WorldWideScience

Sample records for metal-poor dwarf stars

  1. Carbon-enhanced metal-poor stars in dwarf galaxies

    NARCIS (Netherlands)

    Salvadori, Stefania; Skúladóttir, Ása; Tolstoy, Eline

    2015-01-01

    We investigate the frequency and origin of carbon-enhanced metal-poor (CEMP) stars in Local Group dwarf galaxies by means of a statistical, data-calibrated cosmological model for the hierarchical build-up of the Milky Way and its dwarf satellites. The model self-consistently explains the variation

  2. Chemical Abundances of Metal-poor stars in Dwarf Galaxies

    NARCIS (Netherlands)

    Venn, Kim A.; Jablonka, Pascale; Hill, Vanessa; Starkenburg, Else; Lemasle, Bertrand; Shetrone, Matthew; Irwin, Mike; Norris, John; Yong, David; Gilmore, Gerry; Salvadori, Stephania; Skuladottir, Asa; Tolstoy, Eline; Bragaglia, A.; Arnaboldi, M.; Rejkuba, M.; Romano, D.

    2016-01-01

    Stars in low-mass dwarf galaxies show a larger range in their chemical properties than those in the Milky Way halo. The slower star formation efficiency make dwarf galaxies ideal systems for testing nucleosynthetic yields. Not only are alpha-poor stars found at lower metallicities, and a higher

  3. The first carbon-enhanced metal-poor star found in the Sculptor dwarf spheroidal

    NARCIS (Netherlands)

    Skúladóttir, Á.; Tolstoy, E.; Salvadori, S.; Hill, V.; Pettini, M.; Shetrone, M. D.; Starkenburg, E.

    The origin of carbon-enhanced metal-poor (CEMP) stars and their possible connection with the chemical elements produced by the first stellar generation is still highly debated. In contrast to the Galactic halo, not many CEMP stars have been found in the dwarf spheroidal galaxies around the Milky

  4. Linking dwarf galaxies to halo building blocks with the most metal-poor star in Sculptor.

    Science.gov (United States)

    Frebel, Anna; Kirby, Evan N; Simon, Joshua D

    2010-03-04

    Current cosmological models indicate that the Milky Way's stellar halo was assembled from many smaller systems. On the basis of the apparent absence of the most metal-poor stars in present-day dwarf galaxies, recent studies claimed that the true Galactic building blocks must have been vastly different from the surviving dwarfs. The discovery of an extremely iron-poor star (S1020549) in the Sculptor dwarf galaxy based on a medium-resolution spectrum cast some doubt on this conclusion. Verification of the iron-deficiency, however, and measurements of additional elements, such as the alpha-element Mg, are necessary to demonstrate that the same type of stars produced the metals found in dwarf galaxies and the Galactic halo. Only then can dwarf galaxy stars be conclusively linked to early stellar halo assembly. Here we report high-resolution spectroscopic abundances for 11 elements in S1020549, confirming its iron abundance of less than 1/4,000th that of the Sun, and showing that the overall abundance pattern follows that seen in low-metallicity halo stars, including the alpha-elements. Such chemical similarity indicates that the systems destroyed to form the halo billions of years ago were not fundamentally different from the progenitors of present-day dwarfs, and suggests that the early chemical enrichment of all galaxies may be nearly identical.

  5. Ages and Heavy Element Abundances from Very Metal-poor Stars in the Sagittarius Dwarf Galaxy

    Science.gov (United States)

    Hansen, Camilla Juul; El-Souri, Mariam; Monaco, Lorenzo; Villanova, Sandro; Bonifacio, Piercarlo; Caffau, Elisabetta; Sbordone, Luca

    2018-03-01

    Sagittarius (Sgr) is a massive disrupted dwarf spheroidal galaxy in the Milky Way halo that has undergone several stripping events. Previous chemical studies were restricted mainly to a few, metal-rich ([Fe/H] \\gtrapprox -1) stars that suggested a top-light initial mass function (IMF). Here we present the first high-resolution, very metal-poor ([Fe/H] =‑1 to ‑3) sample of 13 giant stars in the main body of Sgr. We derive abundances of 13 elements, namely C, Ca, Co, Fe, Sr, Ba, La, Ce, Nd, Eu, Dy, Pb, and Th, that challenge the interpretation based on previous studies. Our abundances from Sgr mimic those of the metal-poor halo, and our most metal-poor star ([Fe/H] ∼ -3) indicates a pure r-process pollution. Abundances of Sr, Pb, and Th are presented for the first time in Sgr, allowing for age determination using nuclear cosmochronology. We calculate ages of 9+/- 2.5 {Gyr}. Most of the sample stars have been enriched by a range of asymptotic giant branch (AGB) stars with masses between 1.3 and 5 M ⊙. Sgr J190651.47–320147.23 shows a large overabundance of Pb (2.05 dex) and a peculiar abundance pattern best fit by a 3 M ⊙ AGB star. Based on star-to-star scatter and observed abundance patterns, a mixture of low- and high-mass AGB stars and supernovae (15–25 M ⊙) is necessary to explain these patterns. The high level (0.29 ± 0.05 dex) of Ca indicates that massive supernovae must have existed and polluted the early ISM of Sgr before it lost its gas. This result is in contrast with a top-light IMF with no massive stars polluting Sgr. Based on data obtained UVES/VLT ID: 083.B-0774, 075.B-0127.

  6. Extremely metal-poor stars in classical dwarf spheroidal galaxies : Fornax, Sculptor, and Sextans

    NARCIS (Netherlands)

    Tafelmeyer, M.; Jablonka, P.; Hill, V.; Shetrone, M.; Tolstoy, E.; Irwin, M. J.; Battaglia, G.; Helmi, A.; Starkenburg, E.; Venn, K. A.; Abel, T.; Francois, P.; Kaufer, A.; North, P.; Primas, F.; Szeifert, T.

    2010-01-01

    We present the results of a dedicated search for extremely metal-poor stars in the Fornax, Sculptor, and Sextans dSphs. Five stars were selected from two earlier VLT/Giraffe and HET/HRS surveys and subsequently followed up at high spectroscopic resolution with VLT/UVES. All of them turned out to

  7. Extremely metal-poor stars in classical dwarf spheroidal galaxies: Fornax, Sculptor, and Sextans

    NARCIS (Netherlands)

    Tafelmeyer, M.; Jablonka, P.; Hill, V.; Shetrone, M.; Tolstoy, E.; Irwin, M. J.; Battaglia, G.; Helmi, A.; Starkenburg, E.; Venn, K. A.; Abel, T.; Francois, P.; Kaufer, A.; North, P.; Primas, F.; Szeifert, T.

    2010-01-01

    We present the results of a dedicated search for extremely metal-poor stars in the Fornax, Sculptor, and Sextans dSphs. Five stars were selected from two earlier VLT/Giraffe and HET/HRS surveys and subsequently followed up at high spectroscopic resolution with VLT/UVES. All of them turned out to

  8. Detection of a Population of Carbon-enhanced Metal-poor Stars in the Sculptor Dwarf Spheroidal Galaxy

    Science.gov (United States)

    Chiti, Anirudh; Simon, Joshua D.; Frebel, Anna; Thompson, Ian B.; Shectman, Stephen A.; Mateo, Mario; Bailey, John I., III; Crane, Jeffrey D.; Walker, Matthew

    2018-04-01

    The study of the chemical abundances of metal-poor stars in dwarf galaxies provides a venue to constrain paradigms of chemical enrichment and galaxy formation. Here we present metallicity and carbon abundance measurements of 100 stars in Sculptor from medium-resolution (R ∼ 2000) spectra taken with the Magellan/Michigan Fiber System mounted on the Magellan-Clay 6.5 m telescope at Las Campanas Observatory. We identify 24 extremely metal-poor star candidates ([Fe/H] measure a CEMP fraction of 36% for stars below [Fe/H] = ‑3.0, indicating that the prevalence of carbon-enhanced stars in Sculptor is similar to that of the halo (∼43%) after excluding likely CEMP-s and CEMP-r/s stars from our sample. However, we do not detect that any CEMP stars are strongly enhanced in carbon ([C/Fe] > 1.0). The existence of a large number of CEMP stars both in the halo and in Sculptor suggests that some halo CEMP stars may have originated from accreted early analogs of dwarf galaxies. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  9. The Oldest Stars of the Extremely Metal-Poor Local Group Dwarf Irregular Galaxy Leo A

    Science.gov (United States)

    Schulte-Ladbeck, Regina E.; Hopp, Ulrich; Drozdovsky, Igor O.; Greggio, Laura; Crone, Mary M.

    2002-08-01

    We present deep Hubble Space Telescope (HST) single-star photometry of Leo A in B, V, and I. Our new field of view is offset from the centrally located field observed by Tolstoy et al. in order to expose the halo population of this galaxy. We report the detection of metal-poor red horizontal branch stars, which demonstrate that Leo A is not a young galaxy. In fact, Leo A is as least as old as metal-poor Galactic Globular Clusters that exhibit red horizontal branches and are considered to have a minimum age of about 9 Gyr. We discuss the distance to Leo A and perform an extensive comparison of the data with stellar isochrones. For a distance modulus of 24.5, the data are better than 50% complete down to absolute magnitudes of 2 or more. We can easily identify stars with metallicities between 0.0001 and 0.0004, and ages between about 5 and 10 Gyr, in their post-main-sequence phases, but we lack the detection of main-sequence turnoffs that would provide unambiguous proof of ancient (>10 Gyr) stellar generations. Blue horizontal branch stars are above the detection limits but difficult to distinguish from young stars with similar colors and magnitudes. Synthetic color-magnitude diagrams show it is possible to populate the blue horizontal branch in the halo of Leo A. The models also suggest ~50% of the total astrated mass in our pointing to be attributed to an ancient (>10 Gyr) stellar population. We conclude that Leo A started to form stars at least about 9 Gyr ago. Leo A exhibits an extremely low oxygen abundance, only 3% of solar, in its ionized interstellar medium. The existence of old stars in this very oxygen-deficient galaxy illustrates that a low oxygen abundance does not preclude a history of early star formation. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  10. J0023+0307: A Mega Metal-poor Dwarf Star from SDSS/BOSS

    Science.gov (United States)

    Aguado, David S.; Allende Prieto, Carlos; González Hernández, Jonay I.; Rebolo, Rafael

    2018-02-01

    Only a handful of stars have been identified with an iron abundance [Fe/H] zero or very low metal abundance limiting radiative cooling, the formation of low-mass stars could be inhibited. Currently, the star SDSS J1029+1729 sets the potential metallicity threshold for the formation of low-mass stars at {log}Z/{Z}ȯ ∼ -5. In our quest to push down the metallicity threshold we have identified SDSS J0023+0307, a primitive star with T eff = 6188 ± 84 K, and {log}g=4.9+/- 0.5, an upper limit [Fe/H] < ‑6.6, and a carbon abundance A(C) < 6.3. We find J0023+0307 to be one of the two most iron-poor stars known, and it exhibits less carbon that most of the stars at [Fe/H] < ‑5. Based on observations made with William Herschel Telescope (WHT) and the Gran Telescopio de Canarias (GTC), at the Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in La Palma.

  11. Lithium in Very Metal-poor Dwarf Stars -- Problems for Standard Big Bang Nucleosynthesis?

    International Nuclear Information System (INIS)

    Lambert, David L.

    2004-01-01

    The standard model of primordial nucleosynthesis by the Big Bang as selected by the WMAP-based estimate of the baryon density (Ωbh2) predicts an abundance of 7Li that is a factor of three greater than the generally reported abundance for stars on the Spite plateau, and an abundance of 6Li that is about a thousand times less than is found for some stars on the plateau. This review discusses and examines these two discrepancies. They can likely be resolved without major surgery on the standard model of the Big Bang. In particular, stars on the Spite plateau may have depleted their surface lithium abundance over their long lifetime from the WMAP-based predicted abundances down to presently observed abundances, and synthesis of 6Li (and 7Li) via α + α fusion reactions may have occurred in the early Galaxy. Yet, there remain fascinating ways in which to remove the two discrepancies involving aspects of a new cosmology, particularly through the introduction of exotic particles

  12. Chemical Abundance Analysis of Three α-poor, Metal-poor Stars in the Ultrafaint Dwarf Galaxy Horologium I

    Science.gov (United States)

    Nagasawa, D. Q.; Marshall, J. L.; Li, T. S.; Hansen, T. T.; Simon, J. D.; Bernstein, R. A.; Balbinot, E.; Drlica-Wagner, A.; Pace, A. B.; Strigari, L. E.; Pellegrino, C. M.; DePoy, D. L.; Suntzeff, N. B.; Bechtol, K.; Walker, A. R.; Abbott, T. M. C.; Abdalla, F. B.; Allam, S.; Annis, J.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Carnero Rosell, A.; Carrasco Kind, M.; Carretero, J.; Cunha, C. E.; D’Andrea, C. B.; da Costa, L. N.; Davis, C.; Desai, S.; Doel, P.; Eifler, T. F.; Flaugher, B.; Fosalba, P.; Frieman, J.; García-Bellido, J.; Gaztanaga, E.; Gerdes, D. W.; Gruen, D.; Gruendl, R. A.; Gschwend, J.; Gutierrez, G.; Hartley, W. G.; Honscheid, K.; James, D. J.; Jeltema, T.; Krause, E.; Kuehn, K.; Kuhlmann, S.; Kuropatkin, N.; March, M.; Miquel, R.; Nord, B.; Roodman, A.; Sanchez, E.; Santiago, B.; Scarpine, V.; Schindler, R.; Schubnell, M.; Sevilla-Noarbe, I.; Smith, M.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Tarle, G.; Thomas, D.; Tucker, D. L.; Wechsler, R. H.; Wolf, R. C.; Yanny, B.

    2018-01-01

    We present chemical abundance measurements of three stars in the ultrafaint dwarf galaxy Horologium I, a Milky Way satellite discovered by the Dark Energy Survey. Using high-resolution spectroscopic observations, we measure the metallicity of the three stars, as well as abundance ratios of several α-elements, iron-peak elements, and neutron-capture elements. The abundance pattern is relatively consistent among all three stars, which have a low average metallicity of [Fe/H] ∼ ‑2.6 and are not α-enhanced ([α/Fe] ∼ 0.0). This result is unexpected when compared to other low-metallicity stars in the Galactic halo and other ultrafaint dwarfs and suggests the possibility of a different mechanism for the enrichment of Hor I compared to other satellites. We discuss possible scenarios that could lead to this observed nucleosynthetic signature, including extended star formation, enrichment by a Population III supernova, and or an association with the Large Magellanic Cloud. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. This paper also includes data based on observations made with the ESO Very Large Telescope at Paranal Observatory, Chile (ID 096.D-0967(B); PI: E. Balbinot).

  13. Detecting metal-poor gas accretion in the star-forming dwarf galaxies UM 461 and Mrk 600

    Science.gov (United States)

    Lagos, P.; Scott, T. C.; Nigoche-Netro, A.; Demarco, R.; Humphrey, A.; Papaderos, P.

    2018-03-01

    Using VIMOS-IFU observations, we study the interstellar medium (ISM) of two star-forming dwarf galaxies, UM 461 and Mrk 600. Our aim was to search for the existence of metallicity inhomogeneities that might arise from infall of nearly pristine gas feeding ongoing localized star-formation. The IFU data allowed us to study the impact of external gas accretion on the chemical evolution as well as the ionised gas kinematics and morphologies of these galaxies. Both systems show signs of morphological distortions, including cometary-like morphologies. We analysed the spatial variation of 12 + log(O/H) abundances within both galaxies using the direct method (Te), the widely applied HII-CHI-mistry code, as well as by employing different standard calibrations. For UM 461 our results show that the ISM is fairly well mixed, at large scales, however we find an off-centre and low-metallicity region with 12 + log(O/H) ISM in our analysed galaxies are consistent with these systems being at different evolutionary stages.

  14. A New View of the Dwarf Spheroidal Satellites of the Milky Way From VLT/FLAMES: Where are the Very Metal Poor Stars?

    Energy Technology Data Exchange (ETDEWEB)

    Helmi, Amina; Irwin, M.J.; Tolstoy, E.; Battaglia, G.; Hill, V.; Jablonka, P.; Venn, K.; Shetrone, M.; Letarte, B.; Arimoto, N.; Abel, T.; Francois, P.; Kaufer, A.; Primas, F.; Sadakane, K.; Szeifert, T.; /Kapteyn Astron. Inst., Groningen /Cambridge U., Inst. of Astron. /Meudon Observ. /LASTRO Observ. /Victoria U. /Texas U., McDonald Observ.

    2006-11-20

    As part of the Dwarf galaxies Abundances and Radial-velocities Team (DART) Programme, we have measured the metallicities of a large sample of stars in four nearby dwarf spheroidal galaxies (dSph): Sculptor, Sextans, Fornax and Carina. The low mean metal abundances and the presence of very old stellar populations in these galaxies have supported the view that they are fossils from the early Universe. However, contrary to naive expectations, we find a significant lack of stars with metallicities below [Fe/H] {approx} -3 dex in all four systems. This suggests that the gas that made up the stars in these systems had been uniformly enriched prior to their formation. Furthermore, the metal-poor tail of the dSph metallicity distribution is significantly different from that of the Galactic halo. These findings show that the progenitors of nearby dSph appear to have been fundamentally different from the building blocks of the Milky Way, even at the earliest epochs.

  15. Chemical Abundance Analysis of Three α -poor, Metal-poor Stars in the Ultrafaint Dwarf Galaxy Horologium I

    Energy Technology Data Exchange (ETDEWEB)

    Nagasawa, D. Q.; Marshall, J. L.; Li, T. S.; Hansen, T. T.; Simon, J. D.; Bernstein, R. A.; Balbinot, E.; Drlica-Wagner, A.; Pace, A. B.; Strigari, L. E.; Pellegrino, C. M.; DePoy, D. L.; Suntzeff, N. B.; Bechtol, K.; Walker, A. R.; Abbott, T. M. C.; Abdalla, F. B.; Allam, S.; Annis, J.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Rosell, A. Carnero; Kind, M. Carrasco; Carretero, J.; Cunha, C. E.; D’Andrea, C. B.; da Costa, L. N.; Davis, C.; Desai, S.; Doel, P.; Eifler, T. F.; Flaugher, B.; Fosalba, P.; Frieman, J.; García-Bellido, J.; Gaztanaga, E.; Gerdes, D. W.; Gruen, D.; Gruendl, R. A.; Gschwend, J.; Gutierrez, G.; Hartley, W. G.; Honscheid, K.; James, D. J.; Jeltema, T.; Krause, E.; Kuehn, K.; Kuhlmann, S.; Kuropatkin, N.; March, M.; Miquel, R.; Nord, B.; Roodman, A.; Sanchez, E.; Santiago, B.; Scarpine, V.; Schindler, R.; Schubnell, M.; Sevilla-Noarbe, I.; Smith, M.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Tarle, G.; Thomas, D.; Tucker, D. L.; Wechsler, R. H.; Wolf, R. C.; Yanny, B.

    2018-01-10

    We present chemical abundance measurements of three stars in the ultra-faintdwarf galaxy Horologium I, a Milky Way satellite discovered by the Dark EnergySurvey. Using high resolution spectroscopic observations we measure themetallicity of the three stars as well as abundance ratios of several$\\alpha$-elements, iron-peak elements, and neutron-capture elements. Theabundance pattern is relatively consistent among all three stars, which have alow average metallicity of [Fe/H] $\\sim -2.6$ and are not $\\alpha$-enhanced([$\\alpha$/Fe] $\\sim 0.0$). This result is unexpected when compared to otherlow-metallicity stars in the Galactic halo and other ultra-faint dwarfs andhints at an entirely different mechanism for the enrichment of Hor I comparedto other satellites. We discuss possible scenarios that could lead to thisobserved nucleosynthetic signature including extended star formation, aPopulation III supernova, and a possible association with the Large MagellanicCloud.

  16. Mining the Galactic halo for very metal-poor stars

    NARCIS (Netherlands)

    Salvadori, S.; Ferrara, A.; Schneider, R.; Scannapieco, E.; Kawata, D.

    We study the age and metallicity distribution function (MDF) of metal-poor stars in the Milky Way halo as a function of galactocentric radius by combining N-body simulations and semi-analytical methods. We find that the oldest stars populate the innermost region, while extremely metal-poor stars are

  17. Very Metal-poor Stars in the RAVE Spectroscopic Survey

    Science.gov (United States)

    Matijevic, Gal

    2015-08-01

    Metal-poor stars have been the cornerstone of the galactic and stellar archeology for decades. Due to their intact nature they offer a unique insight into the early stages of the galactic evolution and help us understand the nucleosynthesis processes responsible for the creation of chemical elements. The number of discovered very metal-poor stars (metallicity [Fe/H] drops sharply towards even lower metallicities. Only a handful of known stars have [Fe/H] band BVg'r'i'JHKS photometry. All sources of the uncertainty were taken into account which brought the final metallicity uncertainties to ~0.3dex, including for stars with lowest metal abundances. The study enabled us to discover many new very metal poor stars, several of which fall in the extremely metal-poor domain and some of which are possibly ultra metal-poor. For all stars in our sample we also provide updated 6D information.

  18. The Star Formation History of the Very Metal-poor Blue Compact Dwarf I Zw 18 from HST/ACS Data

    Science.gov (United States)

    Annibali, F.; Cignoni, M.; Tosi, M.; van der Marel, R. P.; Aloisi, A.; Clementini, G.; Contreras Ramos, R.; Fiorentino, G.; Marconi, M.; Musella, I.

    2013-12-01

    We have derived the star formation history (SFH) of the blue compact dwarf galaxy I Zw 18 through comparison of deep HST/ACS data with synthetic color-magnitude diagrams (CMDs). A statistical analysis was implemented for the identification of the best-fit SFH and relative uncertainties. We confirm that I Zw 18 is not a truly young galaxy, having started forming stars earlier than ~1 Gyr ago, and possibly at epochs as old as a Hubble time. In I Zw 18's main body we infer a lower limit of ≈2 × 106 M ⊙ for the mass locked up in old stars. I Zw 18's main body has been forming stars very actively during the last ~10 Myr, with an average star formation rate (SFR) as high as ≈1 M ⊙ yr-1 (or ≈2 × 10-5 M ⊙ yr-1 pc-2). On the other hand, the secondary body was much less active at these epochs, in agreement with the absence of significant nebular emission. The high current SFR can explain the very blue colors and the high ionized gas content in I Zw 18, resembling primeval galaxies in the early universe. Detailed chemical evolution models are required to quantitatively check whether the SFH from the synthetic CMDs can explain the low measured element abundances, or if galactic winds with loss of metals are needed. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., for NASA under contract NAS5-26555.

  19. Carbon-enhanced metal-poor stars and thermohaline mixing

    NARCIS (Netherlands)

    Stancliffe, R.J.; Glebbeek, E.|info:eu-repo/dai/nl/30483324X; Izzard, R.G.|info:eu-repo/dai/nl/304836052; Pols, O.R.|info:eu-repo/dai/nl/111811155

    2007-01-01

    One possible scenario for the formation of carbon-enhanced metal-poor stars is the accretion of carbon-rich material from a binary companion which may no longer visible. It is generally assumed that the accreted material remains on the surface of the star and does not mix with the interior until

  20. Origins of carbon-enhanced metal-poor stars

    Science.gov (United States)

    Sharma, Mahavir; Theuns, Tom; Frenk, Carlos S.; Cooke, Ryan J.

    2018-01-01

    We investigate the nature of carbon-enhanced metal-poor (CEMP) stars in Milky Way (MW) analogues selected from the EAGLE cosmological hydrodynamical simulation. The stellar evolution model in EAGLE includes the physics of enrichment by asymptotic giant branch (AGB) stars, winds from massive stars, and Type Ia and Type II supernovae (SNe). In the simulation, star formation in young MW progenitors is bursty due to efficient stellar feedback, which enables poor metal mixing leading to the formation of CEMP stars with extreme abundance patterns. Two classes of CEMP stars emerge: those mostly enriched by low-metallicity Type II SNe with low Fe yields that drive galactic outflows, and those mostly enriched by AGB stars when a gas-poor galaxy accretes pristine gas. The first class resembles CEMP-no stars with high [C/Fe] and low [C/O], the second class resembles CEMP-s stars overabundant in s-process elements and high values of [C/O]. These two enrichment channels explain several trends seen in data: (i) the increase in the scatter and median of [C/O] at low and decreasing [O/H], (ii) the trend of stars with very low [Fe/H] or [C/H] to be of type CEMP-no and (iii) the reduction in the scatter of [α/Fe] with atomic number in metal-poor stars. In this interpretation, CEMP-no stars were enriched by the stars that enabled galaxies to reionize the Universe.

  1. Very metal-poor stars observed by the RAVE survey

    Science.gov (United States)

    Matijevič, G.; Chiappini, C.; Grebel, E. K.; Wyse, R. F. G.; Zwitter, T.; Bienaymé, O.; Bland-Hawthorn, J.; Freeman, K. C.; Gibson, B. K.; Gilmore, G.; Helmi, A.; Kordopatis, G.; Kunder, A.; Munari, U.; Navarro, J. F.; Parker, Q. A.; Reid, W.; Seabroke, G.; Siviero, A.; Steinmetz, M.; Watson, F.

    2017-07-01

    Metal-poor stars trace the earliest phases in the chemical enrichment of the Universe. They give clues about the early assembly of the Galaxy as well as on the nature of the first stellar generations. Multi-object spectroscopic surveys play a key role in finding these fossil records in large volumes. Here we present a novel analysis of the metal-poor star sample in the complete Radial Velocity Experiment (RAVE) Data Release 5 catalog with the goal of identifying and characterizing all very metal-poor stars observed by the survey. Using a three-stage method, we first identified the candidate stars using only their spectra as input information. We employed an algorithm called t-SNE to construct a low-dimensional projection of the spectrum space and isolate the region containing metal-poor stars. Following this step, we measured the equivalent widths of the near-infrared Ca II triplet lines with a method based on flexible Gaussian processes to model the correlated noise present in the spectra. In the last step, we constructed a calibration relation that converts the measured equivalent widths and the color information coming from the 2MASS and WISE surveys into metallicity and temperature estimates. We identified 877 stars with at least a 50% probability of being very metal-poor ([Fe/H] < -2 dex), out of which 43 are likely extremely metal-poor ([Fe/H] < -3 dex). The comparison of the derived values to a small subsample of stars with literature metallicity values shows that our method works reliably and correctly estimates the uncertainties, which typically have valuesσ[Fe/H] ≈ 0.2 dex. In addition, when compared to the metallicity results derived using the RAVE DR5 pipeline, it is evident that we achieve better accuracy than the pipeline and therefore more reliably evaluate the very metal-poor subsample. Based on the repeated observations of the same stars, our method gives very consistent results. We intend to study the identified sample further by acquiring high

  2. Impact of Lyman alpha pressure on metal-poor dwarf galaxies

    Science.gov (United States)

    Kimm, Taysun; Haehnelt, Martin; Blaizot, Jérémy; Katz, Harley; Michel-Dansac, Léo; Garel, Thibault; Rosdahl, Joakim; Teyssier, Romain

    2018-01-01

    Understanding the origin of strong galactic outflows and the suppression of star formation in dwarf galaxies is a key problem in galaxy formation. Using a set of radiation-hydrodynamic simulations of an isolated dwarf galaxy embedded in a 10^{10} M_⊙ halo, we show that the momentum transferred from resonantly scattered Lyman-α (Lyα) photons is an important source of stellar feedback which can shape the evolution of galaxies. We find that Lyα feedback suppresses star formation by a factor of two in metal-poor galaxies by regulating the dynamics of star-forming clouds before the onset of supernova explosions (SNe). This is possible because each Lyα photon resonantly scatters and imparts ˜10-300 times greater momentum than in the single scattering limit. Consequently, the number of star clusters predicted in the simulations is reduced by a factor of ˜5, compared to the model without the early feedback. More importantly, we find that galactic outflows become weaker in the presence of strong Lyα radiation feedback, as star formation and associated SNe become less bursty. We also examine a model in which radiation field is arbitrarily enhanced by a factor of up to 10, and reach the same conclusion. The typical mass loading factors in our metal-poor dwarf system are estimated to be ˜5 - 10 near the mid plane, while it is reduced to ˜1 at larger radii. Finally, we find that the escape of ionizing radiation and hence the reionization history of the Universe is unlikely to be strongly affected by Lyα feedback.

  3. Impact of Lyman alpha pressure on metal-poor dwarf galaxies

    Science.gov (United States)

    Kimm, Taysun; Haehnelt, Martin; Blaizot, Jérémy; Katz, Harley; Michel-Dansac, Léo; Garel, Thibault; Rosdahl, Joakim; Teyssier, Romain

    2018-04-01

    Understanding the origin of strong galactic outflows and the suppression of star formation in dwarf galaxies is a key problem in galaxy formation. Using a set of radiation-hydrodynamic simulations of an isolated dwarf galaxy embedded in a 1010 M⊙ halo, we show that the momentum transferred from resonantly scattered Lyman-α (Lyα) photons is an important source of stellar feedback which can shape the evolution of galaxies. We find that Lyα feedback suppresses star formation by a factor of two in metal-poor galaxies by regulating the dynamics of star-forming clouds before the onset of supernova explosions (SNe). This is possible because each Lyα photon resonantly scatters and imparts ˜10-300 times greater momentum than in the single scattering limit. Consequently, the number of star clusters predicted in the simulations is reduced by a factor of ˜5, compared to the model without the early feedback. More importantly, we find that galactic outflows become weaker in the presence of strong Lyα radiation feedback, as star formation and associated SNe become less bursty. We also examine a model in which radiation field is arbitrarily enhanced by a factor of up to 10, and reach the same conclusion. The typical mass-loading factors in our metal-poor dwarf system are estimated to be ˜5-10 near the mid-plane, while it is reduced to ˜1 at larger radii. Finally, we find that the escape of ionizing radiation and hence the reionization history of the Universe is unlikely to be strongly affected by Lyα feedback.

  4. AN EXTREMELY CARBON-RICH, EXTREMELY METAL-POOR STAR IN THE SEGUE 1 SYSTEM

    International Nuclear Information System (INIS)

    Norris, John E.; Yong, David; Gilmore, Gerard; Wyse, Rosemary F. G.; Frebel, Anna

    2010-01-01

    We report the analysis of high-resolution, high signal-to-noise ratio, spectra of an extremely metal-poor, extremely C-rich red giant, Seg 1-7, in Segue 1-described in the literature alternatively as an unusually extended globular cluster or an ultra-faint dwarf galaxy. The radial velocity of Seg 1-7 coincides precisely with the systemic velocity of Segue 1, and its chemical abundance signature of [Fe/H] = -3.52, [C/Fe] = +2.3, [N/Fe] = +0.8, [Na/Fe] = +0.53, [Mg/Fe] = +0.94, [Al/Fe] = +0.23, and [Ba/Fe] < -1.0 is similar to that of the rare and enigmatic class of Galactic halo objects designated CEMP-no (carbon-rich, extremely metal-poor with no enhancement (over solar ratios) of heavy neutron-capture elements). This is the first star in a Milky Way 'satellite' that unambiguously lies on the metal-poor, C-rich branch of the Aoki et al. bimodal distribution of field halo stars in the ([C/Fe], [Fe/H])-plane. Available data permit us only to identify Seg 1-7 as a member of an ultra-faint dwarf galaxy or as debris from the Sgr dwarf spheroidal galaxy. In either case, this demonstrates that at extremely low abundance, [Fe/H ] <-3.0, star formation and associated chemical evolution proceeded similarly in the progenitors of both the field halo and satellite systems. By extension, this is consistent with other recent suggestions that the most metal-poor dwarf spheroidal and ultra-faint dwarf satellites were the building blocks of the Galaxy's outer halo.

  5. The Extremely Metal-Poor Dwarf Galaxy AGC 198691

    Science.gov (United States)

    Hirschauer, Alec S.; Salzer, John Joseph; Cannon, John M.; Skillman, Evan D.; SHIELD II Team

    2016-01-01

    We present spectroscopic observations of the nearby dwarf irregular galaxy AGC 198691. This object is part of the Survey of HI in Extremely Low-Mass Dwarfs (SHIELD) sample, which consists of ultra-low HI mass galaxies discovered by the Arecibo Legacy Fast-Acting ALFA (ALFALFA) survey. SHIELD is a multi-configuration Expanded Very Large Array (EVLA) study of the neutral gas content and dynamics of galaxies with HI masses in the range of 106-107 M⊙. Our spectral data were obtained using the new high-throughput KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m telescope as part of a systematic study of the nebular abundances in the SHIELD galaxy sample. These observations enable measurement of the temperature sensitive [OIII]λ4363 line and hence the determination of a "direct" oxygen abundance for AGC 198691. We find this system to be an extremely metal-deficient (XMD) galaxy with an oxygen abundance comparable to such objects as I Zw 18, SBS 0335-052W, Leo P, and DDO 68 - the lowest metallicity star-forming systems known. It is worth noting that two of the five lowest-abundance galaxies currently recognized were discovered via the ALFALFA blind HI survey. These XMD galaxies are potential analogues to the first star-forming systems, which through hierarchical accretion processes built up the large galaxies we observe today in the local Universe. Detailed analysis of such XMD systems offers observational constraint to models of galactic evolution and star formation histories to allow a better understanding of the processes that govern the chemical evolution of low-mass galaxies.

  6. Heavy elements abundances in metal-poor stars

    International Nuclear Information System (INIS)

    Magain, P.; Jehin, E.; Neuforge, C.; Noels, A.

    1998-01-01

    A sample of 21 metal-poor stars have been analysed on the basis of high resolution and high signal-to-noise spectra. Correlations between relative abundances of 16 elements have been studied, with a special emphasis on the neutron-capture ones. This analysis reveals the existence of two sub-populations of field halo stars, namely Pop IIa and Pop IIb. They differ by the behaviour of the s-process elements versus the α and r-process elements. We suggest a scenario of formation of these stars, which closely relates the field halo stars to the evolution of globular clusters. The two sub-populations would have evaporated the clusters during two different stages of their chemical evolution

  7. THE KENNICUTT–SCHMIDT RELATION IN EXTREMELY METAL-POOR DWARF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Filho, M. E.; Almeida, J. Sánchez; Muñoz-Tuñón, C. [Instituto Astrofísica de Canarias, E-38200 La Laguna, Tenerife (Spain); Amorín, R. [National Institute for Astrophysics, Astronomical Observatory of Rome, Via Frascati 33, I-00040 Monteporzio Catone (Rome) (Italy); Elmegreen, B. G. [IBM, T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598 (United States); Elmegreen, D. M., E-mail: mfilho@astro.up.pt [Department of Physics and Astronomy, Vassar College, Poughkeepsie, NY 12604 (United States)

    2016-04-01

    The Kennicutt–Schmidt (KS) relation between the gas mass and star formation rate (SFR) describes the star formation regulation in disk galaxies. It is a function of gas metallicity, but the low-metallicity regime of the KS diagram is poorly sampled. We have analyzed data for a representative set of extremely metal-poor galaxies (XMPs), as well as auxiliary data, and compared these to empirical and theoretical predictions. The majority of the XMPs possess high specific SFRs, similar to high-redshift star-forming galaxies. On the KS plot, the XMP H i data occupy the same region as dwarfs and extend the relation for low surface brightness galaxies. Considering the H i gas alone, a considerable fraction of the XMPs already fall off the KS law. Significant quantities of “dark” H{sub 2} mass (i.e., not traced by CO) would imply that XMPs possess low star formation efficiencies (SFE{sub gas}). Low SFE{sub gas} in XMPs may be the result of the metal-poor nature of the H i gas. Alternatively, the H i reservoir may be largely inert, the star formation being dominated by cosmological accretion. Time lags between gas accretion and star formation may also reduce the apparent SFE{sub gas}, as may galaxy winds, which can expel most of the gas into the intergalactic medium. Hence, on global scales, XMPs could be H i-dominated, high-specific-SFR (≳10{sup −10} yr{sup −1}), low-SFE{sub gas} (≲10{sup −9} yr{sup −1}) systems, in which the total H i mass is likely not a good predictor of the total H{sub 2} mass, nor of the SFR.

  8. Searching for dust around hyper metal poor stars

    Energy Technology Data Exchange (ETDEWEB)

    Venn, Kim A.; Divell, Mike; Starkenburg, Else [Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, BC, V8P 5C2 (Canada); Puzia, Thomas H. [Institute of Astrophysics, Pontificia Universidad Catolica de Chile, Av. Vicuna Mackenna 4860, 7820436 Macul, Santiago (Chile); Côté, Stephanie [NRC Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC, V9E 2E7 (Canada); Lambert, David L., E-mail: kvenn@uvic.ca [McDonald Observatory and the Department of Astronomy, University of Texas at Austin, RLM 15.308, Austin, TX 78712 (United States)

    2014-08-20

    We examine the mid-infrared fluxes and spectral energy distributions for stars with iron abundances [Fe/H] <–5, and other metal-poor stars, to eliminate the possibility that their low metallicities are related to the depletion of elements onto dust grains in the formation of a debris disk. Six out of seven stars examined here show no mid-IR excesses. These non-detections rule out many types of circumstellar disks, e.g., a warm debris disk (T ≤ 290 K), or debris disks with inner radii ≤1 AU, such as those associated with the chemically peculiar post-asymptotic giant branch spectroscopic binaries and RV Tau variables. However, we cannot rule out cooler debris disks, nor those with lower flux ratios to their host stars due to, e.g., a smaller disk mass, a larger inner disk radius, an absence of small grains, or even a multicomponent structure, as often found with the chemically peculiar Lambda Bootis stars. The only exception is HE0107-5240, for which a small mid-IR excess near 10 μm is detected at the 2σ level; if the excess is real and associated with this star, it may indicate the presence of (recent) dust-gas winnowing or a binary system.

  9. Quantitative spectroscopy of blue supergiants in metal-poor dwarf galaxy NGC 3109

    International Nuclear Information System (INIS)

    Hosek, Matthew W. Jr.; Kudritzki, Rolf-Peter; Bresolin, Fabio; Urbaneja, Miguel A.; Przybilla, Norbert; Evans, Christopher J.; Pietrzyński, Grzegorz; Gieren, Wolfgang; Carraro, Giovanni

    2014-01-01

    We present a quantitative analysis of the low-resolution (∼4.5 Å) spectra of 12 late-B and early-A blue supergiants (BSGs) in the metal-poor dwarf galaxy NGC 3109. A modified method of analysis is presented which does not require use of the Balmer jump as an independent T eff indicator, as used in previous studies. We determine stellar effective temperatures, gravities, metallicities, reddening, and luminosities, and combine our sample with the early-B-type BSGs analyzed by Evans et al. to derive the distance to NGC 3109 using the flux-weighted gravity-luminosity relation (FGLR). Using primarily Fe-group elements, we find an average metallicity of [ Z-bar ] = –0.67 ± 0.13, and no evidence of a metallicity gradient in the galaxy. Our metallicities are higher than those found by Evans et al. based on the oxygen abundances of early-B supergiants ([ Z-bar ] = –0.93 ± 0.07), suggesting a low α/Fe ratio for the galaxy. We adjust the position of NGC 3109 on the BSG-determined galaxy mass-metallicity relation accordingly and compare it to metallicity studies of H II regions in star-forming galaxies. We derive an FGLR distance modulus of 25.55 ± 0.09 (1.27 Mpc) that compares well with Cepheid and tip of the red giant branch distances. The FGLR itself is consistent with those found in other galaxies, demonstrating the reliability of this method as a measure of extragalactic distances.

  10. Quantitative spectroscopy of blue supergiants in metal-poor dwarf galaxy NGC 3109

    Energy Technology Data Exchange (ETDEWEB)

    Hosek, Matthew W. Jr.; Kudritzki, Rolf-Peter; Bresolin, Fabio [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Urbaneja, Miguel A.; Przybilla, Norbert [Institute for Astro and Particle Physics, A-6020 Innsbruck University (Austria); Evans, Christopher J. [UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh (United Kingdom); Pietrzyński, Grzegorz; Gieren, Wolfgang [Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción (Chile); Carraro, Giovanni, E-mail: mwhosek@ifa.hawaii.edu, E-mail: kud@ifa.hawaii.edu, E-mail: bresolin@ifa.hawaii.edu, E-mail: Miguel.Urbaneja-Perez@uibk.ac.at, E-mail: Norbert.Przybilla@uibk.ac.at, E-mail: chris.evans@stfc.ac.uk, E-mail: pietrzyn@astrouw.edu.pl, E-mail: wgieren@astro-udec.cl, E-mail: gcarraro@eso.org [European Southern Observatory, La Silla Paranal Observatory (Chile)

    2014-04-20

    We present a quantitative analysis of the low-resolution (∼4.5 Å) spectra of 12 late-B and early-A blue supergiants (BSGs) in the metal-poor dwarf galaxy NGC 3109. A modified method of analysis is presented which does not require use of the Balmer jump as an independent T {sub eff} indicator, as used in previous studies. We determine stellar effective temperatures, gravities, metallicities, reddening, and luminosities, and combine our sample with the early-B-type BSGs analyzed by Evans et al. to derive the distance to NGC 3109 using the flux-weighted gravity-luminosity relation (FGLR). Using primarily Fe-group elements, we find an average metallicity of [ Z-bar ] = –0.67 ± 0.13, and no evidence of a metallicity gradient in the galaxy. Our metallicities are higher than those found by Evans et al. based on the oxygen abundances of early-B supergiants ([ Z-bar ] = –0.93 ± 0.07), suggesting a low α/Fe ratio for the galaxy. We adjust the position of NGC 3109 on the BSG-determined galaxy mass-metallicity relation accordingly and compare it to metallicity studies of H II regions in star-forming galaxies. We derive an FGLR distance modulus of 25.55 ± 0.09 (1.27 Mpc) that compares well with Cepheid and tip of the red giant branch distances. The FGLR itself is consistent with those found in other galaxies, demonstrating the reliability of this method as a measure of extragalactic distances.

  11. The metal-poor knee in the Fornax dwarf spheroidal galaxy

    Energy Technology Data Exchange (ETDEWEB)

    Hendricks, Benjamin; Koch, Andreas [Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, D-69117, Heidelberg (Germany); Lanfranchi, Gustavo A. [Núcleo de Astrofísica Teórica, Universidade Cruzeiro do Sul, R. Galvão Bueno 868, Liberdade, 01506-000, São Paulo, SP (Brazil); Boeche, Corrado [Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Mönchhofstr. 12-14, D-69120, Heidelberg (Germany); Walker, Matthew [McWilliams Center for Cosmology, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, PA 15213 (United States); Johnson, Christian I. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-15, Cambridge, MA 02138 (United States); Peñarrubia, Jorge [Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Gilmore, Gerard, E-mail: ben.hendricks@lsw.uni-heidelberg.de [Institute of Astronomy, Cambridge University, Madingley Rd, Cambridge CB3 OHA (United Kingdom)

    2014-04-20

    We present α-element abundances of Mg, Si, and Ti for a large sample of field stars in two outer fields of the Fornax dwarf spheroidal (dSph) galaxy, obtained with Very Large Telescope/GIRAFFE (R ∼ 16, 000). Due to the large fraction of metal-poor (MP) stars in our sample, we are able to follow the α-element evolution from [Fe/H] ≈ –2.5 continuously to [Fe/H] ≈ –0.7. For the first time we are able to resolve the turnover from the Type II supernovae (SNe) dominated, α-enhanced plateau down to subsolar [α/Fe] values, due to the onset of SNe Ia, and thus to trace the chemical enrichment efficiency of the galaxy. Our data support the general concept of an α-enhanced plateau at early epochs, followed by a well-defined 'knee' caused by the onset of SNe Ia, and finally a second plateau with sub-solar [α/Fe] values. We find the position of this knee to be at [Fe/H] ≈ –1.9 and therefore significantly more MP than expected from comparison with other dSphs and standard evolutionary models. Surprisingly, this value is rather comparable to the knee in Sculptor, a dSph ∼10 times less luminous than Fornax. Using chemical evolution models, we find that the position of the knee and the subsequent plateau at the sub-solar level can hardly be explained unless the galaxy experienced several discrete star formation (SF) events with a drastic variation in SF efficiency, while a uniform SF can be ruled out. One possible evolutionary scenario is that Fornax experienced one or several major accretion events from gas-rich systems in the past, so that its current stellar mass is not indicative of the chemical evolution environment at ancient times. If Fornax is the product of several smaller buildings blocks, this may also have implications for the understanding of the formation process of dSphs in general.

  12. The Metal-poor Knee in the Fornax Dwarf Spheroidal Galaxy

    Science.gov (United States)

    Hendricks, Benjamin; Koch, Andreas; Lanfranchi, Gustavo A.; Boeche, Corrado; Walker, Matthew; Johnson, Christian I.; Peñarrubia, Jorge; Gilmore, Gerard

    2014-04-01

    We present α-element abundances of Mg, Si, and Ti for a large sample of field stars in two outer fields of the Fornax dwarf spheroidal (dSph) galaxy, obtained with Very Large Telescope/GIRAFFE (R ~ 16, 000). Due to the large fraction of metal-poor (MP) stars in our sample, we are able to follow the α-element evolution from [Fe/H] ≈ -2.5 continuously to [Fe/H] ≈ -0.7. For the first time we are able to resolve the turnover from the Type II supernovae (SNe) dominated, α-enhanced plateau down to subsolar [α/Fe] values, due to the onset of SNe Ia, and thus to trace the chemical enrichment efficiency of the galaxy. Our data support the general concept of an α-enhanced plateau at early epochs, followed by a well-defined "knee" caused by the onset of SNe Ia, and finally a second plateau with sub-solar [α/Fe] values. We find the position of this knee to be at [Fe/H] ≈ -1.9 and therefore significantly more MP than expected from comparison with other dSphs and standard evolutionary models. Surprisingly, this value is rather comparable to the knee in Sculptor, a dSph ~10 times less luminous than Fornax. Using chemical evolution models, we find that the position of the knee and the subsequent plateau at the sub-solar level can hardly be explained unless the galaxy experienced several discrete star formation (SF) events with a drastic variation in SF efficiency, while a uniform SF can be ruled out. One possible evolutionary scenario is that Fornax experienced one or several major accretion events from gas-rich systems in the past, so that its current stellar mass is not indicative of the chemical evolution environment at ancient times. If Fornax is the product of several smaller buildings blocks, this may also have implications for the understanding of the formation process of dSphs in general. This article is based on observations made with ESO Telescopes at the Paranal Observatory under program 082.B-0940(A).

  13. Rotational mixing in carbon-enhanced metal-poor stars with s-process enrichment

    Science.gov (United States)

    Matrozis, E.; Stancliffe, R. J.

    2017-10-01

    Carbon-enhanced metal-poor (CEMP) stars with s-process enrichment (CEMP-s) are believed to be the products of mass transfer from an asymptotic giant branch (AGB) companion, which has long since become a white dwarf. The surface abundances of CEMP-s stars are thus commonly assumed to reflect the nucleosynthesis output of the first AGB stars. We have previously shown that, for this to be the case, some physical mechanism must counter atomic diffusion (gravitational settling and radiative levitation) in these nearly fully radiative stars, which otherwise leads to surface abundance anomalies clearly inconsistent with observations. Here we take into account angular momentum accretion by these stars. We compute in detail the evolution of typical CEMP-s stars from the zero-age main sequence, through the mass accretion, and up the red giant branch for a wide range of specific angular momentum ja of the accreted material, corresponding to surface rotation velocities, vrot, between about 0.3 and 300 kms-1. We find that only for ja ≳ 1017 cm2s-1 (vrot > 20 kms-1, depending on mass accreted) angular momentum accretion directly causes chemical dilution of the accreted material. This could nevertheless be relevant to CEMP-s stars, which are observed to rotate more slowly, if they undergo continuous angular momentum loss akin to solar-like stars. In models with rotation velocities characteristic of CEMP-s stars, rotational mixing primarily serves to inhibit atomic diffusion, such that the maximal surface abundance variations (with respect to the composition of the accreted material) prior to first dredge-up remain within about 0.4 dex without thermohaline mixing or about 0.5-1.5 dex with thermohaline mixing. Even in models with the lowest rotation velocities (vrot ≲ 1 kms-1), rotational mixing is able to severely inhibit atomic diffusion, compared to non-rotating models. We thus conclude that it offers a natural solution to the problem posed by atomic diffusion and cannot be

  14. Modelling the nucleosynthetic properties of carbon-enhanced metal-poor RR Lyrae stars

    OpenAIRE

    Stancliffe, Richard J.; Kennedy, Catherine R.; Lau, Herbert H. B.; Beers, Timothy C.

    2013-01-01

    Certain carbon-enhanced metal-poor stars likely obtained their composition via pollution from some of the earliest generations of asymptotic giant branch stars and as such provide important clues to early Universe nucleosynthesis. Recently, Kinman et al. discovered that the highly carbon- and barium-enriched metal-poor star SDSS J1707+58 is in fact an RR Lyrae pulsator. This gives us an object in a definite evolutionary state where the effects of dilution of material during the Main Sequence ...

  15. Thermohaline mixing and gravitational settling in carbon-enhanced metal-poor stars

    NARCIS (Netherlands)

    Stancliffe, R.J.; Glebbeek, E.|info:eu-repo/dai/nl/30483324X

    2008-01-01

    We investigate the formation of carbon-enhanced metal-poor (CEMP) stars via the scenario of mass transfer from a carbon-rich asymptotic giant branch primary to a low-mass companion in a binary system. We explore the extent to which material accreted from a companion star mixes with that of the

  16. Formation and Evolution of Carbon-Enhanced Metal-Poor Stars

    NARCIS (Netherlands)

    Abate, C.; Pols, O.R.; Izzard, R.G.

    2010-01-01

    Very metal-poor stars observed in the Galactic halo constitute a window on the primordial conditions under which the Milky Way was formed. A large fraction of these stars show a great enhancement in the abundance of carbon and other heavy elements. One explanation of this observation is that these

  17. Metal-poor star formation triggered by the feedback effects from Pop III stars

    Science.gov (United States)

    Chiaki, Gen; Susa, Hajime; Hirano, Shingo

    2018-04-01

    Metal enrichment by first-generation (Pop III) stars is the very first step of the matter cycle in structure formation and it is followed by the formation of extremely metal-poor (EMP) stars. To investigate the enrichment process by Pop III stars, we carry out a series of numerical simulations including the feedback effects of photoionization and supernovae (SNe) of Pop III stars with a range of masses of minihaloes (MHs), Mhalo, and Pop III stars, MPopIII. We find that the metal-rich ejecta reach neighbouring haloes and external enrichment (EE) occurs when the H II region expands before the SN explosion. The neighbouring haloes are only superficially enriched, and the metallicity of the clouds is [Fe/H] < -5. Otherwise, the SN ejecta fall back and recollapse to form an enriched cloud, i.e. an internal-enrichment (IE) process takes place. In the case where a Pop III star explodes as a core-collapse SN (CCSN), the MH undergoes IE, and the metallicity in the recollapsing region is -5 ≲ [Fe/H] ≲ -3 in most cases. We conclude that IE from a single CCSN can explain the formation of EMP stars. For pair-instability SNe (PISNe), EE takes place for all relevant mass ranges of MHs, consistent with the lack of observational signs of PISNe among EMP stars.

  18. Extremely metal-poor stars from the cosmic dawn in the bulge of the Milky Way.

    Science.gov (United States)

    Howes, L M; Casey, A R; Asplund, M; Keller, S C; Yong, D; Nataf, D M; Poleski, R; Lind, K; Kobayashi, C; Owen, C I; Ness, M; Bessell, M S; Da Costa, G S; Schmidt, B P; Tisserand, P; Udalski, A; Szymański, M K; Soszyński, I; Pietrzyński, G; Ulaczyk, K; Wyrzykowski, Ł; Pietrukowicz, P; Skowron, J; Kozłowski, S; Mróz, P

    2015-11-26

    The first stars are predicted to have formed within 200 million years after the Big Bang, initiating the cosmic dawn. A true first star has not yet been discovered, although stars with tiny amounts of elements heavier than helium ('metals') have been found in the outer regions ('halo') of the Milky Way. The first stars and their immediate successors should, however, preferentially be found today in the central regions ('bulges') of galaxies, because they formed in the largest over-densities that grew gravitationally with time. The Milky Way bulge underwent a rapid chemical enrichment during the first 1-2 billion years, leading to a dearth of early, metal-poor stars. Here we report observations of extremely metal-poor stars in the Milky Way bulge, including one star with an iron abundance about 10,000 times lower than the solar value without noticeable carbon enhancement. We confirm that most of the metal-poor bulge stars are on tight orbits around the Galactic Centre, rather than being halo stars passing through the bulge, as expected for stars formed at redshifts greater than 15. Their chemical compositions are in general similar to typical halo stars of the same metallicity although intriguing differences exist, including lower abundances of carbon.

  19. Metallicity inhomogeneities in local star-forming galaxies as a sign of recent metal-poor gas accretion

    International Nuclear Information System (INIS)

    Sánchez Almeida, J.; Morales-Luis, A. B.; Muñoz-Tuñón, C.; Méndez-Abreu, J.; Elmegreen, D. M.; Elmegreen, B. G.

    2014-01-01

    We measure the oxygen metallicity of the ionized gas along the major axis of seven dwarf star-forming galaxies. Two of them, SDSSJ1647+21 and SDSSJ2238+14, show ≅0.5 dex metallicity decrements in inner regions with enhanced star formation activity. This behavior is similar to the metallicity drop observed in a number of local tadpole galaxies by Sánchez Almeida et al., and was interpreted as showing early stages of assembling in disk galaxies, with the star formation sustained by external metal-poor gas accretion. The agreement with tadpoles has several implications. (1) It proves that galaxies other than the local tadpoles present the same unusual metallicity pattern. (2) Our metallicity inhomogeneities were inferred using the direct method, thus discarding systematic errors usually attributed to other methods. (3) Taken together with the tadpole data, our findings suggest a threshold around one-tenth the solar value for the metallicity drops to show up. Although galaxies with clear metallicity drops are rare, the physical mechanism responsible for them may sustain a significant part of the star formation activity in the local universe. We argue that the star formation dependence of the mass-metallicity relationship, as well as other general properties followed by most local disk galaxies, is naturally interpreted as side effects of pristine gas infall. Alternatives to the metal-poor gas accretion are examined as well.

  20. The Pristine survey - III. Spectroscopic confirmation of an efficient search for extremely metal-poor stars

    Science.gov (United States)

    Youakim, K.; Starkenburg, E.; Aguado, D. S.; Martin, N. F.; Fouesneau, M.; González Hernández, J. I.; Allende Prieto, C.; Bonifacio, P.; Gentile, M.; Kielty, C.; Côté, P.; Jablonka, P.; McConnachie, A.; Sánchez Janssen, R.; Tolstoy, E.; Venn, K.

    2017-12-01

    The Pristine survey is a narrow-band, photometric survey focused around the wavelength region of the Ca II H&K absorption lines, designed to efficiently search for extremely metal-poor stars. In this work, we use the first results of a medium-resolution spectroscopic follow-up to refine the selection criteria for finding extremely metal-poor stars ([Fe/H] ≤ -3.0) in the Pristine survey. We consider methods by which stars can be selected from available broad-band and infrared photometry plus the additional Pristine narrow-band photometry. The sample consists of 205 stars in the magnitude range 14 cuts the sample down to 149 stars, and from these we report a success rate of 70 per cent for finding stars with [Fe/H] ≤ -2.5 and 22 per cent for finding stars with [Fe/H] ≤ -3.0. These statistics compare favourably with other surveys that search for extremely metal-poor stars, namely an improvement by a factor of ∼4 - 5 for recovering stars with [Fe/H] ≤ -3.0. In addition, Pristine covers a fainter magnitude range than its predecessors and can thus probe deeper into the Galactic halo.

  1. A KECK HIRES DOPPLER SEARCH FOR PLANETS ORBITING METAL-POOR DWARFS. II. ON THE FREQUENCY OF GIANT PLANETS IN THE METAL-POOR REGIME

    International Nuclear Information System (INIS)

    Sozzetti, Alessandro; Torres, Guillermo; Latham, David W.; Stefanik, Robert P.; Korzennik, Sylvain G.; Boss, Alan P.; Carney, Bruce W.; Laird, John B.

    2009-01-01

    We present an analysis of three years of precision radial velocity (RV) measurements of 160 metal-poor stars observed with HIRES on the Keck 1 telescope. We report on variability and long-term velocity trends for each star in our sample. We identify several long-term, low-amplitude RV variables worthy of followup with direct imaging techniques. We place lower limits on the detectable companion mass as a function of orbital period. Our survey would have detected, with a 99.5% confidence level, over 95% of all companions on low-eccentricity orbits with velocity semiamplitude K ∼> 100 m s -1 , or M p sin i ∼> 3.0 M J (P/yr) (1/3) , for orbital periods P ∼ p p ≅ 1%. Our results can usefully inform theoretical studies of the process of giant-planet formation across two orders of magnitude in metallicity.

  2. Modelling the nucleosynthetic properties of carbon-enhanced metal-poor RR Lyrae stars

    Science.gov (United States)

    Stancliffe, Richard J.; Kennedy, Catherine R.; Lau, Herbert H. B.; Beers, Timothy C.

    2013-10-01

    Certain carbon-enhanced metal-poor stars likely obtained their composition via pollution from some of the earliest generations of asymptotic giant branch stars and as such provide important clues to early Universe nucleosynthesis. Recently, Kinman et al. discovered that the highly carbon- and barium-enriched metal-poor star SDSS J1707+58 is in fact an RR Lyrae pulsator. This gives us an object in a definite evolutionary state where the effects of dilution of material during the main sequence are minimized owing to the object having passed through first dredge-up. We perform detailed stellar modelling of putative progenitor systems in which we accreted material from asymptotic giant branch stars in the mass range 1-2 M⊙. We investigate how the surface abundances are affected by the inclusion of mechanisms like thermohaline mixing and gravitational settling. While we are able to find a reasonable fit to the carbon and sodium abundances of SDSS J1707+58, suggesting accretion of around 0.1 M⊙ from a 2 M⊙ companion, the strontium and barium abundances remain problematic and this object may have experienced something other than a standard s-process. We have more success in fitting the abundances of the mildly carbon-enriched, metal-poor RR Lyrae pulsator TY Gru (CS 22881-071), which we suggest received 0.1 M⊙ of material from a companion of around 1 M⊙.

  3. THE ORIGIN OF LOW [α/Fe] RATIOS IN EXTREMELY METAL-POOR STARS

    Energy Technology Data Exchange (ETDEWEB)

    Kobayashi, Chiaki [School of Physics, Astronomy and Mathematics, Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB (United Kingdom); Ishigaki, Miho N.; Tominaga, Nozomu; Nomoto, Ken' ichi, E-mail: c.kobayashi@herts.ac.uk [Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo, Kashiwa, Chiba 277-8583 (Japan)

    2014-04-10

    We show that the low ratios of α elements (Mg, Si, and Ca) to Fe recently found for a small fraction of extremely metal-poor stars can be naturally explained with the nucleosynthesis yields of core-collapse supernovae, i.e., 13-25 M {sub ☉} supernovae, or hypernovae. For the case without carbon enhancement, the ejected iron mass is normal, consistent with observed light curves and spectra of nearby supernovae. On the other hand, the carbon enhancement requires much smaller iron production, and the low [α/Fe] of carbon-enhanced metal-poor stars can also be reproduced with 13-25 M {sub ☉} faint supernovae or faint hypernovae. Iron-peak element abundances, in particular Zn abundances, are important to put further constraints on the enrichment sources from galactic archaeology surveys.

  4. BVRI and UBV Photometry of Metal-Poor and Horizontal- Branch Stars in the Galactic Halo

    Science.gov (United States)

    Beers, Timothy C.; Christlieb, Norbert; Smith, Horace; Rossi, Silvia; de Lee, Nathan

    2005-08-01

    We propose to carry out photometry of an additional sample of 750 metal-poor giants, main-sequence turnoff stars, and field horizontal- branch stars selected from the Hamburg/ESO objective prism survey. These stars either have, or soon will have, medium-resolution spectroscopy obtained with various 2.5m - 4m class telescopes, including the SOAR 4.1m. These observations are part of an ongoing search for the most metal-poor stars, which provide fundamental information on the Galaxy's chemical and dynamical history, and horizontal-branch stars, which enable investigations of the kinematics, dynamics, structure, and mass of the Milky Way. We propose to use the SMARTS 0.9m telescope to obtain BVRI and UBV photometry in service (or classical) observing mode. The eventual sample in this long-term program is envisioned to comprise 3000 stars. The first 750 stars on this program will be observed in May during a previously scheduled run.

  5. Lithium isotopic abundances in metal-poor stars: a problem for standard big bang nucleosynthesis?

    International Nuclear Information System (INIS)

    Nissen, P.E.; Asplund, M.; Lambert, D.L.; Primas, F.; Smith, V.V.

    2005-01-01

    Spectral obtained with VLT/UVES suggest the existence of the 6 Li isotope in several metal-poor stars at a level that challenges ideas about its synthesis. The 7 Li abundance is, on the other hand, a factor of three lower than predicted by standard Big Bang nucleosynthesis theory. Both problems may be explained if decaying suppersymmetric particles affect the synthesis of light elements in the Big Bang. (orig.)

  6. Empirical Determination of Dark Matter Velocities Using Metal-Poor Stars.

    Science.gov (United States)

    Herzog-Arbeitman, Jonah; Lisanti, Mariangela; Madau, Piero; Necib, Lina

    2018-01-26

    The Milky Way dark matter halo is formed from the accretion of smaller subhalos. These sub-units also harbor stars-typically old and metal-poor-that are deposited in the Galactic inner regions by disruption events. In this Letter, we show that the dark matter and metal-poor stars in the Solar neighborhood share similar kinematics due to their common origin. Using the high-resolution eris simulation, which traces the evolution of both the dark matter and baryons in a realistic Milky Way analog galaxy, we demonstrate that metal-poor stars are indeed effective tracers for the local, virialized dark matter velocity distribution. The local dark matter velocities can therefore be inferred from observations of the stellar halo made by the Sloan Digital Sky Survey within 4 kpc of the Sun. This empirical distribution differs from the standard halo model in important ways and suggests that the bounds on the spin-independent scattering cross section may be weakened for dark matter masses below ∼10  GeV. Data from Gaia will allow us to further refine the expected distribution for the smooth dark matter component, and to test for the presence of local substructure.

  7. The Pristine survey - I. Mining the Galaxy for the most metal-poor stars

    Science.gov (United States)

    Starkenburg, Else; Martin, Nicolas; Youakim, Kris; Aguado, David S.; Allende Prieto, Carlos; Arentsen, Anke; Bernard, Edouard J.; Bonifacio, Piercarlo; Caffau, Elisabetta; Carlberg, Raymond G.; Côté, Patrick; Fouesneau, Morgan; François, Patrick; Franke, Oliver; González Hernández, Jonay I.; Gwyn, Stephen D. J.; Hill, Vanessa; Ibata, Rodrigo A.; Jablonka, Pascale; Longeard, Nicolas; McConnachie, Alan W.; Navarro, Julio F.; Sánchez-Janssen, Rubén; Tolstoy, Eline; Venn, Kim A.

    2017-11-01

    We present the Pristine survey, a new narrow-band photometric survey focused on the metallicity-sensitive Ca H&K lines and conducted in the Northern hemisphere with the wide-field imager MegaCam on the Canada-France-Hawaii Telescope. This paper reviews our overall survey strategy and discusses the data processing and metallicity calibration. Additionally we review the application of these data to the main aims of the survey, which are to gather a large sample of the most metal-poor stars in the Galaxy, to further characterize the faintest Milky Way satellites, and to map the (metal-poor) substructure in the Galactic halo. The current Pristine footprint comprises over 1000 deg2 in the Galactic halo ranging from b ˜ 30° to ˜78° and covers many known stellar substructures. We demonstrate that, for Sloan Digital Sky Survey (SDSS) stellar objects, we can calibrate the photometry at the 0.02-mag level. The comparison with existing spectroscopic metallicities from SDSS/Sloan Extension for Galactic Understanding and Exploration (SEGUE) and Large Sky Area Multi-Object Fiber Spectroscopic Telescope shows that, when combined with SDSS broad-band g and I photometry, we can use the CaHK photometry to infer photometric metallicities with an accuracy of ˜0.2 dex from [Fe/H] = -0.5 down to the extremely metal-poor regime ([Fe/H] < -3.0). After the removal of various contaminants, we can efficiently select metal-poor stars and build a very complete sample with high purity. The success rate of uncovering [Fe/H]SEGUE < -3.0 stars among [Fe/H]Pristine < -3.0 selected stars is 24 per cent, and 85 per cent of the remaining candidates are still very metal poor ([Fe/H]<-2.0). We further demonstrate that Pristine is well suited to identify the very rare and pristine Galactic stars with [Fe/H] < -4.0, which can teach us valuable lessons about the early Universe.

  8. Near-infrared Stellar Populations in the Metal-poor, Dwarf Irregular Galaxies Sextans A and Leo A

    Science.gov (United States)

    Jones, Olivia C.; Maclay, Matthew T.; Boyer, Martha L.; Meixner, Margaret; McDonald, Iain; Meskhidze, Helen

    2018-02-01

    We present JHK s observations of the metal-poor ([Fe/H] {10}-11 {M}ȯ {yr}}-1, confirming that metal-poor stars can form substantial amounts of dust. We also find tentative evidence for oxygen-rich dust formation at low metallicity, contradicting previous models that suggest oxygen-rich dust production is inhibited in metal-poor environments. The total rates of dust injection into the interstellar medium of Leo A and Sextans A are (8.2+/- 1.8)× {10}-9 {M}ȯ {yr}}-1 and (6.2+/- 0.2)× {10}-7 {M}ȯ {yr}}-1, respectively. The majority of this dust is produced by a few very dusty evolved stars and does not vary strongly with metallicity.

  9. Searching for chemical classes among metal-poor stars using medium-resolution spectroscopy

    Science.gov (United States)

    Cruz, Monique A.; Cogo-Moreira, Hugo; Rossi, Silvia

    2018-04-01

    Astronomy is in the era of large spectroscopy surveys, with the spectra of hundreds of thousands of stars in the Galaxy being collected. Although most of these surveys have low or medium resolution, which makes precise abundance measurements not possible, there is still important information to be extracted from the available data. Our aim is to identify chemically distinct classes among metal-poor stars, observed by the Sloan Digital Sky Survey, using line indices. The present work focused on carbon-enhanced metal-poor (CEMP) stars and their subclasses. We applied the latent profile analysis technique to line indices for carbon, barium, iron and europium, in order to separate the sample into classes with similar chemical signatures. This technique provides not only the number of possible groups but also the probability of each object to belong to each class. The method was able to distinguish at least two classes among the observed sample, with one of them being probable CEMP stars enriched in s-process elements. However, it was not able to separate CEMP-no stars from the rest of the sample. Latent profile analysis is a powerful model-based tool to be used in the identification of patterns in astrophysics. Our tests show the potential of the technique for the attainment of additional chemical information from `poor' data.

  10. Looking for imprints of the first stellar generations in metal-poor bulge field stars

    Science.gov (United States)

    Siqueira-Mello, C.; Chiappini, C.; Barbuy, B.; Freeman, K.; Ness, M.; Depagne, E.; Cantelli, E.; Pignatari, M.; Hirschi, R.; Frischknecht, U.; Meynet, G.; Maeder, A.

    2016-09-01

    Context. Efforts to look for signatures of the first stars have concentrated on metal-poor halo objects. However, the low end of the bulge metallicity distribution has been shown to host some of the oldest objects in the Milky Way and hence this Galactic component potentially offers interesting targets to look at imprints of the first stellar generations. As a pilot project, we selected bulge field stars already identified in the ARGOS survey as having [Fe/H] ≈-1 and oversolar [α/Fe] ratios, and we used FLAMES-UVES to obtain detailed abundances of key elements that are believed to reveal imprints of the first stellar generations. Aims: The main purpose of this study is to analyse selected ARGOS stars using new high-resolution (R ~ 45 000) and high-signal-to-noise (S/N> 100) spectra. We aim to derive their stellar parameters and elemental ratios, in particular the abundances of C, N, the α-elements O, Mg, Si, Ca, and Ti, the odd-Z elements Na and Al, the neutron-capture s-process dominated elements Y, Zr, La, and Ba, and the r-element Eu. Methods: High-resolution spectra of five field giant stars were obtained at the 8 m VLT UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVES configuration. Spectroscopic parameters were derived based on the excitation and ionization equilibrium of Fe I and Fe II. The abundance analysis was performed with a MARCS LTE spherical model atmosphere grid and the Turbospectrum spectrum synthesis code. Results: We confirm that the analysed stars are moderately metal-poor (-1.04 ≤ [Fe/H] ≤-0.43), non-carbon-enhanced (non-CEMP) with [C/Fe] ≤ + 0.2, and α-enhanced. We find that our three most metal-poor stars are nitrogen enhanced. The α-enhancement suggests that these stars were formed from a gas enriched by core-collapse supernovae, and that the values are in agreement with results in the literature for bulge stars in the same metallicity range. No abundance anomalies (Na - O, Al - O, Al - Mg anti-correlations) were

  11. The chemical imprint of silicate dust on the most metal-poor stars

    International Nuclear Information System (INIS)

    Ji, Alexander P.; Frebel, Anna; Bromm, Volker

    2014-01-01

    We investigate the impact of dust-induced gas fragmentation on the formation of the first low-mass, metal-poor stars (<1 M ☉ ) in the early universe. Previous work has shown the existence of a critical dust-to-gas ratio, below which dust thermal cooling cannot cause gas fragmentation. Assuming that the first dust is silicon-based, we compute critical dust-to-gas ratios and associated critical silicon abundances ([Si/H] crit ). At the density and temperature associated with protostellar disks, we find that a standard Milky Way grain size distribution gives [Si/H] crit = –4.5 ± 0.1, while smaller grain sizes created in a supernova reverse shock give [Si/H] crit = –5.3 ± 0.1. Other environments are not dense enough to be influenced by dust cooling. We test the silicate dust cooling theory by comparing to silicon abundances observed in the most iron-poor stars ([Fe/H] < -4.0). Several stars have silicon abundances low enough to rule out dust-induced gas fragmentation with a standard grain size distribution. Moreover, two of these stars have such low silicon abundances that even dust with a shocked grain size distribution cannot explain their formation. Adding small amounts of carbon dust does not significantly change these conclusions. Additionally, we find that these stars exhibit either high carbon with low silicon abundances or the reverse. A silicate dust scenario thus suggests that the earliest low-mass star formation in the most metal-poor regime may have proceeded through two distinct cooling pathways: fine-structure line cooling and dust cooling. This naturally explains both the carbon-rich and carbon-normal stars at extremely low [Fe/H].

  12. Carbon and nitrogen abundances in giant stars of the metal-poor globular cluster M92

    International Nuclear Information System (INIS)

    Carbon, D.F.; Langer, G.E.; Butler, D.; Kraft, R.P.; Suntzeff, N.B.; Kemper, E.; Trefzger, C.F.; Romanishin, W.

    1982-01-01

    Zinn in 1973 and 1977 and Norris and Zinn in 1977 showed that in M92 and several other metal-poor globular clusters the G bands (mostly due to CH) in the spectra of asymptotic giant branch (AGB) stars are systematically weaker than those found in the less highly evolved subgiant branch (SGB) stars. If carbon is depleted in the atmospheres of evolved stars because material at the base of the envelope, processed through the CN cycle, has been mixed with the material above, then the atmospheric nitrogen abundance should be correspondingly increased. In this paper we test the hypothesis that C and N abundances in M92 giants are negatively correlated as the evolutionary state becomes more advanced. We find that this simple hypothesis is not adequate to describe the complex behavior of C and N in the cluster giants

  13. VizieR Online Data Catalog: Properties of metal-poor stars in APOGEE DR13 (Hayes+, 2018)

    Science.gov (United States)

    Hayes, C. R.; Majewski, S. R.; Shetrone, M.; Fernandez-Alvar, E.; Prieto, C. A.; Schuster, W. J.; Carigi, L.; Cunha, K.; Smith, V. V.; Sobeck, J.; Almeida, A.; Beers, T. C.; Carrera, R.; Fernandez-Trincado, J. G.; Garcia-Hernandez, D. A.; Geisler, D.; Lane, R. R.; Lucatello, S.; Matthews, A. M.; Minniti, D.; Nitschelm, C.; Tang, B.; Tissera, P. B.; Zamora, O.

    2018-01-01

    Table 1 contains the properties, stellar parameters, and chemical abundances of the metal-poor stars in reported by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) in the 13th data release of the Sloan Digital Sky survey as presented in the paper. This table also includes population assignments for these metal-poor stars into to the two populations that have been identified. (1 data file).

  14. TESTING THE ASTEROSEISMIC MASS SCALE USING METAL-POOR STARS CHARACTERIZED WITH APOGEE AND KEPLER

    Energy Technology Data Exchange (ETDEWEB)

    Epstein, Courtney R.; Johnson, Jennifer A.; Tayar, Jamie; Pinsonneault, Marc [Department of Astronomy, Ohio State University, 140 W. 18th Avenue, Columbus, OH 43210 (United States); Elsworth, Yvonne P.; Chaplin, William J. [School of Physics and Astronomy, University of Birmingham, Edgbaston Park Road, West Midlands, Birmingham B15 2TT (United Kingdom); Shetrone, Matthew [McDonald Observatory, The University of Texas at Austin, 1 University Station, C1400, Austin, TX 78712-0259 (United States); Mosser, Benoît [LESIA, CNRS, Université Pierre et Marie Curie, Université Denis Diderot, Observatoire de Paris, F-92195 Meudon Cedex (France); Hekker, Saskia [Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany); Harding, Paul [Department of Astronomy, Case Western Reserve University, Cleveland, OH 44106-7215 (United States); Silva Aguirre, Víctor [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Basu, Sarbani [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Beers, Timothy C. [National Optical Astronomy Observatory, Tucson, AZ 85719, USA and JINA: Joint Institute for Nuclear Astrophysics (United States); Bizyaev, Dmitry [Apache Point Observatory, Sunspot, NM 88349 (United States); Bedding, Timothy R. [Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia); Frinchaboy, Peter M. [Department of Physics and Astronomy, Texas Christian University, TCU Box 298840, Fort Worth, TX 76129 (United States); García, Rafael A. [Laboratoire AIM, CEA/DSM-CNRS, Universit Paris 7 Diderot, IRFU/SAp, Centre de Saclay, F-91191, Gif-sur-Yvette (France); Pérez, Ana E. García; Hearty, Fred R., E-mail: epstein@astronomy.ohio-state.edu [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); and others

    2014-04-20

    Fundamental stellar properties, such as mass, radius, and age, can be inferred using asteroseismology. Cool stars with convective envelopes have turbulent motions that can stochastically drive and damp pulsations. The properties of the oscillation frequency power spectrum can be tied to mass and radius through solar-scaled asteroseismic relations. Stellar properties derived using these scaling relations need verification over a range of metallicities. Because the age and mass of halo stars are well-constrained by astrophysical priors, they provide an independent, empirical check on asteroseismic mass estimates in the low-metallicity regime. We identify nine metal-poor red giants (including six stars that are kinematically associated with the halo) from a sample observed by both the Kepler space telescope and the Sloan Digital Sky Survey-III APOGEE spectroscopic survey. We compare masses inferred using asteroseismology to those expected for halo and thick-disk stars. Although our sample is small, standard scaling relations, combined with asteroseismic parameters from the APOKASC Catalog, produce masses that are systematically higher (<ΔM > =0.17 ± 0.05 M {sub ☉}) than astrophysical expectations. The magnitude of the mass discrepancy is reduced by known theoretical corrections to the measured large frequency separation scaling relationship. Using alternative methods for measuring asteroseismic parameters induces systematic shifts at the 0.04 M {sub ☉} level. We also compare published asteroseismic analyses with scaling relationship masses to examine the impact of using the frequency of maximum power as a constraint. Upcoming APOKASC observations will provide a larger sample of ∼100 metal-poor stars, important for detailed asteroseismic characterization of Galactic stellar populations.

  15. Empirical Determination of Dark Matter Velocities Using Metal-Poor Stars

    Science.gov (United States)

    Herzog-Arbeitman, Jonah; Lisanti, Mariangela; Madau, Piero; Necib, Lina

    2018-01-01

    The Milky Way dark matter halo is formed from the accretion of smaller subhalos. These sub-units also harbor stars—typically old and metal-poor—that are deposited in the Galactic inner regions by disruption events. In this Letter, we show that the dark matter and metal-poor stars in the Solar neighborhood share similar kinematics due to their common origin. Using the high-resolution eris simulation, which traces the evolution of both the dark matter and baryons in a realistic Milky Way analog galaxy, we demonstrate that metal-poor stars are indeed effective tracers for the local, virialized dark matter velocity distribution. The local dark matter velocities can therefore be inferred from observations of the stellar halo made by the Sloan Digital Sky Survey within 4 kpc of the Sun. This empirical distribution differs from the standard halo model in important ways and suggests that the bounds on the spin-independent scattering cross section may be weakened for dark matter masses below ˜10 GeV . Data from Gaia will allow us to further refine the expected distribution for the smooth dark matter component, and to test for the presence of local substructure.

  16. DETECTION OF THE SECOND r-PROCESS PEAK ELEMENT TELLURIUM IN METAL-POOR STARS ,

    Energy Technology Data Exchange (ETDEWEB)

    Roederer, Ian U. [Carnegie Observatories, Pasadena, CA 91101 (United States); Lawler, James E. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States); Cowan, John J. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States); Beers, Timothy C. [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States); Frebel, Anna [Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, Cambridge, MA 02139 (United States); Ivans, Inese I. [Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112 (United States); Schatz, Hendrik [Department of Physics and Astronomy, Michigan State University, E. Lansing, MI 48824 (United States); Sobeck, Jennifer S. [Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637 (United States); Sneden, Christopher [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States)

    2012-03-15

    Using near-ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, we detect neutral tellurium in three metal-poor stars enriched by products of r-process nucleosynthesis, BD +17 3248, HD 108317, and HD 128279. Tellurium (Te, Z = 52) is found at the second r-process peak (A Almost-Equal-To 130) associated with the N = 82 neutron shell closure, and it has not been detected previously in Galactic halo stars. The derived tellurium abundances match the scaled solar system r-process distribution within the uncertainties, confirming the predicted second peak r-process residuals. These results suggest that tellurium is predominantly produced in the main component of the r-process, along with the rare earth elements.

  17. NEW HUBBLE SPACE TELESCOPE OBSERVATIONS OF HEAVY ELEMENTS IN FOUR METAL-POOR STARS

    Energy Technology Data Exchange (ETDEWEB)

    Roederer, Ian U.; Thompson, Ian B. [Carnegie Observatories, Pasadena, CA 91101 (United States); Lawler, James E. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States); Sobeck, Jennifer S. [Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637 (United States); Beers, Timothy C. [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States); Cowan, John J. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States); Frebel, Anna [Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, Cambridge, MA 02139 (United States); Ivans, Inese I. [Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112 (United States); Schatz, Hendrik [Department of Physics and Astronomy, Michigan State University, E. Lansing, MI 48824 (United States); Sneden, Christopher [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States)

    2012-12-15

    Elements heavier than the iron group are found in nearly all halo stars. A substantial number of these elements, key to understanding neutron-capture nucleosynthesis mechanisms, can only be detected in the near-ultraviolet. We report the results of an observing campaign using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to study the detailed heavy-element abundance patterns in four metal-poor stars. We derive abundances or upper limits from 27 absorption lines of 15 elements produced by neutron-capture reactions, including seven elements (germanium, cadmium, tellurium, lutetium, osmium, platinum, and gold) that can only be detected in the near-ultraviolet. We also examine 202 heavy-element absorption lines in ground-based optical spectra obtained with the Magellan Inamori Kyocera Echelle Spectrograph on the Magellan-Clay Telescope at Las Campanas Observatory and the High Resolution Echelle Spectrometer on the Keck I Telescope on Mauna Kea. We have detected up to 34 elements heavier than zinc. The bulk of the heavy elements in these four stars are produced by r-process nucleosynthesis. These observations affirm earlier results suggesting that the tellurium found in metal-poor halo stars with moderate amounts of r-process material scales with the rare earth and third r-process peak elements. Cadmium often follows the abundances of the neighboring elements palladium and silver. We identify several sources of systematic uncertainty that must be considered when comparing these abundances with theoretical predictions. We also present new isotope shift and hyperfine structure component patterns for Lu II and Pb I lines of astrophysical interest.

  18. Asteroseismology of White Dwarf Stars

    Science.gov (United States)

    Hansen, Carl J.

    1997-01-01

    The primary purpose of this investigation has been to study various aspects of multimode pulsations in variable white dwarfs. In particular, nonlinear interactions among pulsation modes in white dwarfs (and, to some extent, in other variable stars), analysis of recent observations where such interactions are important, and preliminary work on the effects of crystallization in cool white dwarfs are reported.

  19. White Dwarf Stars

    Science.gov (United States)

    1999-01-01

    Peering deep inside a cluster of several hundred thousand stars, NASA's Hubble Space Telescope has uncovered the oldest burned-out stars in our Milky Way Galaxy, giving astronomers a fresh reading on the age of the universe. Located in the globular cluster M4, these small, burned-out stars -- called white dwarfs -- are about 12 to 13 billion years old. By adding the one billion years it took the cluster to form after the Big Bang, astronomers found that the age of the white dwarfs agrees with previous estimates that the universe is 13 to 14 billion years old. The images, including some taken by Hubble's Wide Field and Planetary Camera 2, are available online at http://oposite.stsci.edu/pubinfo/pr/2002/10/ or http://www.jpl.nasa.gov/images/wfpc . The camera was designed and built by NASA's Jet Propulsion Laboratory, Pasadena, Calif. In the top panel, a ground-based observatory snapped a panoramic view of the entire cluster, which contains several hundred thousand stars within a volume of 10 to 30 light-years across. The Kitt Peak National Observatory's .9-meter telescope took this picture in March 1995. The box at left indicates the region observed by the Hubble telescope. The Hubble telescope studied a small region of the cluster. A section of that region is seen in the picture at bottom left. A sampling of an even smaller region is shown at bottom right. This region is only about one light-year across. In this smaller region, Hubble pinpointed a number of faint white dwarfs. The blue circles indicate the dwarfs. It took nearly eight days of exposure time over a 67-day period to find these extremely faint stars. Globular clusters are among the oldest clusters of stars in the universe. The faintest and coolest white dwarfs within globular clusters can yield a globular cluster's age. Earlier Hubble observations showed that the first stars formed less than 1 billion years after the universe's birth in the big bang. So, finding the oldest stars puts astronomers within

  20. Constraining cosmic scatter in the Galactic halo through a differential analysis of metal-poor stars

    Science.gov (United States)

    Reggiani, Henrique; Meléndez, Jorge; Kobayashi, Chiaki; Karakas, Amanda; Placco, Vinicius

    2017-12-01

    Context. The chemical abundances of metal-poor halo stars are important to understanding key aspects of Galactic formation and evolution. Aims: We aim to constrain Galactic chemical evolution with precise chemical abundances of metal-poor stars (-2.8 ≤ [Fe/H] ≤ -1.5). Methods: Using high resolution and high S/N UVES spectra of 23 stars and employing the differential analysis technique we estimated stellar parameters and obtained precise LTE chemical abundances. Results: We present the abundances of Li, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Zn, Sr, Y, Zr, and Ba. The differential technique allowed us to obtain an unprecedented low level of scatter in our analysis, with standard deviations as low as 0.05 dex, and mean errors as low as 0.05 dex for [X/Fe]. Conclusions: By expanding our metallicity range with precise abundances from other works, we were able to precisely constrain Galactic chemical evolution models in a wide metallicity range (-3.6 ≤ [Fe/H] ≤ -0.4). The agreements and discrepancies found are key for further improvement of both models and observations. We also show that the LTE analysis of Cr II is a much more reliable source of abundance for chromium, as Cr I has important NLTE effects. These effects can be clearly seen when we compare the observed abundances of Cr I and Cr II with GCE models. While Cr I has a clear disagreement between model and observations, Cr II is very well modeled. We confirm tight increasing trends of Co and Zn toward lower metallicities, and a tight flat evolution of Ni relative to Fe. Our results strongly suggest inhomogeneous enrichment from hypernovae. Our precise stellar parameters results in a low star-to-star scatter (0.04 dex) in the Li abundances of our sample, with a mean value about 0.4 dex lower than the prediction from standard Big Bang nucleosynthesis; we also study the relation between lithium depletion and stellar mass, but it is difficult to assess a correlation due to the limited mass range. We

  1. WASP-36b: A NEW TRANSITING PLANET AROUND A METAL-POOR G-DWARF, AND AN INVESTIGATION INTO ANALYSES BASED ON A SINGLE TRANSIT LIGHT CURVE

    Energy Technology Data Exchange (ETDEWEB)

    Smith, A. M. S.; Anderson, D. R.; Hellier, C.; Maxted, P. F. L.; Smalley, B.; Southworth, J. [Astrophysics Group, Keele University, Staffordshire, ST5 5BG (United Kingdom); Collier Cameron, A. [SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, Fife, KY16 9SS (United Kingdom); Gillon, M.; Jehin, E. [Institut d' Astrophysique et de Geophysique, Universite de Liege, Allee du 6 Aout, 17 Bat. B5C, Liege 1 (Belgium); Lendl, M.; Queloz, D.; Triaud, A. H. M. J.; Pepe, F.; Segransan, D.; Udry, S. [Observatoire de Geneve, Universite de Geneve, 51 Chemin des Maillettes, 1290 Sauverny (Switzerland); West, R. G. [Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH (United Kingdom); Barros, S. C. C.; Pollacco, D. [Astrophysics Research Centre, School of Mathematics and Physics, Queen' s University, University Road, Belfast, BT7 1NN (United Kingdom); Street, R. A., E-mail: amss@astro.keele.ac.uk [Las Cumbres Observatory, 6740 Cortona Drive Suite 102, Goleta, CA 93117 (United States)

    2012-04-15

    We report the discovery, from WASP and CORALIE, of a transiting exoplanet in a 1.54 day orbit. The host star, WASP-36, is a magnitude V = 12.7, metal-poor G2 dwarf (T{sub eff} = 5959 {+-} 134 K), with [Fe/H] =-0.26 {+-} 0.10. We determine the planet to have mass and radius, respectively, 2.30 {+-} 0.07 and 1.28 {+-} 0.03 times that of Jupiter. We have eight partial or complete transit light curves, from four different observatories, which allow us to investigate the potential effects on the fitted system parameters of using only a single light curve. We find that the solutions obtained by analyzing each of these light curves independently are consistent with our global fit to all the data, despite the apparent presence of correlated noise in at least two of the light curves.

  2. CHEMICAL ANALYSIS OF A CARBON-ENHANCED VERY METAL-POOR STAR: CD-27 14351

    Energy Technology Data Exchange (ETDEWEB)

    Karinkuzhi, Drisya; Goswami, Aruna [Indian Institute of Astrophysics, Koramangala, Bangalore 560034 (India); Masseron, Thomas [Institute of Astronomy, Madingley Road, Cambridge CB3 0HA (United Kingdom)

    2017-01-01

    We present, for the first time, an abundance analysis of a very metal-poor carbon-enhanced star CD-27 14351 based on a high-resolution ( R  ∼ 48,000) FEROS spectrum. Our abundance analysis performed using local thermodynamic equilibrium model atmospheres shows that the object is a cool star with stellar atmospheric parameters, effective temperature T {sub eff} = 4335 K, surface gravity log g  = 0.5, microturbulence ξ  = 2.42 km s{sup −1}, and metallicity [Fe/H] = −2.6. The star exhibits high carbon and nitrogen abundances with [C/Fe] = 2.89 and [N/Fe] = 1.89. Overabundances of neutron-capture elements are evident in Ba, La, Ce, and Nd, with estimated [X/Fe] > 1, the largest enhancement being seen in Ce with [Ce/Fe] = 2.63. While the first peak s -process elements Sr and Y are found to be enhanced with respect to Fe, ([Sr/Fe] = 1.73 and [Y/Fe] = 1.91), the third peak s -process element Pb could not be detected in our spectrum at the given resolution. Europium, primarily an r -process element also shows an enhancement with [Eu/Fe] = 1.65. With [Ba/Eu] = 0.12, the object CD-27 14351 satisfies the classification criterion for a CEMP-r/s star. The elemental abundance distributions observed in this star are discussed in light of the chemical abundances observed in other CEMP stars in the literature.

  3. THE INTERMEDIATE NEUTRON-CAPTURE PROCESS AND CARBON-ENHANCED METAL-POOR STARS

    Energy Technology Data Exchange (ETDEWEB)

    Hampel, Melanie [Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, D-69117 Heidelberg (Germany); Stancliffe, Richard J. [Argelander-Institut für Astronomie, University of Bonn, Auf dem Hügel 71, D-53121 Bonn (Germany); Lugaro, Maria [Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, H-1121 Budapest (Hungary); Meyer, Bradley S., E-mail: mhampel@lsw.uni-heidelberg.de [Department of Physics and Astronomy, Clemson University, Clemson, SC 29634-0978 (United States)

    2016-11-10

    Carbon-enhanced metal-poor (CEMP) stars in the Galactic Halo display enrichments in heavy elements associated with either the s (slow) or the r (rapid) neutron-capture process (e.g., barium and europium, respectively), and in some cases they display evidence of both. The abundance patterns of these CEMP- s / r stars, which show both Ba and Eu enrichment, are particularly puzzling, since the s and the r processes require neutron densities that are more than ten orders of magnitude apart and, hence, are thought to occur in very different stellar sites with very different physical conditions. We investigate whether the abundance patterns of CEMP- s / r stars can arise from the nucleosynthesis of the intermediate neutron-capture process (the i process), which is characterized by neutron densities between those of the s and the r processes. Using nuclear network calculations, we study neutron capture nucleosynthesis at different constant neutron densities n ranging from 10{sup 7}–10{sup 15} cm{sup -3}. With respect to the classical s process resulting from neutron densities on the lowest side of this range, neutron densities on the highest side result in abundance patterns, which show an increased production of heavy s -process and r -process elements, but similar abundances of the light s -process elements. Such high values of n may occur in the thermal pulses of asymptotic giant branch stars due to proton ingestion episodes. Comparison to the surface abundances of 20 CEMP- s / r stars shows that our modeled i -process abundances successfully reproduce observed abundance patterns, which could not be previously explained by s -process nucleosynthesis. Because the i -process models fit the abundances of CEMP- s / r stars so well, we propose that this class should be renamed as CEMP- i .

  4. New Hubble Space Telescope Observations of Heavy Elements in Four Metal-Poor Stars

    Science.gov (United States)

    Roederer, Ian U.; Lawler, James E.; Sobeck, Jennifer S.; Beers, Timothy C.; Cowan, John J.; Frebel, Anna; Ivans, Inese I.; Schatz, Hendrik; Sneden, Christopher; Thompson, Ian B.

    2012-12-01

    Elements heavier than the iron group are found in nearly all halo stars. A substantial number of these elements, key to understanding neutron-capture nucleosynthesis mechanisms, can only be detected in the near-ultraviolet. We report the results of an observing campaign using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to study the detailed heavy-element abundance patterns in four metal-poor stars. We derive abundances or upper limits from 27 absorption lines of 15 elements produced by neutron-capture reactions, including seven elements (germanium, cadmium, tellurium, lutetium, osmium, platinum, and gold) that can only be detected in the near-ultraviolet. We also examine 202 heavy-element absorption lines in ground-based optical spectra obtained with the Magellan Inamori Kyocera Echelle Spectrograph on the Magellan-Clay Telescope at Las Campanas Observatory and the High Resolution Echelle Spectrometer on the Keck I Telescope on Mauna Kea. We have detected up to 34 elements heavier than zinc. The bulk of the heavy elements in these four stars are produced by r-process nucleosynthesis. These observations affirm earlier results suggesting that the tellurium found in metal-poor halo stars with moderate amounts of r-process material scales with the rare earth and third r-process peak elements. Cadmium often follows the abundances of the neighboring elements palladium and silver. We identify several sources of systematic uncertainty that must be considered when comparing these abundances with theoretical predictions. We also present new isotope shift and hyperfine structure component patterns for Lu II and Pb I lines of astrophysical interest. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs 8111 and

  5. New detections of arsenic, selenium, and other heavy elements in two metal-poor stars

    Energy Technology Data Exchange (ETDEWEB)

    Roederer, Ian U. [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Schatz, Hendrik; Beers, Timothy C. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Lawler, James E. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States); Cowan, John J. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States); Frebel, Anna [Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Ivans, Inese I. [Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112 (United States); Sneden, Christopher [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States); Sobeck, Jennifer S. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States)

    2014-08-10

    We use the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to obtain new high-quality spectra covering the 1900 ≤λ ≤ 2360 Å wavelength range for two metal-poor stars, HD 108317 and HD 128279. We derive abundances of Cu II, Zn II, As I, Se I, Mo II, and Cd II, which have not been detected previously in either star. Abundances derived for Ge I, Te I, Os II, and Pt I confirm those derived from lines at longer wavelengths. We also derive upper limits from the non-detection of W II, Hg II, Pb II, and Bi I. The mean [As/Fe] ratio derived from these two stars and five others in the literature is unchanged over the metallicity range –2.8 < [Fe/H] <–0.6, ([As/Fe]) = +0.28 ± 0.14 (σ = 0.36 dex). The mean [Se/Fe] ratio derived from these two stars and six others in the literature is also constant, ([Se/Fe]) = +0.16 ± 0.09 (σ = 0.26 dex). The As and Se abundances are enhanced relative to a simple extrapolation of the iron-peak abundances to higher masses, suggesting that this mass region (75 ≤A ≤ 82) may be the point at which a different nucleosynthetic mechanism begins to dominate the quasi-equilibrium α-rich freezeout of the iron peak. ([Cu II/Cu I]) = +0.56 ± 0.23 in HD 108317 and HD 128279, and we infer that lines of Cu I may not be formed in local thermodynamic equilibrium in these stars. The [Zn/Fe], [Mo/Fe], [Cd/Fe], and [Os/Fe] ratios are also derived from neutral and ionized species, and each ratio pair agrees within the mutual uncertainties, which range from 0.15 to 0.52 dex.

  6. A search for stars of very low metal abundance. VI. Detailed abundances of 313 metal-poor stars

    International Nuclear Information System (INIS)

    Roederer, Ian U.; Preston, George W.; Thompson, Ian B.; Shectman, Stephen A.; Burley, Gregory S.; Kelson, Daniel D.; Sneden, Christopher

    2014-01-01

    We present radial velocities, equivalent widths, model atmosphere parameters, and abundances or upper limits for 53 species of 48 elements derived from high resolution optical spectroscopy of 313 metal-poor stars. A majority of these stars were selected from the metal-poor candidates of the HK Survey of Beers, Preston, and Shectman. We derive detailed abundances for 61% of these stars for the first time. Spectra were obtained during a 10 yr observing campaign using the Magellan Inamori Kyocera Echelle spectrograph on the Magellan Telescopes at Las Campanas Observatory, the Robert G. Tull Coudé Spectrograph on the Harlan J. Smith Telescope at McDonald Observatory, and the High Resolution Spectrograph on the Hobby-Eberly Telescope at McDonald Observatory. We perform a standard LTE abundance analysis using MARCS model atmospheres, and we apply line-by-line statistical corrections to minimize systematic abundance differences arising when different sets of lines are available for analysis. We identify several abundance correlations with effective temperature. A comparison with previous abundance analyses reveals significant differences in stellar parameters, which we investigate in detail. Our metallicities are, on average, lower by ≈0.25 dex for red giants and ≈0.04 dex for subgiants. Our sample contains 19 stars with [Fe/H] ≤–3.5, 84 stars with [Fe/H] ≤–3.0, and 210 stars with [Fe/H] ≤–2.5. Detailed abundances are presented here or elsewhere for 91% of the 209 stars with [Fe/H] ≤–2.5 as estimated from medium resolution spectroscopy by Beers, Preston, and Shectman. We will discuss the interpretation of these abundances in subsequent papers.

  7. AN INFRARED CENSUS OF DUST IN NEARBY GALAXIES WITH SPITZER (DUSTiNGS). II. DISCOVERY OF METAL-POOR DUSTY AGB STARS

    Energy Technology Data Exchange (ETDEWEB)

    Boyer, Martha L.; Sonneborn, George [Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); McQuinn, Kristen B. W.; Gehrz, Robert D.; Skillman, Evan [Minnesota Institute for Astrophysics, School of Physics and Astronomy, 116 Church Street SE, University of Minnesota, Minneapolis, MN 55455 (United States); Barmby, Pauline [Department of Physics and Astronomy, University of Western Ontario, London, ON N6A 3K7 (Canada); Bonanos, Alceste Z. [IAASARS, National Observatory of Athens, GR-15236 Penteli (Greece); Gordon, Karl D.; Meixner, Margaret [STScI, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Groenewegen, M. A. T. [Royal Observatory of Belgium, Ringlaan 3, B-1180 Brussels (Belgium); Lagadec, Eric [Laboratoire Lagrange, UMR7293, Univ. Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d' Azur, F-06300 Nice (France); Lennon, Daniel [ESA-European Space Astronomy Centre, Apdo. de Correo 78, E-28691 Villanueva de la Cañada, Madrid (Spain); Marengo, Massimo [Department of Physics and Astronomy, Iowa State University, Ames, IA 50011 (United States); McDonald, Iain; Zijlstra, Albert [Jodrell Bank Centre for Astrophysics, Alan Turing Building, University of Manchester, Manchester M13 9PL (United Kingdom); Sloan, G. C. [Astronomy Department, Cornell University, Ithaca, NY 14853-6801 (United States); Van Loon, Jacco Th., E-mail: martha.boyer@nasa.gov [Astrophysics Group, Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BG (United Kingdom)

    2015-02-10

    The DUSTiNGS survey (DUST in Nearby Galaxies with Spitzer) is a 3.6 and 4.5 μm imaging survey of 50 nearby dwarf galaxies designed to identify dust-producing asymptotic giant branch (AGB) stars and massive stars. Using two epochs, spaced approximately six months apart, we identify a total of 526 dusty variable AGB stars (sometimes called ''extreme'' or x-AGB stars; [3.6]-[4.5] > 0.1 mag). Of these, 111 are in galaxies with [Fe/H] < –1.5 and 12 are in galaxies with [Fe/H] < –2.0, making them the most metal-poor dust-producing AGB stars known. We compare these identifications to those in the literature and find that most are newly discovered large-amplitude variables, with the exception of ≈30 stars in NGC 185 and NGC 147, 1 star in IC 1613, and 1 star in Phoenix. The chemical abundances of the x-AGB variables are unknown, but the low metallicities suggest that they are more likely to be carbon-rich than oxygen-rich and comparisons with existing optical and near-IR photometry confirm that 70 of the x-AGB variables are confirmed or likely carbon stars. We see an increase in the pulsation amplitude with increased dust production, supporting previous studies suggesting that dust production and pulsation are linked. We find no strong evidence linking dust production with metallicity, indicating that dust can form in very metal-poor environments.

  8. Abundance patterns of the light neutron-capture elements in very and extremely metal-poor stars

    Science.gov (United States)

    Spite, F.; Spite, M.; Barbuy, B.; Bonifacio, P.; Caffau, E.; François, P.

    2018-03-01

    Aims: The abundance patterns of the neutron-capture elements in metal-poor stars provide a unique record of the nucleosynthesis products of the earlier massive primitive objects. Methods: We measured new abundances of so-called light neutron-capture of first peak elements using local thermodynamic equilibrium (LTE) 1D analysis; this analysis resulted in a sample of 11 very metal-poor stars, from [Fe/H] = -2.5 to [Fe/H] = -3.4, and one carbon-rich star, CS 22949-037 with [Fe/H] = -4.0. The abundances were compared to those observed in two classical metal-poor stars: the typical r-rich star CS 31082-001 ([Eu/Fe] > +1.0) and the r-poor star HD 122563 ([Eu/Fe] combination of at least two mechanisms: one that enriches the forming stars cloud homogeneously through the main r-process and leads to an element pattern similar to the r-rich stars, such as CS 31082-001; and another that forms mainly lighter, first peak elements. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 165.N-0276(A), (PI R.Cayrel).

  9. SEARCHES FOR METAL-POOR STARS FROM THE HAMBURG/ESO SURVEY USING THE CH G BAND

    Energy Technology Data Exchange (ETDEWEB)

    Placco, Vinicius M.; Rossi, Silvia [Departamento de Astronomia-Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Sao Paulo, SP 05508-090 (Brazil); Kennedy, Catherine R.; Beers, Timothy C.; Lee, Young Sun [Department of Physics and Astronomy and JINA (Joint Institute for Nuclear Astrophysics), Michigan State University, East Lansing, MI 48824 (United States); Christlieb, Norbert [Zentrum fuer Astronomie der Universitaet Heidelberg, Landessternwarte, Koenigstuhl 12, 69117 Heidelberg (Germany); Sivarani, Thirupathi [Indian Institute of Astrophysics, 2nd Block, Koramangala, Bangalore 560034 (India); Reimers, Dieter [Hamburger Sternwarte, Universitaet Hamburg, Gojenbergsweg 112, 21029 Hamburg (Germany); Wisotzki, Lutz, E-mail: vmplacco@astro.iag.usp.br [Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Potsdam (Germany)

    2011-12-15

    We describe a new method to search for metal-poor candidates from the Hamburg/ESO objective-prism survey (HES) based on identifying stars with apparently strong CH G-band strengths for their colors. The hypothesis we exploit is that large overabundances of carbon are common among metal-poor stars, as has been found by numerous studies over the past two decades. The selection was made by considering two line indices in the 4300 A region, applied directly to the low-resolution prism spectra. This work also extends a previously published method by adding bright sources to the sample. The spectra of these stars suffer from saturation effects, compromising the index calculations and leading to an undersampling of the brighter candidates. A simple numerical procedure, based on available photometry, was developed to correct the line indices and overcome this limitation. Visual inspection and classification of the spectra from the HES plates yielded a list of 5288 new metal-poor (and by selection, carbon-rich) candidates, which are presently being used as targets for medium-resolution spectroscopic follow-up. Estimates of the stellar atmospheric parameters, as well as carbon abundances, are now available for 117 of the first candidates, based on follow-up medium-resolution spectra obtained with the SOAR 4.1 m and Gemini 8 m telescopes. We demonstrate that our new method improves the metal-poor star fractions found by our pilot study by up to a factor of three in the same magnitude range, as compared with our pilot study based on only one CH G-band index. Our selection scheme obtained roughly a 40% success rate for identification of stars with [Fe/H] <-1.0; the primary contaminant is late-type stars with near-solar abundances and, often, emission line cores that filled in the Ca II K line on the prism spectrum. Because the selection is based on carbon, we greatly increase the numbers of known carbon-enhanced metal-poor stars from the HES with intermediate metallicities -2

  10. Searches for Metal-poor Stars from the Hamburg/ESO Survey Using the CH G Band

    Science.gov (United States)

    Placco, Vinicius M.; Kennedy, Catherine R.; Beers, Timothy C.; Christlieb, Norbert; Rossi, Silvia; Sivarani, Thirupathi; Lee, Young Sun; Reimers, Dieter; Wisotzki, Lutz

    2011-12-01

    We describe a new method to search for metal-poor candidates from the Hamburg/ESO objective-prism survey (HES) based on identifying stars with apparently strong CH G-band strengths for their colors. The hypothesis we exploit is that large overabundances of carbon are common among metal-poor stars, as has been found by numerous studies over the past two decades. The selection was made by considering two line indices in the 4300 Å region, applied directly to the low-resolution prism spectra. This work also extends a previously published method by adding bright sources to the sample. The spectra of these stars suffer from saturation effects, compromising the index calculations and leading to an undersampling of the brighter candidates. A simple numerical procedure, based on available photometry, was developed to correct the line indices and overcome this limitation. Visual inspection and classification of the spectra from the HES plates yielded a list of 5288 new metal-poor (and by selection, carbon-rich) candidates, which are presently being used as targets for medium-resolution spectroscopic follow-up. Estimates of the stellar atmospheric parameters, as well as carbon abundances, are now available for 117 of the first candidates, based on follow-up medium-resolution spectra obtained with the SOAR 4.1 m and Gemini 8 m telescopes. We demonstrate that our new method improves the metal-poor star fractions found by our pilot study by up to a factor of three in the same magnitude range, as compared with our pilot study based on only one CH G-band index. Our selection scheme obtained roughly a 40% success rate for identification of stars with [Fe/H] contaminant is late-type stars with near-solar abundances and, often, emission line cores that filled in the Ca II K line on the prism spectrum. Because the selection is based on carbon, we greatly increase the numbers of known carbon-enhanced metal-poor stars from the HES with intermediate metallicities -2.0 < [Fe/H] <-1

  11. The HARPS search for southern extra-solar planets. XL. Searching for Neptunes around metal-poor stars

    Science.gov (United States)

    Faria, J. P.; Santos, N. C.; Figueira, P.; Mortier, A.; Dumusque, X.; Boisse, I.; Lo Curto, G.; Lovis, C.; Mayor, M.; Melo, C.; Pepe, F.; Queloz, D.; Santerne, A.; Ségransan, D.; Sousa, S. G.; Sozzetti, A.; Udry, S.

    2016-05-01

    Context. As a probe of the metallicity of proto-planetary disks, stellar metallicity is an important ingredient for giant planet formation, most likely through its effect on the timescales in which rocky or icy planet cores can form. Giant planets have been found to be more frequent around metal-rich stars, in agreement with predictions based on the core-accretion theory. In the metal-poor regime, however, the frequency of planets, especially low-mass planets, and the way it depends on metallicity are still largely unknown. Aims: As part of a planet search programme focused on metal-poor stars, we study the targets from this survey that were observed with HARPS on more than 75 nights. The main goals are to assess the presence of low-mass planets and provide a first estimate of the frequency of Neptunes and super-Earths around metal-poor stars. Methods: We performed a systematic search for planetary companions, both by analysing the periodograms of the radial-velocities and by comparing, in a statistically meaningful way, models with an increasing number of Keplerians. Results: A first constraint on the frequency of planets in our metal-poor sample is calculated considering the previous detection (in our sample) of a Neptune-sized planet around HD 175607 and one candidate planet (with an orbital period of 68.42 d and minimum mass Mpsini = 11.14 ± 2.47 M⊕) for HD 87838, announced in the present study. This frequency is determined to be close to 13% and is compared with results for solar-metallicity stars. Based on observations collected at ESO facilities under programs 082.C-0212, 085.C-0063, 086.C-0284, and 190.C-0027 (with the HARPS spectrograph at the ESO 3.6-m telescope, La Silla-Paranal Observatory).

  12. The Little Cub: Discovery of an Extremely Metal-poor Star-forming Galaxy in the Local Universe

    Energy Technology Data Exchange (ETDEWEB)

    Hsyu, Tiffany; Prochaska, J. Xavier; Bolte, Michael [Department of Astronomy and Astrophysics, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95060 (United States); Cooke, Ryan J. [Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom)

    2017-08-20

    We report the discovery of the Little Cub, an extremely metal-poor star-forming galaxy in the local universe, found in the constellation Ursa Major (a.k.a. the Great Bear). We first identified the Little Cub as a candidate metal-poor galaxy based on its Sloan Digital Sky Survey photometric colors, combined with spectroscopy using the Kast spectrograph on the Shane 3 m telescope at Lick Observatory. In this Letter, we present high-quality spectroscopic data taken with the Low Resolution Imaging Spectrometer at Keck Observatory, which confirm the extremely metal-poor nature of this galaxy. Based on the weak [O iii] λ 4363 Å emission line, we estimate a direct oxygen abundance of 12 + log(O/H) = 7.13 ± 0.08, making the Little Cub one of the lowest-metallicity star-forming galaxies currently known in the local universe. The Little Cub appears to be a companion of the spiral galaxy NGC 3359 and shows evidence of gas stripping. We may therefore be witnessing the quenching of a near-pristine galaxy as it makes its first passage about a Milky Way–like galaxy.

  13. Carbon-enhanced Metal-poor Stars in SDSS/SEGUE. I. Carbon Abundance Estimation and Frequency of CEMP Stars

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Young Sun [NMSU, Las Cruces; Beers, Timothy C. [Michigan State U., JINA; Masseron, Thomas [Brussels U.; Plez, Bertrand [U. Montpellier 2, LUPM; Rockosi, Constance M. [Lick Observ.; Sobeck, Jennifer [Chicago U.; Yanny, Brian [Fermilab; Lucatello, Sara [Padua Observ.; Sivarani, Thirupathi [Bangalore, Indian Inst. Astrophys.; Placco, Vinicius M. [Sao Paulo U., IAG; Carollo, Daniela [Macquarie U.

    2013-10-17

    We describe a method for the determination of stellar [C/Fe] abundance ratios using low-resolution (R = 2000) stellar spectra from the SDSS and SEGUE. By means of a star-by-star comparison with a set of SDSS/SEGUE spectra with available estimates of [C/Fe] based on published high-resolution analyses, we demonstrate that we can measure [C/Fe] from SDSS/SEGUE spectra with S/N > 15 to a precision better than 0.35 dex. Using the measured carbon-to-iron abundance ratios obtained by this technique, we derive the frequency of carbon-enhanced stars ([C/Fe] > +0.7) as a function of [Fe/H], for both the SDSS/SEGUE stars and other samples from the literature. We find that the differential frequency slowly rises from almost zero to about 14% at [Fe/H] ~ -2.4, followed by a sudden increase, by about a factor of three, to 39% from [Fe/H] ~ -2.4 to [Fe/H] ~ -3.7. We also examine how the cumulative frequency of CEMP stars varies across different luminosity classes. The giant sample exhibits a cumulative CEMP frequency of 32% for [Fe/H] < -2.5, 31% for [Fe/H] < -3.0, and 33% for [Fe/H] < -3.5. For the main-sequence turnoff stars, we obtain a lower cumulative CEMP frequency, around 10% for [Fe/H] < -2.5. The dwarf population displays a large change in the cumulative frequency for CEMP stars below [Fe/H] = -2.5, jumping from 15% for [Fe/H] < -2.5 to about 75% for [Fe/H] < -3.0. When we impose a restriction with respect to distance from the Galactic mid-plane (|Z| < 5 kpc), the frequency of the CEMP giants does not increase at low metallicity ([Fe/H] < -2.5), but rather, decreases, due to the dilution of C-rich material in stars that have undergone mixing with CNO-processed material from their interiors. The frequency of CEMP stars near the main-sequence turnoff, which are not expected to have experienced mixing, increases for [Fe/H] < -3.0. [abridged

  14. Accurate effective temperatures of the metal-poor benchmark stars HD 140283, HD 122563, and HD 103095 from CHARA interferometry

    Science.gov (United States)

    Karovicova, I.; White, T. R.; Nordlander, T.; Lind, K.; Casagrande, L.; Ireland, M. J.; Huber, D.; Creevey, O.; Mourard, D.; Schaefer, G. H.; Gilmore, G.; Chiavassa, A.; Wittkowski, M.; Jofré, P.; Heiter, U.; Thévenin, F.; Asplund, M.

    2018-03-01

    Large stellar surveys of the Milky Way require validation with reference to a set of `benchmark' stars whose fundamental properties are well determined. For metal-poor benchmark stars, disagreement between spectroscopic and interferometric effective temperatures has called the reliability of the temperature scale into question. We present new interferometric measurements of three metal-poor benchmark stars, HD 140283, HD 122563, and HD 103095, from which we determine their effective temperatures. The angular sizes of all the stars were determined from observations with the PAVO beam combiner at visible wavelengths at the CHARA array, with additional observations of HD 103095 made with the VEGA instrument, also at the CHARA array. Together with photometrically derived bolometric fluxes, the angular diameters give a direct measurement of the effective temperature. For HD 140283, we find θLD = 0.324 ± 0.005 mas, Teff = 5787 ± 48 K; for HD 122563, θLD = 0.926 ± 0.011 mas, Teff = 4636 ± 37 K; and for HD 103095, θLD = 0.595 ± 0.007 mas, Teff = 5140 ± 49 K. Our temperatures for HD 140283 and HD 103095 are hotter than the previous interferometric measurements by 253 and 322 K, respectively. We find good agreement between our temperatures and recent spectroscopic and photometric estimates. We conclude some previous interferometric measurements have been affected by systematic uncertainties larger than their quoted errors.

  15. The Physical Nature of Subdwarf A Stars: White Dwarf Impostors

    Science.gov (United States)

    Brown, Warren R.; Kilic, Mukremin; Gianninas, A.

    2017-04-01

    We address the physical nature of subdwarf A-type (sdA) stars and their possible link to extremely low mass (ELM) white dwarfs (WDs). The two classes of objects are confused in low-resolution spectroscopy. However, colors and proper motions indicate that sdA stars are cooler and more luminous, and thus larger in radius, than published ELM WDs. We demonstrate that surface gravities derived from pure hydrogen models suffer a systematic ˜1 dex error for sdA stars, likely explained by metal line blanketing below 9000 K. A detailed study of five eclipsing binaries with radial velocity orbital solutions and infrared excess establishes that these sdA stars are metal-poor ≃1.2 M ⊙ main sequence stars with ≃0.8 M ⊙ companions. While WDs must exist at sdA temperatures, only ˜1% of a magnitude-limited sdA sample should be ELM WDs. We conclude that the majority of sdA stars are metal-poor A-F type stars in the halo, and that recently discovered pulsating ELM WD-like stars with no obvious radial velocity variations may be SX Phe variables, not pulsating WDs.

  16. The Physical Nature of Subdwarf A Stars: White Dwarf Impostors

    Energy Technology Data Exchange (ETDEWEB)

    Brown, Warren R. [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Kilic, Mukremin; Gianninas, A., E-mail: wbrown@cfa.harvard.edu, E-mail: kilic@ou.edu, E-mail: alexg@nhn.ou.edu [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks Street, Norman, OK, 73019 (United States)

    2017-04-10

    We address the physical nature of subdwarf A-type (sdA) stars and their possible link to extremely low mass (ELM) white dwarfs (WDs). The two classes of objects are confused in low-resolution spectroscopy. However, colors and proper motions indicate that sdA stars are cooler and more luminous, and thus larger in radius, than published ELM WDs. We demonstrate that surface gravities derived from pure hydrogen models suffer a systematic ∼1 dex error for sdA stars, likely explained by metal line blanketing below 9000 K. A detailed study of five eclipsing binaries with radial velocity orbital solutions and infrared excess establishes that these sdA stars are metal-poor ≃1.2 M {sub ⊙} main sequence stars with ≃0.8 M {sub ⊙} companions. While WDs must exist at sdA temperatures, only ∼1% of a magnitude-limited sdA sample should be ELM WDs. We conclude that the majority of sdA stars are metal-poor A–F type stars in the halo, and that recently discovered pulsating ELM WD-like stars with no obvious radial velocity variations may be SX Phe variables, not pulsating WDs.

  17. Ultra-metal-poor Stars: Spectroscopic Determination of Stellar Atmospheric Parameters Using Iron Non-LTE Line Abundances

    Science.gov (United States)

    Ezzeddine, Rana; Frebel, Anna; Plez, Bertrand

    2017-10-01

    We present new ultra-metal-poor stars parameters with [Fe/H] LTE in their atmospheric parameters and show that they can grow up to ˜1.00 dex in [Fe/H], ˜150 K in {T}{eff} and ˜0.5 dex in log g toward the lowest metallicities. Accurate NLTE atmospheric stellar parameters, in particular [Fe/H] being significantly higher, are the first step to eventually providing full NLTE abundance patterns that can be compared with Population III supernova nucleosynthesis yields to derive properties of the first stars. Overall, this maximizes the potential of these likely second-generation stars to investigate the early universe and how the chemical elements were formed.

  18. THE CHEMICAL COMPOSITIONS OF VERY METAL-POOR STARS HD 122563 AND HD 140283: A VIEW FROM THE INFRARED

    Energy Technology Data Exchange (ETDEWEB)

    Afşar, Melike [Department of Astronomy and Space Sciences, Ege University, 35100 Bornova, İzmir (Turkey); Sneden, Christopher; Kim, Hwihyun, E-mail: melike.afsar@ege.edu.tr, E-mail: chris@astro.as.utexas.edu, E-mail: dtj@astro.as.utexas.edu, E-mail: hwihyun@astro.as.utexas.edu, E-mail: mace@astro.as.utexas.edu, E-mail: afrebel@mit.edu [Department of Astronomy and McDonald Observatory, The University of Texas, Austin, TX 78712 (United States); and others

    2016-03-10

    From high resolution (R ≃ 45,000), high signal-to-noise ratio (S/N > 400) spectra gathered with the Immersion Grating Infrared Spectrograph (IGRINS) in the H and K photometric bands, we have derived elemental abundances of two bright, well-known metal-poor halo stars: the red giant HD 122563 and the subgiant HD 140283. Since these stars have metallicities approaching [Fe/H] = −3, their absorption features are generally very weak. Neutral-species lines of Mg, Si, S and Ca are detectable, as well as those of the light odd-Z elements Na and Al. The derived IR-based abundances agree with those obtained from optical-wavelength spectra. For Mg and Si the abundances from the infrared transitions are improvements to those derived from shorter wavelength data. Many useful OH and CO lines can be detected in the IGRINS HD 122563 spectrum, from which derived O and C abundances are consistent to those obtained from the traditional [O i] and CH features. IGRINS high resolutions H- and K-band spectroscopy offers promising ways to determine more reliable abundances for additional metal-poor stars whose optical features are either not detectable, or too weak, or are based on lines with analytical difficulties.

  19. First stars X. The nature of three unevolved carbon-enhanced metal-poor stars

    DEFF Research Database (Denmark)

    Sivarani, T.; Beers, T.C.; Bonifacio, P.

    2006-01-01

    Stars: abundances, stars: population II, Galaxy: abundances, stars: AGB and post-AGB Udgivelsesdato: Nov.......Stars: abundances, stars: population II, Galaxy: abundances, stars: AGB and post-AGB Udgivelsesdato: Nov....

  20. VLT/UVES abundances of individual stars in the Fornax dwarf spheroidal globular clusters

    NARCIS (Netherlands)

    Letarte, B.; Hill, V.; Jablonka, P.; Tolstoy, E.; Randich, S; Pasquini, L

    2006-01-01

    We present high resolution abundance analysis of nine stars belonging to three of the five globular clusters (GCs) of the Fornax dwarf galaxy. The spectra were taken with UVES at a resolution of 43 000. We find them to be slightly more metal-poor than what was previously calculated with other

  1. From strange stars to strange dwarfs

    International Nuclear Information System (INIS)

    Glendenning, N.K.; Kettner, C.; Weber, F.

    1995-01-01

    We determine all possible equilibrium sequences of compact strange-matter stars with nuclear crusts, which range from massive strange stars to strange white dwarf endash like objects (strange dwarfs). The properties of such stars are compared with those of their nonstrange counterparts emdash neutron stars and ordinary white dwarfs. The main emphasis of this paper is on strange dwarfs, which we divide into two distinct categories. The first one consists of a core of strange matter enveloped within ordinary white dwarf matter. Such stars are hydrostatically stable with or without the strange core and are therefore referred to as open-quote open-quote trivial close-quote close-quote strange dwarfs. This is different for the second category which forms an entirely new class of dwarf stars that contain nuclear material up to 4x10 4 times denser than in ordinary white dwarfs of average mass, M∼0.6 M circle-dot , and still about 400 times denser than in the densest white dwarfs. The entire family of such dwarfs, denoted dense strange dwarfs, owes its hydrostatic stability to the strange core. A striking features of strange dwarfs is that the entire sequence from the maximum-mass strange star to the maximum-mass strange dwarf is stable to radial oscillations. The minimum-mass star is only conditionally stable, and the sequences on both sides are stable. Such a stable, continuous connection does not exist between ordinary white dwarfs and neutron stars, which are known to be separated by a broad range of unstable stars. We find an expansive range of very low mass (planetary-like) strange-matter stars (masses even below 10 -4 M circle-dot are possible) that arise as natural dark-matter candidates, which if abundant enough in our Galaxy, should be seen in the gravitational microlensing searches that are presently being performed. copyright 1995 The American Astronomical Society

  2. Star Formation Histories of Nearby Dwarf Galaxies

    OpenAIRE

    Grebel, Eva K.

    2000-01-01

    Properties of nearby dwarf galaxies are briefly discussed. Dwarf galaxies vary widely in their star formation histories, the ages of their subpopulations, and in their enrichment history. Furthermore, many dwarf galaxies show evidence for spatial variations in their star formation history; often in the form of very extended old populations and radial gradients in age and metallicity. Determining factors in dwarf galaxy evolution appear to be both galaxy mass and environment. We may be observi...

  3. Massive stars in the Sagittarius Dwarf Irregular Galaxy

    Science.gov (United States)

    Garcia, Miriam

    2018-02-01

    Low metallicity massive stars hold the key to interpret numerous processes in the past Universe including re-ionization, starburst galaxies, high-redshift supernovae, and γ-ray bursts. The Sagittarius Dwarf Irregular Galaxy [SagDIG, 12+log(O/H) = 7.37] represents an important landmark in the quest for analogues accessible with 10-m class telescopes. This Letter presents low-resolution spectroscopy executed with the Gran Telescopio Canarias that confirms that SagDIG hosts massive stars. The observations unveiled three OBA-type stars and one red supergiant candidate. Pending confirmation from high-resolution follow-up studies, these could be the most metal-poor massive stars of the Local Group.

  4. Something borrowed, something blue: The nature of blue metal-poor stars inferred from their colours and chemical abundances

    Science.gov (United States)

    Hansen, C. J.; Jofré, P.; Koch, A.; McWilliam, A.; Sneden, C. S.

    2017-02-01

    Blue metal-poor (BMP) stars are main sequence stars that appear bluer and more luminous than normal turnoff stars. They were originally singled out by using B-V and U-B colour cuts.Early studies found that a larger fraction of field BMP stars were binaries compared to normal halo stars. Thus, BMP stars are ideal field blue straggler candidates for investigating internal stellar evolution processes and binary interaction. In particular, the presence or depletion in lithium in their spectra is a powerful indicator of their origin. They are either old, halo blue stragglers experiencing internal mixing processes or mass transfer (Li-depletion), or intermediate-age, single stars of possibly extragalactic origin (2.2 dex halo plateau Li). However, we note that internal mixing processes can lead to an increased level of Li. Hence, this study combines photometry and spectroscopy to unveil the origin of various BMP stars. We first show how to separate binaries from young blue stars using photometry, metallicity and lithium. Using a sample of 80 BMP stars (T > 6300 K), we find that 97% of the BMP binaries have V-Ks0 chemical analysis using new high-resolution and high signal-to-noise spectra. Based on their radial velocities, Li, α and s- and r-process abundances we show that BPS CS22874-042 is a single star (A(Li) = 2.38 ± 0.10 dex) while with A(Li)= 2.23 ± 0.07 dex CD-48 2445 is a binary, contrary to earlier findings. Our analysis emphasises that field blue stragglers can be segregated from single metal-poor stars, using (V-Ks) colours with a fraction of single stars polluting the binary sample, but not vice versa. These two groups can only be properly separated by using information from stellar spectra, illustrating the need for accurate and precise stellar parameters and high-resolution, high-S/N spectra in order to fully understand and classify this intriguing class of stars. Our high-resolution spectrum analysis confirms the findings from the colour cuts and shows

  5. Spectroscopic Comparison of Metal-rich RRab Stars of the Galactic Field with their Metal-poor Counterparts

    Energy Technology Data Exchange (ETDEWEB)

    Chadid, Merieme [Université Nice Sophia–Antipolis, Observatoire de la Côte dAzur, UMR 7293, Parc Valrose, F-06108, Nice Cedex 02 (France); Sneden, Christopher [Department of Astronomy and McDonald Observatory, The University of Texas, Austin, TX 78712 (United States); Preston, George W., E-mail: chadid@unice.fr, E-mail: chris@verdi.as.utexas.edu, E-mail: gwp@obs.carnegiescience.edu [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)

    2017-02-01

    We investigate atmospheric properties of 35 stable RRab stars that possess the full ranges of period, light amplitude, and metal abundance found in Galactic RR Lyrae stars. Our results are derived from several thousand echelle spectra obtained over several years with the du Pont telescope of Las Campanas Observatory. Radial velocities of metal lines and the H α line were used to construct curves of radial velocity versus pulsation phase. From these we estimated radial velocity amplitudes for metal lines (formed near the photosphere) and H α Doppler cores (formed at small optical depths). We also measured H α emission fluxes when they appear during primary light rises. Spectra shifted to rest wavelengths, binned into small phase intervals, and co-added were used to perform model atmospheric and abundance analyses. The derived metallicities and those of some previous spectroscopic surveys were combined to produce a new calibration of the Layden abundance scale. We then divided our RRab sample into metal-rich (disk) and metal-poor (halo) groups at [Fe/H] = −1.0; the atmospheres of RRab families, so defined, differ with respect to (a) peak strength of H α emission flux, (b) H α radial velocity amplitude, (c) dynamical gravity, (d) stellar radius variation, (e) secondary acceleration during the photometric bump that precedes minimum light, and (f) duration of H α line-doubling. We also detected H α line-doubling during the “bump” in the metal-poor family, but not in the metal-rich one. Although all RRab probably are core helium-burning horizontal branch stars, the metal-rich group appears to be a species sui generis.

  6. Identification Of (Bright) Carbon-Enhanced Metal-Poor Stars With J-Plus Photometry

    Science.gov (United States)

    Placco, Vinicius

    2017-10-01

    The chemical composition of our bodies, the Earth, the Sun, and the Universe is complex, and the end result of the formation and evolution of numerous stellar generations that contributed all of the elements heavier than helium. One way to understand the possible pathways that led to such complexity is to determine the chemical abundance patterns of ancient low-metallicity stars in the Halo of our Galaxy. However, it is impossible to observe each of the 100 billion stars in the Milky Way in sufficient detail to assess its chemical composition. Hence, astronomers have developed efficient ways to pre-select the most interesting stars for further high-resolution follow-up, based on the understanding that the colors of stars in specific regions of the optical spectrum are affected in predictable ways by changes in their chemical composition. I will discuss the importance of the J-PLUS photometry in selecting low-metallicity and carbon-enhanced stars, using its 12 magnitudes, which will fully exploit this approach, in a manner superior to all previous such efforts.

  7. Metallicity inhomogeneities in local star-forming galaxies as sign of recent metal-poor gas accretion

    OpenAIRE

    Almeida, J. Sanchez; Morales-Luis, A. B.; Munoz-Tunon, C.; Elmegreen, D. M.; Elmegreen, B. G.; Mendez-Abreu, J.

    2014-01-01

    This work was partly funded by the Spanish Ministry for Science, project AYA 2010-21887-C04-04. J.M.A. acknowledges support from the European Research Council Starting Grant (SEDmorph; P.I. V. Wild). We measure the oxygen metallicity of the ionized gas along the major axis of seven dwarf star-forming galaxies. Two of them, SDSSJ1647+21 and SDSSJ2238+14, show ≃0.5 dex metallicity decrements in inner regions with enhanced star formation activity. This behavior is similar to the metallicity d...

  8. VizieR Online Data Catalog: Very metal poor stars in MW halo (Mashonkina+, 2017)

    Science.gov (United States)

    Mashonkina, L.; Jablonka, P.; Sitnova, T.; Pakhomov, Yu; North, P.

    2017-10-01

    Tables 3 and 4 from the article are presented. They include the LTE and NLTE abundances from individual lines and average abundances of the investigated stars in the dSphs Sculptor (Scl), Ursa Minor (UMi), Fornax (Fnx), Sextans (Sex), Bootes I (Boo), UMa II, and Leo IV and the Milky Way (MW) halo. (3 data files).

  9. Stars at Low Metallicity in Dwarf Galaxies

    NARCIS (Netherlands)

    Tolstoy, Eline; Battaglia, Giuseppina; Cole, Andrew; Hunt, LK; Madden, S; Schneider, R

    2008-01-01

    Dwarf galaxies offer an opportunity to understand the properties of low metallicity star formation both today and at the earliest times at the, epoch of the formation of the first stars. Here we concentrate on two galaxies in the Local Group: the dwarf irregular galaxy Leo A, which has been the

  10. New Detections of Arsenic, Selenium, and Other Heavy Elements in Two Metal-poor Stars

    Science.gov (United States)

    Roederer, Ian U.; Schatz, Hendrik; Lawler, James E.; Beers, Timothy C.; Cowan, John J.; Frebel, Anna; Ivans, Inese I.; Sneden, Christopher; Sobeck, Jennifer S.

    2014-08-01

    We use the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to obtain new high-quality spectra covering the 1900 formed in local thermodynamic equilibrium in these stars. The [Zn/Fe], [Mo/Fe], [Cd/Fe], and [Os/Fe] ratios are also derived from neutral and ionized species, and each ratio pair agrees within the mutual uncertainties, which range from 0.15 to 0.52 dex. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs GO-12268 and GO-12976.

  11. Improved Cr II log(gf)s and Cr Abundances in the Photospheres of the Sun and Metal-Poor Star HD 84937

    Science.gov (United States)

    Lawler, James E.; Sneden, Chris; Nave, Gillian; Den Hartog, Elizabeth; Emrahoglu, Nuri; Cowan, John J.

    2017-01-01

    New laser induced fluorescence (LIF) data for eight levels of singly ionized chromium (Cr) and emission branching fraction (BF) measurements for 183 lines of the second spectrum of chromium (Cr II) are reported. A goal of this study is to reconcile Solar and stellar Cr abundance values based on Cr I and Cr II lines. Analyses of eighteen spectra from three Fourier Transform Spectrometers supplemented with ultraviolet spectra from a high resolution echelle spectrometer yield the BF measurements. Radiative lifetimes from LIF measurements are used to convert the BFs to absolute transition probabilities. These new laboratory data are applied to determine the Cr abundance log eps in the Sun and metal-poor star HD 84937. The mean result in the Sun is = 5.624 ± 0.009 compared to = 5.644 ± 0.006 on a scale with the H abundance log eps(H) = 12. Similarily the photosphere of HD 84937 is found to be in Saha balance with = 3.417 ± 0.006 and 0 eV) > = 3.374 ± 0.011 for this dwarf star. The resonance (E.P. = 0 eV) lines of Cr I reveal overionization of the ground level of neutral Cr. We find a correlation of Cr with the iron-peak element Ti, suggesting an associated or related nucleosynthetic production. Four iron-peak elements (Cr along with Ti, V and Sc) appear to have a similar (or correlated) production history - other iron-peak elements appear not to be associated with Cr.This work is supported in part by NASA grant NNX16AE96G (J.E.L.), by NSF grant AST-1516182 (J.E.L. & E.D.H.), by NASA interagency agreement NNH10AN381 (G.N.), and NSF grant AST-1211585 (C.S.). Postdoctoral research support for N. E. is from the Technological and Scientific Research Council of Turkey (TUBITAK).

  12. The role of binaries in the enrichment of the early Galactic halo. II. Carbon-enhanced metal-poor stars: CEMP-no stars

    Science.gov (United States)

    Hansen, T. T.; Andersen, J.; Nordström, B.; Beers, T. C.; Placco, V. M.; Yoon, J.; Buchhave, L. A.

    2016-02-01

    Context. The detailed composition of most metal-poor halo stars has been found to be very uniform. However, a fraction of 20-70% (increasing with decreasing metallicity) exhibit dramatic enhancements in their abundances of carbon; these are the so-called carbon-enhanced metal-poor (CEMP) stars. A key question for Galactic chemical evolution models is whether this non-standard composition reflects that of the stellar natal clouds or is due to local, post-birth mass transfer of chemically processed material from a binary companion; CEMP stars should then all be members of binary systems. Aims: Our aim is to determine the frequency and orbital parameters of binaries among CEMP stars with and without over-abundances of neutron-capture elements - CEMP-s and CEMP-no stars, respectively - as a test of this local mass-transfer scenario. This paper discusses a sample of 24 CEMP-no stars, while a subsequent paper will consider a similar sample of CEMP-s stars. Methods: High-resolution, low S/N spectra of the stars were obtained at roughly monthly intervals over a time span of up to eight years with the FIES spectrograph at the Nordic Optical Telescope. Radial velocities of ~100 m s-1 precision were determined by cross-correlation after each observing night, allowing immediate, systematic follow-up of any variable object. Results: Most programme stars exhibit no statistically significant radial-velocity variation over this period and appear to be single, while four are found to be binaries with orbital periods of 300-2000 days and normal eccentricity; the binary frequency for the sample is 17 ± 9%. The single stars mostly belong to the recently identified low-C band, while the binaries have higher absolute carbon abundances. Conclusions: We conclude that the nucleosynthetic process responsible for the strong carbon excess in these ancient stars is unrelated to their binary status; the carbon was imprinted on their natal molecular clouds in the early Galactic interstellar

  13. METAL-POOR STARS OBSERVED WITH THE MAGELLAN TELESCOPE. I. CONSTRAINTS ON PROGENITOR MASS AND METALLICITY OF AGB STARS UNDERGOING s-PROCESS NUCLEOSYNTHESIS

    Energy Technology Data Exchange (ETDEWEB)

    Placco, Vinicius M.; Rossi, Silvia [Departamento de Astronomia-Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Sao Paulo, SP 05508-900 (Brazil); Frebel, Anna [Massachusetts Institute of Technology and Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Beers, Timothy C. [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States); Karakas, Amanda I.; Kennedy, Catherine R. [Research School of Astronomy and Astrophysics, The Australian National University, Cotter Road, Weston, ACT 2611 (Australia); Christlieb, Norbert [Zentrum fuer Astronomie der Universitaet Heidelberg, Landessternwarte, Koenigstuhl 12, D-69117 Heidelberg (Germany); Stancliffe, Richard J. [Argelander-Institut fuer Astronomie der Universitaet Bonn, Auf dem Huegel 71, D-53121 Bonn (Germany)

    2013-06-20

    We present a comprehensive abundance analysis of two newly discovered carbon-enhanced metal-poor (CEMP) stars. HE 2138-3336 is a s-process-rich star with [Fe/H] = -2.79, and has the highest [Pb/Fe] abundance ratio measured thus far, if non-local thermodynamic equilibrium corrections are included ([Pb/Fe] = +3.84). HE 2258-6358, with [Fe/H] = -2.67, exhibits enrichments in both s- and r-process elements. These stars were selected from a sample of candidate metal-poor stars from the Hamburg/ESO objective-prism survey, and followed up with medium-resolution (R {approx} 2000) spectroscopy with GEMINI/GMOS. We report here on derived abundances (or limits) for a total of 34 elements in each star, based on high-resolution (R {approx} 30, 000) spectroscopy obtained with Magellan-Clay/MIKE. Our results are compared to predictions from new theoretical asymptotic giant branch (AGB) nucleosynthesis models of 1.3 M{sub Sun} with [Fe/H] = -2.5 and -2.8, as well as to a set of AGB models of 1.0 to 6.0 M{sub Sun} at [Fe/H] = -2.3. The agreement with the model predictions suggests that the neutron-capture material in HE 2138-3336 originated from mass transfer from a binary companion star that previously went through the AGB phase, whereas for HE 2258-6358, an additional process has to be taken into account to explain its abundance pattern. We find that a narrow range of progenitor masses (1.0 {<=} M(M{sub Sun }) {<=} 1.3) and metallicities (-2.8 {<=} [Fe/H] {<=}-2.5) yield the best agreement with our observed elemental abundance patterns.

  14. Evidence for a vanishing 6Li/7Li isotopic signature in the metal-poor halo star HD84937

    DEFF Research Database (Denmark)

    Lind, K.; Asplund, M.; Collet, Remo

    2012-01-01

    The claimed detections of 6Li in the atmospheres of some metal-poor halo stars have lead to speculative additions to the standard model of Big Bang nucleosynthesis and the early Universe, as the inferred abundances cannot be explained by Galactic cosmic ray production. A prominent example of a so...

  15. THE EATING HABITS OF MILKY WAY-MASS HALOS: DESTROYED DWARF SATELLITES AND THE METALLICITY DISTRIBUTION OF ACCRETED STARS

    International Nuclear Information System (INIS)

    Deason, Alis J.; Mao, Yao-Yuan; Wechsler, Risa H.

    2016-01-01

    We study the mass spectrum of destroyed dwarfs that contribute to the accreted stellar mass of Milky Way (MW)-mass (M vir  ∼ 10 12.1 M ⊙ ) halos using a suite of 45 zoom-in dissipationless simulations. Empirical models are employed to relate (peak) subhalo mass to dwarf stellar mass, and we use constraints from z = 0 observations and hydrodynamical simulations to estimate the metallicity distribution of the accreted stellar material. The dominant contributors to the accreted stellar mass are relatively massive dwarfs with M star  ∼ 10 8 –10 10 M ⊙ . Halos with more quiescent accretion histories tend to have lower mass progenitors (10 8 –10 9 M ⊙ ), and lower overall accreted stellar masses. Ultra-faint mass (M star  < 10 5 M ⊙ ) dwarfs contribute a negligible amount (≪1%) to the accreted stellar mass and, despite having low average metallicities, supply a small fraction (∼2%–5%) of the very metal-poor stars with [Fe/H] < −2. Dwarfs with masses 10 5  < M star /M ⊙  < 10 8 provide a substantial amount of the very metal-poor stellar material (∼40%–80%), and even relatively metal-rich dwarfs with M star  > 10 8 M ⊙ can contribute a considerable fraction (∼20%–60%) of metal-poor stars if their metallicity distributions have significant metal-poor tails. Finally, we find that the generic assumption of a quiescent assembly history for the MW halo seems to be in tension with the mass spectrum of its surviving dwarfs. We suggest that the MW could be a “transient fossil”; a quiescent halo with a recent accretion event(s) that disguises the preceding formation history of the halo

  16. Metal-Poor, Strongly Star-Forming Galaxies in the DEEP2 Survey: The Relationship Between Stellar Mass, Temperature-Based Metallicity, and Star Formation Rate

    Science.gov (United States)

    Ly, Chun; Rigby, Jane R.; Cooper, Michael; Yan, Renbin

    2015-01-01

    We report on the discovery of 28 redshift (z) approximately equal to 0.8 metal-poor galaxies in DEEP2. These galaxies were selected for their detection of the weak [O (sub III)] lambda 4363 emission line, which provides a "direct" measure of the gas-phase metallicity. A primary goal for identifying these rare galaxies is to examine whether the fundamental metallicity relation (FMR) between stellar mass, gas metallicity, and star formation rate (SFR) holds for low stellar mass and high SFR galaxies. The FMR suggests that higher SFR galaxies have lower metallicity (at fixed stellar mass). To test this trend, we combine spectroscopic measurements of metallicity and dust-corrected SFR with stellar mass estimates from modeling the optical photometry. We find that these galaxies are 1.05 plus or minus 0.61 dex above the redshift (z) approximately 1 stellar mass-SFR relation and 0.23 plus or minus 0.23 dex below the local mass-metallicity relation. Relative to the FMR, the latter offset is reduced to 0.01 dex, but significant dispersion remains dex with 0.16 dex due to measurement uncertainties). This dispersion suggests that gas accretion, star formation, and chemical enrichment have not reached equilibrium in these galaxies. This is evident by their short stellar mass doubling timescale of approximately equal to 100 (sup plus 310) (sub minus 75) million years which suggests stochastic star formation. Combining our sample with other redshift (z) of approximately 1 metal-poor galaxies, we find a weak positive SFR-metallicity dependence (at fixed stellar mass) that is significant at 94.4 percent confidence. We interpret this positive correlation as recent star formation that has enriched the gas but has not had time to drive the metal-enriched gas out with feedback mechanisms.

  17. An overview of white dwarf stars

    Directory of Open Access Journals (Sweden)

    Charpinet S.

    2013-03-01

    Full Text Available We present a brief summary of what is currently known about white dwarf stars, with an emphasis on their evolutionary and internal properties. As is well known, white dwarfs represent the end products of stellar evolution for the vast majority of stars and, as such, bear the signatures of past events (such as mass loss, mixing phases, loss and redistribution of angular momentum, and thermonuclear burning that are of essential importance in the evolution of stars in general. In addition, white dwarf stars represent ideal testbeds for our understanding of matter under extreme conditions, and work on their constitutive physics (neutrino production rates, conductive and radiative opacities, interior liquid/solid equations of state, partially ionized and partially degenerate envelope equations of state, diffusion coefficients, line broadening mechanisms is still being actively pursued. Given a set of constitutive physics, cooling white dwarfs can be used advantageously as cosmochronometers. Moreover, the field has been blessed by the existence of four distinct families of pulsating white dwarfs, each mapping a different evolutionary phase, and this allows the application of the asteroseismological method to probe and test their internal structure and evolutionary state. We set the stage for the reviews that follow on cooling white dwarfs as cosmochronometers and physics laboratories, as well as on the properties of pulsating white dwarfs and the asteroseismological results that can be inferred.

  18. EXTREMELY METAL-POOR GALAXIES: THE ENVIRONMENT

    Energy Technology Data Exchange (ETDEWEB)

    Filho, M. E. [Universidad de Las Palmas de Gran Canaria–Universidad de La Laguna, CIE Canarias: Tri-Continental Atlantic Campus, Canary Islands (Spain); Almeida, J. Sánchez; Muñoz-Tuñón, C. [Instituto Astrofísica de Canarias, E-38200 La Laguna, Tenerife (Spain); Nuza, S. E.; Kitaura, F.; Heß, S., E-mail: mfilho@astro.up.pt [Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam (Germany)

    2015-04-01

    We have analyzed bibliographical observational data and theoretical predictions, in order to probe the environment in which extremely metal-poor dwarf galaxies (XMPs) reside. We have assessed the H i component and its relation to the optical galaxy, the cosmic web type (voids, sheets, filaments and knots), the overdensity parameter and analyzed the nearest galaxy neighbors. The aim is to understand the role of interactions and cosmological accretion flows in the XMP observational properties, particularly the triggering and feeding of the star formation. We find that XMPs behave similarly to Blue Compact Dwarfs; they preferably populate low-density environments in the local universe: ∼60% occupy underdense regions, and ∼75% reside in voids and sheets. This is more extreme than the distribution of irregular galaxies, and in contrast to those regions preferred by elliptical galaxies (knots and filaments). We further find results consistent with previous observations; while the environment does determine the fraction of a certain galaxy type, it does not determine the overall observational properties. With the exception of five documented cases (four sources with companions and one recent merger), XMPs do not generally show signatures of major mergers and interactions; we find only one XMP with a companion galaxy within a distance of 100 kpc, and the H i gas in XMPs is typically well-behaved, demonstrating asymmetries mostly in the outskirts. We conclude that metal-poor accretion flows may be driving the XMP evolution. Such cosmological accretion could explain all the major XMP observational properties: isolation, lack of interaction/merger signatures, asymmetric optical morphology, large amounts of unsettled, metal-poor H i gas, metallicity inhomogeneities, and large specific star formation.

  19. Flaring red dwarf stars: news from Crimea

    International Nuclear Information System (INIS)

    Gershberg, Roald E

    1998-01-01

    Important phenomena are briefly described which have recently been discovered in the Crimean studies of flaring red dwarf stars believed to be the most common type of variable stars in the Galaxy. These phenomena include (i) long-lived radiation from a blueshifted component in the ionized-helium λ 4686 A emission line in the active state of one such star, (ii) a long-lived absorption component in the stellar flare light curves with a lifetime exceeding that of the conventional flare emission, and (iii) solarcycle-like activity periodicity of the star EV Lac, whose mass is only 0.3 solar masses. In theoretical terms, a red dwarf star spot model is constructed which, in contrast to the commonly accepted model, agrees well with the solar spot picture. (physics of our days)

  20. Abundance analysis of SDSS J134338.67+484426.6; an extremely metal-poor star from the MARVELS pre-survey

    Science.gov (United States)

    Susmitha Rani, A.; Sivarani, T.; Beers, T. C.; Fleming, S.; Mahadevan, S.; Ge, J.

    2016-05-01

    We present an elemental-abundance analysis of an extremely metal-poor (EMP; [Fe/H] <-3.0) star, SDSS J134338.67+484426.6, identified during the course of the Multi-object Apache Point Observatory Radial Velocity Exoplanet Large-area Survey spectroscopic pre-survey of some 20 000 stars to identify suitable candidates for exoplanet searches. This star, with an apparent magnitude V = 12.14, is the lowest metallicity star found in the pre-survey, and is one of only ˜20 known EMP stars that are this bright or brighter. Our high-resolution spectroscopic analysis shows that this star is a subgiant with [Fe/H] = -3.42, having `normal' carbon and no enhancement of neutron-capture abundances. Strontium is underabundant, [Sr/Fe] = -0.47, but the derived lower limit on [Sr/Ba] indicates that Sr is likely enhanced relative to Ba. This star belongs to the sparsely populated class of α-poor EMP stars that exhibit low ratios of [Mg/Fe], [Si/Fe], and [Ca/Fe] compared to typical halo stars at similar metallicity. The observed variations in radial velocity from several epochs of (low- and high-resolution) spectroscopic follow-up indicate that SDSS J134338.67+484426.6 is a possible long-period binary. We also discuss the abundance trends in EMP stars for r-process elements, and compare with other magnesium-poor stars.

  1. White dwarfs in Be star binary systems

    Science.gov (United States)

    Apparao, K. M. V.

    1991-01-01

    An evaluation is made of possible reasons for the persistent inability to identify white dwarf stars in the Be binary systems. It is noted that many Be stars exhibiting large optical enhancements may be Be + WD and Be + He systems, and that observations of pulsations in the H-alpha emission, as well as observation of time delays between enhancements of optical line and continuum, can identify such systems.

  2. Lessons for Asteroseismology from White Dwarf Stars

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... The interpretation of pulsation data for sun-like stars is currently facing challenges quite similar to those faced by white dwarf modelers ten years ago. The observational requirements for uninterrupted long-term monitoring are beginning to be satisfied by successful multi-site campaigns and dedicated ...

  3. The r-process Pattern of a Bright, Highly r-process-enhanced Metal-poor Halo Star at [Fe/H] ∼ ‑2

    Science.gov (United States)

    Sakari, Charli M.; Placco, Vinicius M.; Hansen, Terese; Holmbeck, Erika M.; Beers, Timothy C.; Frebel, Anna; Roederer, Ian U.; Venn, Kim A.; Wallerstein, George; Davis, Christopher Evan; Farrell, Elizabeth M.; Yong, David

    2018-02-01

    A high-resolution spectroscopic analysis is presented for a new highly r-process-enhanced ([Eu/Fe] = 1.27, [Ba/Eu] = ‑0.65), very metal-poor ([Fe/H] = ‑2.09), retrograde halo star, RAVE J153830.9–180424, discovered as part of the R-Process Alliance survey. At V = 10.86, this is the brightest and most metal-rich r-II star known in the Milky Way halo. Its brightness enables high-S/N detections of a wide variety of chemical species that are mostly created by the r-process, including some infrequently detected lines from elements like Ru, Pd, Ag, Tm, Yb, Lu, Hf, and Th, with upper limits on Pb and U. This is the most complete r-process census in a very metal-poor r-II star. J1538–1804 shows no signs of s-process contamination, based on its low [Ba/Eu] and [Pb/Fe]. As with many other r-process-enhanced stars, J1538–1804's r-process pattern matches that of the Sun for elements between the first, second, and third peaks, and does not exhibit an actinide boost. Cosmo-chronometric age-dating reveals the r-process material to be quite old. This robust main r-process pattern is a necessary constraint for r-process formation scenarios (of particular interest in light of the recent neutron star merger, GW170817), and has important consequences for the origins of r-II stars. Additional r-I and r-II stars will be reported by the R-Process Alliance in the near future.

  4. Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxies

    Science.gov (United States)

    Hunt, Leslie K.; Madden, Suzanne C.; Schneider, Raffaella

    2008-12-01

    'Shea and Michael L. Norman; 16. Damped Lyα systems as probes of chemical evolution over cosmological timescales Miroslava Dessauges-Zavadsky; 17. Connecting high-redshift galaxy populations through observations of local damped Lyman alpha dwarf galaxies Regina E. Schulte-Ladbeck; 18. Chemical enrichment and feedback in low metallicity environments: constraints on galaxy formation Francesca Matteucci; 19. Effects of reionization on dwarf galaxy formation Massimo Ricotti; 20. The importance of following the evolution of the dust in galaxies on their SEDs A. Schurer, F. Calura, L. Silva, A. Pipino, G. L. Granato, F. Matteucci and R. Maiolino; 21. About the chemical evolution of dSphs (and the peculiar globular cluster ωCen) Andrea Marcolini and Annibale D'Ercole; 22. Young star clusters in the small Magellanic cloud: impact of local and global conditions on star formation Elena Sabbi, Linda J. Smith, Lynn R. Carlson, Antonella Nota, Monca Tosi, Michele Cignoni, Jay S. Gallagher III, Marco Sirianni and Margaret Meixner; 23. Modeling the ISM properties of metal-poor galaxies and gamma-ray burst hosts Emily M. Levesque, Lisa J. Kewley, Kirsten Larson and Leonie Snijders; 24. Dwarf galaxies and the magnetisation of the IGM Uli Klein; Session III. Explosive Events in Low-Metallicity Environments: 25. Supernovae and their evolution in a low metallicity ISM Roger A. Chevalier; 26. First stars - type Ib supernovae connection Ken'ichi Nomoto, Masaomi Tanaka, Yasuomi Kamiya, Nozomu Tominaga and Keiichi Maeda; 27. Supernova nucleosynthesis in the early universe Nozomu Tominaga, Hideyuki Umeda, Keiichi Maeda, Ken'ichi Nomoto and Nobuyuki Iwamoto; 28. Powerful explosions at Z = 0? Sylvia Ekström, Georges Meynet, Raphael Hirschi and André Maeder; 29. Wind anisotropy and stellar evolution Cyril Georgy, Georges Meynet and André Maeder; 30. Low-mass and metal-poor gamma-ray burst

  5. Evidence of heavy element nucleosynthesis early in the history of the galaxy: The ultra-metal-poor star CS 22892-052

    Science.gov (United States)

    Cowan, John J.; Burris, Debra L.; Sneden, Christopher; McWilliam, Andrew; Preston, George W.

    1995-02-01

    We analyze the neutron-capture element (Z greater than 30) abundance distribution of the ultra-metal-poor (but neutron-capture element rich) halo star CS 22892-052. The observed stellar elemental distribution is compared with those produced by the slow and rapid neutron capture processes (i.e., the s- and r-process) in solar system material. This comparison indicates that the elemental abundances, from barium to erbium, in this Galactic halo star, have the same relative proportions as the solar system r-process distirbution. Within the uncertainties of the abundance determinations, the elements strontium and zirconium, but not yttrium, also fall on the same scaled solar r-process curve. The main component of the s-process cannot reproduce the observed neutron-capture abundances in this star. The weak component of the s-process, expected to occur during core helium burning in massive stars, can fit the relative abundance distribution of Sr and Y, but not Zr, suggesting that for the currently observed abundances in CS 22892-052, an admixture of the weak s- and the r-process might be required for production of the elements Sr to Zr. These results give evidence of the occurrence of heavy element nucleosynthesis, particularly the r-process, early in the history of the Galaxy, and further suggest a generation of massive stars (the astrophysical site for the r-process), preceding the formation of this very metal poor halo star, that was responsible for producing the observed heavy elements.

  6. Gas, Stars, and Star Formation in Alfalfa Dwarf Galaxies

    Science.gov (United States)

    Huang, Shan; Haynes, Martha P.; Giovanelli, Riccardo; Brinchmann, Jarle; Stierwalt, Sabrina; Neff, Susan G.

    2012-01-01

    We examine the global properties of the stellar and Hi components of 229 low H i mass dwarf galaxies extracted from the ALFALFA survey, including a complete sample of 176 galaxies with H i masses dwarfs are faint and of low surface brightness; only 56% of those within the SDSS footprint have a counterpart in the SDSS spectroscopic survey. A large fraction of the dwarfs have high specific star formation rates (SSFRs), and estimates of their SFRs and M* obtained by SED fitting are systematically smaller than ones derived via standard formulae assuming a constant SFR. The increased dispersion of the SSFR distribution at M* approximately less than10(exp 8)M(sub 0) is driven by a set of dwarf galaxies that have low gas fractions and SSFRs; some of these are dE/dSphs in the Virgo Cluster. The imposition of an upper Hi mass limit yields the selection of a sample with lower gas fractions for their M* than found for the overall ALFALFA population. Many of the ALFALFA dwarfs, particularly the Virgo members, have H i depletion timescales shorter than a Hubble time. An examination of the dwarf galaxies within the full ALFALFA population in the context of global star formation (SF) laws is consistent with the general assumptions that gas-rich galaxies have lower SF efficiencies than do optically selected populations and that Hi disks are more extended than stellar ones.

  7. Unlocking the secrets of white dwarf stars

    CERN Document Server

    Van Horn, Hugh M

    2015-01-01

    White dwarfs, each containing about as much mass as our Sun but packed into a volume about the size of Earth, are the endpoints of evolution for most stars. Thousands of these faint objects have now been discovered, though only a century ago only three were known. They are among the most common stars in the Milky Way Galaxy, and they have become important tools in understanding the universe. Yet a century ago only three white dwarfs were known.   The existence of these stars completely baffled the scientists of the day, and solving the mysteries of these strange objects required revolutionary advances in science and technology, including the development of quantum physics, the construction and utilization of large telescopes, the invention of the digital computer, and the ability to make astronomical observations from space.   This book tells the story of the growth in our understanding of white dwarf stars, set within the context of the relevant scientific and technological advances. Part popular science, ...

  8. A systematic search for brown dwarfs orbiting nearby stars

    International Nuclear Information System (INIS)

    Henry, T.J.; Mccarthy, D.W. Jr.

    1990-01-01

    Survey data for brown dwarf and stellar companions relative to known M dwarf stars within 5 pc north of -30 deg are analyzed. A region 0.2 to 5 arcsec in radius around 27 stars at the IR H and K bands are examined using IR speckle interferometry. The frequency of binary versus single M dwarfs in the solar neighborhood is examined. The IR mass-magnitude relations and mass-luminosity-age relation are studied. The data reveal that there are 19 single M dwarfs, 8 M dwarf binaries, 1 M dwarf triple system, and 1 M dwarf in a triple system for M dwarfs within 5 pc north of -30 deg. Also of the 27 M dwarfs studied none was found to have a brown dwarf companion. 64 refs

  9. Asteroseismology of DAV White Dwarf Stars

    Energy Technology Data Exchange (ETDEWEB)

    Bradley, Paul A.

    1997-12-31

    The author reviews the seismological structural determinations of ZZ Ceti stars done to date, and supplement these with additional preliminary determinations of his own. He compares the constraints on the hydrogen layer mass to see what trends emerge and also determines if the observed hydrogen layer masses are consistent with proposed theories. He then looks ahead to the prospects of further DAV white dwarf seismology.

  10. Star Formation Histories of Dwarf Irregular Galaxies

    Science.gov (United States)

    Skillman, Evan

    1995-07-01

    We propose to obtain deep WFPC2 `BVI' color-magnitude diagrams {CMDs} for the dwarf irregular {dI} Local Group galaxies GR 8, Leo A, Pegasus, and Sextans A. In addition to resolved stars, we will use star clusters, and especially any globulars, to probe the history of intense star formation. These data will allow us to map the Pop I and Pop II stellar components, and thereby construct the first detailed star formation histories for non-interacting dI galaxies. Our results will bear on a variety of astrophysical problems, including the evolution of small galaxies, distances in the Local Group, age-metallicity distributions in small galaxies, ages of dIs, and the physics of star formation. The four target galaxies are typical dI systems in terms of luminosity, gas content, and H II region abundance, and represent a range in current star forming activity. They are sufficiently near to allow us to reach to stars at M_V = 0, have 0.1 of the luminosity of the SMC and 0.25 of its oxygen abundance. Unlike the SMC, these dIs are not near giant galaxies. This project will allow the extension of our knowledge of stellar populations in star forming galaxies from the spirals in the Local Group down to its smallest members. We plan to take maximum advantage of the unique data which this project will provide. Our investigator team brings extensive and varied experience in studies of dwarf galaxies, stellar populations, imaging photometry, and stellar evolution to this project.

  11. GAS, STARS, AND STAR FORMATION IN ALFALFA DWARF GALAXIES

    International Nuclear Information System (INIS)

    Huang Shan; Haynes, Martha P.; Giovanelli, Riccardo; Brinchmann, Jarle; Stierwalt, Sabrina; Neff, Susan G.

    2012-01-01

    We examine the global properties of the stellar and H I components of 229 low H I mass dwarf galaxies extracted from the ALFALFA survey, including a complete sample of 176 galaxies with H I masses 7.7 M ☉ and H I line widths –1 . Sloan Digital Sky Survey (SDSS) data are combined with photometric properties derived from Galaxy Evolution Explorer to derive stellar masses (M * ) and star formation rates (SFRs) by fitting their UV-optical spectral energy distributions (SEDs). In optical images, many of the ALFALFA dwarfs are faint and of low surface brightness; only 56% of those within the SDSS footprint have a counterpart in the SDSS spectroscopic survey. A large fraction of the dwarfs have high specific star formation rates (SSFRs), and estimates of their SFRs and M * obtained by SED fitting are systematically smaller than ones derived via standard formulae assuming a constant SFR. The increased dispersion of the SSFR distribution at M * ∼ 8 M ☉ is driven by a set of dwarf galaxies that have low gas fractions and SSFRs; some of these are dE/dSphs in the Virgo Cluster. The imposition of an upper H I mass limit yields the selection of a sample with lower gas fractions for their M * than found for the overall ALFALFA population. Many of the ALFALFA dwarfs, particularly the Virgo members, have H I depletion timescales shorter than a Hubble time. An examination of the dwarf galaxies within the full ALFALFA population in the context of global star formation (SF) laws is consistent with the general assumptions that gas-rich galaxies have lower SF efficiencies than do optically selected populations and that H I disks are more extended than stellar ones.

  12. THE EATING HABITS OF MILKY WAY-MASS HALOS: DESTROYED DWARF SATELLITES AND THE METALLICITY DISTRIBUTION OF ACCRETED STARS

    Energy Technology Data Exchange (ETDEWEB)

    Deason, Alis J.; Mao, Yao-Yuan; Wechsler, Risa H., E-mail: adeason@stanford.edu [Kavli Institute for Particle Astrophysics and Cosmology and Physics Department, Stanford University, Stanford, CA 94305 (United States)

    2016-04-10

    We study the mass spectrum of destroyed dwarfs that contribute to the accreted stellar mass of Milky Way (MW)-mass (M{sub vir} ∼ 10{sup 12.1} M{sub ⊙}) halos using a suite of 45 zoom-in dissipationless simulations. Empirical models are employed to relate (peak) subhalo mass to dwarf stellar mass, and we use constraints from z = 0 observations and hydrodynamical simulations to estimate the metallicity distribution of the accreted stellar material. The dominant contributors to the accreted stellar mass are relatively massive dwarfs with M{sub star} ∼ 10{sup 8}–10{sup 10}M{sub ⊙}. Halos with more quiescent accretion histories tend to have lower mass progenitors (10{sup 8}–10{sup 9} M{sub ⊙}), and lower overall accreted stellar masses. Ultra-faint mass (M{sub star} < 10{sup 5} M{sub ⊙}) dwarfs contribute a negligible amount (≪1%) to the accreted stellar mass and, despite having low average metallicities, supply a small fraction (∼2%–5%) of the very metal-poor stars with [Fe/H] < −2. Dwarfs with masses 10{sup 5} < M{sub star}/M{sub ⊙} < 10{sup 8} provide a substantial amount of the very metal-poor stellar material (∼40%–80%), and even relatively metal-rich dwarfs with M{sub star} > 10{sup 8} M{sub ⊙} can contribute a considerable fraction (∼20%–60%) of metal-poor stars if their metallicity distributions have significant metal-poor tails. Finally, we find that the generic assumption of a quiescent assembly history for the MW halo seems to be in tension with the mass spectrum of its surviving dwarfs. We suggest that the MW could be a “transient fossil”; a quiescent halo with a recent accretion event(s) that disguises the preceding formation history of the halo.

  13. Activity-induced radial velocity variation of M dwarf stars

    DEFF Research Database (Denmark)

    Andersen, Jan Marie; Korhonen, Heidi Helena

    2012-01-01

    that can drown out a planetary signature. Cool, low-mass M dwarf stars can be highly active, which can make detection of potentially habitable planets around these stars difficult. We investigate radial velocity variations caused by different activity (spot) patterns on M dwarf stars in order to determine...... the limits of detectability for small planets orbiting active M dwarfs. We report on our progress toward the aim of answering the following questions: What types of spot patterns are realistic for M dwarf stars? What effect will spots have on M dwarf RV measurements? Can jitter from M dwarf spots mimic...... planetary signals? What is the ideal observing wavelength to reduce M dwarf jitter?...

  14. Dwarf Star Erupts in Giant Flare

    Science.gov (United States)

    2005-01-01

    This movie taken by NASA'S Galaxy Evolution Explorer shows one of the largest flares, or star eruptions, ever recorded at ultraviolet wavelengths. The star, called GJ 3685A, just happened to be in the Galaxy Evolution Explorer's field of view while the telescope was busy observing galaxies. As the movie demonstrates, the seemingly serene star suddenly exploded once, then even more intensely a second time, pouring out in total about one million times more energy than a typical flare from our Sun. The second blast of light constituted an increase in brightness by a factor of at least 10,000. Flares are huge explosions of energy stemming from a single location on a star's surface. They are caused by the brief destruction of a star's magnetic fields. Many types of stars experience them, though old, small, rapidly rotating 'red dwarfs' like GJ 3685A tend to flare more frequently and dramatically. These stars, called flare stars, can experience powerful eruptions as often as every few hours. Younger stars, in general, also erupt more often. One of the reasons astronomers study flare stars is to gain a better picture and history of flare events taking place on the Sun. A preliminary analysis of the GJ 3685A flare shows that the mechanisms underlying stellar eruptions may be more complex than previously believed. Evidence for the two most popular flare theories was found. Though this movie has been sped up (the actual flare lasted about 20 minutes), time-resolved data exist for each one-hundredth of a second. These observations were taken at 2 p.m. Pacific time, April 24, 2004. In the still image, the time sequence starts in the upper left panel, continues in the upper right, then moves to the lower left and ends in the lower right. The circular and linear features that appear below and to the right of GJ 3685A during the flare event are detector artifacts caused by the extreme brightness of the flare.

  15. Classification of extremely metal-poor stars: absent region in A(C)-[Fe/H] plane and the role of dust cooling

    Science.gov (United States)

    Chiaki, Gen; Tominaga, Nozomu; Nozawa, Takaya

    2017-11-01

    Extremely metal-poor (EMP) stars are the living fossils with records of chemical enrichment history at the early epoch of galaxy formation. By the recent large observation campaigns, statistical samples of EMP stars have been obtained. This motivates us to reconsider their classification and formation conditions. From the observed lower limits of carbon and iron abundances of Acr(C) ∼ 6 and [Fe/H]cr ∼ -5 for C-enhanced EMP (CE-EMP) and C-normal EMP (CN-EMP) stars, we confirm that gas cooling by dust thermal emission is indispensable for the fragmentation of their parent clouds to form such low mass, i.e. long-lived stars, and that the dominant grain species are carbon and silicate, respectively. We constrain the grain radius r_i^cool of a species i and condensation efficiency fij of a key element j as r_C^cool / f_C,C = 10 {μ m} and r_Sil^cool / f_Sil,Mg = 0.1 {μ m} to reproduce Acr(C) and [Fe/H]cr, which give a universal condition 10[C/H] - 2.30 + 10[Fe/H] > 10-5.07 for the formation of every EMP star. Instead of the conventional boundary [C/Fe] = 0.7 between CE-EMP and CN-EMP stars, this condition suggests a physically meaningful boundary [C/Fe]b = 2.30 above and below which carbon and silicate grains are dominant coolants, respectively.

  16. On the Stability of Strange Dwarf Hybrid Stars

    Energy Technology Data Exchange (ETDEWEB)

    Alford, Mark G.; Harris, Steven P. [Physics Department, Washington University, St. Louis, MO 63130 (United States); Sachdeva, Pratik S., E-mail: harrissp@wustl.edu [Department of Physics, University of California, Berkeley, CA 94720 (United States)

    2017-10-01

    We investigate the stability of “strange dwarfs”: white-dwarf-sized stars with a density discontinuity between a small dense core of quark matter and a thick low-density mantle of degenerate electrons. Previous work on strange dwarfs suggested that such a discontinuity could stabilize stars that would have been classified as unstable by the conventional criteria based on extrema in the mass–radius relation. We investigate the stability of such stars by numerically solving the Sturm–Liouville equations for the lowest-energy modes of the star. We find that the conventional criteria are correct, and strange dwarfs are not stable.

  17. The role of binaries in the enrichment of the early Galactic halo. I. r-process-enhanced metal-poor stars

    Science.gov (United States)

    Hansen, T. T.; Andersen, J.; Nordström, B.; Beers, T. C.; Yoon, J.; Buchhave, L. A.

    2015-11-01

    Context. The detailed chemical composition of most metal-poor halo stars has been found to be highly uniform, but a minority of stars exhibit dramatic enhancements in their abundances of heavy neutron-capture elements and/or of carbon. The key question for Galactic chemical evolution models is whether these peculiarities reflect the composition of the natal clouds, or if they are due to later (post-birth) mass transfer of chemically processed material from a binary companion. If the former case applies, the observed excess of certain elements was implanted within selected clouds in the early ISM from a production site at interstellar distances. Aims: Our aim is to determine the frequency and orbital properties of binaries among these chemically peculiar stars. This information provides the basis for deciding whether local mass transfer from a binary companion is necessary and sufficient to explain their unusual compositions. This paper discusses our study of a sample of 17 moderately (r-I) and highly (r-II) r-process-element enhanced VMP and EMP stars. Methods: High-resolution, low signal-to-noise spectra of the stars were obtained at roughly monthly intervals over eight years with the FIES spectrograph at the Nordic Optical Telescope. From these spectra, radial velocities with an accuracy of ~100 m s-1 were determined by cross-correlation against an optimized template. Results: Fourteen of the programme stars exhibit no significant radial-velocity variation over this temporal window, while three are binaries with orbits of typical eccentricity for their periods, resulting in a normal binary frequency of ~18 ± 6% for the sample. Conclusions: Our results confirm our preliminary conclusion from 2011, based on partial data, that the chemical peculiarity of the r-I and r-II stars is not caused by any putative binary companions. Instead, it was imprinted on the natal molecular clouds of these stars by an external, distant source. Models of the ISM in early galaxies

  18. On the necessity of composition-dependent low-temperature opacity in models of metal-poor asymptotic giant branch stars

    Energy Technology Data Exchange (ETDEWEB)

    Constantino, Thomas; Campbell, Simon; Lattanzio, John [Monash Centre for Astrophysics, School of Mathematical Sciences, Monash University, Victoria 3800 (Australia); Gil-Pons, Pilar, E-mail: thomas.constantino@monash.edu [Department of Applied Physics, Polytechnic University of Catalonia, 08860 Barcelona (Spain)

    2014-03-20

    The vital importance of composition-dependent low-temperature opacity in low-mass (M ≤ 3 M {sub ☉}) asymptotic giant branch (AGB) stellar models of metallicity Z ≥ 0.001 has recently been demonstrated. Its significance to more metal-poor, intermediate-mass (M ≥ 2.5 M {sub ☉}) models has yet to be investigated. We show that its inclusion in lower-metallicity models ([Fe/H] ≤–2) is essential and that there exists no threshold metallicity below which composition-dependent molecular opacity may be neglected. We find it to be crucial in all intermediate-mass models investigated ([Fe/H] ≤–2 and 2.5 ≤ M/M {sub ☉} ≤ 5), because of the evolution of the surface chemistry, including the orders of magnitude increase in the abundance of molecule-forming species. Its effect on these models mirrors that previously reported for higher-metallicity models—increase in radius, decrease in T {sub eff}, faster mass loss, shorter thermally pulsing AGB lifetime, reduced enrichment in third dredge-up products (by a factor of 3-10), and an increase in the mass limit for hot bottom burning. We show that the evolution of low-metallicity models with composition-dependent low-temperature opacity is relatively independent of initial metal abundance because its contribution to the opacity is far outweighed by changes resulting from dredge-up. Our results imply a significant reduction in the expected number of nitrogen-enhanced metal-poor stars, which may help explain their observed paucity. We note that these findings are partially a product of the macrophysics adopted in our models, in particular, the Vassiliadis and Wood mass loss rate which is strongly dependent on radius.

  19. Ages of M Dwarf Stars from their Alpha Enhancement

    Science.gov (United States)

    Muirhead, Philip Steven; Veyette, Mark

    2018-01-01

    M dwarf stars dominate stellar populations, and recent results from NASA's Kepler Mission suggest rocky planets are abundant around M dwarf stars. With so many planets orbiting M dwarfs, exoplanet scientists can now turn to questions about their history and evolution. Unfortunately, measuring fundamental properties of M dwarfs is challenging for a variety of reasons. I will discuss the importance of near-infrared spectroscopy in this effort. With high-resolution near-infrared spectroscopy covering Y to K band, we can measure detailed fundamental properties of low-mass stars. With new techniques to measure stellar alpha and iron abundances, we can begin to measure the most challenging fundamental property of M dwarfs: their age. These efforts are even more exciting in the coming years, when the TESS spacecraft is expected to discover five times as many planets orbiting low-mass stars as Kepler.

  20. Rapid Formation of Gas Giant Planets around M Dwarf Stars

    OpenAIRE

    Boss, Alan P.

    2006-01-01

    Extrasolar planet surveys have begun to detect gas giant planets in orbit around M dwarf stars. While the frequency of gas giant planets around M dwarfs so far appears to be lower than that around G dwarfs, it is clearly not zero. Previous work has shown that the core accretion mechanism does not seem to be able to form gas giant planets around M dwarfs, because the time required for core formation scales with the orbital period, which lengthens for lower mass stars, resulting in failed (gas-...

  1. A radio-pulsing white dwarf binary star.

    Science.gov (United States)

    Marsh, T R; Gänsicke, B T; Hümmerich, S; Hambsch, F-J; Bernhard, K; Lloyd, C; Breedt, E; Stanway, E R; Steeghs, D T; Parsons, S G; Toloza, O; Schreiber, M R; Jonker, P G; van Roestel, J; Kupfer, T; Pala, A F; Dhillon, V S; Hardy, L K; Littlefair, S P; Aungwerojwit, A; Arjyotha, S; Koester, D; Bochinski, J J; Haswell, C A; Frank, P; Wheatley, P J

    2016-09-15

    White dwarfs are compact stars, similar in size to Earth but approximately 200,000 times more massive. Isolated white dwarfs emit most of their power from ultraviolet to near-infrared wavelengths, but when in close orbits with less dense stars, white dwarfs can strip material from their companions and the resulting mass transfer can generate atomic line and X-ray emission, as well as near- and mid-infrared radiation if the white dwarf is magnetic. However, even in binaries, white dwarfs are rarely detected at far-infrared or radio frequencies. Here we report the discovery of a white dwarf/cool star binary that emits from X-ray to radio wavelengths. The star, AR Scorpii (henceforth AR Sco), was classified in the early 1970s as a δ-Scuti star, a common variety of periodic variable star. Our observations reveal instead a 3.56-hour period close binary, pulsing in brightness on a period of 1.97 minutes. The pulses are so intense that AR Sco's optical flux can increase by a factor of four within 30 seconds, and they are also detectable at radio frequencies. They reflect the spin of a magnetic white dwarf, which we find to be slowing down on a 10 7 -year timescale. The spin-down power is an order of magnitude larger than that seen in electromagnetic radiation, which, together with an absence of obvious signs of accretion, suggests that AR Sco is primarily spin-powered. Although the pulsations are driven by the white dwarf's spin, they mainly originate from the cool star. AR Sco's broadband spectrum is characteristic of synchrotron radiation, requiring relativistic electrons. These must either originate from near the white dwarf or be generated in situ at the M star through direct interaction with the white dwarf's magnetosphere.

  2. First stars IX - Mixing in extremely metal-poor giants. Variation of the 12C/13C, [Na/Mg] and [Al/Mg] ratios

    DEFF Research Database (Denmark)

    Spite...[], M.; Cayrel, R.; Hill, V.

    2006-01-01

    Galaxy: abundances, Galaxy: evolution, stars: abundances, stars: interiors, stars: supernovae: general, stars: evolution Udgivelsesdato: August......Galaxy: abundances, Galaxy: evolution, stars: abundances, stars: interiors, stars: supernovae: general, stars: evolution Udgivelsesdato: August...

  3. Lessons for Asteroseismology from White Dwarf Stars Travis S ...

    Indian Academy of Sciences (India)

    Travis S. Metcalfe. High Altitude Observatory, NCAR, P.O. Box 3000, Boulder CO 80307, USA. e-mail: travis@hao.ucar.edu ... and dark areas tend to cancel each other out for higher-l modes. Asteroseismology of white dwarfs has .... age of the universe to form through single-star evolution. Higher mass white dwarfs.

  4. New light on dark stars red dwarfs, low-mass stars, brown dwarfs

    CERN Document Server

    Reid, I Neill

    2000-01-01

    Perhaps the most common question that a child asks when he or she sees the night sky from a dark site for the first time is: 'How many stars are there?' This happens to be a question which has exercised the intellectual skills of many astronomers over the course of most of the last century, including, for the last two decades, one of the authors of this text. Until recently, the most accurate answer was 'We are not certain, but there is a good chance that almost all of them are M dwarfs. ' Within the last three years, results from new sky-surveys - particularly the first deep surveys at near­ infrared wavelengths - have provided a breakthrough in this subject, solidifying our census of the lowest-mass stars and identifying large numbers of the hitherto almost mythical substellar-mass brown dwarfs. These extremely low-luminosity objects are the central subjects of this book, and the subtitle should be interpreted accordingly. The expression 'low-mass stars' carries a wide range of meanings in the astronomical...

  5. The Eating Habits of Milky Way-mass Halos: Destroyed Dwarf Satellites and the Metallicity Distribution of Accreted Stars

    Science.gov (United States)

    Deason, Alis J.; Mao, Yao-Yuan; Wechsler, Risa H.

    2016-04-01

    We study the mass spectrum of destroyed dwarfs that contribute to the accreted stellar mass of Milky Way (MW)-mass (Mvir ˜ 1012.1 M⊙) halos using a suite of 45 zoom-in dissipationless simulations. Empirical models are employed to relate (peak) subhalo mass to dwarf stellar mass, and we use constraints from z = 0 observations and hydrodynamical simulations to estimate the metallicity distribution of the accreted stellar material. The dominant contributors to the accreted stellar mass are relatively massive dwarfs with Mstar ˜ 108-1010M⊙. Halos with more quiescent accretion histories tend to have lower mass progenitors (108-109 M⊙), and lower overall accreted stellar masses. Ultra-faint mass (Mstar 108 M⊙ can contribute a considerable fraction (˜20%-60%) of metal-poor stars if their metallicity distributions have significant metal-poor tails. Finally, we find that the generic assumption of a quiescent assembly history for the MW halo seems to be in tension with the mass spectrum of its surviving dwarfs. We suggest that the MW could be a “transient fossil” a quiescent halo with a recent accretion event(s) that disguises the preceding formation history of the halo.

  6. Gas, Stars, and Star Formation in ALFALFA Dwarf Galaxies

    Science.gov (United States)

    Huang, Shan; Haynes, Martha P.; Giovanelli, Riccardo; Brinchmann, Jarle; Stierwalt, Sabrina; Neff, Susan G.

    2012-06-01

    We examine the global properties of the stellar and H I components of 229 low H I mass dwarf galaxies extracted from the ALFALFA survey, including a complete sample of 176 galaxies with H I masses global star formation (SF) laws is consistent with the general assumptions that gas-rich galaxies have lower SF efficiencies than do optically selected populations and that H I disks are more extended than stellar ones. Based on observations made with the Arecibo Observatory and the NASA Galaxy Evolution Explorer (GALEX). The Arecibo Observatory is operated by SRI International under a cooperative agreement with the National Science Foundation (AST-1100968), and in alliance with Ana G. Méndez-Universidad Metropolitana and the Universities Space Research Association. GALEX is operated for NASA by the California Institute of Technology under NASA contract NAS5-98034.

  7. A Formation Timescale of the Galactic Halo from Mg Isotopes in Dwarf Stars

    Science.gov (United States)

    Carlos, Marília; Karakas, Amanda I.; Cohen, Judith G.; Kobayashi, Chiaki; Meléndez, Jorge

    2018-04-01

    We determine magnesium isotopic abundances of metal-poor dwarf stars from the galactic halo, to shed light on the onset of asymptotic giant branch (AGB) star nucleosynthesis in the galactic halo and constrain the timescale of its formation. We observed a sample of eight new halo K dwarfs in a metallicity range of ‑1.9 ‑1.4 are somewhat higher (1–3σ) than previous chemical evolution model predictions, indicating perhaps higher yields of the neutron-rich isotopes. Our results using only AGB star enrichment suggest a timescale for formation for the galactic halo of about 0.3 Gyr, but considering also supernova enrichment, the upper limit for the timescale formation is about 1.5 Gyr. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  8. Discovery of a Metal-Poor Little Cub

    Science.gov (United States)

    Kohler, Susanna

    2017-09-01

    The discovery of an extremely metal-poor star-forming galaxy in our local universe, dubbed Little Cub, is providing astronomers with front-row seats to the quenching of a near-pristine galaxy.SDSS image of NGC 3359 (left) and Little Cub (right), with overlying contours displaying the location of hydrogen gas. Little Cubs (also shown in the inset) stellar mass lies in the blue contour of the right-hand side. The outer white contours show the extended gas of the galaxy, likely dragged out as a tidal tail by Little Cubs interaction with NGC 3359. [Hsyu et al. 2017]The Hunt for Metal-Poor GalaxiesLow-metallicity, star-forming galaxies can show us the conditions under which the first stars formed. The galaxies with the lowest metallicities, however, also tend to be those with the lowest luminosities making them difficult to detect. Though we know that there should be many low-mass, low-luminosity, low-metallicity galaxies in the universe, weve detected very few of them nearby.In an effort to track down more of these metal-poor galaxies, a team of scientists led by Tiffany Hsyu (University of California Santa Cruz) searched through Sloan Digital Sky Survey data, looking for small galaxies with the correct photometric color to qualify a candidate blue compact dwarfs, a type of small, low-luminosity, star-forming galaxy that is often low-metallicity.Hsyu and collaborators identified more than 2,500 candidate blue compact dwarfs, and next set about obtaining follow-up spectroscopy for many of the candidates from the Keck and Lick Observatories. Though this project is still underway, around 100 new blue compact dwarfs have already been identified via the spectroscopy, including one of particular interest: the Little Cub.Little CubThis tiny star-forming galaxy gained its nickname from its location in the constellation Ursa Major. Little Cub is perhaps 50 or 60 million light-years away, and Hsyu and collaborators find it to be one of the lowest-metallicity star

  9. Star Formation History of Dwarf Galaxies in Cosmological Hydrodynamic Simulations

    Directory of Open Access Journals (Sweden)

    Kentaro Nagamine

    2010-01-01

    Full Text Available We examine the past and current work on the star formation (SF histories of dwarf galaxies in cosmological hydrodynamic simulations. The results obtained from different numerical methods are still somewhat mixed, but the differences are understandable if we consider the numerical and resolution effects. It remains a challenge to simulate the episodic nature of SF history in dwarf galaxies at late times within the cosmological context of a cold dark matter model. More work is needed to solve the mysteries of SF history of dwarf galaxies employing large-scale hydrodynamic simulations on the next generation of supercomputers.

  10. The Universality of the Rapid Neutron-capture Process Revealed by a Possible Disrupted Dwarf Galaxy Star

    Science.gov (United States)

    Casey, Andrew R.; Schlaufman, Kevin C.

    2017-12-01

    The rapid neutron-capture or r-process is thought to produce the majority of the heavy elements (Z> 30) in extremely metal-poor stars. The same process is also responsible for a significant fraction of the heavy elements in the Sun. This universality of the r-process is one of its characteristic features, as well as one of the most important clues to its astrophysical origin. We report the discovery of an extremely metal-poor field giant with [{Sr},{Ba}/{{H}}]≈ -6.0 and [{Sr},{Ba}/{Fe}]≈ -3.0, the lowest abundances of strontium and barium relative to iron ever observed. Despite its low abundances, the star 2MASS J151113.24-213003.0 has [{Sr}/{Ba}]=-0.11+/- 0.14, therefore its neutron-capture abundances are consistent with the main solar r-process pattern that has [{Sr}/{Ba}]=-0.25. It has been suggested that extremely low neutron-capture abundances are a characteristic of dwarf galaxies, and we find that this star is on a highly eccentric orbit with an apocenter ≳100 kpc that lies in the disk of satellites in the halo of the Milky Way. We show that other extremely metal-poor stars with low [Sr, Ba/H] and [Sr, Ba/Fe] plus solar [Sr/Ba] tend to have orbits with large apocenters, consistent with a dwarf galaxy origin for this class of object. The nucleosynthesis event that produced the neutron-capture elements in 2MASS J151113.24-213003.0 must produce both strontium and barium together in the solar ratio. We exclude contributions from the s-process in intermediate-mass asymptotic giant branch or fast-rotating massive metal-poor stars, pair-instability supernovae, the weak r-process, and neutron-star mergers. We argue that the event was a Pop III or extreme Pop II core-collapse supernova explosion. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  11. Numerical simulations of bubble-induced star formation in dwarf irregular galaxies with a novel stellar feedback scheme

    Science.gov (United States)

    Kawata, Daisuke; Gibson, Brad K.; Barnes, David J.; Grand, Robert J. J.; Rahimi, Awat

    2014-02-01

    To study the star formation and feedback mechanism, we simulate the evolution of an isolated dwarf irregular galaxy (dIrr) in a fixed dark matter halo, similar in size to Wolf-Lundmark-Melotte, using a new stellar feedback scheme. We use the new version of our original N-body/smoothed particle chemodynamics code, GCD+, which adopts improved hydrodynamics, metal diffusion between the gas particles and new modelling of star formation and stellar wind and supernovae feedback. Comparing the simulations with and without stellar feedback effects, we demonstrate that the collisions of bubbles produced by strong feedback can induce star formation in a more widely spread area. We also demonstrate that the metallicity in star-forming regions is kept low due to the mixing of the metal-rich bubbles and the metal-poor interstellar medium. Our simulations also suggest that the bubble-induced star formation leads to many counter-rotating stars. The bubble-induced star formation could be a dominant mechanism to maintain star formation in dIrrs, which is different from larger spiral galaxies where the non-axisymmetric structures, such as spiral arms, are a main driver of star formation.

  12. Chemo-orbital evidence from SDSS/SEGUE G dwarf stars for a mixed origin of the Galactic thick disk

    Directory of Open Access Journals (Sweden)

    van de Ven G.

    2012-02-01

    Full Text Available About 13,000 G dwarf within 7stars and smoothly extends into a thick disk with α-enhanced stars, consistent with an in-situ formation through radial migration. On the other hand, the metal-poor population with enhanced α-abundance, higher scale height, and disperse kinematical properties, is difficult to explain with radial migration but might have originated from gas-rich mergers. The thick disk of the Milky Way seems to have a mixed origin.

  13. A Refined Catalogue of Phoenix Dwarf Galaxy Giant Star Candidates

    Science.gov (United States)

    Tobolewski, Joshua; Siegel, M.; Palma, C.; Charlton, J.

    2005-12-01

    Continuing our studies of the Phoenix dwarf irregular galaxy and its extended tidal structure, we present the results of a survey using improved photometry with the Washington M-T2-DDO51 photometric method. The three-filter method has the ability to discriminate low surface-gravity giant stars from high surface gravity dwarfs and has proven successful at showing extended distributions of giant stars in other dSph satellites of the Milky Way. Our survey of Phoenix, the most distant (Rgc > 400kpc) of the Milky Way's bound satellites, was taken over a 0.5 square degree region obtained with the CTIO 4-meter telescope and Mosaic II camera. Relying on conservative cuts in photometric error and stellar shape parameter space, our photometry provides a clean list of extratidal giant star candidates. We find 250 giant candidates in our survey that pass both color-magnitude and color-color constraint cuts. Of these, we have roughly 29 candidate giant stars that lie outside the tidal radius of Phoenix. This number of candidate extratidal stars has not been adjusted for background contamination. Further investigations are required to determine if any of these stars were once bound to Phoenix. Using the entire sample of candidate giant stars associated with Phoenix, we also see structural differences in the spatial distribution of high and low metallicity giant stars within the galaxy. Similar differences in the spatial distribution of young and old stars in Phoenix have been noted by other authors. Finally, we compare our photometric selection of Phoenix stars with spectroscopically verified giant stars from Gallart et al (2001) and find that our selection process is successful in identifying these stars as giants, suggesting a high efficiency in selecting giants. We gratefully acknowledge funding for this work from an NSF REU supplement and grant AST 0306884.

  14. Contrasting Accreting White Dwarf Pulsators with the ZZ Ceti Stars

    Science.gov (United States)

    Mukadam, A. S.; Szkody, P.; Gänsicke, B. T.; Pala, A.

    2017-03-01

    Understanding the similarities and differences between the accreting white dwarf pulsators and their non-interacting counterparts, the ZZ Ceti stars, will eventually help us deduce how accretion affects pulsations. ZZ Ceti stars pulsate in a narrow instability strip in the range 10800-12300 K due to H ionization in their pure H envelopes; their pulsation characteristics depend on their temperature and stellar mass. Models of accreting white dwarfs are found to be pulsationally unstable due to the H/HeI ionization zone, and even show a second instability strip around 15000 K due to HeII ionization. Both these strips are expected to merge for a He abundance higher than 0.48 to form a broad instability strip, which is consistent with the empirical determination of 10500-16000 K. Accreting pulsators undergo outbursts, during which the white dwarf is heated to temperatures well beyond the instability strip and is observed to cease pulsations. The white dwarf then cools to quiescence in a few years as its outer layers cool more than a million times faster than the evolutionary rate. This provides us with an exceptional opportunity to track the evolution of pulsations from the blue edge to quiescence in a few years, while ZZ Ceti stars evolve on Myr timescales. Some accreting pulsators have also been observed to cease pulsations without any apparent evidence of an outburst. This is a distinct difference between this class of pulsators and the non-interacting ZZ Ceti stars. While the ZZ Ceti instability strip is well sampled, the strip for the accreting white dwarfs is sparsely sampled and we hereby add two new potential discoveries to improve the statistics.

  15. SEARCH FOR RED DWARF STARS IN GLOBULAR CLUSTER NGC 6397

    Science.gov (United States)

    2002-01-01

    Left A NASA Hubble Space Telescope image of a small region (1.4 light-years across) in the globular star cluster NGC 6397. Simulated stars (diamonds) have been added to this view of the same region of the cluster to illustrate what astronomers would have expected to see if faint red dwarf stars were abundant in the Milky Way Galaxy. The field would then contain 500 stars, according to theoretical calculations. Right The unmodified HST image shows far fewer stars than would be expected, according to popular theories of star formation. HST resolves about 200 stars. The stellar density is so low that HST can literally see right through the cluster and resolve far more distant background galaxies. From this observation, scientists have identified the surprising cutoff point below which nature apparently doesn't make many stars smaller that 1/5 the mass of our Sun. These HST findings provide new insights into star formation in our Galaxy. Technical detail:The globular cluster NGC 6397, one of the nearest and densest agglomerations of stars, is located 7,200 light-years away in the southern constellation Ara. This visible-light picture was taken on March 3, 1994 with the Wide Field Planetary Camera 2, as part the HST parallel observing program. Credit: F. Paresce, ST ScI and ESA and NASA

  16. Delayed star formation in isolated dwarf galaxies: Hubble space telescope star formation history of the Aquarius dwarf irregular

    Energy Technology Data Exchange (ETDEWEB)

    Cole, Andrew A. [School of Physical Sciences, University of Tasmania, Private Bag 37, Hobart, Tasmania, 7001 Australia (Australia); Weisz, Daniel R. [Department of Astronomy, University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Dolphin, Andrew E. [Raytheon, 1151 East Hermans Road, Tucson, AZ 85706 (United States); Skillman, Evan D. [Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN 55441 (United States); McConnachie, Alan W. [NRC Herzberg Institute of Astrophysics, Dominion Astrophysical Observatory, Victoria, BC, V9E 2E7 Canada (Canada); Brooks, Alyson M. [Department of Physics and Astronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854 (United States); Leaman, Ryan, E-mail: andrew.cole@utas.edu.au, E-mail: drw@ucsc.edu, E-mail: adolphin@raytheon.com, E-mail: skillman@astro.umn.edu, E-mail: alan.mcconnachie@nrc-cnrc.gc.ca, E-mail: abrooks@physics.rutgers.edu, E-mail: rleaman@iac.es [Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife (Spain)

    2014-11-01

    We have obtained deep images of the highly isolated (d = 1 Mpc) Aquarius dwarf irregular galaxy (DDO 210) with the Hubble Space Telescope Advanced Camera for Surveys. The resulting color-magnitude diagram (CMD) reaches more than a magnitude below the oldest main-sequence turnoff, allowing us to derive the star formation history (SFH) over the entire lifetime of the galaxy with a timing precision of ≈10% of the lookback time. Using a maximum likelihood fit to the CMD we find that only ≈10% of all star formation in Aquarius took place more than 10 Gyr ago (lookback time equivalent to redshift z ≈ 2). The star formation rate increased dramatically ≈6-8 Gyr ago (z ≈ 0.7-1.1) and then declined until the present time. The only known galaxy with a more extreme confirmed delay in star formation is Leo A, a galaxy of similar M {sub H} {sub I}/M {sub *}, dynamical mass, mean metallicity, and degree of isolation. The delayed stellar mass growth in these galaxies does not track the mean dark matter accretion rate from CDM simulations. The similarities between Leo A and Aquarius suggest that if gas is not removed from dwarf galaxies by interactions or feedback, it can linger for several gigayears without cooling in sufficient quantity to form stars efficiently. We discuss possible causes for the delay in star formation including suppression by reionization and late-time mergers. We find reasonable agreement between our measured SFHs and select cosmological simulations of isolated dwarfs. Because star formation and merger processes are both stochastic in nature, delayed star formation in various degrees is predicted to be a characteristic (but not a universal) feature of isolated small galaxies.

  17. RUNAWAY DWARF CARBON STARS AS CANDIDATE SUPERNOVA EJECTA

    Energy Technology Data Exchange (ETDEWEB)

    Plant, Kathryn A.; Margon, Bruce; Guhathakurta, Puragra; Cunningham, Emily C.; Toloba, Elisa [Department of Astronomy and Astrophysics and University of California Observatories, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Munn, Jeffrey A., E-mail: kaplant@ucsc.edu [US Naval Observatory, Flagstaff Station, 10391 West Naval Observatory Road, Flagstaff, AZ 86005-8521 (United States)

    2016-12-20

    The dwarf carbon (dC) star SDSS J112801.67+004034.6 has an unusually high radial velocity, 531 ± 4 km s{sup −1}. We present proper motion and new spectroscopic observations which imply a large Galactic rest frame velocity, 425 ± 9 km s{sup −1}. Several other SDSS dC stars are also inferred to have very high galactocentric velocities, again each based on both high heliocentric radial velocity and also confidently detected proper motions. Extreme velocities and the presence of C {sub 2} bands in the spectra of dwarf stars are both rare. Passage near the Galactic center can accelerate stars to such extreme velocities, but the large orbital angular momentum of SDSS J1128 precludes this explanation. Ejection from a supernova in a binary system or disruption of a binary by other stars are possibilities, particularly as dC stars are thought to obtain their photospheric C {sub 2} via mass transfer from an evolved companion.

  18. Theoretical colours for F and G dwarf stars.

    Science.gov (United States)

    Bell, R. A.

    1971-01-01

    Synthetic spectra have been computed for F and G dwarf stars, using a number of values of chemical abundance, Doppler broadening velocity, and damping constant. Metal abundances for a number of such stars have been obtained using computed and observed m(sub 1) and 40-52 colors. These abundances are in good agreement with spectroscopically determined ones. The c(sub 1) colors of such stars with exactly known trigonometric parallaxes have been used in order to determine how accurately absolute magnitudes can be predicted from the colors. Generally reasonable agreement can be obtained between observed and predicted absolute magnitudes for certain of these stars. The effects of interstellar reddening on the colors of the models are examined.

  19. The Ultraviolet Radiation Environment around M Dwarf Exoplanet Host Stars

    Science.gov (United States)

    France, Kevin; Froning, Cynthia S.; Linsky, Jeffrey L.; Roberge, Aki; Stocke, John T.; Tian, Feng; Bushinsky, Rachel; Desert, Jean-Michel; Mauas, Pablo; Mauas, Pablo; hide

    2013-01-01

    The spectral and temporal behavior of exoplanet host stars is a critical input to models of the chemistry and evolution of planetary atmospheres. Ultraviolet photons influence the atmospheric temperature profiles and production of potential biomarkers on Earth-like planets around these stars. At present, little observational or theoretical basis exists for understanding the ultraviolet spectra of M dwarfs, despite their critical importance to predicting and interpreting the spectra of potentially habitable planets as they are obtained in the coming decades. Using observations from the Hubble Space Telescope, we present a study of the UV radiation fields around nearby M dwarf planet hosts that covers both far-UV (FUV) and near-UV (NUV) wavelengths. The combined FUV+NUV spectra are publicly available in machine-readable format. We find that all six exoplanet host stars in our sample (GJ 581, GJ 876, GJ 436, GJ 832, GJ 667C, and GJ 1214) exhibit some level of chromospheric and transition region UV emission. No "UV-quiet" M dwarfs are observed. The bright stellar Lyman-alpha emission lines are reconstructed, and we find that the Lyman-alpha line fluxes comprise approximately 37%-75% of the total 1150-3100 A flux from most M dwarfs; approximately greater than 10(exp3) times the solar value. We develop an empirical scaling relation between Lyman-alpha and Mg II emission, to be used when interstellar H I attenuation precludes the direct observation of Lyman-alpha. The intrinsic unreddened flux ratio is F(Lyman-alpha)/F(Mg II) = 10(exp3). The F(FUV)/F(NUV) flux ratio, a driver for abiotic production of the suggested biomarkers O2 and O3, is shown to be approximately 0.5-3 for all M dwarfs in our sample, greather than 10(exp3) times the solar ratio. For the four stars with moderate signal-to-noise Cosmic Origins Spectrograph time-resolved spectra, we find UV emission line variability with amplitudes of 50%.500% on 10(exp2)-10(exp3) s timescales. This effect should be taken

  20. Atmospheric activity in red dwarf stars

    International Nuclear Information System (INIS)

    Pettersen, B.R.

    1986-01-01

    Active and inactive stars of similar mass and luminosity have similar physical conditions in their photospheres, outside of magnetically disturbed regions. Such field structures give rise to stellar activity, which manifests itself at all heights of the atmosphere. Observations of uneven distributions of flux across the stellar disc have led to the disovery of photospheric starspots, chromospheric plage areas, and coronal holes. Localized transient behavior has been identified in both thermal and non-thermal sources, such as flares, shock waves and particle acceleration. The common element to all active regions is the presence of strong magnetic field structures connecting the violently turbulent deep layers in the convection zones of stars with the tenuous outer atmospheres. Transport and dissipation of energy into the chromospheric and coronal regions are still much debated topics

  1. J0815+4729: A Chemically Primitive Dwarf Star in the Galactic Halo Observed with Gran Telescopio Canarias

    Science.gov (United States)

    Aguado, David S.; González Hernández, Jonay I.; Allende Prieto, Carlos; Rebolo, Rafael

    2018-01-01

    We report the discovery of the carbon-rich hyper metal-poor unevolved star J0815+4729. This dwarf star was selected from SDSS/BOSS as a metal-poor candidate and follow-up spectroscopic observations at medium resolution were obtained with the Intermediate dispersion Spectrograph and Imaging System (ISIS) at William Herschel Telescope and the Optical System for Imaging and low-intermediate-Resolution Integrated Spectroscopy (OSIRIS) at Gran Telescopio de Canarias. We use the FERRE code to derive the main stellar parameters, {T}{eff}=6215+/- 82 K, and {log}g=4.7+/- 0.5, an upper limit to the metallicity of [Fe/H] ≤ ‑5.8, and a carbon abundance of [C/Fe] ≥ +5.0, while [α /{Fe}]=0.4 is assumed. The metallicity upper limit is based on the Ca II K line, which at the resolving power of the OSIRIS spectrograph cannot be resolved from possible interstellar calcium. The star could be the most iron-poor unevolved star known and also be among the ones with the largest overabundances of carbon. High-resolution spectroscopy of J0815+4729 will certainly help to derive other important elemental abundances, possibly providing new fundamental constraints on the early stages of the universe, the formation of the first stars, and the properties of the first supernovae. Based on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, on the island of La Palma. Program ID GTC90-15B and the Discretionary Director Time GTC03-16ADDT and also based on observations made with the William Herschel Telescope (WHT).

  2. UVES Abundances of Stars in Nearby Dwarf Spheroidal Galaxies

    Science.gov (United States)

    Tolstoy, Eline; Venn, Kim; Shetrone, Matt; Primas, Francesca; Hill, Vanessa; Kaufer, Andreas; Szeifert, Thomas

    2002-07-01

    It is a truth universally acknowledged, that a galaxy in possession of a good quantity of gas must want to form stars. It is the details of how and why that baffle us all. The simplest theories either would have this process a carefully self-regulated affair, or one that goes completely out of control and is capable of wrecking the galaxy which hosts it. Of course the majority of galaxies seem to amble along somewhere between these two extremes, and the mean properties tend to favour a quiescent self-regulated evolutionary scenario. But there area variety of observations which require us to invoke transitory ‘bursts’ of star-formation at one time or another in most galaxy types. Several nearby dwarf spheroidal galaxies have clearly determined star-formation histories with apparent periods of zero star formation followed by periods of fairly active star formation. If we are able to understand what separated these bursts we would understand several important phenomena in galaxy evolution. Were these galaxies able to clear out their gas reservoir in a burst of star formation? How did this gas return? or did it? Have these galaxies receieved gas from the IGM instead? Could stars from these types of galaxy contribute significantly to the halo population in our Galaxy? To answer these questions we need to combine accurate stellar photometry and Colour-Magnitude Diagram interpretation with detailed metal abundances to combine a star-formation rate versus time with a range of element abundances with time. Different elements trace different evolutionary process (e.g., relative contributions of type I and II supernovae). We often aren't even sure of the abundance spread in these galaxies. We have collected detailed high resolution UVES spectra of four nearby dwarf spheroidal galaxies (Sculptor, Fornax, Leo I & Carina) to begin to answer these questions. This is a precursor study to a more complete study with FLAMES. We presented at this meeting the initial results for

  3. Star Formation and the ISM in Four Dwarf Irregular Galaxies

    OpenAIRE

    Young, L. M.; van Zee, L.; Lo, K. Y.; Dohm-Palmer, R. C.; Beierle, M. E.

    2003-01-01

    We present new, high sensitivity VLA observations of HI in four dwarf galaxies (UGCA 292, GR8, DDO 210, and DDO 216) and we use these data to study interactions between star formation and the interstellar medium. HI velocity dispersions and line shapes in UGCA 292, GR8, and DDO 210 show that these three galaxies contain both warm and cool or cold HI phases. The presence of the cold neutral medium is indicated by a low-dispersion (3--6 km/s) HI component or by the Gauss-Hermite shape parameter...

  4. Microlensing of unresolved stars as a brown dwarf detection method

    CERN Document Server

    Bouquet, A; Melchior, A L; Giraud-Héraud, Yannick; Baillon, Paul

    1993-01-01

    We describe a project of brown dwarf detection in the dark halo of a galaxy using the microlensing effect. We argue that monitoring pixels instead of stars could provide an enhancement in the number of detectable events. We estimate the detection efficiency with a Monte-Carlo simulation. We expect a ten-fold increase with respect to current experiments. To assess the feasibility of this method we have determined the photometric precision of a pixel by comparing several pictures of a same field in the LMC. To be published in the Proceeding of the workshop 'The dark side of the universe...', Roma, Juin 1993,

  5. Variable Stars in (Not Only) Dwarf Galaxies : Key Tools to Constrain Distances and Stellar Content

    NARCIS (Netherlands)

    Fiorentino, G.; Koleva, M; Prugniel, P; Vauglin,

    2011-01-01

    The important role of Cepheid and RR Lyrae variable stars and what they teach us about dwarf galaxies is discussed. Despite ever improving star formation histories of Local Group dwarf galaxies uncertainties remain, in particular in the identification and characterisation of the oldest stellar

  6. The structure of white dwarf stars | Babaji | Journal of the Nigerian ...

    African Journals Online (AJOL)

    A FORTRAN code to compute the structure of white dwarf Stars has been written. It is assumed that a good model for the matter in white dwarf stars is the free Fermi gas of electrons at zero temperature, treated with relativistic kinematics. The code written essentially solves numerically the two coupled first-order differential ...

  7. Crystallization of Carbon-Oxygen Mixtures in White Dwarf Stars

    International Nuclear Information System (INIS)

    Horowitz, C. J.; Schneider, A. S.; Berry, D. K.

    2010-01-01

    We determine the phase diagram for dense carbon-oxygen mixtures in white dwarf (WD) star interiors using molecular dynamics simulations involving liquid and solid phases. Our phase diagram agrees well with predictions from Ogata et al. and from Medin and Cumming and gives lower melting temperatures than Segretain et al. Observations of WD crystallization in the globular cluster NGC 6397 by Winget et al. suggest that the melting temperature of WD cores is close to that for pure carbon. If this is true, our phase diagram implies that the central oxygen abundance in these stars is less than about 60%. This constraint, along with assumptions about convection in stellar evolution models, limits the effective S factor for the 12 C(α,γ) 16 O reaction to S 300 ≤170 keV b.

  8. The Ultraviolet Radiation Environment around M dwarf Exoplanet Host Stars

    Science.gov (United States)

    France, Kevin; Froning, Cynthia S.; Linsky, Jeffrey L.; Roberge, Aki; Stocke, John T.; Tian, Feng; Bushinsky, Rachel; Désert, Jean-Michel; Mauas, Pablo; Vieytes, Mariela; Walkowicz, Lucianne M.

    2013-02-01

    The spectral and temporal behavior of exoplanet host stars is a critical input to models of the chemistry and evolution of planetary atmospheres. Ultraviolet photons influence the atmospheric temperature profiles and production of potential biomarkers on Earth-like planets around these stars. At present, little observational or theoretical basis exists for understanding the ultraviolet spectra of M dwarfs, despite their critical importance to predicting and interpreting the spectra of potentially habitable planets as they are obtained in the coming decades. Using observations from the Hubble Space Telescope, we present a study of the UV radiation fields around nearby M dwarf planet hosts that covers both far-UV (FUV) and near-UV (NUV) wavelengths. The combined FUV+NUV spectra are publicly available in machine-readable format. We find that all six exoplanet host stars in our sample (GJ 581, GJ 876, GJ 436, GJ 832, GJ 667C, and GJ 1214) exhibit some level of chromospheric and transition region UV emission. No "UV-quiet" M dwarfs are observed. The bright stellar Lyα emission lines are reconstructed, and we find that the Lyα line fluxes comprise ~37%-75% of the total 1150-3100 Å flux from most M dwarfs; gsim103 times the solar value. We develop an empirical scaling relation between Lyα and Mg II emission, to be used when interstellar H I attenuation precludes the direct observation of Lyα. The intrinsic unreddened flux ratio is F(Lyα)/F(Mg II) = 10 ± 3. The F(FUV)/F(NUV) flux ratio, a driver for abiotic production of the suggested biomarkers O2 and O3, is shown to be ~0.5-3 for all M dwarfs in our sample, >103 times the solar ratio. For the four stars with moderate signal-to-noise Cosmic Origins Spectrograph time-resolved spectra, we find UV emission line variability with amplitudes of 50%-500% on 102-103 s timescales. This effect should be taken into account in future UV transiting planet studies, including searches for O3 on Earth-like planets. Finally, we

  9. CALIBRATING UV STAR FORMATION RATES FOR DWARF GALAXIES FROM STARBIRDS

    Energy Technology Data Exchange (ETDEWEB)

    McQuinn, Kristen B. W.; Skillman, Evan D.; Mitchell, Noah P. [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street, S.E., Minneapolis, MN 55455 (United States); Dolphin, Andrew E., E-mail: kmcquinn@astro.umn.edu [Raytheon Company, 1151 E. Hermans Road, Tucson, AZ 85756 (United States)

    2015-08-01

    Integrating our knowledge of star formation (SF) traced by observations at different wavelengths is essential for correctly interpreting and comparing SF activity in a variety of systems and environments. This study compares extinction corrected integrated ultraviolet (UV) emission from resolved galaxies with color–magnitude diagram (CMD) based star formation rates (SFRs) derived from resolved stellar populations and CMD fitting techniques in 19 nearby starburst and post-starburst dwarf galaxies. The data sets are from the panchromatic Starburst Irregular Dwarf Survey and include deep legacy GALEX UV imaging, Hubble Space Telescope optical imaging, and Spitzer MIPS imaging. For the majority of the sample, the integrated near-UV fluxes predicted from the CMD-based SFRs—using four different models—agree with the measured, extinction corrected, integrated near-UV fluxes from GALEX images, but the far-UV (FUV) predicted fluxes do not. Furthermore, we find a systematic deviation between the SFRs based on integrated FUV luminosities and existing scaling relations, and the SFRs based on the resolved stellar populations. This offset is not driven by different SF timescales, variations in SFRs, UV attenuation, nor stochastic effects. This first comparison between CMD-based SFRs and an integrated FUV emission SFR indicator suggests that the most likely cause of the discrepancy is the theoretical FUV–SFR calibration from stellar evolutionary libraries and/or stellar atmospheric models. We present an empirical calibration of the FUV-based SFR relation for dwarf galaxies, with uncertainties, which is ∼53% larger than previous relations.

  10. A STAR FORMATION LAW FOR DWARF IRREGULAR GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Elmegreen, Bruce G. [IBM Research Division, T.J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598 (United States); Hunter, Deidre A., E-mail: bge@us.ibm.com, E-mail: dah@lowell.edu [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, Arizona 86001 (United States)

    2015-06-01

    The radial profiles of gas, stars, and far-ultraviolet radiation in 20 dwarf Irregular galaxies are converted to stability parameters and scale heights for a test of the importance of two-dimensional (2D) instabilities in promoting star formation. A detailed model of this instability involving gaseous and stellar fluids with self-consistent thicknesses and energy dissipation on a perturbation crossing time gives the unstable growth rates. We find that all locations are effectively stable to 2D perturbations, mostly because the disks are thick. We then consider the average volume densities in the midplanes, evaluated from the observed H i surface densities and calculated scale heights. The radial profiles of the star-formation rates are equal to about 1% of the H i surface densities divided by the free fall times at the average midplane densities. This 1% resembles the efficiency per unit free fall time commonly found in other cases. There is a further variation of this efficiency with radius in all of our galaxies, following the exponential disk with a scale length equal to about twice the stellar mass scale length. This additional variation is modeled by the molecular fraction in a diffuse medium using radiative transfer solutions for galaxies with the observed dimensions and properties of our sample. We conclude that star formation is activated by a combination of three-dimensional gaseous gravitational processes and molecule formation. Implications for outer disk structure and formation are discussed.

  11. Comparing the asteroseismic properties of pulsating extremely low-mass pre-white dwarf stars and δ Scuti stars

    Science.gov (United States)

    Arias, J. P. Sánchez; Córsico, A. H.; Romero, A. D.; Althaus, L. G.

    2017-09-01

    We present the first results of a detailed comparison between the pulsation properties of pulsating Extremely Low-Mass pre-white dwarf stars (the pre-ELMV variable stars) and δ Scuti stars. The instability domains of these very different kinds of stars nearly overlap in the log Teff vs. log g diagram, leading to a degeneracy in the classification of the stars. Our aim is to provide asteroseismic tools for their correct classification.

  12. Comparing the asteroseismic properties of pulsating extremely low-mass pre-white dwarf stars and δ Scuti stars

    Directory of Open Access Journals (Sweden)

    Arias J.P.Sánchez

    2017-01-01

    Full Text Available We present the first results of a detailed comparison between the pulsation properties of pulsating Extremely Low-Mass pre-white dwarf stars (the pre-ELMV variable stars and δ Scuti stars. The instability domains of these very different kinds of stars nearly overlap in the log Teff vs. log g diagram, leading to a degeneracy in the classification of the stars. Our aim is to provide asteroseismic tools for their correct classification.

  13. Probing the Extraordinary Ends of Ordinary Stars: White Dwarf Seismology with the Whole Earth Telescope

    OpenAIRE

    Kawaler, Steven D.

    1995-01-01

    During the final evolution of most stars, they shed their outer skin and expose their core of the hot ashes of nuclear burning. As these hot and very dense cores cool into white dwarf stars, they go through episodes of multiperiodic, nonradial g-mode pulsation. The tools of stellar seismology allow us to use the pulsation spectra as powerful probes into the deep interiors of these stars. Progress in white dwarf seismology has required significant international cooperation, since another conse...

  14. Environmental effects on star formation in dwarf galaxies and star clusters

    Science.gov (United States)

    Pasetto, Stefano; Cropper, Mark; fujita, Yutaka; Chiosi, Cesare; Grebel, Eva K.

    2015-08-01

    We investigate the competitive role of the different dissipative phenomena acting on the onset of star formation history of gravitationally bound system in an external environment.Ram pressure, Kelvin-Helmholtz instability, Rayleigh-Taylor, and tidal forces are accounted separately in an analytical framework and compared in their role in influencing the star forming regions. The two-fluids instability at the interface between a stellar system and its surrounding hotter and less dense environment is related to the star formation processes through a set of differential equations. We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system on its surrounding environment useful in theoretical interpretations of numerical results as well as observational applications. We show how spherical coordinates naturally enlighten the interpretation of the two-fluids instability in a geometry that directly applies to astrophysical case. Finally, we consider the different signatures of these phenomena in synthetically realized colour-magnitude diagrams of the orbiting system thus investigating the detectability limits of these different effects for future observational projects and their relevance.The theoretical framework developed has direct applications to the cases of dwarf galaxies in galaxy clusters and dwarf galaxies orbiting our Milky Way system, as well as any primordial gas-rich cluster of stars orbiting within its host galaxy.

  15. THE ACS NEARBY GALAXY SURVEY TREASURY. IX. CONSTRAINING ASYMPTOTIC GIANT BRANCH EVOLUTION WITH OLD METAL-POOR GALAXIES

    International Nuclear Information System (INIS)

    Girardi, Leo; Williams, Benjamin F.; Gilbert, Karoline M.; Rosenfield, Philip; Dalcanton, Julianne J.; Marigo, Paola; Boyer, Martha L.; Dolphin, Andrew; Weisz, Daniel R.; Skillman, Evan; Melbourne, Jason; Olsen, Knut A. G.; Seth, Anil C.

    2010-01-01

    In an attempt to constrain evolutionary models of the asymptotic giant branch (AGB) phase at the limit of low masses and low metallicities, we have examined the luminosity functions and number ratios between AGB and red giant branch (RGB) stars from a sample of resolved galaxies from the ACS Nearby Galaxy Survey Treasury. This database provides Hubble Space Telescope optical photometry together with maps of completeness, photometric errors, and star formation histories for dozens of galaxies within 4 Mpc. We select 12 galaxies characterized by predominantly metal-poor populations as indicated by a very steep and blue RGB, and which do not present any indication of recent star formation in their color-magnitude diagrams. Thousands of AGB stars brighter than the tip of the RGB (TRGB) are present in the sample (between 60 and 400 per galaxy), hence, the Poisson noise has little impact in our measurements of the AGB/RGB ratio. We model the photometric data with a few sets of thermally pulsing AGB (TP-AGB) evolutionary models with different prescriptions for the mass loss. This technique allows us to set stringent constraints on the TP-AGB models of low-mass, metal-poor stars (with M sun , [Fe/H]∼ sun . This is also in good agreement with recent observations of white dwarf masses in the M4 old globular cluster. These constraints can be added to those already derived from Magellanic Cloud star clusters as important mileposts in the arduous process of calibrating AGB evolutionary models.

  16. The ACS Nearby Galaxy Survey Treasury. IX. Constraining Asymptotic Giant Branch Evolution with Old Metal-poor Galaxies

    Science.gov (United States)

    Girardi, Léo; Williams, Benjamin F.; Gilbert, Karoline M.; Rosenfield, Philip; Dalcanton, Julianne J.; Marigo, Paola; Boyer, Martha L.; Dolphin, Andrew; Weisz, Daniel R.; Melbourne, Jason; Olsen, Knut A. G.; Seth, Anil C.; Skillman, Evan

    2010-12-01

    In an attempt to constrain evolutionary models of the asymptotic giant branch (AGB) phase at the limit of low masses and low metallicities, we have examined the luminosity functions and number ratios between AGB and red giant branch (RGB) stars from a sample of resolved galaxies from the ACS Nearby Galaxy Survey Treasury. This database provides Hubble Space Telescope optical photometry together with maps of completeness, photometric errors, and star formation histories for dozens of galaxies within 4 Mpc. We select 12 galaxies characterized by predominantly metal-poor populations as indicated by a very steep and blue RGB, and which do not present any indication of recent star formation in their color-magnitude diagrams. Thousands of AGB stars brighter than the tip of the RGB (TRGB) are present in the sample (between 60 and 400 per galaxy), hence, the Poisson noise has little impact in our measurements of the AGB/RGB ratio. We model the photometric data with a few sets of thermally pulsing AGB (TP-AGB) evolutionary models with different prescriptions for the mass loss. This technique allows us to set stringent constraints on the TP-AGB models of low-mass, metal-poor stars (with M white dwarf masses in the M4 old globular cluster. These constraints can be added to those already derived from Magellanic Cloud star clusters as important mileposts in the arduous process of calibrating AGB evolutionary models.

  17. Star formation rate in Holmberg IX dwarf galaxy

    Directory of Open Access Journals (Sweden)

    Anđelić M.M.

    2011-01-01

    Full Text Available In this paper we use previously determined Hα fluxes for dwarf galaxy Holmberg IX (Arbutina et al. 2009 to calculate star formation rate (SFR in this galaxy. We discuss possible contaminations of Hα flux and, for the first time, we take into account optical emission from supernova remnants (SNRs as a possible source of contamination of Hα flux. Derived SFR for Holmberg IX is 3:4 x 10-4M.yr-1. Our value is lower then in previous studies, due to luminous shock-heated source M&H 9-10, possible hypernova remnant, which we excluded from the total Hα flux in our calculation of SFR.

  18. Star-Formation Histories, Abundances, and Kinematics of Dwarf Galaxies in the Local Group

    NARCIS (Netherlands)

    Tolstoy, Eline; Hill, Vanessa; Tosi, Monica; Blandford, R; Kormendy, J; VanDishoeck, E

    2009-01-01

    Within the Local Universe galaxies can be studied in great detail star by star, and here we review the results of quantitative studies in nearby dwarf galaxies. The color-magnitude diagram synthesis method is well established as the most accurate way to determine star-formation histories of galaxies

  19. Stellar evolution on the borderline of white dwarf and neutron star formation

    NARCIS (Netherlands)

    Poelarends, A.J.T.

    2007-01-01

    This thesis is about the evolution of stars, specifically about the final fate of stars at the borderline between the formation of white dwarfs and neutron stars. It is well known that the mass and the metallicity are the two determining factors in stellar evolution, and for a given initial chemical

  20. The ACS LCID project. IX. Imprints of the early universe in the radial variation of the star formation history of dwarf galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Hidalgo, Sebastian L.; Monelli, Matteo; Aparicio, Antonio; Gallart, Carme, E-mail: shidalgo@iac.es, E-mail: monelli@iac.es, E-mail: aparicio@iac.es, E-mail: carme@iac.es [Instituto de Astrofísica de Canarias, Vía Láctea s/n, E-38200 La Laguna, Tenerife, Canary Islands (Spain); and others

    2013-12-01

    Based on Hubble Space Telescope observations from the Local Cosmology from Isolated Dwarfs project, we present the star formation histories, as a function of galactocentric radius, of four isolated Local Group dwarf galaxies: two dSph galaxies, Cetus and Tucana, and two transition galaxies (dTrs), LGS-3 and Phoenix. The oldest stellar populations of the dSphs and dTrs are, within the uncertainties, coeval (∼13 Gyr) at all galactocentric radii. We find that there are no significative differences between the four galaxies in the fundamental properties (such as the normalized star formation rate or age-metallicity relation) of their outer regions (radii greater than four exponential scale lengths); at large radii, these galaxies consist exclusively of old (≳ 10.5 Gyr) metal-poor stars. The duration of star formation in the inner regions varies from galaxy to galaxy, and the extended central star formation in the dTrs produces the dichotomy between dSph and dTr galaxy types. The dTr galaxies show prominent radial stellar population gradients: The centers of these galaxies host young (≲ 1 Gyr) populations, while the age of the last formation event increases smoothly with increasing radius. This contrasts with the two dSph galaxies. Tucana shows a similar, but milder, gradient, but no gradient in age is detected Cetus. For the three galaxies with significant stellar population gradients, the exponential scale length decreases with time. These results are in agreement with outside-in scenarios of dwarf galaxy evolution, in which a quenching of the star formation toward the center occurs as the galaxy runs out of gas in the outskirts.

  1. Global results from the HARPS metal-poor sample

    Directory of Open Access Journals (Sweden)

    Ségransan D.

    2011-02-01

    Full Text Available In this paper we present the global results of a HARPS-GTO program to search for planets orbiting a sample of metal-poor stars. The detection of several giant planets in long period orbits is discussed in the context of the metallicitygiant planet correlation.

  2. Ages of evolved low mass stars: Central stars of planetary nebulae and white dwarfs

    Directory of Open Access Journals (Sweden)

    Costa R.D.D.

    2013-03-01

    Full Text Available We have developed several methods to estimate the ages of central stars of planetary nebulae (CSPN, which are based either on observed nebular properties or on data from the stars themselves. Our goal is to derive the age distribution of these stars and compare the results with empirical distributions for CSPN and white dwarfs. We have initially developed three methods based on nebular abundances, using (i an age-metallicity relation which is also a function of the galactocentric distance; (ii an age-metallicity relation obtained for the galactic disk, and (iii the central star masses derived from the observed nitrogen abundances. In this work we present two new, more accurate methods, which are based on kinematic properties: (I in this method, the expected rotation velocities of the nebulae around the galactic centre at their galactocentric distances are compared with the predicted values for the galactic rotation curve, and the differences are attributed to the different ages of the evolved stars; (II we determine directly the U, V, W, velocity components of the stars, as well as the velocity dispersions, and use the dispersion-age relation by the Geneva-Copenhagen survey. These methods were applied to two large samples of galactic CSPN. We conclude that most CSPN in the galactic disk have ages under 5 Gyr, and that the age distribution is peaked around 1 to 3 Gyr.

  3. Accretion-induced Collapse from Helium Star + White Dwarf Binaries

    Science.gov (United States)

    Brooks, Jared; Schwab, Josiah; Bildsten, Lars; Quataert, Eliot; Paxton, Bill

    2017-07-01

    Accretion-induced collapse (AIC) occurs when an O/Ne white dwarf (WD) grows to nearly the Chandrasekhar mass ({M}{Ch}), reaching central densities that trigger electron captures in the core. Using Modules for Experiments in Stellar Astrophysics (MESA), we present the first true binary simulations of He star + O/Ne WD binaries, focusing on a 1.5 {M}⊙ He star in a 3 hr orbital period with 1.1{--}1.3 {M}⊙ O/Ne WDs. The helium star fills its Roche lobe after core helium burning is completed and donates helium on its thermal timescale to the WD, \\dot{M}≈ 3× {10}-6 {M}⊙ {{yr}}-1, which is a rate high enough that the accreting helium burns stably on the WD. The accumulated carbon/oxygen ashes from the helium burning undergo an unstable shell flash that initiates an inwardly moving, carbon burning flame. This flame is only quenched when it runs out of carbon at the surface of the original O/Ne core. Subsequent accumulation of fresh carbon/oxygen layers also undergo thermal instabilities, but no mass loss is triggered, which allows {M}{WD}\\to {M}{Ch}, and then triggers the onset of AIC. We also discuss the scenario of accreting C/O WDs that experience shell carbon ignitions to become O/Ne WDs, and then, under continuing mass transfer, lead to AIC. Studies of the AIC event rate using binary population synthesis should include all of these channels, especially this latter channel, which has been previously neglected but might dominate the rate.

  4. Pulsating low-mass white dwarfs in the frame of new evolutionary sequences. V. Asteroseismology of ELMV white dwarf stars

    Science.gov (United States)

    Calcaferro, Leila M.; Córsico, Alejandro H.; Althaus, Leandro G.

    2017-11-01

    Context. Many pulsating low-mass white dwarf stars have been detected in the past years in the field of our Galaxy. Some of them exhibit multiperiodic brightness variation, therefore it is possible to probe their interiors through asteroseismology. Aims: We present a detailed asteroseismological study of all the known low-mass variable white dwarf stars based on a complete set of fully evolutionary models that are representative of low-mass He-core white dwarf stars. Methods: We employed adiabatic radial and nonradial pulsation periods for low-mass white dwarf models with stellar masses ranging from 0.1554 to 0.4352 M⊙ that were derived by simulating the nonconservative evolution of a binary system consisting of an initially 1 M⊙ zero-age main-sequence (ZAMS) star and a 1.4 M⊙ neutron star companion. We estimated the mean period spacing for the stars under study (where this was possible), and then we constrained the stellar mass by comparing the observed period spacing with the average of the computed period spacings for our grid of models. We also employed the individual observed periods of every known pulsating low-mass white dwarf star to search for a representative seismological model. Results: We found that even though the stars under analysis exhibit few periods and the period fits show multiplicity of solutions, it is possible to find seismological models whose mass and effective temperature are in agreement with the values given by spectroscopy for most of the cases. Unfortunately, we were not able to constrain the stellar masses by employing the observed period spacing because, in general, only few periods are exhibited by these stars. In the two cases where we were able to extract the period spacing from the set of observed periods, this method led to stellar mass values that were substantially higher than expected for this type of stars. Conclusions: The results presented in this work show the need for further photometric searches, on the one hand

  5. Determination of the upper mass limit for stars producing white-dwarf remnants

    International Nuclear Information System (INIS)

    Romanishin, W.; Angel, J.R.P.

    1980-01-01

    We have searched ultraviolet and red plates of four open clusters (NGC 2168, 2287, 2422, and 6633) for faint blue objects which might be white dwarf members of the clusters. The most massive stars in these clusters range from 3 to 6 M/sub sun/. We find a definite concentration of faint blue objects in the clusters. This fact, plus initial photoelectric photometry, provides strong support for the identification of many of these objects as cluster white dwarfs. By modeling the expected number of possible white dwarfs in each cluster, we are able to put some limits on m/sub w/, the upper stellar mass limit for formation of white dwarfs. Our data require that some stars of at least 5 M/sub sun/ have evolved into white dwarfs and give a most probable value of 7 M/sub sun/ for m/sub w/

  6. A Deep Study of the Dwarf Satellites Andromeda XXVIII & Andromeda XXIX

    OpenAIRE

    Slater, Colin T.; Bell, Eric F.; Martin, Nicolas F.; Tollerud, Erik J.; Ho, Nhung

    2015-01-01

    We present the results of a deep study of the isolated dwarf galaxies Andromeda XXVIII and Andromeda XXIX with Gemini/GMOS and Keck/DEIMOS. Both galaxies are shown to host old, metal-poor stellar populations with no detectable recent star formation, conclusively identifying both of them as dwarf spheroidal galaxies (dSphs). And XXVIII exhibits a complex horizontal branch morphology, which is suggestive of metallicity enrichment and thus an extended period of star formation in the past. Decomp...

  7. Deposition of steeply infalling debris around white dwarf stars

    Science.gov (United States)

    Brown, John C.; Veras, Dimitri; Gänsicke, Boris T.

    2017-06-01

    High-metallicity pollution is common in white dwarf (WD) stars hosting remnant planetary systems. However, they rarely have detectable debris accretion discs, possibly because much of the influx is fast steeply infalling debris in star-grazing orbits, producing a more tenuous signature than a slowly accreting disc. Processes governing such deposition between the Roche radius and photosphere have so far received little attention and we model them here analytically by extending recent work on sun-grazing comets to WD systems. We find that the evolution of cm-to-km size (a0) infallers most strongly depends on two combinations of parameters, which effectively measure sublimation rate and binding strength. We then provide an algorithm to determine the fate of infallers for any WD, and apply the algorithm to four limiting combinations of hot versus cool (young/old) WDs with snowy (weak, volatile) versus rocky (strong, refractory) infallers. We find: (I) Total sublimation above the photosphere befalls all small infallers across the entire WD temperature (TWD) range, the threshold size rising with TWD and 100× larger for rock than snow. (II) All very large objects fragment tidally regardless of TWD: for rock, a0 ≽ 105 cm; for snow, a0 ≽ 103-3 × 104 cm across all WD cooling ages. (III) A considerable range of a0 avoids fragmentation and total sublimation, yielding impacts or grazes with cold WDs. This range rapidly narrows with increasing TWD, especially for snowy bodies. Finally, we briefly discuss how the various forms of deposited debris may finally reach the photosphere surface itself.

  8. SPITZER OBSERVATIONS OF WHITE DWARFS: THE MISSING PLANETARY DEBRIS AROUND DZ STARS

    International Nuclear Information System (INIS)

    Xu, S.; Jura, M.

    2012-01-01

    We report a Spitzer/Infrared Array Camera search for infrared excesses around white dwarfs, including 14 newly observed targets and 16 unpublished archived stars. We find a substantial infrared excess around two warm white dwarfs—J220934.84+122336.5 and WD 0843+516, the latter apparently being the hottest white dwarf known to display a close-in dust disk. Extending previous studies, we find that the fraction of white dwarfs with dust disks increases as the star's temperature increases; for stars cooler than 10,000 K, even the most heavily polluted ones do not have ∼1000 K dust. There is tentative evidence that the dust disk occurrence is correlated with the volatility of the accreted material. In the Appendix, we modify a previous analysis to clarify how Poynting-Robertson drag might play an important role in transferring materials from a dust disk into a white dwarf's atmosphere.

  9. PROTOPLANETARY DISK MASSES FROM STARS TO BROWN DWARFS

    International Nuclear Information System (INIS)

    Mohanty, Subhanjoy; Mortlock, Daniel; Greaves, Jane; Pascucci, Ilaria; Apai, Daniel; Scholz, Aleks; Thompson, Mark; Lodato, Giuseppe; Looper, Dagny

    2013-01-01

    We present SCUBA-2 850 μm observations of seven very low mass stars (VLMS) and brown dwarfs (BDs). Three are in Taurus and four in the TW Hydrae Association (TWA), and all are classical T Tauri (cTT) analogs. We detect two of the three Taurus disks (one only marginally), but none of the TWA ones. For standard grains in cTT disks, our 3σ limits correspond to a dust mass of 1.2 M ⊕ in Taurus and a mere 0.2 M ⊕ in the TWA (3-10× deeper than previous work). We combine our data with other submillimeter/millimeter (sub-mm/mm) surveys of Taurus, ρ Oph, and the TWA to investigate the trends in disk mass and grain growth during the cTT phase. Assuming a gas-to-dust mass ratio of 100:1 and fiducial surface density and temperature profiles guided by current data, we find the following. (1) The minimum disk outer radius required to explain the upper envelope of sub-mm/mm fluxes is ∼100 AU for intermediate-mass stars, solar types, and VLMS, and ∼20 AU for BDs. (2) While the upper envelope of apparent disk masses increases with M * from BDs to VLMS to solar-type stars, no such increase is observed from solar-type to intermediate-mass stars. We propose this is due to enhanced photoevaporation around intermediate stellar masses. (3) Many of the disks around Taurus and ρ Oph intermediate-mass and solar-type stars evince an opacity index of β ∼ 0-1, indicating significant grain growth. Of the only four VLMS/BDs in these regions with multi-wavelength measurements, three are consistent with considerable grain growth, though optically thick disks are not ruled out. (4) For the TWA VLMS (TWA 30A and B), combining our 850 μm fluxes with the known accretion rates and ages suggests substantial grain growth by 10 Myr, comparable to that in the previously studied TWA cTTs Hen 3-600A and TW Hya. The degree of grain growth in the TWA BDs (2M1207A and SSPM1102) remains largely unknown. (5) A Bayesian analysis shows that the apparent disk-to-stellar mass ratio has a roughly

  10. The star formation and chemical evolution history of the sculptor dwarf spheroidal galaxy

    NARCIS (Netherlands)

    de Boer, T. J. L.; Tolstoy, E.; Hill, V.; Saha, A.; Olsen, K.; Starkenburg, E.; Lemasle, B.; Irwin, M. J.; Battaglia, G.

    We have combined deep photometry in the B, V and I bands from CTIO/MOSAIC of the Sculptor dwarf spheroidal galaxy, going down to the oldest main sequence turn-offs, with spectroscopic metallicity distributions of red giant branch stars. This allows us to obtain the most detailed and complete star

  11. Black holes, white dwarfs and neutron stars: The physics of compact objects

    International Nuclear Information System (INIS)

    Shapiro, S.L.; Teukolsky, S.A.

    1983-01-01

    The contents include: Star deaths and the formation of compact objects; White dwarfs; Rotation and magnetic fields; Cold equation of state above neutron drip; Pulsars; Accretion onto black holes; Supermassive stars and black holes; Appendices; and Indexes. This book discusses one aspect, compact objects, of astronomy and provides information of astrophysics or general relativity

  12. Constraining the Stellar Populations and Star Formation Histories of Blue Compact Dwarf Galaxies with SED Fits

    Energy Technology Data Exchange (ETDEWEB)

    Janowiecki, Steven [International Center for Radio Astronomy Research, M468, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia, 6009 (Australia); Salzer, John J.; Zee, Liese van [Department of Astronomy, Indiana University, 727 East Third Street, Bloomington, IN 47405 (United States); Rosenberg, Jessica L. [Department of Physics and Astronomy, George Mason University, Fairfax, VA 22030 (United States); Skillman, Evan, E-mail: steven.janowiecki@uwa.edu.au [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street, SE Minneapolis, MN, 55455 (United States)

    2017-02-10

    We discuss and test possible evolutionary connections between blue compact dwarf galaxies (BCDs) and other types of dwarf galaxies. BCDs provide ideal laboratories to study intense star formation episodes in low-mass dwarf galaxies, and have sometimes been considered a short-lived evolutionary stage between types of dwarf galaxies. To test these connections, we consider a sample of BCDs as well as a comparison sample of nearby galaxies from the Local Volume Legacy (LVL) survey for context. We fit the multi-wavelength spectral energy distributions (SED, far-ultra-violet to far-infrared) of each galaxy with a grid of theoretical models to determine their stellar masses and star formation properties. We compare our results for BCDs with the LVL galaxies to put BCDs in the context of normal galaxy evolution. The SED fits demonstrate that the star formation events currently underway in BCDs are at the extreme of the continuum of normal dwarf galaxies, both in terms of the relative mass involved and in the relative increase over previous star formation rates. Today’s BCDs are distinctive objects in a state of extreme star formation that is rapidly transforming them. This study also suggests ways to identify former BCDs whose star formation episodes have since faded.

  13. GD1212: Probing deep into the interior of a pulsating white dwarf star

    Directory of Open Access Journals (Sweden)

    Giammichele N.

    2015-01-01

    Full Text Available We present the first self-consistent seismic analysis of a white dwarf star, GD 1212, in the Kepler2 field. We precisely establish the fundamental parameters of the star using the forward method based on physically sound models. We unravel the internal structure as well as the rotation profile of GD1212 deeper than in any other ZZCeti stars studied so far. This opens up interesting prospects for future analyses of the white dwarf pulsators monitored in the Kepler and Kepler2 fields.

  14. Local Group Dwarf Galaxies and the Star Formation Law at High Redshift.

    Science.gov (United States)

    Gnedin

    2000-06-01

    I show how the existing observational data on Local Group dwarf galaxies can be used to estimate the average star formation law during the first 3 Gyr of the history of the universe. I find that the observational data are consistent with the orthodox Schmidt law with a star formation efficiency of about 4% if the star formation is continuous (during the first 3 Gyr). The efficiency is proportionally higher if most of the gas in the dwarfs was consumed (and never replenished) in a short time interval well before the universe turned 3 Gyr.

  15. SOLAR-LIKE OSCILLATIONS IN A METAL-POOR GLOBULAR CLUSTER WITH THE HUBBLE SPACE TELESCOPE

    International Nuclear Information System (INIS)

    Stello, Dennis; Gilliland, Ronald L.

    2009-01-01

    We present analyses of variability in the red giant stars in the metal-poor globular cluster NGC 6397, based on data obtained with the Hubble Space Telescope. We use a nonstandard data reduction approach to turn a 23 day observing run originally aimed at imaging the white dwarf population, into time-series photometry of the cluster's highly saturated red giant stars. With this technique we obtain noise levels in the final power spectra down to 50 parts per million, which allows us to search for low-amplitude solar-like oscillations. We compare the observed excess power seen in the power spectra with estimates of the typical frequency range, frequency spacing, and amplitude from scaling the solar oscillations. We see evidence that the detected variability is consistent with solar-like oscillations in at least one and perhaps up to four stars. With metallicities 2 orders of magnitude lower than those of the Sun, these stars present so far the best evidence of solar-like oscillations in such a low-metallicity environment.

  16. An age difference of two billion years between a metal-rich and a metal-poor globular cluster.

    Science.gov (United States)

    Hansen, B M S; Kalirai, J S; Anderson, J; Dotter, A; Richer, H B; Rich, R M; Shara, M M; Fahlman, G G; Hurley, J R; King, I R; Reitzel, D; Stetson, P B

    2013-08-01

    Globular clusters trace the formation history of the spheroidal components of our Galaxy and other galaxies, which represent the bulk of star formation over the history of the Universe. The clusters exhibit a range of metallicities (abundances of elements heavier than helium), with metal-poor clusters dominating the stellar halo of the Galaxy, and higher-metallicity clusters found within the inner Galaxy, associated with the stellar bulge, or the thick disk. Age differences between these clusters can indicate the sequence in which the components of the Galaxy formed, and in particular which clusters were formed outside the Galaxy and were later engulfed along with their original host galaxies, and which were formed within it. Here we report an absolute age of 9.9 ± 0.7 billion years (at 95 per cent confidence) for the metal-rich globular cluster 47 Tucanae, determined by modelling the properties of the cluster's white-dwarf cooling sequence. This is about two billion years younger than has been inferred for the metal-poor cluster NGC 6397 from the same models, and provides quantitative evidence that metal-rich clusters like 47 Tucanae formed later than metal-poor halo clusters like NGC 6397.

  17. The Metal-poor non-Sagittarius (?) Globular Cluster NGC 5053: Orbit and Mg, Al, and Si Abundances

    Science.gov (United States)

    Tang, Baitian; Fernández-Trincado, J. G.; Geisler, Doug; Zamora, Olga; Mészáros, Szabolcs; Masseron, Thomas; Cohen, Roger E.; García-Hernández, D. A.; Dell’Agli, Flavia; Beers, Timothy C.; Schiavon, Ricardo P.; Sohn, Sangmo Tony; Hasselquist, Sten; Robin, Annie C.; Shetrone, Matthew; Majewski, Steven R.; Villanova, Sandro; Schiappacasse Ulloa, Jose; Lane, Richard R.; Minnti, Dante; Roman-Lopes, Alexandre; Almeida, Andres; Moreno, E.

    2018-03-01

    Metal-poor globular clusters (GCs) exhibit intriguing Al–Mg anti-correlations and possible Si–Al correlations, which are important clues to decipher the multiple-population phenomenon. NGC 5053 is one of the most metal-poor GCs in the nearby universe and has been suggested to be associated with the Sagittarius (Sgr) dwarf galaxy, due to its similarity in location and radial velocity with one of the Sgr arms. In this work, we simulate the orbit of NGC 5053, and argue against a physical connection between Sgr and NGC 5053. On the other hand, the Mg, Al, and Si spectral lines, which are difficult to detect in the optical spectra of NGC 5053 stars, have been detected in the near-infrared APOGEE spectra. We use three different sets of stellar parameters and codes to derive the Mg, Al, and Si abundances. Regardless of which method is adopted, we see a large Al variation, and a substantial Si spread. Along with NGC 5053, metal-poor GCs exhibit different Mg, Al, and Si variations. Moreover, NGC 5053 has the lowest cluster mass among the GCs that have been identified to exhibit an observable Si spread until now.

  18. Chromospheric and Transition Region Emission Properties of G, K, and M dwarf Exoplanet Host Stars

    Science.gov (United States)

    France, Kevin; Arulanantham, Nicole; Fossati, Luca; Lanza, A. F.; Linsky, Jeffrey L.; Redfield, Seth; Loyd, Robert; Schneider, Christian

    2018-01-01

    Exoplanet magnetic fields have proven notoriously hard to detect, despite theoretical predictions of substantial magnetic field strengths on close-in extrasolar giant planets. It has been suggested that stellar and planetary magnetic field interactions can manifest as enhanced stellar activity relative to nominal age-rotation-activity relationships for main sequence stars or enhanced activity on stars hosting short-period massive planets. In a recent study of M and K dwarf exoplanet host stars, we demonstrated a significant correlation between the relative luminosity in high-temperature stellar emission lines (L(ion)/L_Bol) and the “star-planet interaction strength”, M_plan/a_plan. Here, we expand on that work with a survey of G, K, and M dwarf exoplanet host stars obtained in two recent far-ultraviolet spectroscopic programs with the Hubble Space Telescope. We have measured the relative luminosities of stellar lines C II, Si III, Si IV, and N V (formation temperatures from 30,000 – 150,000 K) in a sample of ~60 exoplanet host stars and an additional ~40 dwarf stars without known planets. We present results on star-planet interaction signals as a function of spectral type and line formation temperature, as well as a statistical comparison of stars with and without planets.

  19. K-band spectroscopic metallicities and temperatures of M-dwarf stars

    Directory of Open Access Journals (Sweden)

    Rojas-Ayala Bárbara

    2013-04-01

    Full Text Available I present the metallicity and effective temperature techniques developed for M dwarf stars by Rojas-Ayala et al. (2010, 2012. These techniques are based on absorption features present in the modest resolution K-band spectra (R∼2700 of M dwarfs and have been calibrated using FGK+M dwarf pairs and synthetic atmosphere models. The H2O-K2 index seems to overestimate the effective temperatures of M dwarfs when compared to interferometric measurements. The metallicity distribution of the M dwarf host candidates by the Kepler Mission hints that jovian-size planets form preferentially around solar and super-solar metallicity environments, while small rocky planet host exhibit a wide range of metallicities, just like in their solar-type counterparts.

  20. The critical binary star separation for a planetary system origin of white dwarf pollution

    Science.gov (United States)

    Veras, Dimitri; Xu, Siyi; Rebassa-Mansergas, Alberto

    2018-01-01

    The atmospheres of between one quarter and one half of observed single white dwarfs in the Milky Way contain heavy element pollution from planetary debris. The pollution observed in white dwarfs in binary star systems is, however, less clear, because companion star winds can generate a stream of matter which is accreted by the white dwarf. Here, we (i) discuss the necessity or lack thereof of a major planet in order to pollute a white dwarf with orbiting minor planets in both single and binary systems, and (ii) determine the critical binary separation beyond which the accretion source is from a planetary system. We hence obtain user-friendly functions relating this distance to the masses and radii of both stars, the companion wind, and the accretion rate on to the white dwarf, for a wide variety of published accretion prescriptions. We find that for the majority of white dwarfs in known binaries, if pollution is detected, then that pollution should originate from planetary material.

  1. Relativistic deflection of background starlight measures the mass of a nearby white dwarf star.

    Science.gov (United States)

    Sahu, Kailash C; Anderson, Jay; Casertano, Stefano; Bond, Howard E; Bergeron, Pierre; Nelan, Edmund P; Pueyo, Laurent; Brown, Thomas M; Bellini, Andrea; Levay, Zoltan G; Sokol, Joshua; Dominik, Martin; Calamida, Annalisa; Kains, Noé; Livio, Mario

    2017-06-09

    Gravitational deflection of starlight around the Sun during the 1919 total solar eclipse provided measurements that confirmed Einstein's general theory of relativity. We have used the Hubble Space Telescope to measure the analogous process of astrometric microlensing caused by a nearby star, the white dwarf Stein 2051 B. As Stein 2051 B passed closely in front of a background star, the background star's position was deflected. Measurement of this deflection at multiple epochs allowed us to determine the mass of Stein 2051 B-the sixth-nearest white dwarf to the Sun-as 0.675 ± 0.051 solar masses. This mass determination provides confirmation of the physics of degenerate matter and lends support to white dwarf evolutionary theory. Copyright © 2017, American Association for the Advancement of Science.

  2. Environmental effects on stellar populations of star clusters and dwarf galaxies

    Science.gov (United States)

    Pasetto, Stefano; Cropper, Mark; Fujita, Yutaka; Chiosi, Cesare; Grebel, Eva K.

    2017-03-01

    We investigate the competitive role of the different dissipative phenomena acting on the onset of star formation of gravitationally bound systems in an external environment. Ram pressure, Kelvin-Helmholtz and Rayleigh-Taylor instabilities, and tidal forces are accounted for separately in an analytical framework and compared in their role in influencing the star forming regions. We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system on its surrounding environment. We consider the different signatures of these phenomena in synthetically realized colour-magnitude diagrams (CMDs) of the orbiting system thus investigating the detectability limits of these different effects for future observational projects and their relevance. The developed theoretical framework has direct applications to the cases of massive star clusters, dwarf galaxies in galaxy clusters and dwarf galaxies orbiting our Milky Way system, as well as any primordial gas-rich cluster of stars orbiting within its host galaxy.

  3. Milky Way red dwarfs in the BoRG survey; galactic scale-height and the distribution of dwarf stars in WFC3 imaging

    International Nuclear Information System (INIS)

    Holwerda, B. W.; Bouwens, R.; Trenti, M.; Clarkson, W.; Sahu, K.; Bradley, L.; Stiavelli, M.; Pirzkal, N.; Ryan, R.; De Marchi, G.; Andersen, M.

    2014-01-01

    We present a tally of Milky Way late-type dwarf stars in 68 Wide Field Camera 3 (WFC3) pure-parallel fields (227 arcmin 2 ) from the Brightest of Reionizing Galaxies survey for high-redshift galaxies. Using spectroscopically identified M-dwarfs in two public surveys, the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey and the Early Release Science mosaics, we identify a morphological selection criterion using the half-light radius (r 50 ), a near-infrared J – H, G – J color region where M-dwarfs are found, and a V – J relation with M-dwarf subtype. We apply this morphological selection of stellar objects, color-color selection of M-dwarfs, and optical-near-infrared color subtyping to compile a catalog of 274 M-dwarfs belonging to the disk of the Milky Way with a limiting magnitude of m F125W < 24(AB). Based on the M-dwarf statistics, we conclude that (1) the previously identified north-south discrepancy in M-dwarf numbers persists in our sample; there are more M-dwarfs in the northern fields on average than in southern ones, (2) the Milky Way's single disk scale-height for M-dwarfs is 0.3-4 kpc, depending on subtype, (3) the scale-height depends on M-dwarf subtype with early types (M0-4) high scale-height (z 0 = 3-4 kpc) and later types M5 and above in the thin disk (z 0 = 0.3-0.5 kpc), (4) a second component is visible in the vertical distribution, with a different, much higher scale-height in the southern fields compared to the northern ones. We report the M-dwarf component of the Sagittarius stream in one of our fields with 11 confirmed M-dwarfs, seven of which are at the stream's distance. In addition to the M-dwarf catalog, we report the discovery of 1 T-dwarfs and 30 L-dwarfs from their near-infrared colors. The dwarf scale-height and the relative low incidence in our fields of L- and T-dwarfs in these fields makes it unlikely that these stars will be interlopers in great numbers in color-selected samples of high-redshift galaxies

  4. Dwarf Galaxies with Gentle Star Formation and the Counts of Galaxies in the Hubble Deep Field

    OpenAIRE

    Campos, Ana

    1997-01-01

    In this paper the counts and colors of the faint galaxies observed in the Hubble Deep Field are fitted by means of simple luminosity evolution models that incorporate a numerous population of fading dwarfs. The observed color distribution of the very faint galaxies now allows us to put constraints on the star formation history in dwarfs. It is shown that the star-forming activity in these small systems has to proceed in a gentle way, i.e., through episodes where each one lasts much longer tha...

  5. Star Formation at Low Rates: How a Lack of Massive Stars Impacts the Evolution of Dwarf Galaxies

    Science.gov (United States)

    Hensler, Gerhard

    2017-01-01

    In recent years dedicated observations have uncovered star formation at extremely low rates in dwarf galaxies, tidal tails, ram-pressure stripped gas clouds, and the outskirts of galactic disks. At the same time, numerical simulations of galaxy evolution have advanced to higher spatial and mass resolutions, but have yet to account for the underfilling of the uppermost mass bins of stellar initial mass function (IMF) at low star-formation rates. In such situations, simulations may simply scale down the IMF, without realizing that this unrealistically results infractions of massive stars, along with fractions of massive star feedback energy (e.g., radiation and SNII explosions). Not properlyaccounting for such parameters has consequences for the self-regulation of star formation, the energetics of galaxies, as well as for the evolution of chemical abundances.Here we present numerical simulations of dwarf galaxies with low star-formation rates allowing for two extreme cases of the IMF: a "filled" case with fractional massive stars vs. a truncated IMF, at which the IMF is built bottom-up until the gas reservoir allows the formation of a last single star at an uppermost mass. The aim of the study is to demonstrate the different effects on galaxy evolution with respect to self-regulation, feedback, and chemistry. The case of a stochastic sampled IMF is situated somewhere in between these extremes.

  6. ALFALFA DISCOVERY OF THE MOST METAL-POOR GAS-RICH GALAXY KNOWN: AGC 198691

    Energy Technology Data Exchange (ETDEWEB)

    Hirschauer, Alec S.; Salzer, John J.; Rhode, Katherine L., E-mail: ash@astro.indiana.edu, E-mail: slaz@astro.indiana.edu, E-mail: krhode@indiana.edu [Department of Astronomy, Indiana University, 727 East Third Street, Bloomington, IN 47405 (United States); and others

    2016-05-10

    We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part of the Survey of H i in Extremely Low-Mass Dwarfs project, which is a multi-wavelength study of galaxies with H i masses in the range of 10{sup 6}–10{sup 7.2} M {sub ⊙}, discovered by the Arecibo Legacy Fast ALFA (ALFALFA) survey. We have obtained spectra of the lone H ii region in AGC 198691 with the new high-throughput KPNO Ohio State Multi-Object Spectrograph on the Mayall 4 m, as well as with the Blue Channel spectrograph on the MMT 6.5 m telescope. These observations enable the measurement of the temperature-sensitive [O iii] λ 4363 line and hence the determination of a “direct” oxygen abundance for AGC 198691. We find this system to be an extremely metal-deficient (XMD) system with an oxygen abundance of 12+log(O/H) = 7.02 ± 0.03, making AGC 198691 the lowest-abundance star-forming galaxy known in the local universe. Two of the five lowest-abundance galaxies known have been discovered by the ALFALFA blind H i survey; this high yield of XMD galaxies represents a paradigm shift in the search for extremely metal-poor galaxies.

  7. Temperate Earth-sized planets transiting a nearby ultracool dwarf star.

    Science.gov (United States)

    Gillon, Michaël; Jehin, Emmanuël; Lederer, Susan M; Delrez, Laetitia; de Wit, Julien; Burdanov, Artem; Van Grootel, Valérie; Burgasser, Adam J; Triaud, Amaury H M J; Opitom, Cyrielle; Demory, Brice-Olivier; Sahu, Devendra K; Bardalez Gagliuffi, Daniella; Magain, Pierre; Queloz, Didier

    2016-05-12

    Star-like objects with effective temperatures of less than 2,700 kelvin are referred to as 'ultracool dwarfs'. This heterogeneous group includes stars of extremely low mass as well as brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion), and represents about 15 per cent of the population of astronomical objects near the Sun. Core-accretion theory predicts that, given the small masses of these ultracool dwarfs, and the small sizes of their protoplanetary disks, there should be a large but hitherto undetected population of terrestrial planets orbiting them--ranging from metal-rich Mercury-sized planets to more hospitable volatile-rich Earth-sized planets. Here we report observations of three short-period Earth-sized planets transiting an ultracool dwarf star only 12 parsecs away. The inner two planets receive four times and two times the irradiation of Earth, respectively, placing them close to the inner edge of the habitable zone of the star. Our data suggest that 11 orbits remain possible for the third planet, the most likely resulting in irradiation significantly less than that received by Earth. The infrared brightness of the host star, combined with its Jupiter-like size, offers the possibility of thoroughly characterizing the components of this nearby planetary system.

  8. Supernova SN 2011fe from an exploding carbon-oxygen white dwarf star.

    Science.gov (United States)

    Nugent, Peter E; Sullivan, Mark; Cenko, S Bradley; Thomas, Rollin C; Kasen, Daniel; Howell, D Andrew; Bersier, David; Bloom, Joshua S; Kulkarni, S R; Kandrashoff, Michael T; Filippenko, Alexei V; Silverman, Jeffrey M; Marcy, Geoffrey W; Howard, Andrew W; Isaacson, Howard T; Maguire, Kate; Suzuki, Nao; Tarlton, James E; Pan, Yen-Chen; Bildsten, Lars; Fulton, Benjamin J; Parrent, Jerod T; Sand, David; Podsiadlowski, Philipp; Bianco, Federica B; Dilday, Benjamin; Graham, Melissa L; Lyman, Joe; James, Phil; Kasliwal, Mansi M; Law, Nicholas M; Quimby, Robert M; Hook, Isobel M; Walker, Emma S; Mazzali, Paolo; Pian, Elena; Ofek, Eran O; Gal-Yam, Avishay; Poznanski, Dovi

    2011-12-14

    Type Ia supernovae have been used empirically as 'standard candles' to demonstrate the acceleration of the expansion of the Universe even though fundamental details, such as the nature of their progenitor systems and how the stars explode, remain a mystery. There is consensus that a white dwarf star explodes after accreting matter in a binary system, but the secondary body could be anything from a main-sequence star to a red giant, or even another white dwarf. This uncertainty stems from the fact that no recent type Ia supernova has been discovered close enough to Earth to detect the stars before explosion. Here we report early observations of supernova SN 2011fe in the galaxy M101 at a distance from Earth of 6.4 megaparsecs. We find that the exploding star was probably a carbon-oxygen white dwarf, and from the lack of an early shock we conclude that the companion was probably a main-sequence star. Early spectroscopy shows high-velocity oxygen that slows rapidly, on a timescale of hours, and extensive mixing of newly synthesized intermediate-mass elements in the outermost layers of the supernova. A companion paper uses pre-explosion images to rule out luminous red giants and most helium stars as companions to the progenitor.

  9. Lithium abundances in nearby FGK dwarf and subgiant stars: internal destruction, Galactic chemical evolution, and exoplanets

    OpenAIRE

    Ramirez, I.; Fish, J. R.; Lambert, D. L.; Prieto, C. Allende

    2012-01-01

    We derive atmospheric parameters and lithium abundances for 671 stars and include our measurements in a literature compilation of 1381 dwarf and subgiant stars. First, a "lithium desert" in the effective temperature (Teff) versus lithium abundance (A_Li) plane is observed such that no stars with Teff~6075 K and A_Li~1.8 are found. We speculate that most of the stars on the low A_Li side of the desert have experienced a short-lived period of severe surface lithium destruction as main-sequence ...

  10. White dwarf stars exceeding the Chandrasekhar mass limit

    Science.gov (United States)

    Tomaschitz, Roman

    2018-01-01

    The effect of nonlinear ultra-relativistic electron dispersion on the mass-radius relation of high-mass white dwarfs is studied. The dispersion is described by a permeability tensor in the Dirac equation, generated by the ionized high-density stellar matter, which constitutes the neutralizing background of the nearly degenerate electron plasma. The electron dispersion results in a stable mass-radius relation for high-mass white dwarfs, in contrast to a mass limit in the case of vacuum permeabilities. In the ultra-relativistic regime, the dispersion relation is a power law whose amplitude and scaling exponent is inferred from mass and radius estimates of two high-mass white dwarfs, Sirius B and LHS 4033. Evidence for the existence of super-Chandrasekhar mass white dwarfs is provided by several Type Ia supernovae (e.g., SN 2013cv, SN 2003fg, SN 2007if and SN 2009dc), whose mass ejecta exceed the Chandrasekhar limit by up to a factor of two. The dispersive mass-radius relation is used to estimate the radii, central densities, Fermi temperatures, bulk and compression moduli and sound velocities of their white dwarf progenitors.

  11. Stellar Abundances for Galactic Archaeology Database. IV. Compilation of stars in dwarf galaxies

    Science.gov (United States)

    Suda, Takuma; Hidaka, Jun; Aoki, Wako; Katsuta, Yutaka; Yamada, Shimako; Fujimoto, Masayuki Y.; Ohtani, Yukari; Masuyama, Miyu; Noda, Kazuhiro; Wada, Kentaro

    2017-10-01

    We have constructed a database of stars in Local Group galaxies using the extended version of the SAGA (Stellar Abundances for Galactic Archaeology) database that contains stars in 24 dwarf spheroidal galaxies and ultra-faint dwarfs. The new version of the database includes more than 4500 stars in the Milky Way, by removing the previous metallicity criterion of [Fe/H] ≤ -2.5, and more than 6000 stars in the Local Group galaxies. We examined the validity of using a combined data set for elemental abundances. We also checked the consistency between the derived distances to individual stars and those to galaxies as given in the literature. Using the updated database, the characteristics of stars in dwarf galaxies are discussed. Our statistical analyses of α-element abundances show that the change of the slope of the [α/Fe] relative to [Fe/H] (so-called "knee") occurs at [Fe/H] = -1.0 ± 0.1 for the Milky Way. The knee positions for selected galaxies are derived by applying the same method. The star formation history of individual galaxies is explored using the slope of the cumulative metallicity distribution function. Radial gradients along the four directions are inspected in six galaxies where we find no direction-dependence of metallicity gradients along the major and minor axes. The compilation of all the available data shows a lack of CEMP-s population in dwarf galaxies, while there may be some CEMP-no stars at [Fe/H] ≲ -3 even in the very small sample. The inspection of the relationship between Eu and Ba abundances confirms an anomalously Ba-rich population in Fornax, which indicates a pre-enrichment of interstellar gas with r-process elements. We do not find any evidence of anti-correlations in O-Na and Mg-Al abundances, which characterizes the abundance trends in the Galactic globular clusters.

  12. Stellar Archeology: What White Dwarf Stars Tell Us About the History of the Galaxy

    Directory of Open Access Journals (Sweden)

    Terry D. Oswalt

    2012-06-01

    Full Text Available White dwarf stars have played important roles in rather diverse areas of astrophysics. This paper outlines how these stellar remnants, especially those in widely separated “fragile” binaries, have provided unique leverage on difficult astrophysical problems such as the ages of stars, the structure and evolution of the Galaxy, the nature of dark matter and even the discovery of dark energy.

  13. Detection of brown dwarfs by the micro-lensing of unresolved stars

    CERN Document Server

    Baillon, Paul; Giraud-Héraud, Yannick; Kaplan, J; Baillon, Paul; Bouquet, Alain; Giraud-Héraud, Yannick; Kaplan, Jean

    1993-01-01

    The presence of brown dwarfs in the dark galactic halo could be detected through their gravitational lensing effect and experiments under way monitor about one million stars to observe a few lensing events per year. We show that if the photon flux from a galaxy is measured with a good precision, it is not necessary to resolve the stars and besides more events could be observed.

  14. A possible formation scenario for dwarf spheroidal galaxies - III. Adding star formation histories to the fiducial model

    Science.gov (United States)

    Alarcón Jara, A. G.; Fellhauer, M.; Matus Carrillo, D. R.; Assmann, P.; Urrutia Zapata, F.; Hazeldine, J.; Aravena, C. A.

    2018-02-01

    Dwarf spheroidal galaxies are regarded as the basic building blocks in the formation of larger galaxies and are the most dark matter dominated systems in the Universe, known so far. There are several models that attempt to explain their formation and evolution, but they have problems modelling the formation of isolated dwarf spheroidal galaxies. Here, we will explain a possible formation scenario in which star clusters form inside the dark matter halo of a dwarf spheroidal galaxy. These star clusters suffer from low star formation efficiency and dissolve while orbiting inside the dark matter halo. Thereby, they build the faint luminous components that we observe in dwarf spheroidal galaxies. In this paper, we study this model by adding different star formation histories to the simulations and compare the results with our previous work and observational data to show that we can explain the formation of dwarf spheroidal galaxies.

  15. The Star Formation & Chemical Evolution Timescales of Two Nearby Dwarf Spheroidal Galaxies

    NARCIS (Netherlands)

    de Boer, Thomas; Tolstoy, E.; Hill, V.; Saha, A.; Olsen, K.; Starkenburg, E.; Irwin, M.; Battaglia, G.

    We present wide-field photometry of resolved stars in the nearby Sculptor and Fornax dwarf spheroidal galaxies, going down to the oldest Main Sequence Turn-Off. The accurately flux calibrated wide-field Colour-Magnitude Diagrams are used directly in combination with spectroscopic metallicities of

  16. The star formation and chemical evolution history of the Fornax dwarf spheroidal galaxy

    NARCIS (Netherlands)

    de Boer, T. J. L.; Tolstoy, E.; Hill, V.; Saha, A.; Olszewski, E. W.; Mateo, M.; Starkenburg, E.; Battaglia, G.; Walker, M. G.

    We present deep photometry in the B, V and I filters from CTIO/MOSAIC for about 270 000 stars in the Fornax dwarf spheroidal galaxy, out to a radius of rell ≈ 0.8 degrees. By combining the accurately calibrated photometry with the spectroscopic metallicity distributions of individual red giant

  17. REVERSAL OF FORTUNE: INCREASED STAR FORMATION EFFICIENCIES IN THE EARLY HISTORIES OF DWARF GALAXIES?

    International Nuclear Information System (INIS)

    Madau, Piero; Weisz, Daniel R.; Conroy, Charlie

    2014-01-01

    On dwarf galaxy scales, the different shapes of the galaxy stellar mass function and the dark halo mass function require a star-formation efficiency (SFE) in these systems that is currently more than 1 dex lower than that of Milky Way-size halos. Here, we argue that this trend may actually be reversed at high redshift. Specifically, by combining the resolved star-formation histories of nearby isolated dwarfs with the simulated mass-growth rates of dark matter halos, we show that the assembly of these systems occurs in two phases: (1) an early, fast halo accretion phase with a rapidly deepening potential well, characterized by a high SFE; and (2) a late, slow halo accretion phase where, perhaps as a consequence of reionization, the SFE is low. Nearby dwarfs have more old stars than predicted by assuming a constant or decreasing SFE with redshift, a behavior that appears to deviate qualitatively from the trends seen among more massive systems. Taken at face value, the data suggest that at sufficiently early epochs, dwarf galaxy halos above the atomic cooling mass limit can be among the most efficient sites of star formation in the universe

  18. Metallicity and the spectral energy distribution and spectral types of dwarf O-stars

    NARCIS (Netherlands)

    Mokiem, M.R.; Martín-Hernández, N.L.; Lenorzer, A.; de Koter, A.; Tielens, A.G.G.M.

    2004-01-01

    We present a systematic study of the effect of metallicity on the stellar spectral energy distribution (SED) of O main sequence (dwarf) stars, focussing on the hydrogen and helium ionizing continua, and on the optical and near-IR lines used for spectral classification. The spectra are based on

  19. Discovery of a group of star-forming dwarf galaxies in A1367

    NARCIS (Netherlands)

    Sakai, S; Kennicutt, RC; van der Hulst, JM; Moss, C

    2002-01-01

    We describe the properties of a remarkable group of actively star-forming dwarf galaxies and H II galaxies in the A1367 cluster, which were discovered in a large-scale Halpha imaging survey of the cluster. Approximately 30 Halpha-emitting knots were identified in a region approximately 150 kpc

  20. Spectropolarimetric Survey of Hydrogen-rich White Dwarf Stars

    Czech Academy of Sciences Publication Activity Database

    Kawka, Adela; Vennes, S.; Schmidt, G. D.; Wickramasinghe, D.T.; Koch, R.

    2007-01-01

    Roč. 654, č. 1 (2007), s. 499-520 ISSN 0004-637X R&D Projects: GA ČR GP205/05/P186 Institutional research plan: CEZ:AV0Z10030501 Keywords : magnetic fields * white dwarf s Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 6.405, year: 2007

  1. Sulphur in the metal poor globular cluster NGC 6397

    Science.gov (United States)

    Koch, A.; Caffau, E.

    2011-10-01

    Sulphur (S) is a non-refractory α-element that is not locked into dust grains in the interstellar medium. Thus no correction to the measured, interstellar sulphur abundance is needed and it can be readily compared to the S content in stellar photospheres. Here we present the first measurement of sulphur in the metal poor globular cluster (GC) NGC 6397, as detected in a MIKE/Magellan high signal-to-noise, high-resolution spectrum of one red giant star. While abundance ratios of sulphur are available for a larger number of Galactic stars down to an [Fe/H] of ~ -3.5 dex, no measurements in globular clusters more metal poor than -1.5 dex have been reported so far. We find aNLTE, 3-D abundance ratio of [S/Fe] = +0.52 ± 0.20 (stat.) ± 0.08 (sys.), based on theS I, Multiplet 1 line at 9212.8 Å. This value is consistent with a Galactic halo plateau as typical of other α-elements in GCs and field stars, but we cannot rule out its membership with a second branch of increasing [S/Fe] with decreasing [Fe/H], claimed in the literature, which leads to a large scatter at metallicities around - 2 dex. The [S/Mg] and [S/Ca] ratios in this star are compatible with a Solar value to within the (large) uncertainties. Despite the very large scatter in these ratios across Galactic stars between literature samples, this indicates that sulphur traces the chemical imprints of the other α-elements in metal poor GCs. Combined with its moderate sodium abundance ([S/Na]NLTE = 0.48), the [S/Fe] ratio in this GC extends a global, positive S-Na correlation that is not seen in field stars and might indicate that proton-capture reactions contributed to the production of sulphur in the (metal poor) early GC environments. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  2. A detailed study of lithium in 107 CHEPS dwarf stars

    Science.gov (United States)

    Pavlenko, Ya. V.; Jenkins, J. S.; Ivanyuk, O. M.; Jones, H. R. A.; Kaminsky, B. M.; Lyubchik, Yu. P.; Yakovina, L. A.

    2018-03-01

    Context. We report results from lithium abundance determinations using high resolution spectral analysis of the 107 metal-rich stars from the Calan-Hertfordshire Extrasolar Planet Search programme. Aims: We aim to set out to understand the lithium distribution of the population of stars taken from this survey. Methods: The lithium abundance taking account of non-local thermodynamical equilibrium effects was determined from the fits to the Li I 6708 Å resonance doublet profiles in the observed spectra. Results: We find that a) fast rotators tend to have higher lithium abundances; b) log N(Li) is higher in more massive and hot stars; c) log N(Li) is higher in stars of lower log g; d) stars with the metallicities >0.25 dex do not show the lithium lines in their spectra; e) most of our planet hosts rotate slower; and f) a lower limit of lithium isotopic ratio is 7Li/6Li > 10 in the atmospheres of two stars with planets (SWP) and two non-SWP stars. Conclusions: Measurable lithium abundances were found in the atmospheres of 45 stars located at distances of 20-170 pc from the Sun, for the other 62 stars the upper limits of log N(Li) were computed. We found well defined dependences of lithium abundances on Teff, V sin i, and less pronounced for the log g. In case of V sin i we see two sequences of stars: with measurable lithium and with the upper limit of log N(Li). About 10% of our targets are known to host planets. Only two SWP have notable lithium abundances, so we found a lower proportion of stars with detectable Li among known planet hosts than among stars without planets. However, given the small sample size of our planet-host sample, our analysis does not show any statistically significant differences in the lithium abundance between SWP and stars without known planets.

  3. History of the Milky Way star formation rate from the white dwarf luminosity function

    Energy Technology Data Exchange (ETDEWEB)

    Noh, Hyerim; Scalo, J. (Texas Univ., Austin (USA))

    1990-04-01

    Consideration is given to the use of the white dwarf luminosity function (WDLF) to study the history of the star formation rate in the Galaxy. It is shown that the WDLF is much more sensitive to the star formation rate than to variations in the initial mass function. A marginal feature in the WDLF at log(L/solar L) = -2 is found to represent the burst of star formation which occurred 300 million yrs ago, as proposed by Barry (1988) and Scalo (1987, 1988). Observations are used to limit the ratio of recent to past average star formation rates for smoothly decreasing and increasing star formation rates. The star formation rate histories derived from the results of Twarog (1980) and Barry (1988) are compared. 34 refs.

  4. History of the Milky Way star formation rate from the white dwarf luminosity function

    Science.gov (United States)

    Noh, Hye-Rim; Scalo, John

    1990-04-01

    Consideration is given to the use of the white dwarf luminosity function (WDLF) to study the history of the star formation rate in the Galaxy. It is shown that the WDLF is much more sensitive to the star formation rate than to variations in the initial mass function. A marginal feature in the WDLF at log(L/solar L) = -2 is found to represent the burst of star formation which occurred 300 million yrs ago, as proposed by Barry (1988) and Scalo (1987, 1988). Observations are used to limit the ratio of recent to past average star formation rates for smoothly decreasing and increasing star formation rates. The star formation rate histories derived from the results of Twarog (1980) and Barry (1988) are compared.

  5. The evolution of white dwarfs resulting from helium-enhanced, low-metallicity progenitor stars

    Science.gov (United States)

    Althaus, Leandro G.; De Gerónimo, Francisco; Córsico, Alejandro; Torres, Santiago; García-Berro, Enrique

    2017-01-01

    Context. Some globular clusters host multiple stellar populations with different chemical abundance patterns. This is particularly true for ω Centauri, which shows clear evidence of a helium-enriched subpopulation characterized by a helium abundance as high as Y = 0.4 Aims: We present a whole and consistent set of evolutionary tracks from the ZAMS to the white dwarf stage that is appropriate for the study of the formation and evolution of white dwarfs resulting from the evolution of helium-rich progenitors. Methods: We derived white dwarf sequences from progenitors with stellar mass ranging from 0.60 to 2.0 M⊙ and for an initial helium abundance of Y = 0.4. We adopted two values of metallicity: Z = 0.001 and Z = 0.0005. Results: We explored different issues of white dwarf evolution and their helium-rich progenitors. In particular, the final mass of the remnants, the role of overshooting during the thermally pulsing phase, and the cooling of the resulting white dwarfs differ markedly from the evolutionary predictions of progenitor stars with the standard initial helium abundance. Finally, the pulsational properties of the resulting white dwarfs are also explored. Conclusions: We find that, for the range of initial masses explored in this paper, the final mass of the helium-rich progenitors is markedly higher than the final mass expected from progenitors with the usual helium abundance. We also find that progenitors with initial mass lower than M ≃ 0.65 M⊙ evolve directly into helium-core white dwarfs in less than 14 Gyr, and that, for larger progenitor masses, the evolution of the resulting low-mass carbon-oxygen white dwarfs is dominated by residual nuclear burning. For helium-core white dwarfs, we find that they evolve markedly faster than their counterparts coming from standard progenitors. Also, in contrast with what occurs for white dwarfs resulting from progenitors with the standard helium abundance, the impact of residual burning on the cooling time of

  6. White dwarf-red dwarf binaries in the Galaxy

    NARCIS (Netherlands)

    Besselaar, E.J.M. van den

    2007-01-01

    This PhD thesis shows several studies on white dwarf - red dwarf binaries. White dwarfs are the end products of most stars and red dwarfs are normal hydrogen burning low-mass stars. White dwarf - red dwarf binaries are both blue (white dwarf) and red (red dwarf). Together with the fact that they are

  7. Multi-Epoch Hubble Space Telescope Observations of IZw18 : Characterization of Variable Stars at Ultra-Low Metallicities

    NARCIS (Netherlands)

    Fiorentino, G.; Ramos, R. Contreras; Clementini, G.; Marconi, M.; Musella, I.; Aloisi, A.; Annibali, F.; Saha, A.; Tosi, M.; van der Marel, R. P.

    2010-01-01

    Variable stars have been identified for the first time in the very metal-poor blue compact dwarf galaxy IZw18, using deep multi-band (F606W, F814W) time-series photometry obtained with the Advanced Camera for Surveys on board the Hubble Space Telescope. We detected 34 candidate variable stars in the

  8. Compact Objects in Astrophysics White Dwarfs, Neutron Stars and Black Holes

    CERN Document Server

    Camenzind, Max

    2007-01-01

    Compact objects are an important class of astronomical objects in current research. Supermassive black holes play an important role in the understanding of the formation of galaxies in the early Universe. Old white dwarfs are nowadays used to calibrate the age of the Universe. Mergers of neutron stars and black holes are the sources of intense gravitational waves which will be measured in the next ten years by gravitational wave detectors. Camenzind's Compact Objects in Astrophysics gives a comprehensive introduction and up-to-date overview about the physical processes behind these objects, covering the field from the beginning to most recent results, including all relevant observations. After a presentation of the taxonomy of compact objects, the basic principles of general relativity are given. The author then discusses in detail the physics and observations of white dwarfs and neutron stars (including the most recent equations of state for neutron star matter), the gravitational field of rapidly rotating c...

  9. Understanding of variability properties in very low mass stars and brown dwarfs

    Science.gov (United States)

    Mondal, Soumen; Ghosh, Samrat; Khata, Dhrimadri; Joshi, Santosh; Das, Ramkrishna

    2018-04-01

    We report on photometric variability studies of a L3.5 brown dwarf 2MASS J00361617+1821104 (2M0036+18) in the field and of four young brown dwarfs in the star-forming region IC 348. From muti-epoch observations, we found significant periodic variability in 2M0036+18 with a period of 2.66 ± 0.55 hours on one occasion while it seemed to be non-variable on three other occasions. An evolving dust cloud might cause such a scenario. Among four young brown dwarfs of IC 348 in the spectral range M7.25 - M8, one brown dwarf 2MASS J03443921+3208138 shows significant variability. The K-band spectra (2.0-2.4 μm) of nine very low mass stars (M1 - M9 V) are used to characterize the water band index (H20-K2). We found that it is strongly correlated with the surface temperature of M dwarfs.

  10. Evidences of extragalactic origin and planet engulfment in the metal-poor twin pair HD 134439/HD 134440

    Science.gov (United States)

    Reggiani, Henrique; Meléndez, Jorge

    2018-04-01

    Recent studies of chemical abundances in metal-poor halo stars show the existence of different populations, which is important for studies of Galaxy formation and evolution. Here, we revisit the twin pair of chemically anomalous stars HD 134439 and HD 134440, using high resolution (R ˜ 72 000) and high S/N ratio (S/N ˜ 250) HDS/Subaru spectra. We compare them to the well-studied halo star HD 103095, using the line-by-line differential technique to estimate precise stellar parameters and LTE chemical abundances. We present the abundances of C, O, Na, Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Sr, Y, Ba, La, Ce, Nd, and Sm. We compare our results to the precise abundance patterns of Nissen & Schuster (2010) and data from dwarf Spheroidal galaxies (dSphs). We show that the abundance pattern of these stars appears to be closely linked to that of dSphs with [α/Fe] knee below [Fe/H] < -1.5. We also find a systematic difference of 0.06 ± 0.01 dex between the abundances of these twin binary stars, which could be explained by the engulfment of a planet, thus suggesting that planet formation is possible at low metallicities ([Fe/H] = -1.4).

  11. Bursts of star formation in computer simulations of dwarf galaxies

    International Nuclear Information System (INIS)

    Comins, N.F.

    1984-01-01

    A three-dimensional Stochastic Self-Propagating Star Formation (SSPSF) model of compact galacies is presented. Two phases of gas, active and inactive, are present, and permanent depletion of gas in the form of long lived, low mass stars and remnants occurs. Similarly, global infall of gas from a galactic halo or through galactic cannibalism is permitted. We base our parameters on the observed properties of the compact blue galaxy I Zw 36. Our results are that bursts of star formation occur much more frequently in these runs than continuous nonbursting star formation, suggesting that the blue compact galaxies are probably undergoing bursts rather than continuous, nonbursting low-level star formation activity

  12. Chemical abundances of giant stars in NGC 5053 and NGC 5634, two globular clusters associated with the Sagittarius dwarf spheroidal galaxy?

    Science.gov (United States)

    Sbordone, L.; Monaco, L.; Moni Bidin, C.; Bonifacio, P.; Villanova, S.; Bellazzini, M.; Ibata, R.; Chiba, M.; Geisler, D.; Caffau, E.; Duffau, S.

    2015-07-01

    Context. The tidal disruption of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) is producing the most prominent substructure in the Milky Way (MW) halo, the Sagittarius Stream. Aside from field stars, it is suspected that the Sgr dSph has lost a number of globular clusters (GC). Many Galactic GC are thought to have originated in the Sgr dSph. While for some candidates an origin in the Sgr dSph has been confirmed owing to chemical similarities, others exist whose chemical composition has never been investigated. Aims: NGC 5053 and NGC 5634 are two of these scarcely studied Sgr dSph candidate-member clusters. To characterize their composition we analyzed one giant star in NGC 5053, and two in NGC 5634. Methods: We analyze high-resolution and signal-to-noise spectra by means of the MyGIsFOS code, determining atmospheric parameters and abundances for up to 21 species between O and Eu. The abundances are compared with those of MW halo field stars, of unassociated MW halo globulars, and of the metal-poor Sgr dSph main body population. Results: We derive a metallicity of [Fe ii/H] = -2.26 ± 0.10 for NGC 5053, and of [Fe i/H] = -1.99 ± 0.075 and -1.97 ± 0.076 for the two stars in NGC 5634. This makes NGC 5053 one of the most metal-poor globular clusters in the MW. Both clusters display an α enhancement similar to the one of the halo at comparable metallicity. The two stars in NGC 5634 clearly display the Na-O anticorrelation widespread among MW globulars. Most other abundances are in good agreement with standard MW halo trends. Conclusions: The chemistry of the Sgr dSph main body populations is similar to that of the halo at low metallicity. It is thus difficult to discriminate between an origin of NGC 5053 and NGC 5634 in the Sgr dSph, and one in the MW. However, the abundances of these clusters do appear closer to that of Sgr dSph than of the halo, favoring an origin in the Sgr dSph system. Appendix A is available in electronic form at http

  13. Two new pulsating low-mass pre-white dwarfs or SX Phoenicis stars?

    Science.gov (United States)

    Corti, M. A.; Kanaan, A.; Córsico, A. H.; Kepler, S. O.; Althaus, L. G.; Koester, D.; Sánchez Arias, J. P.

    2016-03-01

    Context. The discovery of pulsations in low-mass stars opens an opportunity to probe their interiors and determine their evolution by employing the tools of asteroseismology. Aims: We aim to analyse high-speed photometry of SDSS J145847.02+070754.46 and SDSS J173001.94+070600.25 and discover brightness variabilities. In order to locate these stars in the Teff - log g diagram, we fit optical spectra (SDSS) with synthetic non-magnetic spectra derived from model atmospheres. Methods: To carry out this study, we used the photometric data we obtained for these stars with the 2.15 m telescope at CASLEO, Argentina. We analysed their light curves and applied the discrete Fourier transform (FT) to determine the pulsation frequencies. Finally, we compare both stars in the Teff - log g diagram, with two known pre-white dwarfs and seven pulsating pre-ELM white dwarf stars, δ Scuti, and SX Phe stars Results: We report the discovery of pulsations in SDSS J145847.02+070754.46 and SDSS J173001.94+070600.25. We determine their effective temperature and surface gravity to be Teff = 7972 ± 200 K, log g = 4.25 ± 0.5 and Teff = 7925 ± 200 K, log g = 4.25 ± 0.5, respectively. With these parameters, these new pulsating low-mass stars can be identified with either ELM white dwarfs (with ~0.17 M⊙) or more massive SX Phe stars. We identified pulsation periods of 3278.7 and 1633.9 s for SDSS J145847.02+070754.46 and a pulsation period of 3367.1 s for SDSS J173001.94+070600.25. These two new objects, together with those of Maxted et al. (2013, 2014), indicate the possible existence of a new instability domain towards the late stages of evolution of low-mass white dwarf stars, although their identification with SX Phe stars cannot be discarded. Visiting Astronomer, Complejo Astronómico El Leoncito operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan.

  14. Suppression of star formation in dwarf galaxies by photoelectric grain heating feedback.

    Science.gov (United States)

    Forbes, John C; Krumholz, Mark R; Goldbaum, Nathan J; Dekel, Avishai

    2016-07-28

    Photoelectric heating--heating of dust grains by far-ultraviolet photons--has long been recognized as the primary source of heating for the neutral interstellar medium. Simulations of spiral galaxies have shown some indication that photoelectric heating could suppress star formation; however, simulations that include photoelectric heating have typically shown that it has little effect on the rate of star formation in either spiral galaxies or dwarf galaxies, which suggests that supernovae are responsible for setting the gas depletion time in galaxies. This result is in contrast with recent work indicating that a star formation law that depends on galaxy metallicity--as is expected with photoelectric heating,but not with supernovae--reproduces the present-day galaxy population better than does a metallicity-independent one. Here we report a series of simulations of dwarf galaxies, the class of galaxy in which the effects of both photoelectric heating and supernovae are expected to be strongest. We simultaneously include space and time-dependent photoelectric heating in our simulations, and we resolve the energy-conserving phase of every supernova blast wave, which allows us to directly measure the relative importance of feedback by supernovae and photoelectric heating in suppressing star formation. We find that supernovae are unable to account for the observed large gas depletion times in dwarf galaxies. Instead, photoelectric heating is the dominant means by which dwarf galaxies regulate their star formation rate at any given time,suppressing the rate by more than an order of magnitude relative to simulations with only supernovae.

  15. Lithium abundances in samples of dwarf stars of population II and very old population I

    International Nuclear Information System (INIS)

    Molaro, P.; Beckman, J.; Rebolo, R.

    1986-01-01

    We have used the CCD camera and Intermediate Dispersion Spectrograph of the 2.5m Isaac Newton Telescope to obtain high quality spectra of the 6708 A 7 Li resonance doublet in 22 dwarfs with metallicities ≤ -0.7. We find a mean constant value of Log N(Li)= 2.07 (±0.1) for highly metal deficient dwarfs ([Fe/H] ≤ -1.5) with atmospheric temperatures T eff > 5500 K, and a larger spread with values of Log N(Li) up to 2.4 for the warmer dwarfs with metallicities between -0.7 and -1.2. Our results agree with previous findings showing a highly uniform Li abundance near the inception of the galaxy. Li depletion appears to set in at higher temperatures for the moderately metal deficient stars than for the extremely metal deficient, consistent with metallicity-dependent depletion rates (low metals, low depletion)

  16. New circumstellar disk candidates around young low mass stars and brown dwarfs

    Science.gov (United States)

    Boucher, Anne; Lafrenière, David; Gagné, Jonathan; Malo, Lison; Doyon, Rene

    2015-12-01

    It is now common knowledge that circumstellar disks are signposts of past or ongoing planetary system formation. Their presence and their properties, in relation to those of their host star, also bear valuable information about the process of star formation itself. To address these questions, we started a project to uncover new circumstellar disks around newly identified low mass star and brown dwarf candidates in nearby young kinematic associations. Being near the stellar/substellar mass boundary, these hosts - and their potential disks - are particularly interesting to study both star and planet formation. We used a least squares approach to fit synthetic spectra to the observed photometric data of each star, covering from 0.8 µm up to 22 µm, and then identified candidates showing a significant excess compared to the best fits. We then carefully looked at the data for these candidates to filter out those biased by contaminants or other artefacts. We ended up with a list of 4 young stars and brown dwarfs strongly suspected of being surrounded by a disk. Here we will present our search method and some properties of our newly identified disk-bearing candidates.

  17. White Dwarfs in Cataclysmic Variable Stars: Surface Temperatures and Evolution

    Directory of Open Access Journals (Sweden)

    Edward M. Sion

    2012-06-01

    Full Text Available A summary is presented of what is currently known about the surface temperatures of accreting white dwarfs (WDs detected in non-magnetic and magnetic cataclysmic variables (CVs based upon synthetic spectral analyses of far ultraviolet data. A special focus is placed on WD temperatures above and below the CV period gap as a function of the orbital period, Porb. The principal uncertainty of the temperatures for the CV WDs in the Teff - Porb distribution, besides the distance to the CV, is the mass of the WD. Only in eclipsing CV systems, an area of eclipsing binary studies, which was so central to Robert H. Koch’s career, is it possible to know CV WD masses with high precision.

  18. Lessons for Asteroseismology from White Dwarf Stars Travis S ...

    Indian Academy of Sciences (India)

    idea is that convection generates sound waves at all frequencies (“white noise”, like static on a radio). ... values of the sound speed (or Lamb frequency, L) and the buoyancy frequency (N) from the center of the star to .... in any stellar population (the Galactic disk and halo, open and globular clusters) to determine the age, it ...

  19. UVES abundances of stars in nearby dwarf spheroidal galaxies

    NARCIS (Netherlands)

    Tolstoy, E; Venn, K; Shetrone, M; Primas, F; Hill, [No Value; Kaufer, A; Szeifert, T

    2002-01-01

    It is a truth universally acknowledged, that a galaxy in possession of a good quantity of gas must want to form stars. It is the details of how and why that baffle us all. The simplest theories either would have this process a carefully self-regulated affair, or one that goes completely out of

  20. Rapid Evolution of the Gaseous Exoplanetary Debris around the White Dwarf Star HE 1349–2305

    Science.gov (United States)

    Dennihy, E.; Clemens, J. C.; Dunlap, B. H.; Fanale, S. M.; Fuchs, J. T.; Hermes, J. J.

    2018-02-01

    Observations of heavy metal pollution in white dwarf stars indicate that metal-rich planetesimals are frequently scattered into star-grazing orbits, tidally disrupted, and accreted onto the white dwarf surface, offering direct insight into the dynamical evolution of post-main-sequence exoplanetary systems. Emission lines from the gaseous debris in the accretion disks of some of these systems show variations on timescales of decades, and have been interpreted as the general relativistic precession of a recently formed, elliptical disk. Here we present a comprehensive spectroscopic monitoring campaign of the calcium infrared triplet emission in one system, HE 1349–2305, which shows morphological emission profile variations suggestive of a precessing, asymmetric intensity pattern. The emission profiles are shown to vary on a timescale of one to two years, which is an order of magnitude shorter than what has been observed in other similar systems. We demonstrate that this timescale is likely incompatible with general relativistic precession, and consider alternative explanations for the rapid evolution, including the propagation of density waves within the gaseous debris. We conclude with recommendations for follow-up observations, and discuss how the rapid evolution of the gaseous debris in HE 1349–2305 could be leveraged to test theories of exoplanetary debris disk evolution around white dwarf stars.

  1. Discovery of Temperate Earth-Sized Planets Transiting a Nearby Ultracool Dwarf Star

    Science.gov (United States)

    Jehin, Emmanuel; Gillon, Michael; Lederer, Susan M.; Delrez, Laetitia; De Wit, Julien; Burdanov, Artem; Van Grootel, Valerie; Burgasser, Adam; Triaud, Amaury; Demory, Brice-Olivier; hide

    2016-01-01

    We report the discovery of three short-period Earth-sized planets transiting a nearby ultracool dwarf star using data collected by the Liège TRAPPIST telescope, located in la Silla (Chile). TRAPPIST-1 is an isolated M8.0+/-0.5-type dwarf star at a distance of 12.0+/-0.4 parsecs as measured by its trigonometric parallax, with an age constrained to be > 500 Myr, and with a luminosity, mass, and radius of 0.05%, 8% and 11.5% those of the Sun, respectively. The small size of the host star, only slightly larger than Jupiter, translates into Earth-like radii for the three discovered planets, as deduced from their transit depths. The inner two planets receive four and two times the irradiation of Earth, respectively, placing them close to the inner edge of the habitable zone of the star. Several orbits remain possible for the third planet based on our current data. The infrared brightness of the host star combined with its Jupiter-like size offer the possibility of thoroughly characterizing the components of this nearby planetary system.

  2. The extent of chemically enriched gas around star-forming dwarf galaxies

    Science.gov (United States)

    Johnson, Sean

    2018-01-01

    Supernovae driven winds are often invoked to remove chemically enriched gas from galaxies to match the low metallicities of dwarf galaxies. In such shallow potential wells, outflows may produce massive amounts of enriched halo gas (circum-galactic medium or CGM) and pollute the intergalactic medium (IGM). I will present a survey of the CGM and IGM around 18 star-forming field dwarf galaxies with stellar masses of log M*/M⊙ ≈ 8 ‑ 9 at z ≈ 0.2. Eight of these have CGM probed by quasar absorption spectra at projected distances, d, less than the host virial radius, Rh. Ten are probed at d/Rh = 1 ‑ 3 to study the surrounding IGM. The absorption measurements include neutral hydrogen (H I), the dominant silicon ions for diffuse cool gas (T ∼ 104 K; Si II, Si III, and Si IV), more highly ionized carbon (C IV), and highly ionized oxygen (O VI). The metal absorption from the CGM of the dwarf galaxies is less common and ≈ 4× weaker compared to massive star-forming galaxies though O VI absorption is still common. None of the dwarfs probed at d/Rh = 1 ‑ 3 have definitive metal-line detections. Combining the available silicon ions, we estimate that the cool CGM accounts for only 2 ‑ 6% of the expected silicon budget. CGM absorption from O VI can account for ≈ 8% of the expected oxygen budget. As O VI traces an ion with expected equilibrium ion fractions of 0.2, this highly ionized phase of the CGM may represent a significant metal reservoir even for dwarf galaxies not expected to maintain gravitationally shock heated hot halos.

  3. PROBABILITY OF CME IMPACT ON EXOPLANETS ORBITING M DWARFS AND SOLAR-LIKE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Kay, C. [Solar Physics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Opher, M.; Kornbleuth, M., E-mail: ckay@bu.edu [Astronomy Department, Boston University, Boston, MA 02215 (United States)

    2016-08-01

    Solar coronal mass ejections (CMEs) produce adverse space weather effects at Earth. Planets in the close habitable zone of magnetically active M dwarfs may experience more extreme space weather than at Earth, including frequent CME impacts leading to atmospheric erosion and leaving the surface exposed to extreme flare activity. Similar erosion may occur for hot Jupiters with close orbits around solar-like stars. We have developed a model, Forecasting a CME's Altered Trajectory (ForeCAT), which predicts a CME's deflection. We adapt ForeCAT to simulate CME deflections for the mid-type M dwarf V374 Peg and hot Jupiters with solar-type hosts. V374 Peg's strong magnetic fields can trap CMEs at the M dwarfs's Astrospheric Current Sheet, that is, the location of the minimum in the background magnetic field. Solar-type CMEs behave similarly, but have much smaller deflections and do not become trapped at the Astrospheric Current Sheet. The probability of planetary impact decreases with increasing inclination of the planetary orbit with respect to the Astrospheric Current Sheet: 0.5–5 CME impacts per day for M dwarf exoplanets, 0.05–0.5 CME impacts per day for solar-type hot Jupiters. We determine the minimum planetary magnetic field necessary to shield a planet's atmosphere from CME impacts. M dwarf exoplanets require values between tens and hundreds of Gauss. Hot Jupiters around a solar-type star, however, require a more reasonable <30 G. These values exceed the magnitude required to shield a planet from the stellar wind, suggesting that CMEs may be the key driver of atmospheric losses.

  4. PROBABILITY OF CME IMPACT ON EXOPLANETS ORBITING M DWARFS AND SOLAR-LIKE STARS

    International Nuclear Information System (INIS)

    Kay, C.; Opher, M.; Kornbleuth, M.

    2016-01-01

    Solar coronal mass ejections (CMEs) produce adverse space weather effects at Earth. Planets in the close habitable zone of magnetically active M dwarfs may experience more extreme space weather than at Earth, including frequent CME impacts leading to atmospheric erosion and leaving the surface exposed to extreme flare activity. Similar erosion may occur for hot Jupiters with close orbits around solar-like stars. We have developed a model, Forecasting a CME's Altered Trajectory (ForeCAT), which predicts a CME's deflection. We adapt ForeCAT to simulate CME deflections for the mid-type M dwarf V374 Peg and hot Jupiters with solar-type hosts. V374 Peg's strong magnetic fields can trap CMEs at the M dwarfs's Astrospheric Current Sheet, that is, the location of the minimum in the background magnetic field. Solar-type CMEs behave similarly, but have much smaller deflections and do not become trapped at the Astrospheric Current Sheet. The probability of planetary impact decreases with increasing inclination of the planetary orbit with respect to the Astrospheric Current Sheet: 0.5–5 CME impacts per day for M dwarf exoplanets, 0.05–0.5 CME impacts per day for solar-type hot Jupiters. We determine the minimum planetary magnetic field necessary to shield a planet's atmosphere from CME impacts. M dwarf exoplanets require values between tens and hundreds of Gauss. Hot Jupiters around a solar-type star, however, require a more reasonable <30 G. These values exceed the magnitude required to shield a planet from the stellar wind, suggesting that CMEs may be the key driver of atmospheric losses.

  5. EX-111 Thermal Emission from Hot White Dwarfs: The Suggested He Abundance-Temperature Correlation. EX-112: The Unique Emission Line White Dwarf Star GD 356

    Science.gov (United States)

    Shipman, H. L.

    1986-01-01

    Progress in the EXOSAT data analysis program is reported. EXOSAT observations for four white dwarfs (WD1031-115, WD0004+330, WD1615-154, and WD0109-264) were obtained. Counting rates were unexpectedly low, indicating that these objects have a substantial amount of x-ray absorbing matter in their photosheres. In addition, soft x-ray pulsations characterized by a 9.25 minute cycle were discovered in the DA white dwarf V471 Tauri. A residual x-ray flux from the K dwarf companion can be seen during the white dwarf eclipse at orbital phase 0.0. Pronounced dips in the soft x-ray light curve occur at orbital phases 0.15, 0.18, and 0.85. The dips may be correlated with the triangular Lagrangian points of the binary orbit. Smaller dips at phases near the eclipse may be associated with cool loops in the K star corona. Data for the white dwarf H1504+65 was also analyzed. This object is particularly unusual in that its photoshere is devoid of hydrogen and helium. Finally, existing data on the white dwarf Sirius B were analyzed to see what constraints from other data can be placed on the properties of this star. Interrelationships between radius, rotational velocity, and effective temperature were derived.

  6. The most metal-poor damped Lyα systems: insights into chemical evolution in the very metal-poor regime

    DEFF Research Database (Denmark)

    Cooke, Ryan; Pettini, Max; Steidel, Charles C.

    2011-01-01

    We present a high spectral resolution survey of the most metal-poor damped Lyα absorption systems (DLAs) aimed at probing the nature and nucleosynthesis of the earliest generations of stars. Our survey comprises 22 systems with iron abundance less than 1/100 solar; observations of seven of these ...... measurements are currently available for only a few elements, we cannot yet rule out an additional contribution from Population II stars....

  7. OPTICAL–NEAR-INFRARED PHOTOMETRIC CALIBRATION OF M DWARF METALLICITY AND ITS APPLICATION

    International Nuclear Information System (INIS)

    Hejazi, N.; Robertis, M. M. De; Dawson, P. C.

    2015-01-01

    Based on a carefully constructed sample of dwarf stars, a new optical–near-infrared photometric calibration to estimate the metallicity of late-type K and early-to-mid-type M dwarfs is presented. The calibration sample has two parts; the first part includes 18 M dwarfs with metallicities determined by high-resolution spectroscopy and the second part contains 49 dwarfs with metallicities obtained through moderate-resolution spectra. By applying this calibration to a large sample of around 1.3 million M dwarfs from the Sloan Digital Sky Survey and 2MASS, the metallicity distribution of this sample is determined and compared with those of previous studies. Using photometric parallaxes, the Galactic heights of M dwarfs in the large sample are also estimated. Our results show that stars farther from the Galactic plane, on average, have lower metallicity, which can be attributed to the age–metallicity relation. A scarcity of metal-poor dwarf stars in the metallicity distribution relative to the Simple Closed Box Model indicates the existence of the “M dwarf problem,” similar to the previously known G and K dwarf problems. Several more complicated Galactic chemical evolution models which have been proposed to resolve the G and K dwarf problems are tested and it is shown that these models could, to some extent, mitigate the M dwarf problem as well

  8. Environmental effects on stellar populations of dwarf galaxies and star clusters

    Science.gov (United States)

    Pasetto, Stefano; Cropper, Mark; fujita, Yutaka; Chiosi, Cesare; Grebel, Eva K.

    2015-08-01

    We investigate the competitive role of the different dissipative phenomena acting on the onset of star formation history of gravitationally bound system in an external environment. Ram pressure, Kelvin-Helmholtz instability, Rayleigh-Taylor, and tidal forces are accounted separately in an analytical framework and compared in their role in influencing the star forming regions. We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system on its surrounding environment useful in observational applications as well as theoretical interpretations of numerical results.We consider the different signatures of these phenomena in synthetically realized colour-magnitude diagrams (CMDs) of the orbiting system thus investigating the detectability limits of these different effects for future observational projects and their relevance.The theoretical framework developed has direct applications to the cases of dwarf galaxies in galaxy clusters and dwarf galaxies orbiting our Milky Way system, as well as any primordial gas-rich cluster of stars orbiting within its host galaxy.

  9. Field #3 of the Palomar-Groningen Survey; 1, Variable stars at the edge of the Sagittarius dwarf galaxy

    NARCIS (Netherlands)

    Schultheis, M.

    1996-01-01

    Submitted to: Astron. Astrophys. Abstract: A catalogue is presented with variable (RR Lyrae, semiregular and Mira) stars located inside field #3 of the Palomar-Groningen Survey, at the outer edge of the Sagittarius dwarf galaxy. One of the semiregular variables is a carbon star, comparable with

  10. Mapping the Tidal Destruction of the Hercules Dwarf: A Wide-field DECam Imaging Search for RR Lyrae Stars

    Science.gov (United States)

    Garling, Christopher; Willman, Beth; Sand, David J.; Hargis, Jonathan; Crnojević, Denija; Bechtol, Keith; Carlin, Jeffrey L.; Strader, Jay; Zou, Hu; Zhou, Xu; Nie, Jundan; Zhang, Tianmeng; Zhou, Zhimin; Peng, Xiyan

    2018-01-01

    We investigate the hypothesized tidal disruption of the Hercules ultra-faint dwarf galaxy (UFD). Previous tidal disruption studies of the Hercules UFD have been hindered by the high degree of foreground contamination in the direction of the dwarf. We bypass this issue by using RR Lyrae stars, which are standard candles with a very low field-volume density at the distance of Hercules. We use wide-field imaging from the Dark Energy Camera on CTIO to identify candidate RR Lyrae stars, supplemented with observations taken in coordination with the Beijing–Arizona Sky Survey on the Bok Telescope. Combining color, magnitude, and light-curve information, we identify three new RR Lyrae stars associated with Hercules. All three of these new RR Lyrae stars lie outside its published tidal radius. When considered with the nine RR Lyrae stars already known within the tidal radius, these results suggest that a substantial fraction of Hercules’ stellar content has been stripped. With this degree of tidal disruption, Hercules is an interesting case between a visibly disrupted dwarf (such as the Sagittarius dwarf spheroidal galaxy) and one in dynamic equilibrium. The degree of disruption also shows that we must be more careful with the ways we determine object membership when estimating dwarf masses in the future. One of the three discovered RR Lyrae stars sits along the minor axis of Hercules, but over two tidal radii away. This type of debris is consistent with recent models that suggest Hercules’ orbit is aligned with its minor axis.

  11. A bag of tricks: Using proper motions of Galactic stars to identify the Hercules ultra-faint dwarf galaxy members

    Science.gov (United States)

    Fabrizio, M.; Raimondo, G.; Brocato, E.; Bellini, A.; Libralato, M.; Testa, V.; Cantiello, M.; Musella, I.; Clementini, G.; Carini, R.; Marconi, M.; Piotto, G.; Ripepi, V.; Buonanno, R.; Sani, E.; Speziali, R.

    2014-10-01

    Context. Discovered in the last decade as overdensities of resolved stars, the ultra-faint dwarfs (UFDs) are among the least luminous, most dark-matter dominated, and most metal-poor galaxies known today. They appear as sparse, loose objects with high mass-to-light ratios. Hercules is the prototype of the UFD galaxies. To date, there are still no firm constraints on its total luminosity due to the difficulty of disentangling Hercules bona-fide stars from the severe Galactic field contamination. Aims: To better constrain Hercules properties, we aim at removing foreground and background contaminants in the galaxy field using the proper motions of the Milky Way stars and the colour-colour diagram. Methods: We have obtained images of Hercules in the rSloan , BBessel and Uspec bands with the Large Binocular Telescope (LBT) and LBC-BIN mode capabilities. The rSloan new dataset combined with data from the LBT archive span a time baseline of about 5 yr, allowing us to measure proper motions of stars in the Hercules direction for the first time. The Uspec data along with existing LBT photometry allowed us to use colour-colour diagram to further remove the field contamination. Results: Thanks to a highly-accurate procedure to derive the rSloan -filter geometric distortion solution for the LBC-red, we were able to measure stellar relative proper motions to a precision of better than 5 mas yr-1 down to rSloan≃ 22 mag and disentangle a significant fraction (>90%) of Milky Way contaminants. We ended up with a sample of 528 sources distributed over a large portion of the galaxy body (~0.12 deg2). Of these sources, 171 turned out to be background galaxies and additional foreground stars from the analysis of the Uspec - BBessel vs. BBessel - rSloan colour-colour diagram. This leaves us with a sample of 357 likely members of the Hercules UFD. We compared the cleaned colour-magnitude diagram (CMD) with evolutionary models and synthetic CMDs, confirming the presence in Hercules of

  12. Evidence for halo kinematics among cool carbon-rich dwarfs

    Science.gov (United States)

    Farihi, J.; Arendt, A. R.; Machado, H. S.; Whitehouse, L. J.

    2018-04-01

    This paper reports preliminary yet compelling kinematical inferences for N ≳ 600 carbon-rich dwarf stars that demonstrate around 30% to 60% are members of the Galactic halo. The study uses a spectroscopically and non-kinematically selected sample of stars from the SDSS, and cross-correlates these data with three proper motion catalogs based on Gaia DR1 astrometry to generate estimates of their 3-D space velocities. The fraction of stars with halo-like kinematics is roughly 30% for distances based on a limited number of parallax measurements, with the remainder dominated by the thick disk, but close to 60% of the sample lie below an old, metal-poor disk isochrone in reduced proper motion. An ancient population is consistent with an extrinsic origin for C/O >1 in cool dwarfs, where a fixed mass of carbon pollution more readily surmounts lower oxygen abundances, and with a lack of detectable ultraviolet-blue flux from younger white dwarf companions. For an initial stellar mass function that favors low-mass stars as in the Galactic disk, the dC stars are likely to be the dominant source of carbon-enhanced, metal-poor stars in the Galaxy.

  13. Membership and lithium in the old, metal-poor open cluster Berkeley 32

    Science.gov (United States)

    Randich, S.; Pace, G.; Pastori, L.; Bragaglia, A.

    2009-03-01

    Context: Measurements of lithium (Li) abundances in open clusters provide a unique tool for following the evolution of this element with age, metallicity, and stellar mass. In spite of the plethora of Li data already available, the behavior of Li in solar-type stars has so far been poorly understood. Aims: Using FLAMES/Giraffe on the VLT, we obtained spectra of 157 candidate members of the old, metal-poor cluster Berkeley 32, to determine membership and to study the Li behavior of confirmed members. Methods: Radial velocities were measured, allowing us to derive both the cluster velocity and membership information for the sample stars. The Li abundances were obtained from the equivalent width of the Li i 670.8 nm feature, using curves of growth. Results: We obtained an average radial velocity of 105.2 ± 0.86 km s-1, and 53% of the stars have a radial velocity consistent with membership. The Li - T_eff distribution of unevolved members matches the upper envelope of M 67, as well as that of the slightly older and more metal-rich NGC 188. No major dispersion in Li is detected. When considering the Li distribution as a function of mass, however, Be 32 members with solar-like temperature are less massive and less Li-depleted than their counterparts in the other clusters. The mean Li of stars in the temperature interval 5750 ≤ T_eff ≤ 6050 K is log n(Li) = 2.47±0.16, less than a factor of two below the average Li of the 600 Myr old Hyades, and slightly above the average of intermediate age (1-2 Gyr) clusters, the upper envelope of M 67, and NGC 188. This value is comparable to or slightly higher than the plateau of Pop. ii stars. The similarity of the average Li abundance of clusters of different age and metallicity, along with its closeness to the halo dwarf plateau, is very intriguing and suggests that, whatever the initial Li abundance and the Li depletion histories, old stars converge to almost the same final Li abundance. Based on observations collected at ESO

  14. The First APOKASC Catalog of Kepler Dwarf and Subgiant Stars

    Science.gov (United States)

    Serenelli, Aldo; Johnson, Jennifer; Huber, Daniel; Pinsonneault, Marc; Ball, Warrick H.; Tayar, Jamie; Silva Aguirre, Victor; Basu, Sarbani; Troup, Nicholas; Hekker, Saskia; Kallinger, Thomas; Stello, Dennis; Davies, Guy R.; Lund, Mikkel N.; Mathur, Savita; Mosser, Benoit; Stassun, Keivan G.; Chaplin, William J.; Elsworth, Yvonne; García, Rafael A.; Handberg, Rasmus; Holtzman, Jon; Hearty, Fred; García-Hernández, D. A.; Gaulme, Patrick; Zamora, Olga

    2017-12-01

    We present the first APOKASC catalog of spectroscopic and asteroseismic data for dwarfs and subgiants. Asteroseismic data for our sample of 415 objects have been obtained by the Kepler mission in short (58.5 s) cadence, and light curves span from 30 up to more than 1000 days. The spectroscopic parameters are based on spectra taken as part of the Apache Point Observatory Galactic Evolution Experiment and correspond to Data Release 13 of the Sloan Digital Sky Survey. We analyze our data using two independent {T}{eff} scales, the spectroscopic values from DR13 and those derived from SDSS griz photometry. We use the differences in our results arising from these choices as a test of systematic temperature uncertainties and find that they can lead to significant differences in the derived stellar properties. Determinations of surface gravity ({log}g), mean density ( ), radius (R), mass (M), and age (τ) for the whole sample have been carried out by means of (stellar) grid-based modeling. We have thoroughly assessed random and systematic error sources in the spectroscopic and asteroseismic data, as well as in the grid-based modeling determination of the stellar quantities provided in the catalog. We provide stellar properties determined for each of the two {T}{eff} scales. The median combined (random and systematic) uncertainties are 2% (0.01 dex; {log}g), 3.4% ( ), 2.6% (R), 5.1% (M), and 19% (τ) for the photometric {T}{eff} scale and 2% ({log}g), 3.5% ( ), 2.7% (R), 6.3% (M), and 23% (τ) for the spectroscopic scale. We present comparisons with stellar quantities in the asteroseismic catalog by Chaplin et al. that highlight the importance of having metallicity measurements for determining stellar parameters accurately. Finally, we compare our results with those coming from a variety of sources, including stellar radii determined from TGAS parallaxes and asteroseismic analyses based on individual frequencies. We find a very good agreement for all inferred quantities

  15. Identification and characterization of low mass stars and brown dwarfs using Virtual Observatory tools

    Science.gov (United States)

    Aberasturi, Miriam

    2015-11-01

    Context: Two thirds of the stars in our galactic neighborhood (d Isaac Newton telescope at La Palma, as well as with an astrometric and photometric study. In the third paper we attempted to refine the multiplicity properties of T dwarfs studying the largest sample so far observed with high angular resolution imaging. We undertook two parallel programs using the Wide Field Camera 3 (WFC3) installed on the Hubble Space Telescope (HST). We used a PSF-fitting subtraction technique to reveal the presence of any close companion to the sources in our sample. Monte Carlo simulations were carried out to estimate the capability of WFC3 to detect close binaries in terms of angular separation and magnitude difference. Simulations were also used to determine the fraction of binaries that would have been detected around each source based on assumed separations, mass ratio distributions and orientations of the systems. Results: The main conclusion from this dissertation is that the Virtual Observatory has proved to be an excellent research methodology in the field of low mass stars and brown dwarfs. In particular, it allowed an efficient management of the queries to different catalogues and archives as well as the estimation of physical parameters through VO-tools. In the first publication we present the identification of 31 brown dwarf (25 known and 6 strong candidates not previously reported in the literature) identified in the sky area in common toWISE, 2MASS and SDSS. This is a remarkable number considering that 2MASS has been extensively searched for ultracool dwarfs and clearly show how new surveys and the use of VO tools can help to mine older surveys. The robustness of our methodology was confirmed with the spectroscopic confirmation of our candidate targets making it an ideal technique to identify brown dwarfs and, by extension, other rare objects. In the second paper, we show the potential of the VO and a purely photometric approach for finding new bright, nearby M

  16. Mapping radio emitting-region on low-mass stars and brown dwarfs

    Directory of Open Access Journals (Sweden)

    Hallinan G.

    2011-07-01

    Full Text Available Strong magnetic activity in ultracool dwarfs (UCDs, spectral classes later than M7 have emerged from a number of radio observations, including the periodic beams. The highly (up to 100% circularly polarized nature of the emission point to an effective amplification mechanism of the high-frequency electromagnetic waves – the electron cyclotron maser (ECM instability. Several anisotropic velocity distibution models of electrons, including the horseshoe distribution, ring shell distribution and the loss-cone distribution, are able to generate the ECM instability. A magnetic-field-aligned electric potential would play an significant role in the ECM process. We are developing a theoretical model in order to simulate ECM and apply this model to map the radio-emitting region on low-mass stars and brown dwarfs.

  17. An unusual white dwarf star may be a surviving remnant of a subluminous Type Ia supernova.

    Science.gov (United States)

    Vennes, S; Nemeth, P; Kawka, A; Thorstensen, J R; Khalack, V; Ferrario, L; Alper, E H

    2017-08-18

    Subluminous Type Ia supernovae, such as the Type Iax-class prototype SN 2002cx, are described by a variety of models such as the failed detonation and partial deflagration of an accreting carbon-oxygen white dwarf star or the explosion of an accreting, hybrid carbon-oxygen-neon core. These models predict that bound remnants survive such events with, according to some simulations, a high kick velocity. We report the discovery of a high proper motion, low-mass white dwarf (LP 40-365) that travels at a velocity greater than the Galactic escape velocity and whose peculiar atmosphere is dominated by intermediate-mass elements. Strong evidence indicates that this partially burnt remnant was ejected following a subluminous Type Ia supernova event. This supports the viability of single-degenerate supernova progenitors. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

  18. CHEMICAL ABUNDANCES IN NGC 5053: A VERY METAL-POOR AND DYNAMICALLY COMPLEX GLOBULAR CLUSTER

    Energy Technology Data Exchange (ETDEWEB)

    Boberg, Owen M.; Friel, Eileen D.; Vesperini, Enrico [Astronomy Department, Indiana University, Bloomington, IN 47405 (United States)

    2015-05-10

    NGC 5053 provides a rich environment to test our understanding of the complex evolution of globular clusters (GCs). Recent studies have found that this cluster has interesting morphological features beyond the typical spherical distribution of GCs, suggesting that external tidal effects have played an important role in its evolution and current properties. Additionally, simulations have shown that NGC 5053 could be a likely candidate to belong to the Sagittarius dwarf galaxy (Sgr dSph) stream. Using the Wisconsin–Indiana–Yale–NOAO–Hydra multi-object spectrograph, we have collected high quality (signal-to-noise ratio ∼ 75–90), medium-resolution spectra for red giant branch stars in NGC 5053. Using these spectra we have measured the Fe, Ca, Ti, Ni, Ba, Na, and O abundances in the cluster. We measure an average cluster [Fe/H] abundance of −2.45 with a standard deviation of 0.04 dex, making NGC 5053 one of the most metal-poor GCs in the Milky Way (MW). The [Ca/Fe], [Ti/Fe], and [Ba/Fe] we measure are consistent with the abundances of MW halo stars at a similar metallicity, with alpha-enhanced ratios and slightly depleted [Ba/Fe]. The Na and O abundances show the Na–O anti-correlation found in most GCs. From our abundance analysis it appears that NGC 5053 is at least chemically similar to other GCs found in the MW. This does not, however, rule out NGC 5053 being associated with the Sgr dSph stream.

  19. Chemical Abundances in NGC 5053: A Very Metal-poor and Dynamically Complex Globular Cluster

    Science.gov (United States)

    Boberg, Owen M.; Friel, Eileen D.; Vesperini, Enrico

    2015-05-01

    NGC 5053 provides a rich environment to test our understanding of the complex evolution of globular clusters (GCs). Recent studies have found that this cluster has interesting morphological features beyond the typical spherical distribution of GCs, suggesting that external tidal effects have played an important role in its evolution and current properties. Additionally, simulations have shown that NGC 5053 could be a likely candidate to belong to the Sagittarius dwarf galaxy (Sgr dSph) stream. Using the Wisconsin-Indiana-Yale-NOAO-Hydra multi-object spectrograph, we have collected high quality (signal-to-noise ratio ˜ 75-90), medium-resolution spectra for red giant branch stars in NGC 5053. Using these spectra we have measured the Fe, Ca, Ti, Ni, Ba, Na, and O abundances in the cluster. We measure an average cluster [Fe/H] abundance of -2.45 with a standard deviation of 0.04 dex, making NGC 5053 one of the most metal-poor GCs in the Milky Way (MW). The [Ca/Fe], [Ti/Fe], and [Ba/Fe] we measure are consistent with the abundances of MW halo stars at a similar metallicity, with alpha-enhanced ratios and slightly depleted [Ba/Fe]. The Na and O abundances show the Na-O anti-correlation found in most GCs. From our abundance analysis it appears that NGC 5053 is at least chemically similar to other GCs found in the MW. This does not, however, rule out NGC 5053 being associated with the Sgr dSph stream.

  20. MAGNETIC FIELD TOPOLOGY IN LOW-MASS STARS: SPECTROPOLARIMETRIC OBSERVATIONS OF M DWARFS

    International Nuclear Information System (INIS)

    Phan-Bao, Ngoc; Lim, Jeremy; Donati, Jean-Francois; Johns-Krull, Christopher M.; MartIn, Eduardo L.

    2009-01-01

    The magnetic field topology plays an important role in the understanding of stellar magnetic activity. While it is widely accepted that the dynamo action present in low-mass partially convective stars (e.g., the Sun) results in predominantly toroidal magnetic flux, the field topology in fully convective stars (masses below ∼0.35 M sun ) is still under debate. We report here our mapping of the magnetic field topology of the M4 dwarf G 164-31 (or Gl 490B), which is expected to be fully convective, based on time series data collected from 20 hr of observations spread over three successive nights with the ESPaDOnS spectropolarimeter. Our tomographic imaging technique applied to time series of rotationally modulated circularly polarized profiles reveals an axisymmetric large-scale poloidal magnetic field on the M4 dwarf. We then apply a synthetic spectrum fitting technique for measuring the average magnetic flux on the star. The flux measured in G 164-31 is |Bf| = 3.2 ± 0.4 kG, which is significantly greater than the average value of 0.68 kG determined from the imaging technique. The difference indicates that a significant fraction of the stellar magnetic energy is stored in small-scale structures at the surface of G 164-31. Our Hα emission light curve shows evidence for rotational modulation suggesting the presence of localized structure in the chromosphere of this M dwarf. The radius of the M4 dwarf derived from the rotational period and the projected equatorial velocity is at least 30% larger than that predicted from theoretical models. We argue that this discrepancy is likely primarily due to the young nature of G 164-31 rather than primarily due to magnetic field effects, indicating that age is an important factor which should be considered in the interpretation of this observational result. We also report here our polarimetric observations of five other M dwarfs with spectral types from M0 to M4.5, three of them showing strong Zeeman signatures.

  1. The Binary Fraction of Stars in Dwarf Galaxies: The Case of Leo II

    Science.gov (United States)

    Spencer, Meghin E.; Mateo, Mario; Walker, Matthew G.; Olszewski, Edward W.; McConnachie, Alan W.; Kirby, Evan N.; Koch, Andreas

    2017-06-01

    We combine precision radial velocity data from four different published works of the stars in the Leo II dwarf spheroidal galaxy. This yields a data set that spans 19 years, has 14 different epochs of observation, and contains 372 unique red giant branch stars, 196 of which have repeat observations. Using this multi-epoch data set, we constrain the binary fraction for Leo II. We generate a suite of Monte Carlo simulations that test different binary fractions using Bayesian analysis and determine that the binary fraction for Leo II ranges from {0.30}-0.10+0.09 to {0.34}-0.11+0.11, depending on the distributions of binary orbital parameters assumed. This value is smaller than what has been found for the solar neighborhood (˜0.4-0.6) but falls within the wide range of values that have been inferred for other dwarf spheroidals (0.14-0.69). The distribution of orbital periods has the greatest impact on the binary fraction results. If the fraction we find in Leo II is present in low-mass ultra-faints, it can artificially inflate the velocity dispersion of those systems and cause them to appear more dark matter rich than in actuality. For a galaxy with an intrinsic dispersion of 1 km s-1 and an observational sample of 100 stars, the dispersion can be increased by a factor of 1.5-2 for Leo II-like binary fractions or by a factor of three for binary fractions on the higher end of what has been seen in other dwarf spheroidals.

  2. FORMING HABITABLE PLANETS AROUND DWARF STARS: APPLICATION TO OGLE-06-109L

    International Nuclear Information System (INIS)

    Wang Su; Zhou Jilin

    2011-01-01

    Dwarf stars are believed to have a small protostar disk where planets may grow up. During the planet formation stage, embryos undergoing type I migration are expected to be stalled at an inner edge of the magnetically inactive disk (a crit ∼ 0.2-0.3 AU). This mechanism makes the location around a crit a 'sweet spot' for forming planets. In dwarf stars with masses ∼0.5 M sun , a crit is roughly inside the habitable zone of the system. In this paper, we study the formation of habitable planets due to this mechanism using model system OGLE-06-109L, which has a 0.51 M sun dwarf star with two giant planets in 2.3 and 4.6 AU observed by microlensing. We model the embryos undergoing type I migration in the gas disk with a constant disk-accretion rate ( M-dot ). Giant planets in outside orbits affect the formation of habitable planets through secular perturbations at the early stage and secular resonance at the late stage. We find that the existence and the masses of the habitable planets in the OGLE-06-109L system depend on both M-dot and the speed of type I migration. If planets are formed earlier, so that M-dot is larger (∼10 -7 M sun yr -1 ), terrestrial planets cannot survive unless the type I migration rate is an order of magnitude less. If planets are formed later, so that M-dot is smaller (∼10 -8 M sun yr -1 ), single and high-mass terrestrial planets with high water contents (∼5%) will be formed by inward migration of outer planet cores. A slower-speed migration will result in several planets via collisions of embryos, and thus their water contents will be low (∼2%). Mean motion resonances or apsidal resonances among planets may be observed if multiple planets survive in the inner system.

  3. Intermediate-mass single stars and accreting white dwarfs as sources of neutron-rich isotopes

    International Nuclear Information System (INIS)

    Iben, I. Jr.

    1981-01-01

    During the most luminous portion of the asymptotic giant-branch phase, models of intermediate-mass stars first become carbon stars and then produce s-process isotopes in the solar-system distribution. Recent observations of the optically most luminous carbon stars in the Magellanic Clouds introduce the possibility that real intermediate-mass stars lose their hydrogen-rich envelopes during the asymptotic giant-branch phase before they have made s-process isotopes both in large quantities and in the solar system distribution. This encourages a search for alternate sources of these isotopes. A promising site for the production of some neutron-rich isotopes isthe convective helium-carbon region that appears in accreting white dwarfs during helium shell flashes. For appropriate accretion rates, overlap of matter in successive convective zones may lead to an exponential distribution of exposures. Further, because of a small entropy barrier between the convective shell and the hydrogen-rich envelope, protons enter the shell and provide a source of neutrons that, for appropriate accretion rates, is repetitive in strength and either dominates or is complementary to the 22 Ne(α,n) 25 Mg source. This permits an estimate of the distribution of neutron-rich isotopes that is formed after many flashes. The distribution, in most instances, tends to be weighted more toward heavier elements than is the case when 22 Ne(α, n) 25 Mg is the sole source of neutrons. Hence, accreting white dwarfs cannot be major contributors to the enrichment of the interstellar medium in most s-process isotopes. Considerable effort should be devoted toward demonstrating whether or not the bolometrically most lumious asymptotic giant branch stars in local systems obey M/sub BOL/ /sup min/ -6.5, then either the source of most Galactic s-process isotopes is as yet unknown, or the rate of the 22 Ne(α, n) 25 Mg reaction has been underestimated

  4. Young stars and brown dwarfs surrounding Alnilam (eps Ori) and Mintaka (del Ori)

    OpenAIRE

    Caballero, J. A.; Solano, E.

    2008-01-01

    Aims: We look for new regions for the search of substellar objects. Methods: Two circular areas, 45 arcmin-radius each, centred on the young massive star systems Alnilam and Mintaka in the Orion Belt, have been explored. The regions are very young (less than 10 Ma), have low extinction, and are neighbours to sigma Orionis (~3 Ma), a young open cluster very rich in brown dwarfs and planetary-mass objects. We have used Virtual Observatory tools, the astro-photometric Tycho-2, DENIS and 2MASS ca...

  5. Modular Spectral Inference Framework Applied to Young Stars and Brown Dwarfs

    Science.gov (United States)

    Gully-Santiago, Michael A.; Marley, Mark S.

    2017-01-01

    In practice, synthetic spectral models are imperfect, causing inaccurate estimates of stellar parameters. Using forward modeling and statistical inference, we derive accurate stellar parameters for a given observed spectrum by emulating a grid of precomputed spectra to track uncertainties. Spectral inference as applied to brown dwarfs re: Synthetic spectral models (Marley et al 1996 and 2014) via the newest grid spans a massive multi-dimensional grid applied to IGRINS spectra, improving atmospheric models for JWST. When applied to young stars(10Myr) with large starpots, they can be measured spectroscopically, especially in the near-IR with IGRINS.

  6. Tidal interaction, star formation and chemical evolution in blue compact dwarf galaxy Mrk 22

    Science.gov (United States)

    Paswan, A.; Omar, A.; Jaiswal, S.

    2018-02-01

    The optical spectroscopic and radio interferometric H I 21 cm-line observations of the blue compact dwarf galaxy Mrk 22 are presented. The Wolf-Rayet (WR) emission-line features corresponding to high ionization lines of He II λ4686 and C IV λ5808 from young massive stars are detected. The ages of two prominent star-forming regions in the galaxy are estimated as ∼10 and ∼ 4 Myr. The galaxy has non-thermal radio deficiency, which also indicates a young starburst and lack of supernovae events from the current star formation activities, consistent with the detection of WR emission-line features. A significant N/O enrichment is seen in the fainter star-forming region. The gas-phase metallicities [12 + log(O/H)] for the bright and faint regions are estimated as 7.98±0.07 and 7.46±0.09, respectively. The galaxy has a large diffuse H I envelop. The H I images reveal disturbed gas kinematics and H I clouds outside the optical extent of the galaxy, indicating recent tidal interaction or merger in the system. The results strongly indicate that Mrk 22 is undergoing a chemical and morphological evolution due to ongoing star formation, most likely triggered by a merger.

  7. THE STELLAR POPULATION AND STAR FORMATION PROPERTIES OF BLUE COMPACT DWARF GALAXIES

    International Nuclear Information System (INIS)

    Zhao Yinghe; Gao Yu; Gu Qiusheng

    2011-01-01

    We study stellar populations, star formation histories (SFHs), and star formation properties for a sample of blue compact dwarf galaxies (BCDs) selected by cross-correlating the Gil de Paz et al. sample with the Sloan Digital Sky Survey Data Release 6. The sample includes 31 BCDs, which span a large range of galactic parameters. Using a stellar population synthesis method, we derive stellar populations and reconstruct SFHs for these BCDs. Our studies confirm that BCDs are not young systems experiencing their first star formation, but old systems undergoing a starburst activity. The stellar mass-weighted ages can be up to 10 Gyr, while the luminosity-weighted ages might be up to approximately three orders of magnitude younger (∼10 Myr) for most galaxies. Based on multiwavelength data, we also study the integrated star formation properties. The star formation rate (SFR) for our sample galaxies spans nearly three orders of magnitude, from a few 10 -3 to ∼1 M sun yr -1 , with a median value of ∼0.1 M sun yr -1 . We find that about 90% of BCDs in our sample have their birthrate parameter (the ratio of the current SFR to the averaged past SFR) b>2-3. We further discuss correlations of the current SFR with the integrated galactic stellar mass and explore the connection between SFR and metallicity.

  8. A Study of Two Dwarf Irregular Galaxies with Asymmetrical Star Formation Distributions

    Science.gov (United States)

    Hunter, Deidre A.; Gallardo, Samavarti; Zhang, Hong-Xin; Adamo, Angela; Cook, David O.; Oh, Se-Heon; Elmegreen, Bruce G.; Kim, Hwihyun; Kahre, Lauren; Ubeda, Leonardo; Bright, Stacey N.; Ryon, Jenna E.; Fumagalli, Michele; Sacchi, Elena; Kennicutt, R. C.; Tosi, Monica; Dale, Daniel A.; Cignoni, Michele; Messa, Matteo; Grebel, Eva K.; Gouliermis, Dimitrios A.; Sabbi, Elena; Grasha, Kathryn; Gallagher, John S., III; Calzetti, Daniela; Lee, Janice C.

    2018-03-01

    Two dwarf irregular galaxies, DDO 187 and NGC 3738, exhibit a striking pattern of star formation: intense star formation is taking place in a large region occupying roughly half of the inner part of the optical galaxy. We use data on the H I distribution and kinematics and stellar images and colors to examine the properties of the environment in the high star formation rate (HSF) halves of the galaxies in comparison with the low star formation rate halves. We find that the pressure and gas density are higher on the HSF sides by 30%–70%. In addition we find in both galaxies that the H I velocity fields exhibit significant deviations from ordered rotation and there are large regions of high-velocity dispersion and multiple velocity components in the gas beyond the inner regions of the galaxies. The conditions in the HSF regions are likely the result of large-scale external processes affecting the internal environment of the galaxies and enabling the current star formation there.

  9. Young stars and brown dwarfs surrounding Alnilam (ɛ Orionis) and Mintaka (δ Orionis)

    Science.gov (United States)

    Caballero, J. A.; Solano, E.

    2008-07-01

    Aims: We look for new regions to search for substellar objects. Methods: Two circular areas, 45 arcmin-radius each, centred on the young massive star systems Alnilam and Mintaka in the Orion Belt, were explored. The regions are very young (less than 10 Ma), have low extinction, and are neighbours to σ Orionis (~3 Ma), a young open cluster very rich in brown dwarfs and planetary-mass objects. We used Virtual Observatory tools, the astro-photometric Tycho-2, DENIS and 2MASS catalogues, 10 control fields at similar galactic latitudes, as well as X-ray, mid-infrared, and spectroscopic data from the literature. Results: We compiled exhaustive lists of known young stars and new candidate members in the Ori OB1b association and of fore- and background sources. A total of 136 stars display features of extreme youth, like early spectral types, lithium in absorption, or mid-infrared flux excess. Other two young brown dwarf and 289 star candidates have been identified from an optical/near-infrared colour-magnitude diagram. We list another 74 known objects that might belong to the association. This catalogue can serve as input for characterising the stellar and high-mass substellar populations in the Orion Belt. Finally, we investigated the surface densities and radial distributions of young objects surrounding Alnilam and Mintaka and compared them with those in the σ Orionis cluster. We report on a new open cluster centred on Mintaka. Conclusions: Both regions can be analogues to the σ Orionis cluster, but more massive, more extended, slightly older, and less radially concentrated. Tables A.1 to A.18 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/485/931

  10. MAPPING THE SHORES OF THE BROWN DWARF DESERT. II. MULTIPLE STAR FORMATION IN TAURUS-AURIGA

    International Nuclear Information System (INIS)

    Kraus, Adam L.; Ireland, Michael J.; Martinache, Frantz; Hillenbrand, Lynne A.

    2011-01-01

    We have conducted a high-resolution imaging study of the Taurus-Auriga star-forming region in order to characterize the primordial outcome of multiple star formation and the extent of the brown dwarf desert. Our survey identified 16 new binary companions to primary stars with masses of 0.25-2.5 M sun , raising the total number of binary pairs (including components of high-order multiples) with separations of 3-5000 AU to 90. We find that ∼2/3-3/4 of all Taurus members are multiple systems of two or more stars, while the other ∼1/4-1/3 appear to have formed as single stars; the distribution of high-order multiplicity suggests that fragmentation into a wide binary has no impact on the subsequent probability that either component will fragment again. The separation distribution for solar-type stars (0.7-2.5 M sun ) is nearly log-flat over separations of 3-5000 AU, but lower-mass stars (0.25-0.7 M sun ) show a paucity of binary companions with separations of ∼>200 AU. Across this full mass range, companion masses are well described with a linear-flat function; all system mass ratios (q = M B /M A ) are equally probable, apparently including substellar companions. Our results are broadly consistent with the two expected modes of binary formation (free-fall fragmentation on large scales and disk fragmentation on small scales), but the distributions provide some clues as to the epochs at which the companions are likely to form.

  11. Merger of white dwarf-neutron star binaries: Prelude to hydrodynamic simulations in general relativity

    International Nuclear Information System (INIS)

    Paschalidis, Vasileios; MacLeod, Morgan; Baumgarte, Thomas W.; Shapiro, Stuart L.

    2009-01-01

    White dwarf-neutron star binaries generate detectable gravitational radiation. We construct Newtonian equilibrium models of corotational white dwarf-neutron star (WDNS) binaries in circular orbit and find that these models terminate at the Roche limit. At this point the binary will undergo either stable mass transfer (SMT) and evolve on a secular time scale, or unstable mass transfer (UMT), which results in the tidal disruption of the WD. The path a given binary will follow depends primarily on its mass ratio. We analyze the fate of known WDNS binaries and use population synthesis results to estimate the number of LISA-resolved galactic binaries that will undergo either SMT or UMT. We model the quasistationary SMT epoch by solving a set of simple ordinary differential equations and compute the corresponding gravitational waveforms. Finally, we discuss in general terms the possible fate of binaries that undergo UMT and construct approximate Newtonian equilibrium configurations of merged WDNS remnants. We use these configurations to assess plausible outcomes of our future, fully relativistic simulations of these systems. If sufficient WD debris lands on the NS, the remnant may collapse, whereby the gravitational waves from the inspiral, merger, and collapse phases will sweep from LISA through LIGO frequency bands. If the debris forms a disk about the NS, it may fragment and form planets.

  12. An extended star formation history in an ultra-compact dwarf

    Science.gov (United States)

    Norris, Mark A.; Escudero, Carlos G.; Faifer, Favio R.; Kannappan, Sheila J.; Forte, Juan Carlos; van den Bosch, Remco C. E.

    2015-08-01

    There has been significant controversy over the mechanisms responsible for forming compact stellar systems like ultra-compact dwarfs (UCDs), with suggestions that UCDs are simply the high-mass extension of the globular cluster population, or alternatively, the liberated nuclei of galaxies tidally stripped by larger companions. Definitive examples of UCDs formed by either route have been difficult to find, with only a handful of persuasive examples of stripped-nucleus-type UCDs being known. In this paper, we present very deep Gemini/GMOS spectroscopic observations of the suspected stripped-nucleus UCD NGC 4546-UCD1 taken in good seeing conditions (noise spectrum to detect a temporally extended star formation history for this UCD. We find that the UCD was forming stars since the earliest epochs until at least 1-2 Gyr ago. Taken together these observations confirm that NGC 4546-UCD1 is the remnant nucleus of a nucleated dwarf galaxy that was tidally destroyed by NGC 4546 within the last 1-2 Gyr.

  13. Galactic Outflows, Star Formation Histories, and Timescales in Starburst Dwarf Galaxies from STARBIRDS

    Science.gov (United States)

    McQuinn, Kristen B. W.; Skillman, Evan D.; Heilman, Taryn N.; Mitchell, Noah P.; Kelley, Tyler

    2018-03-01

    Winds are predicted to be ubiquitous in low-mass, actively star-forming galaxies. Observationally, winds have been detected in relatively few local dwarf galaxies, with even fewer constraints placed on their timescales. Here, we compare galactic outflows traced by diffuse, soft X-ray emission from Chandra Space Telescope archival observations to the star formation histories derived from Hubble Space Telescope imaging of the resolved stellar populations in six starburst dwarfs. We constrain the longevity of a wind to have an upper limit of 25 Myr based on galaxies whose starburst activity has already declined, although a larger sample is needed to confirm this result. We find an average 16% efficiency for converting the mechanical energy of stellar feedback to thermal, soft X-ray emission on the 25 Myr timescale, somewhat higher than simulations predict. The outflows have likely been sustained for timescales comparable to the duration of the starbursts (i.e., 100's Myr), after taking into account the time for the development and cessation of the wind. The wind timescales imply that material is driven to larger distances in the circumgalactic medium than estimated by assuming short, 5-10 Myr starburst durations, and that less material is recycled back to the host galaxy on short timescales. In the detected outflows, the expelled hot gas shows various morphologies which are not consistent with a simple biconical outflow structure. The sample and analysis are part of a larger program, the STARBurst IRregular Dwarf Survey (STARBIRDS), aimed at understanding the lifecycle and impact of starburst activity in low-mass systems.

  14. Extrasolar planets and brown dwarfs around AF-type stars. IX. The HARPS southern sample

    Science.gov (United States)

    Borgniet, S.; Lagrange, A.-M.; Meunier, N.; Galland, F.

    2017-03-01

    Context. Massive, main-sequence (MS) AF-type stars have so far remained unexplored in past radial velocities (RV) surveys due to their small number of spectral lines and high rotational velocities that prevent the classic RV computation method. Aims: Our aim is to search for giant planets (GPs) around AF MS stars, to get primary statistical information on their occurrence rate and to compare the results with evolved stars and lower-mass MS stars. Methods: We used the HARPS spectrograph located on the 3.6 m telescope at ESO La Silla Observatory to observe 108 AF MS stars with B-V in the range -0.04 to 0.58 and masses in the range 1.1 to 3.6 M⊙. We used our SAFIR software developed to compute the RV and other spectroscopic observables of these early-type stars. We characterized the detected companions as well as the intrinsic stellar variability. We computed the detection limits and used them as well as the detected companions to derive the first estimates of the close-in brown dwarf (BD) and GP frequencies around AF stars. Results: We report the detection of a mpsini = 4.51MJup planetary companion with an 826-day period to the F6V dwarf HD 111998. We also present new data on the two-planet system around the F6IV-V dwarf HD 60532. We also report the detections of 14 binaries with long-term RV trends and/or high-amplitude RV variations combined to a flat RV-bisector span diagram. We constrain the minimal masses and semi-major axes of these companions and check that these constraints are compatible with the stellar companions previously detected by direct imaging or astrometry for six of these targets. We get detection limits deep into the planetary domain with 70% of our targets showing detection limits between 0.1 and 10 MJup at all orbital periods in the 1- to 103-day range. We derive BD (13 ≤mpsini ≤ 80 MJup) occurrence rates in the 1- to 103-day period range of 2-2+5% and 2.6-2.6+6.7% for stars with M⋆ in the ranges 1.1 to 1.5 and 1.5 to 3 M

  15. Exploring Simulated Early Star Formation in the Context of the Ultrafaint Dwarf Galaxies

    Science.gov (United States)

    Corlies, Lauren; Johnston, Kathryn V.; Wise, John H.

    2018-01-01

    Ultrafaint dwarf galaxies (UFDs) are typically assumed to have simple, stellar populations with star formation ending at reionization. Yet as the observations of these galaxies continue to improve, their star formation histories (SFHs) are revealed to be more complicated than previously thought. In this paper, we study how star formation, chemical enrichment, and mixing proceed in small, dark matter halos at early times using a high-resolution, cosmological, hydrodynamical simulation. The goals are to inform the future use of analytic models and to explore observable properties of the simulated halos in the context of UFD data. Specifically, we look at analytic approaches that might inform metal enrichment within and beyond small galaxies in the early Universe. We find that simple assumptions for modeling the extent of supernova-driven winds agree with the simulation on average whereas inhomogeneous mixing and gas flows have a large effect on the spread in simulated stellar metallicities. In the context of the UFDs, this work demonstrates that simulations can form halos with a complex SFH and a large spread in the metallicity distribution function within a few hundred Myr in the early Universe. In particular, bursty and continuous star formation are seen in the simulation and both scenarios have been argued from the data. Spreads in the simulated metallicities, however remain too narrow and too metal-rich when compared to the UFDs. Future work is needed to help reduce these discrepancies and advance our interpretation of the data.

  16. A system of three transiting super-Earths in a cool dwarf star

    Science.gov (United States)

    Alonso, E. Díez; Suárez Gómez, S. L.; González Hernández, J. I.; Suárez Mascareño, A.; González Gutiérrez, C.; Velasco, S.; Toledo-Padrón, B.; de Cos Juez, F. J.; Rebolo, R.

    2018-03-01

    We present the detection of three super-Earths transiting the cool star LP415-17, monitored by K2 mission in its 13th campaign. High resolution spectra obtained with HARPS-N/TNG showed that the star is a mid-late K dwarf. Using spectral synthesis models we infer its effective temperature, surface gravity and metallicity and subsequently determined from evolutionary models a stellar radius of 0.58 R⊙. The planets have radii of 1.8, 2.6 and 1.9 R⊕ and orbital periods of 6.34, 13.85 and 40.72 days. High resolution images discard any significant contamination by an intervening star in the line of sight. The orbit of the furthest planet has radius of 0.18 AU, close to the inner edge of the habitable zone. The system is suitable to improve our understanding of formation and dynamical evolution of super-Earth systems in the rocky - gaseous threshold, their atmospheres, internal structure, composition and interactions with host stars.

  17. Exploring simulated early star formation in the context of the ultrafaint dwarf galaxies

    Science.gov (United States)

    Corlies, Lauren; Johnston, Kathryn V.; Wise, John H.

    2018-04-01

    Ultrafaint dwarf galaxies (UFDs) are typically assumed to have simple, stellar populations with star formation ending at reionization. Yet as the observations of these galaxies continue to improve, their star formation histories (SFHs) are revealed to be more complicated than previously thought. In this paper, we study how star formation, chemical enrichment, and mixing proceed in small, dark matter haloes at early times using a high-resolution, cosmological, hydrodynamical simulation. The goals are to inform the future use of analytic models and to explore observable properties of the simulated haloes in the context of UFD data. Specifically, we look at analytic approaches that might inform metal enrichment within and beyond small galaxies in the early Universe. We find that simple assumptions for modelling the extent of supernova-driven winds agree with the simulation on average, whereas inhomogeneous mixing and gas flows have a large effect on the spread in simulated stellar metallicities. In the context of the UFDs, this work demonstrates that simulations can form haloes with a complex SFH and a large spread in the metallicity distribution function within a few hundred Myr in the early Universe. In particular, bursty and continuous star formation are seen in the simulation and both scenarios have been argued from the data. Spreads in the simulated metallicities, however, remain too narrow and too metal-rich when compared to the UFDs. Future work is needed to help reduce these discrepancies and advance our interpretation of the data.

  18. The star formation histories of local group dwarf galaxies. II. Searching for signatures of reionization

    Energy Technology Data Exchange (ETDEWEB)

    Weisz, Daniel R. [Department of Astronomy, University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Dolphin, Andrew E. [Raytheon Company, 1151 East Hermans Road, Tucson, AZ 85756 (United States); Skillman, Evan D. [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455 (United States); Holtzman, Jon [Department of Astronomy, New Mexico State University, Box 30001, 1320 Frenger Street, Las Cruces, NM 88003 (United States); Gilbert, Karoline M.; Dalcanton, Julianne J.; Williams, Benjamin F., E-mail: drw@ucsc.edu [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)

    2014-07-10

    We search for signatures of reionization in the star formation histories (SFHs) of 38 Local Group dwarf galaxies (10{sup 4} < M{sub *} < 10{sup 9} M{sub ☉}). The SFHs are derived from color-magnitude diagrams using archival Hubble Space Telescope/Wide Field Planetary Camera 2 imaging. Only five quenched galaxies (And V, And VI, And XIII, Leo IV, and Hercules) are consistent with forming the bulk of their stars before reionization, when full uncertainties are considered. Observations of 13 of the predicted 'true fossils' identified by Bovill and Ricotti show that only two (Hercules and Leo IV) indicate star formation quenched by reionization. However, both are within the virial radius of the Milky Way and evidence of tidal disturbance complicates this interpretation. We argue that the late-time gas capture scenario posited by Ricotti for the low mass, gas-rich, and star-forming fossil candidate Leo T is observationally indistinguishable from simple gas retention. Given the ambiguity between environmental effects and reionization, the best reionization fossil candidates are quenched low mass field galaxies (e.g., KKR 25).

  19. Mass Modelling of Dwarf Spheroidal Galaxies: the Effect of Unbound Stars From Tidal Tails And the Milky Way

    Energy Technology Data Exchange (ETDEWEB)

    Klimentowski, Jaroslaw; Lokas, Ewa L.; /Warsaw, Copernicus Astron. Ctr.; Kazantzidis, Stelios; /KIPAC, Menlo Park; Prada, Francisco; /IAA, Granada; Mayer, Lucio; /Zurich,; Mamon, Gary A.; /Paris, Inst. Astrophys. /Meudon Observ.

    2006-11-14

    We study the origin and properties of the population of unbound stars in the kinematic samples of dwarf spheroidal galaxies. For this purpose we have run a high resolution N- body simulation of a two-component dwarf galaxy orbiting in a Milky Way potential. In agreement with the tidal stirring scenario of Mayer et al., the dwarf is placed on a highly eccentric orbit, its initial stellar component is in the form of an exponential disk and it has a NFW-like dark matter halo. After 10 Gyrs of evolution the dwarf produces a spheroidal stellar component and is strongly tidally stripped so that mass follows light and the stars are on almost isotropic orbits. From this final state, we create mock kinematic data sets for 200 stars by observing the dwarf in different directions.We find that when the dwarf is observed along the tidal tails the kinematic samples are strongly contaminated by unbound stars from the tails.We also study another source of possible contamination by adding stars from the Milky Way. We demonstrate that most of the unbound stars can be removed by the method of interloper rejection proposed by den Hartog & Katgert and recently tested on simulated dark matter haloes. We model the cleaned up kinematic samples using solutions of the Jeans equation with constant mass-to-light ratio and velocity anisotropy parameter. We show that even for such strongly stripped dwarf the Jeans analysis, when applied to cleaned samples, allows us to reproduce the mass and mass-to-light ratio of the dwarf with accuracy typically better than 25 percent and almost exactly in the case when the line of sight is perpendicular to the tidal tails. The analysis was applied to the new data for the Fornax dSph galaxy for which we find a mass-to-light ratio of 11 solar units and isotropic orbits. We demonstrate that most of the contamination in the kinematic sample of Fornax probably originates from the Milky Way.

  20. Stars

    CERN Document Server

    Kukla, Lauren

    2016-01-01

    Climb Aboard! Explore planets and how they are formed! Meet key astronomers! Examine the history of mapping the stars! Investigate red giants, black and white dwarfs, neutron stars, supernovas, and black holes! See an infographic showing our solar system's statistics! Did You Know? facts and a Guidebook of the brightest stars complete your journey. Aligned to Common Core standards and correlated to state standards. Checkerboard Library is an imprint of Abdo Publishing, a division of ABDO.

  1. High resolution spectroscopy of Red Giant Branch stars and the chemical evolution of the Fornax dwarf spheroidal galaxy

    NARCIS (Netherlands)

    Lemasle, B.; de Boer, T. J. L.; Hill, V.; Tolstoy, E.; Irwin, M. J.; Jablonka, P.; Venn, K.; Battaglia, G.; Starkenburg, E.; Shetrone, M.; Letarte, B.; Francois, P.; Helmi, A.; Primas, F.; Kaufer, A.; Szeifert, T.; Ballet, J.; Martins, F.; Bournaud, F.; Monier, R.; Reylé, C.

    2014-01-01

    From VLT-FLAMES high-resolution spectra, we determine the abundances of several α, iron-peak and neutron-capture elements in 47 Red Giant Branch stars in the Fornax dwarf spheroidal galaxy. We confirm that SNe Ia started to contribute to the chemical enrichment of Fornax at [Fe/H] between --2.0 and

  2. High resolution spectroscopy of Red Giant Branch stars and the chemical evolution of the Fornax dwarf spheroidal galaxy

    NARCIS (Netherlands)

    Lemasle, B.; de Boer, T.J.L.; Hill, V.; Tolstoy, E.; Irwin, M.J.; Jablonka, P.; Venn, K.; Battaglia, G.; Starkenburg, E.; Shetrone, M.; Letarte, B.; Francois, P.; Helmi, A.; Primas, F.; Kaufer, A.; Szeifert, T.; Ballet, J.; Bournaud, F.; Martins, F.; Monier, R.; Reyle, C.

    2014-01-01

    From VLT-FLAMES high-resolution spectra, we determine the abundances of several α, iron-peak and neutron-capture elements in 47 Red Giant Branch stars in the Fornax dwarf speroidal galaxy. We confirm that SNe Ia started to contribute to the chemical enrichment of Fornax at [Fe/H] between -2.0 and -

  3. The Shape of Extremely Metal-Poor Galaxies

    Science.gov (United States)

    Putko, Joseph; Sánchez Almeida, Jorge; Muñoz-Tuñón, Casiana; Elmegreen, Bruce; Elmegreen, Debra

    2018-01-01

    This work is the first study on the 3D shape of starbursting extremely metal-poor galaxies (XMPs; a galaxy is said to be an XMP if its ionized gas-phase metallicity is less than 1/10 the solar value). A few hundred XMPs have been identified in the local universe primarily through mining the spectroscopic catalog of the Sloan Digital Sky Survey (SDSS), and follow-up observations have shown that metallicity drops significantly at the starburst (compared to the quiescent component of the galaxy). As the timescale for gas mixing is short, the metal-poor gas triggering the starburst must have been accreted recently. This is strong observational evidence for the cold flow accretion predicted by cosmological models of galaxy formation, and, in this respect, XMPs seem to be the best local analogs of the very first galaxies.The ellipsoidal shape of a class of galaxies can be inferred from the observed axial ratio (q) distribution (q = minor axis/major axis) of a large sample of randomly-oriented galaxies. Fitting ellipses to 200 XMPs using r-band SDSS images, we observe that the axial ratio distribution falls off at q ~0.8, and we determine that these falloffs are not due to biases in the data. The falloff at low axial ratio indicates that the XMPs are thick for their size, and the falloff at high axial ratio suggests the vast majority of XMPs are triaxial. We also observe that smaller XMPs are thicker in proportion to their size, and it is expected that for decreasing galaxy size the ratio of random to rotational motions increases, which correlates with increasing relative thickness. The XMPs are low-redshift dwarf galaxies dominated by dark matter, and our results are compatible with simulations that have shown dark matter halos to be triaxial, with triaxial stellar distributions for low-mass galaxies and with triaxiality increasing over time. We will offer precise constraints on the 3D shape of XMPs via Bayesian analysis of our observed axial ratio distribution.This work

  4. On the Iron Abundance Anomaly in K-dwarf and Hyades Stars

    Energy Technology Data Exchange (ETDEWEB)

    Aleo, Patrick D.; Sobotka, Alexander C. [McDonald Observatory and Department of Astronomy, University of Texas at Austin, 2515 Speedway, Stop C1402, Austin, TX 78712-1205 (United States); Ramírez, Ivan [Tacoma Community College, 6501 South 19th Street, Tacoma, WA 98466-7400 (United States)

    2017-09-01

    Using standard 1D-LTE model atmosphere analysis, we provide an in-depth investigation of iron abundance as derived from neutral and singly ionization iron lines (Fe i, ii) in nearby star clusters. Specifically, we replicate the discrepancy regarding Δ[Fe/H], wherein the difference of Fe ii–Fe i increases for stars of the same cluster with decreasing T {sub eff}, reaching an astonishing 1.0 dex at T {sub eff} ∼ 4000 K. Previous studies have investigated this anomaly in the Pleiades and Hyades clusters with no concrete solution. In this analysis, we probe two samples: 63 wide binary field stars where the primary star is of Sun-like temperatures and the secondary is a K-dwarf, ranging from 4231 K ≤ T {sub eff} ≤ 6453 K, and 33 Hyades stars of temperatures 4268 K ≤ T {sub eff} ≤ 6072 K. Previous studies have found discrepancies on the order of 1.0 dex. However, we find that these studies have neglected line-blending effects of certain Fe ii lines, namely λ = (4508.29 Å, 4993.34 Å, 5197.58 Å, 5325.55 Å, 5425.26 Å, 6456.38 Å). When these lines are removed from the line-list, we find Δ[Fe/H] decreases to ∼0.6 dex in the field binaries and ∼0.3 dex in the Hyades. The reason for this remaining trend is investigated by probing NLTE effects, as well as age and activity considerations using Ca ii H+K emission and Li absorption, but these results appear to be small to negligible.

  5. ON THE SURVIVAL OF BROWN DWARFS AND PLANETS ENGULFED BY THEIR GIANT HOST STAR

    Energy Technology Data Exchange (ETDEWEB)

    Passy, Jean-Claude; Mac Low, Mordecai-Mark [Department of Astrophysics, American Museum of Natural History, New York, NY (United States); De Marco, Orsola [Department of Physics and Astronomy, Macquarie University, Sydney, NSW (Australia)

    2012-11-10

    The recent discovery of two Earth-mass planets in close orbits around an evolved star has raised questions as to whether substellar companions can survive encounters with their host stars. We consider whether these companions could have been stripped of significant amounts of mass during the phase when they orbited through the dense inner envelopes of the giant. We apply the criterion derived by Murray et al. for disruption of gravitationally bound objects by ram pressure to determine whether mass loss may have played a role in the histories of these and other recently discovered low-mass companions to evolved stars. We find that the brown dwarf and Jovian-mass objects circling WD 0137-349, SDSS J08205+0008, and HIP 13044 are most unlikely to have lost significant mass during the common envelope phase. However, the Earth-mass planets found around KIC 05807616 could well be the remnants of one or two Jovian-mass planets that lost extensive mass during the common envelope phase.

  6. Milky Way Tomography with K and M Dwarf Stars: The Vertical Structure of the Galactic Disk

    Energy Technology Data Exchange (ETDEWEB)

    Ferguson, Deborah; Gardner, Susan [Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506-0055 (United States); Yanny, Brian [Fermi National Accelerator Laboratory, Batavia, IL 60510 (United States)

    2017-07-10

    We use the number density distributions of K and M dwarf stars with vertical height from the Galactic disk, determined using observations from the Sloan Digital Sky Survey, to probe the structure of the Milky Way disk across the survey’s footprint. Using photometric parallax as a distance estimator we analyze a sample of several million disk stars in matching footprints above and below the Galactic plane, and we determine the location and extent of vertical asymmetries in the number counts in a variety of thin- and thick-disk subsamples in regions of some 200 square degrees within 2 kpc in vertical distance from the Galactic disk. These disk asymmetries present wave-like features as previously observed on other scales and at other distances from the Sun. We additionally explore the scale height of the disk and the implied offset of the Sun from the Galactic plane at different locations, noting that the scale height of the disk can differ significantly when measured using stars only above or only below the plane. Moreover, we compare the shape of the number density distribution in the north for different latitude ranges with a fixed range in longitude and find the shape to be sensitive to the selected latitude window. We explain why this may be indicative of a change in stellar populations in the latitude regions compared, possibly allowing access to the systematic metallicity difference between thin- and thick-disk populations through photometry.

  7. Milky Way Tomography with K and M Dwarf Stars: The Vertical Structure of the Galactic Disk

    International Nuclear Information System (INIS)

    Ferguson, Deborah; Gardner, Susan; Yanny, Brian

    2017-01-01

    We use the number density distributions of K and M dwarf stars with vertical height from the Galactic disk, determined using observations from the Sloan Digital Sky Survey, to probe the structure of the Milky Way disk across the survey’s footprint. Using photometric parallax as a distance estimator we analyze a sample of several million disk stars in matching footprints above and below the Galactic plane, and we determine the location and extent of vertical asymmetries in the number counts in a variety of thin- and thick-disk subsamples in regions of some 200 square degrees within 2 kpc in vertical distance from the Galactic disk. These disk asymmetries present wave-like features as previously observed on other scales and at other distances from the Sun. We additionally explore the scale height of the disk and the implied offset of the Sun from the Galactic plane at different locations, noting that the scale height of the disk can differ significantly when measured using stars only above or only below the plane. Moreover, we compare the shape of the number density distribution in the north for different latitude ranges with a fixed range in longitude and find the shape to be sensitive to the selected latitude window. We explain why this may be indicative of a change in stellar populations in the latitude regions compared, possibly allowing access to the systematic metallicity difference between thin- and thick-disk populations through photometry.

  8. Milky Way Tomography with K and M Dwarf Stars: The Vertical Structure of the Galactic Disk

    Science.gov (United States)

    Ferguson, Deborah; Gardner, Susan; Yanny, Brian

    2017-07-01

    We use the number density distributions of K and M dwarf stars with vertical height from the Galactic disk, determined using observations from the Sloan Digital Sky Survey, to probe the structure of the Milky Way disk across the survey’s footprint. Using photometric parallax as a distance estimator we analyze a sample of several million disk stars in matching footprints above and below the Galactic plane, and we determine the location and extent of vertical asymmetries in the number counts in a variety of thin- and thick-disk subsamples in regions of some 200 square degrees within 2 kpc in vertical distance from the Galactic disk. These disk asymmetries present wave-like features as previously observed on other scales and at other distances from the Sun. We additionally explore the scale height of the disk and the implied offset of the Sun from the Galactic plane at different locations, noting that the scale height of the disk can differ significantly when measured using stars only above or only below the plane. Moreover, we compare the shape of the number density distribution in the north for different latitude ranges with a fixed range in longitude and find the shape to be sensitive to the selected latitude window. We explain why this may be indicative of a change in stellar populations in the latitude regions compared, possibly allowing access to the systematic metallicity difference between thin- and thick-disk populations through photometry.

  9. ON THE SURVIVAL OF BROWN DWARFS AND PLANETS ENGULFED BY THEIR GIANT HOST STAR

    International Nuclear Information System (INIS)

    Passy, Jean-Claude; Mac Low, Mordecai-Mark; De Marco, Orsola

    2012-01-01

    The recent discovery of two Earth-mass planets in close orbits around an evolved star has raised questions as to whether substellar companions can survive encounters with their host stars. We consider whether these companions could have been stripped of significant amounts of mass during the phase when they orbited through the dense inner envelopes of the giant. We apply the criterion derived by Murray et al. for disruption of gravitationally bound objects by ram pressure to determine whether mass loss may have played a role in the histories of these and other recently discovered low-mass companions to evolved stars. We find that the brown dwarf and Jovian-mass objects circling WD 0137–349, SDSS J08205+0008, and HIP 13044 are most unlikely to have lost significant mass during the common envelope phase. However, the Earth-mass planets found around KIC 05807616 could well be the remnants of one or two Jovian-mass planets that lost extensive mass during the common envelope phase.

  10. On the Survival of Brown Dwarfs and Planets Engulfed by Their Giant Host Star

    Science.gov (United States)

    Passy, Jean-Claude; Mac Low, Mordecai-Mark; De Marco, Orsola

    2012-11-01

    The recent discovery of two Earth-mass planets in close orbits around an evolved star has raised questions as to whether substellar companions can survive encounters with their host stars. We consider whether these companions could have been stripped of significant amounts of mass during the phase when they orbited through the dense inner envelopes of the giant. We apply the criterion derived by Murray et al. for disruption of gravitationally bound objects by ram pressure to determine whether mass loss may have played a role in the histories of these and other recently discovered low-mass companions to evolved stars. We find that the brown dwarf and Jovian-mass objects circling WD 0137-349, SDSS J08205+0008, and HIP 13044 are most unlikely to have lost significant mass during the common envelope phase. However, the Earth-mass planets found around KIC 05807616 could well be the remnants of one or two Jovian-mass planets that lost extensive mass during the common envelope phase.

  11. METAL-POOR LITHIUM-RICH GIANTS IN THE RADIAL VELOCITY EXPERIMENT SURVEY

    Energy Technology Data Exchange (ETDEWEB)

    Ruchti, Gregory R.; Fulbright, Jon P.; Wyse, Rosemary F. G. [Bloomberg Center for Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Gilmore, Gerard F. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Grebel, Eva K. [Astronomisches Rechen-Institut, Zentrum fuer Astronomie der Universitaet Heidelberg, Moenchhofstr. 12-14, D-69120 Heidelberg (Germany); Bienayme, Olivier; Siebert, Arnaud [Observatoire de Strasbourg, 11 Rue de l' Universite, F-67000 Strasbourg (France); Bland-Hawthorn, Joss [Sydney Institute for Astronomy, School of Physics A28, University of Sydney, NSW 2006 (Australia); Freeman, Ken C. [RSAA Australian National University, Mount Stromlo Observatory, Cotter Road, Weston Creek, Canberra, ACT 2611 (Australia); Gibson, Brad K. [Jeremiah Horrocks Institute for Astrophysics and Super-computing, University of Central Lancashire, Preston PR1 2HE (United Kingdom); Munari, Ulisse [INAF Osservatorio Astronomico di Padova, Via dell' Osservatorio 8, I-36012 Asiago (Italy); Navarro, Julio F. [Department of Physics and Astronomy, University of Victoria, P.O. Box 3055, Station CSC, Victoria, BC V8W 3P6 (Canada); Parker, Quentin A.; Watson, Fred G. [Australian Astronomical Observatory, Coonabarabran, NSW 2357 (Australia); Reid, Warren [Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109 (Australia); Seabroke, George M. [Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking RH5 6NT (United Kingdom); Siviero, Alessandro [Department of Astronomy, Padova University, Vicolo dell' Osservatorio 2, I-35122 Padova (Italy); Steinmetz, Matthias; Williams, Mary [Leibniz-Institut fuer Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam (Germany); Zwitter, Tomaz, E-mail: gruchti@mpa-garching.mpg.de [Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SK-1000 Ljubljana (Slovenia)

    2011-12-20

    We report the discovery of eight lithium-rich field giants found in a high-resolution spectroscopic sample of over 700 metal-poor stars ([Fe/H] < -0.5) selected from the Radial Velocity Experiment survey. The majority of the Li-rich giants in our sample are very metal-poor ([Fe/H] {approx}< -1.9), and have a Li abundance (in the form of {sup 7}Li), A(Li) = log (n(Li)/n(H)) + 12, between 2.30 and 3.63, well above the typical upper red giant branch (RGB) limit, A(Li) < 0.5, while two stars, with A(Li) {approx} 1.7-1.8, show similar lithium abundances to normal giants at the same gravity. We further included two metal-poor, Li-rich globular cluster giants in our sample, namely the previously discovered M3-IV101 and newly discovered (in this work) M68-A96. This comprises the largest sample of metal-poor Li-rich giants to date. We performed a detailed abundance analysis of all stars, finding that the majority of our sample stars have elemental abundances similar to that of Li-normal halo giants. Although the evolutionary phase of each Li-rich giant cannot be definitively determined, the Li-rich phase is likely connected to extra mixing at the RGB bump or early asymptotic giant branch that triggers cool bottom processing in which the bottom of the outer convective envelope is connected to the H-burning shell in the star. The surface of a star becomes Li-enhanced as {sup 7}Be (which burns to {sup 7}Li) is transported to the stellar surface via the Cameron-Fowler mechanism. We discuss and discriminate among several models for the extra mixing that can cause Li production, given the detailed abundances of the Li-rich giants in our sample.

  12. MULTI-ELEMENT ABUNDANCE MEASUREMENTS FROM MEDIUM-RESOLUTION SPECTRA. II. CATALOG OF STARS IN MILKY WAY DWARF SATELLITE GALAXIES

    International Nuclear Information System (INIS)

    Kirby, Evan N.; Cohen, Judith G.; Guhathakurta, Puragra; Rockosi, Constance M.; Simon, Joshua D.; Geha, Marla C.; Sneden, Christopher; Sohn, Sangmo Tony; Majewski, Steven R.; Siegel, Michael

    2010-01-01

    We present a catalog of Fe, Mg, Si, Ca, and Ti abundances for 2961 stars in eight dwarf satellite galaxies of the Milky Way (MW): Sculptor, Fornax, Leo I, Sextans, Leo II, Canes Venatici I, Ursa Minor, and Draco. For the purposes of validating our measurements, we also observed 445 red giants in MW globular clusters and 21 field red giants in the MW halo. The measurements are based on Keck/DEIMOS medium-resolution spectroscopy (MRS) combined with spectral synthesis. We estimate uncertainties in [Fe/H] by quantifying the dispersion of [Fe/H] measurements in a sample of stars in monometallic globular clusters (GCs). We estimate uncertainties in Mg, Si, Ca, and Ti abundances by comparing to high-resolution spectroscopic abundances of the same stars. For this purpose, a sample of 132 stars with published high-resolution spectroscopy in GCs, the MW halo field, and dwarf galaxies has been observed with MRS. The standard deviations of the differences in [Fe/H] and ([α/Fe]) (the average of [Mg/Fe], [Si/Fe], [Ca/Fe], and [Ti/Fe]) between the two samples is 0.15 and 0.16, respectively. This catalog represents the largest sample of multi-element abundances in dwarf galaxies to date. The next papers in this series draw conclusions on the chemical evolution, gas dynamics, and star formation histories from the catalog presented here. The wide range of dwarf galaxy luminosity reveals the dependence of dwarf galaxy chemical evolution on galaxy stellar mass.

  13. THE SOLAR NEIGHBORHOOD. XXVIII. THE MULTIPLICITY FRACTION OF NEARBY STARS FROM 5 TO 70 AU AND THE BROWN DWARF DESERT AROUND M DWARFS

    International Nuclear Information System (INIS)

    Dieterich, Sergio B.; Henry, Todd J.; Golimowski, David A.; Krist, John E.; Tanner, Angelle M.

    2012-01-01

    We report on our analysis of Hubble Space Telescope/NICMOS snapshot high-resolution images of 255 stars in 201 systems within ∼10 pc of the Sun. Photometry was obtained through filters F110W, F180M, F207M, and F222M using NICMOS Camera 2. These filters were selected to permit clear identification of cool brown dwarfs through methane contrast imaging. With a plate scale of 76 mas pixel –1 , NICMOS can easily resolve binaries with subarcsecond separations in the 19.''5×19.''5 field of view. We previously reported five companions to nearby M and L dwarfs from this search. No new companions were discovered during the second phase of data analysis presented here, confirming that stellar/substellar binaries are rare. We establish magnitude and separation limits for which companions can be ruled out for each star in the sample, and then perform a comprehensive sensitivity and completeness analysis for the subsample of 138 M dwarfs in 126 systems. We calculate a multiplicity fraction of 0.0 +3.5 –0.0 % for L companions to M dwarfs in the separation range of 5-70 AU, and 2.3 +5.0 –0.7 % for L and T companions to M dwarfs in the separation range of 10-70 AU. We also discuss trends in the color-magnitude diagrams using various color combinations and present astrometry for 19 multiple systems in our sample. Considering these results and results from several other studies, we argue that the so-called brown dwarf desert extends to binary systems with low-mass primaries and is largely independent of primary mass, mass ratio, and separations. While focusing on companion properties, we discuss how the qualitative agreement between observed companion mass functions and initial mass functions suggests that the paucity of brown dwarfs in either population may be due to a common cause and not due to binary formation mechanisms.

  14. Importance of tides for periastron precession in eccentric neutron star-white dwarf binaries

    Energy Technology Data Exchange (ETDEWEB)

    Sravan, N.; Valsecchi, F.; Kalogera, V. [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States); Althaus, L. G., E-mail: niharika.sravan@gmail.com [Grupo de Evolución Estelar y Pulsaciones, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Argentina Instituto de Astrofísica La Plata, CONICET-UNLP, Paseo del Bosque s/n, (1900) La Plata (Argentina)

    2014-09-10

    Although not nearly as numerous as binaries with two white dwarfs, eccentric neutron star-white dwarf (NS-WD) binaries are important gravitational-wave (GW) sources for the next generation of space-based detectors sensitive to low frequency waves. Here we investigate periastron precession in these sources as a result of general relativistic, tidal, and rotational effects; such precession is expected to be detectable for at least some of the detected binaries of this type. Currently, two eccentric NS-WD binaries are known in the galactic field, PSR J1141–6545 and PSR B2303+46, both of which have orbits too wide to be relevant in their current state to GW observations. However, population synthesis studies predict the existence of a significant Galactic population of such systems. Though small in most of these systems, we find that tidally induced periastron precession becomes important when tides contribute to more than 3% of the total precession rate. For these systems, accounting for tides when analyzing periastron precession rate measurements can improve estimates of the inferred WD component mass and, in some cases, will prevent us from misclassifying the object. However, such systems are rare, due to rapid orbital decay. To aid the inclusion of tidal effects when using periastron precession as a mass measurement tool, we derive a function that relates the WD radius and periastron precession constant to the WD mass.

  15. Effect of Generalized Uncertainty Principle on Main-Sequence Stars and White Dwarfs

    Directory of Open Access Journals (Sweden)

    Mohamed Moussa

    2015-01-01

    Full Text Available This paper addresses the effect of generalized uncertainty principle, emerged from different approaches of quantum gravity within Planck scale, on thermodynamic properties of photon, nonrelativistic ideal gases, and degenerate fermions. A modification in pressure, particle number, and energy density are calculated. Astrophysical objects such as main-sequence stars and white dwarfs are examined and discussed as an application. A modification in Lane-Emden equation due to a change in a polytropic relation caused by the presence of quantum gravity is investigated. The applicable range of quantum gravity parameters is estimated. The bounds in the perturbed parameters are relatively large but they may be considered reasonable values in the astrophysical regime.

  16. Constraining the Nature of Dark Matter with the Star-formation History of the Faintest Local Group Dwarf Galaxy Satellites

    Energy Technology Data Exchange (ETDEWEB)

    Chau, Alice; Mayer, Lucio [Center for Theoretical Astrophysics and Cosmology, Institute for Computational Science, University of Zurich, Winterthurerstrasse 190, CH-8057 Zürich (Switzerland); Governato, Fabio [Astronomy Department, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States)

    2017-08-10

    Λ warm dark matter (ΛWDM), realized by collisionless particles of 1–3 keV, has been proposed as an alternative scenario to Λ-Cold-Dark Matter (ΛCDM) for the dwarf galaxy scale discrepancies. We present an approach to test the viability of such WDM models using star-formation histories (SFHs) of the dwarf spheroidal galaxies (dSphs) in the Local Group. We compare their high-time-resolution SFHs with the collapse redshift of their dark halos in CDM and WDM. Collapse redshift is inferred after determining the subhalo infall mass. This is based on the dwarf current mass inferred from stellar kinematics, combined with cosmological simulation results on subhalo evolution. WDM subhalos close to the filtering mass scale, forming significantly later than CDM, are the most difficult to reconcile with early truncation of star formation ( z ≥ 3). The ultra-faint dwarfs (UFDs) provide the most stringent constraints. Using six UFDs and eight classical dSphs, we show that a 1 keV particle is strongly disfavored, consistently with other reported methods. Excluding other models is only hinted for a few UFDs. Other UFDs for which the lack of robust constraints on halo mass prevents us from carrying out our analysis rigorously, show a very early onset of star formation that will strengthen the constraints delivered by our method in the future. We discuss the various caveats, notably the low number of dwarfs with accurately determined SFHs and the uncertainties when determining the subhalo infall mass, most notably the baryonic physics. Our preliminary analysis may serve as a pathfinder for future investigations that will combine accurate SFHs for local dwarfs with direct analysis of WDM simulations with baryons.

  17. AN UNDERSTANDING OF THE SHOULDER OF GIANTS: JOVIAN PLANETS AROUND LATE K DWARF STARS AND THE TREND WITH STELLAR MASS

    Energy Technology Data Exchange (ETDEWEB)

    Gaidos, Eric [Department of Geology and Geophysics, University of Hawai' i at Manoa, Honolulu, HI 96822 (United States); Fischer, Debra A. [Department of Astronomy, Yale University, New Haven, CT 06520 (United States); Mann, Andrew W.; Howard, Andrew W., E-mail: gaidos@hawaii.edu [Institute for Astronomy, University of Hawai' i at Manoa, Honolulu, HI 96822 (United States)

    2013-07-01

    Analyses of exoplanet statistics suggest a trend of giant planet occurrence with host star mass, a clue to how planets like Jupiter form. One missing piece of the puzzle is the occurrence around late K dwarf stars (masses of 0.5-0.75 M{sub Sun} and effective temperatures of 3900-4800 K). We analyzed four years of Doppler radial velocity (RVs) data for 110 late K dwarfs, one of which hosts two previously reported giant planets. We estimate that 4.0% {+-} 2.3% of these stars have Saturn-mass or larger planets with orbital periods <245 days, depending on the planet mass distribution and RV variability of stars without giant planets. We also estimate that 0.7% {+-} 0.5% of similar stars observed by Kepler have giant planets. This Kepler rate is significantly (99% confidence) lower than that derived from our Doppler survey, but the difference vanishes if only the single Doppler system (HIP 57274) with completely resolved orbits is considered. The difference could also be explained by the exclusion of close binaries (without giant planets) from the Doppler but not Kepler surveys, the effect of long-period companions and stellar noise on the Doppler data, or an intrinsic difference between the two populations. Our estimates for late K dwarfs bridge those for solar-type stars and M dwarfs, and support a positive trend with stellar mass. Small sample size precludes statements about finer structure, e.g., a ''shoulder'' in the distribution of giant planets with stellar mass. Future surveys such as the Next Generation Transit Survey and the Transiting Exoplanet Satellite Survey will ameliorate this deficiency.

  18. Hints for Small Disks around Very Low Mass Stars and Brown Dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    Hendler, Nathanial P.; Mulders, Gijs D.; Pascucci, Ilaria [Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721 (United States); Greenwood, Aaron; Kamp, Inga [Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen (Netherlands); Henning, Thomas [Max Planck Institute for Astronomy, Konigstuhl 17, D-69117 Heidelberg (Germany); Ménard, François [Univ. Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble (France); Dent, William R. F. [Department of Engineering, Atacama Large Millimeter/submillimeter Array (ALMA) Santiago Central Offices, Alonso de Córdova 3107, Vitacura, Casilla 763 0355, Santiago (Chile); II, Neal J. Evans, E-mail: equant@lpl.arizona.edu [Department of Astronomy, The University of Texas at Austin, Austin, TX 78712 (United States)

    2017-06-01

    The properties of disks around brown dwarfs and very low mass stars (hereafter VLMOs) provide important boundary conditions on the process of planet formation and inform us about the numbers and masses of planets than can form in this regime. We use the Herschel Space Observatory PACS spectrometer to measure the continuum and [O i] 63 μ m line emission toward 11 VLMOs with known disks in the Taurus and Chamaeleon I star-forming regions. We fit radiative transfer models to the spectral energy distributions of these sources. Additionally, we carry out a grid of radiative transfer models run in a regime that connects the luminosity of our sources with brighter T Tauri stars. We find that VLMO disks with sizes 1.3–78 au, smaller than typical T Tauri disks, fit well the spectral energy distributions assuming that disk geometry and dust properties are stellar mass independent. Reducing the disk size increases the disk temperature, and we show that VLMOs do not follow previously derived disk temperature–stellar luminosity relationships if the disk outer radius scales with stellar mass. Only 2 out of 11 sources are detected in [O i] despite a better sensitivity than was achieved for T Tauri stars, suggesting that VLMO disks are underluminous. Using thermochemical models, we show that smaller disks can lead to the unexpected [O i] 63 μ m nondetections in our sample. The disk outer radius is an important factor in determining the gas and dust observables. Hence, spatially resolved observations with ALMA—to establish if and how disk radii scale with stellar mass—should be pursued further.

  19. The ISLAnds Project. III. Variable Stars in Six Andromeda Dwarf Spheroidal Galaxies

    Science.gov (United States)

    Martínez-Vázquez, Clara E.; Monelli, Matteo; Bernard, Edouard J.; Gallart, Carme; Stetson, Peter B.; Skillman, Evan D.; Bono, Giuseppe; Cassisi, Santi; Fiorentino, Giuliana; McQuinn, Kristen B. W.; Cole, Andrew A.; McConnachie, Alan W.; Martin, Nicolas F.; Dolphin, Andrew E.; Boylan-Kolchin, Michael; Aparicio, Antonio; Hidalgo, Sebastian L.; Weisz, Daniel R.

    2017-12-01

    We present a census of variable stars in six M31 dwarf spheroidal satellites observed with the Hubble Space Telescope. We detect 870 RR Lyrae (RRL) stars in the fields of And I (296), II (251), III (111), XV (117), XVI (8), and XXVIII (87). We also detect a total of 15 Anomalous Cepheids, three eclipsing binaries, and seven field RRL stars compatible with being members of the M31 halo or the Giant Stellar Stream. We derive robust and homogeneous distances to the six galaxies using different methods based on the properties of the RRL stars. Working with the up-to-date set of Period-Wesenheit (I, B-I) relations published by Marconi et al., we obtain distance moduli of μ 0 = [24.49, 24.16, 24.36, 24.42, 23.70, 24.43] mag (respectively), with systematic uncertainties of 0.08 mag and statistical uncertainties systems do not show any significant difference. In particular, we found a strikingly similar correlation between the mean period distribution of the fundamental RRL pulsators (RRab) and the mean metallicities of the galaxies. This indicates that the old RRL progenitors were similar at the early stage in the two environments, suggesting very similar characteristics for the earliest stages of evolution of both satellite systems. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs 13028 and 13739.

  20. Photospheric Spots and Flare on the Active Dwarf Star FR Cnc

    Science.gov (United States)

    Kozhevnikova, A. V.; Kozhevnikov, V. P.; Alekseev, I. Yu.

    2018-03-01

    We perform analysis of new BVRI photometry of young active dwarf star FR Cnc (K7V), obtained at Kourovka astronomical observatory of Ural Federal University with the help of multichannel electrophotometer in February 2010. The lightcurve displays sinusoidal rotation modulation with the amplitude of 0m.15 in V band. Reddening of the brightness at the photometric minimum confirms that this modulation is caused by cold photospheric spots. An analysis of the spottedness distribution in terms of a zonal model based on our own and published data shows that the spots are localized at lower and middle latitudes from 47° to 56°, occupy 10-21% of the star's area, and are colder than the photosphere by 1650 K. A flare was detected on February 3, 2010, at a time corresponding to HJD=2455231. 3136. A maximum amplitude of 0m.11 was observed in the B band, the amplitudes in the V, R, and I bands were 0m.04, 0m.03, and 0m.02, respectively, and the duration of the flare was 32.5 min. It was noted that the flare occurred near the maximum spottedness of the star. The calculated total energy of the flare was 2.4·1033 and 1.3·1033 erg in the B and V bands, respectively. The flare was found to have an afterglow, with an overall increase in the star's brightness by 0m.02 in the B band after the flare compared to the pre-flare level.

  1. Resolving the Connection Between Superluminous Supernovae and Star Formation in Dwarf Galaxies

    Science.gov (United States)

    Lunnan, Ragnhild

    2017-08-01

    Hydrogen-poor superluminous supernovae (SLSN-I) are a rare class of transients with peak luminosities 10-100x those of ordinary SNe and unique spectra. Now a decade after their first discoveries (and even with > 50 objects found), fundamental questions like their energy sources and progenitors are still unknown. A strong clue comes from their host galaxy environments: SLSN-I show an overwhelming preference for low-mass, low-metallicity dwarf galaxies, many of which are also undergoing a starburst. Whether this is purely a metallicity effect or also require extreme star formation conditions is debated, but the latter scenario predicts a correlation between the local SN environments and the host galaxy star formation as traced by UV light. This prediction is testable with resolved HST imaging and precise astrometry, though initial studies have been inconclusive due to small number statistics. Here we propose to remedy this by obtaining resolved rest-frame UV imaging of 22 SLSN-I host galaxies from the Palomar Transient Factory SLSN sample, which will nearly triple the sample with HST imaging compared to previous studies and allow this question to be settled with robust statistics. At the current discovery rate of SLSNe, a similar improvement will not be possible until the LSST era.

  2. A Massive-born Neutron Star with a Massive White Dwarf Companion

    Energy Technology Data Exchange (ETDEWEB)

    Cognard, Ismaël; Guillemot, Lucas; Theureau, Gilles [Laboratoire de Physique et Chimie de l’Environnement et de l’Espace, Université d’Orléans/CNRS, F-45071 Orléans Cedex 02 (France); Freire, Paulo C. C. [Station de radioastronomie de Nançay, Observatoire de Paris, CNRS/INSU, F-18330 Nançay (France); Tauris, Thomas M.; Wex, Norbert; Graikou, Eleni; Kramer, Michael; Desvignes, Gregory; Lazarus, Patrick [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Stappers, Benjamin; Lyne, Andrew G. [Jodrell Bank Center for Astrophysics, School of Physics and Astronomy, The University of Manchester, M13 9PL (United Kingdom); Bassa, Cees [ASTRON, The Netherlands Institute for Radioastronomy, Postbus 2, 7900 AA, Dwingeloo (Netherlands)

    2017-08-01

    We report on the results of a 4 year timing campaign of PSR J2222−0137, a 2.44 day binary pulsar with a massive white dwarf (WD) companion, with the Nançay, Effelsberg, and Lovell radio telescopes. Using the Shapiro delay for this system, we find a pulsar mass m {sub p} = 1.76 ± 0.06 M {sub ⊙} and a WD mass m {sub c} = 1.293 ± 0.025 M {sub ⊙}. We also measure the rate of advance of periastron for this system, which is marginally consistent with the general relativity prediction for these masses. The short lifetime of the massive WD progenitor star led to a rapid X-ray binary phase with little (< 10{sup −2} M {sub ⊙}) mass accretion onto the neutron star; hence, the current pulsar mass is, within uncertainties, its birth mass, which is the largest measured to date. We discuss the discrepancy with previous mass measurements for this system; we conclude that the measurements presented here are likely to be more accurate. Finally, we highlight the usefulness of this system for testing alternative theories of gravity by tightly constraining the presence of dipolar radiation. This is of particular importance for certain aspects of strong-field gravity, like spontaneous scalarization, since the mass of PSR J2222−0137 puts that system into a poorly tested parameter range.

  3. NEAR-IR PHOTOMETRIC PROPERTIES OF HB, MSTO, AND SGB FOR METAL POOR GALACTIC GLOBULAR CLUSTERS

    Directory of Open Access Journals (Sweden)

    J.-W. Kim

    2007-03-01

    Full Text Available We report photometric features of the HB, MSTO, and SGB for a set of metal-poor Galactic globular clusters on the near-IR CMDs. The magnitude and color of the MSTO and SGB are measured on the fiducial normal points of the CMDs by applying a polynomial fit. The near-IR luminosity functions of horizontal branch stars in the classical second parameter pair M3 and M13 indicate that HB stars in M13 are dominated by hot stars that are rotatively faint in the infrared, whereas HB stars in M3 are brighter than those in M13. The luminosity functions of HB stars in the observed bulge clusters, except for NGC 6717, show a trend that the fainter hot HB stars are dominated in the relatively metal-poor clusters while the relatively metal-rich clusters contain the brighter HB stars. It is suggestive that NGC 6717 would be an extreme example of the second-parameter phenomenon for the bulge globular clusters.

  4. "Dark galaxies" and local very metal-poor gas-rich galaxies: possible interrelations

    OpenAIRE

    Pustilnik, Simon A.

    2007-01-01

    There are only a few ``dark galaxy'' candidates discovered to date in the local Universe. One of the most prominent of them is the SW component of a merging system HI 1225+01. On the other hand, the number of known very metal-poor gas-rich dwarfs similar to IZw18 and SBS 0335-052 E,W has grown drastically during the last decade, from a dozen and a half to about five dozen. Many of them are very gas-rich, having from ~90 to 99% of all baryons in gas. For some of such objects that have the deep...

  5. The Development of New Atmospheric Models for K and M DwarfStars with Exoplanets

    Science.gov (United States)

    Linsky, Jeffrey L.

    2018-01-01

    The ultraviolet and X-ray emissions of host stars play critical roles in the survival and chemical composition of the atmospheres of their exoplanets. The need to measure and understand this radiative output, in particular for K and M dwarfs, is the main rationale for computing a new generation of stellar models that includes magnetically heated chromospheres and coronae in addition to their photospheres. We describe our method for computing semi-empirical models that includes solutions of the statistical equilibrium equations for 52 atoms and ions and of the non-LTE radiative transfer equations for all important spectral lines. The code is an offspring of the Solar Radiation Physical Modelling system (SRPM) developed by Fontenla et al. (2007--2015) to compute one-dimensional models in hydrostatic equilibrium to fit high-resolution stellar X-ray to IR spectra. Also included are 20 diatomic molecules and their more than 2 million spectral lines. Our-proof-of-concept model is for the M1.5 V star GJ 832 (Fontenla et al. ApJ 830, 154 (2016)). We will fit the line fluxes and profiles of X-ray lines and continua observed by Chandra and XMM-Newton, UV lines observed by the COS and STIS instruments on HST (N V, C IV, Si IV, Si III, Mg II, C II, and O I), optical lines (including H$\\alpha$, Ca II, Na I), and continua. These models will allow us to compute extreme-UV spectra, which are unobservable but required to predict the hydrodynamic mass-loss rate from exoplanet atmospheres, and to predict panchromatic spectra of new exoplanet host stars discovered after the end of the HST mission.This work is supported by grant HST-GO-15038 from the Space Telescope Science Institute to the Univ. of Colorado

  6. The star formation histories of local group dwarf galaxies. I. Hubble space telescope/wide field planetary camera 2 observations

    Energy Technology Data Exchange (ETDEWEB)

    Weisz, Daniel R. [Department of Astronomy, University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Dolphin, Andrew E. [Raytheon Company, 1151 East Hermans Road, Tucson, AZ 85756 (United States); Skillman, Evan D. [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455 (United States); Holtzman, Jon [Department of Astronomy, New Mexico State University, Box 30001, 1320 Frenger Street, Las Cruces, NM 88003 (United States); Gilbert, Karoline M.; Dalcanton, Julianne J.; Williams, Benjamin F., E-mail: drw@ucsc.edu [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)

    2014-07-10

    We present uniformly measured star formation histories (SFHs) of 40 Local Group (LG) dwarf galaxies based on color-magnitude diagram (CMD) analysis from archival Hubble Space Telescope imaging. We demonstrate that accurate SFHs can be recovered from CMDs that do not reach the oldest main sequence turn-off (MSTO), but emphasize that the oldest MSTO is critical for precisely constraining the earliest epochs of star formation. We find that: (1) the average lifetime SFHs of dwarf spheroidals (dSphs) can be approximated by an exponentially declining SFH with τ ∼ 5 Gyr; (2) lower luminosity dSphs are less likely to have extended SFHs than more luminous dSphs; (3) the average SFHs of dwarf irregulars (dIrrs), transition dwarfs, and dwarf ellipticals can be approximated by the combination of an exponentially declining SFH (τ ∼ 3-4 Gyr) for lookback ages >10-12 Gyr ago and a constant SFH thereafter; (4) the observed fraction of stellar mass formed prior to z = 2 ranges considerably (80% for galaxies with M < 10{sup 5} M{sub ☉} to 30% for galaxies with M > 10{sup 7} M{sub ☉}) and is largely explained by environment; (5) the distinction between 'ultra-faint' and 'classical' dSphs is arbitrary; (6) LG dIrrs formed a significantly higher fraction of stellar mass prior to z = 2 than the Sloan Digital Sky Survey galaxies from Leitner and the SFHs from the abundance matching models of Behroozi et al. This may indicate higher than expected star formation efficiencies at early times in low mass galaxies. Finally, we provide all the SFHs in tabulated electronic format for use by the community.

  7. The Star Formation Histories of Local Group Dwarf Galaxies. I. Hubble Space Telescope/Wide Field Planetary Camera 2 Observations

    Science.gov (United States)

    Weisz, Daniel R.; Dolphin, Andrew E.; Skillman, Evan D.; Holtzman, Jon; Gilbert, Karoline M.; Dalcanton, Julianne J.; Williams, Benjamin F.

    2014-07-01

    We present uniformly measured star formation histories (SFHs) of 40 Local Group (LG) dwarf galaxies based on color-magnitude diagram (CMD) analysis from archival Hubble Space Telescope imaging. We demonstrate that accurate SFHs can be recovered from CMDs that do not reach the oldest main sequence turn-off (MSTO), but emphasize that the oldest MSTO is critical for precisely constraining the earliest epochs of star formation. We find that: (1) the average lifetime SFHs of dwarf spheroidals (dSphs) can be approximated by an exponentially declining SFH with τ ~ 5 Gyr (2) lower luminosity dSphs are less likely to have extended SFHs than more luminous dSphs; (3) the average SFHs of dwarf irregulars (dIrrs), transition dwarfs, and dwarf ellipticals can be approximated by the combination of an exponentially declining SFH (τ ~ 3-4 Gyr) for lookback ages >10-12 Gyr ago and a constant SFH thereafter; (4) the observed fraction of stellar mass formed prior to z = 2 ranges considerably (80% for galaxies with M 107 M ⊙) and is largely explained by environment; (5) the distinction between "ultra-faint" and "classical" dSphs is arbitrary; (6) LG dIrrs formed a significantly higher fraction of stellar mass prior to z = 2 than the Sloan Digital Sky Survey galaxies from Leitner and the SFHs from the abundance matching models of Behroozi et al. This may indicate higher than expected star formation efficiencies at early times in low mass galaxies. Finally, we provide all the SFHs in tabulated electronic format for use by the community. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  8. Radiation of dwarf novae

    International Nuclear Information System (INIS)

    Bruch, A.

    1987-01-01

    The nature of dwarf novae with their components white dwarf star, cool star, accretion disk, boundary layer and hot spot is investigated. It is shown that very different physical states and processes occur in the components of dwarf novae. Spectroscopical and photometrical observations are carried out. For better understanding the radiation portions of the single dwarf novae components are separated from the total electromagnetic spectrum recieved from the dwarf novae. The model assumptions are compared with the observations and verified

  9. Chemical Abundances of M-Dwarfs from the Apogee Survey. I. The Exoplanet Hosting Stars Kepler-138 and Kepler-186

    Energy Technology Data Exchange (ETDEWEB)

    Souto, D.; Cunha, K. [Observatório Nacional, Rua General José Cristino, 77, 20921-400 São Cristóvão, Rio de Janeiro, RJ (Brazil); García-Hernández, D. A.; Zamora, O.; Prieto, C. Allende; Jönsson, H.; Pérez, A. E. García [Instituto de Astrofísica de Canarias (IAC), Vía Lactea S/N, E-38205, La Laguna, Tenerife (Spain); Smith, V. V. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Mahadevan, S. [Department of Astronomy and Astrophysics, The Pennsylvania State University (United States); Blake, C. [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104 (United States); Johnson, J. A.; Pinsonneault, M. [Department of Astronomy, The Ohio State University, Columbus, OH 43210 (United States); Holtzman, J. [New Mexico State University, Las Cruces, NM 88003 (United States); Majewski, S. R.; Sobeck, J. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325 (United States); Shetrone, M. [University of Texas at Austin, McDonald Observatory (United States); Teske, J. [Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington, DC 20015 (United States); Nidever, D. [Department of Astronomy, University of Michigan, Ann Arbor, MI, 48104 (United States); Schiavon, R. [Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool, L3 5RF (United Kingdom); and others

    2017-02-01

    We report the first detailed chemical abundance analysis of the exoplanet-hosting M-dwarf stars Kepler-138 and Kepler-186 from the analysis of high-resolution ( R ∼ 22,500) H -band spectra from the SDSS-IV–APOGEE survey. Chemical abundances of 13 elements—C, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, and Fe—are extracted from the APOGEE spectra of these early M-dwarfs via spectrum syntheses computed with an improved line list that takes into account H{sub 2}O and FeH lines. This paper demonstrates that APOGEE spectra can be analyzed to determine detailed chemical compositions of M-dwarfs. Both exoplanet-hosting M-dwarfs display modest sub-solar metallicities: [Fe/H]{sub Kepler-138} = −0.09 ± 0.09 dex and [Fe/H]{sub Kepler-186} = −0.08 ± 0.10 dex. The measured metallicities resulting from this high-resolution analysis are found to be higher by ∼0.1–0.2 dex than previous estimates from lower-resolution spectra. The C/O ratios obtained for the two planet-hosting stars are near-solar, with values of 0.55±0.10 for Kepler-138 and 0.52±0.12 for Kepler-186. Kepler-186 exhibits a marginally enhanced [Si/Fe] ratio.

  10. NEW M, L, AND T DWARF COMPANIONS TO NEARBY STARS FROM THE WIDE-FIELD INFRARED SURVEY EXPLORER

    International Nuclear Information System (INIS)

    Luhman, Kevin L.; Loutrel, Nicholas P.; McCurdy, Nicholas S.; Melso, Nicole D.; Star, Kimberly M.; Terrien, Ryan C.; Mace, Gregory N.; McLean, Ian S.; Young, Michael D.; Rhode, Katherine L.; Davy Kirkpatrick, J.

    2012-01-01

    We present 11 candidate late-type companions to nearby stars identified with data from the Wide-field Infrared Survey Explorer (WISE) and the Two Micron All Sky Survey (2MASS). Eight of the candidates are likely to be companions based on their common proper motions with the primaries. The remaining three objects are rejected as companions, one of which is a free-floating T7 dwarf. Spectral types are available for five of the companions, which consist of M2V, M8.5V, L5, T8, and T8. Based on their photometry, the unclassified companions are probably two mid-M dwarfs and one late-M/early-L dwarf. One of the T8 companions, WISE J142320.84+011638.0, has already been reported by Pinfield and coworkers. The other T8 companion, ULAS J095047.28+011734.3, was discovered by Burningham and coworkers through the United Kingdom Infrared Telescope Infrared Deep Sky Survey, but its companionship has not been previously recognized in the literature. The L5 companion, 2MASS J17430860+8526594, is a new member of a class of L dwarfs that exhibit unusually blue near-IR colors. Among the possible mechanisms that have been previously proposed for the peculiar colors of these L dwarfs, low metallicity does not appear to be a viable explanation for 2MASS J17430860+8526594 since our spectrum of the primary suggests that its metallicity is not significantly subsolar.

  11. Understanding the physics of gas stripping and star-formation quenching of the satellite dwarf galaxies in the Local Group

    Science.gov (United States)

    Wetzel, Andrew

    2017-08-01

    The Milky Way (MW) and M31 are among the best systems to study the physics of the halo environment on galaxy evolution. Nearly all of the satellite dwarf galaxies of the MW and M31 are gas-poor and have quenched star formation. Over 1200 orbits of HST observations of these satellites now provide detailed star-formation histories and proper-motion velocities for full 6-D orbital phase-space, informing both when and where each satellite quenched. However, the lack of sufficiently realistic theoretical models of gas stripping represents a severe limitation to leveraging the astrophysical returns of these HST observations.We propose to use the new Latte cosmological zoom-in hydrodynamic simulations of MW- and M31-mass systems to understand the environmental processes that strip gas from satellite dwarf galaxies and quench their star formation. Our initial Latte simulations form realistic satellite populations, with star-formation histories that agree well HST measurements. These simulations use the state-of-the-art FIRE model for star formation and feedback: this feedback drives strong gas outflows within dwarf galaxies that can enhance the efficiency of ram-pressure stripping within the halo. We will run a new suite of simulations carefully targeted to the Local Group, and we will investigate how the combination of internal feedback and external stripping leads to rapid quenching, as observed by HST. Finally, we will publicly release our satellite galaxy/subhalo catalogs, including their full orbital and star-formation histories, to compare with existing/upcoming HST observations, providing detailed insight into the physics of environmental quenching.

  12. The Most Massive Star Clusters: Supermassive Globular Clusters or Dwarf Galaxy Nuclei?

    Science.gov (United States)

    Harris, William

    2004-07-01

    Evidence is mounting that the most massive globular clusters, such as Omega Centauri and M31-G1, may be related to the recently discovered "Ultra-Compact Dwarfs" and the dense nuclei of dE, N galaxies. However, no systematic imaging investigation of these supermassive globular clusters - at the level of Omega Cen and beyond - has been done, and we do not know what fraction of them might bear the signatures {such as large effective radii or tidal tails} of having originated as dE nuclei. We propose to use the ACS/WFC to obtain deep images of 18 such clusters in NGC 5128 and M31, the two nearest rich globular cluster systems. These globulars are the richest star clusters that can be found in nature, the biggest of them reaching 10^7 Solar masses, and they are likely to represent the results of star formation under the densest and most extreme conditions known. Using the profiles of the clusters including their faint outer envelopes, we will carry out state-of-the-art dynamical modelling of their structures, and look for any clear evidence which would indicate that they are associated with stripped satellites. This study will build on our previous work with STIS and WFPC2 imaging designed to study the 'Fundamental Plane' of globular clusters. When our new work is combined with Archival WFPC2, STIS, and ACS material, we will also be able to construct the definitive mapping of the Fundamental Plane of globular clusters at its uppermost mass range, and confirm whether or not the UCD and dE, N objects occupy a different structural parameter space.

  13. NuSTAR AND SWIFT Observations of the Fast Rotating Magnetized White Dwarf AE Aquarii

    Science.gov (United States)

    Kitaguchi, Takao; An, Hongjun; Beloborodov, Andrei M.; Gotthelf, Eric V.; Hayashi, Takayuki; Kaspi, Victoria M.; Rana, Vikram R.; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; hide

    2014-01-01

    AE Aquarii is a cataclysmic variable with the fastest known rotating magnetized white dwarf (P(sub spin) = 33.08 s). Compared to many intermediate polars, AE Aquarii shows a soft X-ray spectrum with a very low luminosity (LX (is) approximately 10(exp 31) erg per second). We have analyzed overlapping observations of this system with the NuSTAR and the Swift X-ray observatories in 2012 September. We find the 0.5-30 keV spectra to be well fitted by either an optically thin thermal plasma model with three temperatures of 0.75(+0.18 / -0.45), 2.29(+0.96 / -0.82), and 9.33 (+6.07 / -2.18) keV, or an optically thin thermal plasma model with two temperatures of 1.00 (+0.34 / -0.23) and 4.64 (+1.58 / -0.84) keV plus a power-law component with photon index of 2.50 (+0.17 / -0.23). The pulse profile in the 3-20 keV band is broad and approximately sinusoidal, with a pulsed fraction of 16.6% +/- 2.3%. We do not find any evidence for a previously reported sharp feature in the pulse profile.

  14. THE BIMODALITY OF ACCRETION IN T TAURI STARS AND BROWN DWARFS

    International Nuclear Information System (INIS)

    Vorobyov, E. I.; Basu, Shantanu

    2009-01-01

    We present numerical solutions of the collapse of prestellar cores that lead to the formation and evolution of circumstellar disks. The disk evolution is then followed for up to three million years. A variety of models of different initial masses and rotation rates allow us to study disk accretion around brown dwarfs and low-mass T Tauri stars (TTSs), with central object mass M * sun , as well as intermediate- and upper-mass TTSs (0.2 M sun * sun ). Our models include self-gravity and allow for nonaxisymmetric motions. In addition to the self-consistently generated gravitational torques, we introduce an effective turbulent α-viscosity with α = 0.01, which allows us particularly to model accretion in the low-mass regime where disk self-gravity is diminishing. A range of models with observationally motivated values of the initial ratio of rotational-to-gravitational energy yield a correlation between mass accretion rate M-dot and M * that is relatively steep, as observed. Additionally, our modeling reveals evidence for a bimodality in the M-dot - M * correlation, with a steeper slope at lower masses and a shallower slope at intermediate and upper masses, as also implied by observations. Furthermore, we show that the neglect of disk self-gravity leads to a much steeper M-dot - M * relation for intermediate- and upper-mass TTSs. This demonstrates that an accurate treatment of global self-gravity is essential to understanding observations of circumstellar disks.

  15. Spatially Resolved Dust, Gas, and Star Formation in the Dwarf Magellanic Irregular NGC 4449

    Science.gov (United States)

    Calzetti, D.; Wilson, G. W.; Draine, B. T.; Roussel, H.; Johnson, K. E.; Heyer, M. H.; Wall, W. F.; Grasha, K.; Battisti, A.; Andrews, J. E.; Kirkpatrick, A.; Rosa González, D.; Vega, O.; Puschnig, J.; Yun, M.; Östlin, G.; Evans, A. S.; Tang, Y.; Lowenthal, J.; Sánchez-Arguelles, D.

    2018-01-01

    We investigate the relation between gas and star formation in subgalactic regions, ∼360 pc to ∼1.5 kpc in size, within the nearby starburst dwarf NGC 4449, in order to separate the underlying relation from the effects of sampling at varying spatial scales. Dust and gas mass surface densities are derived by combining new observations at 1.1 mm, obtained with the AzTEC instrument on the Large Millimeter Telescope, with archival infrared images in the range 8–500 μm from the Spitzer Space Telescope and the Herschel Space Observatory. We extend the dynamic range of our millimeter (and dust) maps at the faint end, using a correlation between the far-infrared/millimeter colors F(70)/F(1100) (and F(160)/F(1100)) and the mid-infrared color F(8)/F(24) that we establish for the first time for this and other galaxies. Supplementing our data with maps of the extinction-corrected star formation rate (SFR) surface density, we measure both the SFR–molecular gas and the SFR–total gas relations in NGC 4449. We find that the SFR–molecular gas relation is described by a power law with an exponent that decreases from ∼1.5 to ∼1.2 for increasing region size, while the exponent of the SFR–total gas relation remains constant with a value of ∼1.5 independent of region size. We attribute the molecular law behavior to the increasingly better sampling of the molecular cloud mass function at larger region sizes; conversely, the total gas law behavior likely results from the balance between the atomic and molecular gas phases achieved in regions of active star formation. Our results indicate a nonlinear relation between SFR and gas surface density in NGC 4449, similar to what is observed for galaxy samples. Based on observations obtained with the Large Millimeter Telescope Alfonso Serrano—a binational collaboration between INAOE (Mexico) and the University of Massachusetts–Amherst (USA).

  16. Toward High-precision Seismic Studies of White Dwarf Stars: Parametrization of the Core and Tests of Accuracy

    Science.gov (United States)

    Giammichele, N.; Charpinet, S.; Fontaine, G.; Brassard, P.

    2017-01-01

    We present a prescription for parametrizing the chemical profile in the core of white dwarfs in light of the recent discovery that pulsation modes may sometimes be deeply confined in some cool pulsating white dwarfs. Such modes may be used as unique probes of the complicated chemical stratification that results from several processes that occurred in previous evolutionary phases of intermediate-mass stars. This effort is part of our ongoing quest for more credible and realistic seismic models of white dwarfs using static, parametrized equilibrium structures. Inspired by successful techniques developed in design optimization fields (such as aerodynamics), we exploit Akima splines for the tracing of the chemical profile of oxygen (carbon) in the core of a white dwarf model. A series of tests are then presented to better seize the precision and significance of the results that can be obtained in an asteroseismological context. We also show that the new parametrization passes an essential basic test, as it successfully reproduces the chemical stratification of a full evolutionary model.

  17. TOWARD HIGH-PRECISION SEISMIC STUDIES OF WHITE DWARF STARS: PARAMETRIZATION OF THE CORE AND TESTS OF ACCURACY

    International Nuclear Information System (INIS)

    Giammichele, N.; Fontaine, G.; Brassard, P.; Charpinet, S.

    2017-01-01

    We present a prescription for parametrizing the chemical profile in the core of white dwarfs in light of the recent discovery that pulsation modes may sometimes be deeply confined in some cool pulsating white dwarfs. Such modes may be used as unique probes of the complicated chemical stratification that results from several processes that occurred in previous evolutionary phases of intermediate-mass stars. This effort is part of our ongoing quest for more credible and realistic seismic models of white dwarfs using static, parametrized equilibrium structures. Inspired by successful techniques developed in design optimization fields (such as aerodynamics), we exploit Akima splines for the tracing of the chemical profile of oxygen (carbon) in the core of a white dwarf model. A series of tests are then presented to better seize the precision and significance of the results that can be obtained in an asteroseismological context. We also show that the new parametrization passes an essential basic test, as it successfully reproduces the chemical stratification of a full evolutionary model.

  18. TOWARD HIGH-PRECISION SEISMIC STUDIES OF WHITE DWARF STARS: PARAMETRIZATION OF THE CORE AND TESTS OF ACCURACY

    Energy Technology Data Exchange (ETDEWEB)

    Giammichele, N.; Fontaine, G.; Brassard, P. [Département de Physique, Université de Montréal, Montréal, QC H3C 3J7 (Canada); Charpinet, S. [Université de Toulouse, UPS-OMP, IRAP, Toulouse F-31400 (France)

    2017-01-10

    We present a prescription for parametrizing the chemical profile in the core of white dwarfs in light of the recent discovery that pulsation modes may sometimes be deeply confined in some cool pulsating white dwarfs. Such modes may be used as unique probes of the complicated chemical stratification that results from several processes that occurred in previous evolutionary phases of intermediate-mass stars. This effort is part of our ongoing quest for more credible and realistic seismic models of white dwarfs using static, parametrized equilibrium structures. Inspired by successful techniques developed in design optimization fields (such as aerodynamics), we exploit Akima splines for the tracing of the chemical profile of oxygen (carbon) in the core of a white dwarf model. A series of tests are then presented to better seize the precision and significance of the results that can be obtained in an asteroseismological context. We also show that the new parametrization passes an essential basic test, as it successfully reproduces the chemical stratification of a full evolutionary model.

  19. Star Formation Histories of the LEGUS Dwarf Galaxies. I. Recent History of NGC 1705, NGC 4449, and Holmberg II

    Science.gov (United States)

    Cignoni, M.; Sacchi, E.; Aloisi, A.; Tosi, M.; Calzetti, D.; Lee, J. C.; Sabbi, E.; Adamo, A.; Cook, D. O.; Dale, D. A.; Elmegreen, B. G.; Gallagher, J. S., III; Gouliermis, D. A.; Grasha, K.; Grebel, E. K.; Hunter, D. A.; Johnson, K. E.; Messa, M.; Smith, L. J.; Thilker, D. A.; Ubeda, L.; Whitmore, B. C.

    2018-03-01

    We use Hubble Space Telescope observations from the Legacy Extragalactic UV Survey to reconstruct the recent star formation histories (SFHs) of three actively star-forming dwarf galaxies, NGC 4449, Holmberg II, and NGC 1705, from their UV color–magnitude diagrams (CMDs). We apply a CMD fitting technique using two independent sets of stellar isochrones, PARSEC-COLIBRI and MIST, to assess the uncertainties related to stellar evolution modeling. Irrespective of the adopted stellar models, all three dwarfs are found to have had almost constant star formation rates (SFRs) in the last 100–200 Myr, with modest enhancements (a factor of ∼2) above the 100 Myr averaged SFR. Significant differences among the three dwarfs are found in terms of the overall SFR, the timing of the most recent peak, and the SFR/area. The initial mass function of NGC 1705 and Holmberg II is consistent with a Salpeter slope down to ≈5 M ⊙, whereas it is slightly flatter, s = ‑2.0, in NGC 4449. The SFHs derived with the two different sets of stellar models are consistent with each other, except for some quantitative details, attributable to their input assumptions. They also share the drawback that all synthetic diagrams predict a clear separation in color between the upper main-sequence and helium-burning stars, which is not apparent in the data. Since neither differential reddening, which is significant in NGC 4449, nor unresolved binaries appear to be sufficient to fill the gap, we suggest this calls for a revision of both sets of stellar evolutionary tracks. Based on observations obtained with the NASA/ESA Hubble Space Telescope at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy under NASA Contract NAS 5-26555.

  20. VizieR Online Data Catalog: Young stars and brown dwarfs in Ori OB1b (Caballero+, 2008)

    Science.gov (United States)

    Caballero, J. A.; Solano, E.

    2008-06-01

    We present here exhaustive lists of known young stars and new candidate members around Alnilam and Mintaka in the Ori OB1b association as well as of fore- and background sources. A total of 133 stars display features of extreme youth, including early spectral types, lithium in absorption, or mid-infrared flux excess. Other two young brown dwarf and 289 star candidates have been identified from an optical/near-infrared colour-magnitude diagram. We list additional 74 known objects that might belong to the association. This compilation of tables can serve as an input for characterisation of the stellar and high-mass substellar populations in the Orion Belt. (20 data files).

  1. Quasisoft X-Ray Sources: White Dwarfs? Neutron Stars? Black Holes?

    Science.gov (United States)

    Di Stefano, Rosanne

    Two of the most exciting areas of current research in astrophysics are black holes and Type Ia supernovae. We propose archival work that has the potential to shed light on both areas. The focus of our research is a newly-established class of x-ray sources called Quasisoft X-ray Sources (QSSs). Although they comprise a significant fraction of the x- ray sources in galaxies of all types, including M31, it has proved difficult to identify members of this class in the Milky Way or Magellanic Clouds. We have developed methods to find these sources, and have begun to meet with success in the application of our methods. The three-year project we propose will allow us to identify QSSs. We will then use the full range of archived data to determine which QSS candidates are highly luminous, and which are members of less luminous classes, such as quiescent low-mass x-ray binaries (qLMXBs), or even isolated neutron stars. Many will be nearby x-ray active stars, or else distant AGN, whose discovery will also be of interest to a range of researchers. In the end, we will have a subset of intriguing physical systems, some of which may be accreting black holes and some of which may be unusual states of neutron stars or even of nuclear-burning white dwarfs. The systems identified through this ADAP program will be targets of future observing programs, from space and from the ground. The information we derive from NASA archived data will provide insight into important astrophysical questions. Do intermediate-mass black holes (IMBHs) exist? It has only been during the past 15 years or so that accreting compact objects that were considered as black hole candidates have been promoted to black holes. This achievement required years of observations of candidates in the Milky Way and Magellanic Clouds. The discovery of ultraluminous X- ray source in external galaxies suggests that there are black holes with masses larger than the 10-30 solar masses typical of the known black holes. To

  2. Infrared photometry of the dwarf nova V2051 Ophiuchi - I. The mass-donor star and the distance

    Science.gov (United States)

    Wojcikiewicz, Eduardo; Baptista, Raymundo; Ribeiro, Tiago

    2018-04-01

    We report the analysis of time series of infrared JHKs photometry of the dwarf nova V2051 Oph in quiescence. We modelled the ellipsoidal variations caused by the distorted mass-donor star to infer its JHKs fluxes. From its infrared colours, we estimate a spectral type of M(8.0 ± 1.5) and an equivalent blackbody temperature of TBB = (2700 ± 270) K. We used the Barnes & Evans relation to infer a photometric parallax distance of dBE = (102 ± 16) pc to the binary. At this short distance, the corresponding accretion disc temperatures in outburst are too low to be explained by the disc-instability model for dwarf nova outbursts, underscoring a previous suggestion that the outbursts of this binary are powered by mass-transfer bursts.

  3. CHANDRA DETECTION OF X-RAY EMISSION FROM ULTRACOMPACT DWARF GALAXIES AND EXTENDED STAR CLUSTERS

    International Nuclear Information System (INIS)

    Hou, Meicun; Li, Zhiyuan

    2016-01-01

    We have conducted a systematic study of X-ray emission from ultracompact dwarf (UCD) galaxies and extended star clusters (ESCs), based on archival Chandra observations. Among a sample of 511 UCDs and ESCs complied from the literature, 17 X-ray counterparts with 0.5–8 keV luminosities above ∼5 × 10 36 erg s −1 are identified, which are distributed in eight early-type host galaxies. To facilitate comparison, we also identify X-ray counterparts of 360 globular clusters (GCs) distributed in four of the eight galaxies. The X-ray properties of the UCDs and ESCs are found to be broadly similar to those of the GCs. The incidence rate of X-ray-detected UCDs and ESCs, 3.3% ± 0.8%, while lower than that of the X-ray-detected GCs (7.0% ± 0.4%), is substantially higher than expected from the field populations of external galaxies. A stacking analysis of the individually undetected UCDs/ESCs further reveals significant X-ray signals, which corresponds to an equivalent 0.5–8 keV luminosity of ∼4 × 10 35 erg s −1 per source. Taken together, these provide strong evidence that the X-ray emission from UCDs and ESCs is dominated by low-mass X-ray binaries having formed from stellar dynamical interactions, consistent with the stellar populations in these dense systems being predominantly old. For the most massive UCDs, there remains the possibility that a putative central massive black hole gives rise to the observed X-ray emission

  4. Chromospheric lines in red dwarf flare stars. I - AD Leonis and GX Andromedae

    Science.gov (United States)

    Pettersen, B. R.; Coleman, L. A.

    1981-12-01

    Line profiles with a spectral resolution of 0.45 A have been obtained for Hα(λ6563), the Na D lines (λλ5890, 5896), He I lines (λλ5876, 6678), and the Ca II infrared triplet lines (λλ8498, 8542, 8662) in the flare stars AD Leonis and GX Andromedae. The spectroscopic Reticon diode array observations of AD Leo were obtained simultaneously with high speed photometry, and major influences in the spectra due to flares are avoided by this technique. GX And has photospheric parameters very similar to AD Leo but shows a flare activity level more than one order of magnitude smaller. Simultaneous photometry was not done during spectroscopic observations of GX And because of the small probability that a flare should contaminate the data. Despite apparently equal physical parameters at the photospheric level, the chromospheric lines observed in this program appear very different in AD Leo and GX And. Hα is a prominent emission line in AD Leo with a central absorption, for which the two peaks are separated by 0.6 Å. The FWHM of the line itself is 1.35 Å in AD Leo. In contrast, the Ha line in GX And is an absorption feature with FWHM =0.75 Å. The strength of this line is too large to be formed purely in the photosphere because temperatures are so low in this region that it is transparent to Hα and consequently forms only a very weak Ha absorption line. A collisionally dominated line may strengthen its absorption feature in a chromosphere before turning into emission (Cram and Mullan), and this is probably what is seen in GX And. An emission feature in the blue wing of Hα in AD Leo, 20% above the continuum, is found to be present also in two nonflaring M dwarfs with Ha in absorption, and is associated with less TiO blanketing at that wavelength. The Na D lines are broad absorption features in both stars with equal intensity distributions in the outer wings, reflecting the similarity of photospheric conditions in these stars. In AD Leo, however, the cores of the

  5. Precision modelling of M dwarf stars: the magnetic components of CM Draconis

    Science.gov (United States)

    MacDonald, J.; Mullan, D. J.

    2012-04-01

    The eclipsing binary CM Draconis (CM Dra) contains two nearly identical red dwarfs of spectral class dM4.5. The masses and radii of the two components have been reported with unprecedentedly small statistical errors: for M, these errors are 1 part in 260, while for R, the errors reported by Morales et al. are 1 part in 130. When compared with standard stellar models with appropriate mass and age (≈4 Gyr), the empirical results indicate that both components are discrepant from the models in the following sense: the observed stars are larger in R ('bloated'), by several standard deviations, than the models predict. The observed luminosities are also lower than the models predict. Here, we attempt at first to model the two components of CM Dra in the context of standard (non-magnetic) stellar models using a systematic array of different assumptions about helium abundances (Y), heavy element abundances (Z), opacities and mixing length parameter (α). We find no 4-Gyr-old models with plausible values of these four parameters that fit the observed L and R within the reported statistical error bars. However, CM Dra is known to contain magnetic fields, as evidenced by the occurrence of star-spots and flares. Here we ask: can inclusion of magnetic effects into stellar evolution models lead to fits of L and R within the error bars? Morales et al. have reported that the presence of polar spots results in a systematic overestimate of R by a few per cent when eclipses are interpreted with a standard code. In a star where spots cover a fraction f of the surface area, we find that the revised R and L for CM Dra A can be fitted within the error bars by varying the parameter α. The latter is often assumed to be reduced by the presence of magnetic fields, although the reduction in α as a function of B is difficult to quantify. An alternative magnetic effect, namely inhibition of the onset of convection, can be readily quantified in terms of a magnetic parameter δ≈B2/4

  6. Characterization of star-forming dwarf galaxies at 0.1 ≲z ≲ 0.9 in VUDS: probing the low-mass end of the mass-metallicity relation

    Science.gov (United States)

    Calabrò, A.; Amorín, R.; Fontana, A.; Pérez-Montero, E.; Lemaux, B. C.; Ribeiro, B.; Bardelli, S.; Castellano, M.; Contini, T.; De Barros, S.; Garilli, B.; Grazian, A.; Guaita, L.; Hathi, N. P.; Koekemoer, A. M.; Le Fèvre, O.; Maccagni, D.; Pentericci, L.; Schaerer, D.; Talia, M.; Tasca, L. A. M.; Zucca, E.

    2017-05-01

    agreement with recent studies, we find the subclass of EELGs to be systematically offset to lower metallicity compared to SFDGs at a given stellar mass and SFR, suggesting a younger starburst phase. Compared with simple chemical evolution models we find that most SFDGs do not follow the predictions of a "closed-box" model, but those from a gas-regulating model in which gas flows are considered. While strong stellar feedback may produce large-scale outflows favoring the cessation of vigorous star formation and promoting the removal of metals, younger and more metal-poor dwarfs may have recently accreted large amounts of fresh, very metal-poor gas, that is used to fuel current star formation. Full Tables B.1-B.3 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/601/A95

  7. The Mass-Luminosity-Metallicity Relation for M Dwarfs

    Science.gov (United States)

    Mann, Andrew; Dupuy, Trent; Rizzuto, Aaron; Kraus, Adam; Gaidos, Eric; Ansdell, Megan

    2018-01-01

    One of the most powerful tools for stellar characterization is the mass-luminosity relation (MLR). In addition to its use for characterizing exoplanet hosts, the MLR for late-type stars is critical to measuring the stellar IMF, testing isochrones, and studies of Galactic archeology. However, existing MLRs do not fully account for metallicity effects, do not extend down to the substellar boundary, and are not precise enough to take full advantage of the impending arrival of Gaia parallaxes for millions of late-type stars. For two years we monitored 72 nearby M-dwarf astrometric binaries using adaptive optics and non-redundant aperture masking, with the goal of better constraining the MLR. We combined our astrometry with measurements from the literature and Keck archive to measure orbits, masses, and flux ratios of all binaries in JHK bands. In parallel, we obtained moderate-resolution NIR spectra of all binaries, from which we determine empirical metallicities for each system. We derived an updated MLR-metallicity relation that spans most of the M dwarf sequence (K5 to M7) and the metallicity range expected in the solar neighborhood (-0.5 revised relation and Gaia-precision parallaxes, it will soon be possible to calculate empirical masses of nearby M dwarfs to better than 2%, and future studies will enable us to extend our relation to more metal-poor stars and explore the role of youth and evolution of the MLR for M dwarfs.

  8. EX-111 thermal emission from hot white dwarfs: the suggested He abundance-temperature correlation. EX-112: the unique emission line white dwarf star GD 356. Semiannnual status report, 1 December 1985-1 June 1986

    International Nuclear Information System (INIS)

    Shipman, H.L.

    1986-08-01

    Progress in the EXOSAT data analysis program is reported. EXOSAT observations for four white dwarfs (WD1031-115, WD0004+330, WD1615-154, and WD0109-264) were obtained. Counting rates were unexpectedly low, indicating that these objects have a substantial amount of x-ray absorbing matter in their photosheres. In addition, soft x-ray pulsations characterized by a 9.25 minute cycle were discovered in the DA white dwarf V471 Tauri. A residual x-ray flux from the K dwarf companion can be seen during the white dwarf eclipse at orbital phase 0.0. Pronounced dips in the soft x-ray light curve occur at orbital phases 0.15, 0.18, and 0.85. The dips may be correlated with the triangular Lagrangian points of the binary orbit. Smaller dips at phases near the eclipse may be associated with cool loops in the K star corona. Data for the white dwarf H1504+65 was also analyzed. This object is particularly unusual in that its photoshere is devoid of hydrogen and helium. Finally, existing data on the white dwarf Sirius B were analyzed to see what constraints from other data can be placed on the properties of this star. Interrelationships between radius, rotational velocity, and effective temperature were derived

  9. A high-resolution VLT/FLAMES study of individual stars in the centre of the Fornax dwarf spheroidal galaxy

    Science.gov (United States)

    Letarte, B.; Hill, V.; Tolstoy, E.; Jablonka, P.; Shetrone, M.; Venn, K. A.; Spite, M.; Irwin, M. J.; Battaglia, G.; Helmi, A.; Primas, F.; François, P.; Kaufer, A.; Szeifert, T.; Arimoto, N.; Sadakane, K.

    2010-11-01

    For the first time we show the detailed, late-stage, chemical evolution history of a small nearby dwarf spheroidal galaxy in the Local Group. We present the results of a high-resolution (R ~ 20 000, λ = 5340-5620; 6120-6701) FLAMES/GIRAFFE abundance study at ESO/VLT of 81 photometrically selected, red giant branch stars in the central 25' of the Fornax dwarf spheroidal galaxy. We also carried out a detailed comparison of the effects of recent developments in abundance analysis (e.g., spherical models vs. plane-parallel) and the automation that is required to efficiently deal with such large data sets. We present abundances of α-elements (Mg, Si, Ca, and Ti), iron-peak elements (Fe, Ni, and Cr), and heavy elements (Y, Ba, La, Nd, and Eu). Our sample was randomly selected and is clearly dominated by the younger and more metal-rich component of Fornax, which represents the major fraction of stars in the central region. This means that the majority of our stars are 1-4 Gyr old, and thus represent the end phase of chemical evolution in this system. Our sample of stars has unusually low [ α/Fe] , [Ni/Fe], and [Na/Fe] compared to the Milky Way stellar populations at the same [Fe/H]. The particularly important role of stellar winds from low-metallicity AGB stars in the creation of s-process elements is clearly seen from the high [Ba/Y]. Furthermore, we present evidence of an s-process origin of Eu. Based on FLAMES observations collected at the European Southern Observatory, proposal number 171.B-0588.Tables A1-A5 are only available in electronic form at http://www.aanda.org

  10. Effect of accretion on the pre-main-sequence evolution of low-mass stars and brown dwarfs

    Science.gov (United States)

    Vorobyov, Eduard I.; Elbakyan, Vardan; Hosokawa, Takashi; Sakurai, Yuya; Guedel, Manuel; Yorke, Harold

    2017-09-01

    Aims: The pre-main-sequence evolution of low-mass stars and brown dwarfs is studied numerically starting from the formation of a protostellar or proto-brown dwarf seed and taking into account the mass accretion onto the central object during the initial several Myr of evolution. Methods: The stellar evolution was computed using the STELLAR evolution code with recent modifications. The mass accretion rates were taken from numerical hydrodynamics models by computing the circumstellar disk evolution starting from the gravitational collapse of prestellar cloud cores of various mass and angular momentum. The resulting stellar evolution tracks were compared with the isochrones and isomasses calculated using non-accreting models. Results: We find that mass accretion in the initial several Myr of protostellar evolution can have a strong effect on the subsequent evolution of young stars and brown dwarfs. The disagreement between accreting and non-accreting models in terms of the total stellar luminosity L∗, stellar radius R∗, and effective temperature Teff depends on the thermal efficiency of accretion, that is, on the fraction of accretion energy that is absorbed by the central object. The largest mismatch is found for the cold accretion case, in which essentially all accretion energy is radiated away. The relative deviations in L∗ and R∗ in this case can reach 50% for objects 1.0 Myr old, and they remain notable even for objects 10 Myr old. In the hot and hybrid accretion cases, in which a constant fraction of accretion energy is absorbed, the disagreement between accreting and non-accreting models becomes less pronounced, but still remains notable for objects 1.0 Myr old. These disagreements may lead to an incorrect age estimate for objects of (sub-)solar mass when using the isochrones that are based on non-accreting models, as has also been noted previously. We find that objects with strong luminosity bursts exhibit notable excursions in the L∗-Teff diagram

  11. Efficiency of Metal Mixing in Dwarf Galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Hirai, Yutaka [Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Saitoh, Takayuki R., E-mail: yutaka.hirai@nao.ac.jp [Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551 (Japan)

    2017-04-01

    Metal mixing plays a critical role in the enrichment of metals in galaxies. The abundance of elements such as Mg, Fe, and Ba in metal-poor stars helps us understand the metal mixing in galaxies. However, the efficiency of metal mixing in galaxies is not yet understood. Here we report a series of N -body/smoothed particle hydrodynamics simulations of dwarf galaxies with different efficiencies of metal mixing using a turbulence-induced mixing model. We show that metal mixing apparently occurs in dwarf galaxies from Mg and Ba abundances. We find that a scaling factor for metal diffusion larger than 0.01 is necessary to reproduce the measured abundances of Ba in dwarf galaxies. This value is consistent with the value expected from turbulence theory and experiments. We also find that the timescale of metal mixing is less than 40 Myr. This timescale is shorter than the typical dynamical times of dwarf galaxies. We demonstrate that the determination of a degree of scatters of Ba abundance by the observation will help us to better constrain the efficiency of metal mixing.

  12. Can Oort clouds pollute their parent stars after they become white dwarfs?

    Science.gov (United States)

    Veras, D.; Shannon, A.; Gänsicke, B. T.

    2017-09-01

    Comets impact the Sun frequently. In fact, coronographs like those which are part of Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph Experiment (LASCO) reveal that a comet grazes the Sun every few days, with a total of about 2400 grazers from 1996 to 2008. This frequency underscores an outstanding question in the quest to understand planetary systems: what types of small bodies - pebbles, asteroids, comets or moons - are the primary polluter of white dwarfs? We determine how often remnant exo-Oort clouds, freshly excited from post-main-sequence stellar mass loss, dynamically inject comets inside the white dwarf's Roche radius. We improve upon previous studies by considering a representative range of single white dwarf masses (0.52-1.00 M⊙) and incorporating different cloud architectures, giant branch stellar mass loss, stellar flybys, Galactic tides and a realistic escape ellipsoid in self-consistent numerical simulations that integrate beyond 8 Gyr ages of white dwarf cooling. We find that ˜10^(-5) of the material in an exo-Oort cloud is typically amassed onto the white dwarf, and that hydrogen deposits accumulate even as the cloud dissipates. This accumulation may account for the relatively large amount of trace hydrogen, 10^(22) -10^(25) g, that is determined frequently among white dwarfs with cooling ages ≥1 Gyr. Our results also reaffirm the notion that exo-Oort cloud comets are not the primary agents of the metal budgets observed in polluted white dwarf atmospheres.

  13. Suppression of globular cluster formation in metal-poor gas clouds by Lyman α radiation feedback

    Science.gov (United States)

    Abe, Makito; Yajima, Hidenobu

    2018-03-01

    We study the impact of Ly α radiation feedback on globular cluster (GC) formation. In this Letter, we analytically derive the relation between star formation efficiency (SFE) and metallicity in spherical clouds with the Ly α radiation feedback. Our models show that the SFE becomes small as the metallicity decreases. In metal-poor gas clouds, Ly α photons are trapped for a long time and exert strong radiation force to the gas, resulting in the suppression of star formation. We find that bound star clusters (SFE ≳ 0.5) form only for the metallicity higher than ˜ 10- 2.5 Z⊙ in the case with the initial cloud mass 105 M⊙ and the radius 5 pc. Our models successfully reproduce the lower bound of observed metallicity of GCs. Thus, we suggest that the Ly α radiation feedback can be essential in understanding the formation of GCs.

  14. Globular star cluster systems around galaxies. II. The cases of spiral and dwarf galaxies

    International Nuclear Information System (INIS)

    Tadjibaev, I.U.; Nuritdinov, S.N.; Ganiev, J.M.

    2015-01-01

    Our compiled catalogue of globular cluster systems (GCS) which had studied in pervious part [1] is replenished now essentially as it are not sufficient the data to search for some empirical relationships between physical GCS parameters of the spiral and dwarf galaxies with a glance host galaxy characteristics. A number of empirical relationships for GCS of spiral and dwarf galaxies is first found. These results are differing essentially from analogous relationships for GCS of elliptical and lenticular galaxies which were found in [1]. It is also offered a possible new approach to the origin theory of the poor GCS which occupy a significant portion in our list of dwarf and spiral galaxies

  15. The rarity of dust in metal-poor galaxies.

    Science.gov (United States)

    Fisher, David B; Bolatto, Alberto D; Herrera-Camus, Rodrigo; Draine, Bruce T; Donaldson, Jessica; Walter, Fabian; Sandstrom, Karin M; Leroy, Adam K; Cannon, John; Gordon, Karl

    2014-01-09

    Galaxies observed at redshift z > 6, when the Universe was less than a billion years old, thus far very rarely show evidence of the cold dust that accompanies star formation in the local Universe, where the dust-to-gas mass ratio is around one per cent. A prototypical example is the galaxy Himiko (z = 6.6), which--a mere 840 million years after the Big Bang--is forming stars at a rate of 30-100 solar masses per year, yielding a mass assembly time of about 150 × 10(6) years. Himiko is thought to have a low fraction (2-3 per cent of the Sun's) of elements heavier than helium (low metallicity), and although its gas mass cannot yet be determined its dust-to-stellar mass ratio is constrained to be less than 0.05 per cent. The local dwarf galaxy I Zwicky 18, which has a metallicity about 4 per cent that of the Sun's and is forming stars less rapidly (assembly time about 1.6 × 10(9) years) than Himiko but still vigorously for its mass, is also very dust deficient and is perhaps one of the best analogues of primitive galaxies accessible to detailed study. Here we report observations of dust emission from I Zw 18, from which we determine its dust mass to be 450-1,800 solar masses, yielding a dust-to-stellar mass ratio of about 10(-6) to 10(-5) and a dust-to-gas mass ratio of 3.2-13 × 10(-6). If I Zw 18 is a reasonable analogue of Himiko, then Himiko's dust mass must be around 50,000 solar masses, a factor of 100 below the current upper limit. These numbers are quite uncertain, but if most high-z galaxies are more like Himiko than like the very-high-dust-mass galaxy SDSS J114816.64 + 525150.3 at z ≈ 6, which hosts a quasar, then our prospects for detecting the gas and dust inside such galaxies are much poorer than hitherto anticipated.

  16. A search for companions to brown dwarfs in the Taurus and Chamaeleon star-forming regions

    International Nuclear Information System (INIS)

    Todorov, K. O.; Luhman, K. L.; Konopacky, Q. M.; McLeod, K. K.; Apai, D.; Pascucci, I.; Ghez, A. M.; Robberto, M.

    2014-01-01

    We have used WFPC2 on board the Hubble Space Telescope to obtain images of 47 members of the Taurus and Chamaeleon I star-forming regions that have spectral types of M6-L0 (M ∼ 0.01-0.1 M ☉ ). An additional late-type member of Taurus, FU Tau (M7.25+M9.25), was also observed with adaptive optics at Keck Observatory. In these images, we have identified promising candidate companions to 2MASS J04414489+2301513 (ρ = 0.''105/15 AU), 2MASS J04221332+1934392 (ρ = 0.''05/7 AU), and ISO 217 (ρ = 0.''03/5 AU). We reported the first candidate in a previous study, showing that it has a similar proper motion as the primary in images from WFPC2 and Gemini adaptive optics. We have collected an additional epoch of data with Gemini that further supports that result. By combining our survey with previous high-resolution imaging in Taurus, Chamaeleon I, and Upper Sco (τ ∼ 10 Myr), we measure binary fractions of 14/93 = 0.15 −0.03 +0.05 for M4-M6 (M ∼ 0.1-0.3 M ☉ ) and 4/108 = 0.04 −0.01 +0.03 for >M6 (M ≲ 0.1 M ☉ ) at separations of >10 AU. Given the youth and low density of these regions, the lower binary fraction at later types is probably primordial rather than due to dynamical interactions among association members. The widest low-mass binaries (>100 AU) also appear to be more common in Taurus and Chamaeleon I than in the field, which suggests that the widest low-mass binaries are disrupted by dynamical interactions at >10 Myr, or that field brown dwarfs have been born predominantly in denser clusters where wide systems are disrupted or inhibited from forming.

  17. A search for companions to brown dwarfs in the Taurus and Chamaeleon star-forming regions

    Energy Technology Data Exchange (ETDEWEB)

    Todorov, K. O.; Luhman, K. L. [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Konopacky, Q. M. [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 (United States); McLeod, K. K. [Whitin Observatory, Wellesley College, Wellesley, MA 02481 (United States); Apai, D.; Pascucci, I. [Department of Astronomy, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721 (United States); Ghez, A. M. [Division of Astronomy and Astrophysics, University of California, Los Angeles, CA 90095 (United States); Robberto, M., E-mail: todorovk@phys.ethz.ch [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2014-06-10

    We have used WFPC2 on board the Hubble Space Telescope to obtain images of 47 members of the Taurus and Chamaeleon I star-forming regions that have spectral types of M6-L0 (M ∼ 0.01-0.1 M {sub ☉}). An additional late-type member of Taurus, FU Tau (M7.25+M9.25), was also observed with adaptive optics at Keck Observatory. In these images, we have identified promising candidate companions to 2MASS J04414489+2301513 (ρ = 0.''105/15 AU), 2MASS J04221332+1934392 (ρ = 0.''05/7 AU), and ISO 217 (ρ = 0.''03/5 AU). We reported the first candidate in a previous study, showing that it has a similar proper motion as the primary in images from WFPC2 and Gemini adaptive optics. We have collected an additional epoch of data with Gemini that further supports that result. By combining our survey with previous high-resolution imaging in Taurus, Chamaeleon I, and Upper Sco (τ ∼ 10 Myr), we measure binary fractions of 14/93 = 0.15{sub −0.03}{sup +0.05} for M4-M6 (M ∼ 0.1-0.3 M {sub ☉}) and 4/108 = 0.04{sub −0.01}{sup +0.03} for >M6 (M ≲ 0.1 M {sub ☉}) at separations of >10 AU. Given the youth and low density of these regions, the lower binary fraction at later types is probably primordial rather than due to dynamical interactions among association members. The widest low-mass binaries (>100 AU) also appear to be more common in Taurus and Chamaeleon I than in the field, which suggests that the widest low-mass binaries are disrupted by dynamical interactions at >10 Myr, or that field brown dwarfs have been born predominantly in denser clusters where wide systems are disrupted or inhibited from forming.

  18. The type Ia supernova SNLS-03D3bb from a super-Chandrasekhar-mass white dwarf star.

    Science.gov (United States)

    Howell, D Andrew; Sullivan, Mark; Nugent, Peter E; Ellis, Richard S; Conley, Alexander J; Le Borgne, Damien; Carlberg, Raymond G; Guy, Julien; Balam, David; Basa, Stephane; Fouchez, Dominique; Hook, Isobel M; Hsiao, Eric Y; Neill, James D; Pain, Reynald; Perrett, Kathryn M; Pritchet, Christopher J

    2006-09-21

    The accelerating expansion of the Universe, and the need for dark energy, were inferred from observations of type Ia supernovae. There is a consensus that type Ia supernovae are thermonuclear explosions that destroy carbon-oxygen white dwarf stars that have accreted matter from a companion star, although the nature of this companion remains uncertain. These supernovae are thought to be reliable distance indicators because they have a standard amount of fuel and a uniform trigger: they are predicted to explode when the mass of the white dwarf nears the Chandrasekhar mass of 1.4 solar masses (M(o)). Here we show that the high-redshift supernova SNLS-03D3bb has an exceptionally high luminosity and low kinetic energy that both imply a super-Chandrasekhar-mass progenitor. Super-Chandrasekhar-mass supernovae should occur preferentially in a young stellar population, so this may provide an explanation for the observed trend that overluminous type Ia supernovae occur only in 'young' environments. As this supernova does not obey the relations that allow type Ia supernovae to be calibrated as standard candles, and as no counterparts have been found at low redshift, future cosmology studies will have to consider possible contamination from such events.

  19. Extreme Emission Line Galaxies in CANDELS: Broad-Band Selected, Star-Bursting Dwarf Galaxies at Z greater than 1

    Science.gov (United States)

    vanderWel, A.; Straughn, A. N.; Rix, H.-W.; Finkelstein, S. L.; Koekemoer, A. M.; Weiner, B. J.; Wuyts, S.; Bell, E. F.; Faber, S. M.; Trump, J. R.; hide

    2012-01-01

    We identify an abundant population of extreme emission line galaxies (EELGs) at redshift z approx. 1.7 in the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) imaging from Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3). 69 EELG candidates are selected by the large contribution of exceptionally bright emission lines to their near-infrared broad-band magnitudes. Supported by spectroscopic confirmation of strong [OIII] emission lines . with rest-frame equivalent widths approx. 1000A in the four candidates that have HST/WFC3 grism observations, we conclude that these objects are galaxies with approx.10(exp 8) Solar Mass in stellar mass, undergoing an enormous starburst phase with M*/M* of only approx. 15 Myr. These bursts may cause outflows that are strong enough to produce cored dark matter profiles in low-mass galaxies. The individual star formation rates and the co-moving number density (3.7x10(exp -4) Mpc(sup -3) can produce in approx.4 Gyr much of the stellar mass density that is presently contained in 10(exp 8) - 10(exp 9) Solar Mass dwarf galaxies. Therefore, our observations provide a strong indication that many or even most of the stars in present-day dwarf galaxies formed in strong, short-lived bursts, mostly at z > 1.

  20. Simulating the UV escape fractions from molecular cloud populations in star-forming dwarf and spiral galaxies

    Science.gov (United States)

    Howard, Corey S.; Pudritz, Ralph E.; Harris, William E.; Klessen, Ralf S.

    2018-04-01

    The escape of ultraviolet photons from the densest regions of the interstellar medium (ISM) - giant molecular clouds (GMCs) - is a poorly constrained parameter which is vital to understanding the ionization of the ISM and the intergalactic medium. We characterize the escape fraction, fesc,GMC, from a suite of individual GMC simulations with masses in the range 104-6 M⊙ using the adaptive-mesh refinement code FLASH. We find significantly different fesc,GMC depending on the GMC mass that can reach >90 per cent in the evolution of 5 × 104 and 105 M⊙ clouds or remain low at ˜5 per cent for most of the lifetime of more massive GMCs. All clouds show fluctuations over short, sub-Myr time-scales produced by flickering H II regions. We combine our results to calculate the total escape fraction (fesc,tot) from GMC populations in dwarf starburst and spiral galaxies by randomly drawing clouds from a GMC mass distribution (dN/dM ∝ Mα, where α is either -1.5 or -2.5) over fixed time intervals. We find typical fesc,tot values of 8 per cent for both the dwarf and spiral models. The fluctuations of fesc,tot, however, are much larger for the dwarf models with values as high as 90 per cent. The photons escaping from the 5 × 104 and 105 M⊙ GMCs are the dominant contributors to fesc,tot in all cases. We also show that the accompanying star formation rates (SFRs) of our model (˜2 × 10-2 and 0.73 M⊙yr-1) are consistent with observations of SFRs in dwarf starburst and spiral galaxies, respectively.

  1. KINEMATICS OF EXTREMELY METAL-POOR GALAXIES: EVIDENCE FOR STELLAR FEEDBACK

    Energy Technology Data Exchange (ETDEWEB)

    Olmo-García, A.; Sánchez Almeida, J.; Muñoz-Tuñón, C.; Filho, M. E. [Instituto Astrofísica de Canarias, E-38200 La Laguna, Tenerife (Spain); Elmegreen, B. G. [IBM Research Division, T. J. Watson Research Center, Yorktown Heights, NY 10598 (United States); Elmegreen, D. M. [Department of Physics and Astronomy, Vassar College, Poughkeepsie, NY 12604 (United States); Pérez-Montero, E. [Instituto de Astrofísica de Andalucía, CSIC, Granada (Spain); Méndez-Abreu, J., E-mail: jos@iac.es [School of Physics and Astronomy, University of St Andrews, St Andrews (United Kingdom)

    2017-01-10

    The extremely metal-poor (XMP) galaxies analyzed in a previous paper have large star-forming regions with a metallicity lower than the rest of the galaxy. Such a chemical inhomogeneity reveals the external origin of the metal-poor gas fueling star formation, possibly indicating accretion from the cosmic web. This paper studies the kinematic properties of the ionized gas in these galaxies. Most XMPs have a rotation velocity around a few tens of km s{sup −1}. The star-forming regions appear to move coherently. The velocity is constant within each region, and the velocity dispersion sometimes increases within the star-forming clump toward the galaxy midpoint, suggesting inspiral motion toward the galaxy center. Other regions present a local maximum in velocity dispersion at their center, suggesting a moderate global expansion. The H α line wings show a number of faint emission features with amplitudes around a few per cent of the main H α component, and wavelength shifts between 100 and 400 km s{sup −1}. The components are often paired, so that red and blue emission features with similar amplitudes and shifts appear simultaneously. Assuming the faint emission to be produced by expanding shell-like structures, the inferred mass loading factor (mass loss rate divided by star formation rate) exceeds 10. Since the expansion velocity far exceeds the rotational and turbulent velocities, the gas may eventually escape from the galaxy disk. The observed motions involve energies consistent with the kinetic energy released by individual core-collapse supernovae. Alternative explanations for the faint emission have been considered and discarded.

  2. Probing dark matter with star clusters: a dark matter core in the ultra-faint dwarf Eridanus II

    Science.gov (United States)

    Contenta, Filippo; Balbinot, Eduardo; Petts, James A.; Read, Justin I.; Gieles, Mark; Collins, Michelle L. M.; Peñarrubia, Jorge; Delorme, Maxime; Gualandris, Alessia

    2018-05-01

    We present a new technique to probe the central dark matter (DM) density profile of galaxies that harnesses both the survival and observed properties of star clusters. As a first application, we apply our method to the `ultra-faint' dwarf Eridanus II (Eri II) that has a lone star cluster ˜45 pc from its centre. Using a grid of collisional N-body simulations, incorporating the effects of stellar evolution, external tides and dynamical friction, we show that a DM core for Eri II naturally reproduces the size and the projected position of its star cluster. By contrast, a dense cusped galaxy requires the cluster to lie implausibly far from the centre of Eri II (>1 kpc), with a high inclination orbit that must be observed at a particular orbital phase. Our results, therefore, favour a DM core. This implies that either a cold DM cusp was `heated up' at the centre of Eri II by bursty star formation or we are seeing an evidence for physics beyond cold DM.

  3. Probing dark matter with star clusters: a dark matter core in the ultra-faint dwarf Eridanus II

    Science.gov (United States)

    Contenta, Filippo; Balbinot, Eduardo; Petts, James A.; Read, Justin I.; Gieles, Mark; Collins, Michelle L. M.; Peñarrubia, Jorge; Delorme, Maxime; Gualandris, Alessia

    2018-02-01

    We present a new technique to probe the central dark matter (DM) density profile of galaxies that harnesses both the survival and observed properties of star clusters. As a first application, we apply our method to the `ultra-faint' dwarf Eridanus II (Eri II) that has a lone star cluster ˜45 pc from its centre. Using a grid of collisional N-body simulations, incorporating the effects of stellar evolution, external tides and dynamical friction, we show that a DM core for Eri II naturally reproduces the size and the projected position of its star cluster. By contrast, a dense cusped galaxy requires the cluster to lie implausibly far from the centre of Eri II (>1 kpc), with a high inclination orbit that must be observed at a particular orbital phase. Our results, therefore, favour a dark matter core. This implies that either a cold DM cusp was `heated up' at the centre of Eri II by bursty star formation, or we are seeing an evidence for physics beyond cold DM.

  4. The Araucaria Project: The Distance to the Fornax Dwarf Galaxy from Near-infrared Photometry of RR Lyrae Stars

    Science.gov (United States)

    Karczmarek, Paulina; Pietrzyński, Grzegorz; Górski, Marek; Gieren, Wolfgang; Bersier, David

    2017-12-01

    We have obtained single-phase near-infrared (NIR) magnitudes in the J and K bands for 77 RR Lyrae (RRL) stars in the Fornax Dwarf Spheroidal Galaxy. We have used different theoretical and empirical NIR period-luminosity-metallicity calibrations for RRL stars to derive their absolute magnitudes, and found a true, reddening-corrected distance modulus of 20.818+/- 0.015{{(statistical)}}+/- 0.116{{(systematic)}} mag. This value is in excellent agreement with the results obtained within the Araucaria Project from the NIR photometry of red clump stars (20.858 ± 0.013 mag), the tip of the red giant branch (20.84+/- 0.04+/- 0.14 mag), as well as with other independent distance determinations to this galaxy. The effect of metallicity and reddening is substantially reduced in the NIR domain, making this method a robust tool for accurate distance determination at the 5% level. This precision is expected to reach the level of 3% once the zero points of distance calibrations are refined thanks to the Gaia mission. NIR period-luminosity-metallicity relations of RRL stars are particularly useful for distance determinations to galaxies and globular clusters up to 300 kpc, that lack young standard candles, like Cepheids. Based on data collected with the VLT/HAWK-I instrument at ESO Paranal Observatory, Chile, as a part of programme 082.D-0123(B).

  5. MagAO IMAGING OF LONG-PERIOD OBJECTS (MILO). II. A PUZZLING WHITE DWARF AROUND THE SUN-LIKE STAR HD 11112

    Energy Technology Data Exchange (ETDEWEB)

    Rodigas, Timothy J.; Arriagada, Pamela; Faherty, Jacqueline K.; Weinberger, Alycia; Butler, R. Paul [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015 (United States); Bergeron, P.; Simon, Amélie [Département de Physique, Université de Montréal, C.P. 6128, Succ. Centre-Ville, Montréal, Québec H3C 3J7 (Canada); Anglada-Escudé, Guillem [School of Physics and Astronomy, Queen Mary, University of London, 327 Mile End Road, London (United Kingdom); Mamajek, Eric E. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627-0171 (United States); Males, Jared R.; Morzinski, Katie; Close, Laird M.; Hinz, Philip M. [Steward Observatory, The University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721 (United States); Bailey, Jeremy; Tinney, C. G.; Wittenmyer, Rob [Exoplanetary Science at UNSW, School of Physics, UNSW Australia, Sydney, NSW 2052 (Australia); Carter, Brad [Computational Engineering and Science Research Centre, University of Southern Queensland, Springfield, QLD 4300 (Australia); Jenkins, James S. [Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Las Condes, Santiago (Chile); Jones, Hugh [Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Herts AL10 9AB (United Kingdom); O’Toole, Simon, E-mail: trodigas@carnegiescience.edu [Australian Astronomical Observatory, P.O. Box 915, North Ryde, NSW 1670 (Australia); and others

    2016-11-10

    HD 11112 is an old, Sun-like star that has a long-term radial velocity (RV) trend indicative of a massive companion on a wide orbit. Here we present direct images of the source responsible for the trend using the Magellan Adaptive Optics system. We detect the object (HD 11112B) at a separation of 2.″2 (100 au) at multiple wavelengths spanning 0.6–4 μ m and show that it is most likely a gravitationally bound cool white dwarf. Modeling its spectral energy distribution suggests that its mass is 0.9–1.1 M {sub ⊙}, which corresponds to very high eccentricity, near edge-on orbits from a Markov chain Monte Carlo analysis of the RV and imaging data together. The total age of the white dwarf is >2 σ , which is discrepant with that of the primary star under most assumptions. The problem can be resolved if the white dwarf progenitor was initially a double white dwarf binary that then merged into the observed high-mass white dwarf. HD 11112B is a unique and intriguing benchmark object that can be used to calibrate atmospheric and evolutionary models of cool white dwarfs and should thus continue to be monitored by RV and direct imaging over the coming years.

  6. A High-precision Trigonometric Parallax to an Ancient Metal-poor Globular Cluster

    Science.gov (United States)

    Brown, T. M.; Casertano, S.; Strader, J.; Riess, A.; VandenBerg, D. A.; Soderblom, D. R.; Kalirai, J.; Salinas, R.

    2018-03-01

    Using the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST), we have obtained a direct trigonometric parallax for the nearest metal-poor globular cluster, NGC 6397. Although trigonometric parallaxes have been previously measured for many nearby open clusters, this is the first parallax for an ancient metal-poor population—one that is used as a fundamental template in many stellar population studies. This high-precision measurement was enabled by the HST/WFC3 spatial-scanning mode, providing hundreds of astrometric measurements for dozens of stars in the cluster and also for Galactic field stars along the same sightline. We find a parallax of 0.418 ± 0.013 ± 0.018 mas (statistical, systematic), corresponding to a true distance modulus of 11.89 ± 0.07 ± 0.09 mag (2.39 ± 0.07 ± 0.10 kpc). The V luminosity at the stellar main-sequence turnoff implies an absolute cluster age of 13.4 ± 0.7 ± 1.2 Gyr. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs GO-13817, GO-14336, and GO-14773.

  7. Asteroseismology of ZZ Ceti stars with fully evolutionary white dwarf models: I. The impact of the uncertainties from prior evolution on the period spectrum

    OpenAIRE

    De Gerónimo, Francisco C.; Althaus, Leandro G.; Córsico, Alejandro H.; Romero, Alejandra D.; Kepler, S. O.

    2016-01-01

    ZZ Ceti stars are pulsating white dwarfs with a carbon-oxygen core build up during the core helium burning and thermally pulsing Asymptotic Giant Branch phases. Through the interpretation of their pulsation periods by means of asteroseismology, details about their origin and evolution can be inferred. The whole pulsation spectrum exhibited by ZZ Ceti stars strongly depends on the inner chemical structure. At present, there are several processes affecting the chemical profiles that are still n...

  8. Modeling the Cloudy Atmospheres of Cool Stars, Brown Dwarfs and Hot Exoplanets

    DEFF Research Database (Denmark)

    Juncher, Diana

    M-dwarfs are very attractive targets when searching for new exoplanets. Unfortunately, they are also very difficult to model since their temperatures are low enough for dust clouds to form in their atmospheres. Because the properties of an exoplanet cannot be determined without knowing...... of their clouds and found that their synthetic spectra fit the observed spectra of mid to late type M-dwarfs and early type L-dwarfs well. With additional development into even cooler regimes, they could be used to characterize the atmospheres of exoplanets and aid us in our search for the kind of chemical...... imbalances that suggest the presence of life. I have also directly performed spectroscopic and photometric observations of exoplanets to discover and/or improve our knowledge of their properties and to participate in the development of the techniques that is being used to discover and characterize exoplanets."...

  9. Asteroseismology of ZZ Ceti stars with fully evolutionary white dwarf models. I. The impact of the uncertainties from prior evolution on the period spectrum

    Science.gov (United States)

    De Gerónimo, F. C.; Althaus, L. G.; Córsico, A. H.; Romero, A. D.; Kepler, S. O.

    2017-03-01

    Context. ZZ Ceti stars are pulsating white dwarfs with a carbon-oxygen core build up during the core helium burning and thermally pulsing Asymptotic Giant Branch phases. Through the interpretation of their pulsation periods by means of asteroseismology, details about their origin and evolution can be inferred. The whole pulsation spectrum exhibited by ZZ Ceti stars strongly depends on the inner chemical structure. At present, there are several processes affecting the chemical profiles that are still not accurately determined. Aims: We present a study of the impact of the current uncertainties of the white dwarf formation and evolution on the expected pulsation properties of ZZ Ceti stars. Methods: Our analysis is based on a set of carbon-oxygen core white dwarf models with masses 0.548 and 0.837 M⊙ that are derived from full evolutionary computations from the ZAMS to the ZZ Ceti domain. We considered models in which we varied the number of thermal pulses, the amount of overshooting, and the 12C(α,γ)16O reaction rate within their uncertainties. Results: We explore the impact of these major uncertainties in prior evolution on the chemical structure and expected pulsation spectrum. We find that these uncertainties yield significant changes in the g-mode pulsation periods. Conclusions: We conclude that the uncertainties in the white dwarf progenitor evolution should be taken into account in detailed asteroseismological analyses of these pulsating stars.

  10. COMPARISON OF Hα AND UV STAR FORMATION RATES IN THE LOCAL VOLUME: SYSTEMATIC DISCREPANCIES FOR DWARF GALAXIES

    International Nuclear Information System (INIS)

    Lee, Janice C.; Gil de Paz, Armando; Tremonti, Christy; Walter, Fabian; Kennicutt, Robert C.; Bothwell, Matthew; Johnson, Benjamin; Salim, Samir; Calzetti, Daniela; Dalcanton, Julianne; Dale, Daniel; Engelbracht, Chad; Funes, S. J. Jose G.; Sakai, Shoko; Skillman, Evan; Weisz, Daniel; Van Zee, Liese

    2009-01-01

    Using a complete sample of ∼300 star-forming galaxies within 11 Mpc of the Milky Way, we evaluate the consistency between star formation rates (SFRs) inferred from the far ultraviolet (FUV) non-ionizing continuum and Hα nebular emission, assuming standard conversion recipes in which the SFR scales linearly with luminosity at a given wavelength. Our analysis probes SFRs over 5 orders of magnitude, down to ultra-low activities on the order of ∼10 -4 M sun yr -1 . The data are drawn from the 11 Mpc Hα and Ultraviolet Galaxy Survey (11HUGS), which has obtained Hα fluxes from ground-based narrowband imaging, and UV fluxes from imaging with GALEX. For normal spiral galaxies (SFR ∼ 1 M sun yr -1 ), our results are consistent with previous work which has shown that FUV SFRs tend to be lower than Hα SFRs before accounting for internal dust attenuation, but that there is relative consistency between the two tracers after proper corrections are applied. However, a puzzle is encountered at the faint end of the luminosity function. As lower luminosity dwarf galaxies, roughly less active than the Small Magellanic Cloud, are examined, Hα tends to increasingly underpredict the total SFR relative to the FUV. The trend is evident prior to corrections for dust attenuation, which affects the FUV more than the nebular Hα emission, so this general conclusion is robust to the effects of dust. Although past studies have suggested similar trends, this is the first time this effect is probed with a statistical sample for galaxies with SFR ∼ sun yr -1 . By SFR ∼ 0.003 M sun yr -1 , the average Hα-to-FUV flux ratio is lower than expected by a factor of two, and at the lowest SFRs probed, the ratio exhibits an order of magnitude discrepancy for the handful of galaxies that remain in the sample. A range of standard explanations does not appear to be able to fully account for the magnitude of the systematic. Some recent work has argued for a stellar initial mass function which

  11. Pulsational instability of high-luminosity H-rich pre-white dwarf star

    Science.gov (United States)

    Calcaferro, Leila M.; Córsico, Alejandro H.; Camisassa, María E.; Althaus, Leandro G.; Shibahashi, Hiromoto

    2017-09-01

    We present a pulsational stability analysis on high-luminosity H-rich (DA) white dwarf models evolved from low-metallicity progenitors. We found that the ɛ mechanism due to H-shell burning is able to excite low-order g modes.

  12. Pulsational instability of high-luminosity H-rich pre-white dwarf star

    Directory of Open Access Journals (Sweden)

    Calcaferro Leila M.

    2017-01-01

    Full Text Available We present a pulsational stability analysis on high-luminosity H-rich (DA white dwarf models evolved from low-metallicity progenitors. We found that the ε mechanism due to H-shell burning is able to excite low-order g modes.

  13. Dark influences II. Gas and star formation in minor mergers of dwarf galaxies with dark satellites

    NARCIS (Netherlands)

    Starkenburg, T. K.; Helmi, A.; Sales, L. V.

    2016-01-01

    Context. It has been proposed that mergers induce starbursts and lead to important morphological changes in galaxies. Most studies so far have focused on large galaxies, but dwarfs might also experience such events, since the halo mass function is scale-free in the concordance cosmological model.

  14. VizieR Online Data Catalog: Rotation periods of M-dwarf stars (McQuillan+, 2013)

    Science.gov (United States)

    McQuillan, A.; Aigrain, S.; Mazeh, T.

    2014-07-01

    We have analysed 10 months of public data from the Kepler space mission to measure rotation periods of main-sequence stars with masses between 0.3 and 0.55M⊙. To derive the rotational period, we introduce the autocorrelation function and show that it is robust against phase and amplitude modulation and residual instrumental systematics. Of the 2483 stars examined, we detected rotation periods in 1570 (63.2%), representing an increase of a factor of ~30 in the number of rotation period determination for field M dwarfs. The periods range from 0.37 to 69.7d, with amplitudes ranging from 1.0 to 140.8mmag. The rotation period distribution is clearly bimodal, with peaks at ~19 and ~33d, hinting at two distinct waves of star formation, a hypothesis that is supported by the fact that slower rotators tend to have larger proper motions. The two peaks of the rotation period distribution form two distinct sequences in period-temperature space, with the period decreasing with increasing temperature, reminiscent of the Vaughan-Preston gap. The period-mass distribution of our sample shows no evidence of a transition at the fully convective boundary. On the other hand, the slope of the upper envelope of the period-mass relation changes sign around 0.55M⊙, below which period rises with decreasing mass. (4 data files).

  15. Post-main-sequence Evolution of Icy Minor Planets. II. Water Retention and White Dwarf Pollution around Massive Progenitor Stars

    Energy Technology Data Exchange (ETDEWEB)

    Malamud, Uri; Perets, Hagai B., E-mail: uri.mal@tx.technion.ac.il, E-mail: hperets@physics.technion.ac.il [Department of Physics, Technion (Israel)

    2017-06-10

    Most studies suggest that the pollution of white dwarf (WD) atmospheres arises from the accretion of minor planets, but the exact properties of polluting material, and in particular the evidence for water in some cases, are not yet understood. Here we study the water retention of small icy bodies in exo-solar planetary systems, as their respective host stars evolve through and off the main sequence and eventually become WDs. We explore, for the first time, a wide range of star masses and metallicities. We find that the mass of the WD progenitor star is of crucial importance for the retention of water, while its metallicity is relatively unimportant. We predict that minor planets around lower-mass WD progenitors would generally retain more water and would do so at closer distances from the WD than compared with high-mass progenitors. The dependence of water retention on progenitor mass and other parameters has direct implications for the origin of observed WD pollution, and we discuss how our results and predictions might be tested in the future as more observations of WDs with long cooling ages become available.

  16. A Survey For Planetary-mass Brown Dwarfs in the Taurus and Perseus Star-forming Regions

    Energy Technology Data Exchange (ETDEWEB)

    Esplin, T. L.; Luhman, K. L., E-mail: taran.esplin@psu.edu [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States)

    2017-10-01

    We present the initial results from a survey for planetary-mass brown dwarfs in the Taurus star-forming region. We have identified brown dwarf candidates in Taurus using proper motions and photometry from several ground- and space-based facilities. Through spectroscopy of some of the more promising candidates, we have found 18 new members of Taurus. They have spectral types ranging from mid-M to early-L, and they include the four faintest known members in extinction-corrected K{sub s}, which should have masses as low as ∼4–5 M {sub Jup} according to evolutionary models. Two of the coolest new members (M9.25, M9.5) have mid-IR excesses that indicate the presence of disks. Two fainter objects with types of M9–L2 and M9–L3 also have red mid-IR colors relative to photospheres at ≤L0, but since the photospheric colors are poorly defined at >L0, it is unclear whether they have excesses from disks. We also have obtained spectra of candidate members of the IC 348 and NGC 1333 clusters in Perseus that were identified by Luhman et al. Eight candidates are found to be probable members, three of which are among the faintest and least-massive known members of the clusters (∼5 M{sub Jup}).

  17. A Survey For Planetary-mass Brown Dwarfs in the Taurus and Perseus Star-forming Regions

    International Nuclear Information System (INIS)

    Esplin, T. L.; Luhman, K. L.

    2017-01-01

    We present the initial results from a survey for planetary-mass brown dwarfs in the Taurus star-forming region. We have identified brown dwarf candidates in Taurus using proper motions and photometry from several ground- and space-based facilities. Through spectroscopy of some of the more promising candidates, we have found 18 new members of Taurus. They have spectral types ranging from mid-M to early-L, and they include the four faintest known members in extinction-corrected K s , which should have masses as low as ∼4–5 M Jup according to evolutionary models. Two of the coolest new members (M9.25, M9.5) have mid-IR excesses that indicate the presence of disks. Two fainter objects with types of M9–L2 and M9–L3 also have red mid-IR colors relative to photospheres at ≤L0, but since the photospheric colors are poorly defined at >L0, it is unclear whether they have excesses from disks. We also have obtained spectra of candidate members of the IC 348 and NGC 1333 clusters in Perseus that were identified by Luhman et al. Eight candidates are found to be probable members, three of which are among the faintest and least-massive known members of the clusters (∼5 M Jup ).

  18. Revisiting the Extended Schmidt Law: The Important Role of Existing Stars in Regulating Star Formation

    Science.gov (United States)

    Shi, Yong; Yan, Lin; Armus, Lee; Gu, Qiusheng; Helou, George; Qiu, Keping; Gwyn, Stephen; Stierwalt, Sabrina; Fang, Min; Chen, Yanmei; Zhou, Luwenjia; Wu, Jingwen; Zheng, Xianzhong; Zhang, Zhi-Yu; Gao, Yu; Wang, Junzhi

    2018-02-01

    We revisit the proposed extended Schmidt law, which posits that the star formation efficiency in galaxies depends on the stellar mass surface density, by investigating spatially resolved star formation rates (SFRs), gas masses, and stellar masses of star formation regions in a vast range of galactic environments, from the outer disks of dwarf galaxies, to spiral disks and to merging galaxies, as well as individual molecular clouds in M33. We find that these regions are distributed in a tight power law as {{{Σ }}}{SFR} ∝ {({{{Σ }}}{star}0.5{{{Σ }}}{gas})}1.09, which is also valid for the integrated measurements of disk and merging galaxies at high-z. Interestingly, we show that star formation regions in the outer disks of dwarf galaxies with {{{Σ }}}{SFR} down to 10‑5 {M}ȯ yr‑1 kpc‑2, which are outliers of both the Kennicutt–Schmidt and Silk–Elmegreen laws, also follow the extended Schmidt law. Other outliers in the Kennicutt–Schmidt law, such as extremely metal-poor star formation regions, also show significantly reduced deviation from the extended Schmidt law. These results suggest an important role for existing stars in helping to regulate star formation through the effect of their gravity on the midplane pressure in a wide range of galactic environments.

  19. Dark-ages Reionization and Galaxy Formation Simulation - XIV. Gas accretion, cooling and star formation in dwarf galaxies at high redshift

    Science.gov (United States)

    Qin, Yuxiang; Duffy, Alan R.; Mutch, Simon J.; Poole, Gregory B.; Geil, Paul M.; Mesinger, Andrei; Wyithe, J. Stuart B.

    2018-03-01

    We study dwarf galaxy formation at high redshift (z ≥ 5) using a suite of high-resolution, cosmological hydrodynamic simulations and a semi-analytic model (SAM). We focus on gas accretion, cooling and star formation in this work by isolating the relevant process from reionization and supernova feedback, which will be further discussed in a companion paper. We apply the SAM to halo merger trees constructed from a collisionless N-body simulation sharing identical initial conditions to the hydrodynamic suite, and calibrate the free parameters against the stellar mass function predicted by the hydrodynamic simulations at z = 5. By making comparisons of the star formation history and gas components calculated by the two modelling techniques, we find that semi-analytic prescriptions that are commonly adopted in the literature of low-redshift galaxy formation do not accurately represent dwarf galaxy properties in the hydrodynamic simulation at earlier times. We propose 3 modifications to SAMs that will provide more accurate high-redshift simulations. These include 1) the halo mass and baryon fraction which are overestimated by collisionless N-body simulations; 2) the star formation efficiency which follows a different cosmic evolutionary path from the hydrodynamic simulation; and 3) the cooling rate which is not well defined for dwarf galaxies at high redshift. Accurate semi-analytic modelling of dwarf galaxy formation informed by detailed hydrodynamical modelling will facilitate reliable semi-analytic predictions over the large volumes needed for the study of reionization.

  20. Role of ocean heat transport in climates of tidally locked exoplanets around M dwarf stars.

    Science.gov (United States)

    Hu, Yongyun; Yang, Jun

    2014-01-14

    The distinctive feature of tidally locked exoplanets is the very uneven heating by stellar radiation between the dayside and nightside. Previous work has focused on the role of atmospheric heat transport in preventing atmospheric collapse on the nightside for terrestrial exoplanets in the habitable zone around M dwarfs. In the present paper, we carry out simulations with a fully coupled atmosphere-ocean general circulation model to investigate the role of ocean heat transport in climate states of tidally locked habitable exoplanets around M dwarfs. Our simulation results demonstrate that ocean heat transport substantially extends the area of open water along the equator, showing a lobster-like spatial pattern of open water, instead of an "eyeball." For sufficiently high-level greenhouse gases or strong stellar radiation, ocean heat transport can even lead to complete deglaciation of the nightside. Our simulations also suggest that ocean heat transport likely narrows the width of M dwarfs' habitable zone. This study provides a demonstration of the importance of exooceanography in determining climate states and habitability of exoplanets.

  1. STAR FORMATION HISTORY AND CHEMICAL EVOLUTION OF THE SEXTANS DWARF SPHEROIDAL GALAXY

    International Nuclear Information System (INIS)

    Lee, Myung Gyoon; Yuk, In-Soo; Park, Hong Soo; Harris, Jason; Zaritsky, Dennis

    2009-01-01

    We present the star formation history (SFH) and chemical evolution of the Sextans dSph galaxy as a function of a galactocentric distance. We derive these from the VI photometry of stars in the 42' x 28' field using the SMART model developed by Yuk and Lee and adopting a closed-box model for chemical evolution. For the adopted age of Sextans 15 Gyr, we find that >84% of the stars formed prior to 11 Gyr ago, significant star formation extends from 15 to 11 Gyr ago (∼ 65% of the stars formed 13-15 Gyr ago, while ∼ 25% formed 11-13 Gyr ago), detectable star formation continued to at least 8 Gyr ago, the SFH is more extended in the central regions than the outskirts, and the difference in star formation rates between the central and outer regions is most marked 11-13 Gyr ago. Whether blue straggler stars are interpreted as intermediate-age main-sequence stars affects conclusions regarding the SFH for times 4-8 Gyr ago, but this is at most only a trace population. We find that the metallicity of the stars increased rapidly up to [Fe/H] = -1.6 in the central region and to [Fe/H] = -1.8 in the outer region within the first Gyr, and has varied slowly since then. The abundance ratios of several elements derived in this study are in good agreement with the observational data based on the high-resolution spectroscopy in the literature. We conclude that the primary driver for the radial gradient of the stellar population in this galaxy is the SFH, which self-consistently drives the chemical enrichment history.

  2. Large-scale environmental dependence of chemical abundances in dwarf galaxies and implications for connecting star formation and halo mass

    OpenAIRE

    Douglass, Kelly A.; Vogeley, Michael S.; Cen, Renyue

    2017-01-01

    We study how the void environment affects the chemical evolution of galaxies in the universe by comparing the oxygen and nitrogen abundances of dwarf galaxies in voids with dwarf galaxies in denser regions. Using spectroscopic observations from SDSS DR7, we estimate the oxygen and nitrogen abundances of 993 void dwarf galaxies and 759 dwarf galaxies in denser regions. We use the Direct Te method for calculating the gas-phase chemical abundances in the dwarf galaxies because it is best suited ...

  3. METALLICITIES OF PLANET-HOSTING STARS: A SAMPLE OF GIANTS AND SUBGIANTS

    International Nuclear Information System (INIS)

    Ghezzi, L.; Cunha, K.; Schuler, S. C.; Smith, V. V.

    2010-01-01

    This work presents a homogeneous derivation of atmospheric parameters and iron abundances for a sample of giant and subgiant stars which host giant planets, as well as a control sample of subgiant stars not known to host giant planets. The analysis is done using the same technique as for our previous analysis of a large sample of planet-hosting and control sample dwarf stars. A comparison between the distributions of [Fe/H] in planet-hosting main-sequence (MS) stars, subgiants, and giants within these samples finds that the MS stars and subgiants have the same mean metallicity of ([Fe/H])≅ +0.11 dex, while the giant sample is typically more metal poor, having an average metallicity of [Fe/H] = -0.06 dex. The fact that the subgiants have the same average metallicities as the dwarfs indicates that significant accretion of solid metal-rich material onto the planet-hosting stars has not taken place, as such material would be diluted in the evolution from dwarf to subgiant. The lower metallicity found for the planet-hosting giant stars in comparison with the planet-hosting dwarfs and subgiants is interpreted as being related to the underlying stellar mass, with giants having larger masses and thus, on average, larger-mass protoplanetary disks. In core accretion models of planet formation, larger disk masses can contain the critical amount of metals necessary to form giant planets even at lower metallicities.

  4. METALLICITY DISTRIBUTION FUNCTIONS OF FOUR LOCAL GROUP DWARF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Ross, Teresa L.; Holtzman, Jon [Department of Astronomy, New Mexico State University, P.O. Box 30001, MSC 4500, Las Cruces, NM 88003-8001 (United States); Saha, Abhijit [NOAO, 950 Cherry Avenue, Tucson, AZ 85726-6732 (United States); Anthony-Twarog, Barbara J., E-mail: rosst@nmsu.edu, E-mail: holtz@nmsu.edu, E-mail: bjat@ku.edu [Department of Physics and Astronomy, University of Kansas, Lawrence, KS 66045-7582 (United States)

    2015-06-15

    We present stellar metallicities in Leo I, Leo II, IC 1613, and Phoenix dwarf galaxies derived from medium (F390M) and broad (F555W, F814W) band photometry using the Wide Field Camera 3 instrument on board the Hubble Space Telescope. We measured metallicity distribution functions (MDFs) in two ways, (1) matching stars to isochrones in color–color diagrams and (2) solving for the best linear combination of synthetic populations to match the observed color–color diagram. The synthetic technique reduces the effect of photometric scatter and produces MDFs 30%–50% narrower than the MDFs produced from individually matched stars. We fit the synthetic and individual MDFs to analytical chemical evolution models (CEMs) to quantify the enrichment and the effect of gas flows within the galaxies. Additionally, we measure stellar metallicity gradients in Leo I and II. For IC 1613 and Phoenix our data do not have the radial extent to confirm a metallicity gradient for either galaxy. We find the MDF of Leo I (dwarf spheroidal) to be very peaked with a steep metal-rich cutoff and an extended metal-poor tail, while Leo II (dwarf spheroidal), Phoenix (dwarf transition), and IC 1613 (dwarf irregular) have wider, less peaked MDFs than Leo I. A simple CEM is not the best fit for any of our galaxies; therefore we also fit the “Best Accretion Model” of Lynden-Bell. For Leo II, IC 1613, and Phoenix we find similar accretion parameters for the CEM even though they all have different effective yields, masses, star formation histories, and morphologies. We suggest that the dynamical history of a galaxy is reflected in the MDF, where broad MDFs are seen in galaxies that have chemically evolved in relative isolation and narrowly peaked MDFs are seen in galaxies that have experienced more complicated dynamical interactions concurrent with their chemical evolution.

  5. Library of high-resolution UES echelle spectra of F, G, K and M field dwarf stars

    Science.gov (United States)

    Montes, D.; Martin, E. L.

    1998-03-01

    We present a library of Utrecht echelle spectrograph (UES) observations of a sample of F, G, K and M field dwarf stars covering the spectral range from 4800 \\ Angstroms to 10600 \\ Angstroms with a resolution of 55000. These spectra include some of the spectral lines most widely used as optical and near-infrared indicators of chromospheric activity such as Hβ , Mg i b triplet, Na i D1, D2, He i D3, Hα , and Ca ii IRT lines, as well as a large number of photospheric lines which can also be affected by chromospheric activity. The spectra have been compiled with the aim of providing a set of standards observed at high-resolution to be used in the application of the spectral subtraction technique to obtain the active-chromosphere contribution to these lines in chromospherically active single and binary stars. This library can also be used for spectral classification purposes. A digital version with all the spectra is available via ftp and the World Wide Web (WWW) in both ASCII and FITS formats. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group at the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrof\\'{\\i

  6. THE INTERACTION OF VENUS-LIKE, M-DWARF PLANETS WITH THE STELLAR WIND OF THEIR HOST STAR

    International Nuclear Information System (INIS)

    Cohen, O.; Drake, J. J.; Garraffo, C.; Ma, Y.; Glocer, A.; Bell, J. M.; Gombosi, T. I.

    2015-01-01

    We study the interaction between the atmospheres of Venus-like, non-magnetized exoplanets orbiting an M-dwarf star, and the stellar wind using a multi-species MHD model. We focus our investigation on the effect of enhanced stellar wind and enhanced EUV flux as the planetary distance from the star decreases. Our simulations reveal different topologies of the planetary space environment for sub- and super-Alfvénic stellar wind conditions, which could lead to dynamic energy deposition into the atmosphere during the transition along the planetary orbit. We find that the stellar wind penetration for non-magnetized planets is very deep, up to a few hundreds of kilometers. We estimate a lower limit for the atmospheric mass-loss rate and find that it is insignificant over the lifetime of the planet. However, we predict that when accounting for atmospheric ion acceleration, a significant amount of the planetary atmosphere could be eroded over the course of a billion years

  7. DETERMINING THE LARGE-SCALE ENVIRONMENTAL DEPENDENCE OF GAS-PHASE METALLICITY IN DWARF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Douglass, Kelly A.; Vogeley, Michael S., E-mail: kelly.a.douglass@drexel.edu [Department of Physics, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104 (United States)

    2017-01-10

    We study how the cosmic environment affects galaxy evolution in the universe by comparing the metallicities of dwarf galaxies in voids with dwarf galaxies in more dense regions. Ratios of the fluxes of emission lines, particularly those of the forbidden [O iii] and [S ii] transitions, provide estimates of a region’s electron temperature and number density. From these two quantities and the emission line fluxes [O ii] λ 3727, [O iii] λ 4363, and [O iii] λλ 4959, 5007, we estimate the abundance of oxygen with the direct T{sub e}  method. We estimate the metallicity of 42 blue, star-forming void dwarf galaxies and 89 blue, star-forming dwarf galaxies in more dense regions using spectroscopic observations from the Sloan Digital Sky Survey Data Release 7, as reprocessed in the MPA-JHU value-added catalog. We find very little difference between the two sets of galaxies, indicating little influence from the large-scale environment on their chemical evolution. Of particular interest are a number of extremely metal-poor dwarf galaxies that are less prevalent in voids than in the denser regions.

  8. Suppression of the water ice and snow albedo feedback on planets orbiting red dwarf stars and the subsequent widening of the habitable zone.

    Science.gov (United States)

    Joshi, Manoj M; Haberle, Robert M

    2012-01-01

    M stars comprise 80% of main sequence stars, so their planetary systems provide the best chance for finding habitable planets, that is, those with surface liquid water. We have modeled the broadband albedo or reflectivity of water ice and snow for simulated planetary surfaces orbiting two observed red dwarf stars (or M stars), using spectrally resolved data of Earth's cryosphere. The gradual reduction of the albedos of snow and ice at wavelengths greater than 1 μm, combined with M stars emitting a significant fraction of their radiation at these same longer wavelengths, means that the albedos of ice and snow on planets orbiting M stars are much lower than their values on Earth. Our results imply that the ice/snow albedo climate feedback is significantly weaker for planets orbiting M stars than for planets orbiting G-type stars such as the Sun. In addition, planets with significant ice and snow cover will have significantly higher surface temperatures for a given stellar flux if the spectral variation of cryospheric albedo is considered, which in turn implies that the outer edge of the habitable zone around M stars may be 10-30% farther away from the parent star than previously thought.

  9. A carbon-enhanced metal-poor damped Lyα system: probing gas from Population III nucleosynthesis?

    Science.gov (United States)

    Cooke, Ryan; Pettini, Max; Steidel, Charles C.; Rudie, Gwen C.; Jorgenson, Regina A.

    2011-04-01

    We present high-resolution observations of an extremely metal-poor damped Lyα system (DLA), at zabs= 2.340 0972 in the spectrum of the QSO J0035-0918, exhibiting an abundance pattern consistent with model predictions for the supernova yields of Population III stars. Specifically, this DLA has [Fe/H]≃-3, shows a clear ‘odd-even’ effect, and is C-rich with [C/Fe]=+1.53, a factor of ˜20 greater than reported in any other DLA. In analogy to the carbon-enhanced metal-poor stars in the Galactic halo (with [C/Fe] > +1.0), this is the first known case of a carbon-enhanced DLA. We determine an upper limit to the mass of 12C, M(12C) ≤ 200 M⊙, which depends on the unknown gas density n(H); if n(H) > 1 cm-3 (which is quite likely for this DLA given its low velocity dispersion), then M(12C) ≤ 2 M⊙, consistent with pollution by only a few prior supernovae. We speculate that DLAs such as the one discovered here may represent the ‘missing link’ between the yields of Population III stars and their later incorporation in the class of carbon-enhanced metal-poor stars which show no enhancement of neutron-capture elements (CEMP-no stars). Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation.

  10. H i in Virgo’s “Red and Dead” Dwarf Ellipticals—A Tidal Tail and Central Star Formation

    Energy Technology Data Exchange (ETDEWEB)

    Hallenbeck, Gregory; Koopmann, Rebecca [Union College, Department of Physics and Astronomy, 807 Union Street, Schenectady NY 12308 (United States); Giovanelli, Riccardo; Haynes, Martha P.; Leisman, Lukas [Cornell Center for Astrophysics and Planetary Science (CCAPS), Space Sciences Building, Cornell University, Ithaca, NY 14853 (United States); Huang, Shan [CCPP, New York University, 4 Washington Place, New York, NY 10003 (United States); Papastergis, Emmanouil, E-mail: hallenbg@union.edu, E-mail: koopmanr@union.edu, E-mail: riccardo@astro.cornell.edu, E-mail: haynes@astro.cornell.edu, E-mail: leisman@astro.cornell.edu, E-mail: shan.huang@nyu.edu, E-mail: papastergis@astro.rug.nl [Kapteyn Astronomical Institute, University of Groningen, Landleven 12, Groningen NL-9747AD (Netherlands)

    2017-08-01

    We investigate a sample of three dwarf elliptical galaxies in the Virgo Cluster that have significant reservoirs of H i. We present deep optical imaging (from CFHT and KPNO), H i spectra (Arecibo), and resolved H i imaging (VLA) of this sample. These observations confirm their H i content and optical morphologies, and indicate that the gas is unlikely to be recently accreted. The sample has more in common with dwarf transitionals, though dwarf transitionals are generally lower in stellar mass and gas fraction. VCC 190 has an H i tidal tail from a recent encounter with the massive spiral galaxy NGC 4224. In VCC 611, blue star-forming features are observed that were not seen by shallower SDSS imaging.

  11. HAT-P-68b: A Transiting Hot Jupiter Around a K5 Dwarf Star

    Science.gov (United States)

    Lindor, Bethlee; Hartman, Joel D.

    2018-01-01

    One of the main goals of the astrophysical society has been to detect sources of life outside of Earth. To aid this search, astronomers have spent the last 2 decades focused on the discovery and characterization of exoplanets. The most effective method for doing so has been transit photometry, wherein we measure the brightness of stars over periods of time. These measurements, or light curves, are later analyzed for dips in brightness caused by objects passing in front of the star. However, variations in these time series can also occur due to non-planetary systems and a meticulous process is needed to distinguish the planets from the various false positives that are detected. HATNet is one of many surveys involved in this endeavor, and in this work I analyze HAT-P-68. First, I model the system as a single star with a transiting planet and derive estimates of the stellar and planetary physical parameters. I also model HAT-P-68 as a number of a false positives such as a pair of stars in an eclipsing binary blended with a background star, and a planet-sized star orbiting a Sun-like star. In order to rule out the possibility that HAT-P-68 is a blend, I carried out a statistical blend analysis of the photometric data and find that all blend models tested can be ruled out. Thus, I conclude that HAT-P-68 is a system with a transiting hot jupiter and consider what future observations would be most promising to further characterize the system.

  12. Dwarf galaxies with ionizing radiation feedback. II. Spatially resolved star formation relation

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ji-hoon; Krumholz, Mark R.; Wise, John H.; Turk, Matthew J.; Goldbaum, Nathan J.; Abel, Tom

    2013-11-15

    AWe investigate the spatially resolved star formation relation using a galactic disk formed in a comprehensive high-resolution (3.8 pc) simulation. Our new implementation of stellar feedback includes ionizing radiation as well as supernova explosions, and we handle ionizing radiation by solving the radiative transfer equation rather than by a subgrid model. Photoheating by stellar radiation stabilizes gas against Jeans fragmentation, reducing the star formation rate (SFR). Because we have self-consistently calculated the location of ionized gas, we are able to make simulated, spatially resolved observations of star formation tracers, such as Hα emission. We can also observe how stellar feedback manifests itself in the correlation between ionized and molecular gas. Applying our techniques to the disk in a galactic halo of 2.3 × 1011 M , we find that the correlation between SFR density (estimated from mock Hα emission) and H2 density shows large scatter, especially at high resolutions of ≲ 75 pc that are comparable to the size of giant molecular clouds (GMCs). This is because an aperture of GMC size captures only particular stages of GMC evolution and because Hα traces hot gas around star-forming regions and is displaced from the H2 peaks themselves. By examining the evolving environment around star clusters, we speculate that the breakdown of the traditional star formation laws of the Kennicutt-Schmidt type at small scales is further aided by a combination of stars drifting from their birthplaces and molecular clouds being dispersed via stellar feedback.

  13. Detailed chemical abundances in NGC 5824: another metal-poor globular cluster with internal heavy element abundance variations

    Science.gov (United States)

    Roederer, Ian U.; Mateo, Mario; Bailey, John I.; Spencer, Meghin; Crane, Jeffrey D.; Shectman, Stephen A.

    2016-01-01

    We present radial velocities, stellar parameters, and detailed abundances of 39 elements derived from high-resolution spectroscopic observations of red giant stars in the luminous, metal-poor globular cluster NGC 5824. We observe 26 stars in NGC 5824 using the Michigan/Magellan Fiber System (M2FS) and two stars using the Magellan Inamori Kyocera Echelle spectrograph. We derive a mean metallicity of [Fe/H] = -1.94 ± 0.02 (statistical) ±0.10 (systematic). The metallicity dispersion of this sample of stars, 0.08 dex, is in agreement with previous work and does not exceed the expected observational errors. Previous work suggested an internal metallicity spread only when fainter samples of stars were considered, so we cannot exclude the possibility of an intrinsic metallicity dispersion in NGC 5824. The M2FS spectra reveal a large internal dispersion in [Mg/Fe], 0.28 dex, which is found in a few other luminous, metal-poor clusters. [Mg/Fe] is correlated with [O/Fe] and anticorrelated with [Na/Fe] and [Al/Fe]. There is no evidence for internal dispersion among the other α- or Fe-group abundance ratios. 25 of the 26 stars exhibit a n-capture enrichment pattern dominated by r-process nucleosynthesis ( = +0.11 ± 0.12; = -0.66 ± 0.05). Only one star shows evidence of substantial s-process enhancement ([Ba/Fe] = +0.56 ± 0.12; [Ba/Eu] = +0.38 ± 0.14), but this star does not exhibit other characteristics associated with s-process enhancement via mass transfer from a binary companion. The Pb and other heavy elements produced by the s-process suggest a time-scale of no more than a few hundred Myr for star formation and chemical enrichment, like the complex globular clusters M2, M22, and NGC 5286.

  14. Role of ocean heat transport in climates of tidally locked exoplanets around M dwarf stars

    Science.gov (United States)

    Hu, Yongyun; Yang, Jun

    2014-01-01

    The distinctive feature of tidally locked exoplanets is the very uneven heating by stellar radiation between the dayside and nightside. Previous work has focused on the role of atmospheric heat transport in preventing atmospheric collapse on the nightside for terrestrial exoplanets in the habitable zone around M dwarfs. In the present paper, we carry out simulations with a fully coupled atmosphere–ocean general circulation model to investigate the role of ocean heat transport in climate states of tidally locked habitable exoplanets around M dwarfs. Our simulation results demonstrate that ocean heat transport substantially extends the area of open water along the equator, showing a lobster-like spatial pattern of open water, instead of an “eyeball.” For sufficiently high-level greenhouse gases or strong stellar radiation, ocean heat transport can even lead to complete deglaciation of the nightside. Our simulations also suggest that ocean heat transport likely narrows the width of M dwarfs’ habitable zone. This study provides a demonstration of the importance of exooceanography in determining climate states and habitability of exoplanets. PMID:24379386

  15. Numerical Simulations of Collisional Cascades at the Roche Limits of White Dwarf Stars

    Science.gov (United States)

    Kenyon, Scott J.; Bromley, Benjamin C.

    2017-08-01

    We consider the long-term collisional and dynamical evolution of solid material orbiting in a narrow annulus near the Roche limit of a white dwarf. With orbital velocities of 300 {km} {{{s}}}-1, systems of solids with initial eccentricity e≳ {10}-3 generate a collisional cascade where objects with radii r ≲ 100{--}300 {km} are ground to dust. This process converts 1-100 km asteroids into 1 μm particles in 102-106 yr. Throughout this evolution, the swarm maintains an initially large vertical scale height H. Adding solids at a rate \\dot{M} enables the system to find an equilibrium where the mass in solids is roughly constant. This equilibrium depends on \\dot{M} and {r}0, the radius of the largest solid added to the swarm. When {r}0 ≲ 10 km, this equilibrium is stable. For larger {r}0, the mass oscillates between high and low states; the fraction of time spent in high states ranges from 100% for large \\dot{M} to much less than 1% for small \\dot{M}. During high states, the stellar luminosity reprocessed by the solids is comparable to the excess infrared emission observed in many metallic line white dwarfs.

  16. BANYAN. V. A SYSTEMATIC ALL-SKY SURVEY FOR NEW VERY LATE-TYPE LOW-MASS STARS AND BROWN DWARFS IN NEARBY YOUNG MOVING GROUPS

    Energy Technology Data Exchange (ETDEWEB)

    Gagné, Jonathan; Lafrenière, David; Doyon, René; Malo, Lison; Artigau, Étienne [Département de Physique, Université de Montréal, C.P. 6128 Succ. Centre-ville, Montréal, QC H3C 3J7 (Canada)

    2015-01-10

    We present the BANYAN All-Sky Survey (BASS) catalog, consisting of 228 new late-type (M4-L6) candidate members of nearby young moving groups (YMGs) with an expected false-positive rate of ∼13%. This sample includes 79 new candidate young brown dwarfs and 22 planetary-mass objects. These candidates were identified through the first systematic all-sky survey for late-type low-mass stars and brown dwarfs in YMGs. We cross-matched the Two Micron All Sky Survey and AllWISE catalogs outside of the galactic plane to build a sample of 98,970 potential ≥M5 dwarfs in the solar neighborhood and calculated their proper motions with typical precisions of 5-15 mas yr{sup –1}. We selected highly probable candidate members of several YMGs from this sample using the Bayesian Analysis for Nearby Young AssociatioNs II tool (BANYAN II). We used the most probable statistical distances inferred from BANYAN II to estimate the spectral type and mass of these candidate YMG members. We used this unique sample to show tentative signs of mass segregation in the AB Doradus moving group and the Tucana-Horologium and Columba associations. The BASS sample has already been successful in identifying several new young brown dwarfs in earlier publications, and will be of great interest in studying the initial mass function of YMGs and for the search of exoplanets by direct imaging; the input sample of potential close-by ≥M5 dwarfs will be useful to study the kinematics of low-mass stars and brown dwarfs and search for new proper motion pairs.

  17. HI properties and star formation history of a fly-by pair of blue compact dwarf galaxies

    Science.gov (United States)

    Kim, Jinhyub; Chung, Aeree; Wong, O. Ivy; Lee, Bumhyun; Sung, Eon-Chang; Staveley-Smith, Lister

    2017-09-01

    A fly-by interaction has been suggested to be one of the major explanations for enhanced star formation in blue compact dwarf (BCD) galaxies, yet no direct evidence for this scenario has been found to date. In the Hi Parkes all-sky survey (HIPASS), ESO 435-IG 020 and ESO 435-G 016, a BCD pair were found in a common, extended gas envelope of atomic hydrogen, providing an ideal case to test the hypothesis that the starburst in BCDs can be indeed triggered by a fly-by interaction. Using high-resolution data from the Australia Telescope Compact Array (ATCA), we investigated Hi properties and the spectral energy distribution (SED) of the BCD pair to study their interaction and star formation histories. The high-resolution Hi data of both BCDs reveal a number of peculiarities, which are suggestive of tidal perturbation. Meanwhile, 40% of the HIPASS flux is not accounted for in the ATCA observations with no Hi gas bridge found between the two BCDs. Intriguingly, in the residual of the HIPASS and the ATCA data, 10% of the missing flux appears to be located between the two BCDs. While the SED-based age of the most dominant young stellar population is old enough to have originated from the interaction with any neighbors (including the other of the two BCDs), the most recent star formation activity traced by strong Hα emission in ESO 435-IG 020 and the shear motion of gas in ESO 435-G 016, suggest a more recent or current tidal interaction. Based on these and the residual emission between the HIPASS and the ATCA data, we propose an interaction between the two BCDs as the origin of their recently enhanced star formation activity. The shear motion on the gas disk, potentially with re-accretion of the stripped gas, could be responsible for the active star formation in this BCD pair. The reduced datacube (FITS file) is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/605/A54

  18. THE GAS PHASE MASS METALLICITY RELATION FOR DWARF GALAXIES: DEPENDENCE ON STAR FORMATION RATE AND HI GAS MASS

    Energy Technology Data Exchange (ETDEWEB)

    Jimmy; Tran, Kim-Vy [George P. and Cynthia W. Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, College Station, TX 77843 (United States); Saintonge, Amélie; Accurso, Gioacchino [Department of Physics and Astronomy, University College London, Gower Place, London WC1E 6BT (United Kingdom); Brough, Sarah; Oliva-Altamirano, Paola [Australian Astronomical Observatory, P.O. Box 915, North Ryde, NSW 1670 (Australia)

    2015-10-20

    Using a sample of dwarf galaxies observed using the VIMOS IFU on the Very Large Telescope, we investigate the mass–metallicity relation (MZR) as a function of star formation rate (FMR{sub SFR}) as well as HI-gas mass (FMR{sub HI}). We combine our IFU data with a subsample of galaxies from the ALFALFA HI survey crossmatched to the Sloan Digital Sky Survey (SDSS) to study the FMR{sub SFR} and FMR{sub HI} across the stellar mass range 10{sup 6.6}–10{sup 8.8} M{sub ⊙}, with metallicities as low as 12 + log(O/H) = 7.67. We find the 1σ mean scatter in the MZR to be 0.05 dex. The 1σ mean scatter in the FMR{sub SFR} (0.02 dex) is significantly lower than that of the MZR. The FMR{sub SFR} is not consistent between the IFU observed galaxies and the ALFALFA/SDSS galaxies for SFRs lower than 10{sup −2.4} M{sub ⊙} yr{sup −1}, however, this could be the result of limitations of our measurements in that regime. The lowest mean scatter (0.01 dex) is found in the FMR{sub HI}. We also find that the FMR{sub HI} is consistent between the IFU observed dwarf galaxies and the ALFALFA/SDSS crossmatched sample. We introduce the fundamental metallicity luminosity counterpart to the FMR, again characterized in terms of SFR (FML{sub SFR}) and HI-gas mass (FML{sub HI}). We find that the FML{sub HI} relation is consistent between the IFU observed dwarf galaxy sample and the larger ALFALFA/SDSS sample. However, the 1σ scatter for the FML{sub HI} relation is not improved over the FMR{sub HI} scenario. This leads us to conclude that the FMR{sub HI} is the best candidate for a physically motivated fundamental metallicity relation.

  19. Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1.

    Science.gov (United States)

    Gillon, Michaël; Triaud, Amaury H M J; Demory, Brice-Olivier; Jehin, Emmanuël; Agol, Eric; Deck, Katherine M; Lederer, Susan M; de Wit, Julien; Burdanov, Artem; Ingalls, James G; Bolmont, Emeline; Leconte, Jeremy; Raymond, Sean N; Selsis, Franck; Turbet, Martin; Barkaoui, Khalid; Burgasser, Adam; Burleigh, Matthew R; Carey, Sean J; Chaushev, Aleksander; Copperwheat, Chris M; Delrez, Laetitia; Fernandes, Catarina S; Holdsworth, Daniel L; Kotze, Enrico J; Van Grootel, Valérie; Almleaky, Yaseen; Benkhaldoun, Zouhair; Magain, Pierre; Queloz, Didier

    2017-02-22

    One aim of modern astronomy is to detect temperate, Earth-like exoplanets that are well suited for atmospheric characterization. Recently, three Earth-sized planets were detected that transit (that is, pass in front of) a star with a mass just eight per cent that of the Sun, located 12 parsecs away. The transiting configuration of these planets, combined with the Jupiter-like size of their host star-named TRAPPIST-1-makes possible in-depth studies of their atmospheric properties with present-day and future astronomical facilities. Here we report the results of a photometric monitoring campaign of that star from the ground and space. Our observations reveal that at least seven planets with sizes and masses similar to those of Earth revolve around TRAPPIST-1. The six inner planets form a near-resonant chain, such that their orbital periods (1.51, 2.42, 4.04, 6.06, 9.1 and 12.35 days) are near-ratios of small integers. This architecture suggests that the planets formed farther from the star and migrated inwards. Moreover, the seven planets have equilibrium temperatures low enough to make possible the presence of liquid water on their surfaces.

  20. Low-mass Pre-He White Dwarf Stars in Kepler Eclipsing Binaries with Multi-periodic Pulsations

    Science.gov (United States)

    Zhang, X. B.; Fu, J. N.; Liu, N.; Luo, C. Q.; Ren, A. B.

    2017-12-01

    We report the discovery of two thermally bloated low-mass pre-He white dwarfs (WDs) in two eclipsing binaries, KIC 10989032 and KIC 8087799. Based on the Kepler long-cadence photometry, we determined comprehensive photometric solutions of the two binary systems. The light curve analysis reveals that KIC 10989032 is a partially eclipsed detached binary system containing a probable low-mass WD with the temperature of about 10,300 K. Having a WD with the temperature of about 13,300, KKIC 8087799 is typical of an EL CVn system. By utilizing radial velocity measurements available for the A-type primary star of KIC 10989032, the mass and radius of the WD component are determined to be 0.24+/- 0.02 {M}⊙ and 0.50+/- 0.01 {R}⊙ , respectively. The values of mass and radius of the WD in KIC 8087799 are estimated as 0.16 ± 0.02 M ⊙ and 0.21 ± 0.01 R ⊙, respectively, according to the effective temperature and mean density of the A-type star derived from the photometric solution. We therefore introduce KIC 10989032 and KIC 8087799 as the eleventh and twelfth dA+WD eclipsing binaries in the Kepler field. Moreover, both binaries display marked multi-periodic pulsations superimposed on binary effects. A preliminary frequency analysis is applied to the light residuals when subtracting the synthetic eclipsing light curves from the observations, revealing that the light pulsations of the two systems are both due to the δ Sct-type primaries. We hence classify KIC 10989032 and KIC 8087799 as two WD+δ Sct binaries.

  1. Warm dust around cool stars: field M dwarfs with Wise 12 or 22 μm excess emission

    International Nuclear Information System (INIS)

    Theissen, Christopher A.; West, Andrew A.

    2014-01-01

    Using the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) spectroscopic catalog, we searched the WISE AllWISE catalog to investigate the occurrence of warm dust, as inferred from IR excesses, around field M dwarfs (dMs). We developed SDSS/WISE color selection criteria to identify 175 dMs (from 70,841) that show IR flux greater than the typical dM photosphere levels at 12 and/or 22 μm, including seven new stars within the Orion OB1 footprint. We characterize the dust populations inferred from each IR excess and investigate the possibility that these excesses could arise from ultracool binary companions by modeling combined spectral energy distributions. Our observed IR fluxes are greater than levels expected from ultracool companions (>3σ). We also estimate that the probability the observed IR excesses are due to chance alignments with extragalactic sources is <0.1%. Using SDSS spectra we measure surface gravity-dependent features (K, Na, and CaH 3) and find <15% of our sample indicates low surface gravities. Examining tracers of youth (Hα, UV fluxes, and Li absorption), we find <3% of our sample appear young, indicating we are observing a population of field stars ≳1 Gyr, likely harboring circumstellar material. We investigate age-dependent properties probed by this sample, studying the disk fraction as a function of Galactic height. The fraction remains small and constant to |Z| ∼ 700 pc and then drops, indicating little to no trend with age. Possible explanations for disks around field dMs include (1) collisions of planetary bodies, (2) tidal disruption of planetary bodies, or (3) failed planet formation.

  2. The Origin of Superflares on G-Type Dwarf Stars of Various Ages

    Science.gov (United States)

    Katsova, M. M.; Livshits, M. A.

    2015-12-01

    We analyze new observations of superflares on G-stars discovered in the optical and near-IR ranges with the Kepler mission. An evolution of solar-type activity is discussed. We give an estimate of the maximal total energy, E_{tot} = 10^{34} erg, of a flare that could have occurred on the young Sun at its age of 1 Gyr when the cycle was formed. We believe that the main source of the flare optical continuum is a low-temperature condensation forming in the course of the response of the chromosphere to an impulsive heating. For a superflare on the young Sun, we adopt an accelerated electron flux, Fe (E> 20 keV) = 3 × 10^{11} erg cm^{-2} s^{-1}, that is limited by the return current and obtain that the area of the optical continuum source on a G-star is S ≈ 10^{19} cm2. This value is close to the area of the Hα ribbons in the largest solar flares, while the area of bright patches of a white-light flare on the contemporary Sun is lower by about two orders of magnitude. At the same electron flux and hard electron spectrum, a stellar flare of similar energy should be accompanied by a microwave source of about 2 mJy at frequencies 10 - 100 GHz at a distance of 100 pc. We discuss the possible detection of the flare-produced lithium in the course of spallation reactions. The detection of the flare microwave source and the emission in the Li resonant line could demonstrate how effective particle acceleration can be on stars in the lower part of the main sequence.

  3. VizieR Online Data Catalog: Metallicity of MPA-JHU SDSS-DR7 dwarf galaxies (Douglass+, 2017)

    Science.gov (United States)

    Douglass, K. A.; Vogeley, M. S.

    2017-07-01

    We study how the cosmic environment affects galaxy evolution in the universe by comparing the metallicities of dwarf galaxies in voids with dwarf galaxies in more dense regions. Ratios of the fluxes of emission lines, particularly those of the forbidden [OIII] and [SII] transitions, provide estimates of a region's electron temperature and number density. From these two quantities and the emission line fluxes [OII]λ3727, [OIII]λ4363, and [OIII]λλ4959,5007, we estimate the abundance of oxygen with the direct Te method. We estimate the metallicity of 42 blue, star-forming void dwarf galaxies and 89 blue, star-forming dwarf galaxies in more dense regions using spectroscopic observations from the Sloan Digital Sky Survey Data Release 7, as reprocessed in the MPA-JHU value-added catalog. We find very little difference between the two sets of galaxies, indicating little influence from the large-scale environment on their chemical evolution. Of particular interest are a number of extremely metal-poor dwarf galaxies that are less prevalent in voids than in the denser regions. (1 data file).

  4. Eight per cent leakage of Lyman continuum photons from a compact, star-forming dwarf galaxy.

    Science.gov (United States)

    Izotov, Y I; Orlitová, I; Schaerer, D; Thuan, T X; Verhamme, A; Guseva, N G; Worseck, G

    2016-01-14

    One of the key questions in observational cosmology is the identification of the sources responsible for ionization of the Universe after the cosmic 'Dark Ages', when the baryonic matter was neutral. The currently identified distant galaxies are insufficient to fully reionize the Universe by redshift z ≈ 6 (refs 1-3), but low-mass, star-forming galaxies are thought to be responsible for the bulk of the ionizing radiation. As direct observations at high redshift are difficult for a variety of reasons, one solution is to identify local proxies of this galaxy population. Starburst galaxies at low redshifts, however, generally are opaque to Lyman continuum photons. Small escape fractions of about 1 to 3 per cent, insufficient to ionize much surrounding gas, have been detected only in three low-redshift galaxies. Here we report far-ultraviolet observations of the nearby low-mass star-forming galaxy J0925+1403. The galaxy is leaking ionizing radiation with an escape fraction of about 8 per cent. The total number of photons emitted during the starburst phase is sufficient to ionize intergalactic medium material that is about 40 times as massive as the stellar mass of the galaxy.

  5. Exploring the Evolution of Star Formation and Dwarf Galaxy Properties with JWST /MIRI Serendipitous Spectroscopic Surveys

    Energy Technology Data Exchange (ETDEWEB)

    Bonato, Matteo; Sajina, Anna; McKinney, Jed; Marchesini, Danilo; Roebuck, Eric; Shipley, Heath [Department of Physics and Astronomy, Tufts University, 574 Boston Avenue, Medford, MA (United States); Zotti, Gianfranco De [INAF, Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, I-35122 Padova (Italy); Baronchelli, Ivano; Yan, Lin [California Institute of Technology, Pasadena, CA (United States); Negrello, Mattia [School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA (United Kingdom); Kurinsky, Noah [Department of Physics, Stanford University, Stanford, CA (United States); Pope, Alexandra [Department of Astronomy, University of Massachusetts Amherst, Amherst, MA (United States); Noriega-Crespo, Alberto [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD (United States); Kirkpatrick, Allison [Department of Astronomy, Yale University, New Haven, CT (United States)

    2017-02-20

    The James Webb Space Telescope ’s Medium Resolution Spectrometer (MRS), will offer nearly two orders of magnitude improvement in sensitivity and >3× improvement in spectral resolution over our previous space-based mid-IR spectrometer, the Spitzer IRS. In this paper, we make predictions for spectroscopic pointed observations and serendipitous detections with the MRS. Specifically, pointed observations of Herschel sources require only a few minutes on source integration for detections of several star-forming and active galactic nucleus lines, out to z = 3 and beyond. But the same data will also include tens of serendipitous 0 ≲ z ≲ 4 galaxies per field with infrared luminosities ranging ∼10{sup 6}–10{sup 13} L {sub ☉}. In particular, for the first time and for free we will be able to explore the L {sub IR} < 10{sup 9} L {sub ☉} regime out to z ∼ 3. We estimate that with ∼ 100 such fields, statistics of these detections will be sufficient to constrain the evolution of the low- L end of the infrared luminosity function, and hence the star formation rate function. The above conclusions hold for a wide range in the potential low- L end of the IR luminosity function, and account for the PAH deficit in low- L , low-metallicity galaxies.

  6. A DEEP STUDY OF THE DWARF SATELLITES ANDROMEDA XXVIII AND ANDROMEDA XXIX

    Energy Technology Data Exchange (ETDEWEB)

    Slater, Colin T.; Bell, Eric F. [Department of Astronomy, University of Michigan, 1085 S. University Ave., Ann Arbor, MI 48109 (United States); Martin, Nicolas F. [Observatoire astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de l’Université, F-67000 Strasbourg (France); Tollerud, Erik J.; Ho, Nhung [Astronomy Department, Yale University, P.O. Box 208101, New Haven, CT 06510 (United States)

    2015-06-20

    We present the results of a deep study of the isolated dwarf galaxies Andromeda XXVIII and Andromeda XXIX with Gemini/GMOS and Keck/DEIMOS. Both galaxies are shown to host old, metal-poor stellar populations with no detectable recent star formation, conclusively identifying both of them as dwarf spheroidal galaxies (dSphs). And XXVIII exhibits a complex horizontal branch morphology, which is suggestive of metallicity enrichment and thus an extended period of star formation in the past. Decomposing the horizontal branch into blue (metal-poor, assumed to be older) and red (relatively more metal-rich, assumed to be younger) populations shows that the metal-rich are also more spatially concentrated in the center of the galaxy. We use spectroscopic measurements of the calcium triplet, combined with the improved precision of the Gemini photometry, to measure the metallicity of the galaxies, confirming the metallicity spread and showing that they both lie on the luminosity–metallicity relation for dwarf satellites. Taken together, the galaxies exhibit largely typical properties for dSphs despite their significant distances from M31. These dwarfs thus place particularly significant constraints on models of dSph formation involving environmental processes such as tidal or ram pressure stripping. Such models must be able to completely transform the two galaxies into dSphs in no more than two pericentric passages around M31, while maintaining a significant stellar population gradient. Reproducing these features is a prime requirement for models of dSph formation to demonstrate not just the plausibility of environmental transformation but the capability of accurately recreating real dSphs.

  7. A DEEP STUDY OF THE DWARF SATELLITES ANDROMEDA XXVIII AND ANDROMEDA XXIX

    International Nuclear Information System (INIS)

    Slater, Colin T.; Bell, Eric F.; Martin, Nicolas F.; Tollerud, Erik J.; Ho, Nhung

    2015-01-01

    We present the results of a deep study of the isolated dwarf galaxies Andromeda XXVIII and Andromeda XXIX with Gemini/GMOS and Keck/DEIMOS. Both galaxies are shown to host old, metal-poor stellar populations with no detectable recent star formation, conclusively identifying both of them as dwarf spheroidal galaxies (dSphs). And XXVIII exhibits a complex horizontal branch morphology, which is suggestive of metallicity enrichment and thus an extended period of star formation in the past. Decomposing the horizontal branch into blue (metal-poor, assumed to be older) and red (relatively more metal-rich, assumed to be younger) populations shows that the metal-rich are also more spatially concentrated in the center of the galaxy. We use spectroscopic measurements of the calcium triplet, combined with the improved precision of the Gemini photometry, to measure the metallicity of the galaxies, confirming the metallicity spread and showing that they both lie on the luminosity–metallicity relation for dwarf satellites. Taken together, the galaxies exhibit largely typical properties for dSphs despite their significant distances from M31. These dwarfs thus place particularly significant constraints on models of dSph formation involving environmental processes such as tidal or ram pressure stripping. Such models must be able to completely transform the two galaxies into dSphs in no more than two pericentric passages around M31, while maintaining a significant stellar population gradient. Reproducing these features is a prime requirement for models of dSph formation to demonstrate not just the plausibility of environmental transformation but the capability of accurately recreating real dSphs

  8. Dense cloud cores revealed by CO in the low metallicity dwarf galaxy WLM.

    Science.gov (United States)

    Rubio, Monica; Elmegreen, Bruce G; Hunter, Deidre A; Brinks, Elias; Cortés, Juan R; Cigan, Phil

    2015-09-10

    Understanding stellar birth requires observations of the clouds in which they form. These clouds are dense and self-gravitating, and in all existing observations they are molecular, with H2 the dominant species and carbon monoxide (CO) the best available tracer. When the abundances of carbon and oxygen are low compared with that of hydrogen, and the opacity from dust is also low, as in primeval galaxies and local dwarf irregular galaxies, CO forms slowly and is easily destroyed, so it is difficult for it to accumulate inside dense clouds. Here we report interferometric observations of CO clouds in the local group dwarf irregular galaxy Wolf-Lundmark-Melotte (WLM), which has a metallicity that is 13 per cent of the solar value and 50 per cent lower than the previous CO detection threshold. The clouds are tiny compared to the surrounding atomic and H2 envelopes, but they have typical densities and column densities for CO clouds in the Milky Way. The normal CO density explains why star clusters forming in dwarf irregulars have similar densities to star clusters in giant spiral galaxies. The low cloud masses suggest that these clusters will also be low mass, unless some galaxy-scale compression occurs, such as an impact from a cosmic cloud or other galaxy. If the massive metal-poor globular clusters in the halo of the Milky Way formed in dwarf galaxies, as is commonly believed, then they were probably triggered by such an impact.

  9. Cloud Atlas: Discovery of Rotational Spectral Modulations in a Low-mass, L-type Brown Dwarf Companion to a Star

    Science.gov (United States)

    Manjavacas, Elena; Apai, Dániel; Zhou, Yifan; Karalidi, Theodora; Lew, Ben W. P.; Schneider, Glenn; Cowan, Nicolas; Metchev, Stan; Miles-Páez, Paulo A.; Burgasser, Adam J.; Radigan, Jacqueline; Bedin, Luigi R.; Lowrance, Patrick J.; Marley, Mark S.

    2018-01-01

    Observations of rotational modulations of brown dwarfs and giant exoplanets allow the characterization of condensate cloud properties. As of now, rotational spectral modulations have only been seen in three L-type brown dwarfs. We report here the discovery of rotational spectral modulations in LP261-75B, an L6-type intermediate surface gravity companion to an M4.5 star. As a part of the Cloud Atlas Treasury program, we acquired time-resolved Wide Field Camera 3 grism spectroscopy (1.1–1.69 μm) of LP261-75B. We find gray spectral variations with the relative amplitude displaying only a weak wavelength dependence and no evidence for lower-amplitude modulations in the 1.4 μm water band than in the adjacent continuum. The likely rotational modulation period is 4.78 ± 0.95 hr, although the rotational phase is not well sampled. The minimum relative amplitude in the white light curve measured over the whole wavelength range is 2.41% ± 0.14%. We report an unusual light curve, which seems to have three peaks approximately evenly distributed in rotational phase. The spectral modulations suggests that the upper atmosphere cloud properties in LP261-75B are similar to two other mid-L dwarfs of typical infrared colors, but differ from that of the extremely red L-dwarf WISE0047.

  10. Fast Variability in Selected Chromospherically Active Dwarf Stars and Observational Equipment for Their Study

    Science.gov (United States)

    Bogdanovski, Rumen G.

    2015-06-01

    The observations of variable stars, especially those which show fast changes in their brightness, require high speed and high precision photometry. In order to study events like low amplitude optical oscillations and small scale fluctuations in the light curves, synchronous observations are required. These observations have to be carried out simultaneously at two or more, preferably distant, sites (Romanyuk et al., 2001), which allows the identification and elimination of artifacts produced by the equipment and the atmospheric interferences. In this way the fine structure of the light curve is revealed with a significant certainty. In order to study these events a new high speed time synchronized photometric system had to be designed, which addresses the requirements of the observations of high frequency subtle phenomena during stellar flares. It provides remote automatedand centralized control of the photometric equipment over a computer network,as well as remotemonitoring. Furthermore, some preliminary data processing can be performed at the time the data is obtained.

  11. ROTATIONAL DYNAMICS AND STAR FORMATION IN THE NEARBY DWARF GALAXY NGC 5238

    Energy Technology Data Exchange (ETDEWEB)

    Cannon, John M.; McNichols, Andrew T.; Teich, Yaron G., E-mail: jcannon@macalester.edu, E-mail: amcnicho@nrao.edu, E-mail: yateich@gmail.com; and others

    2016-12-01

    We present new H i spectral-line images of the nearby low-mass galaxy NGC 5238, acquired with the Karl G. Jansky Very Large Array. Located at a distance of 4.51 ± 0.04 Mpc, NGC 5238 is an actively star-forming galaxy with widespread H α and ultraviolet (UV) continuum emission. The source is included in many ongoing and recent nearby galaxy surveys, but until this work the spatially resolved qualities of its neutral interstellar medium have remained unstudied. Our H i images resolve the disk on physical scales of ∼400 pc, allowing us to undertake a detailed comparative study of the gaseous and stellar components. The H i disk is asymmetric in the outer regions, and the areas of high H i mass surface density display a crescent-shaped morphology that is slightly offset from the center of the stellar populations. The H i column density exceeds 10{sup 21} cm{sup −2} in much of the disk. We quantify the degree of co-spatiality of dense H i gas and sites of ongoing star formation as traced by far-UV and H α emission. The neutral gas kinematics are complex; using a spatially resolved position–velocity analysis, we infer a rotational velocity of 31 ± 5 km s{sup −1}. We place NGC 5238 on the baryonic Tully–Fisher relation and contextualize the system among other low-mass galaxies.

  12. The Unexpected Past of a Dwarf Galaxy

    Science.gov (United States)

    1996-08-01

    New Light on Cannibalism in the Local Group of Galaxies The Local Group of Galaxies consists of a few large spiral galaxies - for instance the Milky Way galaxy in which we live, and the Andromeda galaxy that is visible to the unaided eye in the northern constellation of the same name - as well as two dozen much smaller galaxies of mostly irregular shape. Whereas the larger galaxies have extended halos of very old stars, no such halos have ever been seen around the smaller ones. Now, however, Dante Minniti and Albert Zijlstra [1], working at the ESO 3.5-metre New Technology Telescope (NTT), have found a large halo of old and metal-poor stars around one of the dwarf galaxies in the Local Group. This finding is quite unexpected. It revises our understanding of star formation in these galaxies and provides important information about the past evolution of galaxies [2]. Galaxy halos The Milky Way galaxy is surrounded by a large, roughly spherical halo of old stars. The diameter is about 100,000 light years and the stars therein, known as Population II stars, are among the oldest known, with ages of 10 billion years or even more. They also differ from the younger stars nearer to the main plane of the Milky Way (in which our 4.7 billion year old Sun is located) by being very metal-poor. Many of the halo stars consist almost solely of hydrogen and helium, reflecting the composition of matter in the young Universe. This halo is important for our understanding of the processes that led to the formation of the Milky Way galaxy. It is believed that many of the halo stars and those of the same type found in globular clusters existed already before the Milky Way had fully formed. Galaxy cannibalism Many astronomers suspect that galaxies evolve and gradually grow larger and heavier by practising cannibalism on their own kind. In this picture, when two galaxies collide in space, the stars and nebulae in the smaller one will disperse and soon be taken over by the larger one, which

  13. Exploring the making of a galactic wind in the star-bursting dwarf irregular galaxy IC 10 with LOFAR

    Science.gov (United States)

    Heesen, V.; Rafferty, D. A.; Horneffer, A.; Beck, R.; Basu, A.; Westcott, J.; Hindson, L.; Brinks, E.; ChyŻy, K. T.; Scaife, A. M. M.; Brüggen, M.; Heald, G.; Fletcher, A.; Horellou, C.; Tabatabaei, F. S.; Paladino, R.; Nikiel-Wroczyński, B.; Hoeft, M.; Dettmar, R.-J.

    2018-02-01

    Low-mass galaxies are subject to strong galactic outflows, in which cosmic rays may play an important role; they can be best traced with low-frequency radio continuum observations, which are less affected by spectral ageing. We present a study of the nearby star burst dwarf irregular galaxy IC 10 using observations at 140 MHz with the LOw-Frequency ARray (LOFAR), at 1580 MHz with the Very Large Array (VLA) and at 6200 MHz with the VLA and the 100-m Effelsberg telescope. We find that IC 10 has a low-frequency radio halo, which manifests itself as a second component (thick disc) in the minor axis profiles of the non-thermal radio continuum emission at 140 and 1580 MHz. These profiles are then fitted with 1D cosmic-ray transport models for pure diffusion and advection. We find that a diffusion model fits best, with a diffusion coefficient of D = (0.4-0.8) × 1026(E/GeV)0.5 cm2 s-1, which is at least an order of magnitude smaller than estimates both from anisotropic diffusion and the diffusion length. In contrast, advection models, which cannot be ruled out due to the mild inclination, while providing poorer fits, result in advection speeds close to the escape velocity of ≈50 km s^{-1}, as expected for a cosmic-ray driven wind. Our favoured model with an accelerating wind provides a self-consistent solution, where the magnetic field is in energy equipartition with both the warm neutral and warm ionized medium with an important contribution from cosmic rays. Consequently, cosmic rays can play a vital role for the launching of galactic winds in the disc-halo interface.

  14. Star Formation Histories of Dwarf Galaxies from the Colour-Magnitude Diagrams of Their Resolved Stellar Populations

    Directory of Open Access Journals (Sweden)

    Michele Cignoni

    2010-01-01

    build synthetic CMDs and to exploit them to derive the SF histories (SFHs are described, as well as the corresponding uncertainties. The SFHs of resolved dwarf galaxies of all morphological types, obtained from the application of the synthetic CMD method, are reviewed and discussed. To summarize: (1 only early-type galaxies show evidence of long interruptions in the SF activity; late-type dwarfs present rather continuous, or gasping, SF regimes; (2 a few early-type dwarfs have experienced only one episode of SF activity concentrated at the earliest epochs, whilst many others show extended or recurrent SF activity; (3 no galaxy experiencing now its first SF episode has been found yet; (4 no frequent evidence of strong SF bursts is found; (5 there is no significant difference in the SFH of dwarf irregulars and blue compact dwarfs, except for the current SF rates. Implications of these results on the galaxy formation scenarios are briefly discussed.

  15. Spectroscopy of dwarf elliptical galaxies in the Fornax cluster

    Science.gov (United States)

    Held, Enrico V.; Mould, Jeremy R.

    1994-01-01

    We present the results of spectroscopic observations of 10 nucleated dwarf elliptical galaxies (dE's) in the Fornax cluster. The blue spectra of Fornax dE galaxies indicate a wide range of metallicities at a given luminosity, similar to those of intermediate to metal-rich globular clusters. Metal abundances derived in this paper are well correlated with optical colors and agree with previous spectroscopic results. A discrepancy with metallicities inferred from infrared colors is evident; possible causes include an intermediate age population and dilution of spectral features by a blue light excess. Dwarf ellipticals exhibit a wide variation of hydrogen line strength which points to a complex star formation history. Prominent Balmer absorption lines are the signature of a young stellar population in the nuclei of some (but not all) dE's, while moderately strong Balmer lines in relatively metal-rich dE's are more consistent with an extended main sequence. In a few metal-poor dE galaxies, the hydrogen lines are consisent with, or perhaps weaker than, those found in Galactic globulars of similar metallicity. In the limited magnitude range of this sample, there is no apparent correlation of metallicity either with effective and central surface brightness, or with total and nuclear magnitudes. The velocity distribution of the Fornax dwarfs is flatter than that of brighter galaxies at the 75% confidence level, possibly indicating a difference in the kinematics of the two samples.

  16. Axion cooling of white dwarfs

    OpenAIRE

    Isern, J.; Catalan, S.; Garcia--Berro, E.; Salaris, M.; Torres, S.

    2013-01-01

    The evolution of white dwarfs is a simple gravothermal process. This process can be tested in two ways, through the luminosity function of these stars and through the secular variation of the period of pulsation of those stars that are variable. Here we show how the mass of the axion can be constrained using the white dwarf luminosity function.

  17. Carbon Stars Identified from LAMOST DR4 Using Machine Learning

    Science.gov (United States)

    Li, Yin-Bi; Luo, A.-Li; Du, Chang-De; Zuo, Fang; Wang, Meng-Xin; Zhao, Gang; Jiang, Bi-Wei; Zhang, Hua-Wei; Liu, Chao; Qin, Li; Wang, Rui; Du, Bing; Guo, Yan-Xin; Wang, Bo; Han, Zhan-Wen; Xiang, Mao-Sheng; Huang, Yang; Chen, Bing-Qiu; Chen, Jian-Jun; Kong, Xiao; Hou, Wen; Song, Yi-Han; Wang, You-Fen; Wu, Ke-Fei; Zhang, Jian-Nan; Zhang, Yong; Wang, Yue-Fei; Cao, Zi-Huang; Hou, Yong-Hui; Zhao, Yong-Heng

    2018-02-01

    In this work, we present a catalog of 2651 carbon stars from the fourth Data Release (DR4) of the Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST). Using an efficient machine-learning algorithm, we find these stars from more than 7 million spectra. As a by-product, 17 carbon-enhanced metal-poor turnoff star candidates are also reported in this paper, and they are preliminarily identified by their atmospheric parameters. Except for 176 stars that could not be given spectral types, we classify the other 2475 carbon stars into five subtypes: 864 C-H, 226 C-R, 400 C-J, 266 C-N, and 719 barium stars based on a series of spectral features. Furthermore, we divide the C-J stars into three subtypes, C-J(H), C-J(R), and C-J(N), and about 90% of them are cool N-type stars as expected from previous literature. Besides spectroscopic classification, we also match these carbon stars to multiple broadband photometries. Using ultraviolet photometry data, we find that 25 carbon stars have FUV detections and that they are likely to be in binary systems with compact white dwarf companions.

  18. STELLAR POPULATIONS IN COMPACT GALAXY GROUPS: A MULTI-WAVELENGTH STUDY OF HCGs 16, 22, AND 42, THEIR STAR CLUSTERS, AND DWARF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Konstantopoulos, I. S. [Australian Astronomical Observatory, P.O. Box 915, North Ryde, NSW 1670 (Australia); Maybhate, A. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Charlton, J. C.; Gronwall, C. [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); Fedotov, K.; Desjardins, T. D.; Gallagher, S. C. [Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7 (Canada); Durrell, P. R. [Department of Physics and Astronomy, Youngstown State University, Youngstown, OH 44555 (United States); Mulchaey, J. S. [Carnegie Observatories, Pasadena, CA 91101 (United States); English, J. [Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada); Walker, L. M.; Johnson, K. E. [Department of Astronomy, University of Virginia, P.O. Box 3813, Charlottesville, VA 22904 (United States); Tzanavaris, P., E-mail: iraklis@aao.gov.au [Laboratory for X-ray Astrophysics, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

    2013-06-20

    We present a multi-wavelength analysis of three compact galaxy groups, Hickson compact groups (HCGs) 16, 22, and 42, which describe a sequence in terms of gas richness, from space- (Swift, Hubble Space Telescope (HST), and Spitzer) and ground-based (Las Campanas Observatory and Cerro Tololo Inter-American Observatory) imaging and spectroscopy. We study various signs of past interactions including a faint, dusty tidal feature about HCG 16A, which we tentatively age-date at <1 Gyr. This represents the possible detection of a tidal feature at the end of its phase of optical observability. Our HST images also resolve what were thought to be double nuclei in HCG 16C and D into multiple, distinct sources, likely to be star clusters. Beyond our phenomenological treatment, we focus primarily on contrasting the stellar populations across these three groups. The star clusters show a remarkable intermediate-age population in HCG 22, and identify the time at which star formation was quenched in HCG 42. We also search for dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27 ''associates'' (possible members) radically changes group dynamical masses, which in turn may affect previous evolutionary classifications. The extended membership paints a picture of relative isolation in HCGs 16 and 22, but shows HCG 42 to be part of a larger structure, following a dichotomy expected from recent studies. We conclude that (1) star cluster populations provide an excellent metric of evolutionary state, as they can age-date the past epochs of star formation; and (2) the extended dwarf galaxy population must be considered in assessing the dynamical state of a compact group.

  19. Kinematic, Photometric, and Spectroscopic Properties of Faint White Dwarf Stars Discovered in the HALO7D Survey of the Milky Way Galaxy

    Science.gov (United States)

    Harris, Madison; Cunningham, Emily; Guhathakurta, Puragra; Cheshire, Ishani; Gupta, Nandita

    2018-01-01

    White dwarf (WD) stars represent the final phase in the life of solar-mass stars. The extreme low luminosity of WDs means that most detailed measurements of such stars are limited to samples in the immediate neighborhood of the Sun in the thin disk of the Milky Way galaxy. We present spectra, line-of-sight (LOS) velocities, and proper motions (PMs) of a sample of faint (m_V ~ 19.0–24.5) white dwarfs (WDs) from the HALO7D survey. HALO7D is a Keck II/DEIMOS spectroscopic survey of unprecedented depth (8–24 hour integrations) in the CANDELS fields of main sequence turnoff stars in the Milky Way's outer halo. Faint WD stars are rare but useful by-products of this survey. We identify the sample of WDs based on their characteristic broad spectral Balmer absorption features, and present a Bayesian method for measuring their LOS velocities. Using their broadband colors, LOS velocities and PMs measured with the Hubble Space Telescope, we identify candidate halo members among the WDs based on the predicted velocity distributions from the Besançon numerical model of stellar populations in the Milky Way galaxy. The WDs found in the HALO7D survey will yield new insights on the old stellar population associated with the Milky Way's thick disk and halo. Funding for this research was provided by the National Science Foundation and NASA/STScI. NG and IC's participation in this research was under the auspices of the Science Internship Program at the University of California Santa Cruz.

  20. STELLAR POPULATIONS IN COMPACT GALAXY GROUPS: A MULTI-WAVELENGTH STUDY OF HCGs 16, 22, AND 42, THEIR STAR CLUSTERS, AND DWARF GALAXIES

    International Nuclear Information System (INIS)

    Konstantopoulos, I. S.; Maybhate, A.; Charlton, J. C.; Gronwall, C.; Fedotov, K.; Desjardins, T. D.; Gallagher, S. C.; Durrell, P. R.; Mulchaey, J. S.; English, J.; Walker, L. M.; Johnson, K. E.; Tzanavaris, P.

    2013-01-01

    We present a multi-wavelength analysis of three compact galaxy groups, Hickson compact groups (HCGs) 16, 22, and 42, which describe a sequence in terms of gas richness, from space- (Swift, Hubble Space Telescope (HST), and Spitzer) and ground-based (Las Campanas Observatory and Cerro Tololo Inter-American Observatory) imaging and spectroscopy. We study various signs of past interactions including a faint, dusty tidal feature about HCG 16A, which we tentatively age-date at <1 Gyr. This represents the possible detection of a tidal feature at the end of its phase of optical observability. Our HST images also resolve what were thought to be double nuclei in HCG 16C and D into multiple, distinct sources, likely to be star clusters. Beyond our phenomenological treatment, we focus primarily on contrasting the stellar populations across these three groups. The star clusters show a remarkable intermediate-age population in HCG 22, and identify the time at which star formation was quenched in HCG 42. We also search for dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27 ''associates'' (possible members) radically changes group dynamical masses, which in turn may affect previous evolutionary classifications. The extended membership paints a picture of relative isolation in HCGs 16 and 22, but shows HCG 42 to be part of a larger structure, following a dichotomy expected from recent studies. We conclude that (1) star cluster populations provide an excellent metric of evolutionary state, as they can age-date the past epochs of star formation; and (2) the extended dwarf galaxy population must be considered in assessing the dynamical state of a compact group.

  1. Redshifts of high-temperature emission lines in the far-ultraviolet spectra of late-type stars. II - New, precise measurements of dwarfs and giants

    Science.gov (United States)

    Ayres, Thomas R.; Jensen, Eberhard; Engvold, Oddbjorn

    1988-01-01

    Results are presented from an IUE SWP camera investigation of the occurrence of gasdynamic flows, analogous to the downdrafts of 10 to the 5th K material observed over magnetic active regions of the sun, among stars of late spectral type. The SWP calibration spectra study conducted documents the existence of local, small, persistent distortions of the echelle wavelength scales that are of unknown origin. Attention is given to the enormous widths of the stellar high-excitation emission lines in both the dwarfs and the giants, with respect to the comparatively small, subsonic Doppler shifts; the widths are typically an order of magnitude greater than the redshifts.

  2. Ca II triplet spectroscopy of RGB stars in NGC 6822: kinematics and metallicities

    Science.gov (United States)

    Swan, J.; Cole, A. A.; Tolstoy, E.; Irwin, M. J.

    2016-03-01

    We present a detailed analysis of the chemistry and kinematics of red giants in the dwarf irregular galaxy NGC 6822. Spectroscopy at ≈8500 Å was acquired for 72 red giant stars across two fields using FORS2 at the VLT. Line-of-sight extinction was individually estimated for each target star to accommodate the variable reddening across NGC 6822. The mean radial velocity was found to be = -52.8 ± 2.2 km s-1 with dispersion σv = 24.1 km s-1, in agreement with other studies. Ca II triplet equivalent widths were converted into [Fe/H] metallicities using a V magnitude proxy for surface gravity. The average metallicity was = -0.84 ± 0.04 with dispersion σ = 0.31 dex and interquartile range 0.48. Our assignment of individual reddening values makes our analysis more sensitive to spatial variations in metallicity than previous studies. We divide our sample into metal-rich and metal-poor stars; the former were found to cluster towards small radii with the metal-poor stars more evenly distributed across the galaxy. The velocity dispersion of the metal-poor stars was found to be higher than that of the metal-rich stars (σ _{v_MP}=27.4 km s-1; σ _{v_MR}=21.1 km s-1); combined with the age-metallicity relation this indicates that the older populations have either been dynamically heated during their lifetimes or were born in a less disc-like distribution than the younger stars.. The low ratio vrot/σv suggests that within the inner 10 arcmin, NGC 6822's stars are dynamically decoupled from the H I gas, and possibly distributed in a thick disc or spheroid structure.

  3. An Infrared High Resolution Spectroscopic Abundance Study of the Metal-Poor Giant HD 122563

    Science.gov (United States)

    Sneden, Christopher; Afsar, Melike; Jaffe, Daniel Thomas; Kim, Hwiyun; Mace, Gregory

    2015-01-01

    A high resolution, high signal-to-noise spectrum of the very metal-poor giant star HD 122563 has been obtained with the newly commissioned IGRINS H- and K-band high resolution (R = 40,000) spectrograph on the McDonald Observatory 2.7m Smith telescope. With complete spectral coverage in the range 1.5-1.8 and 1.9-2.4 microns and high signal-to-noise (S/N > 200) in the reduced spectrum, we have so far detected about 50neutral-species transitions of elements Na, Mg, Al, Si, Ca, and Fe, as well as many transitions of OH and CO.Assuming atmosphere parameters from the literature of this well-studied bright giant (Teff~4600K, log(g)~1.3) we have derived a metallicity of [Fe/H] = -2.8, in agreement with past results. The alpha-elements are enhanced: [(Mg,Si,Ca)/Fe] = +0.3 to +0.4. The OH lines yield an O abundance in good accord with past claims from analyses of the [O I] lines in the visible part of the spectrum. Study of other features in the IGRINSspectrum is ongoing.Support for this research from the US National Science Foundation (AST-1211585) and the The Scientific and Technological Research Council of Turkey (TÜBITAK, project No. 112T929) are acknowledged with thanks.

  4. On the Spectral Evolution of Cool, Helium-Atmosphere White Dwarfs: Detailed Spectroscopic and Photometric Analysis of DZ Stars

    National Research Council Canada - National Science Library

    Dufour, P; Bergeron, P; Liebert, James; Harris, H. C; Knapp, G. R; Anderson, S. F; Hall, Patrick B; Strauss, Michael A; Collinge, Matthew J; Edwards, Matt C

    2007-01-01

    ...) and analyze 147 new DZ white dwarfs discovered in the SDSS. The inclusion of metals and hydrogen in our model atmosphere calculations leads to different atmospheric parameters than those derived from pure helium models...

  5. A support vector machine to search for metal-poor galaxies

    Science.gov (United States)

    Shi, Fei; Liu, Yu-Yan; Kong, Xu; Chen, Yang; Li, Zhong-Hua; Zhi, Shu-Teng

    2014-10-01

    To develop a fast and reliable method for selecting metal-poor galaxies (MPGs), especially in large surveys and huge data bases, a support vector machine (SVM) supervized learning algorithms is applied to a sample of star-forming galaxies from the Sloan Digital Sky Survey data release 9 provided by the Max Planck Institute and the Johns Hopkins University (http://www.sdss3.org/dr9/spectro/spectroaccess.php). A two-step approach is adopted: (i) the SVM must be trained with a subset of objects that are known to be either MPGs or metal-rich galaxies (MRGs), treating the strong emission line flux measurements as input feature vectors in n-dimensional space, where n is the number of strong emission line flux ratios. (ii) After training on a sample of star-forming galaxies, the remaining galaxies are classified in the automatic test analysis as either MPGs or MRGs using a 10-fold cross-validation technique. For target selection, we have achieved an acquisition accuracy for MPGs of ˜96 and ˜95 per cent for an MPG threshold of 12 + log(O/H) = 8.00 and 12 + log(O/H) = 8.39, respectively. Running the code takes minutes in most cases under the MATLAB 2013a software environment. The code in the Letter is available on the web (http://fshi5388.blog.163.com). The SVM method can easily be extended to any MPGs target selection task and can be regarded as an efficient classification method particularly suitable for modern large surveys.

  6. Forming Stars From the Cosmic Web

    Science.gov (United States)

    Kohler, Susanna

    2015-09-01

    Scientists have recently identified a connection between metal-poor regions in a set of dwarf galaxies and bursts of star-formation activity within them. These observations provide long-awaited evidence supporting predictions of how stars formed in the early universe and in dwarf galaxies today. Metal-Poor Clues: The primary driver of star formation over cosmic history is thought to be the accretion onto galaxies of cold gas streaming from the cosmic web. The best way to confirm this model would be to observe a cloud of cosmic gas flowing into an otherwise-quiescent galaxy and launching a wave of star formation. But because cold gas doesnt emit much radiation, its difficult to detect directly.Now, a team of scientists have found a clever way around this problem: they searched galaxies for a correlation between areas of active star formation and metal-poor regions. Why? Because metal-poor regions could be a smoking gun indicating a recently accreted cloud of cold gas from the cosmic web. Impacting Clouds: Distribution of metallicity along the major axis of one of the target galaxies. The red bar in the top image shows the position of the spectrograph slit along the galaxy, with the arrow showing the direction of growing distance in the plot below. The plot shows the metallicity variation (red symbols) and star-formation rate (blue line) along the galaxys major axis. The metallicity drop coincides with the brightest knot of the galaxy. [Snchez Almeida et al. 2015]The authors of this study, led by Jorge Snchez Almeida (Instituto de Astrofisica de Canarias and University of La Laguna, Spain), used the Great Canary Telescope to obtain high-quality spectra of ten dwarf galaxies with especially low average metallicities. They aligned the spectrograph slit along the major axes of the galaxies in order to measure abundances as a function of position within each galaxy.The team found that, in nine out of the ten cases, the galaxies displayed sharp drops (by factors of 310

  7. Improved wavelengths for Fe V and Ni V for analysis of spectra of white dwarf stellar stars

    Science.gov (United States)

    Ward, Jacob; Nave, Gillian

    2015-08-01

    A recent paper by J.C. Berengut et al. tests for a potential variation in the fine-structure constant, α, in the presence of a high gravitational field through spectral analysis of white-dwarf stars. The spectrum of G191-B2B has prominent Fe V and Ni V lines in the vacuum ultraviolet (VUV) region that were used to determine any variation in α via observed shifts in their wavelengths. Although no strong evidence for a variation was found, the authors did find a difference between values obtained for Fe V and Ni V that were indicative of a problem with the laboratory wavelengths. The laboratory wavelengths dominate the uncertainty of the measured variation, so improved values would tighten the constraints on the variation of α.We have re-measured the spectra of Fe V and Ni V spectra in the VUV in order to reduce the wavelength uncertainties and put the two spectra on a consistent wavelength scale. The spectra were produced by a sliding spark light source with electrodes made of invar, an iron nickel alloy. Spectra of Fe V and Ni V were obtained using peak currents of 750-2000 A. The spectra were recorded using the NIST Normal Incidence Vacuum Spectrograph with phosphor image plates and photographic plates as detectors. Wavelengths from 1100 Å to 1800 Å were covered in a single exposure. A spectrum of a Pt/Ne hollow cathode lamp was also recorded for wavelength calibration.The spectra recorded on photographic plates are better resolved than the phosphor image plate spectra and are being measured in two ways. The first measures the positions of the spectral lines on a comparator, traditionally used to measure many archival spectra at NIST. The second uses a commercial image scanner to obtain a digital image of the plate that can be analyzed using line fitting software. Preliminary analysis of these spectra indicates that the literature values of the Fe V and Ni V wavelengths are not on the same scale and differ from our new measurements by up to 0.02 Å in some

  8. Dwarf Elliptical Galaxies

    Science.gov (United States)

    Caldwell, N.; Murdin, P.

    2000-11-01

    DWARF SPHEROIDAL GALAXIES were first identified by Shapley, who had noticed two very diffuse collections of stars on Harvard patrol plates. Although these systems had about as many stars as a GLOBULAR CLUSTER, they were of much lower density, and hence much larger radius, and thus were considered distinct galaxies. These two, named Fornax and Sculptor after the constellations in which they ap...

  9. Stellar Populations in Compact Galaxy Groups: a Multi-wavelength Study of HCGs 16, 22, and 42, Their Star Clusters, and Dwarf Galaxies

    Science.gov (United States)

    Konstantopoulos, I. S.; Maybhate, A.; Charlton, J. C.; Fedotov, K.; Durrell, P. R.; Mulchaey, J. S.; English, J.; Desjardins, T. D.; Gallagher, S. C.; Walker, L. M.; hide

    2013-01-01

    We present a multi-wavelength analysis of three compact galaxy groups, Hickson compact groups (HCGs) 16, 22, and 42, which describe a sequence in terms of gas richness, from space- (Swift, Hubble Space Telescope (HST), and Spitzer) and ground-based (Las Campanas Observatory and Cerro Tololo Inter-American Observatory) imaging and spectroscopy.We study various signs of past interactions including a faint, dusty tidal feature about HCG 16A, which we tentatively age-date at dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27 "associates" (possible members) radically changes group dynamical masses, which in turn may affect previous evolutionary classifications. The extended membership paints a picture of relative isolation in HCGs 16 and 22, but shows HCG 42 to be part of a larger structure, following a dichotomy expected from recent studies. We conclude that (1) star cluster populations provide an excellent metric of evolutionary state, as they can age-date the past epochs of star formation; and (2) the extended dwarf galaxy population must be considered in assessing the dynamical state of a compact group.

  10. Planets around Low-mass Stars. III. A Young Dusty L Dwarf Companion at the Deuterium-burning Limit

    Science.gov (United States)

    Bowler, Brendan P.; Liu, Michael C.; Shkolnik, Evgenya L.; Dupuy, Trent J.

    2013-09-01

    We report the discovery of an L-type companion to the young M3.5V star 2MASS J01225093-2439505 at a projected separation of 1.''45 (≈52 AU) as part of our adaptive optics imaging search for extrasolar giant planets around young low-mass stars. 2MASS 0122-2439 B has very red near-infrared colors similar to the HR 8799 planets and the reddest known young/dusty L dwarfs in the field. Moderate-resolution (R ≈ 3800) 1.5-2.4 μm spectroscopy reveals a near-infrared spectral type of L4-L6 and an angular H-band shape, confirming its cool temperature and young age. The kinematics of 2MASS 0122-2439 AB are marginally consistent with members of the ~120 Myr AB Dor young moving group based on the photometric distance to the primary (36 ± 4 pc) and our radial velocity measurement of 2MASS 0122-2439 A from Keck/HIRES. We adopt the AB Dor group age for the system, but the high energy emission, lack of Li I λ6707 absorption, and spectral shape of 2MASS 0122-2439 B suggest a range of ~10-120 Myr is possible. The age and luminosity of 2MASS 0122-2439 B fall in a strip where "hot-start" evolutionary model mass tracks overlap as a result of deuterium burning. Several known substellar companions also fall in this region (2MASS J0103-5515 ABb, AB Pic b, κ And b, G196-3 B, SDSS 2249+0044 B, LP 261-75 B, HD 203030 B, and HN Peg B), but their dual-valued mass predictions have largely been unrecognized. The implied mass of 2MASS 0122-2439 B is ≈12-13 M Jup or ≈22-27 M Jup if it is an AB Dor member, or possibly as low as 11 M Jup if the wider age range is adopted. Evolutionary models predict an effective temperature for 2MASS 0122-2439 B that corresponds to spectral types near the L/T transition (≈1300-1500 K) for field objects. However, we find a mid-L near-infrared spectral type, indicating that 2MASS 0122-2439 B represents another case of photospheric dust being retained to cooler temperatures at low surface gravities, as seen in the spectra of young (8-30 Myr) planetary

  11. How to find and type red/brown dwarf stars in near-infrared imaging space observatories

    Science.gov (United States)

    Willemn Holwerda, Benne; Ryan, Russell; Bridge, Joanna; Pirzkal, Nor; Kenworthy, Matthew; Andersen, Morten; Wilkins, Stephen; Trenti, Michele; Meshkat, Tiffany; Bernard, Stephanie; Smit, Renske

    2018-01-01

    Here we evaluate the near-infrared colors of brown dwarfs as observed with four major infrared imaging space observatories: the Hubble Space Telescope (HST), the James Webb Space Telescope (JWST), the EUCLID mission, and the WFIRST telescope. We use the splat ISPEX spectroscopic library to map out the colors of the M, L, and T-type brown dwarfs. We identify which color-color combination is optimal for identifying broad type and which single color is optimal to then identify the subtype (e.g., T0-9). We evaluate each observatory separately as well as the the narrow-field (HST and JWST) and wide-field (EULID and WFIRST) combinations.HST filters used thus far for high-redshift searches (e.g. CANDELS and BoRG) are close to optimal within the available filter combinations. A clear improvement over HST is one of two broad/medium filter combinations on JWST: pairing F140M with either F150W or F162M discriminates well between brown dwarf subtypes. The improvement of JWST the filter set over the HST one is so marked that any combination of HST and JWST filters does not improve the classification.The EUCLID filter set alone performs poorly in terms of typing brown dwarfs and WFIRST performs only marginally better, despite a wider selection of filters. A combined EUCLID and WFIRST observation, using WFIRST's W146 and F062 and EUCLID's Y-band, allows for a much better discrimination between broad brown dwarf categories. In this respect, WFIRST acts as a targeted follow-up observatory for the all-sky EUCLID survey. However, subsequent subtyping with the combination of EUCLID and WFIRST observations remains uncertain due to the lack of medium or narrow-band filters in this wavelength range. We argue that a medium band added to the WFIRST filter selection would greatly improve its ability to preselect against brown dwarfs in high-latitude surveys.

  12. Planets around Low-mass Stars (PALMS). I. A Substellar Companion to the Young M Dwarf 1RXS J235133.3+312720

    Science.gov (United States)

    Bowler, Brendan P.; Liu, Michael C.; Shkolnik, Evgenya L.; Dupuy, Trent J.; Cieza, Lucas A.; Kraus, Adam L.; Tamura, Motohide

    2012-07-01

    We report the discovery of a brown dwarf companion to the young M dwarf 1RXS J235133.3+312720 as part of a high contrast imaging search for planets around nearby young low-mass stars with Keck-II/NIRC2 and Subaru/HiCIAO. The 2farcs4 (~120 AU) pair is confirmed to be comoving from two epochs of high-resolution imaging. Follow-up low- and moderate-resolution near-infrared spectroscopy of 1RXS J2351+3127 B with IRTF/SpeX and Keck-II/OSIRIS reveals a spectral type of L0+2 -1. The M2 primary star 1RXS J2351+3127 A exhibits X-ray and UV activity levels comparable to young moving group members with ages of ~10-100 Myr. UVW kinematics based the measured radial velocity of the primary and the system's photometric distance (50 ± 10 pc) indicate it is likely a member of the ~50-150 Myr AB Dor moving group. The near-infrared spectrum of 1RXS J2351+3127 B does not exhibit obvious signs of youth, but its H-band morphology shows subtle hints of intermediate surface gravity. The spectrum is also an excellent match to the ~200 Myr M9 brown dwarf LP 944-20. Assuming an age of 50-150 Myr, evolutionary models imply a mass of 32 ± 6 M Jup for the companion, making 1RXS J2351+3127 B the second lowest-mass member of the AB Dor moving group after the L4 companion CD-35 2722 B and one of the few benchmark brown dwarfs known at young ages. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  13. THE DYNAMICAL EVOLUTION OF LOW-MASS HYDROGEN-BURNING STARS, BROWN DWARFS, AND PLANETARY-MASS OBJECTS FORMED THROUGH DISK FRAGMENTATION

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yun; Kouwenhoven, M. B. N. [Department of Astronomy, School of Physics, Peking University, Yiheyuan Lu 5, Haidian Qu, Beijing 100871 (China); Stamatellos, D. [Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, University of Central Lancashire, Preston, PR1 2HE (United Kingdom); Goodwin, S. P., E-mail: yunli@pku.edu.cn [Department of Physics and Astronomy, The University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH (United Kingdom)

    2015-06-01

    Theory and simulations suggest that it is possible to form low-mass hydrogen-burning stars, brown dwarfs (BDs), and planetary-mass objects (PMOs) via disk fragmentation. As disk fragmentation results in the formation of several bodies at comparable distances to the host star, their orbits are generally unstable. Here, we study the dynamical evolution of these objects. We set up the initial conditions based on the outcomes of the smoothed-particle hydrodynamics simulations of Stamatellos and Whitworth, and for comparison we also study the evolution of systems resulting from lower-mass fragmenting disks. We refer to these two sets of simulations as set 1 and set 2, respectively. At 10 Myr, approximately half of the host stars have one companion left, and approximately 22% (set 1) to 9.8% (set 2) of the host stars are single. Systems with multiple secondaries in relatively stable configurations are common (about 30% and 44%, respectively). The majority of the companions are ejected within 1 Myr with velocities mostly below 5 km s{sup −1}, with some runaway escapers with velocities over 30 km s{sup −1}. Roughly 6% (set 1) and 2% (set 2) of the companions pair up into very low-mass binary systems, resulting in respective binary fractions of 3.2% and 1.2%. The majority of these pairs escape as very low-mass binaries, while others remain bound to the host star in hierarchical configurations (often with retrograde inner orbits). Physical collisions with the host star (0.43 and 0.18 events per host star for set 1 and set 2, respectively) and between companions (0.08 and 0.04 events per host star for set 1 and set 2, respectively) are relatively common and their frequency increases with increasing disk mass. Our study predicts observable properties of very low-mass binaries, low-mass hierarchical systems, the BD desert, and free-floating BDs and PMOs in and near young stellar groupings, which can be used to distinguish between different formation scenarios of very low

  14. DISCOVERY OF A GAS-RICH COMPANION TO THE EXTREMELY METAL-POOR GALAXY DDO 68

    Energy Technology Data Exchange (ETDEWEB)

    Cannon, John M.; Alfvin, Erik D. [Department of Physics and Astronomy, Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105 (United States); Johnson, Megan; Koribalski, Baerbel [Australia Telescope National Facility, CSIRO Astronomy and Space Science, P.O. Box 76, NSW 1710, Epping (Australia); McQuinn, Kristen B. W.; Skillman, Evan D. [Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN 55455 (United States); Bailin, Jeremy [Department of Physics and Astronomy, University of Alabama, P.O. Box 870324, Tuscaloosa, AL 35487-0324 (United States); Ford, H. Alyson [National Radio Astronomy Observatory, P.O. Box 2, Green Bank, WV 24944 (United States); Girardi, Léo [Osservatorio Astronomico di Padova—INAF, Vicolo dell' Osservatorio 5, I-35122 Padova (Italy); Hirschauer, Alec S.; Janowiecki, Steven; Salzer, John J.; Van Sistine, Angela [Department of Astronomy, Indiana University, 727 East Third Street, Bloomington, IN 47405 (United States); Dolphin, Andrew [Raytheon Company, 1151 E. Hermans Road, Tucson, AZ 85756 (United States); Elson, E. C. [Astrophysics, Cosmology and Gravity Centre (ACGC), Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701 (South Africa); Marigo, Paola; Rosenfield, Philip [Dipartimento di Fisica e Astronomia Galileo Galilei, Universitá degli Studi di Padova, Vicolo dell' Osservatorio 3, I-35122 Padova (Italy); Rosenberg, Jessica L. [School of Physics, Astronomy, and Computational Science, George Mason University, Fairfax, VA 22030 (United States); Venkatesan, Aparna [Department of Physics and Astronomy, University of San Francisco, 2130 Fulton Street, San Francisco, CA 94117 (United States); Warren, Steven R., E-mail: jcannon@macalester.edu [Department of Astronomy, University of Maryland, CSS Bldg., Rm. 1024, Stadium Drive, College Park, MD 20742-2421 (United States)

    2014-05-20

    We present H I spectral-line imaging of the extremely metal-poor galaxy DDO 68. This system has a nebular oxygen abundance of only ∼3% Z {sub ☉}, making it one of the most metal-deficient galaxies known in the local volume. Surprisingly, DDO 68 is a relatively massive and luminous galaxy for its metal content, making it a significant outlier in the mass-metallicity and luminosity-metallicity relationships. The origin of such a low oxygen abundance in DDO 68 presents a challenge for models of the chemical evolution of galaxies. One possible solution to this problem is the infall of pristine neutral gas, potentially initiated during a gravitational interaction. Using archival H I spectral-line imaging obtained with the Karl G. Jansky Very Large Array, we have discovered a previously unknown companion of DDO 68. This low-mass (M{sub H} {sub I} = 2.8 × 10{sup 7} M {sub ☉}), recently star-forming (SFR{sub FUV} = 1.4 × 10{sup –3} M {sub ☉} yr{sup –1}, SFR{sub Hα} < 7 × 10{sup –5} M {sub ☉} yr{sup –1}) companion has the same systemic velocity as DDO 68 (V {sub sys} = 506 km s{sup –1}; D = 12.74 ± 0.27 Mpc) and is located at a projected distance of ∼42 kpc. New H I maps obtained with the 100 m Robert C. Byrd Green Bank Telescope provide evidence that DDO 68 and this companion are gravitationally interacting at the present time. Low surface brightness H I gas forms a bridge between these objects.

  15. A high-resolution VLT/FLAMES study of individual stars in the centre of the Fornax dwarf spheroidal galaxy

    NARCIS (Netherlands)

    Letarte, B.; Hill, V.; Tolstoy, E.; Jablonka, P.; Shetrone, M.; Venn, K. A.; Spite, M.; Irwin, M. J.; Battaglia, G.; Helmi, A.; Primas, F.; François, P.; Kaufer, A.; Szeifert, T.; Arimoto, N.; Sadakane, K.

    2010-01-01

    For the first time we show the detailed, late-stage, chemical evolution history of a small nearby dwarf spheroidal galaxy in the Local Group. We present the results of a high-resolution (R similar to 20 000, lambda = 5340-5620; 6120-6701) FLAMES/GIRAFFE abundance study at ESO/VLT of 81

  16. Numerical Simulations of Gaseous Disks Generated from Collisional Cascades at the Roche Limits of White Dwarf Stars

    Science.gov (United States)

    Kenyon, Scott J.; Bromley, Benjamin C.

    2017-11-01

    We consider the long-term evolution of gaseous disks fed by the vaporization of small particles produced in a collisional cascade inside the Roche limit of a 0.6 {M}⊙ white dwarf. Adding solids with radius {r}0 at a constant rate {\\dot{M}}0 into a narrow annulus leads to two distinct types of evolution. When {\\dot{M}}0≳ {\\dot{M}}0,{crit}≈ 3× {10}4 {({r}0/1{km})}3.92 {{g}} {{{s}}}-1, the cascade generates a fairly steady accretion disk where the mass transfer rate of gas onto the white dwarf is roughly {\\dot{M}}0 and the mass in gas is {M}g≈ 2.3× {10}22 ({\\dot{M}}0/{10}10 {{g}} {{{s}}}-1) (1500 {{K}}/{T}0) ({10}-3/α ) g, where T 0 is the temperature of the gas near the Roche limit and α is the dimensionless viscosity parameter. If {\\dot{M}}0≲ {\\dot{M}}0,{crit}, the system alternates between high states with large mass transfer rates and low states with negligible accretion. Although either mode of evolution adds significant amounts of metals to the white dwarf photosphere, none of our calculations yield a vertically thin ensemble of solids inside the Roche limit. X-ray observations can place limits on the mass transfer rate and test this model for metallic line white dwarfs.

  17. VERY LOW MASS STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE STARS FROM MARVELS. IV. A CANDIDATE BROWN DWARF OR LOW-MASS STELLAR COMPANION TO HIP 67526

    International Nuclear Information System (INIS)

    Jiang Peng; Ge Jian; De Lee, Nathan; Fleming, Scott W.; Lee, Brian L.; Ma Bo; Wang, Ji; Cargile, Phillip; Hebb, Leslie; Stassun, Keivan G.; Crepp, Justin R.; Porto de Mello, Gustavo F.; Ferreira, Letícia D.; Esposito, Massimiliano; Femenia, Bruno; González Hernández, Jonay I.; Gaudi, B. Scott; Ghezzi, Luan; Wisniewski, John P.; Agol, Eric

    2013-01-01

    We report the discovery of a candidate brown dwarf (BD) or a very low mass stellar companion (MARVELS-5b) to the star HIP 67526 from the Multi-object Apache point observatory Radial Velocity Exoplanet Large-area Survey (MARVELS). The radial velocity curve for this object contains 31 epochs spread over 2.5 yr. Our Keplerian fit, using a Markov Chain Monte Carlo approach, reveals that the companion has an orbital period of 90.2695 +0.0188 -0.0187 days, an eccentricity of 0.4375 ± 0.0040, and a semi-amplitude of 2948.14 +16.65 -16.55 m s –1 . Using additional high-resolution spectroscopy, we find the host star has an effective temperature T eff = 6004 ± 34 K, a surface gravity log g (cgs) =4.55 ± 0.17, and a metallicity [Fe/H] =+0.04 ± 0.06. The stellar mass and radius determined through the empirical relationship of Torres et al. yields 1.10 ± 0.09 M ☉ and 0.92 ± 0.19 R ☉ . The minimum mass of MARVELS-5b is 65.0 ± 2.9M Jup , indicating that it is likely to be either a BD or a very low mass star, thus occupying a relatively sparsely populated region of the mass function of companions to solar-type stars. The distance to this system is 101 ± 10 pc from the astrometric measurements of Hipparcos. No stellar tertiary is detected in the high-contrast images taken by either FastCam lucky imaging or Keck adaptive optics imaging, ruling out any star with mass greater than 0.2 M ☉ at a separation larger than 40 AU

  18. What fraction of white dwarfs are members of binary systems?

    International Nuclear Information System (INIS)

    Holberg, J B

    2009-01-01

    White dwarfs were originally discovered as the subordinate faint companions of bright nearby stars (i.e. Sirius B and 40 Eri B). Several general categories of binary systems involving white dwarfs are recognized: Sirius-like systems, where the white dwarf may be difficult to detect, binary systems containing white dwarfs and low mass stars, where the white dwarf is often readily discerned; and double degenerate systems. Different modes of white dwarf discovery influence our perception of both the overall binary fraction and the nature of these systems; proper motion surveys emphasize resolved systems, while photometric surveys emphasize unresolved systems containing relatively hot white dwarfs. Recent studies of the local white dwarf population offer some hope of achieving realistic estimates of the relative number of binary systems containing white dwarfs. A sample of 132 white dwarfs within 20 pc indicates that an individual white dwarf has a probability of 32 ± 8% of occurring within a binary or multiple star system.

  19. UTILIZING SYNTHETIC UV SPECTRA TO EXPLORE THE PHYSICAL BASIS FOR THE CLASSIFICATION OF LAMBDA BOÖTIS STARS

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, Kwang-Ping; Johnson, Dustin M.; Tarbell, Erik S.; Romo, Christopher A.; Prabhaker, Arvind [Cal. State Univ., Fullerton, Fullerton, CA (United States); Neff, James E.; Steele, Patricia A. [College of Charleston, Charleston, SC (United States); Gray, Richard O. [Appalachian State Univ., Boone, NC (United States); Corbally, Christopher J. [Vatican Observatory, Tucson, AZ (United States)

    2016-04-15

    Lambda Boo-type stars are a group of late B to early F-type Population I dwarfs that show mild to extreme deficiencies of iron-peak elements (up to 2 dex), but their C, N, O, and S abundances are near solar. This intriguing stellar class has recently regained the spotlight because of the directly imaged planets around a confirmed Lambda Boo star, HR 8799, and a suggested Lambda Boo star, Beta Pictoris. The discovery of a giant asteroid belt around Vega, another possible Lambda Boo star, also suggests hidden planets. The possible link between Lambda Boo stars and planet-bearing stars motivates us to study Lambda Boo stars systematically. Since the peculiar nature of the prototype Lambda Boötis was first noticed in 1943, Lambda Boo candidates published in the literature have been selected using widely different criteria. In order to determine the origin of Lambda Boo stars’ unique abundance pattern and to better discriminate between theories explaining the Lambda Boo phenomenon, a consistent working definition of Lambda Boo stars is needed. We have re-evaluated all published Lambda Boo candidates and their available ultraviolet and visible spectra. In this paper, using observed and synthetic spectra, we explore the physical basis for the classification of Lambda Boo stars, and develop quantitative criteria that discriminate metal-poor stars from bona fide Lambda Boo stars. Based on these stricter Lambda Boo classification criteria, we conclude that neither Beta Pictoris nor Vega should be classified as Lambda Boo stars.

  20. VizieR Online Data Catalog: Abundances of two very metal-poor stars (Afsar+, 2016)

    Science.gov (United States)

    Afsar, M.; Sneden, C.; Frebel, A.; Kim, H.; Mace, G. N.; Kaplan, K. F.; Lee, H.-I.; Oh, H.; Oh, J. S.; Pak, S.; Park, C.; Pavel, M. D.; Yuk, I.-S.; Jaffe, D. T.

    2016-05-01

    We obtained high-resolution (R~45000), high S/N (S/N>400, per resolution element) spectra of HD 122563 and HD 140283 with the H and K band Immersion Grating Infrared Spectrograph (IGRINS) during an instrument commissioning run on the night of 2014 May 23 at the McDonald Observatory with the 2.7m Smith Telescope. (3 data files).

  1. The Pristine survey - I. Mining the Galaxy for the most metal-poor stars

    NARCIS (Netherlands)

    Starkenburg, Else; Martin, Nicolas; Youakim, Kris; Aguado, David S.; Allende Prieto, Carlos; Arentsen, Anke; Bernard, Edouard J.; Bonifacio, Piercarlo; Caffau, Elisabetta; Carlberg, Raymond G.; Côté, Patrick; Fouesneau, Morgan; François, Patrick; Franke, Oliver; González Hernández, Jonay I.; Gwyn, Stephen D. J.; Hill, Vanessa; Ibata, Rodrigo A.; Jablonka, Pascale; Longeard, Nicolas; McConnachie, Alan W.; Navarro, Julio F.; Sánchez-Janssen, Rubén; Tolstoy, Eline; Venn, Kim A.

    2017-01-01

    We present the Pristine survey, a new narrow-band photometric survey focused on the metallicity-sensitive Ca H&K lines and conducted in the Northern hemisphere with the wide-field imager MegaCam on the Canada-France-Hawaii Telescope. This paper reviews our overall survey strategy and discusses the

  2. Non-local thermodynamic equilibrium stellar spectroscopy with 1D and 3D models - II. Chemical properties of the Galactic metal-poor disk and the halo

    DEFF Research Database (Denmark)

    Bergemann, Maria; Collet, Remo; Schönrich, Ralph

    2016-01-01

    We have analysed high-resolution spectra of 328 stars and derived Mg abundances using non-local thermodynamic equilibrium (NLTE) spectral line formation calculations and plane-parallel model stellar atmospheres derived from the mean stratification of 3D hydrodynamical surface convection simulations...... of late-type stars. The distribution of Mg abundances in the Galactic disk is analysed from the perspective of Galactic chemical evolution. We find that the trend of [Mg/Fe] shows a mild decline with decreasing metallicity below [Fe/H]~-1.2 and that a significant fraction of low-metallicity stars have [Mg....../Fe] ratios close to solar even at [Fe/H] ~ -2. This is at variance with results of classical abundance analyses based on local thermodynamic equilibrium (LTE) and 1D model stellar atmospheres, which argue for a constant elevated [Mg/Fe] in metal-poor stars of the Galactic thick disk and halo....

  3. The Distance to M54 using Infrared Photometry of RR Lyrae Variable Stars and the Implications of its Relation to the Sagittarius Dwarf Galaxy

    Science.gov (United States)

    Gupta, Arvind F.; Beaton, Rachael L.; Majewski, Steven R.; SMHASH Team

    2018-01-01

    CDM cosmological models predict that dark matter halo density profiles will have central cusps. Yet for many dwarf spheroidal galaxies (dSphs), this expectation is in contrast with observations of cored, rather than cusped, halos. This 'cusp-core problem' is apparent in the Sagittarius Dwarf Galaxy (Sgr), one of the largest satellites of the Milky Way. The globular cluster M54, one of several clusters associated with Sgr, coincides in on-sky position with the center of the main body of Sgr. While several studies find that M54 lies within the center of Sgr, other findings show that M54 is offset from the center by several kiloparsecs along our line of sight. The latter requires Sgr to have a cored dark matter distribution. In the presence of a cuspy halo, the orbit of M54 would have decayed via dynamical friction and the cluster would have fallen to the center of Sgr. A clear determination of the relation of the two bodies may help us better understand the distribution of dark matter in Sgr and other dSphs. Here we present a measurement of the distance modulus to M54 using a set of RR Lyrae variable stars in near-infrared Magellan data mid-infrared Spitzer data. The magnitudes of individual stars are measured using multi-epoch PSF photometry and light curve fitting. From precise RR Lyrae period-luminosity relations at these wavelengths, we then find the mean M54 distance modulus to be 17.126 ± 0.023 (ran) ± 0.080 (sys). Our result is consistent with a distance measurement to Sgr derived via nearly identical methods and thus also consistent with the expectation of a central cusp in the dark matter density profile of Sgr.

  4. Disentangling the Galactic Halo with APOGEE. I. Chemical and Kinematical Investigation of Distinct Metal-poor Populations

    Science.gov (United States)

    Hayes, Christian R.; Majewski, Steven R.; Shetrone, Matthew; Fernández-Alvar, Emma; Allende Prieto, Carlos; Schuster, William J.; Carigi, Leticia; Cunha, Katia; Smith, Verne V.; Sobeck, Jennifer; Almeida, Andres; Beers, Timothy C.; Carrera, Ricardo; Fernández-Trincado, J. G.; García-Hernández, D. A.; Geisler, Doug; Lane, Richard R.; Lucatello, Sara; Matthews, Allison M.; Minniti, Dante; Nitschelm, Christian; Tang, Baitian; Tissera, Patricia B.; Zamora, Olga

    2018-01-01

    We find two chemically distinct populations separated relatively cleanly in the [Fe/H]–[Mg/Fe] plane, but also distinguished in other chemical planes, among metal-poor stars (primarily with metallicities [{Fe}/{{H}}]C+N, Al, and Ni. In addition to these populations having differing chemistry, the low metallicity high-Mg population (which we denote “the HMg population”) exhibits a significant net Galactic rotation, whereas the low-Mg population (or “the LMg population”) has halo-like kinematics with little to no net rotation. Based on its properties, the origin of the LMg population is likely an accreted population of stars. The HMg population shows chemistry (and to an extent kinematics) similar to the thick disk, and is likely associated with in situ formation. The distinction between the LMg and HMg populations mimics the differences between the populations of low- and high-α halo stars found in previous studies, suggesting that these are samples of the same two populations.

  5. Enrichment in r-process Elements from Multiple Distinct Events in the Early Draco Dwarf Spheroidal Galaxy

    Science.gov (United States)

    Tsujimoto, Takuji; Matsuno, Tadafumi; Aoki, Wako; Ishigaki, Miho N.; Shigeyama, Toshikazu

    2017-11-01

    The stellar record of elemental abundances in satellite galaxies is important to identify the origin of r-process because such a small stellar system could have hosted a single r-process event, which would distinguish member stars that are formed before and after the event through the evidence of a considerable difference in the abundances of r-process elements, as found in the ultra-faint dwarf galaxy Reticulum II (Ret II). However, the limited mass of these systems prevents us from collecting information from a sufficient number of stars in individual satellites. Hence, it remains unclear whether the discovery of a remarkable r-process enrichment event in Ret II explains the nature of r-process abundances or is an exception. We perform high-resolution spectroscopic measurements of r-process abundances for 12 metal-poor stars in the Draco dwarf galaxy in the metallicity range of -2.5populations of stars with different r-process abundances, which are built by two r-process events that enriched gases at levels that differ by more than one order of magnitude. This work is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

  6. Slowly Spinning Southern M Dwarfs

    Science.gov (United States)

    Newton, Elisabeth; Mondrik, Nicholas; Irwin, Jonathan; Charbonneau, David

    2018-01-01

    M dwarf stars are the most common type of star in the galaxy, but their ages are challenging to determine due to their trillion-year lifetimes on the main sequence. Consequently, the evolution of rotation and magnetism at field ages is difficult to investigate observationally. M dwarfs in the Solar Neighborhood provide a unique opportunity to make progress in this area due to the availability of parallaxes and the accessibility of spectroscopy. We have used new rotation period measurements and our compilation of H-alpha emission for nearby M dwarfs to explore two questions: 1) What is the longest rotation period an M dwarf can have? And 2) Do M dwarfs undergo an era of rapid angular momentum evolution? Here, we focus on the view from the Southern hemisphere, presenting approximately 200 new rotation periods for fully convective M dwarfs. Amongst the highest-quality datasets, we identify rotation periods in three-quarters of all stars; of these, half have rotation periods longer than 70 days. The longest rotation period we detect is 148 days, which is for a 0.15 solar-mass star. The lack of M dwarfs with intermediate rotation periods that we previously identified persists, supporting our hypothesis that M dwarfs rapidly spin down from 10-day to 100-day periods.ERN is supported by the National Science Foundation Astronomy & Astrophysics Postdoctoral Fellowship. We gratefully acknowledge support from the David and Lucille Packard Foundation, the National Science Foundation, and the John Templeton Foundation.

  7. PAndAS' PROGENY: EXTENDING THE M31 DWARF GALAXY CABAL

    International Nuclear Information System (INIS)

    Richardson, Jenny C.; Irwin, Mike J.; Chapman, Scott C.; McConnachie, Alan W.; Martin, Nicolas F.; Dotter, Aaron L.; Ferguson, Annette M. N.; Ibata, Rodrigo A.; Lewis, Geraint F.; Tanvir, Nial R.; Rich, R. Michael

    2011-01-01

    We present the discovery of five new dwarf galaxies, Andromeda XXIII-XXVII, located in the outer halo of M31. These galaxies were discovered during the second year of data from the Pan-Andromeda Archaeological Survey (PAndAS), a photometric survey of the M31/M33 subgroup conducted with the MegaPrime/MegaCam wide-field camera on the Canada-France-Hawaii Telescope. The current PAndAS survey now provides an almost complete panoramic view of the M31 halo out to an average projected radius of ∼150 kpc. Here we present for the first time the metal-poor stellar density map for this whole region, not only as an illustration of the discovery space for satellite galaxies, but also as a birds-eye view of the ongoing assembly process of an L * disk galaxy. Four of the newly discovered satellites appear as well-defined spatial overdensities of stars lying on the expected locus of metal-poor (-2.5 V = -7.1 ± 0.5 to M V = -10.2 ± 0.5. These five additional satellites bring the number of dwarf spheroidal galaxies in this region to 25 and continue the trend whereby the brighter dwarf spheroidal satellites of M31 generally have much larger half-light radii than their Milky Way counterparts. With an extended sample of M31 satellite galaxies, we also revisit the spatial distribution of this population and in particular we find that, within the current projected limits of the PAndAS survey, the surface density of satellites is essentially constant out to 150 kpc. This corresponds to a radial density distribution of satellites varying as r -1 , a result seemingly in conflict with the predictions of cosmological simulations.

  8. STELLAR PARAMETERS AND METALLICITIES OF STARS HOSTING JOVIAN AND NEPTUNIAN MASS PLANETS: A POSSIBLE DEPENDENCE OF PLANETARY MASS ON METALLICITY

    International Nuclear Information System (INIS)

    Ghezzi, L.; Cunha, K.; De Araujo, F. X.; De la Reza, R.; Smith, V. V.; Schuler, S. C.

    2010-01-01

    The metal content of planet-hosting stars is an important ingredient that may affect the formation and evolution of planetary systems. Accurate stellar abundances require the determinations of reliable physical parameters, namely, the effective temperature, surface gravity, microturbulent velocity, and metallicity. This work presents the homogeneous derivation of such parameters for a large sample of stars hosting planets (N = 117), as well as a control sample of disk stars not known to harbor giant, closely orbiting planets (N = 145). Stellar parameters and iron abundances are derived from an automated analysis technique developed for this work. As previously found in the literature, the results in this study indicate that the metallicity distribution of planet-hosting stars is more metal rich by ∼0.15 dex when compared to the control sample stars. A segregation of the sample according to planet mass indicates that the metallicity distribution of stars hosting only Neptunian-mass planets (with no Jovian-mass planets) tends to be more metal poor in comparison with that obtained for stars hosting a closely orbiting Jovian planet. The significance of this difference in metallicity arises from a homogeneous analysis of samples of FGK dwarfs which do not include the cooler and more problematic M dwarfs. This result would indicate that there is a possible link between planet mass and metallicity such that metallicity plays a role in setting the mass of the most massive planet. Further confirmation, however, must await larger samples.

  9. PAndAS' Progeny: Extending the M31 Dwarf Galaxy Cabal

    Science.gov (United States)

    Richardson, Jenny C.; Irwin, Mike J.; McConnachie, Alan W.; Martin, Nicolas F.; Dotter, Aaron L.; Ferguson, Annette M. N.; Ibata, Rodrigo A.; Chapman, Scott C.; Lewis, Geraint F.; Tanvir, Nial R.; Rich, R. Michael

    2011-05-01

    We present the discovery of five new dwarf galaxies, Andromeda XXIII-XXVII, located in the outer halo of M31. These galaxies were discovered during the second year of data from the Pan-Andromeda Archaeological Survey (PAndAS), a photometric survey of the M31/M33 subgroup conducted with the MegaPrime/MegaCam wide-field camera on the Canada-France-Hawaii Telescope. The current PAndAS survey now provides an almost complete panoramic view of the M31 halo out to an average projected radius of ~150 kpc. Here we present for the first time the metal-poor stellar density map for this whole region, not only as an illustration of the discovery space for satellite galaxies, but also as a birds-eye view of the ongoing assembly process of an L * disk galaxy. Four of the newly discovered satellites appear as well-defined spatial overdensities of stars lying on the expected locus of metal-poor (-2.5 giant branch stars at the distance of M31. The fifth overdensity, And XXVII, is embedded in an extensive stream of such stars and is possibly the remnant of a strong tidal disruption event. Based on distance estimates from horizontal branch magnitudes, all five have metallicities typical of dwarf spheroidal galaxies ranging from [Fe/H] =-1.7 ± 0.2 to [Fe/H] =-1.9 ± 0.2 and absolute magnitudes ranging from MV = -7.1 ± 0.5 to MV = -10.2 ± 0.5. These five additional satellites bring the number of dwarf spheroidal galaxies in this region to 25 and continue the trend whereby the brighter dwarf spheroidal satellites of M31 generally have much larger half-light radii than their Milky Way counterparts. With an extended sample of M31 satellite galaxies, we also revisit the spatial distribution of this population and in particular we find that, within the current projected limits of the PAndAS survey, the surface density of satellites is essentially constant out to 150 kpc. This corresponds to a radial density distribution of satellites varying as r -1, a result seemingly in conflict with

  10. The late-M dwarfs

    International Nuclear Information System (INIS)

    Bessell, M.S.

    1991-01-01

    Far-red spectra and VRIJHK photometry have been obtained for a sample of late-M dwarfs selected on the basis of large reduced red magnitudes from the LHS Catalog. Half of the stars in the three faintest 1 mag bins are late-M stars, the other red stars are metallic-hydride subdwarfs. Relations between various colors for the late-M dwarfs are investigated. Of all the colors I - K most reliably correlates with spectral type. FeH bands near 9900 A are clearly seen in the spectra of all dwarf stars later than M5. Two stars cooler than VB10, and similar in temperature to LHS2924 have been identified; both have H-alpha in emission and appear variable in magnitude and R - I color; one is a flare star. The other stars are of earlier spectral type and resemble W359 and VB8. The observed MI, I - K main sequence is in good agreement with the IG theoretical main sequence of Stringfellow, and the faintest stars could be about 0.09 solar mass red dwarfs or lower mass brown dwarfs. 65 refs

  11. Chemical analysis of carbon stars in the local group - l.  The small magnetic cloud and the Sagittarius Dwarf Spheroidal galaxy

    DEFF Research Database (Denmark)

    de Laverny...[], P.; Abia, C.; Dominguez, I

    2006-01-01

    Stars: abundances, stars: carbon, nuclear reactions, nucleosynthesis, abundances, galaxies: Local Group Udgivelsesdato: Feb.......Stars: abundances, stars: carbon, nuclear reactions, nucleosynthesis, abundances, galaxies: Local Group Udgivelsesdato: Feb....

  12. The Dwarf Project: Vidojevica

    Science.gov (United States)

    Vince, O.

    2013-05-01

    The DWARF project is an important international project for observing eclipsing binary stars and searching for third companion which orbit around both stars. Recently, a group of researchers at the Astronomical Observatory of Belgrade joined this project using the 60 cm telescope at the Astronomical Station Vidojevica for observations. All the equipment and the human potential involved with this project from Serbia will be described in this paper.

  13. The evolution of C/O in dwarf galaxies from Hubble Space Telescope FOS observations

    Science.gov (United States)

    Garnett, D. R.; Skillman, E. D.; Dufour, R. J.; Peimbert, M.; Torres-Peimbert, S.; Terlevich, R.; Terlevich, E.; Shields, G. A.

    1995-01-01

    We present UV observations of seven H II regions in low-luminosity dwarf irregular galaxies and the Magellanic Clouds obtained with the Faint Object Spectrograph (FOS) on the Hubble Space Telescope (HST) in order to measure the C/O abundance ratio in the interstellar medium (ISM) of those galaxies. We measure both O III 1666 A and C III 1909 A in our spectra, enabling us to determine C(+2)/O(+2) with relatively small uncertainties. The results from our HST observations show a continuous increase in C/O with increasing O/H, consistent with a power law having an index of 0.43 +/- 0.09 over the range -4.7 to -3.6 in log (O/H). One possible interpretation of this trend is that the most metal-poor galaxies are the youngest and dominated by the products of early enrichment by massive stars, while more metal-rich galaxies show increasing, delayed contributions of carbon from intermediate-mass stars. Our results also suggest that it may not be appropiate to combine abundances in irregular galaxies with those in spiral galaxies to study the evolution of chemical abundances. Our measured C/O ratios in the most metal-poor galaxies are consistent with predictions of nucleosynthesis from massive stars for Weaver & Woosley's best estimate for the 12C(alpha, gamma) 16O nuclear reaction rate, assuming negligible contanmination from carbon produced in intermediate-mass stars in these galaxies. We detect a weak N III 1750 A multiplet in SMC N88A and obtain interesting upper limits for two other objects. Our 2 sigma uppr limits on the 1750 A feature indicate that the N(+2)/O(+2) ratios in these objects are not significantly larger than the N(+)/O(+) ratios measured from optical spectra. This behavior is consistent with predictions of photionization models, although better detections of N III are needed to confirm the results.

  14. Non-LTE line-blanketed model atmospheres of hot stars. 2: Hot, metal-rich white dwarfs

    Science.gov (United States)

    Lanz, T.; Hubeny, I.

    1995-01-01

    We present several model atmospheres for a typical hot metal-rich DA white dwarf, T(sub eff) = 60,000 K, log g = 7.5. We consider pure hydrogen models, as well as models with various abundances of two typical 'trace' elements-carbon and iron. We calculte a number of Local Thermodynamic Equilibrium (LTE) and non-LTE models, taking into account the effect of numerous lines of these elements on the atmospheric structure. We demostrate that while the non-LTE effects are notvery significant for pure hydrogen models, except for describing correctly the central emission in H-alpha they are essential for predicting correctly the ionization balance of metals, such as carbon and iron. Previously reported discrepancies in LTE abundances determinations using C III and C IV lines are easily explained by non-LTE effects. We show that if the iron abundance is larger than 10(exp -5), the iron line opacity has to be considered not only for the spectrum synthesis, but also in the model construction itself. For such metal abundances, non-LTE metal line-blanketed models are needed for detailed abundance studies of hot, metal-rich white dwarfs. We also discuss the predicted Extreme Ultraviolet (EUV) spectrum and show that it is very sensitive to metal abundances, as well as to non-LTE effects.

  15. Predicting the locations of possible long-lived low-mass first stars: importance of satellite dwarf galaxies

    Science.gov (United States)

    Magg, Mattis; Hartwig, Tilman; Agarwal, Bhaskar; Frebel, Anna; Glover, Simon C. O.; Griffen, Brendan F.; Klessen, Ralf S.

    2018-02-01

    The search for metal-free stars has so far been unsuccessful, proving that if there are surviving stars from the first generation, they are rare, they have been polluted or we have been looking in the wrong place. To predict the likely location of Population III (Pop III) survivors, we semi-analytically model early star formation in progenitors of Milky Way-like galaxies and their environments. We base our model on merger trees from the high-resolution dark matter only simulation suite Caterpillar. Radiative and chemical feedback are taken into account self-consistently, based on the spatial distribution of the haloes. Our results are consistent with the non-detection of Pop III survivors in the Milky Way today. We find that possible surviving Pop III stars are more common in Milky Way satellites than in the main Galaxy. In particular, low-mass Milky Way satellites contain a much larger fraction of Pop III stars than the Milky Way. Such nearby, low-mass Milky Way satellites are promising targets for future attempts to find Pop III survivors, especially for high-resolution, high signal-to-noise spectroscopic observations. We provide the probabilities of finding a Pop III survivor in the red giant branch phase for all known Milky Way satellites to guide future observations.

  16. Stars

    CERN Document Server

    Hansen, Grace

    2017-01-01

    This title will cover how stars form, different types of stars, their lifecycle, and the most important star to us--the Sun! Aligned to Common Core Standards and correlated to state standards. Abdo Kids Jumbo is an imprint of Abdo Kids, a division of ABDO.

  17. The VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits . III. The frequency of brown dwarfs and giant planets as companions to solar-type stars

    Science.gov (United States)

    Reggiani, M.; Meyer, M. R.; Chauvin, G.; Vigan, A.; Quanz, S. P.; Biller, B.; Bonavita, M.; Desidera, S.; Delorme, P.; Hagelberg, J.; Maire, A.-L.; Boccaletti, A.; Beuzit, J.-L.; Buenzli, E.; Carson, J.; Covino, E.; Feldt, M.; Girard, J.; Gratton, R.; Henning, T.; Kasper, M.; Lagrange, A.-M.; Mesa, D.; Messina, S.; Montagnier, G.; Mordasini, C.; Mouillet, D.; Schlieder, J. E.; Segransan, D.; Thalmann, C.; Zurlo, A.

    2016-02-01

    Context. In recent years there have been many attempts to characterize the occurrence and distribution of stellar, brown dwarf (BD), and planetary-mass companions to solar-type stars with the aim of constraining formation mechanisms. From radial velocity observations a dearth of companions with masses between 10-40 MJupiter has been noticed at close separations, suggesting the possibility of a distinct formation mechanism for objects above and below this range. Aims: We present a model for the substellar companion mass function (CMF). This model consists of the superposition of the planet and BD companion mass distributions, assuming that we can extrapolate the radial velocity measured CMF for planets to larger separations and the stellar companion mass-ratio distribution over all separations into the BD mass regime. By using both the results of the VLT/NaCo large program (NaCo-LP) and the complementary archive datasets, which probe the occurrence of planets and BDs on wide orbits around solar-type stars, we place some constraints on the planet and BD distributions. Methods: We developed a Monte Carlo simulation tool to predict the outcome of a given survey, depending on the shape of the orbital parameter distributions (mass, semimajor axis, eccentricity, and inclination). Comparing the predictions with the results of the observations, we calculate the likelihood of different models and which models can be ruled out. Results: Current observations are consistent with the proposed model for the CMF, as long as a sufficiently small outer truncation radius (≲100 AU) is introduced for the planet separation distribution. Some regions of parameter space can be excluded by the observations. Conclusions: We conclude that the results of the direct imaging surveys searching for substellar companions around Sun-like stars are consistent with a combined substellar mass spectrum of planets and BDs. This mass distribution has a minimum between 10 and 50 MJupiter, in agreement

  18. LUMINOUS SUPERNOVA-LIKE UV/OPTICAL/INFRARED TRANSIENTS ASSOCIATED WITH ULTRA-LONG GAMMA-RAY BURSTS FROM METAL-POOR BLUE SUPERGIANTS

    Energy Technology Data Exchange (ETDEWEB)

    Kashiyama, Kazumi; Yajima, Hidenobu [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States); Nakauchi, Daisuke; Nakamura, Takashi [Department of Physics, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502 (Japan); Suwa, Yudai, E-mail: kzk15@psu.edu [Yukawa Institute for Theoretical Physics, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502 (Japan)

    2013-06-10

    Metal-poor massive stars typically end their lives as blue supergiants (BSGs). Gamma-ray bursts (GRBs) from such progenitors could have an ultra-long duration of relativistic jets. For example, Population III (Pop III) GRBs at z {approx} 10-20 might be observable as X-ray-rich events with a typical duration of T{sub 90} {approx} 10{sup 4}(1 + z) s. The recent GRB111209A at z = 0.677 has an ultra-long duration of T{sub 90} {approx} 2.5 Multiplication-Sign 10{sup 4} s and it has been suggested that its progenitor might have been a metal-poor BSG in the local universe. Here, we suggest that luminous UV/optical/infrared emission is associated with this new class of GRBs from metal-poor BSGs. Before the jet head breaks out of the progenitor envelope, the energy injected by the jet is stored in a hot plasma cocoon, which finally emerges and expands as a baryon-loaded fireball. We show that the photospheric emissions from the cocoon fireball could be intrinsically very bright (L{sub peak} {approx} 10{sup 42}-10{sup 44} erg s{sup -1}) in UV/optical bands ({epsilon}{sub peak} {approx} 10 eV) with a typical duration of {approx}100 days in the rest frame. Such cocoon emissions from Pop III GRBs might be detectable in infrared bands at {approx}years after Pop III GRBs at up to z {approx} 15 by upcoming facilities such as the James Webb Space Telescope. We also suggest that GRB111209A might have been rebrightening in UV/optical bands up to an AB magnitude of {approx}< 26. The cocoon emission from local metal-poor BSGs might have been observed previously as luminous supernovae without GRBs since they can be seen from the off-axis direction of the jet.

  19. Luminous Supernova-like UV/Optical/Infrared Transients Associated with Ultra-long Gamma-Ray Bursts from Metal-poor Blue Supergiants

    Science.gov (United States)

    Kashiyama, Kazumi; Nakauchi, Daisuke; Suwa, Yudai; Yajima, Hidenobu; Nakamura, Takashi

    2013-06-01

    Metal-poor massive stars typically end their lives as blue supergiants (BSGs). Gamma-ray bursts (GRBs) from such progenitors could have an ultra-long duration of relativistic jets. For example, Population III (Pop III) GRBs at z ~ 10-20 might be observable as X-ray-rich events with a typical duration of T 90 ~ 104(1 + z) s. The recent GRB111209A at z = 0.677 has an ultra-long duration of T 90 ~ 2.5 × 104 s and it has been suggested that its progenitor might have been a metal-poor BSG in the local universe. Here, we suggest that luminous UV/optical/infrared emission is associated with this new class of GRBs from metal-poor BSGs. Before the jet head breaks out of the progenitor envelope, the energy injected by the jet is stored in a hot plasma cocoon, which finally emerges and expands as a baryon-loaded fireball. We show that the photospheric emissions from the cocoon fireball could be intrinsically very bright (L peak ~ 1042-1044 erg s-1) in UV/optical bands (ɛpeak ~ 10 eV) with a typical duration of ~100 days in the rest frame. Such cocoon emissions from Pop III GRBs might be detectable in infrared bands at ~years after Pop III GRBs at up to z ~ 15 by upcoming facilities such as the James Webb Space Telescope. We also suggest that GRB111209A might have been rebrightening in UV/optical bands up to an AB magnitude of <~ 26. The cocoon emission from local metal-poor BSGs might have been observed previously as luminous supernovae without GRBs since they can be seen from the off-axis direction of the jet.

  20. FIRST DIRECT EVIDENCE THAT BARIUM DWARFS HAVE WHITE DWARF COMPANIONS

    International Nuclear Information System (INIS)

    Gray, R. O.; McGahee, C. E.; Griffin, R. E. M.; Corbally, C. J.

    2011-01-01

    Barium II (Ba) stars are chemically peculiar F-, G-, and K-type objects that show enhanced abundances of s-process elements. Since s-process nucleosynthesis is unlikely to take place in stars prior to the advanced asymptotic giant branch (AGB) stage, the prevailing hypothesis is that each present Ba star was contaminated by an AGB companion which is now a white dwarf (WD). Unless the initial mass ratio of such a binary was fairly close to unity, the receiving star is thus at least as likely to be a dwarf as a giant. So although most known Ba stars appear to be giants, the hypothesis requires that Ba dwarfs be comparably plentiful and moreover that they should all have WD companions. However, despite dedicated searches with the IUE satellite, no WD companions have been directly detected to date among the classical Ba dwarfs, even though some 90% of those stars are spectroscopic binaries, so the contamination hypothesis is therefore presently in some jeopardy. In this paper, we analyze recent deep, near-UV and far-UV Galaxy Evolution Explorer (GALEX) exposures of four of the brightest of the class (HD 2454, 15360, 26367, and 221531), together with archived GALEX data for two newly recognized Ba dwarfs: HD 34654 and HD 114520 (which also prove to be spectroscopic binaries). The GALEX observations of the Ba dwarfs as a group show a significant far-UV excess compared to a control sample of normal F-type dwarfs. We suggest that this ensemble far-UV excess constitutes the first direct evidence that Ba dwarfs have WD companions.

  1. Emission line diagnostics for accretion and outflows in young very low-mass stars and brown dwarfs

    Directory of Open Access Journals (Sweden)

    Stelzer B.

    2014-01-01

    Full Text Available We discuss accretion and outflow properties of three very low-mass young stellar objects based on broad-band mid-resolution X-Shooter/VLT spectra. Our targets (FU Tau A, 2M1207-39, and Par-Lup3-4 have spectral types between M5 and M8, ages between 1Myr and ~ 10Myr, and are known to be accreting from previous studies. The final objective of our project is the determination of mass outflow to accretion rate for objects near or within the substellar regime as a probe for the T Tauri phase of brown dwarfs and the investigation of variability in the accretion and outflow processes.

  2. Satellite dwarf galaxies in a hierarchical universe: the prevalence of dwarf-dwarf major mergers

    International Nuclear Information System (INIS)

    Deason, Alis; Wetzel, Andrew; Garrison-Kimmel, Shea

    2014-01-01

    Mergers are a common phenomenon in hierarchical structure formation, especially for massive galaxies and clusters, but their importance for dwarf galaxies in the Local Group remains poorly understood. We investigate the frequency of major mergers between dwarf galaxies in the Local Group using the ELVIS suite of cosmological zoom-in dissipationless simulations of Milky Way- and M31-like host halos. We find that ∼10% of satellite dwarf galaxies with M star > 10 6 M ☉ that are within the host virial radius experienced a major merger of stellar mass ratio closer than 0.1 since z = 1, with a lower fraction for lower mass dwarf galaxies. Recent merger remnants are biased toward larger radial distance and more recent virial infall times, because most recent mergers occurred shortly before crossing within the virial radius of the host halo. Satellite-satellite mergers also occur within the host halo after virial infall, catalyzed by the large fraction of dwarf galaxies that fell in as part of a group. The merger fraction doubles for dwarf galaxies outside of the host virial radius, so the most distant dwarf galaxies in the Local Group are the most likely to have experienced a recent major merger. We discuss the implications of these results on observable dwarf merger remnants, their star formation histories, the gas content of mergers, and massive black holes in dwarf galaxies.

  3. HIP 38939B: A NEW BENCHMARK T DWARF IN THE GALACTIC PLANE DISCOVERED WITH Pan-STARRS1

    International Nuclear Information System (INIS)

    Deacon, Niall R.; Liu, Michael C.; Magnier, Eugene A.; Bowler, Brendan P.; Burgett, W. S.; Chambers, K. C.; Flewelling, H.; Kaiser, N.; Morgan, J. S.; Sweeney, W. E.; Tonry, J. L.; Wainscoat, R. J.; Waters, C.; Redstone, Joshua; Goldman, Bertrand; Price, P. A.

    2012-01-01

    We report the discovery of a wide brown dwarf companion to the mildly metal-poor ([Fe/H] = –0.24), low Galactic latitude (b = 1. 0 88) K4V star HIP 38939. The companion was discovered by its common proper motion with the primary and its red optical (Pan-STARRS1) and blue infrared (Two Micron All Sky Survey) colors. It has a projected separation of 1630 AU and a near-infrared spectral type of T4.5. As such it is one of only three known companions to a main-sequence star which have early/mid T spectral types of (the others being HN Peg B and ε Indi B). Using chromospheric activity we estimate an age for the primary of 900± 1900 600 Myr. This value is also in agreement with the age derived from the star's weak ROSAT detection. Comparison with evolutionary models for this age range indicates that HIP 38939B falls in the mass range 38 ± 20 M Jup with an effective temperature range of 1090 ± 60 K. Fitting our spectrum with atmospheric models gives a best-fitting temperature of 1100 K. We include our object in an analysis of the population of benchmark T dwarfs and find that while older atmospheric models appeared to overpredict the temperature of the coolest objects compared to evolutionary models, more recent atmospheric models provide better agreement.

  4. A PLANETARY SYSTEM AROUND THE NEARBY M DWARF GJ 667C WITH AT LEAST ONE SUPER-EARTH IN ITS HABITABLE ZONE

    Energy Technology Data Exchange (ETDEWEB)

    Anglada-Escude, Guillem; Butler, R. Paul [Carnegie Institution of Washington, Department of Terrestrial Magnetism, 5241 Broad Branch Rd. NW, Washington, DC 20015 (United States); Arriagada, Pamela; Minniti, Dante [Department of Astronomy, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile); Vogt, Steven S.; Rivera, Eugenio J. [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States); Crane, Jeffrey D.; Shectman, Stephen A.; Thompson, Ian B. [Carnegie Observatories, 813 Santa Barbara St., Pasadena, CA 91101-1292 (United States); Haghighipour, Nader [Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii-Monoa, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Carter, Brad D. [Faculty of Sciences, University of Southern Queensland, Toowoomba 4350 (Australia); Tinney, C. G.; Wittenmyer, Robert A.; Bailey, Jeremy A. [Department of Astrophysics, School of Physics, University of New South Wales, Sydney 2052 (Australia); O' Toole, Simon J. [Australian Astronomical Observatory, P.O. Box 296, Epping 1710 (Australia); Jones, Hugh R. A. [Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Herts, AL10 9AB (United Kingdom); Jenkins, James S., E-mail: anglada@dtm.ciw.edu [Departamento de Astronomia, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago (Chile)

    2012-05-20

    We re-analyze 4 years of HARPS spectra of the nearby M1.5 dwarf GJ 667C available through the European Southern Observatory public archive. The new radial velocity (RV) measurements were obtained using a new data analysis technique that derives the Doppler measurement and other instrumental effects using a least-squares approach. Combining these new 143 measurements with 41 additional RVs from the Magellan/Planet Finder Spectrograph and Keck/High Resolution Echelle Spectrometer spectrometers reveals three additional signals beyond the previously reported 7.2 day candidate, with periods of 28 days, 75 days, and a secular trend consistent with the presence of a gas giant (period {approx}10 years). The 28 day signal implies a planet candidate with a minimum mass of 4.5 M{sub Circled-Plus} orbiting well within the canonical definition of the star's liquid water habitable zone (HZ), that is, the region around the star at which an Earth-like planet could sustain liquid water on its surface. Still, the ultimate water supporting capability of this candidate depends on properties that are unknown such as its albedo, atmospheric composition, and interior dynamics. The 75 day signal is less certain, being significantly affected by aliasing interactions among a potential 91 day signal, and the likely rotation period of the star at 105 days detected in two activity indices. GJ 667C is the common proper motion companion to the GJ 667AB binary, which is metal-poor compared to the Sun. The presence of a super-Earth in the HZ of a metal-poor M dwarf in a triple star system supports the evidence that such worlds should be ubiquitous in the Galaxy.

  5. STELLAR ARCHEOLOGY IN THE GALACTIC HALO WITH ULTRA-FAINT DWARFS. VII. HERCULES

    Energy Technology Data Exchange (ETDEWEB)

    Musella, Ilaria; Ripepi, Vincenzo; Marconi, Marcella, E-mail: ilaria@na.astro.it, E-mail: ripepi@na.astro.it, E-mail: marcella@na.astro.it [INAF, Osservatorio Astronomico di Capodimonte, I-8013 Napoli (Italy); and others

    2012-09-10

    We present the first time-series study of the ultra-faint dwarf galaxy Hercules. Using a variety of telescope/instrument facilities we secured about 50 V and 80 B epochs. These data allowed us to detect and characterize 10 pulsating variable stars in Hercules. Our final sample includes six fundamental-mode (ab-type) and three first-overtone (c-type) RR Lyrae stars, and one Anomalous Cepheid. The average period of the ab-type RR Lyrae stars, (P{sub ab}) = 0.68 days ({sigma} = 0.03 days), places Hercules in the Oosterhoff II group, as found for almost the totality of the ultra-faint dwarf galaxies investigated so far for variability. The RR Lyrae stars were used to obtain independent estimates of the metallicity, reddening, and distance to Hercules, for which we find [Fe/H] = -2.30 {+-} 0.15 dex, E(B - V) = 0.09 {+-} 0.02 mag, and (m - M){sub 0} = 20.6 {+-} 0.1 mag, in good agreement with the literature values. We have obtained a V, B - V color-magnitude diagram (CMD) of Hercules that reaches V {approx} 25 mag and extends beyond the galaxy's half-light radius over a total area of 40' Multiplication-Sign 36'. The CMD and the RR Lyrae stars indicate the presence of a population as old and metal-poor as (at least) the Galactic globular cluster M68.

  6. SN 2010jl IN UGC 5189: YET ANOTHER LUMINOUS TYPE IIn SUPERNOVA IN A METAL-POOR GALAXY

    International Nuclear Information System (INIS)

    Stoll, R.; Stanek, K. Z.; Pogge, R. W.; Szczygiel, D. M.; Antognini, J.; Prieto, J. L.; Pojmanski, G.; Yan, H.

    2011-01-01

    We present All-Sky Automated Survey data starting 25 days before the discovery of the recent type IIn SN 2010jl, and we compare its light curve to other luminous IIn supernovae (SNe), showing that it is a luminous (M I ∼ -20.5) event. Its host galaxy, UGC 5189, has a low gas-phase oxygen abundance (12 + log(O/H) = 8.2 ± 0.1), which reinforces the emerging trend that overluminous core-collapse supernovae (CCSNe) are found in the low-metallicity tail of the galaxy distribution, similar to the known trend for the hosts of long GRBs. We compile oxygen abundances from the literature and from our own observations of UGC 5189, and we present an unpublished spectrum of the luminous type Ic SN 2010gx that we use to estimate its host metallicity. We discuss these in the context of host metallicity trends for different classes of core-collapse objects. The earliest generations of stars are known to be enhanced in [O/Fe] relative to the solar mixture; it is therefore likely that the stellar progenitors of these overluminous SNe are even more iron-poor than they are oxygen-poor. A number of mechanisms and massive star progenitor systems have been proposed to explain the most luminous CCSNe. Any successful theory that tries to explain these very luminous events will need to include the emerging trend that points toward low metallicity for the massive progenitor stars. This trend for very luminous SNe to strongly prefer low-metallicity galaxies should be taken into account when considering various aspects of the evolution of the metal-poor early universe, such as enrichment and reionization.

  7. White dwarf planets

    Directory of Open Access Journals (Sweden)

    Bonsor Amy

    2013-04-01

    Full Text Available The recognition that planets may survive the late stages of stellar evolution, and the prospects for finding them around White Dwarfs, are growing. We discuss two aspects governing planetary survival through stellar evolution to the White Dwarf stage. First we discuss the case of a single planet, and its survival under the effects of stellar mass loss, radius expansion, and tidal orbital decay as the star evolves along the Asymptotic Giant Branch. We show that, for stars initially of 1 − 5 M⊙, any planets within about 1 − 5 AU will be engulfed, this distance depending on the stellar and planet masses and the planet's eccentricity. Planets engulfed by the star's envelope are unlikely to survive. Hence, planets surviving the Asymptotic Giant Branch phase will probably be found beyond ∼ 2 AU for a 1  M⊙ progenitor and ∼ 10 AU for a 5 M⊙ progenitor. We then discuss the evolution of two-planet systems around evolving stars. As stars lose mass, planet–planet interactions become stronger, and many systems stable on the Main Sequence become destabilised following evolution of the primary. The outcome of such instabilities is typically the ejection of one planet, with the survivor being left on an eccentric orbit. These eccentric planets could in turn be responsible for feeding planetesimals into the neighbourhood of White Dwarfs, causing observed pollution and circumstellar discs.

  8. THE C-FLAME QUENCHING BY CONVECTIVE BOUNDARY MIXING IN SUPER-AGB STARS AND THE FORMATION OF HYBRID C/O/Ne WHITE DWARFS AND SN PROGENITORS

    Energy Technology Data Exchange (ETDEWEB)

    Denissenkov, P. A.; Herwig, F. [Department of Physics and Astronomy, University of Victoria, P.O. Box 3055, Victoria, BC V8W 3P6 (Canada); Truran, J. W. [The Joint Institute for Nuclear Astrophysics, Notre Dame, IN 46556 (United States); Paxton, B., E-mail: pavelden@uvic.ca, E-mail: fherwig@uvic.ca [Kavli Institute for Theoretical Physics and Department of Physics, Kohn Hall, University of California, Santa Barbara, CA 93106 (United States)

    2013-07-20

    After off-center C ignition in the cores of super asymptotic giant branch (SAGB) stars, the C flame propagates all the way down to the center, trailing behind it the C-shell convective zone, and thus building a degenerate ONe core. This standard picture is obtained in stellar evolution simulations if the bottom C-shell convection boundary is assumed to be a discontinuity associated with a strict interpretation of the Schwarzschild condition for convective instability. However, this boundary is prone to additional mixing processes, such as thermohaline convection and convective boundary mixing. Using hydrodynamic simulations, we show that contrary to previous results, thermohaline mixing is too inefficient to interfere with the C-flame propagation. However, even a small amount of convective boundary mixing removes the physical conditions required for the C-flame propagation all the way to the center. This result holds even if we allow for some turbulent heat transport in the CBM region. As a result, SAGB stars build in their interiors hybrid C-O-Ne degenerate cores composed of a relatively large CO core (M{sub CO} Almost-Equal-To 0.2 M{sub Sun }) surrounded by a thick ONe zone ({Delta}M{sub ONe} {approx}> 0.85 M{sub Sun }) with another thin CO layer above. If exposed by mass loss, these cores will become hybrid C-O-Ne white dwarfs. Otherwise, the ignition of C-rich material in the central core, surrounded by the thick ONe zone, may trigger a thermonuclear supernova (SN) explosion. The quenching of the C-flame may have implications for the ignition mechanism of SN Ia in the double-degenerate merger scenario.

  9. A THERMAL INFRARED IMAGING STUDY OF VERY LOW MASS, WIDE-SEPARATION BROWN DWARF COMPANIONS TO UPPER SCORPIUS STARS: CONSTRAINING CIRCUMSTELLAR ENVIRONMENTS

    Energy Technology Data Exchange (ETDEWEB)

    Bailey, Vanessa; Hinz, Philip M.; Su, Kate Y. L.; Hoffmann, William F.; Rieke, George; Rodigas, Timothy; Skemer, Andrew; Vaitheeswaran, Vidhya [Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721 (United States); Currie, Thayne [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada); Esposito, Simone; Pinna, Enrico; Puglisi, Alfio [Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125 Firenze (Italy); Hill, John M. [Large Binocular Telescope Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721 (United States); Jones, Terry [School of Physics and Astronomy, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455 (United States); Kim, Jihun [College of Optical Sciences, University of Arizona, 1630 E. University Blvd., Tucson, AZ 85721 (United States); Leisenring, Jarron; Meyer, Michael [Institut fuer Angewandte Physik, Eidgenoessische Technische Hochschule-Zuerich, CH-8093 (Switzerland); Murray-Clay, Ruth; Skrutskie, Michael F. [Harvard-Smithsonian Center for Astrophysics, Harvard University, 60 Garden St., Cambridge, MA 02138 (United States); Nelson, Matthew J., E-mail: vbailey@as.arizona.edu [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); and others

    2013-04-10

    We present a 3-5 {mu}m LBT/MMT adaptive optics imaging study of three Upper Scorpius stars with brown dwarf (BD) companions with very low masses/mass ratios (M{sub BD} <25 M{sub Jup}; M{sub BD}/M{sub *} Almost-Equal-To 1%-2%) and wide separations (300-700 AU): GSC 06214, 1RXS 1609, and HIP 78530. We combine these new thermal IR data with existing 1-4 {mu}m and 24 {mu}m photometry to constrain the properties of the BDs and identify evidence for circumprimary/circumsecondary disks in these unusual systems. We confirm that GSC 06214B is surrounded by a disk, further showing that this disk produces a broadband IR excess due to small dust near the dust sublimation radius. An unresolved 24 {mu}m excess in the system may be explained by the contribution from this disk. 1RXS 1609B exhibits no 3-4 {mu}m excess, nor does its primary; however, the system as a whole has a modest 24 {mu}m excess, which may come from warm dust around the primary and/or BD. Neither object in the HIP 78530 system exhibits near- to mid-IR excesses. We additionally find that the 1-4 {mu}m colors of HIP 78530B match a spectral type of M3 {+-} 2, inconsistent with the M8 spectral type assigned based on its near-IR spectrum, indicating that it may be a low-mass star rather than a BD. We present new upper limits on additional low-mass companions in the system (<5 M{sub Jup} beyond 175 AU). Finally, we examine the utility of circumsecondary disks as probes of the formation histories of wide BD companions, finding that the presence of a disk may disfavor BD formation near the primary with subsequent outward scattering.

  10. Exploring the Milky Way stellar disk. A detailed elemental abundance study of 714 F and G dwarf stars in the solar neighbourhood

    Science.gov (United States)

    Bensby, T.; Feltzing, S.; Oey, M. S.

    2014-02-01

    Aims: The aim of this paper is to explore and map the age and abundance structure of the stars in the nearby Galactic disk. Methods: We have conducted a high-resolution spectroscopic study of 714 F and G dwarf and subgiant stars in the Solar neighbourhood. The star sample has been kinematically selected to trace the Galactic thin and thick disks to their extremes, the metal-rich stellar halo, sub-structures in velocity space such as the Hercules stream and the Arcturus moving group, as well as stars that cannot (kinematically) be associated with either the thin disk or the thick disk. The determination of stellar parameters and elemental abundances is based on a standard analysis using equivalent widths and one-dimensional, plane-parallel model atmospheres calculated under the assumption of local thermodynamical equilibrium (LTE). The spectra have high resolution (R = 40 000-110 000) and high signal-to-noise (S/N = 150-300) and were obtained with the FEROS spectrograph on the ESO 1.5 m and 2.2 m telescopes, the SOFIN and FIES spectrographs on the Nordic Optical Telescope, the UVES spectrograph on the ESO Very Large Telescope, the HARPS spectrograph on the ESO 3.6 m telescope, and the MIKE spectrograph on the Magellan Clay telescope. The abundances from individual Fe i lines were were corrected for non-LTE effects in every step of the analysis. Results: We present stellar parameters, stellar ages, kinematical parameters, orbital parameters, and detailed elemental abundances for O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, Y, and Ba for 714 nearby F and G dwarf stars. Our data show that there is an old and α-enhanced disk population, and a younger and less α-enhanced disk population. While they overlap greatly in metallicity between -0.7 < [Fe/H] ≲ +0.1, they show a bimodal distribution in [α/Fe]. This bimodality becomes even clearer if stars where stellar parameters and abundances show larger uncertainties (Teff ≲ 5400 K) are discarded, showing that it is

  11. Low-metallicity Star Formation (IAU S255)

    Science.gov (United States)

    Hunt, Leslie K.; Madden, Suzanne C.; Schneider, Raffaella

    2009-01-01

    'Shea and Michael L. Norman; 16. Damped Lyα systems as probes of chemical evolution over cosmological timescales Miroslava Dessauges-Zavadsky; 17. Connecting high-redshift galaxy populations through observations of local damped Lyman alpha dwarf galaxies Regina E. Schulte-Ladbeck; 18. Chemical enrichment and feedback in low metallicity environments: constraints on galaxy formation Francesca Matteucci; 19. Effects of reionization on dwarf galaxy formation Massimo Ricotti; 20. The importance of following the evolution of the dust in galaxies on their SEDs A. Schurer, F. Calura, L. Silva, A. Pipino, G. L. Granato, F. Matteucci and R. Maiolino; 21. About the chemical evolution of dSphs (and the peculiar globular cluster ωCen) Andrea Marcolini and Annibale D'Ercole; 22. Young star clusters in the small Magellanic cloud: impact of local and global conditions on star formation Elena Sabbi, Linda J. Smith, Lynn R. Carlson, Antonella Nota, Monca Tosi, Michele Cignoni, Jay S. Gallagher III, Marco Sirianni and Margaret Meixner; 23. Modeling the ISM properties of metal-poor galaxies and gamma-ray burst hosts Emily M. Levesque, Lisa J. Kewley, Kirsten Larson and Leonie Snijders; 24. Dwarf galaxies and the magnetisation of the IGM Uli Klein; Session III. Explosive Events in Low-Metallicity Environments: 25. Supernovae and their evolution in a low metallicity ISM Roger A. Chevalier; 26. First stars - type Ib supernovae connection Ken'ichi Nomoto, Masaomi Tanaka, Yasuomi Kamiya, Nozomu Tominaga and Keiichi Maeda; 27. Supernova nucleosynthesis in the early universe Nozomu Tominaga, Hideyuki Umeda, Keiichi Maeda, Ken'ichi Nomoto and Nobuyuki Iwamoto; 28. Powerful explosions at Z = 0? Sylvia Ekström, Georges Meynet, Raphael Hirschi and André Maeder; 29. Wind anisotropy and stellar evolution Cyril Georgy, Georges Meynet and André Maeder; 30. Low-mass and metal-poor gamma-ray burst

  12. Halo white dwarfs in the Gaia era

    NARCIS (Netherlands)

    van Oirschot, P.; Nelemans, G.; Pols, O.; Helmi, A.; Tolstoy, E.; Brown, A. G. A.; Pugliese, G.; de Koter, A.; Wijburg, M.

    The Galactic Halo is the oldest and most metal-poor component of the Galaxy. It is studied in detail both to understand the formation and evolution of galaxies, as well as the formation and evolution of the earliest stars. With this aim in mind, we plan to couple a population synthesis model to a

  13. THE COLOR-MAGNITUDE RELATION FOR METAL-POOR GLOBULAR CLUSTERS IN M87: CONFIRMATION FROM DEEP HST/ACS IMAGING

    International Nuclear Information System (INIS)

    Peng, Eric W.; Jordan, Andres; Blakeslee, John P.; Cote, Patrick; Ferrarese, Laura; Mieske, Steffen; Harris, William E.; Madrid, Juan P.; Meurer, Gerhardt R.

    2009-01-01

    Metal-poor globular clusters (GCs) are our local link to the earliest epochs of star formation and galaxy building. Studies of extragalactic GC systems using deep, high-quality imaging have revealed a small but significant slope to the color-magnitude relation for metal-poor GCs in a number of galaxies. We present a study of the M87 GC system using deep, archival HST/ACS imaging with the F606W and F814W filters, in which we find a significant color-magnitude relation for the metal-poor GCs. The slope of this relation in the I versus V-I color-magnitude diagram (γ I = -0.024 ± 0.006) is perfectly consistent with expectations based on previously published results using data from the ACS Virgo Cluster Survey. The relation is driven by the most luminous GCs, those with M I ∼ I = -7.8, a luminosity which is ∼1 mag fainter than our fitted Gaussian mean for the luminosity function (LF) of blue, metal-poor GCs (∼0.8 mag fainter than the mean for all GCs). These results indicate that there is a mass scale at which the correlation begins, and is consistent with a scenario where self-enrichment drives a mass-metallicity relationship. We show that previously measured half-light radii of M87 GCs from best-fit PSF-convolved King models are consistent with the more accurate measurements in this study, and we also explain how the color-magnitude relation for metal-poor GCs is real and cannot be an artifact of the photometry. We fit Gaussian and evolved Schechter functions to the luminosity distribution of GCs across all colors, as well as divided into blue and red subpopulations, finding that the blue GCs have a brighter mean luminosity and a narrower distribution than the red GCs. Finally, we present a catalog of astrometry and photometry for 2250 M87 GCs.

  14. Numerical simulations of the metallicity distribution in dwarf spheroidal galaxies

    NARCIS (Netherlands)

    Ripamonti, E.; Tolstoy, E.; Helmi, A.; Battaglia, G.; Abel, T.

    2006-01-01

    Abstract: Recent observations show that the number of stars with very low metallicities in the dwarf spheroidal satellites of the Milky Way is low, despite the low average metallicities of stars in these systems. We undertake numerical simulations of star formation and metal enrichment of dwarf

  15. The distribution of stars around the Milky Way's central black hole. II. Diffuse light from sub-giants and dwarfs

    Science.gov (United States)

    Schödel, R.; Gallego-Cano, E.; Dong, H.; Nogueras-Lara, F.; Gallego-Calvente, A. T.; Amaro-Seoane, P.; Baumgardt, H.

    2018-01-01

    Context. This is the second of three papers that search for the predicted stellar cusp around the Milky Way's central black hole, Sagittarius A*, with new data and methods. Aims: We aim to infer the distribution of the faintest stellar population currently accessible through observations around Sagittarius A*. Methods: We used adaptive optics assisted high angular resolution images obtained with the NACO instrument at the ESO VLT. Through optimised PSF fitting we removed the light from all detected stars above a given magnitude limit. Subsequently we analysed the remaining, diffuse light density. Systematic uncertainties were constrained by the use of data from different observing epochs and obtained with different filters. We show that it is necessary to correct for the diffuse emission from the mini-spiral, which would otherwise lead to a systematically biased light density profile. We used a Paschen α map obtained with the Hubble Space Telescope for this purpose. Results: The azimuthally averaged diffuse surface light density profile within a projected distance of R ≲ 0.5 pc from Sagittarius A* can be described consistently by a single power law with an exponent of Γ = 0.26 ± 0.02stat ± 0.05sys, similar to what has been found for the surface number density of faint stars in Paper I. Conclusions: The analysed diffuse light arises from sub-giant and main-sequence stars with Ks ≈ 19-22 with masses of 0.8-1.5 M⊙. These stars can be old enough to be dynamically relaxed. The observed power-law profile and its slope are consistent with the existence of a relaxed stellar cusp around the Milky Way's central black hole. We find that a Nuker law provides an adequate description of the nuclear cluster's intrinsic shape (assuming spherical symmetry). The 3D power-law slope near Sgr A* is γ = 1.13 ± 0.03model ± 0.05sys. The stellar density decreases more steeply beyond a break radius of about 3 pc, which corresponds roughly to the radius of influence of the

  16. Response of atmospheric biomarkers to NO(x)-induced photochemistry generated by stellar cosmic rays for earth-like planets in the habitable zone of M dwarf stars.

    Science.gov (United States)

    Grenfell, John Lee; Grießmeier, Jean-Mathias; von Paris, Philip; Patzer, A Beate C; Lammer, Helmut; Stracke, Barbara; Gebauer, Stefanie; Schreier, Franz; Rauer, Heike

    2012-12-01

    Understanding whether M dwarf stars may host habitable planets with Earth-like atmospheres and biospheres is a major goal in exoplanet research. If such planets exist, the question remains as to whether they could be identified via spectral signatures of biomarkers. Such planets may be exposed to extreme intensities of cosmic rays that could perturb their atmospheric photochemistry. Here, we consider stellar activity of M dwarfs ranging from quiet up to strong flaring conditions and investigate one particular effect upon biomarkers, namely, the ability of secondary electrons caused by stellar cosmic rays to break up atmospheric molecular nitrogen (N(2)), which leads to production of nitrogen oxides (NO(x)) in the planetary atmosphere, hence affecting biomarkers such as ozone (O(3)). We apply a stationary model, that is, without a time dependence; hence we are calculating the limiting case where the atmospheric chemistry response time of the biomarkers is assumed to be slow and remains constant compared with rapid forcing by the impinging stellar flares. This point should be further explored in future work with time-dependent models. We estimate the NO(x) production using an air shower approach and evaluate the implications using a climate-chemical model of the planetary atmosphere. O(3) formation proceeds via the reaction O+O(2)+M→O(3)+M. At high NO(x) abundances, the O atoms arise mainly from NO(2) photolysis, whereas on Earth this occurs via the photolysis of molecular oxygen (O(2)). For the flaring case, O(3) is mainly destroyed via direct titration, NO+O(3)→NO(2)+O(2), and not via the familiar catalytic cycle photochemistry, which occurs on Earth. For scenarios with low O(3), Rayleigh scattering by the main atmospheric gases (O(2), N(2), and CO(2)) became more important for shielding the planetary surface from UV radiation. A major result of this work is that the biomarker O(3) survived all the stellar-activity scenarios considered except for the strong

  17. Calibrating Detailed Chemical Analysis of M dwarfs

    Science.gov (United States)

    Veyette, Mark; Muirhead, Philip Steven; Mann, Andrew; Brewer, John; Allard, France; Homeier, Derek

    2018-01-01

    The ability to perform detailed chemical analysis of Sun-like F-, G-, and K-type stars is a powerful tool with many applications including studying the chemical evolution of the Galaxy, assessing membership in stellar kinematic groups, and constraining planet formation theories. Unfortunately, complications in modeling cooler stellar atmospheres has hindered similar analysis of M-dwarf stars. Large surveys of FGK abundances play an important role in developing methods to measure the compositions of M dwarfs by providing benchmark FGK stars that have widely-separated M dwarf companions. These systems allow us to empirically calibrate metallicity-sensitive features in M dwarf spectra. However, current methods to measure metallicity in M dwarfs from moderate-resolution spectra are limited to measuring overall metallicity and largely rely on astrophysical abundance correlations in stellar populations. In this talk, I will discuss how large, homogeneous catalogs of precise FGK abundances are crucial to advancing chemical analysis of M dwarfs beyond overall metallicity to direct measurements of individual elemental abundances. I will present a new method to analyze high-resolution, NIR spectra of M dwarfs that employs an empirical calibration of synthetic M dwarf spectra to infer effective temperature, Fe abundance, and Ti abundance. This work is a step toward detailed chemical analysis of M dwarfs at a similar precision achieved for FGK stars.

  18. A study of rotating globular clusters. The case of the old, metal-poor globular cluster NGC 4372

    Science.gov (United States)

    Kacharov, N.; Bianchini, P.; Koch, A.; Frank, M. J.; Martin, N. F.; van de Ven, G.; Puzia, T. H.; McDonald, I.; Johnson, C. I.; Zijlstra, A. A.

    2014-07-01

    Context. NGC 4372 is a poorly studied old, very metal-poor globular cluster (GC) located in the inner Milky Way halo. Aims: We present the first in-depth study of the kinematic properties and derive the structural parameters of NGC 4372 based on the fit of a Plummer profile and a rotating, physical model. We explore the link between internal rotation to different cluster properties and together with similar studies of more GCs, we put these in the context of globular cluster formation and evolution. Methods: We present radial velocities for 131 cluster member stars measured from high-resolution FLAMES/GIRAFFE observations. Their membership to the GC is additionally confirmed from precise metallicity estimates. We build a velocity dispersion profile and a systemic rotation curve using this kinematic data set. Additionally, we obtain an elliptical number density profile of NGC 4372 based on optical images using a Markov chain Monte Carlo fitting algorithm. From this, we derive the cluster's half-light radius and ellipticity as rh = 3.44' ± 0.04' and ɛ = 0.08 ± 0.01. Finally, we give a physical interpretation of the observed morphological and kinematic properties of this GC by fitting an axisymmetric, differentially rotating, dynamical model. Results: Our results show that NGC 4372 has an unusually high ratio of rotation amplitude to velocity dispersion (1.2 vs. 4.5 km s-1) for its metallicity. This puts it in line, however, with two other exceptional, very metal-poor GCs: M 15 and NGC 4590. We also find a mild flattening of NGC 4372 in the direction of its rotation. Given its old age, this suggests that the flattening is indeed caused by the systemic rotation rather than tidal interactions with the Galaxy. Additionally, we estimate the dynamical mass of the GC Mdyn = 2.0 ± 0.5 × 105M⊙ based on the dynamical model, which constrains the mass-to-light ratio of NGC 4372 between 1.4 and 2.3 M⊙/L⊙, representative of an old, purely stellar population. Based on

  19. Extended Schmidt law holds for faint dwarf irregular galaxies

    Science.gov (United States)

    Roychowdhury, Sambit; Chengalur, Jayaram N.; Shi, Yong

    2017-12-01

    Context. The extended Schmidt law (ESL) is a variant of the Schmidt which relates the surface densities of gas and star formation, with the surface density of stellar mass added as an extra parameter. Although ESL has been shown to be valid for a wide range of galaxy properties, its validity in low-metallicity galaxies has not been comprehensively tested. This is important because metallicity affects the crucial atomic-to-molecular transition step in the process of conversion of gas to stars. Aims: We empirically investigate for the first time whether low metallicity faint dwarf irregular galaxies (dIrrs) from the local universe follow the ESL. Here we consider the "global" law where surface densities are averaged over the galactic discs. dIrrs are unique not only because they are at the lowest end of mass and star formation scales for galaxies, but also because they are metal-poor compared to the general population of galaxies. Methods: Our sample is drawn from the Faint Irregular Galaxy GMRT Survey (FIGGS) which is the largest survey of atomic hydrogen in such galaxies. The gas surface densities are determined using their atomic hydrogen content. The star formation rates are calculated using GALEX far ultraviolet fluxes after correcting for dust extinction, whereas the stellar surface densities are calculated using Spitzer 3.6 μm fluxes. The surface densities are calculated over the stellar discs defined by the 3.6 μm images. Results: We find dIrrs indeed follow the ESL. The mean deviation of the FIGGS galaxies from the relation is 0.01 dex, with a scatter around the relation of less than half that seen in the original relation. In comparison, we also show that the FIGGS galaxies are much more deviant when compared to the "canonical" Kennicutt-Schmidt relation. Conclusions: Our results help strengthen the universality of the ESL, especially for galaxies with low metallicities. We suggest that models of star formation in which feedback from previous generations

  20. Discovery of a Highly Unequal-mass Binary T Dwarf with Keck Laser Guide Star Adaptive Optics: A Coevality Test of Substellar Theoretical Models and Effective Temperatures

    Science.gov (United States)

    Liu, Michael C.; Dupuy, Trent J.; Leggett, S. K.

    2010-10-01

    Highly unequal-mass ratio binaries are rare among field brown dwarfs, with the mass ratio distribution of the known census described by q (4.9±0.7). However, such systems enable a unique test of the joint accuracy of evolutionary and atmospheric models, under the constraint of coevality for the individual components (the "isochrone test"). We carry out this test using two of the most extreme field substellar binaries currently known, the T1 + T6 epsilon Ind Bab binary and a newly discovered 0farcs14 T2.0 + T7.5 binary, 2MASS J12095613-1004008AB, identified with Keck laser guide star adaptive optics. The latter is the most extreme tight binary resolved to date (q ≈ 0.5). Based on the locations of the binary components on the Hertzsprung-Russell (H-R) diagram, current models successfully indicate that these two systems are coeval, with internal age differences of log(age) = -0.8 ± 1.3(-1.0+1.2 -1.3) dex and 0.5+0.4 -0.3(0.3+0.3 -0.4) dex for 2MASS J1209-1004AB and epsilon Ind Bab, respectively, as inferred from the Lyon (Tucson) models. However, the total mass of epsilon Ind Bab derived from the H-R diagram (≈ 80 M Jup using the Lyon models) is strongly discrepant with the reported dynamical mass. This problem, which is independent of the assumed age of the epsilon Ind Bab system, can be explained by a ≈ 50-100 K systematic error in the model atmosphere fitting, indicating slightly warmer temperatures for both components; bringing the mass determinations from the H-R diagram and the visual orbit into consistency leads to an inferred age of ≈ 6 Gyr for epsilon Ind Bab, older than previously assumed. Overall, the two T dwarf binaries studied here, along with recent results from T dwarfs in age and mass benchmark systems, yield evidence for small (≈100 K) errors in the evolutionary models and/or model atmospheres, but not significantly larger. Future parallax, resolved spectroscopy, and dynamical mass measurements for 2MASS J1209-1004AB will enable a more

  1. PAndAS' CUBS: DISCOVERY OF TWO NEW DWARF GALAXIES IN THE SURROUNDINGS OF THE ANDROMEDA AND TRIANGULUM GALAXIES

    International Nuclear Information System (INIS)

    Martin, Nicolas F.; McConnachie, Alan W.; Irwin, Mike; Chapman, Scott; Widrow, Lawrence M.; Ferguson, Annette M. N.; Ibata, Rodrigo A.; Dubinski, John; Babul, Arif; Navarro, Julio; Fardal, Mark; Lewis, Geraint F.; Rich, R. Michael

    2009-01-01

    We present the discovery of two new dwarf galaxies, Andromeda XXI and Andromeda XXII, located in the surroundings of the Andromeda and Triangulum galaxies (M31 and M33). These discoveries stem from the first year data of the Pan-Andromeda Archaeological Survey, a photometric survey of the M31/M33 group conducted with the Megaprime/MegaCam Wide-Field Camera mounted on the Canada-France-Hawaii Telescope. Both satellites appear as spatial overdensities of stars which, when plotted in a color-magnitude diagram, follow metal-poor, [Fe/H] = -1.8, red giant branches at the distance of M31/M33. Andromeda XXI is a moderately bright dwarf galaxy (M V = -9.9 ± 0.6), albeit with low surface brightness, emphasizing again that many relatively luminous M31 satellites still remain to be discovered. It is also a large satellite, with a half-light radius close to 1 kpc, making it the fourth largest Local Group dwarf spheroidal galaxy after the recently discovered Andromeda XIX, Andromeda II, and Sagittarius around the Milky Way, and supports the trend that M31 satellites are larger than their Milky Way counterparts. Andromeda XXII is much fainter (M V = -6.5 ± 0.8) and lies a lot closer in projection to M33 than it does to M31 (42 versus 224 kpc), suggesting that it could be the first Triangulum satellite to be discovered. Although this is a very exciting possibility in the context of a past interaction of M33 with M31 and the fate of its satellite system, a confirmation will have to await a good distance estimate to confirm its physical proximity to M33. Along with the dwarf galaxies found in previous surveys of the M31 surroundings, these two new satellites bring the number of dwarf spheroidal galaxies in this region to 20.

  2. SDSS DR7 WHITE DWARF CATALOG

    Energy Technology Data Exchange (ETDEWEB)

    Kleinman, S. J.; Nitta, A. [Gemini Observatory, 670 North A' ohoku Place, Hilo, HI 96720 (United States); Kepler, S. O.; Pelisoli, Ingrid; Pecanha, Viviane; Costa, J. E. S. [Instituto de Fisica, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS (Brazil); Koester, D. [Institut fuer Theoretische Physik und Astrophysik, Universitaet Kiel, D-24098 Kiel (Germany); Krzesinski, J. [Mt. Suhora Observatory, Pedagogical University of Cracow, ul. Podchorazych 2, 30-084 Cracow (Poland); Dufour, P.; Lachapelle, F.-R.; Bergeron, P. [Departement de Physique, Universite de Montreal, C. P. 6128, Succ. Centre-Ville, Montreal, Quebec H3C 3J7 (Canada); Yip, Ching-Wa [Department of Physics and Astronomy, The Johns Hopkins University, 3701 San Martin Drive, Baltimore, MD 21218 (United States); Harris, Hugh C. [United States Naval Observatory, Flagstaff Station, 10391 West Naval Observatory Road, Flagstaff, AZ 86001-8521 (United States); Eisenstein, Daniel J. [Harvard Smithsonian Center for Astrophysics, 60 Garden Street, MS 20, Cambridge, MA 02138 (United States); Althaus, L.; Corsico, A., E-mail: hch@nofs.navy.mil [Facultad de Ciencias Astronomicas y Geofisicas, Paseo del Bosque S/N, (1900) La Plata (Argentina)

    2013-01-15

    We present a new catalog of spectroscopically confirmed white dwarf stars from the Sloan Digital Sky Survey (SDSS) Data Release 7 spectroscopic catalog. We find 20,407 white dwarf spectra, representing 19,712 stars, and provide atmospheric model fits to 14,120 DA and 1011 DB white dwarf spectra from 12,843 and 923 stars, respectively. These numbers represent more than a factor of two increase in the total number of white dwarf stars from the previous SDSS white dwarf catalogs based on DR4 data. Our distribution of subtypes varies from previous catalogs due to our more conservative, manual classifications of each star in our catalog, supplementing our automatic fits. In particular, we find a large number of magnetic white dwarf stars whose small Zeeman splittings mimic increased Stark broadening that would otherwise result in an overestimated log g if fit as a non-magnetic white dwarf. We calculate mean DA and DB masses for our clean, non-magnetic sample and find the DB mean mass is statistically larger than that for the DAs.

  3. Massive star formation within the Leo 'primordial' ring.

    Science.gov (United States)

    Thilker, David A; Donovan, Jennifer; Schiminovich, David; Bianchi, Luciana; Boissier, Samuel; de Paz, Armando Gil; Madore, Barry F; Martin, D Christopher; Seibert, Mark

    2009-02-19

    Few intergalactic, plausibly primordial clouds of neutral atomic hydrogen (H(i)) have been found in the local Universe, suggesting that such structures have either dispersed, become ionized or produced a stellar population on gigayear timescales. The Leo ring, a massive (M(H(i)) approximately 1.8 x 10(9)M[symbol: see text], M[symbol: see text] denoting the solar mass), 200-kpc-wide structure orbiting the galaxies M105 and NGC 3384 with a 4-Gyr period, is a candidate primordial cloud. Despite repeated atttempts, it has previously been seen only from H i emission, suggesting the absence of a stellar population. Here we report the detection of ultraviolet light from gaseous substructures of the Leo ring, which we attribute to recent massive star formation. The ultraviolet colour of the detected complexes is blue, implying the onset of a burst of star formation or continuous star formation of moderate (approximately 10(8)-yr) duration. Measured ultraviolet-visible photometry favours models with low metallicity (Z approximately Z[symbol: see text]/50-Z[symbol: see text]/5, Z[symbol: see text] denoting the solar metallicity), that is, a low proportion of elements heavier than helium, although spectroscopic confirmation is needed. We speculate that the complexes are dwarf galaxies observed during their formation, but distinguished by their lack of a dark matter component. In this regard, they resemble tidal dwarf galaxies, although without the enrichment preceding tidal stripping. If structures like the Leo ring were common in the early Universe, they may have produced a large, yet undetected, population of faint, metal-poor, halo-lacking dwarf galaxies.

  4. Branes constrictions with White Dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    García-Aspeitia, Miguel A., E-mail: aspeitia@fisica.uaz.edu.mx [Consejo Nacional de Ciencia y Tecnología, Av, Insurgentes Sur 1582, Colonia Crédito Constructor, Del. Benito Juárez, C.P. 03940, Mexico, D.F. (Mexico); Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad esquina con Paseo a la Bufa S/N, C.P. 98060, Zacatecas (Mexico)

    2015-11-06

    We consider here a robust study of stellar dynamics for white dwarf stars with polytropic matter in the weak-field approximation using the Lane–Emden equation from the brane-world scenario. We also derive an analytical solution to the nonlocal energy density and show the behavior and sensitivity of these stars to the presence of extra dimensions. Similarly, we analyze stability and compactness, in order to show whether it is possible to agree with the conventional wisdom of white dwarfs dynamics. Our results predict an average value of the brane tension of <λ>≳84.818 MeV{sup 4}, with a standard deviation σ≃82.021 MeV{sup 4}, which comes from a sample of dwarf stars, being weaker than other astrophysical observations but remaining higher than cosmological results provided by nucleosynthesis among others.

  5. White Dwarfs Cosmological and Galactic Probes

    CERN Document Server

    Sion, Edward M; Vennes, Stéphane

    2005-01-01

    The emphasis on white dwarf stars and cosmology arises from the most recent advances in cosmological and galactic structure research in which white dwarf stars are playing a very prominent role. Examples are Type Ia supernovae (i.e. white dwarf supernovae), the origin and evolution of the universe, the age of the galactic disk, cosmochronology using white dwarfs in globular clusters and galactic clusters, and the physics of accretion onto compact (very dense) stars. As an assisting guide to the reader, we have included, by invitation, comprehensive review articles in each of the four major areas of the book, white dwarf supernovae, cosmology, accretion physics and galactic structure. The reviews include introductory material that they build upon. The book is suitable and most useful to advanced undergraduates, graduate students and scientific professionals (e.g. astronomers, astrophysicists, cosmologists, physicists).

  6. Searching for Tidal Tails in Galactic Dwarf Spheroidal Galaxies

    Science.gov (United States)

    Martínez-Delgado, David; Aparicio, A.; Gomez-Flechoso, Maria A.

    The formation of the Galactic halo is currently best explained by the combination of two scenarios which previously were regarded as competing models. Based on the kinematics of metal-poor halo field stars, Eggen, Lynden-Bell & Sandage (ELS, 1962) proposed that the halo formed during a rapid, smooth collapse from a homogeneous primordial medium. Searle & Zinn (SZ, 1978) argued a halo formation via the gradual merging of many sub-galactic fragments. The SZ scenario has been strengthened by the observational evidence accumulated during the past decade. The discovery of the Sagittarius dwarf galaxy (Ibata, Gilmore & Irwin 1994), in a process of dissolving into the Galactic halo, argued in favour that accretion events can take place in the Milky Way. The possibility that accretion events may leave observable fossil records in the halo is also supported by theoretical models of tidally disrupted dSph satellites (Johnston, Spergel & Hernquist 1995; Oh, Lin & Aarseth 1995; Piatek & Pryor 1995). We present our preliminary results of a long-term project to investigate the process of accretion and tidal disruption of dSph satellites in the Galactic halo and, in particular, to search for new tidal tails in a sample of nearby dSph satellites of the Milky Way. The presence of a possible tidal debris in Ursa Minor and Sculptor dSphs and the results of our survey for a tidal extension along the NW semimajor axis of Saggitarius is discussed.

  7. The DART Imaging And CaT Survey of the Fornax Dwarf Spheroidal Galaxy

    Energy Technology Data Exchange (ETDEWEB)

    Battaglia, Giuseppina; Tolstoy, E.; Helmi, A.; /Kapteyn Astron. Inst., Groningen; Irwin, M.J.; /Cambridge U., Inst. of Astron.; Letarte, B.; /Kapteyn Astron. Inst.,; Jablonka, P.; /LASTRO Observ.; Hill, V.; /Meudon Observ.; Venn, K.A.; /Victoria U.; Shetrone, M.D.; /Texas U., McDonald Observ.; Arimoto, N.; /Tokyo, Astron. Observ.; Primas,; /European Southern Observ.; Kaufer, A.; /European Southern Obs., Chile; Francois, P.; /Meudon Observ.; Szeifert, T.; /European Southern Obs., Chile; Abel, T.; /KIPAC, Menlo Park; Sadakane, K.; /Osaka Kyoiku U.

    2006-08-28

    As part of the DART project we have used the ESO/2.2m Wide Field Imager in conjunction with the VLT/FLAMES* GIRAFFE spectrograph to study the detailed properties of the resolved stellar population of the Fornax dwarf spheroidal galaxy out to and beyond its tidal radius. Fornax dSph has had a complicated evolution and contains significant numbers of young, intermediate age and old stars. We investigate the relation between these different components by studying their photometric, kinematic and abundance distributions. We re-derived the structural parameters of the Fornax dwarf spheroidal using our wide field imaging covering the galaxy out to its tidal radius, and analyzed the spatial distribution of the Fornax stars of different ages as selected from Colour-Magnitude Diagram analysis. We have obtained accurate velocities and metallicities from spectra in the Ca II triplet wavelength region for 562 Red Giant Branch stars which have velocities consistent with membership in Fornax dwarf spheroidal. We have found evidence for the presence of at least three distinct stellar components: a young population (few 100 Myr old) concentrated in the center of the galaxy, visible as a Main Sequence in the Colour-Magnitude Diagram; an intermediate age population (2-8 Gyr old); and an ancient population (> 10Gyr), which are distinguishable from each other kinematically, from the metallicity distribution and in the spatial distribution of stars found in the Colour-Magnitude Diagram. From our spectroscopic analysis we find that the ''metal rich'' stars ([Fe/H] > -1.3) show a less extended and more concentrated spatial distribution, and display a colder kinematics than the ''metal poor'' stars ([Fe/H] < -1.3). There is tentative evidence that the ancient stellar population in the center of Fornax does not exhibit equilibrium kinematics. This could be a sign of a relatively recent accretion of external material, such as the merger of another

  8. The most metal-poor damped Ly alpha system at z<3: constraints on early nucleosynthesis

    OpenAIRE

    Erni, P.; Richter, P.; Ledoux, C.; Petitjean, P.

    2006-01-01

    To constrain the conditions for very early nucleosynthesis in the Universe we compare the chemical enrichment pattern of an extremely metal-poor damped Lyman alpha (DLA) absorber with predictions from recent explosive nucleosynthesis model calculations. For this, we have analyzed chemical abundances in the DLA system at z_abs=2.6183 toward the quasar Q0913+072 (z_em=2.785) using public UVES/VLT high spectral resolution data. The total neutral hydrogen column density in this absorber is logN(H...

  9. A brown dwarf orbiting an M-dwarf

    DEFF Research Database (Denmark)

    Bachelet, E.; Fouque, P.; Han, C.

    2012-01-01

    gives two local minima, which correspond to the theoretical degeneracy s ≡ s-1. We find that the lens is composed of a brown dwarf secondary of mass MS = 0.05 M⊙ orbiting a primary M-star of mass MP = 0.18 M⊙. We also reveal a new mass-ratio degeneracy for the central caustics of close binaries....... Conclusions. As far as we are aware, this is the first detection using the microlensing technique of a binary system in our Galaxy composed of an M-star and a brown dwarf....

  10. Probing star formation and feedback in dwarf galaxies. Integral field view of the blue compact galaxy Tololo 1937-423

    Science.gov (United States)

    Cairós, L. M.; González-Pérez, J. N.

    2017-12-01

    Context. Blue compact galaxies (BCG) are gas-rich, low-mass, small systems that form stars at unusually high rates. This makes them excellent laboratories for investigating the process of star-formation (SF) at galactic scales and the effects of massive stellar feedback on the interstellar (and intergalactic) medium. Aims: We analyzed the BCG Tololo 1937-423 using optical integral field spectroscopy to probe its morphology, stellar content, nebular excitation and ionization properties, and the kinematics of its warm ionized gas. Methods: Tololo 1937-423 was observed with the Visible Multi-Object Spectrograph at the Very Large Telescope. We took data in the wavelength range 4150-7400 Å, covering a field of view of 27″× 27″ on the sky with a spatial sampling of 0.̋67. From these data we built maps in the continuum and brighter emission lines, diagnostic line ratio maps, and velocity dispersion fields. We also generated the integrated spectrum of the main H II regions and young stellar clusters to determine reliable physical parameters and oxygen abundances. Results: We found that Tololo 1937-423 is currently undergoing an extended starburst. In the Hα maps we identified nine major clumps, aligned mostly northeast-southwest, and stretching to galactocentric distances ≥2 kpc. The galaxy presents a single continuum peak that is not cospatial with any knot in emission lines, indicating at least two relatively recent episodes of SF. The inhomogeneous dust distribution reachs its maximum (E(B-V) 0.97) roughly at the position of the continuum peak. We found shocked regions in the galaxy outer regions and at the ed