WorldWideScience

Sample records for main-sequence stars effects

  1. Effects of magnetic fields on main sequence stars

    International Nuclear Information System (INIS)

    Hubbard, E.N.

    1981-01-01

    A number of effects of low to medium strength ( 2 /8π) magnetic field pressure term so that the only effect of such a field may come from its inhibiting convection in the core. Isochrones of both convective and radiative core models of 2-5 M are presented. In the deep envelope, mixing of partially nuclear processed material driven by rising and falling magnetic flux tubes may be seen. The effects of this mixing will be brought to the surface during the deep convection phase of the star's tenure as a red giant. This model is used to predict a signature for magnetic mixing based on the CNO isotope and abundance ratios. In the outer envelope the gas pressure is low enough that one might expect to see a perturbation of the stellar structure due to the magnetic field pressure itself. This perturbation is calculated under several physical models for intermediate and high mass stars and it is determined that sufficient magnetic field energy may be available in the outer envelope to expand a star by about 20% over its unperturbed radius. Finally the evidence for the existence of non-magnetic neutron stars is considered, concluding that while no non-magnetic neutron stars have ever been positively identified, there is no evidence that prevents the existence of at least as many non-magnetic as magnetic neutron stars

  2. Nitrogen chronology of massive main sequence stars

    NARCIS (Netherlands)

    Köhler, K.; Borzyszkowski, M.; Brott, I.; Langer, N.; de Koter, A.

    2012-01-01

    Context. Rotational mixing in massive main sequence stars is predicted to monotonically increase their surface nitrogen abundance with time. Aims. We use this effect to design a method for constraining the age and the inclination angle of massive main sequence stars, given their observed luminosity,

  3. Effects of mass loss on the evolution of massive stars. I. Main-sequence evolution

    International Nuclear Information System (INIS)

    Dearborn, D.S.P.; Blake, J.B.; Hainebach, K.L.; Schramm, D.N.

    1978-01-01

    The effect of mass loss on the evolution and surface composition of massive stars during main-sequence evolution are examined. While some details of the evolutionary track depend on the formula used for the mass loss, the results appear most sensitive to the total mass removed during the main-sequence lifetime. It was found that low mass-loss rates have very little effect on the evolution of a star; the track is slightly subluminous, but the lifetime is almost unaffected. High rates of mass loss lead to a hot, high-luminosity stellar model with a helium core surrounded by a hydrogen-deficient (Xapprox.0.1) envelope. The main-sequence lifetime is extended by a factor of 2--3. These models may be identified with Wolf-Rayet stars. Between these mass-loss extremes are intermediate models which appear as OBN stars on the main sequence. The mass-loss rates required for significant observable effects range from 8 x 10 -7 to 10 -5 M/sub sun/ yr -1 , depending on the initial stellar mass. It is found that observationally consistent mass-loss rates for stars with M> or =30 M/sub sun/ may be sufficiently high that these stars lose mass on a time scale more rapidly than their main-sequence core evolution time. This result implies that the helium cores resulting from the main-sequence evolution of these massive stars may all be very similar to that of a star of Mapprox.30 M/sub sun/ regardless of the zero-age mass

  4. 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.

  5. Main sequences defined by Hyades and field stars

    International Nuclear Information System (INIS)

    Upgren, A.R.

    1978-01-01

    The author reviews the main sequences defined by members of the Hyades cluster and by the field stars in the solar neighborhood. For this purpose, the discussion is limited primarily to the stars of the lower portions of the main sequence, especially those of spectral classes K and early M. There are two reasons for emphasis on the faint red dwarf stars. First, the value of a parallax depends on its size or, more accurately, on the error in parallax divided by the parallax itself. Large parallaxes of high precision occur in large numbers only for stars inhabiting the lower main sequence. Furthermore, brighter stars of earlier spectral classes are more likely to be influenced by evolutionary effects which may differ between the Hyades and field stars, and which are difficult to calibrate. (Auth.)

  6. Lithium depletion and rotation in main-sequence stars

    International Nuclear Information System (INIS)

    Balachandran, S.

    1990-01-01

    Lithium abundances were measured in nearly 200 old disk-population F stars to examine the effects of rotational braking on the depletion of Li. The sample was selected to be slightly evolved off the main sequence so that the stars have completed all the Li depletion they will undergo on the main sequence. A large scatter in Li abundances in the late F stars is found, indicating that the Li depletion is not related to age and spectral type alone. Conventional depletion mechanisms like convective overshoot and microscopic diffusion are unable to explain Li depletion in F stars with thin convective envelopes and are doubly taxed to explain such a scatter. No correlation is found between Li abundance and the present projected rotational velocity and some of the most rapid rotators are undepleted, ruling out meridional circulation as the cause of Li depletion. There is a somewhat larger spread in Li abundances in the spun-down late F stars compared to the early F stars which should remain rotationally unaltered on the main sequence. 85 refs

  7. The evolution of coronal activity in main sequence cool stars

    International Nuclear Information System (INIS)

    Stern, R.A.

    1984-01-01

    Stars spend most of their lifetime and show the least amount of nuclear evolution on the main sequence. However, the x-ray luminosities of cool star coronas change by orders of magnitude as a function of main sequence age. Such coronal evolution is discussed in relation to our knowledge of the solar corona, solar and stellar flares, stellar rotation and binarity. The relevance of X-ray observations to current speculations on stellar dynamos is also considered

  8. Solar-Type Activity in Main-Sequence Stars

    CERN Document Server

    Gershberg, Roald E

    2005-01-01

    Solar-type activity over the whole range of the electromagnetic spectrum is a phenomenon inherent in the majority of low- and moderate-mass main sequence stars. In this monograph observational results are summarized in a systematic and comprehensive fashion. The analysis of the various manifestations of such stellar activity leads to the identification of these phenomena with macroscopic non-linear processes in a magnetized plasma. Comparative study of flare stars and the Sun has become increasingly fruitful and is presently an active field of research involving stellar and solar physicists, experts in plasma physics and high-energy astrophysicists. This book will provide them with both an introduction and overview of observational results from the first optical photometry and spectroscopy, from the satellite telescopes International Ultraviolet Explorer to Hubble Space Telescope, XMM-Newton and Chandra, as well as with the present physical interpretation of solar-type activity in main sequence stars. Gershbe...

  9. Infrared photometry of upper main sequence stars in M39

    International Nuclear Information System (INIS)

    Manteiga, M.; Martinez-Roger, C.; Morales, C.; Sabau, L.

    1991-01-01

    Infrared photometry of 19 Main sequence stars in the open cluster M39 is presented. Infrared-infrared and optical-infrared colour-colour and colour-magnitude diagrams are presented and compared with mean intrinsic colours for Population I stars. An interstellar reddening of E(B - V) = 0.01 is obtained by analysis of the colour-colour diagrams. Comparison with a set of theoretical isochrones leads to an age estimate for the cluster between 2.4 and 4.8 x 10 8 years

  10. Infrared photometry of upper main sequence stars in M39

    Energy Technology Data Exchange (ETDEWEB)

    Manteiga, M.; Martinez-Roger, C. (Instituto de Astrofisica de Canarias, Tenerife, (ES)); Morales, C.; Sabau, L. (Instituto de Tecnica Aeroespacial, Madrid, (ES))

    1991-03-01

    Infrared photometry of 19 Main sequence stars in the open cluster M39 is presented. Infrared-infrared and optical-infrared colour-colour and colour-magnitude diagrams are presented and compared with mean intrinsic colours for Population I stars. An interstellar reddening of E(B - V) = 0.01 is obtained by analysis of the colour-colour diagrams. Comparison with a set of theoretical isochrones leads to an age estimate for the cluster between 2.4 and 4.8 x 10{sup 8} years.

  11. Lithium evolution in metal-poor stars: from Pre-Main Sequence to the Spite plateau

    OpenAIRE

    Fu, Xiaoting; Bressan, Alessandro; Molaro, Paolo; Marigo, Paola

    2015-01-01

    Lithium abundance derived in metal-poor main sequence stars is about three times lower than the value of primordial Li predicted by the standard Big Bang nucleosynthesis when the baryon density is taken from the CMB or the deuterium measurements. This disagreement is generally referred as the lithium problem. We here reconsider the stellar Li evolution from the pre-main sequence to the end of the main sequence phase by introducing the effects of convective overshooting and residual mass accre...

  12. Photometric monitoring of pre-main sequence stars - 2

    International Nuclear Information System (INIS)

    Evans, A.; Davies, J.K.; Kilkenny, D.; Bode, M.F.

    1989-01-01

    A discussion is presented of the infrared and optical photometric variability of the pre-main sequence stars BF Ori and UX Ori. In the former case, the reddening that occurs during decline, at both optical and infrared wavelengths, is consistent with variable extinction by circumstellar grains having an interstellar-like reddening law. While in the case of UX Ori, the data suggest variability due to starspots. In both cases, a study of the polarimetric variability would be valuable to confirm these conclusions. (author)

  13. Common Warm Dust Temperatures Around Main Sequence Stars

    Science.gov (United States)

    Morales, Farisa; Rieke, George; Werner, Michael; Stapelfeldt, Karl; Bryden, Geoffrey; Su, Kate

    2011-01-01

    We compare the properties of warm dust emission from a sample of main-sequence A-type stars (B8-A7) to those of dust around solar-type stars (F5-KO) with similar Spitzer Space Telescope Infrared Spectrograph/MIPS data and similar ages. Both samples include stars with sources with infrared spectral energy distributions that show evidence of multiple components. Over the range of stellar types considered, we obtain nearly the same characteristic dust temperatures (∼ 190 K and ∼60 K for the inner and outer dust components, respectively)-slightly above the ice evaporation temperature for the inner belts. The warm inner dust temperature is readily explained if populations of small grains are being released by sublimation of ice from icy planetesimals. Evaporation of low-eccentricity icy bodies at ∼ 150 K can deposit particles into an inner/warm belt, where the small grains are heated to dust Temperatures of -190 K. Alternatively, enhanced collisional processing of an asteroid belt-like system of parent planetesimals just interior to the snow line may account for the observed uniformity in dust temperature. The similarity in temperature of the warmer dust across our B8-KO stellar sample strongly suggests that dust-producing planetesimals are not found at similar radial locations around all stars, but that dust production is favored at a characteristic temperature horizon.

  14. HABITABLE ZONES OF POST-MAIN SEQUENCE STARS

    International Nuclear Information System (INIS)

    Ramirez, Ramses M.; Kaltenegger, Lisa

    2016-01-01

    Once a star leaves the main sequence and becomes a red giant, its Habitable Zone (HZ) moves outward, promoting detectable habitable conditions at larger orbital distances. We use a one-dimensional radiative-convective climate and stellar evolutionary models to calculate post-MS HZ distances for a grid of stars from 3700 to 10,000 K (∼M1 to A5 stellar types) for different stellar metallicities. The post-MS HZ limits are comparable to the distances of known directly imaged planets. We model the stellar as well as planetary atmospheric mass loss during the Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) phases for super-Moons to super-Earths. A planet can stay between 200 million years up to 9 Gyr in the post-MS HZ for our hottest and coldest grid stars, respectively, assuming solar metallicity. These numbers increase for increased stellar metallicity. Total atmospheric erosion only occurs for planets in close-in orbits. The post-MS HZ orbital distances are within detection capabilities of direct imaging techniques.

  15. HABITABLE ZONES OF POST-MAIN SEQUENCE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Ramirez, Ramses M.; Kaltenegger, Lisa [Carl Sagan Institute, Cornell University, Ithaca, NY (United States)

    2016-05-20

    Once a star leaves the main sequence and becomes a red giant, its Habitable Zone (HZ) moves outward, promoting detectable habitable conditions at larger orbital distances. We use a one-dimensional radiative-convective climate and stellar evolutionary models to calculate post-MS HZ distances for a grid of stars from 3700 to 10,000 K (∼M1 to A5 stellar types) for different stellar metallicities. The post-MS HZ limits are comparable to the distances of known directly imaged planets. We model the stellar as well as planetary atmospheric mass loss during the Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) phases for super-Moons to super-Earths. A planet can stay between 200 million years up to 9 Gyr in the post-MS HZ for our hottest and coldest grid stars, respectively, assuming solar metallicity. These numbers increase for increased stellar metallicity. Total atmospheric erosion only occurs for planets in close-in orbits. The post-MS HZ orbital distances are within detection capabilities of direct imaging techniques.

  16. Be ABUNDANCES IN COOL MAIN-SEQUENCE STARS WITH EXOPLANETS

    Energy Technology Data Exchange (ETDEWEB)

    Delgado Mena, E.; Israelian, G.; Gonzalez Hernandez, J. I.; Rebolo, R. [Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife (Spain); Santos, N. C., E-mail: edm@iac.es [Centro de Astrofisica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal)

    2012-02-10

    We present new Ultraviolet and Visual Echelle Spectrograph (UVES) spectra of a sample of 15 cool unevolved stars with and without detected planetary companions. Together with previous determinations, we study Be depletion and possible differences in Be abundances between the two groups of stars. We obtain a final sample of 89 and 40 stars with and without planets, respectively, which covers a wide range of effective temperatures, from 4700 K to 6400 K, and includes several cool dwarf stars for the first time. We determine Be abundances for these stars and find that for most of them (the coolest ones) the Be II resonance lines are often undetectable, implying significant Be depletion. While for hot stars Be abundances are approximately constant, with a slight fall as T{sub eff} decreases and the Li-Be gap around 6300 K, we find a steep drop of Be content as T{sub eff} decreases for T{sub eff} < 5500 K, confirming the results of previous papers. Therefore, for these stars there is an unknown mechanism destroying Be that is not reflected in current models of Be depletion. Moreover, this strong Be depletion in cool objects takes place for all the stars regardless of the presence of planets; thus, the effect of extra Li depletion in solar-type stars with planets when compared with stars without detected planets does not seem to be present for Be, although the number of stars at those temperatures is still small to reach a final conclusion.

  17. Be ABUNDANCES IN COOL MAIN-SEQUENCE STARS WITH EXOPLANETS

    International Nuclear Information System (INIS)

    Delgado Mena, E.; Israelian, G.; González Hernández, J. I.; Rebolo, R.; Santos, N. C.

    2012-01-01

    We present new Ultraviolet and Visual Echelle Spectrograph (UVES) spectra of a sample of 15 cool unevolved stars with and without detected planetary companions. Together with previous determinations, we study Be depletion and possible differences in Be abundances between the two groups of stars. We obtain a final sample of 89 and 40 stars with and without planets, respectively, which covers a wide range of effective temperatures, from 4700 K to 6400 K, and includes several cool dwarf stars for the first time. We determine Be abundances for these stars and find that for most of them (the coolest ones) the Be II resonance lines are often undetectable, implying significant Be depletion. While for hot stars Be abundances are approximately constant, with a slight fall as T eff decreases and the Li-Be gap around 6300 K, we find a steep drop of Be content as T eff decreases for T eff < 5500 K, confirming the results of previous papers. Therefore, for these stars there is an unknown mechanism destroying Be that is not reflected in current models of Be depletion. Moreover, this strong Be depletion in cool objects takes place for all the stars regardless of the presence of planets; thus, the effect of extra Li depletion in solar-type stars with planets when compared with stars without detected planets does not seem to be present for Be, although the number of stars at those temperatures is still small to reach a final conclusion.

  18. Oscillation mode linewidths of main-sequence and subgiant stars observed by Kepler

    DEFF Research Database (Denmark)

    Appourchaux, T.; Benomar, O.; Gruberbauer, M.

    2012-01-01

    Solar-like oscillations have been observed by {{\\it Kepler}} and CoRoT in several solar-type stars. We study the variations of stellar p-mode linewidth as a function of effective temperature. Time series of 9 months of Kepler data have been used. The power spectra of 42 cool main-sequence stars a...

  19. Metallicity and ultraviolet excesses of late main sequence stars

    International Nuclear Information System (INIS)

    Suchkov, A.A.; Marsakov, V.A.; Shevelev, Yu.G.

    1987-01-01

    The comparison of the characteristics of ultraviolet (UV) excesses δ(U-B) and metallicity [Fe/H] distributions of F, G, and K dwarfs reveals a number of discrepancies. It is shown that they can be eliminated if we assume that UV excesses of K and late G dwarfs, and [Fe/H] values from detailed analysis for F dwarfs are underestimated. Such an assumption enables to account for low values of for F, K and late G dwarfs, and for the difference of the free terms in the metallicity - UV-excess relation for these stars as compared to early G dwarfs. In this case the F5-F9 dwarfs turn out to be more metal-rich (by 0.1 in [Fe/H]) than G and K dwarfs, and the metallicity of the Hyades cluster turns out to be larger than the solar one, [Fe/H] Hyades =+0.1. The ''conditional'' metallicity - UV-excess calibrations are obtained for four groups of main-sequence stars: F5-F9, G0-G4, G5-G9, K0-K5

  20. HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: NEW ESTIMATES

    Energy Technology Data Exchange (ETDEWEB)

    Kopparapu, Ravi Kumar; Ramirez, Ramses; Kasting, James F. [Department of Geosciences, Penn State University, 443 Deike Building, University Park, PA 16802 (United States); Eymet, Vincent [Laboratoire d' Astrophysique de Bordeaux, Universite de Bordeaux 1, UMR 5804, F-33270 Floirac (France); Robinson, Tyler D.; Domagal-Goldman, Shawn; Meadows, Victoria [NASA Astrobiology Institute' s Virtual Planetary Laboratory (United States); Mahadevan, Suvrath; Terrien, Ryan C.; Deshpande, Rohit [Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA 16802 (United States)

    2013-03-10

    Identifying terrestrial planets in the habitable zones (HZs) of other stars is one of the primary goals of ongoing radial velocity (RV) and transit exoplanet surveys and proposed future space missions. Most current estimates of the boundaries of the HZ are based on one-dimensional (1D), cloud-free, climate model calculations by Kasting et al. However, this model used band models that were based on older HITRAN and HITEMP line-by-line databases. The inner edge of the HZ in the Kasting et al. model was determined by loss of water, and the outer edge was determined by the maximum greenhouse provided by a CO{sub 2} atmosphere. A conservative estimate for the width of the HZ from this model in our solar system is 0.95-1.67 AU. Here an updated 1D radiative-convective, cloud-free climate model is used to obtain new estimates for HZ widths around F, G, K, and M stars. New H{sub 2}O and CO{sub 2} absorption coefficients, derived from the HITRAN 2008 and HITEMP 2010 line-by-line databases, are important improvements to the climate model. According to the new model, the water-loss (inner HZ) and maximum greenhouse (outer HZ) limits for our solar system are at 0.99 and 1.70 AU, respectively, suggesting that the present Earth lies near the inner edge. Additional calculations are performed for stars with effective temperatures between 2600 and 7200 K, and the results are presented in parametric form, making them easy to apply to actual stars. The new model indicates that, near the inner edge of the HZ, there is no clear distinction between runaway greenhouse and water-loss limits for stars with T{sub eff} {approx}< 5000 K, which has implications for ongoing planet searches around K and M stars. To assess the potential habitability of extrasolar terrestrial planets, we propose using stellar flux incident on a planet rather than equilibrium temperature. This removes the dependence on planetary (Bond) albedo, which varies depending on the host star's spectral type. We suggest

  1. HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: NEW ESTIMATES

    International Nuclear Information System (INIS)

    Kopparapu, Ravi Kumar; Ramirez, Ramses; Kasting, James F.; Eymet, Vincent; Robinson, Tyler D.; Domagal-Goldman, Shawn; Meadows, Victoria; Mahadevan, Suvrath; Terrien, Ryan C.; Deshpande, Rohit

    2013-01-01

    Identifying terrestrial planets in the habitable zones (HZs) of other stars is one of the primary goals of ongoing radial velocity (RV) and transit exoplanet surveys and proposed future space missions. Most current estimates of the boundaries of the HZ are based on one-dimensional (1D), cloud-free, climate model calculations by Kasting et al. However, this model used band models that were based on older HITRAN and HITEMP line-by-line databases. The inner edge of the HZ in the Kasting et al. model was determined by loss of water, and the outer edge was determined by the maximum greenhouse provided by a CO 2 atmosphere. A conservative estimate for the width of the HZ from this model in our solar system is 0.95-1.67 AU. Here an updated 1D radiative-convective, cloud-free climate model is used to obtain new estimates for HZ widths around F, G, K, and M stars. New H 2 O and CO 2 absorption coefficients, derived from the HITRAN 2008 and HITEMP 2010 line-by-line databases, are important improvements to the climate model. According to the new model, the water-loss (inner HZ) and maximum greenhouse (outer HZ) limits for our solar system are at 0.99 and 1.70 AU, respectively, suggesting that the present Earth lies near the inner edge. Additional calculations are performed for stars with effective temperatures between 2600 and 7200 K, and the results are presented in parametric form, making them easy to apply to actual stars. The new model indicates that, near the inner edge of the HZ, there is no clear distinction between runaway greenhouse and water-loss limits for stars with T eff ∼ ⊕ , so that future flagship missions like TPF-C and Darwin are not undersized. Our model does not include the radiative effects of clouds; thus, the actual HZ boundaries may extend further in both directions than the estimates just given.

  2. Possible evidence for metal accretion onto the surfaces of metal-poor main-sequence stars

    Energy Technology Data Exchange (ETDEWEB)

    Hattori, Kohei; Yoshii, Yuzuru [Institute of Astronomy, School of Science, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan); Beers, Timothy C. [National Optical Astronomy Observatories, Tucson, AZ 85719 (United States); Carollo, Daniela [Department of Physics and Astronomy, Macquarie University, Sydney, 2109 NSW (Australia); Lee, Young Sun, E-mail: khattori@ioa.s.u-tokyo.ac.jp [Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States)

    2014-04-01

    The entire evolution of the Milky Way, including its mass-assembly and star-formation history, is imprinted onto the chemo-dynamical distribution function of its member stars, f(x, v, [X/H]), in the multi-dimensional phase space spanned by position, velocity, and elemental abundance ratios. In particular, the chemo-dynamical distribution functions for low-mass stars (e.g., G- or K-type dwarfs) are precious tracers of the earliest stages of the Milky Way's formation, since their main-sequence lifetimes approach or exceed the age of the universe. A basic tenet of essentially all previous analyses is that the stellar metallicity, usually parameterized as [Fe/H], is conserved over time for main-sequence stars (at least those that have not been polluted due to mass transfer from binary companions). If this holds true, any correlations between metallicity and kinematics for long-lived main-sequence stars of different masses, effective temperatures, or spectral types must strictly be the same, since they reflect the same mass-assembly and star-formation histories. By analyzing a sample of nearby metal-poor halo and thick-disk stars on the main sequence, taken from Data Release 8 of the Sloan Digital Sky Survey, we find that the median metallicity of G-type dwarfs is systematically higher (by about 0.2 dex) than that of K-type dwarfs having the same median rotational velocity about the Galactic center. If it can be confirmed, this finding may invalidate the long-accepted assumption that the atmospheric metallicities of long-lived stars are conserved over time.

  3. Dust discs around low-mass main-sequence stars

    International Nuclear Information System (INIS)

    Wolstencroft, R.D.; Walker, H.J.

    1988-01-01

    Current understanding of the formation of circumstellar discs as a natural accompaniment to the process of low-mass star formation is briefly reviewed. Models of the thermal emission from the dust discs around the prototype stars α Lyr, α PsA, β Pic and ε Eri are discussed, which indicate that the central regions of three of these discs are almost devoid of dust within radii ranging between 17 and 26 AU, with the temperature of the hottest dust lying between about 115 and 210 K. One possible explanation of the dust-free zones is the presence of a planet at the inner boundary of each cloud that sweeps up grains crossing its orbit. The colour, diameter and thickness of the optical image of β Pic, obtained by coronagraphic techniques, have provided further information on the size, radial distribution of number density and orbital inclination of the grains. The difference in surface brightness on the two sides of the disc is puzzling, but might be explained if the grains are elongated and aligned by the combined effects of a stellar wind and a magnetic field of spiral configuration. Finally, we discuss the orbital evolution and lifetimes of particles in these discs, which are governed primarily by radiation pressure, Poynting-Robertson drag and grain-grain collisions. (author)

  4. Cyanogen strengths of globular cluster post-main-sequence stars

    International Nuclear Information System (INIS)

    Hesser, J.E.; Hartwick, F.D.A.; McClure, R.D.

    1976-01-01

    CN strengths in the peculiar clusters ω Cen and M22 and the metal-rich clusters 47 Tuc, M71, and NGC 6352 are found to vary markedly from star to star. The strong variations in CN strength found earlier for ω Cen by Norris and Bessell and by Dickens and Bell are shown to extend to fainter stars, although expected correlations of CN strength with position in the color-magnitude (C-M) diagram are less evident in our sample. Several CN and metal-strong stars were also observed in M22. We conclude that CN, once it appears in globular clusters, can vary much more than it does in equivalent Population I samples, a result we briefly examine in light of current understanding regarding physical processes in the stars themselves and of models of galactic chemical evolution

  5. Impacts of WIMP dark matter upon stellar evolution: main-sequence stars

    CERN Document Server

    Scott, Pat; Edsjo, Joakim

    2008-01-01

    The presence of large amounts of WIMP dark matter in stellar cores has been shown to have significant effects upon models of stellar evolution. We present a series of detailed grids of WIMP-influenced stellar models for main sequence stars, computed using the DarkStars code. We describe the changes in stellar structure and main sequence evolution which occur for masses ranging from 0.3 to 2.0 solar masses and metallicities from Z = 0.0003-0.02, as a function of the rate of energy injection by WIMPs. We then go on to show what rates of energy injection can be obtained using realistic orbital parameters for stars near supermassive black holes, including detailed considerations of dark matter halo velocity and density profiles. Capture and annihilation rates are strongly boosted when stars follow elliptical rather than circular orbits, causing WIMP annihilation to provide up to 100 times the energy of hydrogen fusion in stars at the Galactic centre.

  6. Tracing early stellar evolution with asteroseismology: pre-main sequence stars in NGC 2264

    Directory of Open Access Journals (Sweden)

    Zwintz Konstanze

    2015-01-01

    Full Text Available Asteroseismology has been proven to be a successful tool to unravel details of the internal structure for different types of stars in various stages of their main sequence and post-main sequence evolution. Recently, we found a relation between the detected pulsation properties in a sample of 34 pre-main sequence (pre-MS δ Scuti stars and the relative phase in their pre-MS evolution. With this we are able to demonstrate that asteroseismology is similarly powerful if applied to stars in the earliest stages of evolution before the onset of hydrogen core burning.

  7. Carbon, nitrogen, and oxygen abundances in main-sequence stars. II. 20 F and G stars

    International Nuclear Information System (INIS)

    Clegg, R.E.S.; Lambert, D.L.; Tomkin, J.

    1981-01-01

    High-resolution Reticon spectra of red and near-infrared C I, N I, and O I lines have been analyzed to determine C, N, and O abundances in a sample of 20 F and G main-sequence stars. Their iron abundances, which have been determined from analysis of additional Reticon spectra of red Fe I lines, cover the range -0.9< or =[Fe/H]< or =+0.4. Sulfur abundances have also been obtained

  8. Turbulence and the Li abundance in main sequence and giant stars

    International Nuclear Information System (INIS)

    Charbonneau, P.; Michaud, G.

    1990-01-01

    Calculations of Li burning via turbulent transport are conducted to determine the extent to which observed Li abundances in first ascent giants constrain the various turbulence parameterizations used to model the main-sequence surface Li abundance evolution. A full time-dependent solution to the transport equation is performed, including nuclear reaction terms and evolutionary effects. It is found that turbulence can lead to the extreme Li underabundances observed in giants of M67 and NGC 752. Consideration is given to the possibility of using observations of Li abundances to discriminate between turbulent particle transport and meridional circulation transport. Numerical solutions of the turbulent diffusion coefficient of Vauclair (1988) is used to model the Hyades Li abundance gap. The astrophysical implications of the results for main-sequence and giant stars are discussed. 36 refs

  9. Magnetic fields in O-, B- and A-type stars on the main sequence

    Directory of Open Access Journals (Sweden)

    Briquet Maryline

    2015-01-01

    Full Text Available In this review, the latest observational results on magnetic fields in main-sequence stars with radiative envelopes are summarised together with the theoretical works aimed at explaining them.

  10. Reconciling mass functions with the star-forming main sequence via mergers

    Science.gov (United States)

    Steinhardt, Charles L.; Yurk, Dominic; Capak, Peter

    2017-06-01

    We combine star formation along the 'main sequence', quiescence and clustering and merging to produce an empirical model for the evolution of individual galaxies. Main-sequence star formation alone would significantly steepen the stellar mass function towards low redshift, in sharp conflict with observation. However, a combination of star formation and merging produces a consistent result for correct choice of the merger rate function. As a result, we are motivated to propose a model in which hierarchical merging is disconnected from environmentally independent star formation. This model can be tested via correlation functions and would produce new constraints on clustering and merging.

  11. A near-infrared survey for pre-main sequence stars in Taurus

    Science.gov (United States)

    Gomez, Mercedes; Kenyon, Scott J.; Hartmann, Lee

    1994-01-01

    We present a near-infrared survey of approximately 2 sq deg covering parts of L1537, L1538, and Heiles cloud 2 in the Taurus-Auriga molecular cloud. Although this study is more sensitive than previous attempts to identify pre-main sequence stars in Taurus-Auriga, our survey regions contain only one new optically visible, young star. We did find several candidate embedded protostars; additional 10 micrometer photometry is necessary to verify the pre-main sequence nature of these sources. Our results--combined with those of previous surveys--show that the L1537/L1538 clouds contain no pre-main sequence stars. These two clouds are less dense than the active star formation sites in Taurus-Auriga, which suggests a cloud must achieve a threshold density to form stars.

  12. The V Band Empirical Mass-Luminosity Relation for Main Sequence Stars

    Science.gov (United States)

    Xia, F.; Fu, Y. N.

    2010-01-01

    Stellar mass is an indispensable parameter in the studies of stellar physics and stellar dynamics. On the one hand, the most reliable way to determine the stellar dynamical mass is via orbital determination of binaries. On the other hand, however, most stellar masses have to be estimated by using the mass-luminosity relation (MLR). Therefore, it is important to obtain the empirical MLR through fitting the data of stellar dynamical mass and luminosity. The effect of metallicity can make this relation disperse in the V-band, but studies show that this is mainly limited to the case when the stellar mass is less than 0.6M⊙. Recently, many relevant data have been accumulated for main sequence stars with larger mass, which make it possible to significantly improve the corresponding MLR. Using a fitting method which can reasonably assign weight to the observational data including two quantities with different dimensions, we obtain a V-band MLR based on the dynamical masses and luminosities of 203 main sequence stars. Compared with the previous work, the improved MLR is statistically significant, and the relative error of mass estimation reaches about 5%. Therefore, our MLR is useful not only in studies of statistical nature, but also in studies of concrete stellar systems, such as the long-term dynamical study and the short-term positioning study of a specific multiple star system.

  13. The V-band Empirical Mass-luminosity Relation for Main Sequence Stars

    Science.gov (United States)

    Xia, Fang; Fu, Yan-Ning

    2010-07-01

    Stellar mass is an indispensable parameter in the studies of stellar physics and stellar dynamics. On the one hand, the most reliable way to determine the stellar dynamical mass is via orbital determinations of binaries. On the other hand, however, most stellar masses have to be estimated by using the mass luminosity relation (MLR). Therefore, it is important to obtain the empirical MLR through fitting the data of stellar dynamical mass and luminosity. The effect of metallicity can make this relation disperse in the V-band, but studies show that this is mainly limited to the case when the stellar mass is less than 0.6M⊙ Recently, many relevant data have been accumulated for main sequence stars with larger masses, which make it possible to significantly improve the corresponding MLR. Using a fitting method which can reasonably assign weights to the observational data including two quantities with different dimensions, we obtain a V-band MLR based on the dynamical masses and luminosities of 203 main sequence stars. In comparison with the previous work, the improved MLR is statistically significant, and the relative error of mass estimation reaches about 5%. Therefore, our MLR is useful not only in the studies of statistical nature, but also in the studies of concrete stellar systems, such as the long-term dynamical study and the short-term positioning study of a specific multiple star system.

  14. The SAMI Galaxy Survey: spatially resolving the main sequence of star formation

    Science.gov (United States)

    Medling, Anne M.; Cortese, Luca; Croom, Scott M.; Green, Andrew W.; Groves, Brent; Hampton, Elise; Ho, I.-Ting; Davies, Luke J. M.; Kewley, Lisa J.; Moffett, Amanda J.; Schaefer, Adam L.; Taylor, Edward; Zafar, Tayyaba; Bekki, Kenji; Bland-Hawthorn, Joss; Bloom, Jessica V.; Brough, Sarah; Bryant, Julia J.; Catinella, Barbara; Cecil, Gerald; Colless, Matthew; Couch, Warrick J.; Drinkwater, Michael J.; Driver, Simon P.; Federrath, Christoph; Foster, Caroline; Goldstein, Gregory; Goodwin, Michael; Hopkins, Andrew; Lawrence, J. S.; Leslie, Sarah K.; Lewis, Geraint F.; Lorente, Nuria P. F.; Owers, Matt S.; McDermid, Richard; Richards, Samuel N.; Sharp, Robert; Scott, Nicholas; Sweet, Sarah M.; Taranu, Dan S.; Tescari, Edoardo; Tonini, Chiara; van de Sande, Jesse; Walcher, C. Jakob; Wright, Angus

    2018-04-01

    We present the ˜800 star formation rate maps for the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey based on H α emission maps, corrected for dust attenuation via the Balmer decrement, that are included in the SAMI Public Data Release 1. We mask out spaxels contaminated by non-stellar emission using the [O III]/H β, [N II]/H α, [S II]/H α, and [O I]/H α line ratios. Using these maps, we examine the global and resolved star-forming main sequences of SAMI galaxies as a function of morphology, environmental density, and stellar mass. Galaxies further below the star-forming main sequence are more likely to have flatter star formation profiles. Early-type galaxies split into two populations with similar stellar masses and central stellar mass surface densities. The main-sequence population has centrally concentrated star formation similar to late-type galaxies, while galaxies >3σ below the main sequence show significantly reduced star formation most strikingly in the nuclear regions. The split populations support a two-step quenching mechanism, wherein halo mass first cuts off the gas supply and remaining gas continues to form stars until the local stellar mass surface density can stabilize the reduced remaining fuel against further star formation. Across all morphologies, galaxies in denser environments show a decreased specific star formation rate from the outside in, supporting an environmental cause for quenching, such as ram-pressure stripping or galaxy interactions.

  15. An extensive VLT/X-shooter library of photospheric templates of pre-main sequence stars

    Science.gov (United States)

    Manara, C. F.; Frasca, A.; Alcalá, J. M.; Natta, A.; Stelzer, B.; Testi, L.

    2017-09-01

    Context. Studies of the formation and evolution of young stars and their disks rely on knowledge of the stellar parameters of the young stars. The derivation of these parameters is commonly based on comparison with photospheric template spectra. Furthermore, chromospheric emission in young active stars impacts the measurement of mass accretion rates, a key quantity for studying disk evolution. Aims: Here we derive stellar properties of low-mass (M⋆≲ 2 M⊙) pre-main sequence stars without disks, which represent ideal photospheric templates for studies of young stars. We also use these spectra to constrain the impact of chromospheric emission on the measurements of mass accretion rates. The spectra are reduced, flux-calibrated, and corrected for telluric absorption, and are made available to the community. Methods: We derive the spectral type for our targets by analyzing the photospheric molecular features present in their VLT/X-shooter spectra by means of spectral indices and comparison of the relative strength of photospheric absorption features. We also measure effective temperature, gravity, projected rotational velocity, and radial velocity from our spectra by fitting them with synthetic spectra with the ROTFIT tool. The targets have negligible extinction (AVpresented in our previous publication. We perform synthetic photometry on the spectra to derive the typical colors of young stars in different filters. We measure the luminosity of the emission lines present in the spectra and estimate the noise due to chromospheric emission in the measurements of accretion luminosity in accreting stars. Results: We provide a calibration of the photospheric colors of young pre-main sequence stars as a function of their spectral type in a set of standard broad-band optical and near-infrared filters. The logarithm of the noise on the accretion luminosity normalized to the stellar luminosity is roughly constant and equal to -2.3 for targets with masses larger than 1 solar

  16. Rotation in moderate-mass pre-main-sequence radiative track G stars

    International Nuclear Information System (INIS)

    Mcnamara, B.

    1990-01-01

    Recent studies suggest that the observed high-mass radiative track velocity histograms for pre-main-sequence stars differ significantly. In the Vogel and Kuhi (1981) study, these stars were found to possess a rather broad distribution of rotational velocities with a moderate peak at low velocities. In contrast, Smith et al. (1983), found a very sharply peaked distribution located at low values of v sin i. The difference in these velocity distributions is shown to be due to inadequate allowance for field stars in the Smith, et al., work. Once these stars are removed, the high-mass velocity distributions of the two regions are remarkably similar. This result suggests that a unique velocity distribution might be used in modeling very young stars. Assuming that the Orion Ic proto-F stars continue to contract in a homologous fashion, their average current rotational velocity is in agreement with that expected for zero-age main sequence F stars. 27 refs

  17. INTRINSIC COLORS, TEMPERATURES, AND BOLOMETRIC CORRECTIONS OF PRE-MAIN-SEQUENCE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Pecaut, Mark J.; Mamajek, Eric E. [University of Rochester, Department of Physics and Astronomy, Rochester, NY 14627-0171 (United States)

    2013-09-01

    We present an analysis of the intrinsic colors and temperatures of 5-30 Myr old pre-main-sequence (pre-MS) stars using the F0- through M9-type members of nearby, negligibly reddened groups: the η Cha cluster, the TW Hydra Association, the β Pic Moving Group, and the Tucana-Horologium Association. To check the consistency of spectral types from the literature, we estimate new spectral types for 52 nearby pre-MS stars with spectral types F3 through M4 using optical spectra taken with the SMARTS 1.5 m telescope. Combining these new types with published spectral types and photometry from the literature (Johnson-Cousins BVI{sub C} , 2MASS JHK{sub S} and WISE W1, W2, W3, and W4), we derive a new empirical spectral type-color sequence for 5-30 Myr old pre-MS stars. Colors for pre-MS stars match dwarf colors for some spectral types and colors, but for other spectral types and colors, deviations can exceed 0.3 mag. We estimate effective temperatures (T {sub eff}) and bolometric corrections (BCs) for our pre-MS star sample through comparing their photometry to synthetic photometry generated using the BT-Settl grid of model atmosphere spectra. We derive a new T {sub eff} and BC scale for pre-MS stars, which should be a more appropriate match for T Tauri stars than often-adopted dwarf star scales. While our new T {sub eff} scale for pre-MS stars is within ≅100 K of dwarfs at a given spectral type for stars stars are ∼250 K cooler than their MS counterparts. Lastly, we present (1) a modern T {sub eff}, optical/IR color, and BC sequence for O9V-M9V MS stars based on an extensive literature survey, (2) a revised Q-method relation for dereddening UBV photometry of OB-type stars, and (3) introduce two candidate spectral standard stars as representatives of spectral types K8V and K9V.

  18. STELLAR DIAMETERS AND TEMPERATURES. II. MAIN-SEQUENCE K- AND M-STARS

    Energy Technology Data Exchange (ETDEWEB)

    Boyajian, Tabetha S.; McAlister, Harold A.; Jones, Jeremy; White, Russel; Henry, Todd; Gies, Douglas; Jao, Wei-Chun; Parks, J. Robert [Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, P.O. Box 4106, Atlanta, GA 30302-4106 (United States); Von Braun, Kaspar; Kane, Stephen R.; Ciardi, David [NASA Exoplanet Science Institute, California Institute of Technology, MC 100-22, Pasadena, CA 91125 (United States); Van Belle, Gerard [Lowell Observatory, Flagstaff, AZ 86001 (United States); Ten Brummelaar, Theo A.; Schaefer, Gail; Sturmann, Laszlo; Sturmann, Judit [The CHARA Array, Mount Wilson Observatory, Mount Wilson, CA 91023 (United States); Muirhead, Philip S. [Department of Astronomy, California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States); Lopez-Morales, Mercedes [Institut de Ciencies de L' Espai (CSIC-IEEC), E-08193 Bellaterra (Spain); Ridgway, Stephen [National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726-6732 (United States); Rojas-Ayala, Barbara [Department of Astrophysics, Division of Physical Sciences, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States); and others

    2012-10-01

    We present interferometric angular diameter measurements of 21 low-mass, K- and M-dwarfs made with the CHARA Array. This sample is enhanced by adding a collection of radius measurements published in the literature to form a total data set of 33 K-M-dwarfs with diameters measured to better than 5%. We use these data in combination with the Hipparcos parallax and new measurements of the star's bolometric flux to compute absolute luminosities, linear radii, and effective temperatures for the stars. We develop empirical relations for {approx}K0 to M4 main-sequence stars that link the stellar temperature, radius, and luminosity to the observed (B - V), (V - R), (V - I), (V - J), (V - H), and (V - K) broadband color index and stellar metallicity [Fe/H]. These relations are valid for metallicities ranging from [Fe/H] = -0.5 to +0.1 dex and are accurate to {approx}2%, {approx}5%, and {approx}4% for temperature, radius, and luminosity, respectively. Our results show that it is necessary to use metallicity-dependent transformations in order to properly convert colors into stellar temperatures, radii, and luminosities. Alternatively, we find no sensitivity to metallicity on relations we construct to the global properties of a star omitting color information, e.g., temperature-radius and temperature-luminosity. Thus, we are able to empirically quantify to what order the star's observed color index is impacted by the stellar iron abundance. In addition to the empirical relations, we also provide a representative look-up table via stellar spectral classifications using this collection of data. Robust examinations of single star temperatures and radii compared to evolutionary model predictions on the luminosity-temperature and luminosity-radius planes reveal that models overestimate the temperatures of stars with surface temperatures <5000 K by {approx}3%, and underestimate the radii of stars with radii <0.7 R{sub Sun} by {approx}5%. These conclusions additionally

  19. 13-colour photometry of pre-main sequence stars: preliminary report and results

    Energy Technology Data Exchange (ETDEWEB)

    Chavarria-K, C; de Lara, E [Universidad Nacional Autonoma de Mexico, Mexico City. Inst. de Astronomia

    1981-01-01

    Broad (UBVRI) and intermediate (13-colour) band photometry of 160 stars selected mainly from the Herbig Rao catalogue are being carried on currently, mainly to complement the published data of these stars in the optical window (for example shortward of the Balmer and longward of the Paschen discontinuities). The 13-colour photometric system and its applications to pre-main sequences stars are briefly discussed. First results are presented.

  20. The Star-forming Main Sequence of Dwarf Low Surface Brightness Galaxies

    Science.gov (United States)

    McGaugh, Stacy S.; Schombert, James M.; Lelli, Federico

    2017-12-01

    We explore the star-forming properties of late-type, low surface brightness (LSB) galaxies. The star-forming main sequence ({SFR}-{M}* ) of LSB dwarfs has a steep slope, indistinguishable from unity (1.04 ± 0.06). They form a distinct sequence from more massive spirals, which exhibit a shallower slope. The break occurs around {M}* ≈ {10}10 {M}⊙ , and can also be seen in the gas mass—stellar mass plane. The global Kennicutt-Schmidt law ({SFR}-{M}g) has a slope of 1.47 ± 0.11 without the break seen in the main sequence. There is an ample supply of gas in LSB galaxies, which have gas depletion times well in excess of a Hubble time, and often tens of Hubble times. Only ˜ 3 % of this cold gas needs be in the form of molecular gas to sustain the observed star formation. In analogy with the faint, long-lived stars of the lower stellar main sequence, it may be appropriate to consider the main sequence of star-forming galaxies to be defined by thriving dwarfs (with {M}* {10}10 {M}⊙ ) are weary giants that constitute more of a turn-off population.

  1. The Lower Main Sequence of Stars in the Solar Neighborhood: Model Predictions Versus Observation

    Directory of Open Access Journals (Sweden)

    Bartašiūtė S.

    2012-09-01

    Full Text Available We have used the Simbad database and VizieR catalogue access tools to construct the observational color-absolute magnitude diagrams of nearby K-M dwarfs with precise Hipparcos parallaxes (σπ/π ≤ 0:05. Particular attention has been paid to removing unresolved double/multiple stars and variables. In addition to archival data, we have made use of nearly 2000 new radial-velocity measurements of K-M dwarfs to identify spectroscopic binary candidates. The main sequences, cleaned from unresolved binaries, variable stars, and old population stars which can also widen the sequence due to their presumably lower metallicity, were compared to available solar-metallicity models. Significant offsets of most of the model main-sequence lines are seen with respect to observational data, especially for the lower-mass stars. Only the location and slope of the Victoria-Regina and, partly, BaSTI isochrones match the data quite well.

  2. On the mass-spectrum relation for the main sequence stars

    International Nuclear Information System (INIS)

    Svechnikov, M.A.; Tajdakova, T.A.

    1984-01-01

    From 240 main-sequence stars with well-determined masses, a new mass-spectrum relation is obtained, which differs appreciably in certain intervals of spectral types from the mass-spectrum relations of Allen and Trimble. The accuracy of mass determination for the components of eclipsing binary systems of different types from their spectra given in the General Catalogue of Variable Stars (3rd edition) and in its supplements is evaluated

  3. Discovery of three x-ray luminous pre-main-sequence stars

    International Nuclear Information System (INIS)

    Feigelson, E.D.; Kriss, G.A.

    1981-01-01

    Three X-ray sources found serendipitously in Einstein images of the Taurus-Auriga cloud complex were observed at the McGraw-Hill Observatory and are found to be associated with approx.12 mag stars with weak Hα emission. The stars lie on the edges of dark clouds and are spectroscopically similar to the least active emission-line pre-main-sequence stars. Although they lie well above the ZAMS in the H-R diagram, they do not exhibit ultraviolet excess, strong optical variability, or evidence for mass outflow/inflow characteristics of the more active T Tauri stars. Their only unusual property is high X-ray luminosity (approx.10 30 ergs s1). It is suggested that the X-ray emission from pre-main-sequence stars is not closely linked to the conditions giving rise to their unusual spectroscopic properties. The emission may instead represent an enhanced form of the coronal activity producing X-rays observed in late-type main-sequence stars

  4. Binary pulsar PSR 1718-19 contains a stripped main-sequence turn-off star

    International Nuclear Information System (INIS)

    Zwitter, T.

    1993-05-01

    Lyne et al. (1993) have recently announced the discovery of a 1-second globular cluster pulsar, 1718-19, in a 6.2-hour binary system which is embedded in a cloud of material originating from the companion star. However the incident flux of the pulsar's radiation on the companion is too low to ablate it and a main sequence companion is too small to fill its Roche lobe. Here I argue that the companion is a stripped turn-off star of 0.2-0.4 solar masses (M sun ) and with approx. 0.1M sun helium core. It has approx. 1.8-times larger radius than a main sequence star of equal mass. Its position in the Hertzsprung-Russell diagram overlaps that of a ∼ 0.65M sun main-sequence star. The evolutionary state of the companion and the highly magnetized slowly rotating neutron star place the system on the verge of the low mass X-ray binary phase. (author). 19 refs, 2 figs

  5. Radio emission from pre-main-sequence stars in Corona Australis

    International Nuclear Information System (INIS)

    Brown, A.

    1987-01-01

    The central region of the Corona Australis molecular cloud surrounding the stars R and TY CrA has been studied using the VLA at 6 cm. Eleven radio sources are detected including five associated with pre-main-sequence objects. The most striking is associated with the near-IR source IRS 7 and shows a complex structure comprising two strong pointlike sources positioned either side of the deeply embedded IR source and two extended lobes of radio emission. The IRS 7 radio source appears to be similar to that associated with Lynds 1551 IRS 5 but has a considerably larger angular size. The other detected sources include the massive pre-main-sequence star TY CrA, the near-IR sources IRS 1 and IRS 5, and the Herbig-Haro object HH 101. The stars R and T CrA were not detected. 35 references

  6. Characterizing Intermediate-Mass, Pre-Main-Sequence Stars via X-Ray Emision

    Science.gov (United States)

    Haze Nunez, Evan; Povich, Matthew Samuel; Binder, Breanna Arlene; Broos, Patrick; Townsley, Leisa K.

    2018-01-01

    The X-ray emission from intermediate-mass, pre-main-sequence stars (IMPS) can provide useful constraints on the ages of very young (${getting power from the gravitational contraction of the star. Main-sequence late-B and A-type stars are not expected to be strong X-ray emitters, because they lack the both strong winds of more massive stars and the magneto-coronal activity of lower-mass stars. There is, however, mounting evidence that IMPS are powerful intrinsic x-ray emitters during their convection-dominated early evolution, before the development and rapid growth of a radiation zone. We present our prime candidates for intrinsic, coronal X-ray emission from IMPS identified in the Chandra Carina Complex Project. The Carina massive star-forming complex is of special interest due to the wide variation of star formation stages within the region. Candidate IMPS were identified using infrared spectral energy distribution (SED) models. X-ray properties, including thermal plasma temperatures and absorption-corrected fluxes, were derived from XSPEC fits performed using absorption ($N_{H}$) constrained by the extinction values returned by the infrared SED fits. We find that IMPS have systematically higher X-ray luminosities compared to their lower-mass cousins, the TTauri stars.This work is supported by the National Science Foundation under grant CAREER-1454334 and by NASA through Chandra Award 18200040.

  7. Elevation or Suppression? The Resolved Star Formation Main Sequence of Galaxies with Two Different Assembly Modes

    Science.gov (United States)

    Liu, Qing; Wang, Enci; Lin, Zesen; Gao, Yulong; Liu, Haiyang; Berhane Teklu, Berzaf; Kong, Xu

    2018-04-01

    We investigate the spatially resolved star formation main sequence in star-forming galaxies using Integral Field Spectroscopic observations from the Mapping Nearby Galaxies at the Apache Point Observatory survey. We demonstrate that the correlation between the stellar mass surface density (Σ*) and star formation rate surface density (ΣSFR) holds down to the sub-galactic scale, leading to the sub-galactic main sequence (SGMS). By dividing galaxies into two populations based on their recent mass assembly modes, we find the resolved main sequence in galaxies with the “outside-in” mode is steeper than that in galaxies with the “inside-out” mode. This is also confirmed on a galaxy-by-galaxy level, where we find the distributions of SGMS slopes for individual galaxies are clearly separated for the two populations. When normalizing and stacking the SGMS of individual galaxies on one panel for the two populations, we find that the inner regions of galaxies with the “inside-out” mode statistically exhibit a suppression in star formation, with a less significant trend in the outer regions of galaxies with the “outside-in” mode. In contrast, the inner regions of galaxies with “outside-in” mode and the outer regions of galaxies with “inside-out” mode follow a slightly sublinear scaling relation with a slope ∼0.9, which is in good agreement with previous findings, suggesting that they are experiencing a universal regulation without influences of additional physical processes.

  8. HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: DEPENDENCE ON PLANETARY MASS

    International Nuclear Information System (INIS)

    Kopparapu, Ravi Kumar; Ramirez, Ramses M.; Kasting, James F.; SchottelKotte, James; Domagal-Goldman, Shawn; Eymet, Vincent

    2014-01-01

    The ongoing discoveries of extra-solar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this Letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K-7200 K, for planetary masses between 0.1 M ⊕ and 5 M ⊕ . Assuming H 2 O-(inner HZ) and CO 2 -(outer HZ) dominated atmospheres, and scaling the background N 2 atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets will have less dense atmospheres, the inner edge of the HZ (runaway greenhouse limit) moves outward (∼10% lower than Earth flux) for low mass planets due to larger greenhouse effect arising from the increased H 2 O column depth. For larger planets, the H 2 O column depth is smaller, and higher temperatures are needed before water vapor completely dominates the outgoing longwave radiation. Hence the inner edge moves inward (∼7% higher than Earth's flux). The outer HZ changes little due to the competing effects of the greenhouse effect and an increase in albedo. New, three-dimensional climate model results from other groups are also summarized, and we argue that further, independent studies are needed to verify their predictions. Combined with our previous work, the results presented here provide refined estimates of HZs around main-sequence stars and provide a step toward a more comprehensive analysis of HZs

  9. Habitable Zones Around Main-Sequence Stars: Dependence on Planetary Mass

    Science.gov (United States)

    Kopparapu, Ravi Kumar; Ramirez, Ramses M.; Kotte, James Schottel; Kasting, James F.; Domagal-Goldman, Shawn; Eymet, Vincent

    2014-01-01

    The ongoing discoveries of extra-solar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this Letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K-7200 K, for planetary masses between 0.1M and 5M. Assuming H2O-(inner HZ) and CO2-(outer HZ) dominated atmospheres, and scaling the background N2 atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets will have less dense atmospheres, the inner edge of the HZ (runaway greenhouse limit) moves outward (approx.10% lower than Earth flux) for low mass planets due to larger greenhouse effect arising from the increased H2O column depth. For larger planets, the H2O column depth is smaller, and higher temperatures are needed before water vapor completely dominates the outgoing long-wave radiation. Hence the inner edge moves inward (approx.7% higher than Earth's flux). The outer HZ changes little due to the competing effects of the greenhouse effect and an increase in albedo. New, three-dimensional climate model results from other groups are also summarized, and we argue that further, independent studies are needed to verify their predictions. Combined with our previous work, the results presented here provide refined estimates of HZs around main-sequence stars and provide a step toward a more comprehensive analysis of HZs.

  10. HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: DEPENDENCE ON PLANETARY MASS

    Energy Technology Data Exchange (ETDEWEB)

    Kopparapu, Ravi Kumar; Ramirez, Ramses M.; Kasting, James F. [Department of Geosciences, Penn State University, 443 Deike Building, University Park, PA 16802 (United States); SchottelKotte, James [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States); Domagal-Goldman, Shawn [NASA Astrobiology Institute' s Virtual Planetary Laboratory, P.O. Box 351580, Seattle, WA 98195 (United States); Eymet, Vincent, E-mail: ruk15@psu.edu [Laboratoire d' Astrophysique de Bordeaux, Universite de Bordeaux 1, UMR 5804, F-33270 Floirac (France)

    2014-06-01

    The ongoing discoveries of extra-solar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this Letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K-7200 K, for planetary masses between 0.1 M {sub ⊕} and 5 M {sub ⊕}. Assuming H{sub 2}O-(inner HZ) and CO{sub 2}-(outer HZ) dominated atmospheres, and scaling the background N{sub 2} atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets will have less dense atmospheres, the inner edge of the HZ (runaway greenhouse limit) moves outward (∼10% lower than Earth flux) for low mass planets due to larger greenhouse effect arising from the increased H{sub 2}O column depth. For larger planets, the H{sub 2}O column depth is smaller, and higher temperatures are needed before water vapor completely dominates the outgoing longwave radiation. Hence the inner edge moves inward (∼7% higher than Earth's flux). The outer HZ changes little due to the competing effects of the greenhouse effect and an increase in albedo. New, three-dimensional climate model results from other groups are also summarized, and we argue that further, independent studies are needed to verify their predictions. Combined with our previous work, the results presented here provide refined estimates of HZs around main-sequence stars and provide a step toward a more comprehensive analysis of HZs.

  11. Effects of main-sequence mass loss on stellar and galactic chemical evolution

    International Nuclear Information System (INIS)

    Guzik, J.A.

    1988-01-01

    L.A. Willson, G.H. Bowen and C. Struck-Marcell have proposed that 1 to 3 solar mass stars may experience evolutionarily significant mass loss during the early part of their main-sequence phase. The suggested mass-loss mechanism is pulsation, facilitated by rapid rotation. Initial mass-loss rates may be as large as several times 10 -9 M mass of sun/yr, diminishing over several times 10 8 years. The author attempts to test this hypothesis by comparing some theoretical implications with observations. Three areas are addressed: Solar models, cluster HR diagrams, and galactic chemical evolution. Mass-losing solar models were evolved that match the Sun's luminosity and radius at its present age. The most extreme viable models have initial mass 2.0 M 0 , and mass-loss rates decreasing exponentially over 2-3 x 10 8 years. Evolution calculations incorporating main-sequence mass loss were completed for a grid of models with initial masses 1.25 to 2.0 M mass of sun and mass loss timescales 0.2 to 2.0 Gry. Cluster HR diagrams synthesized with these models confirm the potential for the hypothesis to explain observed spreads or bifurcations in the upper main sequence, blue stragglers, anomalous giants, and poor fits of main-sequence turnoffs by standard isochrones. Simple closed galactic chemical evolution models were used to test the effects of main-sequence mass loss on the F and G dwarf distribution. Stars between 3.0 M mass of sun and a metallicity-dependent lower mass are assumed to lose mass. The models produce a 30 to 60% increase in the stars to stars-plus-remnants ratio, with fewer early-F dwarfs and many more late-F dwarfs remaining on the main sequence to the present

  12. The Star Formation Main Sequence in the Hubble Space Telescope Frontier Fields

    Science.gov (United States)

    Santini, Paola; Fontana, Adriano; Castellano, Marco; Di Criscienzo, Marcella; Merlin, Emiliano; Amorin, Ricardo; Cullen, Fergus; Daddi, Emanuele; Dickinson, Mark; Dunlop, James S.; Grazian, Andrea; Lamastra, Alessandra; McLure, Ross J.; Michałowski, Michał. J.; Pentericci, Laura; Shu, Xinwen

    2017-09-01

    We investigate the relation between star formation rate (SFR) and stellar mass (M), I.e., the main sequence (MS) relation of star-forming galaxies, at 1.3≤slant zFrontier Fields, on the basis of rest-frame UV observations. Gravitational lensing combined with deep HST observations allows us to extend the analysis of the MS down to {log} M/{M}⊙ ˜ 7.5 at z≲ 4 and {log} M/{M}⊙ ˜ 8 at higher redshifts, a factor of ˜10 below most previous results. We perform an accurate simulation to take into account the effect of observational uncertainties and correct for the Eddington bias. This step allows us to reliably measure the MS and in particular its slope. While the normalization increases with redshift, we fit an unevolving and approximately linear slope. We nicely extend to lower masses the results of brighter surveys. Thanks to the large dynamic range in mass and by making use of the simulation, we analyzed any possible mass dependence of the dispersion around the MS. We find tentative evidence that the scatter decreases with increasing mass, suggesting a larger variety of star formation histories in low-mass galaxies. This trend agrees with theoretical predictions and is explained as either a consequence of the smaller number of progenitors of low-mass galaxies in a hierarchical scenario and/or of the efficient but intermittent stellar feedback processes in low-mass halos. Finally, we observe an increase in the SFR per unit stellar mass with redshift milder than predicted by theoretical models, implying a still incomplete understanding of the processes responsible for galaxy growth.

  13. Hubble Tarantula Treasury Project - VI. Identification of Pre-Main-Sequence Stars using Machine Learning techniques

    Science.gov (United States)

    Ksoll, Victor F.; Gouliermis, Dimitrios A.; Klessen, Ralf S.; Grebel, Eva K.; Sabbi, Elena; Anderson, Jay; Lennon, Daniel J.; Cignoni, Michele; de Marchi, Guido; Smith, Linda J.; Tosi, Monica; van der Marel, Roeland P.

    2018-05-01

    The Hubble Tarantula Treasury Project (HTTP) has provided an unprecedented photometric coverage of the entire star-burst region of 30 Doradus down to the half Solar mass limit. We use the deep stellar catalogue of HTTP to identify all the pre-main-sequence (PMS) stars of the region, i.e., stars that have not started their lives on the main-sequence yet. The photometric distinction of these stars from the more evolved populations is not a trivial task due to several factors that alter their colour-magnitude diagram positions. The identification of PMS stars requires, thus, sophisticated statistical methods. We employ Machine Learning Classification techniques on the HTTP survey of more than 800,000 sources to identify the PMS stellar content of the observed field. Our methodology consists of 1) carefully selecting the most probable low-mass PMS stellar population of the star-forming cluster NGC2070, 2) using this sample to train classification algorithms to build a predictive model for PMS stars, and 3) applying this model in order to identify the most probable PMS content across the entire Tarantula Nebula. We employ Decision Tree, Random Forest and Support Vector Machine classifiers to categorise the stars as PMS and Non-PMS. The Random Forest and Support Vector Machine provided the most accurate models, predicting about 20,000 sources with a candidateship probability higher than 50 percent, and almost 10,000 PMS candidates with a probability higher than 95 percent. This is the richest and most accurate photometric catalogue of extragalactic PMS candidates across the extent of a whole star-forming complex.

  14. Asteroseismic measurement of surface-to-core rotation in a main-sequence star*

    Directory of Open Access Journals (Sweden)

    Kurtz Donald W.

    2015-01-01

    Full Text Available We have discovered rotationally split core g-mode triplets and surface p-mode triplets and quintuplets in a terminal age main-sequence A star, KIC 11145123, that shows both δ Sct p-mode pulsations and γ Dor g-mode pulsations. This gives the first robust determination of the rotation of the deep core and surface of a main-sequence star, essentially model-independently. We find its rotation to be nearly uniform with a period near 100 d, but we show with high confidence that the surface rotates slightly faster than the core. A strong angular momentum transfer mechanism must be operating to produce the nearly rigid rotation, and a mechanism other than viscosity must be operating to produce a more rapidly rotating surface than core. Our asteroseismic result, along with previous asteroseismic constraints on internal rotation in some B stars, and measurements of internal rotation in some subgiant, giant and white dwarf stars, has made angular momentum transport in stars throughout their lifetimes an observational science.

  15. ABSOLUTE PROPERTIES OF THE PRE-MAIN-SEQUENCE ECLIPSING BINARY STAR NP PERSEI

    Energy Technology Data Exchange (ETDEWEB)

    Lacy, Claud H. Sandberg [Physics Department, University of Arkansas, Fayetteville, AR 72701 (United States); Fekel, Francis C.; Muterspaugh, Matthew W. [Center of Excellence in Information Systems, Tennessee State University, Nashville, TN 37209 (United States); Pavlovski, Krešimir [Department of Physics, Faculty of Science, University of Zagreb, Bijenička cesta 32, 10000 Zagreb (Croatia); Torres, Guillermo, E-mail: clacy@uark.edu, E-mail: fekel@evans.tsuniv.edu, E-mail: pavlovski@phy.hr, E-mail: gtorres@cfa.harvard.edu, E-mail: matthew1@coe.tsuniv.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2016-07-01

    NP Per is a well-detached, 2.2 day eclipsing binary whose components are both pre-main-sequence stars that are still contracting toward the main-sequence phase of evolution. We report extensive photometric and spectroscopic observations with which we have determined their properties accurately. Their surface temperatures are quite different: 6420 ± 90 K for the larger F5 primary star and 4540 ± 160 K for the smaller K5e star. Their masses and radii are 1.3207 ± 0.0087 solar masses and 1.372 ± 0.013 solar radii for the primary, and 1.0456 ± 0.0046 solar masses and 1.229 ± 0.013 solar radii for the secondary. The orbital period is variable over long periods of time. A comparison of the observations with current stellar evolution models from MESA indicates that the stars cannot be fit at a single age: the secondary appears significantly younger than the primary. If the stars are assumed to be coeval and to have the age of the primary (17 Myr), then the secondary is larger and cooler than predicted by current models. The H α spectral line of the secondary component is completely filled by, presumably, chromospheric emission due to a magnetic activity cycle.

  16. X-ray sources in regions of star formation. II. The pre-main-sequence G star HDE 283572

    International Nuclear Information System (INIS)

    Walter, F.M.; Brown, A.; Linsky, J.L.; Rydgren, A.E.; Vrba, F.; Joint Institute for Laboratory Astrophysics, Boulder, CO; Computer Sciences Corp., El Segundo, CA; Naval Observatory, Flagstaff, AZ)

    1987-01-01

    This paper reports the detection of HDE 283572, a ninth-magnitude G star 8 arcmin south of RY Tau, as a bright X-ray source. The observations reveal this object to be a fairly massive (about 2 solar masses) pre-main-sequence star associated with the Taurus-Auriga star formation complex. It exhibits few of the characteristics of the classical T Tauri stars and is a good example of a naked T Tauri star. The star is a mid-G subgiant, of about three solar radii and rotates with a period of 1.5 d. The coronal and chromospheric surface fluxes are similar to those of the most active late type stars (excluding T Tauri stars). The X-ray and UV lines most likely arise in different atmospheric structures. Radiative losses are some 1000 times the quiet solar value and compare favorably with those of T Tauri stars. 49 references

  17. Globules, dark clouds, and low mass pre-main sequence stars

    International Nuclear Information System (INIS)

    Hyland, A.R.

    1981-01-01

    The current observational and theoretical literature on Bok globules and their relationship to star formation is reviewed. Recent observations of globules at optical, infrared, and far infrared wavelengths are shown to provide important constraints on their structure and evolutionary status, and the suggestion that many globules are gravitationally unstable is seriously questioned. Dark clouds associated with T associations are well-known sites of recent and continuing star formation. In recent years molecular observations and far infrared surveys have provided maps of such regions from which possible sites of star formation may be identified. Optical (Hα) and near infrared surveys have enabled a clear identification of pre-main sequence (PMS) objects within the clouds. Methods of distinguishing these from background objects and the nature of their infrared excesses are examined in the light of recent observations in the near and far infrared. The perennial question as to the existence of anomalous reddening within dark clouds is also investigated. (Auth.)

  18. Evolution Models of Helium White Dwarf–Main-sequence Star Merger Remnants

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xianfei; Bi, Shaolan [Department of Astronomy, Beijing Normal University, Beijing, 100875 (China); Hall, Philip D.; Jeffery, C. Simon, E-mail: zxf@bnu.edu.cn [Armagh Observatory, College Hill, Armagh BT61 9DG (United Kingdom)

    2017-02-01

    It is predicted that orbital decay by gravitational-wave radiation and tidal interaction will cause some close binary stars to merge within a Hubble time. The merger of a helium-core white dwarf with a main-sequence (MS) star can produce a red giant branch star that has a low-mass hydrogen envelope when helium is ignited and thus become a hot subdwarf. Because detailed calculations have not been made, we compute post-merger models with a stellar evolution code. We find the evolutionary paths available to merger remnants and find the pre-merger conditions that lead to the formation of hot subdwarfs. We find that some such mergers result in the formation of stars with intermediate helium-rich surfaces. These stars later develop helium-poor surfaces owing to diffusion. Combining our results with a model population and comparing to observed stars, we find that some observed intermediate helium-rich hot subdwarfs can be explained as the remnants of the mergers of helium-core white dwarfs with low-mass MS stars.

  19. Evolution Models of Helium White Dwarf–Main-sequence Star Merger Remnants

    International Nuclear Information System (INIS)

    Zhang, Xianfei; Bi, Shaolan; Hall, Philip D.; Jeffery, C. Simon

    2017-01-01

    It is predicted that orbital decay by gravitational-wave radiation and tidal interaction will cause some close binary stars to merge within a Hubble time. The merger of a helium-core white dwarf with a main-sequence (MS) star can produce a red giant branch star that has a low-mass hydrogen envelope when helium is ignited and thus become a hot subdwarf. Because detailed calculations have not been made, we compute post-merger models with a stellar evolution code. We find the evolutionary paths available to merger remnants and find the pre-merger conditions that lead to the formation of hot subdwarfs. We find that some such mergers result in the formation of stars with intermediate helium-rich surfaces. These stars later develop helium-poor surfaces owing to diffusion. Combining our results with a model population and comparing to observed stars, we find that some observed intermediate helium-rich hot subdwarfs can be explained as the remnants of the mergers of helium-core white dwarfs with low-mass MS stars.

  20. Systematic main sequence photometry of globular cluster stars for age determination

    International Nuclear Information System (INIS)

    Alcaino, G.; Liller, W.

    1984-01-01

    The individual photometric study of the coeval stars in globular clusters presents one of the best observational tests of the stellar evolution theory. Our own globular cluster system provides fundamental clues to the dynamical and chemical evolutionary history of the galaxy, and the study of their ages give a lower limit to the age of the galaxy as well as to that of the universe. The authors have undertaken a systematic research program, and discuss the ages deduced by fitting main sequence photometry to theoretical isochrones of six galactic globular clusters: M4, M22, M30, NGC 288, NGC 3201 and NGC 6397. (Auth.)

  1. Spectroscopic and asteroseismic analysis of the remarkable main-sequence A star KIC 11145123

    DEFF Research Database (Denmark)

    Takada-Hidai, Masahide; Kurtz, Donald W.; Shibahashi, Hiromoto

    2017-01-01

    A spectroscopic analysis was carried out to clarify the properties of KIC 11145123 - the first main-sequence star with a directly measured core-to-surface rotation profile - based on spectra observed with the High Dispersion Spectrograph (HDS) of the Subaru telescope. The atmospheric parameters (T......-eff = 7600 K, log g = 4.2, xi = 3.1 kms(-1) and [Fe/H] = -0.71 dex), the radial and rotation velocities, and elemental abundances were obtained by analysing line strengths and fitting line profiles, which were calculated with a 1D LTE model atmosphere. The main properties of KIC 11145123 are: (1) a low [Fe...

  2. Verifying reddening and extinction for Gaia DR1 TGAS main sequence stars

    Science.gov (United States)

    Gontcharov, George A.; Mosenkov, Aleksandr V.

    2017-12-01

    We compare eight sources of reddening and extinction estimates for approximately 60 000 Gaia DR1 Tycho-Gaia Astrometric Solution (TGAS) main sequence stars younger than 3 Gyr with a relative error of the Gaia parallax less than 0.1. For the majority of the stars, the best 2D dust emission-based reddening maps show considerable differences between the reddening to infinity and the one calculated to the stellar distance using the barometric law of the dust distribution. This proves that the majority of the TGAS stars are embedded in the Galactic dust layer and a proper 3D treatment of the reddening/extinction is required to calculate their dereddened colours and absolute magnitudes reliably. Sources with 3D estimates of reddening are tested in their ability to put the stars among the PARSEC and MIST theoretical isochrones in the Hertzsprung-Russell diagram based on the precise Gaia, Tycho-2, 2MASS and WISE photometry. Only the reddening/extinction estimates by Arenou et al. and Gontcharov, being appropriate for nearby stars within 280 pc, provide both the minimal number of outliers bluer than any reasonable isochrone and the correct number of stars younger than 3 Gyr in agreement with the Besançon Galaxy model.

  3. Magnetic inhibition of convection and the fundamental properties of low-mass stars. II. Fully convective main-sequence stars

    Energy Technology Data Exchange (ETDEWEB)

    Feiden, Gregory A. [Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala (Sweden); Chaboyer, Brian, E-mail: gregory.a.feiden@gmail.com, E-mail: brian.chaboyer@dartmouth.edu [Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, NH 03755 (United States)

    2014-07-01

    We examine the hypothesis that magnetic fields are inflating the radii of fully convective main-sequence stars in detached eclipsing binaries (DEBs). The magnetic Dartmouth stellar evolution code is used to analyze two systems in particular: Kepler-16 and CM Draconis. Magneto-convection is treated assuming stabilization of convection and also by assuming reductions in convective efficiency due to a turbulent dynamo. We find that magnetic stellar models are unable to reproduce the properties of inflated fully convective main-sequence stars, unless strong interior magnetic fields in excess of 10 MG are present. Validation of the magnetic field hypothesis given the current generation of magnetic stellar evolution models therefore depends critically on whether the generation and maintenance of strong interior magnetic fields is physically possible. An examination of this requirement is provided. Additionally, an analysis of previous studies invoking the influence of star spots is presented to assess the suggestion that star spots are inflating stars and biasing light curve analyses toward larger radii. From our analysis, we find that there is not yet sufficient evidence to definitively support the hypothesis that magnetic fields are responsible for the observed inflation among fully convective main-sequence stars in DEBs.

  4. A Population Study of Wide-Separation Brown Dwarf Companions to Main Sequence Stars

    Science.gov (United States)

    Smith, Jeffrey J.

    2005-01-01

    Increased interest in infrared astronomy has opened the frontier to study cooler objects that shed significant light on the formation of planetary systems. Brown dwarf research provides a wealth of information useful for sorting through a myriad of proposed formation theories. Our study combines observational data from 2MASS with rigorous computer simulations to estimate the true population of long-range (greater than 1000 AU) brown dwarf companions in the solar neighborhood (less than 25 pc from Earth). Expanding on Gizis et al. (2001), we have found the margin of error in previous estimates to be significantly underestimated after we included orbit eccentricity, longitude of pericenter, angle of inclination, field star density, and primary and secondary luminosities as parameters influencing the companion systems in observational studies. We apply our simulation results to current L- and T-dwarf catalogs to provide updated estimates on the frequency of wide-separation brown dwarf companions to main sequence stars.

  5. New radio detections of early-type pre-main-sequence stars

    Science.gov (United States)

    Skinner, Stephen L.; Brown, Alexander; Linsky, Jeffrey L.

    1990-01-01

    Results of VLA radio continuum observations of 13 early-type pre-main-sequence stars selected from the 1984 catalog of Finkenzeller and Mundt are presented. The stars HD 259431 and MWC 1080 were detected at 3.6 cm, while HD 200775 and TY CrA were detected at both 3.6 and 6 cm. The flux density of HD 200775 has a frequency dependence consistent with the behavior expected for free-free emission originating in a fully ionized wind. However, an observation in A configuration suggests that the source geometry may not be spherically symmetric. In contrast, the spectral index of TY CrA is negative with a flux behavior implying nonthermal emission. The physical mechanism responsible for the nonthermal emission has not yet been identified, although gyrosynchrotron and synchrotron processes cannot be ruled out.

  6. ON THE MULTIPLICITY OF THE ZERO-AGE MAIN-SEQUENCE O STAR HERSCHEL 36

    International Nuclear Information System (INIS)

    Arias, Julia I.; Barba, Rodolfo H.; Gamen, Roberto C.; Morrell, Nidia I.; Apellaniz, Jesus MaIz; Alfaro, Emilio J.; Sota, Alfredo; Walborn, Nolan R.; Bidin, Christian Moni

    2010-01-01

    We present the analysis of high-resolution optical spectroscopic observations of the zero-age main-sequence O star Herschel 36 spanning six years. This star is definitely a multiple system, with at least three components detected in its spectrum. Based on our radial-velocity (RV) study, we propose a picture of a close massive binary and a more distant companion, most probably in wide orbit about each other. The orbital solution for the binary, whose components we identify as O9 V and B0.5 V, is characterized by a period of 1.5415 ± 0.0006 days. With a spectral type O7.5 V, the third body is the most luminous component of the system and also presents RV variations with a period close to 498 days. Some possible hypotheses to explain the variability are briefly addressed and further observations are suggested.

  7. New radio detections of early-type pre-main-sequence stars

    International Nuclear Information System (INIS)

    Skinner, S.L.; Brown, A.; Linsky, J.L.

    1990-01-01

    Results of VLA radio continuum observations of 13 early-type pre-main-sequence stars selected from the 1984 catalog of Finkenzeller and Mundt are presented. The stars HD 259431 and MWC 1080 were detected at 3.6 cm, while HD 200775 and TY CrA were detected at both 3.6 and 6 cm. The flux density of HD 200775 has a frequency dependence consistent with the behavior expected for free-free emission originating in a fully ionized wind. However, an observation in A configuration suggests that the source geometry may not be spherically symmetric. In contrast, the spectral index of TY CrA is negative with a flux behavior implying nonthermal emission. The physical mechanism responsible for the nonthermal emission has not yet been identified, although gyrosynchrotron and synchrotron processes cannot be ruled out. 32 refs

  8. THE ORIGIN OF HVS17, AN UNBOUND MAIN SEQUENCE B STAR AT 50 kpc

    Energy Technology Data Exchange (ETDEWEB)

    Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J. [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Cohen, Judith G., E-mail: wbrown@cfa.harvard.edu, E-mail: mgeller@cfa.harvard.edu, E-mail: skenyon@cfa.harvard.edu, E-mail: jlc@astro.caltech.edu [Palomar Observatory, Mail Stop 249-17, California Institute of Technology, Pasadena, CA 91125 (United States)

    2013-09-20

    We analyze Keck Echellette Spectrograph and Imager spectroscopy of HVS17, a B-type star traveling with a Galactic rest frame radial velocity of +445 km s{sup –1} in the outer halo of the Milky Way. HVS17 has the projected rotation of a main sequence B star and is chemically peculiar, with solar iron abundance and sub-solar alpha abundance. Comparing measured T{sub eff} and log g with stellar evolution tracks implies that HVS17 is a 3.91 ± 0.09 M{sub ☉}, 153 ± 9 Myr old star at a Galactocentric distance of r = 48.5 ± 4.6 kpc. The time between its formation and ejection significantly exceeds 10 Myr and thus is difficult to reconcile with any Galactic disk runaway scenario involving massive stars. The observations are consistent, on the other hand, with a hypervelocity star ejection from the Galactic center. We show that Gaia proper motion measurements will easily discriminate between a disk and Galactic center origin, thus allowing us to use HVS17 as a test particle to probe the shape of the Milky Way's dark matter halo.

  9. THE ORIGIN OF HVS17, AN UNBOUND MAIN SEQUENCE B STAR AT 50 kpc

    International Nuclear Information System (INIS)

    Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J.; Cohen, Judith G.

    2013-01-01

    We analyze Keck Echellette Spectrograph and Imager spectroscopy of HVS17, a B-type star traveling with a Galactic rest frame radial velocity of +445 km s –1 in the outer halo of the Milky Way. HVS17 has the projected rotation of a main sequence B star and is chemically peculiar, with solar iron abundance and sub-solar alpha abundance. Comparing measured T eff and log g with stellar evolution tracks implies that HVS17 is a 3.91 ± 0.09 M ☉ , 153 ± 9 Myr old star at a Galactocentric distance of r = 48.5 ± 4.6 kpc. The time between its formation and ejection significantly exceeds 10 Myr and thus is difficult to reconcile with any Galactic disk runaway scenario involving massive stars. The observations are consistent, on the other hand, with a hypervelocity star ejection from the Galactic center. We show that Gaia proper motion measurements will easily discriminate between a disk and Galactic center origin, thus allowing us to use HVS17 as a test particle to probe the shape of the Milky Way's dark matter halo

  10. Effects of Main-Sequence Mass Loss on Stellar and Galactic Chemical Evolution.

    Science.gov (United States)

    Guzik, Joyce Ann

    1988-06-01

    L. A. Willson, G. H. Bowen and C. Struck -Marcell have proposed that 1 to 3 solar mass stars may experience evolutionarily significant mass loss during the early part of their main-sequence phase. The suggested mass-loss mechanism is pulsation, facilitated by rapid rotation. Initial mass-loss rates may be as large as several times 10^{-9}M o/yr, diminishing over several times 10^8 years. We attempted to test this hypothesis by comparing some theoretical implications with observations. Three areas are addressed: Solar models, cluster HR diagrams, and galactic chemical evolution. Mass-losing solar models were evolved that match the Sun's luminosity and radius at its present age. The most extreme viable models have initial mass 2.0 M o, and mass-loss rates decreasing exponentially over 2-3 times 10^8 years. Compared to a constant -mass model, these models require a reduced initial ^4He abundance, have deeper envelope convection zones and higher ^8B neutrino fluxes. Early processing of present surface layers at higher interior temperatures increases the surface ^3He abundance, destroys Li, Be and B, and decreases the surface C/N ratio following first dredge-up. Evolution calculations incorporating main-sequence mass loss were completed for a grid of models with initial masses 1.25 to 2.0 Mo and mass loss timescales 0.2 to 2.0 Gyr. Cluster HR diagrams synthesized with these models confirm the potential for the hypothesis to explain observed spreads or bifurcations in the upper main sequence, blue stragglers, anomalous giants, and poor fits of main-sequence turnoffs by standard isochrones. Simple closed galactic chemical evolution models were used to test the effects of main-sequence mass loss on the F and G dwarf distribution. Stars between 3.0 M o and a metallicity -dependent lower mass are assumed to lose mass. The models produce a 30 to 60% increase in the stars to stars-plus -remnants ratio, with fewer early-F dwarfs and many more late-F dwarfs remaining on the main

  11. Variations of the ISM conditions accross the Main Sequence of star forming galaxies: observations and simulations.

    Science.gov (United States)

    Martinez Galarza, Juan R.; Smith, Howard Alan; Lanz, Lauranne; Hayward, Christopher C.; Zezas, Andreas; Hung, Chao-Ling; Rosenthal, Lee; Weiner, Aaron

    2015-01-01

    A significant amount of evidence has been gathered that leads to the existence of a main sequence (MS) of star formation in galaxies. This MS is expressed in terms of a correlation between the SFR and the stellar mass of the form SFR ∝ M* and spans a few orders of magnitude in both quantities. Several ideas have been suggested to explain fundamental properties of the MS, such as its slope, its dispersion, and its evolution with redshift, but no consensus has been reached regarding its true nature, and whether the membership or not of particular galaxies to this MS underlies the existence of two different modes of star formation. In order to advance in the understanding of the MS, here we use a statistically robust Bayesian SED analysis method (CHIBURST) to consistently analyze the star-forming properties of a set of hydro-dynamical simulations of mergers, as well as observations of real mergers, both local and at intermediate redshift. We find a remarkable, very tight correlation between the specific star formation rate (sSFR) of galaxies, and the typical ISM conditions near their inernal star-forming regions, parametrized via a novel quantity: the compactness parameter (C). The evolution of mergers along this correlation explains the spread of the MS, and implies that the physical conditions of the ISM smoothly evolve between on-MS (secular) conditions and off-MS (coalescence/starburst) conditions. Furthermore, we show that the slope of the correlation can be interpreted in terms of the efficiency in the conversion of gas into stars, and that this efficiency remains unchanged along and across the MS. Finally, we discuss differences in the normalization of the correlation as a function of merger mass and redshift, and conclude that these differences imply the existence of two different modes of star formation, unrelated to the smooth evolution across the MS: a disk-like, low pressure mode and a compact nuclear-starburst mode.

  12. Lithium abundances for 185 main-sequence stars: Galactic evolution and stellar depletion of lithium

    Science.gov (United States)

    Chen, Y. Q.; Nissen, P. E.; Benoni, T.; Zhao, G.

    2001-06-01

    We present a survey of lithium abundances in 185 main-sequence field stars with 5600 interesting result from this study is the presence of a large gap in the log varepsilon (Li) - Teff plane, which distinguishes ``Li-dip'' stars like those first identified in the Hyades cluster by Boesgaard & Tripicco (\\cite{Boesgaard86}) from other stars with a much higher Li abundance. The Li-dip stars concentrate on a certain mass, which decreases with metallicity from about 1.4 Msun at solar metallicity to 1.1 Msun at [Fe/H] =~ -1.0. Excluding the Li-dip stars and a small group of lower mass stars with Teff rate of angular momentum loss. It cannot be excluded, however, that a cosmic scatter of the Li abundance in the Galaxy at a given metallicity contributes to the dispersion in Li abundance. These problems make it difficult to determine the Galactic evolution of Li from the data, but a comparison of the upper envelope of the distribution of stars in the log varepsilon (Li) - [Fe/H] plane with recent Galactic evolutionary models by Romano et al. (\\cite{Romano99}) suggests that novae are a major source for the Li production in the Galactic disk; their occurrence seems to be the explanation for the steep increase of Li abundance at [Fe/H] =~ -0.4. Based on observations carried out at Beijing Astronomical Observatory (Xinglong, PR China) and European Southern Observatory, La Silla, Chile. Table 1 is 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/371/943 and at http://www.edpsciences.org

  13. Spectroscopic and asteroseismic analysis of the remarkable main-sequence A star KIC 11145123

    Science.gov (United States)

    Takada-Hidai, Masahide; Kurtz, Donald W.; Shibahashi, Hiromoto; Murphy, Simon J.; Takata, Masao; Saio, Hideyuki; Sekii, Takashi

    2017-10-01

    A spectroscopic analysis was carried out to clarify the properties of KIC 11145123 - the first main-sequence star with a directly measured core-to-surface rotation profile - based on spectra observed with the High Dispersion Spectrograph (HDS) of the Subaru telescope. The atmospheric parameters (Teff = 7600 K, log g = 4.2, ξ = 3.1 km s-1 and [Fe/H] = -0.71 dex), the radial and rotation velocities, and elemental abundances were obtained by analysing line strengths and fitting line profiles, which were calculated with a 1D LTE model atmosphere. The main properties of KIC 11145123 are: (1) a low [Fe/H] = -0.71 ± 0.11 dex and a high radial velocity of -135.4 ± 0.2 km s-1. These are remarkable among late-A stars. Our best asteroseismic models with this low [Fe/H] have slightly high helium abundance and low masses of 1.4 M⊙. All of these results strongly suggest that KIC 11145123 is a Population II blue straggler; (2) the projected rotation velocity confirms the asteroseismically predicted slow rotation of the star; (3) comparisons of abundance patterns between KIC 11145123 and Am, Ap, and blue stragglers show that KIC 11145123 is neither an Am star nor an Ap star, but has abundances consistent with a blue straggler. We conclude that the remarkably long 100-d rotation period of this star is a consequence of it being a blue straggler, but both pathways for the formation of blue stragglers - merger and mass loss in a binary system - pose difficulties for our understanding of the exceedingly slow rotation. In particular, we show that there is no evidence of any secondary companion star, and we put stringent limits on the possible mass of any such purported companion through the phase modulation technique.

  14. STELLAR AGES AND CONVECTIVE CORES IN FIELD MAIN-SEQUENCE STARS: FIRST ASTEROSEISMIC APPLICATION TO TWO KEPLER TARGETS

    Energy Technology Data Exchange (ETDEWEB)

    Silva Aguirre, V.; Christensen-Dalsgaard, J.; Chaplin, W. J. [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Basu, S.; Deheuvels, S. [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Brandao, I. M.; Cunha, M. S.; Sousa, S. G. [Centro de Astrofisica and Faculdade de Ciencias, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Dogan, G. [High Altitude Observatory, NCAR, P.O. Box 3000, Boulder, CO 80307 (United States); Metcalfe, T. S. [Space Science Institute, Boulder, CO 80301 (United States); Serenelli, A. M.; Garcia, R. A. [Kavli Institute for Theoretical Physics, Santa Barbara, CA 93106 (United States); Ballot, J. [Institut de Recherche en Astrophysique et Planetologie, CNRS, 14 avenue Edouard Belin, F-31400 Toulouse (France); Weiss, A. [Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85748 Garching bei Muenchen (Germany); Appourchaux, T. [Institut d' Astrophysique Spatiale, Universite Paris Sud-CNRS (UMR8617) Batiment 121, F-91405 Orsay Cedex (France); Casagrande, L. [Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, The Australian National University, ACT 2611 (Australia); Cassisi, S. [INAF-Astronomical Observatory of Teramo, Via M. Maggini sn, I-64100 Teramo (Italy); Creevey, O. L. [Laboratoire Lagrange, Universite de Nice Sophia-Antipolis, CNRS, I-06300 Nice, France. (France); Lebreton, Y. [Observatoire de Paris, GEPI, CNRS UMR 8111, F-92195 Meudon (France); Noels, A. [Institute of Astrophysics and Geophysics, University of Liege, B-4000 Liege (Belgium); and others

    2013-06-01

    Using asteroseismic data and stellar evolution models we obtain the first detection of a convective core in a Kepler field main-sequence star, putting a stringent constraint on the total size of the mixed zone and showing that extra mixing beyond the formal convective boundary exists. In a slightly less massive target the presence of a convective core cannot be conclusively discarded, and thus its remaining main-sequence lifetime is uncertain. Our results reveal that best-fit models found solely by matching individual frequencies of oscillations corrected for surface effects do not always properly reproduce frequency combinations. Moreover, slightly different criteria to define what the best-fit model is can lead to solutions with similar global properties but very different interior structures. We argue that the use of frequency ratios is a more reliable way to obtain accurate stellar parameters, and show that our analysis in field main-sequence stars can yield an overall precision of 1.5%, 4%, and 10% in radius, mass, and age, respectively. We compare our results with those obtained from global oscillation properties, and discuss the possible sources of uncertainties in asteroseismic stellar modeling where further studies are still needed.

  15. ULTRAVIOLET-SELECTED FIELD AND PRE-MAIN-SEQUENCE STARS TOWARD TAURUS AND UPPER SCORPIUS

    International Nuclear Information System (INIS)

    Findeisen, K.; Hillenbrand, L.

    2010-01-01

    We have carried out a Galaxy Evolution Explorer (GALEX) Cycle 1 guest investigator program covering 56 deg 2 near the Taurus T association and 12 deg 2 along the northern edge of the Upper Scorpius OB association. We combined photometry in the GALEX far-ultraviolet and near-ultraviolet bands with data from the Two Micron All Sky Survey to identify candidate young (∼<100 Myr old) stars as those with an ultraviolet excess relative to older main-sequence stars. Follow-up spectroscopy of a partial sample of these candidates suggests five new members of Taurus, with 8-20 expected from additional observations, and five new members of Upper Scorpius, with three to six expected from additional observations. These candidate new members appear to represent a distributed, non-clustered population in either region, although our sample statistics are as of yet too poor to constrain the nature or extent of this population. Rather, our study demonstrates the ability of GALEX observations to identify young stellar populations distributed over a wide area of the sky. We also highlight the necessity of a better understanding of the Galactic ultraviolet source population to support similar investigations. In particular, we report a large population of stars with an ultraviolet excess but no optical indicators of stellar activity or accretion, and briefly argue against several interpretations of these sources.

  16. AN OBJECTIVE DEFINITION FOR THE MAIN SEQUENCE OF STAR-FORMING GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Renzini, Alvio [INAF—Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122 Padova (Italy); Peng, Ying-jie, E-mail: alvio.renzini@oapd.inaf.it, E-mail: y.peng@mrao.cam.ac.uk [Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom)

    2015-03-10

    The main sequence (MS) of star-forming (SF) galaxies plays a fundamental role in driving galaxy evolution and our efforts to understand it. However, different studies find significant differences in the normalization, slope, and shape of the MS. These discrepancies arise mainly from the different selection criteria adopted to isolate SF galaxies, which may include or exclude galaxies with a specific star formation rate (SFR) substantially below the MS value. To obviate this limitation of all current criteria, we propose an objective definition of the MS that does not rely at all on a pre-selection of SF galaxies. Constructing the 3D SFR–mass–number plot, the MS is then defined as the ridge line of the SF peak, as illustrated with various figures. The advantages of such a definition are manifold. If generally adopted, it will facilitate the inter-comparison of results from different groups using the same SFR and stellar mass diagnostics, or it will highlight the relative systematics of different diagnostics. All of this could help to understand MS galaxies as systems in a quasi-steady state equilibrium and would also provide a more objective criterion for identifying quenching galaxies.

  17. AN OBJECTIVE DEFINITION FOR THE MAIN SEQUENCE OF STAR-FORMING GALAXIES

    International Nuclear Information System (INIS)

    Renzini, Alvio; Peng, Ying-jie

    2015-01-01

    The main sequence (MS) of star-forming (SF) galaxies plays a fundamental role in driving galaxy evolution and our efforts to understand it. However, different studies find significant differences in the normalization, slope, and shape of the MS. These discrepancies arise mainly from the different selection criteria adopted to isolate SF galaxies, which may include or exclude galaxies with a specific star formation rate (SFR) substantially below the MS value. To obviate this limitation of all current criteria, we propose an objective definition of the MS that does not rely at all on a pre-selection of SF galaxies. Constructing the 3D SFR–mass–number plot, the MS is then defined as the ridge line of the SF peak, as illustrated with various figures. The advantages of such a definition are manifold. If generally adopted, it will facilitate the inter-comparison of results from different groups using the same SFR and stellar mass diagnostics, or it will highlight the relative systematics of different diagnostics. All of this could help to understand MS galaxies as systems in a quasi-steady state equilibrium and would also provide a more objective criterion for identifying quenching galaxies

  18. Transit detections of extrasolar planets around main-sequence stars. I. Sky maps for hot Jupiters

    Science.gov (United States)

    Heller, R.; Mislis, D.; Antoniadis, J.

    2009-12-01

    Context: The findings of more than 350 extrasolar planets, most of them nontransiting Hot Jupiters, have revealed correlations between the metallicity of the main-sequence (MS) host stars and planetary incidence. This connection can be used to calculate the planet formation probability around other stars, not yet known to have planetary companions. Numerous wide-field surveys have recently been initiated, aiming at the transit detection of extrasolar planets in front of their host stars. Depending on instrumental properties and the planetary distribution probability, the promising transit locations on the celestial plane will differ among these surveys. Aims: We want to locate the promising spots for transit surveys on the celestial plane and strive for absolute values of the expected number of transits in general. Our study will also clarify the impact of instrumental properties such as pixel size, field of view (FOV), and magnitude range on the detection probability. Methods: We used data of the Tycho catalog for ≈1 million objects to locate all the stars with 0^m~≲~m_V~≲~11.5m on the celestial plane. We took several empirical relations between the parameters listed in the Tycho catalog, such as distance to Earth, m_V, and (B-V), and those parameters needed to account for the probability of a star to host an observable, transiting exoplanet. The empirical relations between stellar metallicity and planet occurrence combined with geometrical considerations were used to yield transit probabilities for the MS stars in the Tycho catalog. Magnitude variations in the FOV were simulated to test whether this fluctuations would be detected by BEST, XO, SuperWASP and HATNet. Results: We present a sky map of the expected number of Hot Jupiter transit events on the basis of the Tycho catalog. Conditioned by the accumulation of stars towards the galactic plane, the zone of the highest number of transits follows the same trace, interrupted by spots of very low and high

  19. STELLAR DIAMETERS AND TEMPERATURES. III. MAIN-SEQUENCE A, F, G, AND K STARS: ADDITIONAL HIGH-PRECISION MEASUREMENTS AND EMPIRICAL RELATIONS

    International Nuclear Information System (INIS)

    Boyajian, Tabetha S.; Jones, Jeremy; White, Russel; McAlister, Harold A.; Gies, Douglas; Von Braun, Kaspar; Van Belle, Gerard; Farrington, Chris; Schaefer, Gail; Ten Brummelaar, Theo A.; Sturmann, Laszlo; Sturmann, Judit; Turner, Nils H.; Goldfinger, P. J.; Vargas, Norm; Ridgway, Stephen

    2013-01-01

    Based on CHARA Array measurements, we present the angular diameters of 23 nearby, main-sequence stars, ranging from spectral types A7 to K0, 5 of which are exoplanet host stars. We derive linear radii, effective temperatures, and absolute luminosities of the stars using Hipparcos parallaxes and measured bolometric fluxes. The new data are combined with previously published values to create an Angular Diameter Anthology of measured angular diameters to main-sequence stars (luminosity classes V and IV). This compilation consists of 125 stars with diameter uncertainties of less than 5%, ranging in spectral types from A to M. The large quantity of empirical data is used to derive color-temperature relations to an assortment of color indices in the Johnson (BVR J I J JHK), Cousins (R C I C ), Kron (R K I K ), Sloan (griz), and WISE (W 3 W 4 ) photometric systems. These relations have an average standard deviation of ∼3% and are valid for stars with spectral types A0-M4. To derive even more accurate relations for Sun-like stars, we also determined these temperature relations omitting early-type stars (T eff > 6750 K) that may have biased luminosity estimates because of rapid rotation; for this subset the dispersion is only ∼2.5%. We find effective temperatures in agreement within a couple of percent for the interferometrically characterized sample of main-sequence stars compared to those derived via the infrared flux method and spectroscopic analysis.

  20. Important consequences of atomic diffusion inside main-sequence stars: opacities, extra-mixing, oscillations

    Directory of Open Access Journals (Sweden)

    Deal M.

    2017-01-01

    Full Text Available Atomic diffusion, including the effects of radiative accelerations on individual elements, leads to important variations of the chemical composition inside stars. The accumulation of important elements in specific layers leads to a local increase of the average opacity and to hydrodynamic instabilities that modify the internal stellar structure. This can also have important consequences for asteroseismology.

  1. The SFR-M∗ main sequence archetypal star-formation history and analytical models

    Science.gov (United States)

    Ciesla, L.; Elbaz, D.; Fensch, J.

    2017-12-01

    The star-formation history (SFH) of galaxies is a key assumption to derive their physical properties and can lead to strong biases. In this work, we derive the SFH of main sequence (MS) galaxies and show how the peak SFH of a galaxy depends on its seed mass at, for example, z = 5. This seed mass reflects the galaxy's underlying dark matter (DM) halo environment. We show that, following the MS, galaxies undergo a drastic slow down of their stellar mass growth after reaching the peak of their SFH. According to abundance matching, these masses correspond to hot and massive DM halos which state could result in less efficient gas inflows on the galaxies and thus could be the origin of limited stellar mass growth. As a result, we show that galaxies, still on the MS, can enter the passive region of the UVJ diagram while still forming stars. The best fit to the MS SFH is provided by a right skew peak function for which we provide parameters depending on the seed mass of the galaxy. The ability of the classical analytical SFHs to retrieve the star-formation rate (SFR) of galaxies from spectral energy distribution (SED) fitting is studied. Due to mathematical limitations, the exponentially declining and delayed SFH struggle to model high SFR, which starts to be problematic at z > 2. The exponentially rising and log-normal SFHs exhibit the opposite behavior with the ability to reach very high SFR, and thus model starburst galaxies, but they are not able to model low values such as those expected at low redshift for massive galaxies. By simulating galaxies SED from the MS SFH, we show that these four analytical forms recover the SFR of MS galaxies with an error dependent on the model and the redshift. They are, however, sensitive enough to probe small variations of SFR within the MS, with an error ranging from 5 to 40% depending on the SFH assumption and redshift; but all the four fail to recover the SFR of rapidly quenched galaxies. However, these SFHs lead to an artificial

  2. IRAS IDENTIFICATION OF PRE-MAIN-SEQUENCE STARS IN THE CHAMELEON-II ASSOCIATION

    NARCIS (Netherlands)

    PRUSTI, T; WHITTET, DCB; ASSENDORP, R; WESSELIUS, PR

    We report the results of a search for new pre-main sequence candidates in the Chamaeleon II dark cloud based on three IRAS catalogues (the Point Source Catalog, the Serendipitous Survey Catalog and the Faint Source Survey). A total of 30 sources were selected. Twelve of these display IRAS colours

  3. Lithium abundances and metallicities in stars near the main-sequence turnoff and a giant in M67

    International Nuclear Information System (INIS)

    Garcia Lopez, R.J.; Rebolo, R.; Beckman, J.E.

    1988-01-01

    The iron abundance of seven stars near the main-sequence (MS) turnoff and a giant in M67 are spectroscopically derived, and the results are discussed. The resulting mean iron abundance of the turnoff stars is (Fe/H) = 0.04 + or - 0.04. Taken together with previous determinations for younger clusters, this shows that there has been relatively little change of the iron abundance in the solar neighborhood during the last 5 Gyr. Lithium was detected in one unevolved star and marginally in the giant, while in the other MS stars only upper limits were found. The considerable differences in Li abundances for stars with similar surface temperature imply that there is at least one parameter affecting Li depletion apart from stellar mass and metallicity. Nonsimultaneous star formation in the cluster cloud explain the scatter in lithium abundances. 50 references

  4. Oscillation mode frequencies of 61 main-sequence and subgiant stars observed by Kepler

    DEFF Research Database (Denmark)

    Appourchaux, T.; Chaplin, W. J.; García, R. A.

    2012-01-01

    Solar-like oscillations have been observed by Kepler and CoRoT in several solar-type stars, thereby providing a way to probe the stars using asteroseismology Aims. We provide the mode frequencies of the oscillations of various stars required to perform a comparison with those obtained from stella...

  5. THE DUSTIEST POST-MAIN SEQUENCE STARS IN THE MAGELLANIC CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Jones, Olivia C.; Meixner, Margaret; Roman-Duval, Julia [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Sargent, Benjamin A. [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States); Boyer, Martha L. [Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Sewiło, Marta [The Johns Hopkins University, Department of Physics and Astronomy, 366 Bloomberg Center, 3400 N. Charles Street, Baltimore, MD 21218 (United States); Hony, Sacha [Institut für Theoretische Astrophysik, Zentrum für Astronomie, Universitt Heidelberg, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany)

    2015-10-01

    Using observations from the Herschel Inventory of The Agents of Galaxy Evolution (HERITAGE) survey of the Magellanic Clouds (MC), we have found 35 evolved stars and stellar end products that are bright in the far-infrared. These 28 (LMC) and 7 (SMC) sources were selected from the 529 evolved star candidates in the HERITAGE far-infrared point source catalogs. Our source identification method is based on spectral confirmation, spectral energy distribution characteristics, careful examination of the multiwavelength images and includes constraints on the luminosity, resulting in a thoroughly vetted list of evolved stars. These sources span a wide range in luminosity and hence initial mass. We found 13 low- to intermediate-mass evolved stars, including asymptotic giant branch (AGB) stars, post-AGB stars, planetary nebulae, and a symbiotic star. We also identify 10 high mass stars, including 4 of the 15 known B[e] stars in the MC, 3 extreme red supergiants that are highly enshrouded by dust, a Luminous Blue Variable, a Wolf–Rayet star, and two supernova remnants. Further, we report the detection of 9 probable evolved objects which were previously undescribed in the literature. These sources are likely to be among the dustiest evolved objects in the MC. The Herschel emission may either be due to dust produced by the evolved star or it may arise from swept-up interstellar medium material.

  6. Radio-emission of pre-main sequence stars of the Rho Ophiuchi cloud: observations and interpretation

    International Nuclear Information System (INIS)

    Andre, P.

    1987-11-01

    Observations of the radio continuum emission of a young star population have been made at VLA on the whole molecular cloud Rho Ophiuchi, one of the closest site of star formation. A dozen of stellar sources have been detected. Radio emission of some identified objects seems to have a magnetic nature and be produced by gyrosynchrotron mechanism. In particular, one of the sources shows a radio radiation circularly polarized; two other stars have a radiation strongly variable probably due to magnetic eruptions more important than those detected in X radiation. More generally, radio observations select probably a specific population of young stars characterized by magnetic field presence extended on several stellar radii and by absence of dense circumstellar environment. Spatial distribution of these objects suggest, they are younger than most of the pre-main sequence stars [fr

  7. A catalog of pre-main-sequence emission-line stars with IRAS source associations

    International Nuclear Information System (INIS)

    Weintraub, D.A.

    1990-01-01

    To aid in finding premain-sequence (PMS) emission-line stars that might have dusty circumstellar environments, 361 PMS stars that are associated with 304 separate IRAS sources were identified. These stars include 200 classical T Tauri stars, 25 weak-lined (naked) T Tauri stars, 56 Herbig Ae/Be stars, six FU Orionis stars, and two SU Aurigae stars. All six of the FU Orionis stars surveyed by IRAS were detected. Of the PMS-IRAS Point Source Catalog (PSC) associations, 90 are new and are not noted in the PSC. The other 271 entries include 104 that are correctly identified in the PSC but have not yet appeared in the literature, 56 more that can be found in both the PSC and in the published and unpublished iterature, and 111 that are in the literature but not in the PSC. Spectral slope diagrams constructed from the 12-, 25-, and 60-micron flux densities reveal unique distributions for the different PMS subclasses; these diagrams may help identify the best candidate PMS stars for observations of circumstellar dust. 30 refs

  8. Stars of type MS with evidence of white dwarf companions. [IUE, Main Sequence (MS)

    Science.gov (United States)

    Peery, Benjamin F., Jr.

    1986-01-01

    A search for white dwarf companions of MS-type stars was conducted, using IUE. The overendowments of these stars in typical S-process nuclides suggest that they, like the Ba II stars, may owe their peculiar compositions to earlier mass transfer. Short-wavelength IUE spectra show striking emission line variability in HD35155, HD61913, and 4 Ori; HD35155 and 4 Ori show evidence of white dwarf companions.

  9. STELLAR DIAMETERS AND TEMPERATURES. III. MAIN-SEQUENCE A, F, G, AND K STARS: ADDITIONAL HIGH-PRECISION MEASUREMENTS AND EMPIRICAL RELATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Boyajian, Tabetha S.; Jones, Jeremy; White, Russel; McAlister, Harold A.; Gies, Douglas [Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, P.O. Box 4106, Atlanta, GA 30302-4106 (United States); Von Braun, Kaspar [NASA Exoplanet Science Institute, California Institute of Technology, MC 100-22, Pasadena, CA 91125 (United States); Van Belle, Gerard [Lowell Observatory, Flagstaff, AZ 86001 (United States); Farrington, Chris; Schaefer, Gail; Ten Brummelaar, Theo A.; Sturmann, Laszlo; Sturmann, Judit; Turner, Nils H.; Goldfinger, P. J.; Vargas, Norm [CHARA Array, Mount Wilson Observatory, Mount Wilson, CA 91023 (United States); Ridgway, Stephen [National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726-6732 (United States)

    2013-07-01

    Based on CHARA Array measurements, we present the angular diameters of 23 nearby, main-sequence stars, ranging from spectral types A7 to K0, 5 of which are exoplanet host stars. We derive linear radii, effective temperatures, and absolute luminosities of the stars using Hipparcos parallaxes and measured bolometric fluxes. The new data are combined with previously published values to create an Angular Diameter Anthology of measured angular diameters to main-sequence stars (luminosity classes V and IV). This compilation consists of 125 stars with diameter uncertainties of less than 5%, ranging in spectral types from A to M. The large quantity of empirical data is used to derive color-temperature relations to an assortment of color indices in the Johnson (BVR{sub J} I{sub J} JHK), Cousins (R{sub C} I{sub C}), Kron (R{sub K} I{sub K}), Sloan (griz), and WISE (W{sub 3} W{sub 4}) photometric systems. These relations have an average standard deviation of {approx}3% and are valid for stars with spectral types A0-M4. To derive even more accurate relations for Sun-like stars, we also determined these temperature relations omitting early-type stars (T{sub eff} > 6750 K) that may have biased luminosity estimates because of rapid rotation; for this subset the dispersion is only {approx}2.5%. We find effective temperatures in agreement within a couple of percent for the interferometrically characterized sample of main-sequence stars compared to those derived via the infrared flux method and spectroscopic analysis.

  10. AN M DWARF COMPANION TO AN F-TYPE STAR IN A YOUNG MAIN-SEQUENCE BINARY

    Energy Technology Data Exchange (ETDEWEB)

    Eigmüller, Ph.; Csizmadia, Sz.; Erikson, A.; Fridlund, M.; Pasternacki, Th.; Rauer, H. [Institute of Planetary Research, German Aerospace Center Rutherfordstr. 2, D-12489 Berlin (Germany); Eislöffel, J.; Lehmann, H.; Hartmann, M.; Hatzes, A. [Thüringer Landessternwarte Tautenburg Sternwarte 5, D-07778 Tautenburg (Germany); Tkachenko, A. [Instituut voor Sterrenkunde, KU Leuven Celestijnenlaan 200D, 3001 Leuven (Belgium); Voss, H., E-mail: philipp.eigmueller@dlr.de [Universitat de Barcelona, Department of Astronomy and Meteorology Martí i Franquès, 1, E-08028 Barcelona (Spain)

    2016-03-15

    Only a few well characterized very low-mass M dwarfs are known today. Our understanding of M dwarfs is vital as these are the most common stars in our solar neighborhood. We aim to characterize the properties of a rare F+dM stellar system for a better understanding of the low-mass end of the Hertzsprung–Russel diagram. We used photometric light curves and radial velocity follow-up measurements to study the binary. Spectroscopic analysis was used in combination with isochrone fitting to characterize the primary star. The primary star is an early F-type main-sequence star with a mass of (1.493 ± 0.073) M{sub ⊙} and a radius of (1.474 ± 0.040) R{sub ⊙}. The companion is an M dwarf with a mass of (0.188 ± 0.014) M{sub ⊙} and a radius of (0.234 ± 0.009) R{sub ⊙}. The orbital period is (1.35121 ± 0.00001) days. The secondary star is among the lowest-mass M dwarfs known to date. The binary has not reached a 1:1 spin–orbit synchronization. This indicates a young main-sequence binary with an age below ∼250 Myr. The mass–radius relation of both components are in agreement with this finding.

  11. Main sequence mass loss

    International Nuclear Information System (INIS)

    Brunish, W.M.; Guzik, J.A.; Willson, L.A.; Bowen, G.

    1987-01-01

    It has been hypothesized that variable stars may experience mass loss, driven, at least in part, by oscillations. The class of stars we are discussing here are the δ Scuti variables. These are variable stars with masses between about 1.2 and 2.25 M/sub θ/, lying on or very near the main sequence. According to this theory, high rotation rates enhance the rate of mass loss, so main sequence stars born in this mass range would have a range of mass loss rates, depending on their initial rotation velocity and the amplitude of the oscillations. The stars would evolve rapidly down the main sequence until (at about 1.25 M/sub θ/) a surface convection zone began to form. The presence of this convective region would slow the rotation, perhaps allowing magnetic braking to occur, and thus sharply reduce the mass loss rate. 7 refs

  12. SDSS-IV MaNGA: Spatially Resolved Star Formation Main Sequence and LI(N)ER Sequence

    Science.gov (United States)

    Hsieh, B. C.; Lin, Lihwai; Lin, J. H.; Pan, H. A.; Hsu, C. H.; Sánchez, S. F.; Cano-Díaz, M.; Zhang, K.; Yan, R.; Barrera-Ballesteros, J. K.; Boquien, M.; Riffel, R.; Brownstein, J.; Cruz-González, I.; Hagen, A.; Ibarra, H.; Pan, K.; Bizyaev, D.; Oravetz, D.; Simmons, A.

    2017-12-01

    We present our study on the spatially resolved Hα and M * relation for 536 star-forming and 424 quiescent galaxies taken from the MaNGA survey. We show that the star formation rate surface density ({{{Σ }}}{SFR}), derived based on the Hα emissions, is strongly correlated with the M * surface density ({{{Σ }}}* ) on kiloparsec scales for star-forming galaxies and can be directly connected to the global star-forming sequence. This suggests that the global main sequence may be a consequence of a more fundamental relation on small scales. On the other hand, our result suggests that ∼20% of quiescent galaxies in our sample still have star formation activities in the outer region with lower specific star formation rate (SSFR) than typical star-forming galaxies. Meanwhile, we also find a tight correlation between {{{Σ }}}{{H}α } and {{{Σ }}}* for LI(N)ER regions, named the resolved “LI(N)ER” sequence, in quiescent galaxies, which is consistent with the scenario that LI(N)ER emissions are primarily powered by the hot, evolved stars as suggested in the literature.

  13. Some aspects of cool main sequence star ages derived from stellar rotation (gyrochronology)

    Science.gov (United States)

    Barnes, S. A.; Spada, F.; Weingrill, J.

    2016-09-01

    Rotation periods for cool stars can be measured with good precision by monitoring starspot light modulation. Observations have shown that the rotation periods of dwarf stars of roughly solar metallicity have such systematic dependencies on stellar age and mass that they can be used to derive reliable ages, a procedure called gyrochronology. We review the method and show illustrative cases, including recent ground- and space-based data. The age uncertainties approach 10 % in the best cases, making them a valuable complement to, and constraint on, asteroseismic or other ages. Edited, updated, and refereed version of a presentation at the WE-Heraeus-Seminar in Bad Honnef, Germany: Reconstructing the Milky Way's History: Spectroscopic Surveys, Asteroseismology and Chemodynamical Models

  14. Carbon Monoxide and the Potential for Prebiotic Chemistry on Habitable Planets Around Main Sequence M Stars

    Science.gov (United States)

    Nava-Sedeno, J. Manik; Ortiz-Cervantes, Adrian; Segura, Antigona; Domagal-Goldman, Shawn D.

    2016-01-01

    Lifeless planets with CO2 atmospheres produce CO by CO2 photolysis. On planets around M dwarfs, CO is a long-lived atmospheric compound, as long as UV emission due to the stars chromospheric activity lasts, and the sink of CO and O2 in seawater is small compared to its atmospheric production. Atmospheres containing reduced compounds, like CO, may undergo further energetic and chemical processing to give rise to organic compounds of potential importance for the origin of life. We calculated the yield of organic compounds from CO2-rich atmospheres of planets orbiting M dwarf stars, which were previously simulated by Domagal- Goldman et al. (2014) and Harman et al. (2015), by cosmic rays and lightning using results of experiments by Miyakawaet al. (2002) and Schlesinger and Miller (1983a, 1983b). Stellar protons from active stars may be important energy sources for abiotic synthesis and increase production rates of biological compounds by at least 2 orders of magnitude compared to cosmic rays. Simple compounds such as HCN and H2CO are more readily synthesized than more complex ones, such as amino acids and uracil (considered here as an example), resulting in higher yields for the former and lower yields for the latter. Electric discharges are most efficient when a reducing atmosphere is present. Nonetheless, atmospheres with high quantities of CO2 are capable of producing higher amounts of prebiotic compounds, given that CO is constantly produced in the atmosphere. Our results further support planetary systems around M dwarf stars as candidates for supporting life or its origin.

  15. Relative stellar occurrence of exoplanets in habitable zones of the main sequence F, G, K stars

    Czech Academy of Sciences Publication Activity Database

    Pintr, Pavel; Peřinová, V.; Lukš, A.; Pathak, A.

    2014-01-01

    Roč. 99, sept2014 (2014), s. 1-6 ISSN 0032-0633 R&D Projects: GA MŠk(CZ) ED2.1.00/03.0079 Institutional support: RVO:61389021 Keywords : Exoplanets * Methods: statistical * Stars: planetary systems Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.875, year: 2014 http://www.sciencedirect.com/science/article/pii/S003206331400172X#

  16. Grain temperature, radiation pressure and electric potential in the vicinity of main sequence and white dwarf stars

    Energy Technology Data Exchange (ETDEWEB)

    Leiknes, J.; Havnes, O. (University of Tromso, Auroral Observatory (Norway))

    1984-08-01

    We present results of calculations of the grain physical parameters temperature, lifetime against evaporation, radiation pressure and electric potential for spherical grains near main sequence stars, hydrogen type (DA) white dwarfs and helium type (DB) white dwarfs. These parameters are essential in determining the behaviour of grains near such stars. The grain temperature as a function of stellar distance is calculated for grains of sizes 0.1 and 1 ..mu.. (micron) for grain materials of silicate (obsidian), iron and graphite. The lifetime due to thermal evaporation as a function of grain temperature of these materials is also given. The radiation pressure is given for grain sizes from 0.01 to 10 ..mu.. for the same three grain materials. Grain potentials have been calculated as functions of stellar distance for one photoelectron high yield material (silicate) and one low yield material (graphite) for grains of radius 0.1 ..mu.. embedded in a thermal plasma of temperature T = 10/sup 4/ K.

  17. MASS LOSS IN PRE-MAIN-SEQUENCE STARS VIA CORONAL MASS EJECTIONS AND IMPLICATIONS FOR ANGULAR MOMENTUM LOSS

    Energy Technology Data Exchange (ETDEWEB)

    Aarnio, Alicia N. [Astronomy Department, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Matt, Sean P. [Laboratoire AIM Paris-Saclay, CEA/Irfu Universite Paris-Diderot CNRS/INSU, F-91191 Gif-sur-Yvette (France); Stassun, Keivan G., E-mail: aarnio@umich.edu [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States)

    2012-11-20

    We develop an empirical model to estimate mass-loss rates via coronal mass ejections (CMEs) for solar-type pre-main-sequence (PMS) stars. Our method estimates the CME mass-loss rate from the observed energies of PMS X-ray flares, using our empirically determined relationship between solar X-ray flare energy and CME mass: log (M {sub CME}[g]) = 0.63 Multiplication-Sign log (E {sub flare}[erg]) - 2.57. Using masses determined for the largest flaring magnetic structures observed on PMS stars, we suggest that this solar-calibrated relationship may hold over 10 orders of magnitude in flare energy and 7 orders of magnitude in CME mass. The total CME mass-loss rate we calculate for typical solar-type PMS stars is in the range 10{sup -12}-10{sup -9} M {sub Sun} yr{sup -1}. We then use these CME mass-loss rate estimates to infer the attendant angular momentum loss leading up to the main sequence. Assuming that the CME outflow rate for a typical {approx}1 M {sub Sun} T Tauri star is <10{sup -10} M {sub Sun} yr{sup -1}, the resulting spin-down torque is too small during the first {approx}1 Myr to counteract the stellar spin-up due to contraction and accretion. However, if the CME mass-loss rate is {approx}> 10{sup -10} M {sub Sun} yr{sup -1}, as permitted by our calculations, then the CME spin-down torque may influence the stellar spin evolution after an age of a few Myr.

  18. Extreme value statistics for two-dimensional convective penetration in a pre-main sequence star

    Science.gov (United States)

    Pratt, J.; Baraffe, I.; Goffrey, T.; Constantino, T.; Viallet, M.; Popov, M. V.; Walder, R.; Folini, D.

    2017-08-01

    Context. In the interior of stars, a convectively unstable zone typically borders a zone that is stable to convection. Convective motions can penetrate the boundary between these zones, creating a layer characterized by intermittent convective mixing, and gradual erosion of the density and temperature stratification. Aims: We examine a penetration layer formed between a central radiative zone and a large convection zone in the deep interior of a young low-mass star. Using the Multidimensional Stellar Implicit Code (MUSIC) to simulate two-dimensional compressible stellar convection in a spherical geometry over long times, we produce statistics that characterize the extent and impact of convective penetration in this layer. Methods: We apply extreme value theory to the maximal extent of convective penetration at any time. We compare statistical results from simulations which treat non-local convection, throughout a large portion of the stellar radius, with simulations designed to treat local convection in a small region surrounding the penetration layer. For each of these situations, we compare simulations of different resolution, which have different velocity magnitudes. We also compare statistical results between simulations that radiate energy at a constant rate to those that allow energy to radiate from the stellar surface according to the local surface temperature. Results: Based on the frequency and depth of penetrating convective structures, we observe two distinct layers that form between the convection zone and the stable radiative zone. We show that the probability density function of the maximal depth of convective penetration at any time corresponds closely in space with the radial position where internal waves are excited. We find that the maximal penetration depth can be modeled by a Weibull distribution with a small shape parameter. Using these results, and building on established scalings for diffusion enhanced by large-scale convective motions, we

  19. LINEAR RELATION FOR WIND-BLOWN BUBBLE SIZES OF MAIN-SEQUENCE OB STARS IN A MOLECULAR ENVIRONMENT AND IMPLICATION FOR SUPERNOVA PROGENITORS

    Energy Technology Data Exchange (ETDEWEB)

    Chen Yang; Zhou Ping [Department of Astronomy, Nanjing University, Nanjing 210093 (China); Chu Youhua [Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801 (United States)

    2013-05-20

    We find a linear relationship between the size of a massive star's main-sequence bubble in a molecular environment and the star's initial mass: R{sub b} Almost-Equal-To 1.22 M/M{sub Sun} - 9.16 pc, assuming a constant interclump pressure. Since stars in the mass range of 8 to 25-30 M{sub Sun} will end their evolution in the red supergiant phase without launching a Wolf-Rayet wind, the main-sequence wind-blown bubbles are mainly responsible for the extent of molecular gas cavities, while the effect of the photoionization is comparatively small. This linear relation can thus be used to infer the masses of the massive star progenitors of supernova remnants (SNRs) that are discovered to evolve in molecular cavities, while few other means are available for inferring the properties of SNR progenitors. We have used this method to estimate the initial masses of the progenitors of eight SNRs: Kes 69, Kes 75, Kes 78, 3C 396, 3C 397, HC 40, Vela, and RX J1713-3946.

  20. Effects of main-sequence mass loss on the turnoff ages of globular clusters

    International Nuclear Information System (INIS)

    Guzik, J.A.

    1989-01-01

    Willson, Bowen, and Struck-Marcell have proposed that globular cluster main-sequence turnoff ages can be reconciled with the lower ages of the Galaxy and universe deduced from other methods by incorporating an epoch of early main-sequence mass-loss by stars of spectral types A through early-F. The proposed mass loss is pulsation-driven, and facilitated by rapid rotation. This paper presents stellar evolution calculations of Pop. II (Z = 0.001) mass-losing stars of initial mass 0.8 to 1.6 M circle dot , with exponentially-decreasing mass loss rates of e-folding times 0.5 to 2.0 Gyr, evolving to a final mass of 0.7 M circle dot . The calculations indicate that a globular cluster with apparent turnoff age 18 Gyr could have an actual age as low as ∼12 Gyr. Observational implications that may help to verify the hypothesis, e.g. low C/N abundance ratios among red giants following first dredge-up, blue stragglers, red giant deficiencies, and signatures in cluster mass/luminosity functions, are also discussed.25 refs., 4 figs., 3 tabs

  1. 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.

  2. How Dusty Is Alpha Centauri? Excess or Non-excess over the Infrared Photospheres of Main-sequence Stars

    Science.gov (United States)

    Wiegert, J.; Liseau, R.; Thebault, P.; Olofsson, G.; Mora, A.; Bryden, G.; Marshall, J. P.; Eiroa, C.; Montesinos, B.; Ardila, D.; hide

    2014-01-01

    Context. Debris discs around main-sequence stars indicate the presence of larger rocky bodies. The components of the nearby, solar-type binary Centauri have metallicities that are higher than solar, which is thought to promote giant planet formation. Aims. We aim to determine the level of emission from debris around the stars in the Cen system. This requires knowledge of their photospheres.Having already detected the temperature minimum, Tmin, of CenA at far-infrared wavelengths, we here attempt to do the same for the moreactive companion Cen B. Using the Cen stars as templates, we study the possible eects that Tmin may have on the detectability of unresolveddust discs around other stars. Methods.We used Herschel-PACS, Herschel-SPIRE, and APEX-LABOCA photometry to determine the stellar spectral energy distributions in thefar infrared and submillimetre. In addition, we used APEX-SHeFI observations for spectral line mapping to study the complex background around Cen seen in the photometric images. Models of stellar atmospheres and of particulate discs, based on particle simulations and in conjunctionwith radiative transfer calculations, were used to estimate the amount of debris around these stars. Results. For solar-type stars more distant than Cen, a fractional dust luminosity fd LdustLstar 2 107 could account for SEDs that do not exhibit the Tmin eect. This is comparable to estimates of fd for the Edgeworth-Kuiper belt of the solar system. In contrast to the far infrared,slight excesses at the 2:5 level are observed at 24 m for both CenA and B, which, if interpreted as due to zodiacal-type dust emission, wouldcorrespond to fd (13) 105, i.e. some 102 times that of the local zodiacal cloud. Assuming simple power-law size distributions of the dustgrains, dynamical disc modelling leads to rough mass estimates of the putative Zodi belts around the Cen stars, viz.4106 M$ of 4 to 1000 msize grains, distributed according to n(a) a3:5. Similarly, for filled-in Tmin

  3. Extended Main-sequence Turn-offs in Intermediate-age Star Clusters: Stellar Rotation Diminishes, but Does Not Eliminate, Age Spreads

    Energy Technology Data Exchange (ETDEWEB)

    Goudfrooij, Paul; Correnti, Matteo [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Girardi, Léo, E-mail: goudfroo@stsci.edu [Osservatorio Astronomico di Padova—INAF, Vicolo dell’Osservatorio 5, I-35122 Padova (Italy)

    2017-09-01

    Extended main-sequence turn-off (eMSTO) regions are a common feature in color–magnitude diagrams of young- and intermediate-age star clusters in the Magellanic Clouds. The nature of eMSTOs remains debated in the literature. The currently most popular scenarios are extended star formation activity and ranges of stellar rotation rates. Here we study details of differences in main-sequence turn-off (MSTO) morphology expected from spreads in age versus spreads in rotation rates, using Monte Carlo simulations with the Geneva syclist isochrone models that include the effects of stellar rotation. We confirm a recent finding of Niederhofer et al. that a distribution of stellar rotation velocities yields an MSTO extent that is proportional to the cluster age, as observed. However, we find that stellar rotation yields MSTO crosscut widths that are generally smaller than observed ones at a given age. We compare the simulations with high-quality Hubble Space Telescope data of NGC 1987 and NGC 2249, which are the two only relatively massive star clusters with an age of ∼1 Gyr for which such data is available. We find that the distribution of stars across the eMSTOs of these clusters cannot be explained solely by a distribution of stellar rotation velocities, unless the orientations of rapidly rotating stars are heavily biased toward an equator-on configuration. Under the assumption of random viewing angles, stellar rotation can account for ∼60% and ∼40% of the observed FWHM widths of the eMSTOs of NGC 1987 and NGC 2249, respectively. In contrast, a combination of distributions of stellar rotation velocities and stellar ages fits the observed eMSTO morphologies very well.

  4. THE CONTRIBUTIONS OF INTERACTIVE BINARY STARS TO DOUBLE MAIN-SEQUENCE TURNOFFS AND DUAL RED CLUMP OF INTERMEDIATE-AGE STAR CLUSTERS

    International Nuclear Information System (INIS)

    Yang Wuming; Bi Shaolan; Tian Zhijia; Li Tanda; Liu Kang; Meng Xiangcun

    2011-01-01

    Double or extended main-sequence turnoffs (DMSTOs) and dual red clump (RC) were observed in intermediate-age clusters, such as in NGC 1846 and 419. The DMSTOs are interpreted as that the cluster has two distinct stellar populations with differences in age of about 200-300 Myr but with the same metallicity. The dual RC is interpreted as a result of a prolonged star formation. Using a stellar population-synthesis method, we calculated the evolution of a binary-star stellar population. We found that binary interactions and merging can reproduce the dual RC in the color-magnitude diagrams of an intermediate-age cluster, whereas in actuality only a single population exists. Moreover, the binary interactions can lead to an extended main-sequence turnoff (MSTO) rather than DMSTOs. However, the rest of the main sequence, subgiant branch, and first giant branch are hardly spread by the binary interactions. Part of the observed dual RC and extended MSTO may be the results of binary interactions and mergers.

  5. EXTENDED MAGNETOSPHERES IN PRE-MAIN-SEQUENCE EVOLUTION: FROM T TAURI STARS TO THE BROWN DWARF LIMIT

    Energy Technology Data Exchange (ETDEWEB)

    Gomez de Castro, Ana I.; Marcos-Arenal, Pablo [Grupo de Investigacion Complutense AEGORA, Universidad Complutense de Madrid, 28040 Madrid (Spain)

    2012-04-20

    Low-mass pre-main-sequence stars, i.e., T Tauri stars (TTSs), strongly radiate at high energies, from X-rays to the ultraviolet (UV). This excess radiation with respect to main-sequence cool stars (MSCSs) is associated with the accretion process, i.e., it is produced in the extended magnetospheres, in the accretion shocks on the stellar surface, and in the outflows. Although evidence of accretion shocks and outflow contribution to the high-energy excess have been recently addressed, there is not an updated revision of the magnetospheric contribution. This article addresses this issue. The UV observations of the TTSs in the well-known Taurus region have been analyzed together with the XMM-Newton observations compiled in the XEST survey. For the first time the high sensitivity of the Hubble Space Telescope UV instrumentation has allowed measurement of the UV line fluxes of TTSs to M8 type. UV- and X-ray-normalized fluxes have been determined to study the extent and properties of the TTS magnetospheres as a class. They have been compared with the atmospheres of the MSCSs. The main results from this analysis are (1) the normalized fluxes of all the tracers are correlated; this correlation is independent of the broad mass range and the hardness of the X-ray radiation field; (2) the TTS correlations are different than the MSCS correlations; (3) there is a very significant excess emission in O I in the TTSs compared with MSCSs that seems to be caused by recombination radiation from the disk atmosphere after photoionization by extreme UV radiation; the Fe II/Mg II recombination continuum has also been detected in several TTSs and most prominently in AA Tau; and (4) the normalized flux of the UV tracers anticorrelates with the strength of the X-ray flux, i.e., the stronger the X-ray surface flux is, the weaker the observed UV flux. This last behavior is counterintuitive within the framework of stellar dynamo theory and suggests that UV emission can be produced in the

  6. 2D and 3D Models of Convective Turbulence and Oscillations in Intermediate-Mass Main-Sequence Stars

    Science.gov (United States)

    Guzik, Joyce Ann; Morgan, Taylor H.; Nelson, Nicholas J.; Lovekin, Catherine; Kitiashvili, Irina N.; Mansour, Nagi N.; Kosovichev, Alexander

    2015-08-01

    We present multidimensional modeling of convection and oscillations in main-sequence stars somewhat more massive than the sun, using three separate approaches: 1) Applying the spherical 3D MHD ASH (Anelastic Spherical Harmonics) code to simulate the core convection and radiative zone. Our goal is to determine whether core convection can excite low-frequency gravity modes, and thereby explain the presence of low frequencies for some hybrid gamma Dor/delta Sct variables for which the envelope convection zone is too shallow for the convective blocking mechanism to drive g modes; 2) Using the 3D planar ‘StellarBox’ radiation hydrodynamics code to model the envelope convection zone and part of the radiative zone. Our goals are to examine the interaction of stellar pulsations with turbulent convection in the envelope, excitation of acoustic modes, and the role of convective overshooting; 3) Applying the ROTORC 2D stellar evolution and dynamics code to calculate evolution with a variety of initial rotation rates and extents of core convective overshooting. The nonradial adiabatic pulsation frequencies of these nonspherical models will be calculated using the 2D pulsation code NRO of Clement. We will present new insights into gamma Dor and delta Sct pulsations gained by multidimensional modeling compared to 1D model expectations.

  7. A Constraint on the Formation Timescale of the Young Open Cluster NGC 2264: Lithium Abundance of Pre-main Sequence Stars

    Science.gov (United States)

    Lim, Beomdu; Sung, Hwankyung; Kim, Jinyoung S.; Bessell, Michael S.; Hwang, Narae; Park, Byeong-Gon

    2016-11-01

    The timescale of cluster formation is an essential parameter in order to understand the formation process of star clusters. Pre-main sequence (PMS) stars in nearby young open clusters reveal a large spread in brightness. If the spread were considered to be a result of a real spread in age, the corresponding cluster formation timescale would be about 5-20 Myr. Hence it could be interpreted that star formation in an open cluster is prolonged for up to a few tens of Myr. However, difficulties in reddening correction, observational errors, and systematic uncertainties introduced by imperfect evolutionary models for PMS stars can result in an artificial age spread. Alternatively, we can utilize Li abundance as a relative age indicator of PMS star to determine the cluster formation timescale. The optical spectra of 134 PMS stars in NGC 2264 have been obtained with MMT/Hectochelle. The equivalent widths have been measured for 86 PMS stars with a detectable Li line (3500\\lt {T}{eff}[{{K}}]≤slant 6500). Li abundance under the condition of local thermodynamic equilibrium (LTE) was derived using the conventional curve of growth method. After correction for non-LTE effects, we find that the initial Li abundance of NGC 2264 is A({Li})=3.2+/- 0.2. From the distribution of the Li abundances, the underlying age spread of the visible PMS stars is estimated to be about 3-4 Myr and this, together with the presence of embedded populations in NGC 2264, suggests that the cluster formed on a timescale shorter than 5 Myr.

  8. THE CLUSTERED NATURE OF STAR FORMATION. PRE-MAIN-SEQUENCE CLUSTERS IN THE STAR-FORMING REGION NGC 602/N90 IN THE SMALL MAGELLANIC CLOUD

    International Nuclear Information System (INIS)

    Gouliermis, Dimitrios A.; Gennaro, Mario; Schmeja, Stefan; Dolphin, Andrew E.; Tognelli, Emanuele; Prada Moroni, Pier Giorgio

    2012-01-01

    Located at the tip of the wing of the Small Magellanic Cloud (SMC), the star-forming region NGC 602/N90 is characterized by the H II nebular ring N90 and the young cluster of pre-main-sequence (PMS) and early-type main-sequence stars NGC 602, located in the central area of the ring. We present a thorough cluster analysis of the stellar sample identified with Hubble Space Telescope/Advanced Camera for Surveys in the region. We show that apart from the central cluster low-mass PMS stars are congregated in 13 additional small, compact sub-clusters at the periphery of NGC 602, identified in terms of their higher stellar density with respect to the average background density derived from star counts. We find that the spatial distribution of the PMS stars is bimodal, with an unusually large fraction (∼60%) of the total population being clustered, while the remaining is diffusely distributed in the intercluster area, covering the whole central part of the region. From the corresponding color-magnitude diagrams we disentangle an age difference of ∼2.5 Myr between NGC 602 and the compact sub-clusters, which appear younger, on the basis of comparison of the brighter PMS stars with evolutionary models, which we accurately calculated for the metal abundance of the SMC. The diffuse PMS population appears to host stars as old as those in NGC 602. Almost all detected PMS sub-clusters appear to be centrally concentrated. When the complete PMS stellar sample, including both clustered and diffused stars, is considered in our cluster analysis, it appears as a single centrally concentrated stellar agglomeration, covering the whole central area of the region. Considering also the hot massive stars of the system, we find evidence that this agglomeration is hierarchically structured. Based on our findings, we propose a scenario according to which the region NGC 602/N90 experiences an active clustered star formation for the last ∼5 Myr. The central cluster NGC 602 was formed first

  9. POPULATION PARAMETERS OF INTERMEDIATE-AGE STAR CLUSTERS IN THE LARGE MAGELLANIC CLOUD. II. NEW INSIGHTS FROM EXTENDED MAIN-SEQUENCE TURNOFFS IN SEVEN STAR CLUSTERS

    International Nuclear Information System (INIS)

    Goudfrooij, Paul; Kozhurina-Platais, Vera; Puzia, Thomas H.; Chandar, Rupali

    2011-01-01

    We discuss new photometry from high-resolution images of seven intermediate-age (1-2 Gyr) star clusters in the Large Magellanic Cloud taken with the Advanced Camera for Surveys on board the Hubble Space Telescope. We fit color-magnitude diagrams (CMDs) with several different sets of theoretical isochrones and determine systematic uncertainties for population parameters when derived using any one set of isochrones. The cluster CMDs show several interesting features, including extended main-sequence turnoff (MSTO) regions, narrow red giant branches, and clear sequences of unresolved binary stars. We show that the extended MSTOs are not caused by photometric uncertainties, contamination by field stars, or the presence of binary stars. Enhanced helium abundances in a fraction of cluster stars are also ruled out as the reason for the extended MSTOs. Quantitative comparisons with simulations indicate that the MSTO regions are better described by a spread in ages than by a bimodal age distribution, although we cannot formally rule out the latter for the three lowest-mass clusters in our sample (which have masses lower than ∼3 x 10 4 M sun ). This conclusion differs from that of some previous works which suggested that the age distribution in massive clusters in our sample is bimodal. This suggests that any secondary star formation occurred in an extended fashion rather than through short bursts. We discuss these results in the context of the nature of multiple stellar populations in star clusters.

  10. OLD MAIN-SEQUENCE TURNOFF PHOTOMETRY IN THE SMALL MAGELLANIC CLOUD. II. STAR FORMATION HISTORY AND ITS SPATIAL GRADIENTS

    International Nuclear Information System (INIS)

    Noel, Noelia E. D.; Gallart, Carme; Hidalgo, Sebastian L.; Aparicio, Antonio; Costa, Edgardo; Mendez, Rene A.

    2009-01-01

    We present a quantitative analysis of the star formation history (SFH) of 12 fields in the Small Magellanic Cloud (SMC) based on unprecedented deep [(B - R), R] color-magnitude diagrams (CMDs). Our fields reach down to the oldest main-sequence turnoff with a high photometric accuracy, which is vital for obtaining accurate SFHs, particularly at intermediate and old ages. We use the IAC-pop code to obtain the SFH, using synthetic CMDs generated with IAC-star. We obtain the SFH as a function ψ(t, z) of age and metallicity. We also consider several auxiliary functions: the initial mass function (IMF), φ(m), and a function accounting for the frequency and relative mass distribution of binary stars, β(f, q). We find that there are several main periods of enhancement of star formation: a young one peaked at ∼0.2-0.5 Gyr old, only present in the eastern and in the central-most fields; two at intermediate ages present in all fields: a conspicuous one peaked at ∼4-5 Gyr, and a less significant one peaked at ∼1.5-2.5; and an old one, peaked at ∼10 Gyr in all fields but the western ones. In the western fields, this old enhancement splits into two, one peaked at ∼8 Gyr old and another at ∼12 Gyr old. This 'two-enhancement' zone is unaffected by our choice of stellar evolutionary library but more data covering other fields of the SMC are necessary in order to ascertain its significancy. Correlation between star formation rate enhancements and SMC-Milky Way encounters is not clear. Some correlation could exist with encounters taken from the orbit determination of Kallivayalil et al. But our results would also fit in a first pericenter passage scenario like the one claimed by Besla et al. For SMC-Large Magellanic Cloud encounters, we find a correlation only for the most recent encounter ∼0.2 Gyr ago. This coincides with the youngest ψ(t) enhancement peaked at these ages in our eastern fields. The population younger than 1 Gyr represents ∼7%-12% of the total

  11. A HIGHER EFFICIENCY OF CONVERTING GAS TO STARS PUSHES GALAXIES AT z ∼ 1.6 WELL ABOVE THE STAR-FORMING MAIN SEQUENCE

    Energy Technology Data Exchange (ETDEWEB)

    Silverman, J. D.; Rujopakarn, W. [Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, The University of Tokyo, Kashiwa, Chiba 277-8583 (Japan); Daddi, E.; Liu, D. [Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, Irfu/Service d’Astrophysique, CEA Saclay (France); Rodighiero, G. [Dipartimento di Fisica e Astronomia, Universita di Padova, vicolo Osservatorio, 3, I-35122 Padova (Italy); Sargent, M. [Astronomy Centre, Department of Physics and Astronomy, University of Sussex, Brighton BN1 9QH (United Kingdom); Renzini, A. [Instituto Nazionale de Astrofisica, Osservatorio Astronomico di Padova, v.co dell’Osservatorio 5, I-35122 Padova (Italy); Feruglio, C. [IRAM—Institut de RadioAstronomie Millimétrique, 300 rue de la Piscine, F-38406 Saint Martin d’Hères (France); Kashino, D. [Division of Particle and Astrophysical Science, Graduate School of Science, Nagoya University, Nagoya 464-8602 (Japan); Sanders, D. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Kartaltepe, J. [National Optical Astronomy Observatory, 950 N. Cherry Avenue, Tucson, AZ 85719 (United States); Nagao, T. [Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577 (Japan); Arimoto, N. [Subaru Telescope, 650 North A’ohoku Place, Hilo, HI-96720 (United States); Berta, S.; Lutz, D. [Max-Planck-Institut für extraterrestrische Physik, D-84571 Garching (Germany); Béthermin, M. [European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching (Germany); Koekemoer, A., E-mail: john.silverman@ipmu.jp [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218 (United States); and others

    2015-10-20

    Local starbursts have a higher efficiency of converting gas into stars, as compared to typical star-forming galaxies at a given stellar mass, possibly indicative of different modes of star formation. With the peak epoch of galaxy formation occurring at z > 1, it remains to be established whether such an efficient mode of star formation is occurring at high redshift. To address this issue, we measure the molecular gas content of seven high-redshift (z ∼ 1.6) starburst galaxies with the Atacama Large Millimeter/submillimeter Array and IRAM/Plateau de Bure Interferometer. Our targets are selected from the sample of Herschel far-infrared-detected galaxies having star formation rates (∼300–800 M{sub ⊙} yr{sup −1}) elevated (≳4×) above the star-forming main sequence (MS) and included in the FMOS-COSMOS near-infrared spectroscopic survey of star-forming galaxies at z ∼ 1.6 with Subaru. We detect CO emission in all cases at high levels of significance, indicative of high gas fractions (∼30%–50%). Even more compelling, we firmly establish with a clean and systematic selection that starbursts, identified as MS outliers, at high redshift generally have a lower ratio of CO to total infrared luminosity as compared to typical MS star-forming galaxies, although with a smaller offset than expected based on past studies of local starbursts. We put forward a hypothesis that there exists a continuous increase in star formation efficiency with elevation from the MS with galaxy mergers as a possible physical driver. Along with a heightened star formation efficiency, our high-redshift sample is similar in other respects to local starbursts, such as being metal rich and having a higher ionization state of the interstellar medium.

  12. A search for pre-main-sequence stars in high-latitude molecular clouds. 3: A survey of the Einstein database

    Science.gov (United States)

    Caillault, Jean-Pierre; Magnani, Loris; Fryer, Chris

    1995-01-01

    In order to discern whether the high-latitude molecular clouds are regions of ongoing star formation, we have used X-ray emission as a tracer of youthful stars. The entire Einstein database yields 18 images which overlap 10 of the clouds mapped partially or completely in the CO (1-0) transition, providing a total of approximately 6 deg squared of overlap. Five previously unidentified X-ray sources were detected: one has an optical counterpart which is a pre-main-sequence (PMS) star, and two have normal main-sequence stellar counterparts, while the other two are probably extragalactic sources. The PMS star is located in a high Galactic latitude Lynds dark cloud, so this result is not too suprising. The translucent clouds, though, have yet to reveal any evidence of star formation.

  13. A search for pre-main sequence stars in the high-latitude molecular clouds. II - A survey of the Einstein database

    Science.gov (United States)

    Caillault, Jean-Pierre; Magnani, Loris

    1990-01-01

    The preliminary results are reported of a survey of every EINSTEIN image which overlaps any high-latitude molecular cloud in a search for X-ray emitting pre-main sequence stars. This survey, together with complementary KPNO and IRAS data, will allow the determination of how prevalent low mass star formation is in these clouds in general and, particularly, in the translucent molecular clouds.

  14. PHIBSS: MOLECULAR GAS CONTENT AND SCALING RELATIONS IN z ∼ 1-3 MASSIVE, MAIN-SEQUENCE STAR-FORMING GALAXIES

    International Nuclear Information System (INIS)

    Tacconi, L. J.; Genzel, R.; Wuyts, S.; Förster Schreiber, N. M.; Gracia-Carpio, J.; Lutz, D.; Saintonge, A.; Neri, R.; Cox, P.; Combes, F.; Bolatto, A.; Cooper, M. C.; Bournaud, F.; Burkert, A.; Comerford, J.; Davis, M.; Newman, S.; García-Burillo, S.; Naab, T.; Omont, A.

    2013-01-01

    We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO 3-2 survey of the molecular gas properties in massive, main-sequence star-forming galaxies (SFGs) near the cosmic star formation peak. PHIBSS provides 52 CO detections in two redshift slices at z ∼ 1.2 and 2.2, with log(M * (M ☉ )) ≥ 10.4 and log(SFR(M ☉ /yr)) ≥ 1.5. Including a correction for the incomplete coverage of the M * -SFR plane, and adopting a ''Galactic'' value for the CO-H 2 conversion factor, we infer average gas fractions of ∼0.33 at z ∼ 1.2 and ∼0.47 at z ∼ 2.2. Gas fractions drop with stellar mass, in agreement with cosmological simulations including strong star formation feedback. Most of the z ∼ 1-3 SFGs are rotationally supported turbulent disks. The sizes of CO and UV/optical emission are comparable. The molecular-gas-star-formation relation for the z = 1-3 SFGs is near-linear, with a ∼0.7 Gyr gas depletion timescale; changes in depletion time are only a secondary effect. Since this timescale is much less than the Hubble time in all SFGs between z ∼ 0 and 2, fresh gas must be supplied with a fairly high duty cycle over several billion years. At given z and M * , gas fractions correlate strongly with the specific star formation rate (sSFR). The variation of sSFR between z ∼ 0 and 3 is mainly controlled by the fraction of baryonic mass that resides in cold gas.

  15. GOODS-HERSCHEL: STAR FORMATION, DUST ATTENUATION, AND THE FIR–RADIO CORRELATION ON THE MAIN SEQUENCE OF STAR-FORMING GALAXIES UP TO z ≃ 4

    Energy Technology Data Exchange (ETDEWEB)

    Pannella, M.; Elbaz, D.; Daddi, E.; Hwang, H. S.; Schreiber, C.; Strazzullo, V.; Aussel, H.; Bethermin, M.; Cibinel, A.; Juneau, S.; Floc’h, E. Le; Leiton, R. [Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu—CNRS—Université Paris Diderot, CEA-Saclay, F-91191 Gif-sur-Yvette (France); Dickinson, M. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Buat, V. [Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR7326, F-13388, Marseille (France); Charmandaris, V.; Magdis, G. [Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, 15236, Penteli (Greece); Ivison, R. J. [European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching (Germany); Borgne, D. Le [Institut d’Astrophysique de Paris, UMR 7095, CNRS, 98bis boulevard Arago, F-75005 Paris (France); Lin, L. [Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 106, Taiwan (China); Morrison, G. E. [Institute for Astronomy, University of Hawaii, Honolulu, Hawaii, HI-96822 (United States); and others

    2015-07-10

    We use deep panchromatic data sets in the GOODS-N field, from GALEX to the deepest Herschel far-infrared (FIR) and VLA radio continuum imaging, to explore the evolution of star-formation activity and dust attenuation properties of star-forming galaxies to z ≃ 4, using mass-complete samples. Our main results can be summarized as follows: (i) the slope of the star-formation rate–M{sub *} correlation is consistent with being constant ≃0.8 up to z ≃ 1.5, while its normalization keeps increasing with redshift; (ii) for the first time we are able to explore the FIR–radio correlation for a mass-selected sample of star-forming galaxies: the correlation does not evolve up to z ≃ 4; (iii) we confirm that galaxy stellar mass is a robust proxy for UV dust attenuation in star-forming galaxies, with more massive galaxies being more dust attenuated. Strikingly, we find that this attenuation relation evolves very weakly with redshift, with the amount of dust attenuation increasing by less than 0.3 mag over the redshift range [0.5–4] for a fixed stellar mass; (iv) the correlation between dust attenuation and the UV spectral slope evolves with redshift, with the median UV slope becoming bluer with redshift. By z ≃ 3, typical UV slopes are inconsistent, given the measured dust attenuations, with the predictions of commonly used empirical laws. (v) Finally, building on existing results, we show that gas reddening is marginally larger (by a factor of around 1.3) than the stellar reddening at all redshifts probed. Our results support a scenario where the ISM conditions of typical star-forming galaxies evolve with redshift, such that at z ≥ 1.5 Main Sequence galaxies have ISM conditions moving closer to those of local starbursts.

  16. Luminosity and Intrinsic Color Calibration of Main-Sequence Stars With 2Mass Photometry: All Sky Local Extinction

    Directory of Open Access Journals (Sweden)

    Knude Jens

    2003-12-01

    Full Text Available We present a new color index vs. absolute magnitude calibration of 2MASS JHK photometry. For the A0 to ~G5 and M segments of the main sequence information on the amount of interstellar extinction and its location in space may be obtained.

  17. Stochastically excited oscillations on the upper main sequence

    DEFF Research Database (Denmark)

    Antoci, Victoria

    2013-01-01

    Convective envelopes in stars on the main sequence are usually connected only with stars of spectral types F5 or later. However, observations as well as theory indicate that the convective outer layers in earlier stars, despite being shallow, are still effective and turbulent enough to stochastic......Convective envelopes in stars on the main sequence are usually connected only with stars of spectral types F5 or later. However, observations as well as theory indicate that the convective outer layers in earlier stars, despite being shallow, are still effective and turbulent enough...... Pulsating B and Be stars, all in the context of solar-like oscillations....

  18. Photometric Determination of the Mass Accretion Rates of Pre-main-sequence Stars. V. Recent Star Formation in the 30 Dor Nebula

    Science.gov (United States)

    De Marchi, Guido; Panagia, Nino; Beccari, Giacomo

    2017-09-01

    We report on the properties of the low-mass stars that recently formed in the central ˜ 2\\buildrel{ \\prime}\\over{.} 7× 2\\buildrel{ \\prime}\\over{.} 7 of 30 Dor, including the R136 cluster. Using the photometric catalog of De Marchi et al., based on observations with the Hubble Space Telescope, and the most recent extinction law for this field, we identify 1035 bona fide pre-main-sequence (PMS) stars showing {{H}}α excess emission at the 4σ level with an {{H}}α equivalent width of 20 Å or more. We find a wide spread in age spanning the range ˜ 0.1{--}50 {Myr}. We also find that the older PMS objects are placed in front of the R136 cluster and are separated from it by a conspicuous amount of absorbing material, indicating that star formation has proceeded from the periphery into the interior of the region. We derive physical parameters for all PMS stars, including masses m, ages t, and mass accretion rates {\\dot{M}}{acc}. To identify reliable correlations between these parameters, which are intertwined, we use a multivariate linear regression fit of the type {log}{\\dot{M}}{acc}=a× {log}t+b× {log}m+c. The values of a and b for 30 Dor are compatible with those found in NGC 346 and NGC 602. We extend the fit to a uniform sample of 1307 PMS stars with 0.5contract NAS5-26555.

  19. Evolution models of helium white dwarf-main-sequence star merger remnants: the mass distribution of single low-mass white dwarfs

    Science.gov (United States)

    Zhang, Xianfei; Hall, Philip D.; Jeffery, C. Simon; Bi, Shaolan

    2018-02-01

    It is not known how single white dwarfs with masses less than 0.5Msolar -- low-mass white dwarfs -- are formed. One way in which such a white dwarf might be formed is after the merger of a helium-core white dwarf with a main-sequence star that produces a red giant branch star and fails to ignite helium. We use a stellar-evolution code to compute models of the remnants of these mergers and find a relation between the pre-merger masses and the final white dwarf mass. Combining our results with a model population, we predict that the mass distribution of single low-mass white dwarfs formed through this channel spans the range 0.37 to 0.5Msolar and peaks between 0.45 and 0.46Msolar. Helium white dwarf--main-sequence star mergers can also lead to the formation of single helium white dwarfs with masses up to 0.51Msolar. In our model the Galactic formation rate of single low-mass white dwarfs through this channel is about 8.7X10^-3yr^-1. Comparing our models with observations, we find that the majority of single low-mass white dwarfs (<0.5Msolar) are formed from helium white dwarf--main-sequence star mergers, at a rate which is about $2$ per cent of the total white dwarf formation rate.

  20. IRAS 18153-1651: an H II region with a possible wind bubble blown by a young main-sequence B star

    Science.gov (United States)

    Gvaramadze, V. V.; Mackey, J.; Kniazev, A. Y.; Langer, N.; Chené, A.-N.; Castro, N.; Haworth, T. J.; Grebel, E. K.

    2017-04-01

    We report the results of spectroscopic observations and numerical modelling of the H II region IRAS 18153-1651. Our study was motivated by the discovery of an optical arc and two main-sequence stars of spectral type B1 and B3 near the centre of IRAS 18153-1651. We interpret the arc as the edge of the wind bubble (blown by the B1 star), whose brightness is enhanced by the interaction with a photoevaporation flow from a nearby molecular cloud. This interpretation implies that we deal with a unique case of a young massive star (the most massive member of a recently formed low-mass star cluster) caught just tens of thousands of years after its stellar wind has begun to blow a bubble into the surrounding dense medium. Our 2D, radiation-hydrodynamics simulations of the wind bubble and the H II region around the B1 star provide a reasonable match to observations, both in terms of morphology and absolute brightness of the optical and mid-infrared emission, and verify the young age of IRAS 18153-1651. Taken together our results strongly suggest that we have revealed the first example of a wind bubble blown by a main-sequence B star.

  1. Evolution models of helium white dwarf--main-sequence star merger remnants: the mass distribution of single low-mass white dwarfs

    OpenAIRE

    Zhang, Xianfei; Hall, Philip D.; Jeffery, C. Simon; Bi, Shaolan

    2017-01-01

    It is not known how single white dwarfs with masses less than 0.5Msolar -- low-mass white dwarfs -- are formed. One way in which such a white dwarf might be formed is after the merger of a helium-core white dwarf with a main-sequence star that produces a red giant branch star and fails to ignite helium. We use a stellar-evolution code to compute models of the remnants of these mergers and find a relation between the pre-merger masses and the final white dwarf mass. Combining our results with ...

  2. The evolution of surface magnetic fields in young solar-type stars II: the early main sequence (250-650 Myr)

    Science.gov (United States)

    Folsom, C. P.; Bouvier, J.; Petit, P.; Lèbre, A.; Amard, L.; Palacios, A.; Morin, J.; Donati, J.-F.; Vidotto, A. A.

    2018-03-01

    There is a large change in surface rotation rates of sun-like stars on the pre-main sequence and early main sequence. Since these stars have dynamo-driven magnetic fields, this implies a strong evolution of their magnetic properties over this time period. The spin-down of these stars is controlled by interactions between stellar and magnetic fields, thus magnetic evolution in turn plays an important role in rotational evolution. We present here the second part of a study investigating the evolution of large-scale surface magnetic fields in this critical time period. We observed stars in open clusters and stellar associations with known ages between 120 and 650 Myr, and used spectropolarimetry and Zeeman Doppler Imaging to characterize their large-scale magnetic field strength and geometry. We report 15 stars with magnetic detections here. These stars have masses from 0.8 to 0.95 M⊙, rotation periods from 0.326 to 10.6 d, and we find large-scale magnetic field strengths from 8.5 to 195 G with a wide range of geometries. We find a clear trend towards decreasing magnetic field strength with age, and a power law decrease in magnetic field strength with Rossby number. There is some tentative evidence for saturation of the large-scale magnetic field strength at Rossby numbers below 0.1, although the saturation point is not yet well defined. Comparing to younger classical T Tauri stars, we support the hypothesis that differences in internal structure produce large differences in observed magnetic fields, however for weak-lined T Tauri stars this is less clear.

  3. The environmental impacts on the star formation main sequence: An Hα study of the newly discovered rich cluster at z = 1.52

    Energy Technology Data Exchange (ETDEWEB)

    Koyama, Yusei; Kodama, Tadayuki; Tadaki, Ken-ichi; Hayashi, Masao [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Tanaka, Ichi [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A' ohoku Place, Hilo, HI 96720 (United States); Shimakawa, Rhythm, E-mail: koyama.yusei@nao.ac.jp [Department of Astronomical Science, The Graduate University for Advanced Studies, Mitaka, Tokyo 181-8588 (Japan)

    2014-07-01

    We report the discovery of a strong over-density of galaxies in the field of a radio galaxy at z = 1.52 (4C 65.22) based on our broadband and narrow-band (Hα) photometry with the Subaru Telescope. We find that Hα emitters are located in the outskirts of the density peak (cluster core) dominated by passive red-sequence galaxies. This resembles the situation in lower-redshift clusters, suggesting that the newly discovered structure is a well-evolved rich galaxy cluster at z = 1.5. Our data suggest that the color-density and stellar mass-density relations are already in place at z ∼ 1.5, mostly driven by the passive red massive galaxies residing within r{sub c} ≲ 200 kpc from the cluster core. These environmental trends almost disappear when we consider only star-forming (SF) galaxies. We do not find SFR-density or SSFR-density relations amongst SF galaxies, and the location of the SF main sequence does not significantly change with environment. Nevertheless, we find a tentative hint that star-bursting galaxies (up-scattered objects from the main sequence) are preferentially located in a small group at ∼1 Mpc away from the main body of the cluster. We also argue that the scatter of the SF main sequence could be dependent on the distance to the nearest neighboring galaxy.

  4. The pre- versus post-main sequence evolutionary phase of B[e] stars. Constraints from 13CO band emission

    Czech Academy of Sciences Publication Activity Database

    Kraus, Michaela

    2009-01-01

    Roč. 494, č. 1 (2009), s. 253-262 ISSN 0004-6361 R&D Projects: GA AV ČR KJB300030701 Institutional research plan: CEZ:AV0Z10030501 Keywords : star s * winds * circumstellar matter Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.179, year: 2009

  5. Using the phase shift to asymptotically characterize the dipolar mixed modes in post-main-sequence stars

    DEFF Research Database (Denmark)

    Jiang, C.; Christensen-Dalsgaard, J.; Cunha, M.

    2018-01-01

    from the eigenvalue condition for mixed modes as a tool to characterize dipolar mixed modes from the theoretical as well as the practical point of view. Unlike the coupling strength, whose variation in a given star is very small over the relevant frequency range, the phase shifts vary significantly...

  6. The evolution of stellar metallicity gradients of the Milky Way disk from LSS-GAC main sequence turn-off stars: a two-phase disk formation history?

    International Nuclear Information System (INIS)

    Xiang, Mao-Sheng; Liu, Xiao-Wei; Huang, Yang; Wang, Chun; Ren, Juan-Juan; Chen, Bing-Qiu; Sun, Ning-Chen; Zhang, Hua-Wei; Yuan, Hai-Bo; Rebassa-Mansergas, Alberto; Huo, Zhi-Ying

    2015-01-01

    Accurate measurements of stellar metallicity gradients in the radial and vertical directions of the disk and their temporal variations provide important constraints on the formation and evolution of the Milky Way disk. We use 297 042 main sequence turn-off stars selected from the LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC) to determine the radial and vertical gradients of stellar metallicity, Δ[Fe/H]/ΔR and Δ[Fe/H]/Δ|Z| of the Milky Way disk in the direction of the anticenter. We determine ages of those turn-off stars by isochrone fitting and measure the temporal variations of metallicity gradients. We have carried out a detailed analysis of the selection effects resulting from the selection, observation and data reduction of LSS-GAC targets and the potential biases of a magnitude limited sample on the determinations of metallicity gradients. Our results show that the gradients, both in the radial and vertical directions, exhibit significant spatial and temporal variations. The radial gradients yielded by stars with the oldest ages (≳ 11 Gyr) are essentially zero at all heights from the disk midplane, while those given by younger stars are always negative. The vertical gradients deduced from stars with the oldest ages (≳ 11 Gyr) are negative and only show very weak variations with Galactocentric distance in the disk plane, R, while those yielded by younger stars show strong variations with R. After being essentially flat at the earliest epochs of disk formation, the radial gradients steepen as age decreases, reaching a maximum (steepest) at age 7–8 Gyr, and then they flatten again. Similar temporal trends are also found for the vertical gradients. We infer that the assembly of the Milky Way disk may have experienced at least two distinct phases. The earlier phase is probably related to a slow, pressure-supported collapse of gas, when the gas settles down to the disk mainly in the vertical direction. In the later phase, there are

  7. IN-SYNC. II. VIRIAL STARS FROM SUBVIRIAL CORES—THE VELOCITY DISPERSION OF EMBEDDED PRE-MAIN-SEQUENCE STARS IN NGC 1333

    International Nuclear Information System (INIS)

    Foster, Jonathan B.; Cottaar, Michiel; Meyer, Michael R.; Covey, Kevin R.; Arce, Héctor G.; Nidever, David L.; Stassun, Keivan G.; Tan, Jonathan C.; Da Rio, Nicola; Chojnowski, S. Drew; Majewski, Steven R.; Skrutskie, Michael; Wilson, John C.; Flaherty, Kevin M.; Rebull, Luisa; Frinchaboy, Peter M.; Zasowski, Gail

    2015-01-01

    The initial velocity dispersion of newborn stars is a major unconstrained aspect of star formation theory. Using near-infrared spectra obtained with the APOGEE spectrograph, we show that the velocity dispersion of young (1-2 Myr) stars in NGC 1333 is 0.92 ± 0.12 km s –1 after correcting for measurement uncertainties and the effect of binaries. This velocity dispersion is consistent with the virial velocity of the region and the diffuse gas velocity dispersion, but significantly larger than the velocity dispersion of the dense, star-forming cores, which have a subvirial velocity dispersion of 0.5 km s –1 . Since the NGC 1333 cluster is dynamically young and deeply embedded, this measurement provides a strong constraint on the initial velocity dispersion of newly formed stars. We propose that the difference in velocity dispersion between stars and dense cores may be due to the influence of a 70 μG magnetic field acting on the dense cores or be the signature of a cluster with initial substructure undergoing global collapse

  8. EFFECT OF METALLICITY ON THE EVOLUTION OF THE HABITABLE ZONE FROM THE PRE-MAIN SEQUENCE TO THE ASYMPTOTIC GIANT BRANCH AND THE SEARCH FOR LIFE

    Energy Technology Data Exchange (ETDEWEB)

    Danchi, William C. [Exoplanets and Stellar Astrophysics Laboratory, NASA Goddard Space Flight Center, Code 667, Greenbelt, MD 20771 (United States); Lopez, Bruno, E-mail: william.c.danchi@nasa.gov, E-mail: bruno.lopez@oca.eu [Observatoire de la Cote d' Azur, Laboratoire Lagrange UMR 7293, BP 4229, F-06034 Nice Cedex 4 (France)

    2013-05-20

    During the course of stellar evolution, the location and width of the habitable zone changes as the luminosity and radius of the star evolves. The duration of habitability for a planet located at a given distance from a star is greatly affected by the characteristics of the host star. A quantification of these effects can be used observationally in the search for life around nearby stars. The longer the duration of habitability, the more likely it is that life has evolved. The preparation of observational techniques aimed at detecting life would benefit from the scientific requirements deduced from the evolution of the habitable zone. We present a study of the evolution of the habitable zone around stars of 1.0, 1.5, and 2.0 M{sub Sun} for metallicities ranging from Z = 0.0001 to Z = 0.070. We also consider the evolution of the habitable zone from the pre-main sequence until the asymptotic giant branch is reached. We find that metallicity strongly affects the duration of the habitable zone for a planet as well as the distance from the host star where the duration is maximized. For a 1.0 M{sub Sun} star with near solar metallicity, Z = 0.017, the duration of the habitable zone is >10 Gyr at distances 1.2-2.0 AU from the star, whereas the duration is >20 Gyr for high-metallicity stars (Z = 0.070) at distances of 0.7-1.8 AU, and {approx}4 Gyr at distances of 1.8-3.3 AU for low-metallicity stars (Z = 0.0001). Corresponding results have been obtained for stars of 1.5 and 2.0 solar masses.

  9. EFFECT OF METALLICITY ON THE EVOLUTION OF THE HABITABLE ZONE FROM THE PRE-MAIN SEQUENCE TO THE ASYMPTOTIC GIANT BRANCH AND THE SEARCH FOR LIFE

    International Nuclear Information System (INIS)

    Danchi, William C.; Lopez, Bruno

    2013-01-01

    During the course of stellar evolution, the location and width of the habitable zone changes as the luminosity and radius of the star evolves. The duration of habitability for a planet located at a given distance from a star is greatly affected by the characteristics of the host star. A quantification of these effects can be used observationally in the search for life around nearby stars. The longer the duration of habitability, the more likely it is that life has evolved. The preparation of observational techniques aimed at detecting life would benefit from the scientific requirements deduced from the evolution of the habitable zone. We present a study of the evolution of the habitable zone around stars of 1.0, 1.5, and 2.0 M ☉ for metallicities ranging from Z = 0.0001 to Z = 0.070. We also consider the evolution of the habitable zone from the pre-main sequence until the asymptotic giant branch is reached. We find that metallicity strongly affects the duration of the habitable zone for a planet as well as the distance from the host star where the duration is maximized. For a 1.0 M ☉ star with near solar metallicity, Z = 0.017, the duration of the habitable zone is >10 Gyr at distances 1.2-2.0 AU from the star, whereas the duration is >20 Gyr for high-metallicity stars (Z = 0.070) at distances of 0.7-1.8 AU, and ∼4 Gyr at distances of 1.8-3.3 AU for low-metallicity stars (Z = 0.0001). Corresponding results have been obtained for stars of 1.5 and 2.0 solar masses.

  10. RADIO PROPERTIES OF THE BAT AGNs: THE FIR–RADIO RELATION, THE FUNDAMENTAL PLANE, AND THE MAIN SEQUENCE OF STAR FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Krista Lynne; Mushotzky, Richard F.; Vogel, Stuart; Shimizu, Thomas T. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Miller, Neal, E-mail: klsmith@astro.umd.edu [Department of Mathematics and Physics, Stevenson University, Stevenson, MD 21117 (United States)

    2016-12-01

    We conducted 22 GHz 1″ JVLA imaging of 70 radio-quiet active galactic nuclei (AGNs) from the Swift -BAT survey. We find radio cores in all but three objects. The radio morphologies of the sample fall into three groups: compact and core-dominated, extended, and jet-like. We spatially decompose each image into core flux and extended flux, and compare the extended radio emission with that predicted from previous Herschel observations using the canonical FIR–radio relation. After removing the AGN contribution to the FIR and radio flux densities, we find that the relation holds remarkably well despite the potentially different star formation physics in the circumnuclear environment. We also compare our core radio flux densities with predictions of coronal models and scale-invariant jet models for the origin of radio emission in radio-quiet AGNs, and find general consistency with both models. However, we find that the L {sub R}/ L {sub X} relation does not distinguish between star formation and non-relativistic AGN-driven outflows as the origin of radio emission in radio-quiet AGNs. Finally, we examine where objects with different radio morphologies fall in relation to the main sequence (MS) of star formation, and conclude that those AGNs that fall below the MS, as X-ray selected AGNs have been found to do, have core-dominated or jet-like 22 GHz morphologies.

  11. Hydrodynamic ejection of bipolar flows from objects undergoing disk accretion: T Tauri stars, massive pre-main-sequence objects, and cataclysmic variables

    International Nuclear Information System (INIS)

    Torbett, M.V.

    1984-01-01

    A general mechanism is presented for generating pressure-driven winds that are intrinsically bipolar from objects undergoing disk accretion. The energy librated in a boundary layer shock as the disk matter impacts the central object is shown to be sufficient to eject a fraction βapprox.10 -2 to 10 -3 of the accreted mass. These winds are driven by a mechanism that accelerates the flow perpendicular to the plane of the disk and can therefore account for the bipolar geometry of the mass loss observed near young stars. The mass loss contained in these winds is comparable to that inferred for young stars. Thus, disk accretion-driven winds may constitute the T Tauri phase of stellar evolution. This mechanism is generally applicable, and thus massive pre-main-sequence objects as well as cataclysmic variables at times of enhanced accretion are predicted to eject bipolar outflows as well. Unmagnetized accreting neutron stas are also expected to eject bipolar flows. Since this mechanism requires stellar surfaces, however, it will not operate in disk accretion onto black holes

  12. A HIGHLY CONSISTENT FRAMEWORK FOR THE EVOLUTION OF THE STAR-FORMING ''MAIN SEQUENCE'' FROM z ∼ 0-6

    Energy Technology Data Exchange (ETDEWEB)

    Speagle, J. S. [Harvard University Department of Astronomy, 60 Garden Street, MS 46, Cambridge, MA 02138 (United States); Steinhardt, C. L.; Silverman, J. D. [Kavli IPMU, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa-shi, Chiba 277-8583 (Japan); Capak, P. L., E-mail: jspeagle@cfa.harvard.edu [California Institute of Technology, MC 105-24, 1200 East California Boulevard, Pasadena, CA 91125 (United States)

    2014-10-01

    Using a compilation of 25 studies from the literature, we investigate the evolution of the star-forming galaxy (SFG) main sequence (MS) in stellar mass and star formation rate (SFR) out to z ∼ 6. After converting all observations to a common set of calibrations, we find a remarkable consensus among MS observations (∼0.1 dex 1σ interpublication scatter). By fitting for time evolution of the MS in bins of constant mass, we deconvolve the observed scatter about the MS within each observed redshift bin. After accounting for observed scatter between different SFR indicators, we find the width of the MS distribution is ∼0.2 dex and remains constant over cosmic time. Our best fits indicate the slope of the MS is likely time-dependent, with our best-fit log SFR(M {sub *}, t) = (0.84 ± 0.02 – 0.026 ± 0.003 × t)log M {sub *} – (6.51 ± 0.24 – 0.11 ± 0.03 × t), where t is the age of the universe in Gyr. We use our fits to create empirical evolutionary tracks in order to constrain MS galaxy star formation histories (SFHs), finding that (1) the most accurate representations of MS SFHs are given by delayed-τ models, (2) the decline in fractional stellar mass growth for a ''typical'' MS galaxy today is approximately linear for most of its lifetime, and (3) scatter about the MS can be generated by galaxies evolving along identical evolutionary tracks assuming an initial 1σ spread in formation times of ∼1.4 Gyr.

  13. IN-SYNC I: Homogeneous stellar parameters from high-resolution apogee spectra for thousands of pre-main sequence stars

    International Nuclear Information System (INIS)

    Cottaar, Michiel; Meyer, Michael R.; Covey, Kevin R.; Nidever, David L.; Stassun, Keivan G.; Foster, Jonathan B.; Tan, Jonathan C.; Da Rio, Nicola; Chojnowski, S. Drew; Skrutskie, Michael; Majewski, Steven R.; Wilson, John C.; Zasowski, Gail; Flaherty, Kevin M.; Frinchaboy, Peter M.

    2014-01-01

    Over two years, 8859 high-resolution H-band spectra of 3493 young (1-10 Myr) stars were gathered by the multi-object spectrograph of the APOGEE project as part of the IN-SYNC ancillary program of the SDSS-III survey. Here we present the forward modeling approach used to derive effective temperatures, surface gravities, radial velocities, rotational velocities, and H-band veiling from these near-infrared spectra. We discuss in detail the statistical and systematic uncertainties in these stellar parameters. In addition, we present accurate extinctions by measuring the E(J – H) of these young stars with respect to the single-star photometric locus in the Pleiades. Finally, we identify an intrinsic stellar radius spread of about 25% for late-type stars in IC 348 using three (nearly) independent measures of stellar radius, namely, the extinction-corrected J-band magnitude, the surface gravity, and the Rsin i from the rotational velocities and literature rotation periods. We exclude that this spread is caused by uncertainties in the stellar parameters by showing that the three estimators of stellar radius are correlated, so that brighter stars tend to have lower surface gravities and larger Rsin i than fainter stars at the same effective temperature. Tables providing the spectral and photometric parameters for the Pleiades and IC 348 have been provided online.

  14. TIME-SERIES PHOTOMETRY OF STARS IN AND AROUND THE LAGOON NEBULA. I. ROTATION PERIODS OF 290 LOW-MASS PRE-MAIN-SEQUENCE STARS IN NGC 6530

    International Nuclear Information System (INIS)

    Henderson, Calen B.; Stassun, Keivan G.

    2012-01-01

    We have conducted a long-term, wide-field, high-cadence photometric monitoring survey of ∼50,000 stars in the Lagoon Nebula H II region. This first paper presents rotation periods for 290 low-mass stars in NGC 6530, the young cluster illuminating the nebula, and for which we assemble a catalog of infrared and spectroscopic disk indicators, estimated masses and ages, and X-ray luminosities. The distribution of rotation periods we measure is broadly uniform for 0.5 days X /L bol ≈ –3.3). However, we find a significant positive correlation between L X /L bol and corotation radius, suggesting that the observed X-ray luminosities are regulated by centrifugal stripping of the stellar coronae. The period-mass relationship in NGC 6530 is broadly similar to that of the Orion Nebula Cluster (ONC), but the slope of the relationship among the slowest rotators differs from that in the ONC and other young clusters. We show that the slope of the period-mass relationship for the slowest rotators can be used as a proxy for the age of a young cluster, and we argue that NGC 6530 may be slightly younger than the ONC, making it a particularly important touchstone for models of angular momentum evolution in young, low-mass stars.

  15. Stellar evolution IV: evolution of a star of 1.5 M(S) from the main-sequence to the red-giant branch with and without overshooting from convective core

    International Nuclear Information System (INIS)

    Maeder, A.

    1975-01-01

    For a star of 1.5 M(S) with an initial composition given by X=0.70 and Z=0.03, three sets of evolutionary models are computed with different assumptions on the non-local effects characterizing the turbulent motions in the convective core. Some overshooting from the convective core may occur during Main-sequence evolution. The changes in the stellar structure, lifetimes and evolutionary tracks brought about by this process are studied. Some characteristics of the evolutionary tracks in the theoretical HR diagram have a very high sensitivity to the exact extent of the convective core, and this may provide powerful tests of events occurring in the deep stellar interior. (orig./BJ) [de

  16. Variability of Disk Emission in Pre-Main Sequence and Related Stars. II. Variability in the Gas and Dust Emission of the Herbig Fe Star SAO 206462

    Science.gov (United States)

    Sitko, Michael L.; Day, Amanda N.; Kimes, Robin L.; Beerman, Lori C.; Martus, Cameron; Lynch, David K.; Russell, Ray W.; Grady, Carol A.; Schneider, Glenn; Lisse, Carey M.; hide

    2011-01-01

    We present thirteen epochs of near-infrared (0.8-5 microns) spectroscopic observations of the pre-transitional, "gapped" disk system in SAO 206462 (=HD 135344B). In all, six gas emission lines (Br(alpha) , Br(gamma), Pa(beta), Pa(delta), Pa(epsilon), and the 0.8446 microns line of O I) along with continuum measurements made near the standard J, H, K, and L photometric bands were measured. A mass accretion rate of approximately 2 x 10(exp 8)Solar Mass/yr was derived from the Br(gamma) and Pa(beta) lines. However, the fluxes of these lines varied by a factor of over two during the course of a few months. The continuum also varied, but by only approx.30%, and even decreased at a time when the gas emission was increasing. The H I line at 1.083 microns was also found to vary in a manner inconsistent with that of either the hydrogen lines or the dust. Both the gas and dust variabilities indicate significant changes in the region of the inner gas and the inner dust belt that may be common to many young disk systems. If planets are responsible for defining the inner edge of the gap, they could interact with the material on time scales commensurate with what is observed for the variations in the dust, while other disk instabilities (thermal, magneto-rotational) would operate there on longer time scales than we observe for the inner dust belt. For SAO 206462, the orbital period would likely be 1-3 years. If the changes are being induced in the disk material closer to the star than the gap, a variety of mechanisms (disk instabilities, interactions via planets) might be responsible for the changes seen. The He I feature is most likely due to a wind whose orientation changes with respect to the observer on time scales of a day or less. To further constrain the origin of the gas and dust emission will require multiple spectroscopic and interferometric observations on both shorter and longer time scales that have been sampled so far.

  17. Post-main-sequence planetary system evolution

    Science.gov (United States)

    Veras, Dimitri

    2016-01-01

    The fates of planetary systems provide unassailable insights into their formation and represent rich cross-disciplinary dynamical laboratories. Mounting observations of post-main-sequence planetary systems necessitate a complementary level of theoretical scrutiny. Here, I review the diverse dynamical processes which affect planets, asteroids, comets and pebbles as their parent stars evolve into giant branch, white dwarf and neutron stars. This reference provides a foundation for the interpretation and modelling of currently known systems and upcoming discoveries. PMID:26998326

  18. A white dwarf companion to the main-sequence star 4 Omicron(1) Orionis and the binary hypothesis for the origin of peculiar red giants

    Science.gov (United States)

    Ake, Thomas B.; Johnson, Hollis R.

    1988-01-01

    Ultraviolet spectra of the peculiar red giants (PRGs) called MS stars are investigated, and the discovery of a white dwarf (WD) companion to the MS star 4 Omicron(1) Orionis is reported. The observations and data analysis are discussed and compared with those for field WDs in order to derive parameters for the WD and the luminosity of the primary. Detection limits for the other MS stars investigated are derived, and the binary hypothesis for PRGs is reviewed.

  19. A main sequence for quasars

    Science.gov (United States)

    Marziani, Paola; Dultzin, Deborah; Sulentic, Jack W.; Del Olmo, Ascensión; Negrete, C. A.; Martínez-Aldama, Mary L.; D'Onofrio, Mauro; Bon, Edi; Bon, Natasa; Stirpe, Giovanna M.

    2018-03-01

    The last 25 years saw a major step forward in the analysis of optical and UV spectroscopic data of large quasar samples. Multivariate statistical approaches have led to the definition of systematic trends in observational properties that are the basis of physical and dynamical modeling of quasar structure. We discuss the empirical correlates of the so-called “main sequence” associated with the quasar Eigenvector 1, its governing physical parameters and several implications on our view of the quasar structure, as well as some luminosity effects associated with the virialized component of the line emitting regions. We also briefly discuss quasars in a segment of the main sequence that includes the strongest FeII emitters. These sources show a small dispersion around a well-defined Eddington ratio value, a property which makes them potential Eddington standard candles.

  20. A Main Sequence for Quasars

    Directory of Open Access Journals (Sweden)

    Paola Marziani

    2018-03-01

    Full Text Available The last 25 years saw a major step forward in the analysis of optical and UV spectroscopic data of large quasar samples. Multivariate statistical approaches have led to the definition of systematic trends in observational properties that are the basis of physical and dynamical modeling of quasar structure. We discuss the empirical correlates of the so-called “main sequence” associated with the quasar Eigenvector 1, its governing physical parameters and several implications on our view of the quasar structure, as well as some luminosity effects associated with the virialized component of the line emitting regions. We also briefly discuss quasars in a segment of the main sequence that includes the strongest FeII emitters. These sources show a small dispersion around a well-defined Eddington ratio value, a property which makes them potential Eddington standard candles.

  1. A deep x-ray survey of the Pleiades cluster and the B6-A3 main sequence stars in Orion

    Science.gov (United States)

    Caillault, Jean-Pierre

    1993-01-01

    We have obtained deep ROSAT images of three regions within the Pleiades open cluster. We have detected 317 X-ray sources in these ROSAT PSPC images, 171 of which we associate with certain probable members of the Pleiades cluster. We detect nearly all Pleiades members with spectral types later than G0 and within 25 arcminutes of our three field centers where our sensitivity is highest. This has allowed us to derive for the first time the luminosity function for the G, K, and M dwarfs of an open cluster without the need to use statistical techniques to account for the presence of upper limits in the data sample. Because of our high X-ray detection frequency down to the faint limit of the optical catalog, we suspect that some of our unidentified X-ray sources are previously unknown, very low-mass members of the Pleiades. A large fraction of the Pleiades members detected with ROSAT have published rotational velocities. Plots of L(sub x)/L(sub bol) versus spectroscopic rotational velocity show tightly correlated 'saturation' type relations for stars with (B - V)(sub O) greater than 0.60. For each of several color ranges, X-ray luminosities rise rapidly with increasing rotation rate until v sin i approximately equals 15 km/s, and then remain essentially flat for rotation rates up to at least v sin i approximately equal to 100 km/s. The dispersion in rotation among low-mass stars in the Pleiades is by far the dominant contributor to the dispersion in L(subx) at a given mass. Only about 35 percent of the B.A. and early F stars in the Pleiades are detected as X-ray sources in our survey. There is no correlation between X-ray flux and rotation for these stars. The X-ray luminosity function for the early-type Pleiades stars appears to be bimodal, with only a few exceptions. We either detect these stars at fluxes in the range found for low-mass stars or we derive X-ray limits below the level found for most Pleiades dwarfs. The X-ray spectra for the early-type Pleiades stars

  2. Chemical Abundances of Main-sequence, Turnoff, Subgiant, and Red Giant Stars from APOGEE Spectra. I. Signatures of Diffusion in the Open Cluster M67

    Science.gov (United States)

    Souto, Diogo; Cunha, Katia; Smith, Verne V.; Allende Prieto, C.; García-Hernández, D. A.; Pinsonneault, Marc; Holzer, Parker; Frinchaboy, Peter; Holtzman, Jon; Johnson, J. A.; Jönsson, Henrik; Majewski, Steven R.; Shetrone, Matthew; Sobeck, Jennifer; Stringfellow, Guy; Teske, Johanna; Zamora, Olga; Zasowski, Gail; Carrera, Ricardo; Stassun, Keivan; Fernandez-Trincado, J. G.; Villanova, Sandro; Minniti, Dante; Santana, Felipe

    2018-04-01

    Detailed chemical abundance distributions for 14 elements are derived for eight high-probability stellar members of the solar metallicity old open cluster M67 with an age of ∼4 Gyr. The eight stars consist of four pairs, with each pair occupying a distinct phase of stellar evolution: two G dwarfs, two turnoff stars, two G subgiants, and two red clump (RC) K giants. The abundance analysis uses near-IR high-resolution spectra (λ1.5–1.7 μm) from the Apache Point Observatory Galactic Evolution Experiment survey and derives abundances for C, N, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, and Fe. Our derived stellar parameters and metallicity for 2M08510076+1153115 suggest that this star is a solar twin, exhibiting abundance differences relative to the Sun of ≤0.04 dex for all elements. Chemical homogeneity is found within each class of stars (∼0.02 dex), while significant abundance variations (∼0.05–0.20 dex) are found across the different evolutionary phases; the turnoff stars typically have the lowest abundances, while the RCs tend to have the largest. Non-LTE corrections to the LTE-derived abundances are unlikely to explain the differences. A detailed comparison of the derived Fe, Mg, Si, and Ca abundances with recently published surface abundances from stellar models that include chemical diffusion provides a good match between the observed and predicted abundances as a function of stellar mass. Such agreement would indicate the detection of chemical diffusion processes in the stellar members of M67.

  3. A CENSUS OF ROTATION AND VARIABILITY IN L1495: A UNIFORM ANALYSIS OF TRANS-ATLANTIC EXOPLANET SURVEY LIGHT CURVES FOR PRE-MAIN-SEQUENCE STARS IN TAURUS

    International Nuclear Information System (INIS)

    Xiao Hongyu; Covey, Kevin R.; Lloyd, James P.; Rebull, Luisa; Charbonneau, David; Mandushev, Georgi; O'Donovan, Francis; Slesnick, Catherine

    2012-01-01

    We analyze light curves obtained by the Trans-atlantic Exoplanet Survey (TrES) for a field centered on the L1495 dark cloud in Taurus. The Spitzer Taurus Legacy Survey catalog identifies 179 bona fide Taurus members within the TrES field; 48 of the known Taurus members are detected by TrES, as well as 26 candidate members identified by the Spitzer Legacy team. We quantify the variability of each star in our sample using the ratio of the standard deviation of the original light curve (σ orig. ) to the standard deviation of a light curve that has been smoothed by 9 or 1001 epochs (σ 9 and σ 1001 , respectively). Known Taurus members typically demonstrate (σ orig. /σ 9 ) orig. /σ 1001 ) orig. /σ 9 ) ∼ 3.0 and (σ orig. /σ 1001 ) ∼ 10, as expected for light curves dominated by unstructured white noise. Of the 74 Taurus members/candidates with TrES light curves, we detect significant variability in 49 sources. Adapting a quantitative metric originally developed to assess the reliability of transit detections, we measure the amount of red and white noise in each light curve and identify 18 known or candidate Taurus members with highly significant period measurements. These appear to be the first periods measured for four of these sources (HD 282276, CX Tau, FP Tau, TrES J042423+265008), and in two other cases, the first non-aliased periods (LkCa 21 and DK Tau AB). For the remainder, the TrES measurements typically agree very well (δP < 1%) with previously reported values. Including periods measured at lower confidence for 15 additional sources, we report periods for 11 objects where no previous periods were found, including 8 confirmed Taurus members. We also identify 10 of the 26 candidate Taurus members that demonstrate variability levels consistent with being bona fide T Tauri stars. A Kolomgorov-Smirnov (K-S) test confirms that these new periods confirm the distinction between the rotation period distributions of stars with and without circumstellar

  4. A Search for Coronal Emission at the Bottom of the Main-Sequence: Stars and Brown Dwarf Candidates with Spectral Types Later than M7 and the Rotation-Activity Relation

    Science.gov (United States)

    Stringfellow, Guy

    2004-01-01

    This program intended to test whether the lowest mass stars at the bottom end of the main sequence and the lower mass brown dwarfs have coronae. If they have coronae, what are the coronal characteristics and what drives them? In the classical dynamo picture, the closed magnetic loop structure is generated near the boundary of the convective envelope and the radiative core. Stars with mass below 0.30 Msun however are fully convective, and the nature of the dynamo responsible for the generation of the coronae in this regime is poorly understood. Previous results from the ROSAT mission (e.g., Fleming et al. 1993, 1995; Schmitt et al. 1995) had confirmed three very important characteristics of M-star coronae: (1) a very high percentage of all M dwarfs have coronae (of order 85% in the local 7 pc sample), (2) those M dwarfs showing high chromospheric activity, such as having the Balmer series in emission or large/numerous optical flaring, indeed exhibit the highest coronal activity, and (3) that the maximum saturation boundary in X-ray luminosity, which amounts to 0.0001-0.001 for Lx/Lbol for the dMe stars, extends down to the current detection limit, through spectral types M7. It was likely that the incompleteness noted for result (1) above was simply a detection limit problem; for more distant sources, the X-ray fainter dM stars will drop below detection thresholds before the more X-ray luminous dMe stars. The latest stars for which direct detection of the corona had been successful were of spectral type dM7 (e.g., VB8, LHS 3003). This program proposed to obtain ROSAT HRI observations for a large number of the coolest known (at that time) stars at the bottom of the main-sequence, which had spectral types of M9 or later. Three stars were approved for observations with ROSAT-HRI totaling 180 ksec. The goal was to obtain X-ray detections or low upper limits for the three approved stars.

  5. Variability of Disk Emission in Pre-main-sequence and Related Stars. IV. Investigating the Structural Changes in the Inner Disk Region of MWC 480

    Science.gov (United States)

    Fernandes, Rachel B.; Long, Zachary C.; Pikhartova, Monika; Sitko, Michael L.; Grady, Carol A.; Russell, Ray W.; Luria, David M.; Tyler, Dakotah B.; Bayyari, Ammar; Danchi, William; Wisniewski, John P.

    2018-04-01

    We present five epochs of near-IR observations of the protoplanetary disk around MWC 480 (HD 31648) obtained with the SpeX spectrograph on NASA’s Infrared Telescope Facility between 2007 and 2013, inclusive. Using the measured line fluxes in the Pa β and Br γ lines, we found the mass accretion rates to be (1.26–2.30) × 10‑7 M ⊙ yr‑1 and (1.4–2.01) × 10‑7 M ⊙ yr‑1, respectively, but which varied by more than 50% from epoch to epoch. The spectral energy distribution reveals a variability of about 30% between 1.5 and 10 μm during this same period of time. We investigated the variability using of the continuum emission of the disk in using the Monte-Carlo Radiative Transfer Code HOCHUNK3D. We find that varying the height of the inner rim successfully produces a change in the NIR flux but lowers the far-IR emission to levels below all measured fluxes. Because the star exhibits bipolar flows, we utilized a structure that simulates an inner disk wind to model the variability in the near-IR, without producing flux levels in the far-IR that are inconsistent with existing data. For this object, variable near-IR emission due to such an outflow is more consistent with the data than changing the scale height of the inner rim of the disk.

  6. VARIABILITY OF DISK EMISSION IN PRE-MAIN SEQUENCE AND RELATED STARS. III. EXPLORING STRUCTURAL CHANGES IN THE PRE-TRANSITIONAL DISK IN HD 169142

    Energy Technology Data Exchange (ETDEWEB)

    Wagner, Kevin R.; Sitko, Michael L.; Swearingen, Jeremy R.; Champney, Elizabeth H.; Johnson, Alexa N.; Werren, Chelsea [Department of Physics, University of Cincinnati, Cincinnati, OH 45221 (United States); Grady, Carol A. [Eureka Scientific, 2452 Delmer, Suite 100, Oakland, CA 96002 (United States); Whitney, Barbara A. [Department of Astronomy, University of Wisconsin, 475 North CharterStreet, Madison, WI 53706-1582 (United States); Russell, Ray W. [The Aerospace Corporation, Los Angeles, CA 90009 (United States); Schneider, Glenn H. [Steward Observatory, 933 North Cherry Avenue, University of Arizona, Tucson, AZ 85721 (United States); Momose, Munetake [Ibaraki University, 310-0056 Ibaraki, Mito, Bunkyo, 11 (Japan); Muto, Takayuki [Kogakuin University, 1-24-2 Nishishinjuku, Shinjuku, Tokyo 163-8677 (Japan); Inoue, Akio K. [Osaka Sangyo University, College of General Education, 3-1-1 Nakagaito, Daito, Osaka 574-8530 (Japan); Lauroesch, James T.; Hornbeck, Jeremy [University of Louisville Research Foundation, Inc., 2301 South 3rd Street, Louisville, KY 40292 (United States); Brown, Alexander [Center for Astrophysics and Space Astronomy, Astrophysics Research Laboratory, 593 UCB, University of Colorado, Boulder, CO 80309-0593 (United States); Fukagawa, Misato [Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1, Machikaneyama, Toyonaka, Osaka 560-0043 (Japan); Currie, Thayne M. [Oak Ridge Associated Universities, 100 ORAU Way, Oak Ridge, TN 37830-6218 (United States); Wisniewski, John P. [University of Oklahoma, 660 Parrington Oval, Norman, OK 73019 (United States); Woodgate, Bruce E., E-mail: wagnekr@mail.uc.edu, E-mail: sitkoml@ucmail.uc.edu, E-mail: swearijr@mail.uc.edu, E-mail: ehchampney@gmail.com, E-mail: astefank@andrew.cmu.edu, E-mail: ccwerren@yahoo.com, E-mail: carol.a.grady@nasa.gov, E-mail: bwhitney@astro.wisc.edu, E-mail: Ray.W.Russell@aero.org [NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States)

    2015-01-10

    We present near-IR (NIR) and far-UV observations of the pre-transitional (gapped) disk in HD 169142 using NASA's Infrared Telescope Facility and Hubble Space Telescope. The combination of our data along with existing data sets into the broadband spectral energy distribution reveals variability of up to 45% between ∼1.5-10 μm over a maximum timescale of 10 yr. All observations known to us separate into two distinct states corresponding to a high near-IR state in the pre-2000 epoch and a low state in the post-2000 epoch, indicating activity within the ≲1 AU region of the disk. Through analysis of the Pa β and Br γ lines in our data we derive a mass accretion rate in 2013 May of M-dot ≈ (1.5-2.7) × 10{sup –9} M {sub ☉} yr{sup –1}. We present a theoretical modeling analysis of the disk in HD 169142 using Monte-Carlo radiative transfer simulation software to explore the conditions and perhaps signs of planetary formation in our collection of 24 yr of observations. We find that shifting the outer edge (r ≈ 0.3 AU) of the inner disk by 0.05 AU toward the star (in simulation of accretion and/or sculpting by forming planets) successfully reproduces the shift in NIR flux. We establish that the ∼40-70 AU dark ring imaged in the NIR by Quanz et al. and Momose et al. and at 7 mm by Osorio et al. may be reproduced with a 30% scaled density profile throughout the region, strengthening the link to this structure being dynamically cleared by one or more planetary mass bodies.

  7. VARIABILITY OF DISK EMISSION IN PRE-MAIN SEQUENCE AND RELATED STARS. III. EXPLORING STRUCTURAL CHANGES IN THE PRE-TRANSITIONAL DISK IN HD 169142

    International Nuclear Information System (INIS)

    Wagner, Kevin R.; Sitko, Michael L.; Swearingen, Jeremy R.; Champney, Elizabeth H.; Johnson, Alexa N.; Werren, Chelsea; Grady, Carol A.; Whitney, Barbara A.; Russell, Ray W.; Schneider, Glenn H.; Momose, Munetake; Muto, Takayuki; Inoue, Akio K.; Lauroesch, James T.; Hornbeck, Jeremy; Brown, Alexander; Fukagawa, Misato; Currie, Thayne M.; Wisniewski, John P.; Woodgate, Bruce E.

    2015-01-01

    We present near-IR (NIR) and far-UV observations of the pre-transitional (gapped) disk in HD 169142 using NASA's Infrared Telescope Facility and Hubble Space Telescope. The combination of our data along with existing data sets into the broadband spectral energy distribution reveals variability of up to 45% between ∼1.5-10 μm over a maximum timescale of 10 yr. All observations known to us separate into two distinct states corresponding to a high near-IR state in the pre-2000 epoch and a low state in the post-2000 epoch, indicating activity within the ≲1 AU region of the disk. Through analysis of the Pa β and Br γ lines in our data we derive a mass accretion rate in 2013 May of M-dot ≈ (1.5-2.7) × 10 –9 M ☉ yr –1 . We present a theoretical modeling analysis of the disk in HD 169142 using Monte-Carlo radiative transfer simulation software to explore the conditions and perhaps signs of planetary formation in our collection of 24 yr of observations. We find that shifting the outer edge (r ≈ 0.3 AU) of the inner disk by 0.05 AU toward the star (in simulation of accretion and/or sculpting by forming planets) successfully reproduces the shift in NIR flux. We establish that the ∼40-70 AU dark ring imaged in the NIR by Quanz et al. and Momose et al. and at 7 mm by Osorio et al. may be reproduced with a 30% scaled density profile throughout the region, strengthening the link to this structure being dynamically cleared by one or more planetary mass bodies

  8. On the Roche constants for main-sequence binaries

    International Nuclear Information System (INIS)

    Giannuzzi, M.A.

    1979-01-01

    The ratios C 1 /C 2 of the constants defining the equipotential surfaces which describe the external forms of the components of a close binary system have been calculated on the basis of evolutionary models. Theoretical systems have been considered allowing for a wide range of input parameters (masses and separation) and taking into account the evolutionary effects on the radii of the stars during their Main-Sequence lifetime. The systems have not undergone any transfer of matter and are representative of detached binaries with Main-sequence components. The ratios of the constants are confined in limited intervals and, for the highest values of the mass-ratios, they are clustered around the unit. (Auth.)

  9. Pre-main sequence masses and the age spread in the Orion cluster

    International Nuclear Information System (INIS)

    McNamara, B.J.

    1975-01-01

    The spread in formation times for stars earlier than GO in the Orion cluster is investigated. The range of stellar ages in this cluster is found to extend from at least 10 6 years to about 10 7 years. On the basis of this evidence and the similarity of the color--magnitude diagrams of other young clusters to the Orion cluster, it is suggested that the current method of dating these clusters (from the point at which the most massive stars just reach the zero-age main sequence) might not be valid. The masses of forty-one pre-main sequence stars within the ranges 4.05 less than or equal to log(Te) less than or equal to 3.77 and 0.6 less than or equal to log (L/L/sub sun/) less than or equal to 2.1 are determined from observed effective temperatures, luminosities, and gravities. These masses were then compared with those expected from Iben's (1965) pre-main sequence evolutionary calculations. In most cases, the agreement between these values was found to be within the observational errors. Finally, the pre-main sequence stars possessing infrared excesses are found to be apparently among the most massive and youngest stars still contracting toward the zero-age main sequence

  10. Main-sequence photometry in NGC 2808

    International Nuclear Information System (INIS)

    Buonanno, R.; Corsi, C.E.; Fusi Pecci, F.; Harris, W.E.

    1984-01-01

    We have obtained a color-magnitude diagram for the southern globular cluster NGC 2808, to V/sub lim/approx. =21 (about 2 mag below the main-sequence turnoff). The internal photographic errors are sigma/sub V/approx. =0.02, sigma/sub B/-Vapprox. =0.03, small enough to permit a precise definition of the turnoff region and an estimate of the ''cosmic scatter'' along the main sequence. Fitting of the CMD to VandenBerg's [Astrophys. J. Suppl. 51, 29 (1983)] isochrones shows that an excellent match to the observations is achieved for model parameters of Yapprox. =0.2, Zapprox. =0.003 ([Fe/H]approx. =-0.8), and an age of (16 +- 2) billion years. All these characteristics are within the expected range from other observational constraints; no new clues from the main-sequence data alone have arisen to help explain the presence of the anomalous blue horizontal-branch stars

  11. Relation of chromospheric activity to convection, rotation, and pre-main-sequence evolution

    International Nuclear Information System (INIS)

    Gilliland, R.L.

    1986-01-01

    Pre-main-sequence, or T Tauri, stars are characterized by much larger fluxes of nonradiative origin than their main-sequence counterparts. As a class, the T Tauri stars have only moderate rotation rates, making an explanation of their chromospheric properties based on rapid rotation problematic. The recent success of correlating nonradiative fluxes to the Rossby number, Ro = P/sub rot//tau/sub conv/, a central parameter of simple dynamo theories of magnetic field generation, has led to the suggestion that the same relation might be of use in explaining the pre-main-sequence (PMS) stars if tau/sub conv/ is very large. We show that tau/sub conv/ does depend strongly on evolutionary effects above the main sequence (MS), but that this dependence alone cannot account for the high observed nonradiative fluxes. The acoustic flux is also strongly dependent on PMS evolutionary state, and when coupled to the parameterization of magnetic activity based on Ro, these two mechanisms seem capable of explaining the high observed level of chromospheric activity in T Tauri stars. The moment of inertia decreases by two to three order of magnitude during PMS evolution. Since young MS stars do not rotate two to three orders of magnitude faster than PMS stars, rapid loss or redistribution of angular momentum must occur

  12. Additional measurements of pre-main-sequence stellar rotation

    International Nuclear Information System (INIS)

    Hartmann, L.; Stauffer, J.R.

    1989-01-01

    New rotational-velocity measurements for pre-main-sequence stars in the Taurus-Auriga molecular cloud are reported. Rotational velocities or upper limits of 10 km/s are now available for 90 percent of the T Tauri stars with V less than 14.7 in the catalog of Cohen and Kuhi. Measurements of 'continuum emission' stars, thought to be accreting high-angular-momentum material from a circumstellar disk, show that these objects are not especially rapid rotators. The results confirm earlier findings that angular-momentum loss proceeds very efficiently in the earliest stages of star formation, and suggest that stars older than about one million yr contract to the main sequence at nearly constant angular momentum. The slow rotation of T Tauri stars probably requires substantial angular-momentum loss via a magnetically coupled wind. 35 references

  13. AK Sco: a tidally induced atmospheric dynamo in a pre-main sequence binary?

    Science.gov (United States)

    Gómez de Castro, A. I.

    2009-02-01

    AK Sco is a unique source: a 10-30 Myrs old pre-main sequence spectroscopic binary composed by two nearly equal F5 stars that at periastron are separated by barely eleven stellar radii so, the stellar magnetospheres fill the Roche lobe at periastron. The orbit is not yet circularized (e = 0.47) and very strong tides are expected. This makes of AK Sco, the ideal laboratory to study the effect of gravitational tides in the stellar magnetic field building up during pre-main sequence evolution. Evidence of this effect is reported in this contribution.

  14. Circumstellar Material on and off the Main Sequence

    Science.gov (United States)

    Steele, Amy; Debes, John H.; Deming, Drake

    2017-06-01

    There is evidence of circumstellar material around main sequence, giant, and white dwarf stars that originates from the small-body population of planetary systems. These bodies tell us something about the chemistry and evolution of protoplanetary disks and the planetary systems they form. What happens to this material as its host star evolves off the main sequence, and how does that inform our understanding of the typical chemistry of rocky bodies in planetary systems? In this talk, I will discuss the composition(s) of circumstellar material on and off the main sequence to begin to answer the question, “Is Earth normal?” In particular, I look at three types of debris disks to understand the typical chemistry of planetary systems—young debris disks, debris disks around giant stars, and dust around white dwarfs. I will review the current understanding on how to infer dust composition for each class of disk, and present new work on constraining dust composition from infrared excesses around main sequence and giant stars. Finally, dusty and polluted white dwarfs hold a unique key to our understanding of the composition of rocky bodies around other stars. In particular, I will discuss WD1145+017, which has a transiting, disintegrating planetesimal. I will review what we know about this system through high speed photometry and spectroscopy and present new work on understanding the complex interplay of physics that creates white dwarf pollution from the disintegration of rocky bodies.

  15. Three aspects of stellar evolution near the main sequence

    International Nuclear Information System (INIS)

    Morgan, J.C.

    1979-05-01

    Three problems of stellar evolution are considered: the gap in the HR diagram of M67, the evolutionary status of RS CVn binaries and the solar neutrino problem. The physical basis of the Eggleton stellar evolution computer program is described. The program was used to calculate a grid of evolutionary tracks for models with masses between 0.7 and 1.29 solar masses. The more massive stars considered here have expanding convective cores during their main sequence evolution. The isochrone of the old galactic cluster M67 has a gap at the top of its main sequence because of the rapid evolution of stars at hydrogen exhaustion. RS CVn binaries present a complex collection of observational phenomena although they appear to be detached binaries. Their evolutionary status has remained controversial because of their high space density. Here it is shown that a post main sequence interpretation is satisfactory. Models of the Sun with metal poor interiors have been proposed in an attempt to resolve the solar neutrino problem. Here the evolution of two such models is calculated in detail, including a gradual contamination of the surface convection zone to produce the observed metal abundance, giving fully consistent models of the Sun as it is observed. (author)

  16. Solar Luminosity on the Main Sequence, Standard Model and Variations

    Science.gov (United States)

    Ayukov, S. V.; Baturin, V. A.; Gorshkov, A. B.; Oreshina, A. V.

    2017-05-01

    Our Sun became Main Sequence star 4.6 Gyr ago according Standard Solar Model. At that time solar luminosity was 30% lower than current value. This conclusion is based on assumption that Sun is fueled by thermonuclear reactions. If Earth's albedo and emissivity in infrared are unchanged during Earth history, 2.3 Gyr ago oceans had to be frozen. This contradicts to geological data: there was liquid water 3.6-3.8 Gyr ago on Earth. This problem is known as Faint Young Sun Paradox. We analyze luminosity change in standard solar evolution theory. Increase of mean molecular weight in the central part of the Sun due to conversion of hydrogen to helium leads to gradual increase of luminosity with time on the Main Sequence. We also consider several exotic models: fully mixed Sun; drastic change of pp reaction rate; Sun consisting of hydrogen and helium only. Solar neutrino observations however exclude most non-standard solar models.

  17. The double main sequence of Omega Centauri

    Science.gov (United States)

    Bedin, L. R.; Piotto, G.; Anderson, J.; King, I. R.; Cassisi, S.; Momany, Y.

    Recent, high precision photometry of Omega Centauri, the biggest Galactic globular cluster, has been obtained with Hubble Space Telescope (HST). The color magnitude diagram reveals an unexpected bifurcation of colors in the main sequence (MS). The newly found double MS, the multiple turnoffs and subgiant branches, and other sequences discovered in the past along the red giant branch of this cluster add up to a fascinating but frustrating puzzle. Among the possible explanations for the blue main sequence an anomalous overabundance of helium is suggested. The hypothesis will be tested with a set of FLAMES@VLT data we have recently obtained (ESO DDT program), and with forthcoming ACS@HST images. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

  18. Testing Scaling Relations for Solar-like Oscillations from the Main Sequence to Red Giants Using Kepler Data

    DEFF Research Database (Denmark)

    Huber, D.; Bedding, T.R.; Stello, D.

    2011-01-01

    ), and oscillation amplitudes. We show that the difference of the Δν-νmax relation for unevolved and evolved stars can be explained by different distributions in effective temperature and stellar mass, in agreement with what is expected from scaling relations. For oscillation amplitudes, we show that neither (L/M) s......We have analyzed solar-like oscillations in ~1700 stars observed by the Kepler Mission, spanning from the main sequence to the red clump. Using evolutionary models, we test asteroseismic scaling relations for the frequency of maximum power (νmax), the large frequency separation (Δν...... scaling nor the revised scaling relation by Kjeldsen & Bedding is accurate for red-giant stars, and demonstrate that a revised scaling relation with a separate luminosity-mass dependence can be used to calculate amplitudes from the main sequence to red giants to a precision of ~25%. The residuals show...

  19. Effects of back warming in cocoon stars

    International Nuclear Information System (INIS)

    Donnison, J.R.; Williams, I.P.

    1976-01-01

    It is stated that dust shells frequently surround young stars, and attempts have been made to determine some of the properties of these shells. It is probable that the dust absorbs the outgoing radiation from the star and re-emits it in the infrared. If the dust shell does absorb radiation both its inner and outer surfaces will re-emit a certain proportion and some radiation will return to the central star, causing what amounts to 'warming of its own back'. It is interesting to consider how such a star evolves, compared with evolution of a normal pre-main-sequence star. A model for a contracting star that is receiving radiation from an external source has been developed by the authors in connection with the evolution of Jupiter within the radiation field of the Sun (Astrophys. Space Sci., 29:387 (1974)), and this model is here applied to the situation just described. It is emphasised that the discussion is concerned only with the evolution of the central star, the dust being regarded merely as a means of redirecting radiation back on to the surface of this star. Amongst conclusions reached is that a thin shell will cause no significant change in the structure and evolution of the central star, whilst the presence of a thick shell has a substantial effect on the star, slowing down is evolution. Whilst a dust shell is present the star cannot be seen, but only the dust shell emitting in the infrared, but once the dust shell clears the star is seen in a position and with an age that differs considerably from what it would have had if it had evolved without 'back warming' from the dust shell. (U.K.)

  20. Main-sequence turnoff of the Draco dwarf galaxy

    International Nuclear Information System (INIS)

    Stetson, P.B.; Mcclure, R.D.; Vandenberg, D.A.; Victoria Univ., Canada)

    1985-01-01

    Deep photometry on the B,V system for 182 stars in the dwarf spheroidal galaxy in Draco was obtained with a CCD camera at the Cassegrain focus of the Canada-France-Hawaii 3.6-m telescope. Draco's main-sequence turnoff if found near V(to) = 23.5, which is about 3.4 magnitudes below the galaxy's horizontal branch. This leads to the interpretation that Draco is not measurably younger than the clusters or Ursa Minor: the age of Draco is about 18 Gyr according to current star-revolution chronologies. No blue stragglers are definitely detected in Draco, and it is concluded that any young population in Draco probably represents less than 10 percent of the total. 30 references

  1. Orbital motion in pre-main sequence binaries

    Energy Technology Data Exchange (ETDEWEB)

    Schaefer, G. H. [The CHARA Array of Georgia State University, Mount Wilson Observatory, Mount Wilson, CA 91023 (United States); Prato, L. [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Simon, M. [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794 (United States); Patience, J., E-mail: schaefer@chara-array.org [Astrophysics Group, School of Physics, University of Exeter, Exeter, EX4 4QL (United Kingdom)

    2014-06-01

    We present results from our ongoing program to map the visual orbits of pre-main sequence (PMS) binaries in the Taurus star forming region using adaptive optics imaging at the Keck Observatory. We combine our results with measurements reported in the literature to analyze the orbital motion for each binary. We present preliminary orbits for DF Tau, T Tau S, ZZ Tau, and the Pleiades binary HBC 351. Seven additional binaries show curvature in their relative motion. Currently, we can place lower limits on the orbital periods for these systems; full solutions will be possible with more orbital coverage. Five other binaries show motion that is indistinguishable from linear motion. We suspect that these systems are bound and might show curvature with additional measurements in the future. The observations reported herein lay critical groundwork toward the goal of measuring precise masses for low-mass PMS stars.

  2. On the Statistical Properties of the Lower Main Sequence

    International Nuclear Information System (INIS)

    Angelou, George C.; Bellinger, Earl P.; Hekker, Saskia; Basu, Sarbani

    2017-01-01

    Astronomy is in an era where all-sky surveys are mapping the Galaxy. The plethora of photometric, spectroscopic, asteroseismic, and astrometric data allows us to characterize the comprising stars in detail. Here we quantify to what extent precise stellar observations reveal information about the properties of a star, including properties that are unobserved, or even unobservable. We analyze the diagnostic potential of classical and asteroseismic observations for inferring stellar parameters such as age, mass, and radius from evolutionary tracks of solar-like oscillators on the lower main sequence. We perform rank correlation tests in order to determine the capacity of each observable quantity to probe structural components of stars and infer their evolutionary histories. We also analyze the principal components of classic and asteroseismic observables to highlight the degree of redundancy present in the measured quantities and demonstrate the extent to which information of the model parameters can be extracted. We perform multiple regression using combinations of observable quantities in a grid of evolutionary simulations and appraise the predictive utility of each combination in determining the properties of stars. We identify the combinations that are useful and provide limits to where each type of observable quantity can reveal information about a star. We investigate the accuracy with which targets in the upcoming TESS and PLATO missions can be characterized. We demonstrate that the combination of observations from GAIA and PLATO will allow us to tightly constrain stellar masses, ages, and radii with machine learning for the purposes of Galactic and planetary studies.

  3. On the Statistical Properties of the Lower Main Sequence

    Energy Technology Data Exchange (ETDEWEB)

    Angelou, George C.; Bellinger, Earl P.; Hekker, Saskia [Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany); Basu, Sarbani [Department of Astronomy, Yale University, New Haven, CT 06520 (United States)

    2017-04-20

    Astronomy is in an era where all-sky surveys are mapping the Galaxy. The plethora of photometric, spectroscopic, asteroseismic, and astrometric data allows us to characterize the comprising stars in detail. Here we quantify to what extent precise stellar observations reveal information about the properties of a star, including properties that are unobserved, or even unobservable. We analyze the diagnostic potential of classical and asteroseismic observations for inferring stellar parameters such as age, mass, and radius from evolutionary tracks of solar-like oscillators on the lower main sequence. We perform rank correlation tests in order to determine the capacity of each observable quantity to probe structural components of stars and infer their evolutionary histories. We also analyze the principal components of classic and asteroseismic observables to highlight the degree of redundancy present in the measured quantities and demonstrate the extent to which information of the model parameters can be extracted. We perform multiple regression using combinations of observable quantities in a grid of evolutionary simulations and appraise the predictive utility of each combination in determining the properties of stars. We identify the combinations that are useful and provide limits to where each type of observable quantity can reveal information about a star. We investigate the accuracy with which targets in the upcoming TESS and PLATO missions can be characterized. We demonstrate that the combination of observations from GAIA and PLATO will allow us to tightly constrain stellar masses, ages, and radii with machine learning for the purposes of Galactic and planetary studies.

  4. Did A Planet Survive A Post-Main Sequence Evolutionary Event?

    Science.gov (United States)

    Sorber, Rebecca; Jang-Condell, Hannah; Zimmerman, Mara

    2018-06-01

    The GL86 is star system approximately 10 pc away with a main sequence K- type ~ 0.77 M⊙ star (GL 86A) with a white dwarf ~0.49 M⊙ companion (GL86 B). The system has a ~ 18.4 AU semi-major axis, an orbital period of ~353 yrs, and an eccentricity of ~ 0.39. A 4.5 MJ planet orbits the main sequence star with a semi-major axis of 0.113 AU, an orbital period of 15.76 days, in a near circular orbit with an eccentricity of 0.046. If we assume that this planet was formed during the time when the white dwarf was a main sequence star, it would be difficult for the planet to have remained in a stable orbit during the post-main sequence evolution of GL86 B. The post-main sequence evolution with planet survival will be examined by modeling using the program Mercury (Chambers 1999). Using the model, we examine the origins of the planet: whether it formed before or after the post-main sequence evolution of GL86B. The modeling will give us insight into the dynamical evolution of, not only, the binary star system, but also the planet’s life cycle.

  5. Pre-main-sequence evolution of the sun

    International Nuclear Information System (INIS)

    Gough, D.

    1980-01-01

    The phase of solar evolution after the dynamical collapse is considered. The physics of the Kelvin-Helmholtz phase of gravitational collapse is described, attention being given to the early stages of the star when it was completely convective. It is noted that subsequently, a radiative core developed and evolution was controlled by the rate at which heat can diffuse through it by radiative transfer. Since the study of the Kelvin-Helmholtz contraction alone does not give enough information regarding the state of the sun when it first settled down to approximate hydrostatic equilibrium, other stars are studied, and information on the sun is obtained by analogy. Many young solar-type stars, such as the T Tauri stars, are not in the completely convective Hayashi (1961) phase hence it is proposed that the sun was completely mixed soon after its formation, which has some bearing on the sun's chemical structure. It is suggested that the surface of the sun was very nonuniform compared with the photosphere of today. The simple solar evolution model presented gives a good guide to the general way in which the sun contracted to the main sequence

  6. Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars

    International Nuclear Information System (INIS)

    Underhill, A.B.; Divan, L.; Prevot-Burnichon, M.L.; Doazan, V.

    1979-01-01

    The significance is explained of the effective temperatures, angular diameters, distances and linear diameters which have been found from published ultraviolet spectrophotometry, visible and near infrared intermediate-band photometry and model-atmosphere fluxes for 160 O and B stars using a method which is fully explained and evaluated in the full paper which is reproduced on Microfiche MN 189/1. An appendix to the full paper presents BCD spectrophotometry for 77 of the program stars. The angular diameters are systematically the same as those measured previously, and the flux effective temperatures of the main-sequence and giant stars reproduce well the relationship established by other authors, for main-sequence and giant O and B stars. The O8 - B9 supergiants have systematically lower temperatures than do main-sequence stars of the same subtype. The Beta Cephei stars and most Be stars have the same effective temperature as normal stars of the same spectral type. The radii of O and B stars increase from main-sequence to supergiant. The late B supergiants are about twice as large as the O9 supergiants. (author)

  7. TESTING SCALING RELATIONS FOR SOLAR-LIKE OSCILLATIONS FROM THE MAIN SEQUENCE TO RED GIANTS USING KEPLER DATA

    Energy Technology Data Exchange (ETDEWEB)

    Huber, D.; Bedding, T. R.; Stello, D. [Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia); Hekker, S. [Astronomical Institute ' Anton Pannekoek' , University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands); Mathur, S. [High Altitude Observatory, NCAR, P.O. Box 3000, Boulder, CO 80307 (United States); Mosser, B. [LESIA, CNRS, Universite Pierre et Marie Curie, Universite Denis, Diderot, Observatoire de Paris, 92195 Meudon cedex (France); Verner, G. A.; Elsworth, Y. P.; Hale, S. J.; Chaplin, W. J. [School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom); Bonanno, A. [INAF Osservatorio Astrofisico di Catania (Italy); Buzasi, D. L. [Eureka Scientific, 2452 Delmer Street Suite 100, Oakland, CA 94602-3017 (United States); Campante, T. L. [Centro de Astrofisica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Kallinger, T. [Department of Physics and Astronomy, University of British Columbia, Vancouver (Canada); Silva Aguirre, V. [Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching (Germany); De Ridder, J. [Instituut voor Sterrenkunde, K.U.Leuven (Belgium); Garcia, R. A. [Laboratoire AIM, CEA/DSM-CNRS, Universite Paris 7 Diderot, IRFU/SAp, Centre de Saclay, 91191, Gif-sur-Yvette (France); Appourchaux, T. [Institut d' Astrophysique Spatiale, UMR 8617, Universite Paris Sud, 91405 Orsay Cedex (France); Frandsen, S. [Danish AsteroSeismology Centre (DASC), Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Houdek, G., E-mail: dhuber@physics.usyd.edu.au [Institute of Astronomy, University of Vienna, 1180 Vienna (Austria); and others

    2011-12-20

    We have analyzed solar-like oscillations in {approx}1700 stars observed by the Kepler Mission, spanning from the main sequence to the red clump. Using evolutionary models, we test asteroseismic scaling relations for the frequency of maximum power ({nu}{sub max}), the large frequency separation ({Delta}{nu}), and oscillation amplitudes. We show that the difference of the {Delta}{nu}-{nu}{sub max} relation for unevolved and evolved stars can be explained by different distributions in effective temperature and stellar mass, in agreement with what is expected from scaling relations. For oscillation amplitudes, we show that neither (L/M){sup s} scaling nor the revised scaling relation by Kjeldsen and Bedding is accurate for red-giant stars, and demonstrate that a revised scaling relation with a separate luminosity-mass dependence can be used to calculate amplitudes from the main sequence to red giants to a precision of {approx}25%. The residuals show an offset particularly for unevolved stars, suggesting that an additional physical dependency is necessary to fully reproduce the observed amplitudes. We investigate correlations between amplitudes and stellar activity, and find evidence that the effect of amplitude suppression is most pronounced for subgiant stars. Finally, we test the location of the cool edge of the instability strip in the Hertzsprung-Russell diagram using solar-like oscillations and find the detections in the hottest stars compatible with a domain of hybrid stochastically excited and opacity driven pulsation.

  8. ON THE RELIABILITY OF STELLAR AGES AND AGE SPREADS INFERRED FROM PRE-MAIN-SEQUENCE EVOLUTIONARY MODELS

    International Nuclear Information System (INIS)

    Hosokawa, Takashi; Offner, Stella S. R.; Krumholz, Mark R.

    2011-01-01

    We revisit the problem of low-mass pre-main-sequence stellar evolution and its observational consequences for where stars fall on the Hertzsprung-Russell diagram (HRD). In contrast to most previous work, our models follow stars as they grow from small masses via accretion, and we perform a systematic study of how the stars' HRD evolution is influenced by their initial radius, by the radiative properties of the accretion flow, and by the accretion history, using both simple idealized accretion histories and histories taken from numerical simulations of star cluster formation. We compare our numerical results to both non-accreting isochrones and to the positions of observed stars in the HRD, with a goal of determining whether both the absolute ages and the age dispersions inferred from non-accreting isochrones are reliable. We show that non-accreting isochrones can sometimes overestimate stellar ages for more massive stars (those with effective temperatures above ∼3500 K), thereby explaining why non-accreting isochrones often suggest a systematic age difference between more and less massive stars in the same cluster. However, we also find the only way to produce a similar overestimate for the ages of cooler stars is if these stars grow from ∼0.01 M sun seed protostars that are an order of magnitude smaller than predicted by current theoretical models, and if the size of the seed protostar correlates systematically with the final stellar mass at the end of accretion. We therefore conclude that, unless both of these conditions are met, inferred ages and age spreads for cool stars are reliable, at least to the extent that the observed bolometric luminosities and temperatures are accurate. Finally, we note that the time dependence of the mass accretion rate has remarkably little effect on low-mass stars' evolution on the HRD, and that such time dependence may be neglected for all stars except those with effective temperatures above ∼4000 K.

  9. On precise ZAMSs, the solar color, and pre-main-sequence lithium depletion

    International Nuclear Information System (INIS)

    Vandenberg, D.A.; Poll, H.E.

    1989-01-01

    This paper describes a semiempirical main-sequence-fitting method for the determination of distances to stellar systems, which uses a ZAMS locus carefully normalized to the sun, and whose shape is defined by a quartic over the color range for (B-V)0 values between 0.2 and 1.0 such that the morphology of the Pleiades C-M diagram is accurately reproduced. Using this technique, distances were derived for a number of star clusters. It was found that the observed depletion of lithium among cool main-sequence stars in the Hyades and Pleiades can be matched quite well by the present models. Calculations also show that the depletion of Li at a fixed T(eff) along the main sequence is a sensitive function of Fe/H. 98 refs

  10. Observational Effects of Magnetism in O Stars: Surface Nitrogen Abundances

    Science.gov (United States)

    Martins, F.; Escolano, C.; Wade, G. A.; Donati, J. F.; Bouret, J. C.

    2011-01-01

    Aims. We investigate the surface nitrogen content of the six magnetic O stars known to date as well as of the early B-type star Tau Sco.. We compare these abundances to predictions of evolutionary models to isolate the effects of magnetic field on the transport of elements in stellar interiors. Methods. We conduct a quantitative spectroscopic analysis of the ample stars with state-of-the-art atmosphere models. We rely on high signal-to-noise ratio, high resolution optical spectra obtained with ESPADONS at CFHT and NARVAL at TBL. Atmosphere models and synthetic spectra are computed with the code CMFGEN. Values of N/H together with their uncertainties are determined and compared to predictions of evolutionary models. Results. We find that the magnetic stars can be divided into two groups: one with stars displaying no N enrichment (one object); and one with stars most likely showing extra N enrichment (5 objects). For one star (Ori C) no robust conclusion can be drawn due to its young age. The star with no N enrichment is the one with the weakest magnetic field, possibly of dynamo origin. It might be a star having experienced strong magnetic braking under the condition of solid body rotation, but its rotational velocity is still relatively large. The five stars with high N content were probably slow rotators on the zero age main sequence, but they have surface N/H typical of normal O stars, indicating that the presence of a (probably fossil) magnetic field leads to extra enrichment. These stars may have a strong differential rotation inducing shear mixing. Our results shOuld be viewed as a basis on which new theoretical simulations can rely to better understand the effect of magnetism on the evolution of massive stars.

  11. Stellar Variability at the Main-sequence Turnoff of the Intermediate-age LMC Cluster NGC 1846

    Science.gov (United States)

    Salinas, R.; Pajkos, M. A.; Vivas, A. K.; Strader, J.; Contreras Ramos, R.

    2018-04-01

    Intermediate-age (IA) star clusters in the Large Magellanic Cloud (LMC) present extended main-sequence turn-offs (MSTO) that have been attributed to either multiple stellar populations or an effect of stellar rotation. Recently it has been proposed that these extended main sequences can also be produced by ill-characterized stellar variability. Here we present Gemini-S/Gemini Multi-Object Spectrometer (GMOS) time series observations of the IA cluster NGC 1846. Using differential image analysis, we identified 73 new variable stars, with 55 of those being of the Delta Scuti type, that is, pulsating variables close the MSTO for the cluster age. Considering completeness and background contamination effects, we estimate the number of δ Sct belonging to the cluster between 40 and 60 members, although this number is based on the detection of a single δ Sct within the cluster half-light radius. This amount of variable stars at the MSTO level will not produce significant broadening of the MSTO, albeit higher-resolution imaging will be needed to rule out variable stars as a major contributor to the extended MSTO phenomenon. Though modest, this amount of δ Sct makes NGC 1846 the star cluster with the highest number of these variables ever discovered. Lastly, our results present a cautionary tale about the adequacy of shallow variability surveys in the LMC (like OGLE) to derive properties of its δ Sct population. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil).

  12. RADIO AND MID-INFRARED PROPERTIES OF COMPACT STARBURSTS: DISTANCING THEMSELVES FROM THE MAIN SEQUENCE

    Energy Technology Data Exchange (ETDEWEB)

    Murphy, E. J. [Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Stierwalt, S.; Armus, L. [Spitzer Science Center, California Institute of Technology, MC 314-6, Pasadena, CA 91125 (United States); Condon, J. J. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Evans, A. S., E-mail: emurphy@obs.carnegiescience.edu [Department of Astronomy, University of Virginia, 530 McCormick Road, Charlottesville, VA 22904 (United States)

    2013-05-01

    We investigate the relationship between 8.44 GHz brightness temperatures and 1.4 to 8.44 GHz radio spectral indices with 6.2 {mu}m polycyclic aromatic hydrocarbon (PAH) emission and 9.7 {mu}m silicate absorption features for a sample of 36 local luminous and ultraluminous infrared galaxies. We find that galaxies having small 6.2 {mu}m PAH equivalent widths (EQWs), which signal the presence of weak PAH emission and/or an excess of very hot dust, also have flat spectral indices. The three active galactic nuclei (AGN) identified through their excessively large 8.44 GHz brightness temperatures are also identified as AGN via their small 6.2 {mu}m PAH EQWs. We also find that the flattening of the radio spectrum increases with increasing silicate optical depth, 8.44 GHz brightness temperature, and decreasing size of the radio source even after removing potential AGN, supporting the idea that compact starbursts show spectral flattening as the result of increased free-free absorption. These correlations additionally suggest that the dust obscuration in these galaxies must largely be coming from the vicinity of the compact starburst itself, and is not distributed throughout the (foreground) disk of the galaxy. Finally, we investigate the location of these infrared-bright systems relative to the main sequence (star formation rate versus stellar mass) of star-forming galaxies in the local universe. We find that the radio spectral indices of galaxies flatten with increasing distance above the main sequence, or in other words, with increasing specific star formation rate. This indicates that galaxies located above the main sequence, having high specific star formation rates, are typically compact starbursts hosting deeply embedded star formation that becomes more optically thick in the radio and infrared with increased distance above the main sequence.

  13. Giant CP stars

    International Nuclear Information System (INIS)

    Loden, L.O.; Sundman, A.

    1989-01-01

    This study is part of an investigation of the possibility of using chemically peculiar (CP) stars to map local galactic structure. Correct luminosities of these stars are therefore crucial. CP stars are generally regarded as main-sequence or near-main-sequence objects. However, some CP stars have been classified as giants. A selection of stars, classified in literature as CP giants, are compared to normal stars in the same effective temperature interval and to ordinary 'non giant' CP stars. There is no clear confirmation of a higher luminosity for 'CP giants', than for CP stars in general. In addition, CP characteristics seem to be individual properties not repeated in a component star or other cluster members. (author). 50 refs., 5 tabs., 3 figs

  14. Chemically Dissected Rotation Curves of the Galactic Bulge from Main-sequence Proper Motions

    Science.gov (United States)

    Clarkson, William I.; Calamida, Annalisa; Sahu, Kailash C.; Brown, Thomas M.; Gennaro, Mario; Avila, Roberto J.; Valenti, Jeff; Debattista, Victor P.; Rich, R. Michael; Minniti, Dante; Zoccali, Manuela; Aufdemberge, Emily R.

    2018-05-01

    We report results from an exploratory study implementing a new probe of Galactic evolution using archival Hubble Space Telescope imaging observations. Precise proper motions are combined with photometric relative metallicity and temperature indices, to produce the proper-motion rotation curves of the Galactic bulge separately for metal-poor and metal-rich main-sequence samples. This provides a “pencil-beam” complement to large-scale wide-field surveys, which to date have focused on the more traditional bright giant branch tracers. We find strong evidence that the Galactic bulge rotation curves drawn from “metal-rich” and “metal-poor” samples are indeed discrepant. The “metal-rich” sample shows greater rotation amplitude and a steeper gradient against line-of-sight distance, as well as possibly a stronger central concentration along the line of sight. This may represent a new detection of differing orbital anisotropy between metal-rich and metal-poor bulge objects. We also investigate selection effects that would be implied for the longitudinal proper-motion cut often used to isolate a “pure-bulge” sample. Extensive investigation of synthetic stellar populations suggests that instrumental and observational artifacts are unlikely to account for the observed rotation curve differences. Thus, proper-motion-based rotation curves can be used to probe chemodynamical correlations for main-sequence tracer stars, which are orders of magnitude more numerous in the Galactic bulge than the bright giant branch tracers. We discuss briefly the prospect of using this new tool to constrain detailed models of Galactic formation and evolution. Based on observations made with the NASA/ESA Hubble Space Telescope and obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  15. THE QUADRUPLE PRE-MAIN-SEQUENCE SYSTEM LkCa 3: IMPLICATIONS FOR STELLAR EVOLUTION MODELS

    International Nuclear Information System (INIS)

    Torres, Guillermo; Latham, David W.; Ruíz-Rodríguez, Dary; Prato, L.; Wasserman, Lawrence H.; Badenas, Mariona; Schaefer, G. H.; Mathieu, Robert D.

    2013-01-01

    We report the discovery that the pre-main-sequence (PMS) object LkCa 3 in the Taurus-Auriga star-forming region is a hierarchical quadruple system of M stars. It was previously known to be a close (∼0.''5) visual pair, with one component being a moderately eccentric 12.94 day single-lined spectroscopic binary. A re-analysis of archival optical spectra complemented by new near-infrared (NIR) spectroscopy shows both visual components to be double lined; the second one has a period of 4.06 days and a circular orbit. In addition to the orbital elements, we determine optical and NIR flux ratios, effective temperatures, and projected rotational velocities for all four stars. Using existing photometric monitoring observations of the system that had previously revealed the rotational period of the primary in the longer-period binary, we also detect the rotational signal of the primary in the 4.06 day binary, which is synchronized with the orbital motion. With only the assumption of coevality, a comparison of all of these constraints with current stellar evolution models from the Dartmouth series points to an age of 1.4 Myr and a distance of 133 pc, consistent with previous estimates for the region and suggesting that the system is on the near side of the Taurus complex. Similar comparisons of the properties of LkCa 3 and the well-known quadruple PMS system GG Tau with the widely used models from the Lyon series for a mixing length parameter of α ML = 1.0 strongly favor the Dartmouth models

  16. Pre-main-sequence depletion of Li-6 and Li-7

    International Nuclear Information System (INIS)

    Proffitt, C.R.; Michaud, G.

    1989-01-01

    Depletion of Li-6 and Li-7 during premain-sequence contraction has been calculated for several evolutionary sequences. Slightly greater Li-7 depletion was found than by other recent workers. On the premain sequence, Li-6 is depleted by a factor of at least 10 in the present models for stars with T(eff) lower than 6800 K on the main sequence. Because of the shorter destruction time scale for Li-6 as compared to Li-7, the determination of the abundances of these two isotopes would place strict constraints on the structure of premain-sequence stars. 39 refs

  17. Acne at The Bottom Of The Main Sequence

    Science.gov (United States)

    Barnes, John; Haswell, C.; Jenkins, J.; Jeffers, S.; Jones, H. R. A.; Lohr, M.; Pavlenko, Y.

    2016-08-01

    Starspots are an important manifestation of stellar activity and yet their distribution patterns on the lowest mass stars is not well known. Time series spectra of fully convective M dwarfs taken in the red-optical with UVES reveal numerous line profile distortions which are interpreted as starspots. We derive Doppler images for four M4.5V - M9V stars and find that contrast ratios corresponding to photosphere-spot temperature differences of only 200-300 K are sufficient to model the timeseries spectra. Although more starspot structure is found at high latitudes, spots are reconstructed at a range of phases and latitudes with mean spot filling factors of only a few per cent. The occurrence of low-contrast spots at predominantly high latitudes is in general likely to be responsible for the low amplitude photometric variability seen in late-M dwarfs. The recovered starspot patterns are used to assess their effect on precision radial velocity surveys aimed at detecting planets around this population of stars.

  18. Rotation-induced YORP break-up of small bodies to produce post-main-sequence debris

    Science.gov (United States)

    Veras, D.; Jacobson, S. A.; Gänsicke, B. T.

    2017-09-01

    We hypothesize that the in situ break-up of small bodies such as asteroids spun to fission during the giant branch phases of stellar evolution provides an important contribution to the debris orbiting and ultimately polluting white dwarfs. The YORP (Yarkovsky-O'Keefe-Radviesvki-Paddock) effect, which arises from radiation pressure, accelerates the spin rate of asymmetric asteroids, which can eventually shear themselves apart. This pressure is maintained and enhanced around dying stars because the outward push of an asteroid due to stellar mass loss is insignificant compared to the resulting stellar luminosity increase. Consequently, giant star radiation will destroy nearly all bodies with radii in the range 100 m-10 km that survive their parent star's main-sequence lifetime within a distance of about 7 au; smaller bodies are spun apart to their strongest, competent components. This estimate is conservative and would increase for highly asymmetric shapes or incorporation of the inward drag due to giant star stellar wind. The resulting debris field, which could extend to thousands of au, may be perturbed by remnant planetary systems to reproduce the observed dusty and gaseous discs which accompany polluted white dwarfs.

  19. Discovery and characterization of 3000+ main-sequence binaries from APOGEE spectra

    Science.gov (United States)

    El-Badry, Kareem; Ting, Yuan-Sen; Rix, Hans-Walter; Quataert, Eliot; Weisz, Daniel R.; Cargile, Phillip; Conroy, Charlie; Hogg, David W.; Bergemann, Maria; Liu, Chao

    2018-05-01

    We develop a data-driven spectral model for identifying and characterizing spatially unresolved multiple-star systems and apply it to APOGEE DR13 spectra of main-sequence stars. Binaries and triples are identified as targets whose spectra can be significantly better fit by a superposition of two or three model spectra, drawn from the same isochrone, than any single-star model. From an initial sample of ˜20 000 main-sequence targets, we identify ˜2500 binaries in which both the primary and secondary stars contribute detectably to the spectrum, simultaneously fitting for the velocities and stellar parameters of both components. We additionally identify and fit ˜200 triple systems, as well as ˜700 velocity-variable systems in which the secondary does not contribute detectably to the spectrum. Our model simplifies the process of simultaneously fitting single- or multi-epoch spectra with composite models and does not depend on a velocity offset between the two components of a binary, making it sensitive to traditionally undetectable systems with periods of hundreds or thousands of years. In agreement with conventional expectations, almost all the spectrally identified binaries with measured parallaxes fall above the main sequence in the colour-magnitude diagram. We find excellent agreement between spectrally and dynamically inferred mass ratios for the ˜600 binaries in which a dynamical mass ratio can be measured from multi-epoch radial velocities. We obtain full orbital solutions for 64 systems, including 14 close binaries within hierarchical triples. We make available catalogues of stellar parameters, abundances, mass ratios, and orbital parameters.

  20. MAGNETIC ACTIVITY ANALYSIS FOR A SAMPLE OF G-TYPE MAIN SEQUENCE KEPLER TARGETS

    Energy Technology Data Exchange (ETDEWEB)

    Mehrabi, Ahmad [Department of Physics, Bu Ali Sina University, 65178, 016016, Hamedan (Iran, Islamic Republic of); He, Han [National Astronomical Observatories, Chinese Academy of Sciences, Beijing (China); Khosroshahi, Habib, E-mail: mehrabi@basu.ac.ir [School of Astronomy, Institute for Research in Fundamental Sciences (IPM), 19395-5531, Tehran (Iran, Islamic Republic of)

    2017-01-10

    The variation of a stellar light curve owing to rotational modulation by magnetic features (starspots and faculae) on the star’s surface can be used to investigate the magnetic properties of the host star. In this paper, we use the periodicity and magnitude of the light-curve variation as two proxies to study the stellar magnetic properties for a large sample of G-type main sequence Kepler targets, for which the rotation periods were recently determined. By analyzing the correlation between the two magnetic proxies, it is found that: (1) the two proxies are positively correlated for most of the stars in our sample, and the percentages of negative, zero, and positive correlations are 4.27%, 6.81%, and 88.91%, respectively; (2) negative correlation stars cannot have a large magnitude of light-curve variation; and (3) with the increase of rotation period, the relative number of positive correlation stars decreases and the negative correlation one increases. These results indicate that stars with shorter rotation period tend to have positive correlation between the two proxies, and a good portion of the positive correlation stars have a larger magnitude of light-curve variation (and hence more intense magnetic activities) than negative correlation stars.

  1. THE EXTENDED MAIN-SEQUENCE TURNOFF CLUSTERS OF THE LARGE MAGELLANIC CLOUD-MISSING LINKS IN GLOBULAR CLUSTER EVOLUTION

    International Nuclear Information System (INIS)

    Keller, Stefan C.; Mackey, A. Dougal; Da Costa, Gary S.

    2011-01-01

    Recent observations of intermediate-age (1-3 Gyr) massive star clusters in the Large Magellanic Cloud have revealed that the majority possess bifurcated or extended main-sequence turnoff (EMSTO) morphologies. This effect can be understood to arise from subsequent star formation among the stellar population with age differences between constituent stars amounting to 50-300 Myr. Age spreads of this order are similarly invoked to explain the light-element abundance variations witnessed in ancient globular clusters (GCs). In this paper, we explore the proposition that the clusters exhibiting the EMSTO phenomenon are a general phase in the evolution of massive clusters, one that naturally leads to the particular chemical properties of the ancient GC population. We show that the isolation of EMSTO clusters to intermediate ages is the consequence of observational selection effects. In our proposed scenario, the EMSTO phenomenon is identical to that which establishes the light-element abundance variations that are ubiquitous in the ancient GC population. Our scenario makes a strong prediction: EMSTO clusters will exhibit abundance variations in the light-elements characteristic of the ancient GC population.

  2. THE 'MAIN SEQUENCE' OF EXPLOSIVE SOLAR ACTIVE REGIONS: DISCOVERY AND INTERPRETATION

    Energy Technology Data Exchange (ETDEWEB)

    Falconer, David A; Moore, Ronald L; Adams, Mitzi [Space Science Office, VP62, Marshall Space Flight Center, Huntsville, AL 35812 (United States); Gary, G. Allen [Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL 35899 (United States)], E-mail: David.falconer@msfc.nasa.gov

    2009-08-01

    We examine the location and distribution of the production of coronal mass ejections (CMEs) and major flares by sunspot active regions in the phase space of two whole-active-region magnetic quantities measured from 1897 SOHO/MDI magnetograms. These magnetograms track the evolution of 44 active regions across the central disk of radius 0.5 R {sub Sun}. The two quantities are {sup L}WL{sub SG}, a gauge of the total free energy in an active region's magnetic field, and {sup L}{phi}, a measure of the active region's total magnetic flux. From these data and each active region's history of production of CMEs, X flares, and M flares, we find (1) that CME/flare-productive active regions are concentrated in a straight-line 'main sequence' in (log {sup L}WL{sub SG}, log {sup L}{phi}) space, (2) that main-sequence active regions have nearly their maximum attainable free magnetic energy, and (3) evidence that this arrangement plausibly results from equilibrium between input of free energy to an explosive active region's magnetic field in the chromosphere and corona by contortion of the field via convection in and below the photosphere and loss of free energy via CMEs, flares, and coronal heating, an equilibrium between energy gain and loss that is analogous to that of the main sequence of hydrogen-burning stars in (mass, luminosity) space.

  3. THE 'MAIN SEQUENCE' OF EXPLOSIVE SOLAR ACTIVE REGIONS: DISCOVERY AND INTERPRETATION

    International Nuclear Information System (INIS)

    Falconer, David A.; Moore, Ronald L.; Adams, Mitzi; Gary, G. Allen

    2009-01-01

    We examine the location and distribution of the production of coronal mass ejections (CMEs) and major flares by sunspot active regions in the phase space of two whole-active-region magnetic quantities measured from 1897 SOHO/MDI magnetograms. These magnetograms track the evolution of 44 active regions across the central disk of radius 0.5 R Sun . The two quantities are L WL SG , a gauge of the total free energy in an active region's magnetic field, and L Φ, a measure of the active region's total magnetic flux. From these data and each active region's history of production of CMEs, X flares, and M flares, we find (1) that CME/flare-productive active regions are concentrated in a straight-line 'main sequence' in (log L WL SG , log L Φ) space, (2) that main-sequence active regions have nearly their maximum attainable free magnetic energy, and (3) evidence that this arrangement plausibly results from equilibrium between input of free energy to an explosive active region's magnetic field in the chromosphere and corona by contortion of the field via convection in and below the photosphere and loss of free energy via CMEs, flares, and coronal heating, an equilibrium between energy gain and loss that is analogous to that of the main sequence of hydrogen-burning stars in (mass, luminosity) space.

  4. Empirical tests of pre-main-sequence stellar evolution models with eclipsing binaries

    Science.gov (United States)

    Stassun, Keivan G.; Feiden, Gregory A.; Torres, Guillermo

    2014-06-01

    We examine the performance of standard pre-main-sequence (PMS) stellar evolution models against the accurately measured properties of a benchmark sample of 26 PMS stars in 13 eclipsing binary (EB) systems having masses 0.04-4.0 M⊙ and nominal ages ≈1-20 Myr. We provide a definitive compilation of all fundamental properties for the EBs, with a careful and consistent reassessment of observational uncertainties. We also provide a definitive compilation of the various PMS model sets, including physical ingredients and limits of applicability. No set of model isochrones is able to successfully reproduce all of the measured properties of all of the EBs. In the H-R diagram, the masses inferred for the individual stars by the models are accurate to better than 10% at ≳1 M⊙, but below 1 M⊙ they are discrepant by 50-100%. Adjusting the observed radii and temperatures using empirical relations for the effects of magnetic activity helps to resolve the discrepancies in a few cases, but fails as a general solution. We find evidence that the failure of the models to match the data is linked to the triples in the EB sample; at least half of the EBs possess tertiary companions. Excluding the triples, the models reproduce the stellar masses to better than ∼10% in the H-R diagram, down to 0.5 M⊙, below which the current sample is fully contaminated by tertiaries. We consider several mechanisms by which a tertiary might cause changes in the EB properties and thus corrupt the agreement with stellar model predictions. We show that the energies of the tertiary orbits are comparable to that needed to potentially explain the scatter in the EB properties through injection of heat, perhaps involving tidal interaction. It seems from the evidence at hand that this mechanism, however it operates in detail, has more influence on the surface properties of the stars than on their internal structure, as the lithium abundances are broadly in good agreement with model predictions. The

  5. Pre-main sequence sun: a dynamic approach

    International Nuclear Information System (INIS)

    Newman, M.J.; Winkler, K.H.A.

    1979-01-01

    The classical pre-main sequence evolutionary behavior found by Hayashi and his coworkers for the Sun depends crucially on the choice of initial conditions. The Hayashi picture results from beginning the calculation with an already centrally condensed, highly Jeans unstable object not terribly far removed from the stellar state initially. The present calculation follows the work of Larson in investigating the hydrodynamic collapse and self-gravitational accretion of an initially uniform, just Jeans unstable interstellar gas-dust cloud. The resulting picture for the early history of the Sun is quite different from that found by Hayashi. A rather small (R approx. = 2 R/sub sun/), low-luminosity (L greater than or equal to L/sub sun/) protostellar core develops. A fully convective stellar core, characteristic of Hayashi's work, is not found during the accretion process, and can only develop, if at all, in the subsequent pre-main sequence Kelvin-Helmholtz contraction of the core. 3 figures, 1 table

  6. BVRI main-sequence photometry of the globular cluster M4

    International Nuclear Information System (INIS)

    Alcaino, G.; Liller, W.

    1984-01-01

    We present BV and RI photographic photometry of 1421 and 189 stars, respectively, in the intermediate metallicity globular cluster M4 (NGC 6121). This investigation includes the first results of RI main-sequence photometry of a globular cluster. The use of longer wavelengths and longer color baselines provides the potential of improved isochrone fittings and underscores the urgent need for calculations of RI synthetic isochrones to be compared with observations. The Pickering-Racine wedge was used with the ESO 3.6 m telescope, the Las Campanas 2.5 m du Pont telescope, and the CTIO 1 m Yale telescope to extend the photoelectric limit from Vroughly-equal16.1 to Vroughly-equal19.1. We have determined the position of the main-sequence turnoff to lie at V = 16.6 +- 0.2 (m.e.) and B-V = 0.80 +- 0.03 (m.e.). A comparison of our BV observations with the CCD data of Richer and Fahlman shows excellent agreement: the two fifucial main sequences agree at all points to within 0.025 mag and, on average, to 0.013 mag. For the cluster we derive a distance modulus (m-M)/sub V/ = 12.52 +- 0.2 and reddening E(B-V) = 0.44 +- 0.03, results which confirm that at a distance of 2 kpc, M4 is the closest globular clusters to the Sun. Using the isochrones of VandenBerg, we deduce an age 13 +- 2 Gyr. As noted in several other investigations, there is a striking deficiency of stars in certain parts of the color-magnitude diagram; in M4 we find a pronounced gap over approx.0.6 mag at the base of the subgiant branch

  7. Discovery of Extended Main-sequence Turnoffs in Four Young Massive Clusters in the Magellanic Clouds

    Energy Technology Data Exchange (ETDEWEB)

    Li, Chengyuan [Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109 (Australia); De Grijs, Richard [Kavli Institute for Astronomy and Astrophysics and Department of Astronomy, Peking University, Yi He Yuan Lu 5, Hai Dian District, Beijing 100871 (China); Deng, Licai [Key Laboratory for Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012 (China); Milone, Antonino P. [Research School of Astronomy and Astrophysics, Australian National University, Mt. Stromlo Observatory, Cotter Road, Weston, ACT 2611 (Australia)

    2017-08-01

    An increasing number of young massive clusters (YMCs) in the Magellanic Clouds have been found to exhibit bimodal or extended main sequences (MSs) in their color–magnitude diagrams (CMDs). These features are usually interpreted in terms of a coeval stellar population with different stellar rotational rates, where the blue and red MS stars are populated by non- (or slowly) and rapidly rotating stellar populations, respectively. However, some studies have shown that an age spread of several million years is required to reproduce the observed wide turnoff regions in some YMCs. Here we present the ultraviolet–visual CMDs of four Large and Small Magellanic Cloud YMCs, NGC 330, NGC 1805, NGC 1818, and NGC 2164, based on high-precision Hubble Space Telescope photometry. We show that they all exhibit extended main-sequence turnoffs (MSTOs). The importance of age spreads and stellar rotation in reproducing the observations is investigated. The observed extended MSTOs cannot be explained by stellar rotation alone. Adopting an age spread of 35–50 Myr can alleviate this difficulty. We conclude that stars in these clusters are characterized by ranges in both their ages and rotation properties, but the origin of the age spread in these clusters remains unknown.

  8. New Insights into the Formation of the Blue Main Sequence in NGC 1850

    Science.gov (United States)

    Yang, Yujiao; Li, Chengyuan; Deng, Licai; de Grijs, Richard; Milone, Antonino P.

    2018-06-01

    Recent discoveries of bimodal main sequences (MSs) associated with young clusters (with ages ≲1 Gyr) in the Magellanic Clouds have drawn a lot of attention. One of the prevailing formation scenarios attributes these split MSs to a bimodal distribution in stellar rotation rates, with most stars belonging to a rapidly rotating population. In this scenario, only a small fraction of stars populating a secondary blue sequence are slowly or non-rotating stars. Here, we focus on the blue MS in the young cluster NGC 1850. We compare the cumulative number fraction of the observed blue-MS stars to that of the high-mass-ratio binary systems at different radii. The cumulative distributions of both populations exhibit a clear anti-correlation, characterized by a highly significant Pearson coefficient of ‑0.97. Our observations are consistent with the possibility that blue-MS stars are low-mass-ratio binaries, and therefore their dynamical disruption is still ongoing. High-mass-ratio binaries, on the other hand, are more centrally concentrated.

  9. Pre-main-sequence disk accretion in Z Canis Majoris

    International Nuclear Information System (INIS)

    Hartmann, L.; Kenyon, S.J.; Hewett, R.; Edwards, S.; Strom, K.M.; Strom, S.E.; Stauffer, J.R.

    1989-01-01

    It is suggested that the pre-main-sequence object Z CMa is a luminous accretion disk, similar in many respects to the FU Orionis variables. Z CMa shows the broad, doubled optical absorption lines expected from a rapidly rotating accretion disk. The first overtone CO absorption detected in Z CMa is blue-shifted, suggesting line formation in a disk wind. Accretion at rates about 0.001 solar mass/yr over 100 yr is required to explain the luminosity of Z CMa. The large amount of material accreted (0.1 solar mass/yr) indicates that Z CMa is in a very early stage of stellar evolution, possibly in an initial phase of massive disk accretion. 41 references

  10. Pre-main-sequence disk accretion in Z Canis Majoris

    Science.gov (United States)

    Hartmann, L.; Kenyon, S. J.; Hewett, R.; Edwards, S.; Strom, K. M.; Strom, S. E.; Stauffer, J. R.

    1989-01-01

    It is suggested that the pre-main-sequence object Z CMa is a luminous accretion disk, similar in many respects to the FU Orionis variables. Z CMa shows the broad, doubled optical absorption lines expected from a rapidly rotating accretion disk. The first overtone CO absorption detected in Z CMa is blue-shifted, suggesting line formation in a disk wind. Accretion at rates about 0.001 solar mass/yr over 100 yr is required to explain the luminosity of Z CMa. The large amount of material accreted (0.1 solar mass/yr) indicates that Z CMa is in a very early stage of stellar evolution, possibly in an initial phase of massive disk accretion.

  11. Pleiades and the zero-age main sequence

    International Nuclear Information System (INIS)

    McNamara, B.J.

    1976-01-01

    New four-color uvby observations of the Pleiades are used to calibrate the ZAMS in the spectral range A2 to F5. Although the Pleiades c 0 versus (b - y) 0 calibration is in good agreement with the ZAMS calibration presented by Crawford, its m 0 versus (b - y) 0 relation shows a systematic difference from his values. This difference is believed to be caused by the higher mean rotational velocity of the Pleiades stars in comparison to field stars

  12. AK SCO, FIRST DETECTION OF A HIGHLY DISTURBED ATMOSPHERE IN A PRE-MAIN-SEQUENCE CLOSE BINARY

    International Nuclear Information System (INIS)

    Gomez de Castro, Ana I.

    2009-01-01

    AK Sco is a unique source: a ∼10 Myr old pre-main-sequence (PMS) spectroscopic binary composed of two nearly equal F5 stars that at periastron are separated by barely 11 stellar radii, so the stellar magnetospheres fill the Roche lobe at periastron. The orbit is not yet circularized (e = 0.47) and very strong tides are expected. This makes AK Sco the ideal laboratory to study the effect of gravitational tides in the stellar magnetic field building up during PMS evolution. In this Letter, the detection of a highly disturbed (σ ≅ 100 km s -1 ) and very dense atmosphere (n e = 1.6 x 10 10 cm -3 ) is reported. Significant line broadening blurs any signs of ion belts or bow shocks in the spectrum of the atmospheric plasma. The radiative losses cannot be accounted for solely by the dissipation of energy from the tidal wave propagating in the stellar atmosphere or by the accreting material. The release of internal energy from the star seems to be the most likely source of the plasma heating. This is the first clear indication of a highly disturbed atmosphere surrounding a PMS close binary.

  13. AK Sco, First Detection of a Highly Disturbed Atmosphere in a Pre-Main-Sequence Close Binary

    Science.gov (United States)

    Gómez de Castro, Ana I.

    2009-06-01

    AK Sco is a unique source: a ~10 Myr old pre-main-sequence (PMS) spectroscopic binary composed of two nearly equal F5 stars that at periastron are separated by barely 11 stellar radii, so the stellar magnetospheres fill the Roche lobe at periastron. The orbit is not yet circularized (e = 0.47) and very strong tides are expected. This makes AK Sco the ideal laboratory to study the effect of gravitational tides in the stellar magnetic field building up during PMS evolution. In this Letter, the detection of a highly disturbed (σ sime 100 km s-1) and very dense atmosphere (n e = 1.6 × 1010 cm-3) is reported. Significant line broadening blurs any signs of ion belts or bow shocks in the spectrum of the atmospheric plasma. The radiative losses cannot be accounted for solely by the dissipation of energy from the tidal wave propagating in the stellar atmosphere or by the accreting material. The release of internal energy from the star seems to be the most likely source of the plasma heating. This is the first clear indication of a highly disturbed atmosphere surrounding a PMS close binary.

  14. DISSECTING THE QUASAR MAIN SEQUENCE: INSIGHT FROM HOST GALAXY PROPERTIES

    International Nuclear Information System (INIS)

    Sun, Jiayi; Shen, Yue

    2015-01-01

    The diverse properties of broad-line quasars appear to follow a well-defined main sequence along which the optical Fe ii strength increases. It has been suggested that this sequence is mainly driven by the Eddington ratio (L/L Edd ) of the black hole (BH) accretion. Shen and Ho demonstrated with quasar clustering analysis that the average BH mass decreases with increasing Fe ii strength when quasar luminosity is fixed, consistent with this suggestion. Here we perform an independent test by measuring the stellar velocity dispersion σ * (hence, the BH mass via the M–σ * relation) from decomposed host spectra in low-redshift Sloan Digital Sky Survey quasars. We found that at fixed quasar luminosity, σ * systematically decreases with increasing Fe ii strength, confirming that the Eddington ratio increases with Fe ii strength. We also found that at fixed luminosity and Fe ii strength, there is little dependence of σ * on the broad Hβ FWHM. These new results reinforce the framework that the Eddington ratio and orientation govern most of the diversity seen in broad-line quasar properties

  15. The age-metallicity relation in the solar neighbourhood from a pilot sample of white dwarf-main sequence binaries

    OpenAIRE

    Rebassa-Mansergas, A.; Anguiano, B.; García-Berro, E.; Freeman, K. C.; Cojocaru, R.; Manser, C. J.; Pala, A. F.; Gänsicke, B. T.; Liu, X. -W.

    2016-01-01

    The age–metallicity relation (AMR) is a fundamental observational constraint for understanding how the Galactic disc formed and evolved chemically in time. However, there is not yet an agreement on the observational properties of the AMR for the solar neighbourhood, primarily due to the difficulty in obtaining accurate stellar ages for individual field stars. We have started an observational campaign for providing the much needed observational input by using wide white-dwarf–main-sequence (WD...

  16. THE DISCOVERY OF SOLAR-LIKE ACTIVITY CYCLES BEYOND THE END OF THE MAIN SEQUENCE?

    Energy Technology Data Exchange (ETDEWEB)

    Route, Matthew, E-mail: mroute@purdue.edu [Research Computing, Information Technology at Purdue, Purdue University, 155 S. Grant Street, West Lafayette, IN 47907 (United States)

    2016-10-20

    The long-term magnetic behavior of objects near the cooler end of the stellar main sequence is poorly understood. Most theoretical work on the generation of magnetism in these ultracool dwarfs (spectral type ≥M7 stars and brown dwarfs) suggests that their magnetic fields should not change in strength and direction. Using polarized radio emission measurements of their magnetic field orientations, I demonstrate that these cool, low-mass, fully convective objects appear to undergo magnetic polarity reversals analogous to those that occur on the Sun. This powerful new technique potentially indicates that the patterns of magnetic activity displayed by the Sun continue to exist, despite the fully convective interiors of these objects, in contravention of several leading theories of the generation of magnetic fields by internal dynamos.

  17. Making Sense of Atmospheric Models and Fundamental Stellar Properties at the Bottom of the Main Sequence

    Science.gov (United States)

    Dieterich, Sergio; Henry, Todd; Jao, W.-C.; Washington, Robert; Silverstein, Michele; Winters, J.; RECONS

    2018-01-01

    We present a detailed comparison of atmospheric model predictions and photometric observations for late M and L dwarfs. We discuss which wavelength regions are best for determining the fundamental properties of these cool stellar and substellar atmospheres and use this analysis to refine the HR diagram for the hydrogen burning limit first presented in 2014. We also add several new objects to the HR diagram and find little qualitative difference in the HR diagram's overall morphology when compared to our 2014 results. The L2 dwarf 2MASS 0523-1403 remains the smallest hydrogen burning star for which we calculated a radius, thus likely indicating the end of the stellar main sequence. This work is supported by the NSF Astronomy and Astrophysics Postdoctoral Fellowship program through grant AST-1400680.

  18. THE MULTIPLE PRE-MAIN-SEQUENCE SYSTEM HBC 515 IN L1622

    International Nuclear Information System (INIS)

    Reipurth, Bo; Aspin, Colin; Herbig, George

    2010-01-01

    The bright pre-main-sequence star HBC 515 (HD 288313) located in the L1622 cometary cloud in Orion has been studied extensively with optical/infrared imaging and ultraviolet/optical/infrared spectroscopy. The spectra indicate that HBC 515 is a weakline T Tauri star (TTS) of spectral type K2V. Adaptive optics imaging in the K band reveals that HBC 515 is a binary with two equally bright components separated by 0.''5. A very faint third component is found 5'' to the northwest. Spitzer IRAC and MIPS observations show that at mid-infrared wavelengths this third source dominates the system, suggesting that it is a protostar still embedded in the nascent cloud of HBC 515. The close association of a weakline TTS with a newborn protostar in a multiple system is noteworthy. Two nearby TTSs are likely associated with the HBC 515 multiple system, and the dynamical evolution of the complex that would lead to such a configuration is considered.

  19. PRE-MAIN-SEQUENCE TURN-ON AS A CHRONOMETER FOR YOUNG CLUSTERS: NGC 346 AS A BENCHMARK

    International Nuclear Information System (INIS)

    Cignoni, M.; Tosi, M.; Sabbi, E.; Nota, A.; Degl'Innocenti, S.; Moroni, P. G. Prada; Gallagher, J. S.

    2010-01-01

    We present a novel approach to deriving the age of very young star clusters, by using the Turn-On (TOn). The TOn is the point in the color-magnitude diagram (CMD) where the pre-main sequence (PMS) joins the main sequence (MS). In the MS luminosity function (LF) of the cluster, the TOn is identified as a peak followed by a dip. We propose that by combining the CMD analysis with the monitoring of the spatial distribution of MS stars it is possible to reliably identify the TOn in extragalactic star-forming regions. Compared to alternative methods, this technique is complementary to the turnoff dating and avoids the systematic biases affecting the PMS phase. We describe the method and its uncertainties and apply it to the star-forming region NGC 346, which has been extensively imaged with the Hubble Space Telescope (HST). This study extends the LF approach in crowded extragalactic regions and opens the way for future studies with HST/WFC3, the James Webb Space Telescope and from the ground with adaptive optics.

  20. SPIN EVOLUTION OF ACCRETING YOUNG STARS. II. EFFECT OF ACCRETION-POWERED STELLAR WINDS

    International Nuclear Information System (INIS)

    Matt, Sean P.; Pinzón, Giovanni; Greene, Thomas P.; Pudritz, Ralph E.

    2012-01-01

    We present a model for the rotational evolution of a young, solar-mass star interacting magnetically with an accretion disk. As in a previous paper (Paper I), the model includes changes in the star's mass and radius as it descends the Hayashi track, a decreasing accretion rate, and a prescription for the angular momentum transfer between the star and disk. Paper I concluded that, for the relatively strong magnetic coupling expected in real systems, additional processes are necessary to explain the existence of slowly rotating pre-main-sequence stars. In the present paper, we extend the stellar spin model to include the effect of a spin-down torque that arises from an accretion-powered stellar wind (APSW). For a range of magnetic field strengths, accretion rates, initial spin rates, and mass outflow rates, the modeled stars exhibit rotation periods within the range of 1-10 days in the age range of 1-3 Myr. This range coincides with the bulk of the observed rotation periods, with the slow rotators corresponding to stars with the lowest accretion rates, strongest magnetic fields, and/or highest stellar wind mass outflow rates. We also make a direct, quantitative comparison between the APSW scenario and the two types of disk-locking models (namely, the X-wind and Ghosh and Lamb type models) and identify some remaining theoretical issues for understanding young star spins.

  1. Are sdAs helium core stars?

    Directory of Open Access Journals (Sweden)

    Pelisoli Ingrid

    2017-12-01

    Full Text Available Evolved stars with a helium core can be formed by non-conservative mass exchange interaction with a companion or by strong mass loss. Their masses are smaller than 0.5 M⊙. In the database of the Sloan Digital Sky Survey (SDSS, there are several thousand stars which were classified by the pipeline as dwarf O, B and A stars. Considering the lifetimes of these classes on the main sequence, and their distance modulus at the SDSS bright saturation, if these were common main sequence stars, there would be a considerable population of young stars very far from the galactic disk. Their spectra are dominated by Balmer lines which suggest effective temperatures around 8 000-10 000 K. Several thousand have significant proper motions, indicative of distances smaller than 1 kpc. Many show surface gravity in intermediate values between main sequence and white dwarf, 4.75 < log g < 6.5, hence they have been called sdA stars. Their physical nature and evolutionary history remains a puzzle. We propose they are not H-core main sequence stars, but helium core stars and the outcomes of binary evolution. We report the discovery of two new extremely-low mass white dwarfs among the sdAs to support this statement.

  2. DIRECTLY DETERMINED LINEAR RADII AND EFFECTIVE TEMPERATURES OF EXOPLANET HOST STARS

    International Nuclear Information System (INIS)

    Van Belle, Gerard T.; Von Braun, Kaspar

    2009-01-01

    We present interferometric angular sizes for 12 stars with known planetary companions, for comparison with 28 additional main-sequence stars not known to host planets. For all objects we estimate bolometric fluxes and reddenings through spectral-energy distribution (SED) fits, and in conjunction with the angular sizes, measurements of effective temperature. The angular sizes of these stars are sufficiently small that the fundamental resolution limits of our primary instrument, the Palomar Testbed Interferometer, are investigated at the sub-milliarcsecond level and empirically established based upon known performance limits. We demonstrate that the effective temperature scale as a function of dereddened (V - K) 0 color is statistically identical for stars with and without planets. A useful byproduct of this investigation is a direct calibration of the T EFF scale for solarlike stars, as a function of both spectral type and (V - K) 0 color. Additionally, in an Appendix we provide SED fits for the 166 stars with known planets which have sufficient photometry available in the literature for such fits; this derived 'XO-Rad' database includes homogeneous estimates of bolometric flux, reddening, and angular size.

  3. WHITE-DWARF-MAIN-SEQUENCE BINARIES IDENTIFIED FROM THE LAMOST PILOT SURVEY

    International Nuclear Information System (INIS)

    Ren Juanjuan; Luo Ali; Li Yinbi; Wei Peng; Zhao Jingkun; Zhao Yongheng; Song Yihan; Zhao Gang

    2013-01-01

    We present a set of white-dwarf-main-sequence (WDMS) binaries identified spectroscopically from the Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST, also called the Guo Shou Jing Telescope) pilot survey. We develop a color selection criteria based on what is so far the largest and most complete Sloan Digital Sky Survey (SDSS) DR7 WDMS binary catalog and identify 28 WDMS binaries within the LAMOST pilot survey. The primaries in our binary sample are mostly DA white dwarfs except for one DB white dwarf. We derive the stellar atmospheric parameters, masses, and radii for the two components of 10 of our binaries. We also provide cooling ages for the white dwarf primaries as well as the spectral types for the companion stars of these 10 WDMS binaries. These binaries tend to contain hot white dwarfs and early-type companions. Through cross-identification, we note that nine binaries in our sample have been published in the SDSS DR7 WDMS binary catalog. Nineteen spectroscopic WDMS binaries identified by the LAMOST pilot survey are new. Using the 3σ radial velocity variation as a criterion, we find two post-common-envelope binary candidates from our WDMS binary sample

  4. Main sequence of the metal-poor globular cluster M30 (NGC 7099)

    International Nuclear Information System (INIS)

    Alcaino, G.; Liller, W.

    1980-01-01

    We present photographic photometry for 673 stars in the metal-poor globular cluster M30 (NGC 7099). The Racine wedge was used with the CTIO 1-m Yale telescope (Δm=3/sup m/.60), the CTIO 4-m telescope (Δm=6/sup m/.83), and the ESO 3.6-m telescope (Δm=4/sup m/.12) to extend the photoelectric limit from Vapprox. =16.3 to Vapprox. =20.4. For the main-sequence turn-off, we have determined its position to lie at V=18.4 +- 0.1 (m.e.) and B-V=0.49 +- 0.03 (m.e.). From these values, we calculate the intrinsic values M/sub v/ =3.87 and (B-V) 0 =0.47. For the cluster as a whole, we derive a distance modulus (m-M)/sub V/=14.53 +- 0.15 and reddening E(B-V)=0.02 +- 0.02. Using the models of Iben and Rood [Astrophys. J. 159, 605 (1970)] and the isochrones of Demarque and McClure [(1977), in Evolution of Galaxies and Stellar Populations, edited by B. Tinsley and R. B. Larson (Yale University Observatory, New Haven), p. 199], we deduce the cluster's age to be 14.5( +- 4.0) x 10 9 yr. The large uncertainty in this value emphasizes the dire need for more work on cluster evolution

  5. THE EVOLVED MAIN-SEQUENCE CHANNEL: HST AND LBT OBSERVATIONS OF CSS 120422:111127+571239

    Energy Technology Data Exchange (ETDEWEB)

    Kennedy, M.; Callanan, P. [Department of Physics, University College Cork, Cork (Ireland); Garnavich, P.; Littlefield, C. [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Szkody, P. [Department of Astronomy, University of Washington, Seattle, WA (United States); Pogge, R. [Department of Astronomy, The Ohio State University, 140 W. 18th Avenue, Columbus, OH 43202 (United States)

    2015-12-20

    The “evolved main-sequence (EMS)” channel is thought to contribute significantly to the population of AM CVn-type systems in the Galaxy, and also to the number of cataclysmic variables (CVs) detected below the period minimum for hydrogen rich systems. CSS 120422:J111127+571239 was discovered by the Catalina Sky Survey in 2012 April. Its period was found to be 56 minutes, well below the minimum, and the optical spectrum is clearly depleted in hydrogen relative to helium, but still has two orders of magnitude more hydrogen than AM CVn stars. Doppler tomography of the Hα line hinted at a spiral structure existing in the disk. Here we present spectroscopy of CSS 120422:J111127+571239 using the Cosmic Origins Spectrograph FUV instrument on the Hubble Space Telescope and using the MODS spectrograph on the Large Binocular Telescope. The UV spectrum shows Si iv, N v, and He ii, but no detectable C iv. The anomalous nitrogen/carbon ratio is seen in a small number of other CVs and confirms a unique binary evolution. We also present and compare the optical spectrum of V418 Ser and advocate that it is also an EMS system.

  6. Theory and evidence of global Rossby waves in upper main-sequence stars

    DEFF Research Database (Denmark)

    Saio, Hideyuki; Kurtz, Donald W.; Murphy, Simon J.

    2018-01-01

    in the observational frame by considering the visibility of these modes. We find that the frequencies of r modes of azimuthal order m appear as groups at slightly lower frequency than m times the rotation frequency. Comparing the visibility curves for r modes with Fourier amplitude spectra of Kepler light curves...

  7. VizieR Online Data Catalog: Habitable zones around main-sequence stars (Kopparapu+, 2014)

    Science.gov (United States)

    Kopparapu, R. K.; Ramirez, R. M.; Schottelkotte, J.; Kasting, J. F.; Domagal-Goldman, S.; Eymet, V.

    2017-08-01

    Language: Fortran 90 Code tested under the following compilers/operating systems: ifort/CentOS linux Description of input data: No input necessary. Description of output data: Output files: HZs.dat, HZ_coefficients.dat System requirements: No major system requirement. Fortran compiler necessary. Calls to external routines: None. Additional comments: None (1 data file).

  8. The Solar Neighborhood. XLI. A Study of the Wide Main Sequence for M Dwarfs—Long-term Photometric Variability

    Energy Technology Data Exchange (ETDEWEB)

    Clements, Tiffany D.; Jao, Wei-Chun; Silverstein, Michele L. [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303 (United States); Henry, Todd J.; Hosey, Altonio D. [RECONS Institute, Chambersburg, PA 17201 (United States); Winters, Jennifer G. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Dieterich, Sergio B. [Carnegie Institution for Science, Washington, DC 20015 (United States); Riedel, Adric R., E-mail: pewett@astro.gsu.edu, E-mail: jao@astro.gsu.edu, E-mail: silverstein@astro.gsu.edu, E-mail: toddhenry28@gmail.com, E-mail: altoniohosey@gmail.com, E-mail: jennifer.winters@cfa.harvard.edu, E-mail: sdieterich@carnegiescience.edu, E-mail: adric.riedel@gmail.com [Space Telescope Science Institute, Baltimore, MD 21218 (United States)

    2017-09-01

    We report findings from a long-term photometric variability study of M dwarfs carried out at the SMARTS 0.9 m telescope at the Cerro Tololo Inter-American Observatory. As part of a multi-faceted effort to investigate the range of luminosities of M dwarfs of a given color on the Hertzsprung–Russell Diagram, 76 M dwarfs have been observed for 3–17 years in the Johnson–Kron–Cousins V band. We find that stars elevated above the center of the main sequence distribution tend to have higher levels of variability, likely caused by magnetic activity, than their fainter counterparts below the center. This study provides insight into how the long-term magnetic activity of these stars may be affecting their sizes, luminosities, and thus positions on the H-R Diagram.

  9. The Problem of Hipparcos Distances to Open Clusters. Report 1; Constraints from Multicolor a Main-Sequence Fitting

    Science.gov (United States)

    Pinsonneault, Marc H.; Stauffer, John; Soderblom, David R.; King, Jeremy R.; Hanson, Robert B.

    1998-01-01

    Parallax data from the Hipparcos mission allow the direct distance to open clusters to be compared with the distance inferred from main-sequence (MS) fitting. There are surprising differences between the two distance measurements. indicating either the need for changes in the cluster compositions or reddening, underlying problems with the technique of MS fitting, or systematic errors in the Hipparcos parallaxes at the 1 mas level. We examine the different possibilities, focusing on MS fitting in both metallicity-sensitive B-V and metallicity-insensitive V-I for five well-studied systems (the Hyades, Pleiades, alpha Per, Praesepe, and Coma Ber). The Hipparcos distances to the Hyades and alpha Per are within 1 sigma of the MS-fitting distance in B-V and V-I, while the Hipparcos distances to Coma Ber and the Pleiades are in disagreement with the MS-fitting distance at more than the 3 sigma level. There are two Hipparcos measurements of the distance to Praesepe; one is in good agreement with the MS-fitting distance and the other disagrees at the 2 sigma level. The distance estimates from the different colors are in conflict with one another for Coma but in agreement for the Pleiades. Changes in the relative cluster metal abundances, age related effects, helium, and reddening are shown to be unlikely to explain the puzzling behavior of the Pleiades. We present evidence for spatially dependent systematic errors at the 1 mas level in the parallaxes of Pleiades stars. The implications of this result are discussed.

  10. YSOVAR: SIX PRE-MAIN-SEQUENCE ECLIPSING BINARIES IN THE ORION NEBULA CLUSTER

    Energy Technology Data Exchange (ETDEWEB)

    Morales-Calderon, M.; Stauffer, J. R.; Rebull, L. M. [Spitzer Science Center, California Institute of Technology, 1200 E California Blvd., Pasadena, CA 91125 (United States); Stassun, K. G. [Physics and Astronomy Department, Vanderbilt University, 1807 Station B, Nashville, TN 37235 (United States); Vrba, F. J. [U. S. Naval Observatory, Flagstaff Station, 10391 W. Naval Observatory Road, Flagstaff, AZ 86001-8521 (United States); Prato, L. [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Hillenbrand, L. A.; Carpenter, J. M. [Astronomy Department, California Institute of Technology, 1200 E California Blvd., Pasadena, CA 91125 (United States); Terebey, S.; Angione, J. [Department of Physics and Astronomy, California State University at Los Angeles, Los Angeles, CA 90032 (United States); Covey, K. R. [Department of Astronomy, Cornell University, 226 Space Sciences Building, Ithaca, NY 14853 (United States); Terndrup, D. M. [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Gutermuth, R. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Song, I. [Physics and Astronomy Department, University of Georgia, Athens, GA 30602-2451 (United States); Plavchan, P. [NASA Exoplanet Science Institute, California Institute of Technology, Pasadena, CA 91125 (United States); Marchis, F. [SETI Institute, Carl Sagan Center, 189 N San Bernado Av, Mountain View, CA 94043 (United States); Garcia, E. V. [Department of Physics, Fisk University, 1000 17th Ave. N, Nashville, TN 37208 (United States); Margheim, S. [Gemini Observatory, Southern Operations Center, Casilla 603, La Serena (Chile); Luhman, K. L. [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Irwin, J. M., E-mail: mariamc@cab.inta-csic.es [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States)

    2012-07-10

    Eclipsing binaries (EBs) provide critical laboratories for empirically testing predictions of theoretical models of stellar structure and evolution. Pre-main-sequence (PMS) EBs are particularly valuable, both due to their rarity and the highly dynamic nature of PMS evolution, such that a dense grid of PMS EBs is required to properly calibrate theoretical PMS models. Analyzing multi-epoch, multi-color light curves for {approx}2400 candidate Orion Nebula Cluster (ONC) members from our Warm Spitzer Exploration Science Program YSOVAR, we have identified 12 stars whose light curves show eclipse features. Four of these 12 EBs are previously known. Supplementing our light curves with follow-up optical and near-infrared spectroscopy, we establish two of the candidates as likely field EBs lying behind the ONC. We confirm the remaining six candidate systems, however, as newly identified ONC PMS EBs. These systems increase the number of known PMS EBs by over 50% and include the highest mass ({theta}{sup 1} Ori E, for which we provide a complete set of well-determined parameters including component masses of 2.807 and 2.797 M{sub Sun }) and longest-period (ISOY J053505.71-052354.1, P {approx} 20 days) PMS EBs currently known. In two cases ({theta}{sup 1} Ori E and ISOY J053526.88-044730.7), enough photometric and spectroscopic data exist to attempt an orbit solution and derive the system parameters. For the remaining systems, we combine our data with literature information to provide a preliminary characterization sufficient to guide follow-up investigations of these rare, benchmark systems.

  11. YSOVAR: SIX PRE-MAIN-SEQUENCE ECLIPSING BINARIES IN THE ORION NEBULA CLUSTER

    International Nuclear Information System (INIS)

    Morales-Calderón, M.; Stauffer, J. R.; Rebull, L. M.; Stassun, K. G.; Vrba, F. J.; Prato, L.; Hillenbrand, L. A.; Carpenter, J. M.; Terebey, S.; Angione, J.; Covey, K. R.; Terndrup, D. M.; Gutermuth, R.; Song, I.; Plavchan, P.; Marchis, F.; García, E. V.; Margheim, S.; Luhman, K. L.; Irwin, J. M.

    2012-01-01

    Eclipsing binaries (EBs) provide critical laboratories for empirically testing predictions of theoretical models of stellar structure and evolution. Pre-main-sequence (PMS) EBs are particularly valuable, both due to their rarity and the highly dynamic nature of PMS evolution, such that a dense grid of PMS EBs is required to properly calibrate theoretical PMS models. Analyzing multi-epoch, multi-color light curves for ∼2400 candidate Orion Nebula Cluster (ONC) members from our Warm Spitzer Exploration Science Program YSOVAR, we have identified 12 stars whose light curves show eclipse features. Four of these 12 EBs are previously known. Supplementing our light curves with follow-up optical and near-infrared spectroscopy, we establish two of the candidates as likely field EBs lying behind the ONC. We confirm the remaining six candidate systems, however, as newly identified ONC PMS EBs. These systems increase the number of known PMS EBs by over 50% and include the highest mass (θ 1 Ori E, for which we provide a complete set of well-determined parameters including component masses of 2.807 and 2.797 M ☉ ) and longest-period (ISOY J053505.71–052354.1, P ∼ 20 days) PMS EBs currently known. In two cases (θ 1 Ori E and ISOY J053526.88–044730.7), enough photometric and spectroscopic data exist to attempt an orbit solution and derive the system parameters. For the remaining systems, we combine our data with literature information to provide a preliminary characterization sufficient to guide follow-up investigations of these rare, benchmark systems.

  12. White dwarfs: connection with masses of the parent stars

    International Nuclear Information System (INIS)

    Amnuel', P.R.; Guseinov, O.Kh.; Novruzova, Kh.I.; Rustamov, Yu.S.

    1988-01-01

    A relationship between the mass of a white dwarf and the mass of the parent star on the main sequence is established. The white dwarf birth-rate matches the birth-rate (death-rate) of main sequence stars

  13. Detection of [O III] at z ∼ 3: A Galaxy Above the Main Sequence, Rapidly Assembling Its Stellar Mass

    Science.gov (United States)

    Vishwas, Amit; Ferkinhoff, Carl; Nikola, Thomas; Parshley, Stephen C.; Schoenwald, Justin P.; Stacey, Gordon J.; Higdon, Sarah J. U.; Higdon, James L.; Weiss, Axel; Güsten, Rolf; Menten, Karl M.

    2018-04-01

    We detect bright emission in the far-infrared (far-IR) fine structure [O III] 88 μm line from a strong lensing candidate galaxy, H-ATLAS J113526.3-014605, hereafter G12v2.43, at z = 3.127, using the second-generation Redshift (z) and Early Universe Spectrometer (ZEUS-2) at the Atacama Pathfinder Experiment Telescope (APEX). This is only the fifth detection of this far-IR line from a submillimeter galaxy at the epoch of galaxy assembly. The observed [O III] luminosity of 7.1 × 109 ≤ft(\\tfrac{10}{μ }\\right) L ⊙ likely arises from H II regions around massive stars, and the amount of Lyman continuum photons required to support the ionization indicate the presence of (1.2–5.2) × 106 ≤ft(\\tfrac{10}{μ }\\right) equivalent O5.5 or higher stars, where μ would be the lensing magnification factor. The observed line luminosity also requires a minimum mass of ∼2 × 108 ≤ft(\\tfrac{10}{μ }\\right) M ⊙ in ionized gas, that is 0.33% of the estimated total molecular gas mass of 6 × 1010 ≤ft(\\tfrac{10}{μ }\\right) M ⊙. We compile multi-band photometry tracing rest-frame ultraviolet to millimeter continuum emission to further constrain the properties of this dusty high-redshift, star-forming galaxy. Via SED modeling we find G12v2.43 is forming stars at a rate of 916 ≤ft(\\tfrac{10}{μ }\\right) M ⊙ yr‑1 and already has a stellar mass of 8 × 1010 ≤ft(\\tfrac{10}{μ }\\right) M ⊙. We also constrain the age of the current starburst to be ≤slant 5 Myr, making G12v2.43 a gas-rich galaxy lying above the star-forming main sequence at z ∼ 3, undergoing a growth spurt, and it could be on the main sequence within the derived gas depletion timescale of ∼66 Myr.

  14. Effective star tracking method based on optical flow analysis for star trackers.

    Science.gov (United States)

    Sun, Ting; Xing, Fei; Wang, Xiaochu; Li, Jin; Wei, Minsong; You, Zheng

    2016-12-20

    Benefiting from rapid development of imaging sensor technology, modern optical technology, and a high-speed computing chip, the star tracker's accuracy, dynamic performance, and update rate have been greatly improved with low power consumption and miniature size. The star tracker is currently one of the most competitive attitude measurement sensors. However, due to restrictions of the optical imaging system, difficulties still exist in moving star spot detection and star tracking when in special motion conditions. An effective star tracking method based on optical flow analysis for star trackers is proposed in this paper. Spot-based optical flow, based on a gray gradient between two adjacent star images, is analyzed to distinguish the star spot region and obtain an accurate star spot position so that the star tracking can keep continuous under high dynamic conditions. The obtained star vectors and extended Kalman filter (EKF) are then combined to conduct an angular velocity estimation to ensure region prediction of the star spot; this can be combined with the optical flow analysis result. Experiment results show that the method proposed in this paper has advantages in conditions of large angular velocity and large angular acceleration, despite the presence of noise. Higher functional density and better performance can be achieved; thus, the star tracker can be more widely applied in small satellites, remote sensing, and other complex space missions.

  15. MAGNETIC FIELDS OF STARS

    OpenAIRE

    Bychkov, V. D.; Bychkova, L. V.; Madej, J.

    2008-01-01

    Now it is known about 1212 stars of the main sequence and giants (from them 610 stars - it is chemically peculiarity (CP) stars) for which direct measurements of magnetic fields were spent (Bychkov et al.,2008). Let's consider, what representations were generated about magnetic fields (MT) of stars on the basis of available observations data.

  16. STANDARD STARS AND EMPIRICAL CALIBRATIONS FOR Hα AND Hβ PHOTOMETRY

    International Nuclear Information System (INIS)

    Joner, Michael D.; Hintz, Eric G.

    2015-01-01

    We define an Hα photometric system that is designed as a companion to the well established Hβ index. The new system is built on spectrophotometric observations of field stars as well as stars in benchmark open clusters. We present data for 75 field stars, 12 stars from the Coma star cluster, 24 stars from the Hyades, 17 stars from the Pleiades, and 8 stars from NGC 752 to be used as primary standard stars in the new systems. We show that the system transformations are relatively insensitive to the shape of the filter functions. We make comparisons of the Hα index to the Hβ index and illustrate the relationship between the two systems. In addition, we present relations that relate both hydrogen indices to equivalent width and effective temperature. We derive equations to calibrate both systems for Main Sequence stars with spectral types in the range O9 to K2 for equivalent width and A2 to K2 for effective temperature

  17. STANDARD STARS AND EMPIRICAL CALIBRATIONS FOR Hα AND Hβ PHOTOMETRY

    Energy Technology Data Exchange (ETDEWEB)

    Joner, Michael D.; Hintz, Eric G., E-mail: joner@byu.edu, E-mail: hintz@byu.edu [Department of Physics and Astronomy, Brigham Young University, N283 ESC, Provo, UT 84602 (United States)

    2015-12-15

    We define an Hα photometric system that is designed as a companion to the well established Hβ index. The new system is built on spectrophotometric observations of field stars as well as stars in benchmark open clusters. We present data for 75 field stars, 12 stars from the Coma star cluster, 24 stars from the Hyades, 17 stars from the Pleiades, and 8 stars from NGC 752 to be used as primary standard stars in the new systems. We show that the system transformations are relatively insensitive to the shape of the filter functions. We make comparisons of the Hα index to the Hβ index and illustrate the relationship between the two systems. In addition, we present relations that relate both hydrogen indices to equivalent width and effective temperature. We derive equations to calibrate both systems for Main Sequence stars with spectral types in the range O9 to K2 for equivalent width and A2 to K2 for effective temperature.

  18. The main sequence of NGC 6231 and the calibration of absolute magnitudes

    International Nuclear Information System (INIS)

    Garrison, R.F.

    1978-01-01

    The author presents a discussion of a new approach to the calibration of absolute magnitudes for MK spectral types. With the addition of the NGC 6231 main sequence down to A0, the material for the cluster fitting method using very carefully determined MK types is complete. (Auth.)

  19. Life of a star

    International Nuclear Information System (INIS)

    Henbest, Nigel.

    1988-01-01

    The paper concerns the theory of stellar evolution. A description is given of:- how a star is born, main sequence stars, red giants, white dwarfs, supernovae, neutron stars and black holes. A brief explanation is given of how the death of a star as a supernova can trigger off the birth of a new generation of stars. Classification of stars and the fate of our sun, are also described. (U.K.)

  20. White dwarf-main sequence binaries from LAMOST: the DR5 catalogue

    Science.gov (United States)

    Ren, J.-J.; Rebassa-Mansergas, A.; Parsons, S. G.; Liu, X.-W.; Luo, A.-L.; Kong, X.; Zhang, H.-T.

    2018-03-01

    We present the data release (DR) 5 catalogue of white dwarf-main sequence (WDMS) binaries from the Large Area Multi-Object fiber Spectroscopic Telescope (LAMOST). The catalogue contains 876 WDMS binaries, of which 757 are additions to our previous LAMOST DR1 sample and 357 are systems that have not been published before. We also describe a LAMOST-dedicated survey that aims at obtaining spectra of photometrically-selected WDMS binaries from the Sloan Digital Sky Survey (SDSS) that are expected to contain cool white dwarfs and/or early type M dwarf companions. This is a population under-represented in previous SDSS WDMS binary catalogues. We determine the stellar parameters (white dwarf effective temperatures, surface gravities and masses, and M dwarf spectral types) of the LAMOST DR5 WDMS binaries and make use of the parameter distributions to analyse the properties of the sample. We find that, despite our efforts, systems containing cool white dwarfs remain under-represented. Moreover, we make use of LAMOST DR5 and SDSS DR14 (when available) spectra to measure the Na I λλ 8183.27, 8194.81 absorption doublet and/or Hα emission radial velocities of our systems. This allows identifying 128 binaries displaying significant radial velocity variations, 76 of which are new. Finally, we cross-match our catalogue with the Catalina Surveys and identify 57 systems displaying light curve variations. These include 16 eclipsing systems, two of which are new, and nine binaries that are new eclipsing candidates. We calculate periodograms from the photometric data and measure (estimate) the orbital periods of 30 (15) WDMS binaries.

  1. Asteroseismic effects in close binary stars

    Science.gov (United States)

    Springer, Ofer M.; Shaviv, Nir J.

    2013-09-01

    Turbulent processes in the convective envelopes of the Sun and stars have been shown to be a source of internal acoustic excitations. In single stars, acoustic waves having frequencies below a certain cut-off frequency propagate nearly adiabatically and are effectively trapped below the photosphere where they are internally reflected. This reflection essentially occurs where the local wavelength becomes comparable to the pressure scale height. In close binary stars, the sound speed is a constant on equipotentials, while the pressure scale height, which depends on the local effective gravity, varies on equipotentials and may be much greater near the inner Lagrangian point (L1). As a result, waves reaching the vicinity of L1 may propagate unimpeded into low-density regions, where they tend to dissipate quickly due to non-linear and radiative effects. We study the three-dimensional propagation and enhanced damping of such waves inside a set of close binary stellar models using a WKB approximation of the acoustic field. We find that these waves can have much higher damping rates in close binaries, compared to their non-binary counterparts. We also find that the relative distribution of acoustic energy density at the visible surface of close binaries develops a ring-like feature at specific acoustic frequencies and binary separations.

  2. COMBINED EFFECTS OF BINARIES AND STELLAR ROTATION ON THE COLOR-MAGNITUDE DIAGRAMS OF INTERMEDIATE-AGE STAR CLUSTERS

    International Nuclear Information System (INIS)

    Li Zhongmu; Mao Caiyan; Chen Li; Zhang Qian

    2012-01-01

    About 70% of intermediate-age star clusters in the Large Magellanic Clouds have been confirmed to have broad main sequence, multiple or extended turnoffs, and dual red giant clumps. The observed result seems to be at odds with the classical idea that such clusters are simple stellar populations. Although many models have been used to explain the results via factors such as prolonged star formation history, metallicity spread, differential reddening, selection effect, observational uncertainty, stellar rotation, and binary interaction, the reason for the special color-magnitude diagrams is still uncertain. We revisit this question via the combination of stellar rotation and binary effects. As a result, it shows 'golf club' color-magnitude diagrams with broad or multiple turnoffs, dual red clumps, blue stragglers, red stragglers, and extended main sequences. Because both binaries and massive rotators are common, our result suggests that most color-magnitude diagrams, including extended turnoff or multiple turnoffs, can be explained using simple stellar populations including both binary and stellar rotation effects, or composite populations with two components.

  3. BVI CCD photometry of the broad main-sequence globular cluster NGC 1851

    International Nuclear Information System (INIS)

    Alcaino, G.; Liller, W.; Alvarado, F.; Wenderoth, E.

    1990-01-01

    Three-color CCD C-M diagrams are presented for the globular cluster NGC 1851, showing an extreme breadth of the main-sequence, similar to that of Omega Centauri. It is found that the main-sequence turnoff points are located at V(TO) = 19.44 + or - 0.10, with colors at B-V = 0.54 + or - 0.02, V-I = 0.61 + or - 0.02, and B-I = 1.15 + or - 0.03. The best fit to the VandenBerg and Bell (1985) isochrones is shown to be all C-M diagrams with Y = 0.20, Fe/H abundance ratio = -1.27, and (m-M)v = 15.45. It is concluded that NGC 1851 has a Delta V(TO - HB) = 3.34 + or - 0.10 and an age of 16 + or - 2 Gyr. 29 refs

  4. Mass loss from pre-main-sequence accretion disks. I - The accelerating wind of FU Orionis

    Science.gov (United States)

    Calvet, Nuria; Hartmann, Lee; Kenyon, Scott J.

    1993-01-01

    We present evidence that the wind of the pre-main-sequence object FU Orionis arises from the surface of the luminous accretion disk. A disk wind model calculated assuming radiative equilibrium explains the differential behavior of the observed asymmetric absorption-line profiles. The model predicts that strong lines should be asymmetric and blueshifted, while weak lines should be symmetric and double-peaked due to disk rotation, in agreement with observations. We propose that many blueshifted 'shell' absorption features are not produced in a true shell of material, but rather form in a differentially expanding wind that is rapidly rotating. The inference of rapid rotation supports the proposal that pre-main-sequence disk winds are rotationally driven.

  5. Gravitomagnetic effect in magnetized neutron stars

    Energy Technology Data Exchange (ETDEWEB)

    Chatterjee, Debarati [LPC/ENSICAEN, 6 Boulevard Maréchal Juin, Caen, 14050 France (France); Chakraborty, Chandrachur [Department of Astronomy and Astrophysics, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, 400005 India (India); Bandyopadhyay, Debades, E-mail: dchatterjee@lpccaen.in2p3.fr, E-mail: chandrachur.chakraborty@tifr.res.in, E-mail: debades.bandyopadhyay@saha.ac.in [Astroparticle Physics and Cosmology Division, Saha Institute of Nuclear Physics, HBNI, 1/AF Bidhannagar, Kolkata, 700064 India (India)

    2017-01-01

    Rotating bodies in General Relativity produce frame dragging, also known as the gravitomagnetic effect in analogy with classical electromagnetism. In this work, we study the effect of magnetic field on the gravitomagnetic effect in neutron stars with poloidal geometry, which is produced as a result of its rotation. We show that the magnetic field has a non-negligible impact on frame dragging. The maximum effect of the magnetic field appears along the polar direction, where the frame-dragging frequency decreases with increase in magnetic field, and along the equatorial direction, where its magnitude increases. For intermediate angles, the effect of the magnetic field decreases, and goes through a minimum for a particular angular value at which magnetic field has no effect on gravitomagnetism. Beyond that particular angle gravitomagnetic effect increases with increasing magnetic field. We try to identify this 'null region' for the case of magnetized neutron stars, both inside and outside, as a function of the magnetic field, and suggest a thought experiment to find the null region of a particular pulsar using the frame dragging effect.

  6. Interstellar Reddening Effect on the Age Dating of Population II Stars

    Directory of Open Access Journals (Sweden)

    Sergio Ortolani

    2017-06-01

    Full Text Available The age measurement of the stellar halo component of the Galaxy is based mainly on the comparison of the main sequence turn-off luminosity of the globular cluster (GC stars with theoretical isochrones. The standard procedure includes a vertical shift, in order to account for the distance and extinction to the cluster, and a horizontal one, to compensate the reddening. However, the photometry is typically performed with broad-band filters where the shape of the stellar spectra introduces a shift of the effective wavelength response of the system, dependent on the effective temperature (or color index of the star. The result is an increasing distortion—actually a rotation and a progressive compression with the temperature—of the color-magnitude diagrams relatively to the standard unreddened isochrones, with increasing reddening. This effect is usually negligible for reddening E ( B - V on the order of or smaller than 0.15, but it can be quite relevant at larger extinction values. While the ratio of the absorption to the reddening is widely discussed in the literature, the importance of the latter effect is often overlooked. In this contribution, we present isochron simulations and discuss the expected effects on age dating of high-reddening globular clusters.

  7. Atomic diffusion in stars

    CERN Document Server

    Michaud, Georges; Richer, Jacques

    2015-01-01

    This book gives an overview of atomic diffusion, a fundamental physical process, as applied to all types of stars, from the main sequence to neutron stars. The superficial abundances of stars as well as their evolution can be significantly affected. The authors show where atomic diffusion plays an essential role and how it can be implemented in modelling.  In Part I, the authors describe the tools that are required to include atomic diffusion in models of stellar interiors and atmospheres. An important role is played by the gradient of partial radiative pressure, or radiative acceleration, which is usually neglected in stellar evolution. In Part II, the authors systematically review the contribution of atomic diffusion to each evolutionary step. The dominant effects of atomic diffusion are accompanied by more subtle effects on a large number of structural properties throughout evolution. One of the goals of this book is to provide the means for the astrophysicist or graduate student to evaluate the importanc...

  8. Evolutionary effects of mass loss in low-mass stars

    International Nuclear Information System (INIS)

    Renzini, A.

    1981-01-01

    The effects of mass loss on the evolution of low-mass stars (actual mass smaller than 1.4 solar masses) are reviewed. The case of globular cluster stars is discussed in some detail, and it is shown that evolutionary theory sets quite precise limits to the mass-loss rate in population II red giants. The effects of mass loss on the final evolutionary stages of stars producing white dwarfs is also discussed. In particular, the interaction of the wind from the hot central star with the surrounding planetary nebula is considered. Finally, the problem of the origin of hydrogen-deficient stars is briefly discussed. (Auth.)

  9. Lithium Depletion in Solar-like Stars: Effect of Overshooting Based on Realistic Multi-dimensional Simulations

    Science.gov (United States)

    Baraffe, I.; Pratt, J.; Goffrey, T.; Constantino, T.; Folini, D.; Popov, M. V.; Walder, R.; Viallet, M.

    2017-08-01

    We study lithium depletion in low-mass and solar-like stars as a function of time, using a new diffusion coefficient describing extra-mixing taking place at the bottom of a convective envelope. This new form is motivated by multi-dimensional fully compressible, time-implicit hydrodynamic simulations performed with the MUSIC code. Intermittent convective mixing at the convective boundary in a star can be modeled using extreme value theory, a statistical analysis frequently used for finance, meteorology, and environmental science. In this Letter, we implement this statistical diffusion coefficient in a one-dimensional stellar evolution code, using parameters calibrated from multi-dimensional hydrodynamic simulations of a young low-mass star. We propose a new scenario that can explain observations of the surface abundance of lithium in the Sun and in clusters covering a wide range of ages, from ˜50 Myr to ˜4 Gyr. Because it relies on our physical model of convective penetration, this scenario has a limited number of assumptions. It can explain the observed trend between rotation and depletion, based on a single additional assumption, namely, that rotation affects the mixing efficiency at the convective boundary. We suggest the existence of a threshold in stellar rotation rate above which rotation strongly prevents the vertical penetration of plumes and below which rotation has small effects. In addition to providing a possible explanation for the long-standing problem of lithium depletion in pre-main-sequence and main-sequence stars, the strength of our scenario is that its basic assumptions can be tested by future hydrodynamic simulations.

  10. Lithium Depletion in Solar-like Stars: Effect of Overshooting Based on Realistic Multi-dimensional Simulations

    International Nuclear Information System (INIS)

    Baraffe, I.; Pratt, J.; Goffrey, T.; Constantino, T.; Viallet, M.; Folini, D.; Popov, M. V.; Walder, R.

    2017-01-01

    We study lithium depletion in low-mass and solar-like stars as a function of time, using a new diffusion coefficient describing extra-mixing taking place at the bottom of a convective envelope. This new form is motivated by multi-dimensional fully compressible, time-implicit hydrodynamic simulations performed with the MUSIC code. Intermittent convective mixing at the convective boundary in a star can be modeled using extreme value theory, a statistical analysis frequently used for finance, meteorology, and environmental science. In this Letter, we implement this statistical diffusion coefficient in a one-dimensional stellar evolution code, using parameters calibrated from multi-dimensional hydrodynamic simulations of a young low-mass star. We propose a new scenario that can explain observations of the surface abundance of lithium in the Sun and in clusters covering a wide range of ages, from ∼50 Myr to ∼4 Gyr. Because it relies on our physical model of convective penetration, this scenario has a limited number of assumptions. It can explain the observed trend between rotation and depletion, based on a single additional assumption, namely, that rotation affects the mixing efficiency at the convective boundary. We suggest the existence of a threshold in stellar rotation rate above which rotation strongly prevents the vertical penetration of plumes and below which rotation has small effects. In addition to providing a possible explanation for the long-standing problem of lithium depletion in pre-main-sequence and main-sequence stars, the strength of our scenario is that its basic assumptions can be tested by future hydrodynamic simulations.

  11. Lithium Depletion in Solar-like Stars: Effect of Overshooting Based on Realistic Multi-dimensional Simulations

    Energy Technology Data Exchange (ETDEWEB)

    Baraffe, I.; Pratt, J.; Goffrey, T.; Constantino, T.; Viallet, M. [Astrophysics Group, University of Exeter, Exeter EX4 4QL (United Kingdom); Folini, D.; Popov, M. V.; Walder, R., E-mail: i.baraffe@ex.ac.uk [Ecole Normale Supérieure de Lyon, CRAL, UMR CNRS 5574, F-69364 Lyon Cedex 07 (France)

    2017-08-10

    We study lithium depletion in low-mass and solar-like stars as a function of time, using a new diffusion coefficient describing extra-mixing taking place at the bottom of a convective envelope. This new form is motivated by multi-dimensional fully compressible, time-implicit hydrodynamic simulations performed with the MUSIC code. Intermittent convective mixing at the convective boundary in a star can be modeled using extreme value theory, a statistical analysis frequently used for finance, meteorology, and environmental science. In this Letter, we implement this statistical diffusion coefficient in a one-dimensional stellar evolution code, using parameters calibrated from multi-dimensional hydrodynamic simulations of a young low-mass star. We propose a new scenario that can explain observations of the surface abundance of lithium in the Sun and in clusters covering a wide range of ages, from ∼50 Myr to ∼4 Gyr. Because it relies on our physical model of convective penetration, this scenario has a limited number of assumptions. It can explain the observed trend between rotation and depletion, based on a single additional assumption, namely, that rotation affects the mixing efficiency at the convective boundary. We suggest the existence of a threshold in stellar rotation rate above which rotation strongly prevents the vertical penetration of plumes and below which rotation has small effects. In addition to providing a possible explanation for the long-standing problem of lithium depletion in pre-main-sequence and main-sequence stars, the strength of our scenario is that its basic assumptions can be tested by future hydrodynamic simulations.

  12. 3D Realistic Radiative Hydrodynamic Modeling of a Moderate-Mass Star: Effects of Rotation

    Science.gov (United States)

    Kitiashvili, Irina; Kosovichev, Alexander G.; Mansour, Nagi N.; Wray, Alan A.

    2018-01-01

    Recent progress in stellar observations opens new perspectives in understanding stellar evolution and structure. However, complex interactions in the turbulent radiating plasma together with effects of magnetic fields and rotation make inferences of stellar properties uncertain. The standard 1D mixing-length-based evolutionary models are not able to capture many physical processes of stellar interior dynamics, but they provide an initial approximation of the stellar structure that can be used to initialize 3D time-dependent radiative hydrodynamics simulations, based on first physical principles, that take into account the effects of turbulence, radiation, and others. In this presentation we will show simulation results from a 3D realistic modeling of an F-type main-sequence star with mass 1.47 Msun, in which the computational domain includes the upper layers of the radiation zone, the entire convection zone, and the photosphere. The simulation results provide new insight into the formation and properties of the convective overshoot region, the dynamics of the near-surface, highly turbulent layer, the structure and dynamics of granulation, and the excitation of acoustic and gravity oscillations. We will discuss the thermodynamic structure, oscillations, and effects of rotation on the dynamics of the star across these layers.

  13. Effect of mass loss on the driving of g-modes in B supergiant stars

    Energy Technology Data Exchange (ETDEWEB)

    Godart, Melanie; Noels, Arlette [Institut d' Astrophysique et de Geophysique, Liege (Belgium); Dupret, Marc-Antoine [Observatoire de Paris-Meudon, LESIA (France)], E-mail: Helanie.Godart@ulg.ac.be, E-mail: Arlette.Noels@ulg.ac.be, E-mail: ma.dupret@obspm.fr

    2008-10-15

    MOST has detected p and g-modes in the B supergiant star HD163899. Saio et al. (2006) have explained the driving of g-modes in a post main sequence star by the presence of a convective shell which prevents some modes from entering the damping radiative core. We show that this scenario depends on the evolution of the star, with or without mass loss. If the mass loss rate is high enough, the convective shell disappears and all the g-modes are stable.

  14. Effect of mass loss on the driving of g-modes in B supergiant stars

    International Nuclear Information System (INIS)

    Godart, Melanie; Noels, Arlette; Dupret, Marc-Antoine

    2008-01-01

    MOST has detected p and g-modes in the B supergiant star HD163899. Saio et al. (2006) have explained the driving of g-modes in a post main sequence star by the presence of a convective shell which prevents some modes from entering the damping radiative core. We show that this scenario depends on the evolution of the star, with or without mass loss. If the mass loss rate is high enough, the convective shell disappears and all the g-modes are stable.

  15. Evolution of long-lived globular cluster stars. III. Effect of the initial helium spread on the position of stars in a synthetic Hertzsprung-Russell diagram

    Science.gov (United States)

    Chantereau, W.; Charbonnel, C.; Meynet, G.

    2016-08-01

    stars even disappear from the horizontal branch and the asymptotic giant branch at 13 Gyr. Conclusions: The helium constraint is no suitable criterion for clearly distinguishing between the scenarios for GC self-enrichment because only few very helium-rich stars are predicted in the investigated framework and because it is difficult to derive the helium content of GC stars observationally. However, the helium constraint indicates some difficulties of the original FRMS scenario that require the exploration of alternatives. The files containing the relevant evolution characteristics of the complete grid of models from the pre-main sequence up to the end of the stellar life (see Appendix of Chantereau et al. 2015) 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/592/A111 As in Chantereau et al. (2015), we also provide all the tables on the website http://obswww.unige.ch/Recherche/evol/starevol/Globular.php

  16. A consistency test of white dwarf and main sequence ages: NGC 6791

    Directory of Open Access Journals (Sweden)

    Córsico A.H.

    2013-03-01

    Full Text Available NGC 6791 is an open cluster that it is so close to us that can be imaged down to very faint luminosities. The main sequence turn-off age (∼8 Gyr and the age derived from the cut-off of the white dwarf luminosity function (∼6 Gyr were found to be significantly different. Here we demonstrate that the origin of this age discrepancy lies in an incorrect evaluation of the white dwarf cooling ages, and we show that when the relevant physical separation processes are included in the calculation of white dwarf sequences both ages are coincident.

  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. Multiple Stars Across the H-R Diagram

    CERN Document Server

    Hubrig, Swetlana; Tokovinin, Andrei; Proceedings of the ESO Workshop held in Garching, Germany, 12-15 July 2005

    2008-01-01

    Stars show a marked tendency to be in systems of different multiplicity, ranging from simple binaries and triples to globular clusters with several 10,000's of stars. The formation and evolution of multiple systems remains a challenging part of astrophysics, and the contributions in this book report on the significant progress that had been made in this research field in the last years. The reader will find a variety of research topics addressed, such as the dynamical evolution in multiple stars, the effects of the environment on multiple system parameters, stellar evolution within multiple stars, multiplicity of massive stars, pre-main sequence and intermediate mass stars, multiplicity of low-mass stars from embedded protostars to open clusters, and brown dwarfs and extrasolar planets in multiples. This book presents the proceedings of the ESO Workshop on Multiple Stars across the H-R Diagram held in the summer of 2005.

  19. Meridional circulation in rotating stars. VII. The effects of chemical inhomogeneities

    International Nuclear Information System (INIS)

    Tassoul, M.; Tassoul, J.

    1984-01-01

    In this paper we discuss the effects of a gradient of mean molecular weight μ on the rotationally driven currents that pervade the radiative zone of a single, nonmagnetic, main-sequence star. Detailed numerical calculations are made for the hydrogen-burning core of a solar-type star, assuming that departures from spherical symmetry are not too large. It is found that meridional streaming virtually dies out from the center outward as the μ-gradient grows in a leisurely fashion. This prevents a substantial mixing of matter between the inner (inhomogeneous) and outer (homogeneous) regions in the radiative zone, although the inner region may be penetrated to some degree. To first order in the ratio of the centrifugal force to gravity at the equator, this pattern of circulation is independent of the mean angular velocity. To this order, then, there is no critical rotation rate above which unimpeded mixing may take place. These quantitative results are compared with diverse statements that can be found in the phenomenological literature on rotational mixing

  20. Explaining the luminosity spread in young clusters: proto and pre-main sequence stellar evolution in a molecular cloud environment

    Science.gov (United States)

    Jensen, Sigurd S.; Haugbølle, Troels

    2018-02-01

    Hertzsprung-Russell diagrams of star-forming regions show a large luminosity spread. This is incompatible with well-defined isochrones based on classic non-accreting protostellar evolution models. Protostars do not evolve in isolation of their environment, but grow through accretion of gas. In addition, while an age can be defined for a star-forming region, the ages of individual stars in the region will vary. We show how the combined effect of a protostellar age spread, a consequence of sustained star formation in the molecular cloud, and time-varying protostellar accretion for individual protostars can explain the observed luminosity spread. We use a global magnetohydrodynamic simulation including a sub-scale sink particle model of a star-forming region to follow the accretion process of each star. The accretion profiles are used to compute stellar evolution models for each star, incorporating a model of how the accretion energy is distributed to the disc, radiated away at the accretion shock, or incorporated into the outer layers of the protostar. Using a modelled cluster age of 5 Myr, we naturally reproduce the luminosity spread and find good agreement with observations of the Collinder 69 cluster, and the Orion Nebular Cluster. It is shown how stars in binary and multiple systems can be externally forced creating recurrent episodic accretion events. We find that in a realistic global molecular cloud model massive stars build up mass over relatively long time-scales. This leads to an important conceptual change compared to the classic picture of non-accreting stellar evolution segmented into low-mass Hayashi tracks and high-mass Henyey tracks.

  1. The Physical Driver of the Optical Eigenvector 1 in Quasar Main Sequence

    Energy Technology Data Exchange (ETDEWEB)

    Panda, Swayamtrupta; Czerny, Bożena [Center for Theoretical Physics, Polish Academy of Sciences, Warsaw (Poland); Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Warsaw (Poland); Wildy, Conor, E-mail: panda@cft.edu.pl [Center for Theoretical Physics, Polish Academy of Sciences, Warsaw (Poland)

    2017-11-07

    Quasars are complex sources, characterized by broad band spectra from radio through optical to X-ray band, with numerous emission and absorption features. This complexity leads to rich diagnostics. However, Boroson and Green (1992) used Principal Component Analysis (PCA), and with this analysis they were able to show significant correlations between the measured parameters. The leading component, related to Eigenvector 1 (EV1) was dominated by the anticorrelation between the FeII optical emission and [OIII] line and EV1 alone contained 30% of the total variance. It opened a way in defining a quasar main sequence, in close analogy to the stellar main sequence on the Hertzsprung-Russel (HR) diagram (Sulentic et al., 2001). The question still remains which of the basic theoretically motivated parameters of an active nucleus (Eddington ratio, black hole mass, accretion rate, spin, and viewing angle) is the main driver behind the EV1. Here we limit ourselves to the optical waveband, and concentrate on theoretical modeling the FeII to Hβ ratio, and we test the hypothesis that the physical driver of EV1 is the maximum of the accretion disk temperature, reflected in the shape of the spectral energy distribution (SED). We performed computations of the Hβ and optical FeII for a broad range of SED peak position using CLOUDY photoionisation code. We assumed that both Hβ and FeII emission come from the Broad Line Region represented as a constant density cloud in a plane-parallel geometry. We expected that a hotter disk continuum will lead to more efficient production of FeII but our computations show that the FeII to Hβ ratio actually drops with the rise of the disk temperature. Thus either hypothesis is incorrect, or approximations used in our paper for the description of the line emissivity is inadequate.

  2. The Physical Driver of the Optical Eigenvector 1 in Quasar Main Sequence

    Directory of Open Access Journals (Sweden)

    Swayamtrupta Panda

    2017-11-01

    Full Text Available Quasars are complex sources, characterized by broad band spectra from radio through optical to X-ray band, with numerous emission and absorption features. This complexity leads to rich diagnostics. However, Boroson and Green (1992 used Principal Component Analysis (PCA, and with this analysis they were able to show significant correlations between the measured parameters. The leading component, related to Eigenvector 1 (EV1 was dominated by the anticorrelation between the FeII optical emission and [OIII] line and EV1 alone contained 30% of the total variance. It opened a way in defining a quasar main sequence, in close analogy to the stellar main sequence on the Hertzsprung-Russel (HR diagram (Sulentic et al., 2001. The question still remains which of the basic theoretically motivated parameters of an active nucleus (Eddington ratio, black hole mass, accretion rate, spin, and viewing angle is the main driver behind the EV1. Here we limit ourselves to the optical waveband, and concentrate on theoretical modeling the FeII to Hβ ratio, and we test the hypothesis that the physical driver of EV1 is the maximum of the accretion disk temperature, reflected in the shape of the spectral energy distribution (SED. We performed computations of the Hβ and optical FeII for a broad range of SED peak position using CLOUDY photoionisation code. We assumed that both Hβ and FeII emission come from the Broad Line Region represented as a constant density cloud in a plane-parallel geometry. We expected that a hotter disk continuum will lead to more efficient production of FeII but our computations show that the FeII to Hβ ratio actually drops with the rise of the disk temperature. Thus either hypothesis is incorrect, or approximations used in our paper for the description of the line emissivity is inadequate.

  3. Gravitational waves from remnant massive neutron stars of binary neutron star merger: Viscous hydrodynamics effects

    Science.gov (United States)

    Shibata, Masaru; Kiuchi, Kenta

    2017-06-01

    Employing a simplified version of the Israel-Stewart formalism of general-relativistic shear-viscous hydrodynamics, we explore the evolution of a remnant massive neutron star of binary neutron star merger and pay special attention to the resulting gravitational waveforms. We find that for the plausible values of the so-called viscous alpha parameter of the order 10-2 the degree of the differential rotation in the remnant massive neutron star is significantly reduced in the viscous time scale, ≲5 ms . Associated with this, the degree of nonaxisymmetric deformation is also reduced quickly, and as a consequence, the amplitude of quasiperiodic gravitational waves emitted also decays in the viscous time scale. Our results indicate that for modeling the evolution of the merger remnants of binary neutron stars we would have to take into account magnetohydrodynamics effects, which in nature could provide the viscous effects.

  4. Physics of star formation in galaxies

    CERN Document Server

    Palla, F

    2002-01-01

    Begining with a historical introduction, ""Star Formation: The Early History"", this text then presents two long articles on ""Pre-Main-Sequence Evolution of Stars and Young Clusters"" and ""Observations of Young Stellar Objects"".

  5. Effects of rotation on the evolution of primordial stars

    Science.gov (United States)

    Ekström, S.; Meynet, G.; Chiappini, C.; Hirschi, R.; Maeder, A.

    2008-10-01

    Context: Although still beyond our observational abilities, Population III stars are interesting objects from many perspectives. They are responsible for the re-ionisation of the inter-galactic medium. They also left their chemical imprint in the early Universe, which can be deciphered in the most metal-poor stars in the halo of our Galaxy. Aims: Rotation has been shown to play a determinant role at very low metallicity, bringing heavy mass loss where almost none was expected. Is this still true when the metallicity strictly equals zero? The aim of our study is to answer this question, and to determine how rotation changes the evolution and the chemical signature of the primordial stars. Methods: We have calculated seven differentially-rotating stellar models at zero metallicity, with masses between 9 and 200 M⊙. For each mass, we also calculated a corresponding model without rotation. The evolution is followed up to the pre-supernova stage. Results: We find that Z=0 models rotate with an internal profile Ω(r) close to local angular momentum conservation, because of a very weak core-envelope coupling. Rotational mixing drives an H-shell boost due to a sudden onset of the CNO cycle in the shell. This boost leads to a high 14N production, which can be as much as 106 times higher than the production of the non-rotating models. Generally, the rotating models produce much more metal than their non-rotating counterparts. The mass loss is very low, even for the models that reach critical velocity during the main sequence. It may however have an impact on the chemical enrichment of the Universe, because some of the stars are supposed to collapse directly into black holes. They would contribute to the enrichment only through their winds. While in that case non-rotating stars would not contribute at all, rotating stars may leave an imprint on their surrounding. Due to the low mass loss and the weak coupling, the core retains a high angular momentum at the end of the

  6. Kepler-4b: A Hot Neptune-Like Planet of a G0 Star Near Main-Sequence Turnoff

    Science.gov (United States)

    2010-04-20

    events using the procedures described by Jenkins et al. (2010) and by Batalha et al. (2010). One of the transiting planet candidates identified by the...Tillinghast Reflector at the Whipple Obser- vatory showed a velocity variation of less than 150 m s−1 over 5 days. Accordingly, we obtained RV measurements with

  7. Chromospheric Ca II H and K and H-alpha emission in single and binary stars of spectral types F6-M2

    International Nuclear Information System (INIS)

    Strassmeier, K.G.; Fekel, F.C.; Bopp, B.W.; Dempsey, R.C.; Henry, G.W.

    1990-01-01

    New observations of the Ca II H and K and H-epsilon region and/or the Balmer H-alpha line are presented for 100 mostly very active stars but also for weak or inactive stars with suspected activity. Correlations between chromospheric activity at Ca II H and K and H-alpha and effective surface temperature and rotation are identified, and several new stars with chromospheric Ca II H and K emission are discovered. No single activity-rotation relation can be derived for all luminosity classes, and there is clear evidence that evolved stars are generally more active than main-sequence stars of the same rotation period. Binary within the evolved stars appears to play no role, while main-sequence binary stars show generally higher levels of activity than their single counterparts. Chromospheric emission in the Ca II H and K lines depends on surface temperature in that flux declines with cooler temperature. 63 refs

  8. Effective interaction: From nuclear reactions to neutron stars

    Indian Academy of Sciences (India)

    pact stars. The nuclear EoS for β-equilibrated neutron star (NS) matter obtained using density-dependent effective nucleon–nucleon interaction satisfies the constraints from the observed flow data from heavy-ion collisions. The energy density of quark matter is lower than that of the nuclear EoS at higher densities implying ...

  9. Intrinsic width and luminosity function of the M92 main sequence

    International Nuclear Information System (INIS)

    Sandage, A.; Katem, B.

    1983-01-01

    Measurements of B and V magnitudes of approx.475 identified stars in the magnitude interval 18.0 - 4 is too low. The luminosity function, obtained from the present data, is compared with that determined earlier by Tayler, by Hartwick, by van den Bergh, and with Fukuoka and Simoda, with good agreement. The evidence favors that phi(M/sub v/) flattens fainter than M/sub v/approx. =+6 as predicted in some dynamical models, due to loss of low mass stars

  10. A tale of two anomalies: Depletion, dispersion, and the connection between the stellar lithium spread and inflated radii on the pre-main sequence

    Energy Technology Data Exchange (ETDEWEB)

    Somers, Garrett; Pinsonneault, Marc H., E-mail: somers@astronomy.ohio-state.edu, E-mail: pinsono@astronomy.ohio-state.edu [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43201 (United States)

    2014-07-20

    We investigate lithium depletion in standard stellar models (SSMs) and main sequence (MS) open clusters, and explore the origin of the Li dispersion in young, cool stars of equal mass, age, and composition. We first demonstrate that SSMs accurately predict the Li abundances of solar analogs at the zero-age main sequence (ZAMS) within theoretical uncertainties. We then measure the rate of MS Li depletion by removing the [Fe/H]-dependent ZAMS Li pattern from three well-studied clusters, and comparing the detrended data. MS depletion is found to be mass-dependent, in the sense of more depletion at low mass. A dispersion in Li abundance at fixed T{sub eff} is nearly universal, and sets in by ∼200 Myr. We discuss mass and age dispersion trends, and the pattern is mixed. We argue that metallicity impacts the ZAMS Li pattern, in agreement with theoretical expectations but contrary to the findings of some previous studies, and suggest Li as a test of cluster metallicity. Finally, we argue that a radius dispersion in stars of fixed mass and age, during the epoch of pre-MS Li destruction, is responsible for the spread in Li abundances and the correlation between rotation and Li in young cool stars, most well known in the Pleiades. We calculate stellar models, inflated to match observed radius anomalies in magnetically active systems, and the resulting range of Li abundances reproduces the observed patterns of young clusters. We discuss ramifications for pre-MS evolutionary tracks and age measurements of young clusters, and suggest an observational test.

  11. A tale of two anomalies: Depletion, dispersion, and the connection between the stellar lithium spread and inflated radii on the pre-main sequence

    International Nuclear Information System (INIS)

    Somers, Garrett; Pinsonneault, Marc H.

    2014-01-01

    We investigate lithium depletion in standard stellar models (SSMs) and main sequence (MS) open clusters, and explore the origin of the Li dispersion in young, cool stars of equal mass, age, and composition. We first demonstrate that SSMs accurately predict the Li abundances of solar analogs at the zero-age main sequence (ZAMS) within theoretical uncertainties. We then measure the rate of MS Li depletion by removing the [Fe/H]-dependent ZAMS Li pattern from three well-studied clusters, and comparing the detrended data. MS depletion is found to be mass-dependent, in the sense of more depletion at low mass. A dispersion in Li abundance at fixed T eff is nearly universal, and sets in by ∼200 Myr. We discuss mass and age dispersion trends, and the pattern is mixed. We argue that metallicity impacts the ZAMS Li pattern, in agreement with theoretical expectations but contrary to the findings of some previous studies, and suggest Li as a test of cluster metallicity. Finally, we argue that a radius dispersion in stars of fixed mass and age, during the epoch of pre-MS Li destruction, is responsible for the spread in Li abundances and the correlation between rotation and Li in young cool stars, most well known in the Pleiades. We calculate stellar models, inflated to match observed radius anomalies in magnetically active systems, and the resulting range of Li abundances reproduces the observed patterns of young clusters. We discuss ramifications for pre-MS evolutionary tracks and age measurements of young clusters, and suggest an observational test.

  12. Effect of tidal fields on star clusters

    Science.gov (United States)

    Chernoff, David; Weinberg, Martin

    1991-01-01

    We follow the dynamical evolution of a star cluster in a galactic tidal field using a restricted N-body code. We find large asymmetric distortions in the outer profile of the cluster in the first 10 or so crossing times as material is lost. Prograde stars escape preferentially and establish a potentially observable retrograde rotation in the halo. We present the rate of particle loss and compare with the prescription proposed by Lee and Ostriker (1987).

  13. Galactic chemical evolution with main-sequence mass loss and the distribution of F and G dwarfs

    International Nuclear Information System (INIS)

    Guzik, J.A.; Struck-Marcell, C.

    1988-01-01

    Simple closed galactic chemical-evolution models incorporating early main-sequence stellar mass loss have been developed for disk ages of 5, 10, and 15 Gyr. Relative to models without stellar mass loss, the models are shown to produce a 30-60 percent increase in the present mass ratio of dwarfs to dwarfs plus remnants, and a 200-250 percent increase in the total mass of late F dwarfs remaining on the main sequence at the current disk age. For present disk ages 5 and 10 Gyr, the total mass of mid-F dwarfs remaining on the main sequence is also shown to increase by 90-120 percent. It is concluded that models with main-sequence mass loss have a slightly reduced gas metallicity and slightly increased gas fraction midway through the evolution. 30 references

  14. Phylogenetic reconstruction of Bantu kinship challenges Main Sequence Theory of human social evolution.

    Science.gov (United States)

    Opie, Christopher; Shultz, Susanne; Atkinson, Quentin D; Currie, Thomas; Mace, Ruth

    2014-12-09

    Kinship provides the fundamental structure of human society: descent determines the inheritance pattern between generations, whereas residence rules govern the location a couple moves to after they marry. In turn, descent and residence patterns determine other key relationships such as alliance, trade, and marriage partners. Hunter-gatherer kinship patterns are viewed as flexible, whereas agricultural societies are thought to have developed much more stable kinship patterns as they expanded during the Holocene. Among the Bantu farmers of sub-Saharan Africa, the ancestral kinship patterns present at the beginning of the expansion are hotly contested, with some arguing for matrilineal and matrilocal patterns, whereas others maintain that any kind of lineality or sex-biased dispersal only emerged much later. Here, we use Bayesian phylogenetic methods to uncover the history of Bantu kinship patterns and trace the interplay between descent and residence systems. The results suggest a number of switches in both descent and residence patterns as Bantu farming spread, but that the first Bantu populations were patrilocal with patrilineal descent. Across the phylogeny, a change in descent triggered a switch away from patrifocal kinship, whereas a change in residence triggered a switch back from matrifocal kinship. These results challenge "Main Sequence Theory," which maintains that changes in residence rules precede change in other social structures. We also indicate the trajectory of kinship change, shedding new light on how this fundamental structure of society developed as farming spread across the globe during the Neolithic.

  15. Entropy Production of Stars

    Directory of Open Access Journals (Sweden)

    Leonid M. Martyushev

    2015-06-01

    Full Text Available The entropy production (inside the volume bounded by a photosphere of main-sequence stars, subgiants, giants, and supergiants is calculated based on B–V photometry data. A non-linear inverse relationship of thermodynamic fluxes and forces as well as an almost constant specific (per volume entropy production of main-sequence stars (for 95% of stars, this quantity lies within 0.5 to 2.2 of the corresponding solar magnitude is found. The obtained results are discussed from the perspective of known extreme principles related to entropy production.

  16. The effect of host star spectral energy distribution and ice-albedo feedback on the climate of extrasolar planets.

    Science.gov (United States)

    Shields, Aomawa L; Meadows, Victoria S; Bitz, Cecilia M; Pierrehumbert, Raymond T; Joshi, Manoj M; Robinson, Tyler D

    2013-08-01

    coverage. The surface ice-albedo feedback effect becomes less important at the outer edge of the habitable zone, where atmospheric CO(2) could be expected to be high such that it maintains clement conditions for surface liquid water. We showed that ∼3-10 bar of CO(2) will entirely mask the climatic effect of ice and snow, leaving the outer limits of the habitable zone unaffected by the spectral dependence of water ice and snow albedo. However, less CO(2) is needed to maintain open water for a planet orbiting an M-dwarf star than would be the case for hotter main-sequence stars.

  17. Time Variability of the Dust Sublimation Zones in Pre-Main Sequence Disk Systems

    Science.gov (United States)

    Sitko, Michael L.; Carpenter, W. J.; Grady, C. A.; Russel, R. W.; Lynch, D. K.; Rudy, R. J.; Mazuk, S. M.; Venturini, C. C.; Kimes, R. L.; Beerman, L. C.; hide

    2007-01-01

    The dust sublimation zone (DSZ) is the region of pre-main sequence (PMS) disks where dust grains most easily anneal, sublime, and condense out of the gas. Because of this, it is a location where crystalline material may be enhanced and redistributed throughout the rest of the disk. A decade-long program to monitor the thermal emission of the grains located in this region demonstrates that large changes in emitted flux occur in many systems. Changes in the thermal emission between 3 and 13.5 microns were observed in HD 31648 (MWC 480), HD 163296 (MWC 275), and DG Tau. This emission is consistent with it being produced at the DSZ, where the transition from a disk of gas to one of gas+dust occurs. In the case of DG Tau, the outbursts were accompanied by increased emission on the 10 micron silicate band on one occasion, while on another occasion it went into absorption. This requires lofting of the material above the disk into the line of sight. Such changes will affect the determination of the inner disk structure obtained through interferometry measurements, and this has been confirmed in the case of HD 163296. Cyclic variations in the heating of the DSZ will lead to the annealing of large grains, the sublimation of smaller grains, possibly followed by re-condensation as the zone enters a cooling phase. Lofting of dust above the disk plane, and outward acceleration by stellar winds and radiation pressure, can re-distribute the processed material to cooler regions of the disk, where cometesimals form. This processing is consistent with the detection of the preferential concentration of large crystalline grains in the inner few AU of PMS disks using interferometric spectroscopy with the VLTI.

  18. On the Use of the Main-sequence Knee (Saddle) to Measure Globular Cluster Ages

    Science.gov (United States)

    Saracino, S.; Dalessandro, E.; Ferraro, F. R.; Lanzoni, B.; Origlia, L.; Salaris, M.; Pietrinferni, A.; Geisler, D.; Kalirai, J. S.; Correnti, M.; Cohen, R. E.; Mauro, F.; Villanova, S.; Moni Bidin, C.

    2018-06-01

    In this paper, we review the operational definition of the so-called main-sequence knee (MS-knee), a feature in the color-magnitude diagram (CMD) occurring at the low-mass end of the MS. The magnitude of this feature is predicted to be independent of age at fixed chemical composition. For this reason, its difference in magnitude with respect to the MS turn-off (MS-TO) point has been suggested as a possible diagnostic to estimate absolute globular cluster (GC) ages. We first demonstrate that the operational definition of the MS-knee currently adopted in the literature refers to the inflection point of the MS (which we here more appropriately named MS-saddle), a feature that is well distinct from the knee and which cannot be used as its proxy. The MS-knee is only visible in near-infrared CMDs, while the MS-saddle can be also detected in optical–NIR CMDs. By using different sets of isochrones, we then demonstrate that the absolute magnitude of the MS-knee varies by a few tenths of a dex from one model to another, thus showing that at the moment stellar models may not capture the full systematic error in the method. We also demonstrate that while the absolute magnitude of the MS-saddle is almost coincident in different models, it has a systematic dependence on the adopted color combinations which is not predicted by stellar models. Hence, it cannot be used as a reliable reference for absolute age determination. Moreover, when statistical and systematic uncertainties are properly taken into account, the difference in magnitude between the MS-TO and the MS-saddle does not provide absolute ages with better accuracy than other methods like the MS-fitting.

  19. End of the Line for a Star like Ours

    Science.gov (United States)

    Riddle, Bob

    2010-01-01

    Stars of different masses have varying life spans, with the more massive stars "burning out" more quickly than stars of lower masses. How or what they do when they burn out also varies, depending on the mass of the star. All stars are called "main sequence stars" as they continue fusing hydrogen and staying in a state of equilibrium--a balance…

  20. 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.

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

    NARCIS (Netherlands)

    Mokiem, MR; Martin-Hernandez, NL; Lenorzer, A; de Koter, A; Tielens, AGGA

    We present a systematic study of the effect of metallicity on the stellar spectral energy distribution (SED) of 0 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

  2. 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

  3. Some properties of spectral binary stars

    International Nuclear Information System (INIS)

    Krajcheva, Z.T.; Popova, E.I.; Tutukov, A.V.; Yungel'son, L.R.; AN SSSR, Moscow. Astronomicheskij Sovet)

    1978-01-01

    Statistical investigations of spectra binary stars are carried out. Binary systems consisting of main sequence stars are considered. For 826 binary stars masses of components, ratios of component masses, semiaxes of orbits and orbital angular momenta are calculated. The distributions of these parameters and their correlations are analyzed. The dependences of statistical properties of spectral binary stars on their origin and evolution are discussed

  4. Multiple star formation : chemistry, physics and coevality

    NARCIS (Netherlands)

    Murillo, Mejias N.M.

    2017-01-01

    Multiple stars, that is two or more stars composing a gravitationally bound system, are common in the universe.They are the cause of many interesting phenomena, from supernovae and planetary nebulae, to binary black hole mergers. Observations of main sequence stars, young stars and forming

  5. On the evolution of stars

    International Nuclear Information System (INIS)

    Kippenhahn, R.

    1989-01-01

    A popular survey is given of the present knowledge on evolution and ageing of stars. Main sequence stars, white dwarf stars, and red giant stars are classified in the Hertzsprung-Russell (HR)-diagram by measurable quantities: surface temperature and luminosity. From the HR-diagram it can be concluded to star mass and age. Star-forming processes in interstellar clouds as well as stellar burning processes are illustrated. The changes occurring in a star due to the depletion of the nuclear energy reserve are described. In this frame the phenomena of planetary nebulae, supernovae, pulsars, neutron stars as well as of black holes are explained

  6. Prospects for detecting decreasing exoplanet frequency with main-sequence age using PLATO

    Science.gov (United States)

    Veras, D.; Brown, D. J. A.; Mustill, A. J.; Pollacco, D.

    2017-09-01

    The space mission PLATO will usher in a new era of exoplanetary science by expanding our current inventory of transiting systems and constraining host star ages, which are currently highly uncertain. This capability might allow PLATO to detect changes in planetary system architecture with time, particularly because planetary scattering due to Lagrange instability may be triggered long after the system was formed. Here, we utilize previously published instability time-scale prescriptions to determine PLATO's capability to detect a trend of decreasing planet frequency with age for systems with equal- mass planets. For two-planet systems, our results demonstrate that PLATO may detect a trend for planet masses which are at least as massive as super-Earths. For systems with three or more planets, we link their initial compactness to potentially detectable frequency trends in order to aid future investigations when these populations will be better characterized.

  7. YSOVAR: Six Pre-main-sequence Eclipsing Binaries in the Orion Nebula Cluster

    Science.gov (United States)

    2012-06-25

    ISOY J053446.01−044922.1i V1448 Ori 17.43c 15.61c 13.88 13.26 12.95 12.73 12.66 12.91 . . . K5c 0.5424125 ISOY J053605.95−050041.2i 2MASS J05360595...identified 12 EB candidates. Four of them, 2MASS 05352184−0546085 (Stassun et al. 2006), V1174 Ori (Stassun et al. 2004), Par1802 (Cargile et al. 2008...Zero points for the photometry were established by reference to data for non-variable stars in our FOV from the Two Micron All Sky Survey ( 2MASS

  8. The effective temperatures of early Wolf-Rayet stars

    International Nuclear Information System (INIS)

    Schmutz, W.

    1982-01-01

    Nussbaumer et al. (1981) (NSSW) have calculated temperatures of 15 Wolf-Rayet stars, which cover most subtypes in the WN and WC sequences. Some Wolf-Rayet stars are found to have a blackbody-like energy distribution and therefore their effective temperature can be well determined, others show deviation from the blackbody shape. This deviation is probably due to an extended continuum emitting region. In view of these later cases NSSW adopted a temperature which they derived from a Zanstra analysis of the He II recombination lines. According to their analysis there should be a continuum jump at 2050 A. New IUE observations of the WN 5 star HD 50896 however did not show any trace of such an absorption edge. This implies that the effective temperature of this WN 5 star and probably of all WR stars with a non blackbody energy distribution is not yet known accurately. Therefore the author started a detailed analysis with a spherically symmetric atmosphere model. Though the model has not yet reached its final shape he has obtained as a first result that the location of HD 50896 in the HR-diagram is to the left of the ZAMS and that the Zanstra analysis is indeed not valid for this star. (Auth.)

  9. The Baldwin-effect in Wolf-Rayet stars

    NARCIS (Netherlands)

    Gent, Jeroen Ivar van

    2000-01-01

    This thesis investigates the Baldwin-effect in Wolf-Rayet (WR) stars. The Baldwin-effect is a correlation with negative slope between the equivalent width of spectral emission lines and the monochromatic luminosity of the underlying continuum at the line wavelength. This effect has been known to

  10. The incidence of stellar mergers and mass gainers among massive stars

    International Nuclear Information System (INIS)

    De Mink, S. E.; Sana, H.; Langer, N.; Izzard, R. G.; Schneider, F. R. N.

    2014-01-01

    Because the majority of massive stars are born as members of close binary systems, populations of massive main-sequence stars contain stellar mergers and products of binary mass transfer. We simulate populations of massive stars accounting for all major binary evolution effects based on the most recent binary parameter statistics and extensively evaluate the effect of model uncertainties. Assuming constant star formation, we find that 8 −4 +9 % of a sample of early-type stars are the products of a merger resulting from a close binary system. In total we find that 30 −15 +10 % of massive main-sequence stars are the products of binary interaction. We show that the commonly adopted approach to minimize the effects of binaries on an observed sample by excluding systems detected as binaries through radial velocity campaigns can be counterproductive. Systems with significant radial velocity variations are mostly pre-interaction systems. Excluding them substantially enhances the relative incidence of mergers and binary products in the non-radial velocity variable sample. This poses a challenge for testing single stellar evolutionary models. It also raises the question of whether certain peculiar classes of stars, such as magnetic O stars, are the result of binary interaction and it emphasizes the need to further study the effect of binarity on the diagnostics that are used to derive the fundamental properties (star-formation history, initial mass function, mass-to-light ratio) of stellar populations nearby and at high redshift.

  11. The Gaia-ESO Survey: the present-day radial metallicity distribution of the Galactic disc probed by pre-main-sequence clusters

    Science.gov (United States)

    Spina, L.; Randich, S.; Magrini, L.; Jeffries, R. D.; Friel, E. D.; Sacco, G. G.; Pancino, E.; Bonito, R.; Bravi, L.; Franciosini, E.; Klutsch, A.; Montes, D.; Gilmore, G.; Vallenari, A.; Bensby, T.; Bragaglia, A.; Flaccomio, E.; Koposov, S. E.; Korn, A. J.; Lanzafame, A. C.; Smiljanic, R.; Bayo, A.; Carraro, G.; Casey, A. R.; Costado, M. T.; Damiani, F.; Donati, P.; Frasca, A.; Hourihane, A.; Jofré, P.; Lewis, J.; Lind, K.; Monaco, L.; Morbidelli, L.; Prisinzano, L.; Sousa, S. G.; Worley, C. C.; Zaggia, S.

    2017-05-01

    Context. The radial metallicity distribution in the Galactic thin disc represents a crucial constraint for modelling disc formation and evolution. Open star clusters allow us to derive both the radial metallicity distribution and its evolution over time. Aims: In this paper we perform the first investigation of the present-day radial metallicity distribution based on [Fe/H] determinations in late type members of pre-main-sequence clusters. Because of their youth, these clusters are therefore essential for tracing the current interstellar medium metallicity. Methods: We used the products of the Gaia-ESO Survey analysis of 12 young regions (age ages is not easily explained by the models. Our results reveal a complex interplay of several processes (e.g. star formation activity, initial mass function, supernova yields, gas flows) that controlled the recent evolution of the Milky Way. Based on observations made with the ESO/VLT, at Paranal Observatory, under program 188.B-3002 (The Gaia-ESO Public Spectroscopic Survey).Full Table 1 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/601/A70

  12. Star Formation in the Orion Nebula Cluster

    Science.gov (United States)

    Palla, Francesco; Stahler, Steven W.

    1999-11-01

    We study the record of star formation activity within the dense cluster associated with the Orion Nebula. The bolometric luminosity function of 900 visible members is well matched by a simplified theoretical model for cluster formation. This model assumes that stars are produced at a constant rate and distributed according to the field-star initial mass function. Our best-fit age for the system, within this framework, is 2×106 yr. To undertake a more detailed analysis, we present a new set of theoretical pre-main-sequence tracks. These cover all masses from 0.1 to 6.0 Msolar, and start from a realistic stellar birthline. The tracks end along a zero-age main-sequence that is in excellent agreement with the empirical one. As a further aid to cluster studies, we offer an heuristic procedure for the correction of pre-main-sequence luminosities and ages to account for the effects of unresolved binary companions. The Orion Nebula stars fall neatly between our birthline and zero-age main-sequence in the H-R diagram. All those more massive than about 8 Msolar lie close to the main sequence, as also predicted by theory. After accounting for the finite sensitivity of the underlying observations, we confirm that the population between 0.4 and 6.0 Msolar roughly follows a standard initial mass function. We see no evidence for a turnover at lower masses. We next use our tracks to compile stellar ages, also between 0.4 and 6.0 Msolar. Our age histogram reveals that star formation began at a low level some 107 yr ago and has gradually accelerated to the present epoch. The period of most active formation is indeed confined to a few×106 yr, and has recently ended with gas dispersal from the Trapezium. We argue that the acceleration in stellar births, which extends over a wide range in mass, reflects the gravitational contraction of the parent cloud spawning this cluster.

  13. Effective Induction Heating around Strongly Magnetized Stars

    Science.gov (United States)

    Kislyakova, K. G.; Fossati, L.; Johnstone, C. P.; Noack, L.; Lüftinger, T.; Zaitsev, V. V.; Lammer, H.

    2018-05-01

    Planets that are embedded in the changing magnetic fields of their host stars can experience significant induction heating in their interiors caused by the planet’s orbital motion. For induction heating to be substantial, the planetary orbit has to be inclined with respect to the stellar rotation and dipole axes. Using WX UMa, for which the rotation and magnetic axes are aligned, as an example, we show that for close-in planets on inclined orbits, induction heating can be stronger than the tidal heating occurring inside Jupiter’s satellite Io; namely, it can generate a surface heat flux exceeding 2 W m‑2. An internal heating source of such magnitude can lead to extreme volcanic activity on the planet’s surface, possibly also to internal local magma oceans, and to the formation of a plasma torus around the star aligned with the planetary orbit. A strongly volcanically active planet would eject into space mostly SO2, which would then dissociate into oxygen and sulphur atoms. Young planets would also eject CO2. Oxygen would therefore be the major component of the torus. If the O I column density of the torus exceeds ≈1012 cm‑2, the torus could be revealed by detecting absorption signatures at the position of the strong far-ultraviolet O I triplet at about 1304 Å. We estimate that this condition is satisfied if the O I atoms in the torus escape the system at a velocity smaller than 1–10 km s‑1. These estimates are valid also for a tidally heated planet.

  14. The Effect of Quantum Fluctuations in Compact Star Observables

    Science.gov (United States)

    Pósfay, P.; Barnaföldi, G. G.; Jakovác, A.

    2018-05-01

    Astrophysical measurements regarding compact stars are just ahead of a big evolution jump, since the NICER experiment deployed on ISS on 2017 June 14. This will provide soon data that would enable the determination of compact star radius with less than 10% error. This can be further constrained by the new observation of gravitational waves originated from merging neutron stars, GW170817. This poses new challenges to nuclear models aiming to explain the structure of super dense nuclear matter found in neutron stars. Detailed studies of the QCD phase diagram show the importance of bosonic quantum fluctuations in the cold dense matter equation of state. Here we used a demonstrative model with one bosonic and one fermionic degree of freedom coupled by Yukawa coupling, we show the effect of bosonic quantum fluctuations on compact star observables such as mass, radius, and compactness. We have also calculated the difference in the value of compressibility which is caused by quantum fluctuations. The above-mentioned quantities are calculated in the mean field, one-loop, and in high order many loop approximation. The results show that the magnitude of these effects is in the range of 4-5%, which place it into the region where modern measurements may detect it. This forms a base for further investigations that how these results carry over to more complicated models.

  15. On the determination of the He abundance distribution in globular clusters from the width of the main sequence

    Science.gov (United States)

    Cassisi, Santi; Salaris, Maurizio; Pietrinferni, Adriano; Hyder, David

    2017-01-01

    One crucial piece of information to study the origin of multiple stellar populations in globular clusters is the range of initial helium abundances ΔY amongst the sub-populations hosted by each cluster. These estimates are commonly obtained by measuring the width in colour of the unevolved main sequence in an optical colour-magnitude diagram (CMD). The measured colour spread is then compared with predictions from theoretical stellar isochrones with varying initial He abundances to determine ΔY. The availability of UV/optical magnitudes, thanks to the Hubble Space Telescope UV Legacy Survey of Galactic GCs project, will allow the homogeneous determination of ΔY for a large Galactic globular cluster sample. From a theoretical point of view, accurate UV CMDs can efficiently disentangle the various sub-populations, and main sequence colour differences in the ACS F606W - (F606W - F814W) diagram allow an estimate of ΔY. We demonstrate that from a theoretical perspective, the (F606W - F814W) colour is an extremely reliable He-abundance indicator. The derivative dY/d(F606W - F814W), computed at a fixed luminosity along the unevolved main sequence, is largely insensitive to the physical assumptions made in stellar model computations, being more sensitive to the choice of the bolometric correction scale, and is only slightly dependent on the adopted set of stellar models. From a theoretical point of view, the (F606W - F814W) colour width of the cluster main sequence is therefore a robust diagnostic of the ΔY range.

  16. Quark matter inside neutron stars in an effective chiral model

    International Nuclear Information System (INIS)

    Kotlorz, A.; Kutschera, M.

    1994-02-01

    An effective chiral model which describes properties of a single baryon predicts that the quark matter relevant to neutron stars, close to the deconfinement density, is in a chirally broken phase. We find the SU(2) model that pion-condensed up and down quark matter is preferred energetically at neutron star densities. It exhibits spin ordering and can posses a permanent magnetization. The equation of state of quark matter with chiral condensate is very well approximated by bag model equation of the state with suitably chosen parameters. We study quark cores inside neutron stars in this model using realistic nucleon equations of state. The biggest quark core corresponds to the second order phase transition to quark matter. Magnetic moment of the pion-condensed quark core is calculated. (author). 19 refs, 10 refs, 1 tab

  17. The effect of UV stars on the intergalactic medium. II

    International Nuclear Information System (INIS)

    Sonnanstine, A.E.; Hills, J.G.

    1976-01-01

    The effect of ionizing radiation from the UV stars (hot prewhite dwarfs) on the intergalactic medium (IGM) has been investigated. If the UV stars are powered only by gravitational contraction they radiate most of their energy at a typical surface temperature of 1.5 x 10 5 K which produces a very highly ionized IGM in which the elements carbon, nitrogen and oxygen are left with only one or two electrons. This result in these elements being very inefficient coolants. The gas is cooled principally by free-free emission and the collisional ionization of hydrogen and helium. For a typical UV star temperature of T=1.5 x 10 5 K, the temperature of the ionized gas in the IGM is Tsub(g)=1.2 x 10 5 K for a Hubble constant H 0 =75 kms -1 Mpc -1 and a hydrogen density nsub(H)=10 -6 cm -3 . Heating by cosmic rays and X-rays is insignificant in the IGM except perhaps in the H I clouds because when a hydrogen atom recombines in the IGM it is far more likely to be re-ionized by a UV-star photon than by either of the other two types of particles due to the greater space density of UV-star photons and their appreciably larger ionization cross sections. If the UV stars radiate a substantial fraction of their energy in a helium-burning stage in which they have surface temperatures of about 5 x 10 4 K, the temperature of the IGM could be lowered to about 5 x 10 4 K. (Auth.)

  18. STAR FORMATION LAWS: THE EFFECTS OF GAS CLOUD SAMPLING

    International Nuclear Information System (INIS)

    Calzetti, D.; Liu, G.; Koda, J.

    2012-01-01

    Recent observational results indicate that the functional shape of the spatially resolved star formation-molecular gas density relation depends on the spatial scale considered. These results may indicate a fundamental role of sampling effects on scales that are typically only a few times larger than those of the largest molecular clouds. To investigate the impact of this effect, we construct simple models for the distribution of molecular clouds in a typical star-forming spiral galaxy and, assuming a power-law relation between star formation rate (SFR) and cloud mass, explore a range of input parameters. We confirm that the slope and the scatter of the simulated SFR-molecular gas surface density relation depend on the size of the sub-galactic region considered, due to stochastic sampling of the molecular cloud mass function, and the effect is larger for steeper relations between SFR and molecular gas. There is a general trend for all slope values to tend to ∼unity for region sizes larger than 1-2 kpc, irrespective of the input SFR-cloud relation. The region size of 1-2 kpc corresponds to the area where the cloud mass function becomes fully sampled. We quantify the effects of selection biases in data tracing the SFR, either as thresholds (i.e., clouds smaller than a given mass value do not form stars) or as backgrounds (e.g., diffuse emission unrelated to current star formation is counted toward the SFR). Apparently discordant observational results are brought into agreement via this simple model, and the comparison of our simulations with data for a few galaxies supports a steep (>1) power-law index between SFR and molecular gas.

  19. FEEDBACK EFFECTS ON LOW-MASS STAR FORMATION

    International Nuclear Information System (INIS)

    Hansen, Charles E.; Klein, Richard I.; McKee, Christopher F.; Fisher, Robert T.

    2012-01-01

    Protostellar feedback, both radiation and bipolar outflows, dramatically affects the fragmentation and mass accretion from star-forming cores. We use ORION, an adaptive mesh refinement gravito-radiation-hydrodynamics code, to simulate low-mass star formation in a turbulent molecular cloud in the presence of protostellar feedback. We present results of the first simulations of a star-forming cluster that include both radiative transfer and protostellar outflows. We run four simulations to isolate the individual effects of radiation feedback and outflow feedback as well as the combination of the two. We find that outflows reduce protostellar masses and accretion rates each by a factor of three and therefore reduce protostellar luminosities by an order of magnitude. This means that, while radiation feedback suppresses fragmentation, outflows render protostellar radiation largely irrelevant for low-mass star formation above a mass scale of 0.05 M ☉ . We find initial fragmentation of our cloud at half the global Jeans length, around 0.1 pc. With insufficient protostellar radiation to stop it, these 0.1 pc cores fragment repeatedly, forming typically 10 stars each. The accretion rate in these stars scales with mass as predicted from core accretion models that include both thermal and turbulent motions; the accretion rate does not appear to be consistent with either competitive accretion or accretion from an isothermal sphere. We find that protostellar outflows do not significantly affect the overall cloud dynamics, in the absence of magnetic fields, due to their small opening angles and poor coupling to the dense gas. The outflows reduce the mass from the cores by 2/3, giving a core to star efficiency, ε core ≅ 1/3. The simulations are also able to reproduce many observation of local star-forming regions. Our simulation with radiation and outflows reproduces the observed protostellar luminosity function. All of the simulations can reproduce observed core mass

  20. EFFECTS OF ROTATIONALLY INDUCED MIXING IN COMPACT BINARY SYSTEMS WITH LOW-MASS SECONDARIES AND IN SINGLE SOLAR-TYPE STARS

    International Nuclear Information System (INIS)

    Chatzopoulos, E.; Robinson, Edward L.; Wheeler, J. Craig

    2012-01-01

    Many population synthesis and stellar evolution studies have addressed the evolution of close binary systems in which the primary is a compact remnant and the secondary is filling its Roche lobe, thus triggering mass transfer. Although tidal locking is expected in such systems, most studies have neglected the rotationally induced mixing that may occur. Here we study the possible effects of mixing in mass-losing stars for a range of secondary star masses and metallicities. We find that tidal locking can induce rotational mixing prior to contact and thus affect the evolution of the secondary star if the effects of the Spruit-Tayler dynamo are included both for angular momentum and chemical transport. Once contact is made, the effect of mass transfer tends to be more rapid than the evolutionary timescale, so the effects of mixing are no longer directly important, but the mass-transfer strips matter to inner layers that may have been affected by the mixing. These effects are enhanced for secondaries of 1-1.2 M ☉ and for lower metallicities. We discuss the possible implications for the paucity of carbon in the secondaries of the cataclysmic variable SS Cyg and the black hole candidate XTE J1118+480 and for the progenitor evolution of Type Ia supernovae. We also address the issue of the origin of blue straggler stars in globular and open clusters. We find that for models that include rotation consistent with that observed for some blue straggler stars, evolution is chemically homogeneous. This leads to tracks in the H-R diagram that are brighter and bluer than the non-rotating main-sequence turn-off point. Rotational mixing could thus be one of the factors that contribute to the formation of blue stragglers.

  1. STAR FORMATION IN 30 DORADUS

    International Nuclear Information System (INIS)

    De Marchi, Guido; Spezzi, Loredana; Sirianni, Marco; Andersen, Morten; Paresce, Francesco; Panagia, Nino; Mutchler, Max; Whitmore, Bradley C.; Bond, Howard; Beccari, Giacomo; Balick, Bruce; Dopita, Michael A.; Frogel, Jay A.; Calzetti, Daniela; Marcella Carollo, C.; Disney, Michael J.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.

    2011-01-01

    Using observations obtained with the Wide-Field Camera 3 on board the Hubble Space Telescope, we have studied the properties of the stellar populations in the central regions of 30 Dor in the Large Magellanic Cloud. The observations clearly reveal the presence of considerable differential extinction across the field. We characterize and quantify this effect using young massive main-sequence stars to derive a statistical reddening correction for most objects in the field. We then search for pre-main-sequence (PMS) stars by looking for objects with a strong (>4σ) Hα excess emission and find about 1150 of them over the entire field. Comparison of their location in the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for the appropriate metallicity reveals that about one-third of these objects are younger than ∼4 Myr, compatible with the age of the massive stars in the central ionizing cluster R 136, whereas the rest have ages up to ∼30 Myr, with a median age of ∼12 Myr. This indicates that star formation has proceeded over an extended period of time, although we cannot discriminate between an extended episode and a series of short and frequent bursts that are not resolved in time. While the younger PMS population preferentially occupies the central regions of the cluster, older PMS objects are more uniformly distributed across the field and are remarkably few at the very center of the cluster. We attribute this latter effect to photo-evaporation of the older circumstellar disks caused by the massive ionizing members of R 136.

  2. Abundances of the elements in sharp-lined early-type stars from IUE high-dispersion spectrograms; 2, the nitrogen deficiency in mercury- manganese stars

    CERN Document Server

    Roby, S W; Adelman, S J

    1999-01-01

    For pt.I see ibid., vol.419, no.1, p.276-85 (1993). The authors determine nitrogen abundances from co-added IUE high-dispersion SWP spectrograms of four HgMn stars and five normal or superficially normal main-sequence B and A stars. They find N deficiencies in the HgMn stars greater than previously reported (depletion factors of 135-400 relative to the Sun). N abundance discrepancies from UV and IR studies of normal stars are discussed in light of possible non-LTE effects. Their data set for their sample of HgMn stars (observed with a consistent strategy to maximize the benefits of co-additions) is an improvement over the single or few images previously used to derive N abundances for most of these stars. (37 refs).

  3. Magnetic field effects on the crust structure of neutron stars

    Science.gov (United States)

    Franzon, B.; Negreiros, R.; Schramm, S.

    2017-12-01

    We study the effects of high magnetic fields on the structure and on the geometry of the crust in neutron stars. We find that the crust geometry is substantially modified by the magnetic field inside the star. We build stationary and axis-symmetric magnetized stellar models by using well-known equations of state to describe the neutron star crust, namely, the Skyrme model for the inner crust and the Baym-Pethick-Sutherland equation of state for the outer crust. We show that the magnetic field has a dual role, contributing to the crust deformation via the electromagnetic interaction (manifested in this case as the Lorentz force) and by contributing to curvature due to the energy stored in it. We also study a direct consequence of the crust deformation due to the magnetic field: the thermal relaxation time. This quantity, which is of great importance to the thermal evolution of neutron stars, is sensitive to the crust properties, and, as such, we show that it may be strongly affected by the magnetic field.

  4. Medium effects in strange quark matter and strange stars

    International Nuclear Information System (INIS)

    Schertler, K.; Greiner, C.; Thoma, M.H.

    1997-01-01

    We investigate the properties of strange quark matter at zero temperature including medium effects. The quarks are considered as quasiparticles which acquire an effective mass generated by the interaction with the other quarks of the dense system. The effective quark masses are derived from the zero momentum limit of the dispersion relations following from an effective quark propagator obtained from resumming one-loop self-energy diagrams in the hard dense loop approximation. This leads to a thermodynamic self-consistent description of strange quark matter as an ideal Fermi gas of quasiparticles. Within this approach we find that medium effects reduce the overall binding energy with respect to 56 Fe of strange quark matter. For typical values of the strong coupling constant (α s >or∼1) strange quark matter is not absolutely stable. The application to pure strange quark matter stars shows that medium effects have, nevertheless, no impact on the mass-radius relation of the stars. However, a phase transition to hadronic matter at the surface of the stars becomes more likely. (orig.)

  5. The State-of-the-art HST Astro-photometric Analysis of the Core of ω Centauri. III. The Main Sequence's Multiple Populations Galore

    Energy Technology Data Exchange (ETDEWEB)

    Bellini, A.; Anderson, J.; Van der Marel, R. P. [Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States); Milone, A. P.; Marino, A. F. [Research School of Astronomy and Astrophysics, Australian National University, Mt Stromlo Observatory, via Cotter Rd, Weston, ACT 2611 (Australia); Piotto, G.; Bedin, L. R. [Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, Padova, I-35122 (Italy); King, I. R., E-mail: bellini@stsci.edu [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)

    2017-08-01

    We take advantage of the exquisite quality of the Hubble Space Telescope 26-filter astro-photometric catalog of the core of ω Cen presented in the first paper of this series and the empirical differential-reddening correction presented in the second paper in order to distill the main sequence into its constituent populations. To this end, we restrict ourselves to the five most useful filters: the magic “trio” of F275W, F336W, and F438W, along with F606W and F814W. We develop a strategy for identifying color systems where different populations stand out most distinctly, then we isolate those populations and examine them in other filters where their subpopulations also come to light. In this way, we have identified at least 15 subpopulations, each of which has a distinctive fiducial curve through our five-dimensional photometric space. We confirm the MSa to be split into two subcomponents, and find that both the bMS and the rMS are split into three subcomponents. Moreover, we have discovered two additional MS groups: the MSd (which has three subcomponents) shares similar properties with the bMS, and the MSe (which has four subcomponents) has properties more similar to those of the rMS. We examine the fiducial curves together and use synthetic spectra to infer relative heavy-element, light-element, and helium abundances for the populations. Our findings show that the stellar populations and star formation history of ω Cen are even more complex than inferred previously. Finally, we provide as a supplement to the original catalog a list that identifies for each star which population it is most likely associated with.

  6. The State-of-the-art HST Astro-photometric Analysis of the Core of ω Centauri. III. The Main Sequence's Multiple Populations Galore

    Science.gov (United States)

    Bellini, A.; Milone, A. P.; Anderson, J.; Marino, A. F.; Piotto, G.; van der Marel, R. P.; Bedin, L. R.; King, I. R.

    2017-08-01

    We take advantage of the exquisite quality of the Hubble Space Telescope 26-filter astro-photometric catalog of the core of ω Cen presented in the first paper of this series and the empirical differential-reddening correction presented in the second paper in order to distill the main sequence into its constituent populations. To this end, we restrict ourselves to the five most useful filters: the magic “trio” of F275W, F336W, and F438W, along with F606W and F814W. We develop a strategy for identifying color systems where different populations stand out most distinctly, then we isolate those populations and examine them in other filters where their subpopulations also come to light. In this way, we have identified at least 15 subpopulations, each of which has a distinctive fiducial curve through our five-dimensional photometric space. We confirm the MSa to be split into two subcomponents, and find that both the bMS and the rMS are split into three subcomponents. Moreover, we have discovered two additional MS groups: the MSd (which has three subcomponents) shares similar properties with the bMS, and the MSe (which has four subcomponents) has properties more similar to those of the rMS. We examine the fiducial curves together and use synthetic spectra to infer relative heavy-element, light-element, and helium abundances for the populations. Our findings show that the stellar populations and star formation history of ω Cen are even more complex than inferred previously. Finally, we provide as a supplement to the original catalog a list that identifies for each star which population it is most likely associated with. Based on archival observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

  7. UBV Light Curves of ζ AUR Star 32 Cygni

    Directory of Open Access Journals (Sweden)

    Il-Seong Nha

    1992-12-01

    Full Text Available UBV ovservation of ζ Aur star 32 Cyg have been at the Yonsei University Observatory suing the 60-cm Goto reflector and five years, 1988-1992. Observations made during these years cover outside of eclipse phase only. No significant light variation which would represent the secondary eclipse of red supergiant by a hot main sequence star is found. The light levels in three passbands do not show any evidence of the proximate effect of this binary system. Some strong light variations, particularly in U, are discussed with no successful explanation.

  8. Can the periodic spectral modulations observed in 236 Sloan Sky Survey stars be due to dark matter effects?

    Science.gov (United States)

    Tamburini, Fabrizio; Licata, Ignazio

    2017-09-01

    The search for dark matter (DM) is one of the most active and challenging areas of current research. Possible DM candidates are ultralight fields such as axions and weak interacting massive particles (WIMPs). Axions piled up in the center of stars are supposed to generate matter/DM configurations with oscillating geometries at a very rapid frequency, which is a multiple of the axion mass m B (Brito et al (2015); Brito et al (2016)). Borra and Trottier (2016) recently found peculiar ultrafast periodic spectral modulations in 236 main sequence stars in the sample of 2.5 million spectra of galactic halo stars of the Sloan Digital Sky Survey (˜1% of main sequence stars in the F-K spectral range) that were interpreted as optical signals from extraterrestrial civilizations, suggesting them as possible candidates for the search for extraterrestrial intelligence (SETI) program. We argue, instead, that this could be the first indirect evidence of bosonic axion-like DM fields inside main sequence stars, with a stable radiative nucleus, where a stable DM core can be hosted. These oscillations were not observed in earlier stellar spectral classes probably because of the impossibility of starting a stable oscillatory regime due to the presence of chaotic motions in their convective nuclei. The axion mass values, (50< {m}B< 2.4× {10}3) μ {eV}, obtained from the frequency range observed by Borra and Trottier, (0.6070< f< 0.6077) THz, agree with the recent theoretical results from high-temperature lattice quantum chromodynamics (Borsanyi et al (2016); Borsanyi et al (2016b)).

  9. Naturalness in an Effective Field Theory for Neutron Star Matter

    International Nuclear Information System (INIS)

    Razeira, Moises; Vasconcellos, Cesar A.Z.; Bodmann, Bardo E.J.; Coelho, Helio T.; Dillig, Manfred

    2004-01-01

    High density hadronic matter is studied in a generalized relativistic multi-baryon lagrangian density. By comparing the predictions of our model with estimates obtained within a phenomenological naive dimensional analysis based on the naturalness of the coefficients of the theory, we show that naturalness plays a major role in effective field theory and, in combination with experiment, could represent a relevant criterium to select a model among others in the description of global static properties of neutron stars

  10. Towards Measurements of Chiral Effects Using Identified Particles from STAR

    Czech Academy of Sciences Publication Activity Database

    Wen, Lw.; Adamczyk, L.; Adkins, J. K.; Agakishiev, G.; Bielčík, J.; Bielčíková, Jana; Chaloupka, P.; Federič, Pavol; Rusňák, Jan; Rusňáková, O.; Šimko, Miroslav; Šumbera, Michal; Vértési, Robert

    2017-01-01

    Roč. 967, č. 11 (2017), s. 756-759 ISSN 0375-9474 R&D Projects: GA MŠk LG15001; GA MŠk LM2015054 Institutional support: RVO:61389005 Keywords : STAR collaboration * chiral magnetic effect * chiral magnetic wave * gamma correlation * k(K) parameter Subject RIV: BF - Elementary Particles and High Energy Physics OBOR OECD: Particles and field physics Impact factor: 1.916, year: 2016

  11. Spectropolarimetry of magnetic stars. IV. The crossover effect.

    Science.gov (United States)

    Mathys, G.

    1995-01-01

    This paper is devoted to the study of the crossover effect in magnetic Ap stars. It is shown that this effect can be measured by the second order moment about their centre of the profiles of spectral lines recorded in the Stokes parameter V. The interpretation of these measurements in terms of magnetic field is developed. It is shown that one can derive from them a quantity called the mean asymmetry of the longitudinal magnetic field, which is the first moment of the component of the magnetic field along the line of sight, about the plane defined by the line of sight and the stellar rotation axis. The consistency of the determination of this quantity with that of the mean longitudinal magnetic field from measurements of wavelength shifts of lines between right and left circular polarization is demonstrated. This technique of analysis is applied to observations of a sample of 29 stars, among which 10 have a detectable crossover effect. For 8 of them, the available observational data allow the study of the variations of the asymmetry of the longitudinal field with rotation phase. In most cases, this variation is sinusoidal and essentially symmetric about 0, and it occurs in quadrature with the variation of the mean longitudinal field. A more complex behaviour is definitely observed in HD 147010 and HD 175362, where the variation of the asymmetry of the longitudinal field is better represented by the superposition of two sinusoids, one with the rotation frequency of the star, and the other with twice that frequency.

  12. MAGNETIC GRAIN TRAPPING AND THE HOT EXCESSES AROUND EARLY-TYPE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Rieke, G. H.; Gáspár, András; Ballering, N. P., E-mail: grieke@as.arizona.edu, E-mail: agaspar@as.arizona.edu, E-mail: ballerin@email.arizona.edu [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)

    2016-01-10

    A significant fraction of main sequence stars observed interferometrically in the near-infrared have slightly extended components that have been attributed to very hot dust. To match the spectrum appears to require the presence of large numbers of very small (<200 nm in radius) dust grains. However, particularly for the hotter stars, it has been unclear how such grains can be retained close to the star against radiation pressure force. We find that the expected weak stellar magnetic fields are sufficient to trap nm-sized dust grains in epicyclic orbits for a few weeks or longer, sufficient to account for the hot excess emission. Our models provide a natural explanation for the requirement that the hot excess dust grains be smaller than 200 nm. They also suggest that magnetic trapping is more effective for rapidly rotating stars, consistent with the average vsini measurements of stars with hot excesses being larger (at ∼2σ) than those for stars without such excesses.

  13. Asteroseismology of solar-type stars: particular physical effects

    Energy Technology Data Exchange (ETDEWEB)

    Carrier, F [Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven (Belgium); Eggenberger, P; Leyder, J-C [Institut d' Astrophysique et de Geophysique de l' Universite de Liege, 17 Allee du 6 aout, 4000 Liege (Belgium)], E-mail: fabien@ster.kuleuven.be

    2008-10-15

    Since the success of helioseismology, numerous efforts have been made to detect solar-like oscillations on other stars. The measurement of the frequencies of p-mode oscillations provides an insight into the internal structure and is nowadays the most powerful constraint on the theory of stellar evolution. The existing asteroseismic observations were mainly motivated by the need to explore the seismological properties of stars with various global parameters, i.e. various locations in the HR diagram. With the aim of testing different physical effects on solar-like oscillations, we report here detection of acoustic modes on solar-like targets achieved with the spectrograph HARPS installed on the 3.6-m telescope at ESO La Silla Observatory.

  14. The Pisa pre-main sequence tracks and isochrones. A database covering a wide range of Z, Y, mass, and age values

    Science.gov (United States)

    Tognelli, E.; Prada Moroni, P. G.; Degl'Innocenti, S.

    2011-09-01

    Context. In recent years new observations of pre-main sequence stars (pre-MS) with Z ≤ Z⊙ have been made available. To take full advantage of the continuously growing amount of data of pre-MS stars in different environments, we need to develop updated pre-MS models for a wide range of metallicity to assign reliable ages and masses to the observed stars. Aims: We present updated evolutionary pre-MS models and isochrones for a fine grid of mass, age, metallicity, and helium values. Methods: We use a standard and well-tested stellar evolutionary code (i.e. FRANEC), that adopts outer boundary conditions from detailed and realistic atmosphere models. In this code, we incorporate additional improvements to the physical inputs related to the equation of state and the low temperature radiative opacities essential to computing low-mass stellar models. Results: We make available via internet a large database of pre-MS tracks and isochrones for a wide range of chemical compositions (Z = 0.0002-0.03), masses (M = 0.2-7.0 M⊙), and ages (1-100 Myr) for a solar-calibrated mixing length parameter α (i.e. 1.68). For each chemical composition, additional models were computed with two different mixing length values, namely α = 1.2 and 1.9. Moreover, for Z ≥ 0.008, we also provided models with two different initial deuterium abundances. The characteristics of the models have been discussed in detail and compared with other work in the literature. The main uncertainties affecting theoretical predictions have been critically discussed. Comparisons with selected data indicate that there is close agreement between theory and observation. Tracks and isochrones are available on the web at the http://astro.df.unipi.it/stellar-models/Tracks and isochrones are also available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/533/A109

  15. ABOUT EXOBIOLOGY: THE CASE FOR DWARF K STARS

    Energy Technology Data Exchange (ETDEWEB)

    Cuntz, M. [Department of Physics, University of Texas at Arlington, Arlington, TX 76019 (United States); Guinan, E. F., E-mail: cuntz@uta.edu, E-mail: edward.guinan@villanova.edu [Department of Astrophysics and Planetary Science, Villanova University, Villanova, PA 19085 (United States)

    2016-08-10

    One of the most fundamental topics of exobiology concerns the identification of stars with environments consistent with life. Although it is believed that most types of main-sequence stars might be able to support life, particularly extremophiles, special requirements appear to be necessary for the development and sustainability of advanced life forms. From our study, orange main-sequence stars, ranging from spectral type late-G to mid-K (with a maximum at early K), are most promising. Our analysis considers a variety of aspects, including (1) the frequency of the various types of stars, (2) the speed of stellar evolution in their lifetimes, (3) the size of the stellar climatological habitable zones (CLI-HZs), (4) the strengths and persistence of their magnetic-dynamo-generated X-ray–UV emissions, and (5) the frequency and severity of flares, including superflares; both (4) and (5) greatly reduce the suitability of red dwarfs to host life-bearing planets. The various phenomena show pronounced dependencies on the stellar key parameters such as effective temperature and mass, permitting the assessment of the astrobiological significance of various types of stars. Thus, we developed a “Habitable-Planetary-Real-Estate Parameter” (HabPREP) that provides a measure for stars that are most suitable for planets with life. Early K stars are found to have the highest HabPREP values, indicating that they may be “Goldilocks” stars for life-hosting planets. Red dwarfs are numerous, with long lifetimes, but their narrow CLI-HZs and hazards from magnetic activity make them less suitable for hosting exolife. Moreover, we provide X-ray–far-UV irradiances for G0 V–M5 V stars over a wide range of ages.

  16. ABOUT EXOBIOLOGY: THE CASE FOR DWARF K STARS

    International Nuclear Information System (INIS)

    Cuntz, M.; Guinan, E. F.

    2016-01-01

    One of the most fundamental topics of exobiology concerns the identification of stars with environments consistent with life. Although it is believed that most types of main-sequence stars might be able to support life, particularly extremophiles, special requirements appear to be necessary for the development and sustainability of advanced life forms. From our study, orange main-sequence stars, ranging from spectral type late-G to mid-K (with a maximum at early K), are most promising. Our analysis considers a variety of aspects, including (1) the frequency of the various types of stars, (2) the speed of stellar evolution in their lifetimes, (3) the size of the stellar climatological habitable zones (CLI-HZs), (4) the strengths and persistence of their magnetic-dynamo-generated X-ray–UV emissions, and (5) the frequency and severity of flares, including superflares; both (4) and (5) greatly reduce the suitability of red dwarfs to host life-bearing planets. The various phenomena show pronounced dependencies on the stellar key parameters such as effective temperature and mass, permitting the assessment of the astrobiological significance of various types of stars. Thus, we developed a “Habitable-Planetary-Real-Estate Parameter” (HabPREP) that provides a measure for stars that are most suitable for planets with life. Early K stars are found to have the highest HabPREP values, indicating that they may be “Goldilocks” stars for life-hosting planets. Red dwarfs are numerous, with long lifetimes, but their narrow CLI-HZs and hazards from magnetic activity make them less suitable for hosting exolife. Moreover, we provide X-ray–far-UV irradiances for G0 V–M5 V stars over a wide range of ages.

  17. Stellar model chromospheres. IX - Chromospheric activity in dwarf stars

    Science.gov (United States)

    Kelch, W. L.; Worden, S. P.; Linsky, J. L.

    1979-01-01

    High-resolution Ca II K line profiles are used to model the upper photospheres and lower chromospheres of eight main-sequence stars ranging in spectral type from F0 to M0 and exhibiting different degrees of chromospheric activity. The model chromospheres are studied as a function of spectral type and activity for stars of similar spectral type in order to obtain evidence of enhanced nonradiative heating in the upper-photospheric models and in the ratio of minimum temperature at the base of the chromosphere to effective temperature, a correlation between activity and temperature in the lower chromospheres, and a correlation of the width at the base of the K-line emission core and at the K2 features with activity. Chromospheric radiative losses are estimated for the modelled stars and other previously analyzed main-sequence stars. The results obtained strengthen the argument that dMe flare stars exhibit fundamentally solar-type activity but on an increased scale.

  18. Effects of Density-Dependent Bag Constant and Strange Star Rotation

    Institute of Scientific and Technical Information of China (English)

    ZHOU Qiao-Er; GUO Hua

    2003-01-01

    With the emphasis on the effects of the density-dependent bag constant and the rotation of strange star the limiting mass of strange star is calculated. The obtained results show that the limiting mass and the corresponding radius of strange star increase as the rotation frequency increases, and tend to be lowered when the density-dependent bag constant is considered.

  19. Evolution of rotating stars. III. Predicted surface rotation velocities for stars which conserve total angular momentum

    International Nuclear Information System (INIS)

    Endal, A.S.; Sofia, S.

    1979-01-01

    Predicted surface rotation velocities are presented for Population I stars at 10, 7, 5, 3, and 1.5M/sub sun/. The surface velocities have been computed for three different cases of angular momentum redistribution: no radial redistribution (rotation on decoupled shells), complete redistribution (rigid-body rotation), and partial redistribution as predicted by detailed consideration of circulation currents in rotation stars. The velocities for these cases are compared to each other and to observed stellar rotation rates (upsilon sin i).Near the main sequence, rotational effects can substantially reduce the moment of inertia of a star, so nonrotating models consistently underestimate the expected velocities for evolving stars. The magnitude of these effects is sufficient to explain the large numbers of Be stars and, perhaps, to explain the bimodal distribution of velocities observed for the O stars.On the red giant branch, angular momentum redistribution reduces the surface velocity by a factor of 2 or more, relative to the velocity expected for no radial redistribution. This removes the discrepancy between predicted and observed rotation rates for the K giants and makes it unlikely that these stars lose significant amounts of angular momentum by stellar winds. Our calculations indicate that improved observations (by the Fourier-transform technique) of the red giants in the Hyades cluster can be used to determine how angular momentum is redistributed by convection

  20. Nonlinear effects in Pulsations of Compact Stars and Gravitational Waves

    International Nuclear Information System (INIS)

    Passamonti, A

    2007-01-01

    Nonlinear stellar oscillations can be studied by using a multiparameter perturbative approach, which is appropriate for investigating the low and mild nonlinear dynamical regimes. We present the main properties of our perturbative framework for describing, in the time domain, the nonlinear coupling between the radial and nonradial perturbations of spherically symmetric and perfect fluid compact stars. This particular coupling can be described by gauge invariant quantities that obeys a system of partial differential equations with source terms, which are made up of product of first order radial and nonradial perturbations. We report the results of numerical simulations for both the axial and polar coupling perturbations, that exhibit in the stellar dynamics and in the associated gravitational wave signal some interesting nonlinear effects, such as combination harmonics and resonances. In particular, we concentrate on the axial case, where the linear axial perturbations describe a harmonic component of a differentially rotating neutron star. The gravitational wave signal of this stellar configuration mirrors at second perturbative order the spectral features of the linear radial normal modes. In addition, a signal amplification appears when one of the radial frequencies is close to the axial w-mode frequencies of the star

  1. The Effects of Galaxy Interactions on Star Formation

    Science.gov (United States)

    Beverage, Aliza; Weiner, Aaron; Ramos Padilla, Andres; Ashby, Matthew; Smith, Howard A.

    2018-01-01

    Galaxy interactions are key events in galaxy evolution, and are widely thought to trigger significant increases in star formation. However, the mechanisms and timescales for these increases are still not well understood. In order to probe the effects of mergers, we undertook an investigation based on the Spitzer Interacting Galaxies Survey (SIGS), a sample of 102 nearby galaxies in 48 systems ranging from weakly interacting to near coalescence. Our study is unique in that we use both broadband photometry and a large sample of objects chosen to be statistically meaningful. Our data come from 32 broad bands ranging from the UV to far-IR, and we model spectral energy distributions (SEDs) using the Code for Investigating Galaxy Emission (CIGALE) to estimate physical characteristics for each galaxy. We find marginal statistical correlations between galaxy interaction strength and dust luminosity and the distribution of dust mass as a function of heating intensity. The specific star formation rates, however, do not show any enhancement across the interaction stages. This result challenges conventional wisdom that mergers induce star formation throughout galaxy interaction.The SAO REU program is funded in part by the National Science Foundation REU and Department of Defense ASSURE programs under NSF Grant no. 1262851, and by the Smithsonian Institution.

  2. FUNDAMENTAL PROPERTIES OF STARS USING ASTEROSEISMOLOGY FROM KEPLER AND CoRoT AND INTERFEROMETRY FROM THE CHARA ARRAY

    Energy Technology Data Exchange (ETDEWEB)

    Huber, D.; Ireland, M. J.; Bedding, T. R.; Maestro, V.; White, T. R. [Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia); Brandao, I. M.; Sousa, S. G.; Cunha, M. S. [Centro de Astrofo Latin-Small-Letter-Dotless-I sica and Faculdade de Ciencias, Universidade do Porto, Rua das Estrelas, P-4150-762 Porto (Portugal); Piau, L. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48823-2320 (United States); Bruntt, H.; Aguirre, V. Silva; Christensen-Dalsgaard, J. [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Casagrande, L. [Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, The Australian National University, ACT 2611 (Australia); Molenda-Zakowicz, J. [Astronomical Institute of the University of Wroclaw, ul. Kopernika 11, 51-622 Wroclaw (Poland); Barclay, T. [Bay Area Environmental Research Institute/NASA Ames Research Center, Moffett Field, CA 94035 (United States); Burke, C. J. [SETI Institute/NASA Ames Research Center, Moffett Field, CA 94035 (United States); Chaplin, W. J. [School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom); De Ridder, J. [Instituut voor Sterrenkunde, K. U. Leuven, B-3001 Leuven (Belgium); Farrington, C. D. [Center for High Angular Resolution Astronomy, Georgia State University, P.O. Box 3969, Atlanta, GA 30302 (United States); Frasca, A., E-mail: daniel.huber@nasa.gov [INAF Osservatorio Astrofisico di Catania, I-95123 Catania (Italy); and others

    2012-11-20

    We present results of a long-baseline interferometry campaign using the PAVO beam combiner at the CHARA Array to measure the angular sizes of five main-sequence stars, one subgiant and four red giant stars for which solar-like oscillations have been detected by either Kepler or CoRoT. By combining interferometric angular diameters, Hipparcos parallaxes, asteroseismic densities, bolometric fluxes, and high-resolution spectroscopy, we derive a full set of near-model-independent fundamental properties for the sample. We first use these properties to test asteroseismic scaling relations for the frequency of maximum power ({nu}{sub max}) and the large frequency separation ({Delta}{nu}). We find excellent agreement within the observational uncertainties, and empirically show that simple estimates of asteroseismic radii for main-sequence stars are accurate to {approx}< 4%. We furthermore find good agreement of our measured effective temperatures with spectroscopic and photometric estimates with mean deviations for stars between T {sub eff} = 4600-6200 K of -22 {+-} 32 K (with a scatter of 97 K) and -58 {+-} 31 K (with a scatter of 93 K), respectively. Finally, we present a first comparison with evolutionary models, and find differences between observed and theoretical properties for the metal-rich main-sequence star HD 173701. We conclude that the constraints presented in this study will have strong potential for testing stellar model physics, in particular when combined with detailed modeling of individual oscillation frequencies.

  3. From clouds to stars

    International Nuclear Information System (INIS)

    Elmegreen, B.G.

    1982-01-01

    At the present time, the theory of star formation must be limited to what we know about the lowest density gas, or about the pre-main sequence stars themselves. We would like to understand two basic processes: 1) how star-forming clouds are created from the ambient interstellar gas in the first place, and 2) how small parts of these clouds condense to form individual stars. We are interested also in knowing what pre-main sequence stars are like, and how they can interact with their environment. These topics are reviewed in what follows. In this series of lectures, what we know about the formation of stars is tentatively described. The lectures begin with a description of the interstellar medium, and then they proceed along the same direction that a young star would follow during its creation, namely from clouds through the collapse phase and onto the proto-stellar phase. The evolution of viscous disks and two models for the formation of the solar system are described in the last lectures. The longest lectures, and the topics that are covered in most detail, are not necessarily the ones for which we have the most information. Physically intuitive explanations for the various processes are emphasized, rather then mathematical explanations. In some cases, the mathematical aspects are developed as well, but only when the equations can be used to give important numerical values for comparison with the observations

  4. A new interpretation of luminous blue stars

    International Nuclear Information System (INIS)

    Stothers, R.

    1976-01-01

    A major revision of current theoretical ideas about the brightest blue stars must be made if Carson's new radiative opacities are adopted in stellar models. Unlike earlier opacities, the new opacities exhibit a large ''bump'' due to CNO ionization, which leads to very strong central condensation, convective instability, and pulsational instability in hot, diffuse stellar envelopes (typically those in which L/M>10 3 solar units). Despite a number of theoretical uncertainties, the new picture of the structure of very luminous stars is reasonably successful in accounting for a variety of previously unexplained observations. Thus, the new stellar models for the phase of core hydrogen burning predict large radii and rather cool effective temperatures (which are yet to be observationally confirmed) for O stars, and a spreading out of the main-sequence band in the H-R diagram toward luminous cool supergiants for masses higher than approx.20 M/sub sun/, beginning at M/sub v/=-4.5 and Sp=B1. They also predict slower surface rotations for O stars compared with B stars; and, in binary systems, slower apsidal motions, closer rotational-revolutional synchronism, and smaller orbital eccentricities. In massive X-ray binary systems, circular orbits and supergiant-like visual companions are expected to be quite common. Radial pulsations of the models have been calculated by employing linearized nonadiabatic pulsation theory. Long-period variability is predicted to exist for massive blue supergiants of luminosity class Ia. The new models for helium stars predict large radii and rather cool effective temperatures for Wolf-Rayet stars, as well as multimodal pulsational instability and, possibly, surface turbulence for these stars. Ultrashort-period variability, observed in many classes of hot luminous stars, may be due, in part, to high radial overtone pulsations (or, possibly, to nonradial pulsation or convective modes)

  5. POST-MAIN SEQUENCE EVOLUTION OF ICY MINOR PLANETS: IMPLICATIONS FOR WATER RETENTION AND WHITE DWARF POLLUTION

    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)

    2016-12-01

    Most observations of polluted white dwarf atmospheres are consistent with accretion of water-depleted planetary material. Among tens of known cases, merely two involve accretion of objects that contain a considerable mass fraction of water. The purpose of this study is to investigate the relative scarcity of these detections. Based on a new and highly detailed model, we evaluate the retention of water inside icy minor planets during the high-luminosity stellar evolution that follows the main sequence. Our model fully considers the thermal, physical, and chemical evolution of icy bodies, following their internal differentiation as well as water depletion, from the moment of their birth and through all stellar evolution phases preceding the formation of the white dwarf. We also account for different initial compositions and formation times. Our results differ from previous studies, which have either underestimated or overestimated water retention. We show that water can survive in a variety of circumstances and in great quantities, and therefore other possibilities are discussed in order to explain the infrequency of water detection. We predict that the sequence of accretion is such that water accretes earlier, and more rapidly, than the rest of the silicate disk, considerably reducing the chance of its detection in H-dominated atmospheres. In He-dominated atmospheres, the scarcity of water detections could be observationally biased. It implies that the accreted material is typically intrinsically dry, which may be the result of the inside-out depopulation sequence of minor planets.

  6. POST-MAIN SEQUENCE EVOLUTION OF ICY MINOR PLANETS: IMPLICATIONS FOR WATER RETENTION AND WHITE DWARF POLLUTION

    International Nuclear Information System (INIS)

    Malamud, Uri; Perets, Hagai B.

    2016-01-01

    Most observations of polluted white dwarf atmospheres are consistent with accretion of water-depleted planetary material. Among tens of known cases, merely two involve accretion of objects that contain a considerable mass fraction of water. The purpose of this study is to investigate the relative scarcity of these detections. Based on a new and highly detailed model, we evaluate the retention of water inside icy minor planets during the high-luminosity stellar evolution that follows the main sequence. Our model fully considers the thermal, physical, and chemical evolution of icy bodies, following their internal differentiation as well as water depletion, from the moment of their birth and through all stellar evolution phases preceding the formation of the white dwarf. We also account for different initial compositions and formation times. Our results differ from previous studies, which have either underestimated or overestimated water retention. We show that water can survive in a variety of circumstances and in great quantities, and therefore other possibilities are discussed in order to explain the infrequency of water detection. We predict that the sequence of accretion is such that water accretes earlier, and more rapidly, than the rest of the silicate disk, considerably reducing the chance of its detection in H-dominated atmospheres. In He-dominated atmospheres, the scarcity of water detections could be observationally biased. It implies that the accreted material is typically intrinsically dry, which may be the result of the inside-out depopulation sequence of minor planets.

  7. THE EFFECTS OF EPISODIC STAR FORMATION ON THE FUV-NUV COLORS OF STAR FORMING REGIONS IN OUTER DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Barnes, Kate L.; Van Zee, Liese [Department of Astronomy, Indiana University, Bloomington, IN 47405 (United States); Dowell, Jayce D., E-mail: barneskl@astro.indiana.edu, E-mail: vanzee@astro.indiana.edu, E-mail: jdowell@unm.edu [Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87131 (United States)

    2013-09-20

    We run stellar population synthesis models to examine the effects of a recently episodic star formation history (SFH) on UV and Hα colors of star forming regions. Specifically, the SFHs we use are an episodic sampling of an exponentially declining star formation rate (SFR; τ model) and are intended to simulate the SFHs in the outer disks of spiral galaxies. To enable comparison between our models and observational studies of star forming regions in outer disks, we include in our models sensitivity limits that are based on recent deep UV and Hα observations in the literature. We find significant dispersion in the FUV-NUV colors of simulated star forming regions with frequencies of star formation episodes of 1 × 10{sup –8} to 4 × 10{sup –9} yr{sup –1}. The dispersion in UV colors is similar to that found in the outer disk of nearby spiral galaxies. As expected, we also find large variations in L{sub H{sub α}}/L{sub FUV}. We interpret our models within the context of inside-out disk growth, and find that a radially increasing τ and decreasing metallicity with an increasing radius will only produce modest FUV-NUV color gradients, which are significantly smaller than what is found for some nearby spiral galaxies. However, including moderate extinction gradients with our models can better match the observations with steeper UV color gradients. We estimate that the SFR at which the number of stars emitting FUV light becomes stochastic is ∼2 × 10{sup –6} M{sub ☉} yr{sup –1}, which is substantially lower than the SFR of many star forming regions in outer disks. Therefore, we conclude that stochasticity in the upper end of the initial mass function is not likely to be the dominant cause of dispersion in the FUV-NUV colors of star forming regions in outer disks. Finally, we note that if outer disks have had an episodic SFH similar to that used in this study, this should be taken into account when estimating gas depletion timescales and modeling chemical

  8. Neutron star/red giant encounters in globular clusters

    International Nuclear Information System (INIS)

    Bailyn, C.D.

    1988-01-01

    The author presents a simple expression for the amount by which xsub(crit) is diminished as a star evolves xsub(crit) Rsub(crit)/R*, where Rsub(crit) is the maximum distance of closest approach between two stars for which the tidal energy is sufficient to bind the system, and R* is the radius of the star on which tides are being raised. Also it is concluded that tidal capture of giants by neutron stars resulting in binary systems is unlikely in globular clusters. However, collisions between neutron stars and red giants, or an alternative process involving tidal capture of a main-sequence star into an initially detached binary system, may result either in rapidly rotating neutron stars or in white dwarf/neutron star binaries. (author)

  9. Gravitational waves from the collision of tidally disrupted stars with massive black holes

    International Nuclear Information System (INIS)

    East, William E.

    2014-01-01

    We use simulations of hydrodynamics coupled with full general relativity to investigate the gravitational waves produced by a star colliding with a massive black hole when the star's tidal disruption radius lies far outside of the black hole horizon. We consider both main-sequence and white-dwarf compaction stars, and nonspinning black holes, as well as those with near-extremal spin. We study the regime in between where the star can be accurately modeled by a point particle, and where tidal effects completely suppress the gravitational wave signal. We find that nonnegligible gravitational waves can be produced even when the star is strongly affected by tidal forces, as well as when it collides with large angular momentum. We discuss the implications that these results have for the potential observation of gravitational waves from these sources with future detectors.

  10. The evolution of massive stars

    International Nuclear Information System (INIS)

    Loore, C. de

    1980-01-01

    The evolution of stars with masses between 15 M 0 and 100 M 0 is considered. Stars in this mass range lose a considerable fraction of their matter during their evolution. The treatment of convection, semi-convection and the influence of mass loss by stellar winds at different evolutionary phases are analysed as well as the adopted opacities. Evolutionary sequences computed by various groups are examined and compared with observations, and the advanced evolution of a 15 M 0 and a 25 M 0 star from zero-age main sequence (ZAMS) through iron collapse is discussed. The effect of centrifugal forces on stellar wind mass loss and the influence of rotation on evolutionary models is examined. As a consequence of the outflow of matter deeper layers show up and when the mass loss rates are large enough layers with changed composition, due to interior nuclear reactions, appear on the surface. The evolution of massive close binaries as well during the phase of mass loss by stellar wind as during the mass exchange and mass loss phase due to Roche lobe overflow is treated in detail, and the value of the parameters governing mass and angular momentum losses are discussed. The problem of the Wolf-Rayet stars, their origin and the possibilities of their production either as single stars or as massive binaries is examined. Finally, the origin of X-ray binaries is discussed and the scenario for the formation of these objects (starting from massive ZAMS close binaries, through Wolf-Rayet binaries leading to OB-stars with a compact companion after a supernova explosion) is reviewed and completed, including stellar wind mass loss. (orig.)

  11. Low-mass stars with mass loss and low-luminosity carbon star formation

    International Nuclear Information System (INIS)

    Boothroyd, A.I.

    1987-01-01

    The effects of large carbon enrichments in static stellar envelopes were investigated, using new Los Alamos opacities (including low-temperature carbon and molecular opacities) and including carbon ionizations. To search for the production of low-mass,low-luminosity carbon stars, detailed stellar evolutionary computations were carried out for a grid of low-mass stars of two different metallicities. The stars were evolved from the main sequence through all intermediate stages and through helium-shell flashes on the asymptotic giant branch. The effects of the latest nuclear reaction rates, the new Los Alamos opacities, Reimers-type wind mass loss, and detailed treatment of convection and semi-convection were investigated. Two low-luminosity carbon stars were achieved, in excellent agreement with observations. Conditions favoring dredge-up (and thus carbon-star production) include a reasonably large convective mixing length, low metallicity, relatively large envelope mass, and high flash strength. Mass loss was of major importance, tending to oppose dredge-up; the total mass-loss amounts inferred from observations suffice to prevent formation of high-mass, high-luminosity carbon stars

  12. Halo Star Lithium Depletion

    International Nuclear Information System (INIS)

    Pinsonneault, M. H.; Walker, T. P.; Steigman, G.; Narayanan, Vijay K.

    1999-01-01

    The depletion of lithium during the pre-main-sequence and main-sequence phases of stellar evolution plays a crucial role in the comparison of the predictions of big bang nucleosynthesis with the abundances observed in halo stars. Previous work has indicated a wide range of possible depletion factors, ranging from minimal in standard (nonrotating) stellar models to as much as an order of magnitude in models that include rotational mixing. Recent progress in the study of the angular momentum evolution of low-mass stars permits the construction of theoretical models capable of reproducing the angular momentum evolution of low-mass open cluster stars. The distribution of initial angular momenta can be inferred from stellar rotation data in young open clusters. In this paper we report on the application of these models to the study of lithium depletion in main-sequence halo stars. A range of initial angular momenta produces a range of lithium depletion factors on the main sequence. Using the distribution of initial conditions inferred from young open clusters leads to a well-defined halo lithium plateau with modest scatter and a small population of outliers. The mass-dependent angular momentum loss law inferred from open cluster studies produces a nearly flat plateau, unlike previous models that exhibited a downward curvature for hotter temperatures in the 7Li-Teff plane. The overall depletion factor for the plateau stars is sensitive primarily to the solar initial angular momentum used in the calibration for the mixing diffusion coefficients. Uncertainties remain in the treatment of the internal angular momentum transport in the models, and the potential impact of these uncertainties on our results is discussed. The 6Li/7Li depletion ratio is also examined. We find that the dispersion in the plateau and the 6Li/7Li depletion ratio scale with the absolute 7Li depletion in the plateau, and we use observational data to set bounds on the 7Li depletion in main-sequence halo

  13. Convective shells and the core He-burning phase of massive stars

    Energy Technology Data Exchange (ETDEWEB)

    Chiosi, C [Padua Univ. (Italy). Ist. di Astronomia; Nasi, E [Osservatorio Astronomico, Padova, Italy

    1978-07-01

    In this paper the effect of complete homogenization in the intermediate unstable layers of massive stars is briefly discussed on the effective temperature of the core He-burning models. To this end, a 20 solar masses star of Population I chemical composition (X=0.700, Z=0.020) has been allowed to evolve from the Main Sequence into the core He-exhaustion stage without taking into account semiconvective mixing. The results show that the models are systematically bluer than those computed with the same physical parameters but with the inclusion of semiconvection.

  14. Magnetic fields and dense chromospheres in dMe stars

    International Nuclear Information System (INIS)

    Mullan, D.J.

    1975-01-01

    We examine in a semi-quantitative fashion the hypothesis that dense chromospheres of dMe stars are heated by dissipation of hydromagnetic waves. We propose that dMe stars are a set of magnetic stars on the lower main sequence, with strong fields presumably generated by dynamo action in deep convective envelopes. We discuss how the combination of magnetic fields and dense chromospheres in dMe stars provides a consistent interpretation of the following features: 1) The dMe stars which are most likely to be flares stars are those with hydrogen lines in emission. However, it is proposed that in certain conditions, Balmer lines may appear in absorption, and we suggest that 'negative flares' can be explained at least in part by the occurrence of strong absorption in Hα. 2) The propagation of flare-initiated coronal waves can trigger sympathetic stellar flares. 3) Apart from flare activity, emission line strengths in dMe stars must exhibit time variations due to the emergence of new magnetic flux ropes through the stellar surface. 4) The combination of strong magnetic fields with dense chromospheres makes the Faraday rotation measure large enough to have potentially a detectable effect on polarized visible light. 5) It is suggested that grain formation occurs in starspots on dMe stars. (orig./WL) [de

  15. AB Dor Moving Group Stars Resolved with the CHARA Array

    Science.gov (United States)

    Schaefer, G. H.; White, R. J.; Baines, E. K.; Boyajian, T. S.; ten Brummelaar, T. A.; Farrington, C. D.; Sturmann, J.; Sturmann, L.; Turner, N. H.

    2018-05-01

    We present interferometric measurements obtained with the CHARA Array of 13 adolescent-age stars in nearby moving groups. The motivation was to spatially resolve the largest stars and to search for binary companions. Nine stars have diameters smaller than the resolution limit and no evidence for companions within 0.5–50 mas and ΔH group, and former member HD 89744 (0.556 ± 0.032 mas). Combining the angular diameters with their distances and bolometric fluxes, we measured radii and effective temperatures. The temperatures of GJ 159 (6286 ± 123 K) and GJ 393 (3515 ± 68 K) are consistent with spectroscopic measurements. Comparisons with evolutionary models show that HD 89744 has evolved off the main sequence. GJ 159 and GJ 393 lie within 1.5σ of the zero-age main sequence, complicating their age estimates because it is unclear whether the stars are contracting or expanding. GJ 159 has a mass of 1.2 ± 0.1 {M}ȯ with an age spanning 0.021–3.0 Gyr. Its debris disk and lithium abundance favor a young age. GJ 393 has a mass of 0.42 ± 0.03 {M}ȯ and a lower limit on its age 0.06 Gyr. This overlaps with the age of the moving group; however, an older age would be more consistent with its slow rotation, low activity, and luminosity, suggesting that GJ 393 is a kinematic interloper.

  16. Magnetic fields in beta Cep, SPB, and Be stars

    OpenAIRE

    Schoeller, M.; Hubrig, S.; Briquet, M.; Ilyin, I.

    2013-01-01

    Recent observational and theoretical results emphasize the potential significance of magnetic fields for structure, evolution, and environment of massive stars. Depending on their spectral and photometric behavior, the upper main-sequence B-type stars are assigned to different groups, such as beta Cep stars and slowly pulsating B (SPB) stars, He-rich and He-deficient Bp stars, Be stars, BpSi stars, HgMn stars, or normal B-type stars. All these groups are characterized by different magnetic fi...

  17. On the Baldwin effect of He II emission lines in WR (WN) stars

    OpenAIRE

    van Gent, J. I.; Lamers, H. J. G. L. M.; de Koter, A.; Morris, P. W.

    2001-01-01

    We investigate the relation between the equivalent width of He ii emission lines and the monochromatic continuum luminosity at the line wavelength in the spectra of Wolf-Rayet stars. Model stellar atmospheres and spectra are used to show that the equivalent width inversely correlates with the monochromatic continuum luminosity. We find the effect in Wolf-Rayet star models over a large range of stellar parameters. The effect is shown to be connected to density differences among Wolf-Rayet star...

  18. New BVI C photometry of low-mass pleiades stars: Exploring the effects of rotation on broadband colors

    International Nuclear Information System (INIS)

    Kamai, Brittany L.; Stassun, Keivan G.; Vrba, Frederick J.; Stauffer, John R.

    2014-01-01

    We present new BVI C photometry for 350 Pleiades proper motion members with 9 < V ≲ 17. Importantly, our new catalog includes a large number of K- and early M-type stars, roughly doubling the number of low-mass stars with well-calibrated Johnson/Cousins photometry in this benchmark cluster. We combine our new photometry with existing photometry from the literature to define a purely empirical isochrone at Pleiades age (≈100 Myr) extending from V = 9 to 17. We use the empirical isochrone to identify 48 new probable binaries and 14 likely nonmembers. The photometrically identified single stars are compared against their expected positions in the color-magnitude diagram (CMD). At 100 Myr, the mid K and early M stars are predicted to lie above the zero-age main sequence (ZAMS) having not yet reached the ZAMS. We find in the B – V versus V CMD that mid K and early M dwarfs are instead displaced below (or blueward of) the ZAMS. Using the stars' previously reported rotation periods, we find a highly statistically significant correlation between rotation period and CMD displacement, in the sense that the more rapidly rotating stars have the largest displacements in the B – V CMD.

  19. The evolution of the Cepheid stars

    International Nuclear Information System (INIS)

    Chiosi, C.

    1990-01-01

    The evolution of intermediate and high mass stars is reviewed focusing on the interpretation of Pop I Cepheids. First, a summary is given of the classical results of stellar evolution theory for the main evolutionary phases (main sequence and core He-burning) all over the HR diagram, putting into evidence the various points of disagreement with current observational data. Second, models incorporating the effect of convective overshoot, are reviewed, and studies are presented on the rich, young clusters in the Large Magellanic Cloud, in which the models are compared with the observational data. Arguments are given to favor the adoption of models with convective overshoot instead of the classical ones. Third, new results are presented for pulsational models of the Cepheid stars, and the shape of the instability strip in the HR diagram, the number frequency-period distribution, and the mass discrepancy are discussed. 81 refs

  20. SImulator of GAlaxy Millimetre/submillimetre Emission (SIGAME): CO emission from massive z=2 main-sequence galaxies

    DEFF Research Database (Denmark)

    Olsen, Karen P.; Greve, Thomas R.; Brinch, Christian

    2016-01-01

    is condensed out of the hot and partly ionized SPH gas. The gas is subjected to far-UV radiation fields and cosmic ray ionization rates which are set to scale with the local star formation rate volume density. Level populations and radiative transport of the CO lines are solved with the 3D radiative transfer...... code lime. We have applied sígame to cosmological SPH simulations of three disc galaxies at z = 2 with stellar masses in the range ∼0.5–2 × 1011 M⊙ and star formation rates ∼40–140 M⊙ yr−1. Global CO luminosities and line ratios are in agreement with observations of disc galaxies at z ∼ 2 up.......5 and Cloud (GMC) mass spectrum does...

  1. Origin of faint blue stars

    International Nuclear Information System (INIS)

    Tutukov, A.; Iungelson, L.

    1987-01-01

    The origin of field faint blue stars that are placed in the HR diagram to the left of the main sequence is discussed. These include degenerate dwarfs and O and B subdwarfs. Degenerate dwarfs belong to two main populations with helium and carbon-oxygen cores. The majority of the hot subdwarfs most possibly are helium nondegenerate stars that are produced by mass exchange close binaries of moderate mass cores (3-15 solar masses). The theoretical estimates of the numbers of faint blue stars of different types brighter than certain stellar magnitudes agree with star counts based on the Palomar Green Survey. 28 references

  2. Kinematic and spatial distributions of barium stars - are the barium stars and Am stars related?

    International Nuclear Information System (INIS)

    Hakkila, J.

    1989-01-01

    The possibility of an evolutionary link between Am stars and barium stars is considered, and an examination of previous data suggests that barium star precursors are main-sequence stars of intermediate mass, are most likely A and/or F dwarfs, and are intermediate-mass binaries with close to intermediate orbital separations. The possible role of mass transfer in the later development of Am systems is explored. Mass transfer and loss from systems with a range of masses and orbital separations may explain such statistical peculiarities of barium stars as the large dispersion in absolute magnitude, the large range of elemental abundances from star to star, and the small number of stars with large peculiar velocities. 93 refs

  3. A particle dark matter footprint on the first generation of stars

    Energy Technology Data Exchange (ETDEWEB)

    Lopes, Ilídio [Centro Multidisciplinar de Astrofísica, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Silk, Joseph, E-mail: ilidio.lopes@ist.utl.pt, E-mail: silk@astro.ox.ac.uk [Institut d' Astrophysique de Paris, F-75014 Paris (France)

    2014-05-01

    Dark matter particles with properties identical to those of dark matter candidates hinted at by several international collaborations dedicated to the experimental detection of dark matter (DAMA, COGENT, CRESST, and CDMS-II, although not, most notably, by LUX), which also have a dark matter asymmetry that is identical to the observed baryon asymmetry (Planck and Wilkinson Microwave Anisotropy Probe), may produce a significant impact on the evolution of the first generation of low-metallicity stars. The lifetimes of these stars in different phases of stellar evolution are significantly extended, namely, in the pre-main sequence, main sequence, and red giant phases. In particular, intermediate-mass stars in the red giant phase experience significant changes in their luminosity and chemical composition. The annihilations of dark matter particles affect the interior of the star in such a way that the 3α reaction becomes less efficient in the production of carbon and oxygen. This dark matter effect contradicts the excess of carbon and other metals observed today in stars of low mass and low metallicity. Hence, we can impose an upper limit on the dark matter halo density, and therefore on the redshift, at which the first generation of low-metallicity stars formed.

  4. Variable extinction in HD 45677 and the evolution of dust grains in pre-main-sequence disks

    Science.gov (United States)

    Sitko, Michael L.; Halbedel, Elaine M.; Lawrence, Geoffrey F.; Smith, J. Allyn; Yanow, Ken

    1994-01-01

    Changes in the UV extinction and IR emission were sought in the Herbig Ae/Be star candidate HD 45677 (= FS CMa) by comparing UV, optical, and IR observations made approximately 10 yr apart. HD 45677 varied significantly, becoming more than 50% brighter in the UV and optical than it was a decade ago. A comparison of the observations between epochs indicates that if the variations are due to changes in dust obscuration, the dust acts as a gray absorber into the near-IR and must be depleted in grains smaller than 1 micron. This is similar to the results obtained on the circumstellar disks of stars like Vega and Beta Pic, and suggests that radiation pressure may be responsible for the small-grain depletion. In addition, the total IR flux seems to have declined, indicating a decrease in the total mass of the dust envelope that contributes to the IR emission in this part of the spectrum. Due to the anomalous nature of the extinction, the use of normal extinction curves to deredden the spectral energy distributions of stars with circumstellar dust may lead to significant errors and should be used with great caution.

  5. arXiv Dark Matter Effects On Neutron Star Properties

    CERN Document Server

    Ellis, John; Kannike, Kristjan; Marzola, Luca; Raidal, Martti; Vaskonen, Ville

    2018-06-14

    We study possible effects of a dark matter (DM) core on the maximum mass of a neutron star (NS), on the mass-radius relation and on the NS tidal deformability parameter $\\Lambda$. We show that all these quantities would in general be reduced in the presence of a DM core. In particular, our calculations indicate that the presence of a DM core with a mass fraction $\\sim 5\\%$ could affect significantly the interpretation of these NS data as constraints on the nuclear equation of state (EOS), potentially excluding some EOS models on the basis of the measured mass of PSR J0348+0432, while allowing other EOS models to become consistent with the LIGO/Virgo upper limit on $\\Lambda$. Specific scenarios for generating such DM cores are explored in an Appendix.

  6. Effects of stellar evolution and ionizing radiation on the environments of massive stars

    Science.gov (United States)

    Mackey, J.; Langer, N.; Mohamed, S.; Gvaramadze, V. V.; Neilson, H. R.; Meyer, D. M.-A.

    2014-09-01

    We discuss two important effects for the astrospheres of runaway stars: the propagation of ionizing photons far beyond the astropause, and the rapid evolution of massive stars (and their winds) near the end of their lives. Hot stars emit ionizing photons with associated photoheating that has a significant dynamical effect on their surroundings. 3-D simulations show that H ii regions around runaway O stars drive expanding conical shells and leave underdense wakes in the medium they pass through. For late O stars this feedback to the interstellar medium is more important than that from stellar winds. Late in life, O stars evolve to cool red supergiants more rapidly than their environment can react, producing transient circumstellar structures such as double bow shocks. This provides an explanation for the bow shock and linear bar-shaped structure observed around Betelgeuse.

  7. The Intrinsic Characteristics of Galaxies on the SFR–M ∗ Plane at 1.2 < z < 4: I. The Correlation between Stellar Age, Central Density, and Position Relative to the Main Sequence

    Science.gov (United States)

    Lee, Bomee; Giavalisco, Mauro; Whitaker, Katherine; Williams, Christina C.; Ferguson, Henry C.; Acquaviva, Viviana; Koekemoer, Anton M.; Straughn, Amber N.; Guo, Yicheng; Kartaltepe, Jeyhan S.; Lotz, Jennifer; Pacifici, Camilla; Croton, Darren J.; Somerville, Rachel S.; Lu, Yu

    2018-02-01

    We use the deep CANDELS observations in the GOODS North and South fields to revisit the correlations between stellar mass (M *), star formation rate (SFR) and morphology, and to introduce a fourth dimension, the mass-weighted stellar age, in galaxies at 1.2history for each galaxy. Like others, we find that the slope of the main sequence (MS) of star formation in the ({M}* ;{SFR}) plane bends at high mass. We observe clear morphological differences among galaxies across the MS, which also correlate with stellar age. At all redshifts, galaxies that are quenching or quenched, and thus old, have high {{{Σ }}}1 (the projected density within the central 1 kpc), while younger, star-forming galaxies span a much broader range of {{{Σ }}}1, which includes the high values observed for quenched galaxies, but also extends to much lower values. As galaxies age and quench, the stellar age and the dispersion of {{{Σ }}}1 for fixed values of M * shows two different regimes: one at the low-mass end, where quenching might be driven by causes external to the galaxies; the other at the high-mass end, where quenching is driven by internal causes, very likely the mass given the low scatter of {{{Σ }}}1 (mass quenching). We suggest that the monotonic increase of central density as galaxies grow is one manifestation of a more general phenomenon of structural transformation that galaxies undergo as they evolve.

  8. XMM-NEWTON MONITORING OF THE CLOSE PRE-MAIN-SEQUENCE BINARY AK SCO. EVIDENCE OF TIDE-DRIVEN FILLING OF THE INNER GAP IN THE CIRCUMBINARY DISK

    Energy Technology Data Exchange (ETDEWEB)

    Gomez de Castro, Ana Ines [S. D. Astronomia y Geodesia and Instituto de Matematica Interdisciplinar, Fac. de CC Matematicas, Universidad Complutense, E-28040 Madrid (Spain); Lopez-Santiago, Javier [Departamento de Astrofisica, Fac de CC Fisicas, Universidad Complutense, E-28040 Madrid (Spain); Talavera, Antonio [European Space Astronomy Center, Villanueva de la Canada, E-28691, Madrid (Spain); Sytov, A. Yu.; Bisikalo, D. [Institute of Astronomy of the Russian Academy of Sciences, Pyatnitskaya St. 48, 109017 Moscow (Russian Federation)

    2013-03-20

    AK Sco stands out among pre-main-sequence binaries because of its prominent ultraviolet excess, the high eccentricity of its orbit, and the strong tides driven by it. AK Sco consists of two F5-type stars that get as close as 11 R{sub *} at periastron passage. The presence of a dense (n{sub e} {approx} 10{sup 11} cm{sup -3}) extended envelope has been unveiled recently. In this article, we report the results from an XMM-Newton-based monitoring of the system. We show that at periastron, X-ray and UV fluxes are enhanced by a factor of {approx}3 with respect to the apastron values. The X-ray radiation is produced in an optically thin plasma with T {approx} 6.4 Multiplication-Sign 10{sup 6} K and it is found that the N{sub H} column density rises from 0.35 Multiplication-Sign 10{sup 21} cm{sup -2} at periastron to 1.11 Multiplication-Sign 10{sup 21} cm{sup -2} at apastron, in good agreement with previous polarimetric observations. The UV emission detected in the Optical Monitor band seems to be caused by the reprocessing of the high-energy magnetospheric radiation on the circumstellar material. Further evidence of the strong magnetospheric disturbances is provided by the detection of line broadening of 278.7 km s{sup -1} in the N V line with Hubble Space Telescope/Space Telescope Imaging Spectrograph. Numerical simulations of the mass flow from the circumbinary disk to the components have been carried out. They provide a consistent scenario with which to interpret AK Sco observations. We show that the eccentric orbit acts like a gravitational piston. At apastron, matter is dragged efficiently from the inner disk border, filling the inner gap and producing accretion streams that end as ring-like structures around each component of the system. At periastron, the ring-like structures come into contact, leading to angular momentum loss, and thus producing an accretion outburst.

  9. Finite size effects in neutron star and nuclear matter simulations

    Energy Technology Data Exchange (ETDEWEB)

    Giménez Molinelli, P.A., E-mail: pagm@df.uba.ar; Dorso, C.O.

    2015-01-15

    In this work we study molecular dynamics simulations of symmetric nuclear and neutron star matter using a semi-classical nucleon interaction model. Our aim is to gain insight on the nature of the so-called “finite size effects”, unavoidable in this kind of simulations, and to understand what they actually affect. To do so, we explore different geometries for the periodic boundary conditions imposed on the simulation cell: cube, hexagonal prism and truncated octahedron. For nuclear matter simulations we show that, at sub-saturation densities and low temperatures, the solutions are non-homogeneous structures reminiscent of the “nuclear pasta” phases expected in neutron star matter simulations, but only one structure per cell and shaped by specific artificial aspects of the simulations—for the same physical conditions (i.e. number density and temperature) different cells yield different solutions. The particular shape of the solution at low enough temperature and a given density can be predicted analytically by surface minimization. We also show that even if this behavior is due to the imposition of periodic boundary conditions on finite systems, this does not mean that it vanishes for very large systems, and it is actually independent of the system size. We conclude that, for nuclear matter simulations, the cells' size sets the only characteristic length scale for the inhomogeneities, and the geometry of the periodic cell determines the shape of those inhomogeneities. To model neutron star matter we add a screened Coulomb interaction between protons, and perform simulations in the three cell geometries. Our simulations indeed produce the well known nuclear pasta, with (in most cases) several structures per cell. However, we find that for systems not too large results are affected by finite size in different ways depending on the geometry of the cell. In particular, at the same certain physical conditions and system size, the hexagonal prism yields a

  10. A model of SNR evolution for an O-star in a cloudy ISM

    International Nuclear Information System (INIS)

    Shull, P. Jr.

    1988-01-01

    The authors present an analytical model of SNR evolution in a cloudy interstellar medium for a single progenitor star of spectral type 05 V. The model begins with the progenitor on the zero-age main sequence, includes the effects of the star's wind and ionizing photons, and ends with the SNR's assimilation by the ISM. The authors assume that the ISM consists of atomic clouds, molecular clouds, and a hot intercloud phase. The type of SNR that results bears a strong resemblance to N63A in the Large Magellanic Cloud

  11. The effect of the scalar-isovector meson field on hyperon-rich neutron star matter

    International Nuclear Information System (INIS)

    Mi, Aijun; Zuo, Wei; Li, Ang

    2008-01-01

    We investigate the effect of the scalar-isovector δ-meson field on the equation of state (EOS) and composition of hyperonic neutron star matter, and the properties of hyperonic neutron stars within the framework of the relativistic mean field theory. The influence of the δ-field turns out to be quite different and generally weaker for hyperonic neutron star matter as compared to that for npeμ neutron star matter. We find that inclusion of the δ-field enhances the strangeness content slightly and consequently moderately softens the EOS of neutron star matter in its hyperonic phase. As for the composition of hyperonic star matter, the effect of the δ-field is shown to shift the onset of the negatively-charged (positively-charged) hyperons to slightly lower (higher) densities and to enhance (reduce) their abundances. The influence of the δ-field on the maximum mass of hyperonic neutron stars is found to be fairly weak, whereas inclusion of the δ-field turns out to enhance sizably both the radii and the moments of inertia of neutron stars with given masses. It is also shown that the effects of the δ-field on the properties of hyperonic neutron stars remain similar in the case of switching off the Σ hyperons. (author)

  12. Effective field theory for quantum liquid in dwarf stars

    Energy Technology Data Exchange (ETDEWEB)

    Gabadadze, Gregory [Center for Cosmology and Particle Physics, Department of Physics, New York University, 4 Washington Place, New York, NY 10003 (United States); Rosen, Rachel A., E-mail: gg32@nyu.edu, E-mail: rarosen@physik.su.se [Oskar Klein Centre for Cosmoparticle Physics, Department of Physics, Stockholm University, AlbaNova, Roslagstullsbacken 21, SE - 106 91, Stockholm (Sweden)

    2010-04-01

    An effective field theory approach is used to describe quantum matter at greater-than-atomic but less-than-nuclear densities which are encountered in white dwarf stars. We focus on the density and temperature regime for which charged spin-0 nuclei form an interacting charged Bose-Einstein condensate, while the neutralizing electrons form a degenerate fermi gas. After a brief introductory review, we summarize distinctive properties of the charged condensate, such as a mass gap in the bosonic sector as well as gapless fermionic excitations. Charged impurities placed in the condensate are screened with great efficiency, greater than in an equivalent uncondensed plasma. We discuss a generalization of the Friedel potential which takes into account bosonic collective excitations in addition to the fermionic excitations. We argue that the charged condensate could exist in helium-core white dwarf stars and discuss the evolution of these dwarfs. Condensation would lead to a significantly faster rate of cooling than that of carbon- or oxygen-core dwarfs with crystallized cores. This prediction can be tested observationally: signatures of charged condensation may have already been seen in the recently discovered sequence of helium-core dwarfs in the nearby globular cluster NGC 6397. Sufficiently strong magnetic fields can penetrate the condensate within Abrikosov-like vortices. We find approximate analytic vortex solutions and calculate the values of the lower and upper critical magnetic fields at which vortices are formed and destroyed respectively. The lower critical field is within the range of fields observed in white dwarfs, but tends toward the higher end of this interval. This suggests that for a significant fraction of helium-core dwarfs, magnetic fields are entirely expelled within the core.

  13. Star Formation of Merging Disk Galaxies with AGN Feedback Effects

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jongwon; Smith, Rory; Yi, Sukyoung K., E-mail: jw.park@yonsei.ac.kr [Department of Astronomy and Yonsei University Observatory, Yonsei University, Seoul 03722 (Korea, Republic of)

    2017-08-20

    Using a numerical hydrodynamics code, we perform various idealized galaxy merger simulations to study the star formation (SF) of two merging disk galaxies. Our simulations include gas accretion onto supermassive black holes and active galactic nucleus (AGN) feedback. By comparing AGN simulations with those without AGNs, we attempt to understand when the AGN feedback effect is significant. Using ∼70 simulations, we investigate SF with the AGN effect in mergers with a variety of mass ratios, inclinations, orbits, galaxy structures, and morphologies. Using these merger simulations with AGN feedback, we measure merger-driven SF using the burst efficiency parameter introduced by Cox et al. We confirm previous studies which demonstrated that, in galaxy mergers, AGN suppresses SF more efficiently than in isolated galaxies. However, we also find that the effect of AGNs on SF is larger in major than in minor mergers. In minor merger simulations with different primary bulge-to-total ratios, the effect of bulge fraction on the merger-driven SF decreases due to AGN feedback. We create models of Sa-, Sb-, and Sc-type galaxies and compare their SF properties while undergoing mergers. With the current AGN prescriptions, the difference in merger-driven SF is not as pronounced as in the recent observational study of Kaviraj. We discuss the implications of this discrepancy.

  14. Star Formation of Merging Disk Galaxies with AGN Feedback Effects

    International Nuclear Information System (INIS)

    Park, Jongwon; Smith, Rory; Yi, Sukyoung K.

    2017-01-01

    Using a numerical hydrodynamics code, we perform various idealized galaxy merger simulations to study the star formation (SF) of two merging disk galaxies. Our simulations include gas accretion onto supermassive black holes and active galactic nucleus (AGN) feedback. By comparing AGN simulations with those without AGNs, we attempt to understand when the AGN feedback effect is significant. Using ∼70 simulations, we investigate SF with the AGN effect in mergers with a variety of mass ratios, inclinations, orbits, galaxy structures, and morphologies. Using these merger simulations with AGN feedback, we measure merger-driven SF using the burst efficiency parameter introduced by Cox et al. We confirm previous studies which demonstrated that, in galaxy mergers, AGN suppresses SF more efficiently than in isolated galaxies. However, we also find that the effect of AGNs on SF is larger in major than in minor mergers. In minor merger simulations with different primary bulge-to-total ratios, the effect of bulge fraction on the merger-driven SF decreases due to AGN feedback. We create models of Sa-, Sb-, and Sc-type galaxies and compare their SF properties while undergoing mergers. With the current AGN prescriptions, the difference in merger-driven SF is not as pronounced as in the recent observational study of Kaviraj. We discuss the implications of this discrepancy.

  15. Effect of the Curved Spacetime on the Electrostatic Potential Energy Distribution of Strange Stars

    Institute of Scientific and Technical Information of China (English)

    陈次星; 张家铝

    2001-01-01

    The effect of the strong gravitational field of the strange core of a strange star on its surface electrostatic potential energy distribution is discussed. We present the general-relativistic hydrodynamics equations of fluids in the presence of the electric fields and investigate the surface electrostatic potential distribution of the strange core of a strange star in hydrostatic equilibrium to correct Alcock and coworker's result [Astrophys. J. 310 (1986) 261]. Also, we discuss the temperature distribution of the bare strange star surface and give the related formulae, which may be useful if we are concerned further about the physical processes near the quark atter surfaces of strange stars.

  16. Abundance of lithium in Pleiades F stars

    International Nuclear Information System (INIS)

    Pilachowski, C.A.; Booth, J.; Hobbs, L.M.

    1987-01-01

    The abundance of lithium has been determined for 18 stars in the Pleiades cluster with spectral types from A7V to G0V. The pronounced dip in the lithium abundance among the mid-F stars which has been reported for other, older star clusters is not present in the Pleiades. The removal of lithium from the surfaces of middle-F dwarfs therefore occurs principally after about 100 Myr on the main sequence. 25 references

  17. Neutron stars with kaon condensation in relativistic effective model

    International Nuclear Information System (INIS)

    Wu, Chen; Ma, Yugang; Qian, Weiliang; Yang, Jifeng

    2013-01-01

    Relativistic mean-field theory with parameter sets FSUGold and IU-FSU is extended to study the properties of neutron star matter in β equilibrium by including Kaon condensation. The mixed phase of normal baryons and Kaon condensation cannot exist in neutron star matter for the FSUGold model and the IU-FSU model. In addition, it is found that when the optical potential of the K - in normal nuclear matter U K ≳ -100 MeV, the Kaon condensation phase is absent in the inner cores of the neutron stars. (author)

  18. A self-consistent study of magnetic field effects on hybrid stars

    International Nuclear Information System (INIS)

    Dexheimer, V; Franzon, B; Schramm, S

    2017-01-01

    It is understood that strong magnetic fields affect the structure of neutron stars. Nevertheless, many calculations for magnetized neutron stars are still being performed using symmetric solutions of Einstein’s equations. In this conference proceeding, we review why this is not the correct procedure and we also discuss the effects of magnetic fields on the stellar population and temperature profiles. (paper)

  19. Accuracy and efficiency in the binary star reflection effect

    International Nuclear Information System (INIS)

    Wilson, R.E.

    1990-01-01

    The geometric and irradiation heating problems for the binary star reflection effect theory are developed in terms of equipotential level surfaces and are sufficiently general so as to include eccentric orbits and nonsynchronous (even centrifugally limited) rotation and to treat multiple reflection. The requisite physics, mathematics, and logic are then presented and the computations are organized so that a given quantity is computed only as often as necessary, emphasizing the distinction between local surface quantities and aspect-related quantities. The local geometric, bolometric, and wavelength-specific quantities are grouped for storage according to how often they need to be recomputed. Some tests of a computer program based on this reflection model are given in the form of graphs in which program results are compared to a special exact case, and with results from an earlier program. The new program gives intuitively reasonable output for all tests, and the tests give an idea of how accurate the old program is, adopting the detailed reflection computations of the new program as a standard for comparison. A table is given which shows the convergence of the multiple reflection computations to a constant distribution of surface effective temperature. 11 refs

  20. Which of Kepler's Stars Flare?

    Science.gov (United States)

    Kohler, Susanna

    2017-12-01

    The habitability of distant exoplanets is dependent upon many factors one of which is the activity of their host stars. To learn about which stars are most likely to flare, a recent study examines tens of thousands of stellar flares observed by Kepler.Need for a Broader SampleArtists rendering of a flaring dwarf star. [NASAs Goddard Space Flight Center/S. Wiessinger]Most of our understanding of what causes a star to flare is based on observations of the only star near enough to examine in detail the Sun. But in learning from a sample size of one, a challenge arises: we must determine which conclusions are unique to the Sun (or Sun-like stars), and which apply to other stellar types as well.Based on observations and modeling, astronomers think that stellar flares result from the reconnection of magnetic field lines in a stars outer atmosphere, the corona. The magnetic activity is thought to be driven by a dynamo caused by motions in the stars convective zone.HR diagram of the Kepler stars, with flaring main-sequence (yellow), giant (red) and A-star (green) stars in the authors sample indicated. [Van Doorsselaere et al. 2017]To test whether these ideas are true generally, we need to understand what types of stars exhibit flares, and what stellar properties correlate with flaring activity. A team of scientists led by Tom Van Doorsselaere (KU Leuven, Belgium) has now used an enormous sample of flares observed by Kepler to explore these statistics.Intriguing TrendsVan Doorsselaere and collaborators used a new automated flare detection and characterization algorithm to search through the raw light curves from Quarter 15 of the Kepler mission, building a sample of 16,850 flares on 6,662 stars. They then used these to study the dependence of the flare occurrence rate, duration, energy, and amplitude on the stellar spectral type and rotation period.This large statistical study led the authors to several interesting conclusions, including:Flare star incidence rate as a a

  1. Effect of Population III Multiplicity on Dark Star Formation

    Science.gov (United States)

    Stacy, Athena; Pawlik, Andreas H.; Bromm, Volker; Loeb, Abraham

    2012-01-01

    We numerically study the mutual interaction between dark matter (DM) and Population III (Pop III) stellar systems in order to explore the possibility of Pop III dark stars within this physical scenario. We perform a cosmological simulation, initialized at z approx. 100, which follows the evolution of gas and DM. We analyze the formation of the first mini halo at z approx. 20 and the subsequent collapse of the gas to densities of 10(exp 12)/cu cm. We then use this simulation to initialize a set of smaller-scale 'cut-out' simulations in which we further refine the DM to have spatial resolution similar to that of the gas. We test multiple DM density profiles, and we employ the sink particle method to represent the accreting star-forming region. We find that, for a range of DM configurations, the motion of the Pop III star-disk system serves to separate the positions of the protostars with respect to the DM density peak, such that there is insufficient DM to influence the formation and evolution of the protostars for more than approx. 5000 years. In addition, the star-disk system causes gravitational scattering of the central DM to lower densities, further decreasing the influence of DM over time. Any DM-powered phase of Pop III stars will thus be very short-lived for the typical multiple system, and DM will not serve to significantly prolong the life of Pop III stars.

  2. Star formation is boosted (and quenched) from the inside-out: radial star formation profiles from MaNGA

    Science.gov (United States)

    Ellison, Sara L.; Sánchez, Sebastian F.; Ibarra-Medel, Hector; Antonio, Braulio; Mendel, J. Trevor; Barrera-Ballesteros, Jorge

    2018-02-01

    The tight correlation between total galaxy stellar mass and star formation rate (SFR) has become known as the star-forming main sequence. Using ˜487 000 spaxels from galaxies observed as part of the Sloan Digital Sky Survey Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, we confirm previous results that a correlation also exists between the surface densities of star formation (ΣSFR) and stellar mass (Σ⋆) on kpc scales, representing a `resolved' main sequence. Using a new metric (ΔΣSFR), which measures the relative enhancement or deficit of star formation on a spaxel-by-spaxel basis relative to the resolved main sequence, we investigate the SFR profiles of 864 galaxies as a function of their position relative to the global star-forming main sequence (ΔSFR). For galaxies above the global main sequence (positive ΔSFR) ΔΣSFR is elevated throughout the galaxy, but the greatest enhancement in star formation occurs at small radii (<3 kpc, or 0.5Re). Moreover, galaxies that are at least a factor of 3 above the main sequence show diluted gas phase metallicities out to 2Re, indicative of metal-poor gas inflows accompanying the starbursts. For quiescent/passive galaxies that lie at least a factor of 10 below the star-forming main sequence, there is an analogous deficit of star formation throughout the galaxy with the lowest values of ΔΣSFR in the central 3 kpc. Our results are in qualitative agreement with the `compaction' scenario in which a central starburst leads to mass growth in the bulge and may ultimately precede galactic quenching from the inside-out.

  3. 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.

  4. Star formation history: Modeling of visual binaries

    Science.gov (United States)

    Gebrehiwot, Y. M.; Tessema, S. B.; Malkov, O. Yu.; Kovaleva, D. A.; Sytov, A. Yu.; Tutukov, A. V.

    2018-05-01

    Most stars form in binary or multiple systems. Their evolution is defined by masses of components, orbital separation and eccentricity. In order to understand star formation and evolutionary processes, it is vital to find distributions of physical parameters of binaries. We have carried out Monte Carlo simulations in which we simulate different pairing scenarios: random pairing, primary-constrained pairing, split-core pairing, and total and primary pairing in order to get distributions of binaries over physical parameters at birth. Next, for comparison with observations, we account for stellar evolution and selection effects. Brightness, radius, temperature, and other parameters of components are assigned or calculated according to approximate relations for stars in different evolutionary stages (main-sequence stars, red giants, white dwarfs, relativistic objects). Evolutionary stage is defined as a function of system age and component masses. We compare our results with the observed IMF, binarity rate, and binary mass-ratio distributions for field visual binaries to find initial distributions and pairing scenarios that produce observed distributions.

  5. The effect of Livermore OPAL opacities on the evolutionary masses of RR Lyrae stars

    Science.gov (United States)

    Yi, Sukyoung; Lee, Young-Wook; Demarque, Pierre

    1993-01-01

    We have investigated the effect of the new Livermore OPAL opacities on the evolution of horizontal-branch (HB) stars. This work was motivated by the recent stellar pulsation calculations using the new Livermore opacities, which suggest that the masses of double-mode RR Lyrae stars are 0.1-0.2 solar mass larger than those based on earlier opacities. Unlike the pulsation calculations, we find that the effect of opacity change on the evolution of HB stars is not significant. In particular, the effect of the mean masses of RR Lyrae stars is very small, showing a decrease of only 0.01-0.02 solar mass compared to the models based on old Cox-Stewart opacities. Consequently, with the new Livermore OPAL opacities, both the stellar pulsation and evolution models now predict approximately the same masses for the RR Lyrae stars. Our evolutionary models suggest that the mean masses of the RR Lyrae stars are about 0.76 and about 0.71 solar mass for M15 (Oosterhoff group II) and M3 (group I), respectively. If (alpha/Fe) = 0.4, these values are decreased by about 0.03 solar mass. Variations of the mean masses of RR Lyrae stars with HB morphology and metallicity are also presented.

  6. EVIDENCE FOR GRANULATION IN EARLY A-TYPE STARS

    International Nuclear Information System (INIS)

    Kallinger, Thomas; Matthews, Jaymie M.

    2010-01-01

    Stars with spectral types earlier than about F0 on (or close) to the main sequence have long been believed to lack observable surface convection, although evolutionary models of A-type stars do predict very thin surface convective zones. We present evidence for granulation in two δ Scuti stars of spectral type A2: HD 174936 and HD 50844. Recent analyses of space-based CoRoT data revealed up to some 1000 frequencies in the photometry of these stars. The frequencies were interpreted as individual pulsation modes. If true, there must be large numbers of nonradial modes of very high degree l which should suffer cancellation effects in disk-integrated photometry (even of high space-based precision). The p-mode interpretation of all the frequencies in HD 174936 and HD 50844 depends on the assumption of white (frequency-independent) noise. Our independent analyses of the data provide an alternative explanation: most of the peaks in the Fourier spectra are the signature of non-white granulation background noise, and less than about 100 of the frequencies are actual stellar p-modes in each star. We find granulation timescales which are consistent with scaling relations that describe cooler stars with known surface convection. If the granulation interpretation is correct, the hundreds of low-amplitude Fourier peaks reported in recent studies are falsely interpreted as independent pulsation modes and a significantly lower number of frequencies are associated with pulsation, consistent with only modes of low degree.

  7. LUMINOSITY DISCREPANCY IN THE EQUAL-MASS, PRE-MAIN-SEQUENCE ECLIPSING BINARY PAR 1802: NON-COEVALITY OR TIDAL HEATING?

    International Nuclear Information System (INIS)

    Gómez Maqueo Chew, Yilen; Stassun, Keivan G.; Hebb, Leslie; Prša, Andrej; Stempels, Eric; Barnes, Rory; Heller, René; Mathieu, Robert D.

    2012-01-01

    Parenago 1802, a member of the ∼1 Myr Orion Nebula Cluster, is a double-lined, detached eclipsing binary in a 4.674 day orbit, with equal-mass components (M 2 /M 1 = 0.985 ± 0.029). Here we present extensive VI C JHK S light curves (LCs) spanning ∼15 yr, as well as a Keck/High Resolution Echelle Spectrometer (HIRES) optical spectrum. The LCs evince a third light source that is variable with a period of 0.73 days, and is also manifested in the high-resolution spectrum, strongly indicating the presence of a third star in the system, probably a rapidly rotating Classical T Tauri star. We incorporate this third light into our radial velocity and LC modeling of the eclipsing pair, measuring accurate masses (M 1 = 0.391 ± 0.032 and M 2 = 0.385 ± 0.032 M ☉ ), radii (R 1 = 1.73 ± 0.02 and R 2 = 1.62 ± 0.02 R ☉ ), and temperature ratio (T eff,1 /T eff,2 = 1.0924 ± 0.0017). Thus, the radii of the eclipsing stars differ by 6.9% ± 0.8%, the temperatures differ by 9.2% ± 0.2%, and consequently the luminosities differ by 62% ± 3%, despite having masses equal to within 3%. This could be indicative of an age difference of ∼3 × 10 5 yr between the two eclipsing stars, perhaps a vestige of the binary formation history. We find that the eclipsing pair is in an orbit that has not yet fully circularized, e = 0.0166 ± 0.003. In addition, we measure the rotation rate of the eclipsing stars to be 4.629 ± 0.006 days; they rotate slightly faster than their 4.674 day orbit. The non-zero eccentricity and super-synchronous rotation suggest that the eclipsing pair should be tidally interacting, so we calculate the tidal history of the system according to different tidal evolution theories. We find that tidal heating effects can explain the observed luminosity difference of the eclipsing pair, providing an alternative to the previously suggested age difference.

  8. LUMINOSITY DISCREPANCY IN THE EQUAL-MASS, PRE-MAIN-SEQUENCE ECLIPSING BINARY PAR 1802: NON-COEVALITY OR TIDAL HEATING?

    Energy Technology Data Exchange (ETDEWEB)

    Gomez Maqueo Chew, Yilen; Stassun, Keivan G.; Hebb, Leslie [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Prsa, Andrej [Department of Astronomy and Astrophysics, Villanova University, Villanova, PA 19085 (United States); Stempels, Eric [Department of Astronomy and Space Physics, Uppsala University, SE-752 67 Uppsala (Sweden); Barnes, Rory [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States); Heller, Rene [Leibniz-Institut fuer Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam (Germany); Mathieu, Robert D., E-mail: yilen.gomez@vanderbilt.edu [Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706 (United States)

    2012-01-20

    Parenago 1802, a member of the {approx}1 Myr Orion Nebula Cluster, is a double-lined, detached eclipsing binary in a 4.674 day orbit, with equal-mass components (M{sub 2}/M{sub 1} = 0.985 {+-} 0.029). Here we present extensive VI{sub C} JHK{sub S} light curves (LCs) spanning {approx}15 yr, as well as a Keck/High Resolution Echelle Spectrometer (HIRES) optical spectrum. The LCs evince a third light source that is variable with a period of 0.73 days, and is also manifested in the high-resolution spectrum, strongly indicating the presence of a third star in the system, probably a rapidly rotating Classical T Tauri star. We incorporate this third light into our radial velocity and LC modeling of the eclipsing pair, measuring accurate masses (M{sub 1} = 0.391 {+-} 0.032 and M{sub 2} = 0.385 {+-} 0.032 M{sub Sun }), radii (R{sub 1} = 1.73 {+-} 0.02 and R{sub 2} = 1.62 {+-} 0.02 R{sub Sun }), and temperature ratio (T{sub eff,1}/T{sub eff,2} = 1.0924 {+-} 0.0017). Thus, the radii of the eclipsing stars differ by 6.9% {+-} 0.8%, the temperatures differ by 9.2% {+-} 0.2%, and consequently the luminosities differ by 62% {+-} 3%, despite having masses equal to within 3%. This could be indicative of an age difference of {approx}3 Multiplication-Sign 10{sup 5} yr between the two eclipsing stars, perhaps a vestige of the binary formation history. We find that the eclipsing pair is in an orbit that has not yet fully circularized, e = 0.0166 {+-} 0.003. In addition, we measure the rotation rate of the eclipsing stars to be 4.629 {+-} 0.006 days; they rotate slightly faster than their 4.674 day orbit. The non-zero eccentricity and super-synchronous rotation suggest that the eclipsing pair should be tidally interacting, so we calculate the tidal history of the system according to different tidal evolution theories. We find that tidal heating effects can explain the observed luminosity difference of the eclipsing pair, providing an alternative to the previously suggested age

  9. Effects of Neutron-Star Dynamic Tides on Gravitational Waveforms within the Effective-One-Body Approach.

    Science.gov (United States)

    Hinderer, Tanja; Taracchini, Andrea; Foucart, Francois; Buonanno, Alessandra; Steinhoff, Jan; Duez, Matthew; Kidder, Lawrence E; Pfeiffer, Harald P; Scheel, Mark A; Szilagyi, Bela; Hotokezaka, Kenta; Kyutoku, Koutarou; Shibata, Masaru; Carpenter, Cory W

    2016-05-06

    Extracting the unique information on ultradense nuclear matter from the gravitational waves emitted by merging neutron-star binaries requires robust theoretical models of the signal. We develop a novel effective-one-body waveform model that includes, for the first time, dynamic (instead of only adiabatic) tides of the neutron star as well as the merger signal for neutron-star-black-hole binaries. We demonstrate the importance of the dynamic tides by comparing our model against new numerical-relativity simulations of nonspinning neutron-star-black-hole binaries spanning more than 24 gravitational-wave cycles, and to other existing numerical simulations for double neutron-star systems. Furthermore, we derive an effective description that makes explicit the dependence of matter effects on two key parameters: tidal deformability and fundamental oscillation frequency.

  10. Effects of Neutron-Star Dynamic Tides on Gravitational Waveforms within the Effective-One-Body Approach

    Science.gov (United States)

    Hinderer, Tanja; Taracchini, Andrea; Foucart, Francois; Buonanno, Alessandra; Steinhoff, Jan; Duez, Matthew; Kidder, Lawrence E.; Pfeiffer, Harald P.; Scheel, Mark A.; Szilagyi, Bela; Hotokezaka, Kenta; Kyutoku, Koutarou; Shibata, Masaru; Carpenter, Cory W.

    2016-05-01

    Extracting the unique information on ultradense nuclear matter from the gravitational waves emitted by merging neutron-star binaries requires robust theoretical models of the signal. We develop a novel effective-one-body waveform model that includes, for the first time, dynamic (instead of only adiabatic) tides of the neutron star as well as the merger signal for neutron-star-black-hole binaries. We demonstrate the importance of the dynamic tides by comparing our model against new numerical-relativity simulations of nonspinning neutron-star-black-hole binaries spanning more than 24 gravitational-wave cycles, and to other existing numerical simulations for double neutron-star systems. Furthermore, we derive an effective description that makes explicit the dependence of matter effects on two key parameters: tidal deformability and fundamental oscillation frequency.

  11. Advanced evolution of a 15 solar mass star

    International Nuclear Information System (INIS)

    Endal, A.S.

    1974-01-01

    The evolution of a 15 solar mass star has been followed from the zero-age main sequence to the neon-ignition phase by use of the Henyey method for solving the equations of quasi-hydrostatic evolution. The detailed results of nucleosynthesis during carbon burning were calculated by a second-order, backwards-differencing scheme, with the effects of convection included in an approximate manner. The results of the evolution calculations and of the nucleosynthesis calculations are described and a detailed analysis of the effects of convection on nucleosynthesis is presented. The quiescent nature of evolution through the hydrogen, helium, and carbon burning stages is confirmed. Comparison with previous studies of the post-carbon burning evolution of massive stars shows that calculations in which degeneracy is neglected will not yield realistic results

  12. The ionisation parameter of star-forming galaxies evolves with the specific star formation rate

    Science.gov (United States)

    Kaasinen, Melanie; Kewley, Lisa; Bian, Fuyan; Groves, Brent; Kashino, Daichi; Silverman, John; Kartaltepe, Jeyhan

    2018-04-01

    We investigate the evolution of the ionisation parameter of star-forming galaxies using a high-redshift (z ˜ 1.5) sample from the FMOS-COSMOS survey and matched low-redshift samples from the Sloan Digital Sky Survey. By constructing samples of low-redshift galaxies for which the stellar mass (M*), star formation rate (SFR) and specific star formation rate (sSFR) are matched to the high-redshift sample we remove the effects of an evolution in these properties. We also account for the effect of metallicity by jointly constraining the metallicity and ionisation parameter of each sample. We find an evolution in the ionisation parameter for main-sequence, star-forming galaxies and show that this evolution is driven by the evolution of sSFR. By analysing the matched samples as well as a larger sample of z physically consistent with the definition of the ionisation parameter, a measure of the hydrogen ionising photon flux relative to the number density of hydrogen atoms.

  13. Paradoxical gap in the relative ages of T Tauri stars

    International Nuclear Information System (INIS)

    Weaer, W.B.

    1984-01-01

    The frequency distribution of T Tauri stars of different Youth (relative age) shows a pronounced gap at 5% of their time to the zero-age main sequence. This gap, which occurs in all of the four major T Tauri associations, is too large to be filled by unclassifiable veiled stars. It is nearly vertical on the Hertzsprung-Russell diagram, is centered near spectral class K5, and lies close to the transition between the convective and radiative tracks of the pre-main-sequence stars

  14. Revolution evolution: tracing angular momentum during star and planetary system formation

    Science.gov (United States)

    Davies, Claire Louise

    2015-04-01

    Stars form via the gravitational collapse of molecular clouds during which time the protostellar object contracts by over seven orders of magnitude. If all the angular momentum present in the natal cloud was conserved during collapse, stars would approach rotational velocities rapid enough to tear themselves apart within just a few Myr. In contrast to this, observations of pre-main sequence rotation rates are relatively slow (∼ 1 - 15 days) indicating that significant quantities of angular momentum must be removed from the star. I use observations of fully convective pre-main sequence stars in two well-studied, nearby regions of star formation (namely the Orion Nebula Cluster and Taurus-Auriga) to determine the removal rate of stellar angular momentum. I find the accretion disc-hosting stars to be rotating at a slower rate and contain less specific angular momentum than the disc-less stars. I interpret this as indicating a period of accretion disc-regulated angular momentum evolution followed by near-constant rotational evolution following disc dispersal. Furthermore, assuming that the age spread inferred from the Hertzsprung-Russell diagram constructed for the star forming region is real, I find that the removal rate of angular momentum during the accretion-disc hosting phase to be more rapid than that expected from simple disc-locking theory whereby contraction occurs at a fixed rotation period. This indicates a more efficient process of angular momentum removal must operate, most likely in the form of an accretion-driven stellar wind or outflow emanating from the star-disc interaction. The initial circumstellar envelope that surrounds a protostellar object during the earliest stages of star formation is rotationally flattened into a disc as the star contracts. An effective viscosity, present within the disc, enables the disc to evolve: mass accretes inwards through the disc and onto the star while momentum migrates outwards, forcing the outer regions of the

  15. Dynamics of H II regions around exiled O stars

    Science.gov (United States)

    Mackey, Jonathan; Langer, Norbert; Gvaramadze, Vasilii V.

    2013-11-01

    At least 25 per cent of massive stars are ejected from their parent cluster, becoming runaways or exiles, travelling with often-supersonic space velocities through the interstellar medium (ISM). Their overpressurized H II regions impart kinetic energy and momentum to the ISM, compress and/or evaporate dense clouds, and can constrain properties of both the star and the ISM. Here, we present one-, two- and (the first) three-dimensional simulations of the H II region around a massive star moving supersonically through a uniform, magnetized ISM, with properties appropriate for the nearby O star ζ Oph. The H II region leaves an expanding overdense shell behind the star and, inside this, an underdense wake that should be filled with hot gas from the shocked stellar wind. The gas column density in the shell is strongly influenced by the ISM magnetic field strength and orientation. Hα emission maps show that H II region remains roughly circular, although the star is displaced somewhat from the centre of emission. For our model parameters, the kinetic energy feedback from the H II region is comparable to the mechanical luminosity of the stellar wind, and the momentum feedback rate is >100 times larger than that from the wind and ≈10 times larger than the total momentum input rate available from radiation pressure. Compared to the star's eventual supernova explosion, the kinetic energy feedback from the H II region over the star's main-sequence lifetime is >100 times less, but the momentum feedback is up to 4 times larger. H II region dynamics are found to have only a small effect on the ISM conditions that a bow shock close to the star would encounter.

  16. Symmetry Energy Effects in the Neutron Star Properties

    Science.gov (United States)

    Alvarez-Castillo, D. E.; Kubis, S.

    2012-12-01

    The functional form of the nuclear symmetry energy has only been determined in a very narrow range of densities. Uncertainties concern both the low as well as the high density behaviour of this function. In this work different shapes of the symmetry energy, consistent with the experimental data, were introduced and their consequences for the crustal properties of neutron stars are presented. The resulting models are in agreement with astrophysical observations.

  17. Structural Parameters of Star Clusters: Signal to Noise Effects

    Directory of Open Access Journals (Sweden)

    Narbutis D.

    2015-09-01

    Full Text Available We study the impact of photometric signal to noise on the accuracy of derived structural parameters of unresolved star clusters using MCMC model fitting techniques. Star cluster images were simulated as a smooth surface brightness distribution following a King profile convolved with a point spread function. The simulation grid was constructed by varying the levels of sky background and adjusting the cluster’s flux to a specified signal to noise. Poisson noise was introduced to a set of cluster images with the same input parameters at each node of the grid. Model fitting was performed using “emcee” algorithm. The presented posterior distributions of the parameters illustrate their uncertainty and degeneracies as a function of signal to noise. By defining the photometric aperture containing 80% of the cluster’s flux, we find that in all realistic sky background level conditions a signal to noise ratio of ~50 is necessary to constrain the cluster’s half-light radius to an accuracy better than ~20%. The presented technique can be applied to synthetic images simulating various observations of extragalactic star clusters.

  18. Polarimetry of the T Tau and Ae/Be Herbig stars

    Energy Technology Data Exchange (ETDEWEB)

    Bergner, Yu K; Miroshnichenko, A S; Yudin, R V; Yutanov, N Yu; Dzhakuseva, K G; Mukanov, D B

    1987-03-01

    The results of polarimetric observations of stars suspected to be at the Pre-Main-Sequence stage are given. Simple phenomenological models of circumstellar shells are proposed for interpretation of the observed polarization variations.

  19. A fitting LEGACY – modelling Kepler's best stars

    Directory of Open Access Journals (Sweden)

    Aarslev Magnus J.

    2017-01-01

    Full Text Available The LEGACY sample represents the best solar-like stars observed in the Kepler mission[5, 8]. The 66 stars in the sample are all on the main sequence or only slightly more evolved. They each have more than one year's observation data in short cadence, allowing for precise extraction of individual frequencies. Here we present model fits using a modified ASTFIT procedure employing two different near-surface-effect corrections, one by Christensen-Dalsgaard[4] and a newer correction proposed by Ball & Gizon[1]. We then compare the results obtained using the different corrections. We find that using the latter correction yields lower masses and significantly lower χ2 values for a large part of the sample.

  20. Effects of a new 3-alpha reaction on the s-process in massive stars

    International Nuclear Information System (INIS)

    Kikuch, Yukihiro; Ono, Masaomi; Matsuo, Yasuhide; Hashimoto, Masa-aki; Fujimoto, Shin-ichiro

    2012-01-01

    Effect of a new 3-alpha reaction rate on the s-process during the evolution of a massive star of 25 solar mass is investigated for the first time, because the s-process in massive stars have been believed to be established with only minor change. We find that the s-process with use of the new rate during the core helium burning is very inefficient compared to the case with the previous 3-alpha rate. However, the difference of the overproduction is found to be largely compensated by the subsequent carbon burning. Since the s-process in massive stars has been attributed so far to the neutron irradiation during core helium burning, our finding reveals for the first time the importance of the carbon burning for the s-process during the evolution of massive stars.

  1. EXPLANATION OF A SPECIAL COLOR–MAGNITUDE DIAGRAM OF STAR CLUSTER NGC 1651 FROM DIFFERENT MODELS

    International Nuclear Information System (INIS)

    Li, Zhongmu; Mao, Caiyan; Chen, Li

    2015-01-01

    The color–magnitude diagram (CMD) of globular cluster NGC 1651 has special structures including a broad main sequence, an extended main sequence turn-off, and an extended red giant clump. The reason for such a special CMD remains unclear. In order to test the difference among the results from various stellar population assumptions, we study a high-quality CMD of NGC 1651 from the Hubble Space Telescope archive using eight kinds of models. Distance modulus, extinction, age ranges, star formation mode, fraction of binaries, and fraction of rotational stars are determined and then compared. The results show that stellar populations both with and without age spread can reproduce the special structure of the observed CMD. A composite population with extended star formation from 1.8 Gyrs ago to 1.4 Gyrs ago, which contains 50% binaries and 70% rotational stars, fits the observed CMD best. Meanwhile, a 1.5 Gyr-old simple population that consists of rotational stars can also fit the observed CMD well. The results of CMD fitting are shown to depend strongly on stellar population type (simple or composite), and fraction of rotators. If the member stars of NGC 1651 formed in a single star burst, the effect of stellar rotation should be very important for explaining the observed CMDs. Otherwise, the effect may be small. It is also possible that the special observed CMD is a result of the combined effects of stellar binarity, rotation, and age spread. Therefore, further work on stellar population type and fraction of rotational stars of intermediate-age clusters are necessary to understand their observed CMDs

  2. X-ray sources in regions of star formation. I. The naked T Tauri stars

    International Nuclear Information System (INIS)

    Walter, F.M.

    1986-01-01

    Einstein X-ray observations of regions of active star formation in Taurus, Ophiuchus, and Corona Australis show a greatly enhanced surface density of stellar X-ray sources over that seen in other parts of the sky. Many of the X-ray sources are identified with low-mass, pre-main-sequence stars which are not classical T Tauri stars. The X-ray, photometric, and spectroscopic data for these stars are discussed. Seven early K stars in Oph and CrA are likely to be 1-solar-mass post-T Tauri stars with ages of 10-million yr. The late K stars in Taurus are not post-T Tauri, but naked T Tauri stars, which are coeval with the T Tauri stars, differing mainly in the lack of a circumstellar envelope. 72 references

  3. Effect of nuclear stars gravity on quasar radiation feedback on the parsec-scale

    Science.gov (United States)

    Yang, Xiao-Hong; Bu, De-Fu

    2018-05-01

    It is often suggested that a super massive black hole is embedded in a nuclear bulge of size of a few 102 parsec . The nuclear stars gravity is not negligible near ˜10parsec. In order to study the effect of nuclear stars gravity on quasar radiation feedback on the parsec scale, we have simulated the parsec scale flows irradiated by a quasar by taking into account the gravitational potential of both the black hole and the nuclear star cluster. We find that the effect of nuclear stars gravity on the parsec-scale flows is related to the fraction of X-ray photons in quasar radiation. For the models in which the fraction of X-ray photons is not small (e.g. the X-ray photons contribute to 20% of the quasar radiation), the nuclear stars gravity is very helpful to collimate the outflows driven by UV photons, significantly weakens the outflow power at the outer boundary and significantly enhances the net accretion rate onto the black hole. For the models in which X-ray photons are significantly decreased (e.g. the X-ray photons contribute to 5% of the quasar radiation), the nuclear stars gravity can just slightly change properties of outflow and slightly enhance the net accretion rate onto the black hole.

  4. Understanding young stars - A history

    International Nuclear Information System (INIS)

    Stahler, S.W.

    1988-01-01

    The history of pre-main-sequence theory is briefly reviewed. The paper of Henyey et al. (1955) is seen as an important transitional work, one which abandoned previous simplifying assumptions yet failed to incorporate newer insights into the surface structure of late-type stars. The subsequent work of Hayashi and his contemporaries is outlined, with an emphasis on the underlying physical principles. Finally, the recent impact of protostar theory is discussed, and speculations are offered on future developments. 56 references

  5. Neutron stars

    International Nuclear Information System (INIS)

    Irvine, J.M.

    1978-01-01

    The subject is covered in chapters entitled: introduction (resume of stellar evolution, gross characteristics of neutron stars); pulsars (pulsar characteristics, pulsars as neutron stars); neutron star temperatures (neutron star cooling, superfluidity and superconductivity in neutron stars); the exterior of neutron stars (the magnetosphere, the neutron star 'atmosphere', pulses); neutron star structure; neutron star equations of state. (U.K.)

  6. Rotational studies of late-type stars. II. Ages of solar-type stars and the rotational history of the sun

    International Nuclear Information System (INIS)

    Soderblom, D.R.

    1983-01-01

    In the first part of this investigation, age indicators for solar-type stars are discussed. A Li abundance-age calibration is derived; it indicates that 1 M/sub sun/ stars have lost as much as 80% of their initial Li before reaching the main sequence. The e-folding time for Li depletion on the main sequence is 1 1/4 Gyr. The distribution of Li abundances for 1 M/sub sun/ stars is consistent with a uniform initial Li abundance for all stars

  7. Systematic Analysis of the Effects of Mode Conversion on Thermal Radiation from Neutron Stars

    Science.gov (United States)

    Yatabe, Akihiro; Yamada, Shoichi

    2017-12-01

    In this paper, we systematically calculate the polarization in soft X-rays emitted from magnetized neutron stars, which are expected to be observed by next-generation X-ray satellites. Magnetars are one of the targets for these observations. This is because thermal radiation is normally observed in the soft X-ray band, and it is thought to be linearly polarized because of different opacities for two polarization modes of photons in the magnetized atmosphere of neutron stars and the dielectric properties of the vacuum in strong magnetic fields. In their study, Taverna et al. illustrated how strong magnetic fields influence the behavior of the polarization observables for radiation propagating in vacuo without addressing a precise, physical emission model. In this paper, we pay attention to the conversion of photon polarization modes that can occur in the presence of an atmospheric layer above the neutron star surface, computing the polarization angle and fraction and systematically changing the magnetic field strength, radii of the emission region, temperature, mass, and radii of the neutron stars. We confirmed that if plasma is present, the effects of mode conversion cannot be neglected when the magnetic field is relatively weak, B∼ {10}13 {{G}}. Our results indicate that strongly magnetized (B≳ {10}14 {{G}}) neutron stars are suitable to detect polarizations, but not-so-strongly magnetized (B∼ {10}13 {{G}}) neutron stars will be the ones to confirm the mode conversion.

  8. MASS TRANSPORT AND TURBULENCE IN GRAVITATIONALLY UNSTABLE DISK GALAXIES. II. THE EFFECTS OF STAR FORMATION FEEDBACK

    Energy Technology Data Exchange (ETDEWEB)

    Goldbaum, Nathan J. [National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, 1205 W. Clark St., Urbana, IL 61801 (United States); Krumholz, Mark R. [Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2601 (Australia); Forbes, John C., E-mail: ngoldbau@illinois.edu [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

    2016-08-10

    Self-gravity and stellar feedback are capable of driving turbulence and transporting mass and angular momentum in disk galaxies, but the balance between them is not well understood. In the previous paper in this series, we showed that gravity alone can drive turbulence in galactic disks, regulate their Toomre Q parameters to ∼1, and transport mass inwards at a rate sufficient to fuel star formation in the centers of present-day galaxies. In this paper we extend our models to include the effects of star formation feedback. We show that feedback suppresses galaxies’ star formation rates by a factor of ∼5 and leads to the formation of a multi-phase atomic and molecular interstellar medium. Both the star formation rate and the phase balance produced in our simulations agree well with observations of nearby spirals. After our galaxies reach steady state, we find that the inclusion of feedback actually lowers the gas velocity dispersion slightly compared to the case of pure self-gravity, and also slightly reduces the rate of inward mass transport. Nevertheless, we find that, even with feedback included, our galactic disks self-regulate to Q ∼ 1, and transport mass inwards at a rate sufficient to supply a substantial fraction of the inner disk star formation. We argue that gravitational instability is therefore likely to be the dominant source of turbulence and transport in galactic disks, and that it is responsible for fueling star formation in the inner parts of galactic disks over cosmological times.

  9. The effective temperatures and colours of G and K stars

    International Nuclear Information System (INIS)

    Bell, R.A.; Gustafsson, B.

    1989-01-01

    Temperature scales are found for G and K dwarf and giant stars, using new tables of synthetic infrared colours as well as the infrared flux ratio method. The temperatures of 95 individual stars are given. The colours are presented for grids of flux constant, line blanketed models. One grid has been published previously, as have some colours for the visible region of the spectrum. The models of this grid are in the range 4000 K eff < 6000 K, 0.75 < log g < 3.00, - 3.0 < [A/H] < 0.0. A grid of dwarf models, with the same temperature and abundance range but with 3.75 < log g < 4.5 is also used. The colours are computed from two series of overlapping synthetic spectra, which have been calculated with a resolution of 0.1 A between 3000 and 12 000 A and 1.0 A between 0.9 and 6.0 μm. (author)

  10. Robustness of third family solutions for hybrid stars against mixed phase effects

    Science.gov (United States)

    Ayriyan, A.; Bastian, N.-U.; Blaschke, D.; Grigorian, H.; Maslov, K.; Voskresensky, D. N.

    2018-04-01

    We investigate the robustness of third family solutions for hybrid compact stars with a quark matter core that correspond to the occurrence of high-mass twin stars against a softening of the phase transition by means of a construction that mimics the effects of pasta structures in the mixed phase. We consider a class of hybrid equations of state that exploits a relativistic mean-field model for the hadronic as well as for the quark matter phase. We present parametrizations that correspond to branches of high-mass twin star pairs with maximum masses between 2.05 M⊙ and 1.48 M⊙ having radius differences between 3.2 and 1.5 km, respectively. When compared to a Maxwell construction with a fixed value of critical pressure Pc, the effect of the mixed phase construction consists in the occurrence of a region of pressures around Pc belonging to the coexistence of hadronic and quark matter phases between the onset pressure at PH and the end of the transition at PQ. The maximum broadening which would still allow mass-twin compact stars is found to be (PQ-PH)max≈Pc for all parametrizations within the present class of models. At least the heavier of the neutron stars of the binary merger GW170817 could have been a member of the third family of hybrid stars. We present the example of another class of hybrid star equations of state for which the appearance of the third family branch is not as robust against mixed phase effects as that of the present work.

  11. Effects of Pop III to PopII transition on the lowest metallicity stars in dwarf galaxies

    Science.gov (United States)

    Zhang, Yimiao; Keres, Dusan; FIRE Team

    2018-01-01

    We examine the effects of the enrichments from Population III (Pop III) stars on the formation and properties of the first generation of the Population II (Pop II) stars. Pop III stars begin to transition towards Pop II stars when the metals dispersed in Pop III supernovae pollute the nearby gas. However, details of this transition are still largely unknown. We use dwarf galaxy simulations from the Feedback In Realistic Environments (FIRE) project to identify the star-forming gas that is likely to be pre-enriched by Pop III supernovae and follow the stars that form in such gas. This pre-enrichment will leave the signature in the lowest metallicity stars that can be used to better constrain the details of the Pop III-to-Pop II transition.

  12. Multibody neutrino exchange in a neutron star neutrino sea and border effects

    CERN Document Server

    Abada, A; Rodríguez-Quintero, J; Abada, As

    1998-01-01

    The interaction due to the exchange of massless neutrinos between neutrons is a long-range force. Border effects on this multibody exchange inside a dense core are studied and computed analytically in 1 + 1 dimensions. We demonstrate in this work that a proper treatment of the star's border effect automatically incorporates the condensate contribution as a consequence of the appropriate boundary conditions for the neutrino Feynman propagator inside the star. The total multibody exchange contribution is infrared-safe and vanishes exactly in 1 + 1 dimensions. The general conclusion of this work is that the border effect does not modify the result that neutrino exchange is infrared-safe. This toy model prepares the ground and gives the tools for the study of the realistic 3 + 1 star.

  13. DARK STARS: A NEW LOOK AT THE FIRST STARS IN THE UNIVERSE

    International Nuclear Information System (INIS)

    Spolyar, Douglas; Bodenheimer, Peter; Freese, Katherine; Gondolo, Paolo

    2009-01-01

    We have proposed that the first phase of stellar evolution in the history of the universe may be dark (matter powered) stars (DSs), luminous objects powered by dark matter (DM) heating rather than by nuclear fusion, and in this paper we examine the history of these DSs. The power source is annihilation of weakly interacting massive particles (WIMPs) which are their own antiparticles. These WIMPs are the best motivated DM candidates and may be discovered by ongoing direct or indirect detection searches (e.g., Fermi/GLAST) or at the Large Hadron Collider at CERN. A new stellar phase results, powered by DM annihilation as long as there is a DM fuel, from millions to billions of years. We build up the DSs from the time DM heating becomes the dominant power source, accreting more and more matter onto them. We have included many new effects in the current study, including a variety of particle masses and accretion rates, nuclear burning, feedback mechanisms, and possible repopulation of DM density due to capture. Remarkably, we find that in all these cases, we obtain the same result: the first stars are very large, 500-1000 times as massive as the Sun; as well as puffy (radii 1-10 AU), bright (10 6 -10 7 L sun ), and cool (T surf sun and the temperatures are much hotter (T surf > 50,000 K). Hence DSs should be observationally distinct from standard Pop III stars. In addition, DSs avoid the (unobserved) element enrichment produced by the standard first stars. Once the DM fuel is exhausted, the DS becomes a heavy main-sequence star; these stars eventually collapse to form massive black holes that may provide seeds for the supermassive black holes observed at early times as well as explanations for recent ARCADE data and for intermediate-mass black holes.

  14. Evidence for circumstellar obscuration of OB stars

    International Nuclear Information System (INIS)

    Bohannan, B.

    1975-01-01

    Reddish found a strong increase of color excess with increasing stellar luminosity: here referred to as the Reddish Effect: in ten young galactic clusters and associations. New photometric and spectroscopic observations drawn from the literature are combined with data used by Reddish to reconsider the color excess versus intrinsic magnitude diagrams of the same ten stellar groups. The reality of the Effect is questioned in all but one of the systems; this was accomplished by identifying possible foreground stars and by recognizing some of the brightest stars as supergiants, then applying correct intrinsic color indices. After careful reanalysis, the one stellar group to retain an indication of the Reddish Effect is Cygnus OB2. No correlation of reddening with luminosity was found for five additional very young stellar groups in the southern hemisphere; these groups should exhibit the Effect if it is a natural consequence of stellar evolution. Reddish ascribed the correlation to massive circumstellar remnants of material from which the stars formed. However, a peculiar dispersion in color excess could also be attributed to patchy dust within the stellar group. In several stellar systems previously identified as displaying the Reddish Effect, a correlation of observed color excess with dust and gas concentrations is noted on Palomar Sky Survey prints. If present, circumstellar dust clouds should []anifest their existence in modes other than a correlation of color excess with luminosity. The following possibilities are considered and all show negative results: correlation of color excess with spectral type; correlation of reddening slope E/subU//sub -//subB//E/subB//sub -//subV/ with spectral type; observable infrared excess. The preceding astrophysical arguments strongly imply that circumstellar dust remnants from stellar formation do not remain around stars during their main-sequence lifetimes. (auth)

  15. Effectiveness of Expanded Implementation of STAR-VA for Managing Dementia-Related Behaviors Among Veterans.

    Science.gov (United States)

    Karel, Michele J; Teri, Linda; McConnell, Eleanor; Visnic, Stephanie; Karlin, Bradley E

    2016-02-01

    Nonpharmacological, psychosocial approaches are first-line treatments for managing behavioral symptoms in dementia, but they can be challenging to implement in long-term care settings. The Veterans Health Administration implemented STAR-VA, an interdisciplinary behavioral approach for managing challenging dementia-related behaviors in its Community Living Center (CLCs, nursing home care) settings. This study describes how the program was implemented and provides an evaluation of Veteran clinical outcomes and staff feedback on the intervention. One mental health professional and registered nurse team from 17 CLCs completed STAR-VA training, which entailed an experiential workshop followed by 6 months of expert consultation as they worked with their teams to implement STAR-VA with Veterans identified to have challenging dementia-related behaviors. The frequency and severity of target behaviors and symptoms of depression, anxiety, and agitation were evaluated at baseline and at intervention completion. Staff provided feedback regarding STAR-VA feasibility and impact. Seventy-one Veterans completed the intervention. Behaviors clustered into 6 types: care refusal or resistance, agitation, aggression, vocalization, wandering, and other. Frequency and severity of target behaviors and symptoms of depression, anxiety, and agitation all significantly decreased, with overall effect sizes of 1 or greater. Staff rated both benefits for Veterans and program feasibility favorably. This evaluation supports the feasibility and effectiveness of STAR-VA, an interdisciplinary, behavioral intervention for managing challenging behaviors among residents with dementia in CLCs. Published by Oxford University Press on behalf of the Gerontological Society of America 2015.

  16. The anti-proliferative and anti-angiogenic effect of the methanol extract from brittle star.

    Science.gov (United States)

    Baharara, Javad; Amini, Elaheh; Mousavi, Marzieh

    2015-04-01

    Anti-angiogenic therapy is a crucial step in cancer treatment. The discovery of new anti-angiogenic compounds from marine organisms has become an attractive concept in anti-cancer therapy. Because little data correlated to the pro- and anti-angiogenic efficacies of Ophiuroidea, which include brittle star, the current study was designed to explore the anti-angiogenic potential of brittle star methanol extract in vitro and in vivo. The anti-proliferative effect of brittle star extract on A2780cp cells was examined by MTT assays, and transcriptional expression of VEGF and b-FGF was evaluated by RT-PCR. In an in vivo model, 40 fertilized Ross eggs were divided into control and three experimental groups. The experimental groups were incubated with brittle star extract at concentrations of 25, 50 and 100 µg/ml, and photographed by photo-stereomicroscopy. Ultimately, numbers and lengths of vessels were measured by Image J software. Data were analyzed with SPSS software (pstar extract exerted a dose- and time-dependent anti-proliferative effect on A2780cp cancer cells. In addition, VEGF and b-FGF expression decreased with brittle star methanol extract treatment. Macroscopic evaluations revealed significant changes in the second and third experimental group compared to controls (pstar methanol extract in vitro and in vivo confer novel insight into the application of natural marine products in angiogenesis-related pathologies.

  17. Not-so-simple stellar populations in the intermediate-age Large Magellanic Cloud star clusters NGC 1831 and NGC 1868

    Energy Technology Data Exchange (ETDEWEB)

    Li, Chengyuan; De Grijs, Richard [Kavli Institute for Astronomy and Astrophysics and Department of Astronomy, Peking University, Yi He Yuan Lu 5, Hai Dian District, Beijing 100871 (China); Deng, Licai, E-mail: joshuali@pku.edu.cn, E-mail: grijs@pku.edu.cn [Key Laboratory for Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012 (China)

    2014-04-01

    Using a combination of high-resolution Hubble Space Telescope/Wide-Field and Planetary Camera-2 observations, we explore the physical properties of the stellar populations in two intermediate-age star clusters, NGC 1831 and NGC 1868, in the Large Magellanic Cloud based on their color-magnitude diagrams. We show that both clusters exhibit extended main-sequence turn offs. To explain the observations, we consider variations in helium abundance, binarity, age dispersions, and the fast rotation of the clusters' member stars. The observed narrow main sequence excludes significant variations in helium abundance in both clusters. We first establish the clusters' main-sequence binary fractions using the bulk of the clusters' main-sequence stellar populations ≳ 1 mag below their turn-offs. The extent of the turn-off regions in color-magnitude space, corrected for the effects of binarity, implies that age spreads of order 300 Myr may be inferred for both clusters if the stellar distributions in color-magnitude space were entirely due to the presence of multiple populations characterized by an age range. Invoking rapid rotation of the population of cluster members characterized by a single age also allows us to match the observed data in detail. However, when taking into account the extent of the red clump in color-magnitude space, we encounter an apparent conflict for NGC 1831 between the age dispersion derived from that based on the extent of the main-sequence turn off and that implied by the compact red clump. We therefore conclude that, for this cluster, variations in stellar rotation rate are preferred over an age dispersion. For NGC 1868, both models perform equally well.

  18. Effects of Combined Stellar Feedback on Star Formation in Stellar Clusters

    Science.gov (United States)

    Wall, Joshua Edward; McMillan, Stephen; Pellegrino, Andrew; Mac Low, Mordecai; Klessen, Ralf; Portegies Zwart, Simon

    2018-01-01

    We present results of hybrid MHD+N-body simulations of star cluster formation and evolution including self consistent feedback from the stars in the form of radiation, winds, and supernovae from all stars more massive than 7 solar masses. The MHD is modeled with the adaptive mesh refinement code FLASH, while the N-body computations are done with a direct algorithm. Radiation is modeled using ray tracing along long characteristics in directions distributed using the HEALPIX algorithm, and causes ionization and momentum deposition, while winds and supernova conserve momentum and energy during injection. Stellar evolution is followed using power-law fits to evolution models in SeBa. We use a gravity bridge within the AMUSE framework to couple the N-body dynamics of the stars to the gas dynamics in FLASH. Feedback from the massive stars alters the structure of young clusters as gas ejection occurs. We diagnose this behavior by distinguishing between fractal distribution and central clustering using a Q parameter computed from the minimum spanning tree of each model cluster. Global effects of feedback in our simulations will also be discussed.

  19. Effects of hyperon mixing on neutron star properties

    International Nuclear Information System (INIS)

    Takatsuka, Tatsuyuki

    2008-01-01

    From a serious inconsistency between theory and observations for the mass of hyperon-mixed neutron stars (NSs), it is stressed that some "extra repulsion" is missing in hypernuclear systems and three-body force repulsion is tested for the cases with phenomenological Illinoi's type, 2π-exchange via Δ-excitation type (2πΔ) and string-junction quark model(SJM). It is remarked that the "extra repulsion" should have a nature to act universally, i.e., independent of baryon species. The SJM three-body repulsion can meet the condition because of flavor-independence and {2πΔ+SJM} scheme is shown to be a promising candidate for the "extra repulsion". Occurence of Λ and Σ - superfluidities are shown also by a realistic approach, which importantly supports the idea of nonstandard fast "hyperon cooling" scenario to explain colder class NSs. However, less attractive ΛΛ interaction suggested by the "NAGARA event" ( ΛΛ 6 He) leads to the disappearance of Λ superfluidity and the breaking down of the scenario. In this connection, the revival of "Λ superfluidity" due to ΛΣ - pairing instead of ΛΛ one is discussed in a new scheme of "bubble shell" hypothesis where the matching of two different Fermi surfaces is forced. (author)

  20. Study of boundary effect of brightness variations of spherical star with two hot precessing spots

    International Nuclear Information System (INIS)

    Kyurkchieva, D.P.; Shkodrov, V.G.

    1984-01-01

    In order to determine the low governing the total brightness variation of a spherical star for the period α<=Ωt<=π-α', the spots behaviour in the intervals 0<=Ωt<=α', π-α'<=Ωt<=π has to be investigated. The article contains an analysis of the boundary effects at which the hot spots are projected as parts of an ellipse on the star's visible disc. The area of the projections of the hot spots on the tangential plane toward the celestial sphere in the above intervals is determined. The equation obtained is sufficient for the determination of the relative light variation of the star. The equation is applied to the parameters of SS433

  1. Rotational velocities of low-mass stars

    International Nuclear Information System (INIS)

    Stauffer, J.B.; Hartmann, L.W.; Harvard-Smithsonian Center for Astrophysics, Cambridge, MA)

    1986-01-01

    The rotational velocities of stars provide important clues to how stars form and evolve. Yet until recently, studies of stellar rotation were limited to stars more massive than the sun. This is beginning to change, and an observational outline of the rotational velocity evolution of stars less massive than the sun can now be provided. Low-mass stars rotate slowly during the early stages of premain-sequence evolution, and spin up as they contract to the main sequence. This spin-up culminates in a brief period of very rapid rotation at an age of order 50 million years. Physical interpretation of this increase in rotation and the subsequent main-sequence spin-down are complicated by the possibility of differential internal rotation. The observed rapidity of spin-down among G dwarfs suggests that initially only the outer convective envelopes of these stars are slowed. The data suggest an intrinsic spread in angular momentum among young stars of the same mass and age, a spread which is apparently minimized by the angular-momentum loss mechanism in old low-mass stars. 83 references

  2. Zeeman effect in sulfur monoxide: a tool to probe magnetic fields in star forming regions

    DEFF Research Database (Denmark)

    Cazzoli, Gabriele; Lattanzi, Valerio; Coriani, Sonia

    2017-01-01

    Context. Magnetic fields play a fundamental role in star formation processes and the best method to evaluate their intensity is to measure the Zeeman effect of atomic and molecular lines. However, a direct measurement of the Zeeman spectral pattern from interstellar molecular species is challengi...

  3. Nonrobustness of the Carryover Effects of Small Classes in Project STAR

    Science.gov (United States)

    Sohn, Kitae

    2015-01-01

    Background: Class size reduction (CSR) is an enduring school reform undertaken in an effort to improve academic achievement and has been widely encouraged in the United States. Supporters of CSR often cite the positive contemporaneous and carryover effects of Project STAR. Much has been discussed regarding the robustness of the contemporaneous…

  4. Flare-related color effects in UV Ceti stars

    International Nuclear Information System (INIS)

    Flesch, T.R.

    1975-01-01

    The UV Ceti flare stars YZ CMi, BD+16 0 2708, EV Lac, and AD Leo were monitored photoelectrically for flare activity with the 76 centimeter reflecting telescope of the University of Florida's Rosemary Hill Observatory. Observations were carried out from January, 1973 to April, 1975. The instrumentation allowed simultaneous readings to be taken at 3500, 4632, and 6496A with a time resolution of 2 seconds. A total of 15 major events were observed, with 14 of these being observed in all three colors. All events showed the classical fast rise and slower decline that is typical of this type of activity. One event showed peculiar behavior in the red bandpass that may indicate strong dependence of the flare light in some cases on line emission. The data were applied to the fast electron model of flare activity proposed by Gurzadyan. Several serious inconsistencies in the theory were found that would not have been evident in single-channel monitoring. No event could be fitted in all three colors using consistent values of the unknown parameters in the theory. The most serious deficiencies in the theory were the wavelength dependence of the optical depth of the electron cloud and the lack of treatment of line emission behavior. Differential color indices for flare light are calculated and are shown to be essentially constant throughout the entire event for the stronger flares. A color-color plot of the flare light at maximum reveals that 11 of the flares show a linear relation. This relation indicates that the smaller the u-b index, the larger is the b-r index. This is probably directly involved with line emission during flare events. Future research possibilities are discussed, with spectroscopic studies and simultaneous multicolor observations being stressed

  5. UBV-photometry of flare stars in pleiades

    International Nuclear Information System (INIS)

    Chavushyan, O.S.; Garibdzhanyan, A.T.

    1975-01-01

    The results are presented of UBV-photometry of 283 flare stars at the minimum of brightness in the Pleiad region. A new method has been developed and used of taking into account the background in photographic UBV-photometry with an iris microphotometer. The data obtained indicate that the flare Pleiad stars are located on both sides of the main sequence in the light-luminosity (V,B-V) diagram, while in the (U-B,B-V) diagram they are largely located above the main sequence

  6. The impact of Einstein observations on our understanding of low mass star formation

    International Nuclear Information System (INIS)

    Walter, F.M.

    1990-01-01

    Prior to 1980, the world of pre-main sequence stars, if not well understood, was at least well defined. The Herbig and Rao (1972) catalog listed 69 pre-main sequence stars in Tau-Aur, with the vast majority clearly being T Tauri stars. The characteristics of the classical T Tauri stars include strong Hα emission, with W λ (Hα)>5-10A; forbidden line emission; continuum ultraviolet and IR excesses; veiling of the absorption line spectrum; significant stellar variability; Li I λ6707A absorption; and association with dark clouds and/or emission nebulosities. Star forming regions were observed extensively with the Einstein Observatory, and showed the abundance of stellar X-ray sources in the Orion Nebula. About 1/3 of the known T Tauri stars were detected as X-ray sources, yet the vast majority of the X-ray sources detected were coincident with anonymous stars not suspected to be pre-main sequence stars. In the grand tradition of X-ray astronomy, X-ray astronomers trooped to telescopes to identify the optical counterparts. It was shown that 5 of the counterparts were K7-M0 stars, above the main sequence, with strong Li I absorption and that these stars were kinematic members of the Tau-Aur star formation complex. Since then, additional members of this class of naked T Tauri Stars (NTTS) have been studied, and charts provided for X-ray selected pre-main sequence star candidates in the general vicinity of Tau-Aur. Thirty five X-ray sources have been selected and optically confirmed as NTTS in Tau-Aur

  7. Identification and period investigation of pulsation variable star UY Camelopardalis, an RR Lyrae star in binary system

    Science.gov (United States)

    Li, Lin-Jia; Qian, Sheng-Bang; Voloshina, Irina; Metlov, Vladimir G.; Zhu, Li-Ying; Liao, Wen-Ping

    2018-06-01

    We present photometric measurements of the short period variable star UY Cam, which has been classified as a δ Scuti or c-type RR Lyrae (RRc) variable in different catalogs. Based on the analyses on Fourier coefficients and (NUV - V)0, we find that UY Cam is probably an RRc star. We obtain 58 new times of light maximum for UY Cam based on several sky surveys and our observations. Combining these with the times of light maximum in literature, a total of 154 times of light maximum are used to analyze the O - C diagram of UY Cam. The results show that the O - C pattern can be described by a downward parabolic component with a rate of -6.86 ± 0.47 × 10-11 d d-1, and a cyclic variation with a period of 65.7 ± 2.4 yr. We suppose these components are caused by the stellar evolution and the light travel time effect (LiTE) of a companion in elliptical orbit, respectively. By calculation, the minimum mass of the potential companion is about 0.17 M⊙, and its mass should be less than or equal to the pulsation primary star when the inclination i > 22.5°D. Therefore, the companion should be a low-mass star, like a late-type main-sequence star or a white dwarf. Due to the unique property of UY Cam, we suggest that more observations and studies on UY Cam and other RRc stars are needed to check the nature of these stars, including the pulsations and binarities.

  8. New light on faint stars

    International Nuclear Information System (INIS)

    Reid, N.; Gilmore, G.

    1982-01-01

    This paper presents the first purely photometric derivation of the stellar main-sequence luminosity function to absolute magnitude Msub(V) = + 19, which is comparable to the minimum mass for thermonuclear burning. The observations consist of COSMOS measures of UK Schmidt telescope plates in the V, R and I bands. They provide a complete sample of every star in 18.24 square degrees towards the South Galactic Pole, brighter than I = 17.0. Absolute magnitudes and distances are derived by photometric parallax from the Msub(V)/V-I and Msub(V)/I-K relations, which have been carefully calibrated on our photometric system. For +9<=Msub(V)<=+19, the photometrically defined luminosity function is in agreement with that derived from samples of nearby stars, and by proper motion techniques. There is no evidence for any excess of intrinsically faint stars, even though this survey reaches some 5 mag deeper into the luminosity function than previous photometric surveys. Re-analysis of subsamples of other photometric studies of the local stellar density removes any evidence for a significant excess of M dwarfs relative to the kinematically derived luminosity function. The missing mass in the solar neighbourhood, if any, does not reside in main-sequence stars brighter than Msub(V) approx. = + 17 mag. (author)

  9. The embedded young stars in the Taurus-Auriga molecular cloud. I - Models for spectral energy distributions

    Science.gov (United States)

    Kenyon, Scott J.; Calvet, Nuria; Hartmann, Lee

    1993-01-01

    We describe radiative transfer calculations of infalling, dusty envelopes surrounding pre-main-sequence stars and use these models to derive physical properties for a sample of 21 heavily reddened young stars in the Taurus-Auriga molecular cloud. The density distributions needed to match the FIR peaks in the spectral energy distributions of these embedded sources suggest mass infall rates similar to those predicted for simple thermally supported clouds with temperatures about 10 K. Unless the dust opacities are badly in error, our models require substantial departures from spherical symmetry in the envelopes of all sources. These flattened envelopes may be produced by a combination of rotation and cavities excavated by bipolar flows. The rotating infall models of Terebey et al. (1984) models indicate a centrifugal radius of about 70 AU for many objects if rotation is the only important physical effect, and this radius is reasonably consistent with typical estimates for the sizes of circumstellar disks around T Tauri stars.

  10. Structure of neutron star crusts from new Skyrme effective interactions constrained by chiral effective field theory

    Science.gov (United States)

    Lim, Yeunhwan; Holt, Jeremy W.

    2017-06-01

    We investigate the structure of neutron star crusts, including the crust-core boundary, based on new Skyrme mean field models constrained by the bulk-matter equation of state from chiral effective field theory and the ground-state energies of doubly-magic nuclei. Nuclear pasta phases are studied using both the liquid drop model as well as the Thomas-Fermi approximation. We compare the energy per nucleon for each geometry (spherical nuclei, cylindrical nuclei, nuclear slabs, cylindrical holes, and spherical holes) to obtain the ground state phase as a function of density. We find that the size of the Wigner-Seitz cell depends strongly on the model parameters, especially the coefficients of the density gradient interaction terms. We employ also the thermodynamic instability method to check the validity of the numerical solutions based on energy comparisons.

  11. THE ROTATION RATES OF MASSIVE STARS: THE ROLE OF BINARY INTERACTION THROUGH TIDES, MASS TRANSFER, AND MERGERS

    Energy Technology Data Exchange (ETDEWEB)

    De Mink, S. E. [Space Telescope Science Institute, Baltimore, MD (United States); Langer, N.; Izzard, R. G. [Argelander-Institut fuer Astronomie der Universitaet Bonn, D-53121 Bonn (Germany); Sana, H.; De Koter, A. [Astronomical Institute Anton Pannekoek, University of Amsterdam, 1098 XH Amsterdam (Netherlands)

    2013-02-20

    Rotation is thought to be a major factor in the evolution of massive stars-especially at low metallicity-with consequences for their chemical yields, ionizing flux, and final fate. Deriving the birth spin distribution is of high priority given its importance as a constraint on theories of massive star formation and as input for models of stellar populations in the local universe and at high redshift. Recently, it has become clear that the majority of massive stars interact with a binary companion before they die. We investigate how this affects the distribution of rotation rates, through stellar winds, expansion, tides, mass transfer, and mergers. For this purpose, we simulate a massive binary-star population typical for our Galaxy assuming continuous star formation. We find that, because of binary interaction, 20{sup +5} {sub -10}% of all massive main-sequence stars have projected rotational velocities in excess of 200 km s{sup -1}. We evaluate the effect of uncertain input distributions and physical processes and conclude that the main uncertainties are the mass transfer efficiency and the possible effect of magnetic braking, especially if magnetic fields are generated or amplified during mass accretion and stellar mergers. The fraction of rapid rotators we derive is similar to that observed. If indeed mass transfer and mergers are the main cause for rapid rotation in massive stars, little room remains for rapidly rotating stars that are born single. This implies that spin-down during star formation is even more efficient than previously thought. In addition, this raises questions about the interpretation of the surface abundances of rapidly rotating stars as evidence for rotational mixing. Furthermore, our results allow for the possibility that all early-type Be stars result from binary interactions and suggest that evidence for rotation in explosions, such as long gamma-ray bursts, points to a binary origin.

  12. ENERGY STAR Certified Displays

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 7.0 ENERGY STAR Program Requirements for Displays that are effective as of July 1, 2016....

  13. ENERGY STAR Certified Boilers

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 3.0 ENERGY STAR Program Requirements for Boilers that are effective as of October 1,...

  14. ENERGY STAR Certified Televisions

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 7.0 ENERGY STAR Program Requirements for Televisions that are effective as of October 30,...

  15. ENERGY STAR Certified Dehumidifiers

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 4.0 ENERGY STAR Program Requirements for Dehumidifiers that are effective as of October...

  16. O stars and Wolf-Rayet stars

    International Nuclear Information System (INIS)

    Conti, P.S.; Underhill, A.B.; Jordan, S.; Thomas, R.

    1988-01-01

    Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented

  17. O stars and Wolf-Rayet stars

    Science.gov (United States)

    Conti, Peter S.; Underhill, Anne B.; Jordan, Stuart (Editor); Thomas, Richard (Editor)

    1988-01-01

    Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented.

  18. Magnetic braking in young late-type stars. The effect of polar spots

    Science.gov (United States)

    Aibéo, A.; Ferreira, J. M.; Lima, J. J. G.

    2007-10-01

    Context: The existence of rapidly rotating cool stars in young clusters implies a reduction of angular momentum loss rate for a certain period of the star's early life. Recently, the concentration of magnetic flux near the poles of these stars has been proposed as an alternative mechanism to dynamo saturation in order to explain the saturation of angular momentum loss. Aims: In this work we study the effect of magnetic surface flux distribution on the coronal field topology and angular momentum loss rate. We investigate if magnetic flux concentration towards the pole is a reasonable alternative to dynamo saturation. Methods: We construct a 1D wind model and also apply a 2-D self-similar analytical model, to evaluate how the surface field distribution affects the angular momentum loss of the rotating star. Results: From the 1D model we find that, in a magnetically dominated low corona, the concentrated polar surface field rapidly expands to regions of low magnetic pressure resulting in a coronal field with small latitudinal variation. We also find that the angular momentum loss rate due to a uniform field or a concentrated field with equal total magnetic flux is very similar. From the 2D wind model we show that there are several relevant factors to take into account when studying the angular momentum loss from a star. In particular, we show that the inclusion of force balance across the field in a wind model is fundamental if realistic conclusions are to be drawn from the effect of non-uniform surface field distribution on magnetic braking. This model predicts that a magnetic field concentrated at high latitudes leads to larger Alfvén radii and larger braking rates than a smoother field distribution. Conclusions: From the results obtained, we argue that the magnetic surface field distribution towards the pole does not directly limit the braking efficiency of the wind.

  19. 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.

  20. Helium-burning flashes on accreting neutron stars: effects of stellar mass, radius, and magnetic field

    International Nuclear Information System (INIS)

    Joss, P.C.; Li, F.K.

    1980-01-01

    We have computed the evolution of the helium-burning shell in an accreting neutron star for various values of the stellar mass (M), radius (R), and surface magnetic fields strength (B). As shown in previous work, the helium-burning shell is often unstable and undergoes thermonuclear flashes that result in the emission of X-ray bursts from the neutron-star surface. The dependence of the properties of these bursts upon the values of M and R can be described by simple scaling relations. A strong magnetic field decreases the radiative and conductive opacities and inhibits convection in the neutron-star surface layers. For B 12 gauss, these effects are unimportant; for B> or approx. =10 13 gauss, the enhancement of the electron thermal conductivity is sufficiently large to stabilize the helium-burning shell against thermonuclear flashes. For intermediate values of B, the reduced opacities increase the recurrence intervals between bursts and the energy released per burst, while the inhibition of convection increases the burst rise times to about a few seconds. If the magnetic field funnels the accreting matter onto the magnetic polar caps, the instability of the helium-burning shell will be very strongly suppressed. These results suggest that it may eventually be possible to extract information on the macroscopic properties of neutron stars from the observed features of X-ray burst sources

  1. Effect of atomic parameters on determination of aluminium abundance in atmospheres of late-type stars

    Science.gov (United States)

    Menzhevitski, V. S.; Shimanskaya, N. N.; Shimansky, V. V.; Kudryavtsev, D. O.

    2014-04-01

    We study the effect of the photoionization cross sections for the ground state of Al I on the inferred aluminium abundance in stellar atmospheres. We match the theoretical and observed line profiles of the resonance λλ 3944.01, 3961.52 Å and subordinate λλ 6696.03, 6698.68 Å doublets in high-resolution spectra of the metal-poor solar-type stars HD22879 and HD201889. We determine the parameters of these stars from their photometric and spectroscopic data. Our computations show that the profiles can be matched and a single aluminium abundance inferred simultaneously from both groups of spectral lines only with low photoionization cross sections (about 10-12 Mb). Larger cross sections (about 58-65 Mb) make such fits impossible. We therefore conclude that small photoionization cross sections should be preferred for the determination of aluminium abundances in metal-poor stars. We redetermine the aluminium abundances in the atmospheres of halo stars. The resulting abundances prove to be lower by 0.1-0.15 dex than our earlier determinations which does not affect the conclusions based on our earlier estimates. In particular, the NLTE [Al/Fe]-[Fe/H] dependence, on the whole, agrees only qualitatively with the results of theoretical predictions. Therefore further refinement of the theory of nuclear synthesis of aluminium in the process of the chemical evolution of the Galaxy remains a task of current importance.

  2. EXTENDED STAR FORMATION IN THE INTERMEDIATE-AGE LARGE MAGELLANIC CLOUD STAR CLUSTER NGC 2209

    International Nuclear Information System (INIS)

    Keller, Stefan C.; Mackey, A. Dougal; Da Costa, Gary S.

    2012-01-01

    We present observations of the 1 Gyr old star cluster NGC 2209 in the Large Magellanic Cloud made with the GMOS imager on the Gemini South Telescope. These observations show that the cluster exhibits a main-sequence turnoff that spans a broader range in luminosity than can be explained by a single-aged stellar population. This places NGC 2209 amongst a growing list of intermediate-age (1-3 Gyr) clusters that show evidence for extended or multiple epochs of star formation of between 50 and 460 Myr in extent. The extended main-sequence turnoff observed in NGC 2209 is a confirmation of the prediction in Keller et al. made on the basis of the cluster's large core radius. We propose that secondary star formation is a defining feature of the evolution of massive star clusters. Dissolution of lower mass clusters through evaporation results in only clusters that have experienced secondary star formation surviving for a Hubble time, thus providing a natural connection between the extended main-sequence turnoff phenomenon and the ubiquitous light-element abundance ranges seen in the ancient Galactic globular clusters.

  3. Symbiotic stars

    International Nuclear Information System (INIS)

    Boyarchuk, A.A.

    1975-01-01

    There are some arguments that the symbiotic stars are binary, where one component is a red giant and the other component is a small hot star which is exciting a nebula. The symbiotic stars belong to the old disc population. Probably, symbiotic stars are just such an evolutionary stage for double stars as planetary nebulae for single stars. (Auth.)

  4. Nuclear processing during star formation

    International Nuclear Information System (INIS)

    Newman, M.J.

    1978-01-01

    A preliminary survey was conducted of the thermonuclear energy release expected during star formation. The destruction of primordial deuterium provides substantial amounts of energy at surprisingly low temperatures, and must be considered in any meaningful treatment of star formation carried to stages in which the internal temperature exceeds a few hundred thousand degrees. Significant energy generation from consumption of initial lithium requires higher temperatures, of the order of a few million degrees. Depletion of primordial beryllium and boron may never provide an important energy source. The approach to equilibrium of the carbon--nitrogen cycle is dominant at temperatures approaching those characteristic of the central regions of main sequence stars. The present calculation should serve as a useful guide in choosing those nuclear processes to be included in a more detailed study. 8 figures, 2 tables

  5. Presupernova evolution of massive stars

    International Nuclear Information System (INIS)

    Weaver, T.A.; Zimmerman, G.B.; Woosley, S.E.

    1977-01-01

    Population I stars of 15 M/sub mass/ and 25 M/sub mass/ have been evolved from the zero-age main sequence through iron core collapse utilizing a numerical model that incorporates both implicit hydrodynamics and a detailed treatment of nuclear reactions. The stars end their presupernova evolution as red supergiants with photospheric radii of 3.9 x 10 13 cm and 6.7 x 10 13 cm, respectively, and density structures similar to those invoked to explain Type II supernova light curves on a strictly hydrodynamic basis. Both stars are found to form substantially neutronized ''iron'' cores of 1.56 M/sub mass/ and 1.61 M/sub mass/, and central electron abundances of 0.427 and 0.439 moles/g, respectively, during hydrostatic silicon burning. Just prior to collapse, the abundances of the elements in the 25 M/sub mass/ star (excluding the neutronized iron core) have ratios strikingly close to their solar system values over the mass range from oxygen to calcium, while the 15 M/sub mass/ star is characterized by large enhancements of Ne, Mg, and Si. It is pointed out on nucleosynthetic grounds that the mass of the neutronized core must represent a lower limit to the mass of the neutron star or black hole remnant that stars in this mass range can normally produce

  6. Understanding the star formation modes in the distant universe

    International Nuclear Information System (INIS)

    Salmi, Fadia

    2012-01-01

    The goal of my PhD study consists at attempt to understand what are the main processes at the origin of the star formation in the galaxies over the last 10 billion years. While it was proposed in the past that merging of galaxies has a dominant role to explain the triggering of the star formation in the distant galaxies having high star formation rates, in the opposite, more recent studies revealed scaling laws linking the star formation rate in the galaxies to their stellar mass or their gas mass. The small dispersion of these laws seems to be in contradiction with the idea of powerful stochastic events due to interactions, but rather in agreement with the new vision of galaxy history where the latter are continuously fed by intergalactic gas. We were especially interested in one of this scaling law, the relation between the star formation (SFR) and the stellar mass (M*) of galaxies, commonly called the main sequence of star forming galaxies. We studied this main sequence, SFR-M"*, in function of the morphology and other physical parameters like the radius, the colour, the clumpiness. The goal was to understand the origin of the sequence's dispersion related to the physical processes underlying this sequence in order to identify the main mode of star formation controlling this sequence. This work needed a multi-wavelength approach as well as the use of galaxies profile simulation to distinguish between the different galaxy morphological types implied in the main sequence. (author) [fr

  7. Spectral fingerprints of Earth-like planets around FGK stars.

    Science.gov (United States)

    Rugheimer, Sarah; Kaltenegger, Lisa; Zsom, Andras; Segura, Antígona; Sasselov, Dimitar

    2013-03-01

    We present model atmospheres for an Earth-like planet orbiting the entire grid of main sequence FGK stars with effective temperatures ranging from Teff=4250 K to Teff=7000 K in 250 K intervals. We have modeled the remotely detectable spectra of Earth-like planets for clear and cloudy atmospheres at the 1 AU equivalent distance from the VIS to IR (0.4 to 20 μm) to compare detectability of features in different wavelength ranges in accordance with the James Webb Space Telescope and future design concepts to characterize exo-Earths. We have also explored the effect of the stellar UV levels as well as spectral energy distribution on a terrestrial atmosphere, concentrating on detectable atmospheric features that indicate habitability on Earth, namely, H2O, O3, CH4, N2O, and CH3Cl. The increase in UV dominates changes of O3, OH, CH4, N2O, and CH3Cl, whereas the increase in stellar temperature dominates changes in H2O. The overall effect as stellar effective temperatures and corresponding UV increase is a lower surface temperature of the planet due to a bigger part of the stellar flux being reflected at short wavelengths, as well as increased photolysis. Earth-like atmosphere models show more O3 and OH but less stratospheric CH4, N2O, CH3Cl, and tropospheric H2O (but more stratospheric H2O) with increasing effective temperature of main sequence stars. The corresponding detectable spectral features, on the other hand, show different detectability depending on the wavelength observed. We concentrate on directly imaged planets here as a framework to interpret future light curves, direct imaging, and secondary eclipse measurements of atmospheres of terrestrial planets in the habitable zone at varying orbital positions.

  8. STAR FORMATION IN DISK GALAXIES. II. THE EFFECT OF STAR FORMATION AND PHOTOELECTRIC HEATING ON THE FORMATION AND EVOLUTION OF GIANT MOLECULAR CLOUDS

    International Nuclear Information System (INIS)

    Tasker, Elizabeth J.

    2011-01-01

    We investigate the effect of star formation and diffuse photoelectric heating on the properties of giant molecular clouds (GMCs) formed in high-resolution (∼ H,c >100 cm -3 are identified as GMCs. Between 1000 and 1500 clouds are created in the simulations with masses M>10 5 M sun and 180-240 with masses M>10 6 M sun in agreement with estimates of the Milky Way's population. We find that the effect of photoelectric heating is to suppress the fragmentation of the interstellar medium, resulting in a filamentary structure in the warm gas surrounding clouds. This environment suppresses the formation of a retrograde rotating cloud population, with 88% of the clouds rotating prograde with respect to the galaxy after 300 Myr. The diffuse heating also reduces the initial star formation rate (SFR), slowing the conversation of gas into stars. We therefore conclude that the interstellar environment plays an important role in the GMC evolution. Our clouds live between 0 and 20 Myr with a high infant mortality (t' < 3 Myr) due to cloud mergers and star formation. Other properties, including distributions of mass, size, and surface density, agree well with observations. Collisions between our clouds are common, occurring at a rate of ∼ 1/4 of the orbital period. It is not clear whether such collisions trigger or suppress star formation at our current resolution. Our SFR is a factor of 10 higher than observations in local galaxies. This is likely due to the absence of localized feedback in our models.

  9. Evolution of Mass Functions of Coeval Stars through Wind Mass Loss and Binary Interactions

    NARCIS (Netherlands)

    Schneider, F.R.N.; Izzard, R.G.; Langer, N.; de Mink, S.E.

    2015-01-01

    Accurate determinations of stellar mass functions and ages of stellar populations are crucial to much of astrophysics. We analyze the evolution of stellar mass functions of coeval main-sequence stars, including all relevant aspects of single and binary star evolution. We show that the slope of the

  10. An Unbiased Survey of 500 Nearby Stars for Debris Disks: A JCMT Legacy Program

    NARCIS (Netherlands)

    Matthews, B.C.; Greaves, J.S.; Holland, W.S.; Wyatt, M.C.; Barlow, M.J.; Bastien, P.; Beichman, C.A.; Biggs, A.; Butner, H.M.; Dent, W.R.F.; Francesco, J. Di; Dominik, C.; Fissel, L.; Friberg, P.; Gibb, A.G.; Halpern, M.; Ivison, R.J.; Jayawardhana, R.; Jenness, T.; Johnstone, D.; Kavelaars, J.J.; Marshall, J.L.; Phillips, N.; Schieven, G.; Snellen, I.A.G.; Walker, H.J.; Ward-Thompson, D.; Weferling, B.; White, G.J.; Yates, J.; Zhu, M.; Craigon, A.

    2007-01-01

    We present the scientific motivation and observing plan for an upcoming detection survey for debris disks using the James Clerk Maxwell Telescope. The SCUBA-2 Unbiased Nearby Stars (SUNS) survey will observe 500 nearby main-sequence and subgiant stars (100 of each of the A, F, G, K, and M spectral

  11. TIDAL BREAKUP OF BINARY STARS AT THE GALACTIC CENTER. II. HYDRODYNAMIC SIMULATIONS

    International Nuclear Information System (INIS)

    Antonini, Fabio; Merritt, David; Lombardi, James C. Jr

    2011-01-01

    In Paper I, we followed the evolution of binary stars as they orbited near the supermassive black hole (SMBH) at the Galactic center, noting the cases in which the two stars would come close enough together to collide. In this paper, we replace the point-mass stars by fluid realizations, and use a smoothed-particle hydrodynamics code to follow the close interactions. We model the binary components as main-sequence stars with initial masses of 1, 3, and 6 solar masses, and with chemical composition profiles taken from stellar evolution codes. Outcomes of the close interactions include mergers, collisions that leave both stars intact, and ejection of one star at high velocity accompanied by capture of the other star into a tight orbit around the SMBH. For the first time, we follow the evolution of the collision products for many (∼> 100) orbits around the SMBH. Stars that are initially too small to be tidally disrupted by the SMBH can be puffed up by close encounters or collisions, with the result that tidal stripping occurs in subsequent periapse passages. In these cases, mass loss occurs episodically, sometimes for hundreds of orbits before the star is completely disrupted. Repeated tidal flares, of either increasing or decreasing intensity, are a predicted consequence. In collisions involving a low-mass and a high-mass star, the merger product acquires a high core hydrogen abundance from the smaller star, effectively resetting the nuclear evolution 'clock' to a younger age. Elements like Li, Be, and B that can exist only in the outermost envelope of a star are severely depleted due to envelope ejection during collisions and due to tidal forces from the SMBH. Tidal spin-up can occur due to either a collision or tidal torque by the SMBH at periapsis. However, in the absence of collisions, tidal spin-up of stars is only important in a narrow range of periapse distances, r t /2 ∼ per ∼ t , with r t the tidal disruption radius. We discuss the implications of

  12. Pulsations of delta Scuti stars

    International Nuclear Information System (INIS)

    Cox, A.N.

    1990-01-01

    In this paper the authors give a general review of the pulsating δ Scuti variables, including the observed light curves and positions of the stars in the Hertzsprung-Russell diagram. Theoretical interpretations from evolution and pulsation calculations give their masses, radii, luminosities, and even their approximate internal compositions. Then we discuss three models of these stars, and use them to study the nonlinear hydrodynamic behavior of these stars, after which the authors outline the hydrodynamic equations and the Stellingwerf method for obtaining strictly periodic solutions. The authors also present the problems of allowing for time-dependent convection and its great sensitivity to temperature and density. Tentative results to data do not show any tendency for amplitudes to grow to large unobserved amplitudes, in disagreement with an earlier suggestion by Stellingwerf. Finally, the authors find that the very small growth rates of the pulsations may even be too small to be useful in seeking a periodic solution. The δ Scuti variables are the most common type of variable star in our galaxy except for the white dwarfs. This is because stars in the mass range from just over one M circle-dot up to at least several M circle-dot pass through the yellow giant instability strip in the Hertzsprung-Russell diagram as they evolve off the main sequence to the red. Actually, stars up to the maximum main sequence mass also evolve through this region at higher luminosities, but there are so few of them, and they evolve so rapidly to the red, that they are almost unknown. At the higher luminosity, they probably would be called first-instability strip-crossing Cepheids anyway. Such cepheids are difficult to separate from those that are on the second blueward instability strip crossing that is much slower. Really, the δ Scuti variables are just low-luminosity Cepheids

  13. Gravitational Effects on Plasma Waves in Environment of Sun and Neutron Star

    International Nuclear Information System (INIS)

    Lu Quankang; Hsiao-Ling Zhou

    2014-01-01

    Local plasma phenomena in environment of Sun are observed closely by spacecrafts in recent years. We provide a new method to apply general relativity to astro-plasma physics in small local area. The relativistic dispersion relations of Langmuir, electromagnetic and cyclotron waves are obtained. The red shifts of Langmuir and cyclotron frequencies are given analytically. A new equilibrium velocity distribution of particles soaked in local gravitational field is suggested. The gravitational effect of a neutron star is also estimated

  14. Burn out or fade away? On the X-ray and magnetic death of intermediate mass stars

    Energy Technology Data Exchange (ETDEWEB)

    Drake, Jeremy J.; Kashyap, Vinay; Günther, H. Moritz; Wright, Nicholas J. [Smithsonian Astrophysical Observatory, MS-3, 60 Garden Street, Cambridge, MA 02138 (United States); Braithwaite, Jonathan, E-mail: jdrake@cfa.harvard.edu [Argelander Institut für Astronomie, Auf dem Hügel 71, D-53121 Bonn (Germany)

    2014-05-10

    The nature of the mechanisms apparently driving X-rays from intermediate mass stars lacking strong convection zones or massive winds remains poorly understood, and the possible role of hidden, lower mass close companions is still unclear. A 20 ks Chandra HRC-I observation of HR 4796A, an 8 Myr old main sequence A0 star devoid of close stellar companions, has been used to search for a signature or remnant of magnetic activity from the Herbig Ae phase. X-rays were not detected and the X-ray luminosity upper limit was L{sub X} ≤ 1.3 × 10{sup 27} erg s{sup –1}. The result is discussed in the context of various scenarios for generating magnetic activity, including rotational shear and subsurface convection. A dynamo driven by natal differential rotation is unlikely to produce observable X rays, chiefly because of the difficulty in getting the dissipated energy up to the surface of the star. A subsurface convection layer produced by the ionization of helium could host a dynamo that should be effective throughout the main sequence but can only produce X-ray luminosities of the order 10{sup 25} erg s{sup –1}. This luminosity lies only moderately below the current detection limit for Vega. Our study supports the idea that X-ray production in Herbig Ae/Be stars is linked largely to the accretion process rather than the properties of the underlying star, and that early A stars generally decline in X-ray luminosity at least 100,000 fold in only a few million years.

  15. The Star Formation Histories of Disk Galaxies: The Live, the Dead, and the Undead

    Energy Technology Data Exchange (ETDEWEB)

    Oemler, Augustus Jr; Dressler, Alan [The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101-1292 (United States); Abramson, Louis E. [Department of Physics and Astronomy, UCLA, 430 Portola Plaza, Los Angeles CA 90095-1547 (United States); Gladders, Michael D. [Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637 (United States); Poggianti, Bianca M. [INAF-Osservatorio Astronomico di Padova, vicolo dell’Osservatorio 5, I-35122 Padova (Italy); Vulcani, Benedetta [School of Physics, The University of Melbourne, VIC 3010 (Australia)

    2017-07-20

    We reexamine the properties of local galaxy populations using published surveys of star formation, structure, and gas content. After recalibrating star formation measures, we are able to reliably measure specific star formation rates well below that of the so-called “main sequence” of star formation versus mass. We find an unexpectedly large population of quiescent galaxies with star formation rates intermediate between the main sequence and passive populations and with disproportionately high star formation rates. We demonstrate that a tight main sequence is a natural outcome of most histories of star formation and has little astrophysical significance but that the quiescent population requires additional astrophysics to explain its properties. Using a simple model for disk evolution based on the observed dependence of star formation on gas content in local galaxies, and assuming simple histories of cold gas inflow, we show that the evolution of galaxies away from the main sequence can be attributed to the depletion of gas due to star formation after a cutoff of gas inflow. The quiescent population is composed of galaxies in which the density of disk gas has fallen below a threshold for star formation probably set by disk stability. The evolution of galaxies beyond the quiescent state to gas exhaustion and the end of star formation requires another process, probably wind-driven mass loss. The environmental dependence of the three galaxy populations is consistent with recent numerical modeling, which indicates that cold gas inflows into galaxies are truncated at earlier epochs in denser environments.

  16. Effect of catalogues coordinate errors of a star onto determination of the physical libration of the Moon from the observations of stars

    Science.gov (United States)

    Petrova, Natalia; Kocoulin, Valerii; Nefediev, Yurii

    2016-07-01

    the time of observation), this error is reduced by an order, i.e. does not exceed the error of observation selenographic coordinates. 2. The worst thing - errors in coordinates of catalogue causes though a small but constant shift in the ρ and Iσ. So, when Δα, Δδ ˜0.01", then the shift reaches 0.0025". Moreover there is a trend, with a slight, but noticeable slope. 3. Effect of error in declination of a stars is substantially strong than the error in right ascension. Perhaps it is characteristic only for polar observations. For the required accuracy in determination of the physical libration these phenomena must be taken into account when processing the planned observations. Referencies. Nefediev et al., 2013. Uchenye zapiski Kazanskogo universiteta, v. 155, 1, p.188-194. Petrova, N., Abdulmyanov T., Hanada H. Some qualitative manifestations of the physical libration of the Moon by observing stars from the lunar surface. //J. Adv. Space Res., 2012a. V. 50, p. 1702-1711

  17. Effects of Δ baryon in hyperon stars in a modified quark meson coupling model

    International Nuclear Information System (INIS)

    Sahoo, H.S.; Mishra, R.N.; Panda, P.K.; Barik, N.

    2016-01-01

    Recent studies on the appearance of the Δ (1232) isobars in neutron stars has ignited much debate on the possibility of its existence in neutron stars satisfying the observational limit of 2 M_⊙. Given the fact that the presence of the Δ tends to soften the equation of state (EoS) and reduce the maximum mass, theoretical and observational contradictions have given rise to the so called Δ puzzle, similar to the hyperon puzzle. In the present work we develop the EoS for dense matter with the inclusion of the nucleons, hyperons and the Delta isobars and study the effects of such inclusion on stellar properties using a Modified Quark-Meson coupling model (MQMC)

  18. Computer experiments on the effect of retrograde stars in disk galaxies

    International Nuclear Information System (INIS)

    Zang, T.A.; Hohl, F.

    1978-01-01

    Using large-scale N-body calculations for flat disk galaxies, we examine the effect of reversing the angular momentum for various fractions of the stars upon the global bar-forming mode. The initial conditions for these simulations are based on stationary states of two classes of models: the isochrones studied recently by Kalnajs by means of linear theory, and a model resembling the Schmidt model of our own Galaxy. In both cases, as the fraction of retrograde stars is increased, the growth of the bar-forming mode is inhibited (although not eliminated). These N-body results for the isochrones agree with the predictions of linear theory, quantitatively as well as qualitatively

  19. Effects of laser beam propagation and saturation on the spatial shape of sodium laser guide stars.

    Science.gov (United States)

    Marc, Fabien; Guillet de Chatellus, Hugues; Pique, Jean-Paul

    2009-03-30

    The possibility to produce diffraction-limited images by large telescopes through Adaptive Optics is closely linked to the precision of measurement of the position of the guide star on the wavefront sensor. In the case of laser guide stars, many parameters can lead to a strong distortion on the shape of the LGS spot. Here we study the influence of both the saturation of the sodium layer excited by different types of lasers, the spatial quality of the laser mode at the ground and the influence of the atmospheric turbulence on the upward propagation of the laser beam. Both shape and intensity of the LGS spot are found to depend strongly on these three effects with important consequences on the precision on the wavefront analysis.

  20. A study of visual double stars with early type primaries. IV. Astrophysical data

    International Nuclear Information System (INIS)

    Lindroos, K.P.

    1985-01-01

    Astrophysical parameters (MK class, colour excess, absolute magnitude, distance, effective temperature mass and age) are derived from calibrations of the uvbyβ indices for the members of 253 double stars with O or B type primaries and faint secondaries. The photometric spectral classification is compared to the MK classes and the agreement is very good. The derived data together with spectroscopic and JHKL data are used for deciding which pairs are likely to be physical and which are optical and it is shown that 98 (34%) of the secondaries are likely to be members of physical systems. For 90% of the physical pairs the projected separations between the components is less than 25000 AU. A majority of the physical secondaries are late type stars and 50% of them are contracting towards the zero-age main-sequence. Also presented are new uvbyβ data for 43 secondaries and a computer programme for determining astrophysical parameters from uvbyβ data

  1. Gravitational waves, neutrino emissions and effects of hyperons in binary neutron star mergers

    International Nuclear Information System (INIS)

    Kiuchi, Kenta; Sekiguchi, Yuichiro; Kyutoku, Koutarou; Shibata, Masaru

    2012-01-01

    Numerical simulations for the merger of binary neutron stars are performed in full general relativity incorporating both nucleonic and hyperonic finite-temperature equations of state (EOS) and neutrino cooling. It is found that for the nucleonic and hyperonic EOS, a hyper-massive neutron star (HMNS) with a long lifetime (t life ≥ 10 ms) is the outcome for the total mass ≅2.7M sun . For the total mass ≅3 M sun , a long-lived (short-lived with t life ≅ 3 ms) HMNS is the outcome for the nucleonic (hyperonic) EOS. It is shown that the typical total neutrino luminosity of the HMNS is ∼3-6 x 10 53 erg s -1 and the effective amplitude of gravitational waves from the HMNS is 1-4 x 10 -22 at f ≅ 2-3.2 kHz for a source of distance of 100 Mpc. During the HMNS phase, characteristic frequencies of gravitational waves shift to a higher frequency for the hyperonic EOS in contrast to the nucleonic EOS in which they remain constant approximately. Our finding suggests that the effects of hyperons are well imprinted in gravitational waves and their detection will give us a potential opportunity to explore the composition of the neutron star matter. We present the neutrino luminosity curve when a black hole is formed as well. (paper)

  2. Quark-nuclear hybrid star equation of state with excluded volume effects

    Science.gov (United States)

    Kaltenborn, Mark Alexander Randolph; Bastian, Niels-Uwe Friedrich; Blaschke, David Bernhard

    2017-09-01

    A two-phase description of the quark-nuclear matter hybrid equation of state that takes into account the effect of excluded volume in both the hadronic and the quark-matter phases is introduced. The nuclear phase manifests a reduction of the available volume as density increases, leading to a stiffening of the matter. The quark-matter phase displays a reduction of the effective string tension in the confining density functional from available volume contributions. The nuclear equation of state is based upon the relativistic density-functional model DD2 with excluded volume. The quark-matter equation of state is based upon a quasiparticle model derived from a relativistic density-functional approach and will be discussed in greater detail. The interactions are decomposed into mean scalar and vector components. The scalar interaction is motivated by a string potential between quarks, whereas the vector interaction potential is motivated by higher-order interactions of quarks leading to an increased stiffening at high densities. As an application, we consider matter under compact star constraints of electric neutrality and β equilibrium. We obtain mass-radius relations for hybrid stars that form a third family, disconnected from the purely hadronic star branch, and fulfill the 2 M⊙ constraint.

  3. Effect of process variables on the osmotic dehydration of star-fruit slices

    Directory of Open Access Journals (Sweden)

    Camila Dalben Madeira Campos

    2012-06-01

    Full Text Available The objective of this work was to study the effect of blanching and the influence of temperature, solution concentration, and the initial fruit:solution ratio on the osmotic dehydration of star-fruit slices. For blanching, different concentrations of citric and ascorbic acids were studied. The samples immersed in 0.75% citric acid presented little variation in color in relation to the fresh star-fruit. Osmotic dehydration was carried out in an incubator with orbital shaking, controlled temperature, and constant shaking at 120 rpm. The influence of process variables was studied in trials defined by a complete 23 central composite design. In general, water loss and solids gain were positively influenced by temperature and by solution concentration. Nevertheless, lower temperatures reduced water loss throughout the osmotic dehydration process. An increase in the amount of dehydrating solution (initial fruit:solution ratio slightly influenced the evaluated responses. The process carried out at 50 ºC with a solution concentration of 50% resulted in a product with lower solids gain and greater water loss. Under these conditions, blanching minimized the effect of the osmotic treatment on star-fruit browning, and therefore the blanched fruits showed little variation in color in relation to the fresh fruit.

  4. A search for magnetic fields in Lambda Bootis stars

    International Nuclear Information System (INIS)

    Bohlender, D.A.; Landstreet, J.D.

    1990-01-01

    We have searched a sample of λ Boo stars for magnetic fields similar to those observed in the magnetic Ap and Bp stars, using a Balmer-line Zeeman analyser. Apart from one dubious measurement, no fields are detected in our sample. It appears that magnetic fields of the λ Boo stars, if they exist, are significantly smaller than those found in magnetic upper main-sequence stars of similar spectral type; this conclusion is supported at about the 90 or 95 per cent confidence level by the present data. (author)

  5. Monte Carlo simulation of star/linear and star/star blends with chemically identical monomers

    Energy Technology Data Exchange (ETDEWEB)

    Theodorakis, P E [Department of Materials Science and Engineering, University of Ioannina, 45110 Ioannina (Greece); Avgeropoulos, A [Department of Materials Science and Engineering, University of Ioannina, 45110 Ioannina (Greece); Freire, J J [Departamento de Ciencias y Tecnicas FisicoquImicas, Universidad Nacional de Educacion a Distancia, Facultad de Ciencias, Senda del Rey 9, 28040 Madrid (Spain); Kosmas, M [Department of Chemistry, University of Ioannina, 45110 Ioannina (Greece); Vlahos, C [Department of Chemistry, University of Ioannina, 45110 Ioannina (Greece)

    2007-11-21

    The effects of chain size and architectural asymmetry on the miscibility of blends with chemically identical monomers, differing only in their molecular weight and architecture, are studied via Monte Carlo simulation by using the bond fluctuation model. Namely, we consider blends composed of linear/linear, star/linear and star/star chains. We found that linear/linear blends are more miscible than the corresponding star/star mixtures. In star/linear blends, the increase in the volume fraction of the star chains increases the miscibility. For both star/linear and star/star blends, the miscibility decreases with the increase in star functionality. When we increase the molecular weight of linear chains of star/linear mixtures the miscibility decreases. Our findings are compared with recent analytical and experimental results.

  6. Monte Carlo simulation of star/linear and star/star blends with chemically identical monomers

    Science.gov (United States)

    Theodorakis, P. E.; Avgeropoulos, A.; Freire, J. J.; Kosmas, M.; Vlahos, C.

    2007-11-01

    The effects of chain size and architectural asymmetry on the miscibility of blends with chemically identical monomers, differing only in their molecular weight and architecture, are studied via Monte Carlo simulation by using the bond fluctuation model. Namely, we consider blends composed of linear/linear, star/linear and star/star chains. We found that linear/linear blends are more miscible than the corresponding star/star mixtures. In star/linear blends, the increase in the volume fraction of the star chains increases the miscibility. For both star/linear and star/star blends, the miscibility decreases with the increase in star functionality. When we increase the molecular weight of linear chains of star/linear mixtures the miscibility decreases. Our findings are compared with recent analytical and experimental results.

  7. Monte Carlo simulation of star/linear and star/star blends with chemically identical monomers

    International Nuclear Information System (INIS)

    Theodorakis, P E; Avgeropoulos, A; Freire, J J; Kosmas, M; Vlahos, C

    2007-01-01

    The effects of chain size and architectural asymmetry on the miscibility of blends with chemically identical monomers, differing only in their molecular weight and architecture, are studied via Monte Carlo simulation by using the bond fluctuation model. Namely, we consider blends composed of linear/linear, star/linear and star/star chains. We found that linear/linear blends are more miscible than the corresponding star/star mixtures. In star/linear blends, the increase in the volume fraction of the star chains increases the miscibility. For both star/linear and star/star blends, the miscibility decreases with the increase in star functionality. When we increase the molecular weight of linear chains of star/linear mixtures the miscibility decreases. Our findings are compared with recent analytical and experimental results

  8. Asteroseismology of Exoplanet-Host Stars in the TESS Era

    DEFF Research Database (Denmark)

    Campante, Tiago L.; Schofield, Mathew; Chaplin, William J.

    2015-01-01

    -mass main-sequence hosts, as well as for the cohort of “full-frame image” stars (observed at a 30-min cadence). The latter cohort offers the exciting prospect of conducting asteroseismology on a significant number of evolved hosts. Also, the brightest solar-type hosts with asteroseismology will become some...

  9. The early evolution of stars and planets with varying mass

    International Nuclear Information System (INIS)

    Bhattacharjee, S.K.

    1980-09-01

    In this thesis some aspects of stellar and planetary evolution with varying mass are examined. It is divided into two sections. The first section deals with the evolution of stars in the pre-main-sequence phase with mass accretion while in the second section we discuss the spin angular momentum of the planets with mass loss. (author)

  10. Hyperfast pulsars as the remnants of massive stars ejected from young star clusters

    Science.gov (United States)

    Gvaramadze, Vasilii V.; Gualandris, Alessia; Portegies Zwart, Simon

    2008-04-01

    Recent proper motion and parallax measurements for the pulsar PSR B1508+55 indicate a transverse velocity of ~1100kms-1, which exceeds earlier measurements for any neutron star. The spin-down characteristics of PSR B1508+55 are typical for a non-recycled pulsar, which implies that the velocity of the pulsar cannot have originated from the second supernova disruption of a massive binary system. The high velocity of PSR B1508+55 can be accounted for by assuming that it received a kick at birth or that the neutron star was accelerated after its formation in the supernova explosion. We propose an explanation for the origin of hyperfast neutron stars based on the hypothesis that they could be the remnants of a symmetric supernova explosion of a high-velocity massive star which attained its peculiar velocity (similar to that of the pulsar) in the course of a strong dynamical three- or four-body encounter in the core of dense young star cluster. To check this hypothesis, we investigated three dynamical processes involving close encounters between: (i) two hard massive binaries, (ii) a hard binary and an intermediate-mass black hole (IMBH) and (iii) a single stars and a hard binary IMBH. We find that main-sequence O-type stars cannot be ejected from young massive star clusters with peculiar velocities high enough to explain the origin of hyperfast neutron stars, but lower mass main-sequence stars or the stripped helium cores of massive stars could be accelerated to hypervelocities. Our explanation for the origin of hyperfast pulsars requires a very dense stellar environment of the order of 106- 107starspc-3. Although such high densities may exist during the core collapse of young massive star clusters, we caution that they have never been observed.

  11. Formation of a contact binary star system

    International Nuclear Information System (INIS)

    Mullen, E.F.F.

    1974-01-01

    The process of forming a contact binary star system is investigated in the light of current knowledge of the W Ursae Majoris type eclipsing binaries and the current rotational braking theories for contracting stars. A preliminary stage of mass transfer is proposed and studied through the use of a computer program which calculates evolutionary model sequences. The detailed development of both stars is followed in these calculations, and findings regarding the internal structure of the star which is receiving the mass are presented. Relaxation of the mass-gaining star is also studied; for these stars of low mass and essentially zero age, the star eventually settles to a state very similar to a zero-age main sequence star of the new mass. A contact system was formed through these calculations; it exhibits the general properties of a W Ursae Majoris system. The initial masses selected for the calculation were 1.29 M/sub solar mass/ and 0.56 M/sub solar mass/. An initial mass transfer rate of about 10 -10 solar masses per year gradually increased to about 10 -8 solar masses per year. After about 2.5 x 10 7 years, the less massive star filled its Roche lobe and an initial contact system was obtained. The final masses were 1.01359 M/sub solar mass/ and 0.83641 M/sub solar mass/. The internal structure of the secondary component is considerably different from that of a main sequence star of the same mass

  12. Seismology of adolescent neutron stars: Accounting for thermal effects and crust elasticity

    Science.gov (United States)

    Krüger, C. J.; Ho, W. C. G.; Andersson, N.

    2015-09-01

    We study the oscillations of relativistic stars, incorporating key physics associated with internal composition, thermal gradients and crust elasticity. Our aim is to develop a formalism which is able to account for the state-of-the-art understanding of the complex physics associated with these systems. As a first step, we build models using a modern equation of state including composition gradients and density discontinuities associated with internal phase transitions (like the crust-core transition and the point where muons first appear in the core). In order to understand the nature of the oscillation spectrum, we carry out cooling simulations to provide realistic snapshots of the temperature distribution in the interior as the star evolves through adolescence. The associated thermal pressure is incorporated in the perturbation analysis, and we discuss the presence of g -modes arising as a result of thermal effects. We also consider interface modes due to phase-transitions and the gradual formation of the star's crust and the emergence of a set of shear modes.

  13. CLOSE STELLAR ENCOUNTERS IN YOUNG, SUBSTRUCTURED, DISSOLVING STAR CLUSTERS: STATISTICS AND EFFECTS ON PLANETARY SYSTEMS

    International Nuclear Information System (INIS)

    Craig, Jonathan; Krumholz, Mark R.

    2013-01-01

    Both simulations and observations indicate that stars form in filamentary, hierarchically clustered associations, most of which disperse into their galactic field once feedback destroys their parent clouds. However, during their early evolution in these substructured environments, stars can undergo close encounters with one another that might have significant impacts on their protoplanetary disks or young planetary systems. We perform N-body simulations of the early evolution of dissolving, substructured clusters with a wide range of properties, with the aim of quantifying the expected number and orbital element distributions of encounters as a function of cluster properties. We show that the presence of substructure both boosts the encounter rate and modifies the distribution of encounter velocities compared to what would be expected for a dynamically relaxed cluster. However, the boost only lasts for a dynamical time, and as a result the overall number of encounters expected remains low enough that gravitational stripping is unlikely to be a significant effect for the vast majority of star-forming environments in the Galaxy. We briefly discuss the implications of this result for models of the origin of the solar system, and of free-floating planets. We also provide tabulated encounter rates and orbital element distributions suitable for inclusion in population synthesis models of planet formation in a clustered environment.

  14. Phase Transition Effects on the Dynamical Stability of Hybrid Neutron Stars

    Science.gov (United States)

    Pereira, Jonas P.; Flores, César V.; Lugones, Germán

    2018-06-01

    We study radial oscillations of hybrid nonrotating neutron stars composed by a quark matter core and hadronic external layers. At first, we physically deduce the junction conditions that should be imposed between the two phases in these systems when perturbations take place. Then we compute the oscillation spectrum focusing on the effects of slow and rapid phase transitions at the quark-hadron interface. We use a generic MIT-bag model for quark matter and a relativistic mean field theory for hadronic matter. In the case of rapid transitions at the interface, we find a general relativistic version of the reaction mode that has similar properties as its classical counterpart. We also show that the usual static stability condition ∂M/∂ρ c ≥ 0, where ρ c is the central density of a star whose total mass is M, always remains true for rapid transitions but breaks down in general for slow transitions. In fact, for slow transitions, we find that the frequency of the fundamental mode can be a real number (indicating stability) even for some branches of stellar models that verify ∂M/∂ρ c ≤ 0. Thus, when secular instabilities are suppressed, as expected below some critical stellar rotation rate, the existance of twin or even triplet stars with the same gravitational mass but different radii, with one of the counterparts having ∂M/∂ρ c ≤ 0, would be possible. We explore some astrophysical consequences of these results.

  15. CLOSE STELLAR ENCOUNTERS IN YOUNG, SUBSTRUCTURED, DISSOLVING STAR CLUSTERS: STATISTICS AND EFFECTS ON PLANETARY SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Craig, Jonathan; Krumholz, Mark R., E-mail: krumholz@ucolick.org [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

    2013-06-01

    Both simulations and observations indicate that stars form in filamentary, hierarchically clustered associations, most of which disperse into their galactic field once feedback destroys their parent clouds. However, during their early evolution in these substructured environments, stars can undergo close encounters with one another that might have significant impacts on their protoplanetary disks or young planetary systems. We perform N-body simulations of the early evolution of dissolving, substructured clusters with a wide range of properties, with the aim of quantifying the expected number and orbital element distributions of encounters as a function of cluster properties. We show that the presence of substructure both boosts the encounter rate and modifies the distribution of encounter velocities compared to what would be expected for a dynamically relaxed cluster. However, the boost only lasts for a dynamical time, and as a result the overall number of encounters expected remains low enough that gravitational stripping is unlikely to be a significant effect for the vast majority of star-forming environments in the Galaxy. We briefly discuss the implications of this result for models of the origin of the solar system, and of free-floating planets. We also provide tabulated encounter rates and orbital element distributions suitable for inclusion in population synthesis models of planet formation in a clustered environment.

  16. Close Stellar Encounters in Young, Substructured, Dissolving Star Clusters: Statistics and Effects on Planetary Systems

    Science.gov (United States)

    Craig, Jonathan; Krumholz, Mark R.

    2013-06-01

    Both simulations and observations indicate that stars form in filamentary, hierarchically clustered associations, most of which disperse into their galactic field once feedback destroys their parent clouds. However, during their early evolution in these substructured environments, stars can undergo close encounters with one another that might have significant impacts on their protoplanetary disks or young planetary systems. We perform N-body simulations of the early evolution of dissolving, substructured clusters with a wide range of properties, with the aim of quantifying the expected number and orbital element distributions of encounters as a function of cluster properties. We show that the presence of substructure both boosts the encounter rate and modifies the distribution of encounter velocities compared to what would be expected for a dynamically relaxed cluster. However, the boost only lasts for a dynamical time, and as a result the overall number of encounters expected remains low enough that gravitational stripping is unlikely to be a significant effect for the vast majority of star-forming environments in the Galaxy. We briefly discuss the implications of this result for models of the origin of the solar system, and of free-floating planets. We also provide tabulated encounter rates and orbital element distributions suitable for inclusion in population synthesis models of planet formation in a clustered environment.

  17. Orbital Decay in Binaries with Evolved Stars

    Science.gov (United States)

    Sun, Meng; Arras, Phil; Weinberg, Nevin N.; Troup, Nicholas; Majewski, Steven R.

    2018-01-01

    Two mechanisms are often invoked to explain tidal friction in binary systems. The ``dynamical tide” is the resonant excitation of internal gravity waves by the tide, and their subsequent damping by nonlinear fluid processes or thermal diffusion. The ``equilibrium tide” refers to non-resonant excitation of fluid motion in the star’s convection zone, with damping by interaction with the turbulent eddies. There have been numerous studies of these processes in main sequence stars, but less so on the subgiant and red giant branches. Motivated by the newly discovered close binary systems in the Apache Point Observatory Galactic Evolution Experiment (APOGEE-1), we have performed calculations of both the dynamical and equilibrium tide processes for stars over a range of mass as the star’s cease core hydrogen burning and evolve to shell burning. Even for stars which had a radiative core on the main sequence, the dynamical tide may have very large amplitude in the newly radiative core in post-main sequence, giving rise to wave breaking. The resulting large dynamical tide dissipation rate is compared to the equilibrium tide, and the range of secondary masses and orbital periods over which rapid orbital decay may occur will be discussed, as well as applications to close APOGEE binaries.

  18. Identifying Treatment Effect Modifiers in the STarT Back Trial: A Secondary Analysis.

    Science.gov (United States)

    Beneciuk, Jason M; Hill, Jonathan C; Campbell, Paul; Afolabi, Ebenezer; George, Steven Z; Dunn, Kate M; Foster, Nadine E

    2017-01-01

    Identification of patient characteristics influencing treatment outcomes is a top low back pain (LBP) research priority. Results from the STarT Back trial support the effectiveness of prognostic stratified care for LBP compared with current best care, however, patient characteristics associated with treatment response have not yet been explored. The purpose of this secondary analysis was to identify treatment effect modifiers within the STarT Back trial at 4-month follow-up (n = 688). Treatment response was dichotomized using back-specific physical disability measured using the Roland-Morris Disability Questionnaire (≥7). Candidate modifiers were identified using previous literature and evaluated using logistic regression with statistical interaction terms to provide preliminary evidence of treatment effect modification. Socioeconomic status (SES) was identified as an effect modifier for disability outcomes (odds ratio [OR] = 1.71, P = .028). High SES patients receiving prognostic stratified care were 2.5 times less likely to have a poor outcome compared with low SES patients receiving best current care (OR = .40, P = .006). Education level (OR = 1.33, P = .109) and number of pain medications (OR = .64, P = .140) met our criteria for effect modification with weaker evidence (.20 > P ≥ .05). These findings provide preliminary evidence for SES, education, and number of pain medications as treatment effect modifiers of prognostic stratified care delivered in the STarT Back Trial. This analysis provides preliminary exploratory findings about the characteristics of patients who might least likely benefit from targeted treatment using prognostic stratified care for LBP. Copyright © 2016 American Pain Society. Published by Elsevier Inc. All rights reserved.

  19. Photometric search for variable stars in the young open cluster Berkeley 59

    Science.gov (United States)

    Lata, Sneh; Pandey, A. K.; Maheswar, G.; Mondal, Soumen; Kumar, Brijesh

    2011-12-01

    We present the time series photometry of stars located in the extremely young open cluster Berkeley 59. Using the 1.04-m telescope at Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, we have identified 42 variables in a field of ˜13 × 13 arcmin2 around the cluster. The probable members of the cluster have been identified using a (V, V-I) colour-magnitude diagram and a (J-H, H-K) colour-colour diagram. 31 variables have been found to be pre-main-sequence stars associated with the cluster. The ages and masses of the pre-main-sequence stars have been derived from the colour-magnitude diagram by fitting theoretical models to the observed data points. The ages of the majority of the probable pre-main-sequence variable candidates range from 1 to 5 Myr. The masses of these pre-main-sequence variable stars have been found to be in the range of ˜0.3 to ˜3.5 M⊙, and these could be T Tauri stars. The present statistics reveal that about 90 per cent T Tauri stars have period dispersal of the discs of relatively massive stars.

  20. Search for bright stars with infrared excess

    Energy Technology Data Exchange (ETDEWEB)

    Raharto, Moedji, E-mail: moedji@as.itb.ac.id [Astronomy Research Division, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jl. Ganesha 10, Bandung 40132 (Indonesia)

    2014-03-24

    Bright stars, stars with visual magnitude smaller than 6.5, can be studied using small telescope. In general, if stars are assumed as black body radiator, then the color in infrared (IR) region is usually equal to zero. Infrared data from IRAS observations at 12 and 25μm (micron) with good flux quality are used to search for bright stars (from Bright Stars Catalogues) with infrared excess. In magnitude scale, stars with IR excess is defined as stars with IR color m{sub 12}−m{sub 25}>0; where m{sub 12}−m{sub 25} = −2.5log(F{sub 12}/F{sub 25})+1.56, where F{sub 12} and F{sub 25} are flux density in Jansky at 12 and 25μm, respectively. Stars with similar spectral type are expected to have similar color. The existence of infrared excess in the same spectral type indicates the existence of circum-stellar dust, the origin of which is probably due to the remnant of pre main-sequence evolution during star formation or post AGB evolution or due to physical process such as the rotation of those stars.

  1. The onset of chromospheric activity among the A- and F- type stars

    Science.gov (United States)

    Simon, Theodore; Landsman, Wayne

    1987-01-01

    IUE observations of C II lambda1335 and C IV lambda1549 and ground-based observations of He I lambda5876 have previously discovered intense levels of chromospheric activity among early F type stars. Virtually all F dwarfs show stronger chromospheric and transition region emission than do the cooler and more deeply convective dwarf stars like the Sun. The IUE spectra and those of He lambda5876 place the onset of stellar activity along the main sequence near a color B - V = 0.28, which corresponds approximately to spectral type FO and an effective temperature of 7300 K. However, existing X-ray observations of A and F stars suggest that coronal activity may reach a peak blueward of this high temperature boundary at B - V = 0.28 before vanishing among the early and mid A-type stars. Discussed are preliminary results of a new effort to refine the location of the high temperature boundary to chromospheric activity among A- and F- type stars, making use of low dispersion short-wavelength spectra from the IUE archives from which the strengths of C IV, C II, and Lyman alpha emission have been measured.

  2. Evolution of massive close binaries and formation of neutron stars and black holes

    International Nuclear Information System (INIS)

    Massevitch, A.G.; Tutukov, A.V.; Yungelson, L.R.

    1976-01-01

    Main results of computations of evolution for massive close binaries (10 M(Sun)+9.4 M(Sun), 16 M(Sun)+15 M(Sun), 32 M(Sun)+30 M(Sun), 64 M(Sun)+60 M(Sun)) up to oxygen exhaustion in the core are described. Mass exchange starting in core hydrogen, shell hydrogen and core helium burning stages was studied. Computations were performed assuming both the Ledoux and Schwarzschild stability criteria for semiconvection. The influence of UFI-neutrino emission on evolution of close binaries was investigated. The results obtained allow to outline the following evolutionary chain: two detached Main-Sequence stars - mass exchange - Wolf-Rayet star or blue supergiant plus main sequence star - explosion of the initially more massive star appearing as a supernova event - collapsed or neutron star plus Main-Sequence star, that may be observed as a 'runaway star' - mass exchange leading to X-rays emission - collapsed or neutron star plus WR-star or blue supergiant - second explosion of supernova that preferentially disrupts the system and gives birth to two single high spatial velocity pulsars. Numerical estimates concerning the number and properties of WR-stars, pulsars and X-ray sources are presented. The results are in favour of the existence of UFI-neutrino and of the Ledoux criterion for describing semiconvection. Properties of several well-known X-ray sources and the binary pulsar are discussed on base of evolutionary chain of close binaries. (Auth.)

  3. SIGNATURES OF DARK MATTER BURNING IN NUCLEAR STAR CLUSTERS

    International Nuclear Information System (INIS)

    Casanellas, Jordi; Lopes, IlIdio

    2011-01-01

    In order to characterize how dark matter (DM) annihilation inside stars changes the aspect of a stellar cluster, we computed the evolution until the ignition of the He burning of stars from 0.7 M sun to 3.5 M sun within halos of DM with different characteristics. We found that, when a cluster is surrounded by a dense DM halo, the positions of the cluster' stars in the H-R diagram have a brighter and hotter turnoff point than in the classical scenario without DM, therefore giving the cluster a younger appearance. The high DM densities required to produce these effects are expected only in very specific locations, such as near the center of our Galaxy. In particular, if DM is formed by the 8 GeV weakly interacting massive particles recently invoked to reconcile the results from direct detection experiments, then this signature is predicted for halos of DM with a density ρ χ = 3 x 10 5 GeV cm -3 . A DM density gradient inside the stellar cluster would result in a broader main sequence, turnoff, and red giant branch regions. Moreover, we found that for very high DM halo densities the bottom of the isochrones in the H-R diagram rises to higher luminosities, leading to a characteristic signature on the stellar cluster. We argue that this signature could be used to indirectly probe the presence of DM particles in the location of a cluster.

  4. Linear series of stellar models. Pt. 4. Helium-carbon stars of 3.5Msub(o) and 1Msub(o)

    International Nuclear Information System (INIS)

    Kozlowski, M.; Paczynski, B.; Popova, K.

    1973-01-01

    One linear series of models for a star of 3.5Msub(o) and two linear series of models for a star of 1Msub(o) are constructed. Models consist of helium rich envelopes (Y = 0.97, Z = 0.03) and pure carbon cores, and they have a rectangular helium profile, Y(Msub(r)). The linear series for a star of 3.5Msub(o) begins on the normal branch of the helium main sequence and terminates on the normal branch of the carbon main sequence. This series has eight turning points at which the core mass attains a local extremum. One of the two linear series for a star of 1Msub(o) begins on the normal branch of the helium main sequence, terminates on the high density branch of the helium main sequence, and has one turning point. The second linear series for a star of 1Msub(o) begins on the normal branch of the carbon main sequence, terminates on the high density branch of the carbon main sequence, and has three turning points. Two such linear series may have a common bifurcation point for a star of about 1.26Msub(o). (author)

  5. The character and behaviour of circumstellar shells at T Tauri stars

    International Nuclear Information System (INIS)

    Goetz, W.

    1988-01-01

    T Tauri stars are extremely young low-mass stars in the pre-main sequence stage. A brief review of investigations made at the Sonneberg observatory concerning the character and the behaviour of circumstellar shells at T Tauri stars is given. They lead to the construction of a shell model on the basis of observational facts. The idea rests upon the causal connection between the gas and dust shell phenomenon and the cosmogonic mass loss of the stars, which is the connecting link between the stars and their shells and which appears in the early phase of the pre-main sequence stage and decreases, like the accompanying shell phenomena, during the evolution of the stars. (author)

  6. The effect of convection and semi-convection on the C/O yield of massive stars

    International Nuclear Information System (INIS)

    Dearborn, D.S.

    1979-01-01

    The C/O ratio produced during core helium burning affects the future evolution and nucleosynthetic yield of massive stars. This ratio is shown to be sensitive to the treatment of convection as well as uncertainties in nuclear rates. By minimizing the effect of semi-convection and reducing the size of the convective core, mass loss in OB stars increases the C/O ratio. (Author)

  7. Zeeman effect in sulfur monoxide. A tool to probe magnetic fields in star forming regions

    Science.gov (United States)

    Cazzoli, Gabriele; Lattanzi, Valerio; Coriani, Sonia; Gauss, Jürgen; Codella, Claudio; Ramos, Andrés Asensio; Cernicharo, José; Puzzarini, Cristina

    2017-09-01

    Context. Magnetic fields play a fundamental role in star formation processes and the best method to evaluate their intensity is to measure the Zeeman effect of atomic and molecular lines. However, a direct measurement of the Zeeman spectral pattern from interstellar molecular species is challenging due to the high sensitivity and high spectral resolution required. So far, the Zeeman effect has been detected unambiguously in star forming regions for very few non-masing species, such as OH and CN. Aims: We decided to investigate the suitability of sulfur monoxide (SO), which is one of the most abundant species in star forming regions, for probing the intensity of magnetic fields via the Zeeman effect. Methods: We investigated the Zeeman effect for several rotational transitions of SO in the (sub-)mm spectral regions by using a frequency-modulated, computer-controlled spectrometer, and by applying a magnetic field parallel to the radiation propagation (I.e., perpendicular to the oscillating magnetic field of the radiation). To support the experimental determination of the g factors of SO, a systematic quantum-chemical investigation of these parameters for both SO and O2 has been carried out. Results: An effective experimental-computational strategy for providing accurate g factors as well as for identifying the rotational transitions showing the strongest Zeeman effect has been presented. Revised g factors have been obtained from a large number of SO rotational transitions between 86 and 389 GHz. In particular, the rotational transitions showing the largest Zeeman shifts are: N,J = 2, 2 ← 1, 1 (86.1 GHz), N,J = 4, 3 ← 3, 2 (159.0 GHz), N,J = 1, 1 ← 0, 1 (286.3 GHz), N,J = 2, 2 ← 1, 2 (309.5 GHz), and N,J = 2, 1 ← 1, 0 (329.4 GHz). Our investigation supports SO as a good candidate for probing magnetic fields in high-density star forming regions. The complete list of measured Zeeman components is only available at the CDS via anonymous ftp to http

  8. PHIBSS: MOLECULAR GAS, EXTINCTION, STAR FORMATION, AND KINEMATICS IN THE z = 1.5 STAR-FORMING GALAXY EGS13011166

    Energy Technology Data Exchange (ETDEWEB)

    Genzel, R.; Tacconi, L. J.; Kurk, J.; Wuyts, S.; Foerster Schreiber, N. M.; Gracia-Carpio, J. [Max-Planck-Institut fuer extraterrestrische Physik (MPE), Giessenbachstr., D-85748 Garching (Germany); Combes, F.; Freundlich, J. [Observatoire de Paris, LERMA, CNRS, 61 Av. de l' Observatoire, F-75014 Paris (France); Bolatto, A. [Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States); Cooper, M. C. [Department of Physics and Astronomy, Frederick Reines Hall, University of California, Irvine, CA 92697 (United States); Neri, R. [IRAM, 300 Rue de la Piscine, F-38406 St. Martin d' Heres, Grenoble (France); Nordon, R. [Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978 (Israel); Bournaud, F. [Service d' Astrophysique, DAPNIA, CEA/Saclay, F-91191 Gif-sur-Yvette Cedex (France); Burkert, A. [Universitaetssternwarte der Ludwig-Maximiliansuniversitaet, Scheinerstr. 1, D-81679 Muenchen (Germany); Comerford, J. [Department of Astronomy and McDonald Observatory, 1 University Station, C1402 Austin, TX 78712-0259 (United States); Cox, P. [Department of Physics, Le Conte Hall, University of California, 94720 Berkeley, CA (United States); Davis, M. [Department of Astronomy, Campbell Hall, University of California, Berkeley, CA 94720 (United States); Garcia-Burillo, S. [Observatorio Astronomico Nacional-OAN, Observatorio de Madrid, Alfonso XII, 3, E-28014 Madrid (Spain); Naab, T. [Max-Planck Institut fuer Astrophysik, Karl Schwarzschildstrasse 1, D-85748 Garching (Germany); Lutz, D., E-mail: genzel@mpe.mpg.de, E-mail: linda@mpe.mpg.de; and others

    2013-08-10

    We report matched resolution imaging spectroscopy of the CO 3-2 line (with the IRAM Plateau de Bure millimeter interferometer) and of the H{alpha} line (with LUCI at the Large Binocular Telescope) in the massive z = 1.53 main-sequence galaxy EGS 13011166, as part of the ''Plateau de Bure high-z, blue-sequence survey'' (PHIBSS: Tacconi et al.). We combine these data with Hubble Space Telescope V-I-J-H-band maps to derive spatially resolved distributions of stellar surface density, star formation rate, molecular gas surface density, optical extinction, and gas kinematics. The spatial distribution and kinematics of the ionized and molecular gas are remarkably similar and are well modeled by a turbulent, globally Toomre unstable, rotating disk. The stellar surface density distribution is smoother than the clumpy rest-frame UV/optical light distribution and peaks in an obscured, star-forming massive bulge near the dynamical center. The molecular gas surface density and the effective optical screen extinction track each other and are well modeled by a ''mixed'' extinction model. The inferred slope of the spatially resolved molecular gas to star formation rate relation, N = dlog{Sigma}{sub starform}/dlog{Sigma}{sub molgas}, depends strongly on the adopted extinction model, and can vary from 0.8 to 1.7. For the preferred mixed dust-gas model, we find N = 1.14 {+-} 0.1.

  9. SPB stars in the open SMC cluster NGC 371

    Science.gov (United States)

    Karoff, C.; Arentoft, T.; Glowienka, L.; Coutures, C.; Nielsen, T. B.; Dogan, G.; Grundahl, F.; Kjeldsen, H.

    2008-05-01

    Pulsation in β Cep and slowly pulsating B (SPB) stars are driven by the κ mechanism which depends critically on the metallicity. It has therefore been suggested that β Cep and SPB stars should be rare in the Magellanic Clouds which have lower metallicities than the solar neighbourhood. To test this prediction we have observed the open Small Magellanic Cloud (SMC) cluster NGC 371 for 12 nights in order to search for β Cep and SPB stars. Surprisingly, we find 29 short-period B-type variables in the upper part of the main sequence, many of which are probably SPB stars. This result indicates that pulsation is still driven by the κ mechanism even in low-metallicity environments. All the identified variables have periods longer than the fundamental radial period which means that they cannot be β Cep stars. Within an amplitude detection limit of 5 mmag no stars in the top of the Hertzsprung-Russell diagram show variability with periods shorter than the fundamental radial period. So if β Cep stars are present in the cluster they oscillate with amplitudes below 5 mmag, which is significantly lower than the mean amplitude of β Cep stars in the Galaxy. We see evidence that multimode pulsation is more common in the upper part of the main sequence than in the lower. We have also identified five eclipsing binaries and three periodic pulsating Be stars in the cluster field.

  10. Amplitude Modulation of Pulsation Modes in Delta Scuti Stars

    Science.gov (United States)

    Bowman, Dominic M.

    2017-10-01

    first overtone radial modes in KIC 5950759. The observed phase modulation of the radial modes in this star is two orders of magnitude larger than predicted by stellar evolutionary models, yet is consistent with the prediction of increasing periods of radial modes for stars on the main sequence. The statistical analysis of 983 δ Sct stars, including the results from the search for amplitude modulation, is a valuable resource for ongoing and future space missions such as K2, TESS and PLATO, because the high quality 4-yr Kepler data set will not be surpassed for some time. The observational studies of individual stars in this thesis provide strong evidence that non-linear processes are clearly at work in the majority of δ Sct stars, and provide valuable constraints for future asteroseismic modelling.

  11. Hot H2O Emission and Evidence for Turbulence in the Disk of a Young Star

    Science.gov (United States)

    2004-03-01

    matter — infrared: stars — planetary systems: protoplanetary disks — stars: formation — stars: pre–main-sequence 1. INTRODUCTION The presence of hot...in disk gaps . Molecules other than CO are expected to exist at the temperatures and densities in the inner few AU of disks . Water should be very... protoplanetary disks . In addition, non-Gaussian line profiles might be ex- pected, given that a characteristic of turbulence seen in both laboratory experiments

  12. PROGRESSIVE STAR FORMATION IN THE YOUNG GALACTIC SUPER STAR CLUSTER NGC 3603

    International Nuclear Information System (INIS)

    Beccari, Giacomo; Spezzi, Loredana; De Marchi, Guido; Andersen, Morten; Paresce, Francesco; Young, Erick; Panagia, Nino; Bond, Howard; Balick, Bruce; Calzetti, Daniela; Carollo, C. Marcella; Disney, Michael J.; Dopita, Michael A.; Frogel, Jay A.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.; O'Connell, Robert W.; Saha, Abhijit

    2010-01-01

    Early Release Science observations of the cluster NGC 3603 with the WFC3 on the refurbished Hubble Space Telescope allow us to study its recent star formation history. Our analysis focuses on stars with Hα excess emission, a robust indicator of their pre-main sequence (PMS) accreting status. The comparison with theoretical PMS isochrones shows that 2/3 of the objects with Hα excess emission have ages from 1 to 10 Myr, with a median value of 3 Myr, while a surprising 1/3 of them are older than 10 Myr. The study of the spatial distribution of these PMS stars allows us to confirm their cluster membership and to statistically separate them from field stars. This result establishes unambiguously for the first time that star formation in and around the cluster has been ongoing for at least 10-20 Myr, at an apparently increasing rate.

  13. Evolution of variable stars

    International Nuclear Information System (INIS)

    Becker, S.A.

    1986-08-01

    Throughout the domain of the H R diagram lie groupings of stars whose luminosity varies with time. These variable stars can be classified based on their observed properties into distinct types such as β Cephei stars, δ Cephei stars, and Miras, as well as many other categories. The underlying mechanism for the variability is generally felt to be due to four different causes: geometric effects, rotation, eruptive processes, and pulsation. In this review the focus will be on pulsation variables and how the theory of stellar evolution can be used to explain how the various regions of variability on the H R diagram are populated. To this end a generalized discussion of the evolutionary behavior of a massive star, an intermediate mass star, and a low mass star will be presented. 19 refs., 1 fig., 1 tab

  14. Effects of Brown-Rho scalings in nuclear matter, neutron stars and finite nuclei

    Science.gov (United States)

    Kuo, T. T. S.; Dong, Huan

    2011-01-01

    We have carried out calculations for nuclear matter, neutron stars and finite nuclei using NN potentials with and without the medium-dependent modifications based on the Brown-Rho (BR) scalings. Using the Vlow-k low-momentum interactions derived from such potentials, the equations of state (EOS) for symmetric and asymmetric nuclear matter, for densities up to ~ 5ρ0, are calculated using a RPA method where the particle-particle hole-hole ring diagrams are summed to all orders. The medium effects from both a linear BR scaling (BR1) and a non-linear one (BR2) are considered, and they both are essential for our EOSs to reproduce the nuclear matter saturation properties. For densities ρ below ρ0, results from BR1 and BR2 are close to each other. For higher densities, the EOS given by BR2 is more desirable and is well reproduced by that given by the interaction (Vlow-k+TBF) where Vlow-k is the unsealed low-momentum interaction and TBF is an empirical Skyrme three-body force. The moment of inertia of neutron stars is ~ 60 and ~ 25Modotkm2 respectively with and without the inclusion of the above BR2 medium effects. Effects from the BR scaling are important for the long half-life, ~ 5000yrs, of the 14C - 14N β-decay.

  15. Post-main-sequence Evolution of Icy Minor Planets. III. Water Retention in Dwarf Planets and Exomoons and Implications for White Dwarf Pollution

    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)

    2017-11-01

    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. Several previous works studied the possibility of water surviving inside minor planets around evolving stars. However, they all focused on small, comet-sized to moonlet-sized minor planets, when the inferred mass inside the convection zones of He-dominated WDs could actually be compatible with much more massive minor planets. Here we explore for the first time, the water retention inside exoplanetary dwarf planets, or moderate-sized moons, with radii of the order of hundreds of kilometers. This paper concludes a series of papers that has now covered nearly the entire potential mass range of minor planets, in addition to the full mass range of their host stars. We find that water retention is (a) affected by the mass of the WD progenitor, and (b) it is on average at least 5%, irrespective of the assumed initial water composition, if it came from a single accretion event of an icy dwarf planet or moon. The latter prediction strengthens the possibility of habitability in WD planetary systems, and it may also be used in order to distinguish between pollution originating from multiple small accretion events and singular large accretion events. To conclude our work, we provide a code that calculates ice and water retention by interpolation and may be freely used as a service to the community.

  16. Strained coordinate methods in rotating stars. II

    International Nuclear Information System (INIS)

    Smith, B.L.

    1977-01-01

    It was shown in a previous paper (Smith, 1976) that the method of strained coordinates may be usefully employed in the determination of the structure of rotating polytropes. In the present work this idea is extended to Main-Sequence stars with conservative centrifugal fields. The structure variables, pressure, density and temperature are considered pure functions of an auxiliary coordinate s (the strained coordinate) and the governing equations written in a form that closely resembles the structure equations for spherical stars but with the correction factors that are functions of s. A systematic, order-by-order derivation of these factors is outlined and applied in detail to a Cowling-model star in uniform rotation. The techniques can be extended beyond first order and external boundary conditions are applied, as they should be, at the true surface of the star. Roche approximations are not needed. (Auth.)

  17. T Tauri stars - Wild as dust

    International Nuclear Information System (INIS)

    Bertout, C.

    1989-01-01

    T Tauri stars (TTSs), their surroundings, and their common evolution toward the main sequence are discussed. The photospheric properties of TTSs and their solar-type outer atmospheres, recent evidence for circumstellar disks around classical TTSs (CTTSs), and CTTS mass outflows are examined. TTSs are depicted as complex systems whose properties depend mostly on the initial conditions of star formation and on their rotation rates, which appear to control the magnetodynamic activity in the stars. The most exotic traits of CTTSs are primarily due to the disk and its interaction with the star, and the properties of weak-line TTSs (WTTSs) are mainly manifestations of the enhanced solar-type magnetic activity expected from their rotation rates. CTTSs are expected to become WTTSs when their disks dissipate. 217 refs

  18. Star-formation history of very young clusters

    International Nuclear Information System (INIS)

    Stahler, S.W.

    1985-01-01

    The popular idea that star formation has proceeded sequentially from lowest to highest mass members in open clusters is examined critically. For extremely young clusters, such as NGC 2264 and NGC 6530, this sequential hypothesis is a consequence of the assignment of pre-main-sequence contraction ages to all member stars. However, such ages yield a formation history which is implausible from a physical point of view, since the critical time for the onset of formation at any stellar mass is equal to the pre-main-sequence contraction time for that mass. Moreover, these ages are in conflict with the strong observational evidence that a substantial fraction of cluster members have already reached the main sequence. After reconsideration of the probable main-sequence members, the stellar ages in NGC 2264 and NGC 6530 are consistent with a variety of formation histories, and, in particular, with the view that all stellar masses form in approximately the same interval of time within a given cluster, i.e., that there is no mass-age correlation. A notion closely related to the sequential hypothesis, that the total star-formation rate increases exponentially with time, is subject to the same criticism

  19. The characteristics of the IR emission features in the spectra of Herbig Ae stars : evidence for chemical evolution

    NARCIS (Netherlands)

    Boersma, C.; Bouwman, J.; Lahuis, F.; van Kerckhoven, C.; Tielens, A. G. G. M.; Waters, L. B. F. M.; Henning, T.

    Context. Infrared ( IR) spectra provide a prime tool to study the characteristics of polycyclic aromatic hydrocarbon ( PAH) molecules in regions of star formation. Herbig Ae/Be stars are a class of young pre-main sequence stellar objects of intermediate mass. They are known to have varying amounts

  20. Fundamental properties of stars using asteroseismology from Kepler and CoRoT and interferometry from the CHARA Array

    DEFF Research Database (Denmark)

    Huber, D.; Ireland, M.J.; Bedding, T.R.

    2012-01-01

    We present results of a long-baseline interferometry campaign using the PAVO beam combiner at the CHARA Array to measure the angular sizes of five main-sequence stars, one subgiant and four red giant stars for which solar-like oscillations have been detected by either Kepler or CoRoT. By combinin...

  1. The symbiotics as binary stars

    International Nuclear Information System (INIS)

    Plavec, M.J.

    1982-01-01

    The author envisages at least three models that can give a symbiotic object: He has called them, respectively, the PN symbiotic, the Algol symbiotic, and the novalike symbiotic. Their properties are briefly discussed. The most promising model is one of a binary system in the second stage of mass transfer, actually at the beginning of it: The cool component is a red giant ascending the asymptotic branch, expanding but not yet filling its critical lobe. The hot star is a subdwarf located in the same region of the Hertzsprung-Russell diagram as the central stars of planetary nebulae. It may be closely related to them, or it may be a helium star, actually a remnant of an Algol primary which underwent the first stage of mass transfer. In these cases, accretion on this star may not play a significant role (PN symbiotic). Perhaps more often, the subdwarf is a ''rejuvenated'' degenerate dwarf whose nuclear burning shells were ignited and are maintained by accretion of material coming from the red giant in the form of a stellar wind. Eruptions are often inevitable: this is the novalike symbiotic. A third alternative is a system in the first stage of mass transfer, where the photons needed for ionization of the nebula come from an accretion disk surrounding a main sequence star: an Algol symbiotic. In spite of considerable observational effort, the symbiotics are known so poorly that it is hard to decide between the models, or even decide if all three can actually exist. (Auth.)

  2. Realistic limitations of detecting planets around young active stars

    Directory of Open Access Journals (Sweden)

    Pinfield D.

    2013-04-01

    Full Text Available Current planet hunting methods using the radial velocity method are limited to observing middle-aged main-sequence stars where the signatures of stellar activity are much less than on young stars that have just arrived on the main-sequence. In this work we apply our knowledge from the surface imaging of these young stars to place realistic limitations on the possibility of detecting orbiting planets. In general we find that the magnitude of the stellar jitter is directly proportional to the stellar vsini. For G and K dwarfs, we find that it is possible, for models with high stellar activity and low stellar vsini, to be able to detect a 1 MJupiter mass planet within 50 epochs of observations and for the M dwarfs it is possible to detect a habitable zone Earth-like planet in 10s of observational epochs.

  3. The Hot Horizontal-Branch Stars in NGC288 - Effects of Diffusion and Stratification on Their Atmospheric Parameters*

    Science.gov (United States)

    Moehler, S.; Dreizler, S.; LeBlanc, F.; Khalack, V.; Michaud, G.; Richer, J.; Sweigart, Allen V.; Grundahl, F.

    2014-01-01

    Context. NGC288 is a globular cluster with a well developed blue horizontal branch covering the so-called u-jump which indicates the onset of diffusion. It is therefore well suited to study the effects of diffusion in blue horizontal branch (HB) stars. Aims. We compare observed abundances to predictions from stellar evolution models calculated with diffusion and from stratified atmospheric models. We verify the effect of using stratified model spectra to derive atmospheric parameters. In addition we investigate the nature of the overluminous blue HB stars around the u-jump. Methods. We define a new photometric index sz from uvby measurements that is gravity sensitive between 8 000K and 12 000 K. Using medium-resolution spectra and Stroemgren photometry we determine atmospheric parameters (Teff, logg) and abundances for the blue HB stars. We use both homogeneous and stratified model spectra for our spectroscopic analyses. Results. The atmospheric parameters and masses of the hot HB stars in NGC288 show a behaviour seen also in other clusters for temperatures between 9 000K and 14 000 K. Outside this temperature range, however, they follow rather the results found for such stars in (omega)Cen. The abundances derived from our observations are for most elements (except He and P) within the abundance range expected from evolutionary models that include the effects of atomic diffusion and assume a surface mixed mass of 10(exp -7) M. The abundances predicted by stratified model atmospheres are generally significantly more extreme than observed, except for Mg. The use of stratified model spectra to determine effective temperatures, surface gravities and masses moves the hotter stars to a closer agreement with canonical evolutionary predictions. Conclusions. Our results show definite promise towards solving the long-standing issue of surface gravity and mass discrepancies for hot HB stars, but there is still much work needed to arrive at a self-consistent solution.

  4. EXPLORING SYSTEMATIC EFFECTS IN THE RELATION BETWEEN STELLAR MASS, GAS PHASE METALLICITY, AND STAR FORMATION RATE

    International Nuclear Information System (INIS)

    Telford, O. Grace; Dalcanton, Julianne J.; Skillman, Evan D.; Conroy, Charlie

    2016-01-01

    There is evidence that the well-established mass–metallicity relation in galaxies is correlated with a third parameter: star formation rate (SFR). The strength of this correlation may be used to disentangle the relative importance of different physical processes (e.g., infall of pristine gas, metal-enriched outflows) in governing chemical evolution. However, all three parameters are susceptible to biases that might affect the observed strength of the relation between them. We analyze possible sources of systematic error, including sample bias, application of signal-to-noise ratio cuts on emission lines, choice of metallicity calibration, uncertainty in stellar mass determination, aperture effects, and dust. We present the first analysis of the relation between stellar mass, gas phase metallicity, and SFR using strong line abundance diagnostics from Dopita et al. for ∼130,000 star-forming galaxies in the Sloan Digital Sky Survey and provide a detailed comparison of these diagnostics in an appendix. Using these new abundance diagnostics yields a 30%–55% weaker anti-correlation between metallicity and SFR at fixed stellar mass than that reported by Mannucci et al. We find that, for all abundance diagnostics, the anti-correlation with SFR is stronger for the relatively few galaxies whose current SFRs are elevated above their past average SFRs. This is also true for the new abundance diagnostic of Dopita et al., which gives anti-correlation between Z and SFR only in the high specific star formation rate (sSFR) regime, in contrast to the recent results of Kashino et al. The poorly constrained strength of the relation between stellar mass, metallicity, and SFR must be carefully accounted for in theoretical studies of chemical evolution.

  5. EFFECT OF PRE-TREATMENT ON THE DRYING KINETICS AND PRODUCT QUALITY OF STAR FRUIT SLICES

    Directory of Open Access Journals (Sweden)

    CHING LIK HII

    2014-02-01

    Full Text Available Start fruit (Avverhoa carambola is rich in nutrients and contains dietary antioxidants which are beneficial to human health. Currently, the commercial potential of this fruit has not been fully explored especially in its dried form. The objectives of this research were to investigate the effect of pre-treatment on the drying kinetics and product quality of star fruit slices. The various pre-treatment methods investigated were hot water blanching and dipping in sugar solution. The star fruit was cut into thin slices (5 mm for drying (60°C-80°C using a hot air ventilated oven. Mathematical modelling showed that the Page model was able to describe the moisture diffusion process during drying. Effective diffusivity values were found within the order reported for most food materials (10-8-10-12 m2/s. A decreasing trend in shrinkage ratios was observed with decreasing moisture ratios which corresponds to the greater rate of moisture removal especially at the falling rate period. Overall colour changes were more significant in the blanched samples which could be due to the non-enzymatic browning.

  6. Lithium abundance patterns of late-F stars: an in-depth analysis of the lithium desert

    Science.gov (United States)

    Aguilera-Gómez, Claudia; Ramírez, Iván; Chanamé, Julio

    2018-06-01

    Aims: We address the existence and origin of the lithium (Li) desert, a region in the Li-Teff plane sparsely populated by stars. Here we analyze some of the explanations that have been suggested for this region, including mixing in the late main sequence, a Li dip origin for stars with low Li abundances in the region, and a possible relation with the presence of planets. Methods: To study the Li desert, we measured the atmospheric parameters and Li abundance of 227 late-F dwarfs and subgiants, chosen to be in the Teff range of the desert and without previous Li abundance measurements. Subsequently, we complemented those with literature data to obtain a homogeneous catalog of 2318 stars, for which we compute masses and ages. We characterize stars surrounding the region of the Li desert. Results: We conclude that stars with low Li abundances below the desert are more massive and more evolved than stars above the desert. Given the unexpected presence of low Li abundance stars in this effective temperature range, we concentrate on finding their origin. We conclude that these stars with low Li abundance do not evolve from stars above the desert: at a given mass, stars with low Li (i.e., below the desert) are more metal-poor. Conclusions: Instead, we suggest that stars below the Li desert are consistent with having evolved from the Li dip, discarding the need to invoke additional mixing to explain this feature. Thus, stars below the Li desert are not peculiar and are only distinguished from other subgiants evolved from the Li dip in that their combination of atmospheric parameters locates them in a range of effective temperatures where otherwise only high Li abundance stars would be found (i.e., stars above the desert). Full Tables 1 and 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/614/A55This paper includes observations collected at The McDonald Observatory and

  7. THERMAL EFFECTS ON CAMERA FOCAL LENGTH IN MESSENGER STAR CALIBRATION AND ORBITAL IMAGING

    Directory of Open Access Journals (Sweden)

    S. Burmeister

    2018-04-01

    Full Text Available We analyse images taken by the MErcury Surface, Space ENviorment, GEochemistry, and Ranging (MESSENGER spacecraft for the camera’s thermal response in the harsh thermal environment near Mercury. Specifically, we study thermally induced variations in focal length of the Mercury Dual Imaging System (MDIS. Within the several hundreds of images of star fields, the Wide Angle Camera (WAC typically captures up to 250 stars in one frame of the panchromatic channel. We measure star positions and relate these to the known star coordinates taken from the Tycho-2 catalogue. We solve for camera pointing, the focal length parameter and two non-symmetrical distortion parameters for each image. Using data from the temperature sensors on the camera focal plane we model a linear focal length function in the form of f(T = A0 + A1 T. Next, we use images from MESSENGER’s orbital mapping mission. We deal with large image blocks, typically used for the production of a high-resolution digital terrain models (DTM. We analyzed images from the combined quadrangles H03 and H07, a selected region, covered by approx. 10,600 images, in which we identified about 83,900 tiepoints. Using bundle block adjustments, we solved for the unknown coordinates of the control points, the pointing of the camera – as well as the camera’s focal length. We then fit the above linear function with respect to the focal plane temperature. As a result, we find a complex response of the camera to thermal conditions of the spacecraft. To first order, we see a linear increase by approx. 0.0107 mm per degree temperature for the Narrow-Angle Camera (NAC. This is in agreement with the observed thermal response seen in images of the panchromatic channel of the WAC. Unfortunately, further comparisons of results from the two methods, both of which use different portions of the available image data, are limited. If leaving uncorrected, these effects may pose significant difficulties in

  8. Stars and Star Myths.

    Science.gov (United States)

    Eason, Oliver

    Myths and tales from around the world about constellations and facts about stars in the constellations are presented. Most of the stories are from Greek and Roman mythology; however, a few Chinese, Japanese, Polynesian, Arabian, Jewish, and American Indian tales are also included. Following an introduction, myths are presented for the following 32…

  9. High-precision atmospheric parameter and abundance determination of massive stars, and consequences for stellar and Galactic evolution

    International Nuclear Information System (INIS)

    Nieva, Maria-Fernanda; Przybilla, Norbert; Irrgang, Andreas

    2011-01-01

    The derivation of high precision/accuracy parameters and chemical abundances of massive stars is of utmost importance to the fields of stellar evolution and Galactic chemical evolution. We concentrate on the study of OB-type stars near the main sequence and their evolved progeny, the BA-type supergiants, covering masses of ∼6 to 25 solar masses and a range in effective temperature from ∼8000 to 35 000 K. The minimization of the main sources of systematic errors in the atmospheric model computation, the observed spectra and the quantitative spectral analysis play a critical role in the final results. Our self-consistent spectrum analysis technique employing a robust non-LTE line formation allows precise atmospheric parameters of massive stars to be derived, achieving 1σ-uncertainties as low as 1% in effective temperature and ∼0.05–0.10 dex in surface gravity. Consequences on the behaviour of the chemical elements carbon, nitrogen and oxygen are discussed here in the context of massive star evolution and Galactic chemical evolution, showing tight relations covered in previous work by too large statistical and systematic uncertainties. The spectral analysis of larger star samples, like from the upcoming Gaia-ESO survey, may benefit from these findings.

  10. The effect of near-surface convection on oscillation frequencies of stars

    Science.gov (United States)

    Hanasoge, Shravan

    2015-08-01

    Measurements of oscillation frequencies of the Sun and stars can provide important independent constraints on their internal structure and dynamics. Seismic models of these oscillations are used to connect structure and rotation of the star to its resonant frequencies, which are then compared with observations, the goal being that of minimizing the difference between the two. Even in the case of the Sun, for which structure models are highly tuned, observed frequencies show systematic deviations from modelled frequencies, a phenomenon referred to as the “surface term”. The dominant source of this systematic effect is thought to be vigorous near-surface convection, which is not well accounted for in both stellar modelling and mode-oscillation physics. Here we bring to bear the method of homogenization, applicable in the asymptotic limit of large wavelength (in comparison to the correlation scale of convection), to characterize the effect of small-scale surface convection on resonant-mode frequencies in the Sun. We show that the full oscillation equations, in the presence of temporally stationary 3-D flows, can be reduced to an effective “quiet-Sun” wave equation with altered sound speed, Brünt-Väisäla frequency and Lamb frequency. We derive the modified wave equation and relations for the appropriate averaging of three dimensional flows and thermal quantities to obtain the properties of this effective medium. Using flows obtained from three dimensional numerical simulations of near-surface convection, we quantify their effect on solar oscillation frequencies, and find that they are shifted systematically and substantially. We argue therefore that consistent interpretations of resonant frequencies must include modifications to the wave equation that effectively capture the impact of vigorous hydrodynamic convection.

  11. IUE observations of new A star candidate proto-planetary systems

    Science.gov (United States)

    Grady, Carol A.

    1994-01-01

    As a result of the detection of accreting gas in the A5e PMS Herbig Ae star, HR 5999, most of the observations for this IUE program were devoted to Herbig Ae stars rather than to main sequence A stars. Mid-UV emission at optical minimum light was detected for UX Ori (A1e), BF Ori (A5e), and CQ Tau (F2e). The presence of accreting gas in HD 45677 and HD 50138 prompted reclassification of these stars as Herbig Be stars rather than as protoplanetary nebulae. Detailed results are discussed.

  12. A STAR IN THE M31 GIANT STREAM: THE HIGHEST NEGATIVE STELLAR VELOCITY KNOWN

    International Nuclear Information System (INIS)

    Caldwell, Nelson; Kenyon, Scott J.; Morrison, Heather; Harding, Paul; Schiavon, Ricardo; Rose, James A.

    2010-01-01

    We report on a single star, B030D, observed as part of a large survey of objects in M31, which has the unusual radial velocity of -780 km s -1 . Based on details of its spectrum, we find that the star is an F supergiant, with a circumstellar shell. The evolutionary status of the star could be one of a post-main-sequence close binary, a symbiotic nova, or less likely, a post-asymptotic giant branch star, which additional observations could help sort out. Membership of the star in the Andromeda Giant Stream can explain its highly negative velocity.

  13. THE REFLECTION EFFECT IN INTERACTING BINARIES OR IN PLANET-STAR SYSTEMS

    International Nuclear Information System (INIS)

    Budaj, J.

    2011-01-01

    There are many similarities between interacting binary stars and stars with a close-in giant extrasolar planet. The reflection effect is a well-known example. Although the generally accepted treatment of this effect in interacting binaries is successful in fitting light curves of eclipsing binaries, it is not very suitable for studying cold objects irradiated by hot objects or extrasolar planets. The aim of this paper is to develop a model of the reflection effect which could be easily incorporated into the present codes for modeling of interacting binaries so that these can be used to study the aforementioned objects. Our model of the reflection effect takes into account the reflection (scattering), heating, and heat redistribution over the surface of the irradiated object. The shape of the object is described by the non-spherical Roche potential expected for close objects. Limb and gravity darkening are included in the calculations of the light output from the system. The model also accounts for the orbital revolution and rotation of the exoplanet with appropriate Doppler shifts for the scattered and thermal radiation. Subsequently, light curves and/or spectra of several exoplanets have been modeled and the effects of the heat redistribution, limb darkening/brightening, (non-)gray albedo, and non-spherical shape have been studied. Recent observations of planet-to-star flux ratio of HD189733b, WASP12b, and WASP-19b at various phases were reproduced with very good accuracy. It was found that HD189733b has a low Bond albedo and intense heat redistribution, while WASP-19b has a low Bond albedo and low heat redistribution. The exact Roche geometries and temperature distributions over the surface of all 78 transiting extrasolar planets have been determined. Departures from the spherical shape may vary considerably but departures of about 1% in the radius are common within the sample. In some cases, these departures can reach 8%, 12%, or 14%, for WASP-33b, WASP-19b, and

  14. The electromagnetic Christodoulou memory effect and its application to neutron star binary mergers

    International Nuclear Information System (INIS)

    Bieri, Lydia; Chen, PoNing; Yau, Shing-Tung

    2012-01-01

    Gravitational waves are predicted by the general theory of relativity. It has been shown that gravitational waves have a nonlinear memory, displacing test masses permanently. This is called the Christodoulou memory. We proved that the electromagnetic field contributes at highest order to the nonlinear memory effect of gravitational waves, enlarging the permanent displacement of test masses. In experiments like LISA or LIGO which measure distances of test masses, the Christodoulou memory will manifest itself as a permanent displacement of these objects. It has been suggested to detect the Christodoulou memory effect using radio telescopes investigating small changes in pulsar’s pulse arrival times. The latter experiments are based on present-day technology and measure changes in frequency. In the present paper, we study the electromagnetic Christodoulou memory effect and compute it for binary neutron star mergers. These are typical sources of gravitational radiation. During these processes, not only mass and momenta are radiated away in form of gravitational waves, but also very strong magnetic fields are produced and radiated away. Moreover, a large portion of the energy is carried away by neutrinos. We give constraints on the conditions, where the energy transported by electromagnetic radiation is of similar or slightly higher order than the energy radiated in gravitational waves or in form of neutrinos. We find that for coalescing neutron stars, large magnetic fields magnify the Christodoulou memory as long as the gaseous environment is sufficiently rarefied. Thus the observed effect on test masses of a laser interferometer gravitational wave detector will be enlarged by the contribution of the electromagnetic field. Therefore, the present results are important for the planned experiments. Looking at the null asymptotics of spacetimes, which are solutions of the Einstein–Maxwell equations, we derive the electromagnetic Christodoulou memory effect. We obtain

  15. CHROMOSPHERICALLY ACTIVE STARS IN THE RADIAL VELOCITY EXPERIMENT (RAVE) SURVEY. I. THE CATALOG

    International Nuclear Information System (INIS)

    Žerjal, M.; Zwitter, T.; Matijevič, G.; Strassmeier, K. G.; Siviero, A.; Steinmetz, M.; Bienaymé, O.; Bland-Hawthorn, J.; Boeche, C.; Grebel, E. K.; Freeman, K. C.; Kordopatis, G.; Munari, U.; Navarro, J. F.; Parker, Q. A.; Reid, W.; Seabroke, G.; Wyse, R. F. G.

    2013-01-01

    RAVE, the unbiased magnitude limited survey of southern sky stars, contained 456,676 medium-resolution spectra at the time of our analysis. Spectra cover the Ca II infrared triplet (IRT) range, which is a known indicator of chromospheric activity. Our previous work classified all spectra using locally linear embedding. It identified 53,347 cases with a suggested emission component in calcium lines. Here, we use a spectral subtraction technique to measure the properties of this emission. Synthetic templates are replaced by the observed spectra of non-active stars to bypass the difficult computations of non-local thermal equilibrium profiles of the line cores and stellar parameter dependence. We derive both the equivalent width of the excess emission for each calcium line on a 5 Å wide interval and their sum EW IRT for ∼44,000 candidate active dwarf stars with signal-to-noise ratio >20, with no cuts on the basis of the source of their emission flux. From these, ∼14,000 show a detectable chromospheric flux with at least a 2σ confidence level. Our set of active stars vastly enlarges previously known samples. Atmospheric parameters and, in some cases, radial velocities of active stars derived from automatic pipelines suffer from systematic shifts due to their shallower calcium lines. We re-estimate the effective temperature, metallicity, and radial velocities for candidate active stars. The overall distribution of activity levels shows a bimodal shape, with the first peak coinciding with non-active stars and the second with the pre-main-sequence cases. The catalog will be made publicly available with the next RAVE public data releases

  16. Is the Young Star RZ Piscium Consuming Its Own (Planetary) Offspring?

    Science.gov (United States)

    Punzi, K. M.; Kastner, J. H.; Melis, C.; Zuckerman, B.; Pilachowski, C.; Gingerich, L.; Knapp, T.

    2018-01-01

    The erratically variable star RZ Piscium (RZ Psc) displays extreme optical dropout events and strikingly large excess infrared emission. To ascertain the evolutionary status of this intriguing star, we obtained observations of RZ Psc with the European Space Agency’s X-ray Multi-Mirror Mission (XMM-Newton), as well as high-resolution optical spectroscopy with the Hamilton Echelle on the Lick Shane 3 m telescope and with HIRES on the Keck I 10 m telescope. The optical spectroscopy data demonstrate that RZ Psc is a pre-main sequence star with an effective temperature of 5600 ± 75 K and log g of 4.35 ± 0.10. The ratio of X-ray to bolometric luminosity, {log}{L}X/{L}{bol}, lies in the range ‑3.7 to ‑3.2, consistent with ratios typical of young, solar-mass stars, thereby providing strong support for the young star status of RZ Psc. The Li absorption line strength of RZ Psc suggests an age in the range 30–50 Myr, which in turn implies that RZ Psc lies at a distance of ∼170 pc. Adopting this estimated distance, we find the Galactic space velocity of RZ Psc to be similar to the space velocities of stars in young moving groups near the Sun. Optical spectral features indicative of activity and/or circumstellar material are present in our spectra over multiple epochs, which provide evidence for the presence of a significant mass of circumstellar gas associated with RZ Psc. We suggest that the destruction of one or more massive orbiting bodies has recently occurred within 1 au of the star, and we are viewing the aftermath of such an event along the plane of the orbiting debris.

  17. Ultraviolet spectrophotometry from Gemini 11 of stars in Orion

    International Nuclear Information System (INIS)

    Morgan, T.H.; Spear, G.G.; Kondo, Y.; Henize, K.G.

    1975-01-01

    Ultraviolet spectrophotometry in the wavelength region 2600--3600 A is reported for the bright early-type stars β, eta, γ, delta, iota, epsilon, sigma, xi, and kappa Ori. The results are in good agreement with other observations, and with the possible exception of the supergiants, are in good agreement with recent line-blanketed model atmospheres. There is evidence that the supergiants possess a small ultraviolet deficiency shortward of 3000 A relative to main-sequence stars of similar spectral type. The most extreme example of this phenomenon is the star kappa Ori

  18. Multiband Lightcurve of Tabby’s Star: Observations and Modeling

    Science.gov (United States)

    Yin, Yao; Wilcox, Alejandro; Boyajian, Tabetha S.

    2018-06-01

    Since March 2017, The Thacher Observatory in California has been monitoring changes in brightness of KIC 8462852 (Tabby's Star), an F-type main sequence star whose irregular dimming behavior was first discovered by Tabetha Boyajian by examining Kepler data. We obtained over 20k observations over 135 nights in 2017 in 4 photometric bands, and detected 4 dip events greater than 1%. The relative magnitude of each dip compared across our 4 different photometric bands provides critical information regarding the nature of the obscuring material, and we present a preliminary analysis of these events. The Thacher Observatory is continuing its monitoring of Tabby’s Star in 2018.

  19. Pulsating stars in the region of Carina Nebula

    Energy Technology Data Exchange (ETDEWEB)

    Steslicki, Marek [Astronomical Institute, University of Wroclaw (Poland)], E-mail: steslicki@astro.uni.wroc.p1

    2008-10-15

    We present the results of a search for pulsating stars in the region of Carina Nebula which includes three very young open clusters: Trumpler