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Sample records for dependent giant star

  1. Giant star seismology

    CERN Document Server

    Hekker, S

    2016-01-01

    The internal properties of stars in the red-giant phase undergo significant changes on relatively short timescales. Long near-interrupted high-precision photometric timeseries observations from dedicated space missions such as CoRoT and Kepler have provided seismic inferences of the global and internal properties of a large number of evolved stars, including red giants. These inferences are confronted with predictions from theoretical models to improve our understanding of stellar structure and evolution. Our knowledge and understanding of red giants have indeed increased tremendously using these seismic inferences, and we anticipate that more information is still hidden in the data. Unraveling this will further improve our understanding of stellar evolution. This will also have significant impact on our knowledge of the Milky Way Galaxy as well as on exo-planet host stars. The latter is important for our understanding of the formation and structure of planetary systems.

  2. Rotation of Giant Stars

    CERN Document Server

    Kissin, Yevgeni

    2015-01-01

    The internal rotation of post-main sequence stars is investigated, in response to the convective pumping of angular momentum toward the stellar core, combined with a tight magnetic coupling between core and envelope. The spin evolution is calculated using model stars of initial mass 1, 1.5 and $5\\,M_\\odot$, taking into account mass loss on the giant branches and the partitioning of angular momentum between the outer and inner envelope. We also include the deposition of orbital angular momentum from a sub-stellar companion, as influenced by tidal drag as well as the excitation of orbital eccentricity by a fluctuating gravitational quadrupole moment. A range of angular velocity profiles $\\Omega(r)$ is considered in the deep convective envelope, ranging from solid rotation to constant specific angular momentum. We focus on the backreaction of the Coriolis force on the inward pumping of angular momentum, and the threshold for dynamo action in the inner envelope. Quantitative agreement with measurements of core ro...

  3. KEPLER RAPIDLY ROTATING GIANT STARS

    Energy Technology Data Exchange (ETDEWEB)

    Costa, A. D.; Martins, B. L. Canto; Bravo, J. P.; Paz-Chinchón, F.; Chagas, M. L. das; Leão, I. C.; Oliveira, G. Pereira de; Silva, R. Rodrigues da; Roque, S.; Oliveira, L. L. A. de; Silva, D. Freire da; De Medeiros, J. R., E-mail: renan@dfte.ufrn.br [Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, Campus Universitário, Natal RN (Brazil)

    2015-07-10

    Rapidly rotating giant stars are relatively rare and may represent important stages of stellar evolution, resulting from stellar coalescence of close binary systems or accretion of substellar companions by their hosting stars. In the present Letter, we report 17 giant stars observed in the scope of the Kepler space mission exhibiting rapid rotation behavior. For the first time, the abnormal rotational behavior for this puzzling family of stars is revealed by direct measurements of rotation, namely from photometric rotation period, exhibiting a very short rotation period with values ranging from 13 to 55 days. This finding points to remarkable surface rotation rates, up to 18 times the rotation of the Sun. These giants are combined with six others recently listed in the literature for mid-infrared (IR) diagnostics based on Wide-field Infrared Survey Explorer information, from which a trend for an IR excess is revealed for at least one-half of the stars, but at a level far lower than the dust excess emission shown by planet-bearing main-sequence stars.

  4. Kepler rapidly rotating giant stars

    CERN Document Server

    Costa, A D; Bravo, J P; Paz-Chinchón, F; Chagas, M L das; Leão, I C; de Oliveira, G Pereira; da Silva, R Rodrigues; Roque, S; de Oliveira, L L A; da Silva, D Freire; De Medeiros, J R

    2015-01-01

    Rapidly rotating giant stars are relatively rare and may represent important stages of stellar evolution, resulting from stellar coalescence of close binary systems or accretion of sub-stellar companions by their hosting stars. In the present letter we report 17 giant stars observed in the scope of the Kepler space mission exhibiting rapid rotation behavior. For the first time the abnormal rotational behavior for this puzzling family of stars is revealed by direct measurements of rotation, namely from photometric rotation period, exhibiting very short rotation period with values ranging from 13 to 55 days. This finding points for remarkable surface rotation rates, up to 18 times the Sun rotation. These giants are combined with 6 other recently listed in the literature for mid-IR diagnostic based on WISE information, from which a trend for an infrared excess is revealed for at least a half of the stars, but at a level far lower than the dust excess emission shown by planet-bearing main-sequence stars.

  5. On the asymptotic acoustic-mode phase in red-giant stars and its dependence on evolutionary state

    CERN Document Server

    Christensen-Dalsgaard, J; Elsworth, Y; Hekker, S

    2014-01-01

    Asteroseismic investigations based on the wealth of data now available,in particular from the CoRoT and Kepler missions, require a good understanding of the relation between the observed quantities and the properties of the underlying stellar structure. Kallinger et al. 2012 found a relation between their determination of the asymptotic phase of radial oscillations in evolved stars and the evolutionary state, separating ascending-branch red giants from helium-burning stars in the `red clump'. Here we provide a detailed analysis of this relation, which is found to derive from differences between these two classes of stars in the thermodynamic state of the convective envelope. There is potential for distinguishing red giants and clump stars based on the phase determined from observations that are too short to allow distinction based on determination of the period spacing for mixed modes. The analysis of the phase may also point to a better understanding of the potential for using the helium-ionization-induced a...

  6. Asteroseismology of Red Giant stars

    CERN Document Server

    Tarrant, N J; Elsworth, Y P; Spreckley, S A; Stevens, I R

    2008-01-01

    Sun-like oscillations, that is p-modes excited stochastically by convective noise, have now been observed in a number of Red Giant stars. Compared to those seen in the Sun, these modes are of large amplitude and long period, making the oscillations attractive prospects for observation. However, the low Q-factor of these modes, and issues relating to the rising background at low frequencies, present some interesting challenges for identifying modes and determining the related asteroseismic parameters. We report on the analysis procedure adopted for peak-bagging by our group at Birmingham, and the techniques used to robustly ensure these are not a product of noise. I also show results from a number of giants extracted from multi-year observations with the SMEI instrument.

  7. On the metallicity dependence of crystalline silicates in oxygen-rich asymptotic giant branch stars and red supergiants

    CERN Document Server

    Jones, O C; Sargent, B A; McDonald, I; Gielen, C; Woods, Paul M; Sloan, G C; Boyer, M L; Zijlstra, A A; Clayton, G C; Kraemer, K E; Srinivasan, S; Ruffle, P M E

    2012-01-01

    We investigate the occurrence of crystalline silicates in oxygen-rich evolved stars across a range of metallicities and mass-loss rates. It has been suggested that the crystalline silicate feature strength increases with increasing mass-loss rate, implying a correlation between lattice structure and wind density. To test this, we analyse Spitzer IRS and Infrared Space Observatory SWS spectra of 217 oxygen-rich asymptotic giant branch stars and 98 red supergiants in the Milky Way, the Large and Small Magellanic Clouds and Galactic globular clusters. These encompass a range of spectral morphologies from the spectrally-rich which exhibit a wealth of crystalline and amorphous silicate features to 'naked' (dust-free) stars. We combine spectroscopic and photometric observations with the GRAMS grid of radiative transfer models to derive (dust) mass-loss rates and temperature. We then measure the strength of the crystalline silicate bands at 23, 28 and 33 microns. We detect crystalline silicates in stars with dust ma...

  8. Testing planet formation theories with Giant stars

    CERN Document Server

    Pasquini, Luca; Hatzes, A; Setiawan, J; Girardi, L; da Silva, L; De Medeiros, J R

    2008-01-01

    Planet searches around evolved giant stars are bringing new insights to planet formation theories by virtue of the broader stellar mass range of the host stars compared to the solar-type stars that have been the subject of most current planet searches programs. These searches among giant stars are producing extremely interesting results. Contrary to main sequence stars planet-hosting giants do not show a tendency of being more metal rich. Even if limited, the statistics also suggest a higher frequency of giant planets (at least 10 %) that are more massive compared to solar-type main sequence stars. The interpretation of these results is not straightforward. We propose that the lack of a metallicity-planet connection among giant stars is due to pollution of the star while on the main sequence, followed by dilution during the giant phase. We also suggest that the higher mass and frequency of the planets are due to the higher stellar mass. Even if these results do not favor a specific formation scenario, they su...

  9. Kepler Asteroseismology of Red-giant Stars

    DEFF Research Database (Denmark)

    Christensen-Dalsgaard, J.

    2012-01-01

    The Kepler mission, launched in March 2009, has revolutionized asteroseismology, providing detailed observations of thousands of stars. This has allowed in-depth analyses of stars ranging from compact hot subdwarfs to red giants, and including the detection of solar-like oscillations in hundreds...... of stars on or near the main sequence. Here I mainly consider solar-like oscillations in red giants, where Kepler observations are yielding results of a perhaps unexpected richness. In addition to giving a brief overview of the observational and numerical results for these stars, I present a simple...

  10. Surface rotation of Kepler red giant stars

    Science.gov (United States)

    Ceillier, T.; Tayar, J.; Mathur, S.; Salabert, D.; García, R. A.; Stello, D.; Pinsonneault, M. H.; van Saders, J.; Beck, P. G.; Bloemen, S.

    2017-09-01

    Kepler allows the measurement of starspot variability in a large sample of field red giants for the first time. With a new method that combines autocorrelation and wavelet decomposition, we measure 361 rotation periods from the full set of 17 377 oscillating red giants in our sample. This represents 2.08% of the stars, consistent with the fraction of spectroscopically detected rapidly rotating giants in the field. The remaining stars do not show enough variability to allow us to measure a reliable surface rotation period. Because the stars with detected rotation periods have measured oscillations, we can infer their global properties, e.g. mass and radius, and quantitatively evaluate the predictions of standard stellar evolution models as a function of mass. Consistent with results for cluster giants when we consider only the 4881 intermediate-mass stars, M > 2.0 M⊙ from our full red giant sample, we do not find the enhanced rates of rapid rotation expected from angular momentum conservation. We therefore suggest that either enhanced angular momentum loss or radial differential rotation must be occurring in these stars. Finally, when we examine the 575 low-mass (Mhttp://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/605/A111

  11. Red-giant stars in eccentric binaries

    Directory of Open Access Journals (Sweden)

    Beck P. G.

    2015-01-01

    Full Text Available The unparalleled photometric data obtained by NASA’s Kepler Space Telescope has led to improved understanding of red-giant stars and binary stars. We discuss the characterization of known eccentric system, containing a solar-like oscillating red-giant primary component. We also report several new binary systems that are candidates for hosting an oscillating companion. A powerful approach to study binary stars is to combine asteroseimic techniques with light curve fitting. Seismology allows us to deduce the properties of red giants. In addition, by modeling the ellipsoidal modulations we can constrain the parameters of the binary system. An valuable independent source are ground-bases, high-resolution spectrographs.

  12. Mass loss from giant and supergiant stars

    Science.gov (United States)

    Wannier, P. G.; Sahai, R.

    1986-01-01

    The 12 m telescope of the National Radio Astronomy Observatory has been used at the J = 2-1 transition of CO to increase the known list of giant and supergiant stars with observable circumstellar envelopes. The candidate objects were generally M-type giants and supergiants, chosen for their strong infrared luminosities. Of the 35 objects which were previously undetected, or only marginally detected, 10 were found to produce detectable CO emission. Physical parameters of the envelopes are derived by source modeling. Mass-loss rates vary from 10 to the -7th to 4 x 10 to the -5th solar mass/yr.

  13. Spectroscopy of late type giant stars

    Science.gov (United States)

    Spaenhauer, A.; Thevenin, F.

    1984-06-01

    An attempt to calibrate broadband RGU colors of late type giant stars in terms of the physical parameters of the objects is reported. The parameters comprise the effective temperature, surface gravity and global metal abundance with respect to the sun. A selection of 21 giant star candidates in the Basel fields Plaut 1, Centaurus III and near HD 95540 were examined to obtain a two color plot. Attention is focused on the G-R color range 1.5-2.15 mag, i.e., spectral types K0-K5. A relationship between R and the metallicity is quantified and shown to have a correlation coefficient of 0.93. No correlation is found between metallicity and gravity or R and the effective temperature.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-03-20

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

  15. Beryllium abundances in stars hosting giant planets

    CERN Document Server

    Santos, N C; Israelian, G; Mayor, M; Rebolo, R; García-Gíl, A; Pérez de Taoro, M R; Randich, S

    2002-01-01

    We have derived beryllium abundances in a wide sample of stars hosting planets, with spectral types in the range F7V-K0V, aimed at studying in detail the effects of the presence of planets on the structure and evolution of the associated stars. Predictions from current models are compared with the derived abundances and suggestions are provided to explain the observed inconsistencies. We show that while still not clear, the results suggest that theoretical models may have to be revised for stars with Teff<5500K. On the other hand, a comparison between planet host and non-planet host stars shows no clear difference between both populations. Although preliminary, this result favors a ``primordial'' origin for the metallicity ``excess'' observed for the planetary host stars. Under this assumption, i.e. that there would be no differences between stars with and without giant planets, the light element depletion pattern of our sample of stars may also be used to further investigate and constraint Li and Be deple...

  16. Introduction to Asymptotic Giant Branch Stars

    Science.gov (United States)

    El Eid, Mounib F.

    2016-04-01

    A brief introduction on the main characteristics of the asymptotic giant branch stars (briefly: AGB) is presented. We describe a link to observations and outline basic features of theoretical modeling of these important evolutionary phases of stars. The most important aspects of the AGB stars is not only because they are the progenitors of white dwarfs, but also they represent the site of almost half of the heavy element formation beyond iron in the galaxy. These elements and their isotopes are produced by the s-process nucleosynthesis, which is a neutron capture process competing with the β- radioactive decay. The neutron source is mainly due to the reaction 13C(α,n)16O reaction. It is still a challenging problem to obtain the right amount of 13 C that can lead to s-process abundances compatible with observation. Some ideas are presented in this context.

  17. The frequency of giant planets around metal-poor stars

    Science.gov (United States)

    Mortier, A.; Santos, N. C.; Sozzetti, A.; Mayor, M.; Latham, D.; Bonfils, X.; Udry, S.

    2012-07-01

    Context. The discovery of about 700 extrasolar planets, so far, has lead to the first statistics concerning extrasolar planets. The presence of giant planets seems to depend on stellar metallicity and mass. For example, they are more frequent around metal-rich stars, with an exponential increase in planet occurrence rates with metallicity. Aims: We analyzed two samples of metal-poor stars (-2.0 ≤ [Fe/H] ≤ 0.0) to see if giant planets are indeed rare around these objects. Radial velocity datasets were obtained with two different spectrographs (HARPS and HIRES). Detection limits for these data, expressed in minimum planetary mass and period, are calculated. These produce trustworthy numbers for the planet frequency. Methods: A general Lomb-Scargle (GLS) periodogram analysis was used together with a bootstrapping method to produce the detection limits. Planet frequencies were calculated based on a binomial distribution function within metallicity bins. Results: Almost all hot Jupiters and most giant planets should have been found in these data. Hot Jupiters around metal-poor stars have a frequency lower than 1.0% at one sigma. Giant planets with periods up to 1800 days, however, have a higher frequency of fp = 2.63-0.8+2.5%. Taking into account the different metallicities of the stars, we show that giant planets appear to be very frequent (fp = 4.48-1.38+4.04%) around stars with [Fe/H] > - 0.7, while they are rare around stars with [Fe/H] ≤ - 0.7 ( ≤ 2.36% at one sigma). Conclusions: Giant planet frequency is indeed a strong function of metallicity, even in the low-metallicity tail. However, the frequencies are most likely higher than previously thought. The data presented herein are based on observations collected at the La Silla Parana Observatory, ESO (Chile) with the HARPS spectrograph at the 3.6-m telescope (ESO runs ID 72.C-0488, 082.C-0212, and 085.C-0063) and at the W. M. Keck Observatory that is operated as a scientific partnership among the

  18. Giant Black Hole Rips Apart Star

    Science.gov (United States)

    2004-02-01

    Thanks to two orbiting X-ray observatories, astronomers have the first strong evidence of a supermassive black hole ripping apart a star and consuming a portion of it. The event, captured by NASA's Chandra and ESA's XMM-Newton X-ray Observatories, had long been predicted by theory, but never confirmed. Astronomers believe a doomed star came too close to a giant black hole after being thrown off course by a close encounter with another star. As it neared the enormous gravity of the black hole, the star was stretched by tidal forces until it was torn apart. This discovery provides crucial information about how these black holes grow and affect surrounding stars and gas. "Stars can survive being stretched a small amount, as they are in binary star systems, but this star was stretched beyond its breaking point," said Stefanie Komossa of the Max Planck Institute for Extraterrestrial Physics (MPE) in Germany, leader of the international team of researchers. "This unlucky star just wandered into the wrong neighborhood." While other observations have hinted stars are destroyed by black holes (events known as "stellar tidal disruptions"), these new results are the first strong evidence. Evidence already exists for supermassive black holes in many galaxies, but looking for tidal disruptions represents a completely independent way to search for black holes. Observations like these are urgently needed to determine how quickly black holes can grow by swallowing neighboring stars. Animation of Star Ripped Apart by Giant Black Hole Star Ripped Apart by Giant Black Hole Observations with Chandra and XMM-Newton, combined with earlier images from the German Roentgen satellite, detected a powerful X-ray outburst from the center of the galaxy RX J1242-11. This outburst, one of the most extreme ever detected in a galaxy, was caused by gas from the destroyed star that was heated to millions of degrees Celsius before being swallowed by the black hole. The energy liberated in the process

  19. Spectroscopic Study on the Beryllium Abundances of Red Giant Stars

    CERN Document Server

    Takeda, Yoichi

    2014-01-01

    An extensive spectroscopic study was carried out for the beryllium abundances of 200 red giants (mostly of late G and early K type), which were determined from the near-UV Be II 3131.066 line based on high-dispersion spectra obtained by Subaru/HDS, with an aim of investigating the nature of surface Be contents in these evolved giants; e.g., dependence upon stellar parameters, degree of peculiarity along with its origin and build-up timing. We found that Be is considerably deficient (to widely different degree from star to star) in the photosphere of these evolved giants by ~1-3 dex (or more) compared to the initial abundance. While the resulting Be abundances (A(Be)) appear to weakly depend upon T_eff, log g, [Fe/H], M, age, and v_sin i, this may be attributed to the metallicity dependence of A(Be) coupled with the mutual correlation between these stellar parameters, since such tendencies almost disappear in the metallicity-scaled Be abundance ([Be/Fe]). By comparing the Be abundances (as well as their correl...

  20. Constructing stable 3D hydrodynamical models of giant stars

    CERN Document Server

    Ohlmann, Sebastian T; Pakmor, Rüdiger; Springel, Volker

    2016-01-01

    Hydrodynamical simulations of stellar interactions require stable models of stars as initial conditions. Such initial models, however, are difficult to construct for giant stars because of the wide range in spatial scales of the hydrostatic equilibrium and in dynamical timescales between the core and the envelope of the giant. They are needed for, e.g., modeling the common envelope phase where a giant envelope encompasses both the giant core and a companion star. Here, we present a new method of approximating and reconstructing giant profiles from a stellar evolution code to produce stable models for multi-dimensional hydrodynamical simulations. We determine typical stellar stratification profiles with the 1D stellar evolution code MESA. After an appropriate mapping, hydrodynamical simulations are conducted using the moving-mesh code AREPO. The giant profiles are approximated by replacing the core of the giant with a point mass and by constructing a suitable continuation of the profile to the center. Differen...

  1. Giant black hole rips star apart

    Science.gov (United States)

    2004-02-01

    Astronomers believe that a doomed star came too close to a giant black hole after a close encounter with another star threw it off course. As it neared the enormous gravity of the black hole, the star was stretched by tidal forces until it was torn apart. This discovery provides crucial information on how these black holes grow and affect the surrounding stars and gas. "Stars can survive being stretched a small amount, as they are in binary star systems, but this star was stretched beyond its breaking point," said Dr Stefanie Komossa of the Max Planck Institute for Extraterrestrial Physics (MPE) in Germany, who led the international team of researchers. "This unlucky star just wandered into the wrong neighbourhood." While other observations have hinted that stars are destroyed by black holes (events known as ‘stellar tidal disruptions’), these new results are the first strong evidence. Observations with XMM-Newton and Chandra, combined with earlier images from the German Roentgensatellite (ROSAT), detected a powerful X-ray outburst from the centre of the galaxy RXJ1242-11. This outburst, one of the most extreme ever detected in a galaxy, was caused by gas from the destroyed star that was heated to millions of degrees before being swallowed by the black hole. The energy liberated in this process is equivalent to that of a supernova. "Now, with all of the data in hand, we have the smoking gun proof that this spectacular event has occurred," said co-author Prof. Guenther Hasinger, also of MPE. The black hole in the centre of RX J1242-11 is estimated to have a mass about 100 million times that of the Sun. By contrast, the destroyed star probably had a mass about equal to that of the Sun, making it a lopsided battle of gravity. "This is the ultimate ‘David versus Goliath’ battle, but here David loses," said Hasinger. The astronomers estimated that about one hundredth of the mass of the star was ultimately consumed, or accreted, by the black hole. This small

  2. Constructing stable 3D hydrodynamical models of giant stars

    Science.gov (United States)

    Ohlmann, Sebastian T.; Röpke, Friedrich K.; Pakmor, Rüdiger; Springel, Volker

    2017-02-01

    Hydrodynamical simulations of stellar interactions require stable models of stars as initial conditions. Such initial models, however, are difficult to construct for giant stars because of the wide range in spatial scales of the hydrostatic equilibrium and in dynamical timescales between the core and the envelope of the giant. They are needed for, e.g., modeling the common envelope phase where a giant envelope encompasses both the giant core and a companion star. Here, we present a new method of approximating and reconstructing giant profiles from a stellar evolution code to produce stable models for multi-dimensional hydrodynamical simulations. We determine typical stellar stratification profiles with the one-dimensional stellar evolution code mesa. After an appropriate mapping, hydrodynamical simulations are conducted using the moving-mesh code arepo. The giant profiles are approximated by replacing the core of the giant with a point mass and by constructing a suitable continuation of the profile to the center. Different reconstruction methods are tested that can specifically control the convective behaviour of the model. After mapping to a grid, a relaxation procedure that includes damping of spurious velocities yields stable models in three-dimensional hydrodynamical simulations. Initially convectively stable configurations lead to stable hydrodynamical models while for stratifications that are convectively unstable in the stellar evolution code, simulations recover the convective behaviour of the initial model and show large convective plumes with Mach numbers up to 0.8. Examples are shown for a 2 M⊙ red giant and a 0.67 M⊙ asymptotic giant branch star. A detailed analysis shows that the improved method reliably provides stable models of giant envelopes that can be used as initial conditions for subsequent hydrodynamical simulations of stellar interactions involving giant stars.

  3. On dynamo action in the giant star Pollux : first results

    CERN Document Server

    Palacios, A

    2013-01-01

    We present preliminary results of a 3D MHD simulation of the convective envelope of the giant star Pollux for which the rotation period and the magnetic ?eld intensity have been measured from spectroscopic and spectropolarimetric observations. This giant is one of the ?rst single giants with a detected magnetic ?eld, and the one with the weakest ?eld so far. Our aim is to understand the development and the action of the dynamo in its extended convective envelope.

  4. Radio emission from rapidly-rotating cool giant stars

    Science.gov (United States)

    Drake, Stephen A.; Walter, Frederick M.; Florkowski, David R.

    1990-01-01

    The results of a VLA program are reported to examine the radio continuum emission from 11 rapidly-rotating cool giant stars, all of which were originally believed to be single stars. Six of the 11 stars were detected as radio sources, including FK Com and HR 9024, for which there exist multifrequency observations. HD 199178, UZ Lib (now known to be a binary system), and HD 82558, for which there is only 6-cm data. The radio properties of these stars are compared with those of the active, rapidly rotating evolved stars found in the RS CVn binary systems.

  5. A Superwind from Early Post-Red Giant Stars?

    CERN Document Server

    Soker, N; Rood, R T; Harpaz, A; Soker, Noam; Catelan, Marcio; Rood, Robert T.; Harpaz, Amos

    2001-01-01

    We suggest that the gap observed at 20,000 K in the horizontal branches of several Galactic globular clusters is caused by a small amount of extra mass loss which occurs when stars start to "peel off" the red giant branch (RGB), i.e., when their effective temperature starts to increase, even though they may still be on the RGB. We show that the envelope structure of RGB stars which start to peel off is similar to that of late asymptotic giant branch stars known to have a super-wind phase. An analogous super-wind in the RGB peel-off stars could easily lead to the observed gap in the distribution of the hottest HB stars.

  6. Alexander's and Phoebe's stars: Two New Exotic Phoenix Giants

    Science.gov (United States)

    Melis, Carl; Zuckerman, B.; Song, I.; Rhee, J. H.; Bessell, M. S.; Murphy, S. J.

    2011-01-01

    Phoenix Giants are first-ascent giant stars orbited by substantial dusty and gaseous disks that are sometimes accreting onto the central star. We present the characterization of two dusty first-ascent giant stars identified through cross-correlating the Tycho-2 and IRAS catalogs. CD-30 11814 (hereafter Alexander's star) is a high-velocity Pop II star that exhibits rapid accretion and outflowing gas. Multiple epochs of spectroscopic observations show that the double-peaked Ca II infrared triplet emission from this source has variable morphology and strength. TYC 596 145 1 (hereafter Phoebe's star) is a lithium-rich K2.5 III star orbited by a substantial icy disk as indicated by water-ice features detected in Spitzer IRS and IRTF/SpeX infrared spectroscopy. Each source can yield interesting insights into binary star evolution and planetary systems. Funding for this research came from NASA grants and an LLNL-Minigrant to UCLA and from the Spitzer Visiting Graduate Student Program.

  7. Star-planet interactions. II. Is planet engulfment the origin of fast rotating red giants?

    Science.gov (United States)

    Privitera, Giovanni; Meynet, Georges; Eggenberger, Patrick; Vidotto, Aline A.; Villaver, Eva; Bianda, Michele

    2016-10-01

    Context. Fast rotating red giants in the upper part of the red giant branch have surface velocities that cannot be explained by single star evolution. Aims: We check whether tides between a star and a planet followed by planet engulfment can indeed accelerate the surface rotation of red giants for a sufficiently long time to produce these fast rotating red giants. Methods: We studied how the surface rotation velocity at the stellar surface evolves using rotating stellar models, accounting for the redistribution of the angular momentum inside the star by different transport mechanisms, the exchanges of angular momentum between the planet orbit and the star before the engulfment, and for the deposition of angular momentum inside the star at the engulfment. We considered different situations with masses of stars in the range between 1.5 and 2.5 M⊙, masses of the planets between 1 and 15 MJ (Jupiter mass), and initial semimajor axis between 0.5 and 1.5 au. The metallicity Z for our stellar models is 0.02. Results: We show that the surface velocities reached at the end of the orbital decay due to tidal forces and planet engulfment can be similar to values observed for fast rotating red giants. This surface velocity then decreases when the star evolves along the red giant branch but at a sufficiently slow pace to allowing stars to be detected with such a high velocity. More quantitatively, star-planet interaction can produce a rapid acceleration of the surface of the star, above values equal to 8 km s-1, for periods lasting up to more than 30% the red giant branch phase. As found already by previous works, the changes of the surface carbon isotopic ratios produced by the dilution of the planetary material into the convective envelope is modest. The increase of the lithium abundance due to this effect might be much more important, however lithium may be affected by many different, still uncertain, processes. Thus any lithium measurement can hardly be taken as a support

  8. A new method for the asteroseismic determination of the evolutionary state of red-giant stars

    Science.gov (United States)

    Elsworth, Yvonne; Hekker, Saskia; Basu, Sarbani; Davies, Guy R.

    2017-04-01

    Determining the ages of red-giant stars is a key problem in stellar astrophysics. One of the difficulties in this determination is to know the evolutionary state of the individual stars - i.e. have they started to burn Helium in their cores? That is the topic of this paper. Asteroseismic data provide a route to achieving this information. What we present here is a highly autonomous way of determining the evolutionary state from an analysis of the power spectrum of the light curve. The method is fast and efficient and can provide results for a large number of stars. It uses the structure of the dipole-mode oscillations, which have a mixed character in red-giant stars, to determine some measures that are used in the categorization. It does not require that all the individual components of any given mode be separately characterized. Some 6604 red-giant stars have been classified. Of these, 3566 are determined to be on the red-giant branch, 2077 are red-clump and 439 are secondary-clump stars. We do not specifically identify the low-metallicity, horizontal-branch stars. The difference between red-clump and secondary-clump stars is dependent on the manner in which Helium burning is first initiated. We discuss that the way the boundary between these classifications is set may lead to mis-categorization in a small number of stars. The remaining 522 stars were not classified either because they lacked sufficient power in the dipole modes (so-called depressed dipole modes) or because of conflicting values in the parameters.

  9. The Metallicity Dependence of Giant Planet Incidence

    CERN Document Server

    Gonzalez, Guillermo

    2014-01-01

    We describe three corrections that should be applied to the observed relative incidence of nearby stars hosting giant planets. These are diffusion in the stellar atmosphere, use of the [Ref] index in place of [Fe/H] for metallicity, and correction for local sampling with the W velocity. We have applied these corrections to a subset of the SPOCS exoplanet survey with uniform giant planet detectability. Fitting the binned data to a power law of the form, $\\alpha 10^{\\beta [Fe/H]}$, we derived $\\alpha = 0.022 \\pm 0.007$ and $\\beta = 3.0 \\pm 0.5$; this value of $\\beta$ is 50\\% larger than the value determined by \\citet{fv05}. While the statistical significance of this difference is marginal, given the small number statistics, these corrections should be included in future analyses that include larger samples.

  10. Mass Losing Asymptotic Giant Branch Stars and Supergiants

    CERN Document Server

    Whitelock, Patricia A; Höfner, Susanne; Wittkowski, Markus; Zijlstra, Albert A

    2016-01-01

    This paper presents a summary of four invited and twelve contributed presentations on asymptotic giant branch stars and red supergiants, given over the course of two afternoon splinter sessions at the 19th Cool Stars Workshop. It highlights both recent observations and recent theory, with some emphasis on high spatial resolution, over a wide range of wavelengths. Topics covered include 3D models, convection, binary interactions, mass loss, dust formation and magnetic fields.

  11. Hydrodynamic Simulations of the Interaction between Giant Stars and Planets

    CERN Document Server

    Staff, Jan E; Wood, Peter; Galaviz, Pablo; Passy, Jean-Claude

    2016-01-01

    We present the results of hydrodynamic simulations of the interaction between a 10 Jupiter mass planet and a red or asymptotic giant branch stars, both with a zero-age main sequence mass of 3.5 $M_\\odot$. Dynamic in-spiral timescales are of the order of few years and a few decades for the red and asymptotic giant branch stars, respectively. The planets will eventually be destroyed at a separation from the core of the giants smaller than the resolution of our simulations, either through evaporation or tidal disruption. As the planets in-spiral, the giant stars' envelopes are somewhat puffed up. Based on relatively long timescales and even considering the fact that further in-spiral should take place before the planets are destroyed, we predict that the merger would be difficult to observe, with only a relatively small, slow brightening. Very little mass is unbound in the process. These conclusions may change if the planet's orbit enhances the star's main pulsation modes. Based on the angular momentum transfer,...

  12. Cyanogen in NGC 1851 Red Giant Branch and Asymptotic Giant Branch Stars: Quadrimodal Distributions

    DEFF Research Database (Denmark)

    Campbell, S. W.; Yong, D.; Wylie-de Boer, E. C.

    2012-01-01

    The Galactic globular cluster NGC 1851 has raised much interest since Hubble Space Telescope photometry revealed that it hosts a double subgiant branch. Here we report on our homogeneous study into the cyanogen (CN) band strengths in the red giant branch (RGB) population (17 stars) and asymptotic...

  13. Cyanogen in NGC 1851 Red Giant Branch and Asymptotic Giant Branch Stars: Quadrimodal Distributions

    DEFF Research Database (Denmark)

    Campbell, S. W.; Yong, D.; Wylie-de Boer, E. C.;

    2012-01-01

    The Galactic globular cluster NGC 1851 has raised much interest since Hubble Space Telescope photometry revealed that it hosts a double subgiant branch. Here we report on our homogeneous study into the cyanogen (CN) band strengths in the red giant branch (RGB) population (17 stars) and asymptotic...

  14. Hydrodynamic simulations of the interaction between giant stars and planets

    Science.gov (United States)

    Staff, Jan E.; De Marco, Orsola; Wood, Peter; Galaviz, Pablo; Passy, Jean-Claude

    2016-05-01

    We present the results of hydrodynamic simulations of the interaction between a 10 Jupiter mass planet and a red or asymptotic giant branch stars, both with a zero-age main sequence mass of 3.5 M⊙. Dynamic in-spiral time-scales are of the order of few years and a few decades for the red and asymptotic giant branch stars, respectively. The planets will eventually be destroyed at a separation from the core of the giants smaller than the resolution of our simulations, either through evaporation or tidal disruption. As the planets in-spiral, the giant stars' envelopes are somewhat puffed up. Based on relatively long time-scales and even considering the fact that further in-spiral should take place before the planets are destroyed, we predict that the merger would be difficult to observe, with only a relatively small, slow brightening. Very little mass is unbound in the process. These conclusions may change if the planet's orbit enhances the star's main pulsation modes. Based on the angular momentum transfer, we also suspect that this star-planet interaction may be unable to lead to large-scale outflows via the rotation-mediated dynamo effect of Nordhaus and Blackman. Detectable pollution from the destroyed planets would only result for the lightest, lowest metallicity stars. We furthermore find that in both simulations the planets move through the outer stellar envelopes at Mach-3 to Mach-5, reaching Mach-1 towards the end of the simulations. The gravitational drag force decreases and the in-spiral slows down at the sonic transition, as predicted analytically.

  15. Giant eruptions of very massive stars

    CERN Document Server

    Davidson, Kris

    2016-01-01

    Giant eruptions or supernova-impostor events are far more mysterious than true supernovae. An extreme example can release as much radiative energy as a SN, ejecting several M_sun of material. These events involve continuous radiation-driven outflows rather than blast waves. They constitute one of the main unsolved problems in stellar astrophysics, but have received surprisingly little theoretical effort. Here I note some aspects that are not yet familiar to most astronomers.

  16. Massive Stars in the W33 Giant Molecular Complex

    CERN Document Server

    Messineo, Maria; Figer, Donald F; Kudritzki, Rolf-Peter; Najarro, Francisco; Rich, R Michael; Menten, Karl M; Ivanov, Valentin D; Valenti, Elena; Trombley, Christine; Chen, C -H Rosie; Davies, Ben

    2015-01-01

    Rich in HII regions, giant molecular clouds are natural laboratories to study massive stars and sequential star formation. The Galactic star forming complex W33 is located at l=~12.8deg and at a distance of 2.4 kpc, has a size of ~10 pc and a total mass of (~0.8 - ~8.0) X 10^5 Msun. The integrated radio and IR luminosity of W33 - when combined with the direct detection of methanol masers, the protostellar object W33A, and protocluster embedded within the radio source W33 main - mark the region out as a site of vigorous ongoing star formation. In order to assess the long term star formation history, we performed an infrared spectroscopic search for massive stars, detecting for the first time fourteen early-type stars, including one WN6 star and four O4-7 stars. The distribution of spectral types suggests that this population formed during the last ~2-4 Myr, while the absence of red supergiants precludes extensive star formation at ages 6-30 Myr. This activity appears distributed throughout the region and does ...

  17. Spectroscopic and Interferometric Measurements of Nine K Giant Stars

    CERN Document Server

    Baines, Ellyn K; Guenther, Eike W; Hatzes, Artie P; Hrudkovu, Marie; van Belle, Gerard T

    2016-01-01

    We present spectroscopic and interferometric measurements for a sample of nine K giant stars. These targets are of particular interest because they are slated for stellar oscillation observations. Our improved parameters will directly translate into reduced errors in the final masses for these stars when interferometric radii and asteroseismic densities are combined. Here we determine each star's limb-darkened angular diameter, physical radius, luminosity, bolometric flux, effective temperature, surface gravity, metallicity, and mass. When we compare our interferometric and spectroscopic results, we find no systematic offsets in the diameters and the values generally agree within the errors. Our interferometric temperatures for seven of the nine stars are hotter than those determined from spectroscopy with an average difference of about 380 K.

  18. NLTE Strontium and Barium in metal poor red giant stars

    CERN Document Server

    Short, C I

    2006-01-01

    We present atmospheric models of red giant stars of various metallicities, including extremely metal poor (XMP, [Fe/H]<-3.5) models, with many chemical species, including, significantly, the first two ionization stages of Strontium (Sr) and Barium (Ba), treated in Non-Local Thermodynamic Equilibrium (NLTE) with various degrees of realism. We conclude that 1) for all lines that are useful Sr and Ba abundance diagnostics the magnitude and sense of the computed NLTE effect on the predicted line strength is metallicity dependent, 2) the indirect NLTE effect of overlap between Ba and Sr transitions and transitions of other species that are also treated in NLTE non-negligibly enhances NLTE abundance corrections for some lines, 3) the indirect NLTE effect of NLTE opacity of other species on the equilibrium structure of the atmospheric model is not significant, 4) the computed NLTE line strengths differ negligibly if collisional b-b and b-f rates are an order of magnitude smaller or larger than those calculated wi...

  19. CHROMOSPHERIC MODELS AND THE OXYGEN ABUNDANCE IN GIANT STARS

    Energy Technology Data Exchange (ETDEWEB)

    Dupree, A. K.; Avrett, E. H.; Kurucz, R. L., E-mail: dupree@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

    2016-04-10

    Realistic stellar atmospheric models of two typical metal-poor giant stars in Omega Centauri, which include a chromosphere (CHR), influence the formation of optical lines of O i: the forbidden lines (λ6300, λ6363) and the infrared triplet (λλ7771−7775). One-dimensional semi-empirical non-local thermodynamic equilibrium (LTE) models are constructed based on observed Balmer lines. A full non-LTE formulation is applied for evaluating the line strengths of O i, including photoionization by the Lyman continuum and photoexcitation by Lyα and Lyβ. Chromospheric models (CHR) yield forbidden oxygen transitions that are stronger than those in radiative/convective equilibrium (RCE) models. The triplet oxygen lines from high levels also appear stronger than those produced in an RCE model. The inferred oxygen abundance from realistic CHR models for these two stars is decreased by factors of ∼3 as compared to values derived from RCE models. A lower oxygen abundance suggests that intermediate-mass AGB stars contribute to the observed abundance pattern in globular clusters. A change in the oxygen abundance of metal-poor field giants could affect models of deep mixing episodes on the red giant branch. Changes in the oxygen abundance can impact other abundance determinations that are critical to astrophysics, including chemical tagging techniques and galactic chemical evolution.

  20. Chromospheric Models and the Oxygen Abundance in Giant Stars

    Science.gov (United States)

    Dupree, A. K.; Avrett, E. H.; Kurucz, R. L.

    2016-04-01

    Realistic stellar atmospheric models of two typical metal-poor giant stars in Omega Centauri, which include a chromosphere (CHR), influence the formation of optical lines of O i: the forbidden lines (λ6300, λ6363) and the infrared triplet (λλ7771-7775). One-dimensional semi-empirical non-local thermodynamic equilibrium (LTE) models are constructed based on observed Balmer lines. A full non-LTE formulation is applied for evaluating the line strengths of O i, including photoionization by the Lyman continuum and photoexcitation by Lyα and Lyβ. Chromospheric models (CHR) yield forbidden oxygen transitions that are stronger than those in radiative/convective equilibrium (RCE) models. The triplet oxygen lines from high levels also appear stronger than those produced in an RCE model. The inferred oxygen abundance from realistic CHR models for these two stars is decreased by factors of ˜3 as compared to values derived from RCE models. A lower oxygen abundance suggests that intermediate-mass AGB stars contribute to the observed abundance pattern in globular clusters. A change in the oxygen abundance of metal-poor field giants could affect models of deep mixing episodes on the red giant branch. Changes in the oxygen abundance can impact other abundance determinations that are critical to astrophysics, including chemical tagging techniques and galactic chemical evolution.

  1. CHEMICAL ANALYSIS OF ASYMPTOTIC GIANT BRANCH STARS IN M62

    Energy Technology Data Exchange (ETDEWEB)

    Lapenna, E.; Mucciarelli, A.; Ferraro, F. R.; Lanzoni, B.; Dalessandro, E. [Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Viale Berti Pichat 6/2, I-40127 Bologna (Italy); Origlia, L.; Massari, D. [INAF-Osservatorio Astronomico di Bologna, Via Ranzani, 1, I-40127 Bologna (Italy)

    2015-11-10

    We have collected UVES-FLAMES high-resolution spectra for a sample of 6 asymptotic giant branch (AGB) and 13 red giant branch (RGB) stars in the Galactic globular cluster (GC) M62 (NGC 6266). Here we present the detailed abundance analysis of iron, titanium, and light elements (O, Na, Mg, and Al). For the majority (five out of six) of the AGB targets, we find that the abundances of both iron and titanium determined from neutral lines are significantly underestimated with respect to those obtained from ionized features, the latter being, instead, in agreement with those measured for the RGB targets. This is similar to recent findings in other clusters and may suggest the presence of nonlocal thermodynamic equilibrium (NLTE) effects. In the O–Na, Al–Mg, and Na–Al planes, the RGB stars show the typical correlations observed for GC stars. Instead, all the AGB targets are clumped in the regions where first-generation stars are expected to lie, similar to what was recently found for the AGB population of NGC 6752. While the sodium and aluminum abundances could be underestimated as a consequence of the NLTE bias affecting iron and titanium, the oxygen line used does not suffer from the same effects, and the lack of O-poor AGB stars therefore is a solid result. We can thus conclude that none of the investigated AGB stars belongs to the second stellar generation of M62. We also find an RGB star with extremely high sodium abundance ([Na/Fe] = +1.08 dex)

  2. Ultrabass Sounds of the Giant Star xi Hya

    Science.gov (United States)

    2002-05-01

    First Observations of Solar-type Oscillations in a Star Very Different from the Sun Summary About 30 years ago, astronomers realised that the Sun resonates like a giant musical instrument with well-defined periods (frequencies). It forms a sort of large, spherical organ pipe. The energy that excites these sound waves comes from the turbulent region just below the Sun's visible surface. Observations of the solar sound waves (known as " helioseismology ") have resulted in enormous progress in the exploration of the interior of the Sun, otherwise hidden from view. As is the case on Earth, seismic techniques can be applied and the detailed interpretation of the observed oscillation periods has provided quite accurate information about the structure and motions inside the Sun, our central star. It has now also become possible to apply this technique to some solar-type stars. The first observations concerned the northern star eta Bootis (cf. ESO PR 16/94 ). Last year, extensive and much more accurate observations with the 1.2-m Swiss telescope at the ESO La Silla Observatory proved that Alpha Centauri , a solar "twin", behaves very much like the Sun (cf. ESO PR 15/01 ), and that some of the periods are quite similar to those in the Sun. These new observational data were of a superb quality, and that study marked a true break-through in the new research field of " asteroseismology " (seismology of the stars) for solar-type stars. But what about other types of stars, for instance those that are much larger than the Sun? Based on an extremely intensive observing project with the same telescope, an international group of astronomers [1] has found that the giant star xi Hya ("xi" is the small greek letter [2]; "Hya" is an abbreviation of "Hydrae") behaves like a giant sub-ultra-bass instrument . This star is located in the constellation Hydra (the Water-Monster) at a distance of 130 light-years, it has a radius about 10 times that of the Sun and its luminosity is about 60

  3. Chemical analysis of Asymptotic Giant Branch stars in M62

    CERN Document Server

    Lapenna, E; Ferraro, F R; Origlia, L; Lanzoni, B; Massari, D; Dalessandro, E

    2015-01-01

    We have collected UVES-FLAMES high-resolution spectra for a sample of 6 asymptotic giant branch (AGB) and 13 red giant branch (RGB) stars in the Galactic globular cluster M62 (NGC6266). Here we present the detailed abundance analysis of iron, titanium, and light-elements (O, Na, Al and Mg). For the majority (5 out 6) of the AGB targets we find that the abundances, of both iron and titanium, determined from neutral lines are significantly underestimated with respect to those obtained from ionized features, the latter being, instead, in agreement with those measured for the RGB targets. This is similar to recent findings in other clusters and may suggest the presence of Non-Local Thermodynamical Equilibrium (NLTE) effects. In the O-Na, Al-Mg and Na-Al planes, the RGB stars show the typical correlations observed for globular cluster stars. Instead, all the AGB targets are clumped in the regions where first generation stars are expected to lie, similarly to what recently found for the AGB population of NGC6752. W...

  4. Homogeneous abundance analysis of dwarf, subgiant and giant FGK stars with and without giant planets

    CERN Document Server

    da Silva, R; Rocha-Pinto, H J

    2015-01-01

    We have analyzed high-resolution and high signal-to-noise ratio optical spectra of nearby FGK stars with and without detected giant planets in order to homogeneously measure their photospheric parameters, mass, age, and the abundances of volatile (C, N, and O) and refractory (Na, Mg, Si, Ca, Ti, V, Mn, Fe, Ni, Cu, and Ba) elements. Our sample contains 309 stars from the solar neighborhood (up to the distance of 100 pc), out of which 140 are dwarfs, 29 are subgiants, and 140 are giants. The photospheric parameters are derived from the equivalent widths of Fe I and Fe II lines. Masses and ages come from the interpolation in evolutionary tracks and isochrones on the HR diagram. The abundance determination is based on the equivalent widths of selected atomic lines of the refractory elements and on the spectral synthesis of C_2, CN, C I, O I, and Na I features. We apply a set of statistical methods to analyze the abundances derived for the three subsamples. Our results show that: i) giant stars systematically exhi...

  5. Is mass loss from red giant stars dust driven?

    Science.gov (United States)

    Yates, J. A.

    1992-12-01

    Long period variable stars on the Asymptotic Giant Branch are observed to be losing mass in the form of cool dusty molecular stellar winds at rates from 10-7 to 10-4 Msunyr-1. The driving force for this mass loss is thought to be radiation pressure on dust particles. The dust transfers its momentum to gas molecules via collisions. This paper discusses the existing evidence for this scenario. New results, from analysis of 22 GHz H2O maser observations made by Merlin, show that the cruical acceleration past the stellar escape velocity of the central star takes place in the inner circumstellar envelope around the central star. The analysis of the velocity fields of the circumstellar envelopes of VX Sgr and VY CMa using the model described by Chapman and Cohen (1986) are discussed.

  6. Triggered star formation in giant HI supershells: ionized gas

    CERN Document Server

    Egorov, O V; Moiseev, A V

    2015-01-01

    We considered the regions of triggered star formation inside kpc-sized HI supershells in three dwarf galaxies: IC 1613, IC 2574 and Holmberg II. The ionized and neutral gas morphology and kinematics were studied based on our observations with scanning Fabry-Perot interferometer at the SAO RAS 6-m telescope and 21 cm archival data of THINGS and LITTLE THINGS surveys. The qualitative analysis of the observational data performed in order to highlight the two questions: why the star formation occurred very locally in the supershells, and how the ongoing star formation in HI supershells rims influence its evolution? During the investigation we discovered the phenomenon never observed before in galaxies IC 2574 and Holmberg II: we found faint giant (kpc-sized) ionized shells in H-alpha and [SII]6717,6731 lines inside the supergiant HI shells.

  7. Mass loss from red giant stars. II. Carbon stars

    Energy Technology Data Exchange (ETDEWEB)

    Wannier, P.G.; Sahai, R.; Andersson, B.G.; Johnson, H.R. (JPL, Pasadena, CA (USA) Goteborg Universitet (Sweden) Indiana Univ., Bloomington (USA))

    1990-07-01

    A millimeter-wave survey has been made of bright relatively unobscured, carbon stars, chosen on the basis of their optical properties. Out of 26 program objects, (J = 2-1)CO emission is detected from 15. Most of these had not been previously detected. There are many differences among the observed objects, but one rather interesting trend emerges: a positive correlation, at moderate IR excesses, between the IR dust emission and the expansion velocity of the dense wind. A similar, positive correlation with the mass-loss rate implies that stars with larger mass fluxes also accelerate them to larger velocities. At high-IR excesses, both correlations break down, and the momentum rate may be limited by the momentum rate of the stellar radiation. All these effects could be ascribed to differences in the gas-to-dust ratio, assuming that radiation pressure initiates and accelerates the wind. 38 refs.

  8. Mass loss from red giant stars. II - Carbon stars

    Science.gov (United States)

    Wannier, P. G.; Sahai, R.; Andersson, B.-G.; Johnson, H. R.

    1990-01-01

    A millimeter-wave survey has been made of bright relatively unobscured, carbon stars, chosen on the basis of their optical properties. Out of 26 program objects, (J = 2-1)CO emission is detected from 15. Most of these had not been previously detected. There are many differences among the observed objects, but one rather interesting trend emerges: a positive correlation, at moderate IR excesses, between the IR dust emission and the expansion velocity of the dense wind. A similar, positive correlation with the mass-loss rate implies that stars with larger mass fluxes also accelerate them to larger velocities. At high-IR excesses, both correlations break down, and the momentum rate may be limited by the momentum rate of the stellar radiation. All these effects could be ascribed to differences in the gas-to-dust ratio, assuming that radiation pressure initiates and accelerates the wind.

  9. Exploring masses and CNO surface abundances of red giant stars

    Science.gov (United States)

    Halabi, Ghina M.; Eid, Mounib El

    2015-08-01

    A grid of evolutionary sequences of stars in the mass range 1.2-7M⊙, with solar-like initial composition is presented. We focus on this mass range in order to estimate the masses and calculate the CNO surface abundances of a sample of observed red giants. The stellar models are calculated from the zero-age main sequence till the early asymptotic giant branch (AGB) phase. Stars of M ≤ 2.2M⊙ are evolved through the core helium flash. In this work, an approach is adopted that improves the mass determination of an observed sample of 21 RGB and early AGB stars. This approach is based on comparing the observationally derived effective temperatures and absolute magnitudes with the calculated values based on our evolutionary tracks in the Hertzsprung-Russell diagram. A more reliable determination of the stellar masses is achieved by using evolutionary tracks extended to the range of observation. In addition, the predicted CNO surface abundances are compared to the observationally inferred values in order to show how far standard evolutionary calculation can be used to interpret available observations and to illustrate the role of convective mixing. We find that extra mixing beyond the convective boundary determined by the Schwarzschild criterion is needed to explain the observational oxygen isotopic ratios in low-mass stars. The effect of recent determinations of proton capture reactions and their uncertainties on the 16O/17O and 14N/15N ratios is also shown. It is found that the 14N( p, γ)15O reaction is important for predicting the 14N/15N ratio in red giants.

  10. Young alpha-enriched giant stars in the solar neighbourhood

    CERN Document Server

    Martig, Marie; Aguirre, Victor Silva; Hekker, Saskia; Mosser, Benoit; Elsworth, Yvonne; Bovy, Jo; Stello, Dennis; Anders, Friedrich; García, Rafael A; Tayar, Jamie; Rodrigues, Thaíse S; Basu, Sarbani; Carrera, Ricardo; Ceillier, Tugdual; Chaplin, William J; Chiappini, Cristina; Frinchaboy, Peter M; García-Hernández, D A; Hearty, Fred R; Holtzman, Jon; Johnson, Jennifer A; Mathur, Savita; Mészáros, Szabolcs; Miglio, Andrea; Nidever, David; Pinsonneault, Marc; Schiavon, Ricardo P; Schneider, Donald P; Serenelli, Aldo; Shetrone, Matthew; Zamora, Olga

    2014-01-01

    We derive age constraints for 1639 red giants in the APOKASC sample for which seismic parameters from Kepler, as well as effective temperatures, metallicities and [{\\alpha}/Fe] values from APOGEE DR12 are available. We investigate the relation between age and chemical abundances for these stars, using a simple and robust approach to obtain ages. We first derive stellar masses using standard seismic scaling relations, then determine the maximum possible age for each star as function of its mass and metallicity, independently of its evolutionary stage. While the overall trend between maximum age and chemical abundances is a declining fraction of young stars with increasing [{\\alpha}/Fe], at least 14 out of 241 stars with [{\\alpha}/Fe]>0.13 are younger than 6 Gyr. Five stars with [{\\alpha}/Fe]>0.2 have ages below 4 Gyr. We examine the effect of modifications in the standard seismic scaling relations, as well as the effect of very low helium fractions, but these changes are not enough to make these stars as old a...

  11. Kinematics of Tycho-2 Red Giant Clump Stars

    CERN Document Server

    Bobylev, V V; Bajkova, A T; Gontcharov, G A; 10.1134/S1063773709120044

    2009-01-01

    Based on the Ogorodnikov-Milne model, we analyze the proper motions of 95 633 red giant clump (RGC) stars from the Tycho-2 Catalogue. The following Oort constants have been found: A = 15.9+-0.2 km/s/kpc and B = -12.0+-0.2 km/s/kpc. Using 3632 RGC stars with known proper motions, radial velocities, and photometric distances, we show that, apart from the star centroid velocity components relative to the Sun, only the model parameters that describe the stellar motions in the XY plane differ significantly from zero. We have studied the contraction (a negative K-effect) of the system of RGC stars as a function of their heliocentric distance and elevation above the Galactic plane. For a sample of distant (500--1000 pc) RGC stars located near the Galactic plane (|Z|=200 pc), these effects are less pronounced, Kd = -1.7+-0.5 km/s and lxy = 4.9+-0.6 degrees. Using RGC stars, we have found a rotation around the Galactic X axis directed toward the Galactic center with an angular velocity of -2.5+-0.3 km/s/kpc, which we ...

  12. Episodic model for star formation history and chemical abundances in giant and dwarf galaxies

    Science.gov (United States)

    Debsarma, Suma; Chattopadhyay, Tanuka; Das, Sukanta; Pfenniger, Daniel

    2016-11-01

    In search for a synthetic understanding, a scenario for the evolution of the star formation rate and the chemical abundances in galaxies is proposed, combining gas infall from galactic haloes, outflow of gas by supernova explosions, and an oscillatory star formation process. The oscillatory star formation model is a consequence of the modelling of the fractional masses changes of the hot, warm and cold components of the interstellar medium. The derived periods of oscillation vary in the range (0.1-3.0) × 107 yr depending on various parameters existing from giant to dwarf galaxies. The evolution of metallicity varies in giant and dwarf galaxies and depends on the outflow process. Observed abundances in dwarf galaxies can be reproduced under fast outflow together with slow evaporation of cold gases into hot gas whereas slow outflow and fast evaporation is preferred for giant galaxies. The variation of metallicities in dwarf galaxies supports the fact that low rate of SNII production in dwarf galaxies is responsible for variation in metallicity in dwarf galaxies of similar masses as suggested by various authors.

  13. Episodic Model For Star Formation History and Chemical Abundances in Giant and Dwarf Galaxies

    CERN Document Server

    Debsarma, Suma; Das, Sukanta; Pfenniger, Daniel

    2016-01-01

    In search for a synthetic understanding, a scenario for the evolution of the star formation rate and the chemical abundances in galaxies is proposed, combining gas infall from galactic halos, outflow of gas by supernova explosions, and an oscillatory star formation process. The oscillatory star formation model is a consequence of the modelling of the fractional masses changes of the hot, warm and cold components of the interstellar medium. The observed periods of oscillation vary in the range $(0.1-3.0)\\times10^{7}$\\,yr depending on various parameters existing from giant to dwarf galaxies. The evolution of metallicity varies in giant and dwarf galaxies and depends on the outflow process. Observed abundances in dwarf galaxies can be reproduced under fast outflow together with slow evaporation of cold gases into hot gas whereas slow outflow and fast evaporation is preferred for giant galaxies. The variation of metallicities in dwarf galaxies supports the fact that low rate of SNII production in dwarf galaxies i...

  14. Giant pulsar glitches and the inertia of neutron star crusts

    Science.gov (United States)

    Delsate, T.; Chamel, N.; Gürlebeck, N.; Fantina, A. F.; Pearson, J. M.; Ducoin, C.

    2016-07-01

    Giant pulsar frequency glitches as detected in the emblematic Vela pulsar have long been thought to be the manifestation of a neutron superfluid permeating the inner crust of a neutron star. However, this superfluid has been recently found to be entrained by the crust, and as a consequence it does not carry enough angular momentum to explain giant glitches. The extent to which pulsar-timing observations can be reconciled with the standard vortex-mediated glitch theory is studied considering the current uncertainties on dense-matter properties. To this end, the crustal moment of inertia of glitching pulsars is calculated employing a series of different unified dense-matter equations of state.

  15. Exploring masses and CNO surface abundances of red giant stars

    CERN Document Server

    Halabi, Ghina M

    2015-01-01

    A grid of evolutionary sequences of stars in the mass range $1.2$-$7$ M$_{\\odot}$, with solar-like initial composition is presented. We focus on this mass range in order to estimate the masses and calculate the CNO surface abundances of a sample of observed red giants. The stellar models are calculated from the zero-age main sequence till the early asymptotic giant branch (AGB) phase. Stars of M $\\leqslant$ $2.2$M$_{\\odot}$ are evolved through the core helium flash. In this work, an approach is adopted that improves the mass determination of an observed sample of 21 RGB and early AGB stars. This approach is based on comparing the observationally derived effective temperatures and absolute magnitudes with the calculated values based on our evolutionary tracks in the Hertzsprung-Russell diagram. A more reliable determination of the stellar masses is achieved by using evolutionary tracks extended to the range of observation. In addition, the predicted CNO surface abundances are compared to the observationally in...

  16. Lithium and magnetic fields in giants. HD 232862 : a magnetic and lithium-rich giant star

    CERN Document Server

    Lèbre, A; Nascimento, J D do; Konstantinova-Antova, R; Kolev, D; Aurière, M; De Laverny, P; De Medeiros, J R

    2009-01-01

    We report the detection of an unusually high lithium content in HD 232862, a field giant classified as a G8II star, and hosting a magnetic field. With the spectropolarimeters ESPaDOnS at CFHT and NARVAL at TBL, we have collected high resolution and high signal-to-noise spectra of three giants : HD 232862, KU Peg and HD 21018. From spectral synthesis we have inferred stellar parameters and measured lithium abundances that we have compared to predictions from evolutionary models. We have also analysed Stokes V signatures, looking for a magnetic field on these giants. HD 232862, presents a very high abundance of lithium (ALi = 2.45 +/- 0.25 dex), far in excess of the theoretically value expected at this spectral type and for this luminosity class (i.e, G8II). The evolutionary stage of HD 232862 has been precised, and it suggests a mass in the lower part of the [1.0 Msun ; 3.5 Msun ] mass interval, likely 1.5 to 2.0 solar mass, at the bottom of the Red Giant Branch. Besides, a time variable Stokes V signature has...

  17. XUV-driven mass loss from extrasolar giant planets orbiting active stars

    Science.gov (United States)

    Chadney, J. M.; Galand, M.; Unruh, Y. C.; Koskinen, T. T.; Sanz-Forcada, J.

    2015-04-01

    Upper atmospheres of Hot Jupiters are subject to extreme radiation conditions that can result in rapid atmospheric escape. The composition and structure of the upper atmospheres of these planets are affected by the high-energy spectrum of the host star. This emission depends on stellar type and age, which are thus important factors in understanding the behaviour of exoplanetary atmospheres. In this study, we focus on Extrasolar Giant Planets (EPGs) orbiting K and M dwarf stars. XUV spectra for three different stars - ɛ Eridani, AD Leonis and AU Microscopii - are constructed using a coronal model. Neutral density and temperature profiles in the upper atmosphere of hypothetical EGPs orbiting these stars are then obtained from a fluid model, incorporating atmospheric chemistry and taking atmospheric escape into account. We find that a simple scaling based solely on the host star's X-ray emission gives large errors in mass loss rates from planetary atmospheres and so we have derived a new method to scale the EUV regions of the solar spectrum based upon stellar X-ray emission. This new method produces an outcome in terms of the planet's neutral upper atmosphere very similar to that obtained using a detailed coronal model of the host star. Our results indicate that in planets subjected to radiation from active stars, the transition from Jeans escape to a regime of hydrodynamic escape at the top of the atmosphere occurs at larger orbital distances than for planets around low activity stars (such as the Sun).

  18. On the Onset of Secondary Stellar Generations in Giant Star Forming Regions and Massive Star Clusters

    CERN Document Server

    Palouš, Jan; Tenorio-Tagle, Guillermo

    2014-01-01

    Here we consider the strong evolution experienced by the matter reinserted by massive stars, both in giant star forming regions driven by a constant star formation rate, and in massive and coeval superstar clusters. In both cases we take into consideration the changes induced by stellar evolution on the number of massive stars, the number of ionizing photons and the integrated mechanical luminosity of the star forming regions. The latter is at all times compared with the critical luminosity that defines, for a given size, the lower mechanical luminosity limit above which the matter reinserted via strong winds and supernova explosions suffers frequent and recurrent thermal instabilities that reduce its temperature and pressure and inhibit its exit as part of a global wind. Instead, the unstable reinserted matter is compressed by the pervasive hot gas, and photoionization maintains its temperature at T $\\sim$ 10$^4$ K. As the evolution proceeds, more unstable matter accumulates and the unstable clumps grow in s...

  19. The Cool Giant HD 77361 - A Super Li-Rich Star

    CERN Document Server

    Lyubimkov, L S; Metlov, V G; Pavlenko, Ya V; Poklad, D B; Rachkovskaya, T M

    2016-01-01

    Super Li-rich stars form a very small and enigmatic group whose existence cannot be explained in terms of the standard stellar evolution theory. The goal of our study is to check the reality of this group of cool giants based on an independent technique. We have carried out such a check using the K giant HD 77361 (HR 3597), which has previously been assigned to this rare type, as an example. We have redetermined the effective temperature Teff and surface gravity log g for this star. We have applied two different methods, photometric and spectroscopic, to estimate Teff (the accuracy of the Li-abundance determination depends significantly on this parameter). The value of log g has been found from the highly accurate parallax of this nearby star. To apply the photometric method of determining Teff, we have performed UBV observations of the star, which yielded V = 6.18 +/- 0.03, B - V = 1.13 +/- 0.01, and U - B = 1.18+/-0.05. The following parameters of the star have been found: effective temperature Teff = 4370+...

  20. Star Formation Efficiencies and Lifetimes of Giant Molecular Clouds in the Milky Way

    CERN Document Server

    Murray, Norman

    2010-01-01

    We use a sample of the 13 most luminous WMAP Galactic free-free sources, responsible for 33% of the free- free emission of the Milky Way, to investigate star formation. The sample contains 40 star forming complexes; we combine this sample with giant molecular cloud (GMC) catalogs in the literature, to identify the host GMCs of 32 of the complexes. We estimate the star formation efficiency epsilon_GMC and star formation rate per free-fall time epsilon_ff. We find that epsilon_GMC ranges from 0.002 to 0.2, with an ionizing luminosity-weighted average epsilon_GMC = 0.08, compared to the Galactic average = 0.005. Turning to the star formation rate per free-fall time, we find values that range up to epsilon_ff = 1. Weighting by ionizing luminosity, we find an average of epsilon_ff = 0.16 - 0.24 depending on the estimate of the age of the system. Once again, this is much larger than the Galaxy-wide average value epsilon_ff = 0.008. We show that the lifetimes of giant molecular clouds at the mean mass found in our s...

  1. Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars

    NARCIS (Netherlands)

    Bedding, T.R.; Mosser, B.; Huber, D.; Montalbán, J.; Beck, P.; Christensen-Dalsgaard, J.; Elsworth, Y.P.; García, R.A.; Miglio, A.; Stello, D.; White, T.R.; de Ridder, J.; Hekker, S.; Aerts, C.; Barban, C.; Belkacem, K.; Broomhall, A.M.; Brown, T.M.; Buzasi, D.L.; Carrier, F.; Chaplin, W.J.; Di Mauro, M.P.; Dupret, M.-A.; Frandsen, S.; Gilliland, R.L.; Goupil, M.J.; Jenkins, J.M.; Kallinger, T.; Kawaler, S.; Kjeldsen, H.; Mathur, S.; Noels, A.; Silva Aguirre, V.; Ventura, P.

    2011-01-01

    Red giants are evolved stars that have exhausted the supply of hydrogen in their cores and instead burn hydrogen in a surrounding shell. Once a red giant is sufficiently evolved, the helium in the core also undergoes fusion. Outstanding issues in our understanding of red giants include uncertainties

  2. Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars

    DEFF Research Database (Denmark)

    Bedding, Timothy R.; Mosser, Benoit; Huber, Daniel;

    2011-01-01

    Red giants are evolved stars that have exhausted the supply of hydrogen in their cores and instead burn hydrogen in a surrounding shell. Once a red giant is sufficiently evolved, the helium in the core also undergoes fusion. Outstanding issues in our understanding of red giants include uncertaint...

  3. An HI Imaging Survey of Asymptotic Giant Branch Stars

    CERN Document Server

    Matthews, L D; Gerard, E; Johnson, M C

    2013-01-01

    We present an imaging study of a sample of eight asymptotic giant branch (AGB) stars in the HI 21-cm line. Using observations from the Very Large Array, we have unambiguously detected HI emission associated with the extended circumstellar envelopes of six of the targets. The detected HI masses range from M_HI ~ 0.015-0.055 M_sun. The HI morphologies and kinematics are diverse, but in all cases appear to be significantly influenced by the interaction between the circumstellar envelope and the surrounding medium. Four stars (RX Lep, Y UMa, Y CVn, and V1942 Sgr) are surrounded by detached HI shells ranging from 0.36 to 0.76 pc across. We interpret these shells as resulting from material entrained in a stellar outflow being abruptly slowed at a termination shock where it meets the local medium. RX Lep and TX Psc, two stars with moderately high space velocities (V_space>56 km/s), exhibit extended gaseous wakes (~0.3 and 0.6 pc in the plane of the sky), trailing their motion through space. The other detected star, ...

  4. Recovery from Giant Eruptions in Very Massive Stars

    CERN Document Server

    Kashi, Amit; Humphreys, Roberta M

    2015-01-01

    We use a hydro-and-radiative-transfer code to explore the behavior of a very massive star (VMS) after a giant eruption -- i.e., following a supernova impostor event. Beginning with a reasonable model for an evolved VMS, we simulate the change of state caused by a giant eruption via two methods that explicitly conserve total energy: 1. Synthetically removing outer layers of mass while reducing the energy of the inner layers. 2. Synthetically transferring energy from the core to the outer layers, an operation that automatically causes mass ejection. Our focus is on the aftermath, not the poorly-understood eruption itself. Then, using a radiation-hydrodynamic code in 1D with realistic opacities and convection, the interior disequilibrium state is followed for about 200 years. Typically the star develops a $\\sim 400 ~\\rm{km}~\\rm{s}^{-1}$ wind with a mass loss rate that begins around $0.1 ~M_\\odot~\\rm{yr^{-1}}$ and gradually decreases. This outflow is driven by $\\kappa$-mechanism radial pulsations. In some cases a...

  5. The dust condensation sequence in red super-giant stars

    CERN Document Server

    Verhoelst, T; Hony, S; Decin, L; Cami, J; Eriksson, K

    2009-01-01

    Context: Red super-giant (RSG) stars exhibit significant mass loss through a slow and dense wind. They are often considered to be the more massive counter parts of Asymptotic Giant Branch (AGB) stars. While the AGB mass loss is linked to their strong pulsations, the RSG are often only weakly variable. Aim: To study the conditions at the base of the wind, by determining the dust composition in a sample of RSG. The dust composition is thought to be sensitive to the density, temperature and acceleration at the base of the wind. Method: We compile a sample of 27 RSG infrared spectra (ISO-SWS) and supplement these with photometric measurements to obtain the full spectral energy distribution (SED). These data are modelled using a dust radiative transfer code. The results are scrutinised for correlations. Results: We find (1) strong correlations between dust composition, mass-loss rate and stellar luminosity, roughly in agreement with the theoretical dust condensation sequence, (2) the need for a continuous (near-)I...

  6. Aluminum 26 production in asymptotic giant branch stars

    Science.gov (United States)

    Mowlavi, N.; Meynet, G.

    2000-09-01

    The production of 26Al in asymptotic giant branch (AGB) stars is studied based on evolutionary stellar models of different masses (1.5 region follows, at a given metallicity, a very well defined pattern as a function of the H-burning shell temperature TH. Two zones must be distinguished. The first one comprises those He-rich layers containing H-burning ashes which escape pulse in jection. The amount of 26Al in that zone (M\\odot1-2×10-7 at the first pulse in M\\odot1.5-3 Z=0.02 stars) steadily decreases with pulse number. Its contribution to the surface 26Al enhancement can only be important during the first pulses if dredge--up occurs at that stage. The second zone consists of the C-rich material emerging from the pulses. The amount of 26Al available in that zone is higher than that in the first zone (M\\odot3-4×10-7 at the first pulse in M\\odot1.5-3 Z=0.02 stars), and keeps constant during about the first dozen pulses before decreasing when TH~> 55× 106 K. This zone is thus an important potential reservoir for surface 26Al enrichment. Using third dredge-up (3DUP) efficiencies from model calculations, the surface 26Al abundance is predicted to reach 1-2× 10-7 mass fractions in our low-mass solar metallicity stars, with an uncertainty factor of about three. It decreases with increasing stellar mass, being about three times lower in a M\\odot4 than in M\\odot2-3 stars. In massive AGB stars, however, hot bottom burning enables to easily reach surface 26Al mass fractions above 10-6. The 26Al/27Al ratios measured in meteoritic SiC and oxide grains are discussed, as well as that possibly measured in the nearby C-star IRC+10216. We also address the contribution of AGB stars to the 2-3 M\\odot present day mass of 26Al detected in the Galaxy. Finally, we discuss the possibility of directly detecting an AGB star or a planetary nebula as a single source at 1.8 MeV with the future INTEGRAL satellite.

  7. STAR-TO-STAR IRON ABUNDANCE VARIATIONS IN RED GIANT BRANCH STARS IN THE GALACTIC GLOBULAR CLUSTER NGC 3201

    Energy Technology Data Exchange (ETDEWEB)

    Simmerer, Jennifer; Ivans, Inese I.; Filler, Dan [Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112 (United States); Francois, Patrick [Paris-Meudon Observatory, France and Universite de Picardie Jules Verne, F-80080 Amiens (France); Charbonnel, Corinne [Geneva Observatory, University of Geneva, Chemin des Maillettes 51, CH-1290 Versoix (Switzerland); Monier, Richard [Laboratoire Hippolyte Fizeau, Universite Nice Sophia Antipolis, Parc Valrose, F-06000 Nice (France); James, Gaeel, E-mail: jennifer@physics.utah.edu, E-mail: iii@physics.utah.edu, E-mail: dan.filler@utah.edu, E-mail: patrick.francois@obspm.fr, E-mail: corinne.charbonnel@unige.ch, E-mail: richard.monier@unice.fr, E-mail: gjames@eso.org [European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei Munchen (Germany)

    2013-02-10

    We present the metallicity as traced by the abundance of iron in the retrograde globular cluster NGC 3201, measured from high-resolution, high signal-to-noise spectra of 24 red giant branch stars. A spectroscopic analysis reveals a spread in [Fe/H] in the cluster stars at least as large as 0.4 dex. Star-to-star metallicity variations are supported both through photometry and through a detailed examination of spectra. We find no correlation between iron abundance and distance from the cluster core, as might be inferred from recent photometric studies. NGC 3201 is the lowest mass halo cluster to date to contain stars with significantly different [Fe/H] values.

  8. Chemical abundances of giant stars in the Crater stellar system

    CERN Document Server

    Bonifacio, P; Zaggia, S; François, P; Sbordone, L; Andrievsky, S M; Korotin, S A

    2015-01-01

    We obtained spectra for two giants of Crater (Crater J113613-105227 and Crater J113615-105244) using X-Shooter at the VLT. The spectra have been analysed with the MyGIsFoS code using a grid of synthetic spectra computed from one dimensional, Local Thermodynamic Equilibrium (LTE) model atmospheres. Effective temperature and surface gravity have been derived from photometry measured from images obtained by the Dark Energy Survey. The radial velocities are 144.3+-4.0 km/s for Crater J113613-105227 and and 134.1+-4.0 km/s for Crater J113615-105244. The metallicities are [Fe/H]=-1.73 and [Fe/H]=-1.67, respectively. Beside the iron abundance we could determine abundances for nine elements: Na, Mg, Ca, Ti, V, Cr, Mn, Ni and Ba. For Na and Ba we took into account deviations from LTE, since the corrections are significant. The abundance ratios are similar in the two stars and resemble those of Galactic stars of the same metallicity. On the deep photometric images we could detect several stars that lie to the blue of t...

  9. Stellar Models and Yields of Asymptotic Giant Branch Stars

    CERN Document Server

    Karakas, Amanda I

    2007-01-01

    We present stellar yields calculated from detailed models of low and intermediate-mass asymptotic giant branch (AGB) stars. We evolve models with a range of mass from 1 to 6Msun, and initial metallicities from solar to 1/200th of the solar metallicity. Each model was evolved from the zero age main sequence to near the end of the thermally-pulsing AGB phase, and through all intermediate phases including the core He-flash for stars initially less massive than 2.5Msun. For each mass and metallicity, we provide tables containing structural details of the stellar models during the TP-AGB phase, and tables of the stellar yields for 74 species from hydrogen through to sulphur, and for a small number of iron-group nuclei. All tables are available for download. Our results have many applications including use in population synthesis studies and the chemical evolution of galaxies and stellar systems, and for comparison to the composition of AGB and post-AGB stars and planetary nebulae.

  10. Chromospheric Models and the Oxygen Abundance in Giant Stars

    CERN Document Server

    Dupree, A K; Kurucz, R L

    2016-01-01

    Realistic stellar atmospheric models of two typical metal-poor giant stars in Omega Centauri that include a chromosphere influence the formation of optical lines of Oxygen I: the forbidden lines (630nm, 636nm) and the infrared triplet (777.1-777.5 nm). One-dimensional semi-empirical non-LTE models are constructed based on observed Balmer lines. A full non-LTE formulation is applied in evaluating line strengths of O I including photoionization by the Lyman continuum and photoexcitation by Ly-alpha and Ly-beta. Chromospheric models (CHR) yield forbidden oxygen transitions that are stronger than in radiative/convective equilibrium (RCE) models. The triplet oxygen lines from high levels also appear stronger than produced in an RCE model. The inferred oxygen abundance from realistic CHR models for these two stars is decreased by factors ~3 as compared to values derived from RCE models. A lower oxygen abundance suggests that intermediate mass AGB stars contribute to the observed abundance pattern in globular cluste...

  11. Solar-Like Cycle in Asymptotic Giant Branch Stars

    CERN Document Server

    Soker, N

    2000-01-01

    I propose that the mechanism behind the formation of concentric semi-periodic shells found in several planetary nebulae (PNs) and proto-PNs, and around one asymptotic giant branch (AGB) star, is a solar-like magnetic activity cycle in the progenitor AGB stars. The time intervals between consecutive ejection events is about 200-1,000 years, which is assumed to be the cycle period (the full magnetic cycle can be twice as long, as is the 22-year period in the sun). The magnetic field has no dynamical effects; it regulates the mass loss rate by the formation of magnetic cool spots. The enhanced magnetic activity at the cycle maximum results in more magnetic cool spots, which facilitate the formation of dust, hence increasing the mass loss rate. The strong magnetic activity implies that the AGB star is spun up by a companion, via a tidal or common envelope interaction. The strong interaction with a stellar companion explains the observations that the concentric semi-periodic shells are found mainly in bipolar PNs.

  12. Asymptotic Analysis of Mixed Modes in Red Giant Stars

    CERN Document Server

    Jiang, C

    2014-01-01

    High precision space observations, such as made by the kepler and corot missions, allow us to detect mixed modes for $l = 1$ modes in their high signal-to-noise photometry data. By means of asteroseismology, the inner structure of red giant (RG) stars is revealed the first time with the help of mixed modes. We analyse these mixed modes of a 1.3 $M_{sun}$ RG model theoretically from the approximate asymptotic descriptions of oscillations. While fitting observed frequencies with the eigenvalue condition for mixed modes, a good estimate of period spacing and coupling strength is also acquired for more evolved models. We show that the behaviour of the mode inertia in a given mode varies dramatically when the coupling is strong. An approximation of period spacings is also obtained from the asymptotic dispersion relation, which provides a good estimate of the coupling strength as well as period spacing when g-mode-like mixed modes are sufficiently dense.

  13. A compact system of small planets around a former red-giant star.

    Science.gov (United States)

    Charpinet, S; Fontaine, G; Brassard, P; Green, E M; Van Grootel, V; Randall, S K; Silvotti, R; Baran, A S; Ostensen, R H; Kawaler, S D; Telting, J H

    2011-12-21

    Planets that orbit their parent star at less than about one astronomical unit (1 AU is the Earth-Sun distance) are expected to be engulfed when the star becomes a red giant. Previous observations have revealed the existence of post-red-giant host stars with giant planets orbiting as close as 0.116 AU or with brown dwarf companions in tight orbits, showing that these bodies can survive engulfment. What has remained unclear is whether planets can be dragged deeper into the red-giant envelope without being disrupted and whether the evolution of the parent star itself could be affected. Here we report the presence of two nearly Earth-sized bodies orbiting the post-red-giant, hot B subdwarf star KIC 05807616 at distances of 0.0060 and 0.0076 AU, with orbital periods of 5.7625 and 8.2293 hours, respectively. These bodies probably survived deep immersion in the former red-giant envelope. They may be the dense cores of evaporated giant planets that were transported closer to the star during the engulfment and triggered the mass loss necessary for the formation of the hot B subdwarf, which might also explain how some stars of this type did not form in binary systems.

  14. RECOVERY FROM GIANT ERUPTIONS IN VERY MASSIVE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Kashi, Amit; Davidson, Kris; Humphreys, Roberta M., E-mail: kashi@astro.umn.edu [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church St. SE. Minneapolis, MN 55455 (United States)

    2016-01-20

    We use a hydro-and-radiative-transfer code to explore the behavior of a very massive star (VMS) after a giant eruption—i.e., following a supernova impostor event. Beginning with reasonable models for evolved VMSs with masses of 80 M{sub ⊙} and 120 M{sub ⊙}, we simulate the change of state caused by a giant eruption via two methods that explicitly conserve total energy. (1) Synthetically removing outer layers of mass of a few M{sub ⊙} while reducing the energy of the inner layers. (2) Synthetically transferring energy from the core to the outer layers, an operation that automatically causes mass ejection. Our focus is on the aftermath, not the poorly understood eruption itself. Then, using a radiation-hydrodynamic code in 1D with realistic opacities and convection, the interior disequilibrium state is followed for about 200 years. Typically the star develops a ∼400 km s{sup −1} wind with a mass loss rate that begins around 0.1 M{sub ⊙} yr{sup −1} and gradually decreases. This outflow is driven by κ-mechanism radial pulsations. The 1D models have regular pulsations but 3D models will probably be more chaotic. In some cases a plateau in the mass-loss rate may persist about 200 years, while other cases are more like η Car which lost >10 M{sub ⊙} and then had an abnormal mass loss rate for more than a century after its eruption. In our model, the post-eruption outflow carried more mass than the initial eruption. These simulations constitute a useful preliminary reconnaissance for 3D models which will be far more difficult.

  15. Recovery from Giant Eruptions in Very Massive Stars

    Science.gov (United States)

    Kashi, Amit; Davidson, Kris; Humphreys, Roberta M.

    2016-01-01

    We use a hydro-and-radiative-transfer code to explore the behavior of a very massive star (VMS) after a giant eruption—i.e., following a supernova impostor event. Beginning with reasonable models for evolved VMSs with masses of 80 M⊙ and 120 M⊙, we simulate the change of state caused by a giant eruption via two methods that explicitly conserve total energy. (1) Synthetically removing outer layers of mass of a few M⊙ while reducing the energy of the inner layers. (2) Synthetically transferring energy from the core to the outer layers, an operation that automatically causes mass ejection. Our focus is on the aftermath, not the poorly understood eruption itself. Then, using a radiation-hydrodynamic code in 1D with realistic opacities and convection, the interior disequilibrium state is followed for about 200 years. Typically the star develops a ˜400 km s-1 wind with a mass loss rate that begins around 0.1 M⊙ yr-1 and gradually decreases. This outflow is driven by κ-mechanism radial pulsations. The 1D models have regular pulsations but 3D models will probably be more chaotic. In some cases a plateau in the mass-loss rate may persist about 200 years, while other cases are more like η Car which lost >10 M⊙ and then had an abnormal mass loss rate for more than a century after its eruption. In our model, the post-eruption outflow carried more mass than the initial eruption. These simulations constitute a useful preliminary reconnaissance for 3D models which will be far more difficult.

  16. Asymptotic Giant Branch stars at low metallicity: the challenging interplay between mass loss and molecular opacities

    CERN Document Server

    Ventura, Paolo

    2010-01-01

    We investigate the main physical properties of low-metallicity Asymptotic Giant Branch stars, with the aim of quantifying the uncertainties that presently affect the predicted chemical yields of these stars, associated to mass loss and description of molecular opacities. We find that above a threshold mass, M ~ 3.5Msun for Z=0.001, the results are little dependent on the opacity treatment, as long as hot-bottom burning prevents the surface C/O ratio from exceeding unity; the yields of these massive AGB stars are expected to be mostly determined by the efficiency of convection, with a relatively mild dependence on the mass-loss description. A much higher degree of uncertainty is associated to the yields of less massive models, which critically depend on the adopted molecular opacities. An interval of masses exists, say 2.0-3.0Msun, (the exact range depends on mass loss), in which HBB may be even extinguished following the cooling produced by the opacity of C-bearing molecules. The yields of these stars are the...

  17. Population Synthesis of Common Envelope Mergers: I. Giant Stars with Stellar or Substellar Companions

    CERN Document Server

    Politano, Michael; Taam, Ronald E; Willems, Bart

    2010-01-01

    Using a population synthesis technique, we have calculated detailed models of the present-day field population of objects that have resulted from the merger of a giant primary and a main-sequence or brown dwarf secondary during common-envelope evolution. We used a grid of 116 stellar and 32 low-mass/brown dwarf models, a crude model of the merger process, and followed the angular momentum evolution of the binary orbit and the primary's rotation prior to merger, as well as the merged object's rotation after the merger. We find that present-day merged objects that are observable as giant stars or core-helium burning stars in our model population constitute between 0.24% and 0.33% of the initial population of ZAMS binaries, depending upon the input parameters chosen. The median projected rotational velocity of these merged objects is ~16 km/sec, an order of magnitude higher than the median projected rotational velocity in a model population of normal single stars calculated using the same stellar models and init...

  18. Medium-resolution Spectroscopy of Red Giant Branch Stars in ω Centauri

    Science.gov (United States)

    An, Deokkeun; Lee, Young Sun; In Jung, Jae; Rey, Soo-Chang; Rhee, Jaehyon; Lee, Jae-Woo; Lee, Young-Wook; Joe, Young Hoon

    2017-10-01

    We present [Fe/H] and [Ca/Fe] of ∼600 red giant branch (RGB) members of the globular cluster Omega Centauri (ω {Cen}). We collect medium-resolution (R∼ 2000) spectra using the Blanco 4 m telescope at the Cerro Tololo Inter-American Observatory equipped with Hydra, the fiber-fed multi-object spectrograph. We demonstrate that blending of stellar light in optical fibers severely limits the accuracy of spectroscopic parameters in the crowded central region of the cluster. When photometric temperatures are taken in the spectroscopic analysis, our kinematically selected cluster members, excluding those that are strongly affected by flux from neighboring stars, include relatively fewer stars at intermediate metallicity ([{Fe}/{{H}}]∼ -1.5) than seen in the previous high-resolution survey for brighter giants in Johnson & Pilachowski. As opposed to the trend of increasing [Ca/Fe] with [Fe/H] found by those authors, our [Ca/Fe] estimates, based on Ca ii H & K measurements, show essentially the same mean [Ca/Fe] for most of the metal-poor and metal-intermediate populations in this cluster, suggesting that mass- or metallicity-dependent SN II yields may not be necessary in their proposed chemical evolution scenario. Metal-rich cluster members in our sample show a large spread in [Ca/Fe], and do not exhibit a clear bimodal distribution in [Ca/Fe]. We also do not find convincing evidence for a radial metallicity gradient among RGB stars in ω {Cen}.

  19. Asteroseismology and interferometry of the red giant star epsilon Oph

    CERN Document Server

    Mazumdar, A; Demarque, P; Kervella, P; Barban, C; Baudin, F; Foresto, V Coude du; Farrington, C; Goldfinger, P J; Goupil, M -J; Josselin, E; Kuschnig, R; McAlister, H A; Matthews, J; Ridgway, S T; Sturmann, J; Sturmann, L; Brummelaar, T A ten; Turner, N

    2009-01-01

    The GIII red giant star epsilon Oph has been found to exhibit several modes of oscillation by the MOST mission. We interpret the observed frequencies of oscillation in terms of theoretical radial p-mode frequencies of stellar models. Evolutionary models of this star, in both shell H-burning and core He-burning phases of evolution, are constructed using as constraints a combination of measurements from classical ground-based observations (for luminosity, temperature, and chemical composition) and seismic observations from MOST. Radial frequencies of models in either evolutionary phase can reproduce the observed frequency spectrum of epsilon Oph almost equally well. The best-fit models indicate a mass in the range of 1.85 +/- 0.05 Msun with radius of 10.55 +/- 0.15 Rsun. We also obtain an independent estimate of the radius of epsilon Oph using high accuracy interferometric observations in the infrared K' band, using the CHARA/FLUOR instrument. The measured limb darkened disk angular diameter of epsilon Oph is 2...

  20. Four new planets around giant stars and the mass-metallicity correlation of planet-hosting stars

    CERN Document Server

    Jones, M I; Brahm, R; Wittenmyer, R A; Olivares, F E; Melo, C H F; Rojo, P; Jordán, A; Drass, H; Butler, R P; Wang, L

    2016-01-01

    CONTEXT. Exoplanet searches have demonstrated that giant planets are preferentially found around metal-rich stars and that their fraction increases with the stellar mass. AIMS. During the past six years, we have conducted a radial velocity follow-up program of 166 giant stars, to detect substellar companions, and characterizing their orbital properties. Using this information, we aim to study the role of the stellar evolution in the orbital parameters of the companions, and to unveil possible correlations between the stellar properties and the occurrence rate of giant planets. METHODS. Using FEROS and CHIRON spectra, we have computed precision radial velocities and we have derived atmospheric and physical parameters for all of our targets. Additionally, velocities computed from UCLES spectra are presented here. By studying the periodic radial velocity signals, we have detected the presence of several substellar companions. RESULTS. We present four new planetary systems around the giant stars HIP8541, HIP74890...

  1. Pulsating red giant stars in eccentric binary systems discovered from Kepler space-based photometry

    CERN Document Server

    Beck, P G; Vos, J; Kallinger, T; Bloemen, S; Tkachenko, A; García, R A; Østensen, R H; Aerts, C; Kurtz, D W; De Ridder, J; Hekker, S; Pavlovski, K; Mathur, S; De Smedt, K; Derekas, A; Corsaro, E; Mosser, B; Van Winckel, H; Huber, D; Degroote, P; Davies, G R; Prša, A; Debosscher, J; Elsworth, Y; Nemeth, P; Siess, L; Schmid, V S; Pápics, P I; de Vries, B L; van Marle, A J; Marcos-Arenal, P; Lobel, A

    2013-01-01

    The unparalleled photometric data obtained by NASA's Kepler space telescope led to an improved understanding of red giant stars and binary stars. Seismology allows us to constrain the properties of red giants. In addition to eclipsing binaries, eccentric non-eclipsing binaries, exhibiting ellipsoidal modulations, have been detected with Kepler. We aim to study the properties of eccentric binary systems containing a red giant star and derive the parameters of the primary giant component. We apply asteroseismic techniques to determine masses and radii of the primary component of each system. For a selected target, light and radial velocity curve modelling techniques are applied to extract the parameters of the system. The effects of stellar on the binary system are studied. The paper presents the asteroseismic analysis of 18 pulsating red giants in eccentric binary systems, for which masses and radii were constrained. The orbital periods of these systems range from 20 to 440days. From radial velocity measuremen...

  2. Exploring Halo Substructure with Giant Stars III First Results from the Grid Giant Star Survey and Discovery of a Possible Nearby Sagittarius Tidal Structure in Virgo

    CERN Document Server

    Kundu, A; Rhee, J; Rocha-Pinto, H J; Polak, A A; Slesnick, C L; Kunkel, W E; Johnston, K V; Patterson, R J; Geisler, D; Gieren, W P; Seguel, J; Smith, V V; Palma, C; Arenas, J; Crane, J D; Hummels, C B

    2002-01-01

    We describe first results of a spectroscopic probe of selected fields from the Grid Giant Star Survey. Multifiber spectroscopy of several hundred stars in a strip of eleven fields along delta approximately -17^{circ}, in the range 12 <~ alpha <~ 17 hours, reveals a group of 8 giants that have kinematical characteristics differing from the main field population, but that as a group maintain coherent, smoothly varying distances and radial velocities with position across the fields. Moreover, these stars have roughly the same abundance, according to their MgH+Mgb absorption line strengths. Photometric parallaxes place these stars in a semi-loop structure, arcing in a contiguous distribution between 5.7 and 7.9 kpc from the Galactic center. The spatial, kinematical, and abundance coherence of these stars suggests that they are part of a diffuse stream of tidal debris, and one roughly consistent with a wrapped, leading tidal arm of the Sagittarius dwarf spheroidal galaxy.

  3. The location, clustering, and propagation of massive star formation in giant molecular clouds

    CERN Document Server

    Ochsendorf, B B; Chastenet, J; Tielens, A G G M; Roman-Duval, J

    2016-01-01

    Massive stars are key players in the evolution of galaxies, yet their formation pathway remains unclear. In this work, we use data from several galaxy-wide surveys to build an unbiased dataset of ~700 massive young stellar objects (MYSOs), ~200 giant molecular clouds (GMCs), and ~100 young (<10 Myr) optical stellar clusters (SCs) in the Large Magellanic Cloud. We employ this data to quantitatively study the location and clustering of massive star formation and its relation to the internal structure of GMCs. We reveal that massive stars do not typically form at the highest column densities nor centers of their parent GMCs at the ~6 pc resolution of our observations. Massive star formation clusters over multiple generations and on size scales much smaller than the size of the parent GMC. We find that massive star formation is significantly boosted in clouds near SCs. Yet, whether a cloud is associated with a SC does not depend on either the cloud's mass or global surface density. These results reveal a conne...

  4. Observational Evidence of Dynamic Star Formation Rate in Milky Way Giant Molecular Clouds

    CERN Document Server

    Lee, Eve J; Murray, Norman

    2016-01-01

    Star formation on galactic scales is known to be a slow process, but whether it is slow on smaller scales is uncertain. We cross-correlate 5469 giant molecular clouds (GMCs) from a new all-sky catalog with 256 star forming complexes (SFCs) to build a sample of 191 SFC-GMC complexes---collections of multiple clouds each matched to 191 SFCs. The total mass in stars harbored by these clouds is inferred from WMAP free-free fluxes. We measure the GMC mass, the virial parameter, the star formation efficiency $\\epsilon$ and the star formation rate per free-fall time $\\epsilon_{\\rm ff}$. Both $\\epsilon$ and $\\epsilon_{\\rm ff}$ range over 3--4 orders of magnitude. We find that 68.3% of the clouds fall within $\\sigma_{\\log\\epsilon}=0.79\\pm0.22\\,{\\rm dex}$ and $\\sigma_{\\log\\epsilon_{\\rm ff}}=0.91\\pm0.22\\,{\\rm dex}$ about the median. Compared to these observed scatters, a simple model with a time independent $\\epsilon_{\\rm ff}$ that depends on the host GMC properties predicts $\\sigma_{\\log\\epsilon_{\\rm ff}}=0.24$. Allowi...

  5. XUV-driven mass loss from extrasolar giant planets orbiting active stars

    CERN Document Server

    Chadney, J M; Unruh, Y C; Koskinen, T T; Sanz-Forcada, J

    2014-01-01

    Upper atmospheres of Hot Jupiters are subject to extreme radiation conditions that can result in rapid atmospheric escape. The composition and structure of the upper atmospheres of these planets are affected by the high-energy spectrum of the host star. This emission depends on stellar type and age, which are thus important factors in understanding the behaviour of exoplanetary atmospheres. In this study, we focus on Extrasolar Giant Planets (EPGs) orbiting K and M dwarf stars. XUV spectra for three different stars - epsilon Eridani, AD Leonis and AU Microscopii - are constructed using a coronal model. Neutral density and temperature profiles in the upper atmosphere of hypothetical EGPs orbiting these stars are then obtained from a fluid model, incorporating atmospheric chemistry and taking atmospheric escape into account. We find that a simple scaling based solely on the host star's X-ray emission gives large errors in mass loss rates from planetary atmospheres and so we have derived a new method to scale th...

  6. EUV-driven ionospheres and electron transport on extrasolar giant planets orbiting active stars

    CERN Document Server

    Chadney, J M; Koskinen, T T; Miller, S; Sanz-Forcada, J; Unruh, Y C; Yelle, R V

    2016-01-01

    The composition and structure of the upper atmospheres of Extrasolar Giant Planets (EGPs) are affected by the high-energy spectrum of their host stars from soft X-rays to EUV. This emission depends on the activity level of the star, which is primarily determined by its age. We focus upon EGPs orbiting K- and M-dwarf stars of different ages. XUV spectra for these stars are constructed using a coronal model. These spectra are used to drive both a thermospheric model and an ionospheric model, providing densities of neutral and ion species. Ionisation is included through photo-ionisation and electron-impact processes. We find that EGP ionospheres at all orbital distances considered and around all stars selected are dominated by the long-lived H$^+$ ion. In addition, planets with upper atmospheres where H$_2$ is not substantially dissociated have a layer in which H$_3^+$ is the major ion at the base of the ionosphere. For fast-rotating planets, densities of short-lived H$_3^+$ undergo significant diurnal variation...

  7. Dying Stars Indicate Lots of Dark Matter in Giant Galaxy

    Science.gov (United States)

    1994-04-01

    Very difficult and time-consuming observations performed with the ESO 3.5-metre New Technology Telescope (NTT) in November 1993 by an international team of astronomers [1], indicate that up to 90 percent of the matter in a distant giant galaxy may be of a kind that cannot be seen by normal telescopes. The astronomers were able to observe the individual motions of 37 extremely faint Planetary Nebulae [2] in the outskirts of the giant elliptical galaxy NGC 1399 that is located at the centre of the southern Fornax cluster of galaxies, at a distance of about 50 million light-years. The mass of the galaxy can be inferred from these motions: the faster they are, the more massive is the galaxy. Surprisingly, the total mass of NGC 1399 found from these new measurements is about ten times as large as the combined mass of the stars and nebulae seen in this galaxy. These new results also have important implications for the current ideas about the formation of giant galaxies. GIANT GALAXIES Galaxies are the basic building blocks of the Universe. Some look like spinning spirals, like our own Milky Way galaxy, with its several hundreds of billions of stars in a flat, rotating disk. Some galaxies lead a comparatively quiet life, others are violent and explosive. But perhaps the most enigmatic of them all are the largest ones, the giant elliptical galaxies. They are huge collections of stars and hot gas, 100 times brighter than the Milky Way and in many of them, the hot gas is a powerful emitter of radio waves and X-rays. The giant galaxies are mostly found at the centres of vast clusters of hundreds or thousands of smaller galaxies, like swarms of bees about the central hive. How did these great galaxies form at the centres of their clusters? Astronomers who make computer simulations of the early Universe believe they know the answer. In their simulations, they see these giant galaxies forming by gradual aggregation of small clumps of matter falling towards the centre, thereby

  8. Seismic diagnostics for transport of angular momentum in stars 2. Interpreting observed rotational splittings of slowly-rotating red giant stars

    CERN Document Server

    Goupil, M J; Marques, J P; Ouazzani, R M; Belkacem, K; Lebreton, Y; Samadi, R

    2012-01-01

    Asteroseismology with the space-borne missions CoRoT and Kepler provides a powerful mean of testing the modeling of transport processes in stars. Rotational splittings are currently measured for a large number of red giant stars and can provide stringent constraints on the rotation profiles. The aim of this paper is to obtain a theoretical framework for understanding the properties of the observed rotational splittings of red giant stars with slowly rotating cores. This allows us to establish appropriate seismic diagnostics for rotation of these evolved stars. Rotational splittings for stochastically excited dipolar modes are computed adopting a first-order perturbative approach for two $1.3 M_\\odot$ benchmark models assuming slowly rotating cores. For red giant stars with slowly rotating cores, we show that the variation of the rotational splittings of $\\ell=1$ modes with frequency depends only on the large frequency separation, the g-mode period spacing, and the ratio of the average envelope to core rotatio...

  9. A giant planet orbiting the 'extreme horizontal branch' star V 391 Pegasi.

    Science.gov (United States)

    Silvotti, R; Schuh, S; Janulis, R; Solheim, J-E; Bernabei, S; Østensen, R; Oswalt, T D; Bruni, I; Gualandi, R; Bonanno, A; Vauclair, G; Reed, M; Chen, C-W; Leibowitz, E; Paparo, M; Baran, A; Charpinet, S; Dolez, N; Kawaler, S; Kurtz, D; Moskalik, P; Riddle, R; Zola, S

    2007-09-13

    After the initial discoveries fifteen years ago, over 200 extrasolar planets have now been detected. Most of them orbit main-sequence stars similar to our Sun, although a few planets orbiting red giant stars have been recently found. When the hydrogen in their cores runs out, main-sequence stars undergo an expansion into red-giant stars. This expansion can modify the orbits of planets and can easily reach and engulf the inner planets. The same will happen to the planets of our Solar System in about five billion years and the fate of the Earth is matter of debate. Here we report the discovery of a planetary-mass body (Msini = 3.2M(Jupiter)) orbiting the star V 391 Pegasi at a distance of about 1.7 astronomical units (au), with a period of 3.2 years. This star is on the extreme horizontal branch of the Hertzsprung-Russell diagram, burning helium in its core and pulsating. The maximum radius of the red-giant precursor of V 391 Pegasi may have reached 0.7 au, while the orbital distance of the planet during the stellar main-sequence phase is estimated to be about 1 au. This detection of a planet orbiting a post-red-giant star demonstrates that planets with orbital distances of less than 2 au can survive the red-giant expansion of their parent stars.

  10. First stars XII. Abundances in extremely metal-poor turnoff stars,and comparison with the giants

    CERN Document Server

    Bonifacio, P; Cayrel, R; Hill, V; Spite, F; François, P; Plez, B; Ludwig, H -G; Caffau, E; Molaro, P; Depagne, E; Andersen, J; Barbuy, B; Beers, T C; Nordström, B; Primas, F

    2009-01-01

    CONTEXT:The detailed chemical abundances of extremely metal-poor (EMP) stars are key guides to understanding the early chemical evolution of the Galaxy. Most existing data are, however, for giant stars which may have experienced internal mixing later. AIMS: We aim to compare the results for giants with new, accurate abundances for all observable elements in 18 EMP turnoff stars. METHODS:VLT/UVES spectra at R ~45,000 and S/N~ 130 per pixel (330-1000 nm) are analysed with OSMARCS model atmospheres and the TURBOSPECTRUM code to derive abundances for C, Mg, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Zn, Sr, and Ba. RESULTS: For Ca, Ni, Sr, and Ba, we find excellent consistency with our earlier sample of EMP giants, at all metallicities. However, our abundances of C, Sc, Ti, Cr, Mn and Co are ~0.2 dex larger than in giants of similar metallicity. Mg and Si abundances are ~0.2 dex lower (the giant [Mg/Fe] values are slightly revised), while Zn is again ~0.4 dex higher than in giants of similar [Fe/H] (6 stars only). CONCLUSIO...

  11. Multi-band polarimetry of post-asymptotic giant branch stars - I. Optical measurements

    Science.gov (United States)

    Akras, S.; Ramírez Vélez, J. C.; Nanouris, N.; Ramos-Larios, G.; López, J. M.; Hiriart, D.; Panoglou, D.

    2017-04-01

    We present new optical broad-band (UBVRI) aperture polarimetric observations of 53 post-asymptotic giant branch (AGB) stars selected to exhibit a large near-infrared excess. 24 out of the 53 stars (45 per cent of our sample) are presented for the first time. A statistical analysis shows four distinctive groups of polarized post-AGB stars: unpolarized or very lowly polarized (degree of polarization or DoP 8 per cent). 23 out of the 53 (66 per cent) belong to the first group, 10 (19 per cent) to the second, five (9 per cent) to the third and only three (6 per cent) to the last group. Approximately 34 per cent of our sample was found to be unpolarized objects, which is close to the percentage of round planetary nebulae. On average, the low and moderate groups show a wavelength-dependent polarization that increases towards shorter wavelengths, implying an intrinsic origin of the polarization, which signifies a Rayleigh-like scattering spectrum typical for non-symmetrical envelopes composed principally of small dust grains. The moderately polarized stars exhibit higher K - W3 and W1 - W3 colour indices compared with the group of lowly polarized stars, suggesting a possible relation between DoP and mass-loss rate. Moreover, they are found to be systematically colder (redder in B - V), which may be associated with the condensation process close to these stars that results in a higher degree of polarization. We also provide evidence that multiple scattering in optically thin polar outflows is the mechanism that gives high DoP in post-AGB stars with bipolar or multi-polar envelopes.

  12. The Tidal Disruption of Giant Stars and Their Contribution to the Flaring Supermassive Black Hole Population

    CERN Document Server

    MacLeod, Morgan; Ramirez-Ruiz, Enrico

    2012-01-01

    Sun-like stars are thought to be regularly disrupted by supermassive black holes (SMBHs) within galactic nuclei. Yet, as stars evolve off the main sequence their vulnerability to tidal disruption increases drastically as they develop a bifurcated structure consisting of a dense core and a tenuous envelope. Here we present the first hydrodynamic simulations of the tidal disruption of giant stars and show that the core has a substantial influence on the star's ability to survive the encounter. Stars with more massive cores retain large fractions of their envelope mass, even in deep encounters. Accretion flares resulting from the disruption of giant stars should last for tens to hundreds of years. Their characteristic signature in transient searches would not be the $t^{-5/3}$ decay typically associated with tidal disruption events, but a correlated rise over many orders of magnitude in brightness on months to years timescales. We calculate the relative disruption rates of stars of varying evolutionary stages in...

  13. On Carbon Burning in Super Asymptotic Giant Branch Stars

    CERN Document Server

    Farmer, R; Timmes, F X

    2015-01-01

    We explore the detailed and broad properties of carbon burning in Super Asymptotic Giant Branch (SAGB) stars with 2755 MESA stellar evolution models. The location of first carbon ignition, quenching location of the carbon burning flames and flashes, angular frequency of the carbon core, and carbon core mass are studied as a function of the ZAMS mass, initial rotation rate, and mixing parameters such as convective overshoot, semiconvection, thermohaline and angular momentum transport. In general terms, we find these properties of carbon burning in SAGB models are not a strong function of the initial rotation profile, but are a sensitive function of the overshoot parameter. We quasi-analytically derive an approximate ignition density, $\\rho_{ign} \\approx 2.1 \\times 10^6$ g cm$^{-3}$, to predict the location of first carbon ignition in models that ignite carbon off-center. We also find that overshoot moves the ZAMS mass boundaries where off-center carbon ignition occurs at a nearly uniform rate of $\\Delta M_{\\rm...

  14. On the helium flash in low-mass Population III Red Giant stars

    CERN Document Server

    Schlattl, H; Salaris, M; Weiss, A

    2001-01-01

    We investigate the evolution of initially metal-free, low-mass Red Giant stars through the He core flash at the tip of the Red Giant Branch. The low entropy barrier between the helium- and hydrogen-rich layers enables a penetration of the helium flash driven convective zone into the inner tail of the extinguishing H-burning shell. As a consequence, protons are mixed into high-temperature regions triggering a H-burning runaway. The subsequent dredge-up of matter processed by He and H burning enriches the stellar surface with large amounts of helium, carbon and nitrogen. Extending previous results by Hollowell et al. (1990) and Fujimoto et al. (2000), who claimed that the H-burning runaway is an intrinsic property of extremely metal-poor low-mass stars, we found that its occurrence depends on additional parameters like the initial composition and the treatment of various physical processes. We perform some comparisons between predicted surface chemical abundances and observational measurements for extremely met...

  15. The Asymptotic Giant Branch and the Tip of the Red Giant Branch as Probes of Star Formation History: The Nearby Dwarf Irregular Galaxy KKH 98

    OpenAIRE

    Melbourne, J; Williams, B.; Dalcanton, J.; Ammons, S. M.; Max, C.; Koo, D.C.; Girardi, Leo; Dolphin, A.

    2010-01-01

    We investigate the utility of the asymptotic giant branch (AGB) and the red giant branch (RGB) as probes of the star formation history (SFH) of the nearby (D=2.5 Mpc) dwarf irregular galaxy, KKH 98. Near-infrared (IR) Keck Laser Guide Star Adaptive Optics (AO) images resolve 592 IR bright stars reaching over 1 magnitude below the Tip of the Red Giant Branch. Significantly deeper optical (F475W and F814W) Hubble Space Telescope images of the same field contain over 2500 stars, reaching to the ...

  16. Star-planet interactions: II. Is planet engulfment the origin of fast rotating red giants?

    CERN Document Server

    Privitera, Giovanni; Eggenberger, Patrick; Vidotto, Aline A; Villaver, Eva; Bianda, Michele

    2016-01-01

    Context. Fast rotating red giants in the upper part of the red giant branch have surface velocities that cannot be explained by single star evolution. Aims. We check whether tides between a star and a planet followed by planet engulfment can indeed accelerate the surface rotation of red giants for a sufficient long time in order to produce these fast rotating red giants. Methods. Using rotating stellar models, accounting for the redistribution of the angular momentum inside the star by different transport mechanisms, for the exchanges of angular momentum between the planet orbit and the star before the engulfment and for the deposition of angular momentum inside the star at the engulfment, we study how the surface rotation velocity at the stellar surface evolves. Results. We show that the surface velocities reached at the end of the orbital decay due to tidal forces and planet engulfment can be similar to values observed for fast rotating red giants. This surface velocity then decreases when the star evolves ...

  17. The spectroscopic indistinguishability of red giant branch and red clump stars

    Science.gov (United States)

    Masseron, T.; Hawkins, K.

    2017-01-01

    Context. Stellar spectroscopy provides useful information on the physical properties of stars such as effective temperature, metallicity and surface gravity. However, those photospheric characteristics are often hampered by systematic uncertainties. The joint spectro-sismo project (APOGEE+Kepler, aka APOKASC) of field red giants has revealed a puzzling offset between the surface gravities (log g) determined spectroscopically and those determined using asteroseismology, which is largely dependent on the stellar evolutionary status. Aims: Therefore, in this letter, we aim to shed light on the spectroscopic source of the offset. Methods: We used the APOKASC sample to analyse the dependencies of the log g discrepancy as a function of stellar mass and stellar evolutionary status. We discuss and study the impact of some neglected abundances on spectral analysis of red giants, such as He and carbon isotopic ratio. Results: We first show that, for stars at the bottom of the red giant branch where the first dredge-up had occurred, the discrepancy between spectroscopic log g and asteroseismic log g depends on stellar mass. This seems to indicate that the log g discrepancy is related to CN cycling. Among the CN-cycled elements, we demonstrate that the carbon isotopic ratio (12C /13C) has the largest impact on stellar spectrum. In parallel, we observe that this log g discrepancy shows a similar trend as the 12C /13C ratios as expected by stellar evolution theory. Although we did not detect a direct spectroscopic signature of 13C, other corroborating evidences suggest that the discrepancy in log g is tightly correlated to the production of 13C in red giants. Moreover, by running the data-driven algorithm (the Cannon) on a synthetic grid trained on the APOGEE data, we try to evaluate more quantitatively the impact of various 12C /13C ratios. Conclusions: While we have demonstrated that 13C indeed impacts all parameters, the size of the impact is smaller than the observed offset

  18. Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars II. Sulfur and Phosphorus

    CERN Document Server

    Visscher, C

    2005-01-01

    We use thermochemical equilibrium and kinetic calculations to model sulfur and phosphorus chemistry in the atmospheres of giant planets, brown dwarfs, low-mass stars, and extrasolar giant planets (EGPs). The chemical behavior of individual S- and P-bearing gases and condensates is determined as a function of pressure, temperature, and metallicity. Our results are independent of any particular model atmosphere and the behavior of different gases can be used to constrain atmospheric structure and metallicity. Hydrogen sulfide is the dominant sulfur gas in substellar atmospheres and approximately represents the atmospheric sulfur inventory. Depending on the prevailing S and C chemistry, the abundance of minor sulfur gases may constrain atmospheric temperatures or metallicity. Disequilibrium abundances of PH3 are expected in the observable atmospheres of substellar objects, and PH3 is representative of the total P abundance in giant planets and T dwarfs. A number of other phosphorus gases become relatively abunda...

  19. Infrared Survey of Pulsating Giant Stars in the Spiral Galaxy M33: Dust Production, Star Formation History, and Galactic Structure

    CERN Document Server

    Javadi, Atefeh; Mirtorabi, Mohammad Taghi

    2011-01-01

    We introduce a near-IR monitoring campaign of the Local Group spiral galaxy M33, carried out with the UK IR Telescope (UKIRT). The pulsating giant stars are identified and their distributions are used to derive the star formation rate as a function of age. We here present the star formation history for the central square kiloparsec. These stars are also important dust factories; we measure their dust production rates from a combination of our data with Spitzer Space Telescope mid-IR photometry.

  20. The M-giant star candidates identified in the LAMOST data release 1

    CERN Document Server

    Zhong, Jing; Li, Jing; Chen, Li; Hou, Jinliang; Yang, Ming; Li, Guangwei; Zhang, Yong; Hou, Yonghui

    2015-01-01

    We perform a discrimination procedure with the spectral index diagram of TiO5 and CaH2+CaH3 to separate M giants from M dwarfs. Using the M giant spectra identified from the LAMOST DR1 with high signal-to-noise ratio (SNR), we have successfully assembled a set of M giant templates, which show more reliable spectral features. Combining with the M dwarf/subdwarf templates in Zhong et al. (2015), we present an extended M-type templates library which includes not only M dwarfs with well-defined temperature and metallicity grid but also M giants with subtype from M0 to M6. Then, the template-fit algorithm were used to automatically identify and classify M giant stars from the LAMOST DR1. The result of M giant stars catalog is cross-matched with 2MASS JHKs and WISE W1/W2 infrared photometry. In addition, we calculated the heliocentric radial velocity of all M giant stars by using the cross-correlation method with the template spectrum in a zero-velocity restframe. Using the relationship between the absolute infrare...

  1. THE GEMINI PLANET-FINDING CAMPAIGN: THE FREQUENCY OF GIANT PLANETS AROUND DEBRIS DISK STARS

    Energy Technology Data Exchange (ETDEWEB)

    Wahhaj, Zahed [European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago (Chile); Liu, Michael C.; Nielsen, Eric L.; Ftaclas, Christ; Chun, Mark [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Biller, Beth A. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Hayward, Thomas L. [Gemini Observatory, Southern Operations Center, c/o AURA, Casilla 603, La Serena (Chile); Close, Laird M.; Males, Jared R.; Skemer, Andrew [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Thatte, Niranjan; Tecza, Matthias [Department of Astronomy, University of Oxford, DWB, Keble Road, Oxford OX1 3RH (United Kingdom); Shkolnik, Evgenya L. [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Kuchner, Marc [NASA Goddard Space Flight Center, Exoplanets and Stellar Astrophysics Laboratory, Greenbelt, MD 20771 (United States); Reid, I. Neill [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); De Gouveia Dal Pino, Elisabete M.; Gregorio-Hetem, Jane [Departamento de Astronomia, Universidade de Sao Paulo, IAG/USP, Rua do Matao 1226, 05508-900 Sao Paulo, SP (Brazil); Alencar, Silvia H. P. [Departamento de Fisica-ICEx-UFMG, Av. Antonio Carlos 6627, 30270-901 Belo Horizonte, MG (Brazil); Boss, Alan [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015 (United States); Lin, Douglas N. C. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA (United States); and others

    2013-08-20

    We have completed a high-contrast direct imaging survey for giant planets around 57 debris disk stars as part of the Gemini NICI Planet-Finding Campaign. We achieved median H-band contrasts of 12.4 mag at 0.''5 and 14.1 mag at 1'' separation. Follow-up observations of the 66 candidates with projected separation <500 AU show that all of them are background objects. To establish statistical constraints on the underlying giant planet population based on our imaging data, we have developed a new Bayesian formalism that incorporates (1) non-detections, (2) single-epoch candidates, (3) astrometric and (4) photometric information, and (5) the possibility of multiple planets per star to constrain the planet population. Our formalism allows us to include in our analysis the previously known {beta} Pictoris and the HR 8799 planets. Our results show at 95% confidence that <13% of debris disk stars have a {>=}5 M{sub Jup} planet beyond 80 AU, and <21% of debris disk stars have a {>=}3 M{sub Jup} planet outside of 40 AU, based on hot-start evolutionary models. We model the population of directly imaged planets as d {sup 2} N/dMda{proportional_to}m {sup {alpha}} a {sup {beta}}, where m is planet mass and a is orbital semi-major axis (with a maximum value of a{sub max}). We find that {beta} < -0.8 and/or {alpha} > 1.7. Likewise, we find that {beta} < -0.8 and/or a{sub max} < 200 AU. For the case where the planet frequency rises sharply with mass ({alpha} > 1.7), this occurs because all the planets detected to date have masses above 5 M{sub Jup}, but planets of lower mass could easily have been detected by our search. If we ignore the {beta} Pic and HR 8799 planets (should they belong to a rare and distinct group), we find that <20% of debris disk stars have a {>=}3 M{sub Jup} planet beyond 10 AU, and {beta} < -0.8 and/or {alpha} < -1.5. Likewise, {beta} < -0.8 and/or a{sub max} < 125 AU. Our Bayesian constraints are not strong enough to reveal any dependence

  2. Evolution of thermally pulsing asymptotic giant branch stars - III. Dust production at supersolar metallicities

    Science.gov (United States)

    Nanni, Ambra; Bressan, Alessandro; Marigo, Paola; Girardi, Léo

    2014-03-01

    We extend the formalism presented in our recent calculations of dust ejecta from the Thermally Pulsing Asymptotic Giant Branch (TP-AGB) phase to the case of super-solar metallicity stars. The TP-AGB evolutionary models are computed with the COLIBRI code. We adopt our preferred scheme for dust growth. For M-giants, we neglect chemisputtering by H2 molecules and for C-stars we assume a homogeneous growth scheme which is primarily controlled by the carbon over oxygen excess. At super-solar metallicities, dust forms more efficiently and silicates tend to condense significantly closer to the photosphere (r ˜ 1.5R*) - and thus at higher temperatures and densities - than at solar and sub-solar metallicities (r ˜ 2-3R*). In such conditions, the hypothesis of thermal decoupling between gas and dust becomes questionable, while dust heating due to collisions plays an important role. The heating mechanism delays dust condensation to slightly outer regions in the circumstellar envelope. We find that the same mechanism is not significant at solar and sub-solar metallicities. The main dust products at super-solar metallicities are silicates. We calculate the total dust ejecta and dust-to-gas ejecta, for various values of the stellar initial masses and initial metallicities Z = 0.04, 0.06. Merging these new calculations with those for lower metallicities it turns out that, contrary to what is often assumed, the total dust-to-gas ejecta of intermediate-mass stars exhibit only a weak dependence on the initial metal content.

  3. Testing the core of red-giant-branch stars using the period spacing of gravity modes

    Science.gov (United States)

    Lagarde, Nadège; Diego, Bossini; Miglio, Andrea

    2015-08-01

    The blooming of asteroseismology of red-giant stars with the CoRoT and Kepler space missions paves the way to a better understanding of the stellar structure and physical processes occurring in low-mass-giant stars.We investigate the effect of rotation on the asymptotic period spacing of gravity modes (DP) and on the coupling strength between acoustic and gravity modes. We focus on red-giant-branch stars (RGB) which ignite He in degenerate conditions (Mstars below the RGB bump, additional transport processes of chemicals have an impact on DP, hence on the determination of the stellar mass when DP is used as a constraint. Moreover we show that the coupling strength gives a direct signature of rotation occuring in red-giant stars. Whether this signature can be inferred from current data needs however to be investigated further. Finally we show that, irrespective of additional transport processes occurring during the main sequence, the period spacing of red-giant stars brighter than the RGB bump is an accurate proxy for the stellar luminosity, due to the well known relation between MHecore and luminosity.

  4. Star formation in a turbulent framework: from giant molecular clouds to protostars

    Science.gov (United States)

    Guszejnov, Dávid; Hopkins, Philip F.

    2016-06-01

    Turbulence is thought to be a primary driving force behind the early stages of star formation. In this framework large, self-gravitating, turbulent clouds fragment into smaller clouds which in turn fragment into even smaller ones. At the end of this cascade we find the clouds which collapse into protostars. Following this process is extremely challenging numerically due to the large dynamical range, so in this paper we propose a semi-analytic framework which is able to model star formation from the largest, giant molecular cloud scale, to the final protostellar size scale. Because of the simplicity of the framework it is ideal for theoretical experimentation to explore the principal processes behind different aspects of star formation, at the cost of introducing strong assumptions about the collapse process. The basic version of the model discussed in this paper only contains turbulence, gravity and crude assumptions about feedback; nevertheless it can reproduce the observed core mass function and provide the protostellar system mass function (PSMF), which shows a striking resemblance to the observed initial mass function (IMF), if a non-negligible fraction of gravitational energy goes into turbulence. Furthermore we find that to produce a universal IMF protostellar feedback must be taken into account otherwise the PSMF peak shows a strong dependence on the background temperature.

  5. NON-LOCAL THERMODYNAMICAL EQUILIBRIUM EFFECTS ON THE IRON ABUNDANCE OF ASYMPTOTIC GIANT BRANCH STARS IN 47 TUCANAE

    Energy Technology Data Exchange (ETDEWEB)

    Lapenna, E.; Mucciarelli, A.; Lanzoni, B.; Ferraro, F. R.; Dalessandro, E.; Massari, D. [Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Viale Berti Pichat 6/2, I-40127 Bologna (Italy); Origlia, L. [INAF- Osservatorio Astronomico di Bologna, Via Ranzani, 1, 40127 Bologna (Italy)

    2014-12-20

    We present the iron abundance of 24 asymptotic giant branch (AGB) stars, members of the globular cluster 47 Tucanae, obtained with high-resolution spectra collected with the FEROS spectrograph at the MPG/ESO 2.2 m Telescope. We find that the iron abundances derived from neutral lines (with a mean value [Fe I/H] =–0.94 ± 0.01, σ = 0.08 dex) are systematically lower than those derived from single ionized lines ([Fe II/H] =–0.83 ± 0.01, σ = 0.05 dex). Only the latter are in agreement with those obtained for a sample of red giant branch (RGB) cluster stars, for which the Fe I and Fe II lines provide the same iron abundance. This finding suggests that non-local thermodynamical equilibrium (NLTE) effects driven by overionization mechanisms are present in the atmosphere of AGB stars and significantly affect the Fe I lines while leaving Fe II features unaltered. On the other hand, the very good ionization equilibrium found for RGB stars indicates that these NLTE effects may depend on the evolutionary stage. We discuss the impact of this finding on both the chemical analysis of AGB stars and on the search for evolved blue stragglers.

  6. Complex Organic and Inorganic Compounds in Shells of Lithium-rich K Giant Stars

    CERN Document Server

    de la Reza, Ramiro; Oliveira, Isa; Rengaswamy, Sridharan

    2015-01-01

    Hydrocarbon organic material, as found in the interstellar medium, exists in complex mixtures of aromatic and aliphatic forms. It is considered to be originated from carbon enriched giant stars during their final stages of evolution, when very strong mass loss occurs in a few thousand years on their way to become planetary nebulae. We show here that the same organic compounds appear to be formed in previous stages of the evolution of giant stars. More specifically, during the first ascending giant branch K-type stars. According to our model this happens only when these stars are being abruptly enriched with lithium together with the formation of a circumstellar shell with a strong mass loss during just a few thousand years. This sudden mass loss is, on an average, a thousand times larger than that of normal Li-poor K giant stars. This shell would later be detached, specially when the star stops its Li enrichment and a rapid photospheric Li depletion occurs. In order to gain extra carbon-based material to form...

  7. The Weihai Observatory search for close-in planets orbiting giant stars

    CERN Document Server

    Wittenmyer, Robert A; Hu, Shao Ming; Villaver, Eva; Endl, Michael; Wright, Duncan

    2015-01-01

    Planets are known to orbit giant stars, yet there is a shortage of planets orbiting within ~0.5 AU (P<100 days). First-ascent giants have not expanded enough to engulf such planets, but tidal forces can bring planets to the surface of the star far beyond the stellar radius. So the question remains: are tidal forces strong enough in these stars to engulf all the missing planets? We describe a high-cadence observational program to obtain precise radial velocities of bright giants from Weihai Observatory of Shandong University. We present data on the planet host Beta Gem (HD 62509), confirming our ability to derive accurate and precise velocities; our data achieve an rms of 7.3 m/s about the Keplerian orbit fit. This planet-search programme currently receives ~100 nights per year, allowing us to aggressively pursue short-period planets to determine whether they are truly absent.

  8. 3D LTE spectral line formation with scattering in red giant stars

    Science.gov (United States)

    Hayek, W.; Asplund, M.; Collet, R.; Nordlund, Å.

    2011-05-01

    wavelengths, and higher metallicity. Velocity fields increase the effects of scattering by separating emission from granules and intergranular lanes in wavelength. 1D calculations exhibit similar scattering abundance corrections for weak lines, but those for strong lines are generally smaller compared to 3D models and depend on the choice of microturbulence. Conclusions: Continuum scattering should be taken into account for computing realistic spectral line profiles at wavelengths λ ≲ 4000 Å in metal-poor giant stars. Profile shapes are strongly affected by velocity fields and horizontal inhomogeneities, requiring a treatment based on 3D hydrodynamical rather than classical 1D hydrostatic model atmospheres.

  9. 12C/13C in atmospheres of red giants and peculiar stars

    CERN Document Server

    Pavlenko, Ya V

    2005-01-01

    We determine the carbon isotopic ratios in the atmospheres of some evolved stars in both globular clusters and the disk of our Galaxy. Analysis of 12CO and 13CO bands at 2.3 micron was carried out using fits to observed spectra of red giants and Sakurai's object (V4334 Sgr). The dependence of theoretical spectra on the various input parameters was studied in detail. The computation of model atmospheres and a detailed abundance analysis was performed in a self-consistent fashion. A special procedure for determining the best fits to observed spectra was used. We show, that globular cluster giants with [Fe/H] < -1.3 have a low 12C/13C = 4 +/- 1 abundance ration. In the spectra of Sakurai's object (V4334 Sgr) taken between 1997-98, the 2.3 micron spectral region is veiled by hot dust emission. By fitting UKIRT spectra we determined 12C/13C = 4 +/- 1 for the July, 1998 spectrum. CO bands in the spectra of ultracool dwarfs are modelled as well.

  10. The formation and retention of gas giant planets around stars with a range of metallicities

    CERN Document Server

    Ida, S

    2004-01-01

    The apparent dependence of detection frequency of extrasolar planets on the metallicity of their host stars is investigated with Monte Carlo simulations using a deterministic core-accretion planet formation model. According to this model, gas giants formed and acquired their mass $M_{\\rm p}$ through planetesimal coagulation followed by the emergence of cores onto which gas is accreted. These protoplanets migrate and attain their asymptotic semi-major axis $a$ through their tidal interaction with their nascent disk. Based on the observed properties of protostellar disks, we generate $M_{\\rm p}$-$a$ distribution. Our results reproduce the observed lack of planets with intermediate mass $M_{\\rm p} = 10$--100$M_{\\oplus}$ and $a \\la 3$AU and with large mass $M_{\\rm p} \\ga 10^3 M_{\\oplus}$ and $a \\la 0.2$AU. Based on the simulated $M_{\\rm p}$-$a$ distributions, we also evaluate the metallicity dependence of fraction of stars harboring planets that are detectable with current radial velocity survey. If protostellar ...

  11. Asteroseismology of red-giant stars as a novel approach in the search for gravitational waves

    CERN Document Server

    Campante, Tiago L; Bossini, Diego; Miglio, Andrea; Chaplin, William J

    2016-01-01

    Stars are massive resonators that may be used as gravitational-wave (GW) detectors with isotropic sensitivity. New insights on stellar physics are being made possible by asteroseismology, the study of stars by the observation of their natural oscillations. The continuous monitoring of oscillation modes in stars of different masses and sizes (e.g., as carried out by NASA's Kepler mission) opens the possibility of surveying the local Universe for GW radiation. Red-giant stars are of particular interest in this regard. Since the mean separation between red giants in open clusters is small (a few light years), this can in principle be used to look for the same GW imprint on the oscillation modes of different stars as a GW propagates across the cluster. Furthermore, the frequency range probed by oscillations in red giants complements the capabilities of the planned eLISA space interferometer. We propose asteroseismology of red giants as a novel approach in the search for gravitational waves.

  12. Precise radial velocities of giant stars IX. HD 59686 Ab: a massive circumstellar planet orbiting a giant star in a ~13.6 au eccentric binary system

    CERN Document Server

    Ortiz, Mauricio; Trifonov, Trifon; Quirrenbach, Andreas; Mitchell, David; Nowak, Grzegorz; Buenzli, Esther; Zimmerman, Neil; Bonnefoy, Mickael; Skemer, Andy; Defrère, Denis; Lee, Man Hoi; Fischer, Debra; Hinz, Philip

    2016-01-01

    Context: For over 12 years, we have carried out a precise radial velocity survey of a sample of 373 G and K giant stars using the Hamilton \\'Echelle Spectrograph at Lick Observatory. There are, among others, a number of multiple planetary systems in our sample as well as several planetary candidates in stellar binaries. Aims: We aim at detecting and characterizing substellar+stellar companions to the giant star HD 59686 A (HR 2877, HIP 36616). Methods: We obtained high precision radial velocity (RV) measurements of the star HD 59686 A. By fitting a Keplerian model to the periodic changes in the RVs, we can assess the nature of companions in the system. In order to discriminate between RV variations due to non-radial pulsation or stellar spots we used infrared RVs taken with the CRIRES spectrograph at the Very Large Telescope. Additionally, to further characterize the system, we obtain high-resolution images with LMIRCam at the Large Binocular Telescope. Results: We report the likely discovery of a giant plane...

  13. Dust Production from Sub-Solar to Super-Solar Metallicity in Thermally Pulsing Asymptotic Giant Branch Stars

    Science.gov (United States)

    Nanni, A.; Bressan, A.; Marigo, P.; Girardi, L.; Javadi, A.; van Loon, J. Th.

    2015-08-01

    We discuss the dust chemistry and growth in the circumstellar envelopes (CSEs) of Thermally Pulsing Asymptotic Giant Branch (TP-AGB) star models, computed with the COLIBRI code, at varying initial mass and metallicity (Z = 0.001, 0.008, 0.02, 0.04, 0.06). A relevant result of our analysis deals with silicate production in M stars. We show that, in order to reproduce the observed trend between terminal velocities and mass-loss rates in Galactic M giants, one has to significantly reduce the efficiency of chemisputtering by H2 molecules, usually considered the most effective dust destruction mechanism. This conclusion is in agreement with the most recent laboratory results, which show that silicates may condense already at Tcond˜1400 K, rather than only at Tcond˜1000 K, as obtained by models that include chemisputtering. From analysis of the total dust ejecta, we find that the dust-to-gas ratios of the total ejecta from intermediate-mass stars are much less dependent on metallicity than usually assumed. In a broader context, our results are suitable for studying the dust enrichment of the interstellar medium provided by TP-AGB stars in both nearby and high-redshift galaxies.

  14. Precise radial velocities of giant stars. IX. HD 59686 Ab: a massive circumstellar planet orbiting a giant star in a 13.6 au eccentric binary system

    Science.gov (United States)

    Ortiz, Mauricio; Reffert, Sabine; Trifonov, Trifon; Quirrenbach, Andreas; Mitchell, David S.; Nowak, Grzegorz; Buenzli, Esther; Zimmerman, Neil; Bonnefoy, Mickaël; Skemer, Andy; Defrère, Denis; Lee, Man Hoi; Fischer, Debra A.; Hinz, Philip M.

    2016-10-01

    Context. For over 12 yr, we have carried out a precise radial velocity (RV) survey of a sample of 373 G- and K-giant stars using the Hamilton Échelle Spectrograph at the Lick Observatory. There are, among others, a number of multiple planetary systems in our sample as well as several planetary candidates in stellar binaries. Aims: We aim at detecting and characterizing substellar and stellar companions to the giant star HD 59686 A (HR 2877, HIP 36616). Methods: We obtained high-precision RV measurements of the star HD 59686 A. By fitting a Keplerian model to the periodic changes in the RVs, we can assess the nature of companions in the system. To distinguish between RV variations that are due to non-radial pulsation or stellar spots, we used infrared RVs taken with the CRIRES spectrograph at the Very Large Telescope. Additionally, to characterize the system in more detail, we obtained high-resolution images with LMIRCam at the Large Binocular Telescope. Results: We report the probable discovery of a giant planet with a mass of mp sin i = 6.92-0.24+0.18 MJup orbiting at ap = 1.0860-0.0007+0.0006 au from the giant star HD 59686 A. In addition to the planetary signal, we discovered an eccentric (eB = 0.729-0.003+0.004) binary companion with a mass of mB sin i = 0.5296-0.0008+0.0011 M⊙ orbiting at a close separation from the giant primary with a semi-major axis of aB = 13.56-0.14+0.18 au. Conclusions: The existence of the planet HD 59686 Ab in a tight eccentric binary system severely challenges standard giant planet formation theories and requires substantial improvements to such theories in tight binaries. Otherwise, alternative planet formation scenarios such as second-generation planets or dynamical interactions in an early phase of the system's lifetime need to be seriously considered to better understand the origin of this enigmatic planet. Based on observations collected at the Lick Observatory, University of California.Based on observations collected at the

  15. Giants of eclipse the ζ [Zeta] Aurigae stars and other binary systems

    CERN Document Server

    Griffin, Elizabeth

    2015-01-01

    The zeta Aurigae stars are the rare but illustrious sub-group of binary stars that undergo the dramatic phenomenon of "chromospheric eclipse". This book provides detailed descriptions of the ten known systems, illustrates them richly with examples of new spectra, and places them in the context of stellar structure and evolution. Comprised of a large cool giant plus a small hot dwarf, these key eclipsing binaries reveal fascinating changes in their spectra very close to total eclipse, when the hot star shines through differing heights of the "chromosphere", or outer atmosphere, of the giant star. The phenomenon provides astrophysics with the means of analyzing the outer atmosphere of a giant star and how that material is shed into space. The physics of these critical events can be explained qualitatively, but it is more challenging to extract hard facts from the observations, and tough to model the chromosphere in any detail. The book offers current thinking on mechanisms for heating a star's chromosphere an...

  16. New spectroscopic binary companions of giant stars and updated metallicity distribution for binary systems

    CERN Document Server

    Bluhm, P; Vanzi, L; Soto, M G; Vos, J; Wittenmyer, R A; Olivares, F; Drass, H; Mennickent, R E; Vuckovic, M; Rojo, P; Melo, C H F

    2016-01-01

    We report the discovery of 24 spectroscopic binary companions to giant stars. We fully constrain the orbital solution for 6 of these systems. We cannot unambiguously derive the orbital elements for the remaining stars because the phase coverage is incomplete. Of these stars, 6 present radial velocity trends that are compatible with long-period brown dwarf companions.The orbital solutions of the 24 binary systems indicate that these giant binary systems have a wide range in orbital periods, eccentricities, and companion masses. For the binaries with restricted orbital solutions, we find a range of orbital periods of between $\\sim$ 97-1600 days and eccentricities of between $\\sim$ 0.1-0.4. In addition, we studied the metallicity distribution of single and binary giant stars. We computed the metallicity of a total of 395 evolved stars, 59 of wich are in binary systems. We find a flat distribution for these binary stars and therefore conclude that stellar binary systems, and potentially brown dwarfs, have a diffe...

  17. Young α-enriched giant stars in the solar neighbourhood

    DEFF Research Database (Denmark)

    Martig, Marie; Rix, Hans-Walter; Aguirre, Victor Silva

    2015-01-01

    We derive age constraints for 1639 red giants in the APOKASC sample for which seismic parameters from Kepler, as well as effective temperatures, metallicities and [alpha/Fe] values from APOGEE DR12 (Apache Point Observatory Galactic Evolution Experiment Data Release 12) are available. We investig......We derive age constraints for 1639 red giants in the APOKASC sample for which seismic parameters from Kepler, as well as effective temperatures, metallicities and [alpha/Fe] values from APOGEE DR12 (Apache Point Observatory Galactic Evolution Experiment Data Release 12) are available. We...

  18. Young α-enriched giant stars in the solar neighbourhood

    DEFF Research Database (Denmark)

    Martig, Marie; Rix, Hans-Walter; Aguirre, Victor Silva;

    2015-01-01

    We derive age constraints for 1639 red giants in the APOKASC sample for which seismic parameters from Kepler, as well as effective temperatures, metallicities and [alpha/Fe] values from APOGEE DR12 (Apache Point Observatory Galactic Evolution Experiment Data Release 12) are available. We investig......We derive age constraints for 1639 red giants in the APOKASC sample for which seismic parameters from Kepler, as well as effective temperatures, metallicities and [alpha/Fe] values from APOGEE DR12 (Apache Point Observatory Galactic Evolution Experiment Data Release 12) are available. We...

  19. New light on Galactic post-asymptotic giant branch stars. I. First distance catalogue

    CERN Document Server

    Vickers, Shane B; Parker, Ouentin A; Bojicic, Ivan S

    2014-01-01

    We have commenced a detailed analysis of the known sample of Galactic post-asymptotic giant branch (PAGB) objects compiled in the Toru\\'n catalogue of Szczerba et al., and present, for the first time, homogeneously derived distance determinations for the 209 likely and 87 possible catalogued PAGB stars from that compilation. Knowing distances are essential in determining meaningful physical characteristics for these sources and this has been difficult to determine for most objects previously. The distances were determined by modelling their spectral energy distributions (SED) with multiple black-body curves, and integrating under the overall fit to determine the total distance-dependent flux. This method works because the luminosity of these central stars is very nearly constant from the tip of the AGB phase to the beginning of the white-dwarf cooling track. This then enables us to use a standard-candle luminosity to estimate the SED distances. For Galactic thin disk PAGB objects, we use three luminosity bins...

  20. Modeling Kepler Observations of Solar-like Oscillations in the Red Giant Star HD 186355

    DEFF Research Database (Denmark)

    Jiang, C.; Jiang, B.W.; Christensen-Dalsgaard, Jørgen;

    2011-01-01

    We have analyzed oscillations of the red giant star HD 186355 observed by the NASA Kepler satellite. The data consist of the first five quarters of science operations of Kepler, which cover about 13 months. The high-precision time-series data allow us to accurately extract the oscillation...

  1. MASSIVE: A Bayesian analysis of giant planet populations around low-mass stars

    CERN Document Server

    Lannier, J; Lagrange, A M; Borgniet, S; Rameau, J; Schlieder, J E; Gagné, J; Bonavita, M A; Malo, L; Chauvin, G; Bonnefoy, M; Girard, J H

    2016-01-01

    Direct imaging has led to the discovery of several giant planet and brown dwarf companions. These imaged companions populate a mass, separation and age domain (mass>1MJup, orbits>5AU, age2MJup might be independent from the mass of the host star.

  2. Radial velocity variations in red giant stars : pulsations, spots and planets

    NARCIS (Netherlands)

    Hekker, Saskia

    2007-01-01

    Radial velocity variations in K giants are observed on long (order hundreds of days) and short (order hours) time scales. Short term variations are most likely caused by solar-like oscillations, stochastically excited in the turbulent atmosphere of the stars. Long term variations can be caused by e

  3. Detailed Study of the Internal Structure of a Red-giant Star Observed with Kepler

    DEFF Research Database (Denmark)

    Di Mauro, M. P.; Ventura, R.; Cardini, D.;

    2012-01-01

    We study the internal structure and evolutionary state of KIC 4351319, a red-giant star observed with the Kepler satellite. The use of 25 individual oscillation frequencies, together with the accurate atmospheric data provided by ground-based spectroscopic observations, allowed us to estimate the...

  4. The K giant stars from the LAMOST survey data. I. Identification, metallicity, and distance

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Chao; Deng, Li-Cai; Li, Jing; Gao, Shuang; Yang, Fan; Xu, Yan; Zhang, Yue-Yang; Xin, Yu; Wu, Yue [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Datun Road 20A, Beijing 100012 (China); Carlin, Jeffrey L.; Newberg, Heidi Jo [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY 12180 (United States); Smith, Martin C. [Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030 (China); Xue, Xiang-Xiang [Max Planck Institute for Astronomy, Königstuhl 17, Heidelberg D-69117 (Germany); Jin, Ge, E-mail: liuchao@nao.cas.cn [University of Science and Technology of China, Hefei 230026 (China)

    2014-08-01

    We present a support vector machine classifier to identify the K giant stars from the LAMOST survey directly using their spectral line features. The completeness of the identification is about 75% for tests based on LAMOST stellar parameters. The contamination in the identified K giant sample is lower than 2.5%. Applying the classification method to about two million LAMOST spectra observed during the pilot survey and the first year survey, we select 298,036 K giant candidates. The metallicities of the sample are also estimated with an uncertainty of 0.13 ∼ 0.29 dex based on the equivalent widths of Mg{sub b} and iron lines. A Bayesian method is then developed to estimate the posterior probability of the distance for the K giant stars, based on the estimated metallicity and 2MASS photometry. The synthetic isochrone-based distance estimates have been calibrated using 7 globular clusters with a wide range of metallicities. The uncertainty of the estimated distance modulus at K = 11 mag, which is the median brightness of the K giant sample, is about 0.6 mag, corresponding to ∼30% in distance. As a scientific verification case, the trailing arm of the Sagittarius stream is clearly identified with the selected K giant sample. Moreover, at about 80 kpc from the Sun, we use our K giant stars to confirm a detection of stream members near the apo-center of the trailing tail. These rediscoveries of the features of the Sagittarius stream illustrate the potential of the LAMOST survey for detecting substructures in the halo of the Milky Way.

  5. The stable K0 giant star β Gem

    Energy Technology Data Exchange (ETDEWEB)

    Gray, David F., E-mail: dfgray@uwo.ca [Department of Physics and Astronomy, University of Western Ontario, 1151 Richmond Street, London, Ontario, N6A 3K7 (Canada)

    2014-12-01

    A nine-season spectroscopic study of the photosphere of β Gem (K0 III) shows this low-luminosity giant to be stable, with no effective temperature variations above ∼2 K, and no secular temperature variations over the 2002-2010 time span above 0.2 K per year. The radial-velocity variations are consistent with an orbital variation of ∼40 m s{sup –1}. The projected rotation rate is found to be 1.70 ± 0.20 km s{sup –1} with a macroturbulence dispersion of 4.53 ± 0.10 km s{sup –1}. The third-signature plot is also invariant and shows a granulation velocity gradient 20% smaller than the solar gradient. The absolute shift of the third-signature plot gives a blueshift-corrected radial velocity of 3385 ± 70 m s{sup –1}. Bisector mapping of the Fe I λ6253 line yields a flux deficit of 12% ± 1% in area, somewhat smaller than for other giants, but the shape and the position of the peak at 4.8 km s{sup –1} is consistent with other giants. All of the investigated photospheric parameters are consistent with β Gem being a low-luminosity giant in agreement with its absolute magnitude.

  6. Young α-enriched giant stars in the solar neighbourhood

    DEFF Research Database (Denmark)

    Martig, Marie; Rix, Hans-Walter; Aguirre, Victor Silva

    2015-01-01

    We derive age constraints for 1639 red giants in the APOKASC sample for which seismic parameters from Kepler, as well as effective temperatures, metallicities and [alpha/Fe] values from APOGEE DR12 (Apache Point Observatory Galactic Evolution Experiment Data Release 12) are available. We investig...

  7. Temperature Dependence of Spreading Width of Giant Dipole Resonance

    CERN Document Server

    Storozhenko, A N; Ventura, A; Blokhin, A I

    2002-01-01

    The Quasiparticle-Phonon Nuclear Model extended to finite temperature within the framework of Thermo Field Dynamics is applied to calculate a temperature dependence of the spreading width Gamma^{\\downarrow} of a giant dipole resonance. Numerical calculations are made for ^{120}Sn and ^{208}Pb nuclei. It is found that Gamma^{\\downarrow} increases with T. The reason of this effect is discussed as well as a relation of the present approach to other ones, existing in the literature.

  8. An extrasolar giant planet in a close triple-star system.

    Science.gov (United States)

    Konacki, Maciej

    2005-07-14

    Hot Jupiters are gas-giant planets orbiting with periods of 3-9 days around Sun-like stars. They are believed to form in a disk of gas and condensed matter at or beyond approximately 2.7 astronomical units (au-the Sun-Earth distance) from their parent star. At such distances, there exists a sufficient amount of solid material to produce a core capable of capturing enough gas to form a giant planet. Subsequently, they migrate inward to their present close orbits. Here I report the detection of an unusual hot Jupiter orbiting the primary star of a triple stellar system, HD 188753. The planet has an orbital period of 3.35 days and a minimum mass of 1.14 times that of Jupiter. The primary star's mass is 1.06 times that of the Sun, 1.06 M(\\circ). The secondary star, itself a binary stellar system, orbits the primary at an average distance of 12.3 au with an eccentricity of 0.50. The mass of the secondary pair is 1.63 M(\\circ). Such a close and massive secondary would have truncated a disk around the primary to a radius of only approximately 1.3 AU (ref. 4) and might have heated it up to temperatures high enough to prohibit giant-planet formation, leaving the origin of this planet unclear.

  9. Asteroseismology Can Reveal Strong Internal Magnetic Fields in Red Giant Stars

    CERN Document Server

    Fuller, Jim; Stello, Dennis; Garcia, Rafael A; Bildsten, Lars

    2015-01-01

    Internal stellar magnetic fields are inaccessible to direct observations and little is known about their amplitude, geometry and evolution. We demonstrate that strong magnetic fields in the cores of red giant stars can be identified with asteroseismology. The fields can manifest themselves via depressed dipole stellar oscillation modes, which arises from a magnetic greenhouse effect that scatters and traps oscillation mode energy within the core of the star. The Kepler satellite has observed a few dozen red giants with depressed dipole modes which we interpret as stars with strongly magnetized cores. We find field strengths larger than $\\sim\\! 10^5 \\,{\\rm G}$ may produce the observed depression, and in one case we infer a minimum core field strength of $\\approx \\! \\! 10^7 \\,{\\rm G}$.

  10. A Substantial Dust Disk Surrounding an Actively Accreting First-Ascent Giant Star

    CERN Document Server

    Melis, C; Song, I; Rhee, J H; Metchev, S

    2009-01-01

    We report identification of the first unambiguous example of what appears to be a new class of first-ascent giant stars that are actively accreting gas and dust and that are surrounded by substantial dusty disks. These old stars, who are nearing the end of their lives, are experiencing a rebirth into characteristics typically associated with newborn stars. The F2-type first-ascent giant star TYC 4144 329 2 is in a wide separation binary system with an otherwise normal G8 IV star, TYC 4144 329 1. From Keck near-infrared imaging and high-resolution spectroscopy we are able to determine that these two stars are $\\sim$1 Gyr old and reside at a distance of $\\sim$550 pc. One possible explanation for the origin of the accreting material is common-envelope interaction with a low-mass stellar or sub-stellar companion. The gaseous and dusty material around TYC 4144 329 2, as it is similar to the primordial disks observed around young classical T Tauri stars, could potentially give rise to a new generation of planets an...

  11. Sulfur and zinc abundances of red giant stars

    CERN Document Server

    Takeda, Yoichi; Harakawa, Hiroki; Sato, Bun'ei

    2016-01-01

    Sulfur and zinc are chemically volatile elements, which play significant roles as depletion-free tracers in studying galactic chemical evolution. However, regarding red giants having evolved off the main sequence, reliable abundance determinations of S and Zn seem to be difficult despite that a few studies have been reported so far. Given this situation, we tried to establish the abundances of these elements for an extensive sample of 239 field GK giants (-0.8 < [Fe/H] < +0.2), by applying the spectrum-fitting technique to S I 8694-5, S I 6757, and Zn I 6362 lines and by taking into account the non-LTE effect. Besides, similar abundance analysis was done for 160 FGK dwarfs to be used for comparison. The non-LTE corrections for the S and Zn abundances derived from these lines turned out < 0.1(-0.2) dex for most cases and not very significant. It revealed that the S I 6757 feature is more reliable as an abundance indicator than S I 8694-5 for the case of red giants, because the latter suffers blending ...

  12. Globular and Open Clusters Observed by SDSS/SEGUE: the Giant Stars

    CERN Document Server

    Morrison, Heather L; Clem, James L; An, Deokkeun; Connor, Thomas; Schechtman-Rook, Andrew; Harding, Paul; Casagrande, Luca; Rockosi, Constance; Yanny, Brian; Beers, Timothy C; Johnson, Jennifer A; Schneider, Donald P

    2015-01-01

    We present griz observations for the clusters M92, M13 and NGC 6791 and gr photometry for M71, Be 29 and NGC 7789. In addition we present new membership identifications for all these clusters, which have been observed spectroscopically as calibrators for the SDSS/SEGUE survey; this paper focuses in particular on the red giant branch stars in the clusters. In a number of cases, these giants were too bright to be observed in the normal SDSS survey operations, and we describe the procedure used to obtain spectra for these stars. For M71, also present a new variable reddening map and a new fiducial for the gr giant branch. For NGC 7789, we derived a transformation from Teff to g-r for giants of near solar abundance, using IRFM Teff measures of stars with good ugriz and 2MASS photometry and SEGUE spectra. The result of our analysis is a robust list of known cluster members with correctly dereddened and (if needed) transformed gr photometry for crucial calibration efforts for SDSS and SEGUE.

  13. GLOBULAR AND OPEN CLUSTERS OBSERVED BY SDSS/SEGUE: THE GIANT STARS

    Energy Technology Data Exchange (ETDEWEB)

    Morrison, Heather L.; Ma, Zhibo; Connor, Thomas; Schechtman-Rook, Andrew; Harding, Paul [Department of Astronomy, Case Western Reserve University, Cleveland, OH 44106 (United States); Clem, James L. [Department of Physics, Grove City College, 100 Campus Dr., Grove City, PA 16127 (United States); An, Deokkeun [Department of Science Education, Ewha Womans University, Seoul 120-750 (Korea, Republic of); Casagrande, Luca [Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, The Australian National University, ACT 2611 (Australia); Rockosi, Constance [UCO/Lick Observatory, University of California, Santa Cruz, 1156 High St., Santa Cruz, CA 95064 (United States); Yanny, Brian [Fermi National Accelerator Laboratory, P.O. Box 500, Batavia IL 60510 (United States); Beers, Timothy C. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46656 (United States); Johnson, Jennifer A. [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Schneider, Donald P., E-mail: hlm5@case.edu [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States)

    2016-01-15

    We present griz observations for the clusters M92, M13 and NGC 6791 and gr photometry for M71, Be 29 and NGC 7789. In addition we present new membership identifications for all these clusters, which have been observed spectroscopically as calibrators for the Sloan Digital Sky Survey (SDSS)/SEGUE survey; this paper focuses in particular on the red giant branch stars in the clusters. In a number of cases, these giants were too bright to be observed in the normal SDSS survey operations, and we describe the procedure used to obtain spectra for these stars. For M71, we also present a new variable reddening map and a new fiducial for the gr giant branch. For NGC 7789, we derived a transformation from T{sub eff} to g–r for giants of near solar abundance, using IRFM T{sub eff} measures of stars with good ugriz  and 2MASS photometry and SEGUE spectra. The result of our analysis is a robust list of known cluster members with correctly dereddened and (if needed) transformed gr photometry for crucial calibration efforts for SDSS and SEGUE.

  14. Dust production from sub-solar to super-solar metallicity in Thermally Pulsing Asymptotic Giant Branch Stars

    CERN Document Server

    Ambra, Nanni; Paola, Marigo; Léo, Girardi; Atefeh, Javadi; Jacco, van Loon

    2014-01-01

    We discuss the dust chemistry and growth in the circumstellar envelopes (CSEs) of Thermally Pulsing Asymptotic Giant Branch (TP-AGB) star models computed with the COLIBRI code, at varying initial mass and metallicity (Z=0.001, 0.008, 0.02, 0.04, 0.06). A relevant result of our analysis deals with the silicate production in M-stars. We show that, in order to reproduce the observed trend between terminal velocities and mass-loss rates in Galactic M-giants, one has to significantly reduce the efficiency of chemisputtering by H2 molecules, usually considered as the most effective dust destruction mechanism. This indication is also in agreement with the most recent laboratory results, which show that silicates may condense already at T=1400 K, instead than at Tcond=1000 K, as obtained by models that include chemisputtering. From the analysis of the total dust ejecta, we find that the total dust-to-gas ejecta of intermediate-mass stars are much less dependent on metallicity than usually assumed. In a broader contex...

  15. EPIC 211351816.01: A (Re-?)Inflated Planet Orbiting a Red Giant Star

    CERN Document Server

    Grunblatt, Samuel K; Gaidos, Eric J; Lopez, Eric D; Fulton, Benjamin J; Fortney, Jonathan J; Howard, Andrew W; Sinukoff, Evan J; Mann, Andrew W; Isaacson, Howard

    2016-01-01

    Giant planets with high incident fluxes have been observed with radii larger than thermal evolution models would allow. Although these inflated planets have been known for almost two decades, it is unclear whether their inflation is caused by deposition of energy from the host star, or inhibited cooling of the planet. These processes can be distinguished if the planet becomes highly irradiated only when the host star evolves onto the red giant branch. We report the discovery of EPIC 211351816.01, a 1.27 +/- 0.09 RJ, 1.10 +/- 0.11 MJ planet orbiting a 4.20 +/- 0.14 Rsun, 1.16 +/- 0.12 Msun red giant star with an orbital period of 8.4 days. We precisely constrained stellar and planetary parameters by combining asteroseismology, spectroscopy, and granulation noise modeling along with transit and radial velocity measurements. Our calculations suggest the incident flux on this planet was ~200 +/- 100 times the flux on Earth while the star was on the main sequence, comparable to the suggested threshold flux for pla...

  16. Further Results from the Galactic O-Star Spectroscopic Survey: Rapidly Rotating Late ON Giants

    CERN Document Server

    Walborn, Nolan R; Sota, Alfredo; Alfaro, Emilio J; Morrell, Nidia I; Barba, Rodolfo H; Arias, Julia I; Gamen, Roberto C

    2011-01-01

    With new data from the Galactic O-Star Spectroscopic Survey, we confirm and expand the ONn category of late-O, nitrogen-enriched (N), rapidly rotating (n) giants. In particular, we have discovered two "clones" (HD 102415 and HD 117490) of one of the most rapidly rotating O stars previously known (HD 191423, "Howarth's Star"). We compare the locations of these objects in the theoretical HR Diagram to those of slowly rotating ON dwarfs and supergiants. All ON giants known to date are rapid rotators, whereas no ON dwarf or supergiant is; but all ON stars are small fractions of their respective spectral-type/luminosity-class/rotational subcategories. The ONn giants, displaying both substantial processed material and high rotation at an intermediate evolutionary stage, may provide significant information about the development of those properties. They may have preserved high initial rotational velocities or been spun up by TAMS core contraction; but alternatively and perhaps more likely, they may be products of bi...

  17. New models for the evolution of post-asymptotic giant branch stars and central stars of planetary nebulae

    Science.gov (United States)

    Miller Bertolami, Marcelo Miguel

    2016-04-01

    Context. The post-asymptotic giant branch (AGB) phase is arguably one of the least understood phases of the evolution of low- and intermediate- mass stars. The two grids of models presently available are based on outdated micro- and macrophysics and do not agree with each other. Studies of the central stars of planetary nebulae (CSPNe) and post-AGB stars in different stellar populations point to significant discrepancies with the theoretical predictions of post-AGB models. Aims: We study the timescales of post-AGB and CSPNe in the context of our present understanding of the micro- and macrophysics of stars. We want to assess whether new post-AGB models, based on the latter improvements in TP-AGB modeling, can help us to understand the discrepancies between observation and theory and within theory itself. In addition, we aim to understand the impact of the previous AGB evolution for post-AGB phases. Methods: We computed a grid of post-AGB full evolutionary sequences that include all previous evolutionary stages from the zero age main sequence to the white dwarf phase. We computed models for initial masses between 0.8 and 4 M⊙ and for a wide range of initial metallicities (Z0 = 0.02, 0.01, 0.001, 0.0001). This allowed us to provide post-AGB timescales and properties for H-burning post-AGB objects with masses in the relevant range for the formation of planetary nebulae (~0.5-0.8 M⊙). We included an updated treatment of the constitutive microphysics and included an updated description of the mixing processes and winds that play a key role during the thermal pulses (TP) on the AGB phase. Results: We present a new grid of models for post-AGB stars that take into account the improvements in the modeling of AGB stars in recent decades. These new models are particularly suited to be inputs in studies of the formation of planetary nebulae and for the determination of the properties of CSPNe from their observational parameters. We find post-AGB timescales that are at

  18. THE DUST BUDGET OF THE SMALL MAGELLANIC CLOUD: ARE ASYMPTOTIC GIANT BRANCH STARS THE PRIMARY DUST SOURCE AT LOW METALLICITY?

    Energy Technology Data Exchange (ETDEWEB)

    Boyer, M. L.; Gordon, K. D.; Meixner, M.; Sargent, B. A. [STScI, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Srinivasan, S. [UPMC-CNRS UMR7095, Institut d' Astrophysique de Paris, F-75014 Paris (France); Riebel, D. [Department of Physics and Astronomy, The Johns Hopkins University, Homewood Campus, Baltimore, MD 21218 (United States); McDonald, I. [Jodrell Bank Centre for Astrophysics, Alan Turing Building, University of Manchester, Manchester M13 9PL (United Kingdom); Van Loon, J. Th. [Astrophysics Group, Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BG (United Kingdom); Clayton, G. C. [Department of Physics and Astronomy, Louisiana State University, 233-A Nicholson Hall, Tower Dr., Baton Rouge, LA 70803-4001 (United States); Sloan, G. C., E-mail: mboyer@stsci.edu [Astronomy Department, Cornell University, Ithaca, NY 14853-6801 (United States)

    2012-03-20

    We estimate the total dust input from the cool evolved stars in the Small Magellanic Cloud, using the 8 {mu}m excess emission as a proxy for the dust-production rate (DPR). We find that asymptotic giant branch (AGB) and red supergiant (RSG) stars produce (8.6-9.5) Multiplication-Sign 10{sup -7} M{sub Sun} yr{sup -1} of dust, depending on the fraction of far-infrared sources that belong to the evolved star population (with 10%-50% uncertainty in individual DPRs). RSGs contribute the least (<4%), while carbon-rich AGB stars (especially the so-called extreme AGB stars) account for 87%-89% of the total dust input from cool evolved stars. We also estimate the dust input from hot stars and supernovae (SNe), and find that if SNe produce 10{sup -3} M{sub Sun} of dust each, then the total SN dust input and AGB input are roughly equivalent. We consider several scenarios of SN dust production and destruction and find that the interstellar medium (ISM) dust can be accounted for solely by stellar sources if all SNe produce dust in the quantities seen around the dustiest examples and if most SNe explode in dense regions where much of the ISM dust is shielded from the shocks. We find that AGB stars contribute only 2.1% of the ISM dust. Without a net positive contribution from SNe to the dust budget, this suggests that dust must grow in the ISM or be formed by another unknown mechanism.

  19. Detection of solar-like oscillations in the bright red giant stars $\\gamma$ Psc and $\\theta^1$ Tau from a 190-day high-precision spectroscopic multisite campaign

    CERN Document Server

    Beck, P G; Hillen, M; Corsaro, E; Van Winckel, H; Moravveji, E; De Ridder, J; Bloemen, S; Saesen, S; Mathias, P; Degroote, P; Kallinger, T; Verhoelst, T; Ando, H; Carrier, F; Acke, B; Oreiro, R; Miglio, A; Eggenberger, P; Sato, B; Zwintz, K; Pápics, P I; Marcos-Arenal, P; Fuentes, S A Sans; Schmid, V S; Waelkens, C; Østensen, R; Matthews, J M; Yoshida, M; Izumiura, H; Koyano, H; Nagayama, S; Shimizu, Y; Okada, N; Okita, K; Sakamoto, A; Yamamuro, T; Aerts, C

    2014-01-01

    Red giants are evolved stars which exhibit solar-like oscillations. Although a multitude of stars have been observed with space telescopes, only a handful of red-giant stars were targets of spectroscopic asteroseismic observing projects. We search for solar-like oscillations in the two bright red-giant stars $\\gamma$ Psc and $\\theta^1$ Tau from time series of ground-based spectroscopy and determine the frequency of the excess of oscillation power $\

  20. Evolution and nucleosynthesis in low mass Asymptotic Giant Branch stars

    CERN Document Server

    Cristallo, S

    2008-01-01

    People usually smile when astrophysicists assert that we are sons of the stars, but human life confirms this sentence: about 65% of the mass of our body is made up of oxygen, carbon occurs in all organic life and is the basis of organic chemistry, nitrogen is an essential part of amino acids and nucleic acids, calcium is a major component of our bones. Moreover, phosphorus plays a major role in biological molecules such as DNA and RNA (where the chemical codes of life is written) and our blood carries oxygen to tissues by means of the hemoglobin (an iron pigment of red blood cells). All these elements have been created in stars. I just list some examples related to human body, but also common element such as aluminum, nickel, gold, silver and lead come from a pristine generation of stars. The abundances in the Solar System are in fact due to the mixing of material ejected from stars that polluted the Universe in different epochs before the Sun formation, occurred about 5 billion years ago, after the gravitati...

  1. Fingerprints of giant planets in the photospheres of Herbig stars

    CERN Document Server

    Kama, Mihkel; Pinilla, Paola

    2015-01-01

    Around 2% of all A stars have photospheres depleted in refractory elements. This is hypothesized to arise from a preferential accretion of gas rather than dust, but the specific processes and the origin of the material -- circum- or interstellar -- are not known. The same depletion is seen in 30% of young, disk-hosting Herbig Ae/Be stars. We investigate whether the chemical peculiarity originates in a circumstellar disk. Using a sample of systems for which both the stellar abundances and the protoplanetary disk structure are known, we find that stars hosting warm, flaring group I disks typically have Fe, Mg and Si depletions of 0.5 dex compared to the solar-like abundances of stars hosting cold, flat group II disks. The volatile, C and O, abundances in both sets are identical. Group I disks are generally transitional, having radial cavities depleted in millimetre-sized dust grains, while those of group II are usually not. Thus we propose that the depletion of heavy elements emerges as Jupiter-like planets blo...

  2. Gas giants in hot water: inhibiting giant planet formation and planet habitability in dense star clusters through cosmic time

    Science.gov (United States)

    Thompson, Todd A.

    2013-05-01

    I show that the temperature of nuclear star clusters, starburst clusters in M82, compact high-z galaxies and some globular clusters of the Galaxy likely exceeded the ice-line temperature (TIce ≈ 150-170 K) during formation for a time comparable to the planet formation time-scale. The protoplanetary discs within these systems will thus, not have an ice line, decreasing the total material available for building protoplanetary embryos, inhibiting the formation of gas- and ice-giants if they form by core accretion, and prohibiting habitability. Planet formation by gravitational instability is similarly suppressed because Toomre's Q > 1 in all but the most massive discs. I show that cluster irradiation can in many cases dominate the thermodynamics and structure of passive and active protoplanetary discs for semi-major axes larger than ˜1-5 au. I discuss these results in the context of the observed lack of planets in 47 Tuc. I predict that a similar search for planets in the globular cluster NGC 6366 ([Fe/H] = -0.82) should yield detections, whereas (counterintuitively) the relatively metal-rich globular clusters NGC 6440, 6441 and 6388 should be devoid of giant planets. The characteristic stellar surface density above which TIce is exceeded in star clusters is ˜ 6 × 103 M⊙ pc- 2 f- 1/2dg, MW, where fdg, MW is the dust-to-gas ratio of the embedding material, normalized to the Milky Way value. Simple estimates suggest that ˜5-50 per cent of the stars in the universe formed in an environment exceeding this surface density. Future microlensing planet searches that directly distinguish between the bulge and disc planet populations of the Galaxy and M31 can test these predictions. Caveats and uncertainties are detailed.

  3. STAR FORMATION AND YOUNG STELLAR CONTENT IN THE W3 GIANT MOLECULAR CLOUD

    Energy Technology Data Exchange (ETDEWEB)

    Rivera-Ingraham, Alana [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada); Martin, Peter G. [Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8 (Canada); Polychroni, Danae [INAF-IFSI, via Fosso del Cavaliere 100, 00133 Roma (Italy); Moore, Toby J. T. [Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD (United Kingdom)

    2011-12-10

    In this work, we have carried out an in-depth analysis of the young stellar content in the W3 giant molecular cloud (GMC). The young stellar object (YSO) population was identified and classified in the Infrared Array Camera/Multiband Imaging Photometer color-magnitude space according to the 'Class' scheme and compared to other classifications based on intrinsic properties. Class 0/I and II candidates were also compared to low-/intermediate-mass pre-main-sequence (PMS) stars selected through their colors and magnitudes in the Two Micron All Sky Survey. We find that a reliable color/magnitude selection of low-mass PMS stars in the infrared requires prior knowledge of the protostar population, while intermediate-mass objects can be more reliably identified. By means of the minimum spanning tree algorithm and our YSO spatial distribution and age maps, we investigated the YSO groups and the star formation history in W3. We find signatures of clustered and distributed star formation in both triggered and quiescent environments. The central/western parts of the GMC are dominated by large-scale turbulence likely powered by isolated bursts of star formation that triggered secondary star formation events. Star formation in the eastern high-density layer (HDL) also shows signs of quiescent and triggered stellar activity, as well as extended periods of star formation. While our findings support triggering as a key factor for inducing and enhancing some of the major star-forming activity in the HDL (e.g., W3 Main/W3(OH)), we argue that some degree of quiescent or spontaneous star formation is required to explain the observed YSO population. Our results also support previous studies claiming a spontaneous origin for the isolated massive star(s) powering KR 140.

  4. Radial velocities of giant stars: an investigation of line profile variations

    Energy Technology Data Exchange (ETDEWEB)

    Hekker, S; Snellen, I A G [Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden (Netherlands); Aerts, C [Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven (Belgium); Quirrenbach, A; Reffert, S [ZAH, Landessternwarte Heidelberg, Koenigstuhl 12, D-69117 Heidelberg (Germany); Mitchell, D S [California Polytechnic State University, San Luis Obispo, CA 93407 (United States)], E-mail: saskia@strw.leidenuniv.nl

    2008-10-15

    Since 1999, a radial velocity survey of 179 red giant stars is ongoing at Lick Observatory with a one month cadence. At present{approx}20-100 measurements have been collected per star with an accuracy of 5 to 8 ms{sup -1}. Of the stars monitored, 145 (80%) show radial velocity (RV) variations at a level >20 ms{sup -1}, of which 43 exhibit significant periodicities. Here, we investigate the mechanism causing the observed radial velocity variations. Firstly, we search for a correlation between the radial velocity amplitude and an intrinsic parameter of the star, in this case surface gravity (logg). Secondly, we investigate line profile variations and compare these with theoretical predictions.

  5. The pillars of creation giant molecular clouds, star formation, and cosmic recycling

    CERN Document Server

    Beech, Martin

    2017-01-01

    This book explores the mechanics of star formation, the process by which matter pulls together and creates new structures. Written for science enthusiasts, the author presents an accessible explanation of how stars are born from the interstellar medium and giant molecular clouds. Stars produce the chemicals that lead to life, and it is they that have enabled the conditions for planets to form and life to emerge. Although the Big Bang provided the spark of initiation, the primordial universe that it sired was born hopelessly sterile. It is only through the continued recycling of the interstellar medium, star formation, and stellar evolution that the universe has been animated beyond a chaotic mess of elementary atomic particles, radiation, dark matter, dark energy, and expanding spacetime. Using the Milky Way and the Eagle Nebula in particular as case studies, Beech follows every step of this amazing process. .

  6. "Sky Full of Stars" Pattern: Dermoscopic Findings in a Desmoplastic Giant Congenital Melanocytic Nevus.

    Science.gov (United States)

    Martín-Carrasco, Pablo; Bernabeu-Wittel, José; Dominguez-Cruz, Javier; Zulueta Dorado, Teresa; Conejo-Mir Sanchez, Julian

    2017-02-27

    Desmoplastic giant congenital melanocytic nevus (DGCN) is an uncommon variant of congenital nevus, presenting as a progressive induration and hypopigmentation of the lesion that occasionally causes hair loss and even total or partial disappearance of the nevus. A 6-month-old girl with a giant congenital melanocytic nevus that involved the entire posterior side of the right thigh was seen in our department. Nine months later, the peripheral area of the nevus presented as a marked induration with hypopigmentation. Dermoscopy demonstrated a reticular pattern exclusively located in the perifollicular areas, with a radial distribution from the follicular ostium that mimicked a "sky full of stars." We report a case of DGCN, including a dermoscopic description of the findings noted in the indurated and hypopigmented areas that appear as a "sky full of stars" image.

  7. Abundances in red giant stars - Carbon and oxygen isotopes in carbon-rich molecular envelopes

    Science.gov (United States)

    Wannier, P. G.; Sahai, R.

    1987-01-01

    Millimeter-wave observations have been made of isotopically substituted CO toward the envelopes of 11 carbon-rich stars. In every case, C-13O was detected and model calculations were used to estimate the C-12/C-13 abundance ratio. C-17O was detected toward three, and possibly four, envelopes, with sensitive upper limits for two others. The CO-18 variant was detected in two envelopes. New results include determinations of oxygen isotopic ratios in the two carbon-rich protoplanetary nebulae CRL 26688 and CRL 618. As with other classes of red giant stars, the carbon-rich giants seem to be significantly, though variably, enriched in O-17. These results, in combination with observations in interstellar molecular clouds, indicate that current knowledge of stellar production of the CNO nuclides is far from satisfactory.

  8. A Comparative Study of Two 47 Tuc Giant Stars with Different s-process Enrichment

    Science.gov (United States)

    Cordero, M. J.; Hansen, C. J.; Johnson, C. I.; Pilachowski, C. A.

    2015-07-01

    Here we aim to understand the origin of 47 Tuc’s La-rich star Lee 4710. We report abundances for O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Co, Ni, Zn, Y, Zr, Ba, La, Ce, Pr, Nd, and Eu and present a detailed abundance analysis of two 47 Tuc stars with similar stellar parameters but different slow neutron-capture (s-)process enrichment. Star Lee 4710 has the highest known La abundance ratio in this cluster ([La/Fe] = 1.14), and star Lee 4626 is known to have normal s-process abundances (e.g., [Ba/Eu] < 0). The nucleosynthetic pattern of elements with Z ≳ 56 for star Lee 4710 agrees with the predicted yields of a 1.3{M}⊙ asymptotic giant branch (AGB) star. Therefore, Lee 4710 may have been enriched by mass transfer from a more massive AGB companion, which is compatible with its location far away from the center of this relatively metal-rich ([Fe/H] ˜ -0.7) globular cluster. A further analysis comparing the abundance pattern of Lee 4710 with data available in the literature reveals that nine out of the ˜200 47 Tuc stars previously studied show strong s-process enhancements that point toward later enrichment by more massive AGB stars.

  9. Rubidium and lead abundances in giant stars of the globular clusters M 13 and NGC 6752

    CERN Document Server

    Yong, D; Lambert, D L; Paulson, D B; Yong, David; Aoki, Wako; Lambert, David L.; Paulson, Diane B.

    2006-01-01

    We present measurements of the neutron-capture elements Rb and Pb in five giant stars of the globular cluster NGC 6752 and Pb measurements in four giants of the globular cluster M 13. The abundances were derived by comparing synthetic spectra with high resolution, high signal-to-noise ratio spectra obtained using HDS on the Subaru telescope and MIKE on the Magellan telescope. The program stars span the range of the O-Al abundance variation. In NGC 6752, the mean abundances are [Rb/Fe] = -0.17 +/- 0.06 (sigma = 0.14), [Rb/Zr] = -0.12 +/- 0.06 (sigma = 0.13), and [Pb/Fe] = -0.17 +/- 0.04 (sigma = 0.08). In M 13 the mean abundance is [Pb/Fe] = -0.28 +/- 0.03 (sigma = 0.06). Within the measurement uncertainties, we find no evidence for a star-to-star variation for either Rb or Pb within these clusters. None of the abundance ratios [Rb/Fe], [Rb/Zr], or [Pb/Fe] are correlated with the Al abundance. NGC 6752 may have slightly lower abundances of [Rb/Fe] and [Rb/Zr] compared to the small sample of field stars at the ...

  10. Mapping of the extinction in Giant Molecular Clouds using optical star counts

    OpenAIRE

    Cambresy, L.

    1999-01-01

    This paper presents large scale extinction maps of most nearby Giant Molecular Clouds of the Galaxy (Lupus, rho-Ophiuchus, Scorpius, Coalsack, Taurus, Chamaeleon, Musca, Corona Australis, Serpens, IC 5146, Vela, Orion, Monoceros R1 and R2, Rosette, Carina) derived from a star count method using an adaptive grid and a wavelet decomposition applied to the optical data provided by the USNO-Precision Measuring Machine. The distribution of the extinction in the clouds leads to estimate their total...

  11. The infrared excess of cool giant stars - A chromospheric contribution

    Science.gov (United States)

    Lambert, D. L.; Snell, R. L.

    1975-01-01

    The idea that the infrared excesses of evolved M stars may contain a contribution from a chromosphere is explored using alpha Ori and W Hya as test cases. The spectrum of alpha Ori between 8 and 30 millimicrons can be interpreted satisfactorily in terms of three components: a photosphere, a silicate dust cloud, and a cool chromosphere (temperature about 5000 K), which is optically thick at 14 millimicrons. A similar modelling for W Hya suggests a hotter chromosphere (temperature about 8000 K), with unit optical depth at 30 millimicrons. Some consequences of these chromospheres are briefly discussed.

  12. Gas Giants in Hot Water: Inhibiting Giant Planet Formation and Planet Habitability in Dense Star Clusters Through Cosmic Time

    CERN Document Server

    Thompson, Todd A

    2012-01-01

    I show that the temperature of nuclear star clusters, starburst clusters in M82, compact high-z galaxies, and some globular clusters of the Galaxy likely exceeded the ice line temperature (T_Ice ~ 150-170 K) during formation for a time comparable to the planet formation timescale. The protoplanetary disks within these systems will thus not have an ice line, decreasing the total material available for building protoplanetary embryos, inhibiting the formation of gas- and ice-giants if they form by core accretion, and prohibiting habitability. Planet formation by gravitational instability is similarly suppressed because Toomre's Q > 1 in all but the most massive disks. I discuss these results in the context of the observed lack of planets in 47 Tuc. I predict that a similar search for planets in the globular cluster NGC 6366 ([Fe/H] = -0.82) should yield detections, whereas (counterintuitively) the relatively metal-rich globular clusters NGC 6440, 6441, and 6388 should be devoid of giant planets. The characteris...

  13. The s-Process in Rotating Asymptotic Giant Branch Stars

    CERN Document Server

    Herwig, F; Lugaro, M

    2003-01-01

    (abridged) We model the nucleosynthesis during the thermal pulse phase of a rotating, solar metallicity AGB star of 3M_sun. Rotationally induced mixing during the thermal pulses produces a layer (~2E-5M_sun) on top of the CO-core where large amounts of protons and C12 co-exist. We follow the abundance evolution in this layer, in particular that of the neutron source C13 and of the neutron poison N14. In our AGB model mixing persists during the entire interpulse phase due to the steep angular velocity gradient at the core-envelope interface. We follow the neutron production during the interpulse phase, and find a resulting maximum neutron exposure of tau_max =0.04 mbarn^-1, which is too small to produce any significant s-process. In parametric models, we then investigate the combined effects of diffusive overshooting from the convective envelope and rotationally induced mixing. Models with overshoot and weaker interpulse mixing - as perhaps expected from more slowly rotating stars - yield larger neutron exposu...

  14. Embedded Star Clusters in the W51 Giant Molecular Cloud

    CERN Document Server

    Kumar, M S N; Davis, C J

    2004-01-01

    We present sub-arcsecond (0.35"-0.9"), near-infrared J,H,K band photometric observations of six fields along the W51 Giant Molecular Cloud (W51 GMC). Our observations reveal four new, embedded clusters and provide a new high-resolution (0.35") view of the W51IRS2 (G49.5-0.4) region. The cluster associated with G48.9-0.3 is found to be a double cluster enclosed in a nest of near-infrared nebulosity. We construct stellar surface density maps for four major clusters in the W51 GMC. These unveil the underlying hierarchical structure. Color-color and color-magnitude diagrams for each of these clusters show clear differences in the embedded stellar populations and indicate the relative ages of these clusters. In particular, the clusters associated with the HII regions G48.9-0.3 and G49.0-0.3 are found to have a high fraction of YSOs and are therefore considered the youngest of all the near-infrared clusters in the W51 GMC. The estimated masses of the individual clusters, when summed, yield a total stellar mass of ~...

  15. Multiple Outflows in the Giant Eruption of a Massive Star

    CERN Document Server

    Humphreys, Roberta M; Gordon, Michael S; Jones, Terry J

    2016-01-01

    The supernova impostor PSN J09132750+7627410 in NGC 2748 reached a maximum luminosity of approximately -14 mag. It was quickly realized that its was not a true supernova, but another example of a non-terminal giant eruption. PSN J09132750+7627410 is distinguished by multiple P Cygni absorption minima in the Balmer emission lines that correspond to outflow velocities of -400, -1100, and -1600 km/s. Multiple outflows have been observed in only a few other objects. In this paper we describe the evolution of the spectrum and the P Cygni profiles for three months past maximum, the post-maximum formation of a cool, dense wind, and the identification of a possible progenitor. One of the possible progenitors is an infrared source. Its pre-eruption spectral energy distribution suggests a bolometric luminosity of -8.3 mag and a dust temperature of 780 degrees K. If it is the progenitor it is above the AGB limit unlike the intermediate luminosity red transients. The three P Cygni profiles could be due to ejecta from the...

  16. VLT/FLAMES spectroscopy of Red Giant Branch stars in the Carina dwarf spheroidal galaxy

    CERN Document Server

    Lemasle, B; Tolstoy, E; Venn, K A; Shetrone, M D; Irwin, M J; de Boer, T J L; Starkenburg, E; Salvadori, S

    2011-01-01

    The ages of individual Red Giant Branch stars (RGB) can range from 1 Gyr old to the age of the Universe, and it is believed that the abundances of most chemical elements in their photospheres remain unchanged with time (those that are not affected by the 1st dredge-up). This means that they trace the ISM in the galaxy at the time the star formed, and hence the chemical enrichment history of the galaxy. CMD analysis has shown the Carina dwarf spheroidal (dSph) to have had an unusually episodic star formation history (SFH) which is expected to be reflected in the abundances of different chemical elements. We use the VLT-FLAMES spectrograph in HR mode (R~20000) to measure the abundances of several chemical elements in a sample of 35 RGB stars in Carina. We also combine these abundances with photometry to derive age estimates for these stars. This allows us to determine which of two distinct star formation (SF) episodes the stars in our sample belong to, and thus to define the relationship between SF and chemical...

  17. EU Del: exploring the onset of pulsation-driven winds in giant stars

    Science.gov (United States)

    McDonald, I.; Zijlstra, A. A.; Sloan, G. C.; Lagadec, E.; Johnson, C. I.; Uttenthaler, S.; Jones, O. C.; Smith, C. L.

    2016-03-01

    We explore the wind-driving mechanism of giant stars through the nearby (117 pc), intermediate-luminosity (L ≈ 1600 L⊙) star EU Del (HIP 101810, HD 196610). Atacama Pathfinder Experiment observations of the CO (3-2) and (2-1) transitions are used to derive a wind velocity of 9.51 ± 0.02 km s-1, a 12C/13C ratio of 14^{+9}_{-4} and a mass-loss rate of a few × 10-8 M⊙ yr-1. Analysis of published spectra show the star has a metallicity of [Fe/H] = -0.27 ± ˜0.30 dex. The star's dusty envelope lacks a clear 10-μm silicate feature, despite the star's oxygen-rich nature. Radiative transfer modelling cannot fit a wind acceleration model which relies solely on radiation pressure on condensing dust. We compare our results to VY Leo (HIP 53449), a star with similar temperature and luminosity, but different pulsation properties. We suggest the much stronger mass-loss from EU Del may be driven by long-period stellar pulsations, due to its potentially lower mass. We explore the implications for the mass-loss rate and wind velocities of other stars.

  18. Subaru/HDS Abundances in Three Giant Stars in the Ursa Minor Dwarf Spheroidal Galaxy

    CERN Document Server

    Sadakane, K; Ikuta, C; Aoki, W; Jablonka, P; Tajitsu, A

    2004-01-01

    With the HDS (High Dispersion Spectrograph) on the Subaru telescope, we obtained high resolution optical region spectra of three red giant stars (cos 4, cos 82, and cos 347) in the Ursa Minor dwarf spheriodal galaxy. Chemical abundances in these stars have been analysed for 26 elements including alpha-, iron-peak, and neutron capture elements. All three stars show low abundances of alpha-elements (Mg, Si, and Ca) and two stars (cos 82 and cos 347) show high abundance of Mn compared to Galactic halo stars of similar metallicity. One star (cos 4) has been confirmed to be very metal deficient ([Fe/H]=-2.7) and found to show anomalously low abundances of Mn, Cu, and Ba. In another star cos 82 ([Fe/H]=-1.5), we have found large excess of heavy neutron-capture elements with the general abundance pattern similar to the scaled solar system r-process abundance curve. These observational results are rather puzzling: low abundances of alpha-elements and high abundance of Mn seem to sugggest a significant contribution of...

  19. Dust-enshrouded Asymptotic Giant Branch Stars in the Solar Neighbourhood

    CERN Document Server

    Olivier, E A; Marang, F; Olivier, Enrico A.; Whitelock, Patricia; Marang, Fred

    2001-01-01

    A study is made of a sample of 58 dust-enshrouded Asymptotic Giant Branch (AGB) stars (including 2 possible post AGB stars), of which 27 are carbon-rich and 31 are oxygen-rich. These objects were originally identified by Jura & Kleinmann as nearby (within about 1 kpc of the sun) AGB stars with high mass-loss rates, greater than 1E-6 solar masses per year. Ground-based near-infrared photometry, data obtained by IRAS and kinematic data from the literature are combined to investigate the properties of these stars. The light amplitude in the near-infrared is found to be correlated with period, and this amplitude decreases with increasing wavelength. Statistical tests show that there is no reason to suspect any difference in the period distributions of the carbon- and oxygen-rich stars for periods less than 1000 days, and no carbon-rich star has a period longer than 1000 days. The colours are consistent with those of cool stars with evolved circumstellar dust-shells. Luminosities and distances are estimated us...

  20. Mg isotope ratios in giant stars of the globular clusters M 13 and M 71

    CERN Document Server

    Yong, D; Lambert, D L; Yong, David; Aoki, Wako; Lambert, David L.

    2006-01-01

    We present Mg isotope ratios in 4 red giants of the globular cluster M 13 and 1 red giant of the globular cluster M 71 based on spectra obtained with HDS on the Subaru Telescope. We confirm earlier results by Shetrone that for M 13, the ratio varies from (25+26)Mg/24Mg = 1 in stars with the highest Al abundance to (25+26)Mg/24Mg = 0.2 in stars with the lowest Al abundance. However, we separate the contributions of all three isotopes and find a spread in the ratio 24Mg:25Mg:26Mg with values ranging from 48:13:39 to 78:11:11. As in NGC 6752, we find a positive correlation between 26Mg and Al, an anticorrelation between 24Mg and Al, and no correlation between 25Mg and Al. In M 71, our one star has a ratio 70:13:17. For both clusters, the lowest ratios of 25Mg/24Mg and 26Mg/24Mg exceed those observed in field stars at the same metallicity, a result also found in NGC 6752. The contribution of 25Mg to the total Mg abundance is constant within a given cluster and between clusters with 25Mg/(24+25+26)Mg = 0.13. For M...

  1. The K giant stars from the LAMOST survey data II: the Hercules stream in radial migration

    CERN Document Server

    Liu, Chao; Yin, Jun; Zhang, Bo; Deng, Li-Cai; Hou, Yong-Hui; Shao, Zheng-Yi; Wan, Jun-Chen; Wang, Hai-Feng; Wu, Yue; Xin, Yu; Xu, Yan; Yang, Ming; Zhang, Yong

    2015-01-01

    We estimate the age for the individual stars located at the lower part of the red giant branch from the LAMOST DR2 K giant sample. Taking into account the selection effects and the volume completeness, the age--metallicity map for the stars located between 0.3 and 1.5 kpc from the Sun is obtained. A significant substructure (denoted as the \\it{narrow stripe}) located from (age, [Fe/H])$\\sim$(5, 0.4) to (10 Gyr, -0.4 dex) in the age--metallicity map is clearly identified. Moreover, the \\it{narrow stripe} stars are found the dominate contributors to several velocity substructures, including the well-known Hercules stream. The substantially large difference between the observed guiding-center radii and the birth radii inferred from the age--metallicity relation is evident that the \\it{narrow stripe} stars have been radially migrated from about R$\\sim4$ kpc to the solar neighborhood. This implies that the Hercules stream may not be owe to the resonance associated with the bar, but may be the kinematic imprint of ...

  2. The variability behavior of CoRoT M-giant Stars

    CERN Document Server

    Lopes, C E Ferreira; Leão, I C; de Freitas, D B; Martins, B L Canto; da Costa, A D; Paz-Chinchón, F; Chagas, M L Das; Baglin, A; Janot-Pacheco, E; De Medeiros, J R

    2015-01-01

    For 6 years the Convection, Rotation, and Planetary Transits (CoRoT) space mission has acquired photometric data from more than one hundred thousand point sources towards and directly opposite from the inner and outer regions of the Galaxy. The high temporal resolution of the CoRoT data combined with the wide time span of the observations has enabled the study of short and long time variations in unprecedented detail. From the initial sample of 2534 stars classified as M-giants in the CoRoT databasis, we selected 1428 targets that exhibit well defined variability, using visual inspection. The variability period and amplitude of C1 stars (stars having Teff < 4200 K) were computed using Lomb-Scargle and harmonic fit methods. The trends found in the V-I vs J-K color-color diagram are in agreement with standard empirical calibrations for M-giants. The sources located towards the inner regions of the Galaxy are distributed throughout the diagram while the majority of the stars towards the outer regions of the G...

  3. Detection of a Planetary Companion around the giant star \\gam1leo

    CERN Document Server

    Han, Inwoo; Kim, K M; Mkrtichian, D E; Hatzes, A P; Valyavin, G

    2009-01-01

    Aims: Our primary goal is to search for planets around intermediate mass stars. We are also interested in studying the nature of radial velocity (RV) variations of K giant stars. Methods: We selected about 55 early K giant (K0 - K4) stars brighter than fifth magnitude that were observed using BOES, a high resolution spectrograph attached to the 1.8 m telescope at BOAO (Bohyunsan Optical Astronomy Observatory). BOES is equipped with $I_2$ absorption cell for high precision RV measurements. Results: We detected a periodic radial velocity variations in the K0 III star \\gam1leo with a period of P = 429 days. An orbital fit of the observed RVs yields a period of P = 429 days, a semi-amplitude of K = 208 \\mps, and an eccentricity of e = 0.14. To investigate the nature of the RV variations, we analyzed the photometric, CaII $\\lambda$ 8662 equivalent width, and line-bisector variations of \\gam1leo. We conclude that the detected RV variations can be best explained by a planetary companion with an estimated mass of m $...

  4. On the onset of secondary stellar generations in giant star-forming regions and massive star clusters

    Energy Technology Data Exchange (ETDEWEB)

    Palouš, J.; Wünsch, R. [Astronomical Institute, Academy of Sciences of the Czech Republic, Boční II 1401, 14131 Prague (Czech Republic); Tenorio-Tagle, G. [Instituto Nacional de Astrofísica Optica y Electrónica, AP 51, 72000 Puebla (Mexico)

    2014-09-10

    Here we consider the strong evolution experienced by the matter reinserted by massive stars, both in giant star-forming regions driven by a constant star formation rate and in massive and coeval superstar clusters. In both cases we take into consideration the changes induced by stellar evolution on the number of massive stars, the number of ionizing photons, and the integrated mechanical luminosity of the star-forming regions. The latter is at all times compared with the critical luminosity that defines, for a given size, the lower mechanical luminosity limit above which the matter reinserted via strong winds and supernova explosions suffers frequent and recurrent thermal instabilities that reduce its temperature and pressure and inhibit its exit as part of a global wind. Instead, the unstable reinserted matter is compressed by the pervasive hot gas, and photoionization maintains its temperature at T ∼ 10{sup 4} K. As the evolution proceeds, more unstable matter accumulates and the unstable clumps grow in size. Here we evaluate the possible self-shielding of thermally unstable clumps against the UV radiation field. Self-shielding allows for a further compression of the reinserted matter, which rapidly develops a high-density neutral core able to absorb in its outer skin the incoming UV radiation. Under such conditions the cold (T ∼ 10 K) neutral cores soon surpass the Jeans limit and become gravitationally unstable, creating a new stellar generation with the matter reinserted by former massive stars. We present the results of several calculations of this positive star formation feedback scenario promoted by strong radiative cooling and mass loading.

  5. The UK Infrared Telescope M33 monitoring project. IV. Variable red giant stars across the galactic disc

    CERN Document Server

    Javadi, Atefeh; van Loon, Jacco Th; Khosroshahi, Habib; Golabatooni, Najmeh; Mirtorabi, Mohammad Taghi

    2014-01-01

    We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). The main aim was to identify stars in the very final stage of their evolution, and for which the luminosity is more directly related to the birth mass than the more numerous less-evolved giant stars that continue to increase in luminosity. In this fourth paper of the series, we present a search for variable red giant stars in an almost square degree region comprising most of the galaxy's disc, carried out with the WFCAM instrument in the K band. These data, taken during the period 2005--2007, were complemented by J- and H-band images. Photometry was obtained for 403 734 stars in this region; of these, 4643 stars were found to be variable, most of which are Asymptotic Giant Branch (AGB) stars. The variable stars are concentrated towards the centre of M33, more so than low-mass, less-evolved red giants. Our data were matched to optical catalogues of variable stars and ca...

  6. The PTI Giant Star Angular Size Survey: Effective Temperatures & Linear Radii

    Science.gov (United States)

    van Belle, Gerard; von Braun, Kaspar; Ciardi, David R.; Pilyavsky, Genady

    2017-01-01

    We report new interferometric angular diameter observations of over 200 giant stars observed with the Palomar Testbed Interferometer (PTI). These angular diameters are combined with bolometric fluxes derived from detailed spectral energy distribution (SED) fits, to produce robust estimates of effective temperature (T_EFF). These SED fits include reddening estimates and are based upon fits of empirical spectral templates to literature photometry, and narrow-band photometry obtained at the Lowell 31" telescope. The 58 nights of 31" observing have produced over 45,000 new photometric data points on these stars, allowing for flux and reddening determination with unprecident precision. Over the range from G5III to M8III, T_EFF estimates are precise to 50K per spectral type. For the 87 objects in Gaia DR1, radius estimates are improved over the Hipparcos estimates (van Leeuwen 2007) but only by a factor of 1.7 reduction in error, and are typically ~6% per star.

  7. The Astrosphere of the Asymptotic Giant Branch Star Irc+10216

    CERN Document Server

    Sahai, Raghvendra

    2010-01-01

    We have discovered a very extended shock structure (i.e., with a diameter of about 24 arcmin) surrounding the well-known carbon star IRC+10216 in ultraviolet images taken with the GALEX satellite. We conclude that this structure results from the interaction of IRC+10216's molecular wind with the interstellar medium (ISM), as it moves through the latter. All important structural features expected from theoretical models of such interactions are identified: the termination shock, the astrosheath, the astropause, the bowshock, and an astrotail (with vortices). The extent of the astropause provides new lower limits to the envelope age (69,000 years) and mass (1.4 solar masses, for a mass-loss rate of 2 x 10^(-5) solar masses/year). From the termination-shock standoff distance, we find that IRC+10216 is moving at a speed of about > 91 km/s [1 cm^(-3)/n_(ISM)]^1/2 through the local ISM.

  8. The astrosphere of the Asymptotic Giant Branch star CIT 6

    CERN Document Server

    Sahai, Raghvendra

    2014-01-01

    We have discovered two extended half-ring structures in a far-ultraviolet image taken with the GALEX satellite of the well-known mass-losing carbon star CIT 6 (RW LMi). The northern (southern) ring is brighter (fainter) with a diameter of about 15 arcmin (18 arcmin). These structures most likely represent the astrosphere resulting from the shock interaction of CIT 6's molecular wind with the Warm Interstellar Medium, as it moves through the latter. These data provide a direct estimate of the size of CIT 6's circumstellar envelope that is a factor ~20 larger than previous estimates based on CO millimeter-wave line data. We find that CIT 6 has been undergoing heavy mass-loss for at least 93,000 yr and the total envelope mass is 0.29 Msun or larger, assuming a constant mass-loss rate of 3.2 x 10^(-6) Msun/yr. Assuming that the shock front has reached a steady-state and CIT 6's motion relative to the ISM is in the sky-plane, we measure the termination-shock standoff distance directly from the image and find that ...

  9. VLT/FLAMES spectroscopy of red giant branch stars in the Fornax dwarf spheroidal galaxy

    CERN Document Server

    Lemasle, B; Hill, V; Tolstoy, E; Irwin, M; Jablonka, P; Venn, K; Battaglia, G; Starkenburg, E; Shetrone, M; Letarte, B; Francois, P; Helmi, A; Primas, F; Kaufer, A; Szeifert, T

    2014-01-01

    Fornax is one of the most massive dwarf spheroidal galaxies in the Local Group. The Fornax field star population is dominated by intermediate age stars but star formation was going on over almost its entire history. It has been proposed that Fornax experienced a minor merger event. Despite recent progress, only the high metallicity end of Fornax field stars ([Fe/H]>-1.2 dex) has been sampled in larger number via high resolution spectroscopy. We want to better understand the full chemical evolution of this galaxy by better sampling the whole metallicity range, including more metal poor stars. We use the VLT-FLAMES multi-fibre spectrograph in high-resolution mode to determine the abundances of several alpha, iron-peak and neutron-capture elements in a sample of 47 individual Red Giant Branch stars in the Fornax dwarf spheroidal galaxy. We combine these abundances with accurate age estimates derived from the age probability distribution from the colour-magnitude diagram of Fornax. Similar to other dwarf spheroid...

  10. A Spitzer Space Telescope Survey of Extreme Asymptotic Giant Branch Stars in M32

    Science.gov (United States)

    Jones, O.C.; McDonald, I.; Rich, R.M.; Kemper, F.; Boyer, M.L.; Zijlstra, A.A.; Bendo, G.J.

    2014-01-01

    We investigate the population of cool, evolved stars in the Local Group dwarf elliptical galaxy M32, using Infrared Array Camera observations from the Spitzer Space Telescope. We construct deep mid-infrared colour-magnitude diagrams for the resolved stellar populations within 3.5 arcminutes of M32's centre, and identify those stars that exhibit infrared excess. Our data is dominated by a population of luminous, dustproducing stars on the asymptotic giant branch (AGB) and extend to approximately 3 magnitudes below the AGB tip. We detect for the first time a sizeable population of 'extreme' AGB stars, highly enshrouded by circumstellar dust and likely completely obscured at optical wavelengths. The total dust-injection rate from the extreme AGB candidates is measured to be 7.5 x 10 (sup -7) solar masses per year, corresponding to a gas mass-loss rate of 1.5 x 10 (sup -4) solar masses per year. These extreme stars may be indicative of an extended star-formation epoch between 0.2 and 5 billion years ago.

  11. A Spitzer Space Telescope survey of extreme Asymptotic Giant Branch stars in M32

    CERN Document Server

    Jones, O C; Rich, R M; Kemper, F; Boyer, M L; Zijlstra, A A; Bendo, G J

    2014-01-01

    We investigate the population of cool, evolved stars in the Local Group dwarf elliptical galaxy M32, using Infrared Array Camera observations from the Spitzer Space Telescope. We construct deep mid-infrared colour-magnitude diagrams for the resolved stellar populations within 3.5 arcmin of M32's centre, and identify those stars that exhibit infrared excess. Our data is dominated by a population of luminous, dust-producing stars on the asymptotic giant branch (AGB) and extend to approximately 3 mag below the AGB tip. We detect for the first time a sizeable population of `extreme' AGB stars, highly enshrouded by circumstellar dust and likely completely obscured at optical wavelengths. The total dust-injection rate from the extreme AGB candidates is measured to be $7.5 \\times 10^{-7}$ ${\\rm M}_{\\odot} \\, {\\rm yr}^{-1}$, corresponding to a gas mass-loss rate of $1.5 \\times 10^{-4}$ ${\\rm M}_{\\odot} \\, {\\rm yr}^{-1}$. These extreme stars may be indicative of an extended star-formation epoch between 0.2 and 5 Gyr a...

  12. Metallicity calibrations for dwarf stars and giants in the Geneva photometric system

    Science.gov (United States)

    Netopil, Martin

    2017-08-01

    We use the most homogeneous Geneva seven-colour photometric system to derive new metallicity calibrations for early A- to K-type stars that cover both, dwarf stars and giants. The calibrations are based on several spectroscopic data sets that were merged to a common scale, and we applied them to open cluster data to obtain an additional proof of the metallicity scale and accuracy. In total, metallicities of 54 open clusters are presented. The accuracy of the calibrations for single stars is in general below 0.1 dex, but for the open cluster sample with mean values based on several stars we find a much better precision, a scatter as low as about 0.03 dex. Furthermore, we combine the new results with another comprehensive photometric data set to present a catalogue of mean metallicities for more than 3000 F- and G-type dwarf stars with σ ˜ 0.06 dex. The list was extended by more than 1200 hotter stars up to about 8500 K (or spectral type A3) by taking advantage of their almost reddening free characteristic in the new Geneva metallicity calibrations. These two large samples are well suited as primary or secondary calibrators of other data, and we already identified about 20 spectroscopic data sets that show offsets up to about 0.4 dex.

  13. Can Star-Disk Collisions Explain the Missing Red Giants Problem in the Galactic Center?

    CERN Document Server

    Kieffer, Thomas Forrest

    2016-01-01

    Observations have revealed a relative paucity of red giant (RG) stars within the central 0.5pc in the Galactic Center (GC). Motivated by this finding we investigate the hypothesis that collisions of stars with a fragmenting accretion disk are responsible for the observed dearth of evolved stars. We use 3-dimensional hydrodynamic simulations to model a star with radius $10 R_{\\odot}$ and mass $1 M_{\\odot}$, representative of the missing population of RGs, colliding with high density clumps. We find that multiple collisions with clumps of column density $\\gtrsim10^{8}\\, {\\rm g\\,cm^{-2}}$ can strip a substantial fraction of the star's envelope and in principle render it invisible to observations. Simulations confirm that repeated impacts are particularly efficient in driving mass loss as partially stripped RGs expand and have increased cross sections for subsequent collisions. Because the envelope is unbound on account of the kinetic energy of the star, any significant amount of stripping of the RG population in...

  14. Asteroseismology of Red-Giant Stars: Mixed Modes, Differential Rotation, and Eccentric Binaries

    Science.gov (United States)

    Beck, Paul G.

    2013-12-01

    Astronomers are aware of rotation in stars since Galileo Galilei attributed the movement of sunspots to rotation of the Sun in 1613. In contrast to the Sun, whose surface can be resolved by small telescopes or even the (protected) eye, we detect stars as point sources with no spatial information. Numerous techniques have been developed to derive information about stellar rotation. Unfortunately, most observational data allow only for the surface rotational rate to be inferred. The internal rotational profile, which has a great effect on the stellar structure and evolution, remains hidden below the top layers of the star - the essential is hidden to the eyes. Asteroseismology allows us to "sense" indirectly deep below the stellar surface. Oscillations that propagate through the star provide information about the deep stellar interiors while they also distort the stellar surface in characteristic patterns leading to detectable brightness or velocity variations. Also, certain oscillation modes are sensitive to internal rotation and carry information on how the star is spinning deep inside. Thanks to the unprecedented quality of NASA's space telescope Kepler, numerous detailed observations of stars in various evolutionary stages are available. Such high quality data allow that for many stars, rotation can not only be constrained from surface rotation, but also investigated through seismic studies. The work presented in this thesis focuses on the oscillations and internal rotational gradient of evolved single and binary stars. It is shown that the seismic analysis can reach the cores of oscillating red-giant stars and that these cores are rapidly rotating, while nested in a slowly rotating convective envelope.

  15. Internal rotation of the red-giant star KIC 4448777 by means of asteroseismic inversion

    CERN Document Server

    Di Mauro, M P; Cardini, D; Stello, D; Christensen-Dalsgaard, J; Dziembowski, W A; Paterno', L; Beck, P G; Bloemen, S; Davies, G R; De Smedt, K; Elsworth, Y; Garcia, R A; Hekker, S; Mosser, B; Tkachenko, A

    2015-01-01

    In this paper we study the dynamics of the stellar interior of the early red-giant star KIC 4448777 by asteroseismic inversion of 14 splittings of the dipole mixed modes obtained from {\\it Kepler} observations. In order to overcome the complexity of the oscillation pattern typical of red-giant stars, we present a procedure which involves a combination of different methods to extract the rotational splittings from the power spectrum. We find not only that the core rotates faster than the surface, confirming previous inversion results generated for other red giants (Deheuvels et al. 2012,2014), but we also estimate the variation of the angular velocity within the helium core with a spatial resolution of $\\Delta r=0.001R$ and verify the hypothesis of a sharp discontinuity in the inner stellar rotation (Deheuvels et al. 2014). The results show that the entire core rotates rigidly with an angular velocity of about $\\langle\\Omega_c/2\\pi\\rangle=748\\pm18$~nHz and provide evidence for an angular velocity decrease thro...

  16. The Giant Branches of ω Centauri: Multiwavelength Observations of Evolved Stars

    Science.gov (United States)

    Hughes, Joanne; Wallerstein, George; van Leeuwen, Floor; Hilker, Michael

    2004-02-01

    We have obtained photometric observations in a 182 arcmin2 area, 25' to the north of the center of the globular cluster ω Centauri. The Strömgren vby and broadband BI filters were used to obtain measurements for some 2500 stars. Preliminary examinations of parts of the data have been presented previously (Hughes & Wallerstein, published in 2000; Hughes, Wallerstein, & van Leeuwen, published in 2002). Here we present the complete data set, study the giant branches, and use the B-I color index as a tool for assessing the ages of the populations within ω Cen. Our results confirm previous results for the main-sequence turnoff stars: there appears to be an age spread of about 3-5 Gyr among the stars of ω Cen. We use the proper-motion study by van Leeuwen et al. (published in 2000) to confirm cluster membership above B~16.5 and calibrate our photometry to that of Hilker and Hilker & Richtler (both published in 2000) in order to use the improved methods described by these authors for deriving metallicity estimates from the Strömgren photometry. We use data on 25 ROA stars in our field and 40 stars from Hilker to look at the enrichment history of ω Cen. We support previous findings that there is another red giant branch, redder (Lee et al., published in 1999, and Pancino et al., published in 2000), and younger than the main giant branch but containing few stars. Even though this so-called RGB-a population appears to be younger than the bulk of the stellar population, it does not seem to be younger than the most metal-rich tail of the bulk population. This last property suggests that the RGB-a may not have been the last burst of star formation in ω Cen and could support the idea, presented by Ferraro et al. and Pancino et al. (both in 2002), that it represents an accreted stellar system.

  17. The astrosphere of the asymptotic giant branch star CIT 6

    Energy Technology Data Exchange (ETDEWEB)

    Sahai, Raghvendra [Jet Propulsion Laboratory, MS 183-900, California Institute of Technology, Pasadena, CA 91109 (United States); Mack-Crane, Galen P., E-mail: sahai@jpl.nasa.gov [Department of Physics, Occidental College, Los Angeles, CA 90041 (United States)

    2014-10-01

    We have discovered two extended half-ring structures in a far-ultraviolet image taken with the GALEX satellite of the well-known mass-losing carbon star CIT 6 (RW LMi). The northern (southern) ring is brighter (fainter) with a diameter of ∼15' (∼18'). These structures most likely represent the astrosphere resulting from the shock interaction of CIT 6's molecular wind with the warm interstellar medium (ISM), as it moves through the latter. These data provide a direct estimate of the size of CIT 6's circumstellar envelope that is a factor ∼20 larger than previous estimates based on CO millimeter-wave line data. We find that CIT 6 has been undergoing heavy mass-loss for at least 93,000 yr and the total envelope mass is 0.29 M {sub ☉} or larger, assuming a constant mass-loss rate of 3.2 × 10{sup –6} M {sub ☉} yr{sup –1}. Assuming that the shock front has reached a steady state and CIT 6's motion relative to the ISM is in the sky plane, we measure the termination-shock standoff distance directly from the image and find that CIT 6 is moving at a speed of about ≳39 (0.17 cm{sup –3}/n {sub ISM}){sup 1/2} km s{sup –1} through the ISM around it. However, comparisons with published numerical simulations and analytical modeling shows that CIT 6's forward shock (the northern ring) departs from the parabolic shape expected in steady state. We discuss several possible explanations for this departureþ.

  18. The Astrosphere of the Asymptotic Giant Branch Star CIT 6

    Science.gov (United States)

    Sahai, Raghvendra; Mack-Crane, Galen P.

    2014-10-01

    We have discovered two extended half-ring structures in a far-ultraviolet image taken with the GALEX satellite of the well-known mass-losing carbon star CIT 6 (RW LMi). The northern (southern) ring is brighter (fainter) with a diameter of ~15' (~18'). These structures most likely represent the astrosphere resulting from the shock interaction of CIT 6's molecular wind with the warm interstellar medium (ISM), as it moves through the latter. These data provide a direct estimate of the size of CIT 6's circumstellar envelope that is a factor ~20 larger than previous estimates based on CO millimeter-wave line data. We find that CIT 6 has been undergoing heavy mass-loss for at least 93,000 yr and the total envelope mass is 0.29 M ⊙ or larger, assuming a constant mass-loss rate of 3.2 × 10-6 M ⊙ yr-1. Assuming that the shock front has reached a steady state and CIT 6's motion relative to the ISM is in the sky plane, we measure the termination-shock standoff distance directly from the image and find that CIT 6 is moving at a speed of about gsim39 (0.17 cm-3/n ISM)1/2 km s-1 through the ISM around it. However, comparisons with published numerical simulations and analytical modeling shows that CIT 6's forward shock (the northern ring) departs from the parabolic shape expected in steady state. We discuss several possible explanations for this departure.

  19. Lost and found: evidence of Second Generation stars along the Asymptotic Giant Branch of the globular cluster NGC 6752

    CERN Document Server

    Lapenna, E; Mucciarelli, A; Salaris, M; Ferraro, F R; Lanzoni, B; Massari, D; Stetson, P B; Cassisi, S; Savino, A

    2016-01-01

    We derived chemical abundances for C, N, O, Na, Mg and Al in 20 asymptotic giant branch (AGB) stars in the globular cluster NGC 6752. All these elements (but Mg) show intrinsic star-to-star variations and statistically significant correlations or anticorrelations analogous to those commonly observed in red giant stars of globular clusters hosting multiple populations. This demonstrates that, at odds with previous findings, both first and second generation stars populate the AGB of NGC 6752. The comparison with the Na abundances of red giant branch stars in the same cluster reveals that second generation stars (with mild Na and He enrichment) do reach the AGB phase. The only objects that are not observed along the AGB of NGC 6752 are stars with extreme Na enhancement. This is also consistent with standard stellar evolution models, showing that highly Na and He enriched stars populate the bluest portion of the horizontal branch and, because of their low stellar masses, evolve directly to the white dwarf cooling...

  20. Lost and Found: Evidence of Second-generation Stars Along the Asymptotic Giant Branch of the Globular Cluster NGC 6752

    Science.gov (United States)

    Lapenna, E.; Lardo, C.; Mucciarelli, A.; Salaris, M.; Ferraro, F. R.; Lanzoni, B.; Massari, D.; Stetson, P. B.; Cassisi, S.; Savino, A.

    2016-07-01

    We derived chemical abundances for C, N, O, Na, Mg, and Al in 20 asymptotic giant branch (AGB) stars in the globular cluster (GC) NGC 6752. All these elements (but Mg) show intrinsic star-to-star variations and statistically significant correlations or anticorrelations analogous to those commonly observed in red giant stars of GCs hosting multiple populations. This demonstrates that, at odds with previous findings, both first- and second-generation (SG) stars populate the AGB of NGC 6752. The comparison with the Na abundances of red giant branch stars in the same cluster reveals that SG stars (with mild Na and He enrichment) do reach the AGB phase. The only objects that are not observed along the AGB of NGC 6752 are stars with extreme Na enhancement. This is also consistent with standard stellar evolution models, showing that highly Na and He enriched stars populate the bluest portion of the horizontal branch and, because of their low stellar masses, evolve directly to the white dwarf cooling sequence, skipping the AGB phase. Based on observations collected at the ESO-VLT under the program 095.D-0320(A).

  1. Giant Pulsar Glitches and the Inertia of Neutron-Star Crusts

    CERN Document Server

    Delsate, T; Gürlebeck, N; Fantina, A F; Pearson, J M; Ducoin, C

    2016-01-01

    Giant pulsar frequency glitches as detected in the emblematic Vela pulsar have long been thought to be the manifestation of a neutron superfluid permeating the inner crust of a neutron star. However, this superfluid has been recently found to be entrained by the crust, and as a consequence it does not carry enough angular momentum to explain giant glitches. The extent to which pulsar-timing observations can be reconciled with the standard vortex-mediated glitch theory is studied considering the current uncertainties on dense-matter properties. To this end, the crustal moment of inertia of glitching pulsars is calculated employing a series of different unified dense-matter equations of state.

  2. Chemical Compositions of Red Giant Stars in Old Large Magellanic Cloud Globular Clusters

    CERN Document Server

    Johnson, J A; Stetson, P B; Ivans, Inese I.; Johnson, Jennifer A.; Stetson, Peter B.

    2006-01-01

    We have observed ten red giant stars in four old Large Magellanic Cloud globular clusters with the high-resolution spectrograph MIKE on the Magellan Landon Clay 6.5-m telescope. The stars in our sample have up to 20 elemental abundance determinations for the alpha-, iron-peak, and neutron-capture element groups. We have also derived abundances for the light odd-Z elements Na and Al. We find NGC 2005 and NGC 2019 to be more metal-rich than previous estimates from the Ca II triplet, and we derive [Fe/H] values closer to those obtained from the slope of the red giant branch. However, we confirm previous determinations for Hodge 11 and NGC 1898 to within 0.2 dex. The LMC cluster [Mg/Fe] and [Si/Fe] ratios are comparable to the values observed in old Galactic globular cluster stars, as are the abundances [Y/Fe], [Ba/Fe], and [Eu/Fe]. The LMC clusters do not share the low-Y behavior observed in some dwarf spheroidal galaxies. [Ca/Fe], [Ti/Fe], and [V/Fe] in the LMC, however, are significantly lower than what is see...

  3. Modelling chromospheric line profiles as diagnostics of velocity fields in {\\omega} Centauri red giant stars

    CERN Document Server

    Vieytes, M; Cacciari, C; Origlia, L; Pancino, E

    2010-01-01

    Context. Mass loss of ~0.1-0.3 M$_{\\odot}$ from Population II red giant stars (RGB) is a requirement of stellar evolution theory in order to account for several observational evidences in globular clusters. Aims. The aim of this study is to detect the presence of outward velocity fields, which are indicative of mass outflow, in six luminous red giant stars of the stellar cluster {\\omega} Cen. Methods. We compare synthetic line profiles computed using relevant model chromospheres to observed profiles of the H{\\alpha} and Ca II K lines. The spectra were taken with UVES (R=45,000) and the stars were selected so that three of them belong to the metal-rich population and three to the metal-poor population, and sample as far down as 1 to 2.5 magnitudes fainter than the respective RGB tips. Results. We do indeed reveal the presence of low-velocity outward motions in four of our six targets, without any apparent correlation with astrophysical parameters. Conclusions. This provides direct evidence that outward velocit...

  4. The properties of red giant stars along the Sagittarius tidal tails

    Science.gov (United States)

    Zhang, X.; Shi, W. B.; Chen, Y. Q.; Zhao, G.; Carrell, K.; Zhao, J. K.; Ruan, G. P.; Liang, Y. C.; Zhou, L.; Ren, H. B.; Zhang, Y.; Hou, Y. H.; Wang, Y. F.

    2017-01-01

    Aims: We aim to measure the metallicity distribution and velocity distribution of red giant branch (RGB) stars along the Sagittarius dwarf galaxy (Sgr) streams. Thanks to the large number of stars of the Sloan Digital Sky Survey (SDSS) sample, we can study the properties of streams as a function of the Λ⊙ from the Sgr core. Methods: Using the 22 000 RGB stars from the ninth data release of SDSS, we selected 1100 RGB stars belonging to the streams of the Sgr. As compared with red horizontal branch stars (Shi et al. 2012, ApJ, 751, 130) the RGB stars constitute a large sample size and extend to a metal-poor component of [Fe/H] -3.0 dex. In particular, this RGB sample has a significant number of stars in the second wrap of the leading stream of the Sgr (leading arm 2), and thus provides a good opportunity to understand the properties of the leading stream. Results: We derive a metallicity gradient of -(2.3 ± 0.5) × 10-3 dex deg-1 in leading arm 2 for the first time, of -(1.6 ± 0.4) × 10-6 dex deg-1 for the leading arm 1, and of -(1.3 ± 0.3) × 10-3 dex deg-1 for the trailing arm 1. We check the distribution of Sgr stars in phase space and find a velocity dispersion of 21.5 km s-1 for leading arm 1. Finally, we identify a possible new branch in leading arm 1. Full Table A.1 is 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/597/A54

  5. INTERNAL ROTATION OF THE RED-GIANT STAR KIC 4448777 BY MEANS OF ASTEROSEISMIC INVERSION

    Energy Technology Data Exchange (ETDEWEB)

    Di Mauro, M. P.; Cardini, D. [INAF, IAPS Istituto di Astrofisica e Planetologia Spaziali, Roma (Italy); Ventura, R.; Paternò, L. [INAF, Astrophysical Observatory of Catania, Catania (Italy); Stello, D. [Sydney Institute for Astronomy, School of Physics, University of Sydney (Australia); Christensen-Dalsgaard, J.; Hekker, S. [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Dziembowski, W. A. [Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warsaw (Poland); Beck, P. G.; De Smedt, K.; Tkachenko, A. [Instituut voor Sterrenkunde, Katholieke Universiteit Leuven (Belgium); Bloemen, S. [Department of Astrophysics, IMAPP, Radboud University Nijmegen, P.O. Box 9010, NL-6500 GL, Nijmegen (Netherlands); Davies, G. R.; Garcia, R. A. [Laboratoire AIM, CEA/DSM-CNRS-Univ. Paris Diderot, IRFU/Sap, Centre de Saclay, F-91191 Gif-sur-Yvette Cedex (France); Elsworth, Y. [School of Physics and Astronomy, University of Birmingham (United Kingdom); Mosser, B. [LESIA, PSL Research University, CNRS, Universitè Pierre et Marie Curie, Université Denis Diderot, Observatoire de Paris, Meudon Cedex (France)

    2016-01-20

    We study the dynamics of the stellar interior of the early red-giant star KIC 4448777 by asteroseismic inversion of 14 splittings of the dipole mixed modes obtained from Kepler observations. In order to overcome the complexity of the oscillation pattern typical of red-giant stars, we present a procedure to extract the rotational splittings from the power spectrum. We find not only that the core rotates from a minimum of 8 to a maximum of 17 times faster than the surface, confirming previous inversion results generated for other red giants (Deheuvels et al.), but we also estimate the variation of the angular velocity within the helium core with a spatial resolution of 0.001R and verify the hypothesis of a sharp discontinuity in the inner stellar rotation. The results show that the entire core rotates rigidly and provide evidence for an angular velocity gradient around the base of the hydrogen-burning shell; however, we do not succeed in characterizing the rotational slope, due to the intrinsic limits of the applied techniques. The angular velocity, from the edge of the core, appears to decrease with increasing distance from the center, reaching an average value in the convective envelope of 68 ± 22 nHz. We conclude that a set of data that includes only dipolar modes is sufficient to infer quite accurately the rotation of a red giant not only in the dense core but also, with a lower level of confidence, in part of the radiative region and in the convective envelope.

  6. The Asymptotic Giant Branch and the Tip of the Red Giant Branch as Probes of Star Formation History: The Nearby Dwarf Irregular Galaxy KKH 98

    CERN Document Server

    Melbourne, J; Dalcanton, J; Ammons, S M; Max, C; Koo, D C; Girardi, Leo; Dolphin, A

    2010-01-01

    We investigate the utility of the asymptotic giant branch (AGB) and the red giant branch (RGB) as probes of the star formation history (SFH) of the nearby (D=2.5 Mpc) dwarf irregular galaxy, KKH 98. Near-infrared (IR) Keck Laser Guide Star Adaptive Optics (AO) images resolve 592 IR bright stars reaching over 1 magnitude below the Tip of the Red Giant Branch. Significantly deeper optical (F475W and F814W) Hubble Space Telescope images of the same field contain over 2500 stars, reaching to the Red Clump and the Main Sequence turn-off for 0.5 Gyr old populations. Compared to the optical color magnitude diagram (CMD), the near-IR CMD shows significantly tighter AGB sequences, providing a good probe of the intermediate age (0.5 - 5 Gyr) populations. We match observed CMDs with stellar evolution models to recover the SFH of KKH 98. On average, the galaxy has experienced relatively constant low-level star formation (5 x 10^-4 Mo yr^-1) for much of cosmic time. Except for the youngest main sequence populations (age &...

  7. Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars. IV. Oxygen diagnostics in extremely metal-poor red giants with infrared OH lines

    CERN Document Server

    Dobrovolskas, V; Bonifacio, P; Caffau, E; Ludwig, H -G; Steffen, M; Spite, M

    2015-01-01

    Context. Although oxygen is an important tracer of Galactic chemical evolution, measurements of its abundance in the atmospheres of the oldest Galactic stars are still scarce and rather imprecise. At the lowest end of the metallicity scale, oxygen can only be measured in giant stars and in most of cases such measurements rely on a single forbidden [O I] 630 nm line that is very weak and frequently blended with telluric lines. Although molecular OH lines located in the ultraviolet and infrared could also be used for the diagnostics, oxygen abundances obtained from the OH lines and the [O I] 630 nm line are usually discrepant to a level of ~0.3-0.4 dex. Aims. We study the influence of convection on the formation of the infrared (IR) OH lines and the forbidden [O I] 630 nm line in the atmospheres of extremely metal-poor (EMP) red giant stars. Methods. We used high-resolution and high signal-to-noise ratio spectra of four EMP red giant stars obtained with the VLT CRIRES spectrograph. For each EMP star, 4-14 IR OH...

  8. The puzzle of the CNO isotope ratios in asymptotic giant branch carbon stars

    Science.gov (United States)

    Abia, C.; Hedrosa, R. P.; Domínguez, I.; Straniero, O.

    2017-02-01

    Context. The abundance ratios of the main isotopes of carbon, nitrogen and oxygen are modified by the CNO-cycle in the stellar interiors. When the different dredge-up events mix the burning material with the envelope, valuable information on the nucleosynthesis and mixing processes can be extracted by measuring these isotope ratios. Aims: Previous determinations of the oxygen isotopic ratios in asymptotic giant branch (AGB) carbon stars were at odds with the existing theoretical predictions. We aim to redetermine the oxygen ratios in these stars using new spectral analysis tools and further develop discussions on the carbon and nitrogen isotopic ratios in order to elucidate this problem. Methods: Oxygen isotopic ratios were derived from spectra in the K-band in a sample of galactic AGB carbon stars of different spectral types and near solar metallicity. Synthetic spectra calculated in local thermodynamic equillibrium (LTE) with spherical carbon-rich atmosphere models and updated molecular line lists were used. The CNO isotope ratios derived in a homogeneous way, were compared with theoretical predictions for low-mass (1.5-3 M⊙) AGB stars computed with the FUNS code assuming extra mixing both during the RGB and AGB phases. Results: For most of the stars the 16O/17O/18O ratios derived are in good agreement with theoretical predictions confirming that, for AGB stars, are established using the values reached after the first dredge-up (FDU) according to the initial stellar mass. This fact, as far as the oxygen isotopic ratios are concerned, leaves little space for the operation of any extra mixing mechanism during the AGB phase. Nevertheless, for a few stars with large 16O/17O/18O, the operation of such a mechanism might be required, although their observed 12C/13C and 14N/15N ratios would be difficult to reconcile within this scenario. Furthermore, J-type stars tend to have lower 16O/17O ratios than the normal carbon stars, as already indicated in previous studies

  9. Modules for Experiments in Stellar Astrophysics (MESA): Giant Planets, Oscillations, Rotation, and Massive Stars

    CERN Document Server

    Paxton, Bill; Arras, Phil; Bildsten, Lars; Brown, Edward F; Dotter, Aaron; Mankovich, Christopher; Montgomery, M H; Stello, Dennis; Timmes, F X; Townsend, Richard

    2013-01-01

    We substantially update the capabilities of the open source software package Modules for Experiments in Stellar Astrophysics (MESA), and its one-dimensional stellar evolution module, MESA Star. Improvements in MESA Star's ability to model the evolution of giant planets now extends its applicability down to masses as low as one-tenth that of Jupiter. The dramatic improvement in asteroseismology enabled by the space-based Kepler and CoRoT missions motivates our full coupling of the ADIPLS adiabatic pulsation code with MESA Star. This also motivates a numerical recasting of the Ledoux criterion that is more easily implemented when many nuclei are present at non-negligible abundances. This impacts the way in which MESA Star calculates semi-convective and thermohaline mixing. We exhibit the evolution of 3-8 Msun stars through the end of core He burning, the onset of He thermal pulses, and arrival on the white dwarf cooling sequence. We implement diffusion of angular momentum and chemical abundances that enable cal...

  10. MASSIVE: A Bayesian analysis of giant planet populations around low-mass stars

    Science.gov (United States)

    Lannier, J.; Delorme, P.; Lagrange, A. M.; Borgniet, S.; Rameau, J.; Schlieder, J. E.; Gagné, J.; Bonavita, M. A.; Malo, L.; Chauvin, G.; Bonnefoy, M.; Girard, J. H.

    2016-12-01

    Context. Direct imaging has led to the discovery of several giant planet and brown dwarf companions. These imaged companions populate a mass, separation and age domain (mass >1 MJup, orbits > 5 AU, age planetary formation models. Methods: We observed 58 young and nearby M-type dwarfs in L'-band with the VLT/NaCo instrument and used angular differential imaging algorithms to optimize the sensitivity to planetary-mass companions and to derive the best detection limits. We estimate the probability of detecting a planet as a function of its mass and physical separation around each target. We conduct a Bayesian analysis to determine the frequency of substellar companions orbiting low-mass stars, using a homogenous sub-sample of 54 stars. Results: We derive a frequency of for companions with masses in the range of 2-80 MJup, and % for planetary mass companions (2-14 MJup), at physical separations of 8 to 400 AU for both cases. Comparing our results with a previous survey targeting more massive stars, we find evidence that substellar companions more massive than 1 MJup with a low mass ratio Q with respect to their host star (Q 2 MJup might be independent from the mass of the host star.

  11. Evolution of thermally pulsing asymptotic giant branch stars - II. Dust production at varying metallicity

    Science.gov (United States)

    Nanni, Ambra; Bressan, Alessandro; Marigo, Paola; Girardi, Léo

    2013-09-01

    We present the dust ejecta of the new stellar models for the thermally pulsing asymptotic giant branch (TP-AGB) phase computed with the COLIBRI code. We use a formalism of dust growth coupled with a stationary wind for both M- and C-stars. In the original version of this formalism, the most efficient destruction process of silicate dust in M-giants is chemisputtering by H2 molecules. For these stars, we find that dust grains can only form at relatively large radial distances (r ˜ 5R*), where they cannot be efficiently accelerated, in agreement with other investigations. In the light of recent laboratory results, we also consider the alternative case that the condensation temperature of silicates is determined only by the competition between growth and free evaporation processes (i.e. no chemisputtering). With this latter approach we obtain dust condensation temperatures that are significantly higher (up to Tcond ˜ 1400 K) than those found when chemisputtering is included (Tcond ˜ 900 K), and in better agreement with condensation experiments. As a consequence, silicate grains can remain stable in inner regions of the circumstellar envelopes (r ˜ 2 R*), where they can rapidly grow and can be efficiently accelerated. With this modification, our models nicely reproduce the observed trend between terminal velocities and mass-loss rates of Galactic M-giants. For C-stars the formalism is based on the homogeneous growth scheme where the key role is played by the carbon over oxygen excess. The models reproduce fairly well the terminal velocities of Galactic stars and there is no need to invoke changes in the standard assumptions. At decreasing metallicity the carbon excess becomes more pronounced and the efficiency of dust formation increases. This trend could be in tension with recent observational evidence in favour of a decreasing efficiency, at decreasing metallicity. If confirmed by more observational data, it would indicate that either the amount of the carbon

  12. Does feedback help or hinder star formation? The effect of photoionization on star formation in giant molecular clouds

    Science.gov (United States)

    Shima, Kazuhiro; Tasker, Elizabeth J.; Habe, Asao

    2017-05-01

    We investigated the effect of photoionizing feedback inside turbulent star-forming clouds, comparing the resultant star formation in both idealized profiles and more realistic cloud structures drawn from a global galaxy simulation. We performed a series of numerical simulations that compared the effect of star formation alone, photoionization and photoionization plus supernovae feedback. In the idealized cloud, photoionization suppresses gas fragmentation at early times, resulting in the formation of more massive stars and an increase in the star formation efficiency. At later times, the dispersal of the dense gas causes the radiative feedback effect to switch from positive to negative as the star formation efficiency drops. In the cloud extracted from the global simulation, the initial cloud is heavily fragmented prior to the stellar-feedback beginning and is largely structurally unaffected by the late injection of radiation energy. The result is a suppression of the star formation. We conclude that the efficiency of feedback is heavily dependent on the gas structure, with negative feedback dominating when the density is high.

  13. Pulsating red giant stars in eccentric binary systems discovered from Kepler space-based photometry. A sample study and the analysis of KIC 5006817

    NARCIS (Netherlands)

    P.G. Beck; K. Hambleton; J. Vos; T. Kallinger; S. Bloemen; A. Tkachenko; R.A. García; R.H. Østensen; C. Aerts; D.W. Kurtz; J. De Ridder; S. Hekker; K. Pavlovski; S. Mathur; K. De Smedt; A. Derekas; E. Corsaro; B. Mosser; H. Van Winckel; D. Huber; P. Degroote; G.R. Davies; A. Prša; J. Debosscher; Y. Elsworth; P. Nemeth; L. Siess; V.S. Schmid; P.I. Pápics; B.L. de Vries; A.J. van Marle; P. Marcos-Arenal; A. Lobel

    2014-01-01

    Context. The unparalleled photometric data obtained by NASA’s Kepler Space Telescope has led to improved understanding of red giant stars and binary stars. Seismology allows us to constrain the properties of red giants. In addition to eclipsing binaries, eccentric non-eclipsing binaries that exhibit

  14. Testing the cores of first ascent red-giant stars using the period spacing of g modes

    CERN Document Server

    Lagarde, Nadège; Miglio, Andrea; Vrard, Mathieu; Mosser, Benoit

    2015-01-01

    In the context of the determination of stellar properties using asteroseismology, we study the influence of rotation and convective-core overshooting on the properties of red-giant stars. We used models in order to investigate the effects of these mechanisms on the asymptotic period spacing of gravity modes ($\\Delta \\Pi_1$) of red-giant stars that ignite He burning in degenerate conditions (M$\\lesssim$2.0 M$_{\\odot}$). We also compare the predictions of these models with Kepler observations. For a given $\\Delta\

  15. Spiral shocks, triggering of star formation and the velocity dispersion in Giant Molecular Clouds

    CERN Document Server

    Bonnell, I A; Robitaille, T R; Pringle, J E

    2006-01-01

    We present numerical simulations of the passage of clumpy gas through a galactic spiral shock and the subsequent formation of giant molecular clouds (GMCs). The spiral shock forms dense clouds while dissipating kinetic energy, producing regions that are locally gravitationally bound and collapse to form stars. The effect of the clumpiness of gas as it passes through the shock is to generate chaotic internal motions in the gas. The kinematics of these motions are found to agree with the observed velocity-dispersion/size relation found in star-forming regions. In contrast to the standard picture where continuously driven turbulence generates the density inhomogeneities in star-forming clouds, we find here that it is the clumpiness of the interstellar gas that produces the chaotic motions as it passes through the spiral shock and initiates the star formation process. The velocity dispersion can be understood as being due to the random mass loading of clumps as they converge in the spiral shock. In this model the...

  16. Discovery of a stripped red giant core in a bright eclipsing binary star

    CERN Document Server

    Maxted, P F L; Burleigh, M R; Collier-Cameron, A; Heber, U; Gänsicke, B T; Geier, S; Kupfer, T; Marsh, T R; Nelemans, G; O'Toole, S J; Østensen, R H; Smalley, B; West, R G; Bloemen, S

    2012-01-01

    We report the serendipitous discovery from WASP archive photometry of a binary star in which an apparently normal A-type star (J0247-25A) eclipses a smaller, hotter subdwarf star (J0247-25B). The kinematics of J0247-25A show that it is a blue-straggler member of the Galactic thick-disk. We present follow-up photometry and spectroscopy from which we derive approximate values for the mass, radius and luminosity for J0247-25B assuming that J0247-25A has the mass appropriate for a normal thick-disk star. We find that the properties of J0247-25B are well matched by models for a red giant stripped of its outer layers and currently in a shell hydrogen-burning stage. In this scenario, J0247-25B will go on to become a low mass white dwarf (M~0.25 solar masses) composed mostly of helium. J0247-25B can be studied in much greater detail than the handful of pre helium white dwarfs (pre-He-WD) identified to-date. These results have been published by Maxted et al., 2011. We also present a preliminary analysis of more recent...

  17. New tidal debris nearby the Sagittarius leading tail from the LAMOST DR2 M giant stars

    CERN Document Server

    Li, Jing; Carlin, Jeffrey L; Zhong, Jing; Hou, Jinliang; Deng, Licai; Newberg, Heidi Jo; Zhang, Yong; Hou, Yonghui; Wang, Yuefei

    2016-01-01

    We report two new tidal debris nearby the Sagittarius (Sgr) tidal stream in the north Galactic cap identified from the M giant stars in LAMOST DR2 data. The M giant stars with sky area of $210^\\circ<$\\Lambda$<290^\\circ$, distance of 10--20kpc, and [Fe/H]$<-0.75$ show clear bimodality in velocity distribution. We denote the two peaks as Vel-3+83 for the one within mean velocity of -3kms$^{-1}$ with respect to that of the well observed Sgr leading tail at the same $\\Lambda$ and Vel+162+26 for the other one with mean velocity of 162kms$^{-1}$ with respect to the Sgr leading tail. Although the projected $\\Lambda$--$V_{gar}$ relation of Vel-3+83 is very similar to the Sgr leading tail, the opposite trend in $\\Lambda$--distance relation against the Sgr leading tail suggests Vel-3+83 has a different 3D direction of motion with any branch of the simulated Sgr tidal stream from Law & Majewski. Therefore, we propose it to be a new tidal debris not related to the Sgr stream. Similarly, the another substruct...

  18. EK Eridani: the tip of the iceberg of giants which have evolved from magnetic Ap stars

    CERN Document Server

    Aurière, M; Petit, P; Charbonnel, C; Dintrans, B; Lignières, F; Roudier, T; Alecian, E; Donati, J F; Landstreet, J D; Wade, G A

    2008-01-01

    We observe the slowly-rotating, active, single giant, EK Eri, to study and infer the nature of its magnetic field directly. We used the spectropolarimeter NARVAL at the Telescope Bernard Lyot, Pic du Midi Observatory, and the Least Square Deconvolution method to create high signal-to-noise ratio Stokes V profiles. We fitted the Stokes V profiles with a model of the large-scale magnetic field. We studied the classical activity indicators, the CaII H and K lines, the CaII infrared triplet, and H\\alpha line. We detected the Stokes V signal of EK Eri securely and measured the longitudinal magnetic field Bl for seven individual dates spanning 60% of the rotational period. The measured longitudinal magnetic field of EK Eri reached about 100 G and was as strong as fields observed in RSCVn or FK Com type stars: this was found to be extraordinary when compared with the weak fields observed at the surfaces of slowly-rotating MS stars or any single red giant previously observed with NARVAL. From our modeling, we infer t...

  19. Carbon and Nitrogen Abundance Variations Among Red Giant Branch Stars in M10

    Science.gov (United States)

    Gerber, Jeffrey M.; Friel, Eileen D.; Vesperini, Enrico

    2016-06-01

    We present analysis of the CN and CH molecular band strengths derived for red giants in M10 as part of a first pilot study in the WIYN Indiana Northern Globular Survey (WINGS). This survey plans to use a combination of low-resolution spectroscopy taken with Hydra and wide-field SDSS filter photometry taken with the newly upgraded ODI to study the multiple populations and dynamics of a sample of Milky Way globular clusters. Our sample comes from the first in a series of observation runs conducted in Aug. 2014 using Hydra on the WIYN 3.5m telescope. CN and CH bands are measured for ~100 red giant branch stars and used to characterize the distribution in band strength and to derive carbon and nitrogen abundances by comparing observed band strengths to synthetic spectra produced by the Synthetic Spectrum Generator (SSG), which makes use of MARCS model atmospheres. Band strengths and CN abundances are used to investigate the distribution of stars in nitrogen normal and enhanced populations and to compare these to other ways of characterizing multiple stellar populations with other light elements (such as Na and O).

  20. MODELING KEPLER OBSERVATIONS OF SOLAR-LIKE OSCILLATIONS IN THE RED GIANT STAR HD 186355

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, C.; Jiang, B. W. [Department of Astronomy, Beijing Normal University, Beijing 100875 (China); Christensen-Dalsgaard, J.; Frandsen, S.; Kjeldsen, H.; Karoff, C. [Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Bedding, T. R.; Stello, D.; Huber, D. [Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, Sydney, NSW 2006 (Australia); Mosser, B. [LESIA, CNRS, Universite Pierre et Marie Curie, Universite Denis Diderot, Observatoire de Paris, 92195 Meudon (France); Demarque, P. [Department of Astronomy, Yale University, New Haven, CT 06520-8101 (United States); Fanelli, M. N.; Kinemuchi, K. [Bay Area Environmental Research Institute, NASA Ames Research Center, Moffett Field, CA 94035 (United States); Mullally, F., E-mail: jiangchen@mail.bnu.edu.cn [SETI Institute, NASA Ames Research Center, Moffett Field, CA 94035 (United States)

    2011-12-01

    We have analyzed oscillations of the red giant star HD 186355 observed by the NASA Kepler satellite. The data consist of the first five quarters of science operations of Kepler, which cover about 13 months. The high-precision time-series data allow us to accurately extract the oscillation frequencies from the power spectrum. We find that the frequency of the maximum oscillation power, {nu}{sub max}, and the mean large frequency separation, {Delta}{nu}, are around 106 and 9.4 {mu}Hz, respectively. A regular pattern of radial and non-radial oscillation modes is identified by stacking the power spectra in an echelle diagram. We use the scaling relations of {Delta}{nu} and {nu}{sub max} to estimate the preliminary asteroseismic mass, which is confirmed with the modeling result (M = 1.45 {+-} 0.05 M{sub Sun }) using the Yale Rotating stellar Evolution Code (YREC7). In addition, we constrain the effective temperature, luminosity, and radius from comparisons between observational constraints and models. A number of mixed l = 1 modes are also detected and taken into account in our model comparisons. We find a mean observational period spacing for these mixed modes of about 58 s, suggesting that this red giant branch star is in the shell hydrogen-burning phase.

  1. Asteroseismology of 19 low-luminosity red giant stars from Kepler

    CERN Document Server

    Hernandez, F Perez; Corsaro, E; Triana, S A; De Ridder, J

    2016-01-01

    Frequencies of acoustic and mixed modes in red giant stars are now determined with high precision thanks to the long continuous observations provided by the NASA Kepler mission. Here we consider the eigenfrequencies of nineteen low-luminosity red giant stars selected by Corsaro et al. (2015) for a detailed peak-bagging analysis. Our objective is to obtain stellar parameters by using individual mode frequencies and spectroscopic information. We use a forward modelling technique based on a minimization procedure combining the frequencies of the p modes, the period spacing of the dipolar modes, and the spectroscopic data. Consistent results between the forward modelling technique and values derived from the seismic scaling relations are found but the errors derived using the former technique are lower. The average error for log g is 0.002 dex, compared to 0.011 dex from the frequency of maximum power and 0.10 dex from the spectroscopic analysis. Relative errors in the masses and radii are on average 2 and 0.5 pe...

  2. Evolution of Thermally Pulsing Asymptotic Giant Branch Stars III. Dust production at supersolar metallicities

    CERN Document Server

    Nanni, Ambra; Marigo, Paola; Girardi, Léo

    2013-01-01

    We extend the formalism presented in our recent calculations of dust ejecta from the Thermally Pulsing Asymptotic Giant Branch (TP-AGB) phase, to the case of super-solar metallicity stars. The TP-AGB evolutionary models are computed with the COLIBRI code. We adopt our preferred scheme for dust growth. For M-giants, we neglect chemisputtering by H$_2$ molecules and, for C-stars we assume a homogeneous growth scheme which is primarily controlled by the carbon over oxygen excess. At super-solar metallicities, dust forms more efficiently and silicates tend to condense significantly closer to the photosphere (r~1.5 R$_*$) - and thus at higher temperatures and densities - than at solar and sub-solar metallicities (r~2-3 R$_*$). In such conditions, the hypothesis of thermal decoupling between gas and dust becomes questionable, while dust heating due to collisions plays an important role. The heating mechanism delays dust condensation to slightly outer regions in the circumstellar envelope. We find that the same mech...

  3. Evolution of Thermally Pulsing Asymptotic Giant Branch Stars II. Dust production at varying metallicity

    CERN Document Server

    Nanni, Ambra; Marigo, Paola; Girardi, Léo

    2013-01-01

    We present the dust ejecta of the new stellar models for the Thermally Pulsing Asymptotic Giant Branch (TP-AGB) phase computed with the COLIBRI code. We use a formalism of dust growth coupled with a stationary wind for both M and C-stars. In the original version of this formalism, the most efficient destruction process of silicate dust in M-giants is chemisputtering by H2 molecules. For these stars we find that dust grains can only form at relatively large radial distances (r~5 R*), where they cannot be efficiently accelerated, in agreement with other investigations. In the light of recent laboratory results, we also consider the alternative case that the condensation temperature of silicates is determined only by the competition between growth and free evaporation processes (i.e. no chemisputtering). With this latter approach we obtain dust condensation temperatures that are significantly higher (up to Tcond~1400 K) than those found when chemisputtering is included (Tcond~900 K), and in better agreement with...

  4. The Space Interferometry Mission Astrometric Grid Giant-Star Survey. I. Stellar Parameters and Radial Velocity Variability

    CERN Document Server

    Bizyaev, D; Cunha, K; Geisler, D; Gieren, W; Majewski, S R; Pardo, C D; Patterson, R J; Smith, V V; Suntzeff, N B; Arenas, Jose; Bizyaev, Dmitry; Cunha, Katia; Geisler, Doug; Gieren, Wolfgang; Majewski, Steven R.; Pardo, Cecilia Del; Patterson, Richard J.; Smith, Verne V.; Suntzeff, Nicholas B.

    2005-01-01

    We present results from a campaign of multiple epoch echelle spectroscopy of relatively faint (V = 9.5-13.5 mag) red giants observed as potential astrometric grid stars for the Space Interferometry Mission (SIM PlanetQuest). Data are analyzed for 775 stars selected from the Grid Giant Star Survey spanning a wide range of effective temperatures (Teff), gravities and metallicities. The spectra are used to determine these stellar parameters and to monitor radial velocity (RV) variability at the 100 m/s level. The degree of RV variation measured for 489 stars observed two or more times is explored as a function of the inferred stellar parameters. The percentage of radial velocity unstable stars is found to be very high -- about 2/3 of our sample. It is found that the fraction of RV-stable red giants (at the 100 m/s level) is higher among stars with Teff \\sim 4500 K, corresponding to the calibration-independent range of infrared colors 0.59 < (J-K_s)_0 < 0.73. A higher percentage of RV-stable stars is found ...

  5. Temperature-Dependent Giant Magnetoimpedance Effect in Amorphous Soft Magnets

    Science.gov (United States)

    Kurniawan, M.; Roy, R. K.; Panda, A. K.; Greve, D. W.; Ohodnicki, P.; McHenry, M. E.

    2014-12-01

    Giant magnetoimpedance (GMI)-based devices offer potential as next-generation low-cost, flexible, ultrasensitive sensors. They can be used in applications that include current sensors, field sensors, stress sensors, and others. Challenging applications involve operation at high temperatures, and therefore studies of GMI temperature dependence and performance of soft magnetic materials are needed. We present a high-temperature GMI study on an amorphous soft magnetic microwire from room temperature to 560°C. The GMI ratio was observed to be nearly constant at ˜86% at low temperatures and to decrease rapidly at ˜290°C, finally reaching a near-zero value at 500°C. The rapid drop in GMI ratio at 290°C is associated with a reduction in the long-range ferromagnetic order as measured by the spontaneous magnetization ( M) at the Curie temperature ( T c). We also correlated the impedance with the magnetic properties of the material. From room temperature to 290°C, the impedance was found to be proportional to the square root of the magnetization to magnetic anisotropy ratio. Lastly, M( T) has been fit using a Handrich-Kobe model, which describes the system with a modified Brillouin function and an asymmetrical distribution of exchange interactions. We infer that the structural fluctuations of the amorphous phase result in a relatively small asymmetry in the fluctuation parameters.

  6. Solar-like oscillations from the depths of the red-giant star KIC4351319 observed with Kepler

    DEFF Research Database (Denmark)

    di Mauro, M.P.; Cardini, D.; Catanzaro, G.

    2011-01-01

    , is in the hydrogen-shell-burning phase, with a mass of ∼1.3 M⊙, a radius of inline image and an age of ∼5.6 Gyr. The main parameters of this star have been determined with an unprecedented level of precision for a red-giant star, with uncertainties of 2 per cent for mass, 7 per cent for age, 1 per cent for radius...

  7. New models for the evolution of Post-Asymptotic Giant Branch stars and Central Stars of Planetary Nebulae

    CERN Document Server

    Bertolami, Marcelo M Miller

    2015-01-01

    The Post Asymptotic Giant Branch (AGB) phase is arguably one of the least understood phases of the evolution of low- and intermediate- mass stars. The two grids of models presently available are based on outdated micro- and macro-physics and do not agree with each other. We study the timescales of post-AGB and CSPNe in the context of our present understanding of the micro- and macro-physics of stars. We want to assess whether new post-AGB models, based on the latter improvements in TP-AGB modeling, can help to understand the discrepancies between observation and theory and within theory itself. We compute a grid of post-AGB full evolutionary sequences that include all previous evolutionary stages from the Zero Age Main Sequence to the White Dwarf phase. Models are computed for initial masses between 0.8 and 4 $M_\\odot$ and for a wide range of initial metallicities ($Z_0=$0.02, 0.01, 0.001, 0.0001), this allow us to provide post-AGB timescales and properties for H-burning post-AGB objects with masses in the re...

  8. Hot Bottom Burning in Asymptotic Giant Branch Stars and the Turbulent Convection Model

    Science.gov (United States)

    D'Antona, Francesca; Mazzitelli, Italo

    1996-10-01

    We investigate the effect of two different local turbulent convection models on the structure of intermediate-mass stars (IMSs, 3.5 Msun ≤ M ≤7 Msun) in the asymptotic giant branch (AGB) phase where, according to observations, they should experience hot bottom burning (HBB). Evolutionary models adopting either the mixing length theory (MLT) or the Canuto & Mazzitelli (CM) description of stellar convection are discussed. It is found that, while the MLT structures require some degree of tuning to achieve, at the bottom of the convective envelope, the large temperatures required for HBB, the CM structures spontaneously achieve these conditions. Since the observational evidence for HBB (existence of a class of very luminous, lithium-rich AGB stars in the Magellanic Clouds showing low 12C/13C ratios) is quite compelling, the above result provides a further, successful test for the CM convective model, in stellar conditions far from solar. With the aid of the CM model, we then explore a number of problems related to the late evolution of this class of objects, and give first results for (1) the luminosity evolution of IMSs in the AGB phase (core mass-luminosity relation and luminosity range in which HBB occurs) for Population I and Population II structures, (2) the minimum core mass for semidegenerate carbon ignition (˜1.05 Msun), (3) the relation between initial mass and final white dwarf (WD) mass (also based on some observational evidences about the upper AGB stars), and (4) the expected mass function of massive WDs. Confirmation of the theoretical framework could arise from an observational test: the luminosity function of AGB stars is expected to show a gap at Mbol ˜ -6, which would distinguish between the low-luminosity regime, in which AGBs become carbon stars, and the upper luminosities, at which they undergo HBB, have very low 12C/13C ratios, and become lithium rich.

  9. The Core Mass Growth and Stellar Lifetime of Thermally Pulsing Asymptotic Giant Branch Stars

    CERN Document Server

    Kalirai, Jason S; Tremblay, Pier-Emmanuel

    2013-01-01

    We establish new constraints on the intermediate-mass range of the initial-final mass relation by studying white dwarfs in four young star clusters, and apply the results to study the evolution of stars on the thermally pulsing asymptotic giant branch (TP-AGB). We show that the stellar core mass on the AGB grows rapidly from 10% to 30% for stars with $M_{\\rm initial}$ = 1.6 to 2.0 $M_\\odot$. At larger masses, the core-mass growth decreases steadily to $\\sim$10% at $M_{\\rm initial}$ = 3.4 $M_\\odot$. These observations are in excellent agreement with predictions from the latest TP-AGB evolutionary models in Marigo et al. (2013). We also compare to models with varying efficiencies of the third dredge-up and mass loss, and demonstrate that the process governing the growth of the core is largely the stellar wind, while the third dredge-up plays a secondary, but non-negligible role. Based on the new white dwarf measurements, we perform an exploratory calibration of the most popular mass-loss prescriptions in the li...

  10. Luminosities of Carbon-rich Asymptotic Giant Branch stars in the Milky Way

    CERN Document Server

    Guandalini, Roald

    2013-01-01

    Stars evolving along the Asymptotic Giant Branch can become Carbon-rich in the final part of their evolution. They replenish the inter-stellar medium with nuclear processed material via strong radiative stellar winds. The determination of the luminosity function of these stars, even if far from being conclusive, is extremely important to test the reliability of theoretical models. In particular, strong constraints on the mixing treatment and the mass-loss rate can be derived. We present an updated Luminosity Function of Galactic Carbon Stars obtained from a re-analysis of available data already published in previous papers. Starting from available near- and mid-infrared photometric data, we re-determine the selection criteria. Moreover, we take advantage from updated distance estimates and Period-Luminosity relations and we adopt a new formulation for the computation of Bolometric Corrections. This leads us to collect an improved sample of carbon-rich sources from which we construct an updated Luminosity Func...

  11. Regulation of star formation in giant galaxies by precipitation, feedback and conduction.

    Science.gov (United States)

    Voit, G M; Donahue, M; Bryan, G L; McDonald, M

    2015-03-12

    The Universe's largest galaxies reside at the centres of galaxy clusters and are embedded in hot gas that, if left undisturbed, would cool quickly and create many more new stars than are actually observed. Cooling can be regulated by feedback from accretion of cooling gas onto the central black hole, but requires an accretion rate finely tuned to the thermodynamic state of the hot gas. Theoretical models in which cold clouds precipitate out of the hot gas via thermal instability and accrete onto the black hole exhibit the necessary tuning. Recent observational evidence shows that the abundance of cold gas in the centres of clusters increases rapidly near the predicted threshold for instability. Here we report observations showing that this precipitation threshold extends over a large range in cluster radius, cluster mass and cosmic time. We incorporate the precipitation threshold into a framework of theoretical models for the thermodynamic state of hot gas in galaxy clusters. According to that framework, precipitation regulates star formation in some giant galaxies, while thermal conduction prevents star formation in others if it can compensate for radiative cooling and shut off precipitation.

  12. Heavy Element Nucleosynthesis in the Brightest Galactic Asymptotic Giant Branch stars

    CERN Document Server

    Karakas, Amanda I; Lugaro, Maria

    2012-01-01

    We present updated calculations of stellar evolutionary sequences and detailed nucleosynthesis predictions for the brightest asymptotic giant branch (AGB) stars in the Galaxy with masses between 5Msun to 9Msun, with an initial metallicity of Z =0.02 ([Fe/H] = 0.14). In our previous studies we used the Vassiliadis & Wood (1993) mass-loss rate, which stays low until the pulsation period reaches 500 days after which point a superwind begins. Vassiliadis & Wood noted that for stars over 2.5Msun the superwind should be delayed until P ~ 750 days at 5Msun. We calculate evolutionary sequences where we delay the onset of the superwind to pulsation periods of P ~ 700-800 days in models of M = 5, 6, and 7Msun. Post-processing nucleosynthesis calculations show that the 6 and 7Msun models produce the most Rb, with [Rb/Fe] ~ 1 dex, close to the average of most of the Galactic Rb-rich stars ([Rb/Fe] ~ 1.4 plus or minus 0.8 dex). Changing the rate of the 22Ne + alpha reactions results in variations of [Rb/Fe] as lar...

  13. Dynamics of the envelope of a rapidly rotating star or giant planet in gravitational contraction

    CERN Document Server

    Hypolite, Delphine

    2014-01-01

    We wish to understand the processes that control the fluid flows of a gravitationally contracting and rotating star or giant planet. We consider a spherical shell containing an incompressible fluid that is slowly absorbed by the core so as to mimick gravitational contraction. We also consider the effects of a stable stratification that may also modify the dynamics of a pre-main sequence star of intermediate mass. This simple model reveals the importance of both the Stewartson layer attached to the core and the boundary conditions met by the fluid at the surface of the object. In the case of a pre-main sequence star of intermediate mass where the envelope is stably stratified, shortly after the birth line, the spin-up flow driven by contraction overwhelms the baroclinic flow that would take place otherwise.This model also shows that for a contracting envelope, a self-similar flow of growing amplitude controls the dynamics. It suggests that initial conditions on the birth line are most probably forgotten. Final...

  14. On the survival of brown dwarfs and planets engulfed by their giant host star

    CERN Document Server

    Passy, Jean-Claude; De Marco, Orsola

    2012-01-01

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

  15. The UK Infrared Telescope M33 monitoring project. I. Variable red giant stars in the central square kiloparsec

    CERN Document Server

    Javadi, Atefeh; Mirtorabi, Mohammad Taghi

    2010-01-01

    We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). The main aim was to identify stars in the very final stage of their evolution, and for which the luminosity is more directly related to the birth mass than the more numerous less-evolved giant stars that continue to increase in luminosity. The most extensive dataset was obtained in the K-band with the UIST instrument for the central 4'x 4' (1 square kpc) - this contains the nuclear star cluster and inner disc. These data, taken during the period 2003-2007, were complemented by J- and H-band images. Photometry was obtained for 18,398 stars in this region; of these, 812 stars were found to be variable, most of which are Asymptotic Giant Branch (AGB) stars. Our data were matched to optical catalogues of variable stars and carbon stars, and to mid-infrared photometry from the Spitzer Space Telescope. In this first of a series of papers, we present the methodology of the va...

  16. The Penn State - Torun Centre for Astronomy Planet Search stars. II. Lithium abundance analysis of the Red Giant Clump sample

    CERN Document Server

    Adamow, M; Villaver, E; Wolszczan, A; Nowak, G

    2014-01-01

    Using the sample of 348 stars from the PennState-Torun Centre for Astronomy Planet Search, for which uniformly determined atmospheric parameters are available, with chemical abundances and rotational velocities presented here, we investigate various channels of Li enrichment in giants. Our work is based on the HET/HRS spectra. The A(Li) was determined from the 670.8nm line, while we use a more extended set of lines for alpha-elements abundances. In a series of K-S tests, we compare Li-rich giants with other stars in the sample. We also use available IR photometric and kinematical data in search for evidence of mass-loss. We investigate properties of the most Li-abundant giants in more detail by using multi-epoch precise radial velocities. We present Li and alpha-elements abundances, as well as vsini for 348 stars. We detected Li in 92 stars, of which 82 are giants. 11 of them show significant Li abundance A(Li)>1.4 and 7 of them are Li-overabundant objects, according to criterion of A(Li)>1.5 and their locati...

  17. The discovery of a planetary candidate around the evolved low-mass Kepler giant star HD 175370

    Science.gov (United States)

    Hrudková, M.; Hatzes, A.; Karjalainen, R.; Lehmann, H.; Hekker, S.; Hartmann, M.; Tkachenko, A.; Prins, S.; Van Winckel, H.; De Nutte, R.; Dumortier, L.; Frémat, Y.; Hensberge, H.; Jorissen, A.; Lampens, P.; Laverick, M.; Lombaert, R.; Pápics, P. I.; Raskin, G.; Sódor, Á.; Thoul, A.; Van Eck, S.; Waelkens, C.

    2017-01-01

    We report on the discovery of a planetary companion candidate with a minimum mass M sin i = 4.6 ± 1.0 MJupiter orbiting the K2 III giant star HD 175370 (KIC 007940959). This star was a target in our programme to search for planets around a sample of 95 giant stars observed with Kepler. This detection was made possible using precise stellar radial velocity measurements of HD 175370 taken over five years and four months using the coudé echelle spectrograph of the 2-m Alfred Jensch Telescope and the fibre-fed echelle spectrograph High Efficiency and Resolution Mercator Echelle Spectrograph of the 1.2-m Mercator Telescope. Our radial velocity measurements reveal a periodic (349.5 ± 4.5 d) variation with a semi-amplitude K = 133 ± 25 m s- 1, superimposed on a long-term trend. A low-mass stellar companion with an orbital period of ˜88 yr in a highly eccentric orbit and a planet in a Keplerian orbit with an eccentricity e = 0.22 are the most plausible explanation of the radial velocity variations. However, we cannot exclude the existence of stellar envelope pulsations as a cause for the low-amplitude radial velocity variations and only future continued monitoring of this system may answer this uncertainty. From Kepler photometry, we find that HD 175370 is most likely a low-mass red giant branch or asymptotic giant branch star.

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

    NARCIS (Netherlands)

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

    2014-01-01

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

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

    NARCIS (Netherlands)

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

    2014-01-01

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

  20. Solar-like oscillations from the depths of the red-giant star KIC 4351319 observed with Kepler

    NARCIS (Netherlands)

    di Mauro, M. P.; Cardini, D.; Catanzaro, G.; Ventura, R.; Barban, C.; Bedding, T.R.; Christensen-Dalsgaard, J.; de Ridder, J.; Hekker, S.; Huber, D.; Kallinger, T.; Miglio, A.; Montalban, J.; Mosser, B.; Stello, D.; Uytterhoeven, K.; Kinemuchi, K.; Kjeldsen, H.; Mullally, F.; Still, M.

    2011-01-01

    We present the results of the asteroseismic analysis of the red-giant star KIC 4351319 (TYC 3124-914-1), observed for 30 d in short-cadence mode with the Kepler satellite. The analysis has allowed us to determine the large and small frequency separations, Hz and Hz, respectively, and the frequency o

  1. A study of the effect of rotational mixing on massive stars evolution: surface abundances of Galactic O7-8 giant stars

    Science.gov (United States)

    Martins, F.; Simón-Díaz, S.; Barbá, R. H.; Gamen, R. C.; Ekström, S.

    2017-02-01

    Context. Massive star evolution remains only partly constrained. In particular, the exact role of rotation has been questioned by puzzling properties of OB stars in the Magellanic Clouds. Aims: Our goal is to study the relation between surface chemical composition and rotational velocity, and to test predictions of evolutionary models including rotation. Methods: We have performed a spectroscopic analysis of a sample of fifteen Galactic O7-8 giant stars. This sample is homogeneous in terms of mass, metallicity and evolutionary state. It is made of stars with a wide range of projected rotational velocities. Results: We show that the sample stars are located on the second half of the main sequence, in a relatively narrow mass range (25-40 M⊙). Almost all stars with projected rotational velocities above 100 km s-1 have N/C ratios about ten times the initial value. Below 100 km s-1 a wide range of N/C values is observed. The relation between N/C and surface gravity is well reproduced by various sets of models. Some evolutionary models including rotation are also able to consistently explain slowly rotating, highly enriched stars. This is due to differential rotation which efficiently transports nucleosynthesis products and allows the surface to rotate slower than the core. In addition, angular momentum removal by winds amplifies surface braking on the main sequence. Comparison of the surface composition of O7-8 giant stars with a sample of B stars with initial masses about four times smaller reveal that chemical enrichment scales with initial mass, as expected from theory. Conclusions: Although evolutionary models that include rotation face difficulties in explaining the chemical properties of O- and B-type stars at low metallicity, some of them can consistently account for the properties of main-sequence Galactic O stars in the mass range 25-40 M⊙.

  2. A kinematic analysis of the Giant star-forming Region of N11

    Science.gov (United States)

    Torres-Flores, Sergio; Barbá, Rodolfo; Maíz Apellániz, Jesús; Rubio, Mónica; Bosch, Guillermo

    2015-02-01

    In this work we present high resolution spectroscopic data of the giant star-forming region of N11, obtained with the GIRAFFE instrument at the Very Large Telescope. By using this data set, we find that most of the Hα emission lines profiles in this complex can be fitted by a single Gaussian, however, multiple emission line profiles can be observed in the central region of N11. By adding all the spectra, we derive the integrated Hα profile of this complex, which displays a width (σ) of about 12 km s-1 (corrected by instrumental and thermal width). We find that a single Gaussian fit on the integrated Hα profile leaves remaining wings, which can be fitted by a secondary broad Gaussian component. In addition, we find high velocity features, which spatially correlate with soft diffuse X-ray emission.

  3. 3D LTE spectral line formation with scattering in red giant stars

    CERN Document Server

    Hayek, W; Collet, R; Nordlund, Å

    2011-01-01

    We investigate the effects of coherent isotropic continuum scattering on the formation of spectral lines in local thermodynamic equilibrium (LTE) using 3D hydrodynamical and 1D hydrostatic model atmospheres of red giant stars. Continuum flux levels, spectral line profiles and curves of growth for different species are compared with calculations that treat scattering as absorption. Photons may escape from deeper, hotter layers through scattering, resulting in significantly higher continuum flux levels beneath a wavelength of 5000 A. The magnitude of the effect is determined by the importance of scattering opacity with respect to absorption opacity; we observe the largest changes in continuum flux at the shortest wavelengths and lowest metallicities; intergranular lanes of 3D models are more strongly affected than granules. Continuum scattering acts to increase the profile depth of LTE lines: continua gain more brightness than line cores due to their larger thermalization depth in hotter layers. We thus observe...

  4. A kinematic analysis of the Giant star-forming Region of N11

    CERN Document Server

    Torres-Flores, S; Apellániz, J Maíz; Rubio, M; Bosch, G

    2015-01-01

    In this work we present high resolution spectroscopic data of the giant star-forming region of N11, obtained with the GIRAFFE instrument at the Very Large Telescope. By using this data set, we find that most of the H$\\alpha$ emission lines profiles in this complex can be fitted by a single Gaussian, however, multiple emission line profiles can be observed in the central region of N11. By adding all the spectra, we derive the integrated H$\\alpha$ profile of this complex, which displays a width ($\\sigma$) of about 12 km s$^{-1}$ (corrected by instrumental and thermal width). We find that a single Gaussian fit on the integrated H$\\alpha$ profile leaves remaining wings, which can be fitted by a secondary broad Gaussian component. In addition, we find high velocity features, which spatially correlate with soft diffuse X-ray emission.

  5. A kinematic study of the giant star-forming region 30 Doradus

    CERN Document Server

    Torres-Flores, Sergio; Apellániz, Jesús Maíz; Rubio, Mónica; Bosch, Guillermo

    2012-01-01

    We present, for the first time, an optical spectroscopic data cube of the giant star-forming region 30 Doradus, obtained with the GIRAFFE on the VLT at Paranal Observatory. The main emission lines present in this data cube correspond to H{\\alpha}, [NII] 6548 {\\AA} and [NII] 6584 {\\AA}. By using this data set, we found that H{\\alpha} presents from simple to multiple profiles, which suggests that different physical mechanisms act in different ways on the excited gas in 30 Doradus. We found, at least, three unclassified large expanding structures. These structures correlate with peaks in the X-ray distribution. Given the excellent signal-to-noise ratio and the large spatial coverage of this data cube, we have studied in detail the kinematics of 30 Doradus, showing the importance of the small scale phenomena on the integrated properties of 30 Doradus.

  6. Radial Velocity Observations and Light Curve Noise Modeling Confirm That Kepler-91b is a Giant Planet Orbiting a Giant Star

    CERN Document Server

    Barclay, Thomas; Huber, Daniel; Foreman-Mackey, Daniel; Cochran, William D; MacQueen, Phillip J; Rowe, Jason F; Quintana, Elisa V

    2014-01-01

    Kepler-91b is a rare example of a transiting hot Jupiter around a red giant star, providing the possibility to study the formation and composition of hot Jupiters under different conditions compared to main-sequence stars. However, the planetary nature of Kepler-91b, which was confirmed using phase-curve variations by Lillo-Box et al., was recently called into question based on a re-analysis of Kepler data. We have obtained ground-based radial velocity observations from the Hobby-Eberly Telescope and unambiguously confirm the planetary nature of Kepler-91b by simultaneously modeling the Kepler and radial velocity data. The star exhibits temporally correlated noise due to stellar granulation which we model as a Gaussian Process. We hypothesize that it is this noise component that led previous studies to suspect Kepler-91b to be a false positive. Our work confirms the conclusions presented by Lillo-Box et al. that Kepler-91b is a 0.73+/-0.13 Mjup planet orbiting a red giant star.

  7. RADIAL VELOCITY OBSERVATIONS AND LIGHT CURVE NOISE MODELING CONFIRM THAT KEPLER-91b IS A GIANT PLANET ORBITING A GIANT STAR

    Energy Technology Data Exchange (ETDEWEB)

    Barclay, Thomas; Huber, Daniel; Rowe, Jason F.; Quintana, Elisa V. [NASA Ames Research Center, M/S 244-30, Moffett Field, CA 94035 (United States); Endl, Michael; Cochran, William D.; MacQueen, Phillip J. [McDonald Observatory, The University of Texas at Austin, Austin, TX 78712 (United States); Foreman-Mackey, Daniel [New York University, Center for Cosmology and Particle Physics, New York, NY 10003 (United States)

    2015-02-10

    Kepler-91b is a rare example of a transiting hot Jupiter around a red giant star, providing the possibility to study the formation and composition of hot Jupiters under different conditions compared to main-sequence stars. However, the planetary nature of Kepler-91b, which was confirmed using phase-curve variations by Lillo-Box et al., was recently called into question based on a re-analysis of Kepler data. We have obtained ground-based radial velocity observations from the Hobby-Eberly Telescope and unambiguously confirm the planetary nature of Kepler-91b by simultaneously modeling the Kepler and radial velocity data. The star exhibits temporally correlated noise due to stellar granulation which we model as a Gaussian Process. We hypothesize that it is this noise component that led previous studies to suspect Kepler-91b to be a false positive. Our work confirms the conclusions presented by Lillo-Box et al. that Kepler-91b is a 0.73 ± 0.13 M {sub Jup} planet orbiting a red giant star.

  8. Classification study of WISE infrared sources: identification of candidate asymptotic giant branch stars

    Institute of Scientific and Technical Information of China (English)

    Xun Tu; Zhong-Xiang Wang

    2013-01-01

    In the Wide-field Infrared Survey Explorer (WISE) all-sky source catalog there are 76 million mid-infrared point sources that were detected in the first three WISE bands and have association with only one 2MASS near-IR source within 3".We search for their identifications in the SIMBAD database and find 3.2 million identified sources.Based on these known sources,we establish three criteria for selecting candidate asymptotic giant branch (AGB) stars in the Galaxy,which are three defined zones in a color-color diagram,Galactic latitude |b| ≤ 20°,and "corrected" WISE third-band W3c≤ 11.Applying these criteria to the WISE+2MASS sources,1.37 million of them are selected.We analyze the WISE third-band W3 distribution of the selected sources,and further establish that W3≤8 is required in order to exclude a large fraction of normal stars from them.We therefore find 0.47 million candidate AGB stars in our Galaxy from the WISE source catalog.Using W3c,we estimate their distances and derive their Galactic distributions.The candidates are generally distributed around the Galactic center uniformly,with 68% (1-σ) of them within approximately 8 kpc.We discuss the idea that optical spectroscopy can be used to verify the C-rich AGB stars in our candidates,and thus a fraction of them (~10%) will be good targets for the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST)survey that is planned to start in fall of 2012.

  9. Hubble Space Telescope Constraints on the Winds and Astrospheres of Red Giant Stars

    Science.gov (United States)

    Wood, Brian E.; Müller, Hans-Reinhard; Harper, Graham M.

    2016-10-01

    We report on an ultraviolet spectroscopic survey of red giants observed by the Hubble Space Telescope, focusing on spectra of the Mg ii h and k lines near 2800 Å in order to study stellar chromospheric emission, winds, and astrospheric absorption. We focus on spectral types between K2 III and M5 III, a spectral type range with stars that are noncoronal, but possessing strong, chromospheric winds. We find a very tight relation between Mg ii surface flux and photospheric temperature, supporting the notion that all K2-M5 III stars are emitting at a basal flux level. Wind velocities (V w ) are generally found to decrease with spectral type, with V w decreasing from ˜40 km s-1 at K2 III to ˜20 km s-1 at M5 III. We find two new detections of astrospheric absorption, for σ Pup (K5 III) and γ Eri (M1 III). This absorption signature had previously only been detected for α Tau (K5 III). For the three astrospheric detections, the temperature of the wind after the termination shock (TS) correlates with V w , but is lower than predicted by the Rankine-Hugoniot shock jump conditions, consistent with the idea that red giant TSs are radiative shocks rather than simple hydrodynamic shocks. A full hydrodynamic simulation of the γ Eri astrosphere is provided to explore this further. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-13462. This paper also presents observations obtained with the Harlan J. Smith Telescope at McDonald Observatory of the University of Texas at Austin.

  10. Differential chemical abundance analysis of a 47 Tucanæ asymptotic giant branch star with respect to Arcturus

    Science.gov (United States)

    Worley, C. C.; Cottrell, P. L.; Freeman, K. C.; Wylie-de Boer, E. C.

    2009-12-01

    This study resolves a discrepancy in the abundance of Zr in the 47 Tucanæ asymptotic giant branch (AGB) star Lee 2525. This star was observed using the echelle spectrograph on the 2.3-m telescope at Siding Spring Observatory. The analysis was undertaken by calibrating Lee 2525 with respect to the standard giant star Arcturus. This work emphasizes the importance of using a standard star with stellar parameters comparable to the star under analysis rather than a calibration with respect to the Sun as in Koch & McWilliam. Systematic errors in the analysis process are then minimized due to the similarity in atmospheric structure between the standard and programme stars. The abundances derived for Lee 2525 were found to be in general agreement with the Brown & Wallerstein values except for Zr. In this study Zr has a similar enhancement ([Zr/Fe] = +0.51 dex) to another light s-process element, Y ([Y/Fe] = +0.53 dex), which reflects current theory regarding the enrichment of s-process elements by nuclear processes within AGB stars. This is contrary to the results of Brown & Wallerstein where Zr was underabundant ([Zr/Fe] = -0.51 dex) and Y was overabundant ([Y/Fe] = +0.50 dex) with respect to Fe.

  11. On the oxygen abundances of M 67 stars from the turn-off point through the red-giant branch

    CERN Document Server

    Takeda, Yoichi

    2014-01-01

    With an aim to examine whether the surface oxygen composition suffers any appreciable change due to evolution-induced mixing of nuclear-processed material in the envelope of red giants, abundance determinations for O/Fe/Ni based on the synthetic spectrum-fitting method were performed by using the moderate-dispersion spectra in the 7770-7792A region (comprising O I 7771-5, Fe I 7780, and Ni I 7788 lines) for 16 stars of the old open cluster M 67 in various evolutionary stages from the turn-off point through the red giant branch. We could not find any meaningful difference in the oxygen abundances between the non-giant group (T_eff > 5000 K) and the red-giant group (T_eff < 5000 K), which are almost consistent with each other on the average (despite that both have rather large dispersions of a few tenths dex caused by insufficient data quality), though only one giant star (S 1054) appears to show an exceptionally low O abundance and thus needs a more detailed study. This result may suggest that oxygen conten...

  12. Hubble Space Telescope Constraints on the Winds and Astrospheres of Red Giant Stars

    CERN Document Server

    Wood, Brian E; Harper, Graham M

    2016-01-01

    We report on an ultraviolet spectroscopic survey of red giants observed by the Hubble Space Telescope, focusing on spectra of the Mg II h & k lines near 2800 A in order to study stellar chromospheric emission, winds, and astrospheric absorption. We focus on spectral types between K2 III and M5 III, a spectral type range with stars that are noncoronal, but possessing strong, chromospheric winds. We find a very tight relation between Mg II surface flux and photospheric temperature, supporting the notion that all K2-M5 III stars are emitting at a basal flux level. Wind velocities (V_w) are generally found to decrease with spectral type, with V_w decreasing from ~40 km/s at K2 III to ~20 km/s at M5 III. We find two new detections of astrospheric absorption, for Sigma Pup (K5 III) and Gamma Eri (M1 III). This absorption signature had previously only been detected for Alpha Tau (K5 III). For the three astrospheric detections the temperature of the wind after the termination shock correlates with V_w, but is low...

  13. A giant stream of metal-rich stars in the halo of the galaxy M31

    CERN Document Server

    Ibata, R; Lewis, G; Ferguson, A; Tanvir, N R; Ibata, Rodrigo; Irwin, Michael; Lewis, Geraint; Ferguson, Annette; Tanvir, Nial

    2001-01-01

    The Milky Way is a cannibal. Recent observations have revealed the detritus of its digestion of the Sagittarius Dwarf and Magellanic Clouds, apparent as streams of gaseous and stellar debris littering the Galactic Halo. The analysis of this material has shown that the dark matter distribution within our own Galaxy is nearly spherical, and that much of the Galactic Halo is made up of cannibalized satellite galaxies. Yet it remains unclear whether such halo substructures really are as ubiquitous and as numerous as predicted by galaxy formation theory. Here we report the discovery of a giant stream of metal-rich stars within the halo of the Andromeda galaxy (M31), the Milky Way's nearest large neighbour. The source of this stream could be the dwarf galaxies M32 and NGC 205, close companions of M31, which have possibly lost a substantial amount of stars due to their tidal interactions with their large neighbour. These observations clearly demonstrate that the epoch of galaxy building still continues, albeit at a ...

  14. Mapping of the extinction in Giant Molecular Clouds using optical star counts

    CERN Document Server

    Cambresy, L

    1999-01-01

    This paper presents large scale extinction maps of most nearby Giant Molecular Clouds of the Galaxy (Lupus, rho-Ophiuchus, Scorpius, Coalsack, Taurus, Chamaeleon, Musca, Corona Australis, Serpens, IC 5146, Vela, Orion, Monoceros R1 and R2, Rosette, Carina) derived from a star count method using an adaptive grid and a wavelet decomposition applied to the optical data provided by the USNO-Precision Measuring Machine. The distribution of the extinction in the clouds leads to estimate their total individual masses M and their maximum of extinction. I show that the relation between the mass contained within an iso-extinction contour and the extinction is similar from cloud to cloud and allows the extrapolation of the maximum of extinction in the range 5.7 to 25.5 magnitudes. I found that about half of the mass is contained in regions where the visual extinction is smaller than 1 magnitude. The star count method used on large scale (about 250 square degrees) is a powerful and relatively straightforward method to es...

  15. Studying the kinematics of the giant star-forming region 30 Doradus. I. The data

    CERN Document Server

    Torres-Flores, S; Apellániz, J Maíz; Rubio, M; Bosch, G; Hénault-Brunet, V; Evans, C J

    2013-01-01

    We present high-quality VLT-FLAMES optical spectroscopy of the nebular gas in the giant star-forming region 30 Doradus. In this paper, the first of a series, we introduce our observations and discuss the main kinematic features of 30 Dor, as revealed by the spectroscopy of the ionized gas in the region. The primary data set consists of regular grid of nebular observations, which we used to produce a spectroscopic datacube of 30 Dor, centered on the massive star cluster R136 and covering a field-of-view of 10'x10'. The main emission lines present in the datacube are from Halpha and [NII]6548,6584. The Halpha emission-line profile varies across the region from simple single-peaked emission to complex, multiple-component profiles, suggesting that different physical mechanisms are acting on the excited gas. To analyse the gas kinematics we fit Gaussian profiles to the observed Halpha features. Unexpectedly, the narrowest Halpha profile in our sample lies close to the supernova remnant 30 Dor B. We present maps of...

  16. Some Like it Hot: The X-Ray Emission of The Giant Star YY Mensae

    CERN Document Server

    Audard, M; Güdel, M; Skinner, S L; Pallavicini, R; Mitra-Kraev, U; Audard, Marc; Telleschi, Alessandra; Guedel, Manuel; Skinner, Stephen L.; Pallavicini, Roberto; Mitra-Kraev, Urmila

    2004-01-01

    (Abridged abstract) We present an analysis of the X-ray emission of the rapidly rotating giant star YY Mensae observed by Chandra HETGS and XMM-Newton. Although no obvious flare was detected, the X-ray luminosity changed by a factor of two between the XMM-Newton and Chandra observations taken 4 months apart. The coronal abundances and the emission measure distribution have been derived from three different methods using optically thin collisional ionization equilibrium models. The abundances show an inverse first ionization potential (FIP) effect. We further find a high N abundance which we interpret as a signature of material processed in the CNO cycle. The corona is dominated by a very high temperature (20-40 MK) plasma, which places YY Men among the magnetically active stars with the hottest coronae. Lower temperature plasma also coexists, albeit with much lower emission measure. Line broadening is reported, which we interpret as Doppler thermal broadening, although rotational broadening due to X-ray emitt...

  17. Clear evidence for the presence of second-generation asymptotic giant branch stars in metal-poor Galactic globular clusters

    CERN Document Server

    Garcia-Hernandez, D A; Monelli, M; Cassisi, S; Stetson, P B; Zamora, O; Shetrone, M; Lucatello, S

    2015-01-01

    Galactic globular clusters (GCs) are known to host multiple stellar populations: a first generation with a chemical pattern typical of halo field stars and a second generation (SG) enriched in Na and Al and depleted in O and Mg. Both stellar generations are found at different evolutionary stages (e.g., the main-sequence turnoff, the subgiant branch, and the red giant branch). The non detection of SG asymptotic giant branch (AGB) stars in several metal-poor ([Fe/H] < -1) GCs suggests that not all SG stars ascend the AGB phase, and that failed AGB stars may be very common in metal-poor GCs. This observation represents a serious problem for stellar evolution and GC formation/evolution theories. We report fourteen SG-AGB stars in four metal-poor GCs (M 13, M 5, M 3, and M 2) with different observational properties: horizontal branch (HB) morphology, metallicity, and age. By combining the H-band Al abundances obtained by the APOGEE survey with ground-based optical photometry, we identify SG Al-rich AGB stars in...

  18. Asteroseismology of red giants from the first four months of Kepler data: Global oscillation parameters for 800 stars

    CERN Document Server

    Huber, D; Stello, D; Mosser, B; Mathur, S; Kallinger, T; Hekker, S; Elsworth, Y P; Buzasi, D L; De Ridder, J; Gilliland, R L; Kjeldsen, H; Chaplin, W J; Garcia, R A; Hale, S J; Preston, H L; White, T R; Borucki, W J; Christensen-Dalsgaard, J; Clarke, B D; Jenkins, J M; Koch, D

    2010-01-01

    We have studied solar-like oscillations in ~800 red-giant stars using Kepler long-cadence photometry. The sample includes stars ranging in evolution from the lower part of the red-giant branch to the Helium main sequence. We investigate the relation between the large frequency separation (Delta nu) and the frequency of maximum power (nu_max) and show that it is different for red giants than for main-sequence stars, which is consistent with evolutionary models and scaling relations. The distributions of nu_max and Delta nu are in qualitative agreement with a simple stellar population model of the Kepler field, including the first evidence for a secondary clump population characterized by M ~> 2 M_sun and nu_max ~ 40-110 muHz. We measured the small frequency separations delta nu_02 and delta nu_01 in over 400 stars and delta nu_03 in over 40. We present C-D diagrams for l=1, 2 and 3 and show that the frequency separation ratios delta nu_02/Delta nu and delta nu_01/Delta nu have opposite trends as a function of ...

  19. Evolution of thermally pulsing asymptotic giant branch stars - I. The COLIBRI code

    Science.gov (United States)

    Marigo, Paola; Bressan, Alessandro; Nanni, Ambra; Girardi, Léo; Pumo, Maria Letizia

    2013-09-01

    We present the COLIBRI code for computing the evolution of stars along the thermally pulsing asymptotic giant branch (TP-AGB) phase. Compared to purely synthetic TP-AGB codes, COLIBRI relaxes a significant part of their analytic formalism in favour of a detailed physics applied to a complete envelope model, in which the stellar structure equations are integrated from the atmosphere down to the bottom of the hydrogen-burning shell. This allows us to predict self-consistently: (i) the effective temperature, and more generally the convective envelope and atmosphere structures, correctly coupled to the changes in the surface chemical abundances and gas opacities; (ii) the conditions under which sphericity effects may significantly affect the atmospheres of giant stars; (iii) the core mass-luminosity relation and its possible break-down due to the occurrence of hot-bottom burning (HBB) in the most massive AGB stars, by taking properly into account the nuclear energy generation in the H-burning shell and in the deepest layers of the convective envelope; (iv) the HBB nucleosynthesis via the solution of a complete nuclear network (including the pp chains, and the CNO, NeNa and MgAl cycles) coupled to a diffusive description of mixing, suitable to follow also the synthesis of 7Li via the Cameron-Fowler beryllium transport mechanism; (v) the intershell abundances left by each thermal pulse via the solution of a complete nuclear network applied to a simple model of the pulse-driven convective zone (PDCZ); (vi) the onset and quenching of the third dredge-up, with a temperature criterion that is applied, at each thermal pulse, to the result of envelope integrations at the stage of the post-flash luminosity peak. At the same time, COLIBRI pioneers new techniques in the treatment of the physics of stellar interiors, not yet adopted in full TP-AGB models. It is the first evolutionary code ever to use accurate on-the-fly computation of the equation of state (EoS) for roughly 800

  20. The Stellar Mass Distribution in the Giant Star Forming Region NGC 346

    CERN Document Server

    Sabbi, E; Nota, A; Tosi, M; Gallagher, J; Smith, L J; Angeretti, L; Meixner, M; Oey, M S; Walterbos, R; Pasquali, A

    2007-01-01

    Deep F555W and F814W Hubble Space Telescope ACS images are the basis for a study of the present day mass function (PDMF) of NGC346, the largest active star forming region in the Small Magellanic Cloud (SMC). We find a PDMF slope of Gamma=-1.43+/-0.18 in the mass range 0.8-60 Mo, in excellent agreement with the Salpeter Initial Mass Function (IMF) in the solar neighborhood. Caveats on the conversion of the PDMF to the IMF are discussed. The PDMF slope changes, as a function of the radial distance from the center of the NGC 346 star cluster, indicating a segregation of the most massive stars. This segregation is likely primordial considering the young age (~3 Myr) of NGC346, and its clumpy structure which suggests that the cluster has likely not had sufficient time to relax. Comparing our results for NGC346 with those derived for other star clusters in the SMC and the Milky Way (MW), we conclude that, while the star formation process might depend on the local cloud conditions, the IMF does not seem to be affect...

  1. The mass-ratio and eccentricity distributions of barium and S stars, and red giants in open clusters

    Science.gov (United States)

    Van der Swaelmen, M.; Boffin, H. M. J.; Jorissen, A.; Van Eck, S.

    2017-01-01

    Context. A complete set of orbital parameters for barium stars, including the longest orbits, has recently been obtained thanks to a radial-velocity monitoring with the HERMES spectrograph installed on the Flemish Mercator telescope. Barium stars are supposed to belong to post-mass-transfer systems. Aims: In order to identify diagnostics distinguishing between pre- and post-mass-transfer systems, the properties of barium stars (more precisely their mass-function distribution and their period-eccentricity (P-e) diagram) are compared to those of binary red giants in open clusters. As a side product, we aim to identify possible post-mass-transfer systems among the cluster giants from the presence of s-process overabundances. We investigate the relation between the s-process enrichment, the location in the (P-e) diagram, and the cluster metallicity and turn-off mass. Methods: To invert the mass-function distribution and derive the mass-ratio distribution, we used the method pioneered by Boffin et al. (1992) that relies on a Richardson-Lucy deconvolution algorithm. The derivation of s-process abundances in the open-cluster giants was performed through spectral synthesis with MARCS model atmospheres. Results: A fraction of 22% of post-mass-transfer systems is found among the cluster binary giants (with companion masses between 0.58 and 0.87 M⊙, typical for white dwarfs), and these systems occupy a wider area than barium stars in the (P-e) diagram. Barium stars have on average lower eccentricities at a given orbital period. When the sample of binary giant stars in clusters is restricted to the subsample of systems occupying the same locus as the barium stars in the (P-e) diagram, and with a mass function compatible with a WD companion, 33% (=4/12) show a chemical signature of mass transfer in the form of s-process overabundances (from rather moderate - about 0.3 dex - to more extreme - about 1 dex). The only strong barium star in our sample is found in the cluster with

  2. Excitation-energy dependence of the giant dipole resonance width

    Science.gov (United States)

    Enders, G.; Berg, F. D.; Hagel, K.; Kühn, W.; Metag, V.; Novotny, R.; Pfeiffer, M.; Schwalb, O.; Charity, R. J.; Gobbi, A.; Freifelder, R.; Henning, W.; Hildenbrand, K. D.; Holzmann, R.; Mayer, R. S.; Simon, R. S.; Wessels, J. P.; Casini, G.; Olmi, A.; Stefanini, A. A.

    1992-07-01

    High-energy γ rays have been measured in coincidence with heavy fragents in deeply inelastic reactions of 136Xe+48Ti at 18.5 MeV/nucleon. The giant dipole resonance (GDR) strength function is deduced from an analysis of the photon spectra within the statistical model. The GDR width Γ is studied as a function of the fragment excitation energy E*. A saturation at about Γ=10 MeV is observed for E*/A>=1.0 MeV/nucleon.

  3. Excitation-energy dependence of the giant dipole resonance width

    Energy Technology Data Exchange (ETDEWEB)

    Enders, G.; Berg, F.D.; Hagel, K.; Kuehn, W.; Metag, V.; Novotny, R.; Pfeiffer, M.; Schwalb, O. (II. Physikalisches Institut, Universitaet, Giessen, Giessen (Germany)); Charity, R.J.; Gobbi, A.; Freifelder, R.; Henning, W.; Hildenbrand, K.D.; Holzmann, R.; Mayer, R.S.; Simon, R.S.; Wessels, J.P. (Gesellschaft fuer Schwerionenforschung Darmstadt, Darmstadt (Germany)); Casini, G.; Olmi, A.; Stefanini, A.A. (Istituto Nazionale di Fisica Nucleare and University of Florence, Florence (Italy))

    1992-07-13

    High-energy {gamma} rays have been measured in coincidence with heavy fragents in deeply inelastic reactions of {sup 136}Xe+{sup 48}Ti at 18.5 MeV/nucleon. The giant dipole resonance (GDR) strength function is deduced from an analysis of the photon spectra within the statistical model. The GDR width {Gamma} is studied as a function of the fragment excitation energy {ital E}{sup *}. A saturation at about {Gamma}=10 MeV is observed for {ital E}{sup *}/{ital A}{ge}1.0 MeV/nucleon.

  4. Influence of Stellar Multiplicity On Planet Formation. III. Adaptive Optics Imaging of Kepler Stars With Gas Giant Planets

    CERN Document Server

    Wang, Ji; Horch, Elliott P; Xie, Ji-Wei

    2015-01-01

    As hundreds of gas giant planets have been discovered, we study how these planets form and evolve in different stellar environments, specifically in multiple stellar systems. In such systems, stellar companions may have a profound influence on gas giant planet formation and evolution via several dynamical effects such as truncation and perturbation. We select 84 Kepler Objects of Interest (KOIs) with gas giant planet candidates. We obtain high-angular resolution images using telescopes with adaptive optics (AO) systems. Together with the AO data, we use archival radial velocity data and dynamical analysis to constrain the presence of stellar companions. We detect 59 stellar companions around 40 KOIs for which we develop methods of testing their physical association. These methods are based on color information and galactic stellar population statistics. We find evidence of suppressive planet formation within 20 AU by comparing stellar multiplicity. The stellar multiplicity rate for planet host stars is 0$^{+5...

  5. Barium isotopic composition of mainstream silicon carbides from Murchison: Constraints for s-process nucleosynthesis in asymptotic giant branch stars

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Nan; Davis, Andrew M.; Pellin, Michael J.; Dauphas, Nicolas [Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637 (United States); Savina, Michael R. [Chicago Center for Cosmochemistry, Chicago, IL 60637 (United States); Gallino, Roberto; Bisterzo, Sara [Dipartimento di Fisica, Università di Torino, I-10125 Torino (Italy); Straniero, Oscar; Cristallo, Sergio [INAF–Osservatorio Astronomico di Collurania, via Maggini snc, I-64100 Teramo (Italy); Gyngard, Frank [Laboratory for Space Sciences, Washington University, St. Louis, MO 63130 (United States); Willingham, David G. [Materials Science Division, Argonne National Laboratory, Argonne, IL 60439 (United States); Pignatari, Marco [Department of Physics, University of Basel, Basel CH-4056 (Switzerland); Herwig, Falk, E-mail: lnsmile@uchicago.edu [Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P5C2 (Canada)

    2014-05-01

    We present barium, carbon, and silicon isotopic compositions of 38 acid-cleaned presolar SiC grains from Murchison. Comparison with previous data shows that acid washing is highly effective in removing barium contamination. Strong depletions in δ({sup 138}Ba/{sup 136}Ba) values are found, down to –400‰, which can only be modeled with a flatter {sup 13}C profile within the {sup 13}C pocket than is normally used. The dependence of δ({sup 138}Ba/{sup 136}Ba) predictions on the distribution of {sup 13}C within the pocket in asymptotic giant branch (AGB) models allows us to probe the {sup 13}C profile within the {sup 13}C pocket and the pocket mass in AGB stars. In addition, we provide constraints on the {sup 22}Ne(α, n){sup 25}Mg rate in the stellar temperature regime relevant to AGB stars, based on δ({sup 134}Ba/{sup 136}Ba) values of mainstream grains. We found two nominally mainstream grains with strongly negative δ({sup 134}Ba/{sup 136}Ba) values that cannot be explained by any of the current AGB model calculations. Instead, such negative values are consistent with the intermediate neutron capture process (i process), which is activated by the very late thermal pulse during the post-AGB phase and characterized by a neutron density much higher than the s process. These two grains may have condensed around post-AGB stars. Finally, we report abundances of two p-process isotopes, {sup 130}Ba and {sup 132}Ba, in single SiC grains. These isotopes are destroyed in the s process in AGB stars. By comparing their abundances with respect to that of {sup 135}Ba, we conclude that there is no measurable decay of {sup 135}Cs (t {sub 1/2} = 2.3 Ma) to {sup 135}Ba in individual SiC grains, indicating condensation of barium, but not cesium into SiC grains before {sup 135}Cs decayed.

  6. HST Studies of the Chromospheres, Wind, and Mass-Loss Rates of Cool Giant and Supergiant Stars

    Science.gov (United States)

    Carpenter, Kenneth G.

    2000-01-01

    UV spectra of K-M giant and supergiant stars and of carbon stars have been acquired with the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST). These spectra have been used to measure chromospheric flow and turbulent velocities, study the acceleration of their stellar winds, acquire constraints on their outer atmospheric structure, and enable estimates of their mass-loss rates. Results from our observations of the giant stars Gamma Dra (K5 III hybrid), Alpha Tau (K5 III), Gamma Cru (M3.4 III), Mu Gem (M3 IIIab), and 30 Her (MG III), the supergiants Alpha Ori (M2 Iab) and Lambda Vel (K5 Ib), and the carbon stars TX Psc (NO; C6,2) and TW Hor (NO; C7,2) will be summarized and compared. The high resolution and wavelength accuracy of these data have allowed the direct measurement of the acceleration of the stellar winds in the chromospheres of several of these stars (from initial velocities of 3-9 km/s to upper velocities of 15-25 km/s) and of the chromospheric macroturbulence (-25-35 km/s). The high signal-to-noise and large dynamic range of these spectra have allowed the detection and identification of numerous new emission features, including weak C IV emission indicative of hot transition-region plasma in the non-coronal giant Alpha Tau, many new fluorescent lines of Fe II, and the first detection of fluorescent molecular hydrogen emission and of Ca II recombination lines in the UV spectrum of a giant star. The UV spectrum of two carbon stars have been studied with unprecedented resolution and reveal extraordinarily complicated Mg II lines nearly smothered by circumstellar absorptions. Finally, comparison of synthetic UV emission line profiles computed with the Lamers et al. (1987) Sobolev with Exact Integration (SEI) code with observations of chromospheric emission lines overlain with wind absorption features provides estimates of the mass-loss rates for four of these stars.

  7. Revisiting the microlensing event OGLE 2012-BLG-0026: A solar mass star with two cold giant planets

    CERN Document Server

    Beaulieu, J P; Batista, V; Fukui, A; Marquette, J -B; Brillant, S; Cole, A A; Rogers, L A; Sumi, T; Abe, F; Bhattacharya, A; Koshimoto, N; Suzuki, D; Tristram, P J; Han, C; Gould, A; Pogge, R; Yee, J

    2016-01-01

    Two cold, gas giant planets orbiting a G-type main sequence star in the galactic disk have previously been discovered in the high magnification microlensing event OGLE-2012-BLG-0026 (Han et al. 2013). Here we present revised host star flux measurements and a refined model for the two-planet system using additional light curve data. We performed high angular resolution adaptive optics imaging with the Keck and Subaru telescopes at two epochs while the source star was still amplified. We detected the lens flux, $H=16.39 \\pm 0.08$. The lens, a disk star, is brighter than predicted from the modeling in the original study. We revisited the light curve modeling using additional photometric data from the B\\&C telescope in New Zealand and CTIO 1.3m H band light curve. We then include the Keck and Subaru adaptive optic observation constraints. The system is composed of a $\\sim 4-9$ Gyr lens star of $\\rm M_{lens} = 1.06 \\pm 0.05~\\,M_\\odot$ at a distance of $\\rm D_{lens} = 4.0 \\pm 0.3~$kpc, orbited by two giant plan...

  8. TAPAS IV. TYC 3667-1280-1 b - the most massive red giant star hosting a warm Jupiter

    CERN Document Server

    Niedzielski, A; Nowak, G; Adamów, M; Maciejewski, G; Kowalik, K; Wolszczan, A; Deka-Szymankiewicz, B; Adamczyk, M

    2016-01-01

    We present the latest result of the TAPAS project that is devoted to intense monitoring of planetary candidates that are identified within the PennState-Toru\\'n planet search. We aim to detect planetary systems around evolved stars to be able to build sound statistics on the frequency and intrinsic nature of these systems, and to deliver in-depth studies of selected planetary systems with evidence of star-planet interaction processes. The paper is based on precise radial velocity measurements: 13 epochs collected over 1920 days with the Hobby-Eberly Telescope and its High-Resolution Spectrograph, and 22 epochs of ultra-precise HARPS-N data collected over 961 days. We present a warm-Jupiter ($T_{eq}=1350 K$, $m_{2} sin i=5.4\\pm$0.4$M_{J}$) companion with an orbital period of 26.468 days in a circular ($e=0.036$) orbit around a giant evolved ($\\log g=3.11\\pm0.09$, $R=6.26\\pm0.86R_{\\odot}$) star with $M_{\\star}=1.87\\pm0.17M_{\\odot}$. This is the most massive and oldest star found to be hosting a close-in giant p...

  9. Chemical Abundances for Seven Giant Stars in M68 (NGC 4590) A Globular Cluster with Abnormal Silicon and Titanium Abundances

    CERN Document Server

    Lee, J W; Habgood, M J; Lee, Jae-Woo; Carney, Bruce W.

    2004-01-01

    We present a detailed chemical abundance study of seven giant stars in M68 including six red giants and one post-AGB star. We find significant differences in the gravities determined using photometry and those obtained from ionization balance, which suggests that non-LTE effects are important for these low-gravity, metal-poor stars. We adopt an iron abundance using photometric gravities and Fe II lines to minimize those effects, finding [Fe/H] = -2.16 +/- 0.02. For element-to-iron ratios,we rely on neutral lines vs. Fe I and ionized lines vs. FeII (except for [O/Fe]) to also minimize non-LTE effects. We find variations in the abundances of sodium among the program stars. However, there is no correlation (or anti-correlation) with the oxygen abundances. Further, the post-AGB star has a normal (low) abundance of sodium. Both of these facts add further support to the idea that the variations seen among some light elements within individual globular clusters arises from primordial variations, and not from deep mi...

  10. The Large Magellanic Cloud as a laboratory for Hot Bottom Burning in massive Asymptotic Giant Branch stars

    CERN Document Server

    Ventura, P; Dell'Agli, F; Boyer, M L; García-Hernández, D A; Di Criscienzo, M; Schneider, R

    2015-01-01

    We use Spitzer observations of the rich population of Asymptotic Giant Branch stars in the Large Magellanic Cloud (LMC) to test models describing the internal structure and nucleosynthesis of the most massive of these stars, i.e. those with initial mass above $\\sim 4M_{\\odot}$. To this aim, we compare Spitzer observations of LMC stars with the theoretical tracks of Asymptotic Giant Branch models, calculated with two of the most popular evolution codes, that are known to differ in particular for the treatment of convection. Although the physical evolution of the two models are significantly different, the properties of dust formed in their winds are surprisingly similar, as is their position in the colour-colour (CCD) and colour-magnitude (CMD) diagrams obtained with the Spitzer bands. This model independent result allows us to select a well defined region in the ($[3.6]-[4.5], [5.8]-[8.0]$) plane, populated by AGB stars experiencing Hot Bottom Burning, the progeny of stars with mass $M\\sim 5.5M_{\\odot}$. This...

  11. Fine-tuning the basic forces of nature through the triple-alpha process in red giant stars

    CERN Document Server

    Csoto, A; Schlattl, H; Csoto, Attila; Oberhummer, Heinz; Schlattl, Helmut

    2001-01-01

    We show that the synthesis of carbon and oxygen through the triple-alpha process in red giant stars is extremely sensitive to the fine details of the nucleon-nucleon (N-N) interaction. A +/-0.5% change in the strength of the N-N force would reduce either the carbon or oxygen abundance by as much as a factor of 30-1000. This result may be used to constrain some fundamental parameters of the Standard Model.

  12. THE EFFECTS OF ROTATION ON s-PROCESS NUCLEOSYNTHESIS IN ASYMPTOTIC GIANT BRANCH STARS

    Energy Technology Data Exchange (ETDEWEB)

    Piersanti, L.; Cristallo, S.; Straniero, O., E-mail: piersanti@oa-teramo.inaf.it [INAF-Osservatorio Astronomico di Collurania, via Maggini snc, I-64100 Teramo (Italy)

    2013-09-10

    In this paper, we analyze the effects induced by rotation on low-mass asymptotic giant branch stars. We compute two sets of models, M = 2.0 M{sub Sun} at [Fe/H] = 0 and M = 1.5 M{sub Sun} at [Fe/H] = -1.7, by adopting main-sequence rotation velocities in the range 0-120 km s{sup -1}. At high metallicity, we find that the Goldreich-Schubert-Fricke instability, active at the interface between the convective envelope and the rapid rotating core, contaminates the {sup 13}C-pocket (the major neutron source) with {sup 14}N (the major neutron poison), thus reducing the neutron flux available for the synthesis of heavy elements. As a consequence, the yields of heavy-s elements (Ba, La, Nd, Sm) and, to a lesser extent, those of light-s elements (Sr, Y, Zr) decrease with increasing rotation velocities up to 60 km s{sup -1}. However, for larger initial rotation velocities, the production of light-s and, to a lesser extent, that of heavy-s, begins again to increase, due to mixing induced by meridional circulations. At low metallicity, the effects of meridional circulations are important even at rather low rotation velocity. The combined effect of the Goldreich-Schubert-Fricke instability and meridional circulations determines an increase of light-s and, to a lesser extent, heavy-s elements, while lead is strongly reduced. For both metallicities, the rotation-induced instabilities active during the interpulse phase reduce the neutron-to-seed ratio, so that the spectroscopic indexes [hs/ls] and [Pb/hs] decrease by increasing the initial rotation velocity. Our analysis suggests that rotation could explain the spread in the s-process indexes, as observed in s-process enriched stars at different metallicities.

  13. Evolution of Thermally Pulsing Asymptotic Giant Branch Stars V: Constraining the Mass Loss and Lifetimes of Intermediate Mass, Low Metallicity AGB Stars

    CERN Document Server

    Rosenfield, Philip; Girardi, Léo; Dalcanton, Julianne J; Bressan, Alessandro; Williams, Benjamin F; Dolphin, Andrew

    2016-01-01

    Thermally-Pulsing Asymptotic Giant Branch (TP-AGB) stars are relatively short lived (less than a few Myr), yet their cool effective temperatures, high luminosities, efficient mass-loss and dust production can dramatically effect the chemical enrichment histories and the spectral energy distributions of their host galaxies. The ability to accurately model TP-AGB stars is critical to the interpretation of the integrated light of distant galaxies, especially in redder wavelengths. We continue previous efforts to constrain the evolution and lifetimes of TP-AGB stars by modeling their underlying stellar populations. Using Hubble Space Telescope (HST) optical and near-infrared photometry taken of 12 fields of 10 nearby galaxies imaged via the ACS Nearby Galaxy Survey Treasury and the near-infrared HST/SNAP follow-up campaign, we compare the model and observed TP-AGB luminosity functions as well as the number ratio of TP-AGB to red giant branch stars. We confirm the best-fitting mass-loss prescription, introduced by...

  14. Probing interstellar extinction near the 30 Doradus nebula with red giant stars

    CERN Document Server

    De Marchi, Guido; Girardi, Leo

    2013-01-01

    We have studied the interstellar extinction in a field of 3' x 3' located about 6' SW of 30 Doradus in the Large Magellanic Cloud (LMC). Hubble Space Telescope observations in the U, B, V, I and Halpha bands reveal patchy extinction in this field. The colour-magnitude diagram (CMD) shows an elongated stellar sequence, almost parallel to the main sequence (MS), which is in reality made up of stars of the red giant clump (RC) spread across the CMD by the uneven levels of extinction in this region. Since these objects are all at the same distance from us and share very similar physical properties, we can derive quantitatively both the extinction law in the range 3000 - 8000 Angstrom and the absolute extinction towards about 100 objects, setting statistically significant constraints on the dust grains properties in this area. We find an extinction curve considerably flatter than the standard Galactic one and than those obtained before for the LMC. The derived value of Rv = 5.6 +/- 0.3 implies that in this region ...

  15. Chemical analysis of giant stars in the young open cluster NGC 3114

    CERN Document Server

    Santrich, O J Katime; Drake, N A

    2013-01-01

    Context: Open clusters are very useful targets for examining possible trends in galactocentric distance and age, especially when young and old open clusters are compared. Aims: We carried out a detailed spectroscopic analysis to derive the chemical composition of seven red giants in the young open cluster NGC 3114. Abundances of C, N, O, Li, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, and Nd were obtained, as well as the carbon isotopic ratio. Methods: The atmospheric parameters of the studied stars and their chemical abundances were determined using high-resolution optical spectroscopy. We employed the local-thermodynamic-equilibrium model atmospheres of Kurucz and the spectral analysis code MOOG. The abundances of the light elements were derived using the spectral synthesis technique. Results: We found that NGC 3114 has a mean metallicity of [Fe/H] = -0.01+/-0.03. The isochrone fit yielded a turn-off mass of 4.2 Msun. The [N/C] ratio is in good agreement with the models predicted by first dredge-up. We f...

  16. VLTI/AMBER observations of cold giant stars: atmospheric structures and fundamental parameters

    CERN Document Server

    Arroyo-Torres, B; Marcaide, J M; Wittkowski, M; Guirado, J C; Hauschildt, P H; Quirrenbach, A; Fabregat, J

    2014-01-01

    The main goal of this research is to determine the angular size and the atmospheric structures of cool giant stars and to compare them with hydrostatic stellar model atmospheres, to estimate the fundamental parameters, and to obtain a better understanding of the circumstellar environment. We conducted spectro-interferometric observations of epsilon Oct, beta Peg, NU Pav, and psi Peg in the near-infrared K band (2.13-2.47 microm), and gamma Hya (1.9-2.47 microm) with the VLTI/AMBER instrument at medium spectral resolution. To obtain the fundamental parameters, we compared our data with hydrostatic atmosphere models (PHOENIX). We estimated the Rosseland angular diameters of epsilon Oct, beta Peg, NU Pav, psi Peg, and gamma Hya. Together with distances and bolometric fluxes, we estimated radii, effective temperatures, and luminosities of our targets. In the beta Peg visibility, we observed a molecular layer of CO with a size similar to that modeled with PHOENIX. However, there is an additional slope in absorptio...

  17. A Comparison of Copper Abundances in Globular Cluster and Halo Field Giant Stars

    CERN Document Server

    Simmerer, J; Ivans, I I; Kraft, R P; Shetrone, M D; Smith, V V; Simmerer, Jennifer; Sneden, Christopher; Ivans, Inese I.; Kraft, Robert P.; Shetrone, Matthew D.; Smith, Verne V.

    2003-01-01

    We derive [Cu/Fe] for 117 giant stars in ten globular clusters (M3, M4, M5, M10, M13, M15, M71, NGC 7006, NCG 288, and NGC 362) and find that globular cluster Cu abundances appear to follow [Cu/Fe] trends found in the field. This result is interesting in light of recent work which indicates that the globular cluster Omega Centauri shows no trend in [Cu/Fe] with [Fe/H] over the abundance range -2.0 <[Fe/H]< -0.8. Of particular interest are the two clusters M4 and M5. While at a similar metallicity ([Fe/H] ~- 1.2), they differ greatly in some elemental abundances: M4 is largely overabundant in Si, Ba, and La compared to M5. We find that it is also overabundant in Cu with respect to M5, though this overabundance is in accord with [Cu/Fe] ratios found in the field.

  18. Studies of the Long Secondary Periods in Pulsating Red Giants. II. Lower-Luminosity Stars

    CERN Document Server

    Percy, John R

    2016-01-01

    We have used AAVSO visual and photoelectric V data, and the AAVSO time-series package VSTAR and the Lomb-Scargle time-series algorithm to determine improved pulsation periods, "long secondary periods" (LSPs). and their amplitudes in 51 shorter-period pulsating red giants in the AAVSO photoelectric photometry program, and the AAVSO LPV (long period variable) binocular program. As is well known, radial pulsation becomes detectable in red giants at about spectral type M0, with periods of about 20 days. We find that the LSP phenomenon is also first detectable at about M0. Pulsation and LSP amplitudes increase from near zero to about 0.1 at pulsation periods of about 100 days. At longer periods, the pulsation amplitudes continue to increase, but the LSP amplitudes are generally between 0.1 and 0.2 on average. The ratios of LSP to pulsation period cluster around 5 and 10, presumably depending on whether the pulsation period is the fundamental or first overtone. The pulsation and LSP phase curves are generally close...

  19. Detailed abundances for a large sample of giant stars in the globular cluster 47 Tucanae (NGC 104)

    Energy Technology Data Exchange (ETDEWEB)

    Cordero, M. J.; Pilachowski, C. A. [Astronomy Department, Indiana University Bloomington, Swain West 319, 727 East 3rd Street, Bloomington, IN 47405-7105 (United States); Johnson, C. I. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-15, Cambridge, MA 02138 (United States); McDonald, I.; Zijlstra, A. A. [Jodrell Bank Centre for Astrophysics, Alan Turing Building, Manchester M13 9PL (United Kingdom); Simmerer, J., E-mail: majocord@indiana.edu, E-mail: catyp@astro.indiana.edu, E-mail: cjohnson@cfa.harvard.edu, E-mail: mcdonald@jb.man.ac.uk, E-mail: albert.zijlstra@manchester.ac.uk, E-mail: jennifer@physics.utah.edu [University of Utah, Physics and Astronomy, 115 South 1400 East #201, Salt Lake City, UT 84112-0830 (United States)

    2014-01-01

    47 Tuc is an ideal target to study chemical evolution and globular cluster (GC) formation in massive more metal-rich GCs, as it is the closest massive GC. We present chemical abundances for O, Na, Al, Si, Ca, Ti, Fe, Ni, La, and Eu in 164 red giant branch stars in the massive GC 47 Tuc using spectra obtained with both the Hydra multifiber spectrograph at the Blanco 4 m telescope and the FLAMES multiobject spectrograph at the Very Large Telescope. We find an average [Fe/H] = –0.79 ± 0.09 dex, consistent with literature values, as well as overabundances of alpha-elements ([α/Fe] ∼ 0.3 dex). The n-capture process elements indicate that 47 Tuc is r process-dominated ([Eu/La] = +0.24), and the light elements O, Na, and Al exhibit star-to-star variations. The Na-O anticorrelation, a signature typically seen in Galactic GCs, is present in 47 Tuc, and extends to include a small number of stars with [O/Fe] ∼ –0.5. Additionally, the [O/Na] ratios of our sample reveal that the cluster stars can be separated into three distinct populations. A Kolmogorov-Smirnov test demonstrates that the O-poor/Na-rich stars are more centrally concentrated than the O-rich/Na-poor stars. The observed number and radial distribution of 47 Tuc's stellar populations, as distinguished by their light element composition, agrees closely with the results obtained from photometric data. We do not find evidence supporting a strong Na-Al correlation in 47 Tuc, which is consistent with current models of asymptotic giant branch nucleosynthesis yields.

  20. On the Interpretation of Sub-Giant Branch Morphologies of Intermediate-Age Star Clusters with Extended Main Sequence Turnoffs

    CERN Document Server

    Goudfrooij, Paul; Rosenfield, Philip; Bressan, Alessandro; Marigo, Paola; Correnti, Matteo; Puzia, Thomas H

    2015-01-01

    Recent high-quality photometry of many star clusters in the Magellanic Clouds with ages of 1$\\,-\\,$2 Gyr revealed main sequence turnoffs (MSTOs) that are significantly wider than can be accounted for by a simple stellar population (SSP). Such extended MSTOs (eMSTOs) are often interpreted in terms of an age spread of several $10^8$ yr, challenging the traditional view of star clusters as being formed in a single star formation episode. Li et al. and Bastian & Niederhofer recently investigated the sub-giant branches (SGBs) of NGC 1651, NGC 1806, and NGC 1846, three star clusters in the Large Magellanic Cloud (LMC) that exhibit an eMSTO. They argued that the SGB of these star clusters can be explained only by a SSP. We study these and two other similar star clusters in the LMC, using extensive simulations of SSPs including unresolved binaries. We find that the shapes of the cross-SGB profiles of all star clusters in our sample are in fact consistent with their cross-MSTO profiles when the latter are interpre...

  1. Evolution of thermally pulsing asymptotic giant branch stars. IV. Constraining mass loss and lifetimes of low mass, low metallicity AGB stars

    Energy Technology Data Exchange (ETDEWEB)

    Rosenfield, Philip; Dalcanton, Julianne J.; Weisz, Daniel; Williams, Benjamin F. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Marigo, Paola [Department of Physics and Astronomy G. Galilei, University of Padova, Vicolo dell' Osservatorio 3, I-35122 Padova (Italy); Girardi, Léo; Gullieuszik, Marco [Osservatorio Astronomico di Padova—INAF, Vicolo dell' Osservatorio 5, I-35122 Padova (Italy); Bressan, Alessandro [Astrophysics Sector, SISSA, Via Bonomea 265, I-34136 Trieste (Italy); Dolphin, Andrew [Raytheon Company, 1151 East Hermans Road, Tucson, AZ 85756 (United States); Aringer, Bernhard [Department of Astrophysics, University of Vienna, Turkenschanzstraße 17, A-1180 Wien (Austria)

    2014-07-20

    The evolution and lifetimes of thermally pulsating asymptotic giant branch (TP-AGB) stars suffer from significant uncertainties. In this work, we analyze the numbers and luminosity functions of TP-AGB stars in six quiescent, low metallicity ([Fe/H] ≲ –0.86) galaxies taken from the ACS Nearby Galaxy Survey Treasury sample, using Hubble Space Telescope (HST) photometry in both optical and near-infrared filters. The galaxies contain over 1000 TP-AGB stars (at least 60 per field). We compare the observed TP-AGB luminosity functions and relative numbers of TP-AGB and red giant branch (RGB) stars, N{sub TP-AGB}/N{sub RGB}, to models generated from different suites of TP-AGB evolutionary tracks after adopting star formation histories derived from the HST deep optical observations. We test various mass-loss prescriptions that differ in their treatments of mass loss before the onset of dust-driven winds (pre-dust). These comparisons confirm that pre-dust mass loss is important, since models that neglect pre-dust mass loss fail to explain the observed N{sub TP-AGB}/N{sub RGB} ratio or the luminosity functions. In contrast, models with more efficient pre-dust mass loss produce results consistent with observations. We find that for [Fe/H] ≲ –0.86, lower mass TP-AGB stars (M ≲ 1 M{sub ☉}) must have lifetimes of ∼0.5 Myr and higher masses (M ≲ 3 M{sub ☉}) must have lifetimes ≲ 1.2 Myr. In addition, assuming our best-fitting mass-loss prescription, we show that the third dredge-up has no significant effect on TP-AGB lifetimes in this mass and metallicity range.

  2. Evolution of Thermally Pulsing Asymptotic Giant Branch Stars. V. Constraining the Mass Loss and Lifetimes of Intermediate-mass, Low-metallicity AGB Stars

    Science.gov (United States)

    Rosenfield, Philip; Marigo, Paola; Girardi, Léo; Dalcanton, Julianne J.; Bressan, Alessandro; Williams, Benjamin F.; Dolphin, Andrew

    2016-05-01

    Thermally pulsing asymptotic giant branch (TP-AGB) stars are relatively short lived (less than a few Myr), yet their cool effective temperatures, high luminosities, efficient mass loss, and dust production can dramatically affect the chemical enrichment histories and the spectral energy distributions of their host galaxies. The ability to accurately model TP-AGB stars is critical to the interpretation of the integrated light of distant galaxies, especially in redder wavelengths. We continue previous efforts to constrain the evolution and lifetimes of TP-AGB stars by modeling their underlying stellar populations. Using Hubble Space Telescope (HST) optical and near-infrared photometry taken of 12 fields of 10 nearby galaxies imaged via the Advanced Camera for Surveys Nearby Galaxy Survey Treasury and the near-infrared HST/SNAP follow-up campaign, we compare the model and observed TP-AGB luminosity functions as well as the ratio of TP-AGB to red giant branch stars. We confirm the best-fitting mass-loss prescription, introduced by Rosenfield et al., in which two different wind regimes are active during the TP-AGB, significantly improves models of many galaxies that show evidence of recent star formation. This study extends previous efforts to constrain TP-AGB lifetimes to metallicities ranging -1.59 ≲ {{[Fe/H]}} ≲ -0.56 and initial TP-AGB masses up to ˜4 M ⊙, which include TP-AGB stars that undergo hot-bottom burning. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  3. On the interpretation of sub-giant branch morphologies of intermediate-age star clusters with extended main sequence turnoffs

    Science.gov (United States)

    Goudfrooij, Paul; Girardi, Léo; Rosenfield, Philip; Bressan, Alessandro; Marigo, Paola; Correnti, Matteo; Puzia, Thomas H.

    2015-06-01

    High-quality photometry of many star clusters in the Magellanic Clouds with ages of 1-2 Gyr revealed main sequence turnoffs (MSTOs) that are significantly wider than can be accounted for by a simple stellar population (SSP). Such extended MSTOs (eMSTOs) are often interpreted in terms of an age spread of several 108 yr, challenging the traditional view of star clusters as being formed in a single star formation episode. Li et al. and Bastian & Niederhofer recently investigated the sub-giant branches (SGBs) of NGC 1651, NGC 1806, and NGC 1846, three star clusters in the Large Magellanic Cloud (LMC) that exhibit an eMSTO. They argued that the SGB of these star clusters can be explained only by an SSP. We study these and two other similar star clusters in the LMC, using extensive simulations of SSPs including unresolved binaries. We find that the shapes of the cross-SGB profiles of all star clusters in our sample are in fact consistent with their cross-MSTO profiles when the latter are interpreted as age distributions. Conversely, SGB morphologies of star clusters with eMSTOs are found to be inconsistent with those of simulated SSPs. Finally, we create PARSEC isochrones from tracks featuring a grid of convective overshoot levels and a very fine grid of stellar masses. A comparison of the observed photometry with these isochrones shows that the morphology of the red clump (RC) of such star clusters is also consistent with that implied by their MSTO in the age spread scenario. We conclude that the SGB and RC morphologies of star clusters featuring eMSTOs are consistent with the scenario in which the eMSTOs are caused by a distribution of stellar ages.

  4. Spectroscopic confirmation of KOI-1299b: a massive warm Jupiter in a 52-day eccentric orbit transiting a giant star

    CERN Document Server

    Ortiz, Mauricio; Reffert, Sabine; Quirrenbach, Andreas; Deeg, Hans J; Karjalainen, Raine; Montañes-Rodríguez, Pilar; Nespral, Davide; Nowak, Grzegorz; Osorio, Yeisson; Palle, Enric

    2014-01-01

    Context: Planets around evolved stars exhibit different properties than those orbiting main-sequence stars. One of the most notable differences is the paucity of planets orbiting at short distance from giant stars (a < 0.5 AU). Detecting these rare close-in planets can shed light on planetary system formation and evolution mechanisms. Aims: We study the Kepler object KOI-1299, an evolved star ascending the red giant branch. We aim at confirming the planetary nature of the Jupiter-like transit signal recurring every ~52.5 days, and characterizing the orbital elements of the system. Methods: We derive radial velocities from multi-epoch high-resolution spectra of KOI-1299 acquired with CAFE at the 2.2m telescope of Calar Alto Observatory and FIES at the 2.56m Nordic Optical Telescope of Roque de los Muchachos Observatory. Results: We confirm the planetary nature of the transiting object KOI-1299b. We find a planetary mass of Mp=5.86 +\\- 0.05 Mjup and an eccentricity of e=0.479 +\\- 0.004. With a semi-major axi...

  5. Identification of a Class of Low-Mass Asymptotic Giant Branch Stars Struggling to Become Carbon Stars in the Magellanic Clouds

    CERN Document Server

    Boyer, Martha L; Srinivasan, Sundar; Zijlstra, Albert; van Loon, Jacco Th; Olsen, Knut A G; Sonneborn, George

    2015-01-01

    We have identified a new class of Asymptotic Giant Branch (AGB) stars in the Small and Large Magellanic Clouds (SMC/LMC) using optical to infrared photometry, light curves, and optical spectroscopy. The strong dust production and long-period pulsations of these stars indicate that they are at the very end of their AGB evolution. Period-mass-radius relations for the fundamental-mode pulsators give median current stellar masses of 1.14 M_sun in the LMC and 0.94 M_sun in the SMC (with dispersions of 0.21 and 0.18 M_sun, respectively), and models suggest initial masses of <1.5 M_sun and <1.25 M_sun, respectively. This new class of stars includes both O-rich and C-rich chemistries, placing the limit where dredge-up allows carbon star production below these masses. A high fraction of the brightest among them should show S star characteristics indicative of atmospheric C/O ~ 1, and many will form O-rich dust prior to their C-rich phase. These stars can be separated from their less-evolved counterparts by their...

  6. A study of the effect of rotational mixing on massive stars evolution: surface abundances of Galactic O7-8 giant stars

    CERN Document Server

    Martins, F; Barba, R H; Gamen, R C; Ekstroem, S

    2016-01-01

    Massive star evolution remains only partly constrained. In particular, the exact role of rotation has been questioned by puzzling properties of OB stars in the Magellanic Clouds. Our goal is to study the relation between surface chemical composition and rotational velocity, and to test predictions of evolutionary models including rotation. We have performed a spectroscopic analysis of a sample of fifteen Galactic O7-8 giant stars. This sample is homogeneous in terms of mass, metallicity and evolutionary state. It is made of stars with a wide range of projected rotational velocities. We show that the sample stars are located on the second half of the main sequence, in a relatively narrow mass range (25-40 Msun). Almost all stars with projected rotational velocities above 100 km/s have N/C ratios about ten times the initial value. Below 100 km/s a wide range of N/C values is observed. The relation between N/C and surface gravity is well reproduced by various sets of models. Some evolutionary models including ro...

  7. STELLAR METALLICITIES AND KINEMATICS IN A GAS-RICH DWARF GALAXY : FIRST CALCIUM TRIPLET SPECTROSCOPY OF RED GIANT BRANCH STARS IN WLM

    NARCIS (Netherlands)

    Leaman, Ryan; Cole, Andrew A.; Venn, Kim A.; Tolstoy, Eline; Irwin, Mike J.; Szeifert, Thomas; Skillman, Evan D.; McConnachie, Alan W.

    2009-01-01

    We present the first determination of the radial velocities and metallicities of 78 red giant stars in the isolated dwarf irregular galaxy WLM. Observations of the calcium II triplet in these stars were made with FORS2 at the VLT-UT2 in two separated fields of view in WLM, and the [Fe/H] values were

  8. A Spitzer Transit of the Most Inflated Planet Known, Around an Extremely Bright Sub-giant Star

    Science.gov (United States)

    Beatty, Thomas; Collins, Karen; Colon, Knicole; James, David; Kriedberg, Laura; Pepper, Joshua; Rodriguez, Joseph; Siverd, Robert; Stassun, Keivan; Stevens, Daniel

    2015-10-01

    KELT-11b is a newly discovered transiting Saturn-mass planet (Mp~0.22MJ) that promises to become a unique benchmark. KELT-11b orbits HD 93396,the second brightest star in the near-IR (K=6.122) and the third brightest star in the optical (V=8.04) to host a transiting giant planet. This makes KELT-11 comparable to the well-studied benchmarks HD 189733 and HD 209458. But unlike these other bright systems, KELT-11b's host star is a sub-giant, with log(g)~3.7. Thus KELT-11b is the first transiting giant planet known around a sub-giant star bright enough for precise follow-up observations. Furthermore, KELT-11b is the most inflated planet known, with the lowest surface gravity (log[g]~2.5) of any transiting planet. This makes it an exciting target for atmospheric characterization and studying the effect of post main-sequence evolution of a host star on a hot Jupiter. But to correctly interpret any follow-up observations, we will first need to measure accurate stellar and planetary parameters for the system via a precise transit observation. Unfortunately, this is effectively impossible to do from the ground. Spitzer's ability to provide high precision continuous photometry provides the only current way in which we may precisely observe a complete transit of KELT-11b. We therefore propose for 15.5 hours, to observe a single transit KELT-11b at 3.6um. This would reduce the uncertainties on the transit depth and stellar density by at least a factor of twenty, and will improve the model-derived stellar mass by at least a factor of ten, compared to ground-based observations. This will serve two goals. First, it will be a valuable legacy to the community, by providing a precise set of system parameters that will enable future observation and interpretation of this unique, bright, system. Second, an observation of a transit will allow us to strongly constrain the mass of KELT-11, and thus help resolve the disagreement over the true masses of the 'retired A stars' radial

  9. Revisiting the Microlensing Event OGLE 2012-BLG-0026: A Solar Mass Star with Two Cold Giant Planets

    Science.gov (United States)

    Beaulieu, J.-P.; Bennett, D. P.; Batista, V.; Fukui, A.; Marquette, J.-B.; Brillant, S.; Cole, A. A.; Rogers, L. A.; Sumi, T.; Abe, F.

    2016-01-01

    Two cold gas giant planets orbiting a G-type main-sequence star in the galactic disk were previously discovered in the high-magnification microlensing event OGLE-2012-BLG-0026. Here, we present revised host star flux measurements and a refined model for the two-planet system using additional light curve data. We performed high angular resolution adaptive optics imaging with the Keck and Subaru telescopes at two epochs while the source star was still amplified. We detected the lens flux, H = 16.39 +/- 0.08. The lens, a disk star, is brighter than predicted from the modeling in the original study. We revisited the light curve modeling using additional photometric data from the B and C telescope in New Zealand and CTIO 1.3 m H-band light curve. We then include the Keck and Subaru adaptive optic observation constraints. The system is composed of an approximately 4-9 Gyr lens star of M(sub lens) = 1.06 +/- 0.05 solar mass at a distance of D(sub lens) = 4.0 +/- 0.3 kpc, orbited by two giant planets of 0.145 +/- 0.008 M(sub Jup) and 0.86 +/- 0.06 M(sub Jup), with projected separations of 4.0 +/- 0.5 au and 4.8 +/- 0.7 au, respectively. Because the lens is brighter than the source star by 16 +/- 8% in H, with no other blend within one arcsec, it will be possible to estimate its metallicity using subsequent IR spectroscopy with 8-10 m class telescopes. By adding a constraint on the metallicity it will be possible to refine the age of the system.

  10. Revisiting the Microlensing Event OGLE 2012-BLG-0026: A Solar Mass Star with Two Cold Giant Planets

    Science.gov (United States)

    Beaulieu, J.-P.; Bennett, D. P.; Batista, V.; Fukui, A.; Marquette, J.-B.; Brillant, S.; Cole, A. A.; Rogers, L. A.; Sumi, T.; Abe, F.

    2016-01-01

    Two cold gas giant planets orbiting a G-type main-sequence star in the galactic disk were previously discovered in the high-magnification microlensing event OGLE-2012-BLG-0026. Here, we present revised host star flux measurements and a refined model for the two-planet system using additional light curve data. We performed high angular resolution adaptive optics imaging with the Keck and Subaru telescopes at two epochs while the source star was still amplified. We detected the lens flux, H = 16.39 +/- 0.08. The lens, a disk star, is brighter than predicted from the modeling in the original study. We revisited the light curve modeling using additional photometric data from the B and C telescope in New Zealand and CTIO 1.3 m H-band light curve. We then include the Keck and Subaru adaptive optic observation constraints. The system is composed of an approximately 4-9 Gyr lens star of M(sub lens) = 1.06 +/- 0.05 solar mass at a distance of D(sub lens) = 4.0 +/- 0.3 kpc, orbited by two giant planets of 0.145 +/- 0.008 M(sub Jup) and 0.86 +/- 0.06 M(sub Jup), with projected separations of 4.0 +/- 0.5 au and 4.8 +/- 0.7 au, respectively. Because the lens is brighter than the source star by 16 +/- 8% in H, with no other blend within one arcsec, it will be possible to estimate its metallicity using subsequent IR spectroscopy with 8-10 m class telescopes. By adding a constraint on the metallicity it will be possible to refine the age of the system.

  11. Solar-like oscillations from the depths of the red-giant star KIC 4351319 observed with Kepler

    Science.gov (United States)

    di Mauro, M. P.; Cardini, D.; Catanzaro, G.; Ventura, R.; Barban, C.; Bedding, T. R.; Christensen-Dalsgaard, J.; De Ridder, J.; Hekker, S.; Huber, D.; Kallinger, T.; Miglio, A.; Montalban, J.; Mosser, B.; Stello, D.; Uytterhoeven, K.; Kinemuchi, K.; Kjeldsen, H.; Mullally, F.; Still, M.

    2011-08-01

    We present the results of the asteroseismic analysis of the red-giant star KIC 4351319 (TYC 3124-914-1), observed for 30 d in short-cadence mode with the Kepler satellite. The analysis has allowed us to determine the large and small frequency separations, ?Hz and ?Hz, respectively, and the frequency of maximum oscillation power, ?Hz. The high signal-to-noise ratio of the observations allowed us to identify 25 independent pulsation modes whose frequencies range approximately from 300 to ?Hz. The observed oscillation frequencies together with the accurate determination of the atmospheric parameters (effective temperature, gravity and metallicity), provided by additional ground-based spectroscopic observations, enabled us to theoretically interpret the observed oscillation spectrum. KIC 4351319 appears to oscillate with a well-defined solar-type p-mode pattern due to radial acoustic modes and non-radial nearly pure p modes. In addition, several non-radial mixed modes have been identified. Theoretical models well reproduce the observed oscillation frequencies and indicate that this star, located at the base of the ascending red-giant branch, is in the hydrogen-shell-burning phase, with a mass of ˜1.3 M⊙, a radius of ? and an age of ˜5.6 Gyr. The main parameters of this star have been determined with an unprecedented level of precision for a red-giant star, with uncertainties of 2 per cent for mass, 7 per cent for age, 1 per cent for radius and 4 per cent for luminosity.

  12. THE GEMINI NICI PLANET-FINDING CAMPAIGN: THE FREQUENCY OF GIANT PLANETS AROUND YOUNG B AND A STARS

    Energy Technology Data Exchange (ETDEWEB)

    Nielsen, Eric L.; Liu, Michael C.; Chun, Mark; Ftaclas, Christ [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Wahhaj, Zahed [European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago (Chile); Biller, Beth A. [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Hayward, Thomas L.; Hartung, Markus [Gemini Observatory, Southern Operations Center, c/o AURA, Casilla 603, La Serena (Chile); Close, Laird M.; Males, Jared R.; Skemer, Andrew J. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Alencar, Silvia H. P. [Departamento de Fisica, ICEx, Universidade Federal de Minas Gerais, Av. Antonio Carlos 6627, 30270-901 Belo Horizonte, MG (Brazil); Artymowicz, Pawel [University of Toronto at Scarborough, 1265 Military Trail, Toronto, Ontario M1C 1A4 (Canada); Boss, Alan [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, N.W., Washington, DC 20015 (United States); Clarke, Fraser [Department of Astronomy, University of Oxford, DWB, Keble Road, Oxford OX1 3RH (United Kingdom); De Gouveia Dal Pino, Elisabete; Gregorio-Hetem, Jane [Departamento de Astronomia, Universidade de Sao Paulo, IAG/USP, Rua do Matao 1226, 05508-900 Sao Paulo, SP (Brazil); Ida, Shigeru [Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550 (Japan); Kuchner, Marc [NASA Goddard Space Flight Center, Exoplanets and Stellar Astrophysics Laboratory, Greenbelt, MD 20771 (United States); Lin, Douglas N. C. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA (United States); and others

    2013-10-10

    We have carried out high contrast imaging of 70 young, nearby B and A stars to search for brown dwarf and planetary companions as part of the Gemini NICI Planet-Finding Campaign. Our survey represents the largest, deepest survey for planets around high-mass stars (≈1.5-2.5 M{sub ☉}) conducted to date and includes the planet hosts β Pic and Fomalhaut. We obtained follow-up astrometry of all candidate companions within 400 AU projected separation for stars in uncrowded fields and identified new low-mass companions to HD 1160 and HIP 79797. We have found that the previously known young brown dwarf companion to HIP 79797 is itself a tight (3 AU) binary, composed of brown dwarfs with masses 58{sup +21}{sub -20} M{sub Jup} and 55{sup +20}{sub -19} M{sub Jup}, making this system one of the rare substellar binaries in orbit around a star. Considering the contrast limits of our NICI data and the fact that we did not detect any planets, we use high-fidelity Monte Carlo simulations to show that fewer than 20% of 2 M{sub ☉} stars can have giant planets greater than 4 M{sub Jup} between 59 and 460 AU at 95% confidence, and fewer than 10% of these stars can have a planet more massive than 10 M{sub Jup} between 38 and 650 AU. Overall, we find that large-separation giant planets are not common around B and A stars: fewer than 10% of B and A stars can have an analog to the HR 8799 b (7 M{sub Jup}, 68 AU) planet at 95% confidence. We also describe a new Bayesian technique for determining the ages of field B and A stars from photometry and theoretical isochrones. Our method produces more plausible ages for high-mass stars than previous age-dating techniques, which tend to underestimate stellar ages and their uncertainties.

  13. The stellar spectral features of nearby galaxies in the near infrared: tracers of thermally pulsing asymptotic giant branch stars?

    Science.gov (United States)

    Riffel, Rogério; Mason, Rachel E.; Martins, Lucimara P.; Rodríguez-Ardila, Alberto; Ho, Luis C.; Riffel, Rogemar A.; Lira, Paulina; Gonzalez Martin, Omaira; Ruschel-Dutra, Daniel; Alonso-Herrero, Almudena; Flohic, Helene; McDermid, Richard M.; Ramos Almeida, Cristina; Thanjavur, Karun; Winge, Claudia

    2015-07-01

    We analyse the stellar absorption features in high signal-to-noise ratio (S/N) near-infrared (NIR) spectra of the nuclear region of 12 nearby galaxies, mostly spirals. The features detected in some or all of the galaxies in this sample are the TiO (0.843 and 0.886 μm), VO (1.048 μm), CN (1.1 and 1.4 μm), H2O (1.4 and 1.9 μm) and CO (1.6 and 2.3 μm) bands. The C2 (1.17 and 1.76 μm) bands are generally weak or absent, although C2 (1.76 μm) may be weakly present in the mean galaxy spectrum. A deep feature near 0.93 μm, likely caused by CN, TiO and/or ZrO, is also detected in all objects. Fitting a combination of stellar spectra to the mean spectrum shows that the absorption features are produced by evolved stars: cool giants and supergiant stars in the early- or thermally pulsing asymptotic giant branch (E-AGB or TP-AGB) phases. The high luminosity of TP-AGB stars, and the appearance of VO and ZrO features in the data, suggest that TP-AGB stars dominate these spectral features. However, a contribution from other evolved stars is also likely. Comparison with evolutionary population synthesis models shows that models based on empirical libraries that predict relatively strong NIR features provide a more accurate description of the data. However, none of the models tested accurately reproduces all of the features observed in the spectra. To do so, the models will need to not only improve the treatment of TP-AGB stars, but also include good quality spectra of red giant and E-AGB stars. The uninterrupted wavelength coverage, high S/N and quantity of features we present here will provide a benchmark for the next generation of models aiming to explain and predict the NIR properties of galaxies.

  14. Kepler Detected Gravity-Mode Period Spacings in a Red Giant Star

    DEFF Research Database (Denmark)

    Beck, P.G.; Bedding, Timothy R.; Mosser, Benoit;

    2011-01-01

    Stellar interiors are inaccessible through direct observations. For this reason, helioseismologists made use of the Sun’s acoustic oscillation modes to tune models of its structure. The quest to detect modes that probe the solar core has been ongoing for decades. We report the detection of mixed ...... modes penetrating all the way to the core of an evolved star from 320 days of observations with the Kepler satellite. The period spacings of these mixed modes are directly dependent on the density gradient between the core region and the convective envelope....

  15. Stellar encounter driven red-giant star mass loss in globular clusters

    Energy Technology Data Exchange (ETDEWEB)

    Pasquato, Mario; Moraghan, Anthony; Chung, Chul; Lee, Young-Wook [Department of Astronomy and Center for Galaxy Evolution Research, Yonsei University, Seoul 120-749 (Korea, Republic of); De Luca, Andrea [Laboratoire de Physique Théorique, Ecole Normale Supérieure 24, rue Lhomond, F-75231 Paris Cedex 05 (France); Raimondo, Gabriella [INAF-Osservatorio Astronomico di Teramo, Mentore Maggini s.n.c., I-64100 Teramo (Italy); Carini, Roberta; Brocato, Enzo [INAF-Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monte Porzio Catone (Italy)

    2014-07-01

    Globular cluster (GC) color-magnitude diagrams (CMDs) are reasonably well understood in terms of standard stellar evolution. However, there are still some open issues, such as fully accounting for the horizontal branch (HB) morphology in terms of chemical and dynamical parameters. Mass loss on the red giant branch (RGB) shapes the mass distribution of the HB stars, and the color distribution in turn. The physical mechanisms driving mass loss are still unclear, as direct observations fail to reveal a clear correlation between mass-loss rate and stellar properties. The HB mass distribution is further complicated by helium-enhanced multiple stellar populations due to differences in the evolving mass along the HB. We present a simple analytical mass-loss model based on tidal stripping through Roche-Lobe overflow during stellar encounters. Our model naturally results in a non-Gaussian mass-loss distribution with high skewness and contains only two free parameters. We fit it to the HB mass distribution of four Galactic GCs, as obtained from fitting the CMD with zero age HB models. The best-fit model accurately reproduces the observed mass distribution. If confirmed on a wider sample of GCs, our results would account for the effects of dynamics in RGB mass-loss processes and provide a physically motivated procedure for synthetic CMDs of GCs. Our physical modeling of mass loss may result in the ability to disentangle the effects of dynamics and helium-enhanced multiple populations on the HB morphology and is instrumental in making HB morphology a probe of the dynamical state of GCs, leading to an improved understanding of their evolution.

  16. The Dependence of the Galactic Star Formation Laws on Metallicity

    CERN Document Server

    Dib, Sami; Mohanty, Subhanjoy; Braine, Jonathan

    2011-01-01

    We describe results from semi-analytical modelling of star formation in protocluster clumps of different metallicities. In this model, gravitationally bound cores form uniformly in the clump following a prescribed core formation efficiency per unit time. After a contraction timescale which is equal to a few times their free-fall times, the cores collapse into stars and populate the IMF. Feedback from the newly formed OB stars is taken into account in the form of stellar winds. When the ratio of the effective energy of the winds to the gravitational energy of the system reaches unity, gas is removed from the clump and core and star formation are quenched. The power of the radiation driven winds has a strong dependence on metallicity and it increases with increasing metallicity. Thus, winds from stars in the high metallicity models lead to a rapid evacuation of the gas from the protocluster clump and to a reduced star formation efficiency, as compared to their low metallicity counterparts. We derive the metalli...

  17. Evolution of Thermally Pulsing Asymptotic Giant Branch Stars IV. Constraining Mass-Loss & Lifetimes of Low Mass, Low Metallicity AGB Stars

    CERN Document Server

    Rosenfield, Philip; Girardi, Leo; Dalcanton, Julianne J; Bressan, Alessandro; Gullieuszik, Marco; Weisz, Daniel; Williams, Benjamin F; Dolphin, Andrew; Aringer, Bernhard

    2014-01-01

    The evolution and lifetimes of thermally pulsating asymptotic giant branch (TP-AGB) stars suffer from significant uncertainties. In this work, we analyze the numbers and luminosity functions of TP-AGB stars in six quiescent, low metallicity ([Fe/H] $\\lesssim -0.86$) galaxies taken from the ANGST sample, using HST photometry in both optical and near-infrared filters. The galaxies contain over 1000 TP-AGB stars (at least 60 per field). We compare the observed TP-AGB luminosity functions and relative numbers of TP-AGB and RGB stars, to models generated from different suites of TP-AGB evolutionary tracks after adopting star formation histories (SFH) derived from the HST deep optical observations. We test various mass-loss prescriptions that differ in their treatments of mass-loss before the onset of dust-driven winds (pre-dust). These comparisons confirm that pre-dust mass-loss is important, since models that neglect pre-dust mass-loss fail to explain the observed TP-AGB/RGB ratio or the luminosity functions. In ...

  18. The GAPS Programme with HARPS-N@TNG II: No giant planets around the metal-poor star HIP 11952

    CERN Document Server

    Desidera, S; Bonomo, A S; Gratton, R; Poretti, E; Claudi, R; Latham, D W; Affer, L; Cosentino, R; Damasso, M; Esposito, M; Giacobbe, P; Malavolta, L; Nascimbeni, V; Piotto, G; Rainer, M; Scardia, M; Schmid, V S; Lanza, A F; Micela, G; Pagano, I; Bedin, L; Biazzo, K; Borsa, F; Carolo, E; Covino, E; Faedi, F; Hebrard, G; Lovis, C; Maggio, A; Mancini, L; Marzari, F; Messina, S; Molinari, E; Munari, U; Pepe, F; Santos, N; Scandariato, G; Shkolnik, E; Southworth, J

    2013-01-01

    In the context of the program Global Architecture of Planetary Systems (GAPS), we have performed radial velocity monitoring of the metal-poor star HIP 11952 on 35 nights over about 150 days using the newly installed high resolution spectrograph HARPS-N at the TNG and HARPS at ESO 3.6m telescope. The radial velocities show a scatter of 7 m/s, compatible with the measurement errors for such a moderately warm metal-poor star (Teff = 6040+-120K; [Fe/H] =-1.9+-0.1). We then exclude the presence of the two giant planets with periods of 6.95+-0.01 d and 290.0+-16.2 d and radial velocity semi-amplitudes of 100.3+-19.4 m/s and 105.2+-14.7 m/s, respectively, which had recently been announced. This result is important considering that HIP 11952 was thought to be the most metal-poor star hosting a planetary system with giant planets, thus challenging some models of planet formation.

  19. The discovery of a planetary candidate around the evolved low-mass Kepler giant star HD 175370

    CERN Document Server

    Hrudková, M; Karjalainen, R; Lehmann, H; Hekker, S; Hartmann, M; Tkachenko, A; Prins, S; van Winckel, H; de Nutte, R; Dumortier, L; Frémat, Y; Hensberge, H; Jorissen, A; Lampens, P; Laverick, M; Lombaert, R; Pápics, P I; Raskin, G; Sódor, Á; Thoul, A; van Eck, S; Waelkens, C

    2016-01-01

    We report on the discovery of a planetary companion candidate with a minimum mass Msini = 4.6 M_J orbiting the K2 III giant star HD 175370 (KIC 007940959). This star was a target in our program to search for planets around a sample of 95 giant stars observed with Kepler. This detection was made possible using precise stellar radial velocity measurements of HD 175370 taken over five years and four months using the coude echelle spectrograph of the 2-m Alfred Jensch Telescope and the fibre-fed echelle spectrograph HERMES of the 1.2-m Mercator Telescope. Our radial velocity measurements reveal a periodic (349.5 days) variation with a semi-amplitude K = 133 m/s, superimposed on a long-term trend. A low-mass stellar companion with an orbital period of ~88 years in a highly eccentric orbit and a planet in a Keplerian orbit with an eccentricity e = 0.22 are the most plausible explanation of the radial velocity variations. However, we cannot exclude the existence of stellar envelope pulsations as a cause for the low-...

  20. The mass-ratio and eccentricity distributions of red giants in open clusters, barium and S stars

    CERN Document Server

    Van der Swaelmen, Mathieu; Jorissen, Alain; Van Eck, Sophie

    2016-01-01

    In order to identify diagnostics distinguishing between pre- and post-mass-transfer systems, the mass-ratio distribution and period - eccentricity (P - e) diagram of barium and S stars are compared to those of the sample of binary red giants in open clusters from Mermilliod et al. (2007). From the analysis of the mass-ratio distribution for the cluster binary giants, we find an excess of systems with companion masses between 0.58 and 0.87 Msun, typical for white dwarfs. They represent 22% of the sample, which are thus candidate post-mass-transfer systems. Among these candidates which occupy the same locus as the barium and S stars in the (P-e) diagram, only 33% (= 4/12) show a chemical signature of mass transfer in the form of s-process overabundances (from rather moderate -- about 0.3 dex -- to more extreme -- about 1 dex). These s-process-enriched cluster stars show a clear tendency to be in the clusters with the lowest metallicity in the sample, confirming the classical prediction that the s-process nucleo...

  1. Detailed abundances of a large sample of giant stars in M 54 and in the Sagittarius nucleus

    CERN Document Server

    Carretta, E; Gratton, R G; Lucatello, S; Bellazzini, M; Catanzaro, G; Leone, F; Momany, Y; Piotto, G; D'Orazi, V

    2010-01-01

    Homogeneous abundances of light elements, alpha and Fe-group elements from high-resolution FLAMES spectra are presented for 76 red giant stars in M54, a massive globular cluster (GC) lying in the nucleus of the Sagittarius dwarf galaxy. We also derived detailed abundances for 27 red giants belonging to the Sgr nucleus. Our abundances assess the intrinsic metallicity dispersion (~0.19 dex, rms scatter) of M54, with the bulk of stars peaking at [Fe/H]~-1.6 and a long tail extending to higher metallicities, similar to omega Cen. The spread in these probable nuclear star clusters exceeds those of most GCs: these massive clusters are located in a region intermediate between normal GCs and dwarf galaxies. M54 shows the Na-O anticorrelation, typical signature of GCs, which is instead absent in the Sgr nucleus. The light elements (Mg, Al, Si) participating to the high temperature Mg-Al cycle show that the pattern of (anti)correlations produced by proton-capture reactions in H-burning is clearly different between the ...

  2. Mixed modes in red-giant stars observed with CoRoT

    NARCIS (Netherlands)

    Mosser, B.; Barban, C.; Montalban, J.; Beck, P.G.; Miglio, A.; Belkacem, K.; Goupil, M.J.; Hekker, S.; de Ridder, J.; Dupret, M.A.; Elsworth, Y.; Noels, A.; Baudin, F.; Michel, A.E.; Samadi, R.; Auvergne, M.; Baglin, A.; Catala, C.

    2011-01-01

    Context. The CoRoT mission has provided thousands of red-giant light curves. The analysis of their solar-like oscillations allows us to characterize their stellar properties. Aims. Up to now, the global seismic parameters of the pressure modes have been unable to distinguish red-clump giants from

  3. Giant Clumps in Simulated High-z Galaxies: Properties, Evolution and Dependence on Feedback

    CERN Document Server

    Mandelker, Nir; Ceverino, Daniel; DeGraf, Colin; Guo, Yicheng; Primack, Joel

    2015-01-01

    We study the evolution of giant clumps in high-z disc galaxies using AMR cosmological simulations at redshifts z=6-1. Our sample consists of 34 galaxies, of halo masses 10^{11}-10^{12}M_s at z=2, run with and without radiation pressure (RP) feedback from young stars. While RP has little effect on the sizes and global stability of discs, it reduces the amount of star-forming gas by a factor of ~2, leading to a decrease in stellar mass by a similar factor by z~2. Both samples undergo violent disc instability (VDI) and form giant clumps of masses 10^7-10^9M_s at a similar rate, though RP significantly reduces the number of long-lived clumps. When RP is (not) included, clumps with circular velocity <40(20)km/s, baryonic surface density <200(100)M_s/pc^2 and baryonic mass <10^{8.2}(10^{7.3})M_s are short-lived, disrupted in a few free-fall times. The more massive and dense clumps survive and migrate toward the disc centre over a few disc orbital times. In the RP simulations, the distribution of clump mass...

  4. Seismic evidence for a rapidly rotating core in a lower-giant-branch star observed with Kepler

    CERN Document Server

    Deheuvels, S; Chaplin, W J; Basu, S; Antia, H M; Appourchaux, T; Benomar, O; Davies, G R; Elsworth, Y; Gizon, L; Goupil, M J; Reese, D R; Regulo, C; Schou, J; Stahn, T; Casagrande, L; Christensen-Dalsgaard, J; Fischer, D; Hekker, S; Kjeldsen, H; Mathur, S; Mosser, B; Pinsonneault, M; Valenti, J; Christiansen, J L; Kinemuchi, K; Mullally, F

    2012-01-01

    Rotation is expected to have an important influence on the structure and the evolution of stars. However, the mechanisms of angular momentum transport in stars remain theoretically uncertain and very complex to take into account in stellar models. To achieve a better understanding of these processes, we desperately need observational constraints on the internal rotation of stars, which until very recently were restricted to the Sun. In this paper, we report the detection of mixed modes - i.e. modes that behave both as g modes in the core and as p modes in the envelope - in the spectrum of the early red giant KIC7341231, which was observed during one year with the Kepler spacecraft. By performing an analysis of the oscillation spectrum of the star, we show that its non-radial modes are clearly split by stellar rotation and we are able to determine precisely the rotational splittings of 18 modes. We then find a stellar model that reproduces very well the observed atmospheric and seismic properties of the star. ...

  5. Using the Ca II Triplet to Trace Abundance Variations in Individual Red Giant Branch stars in Three Nearby Galaxies

    CERN Document Server

    Tolstoy, E; Cole, A A; Pasquini, L; Gilmozzi, R; Gallagher, J S; Tolstoy, Eline; Irwin, Michael J.; Cole, Andrew A.

    2001-01-01

    Spectroscopic abundance determinations for stars spanning a Hubble time in age are necessary in order to unambiguously determine the evolutionary histories of galaxies. Using FORS1 in Multi-Object Spectroscopy mode on ANTU (UT1) at the ESO-VLT on Paranal we obtained near infrared spectra from which we measured the equivalent widths of the two strongest Ca II triplet lines to determine metal abundances for a sample of Red Giant Branch stars, selected from ESO-NTT optical (I, V-I) photometry of three nearby, Local Group, galaxies: the Sculptor Dwarf Spheroidal, the Fornax Dwarf Spheroidal and the Dwarf Irregular NGC 6822. The summed equivalent width of the two strongest lines in the Ca II triplet absorption line feature, centered at 8500A, can be readily converted into an [Fe/H] abundance using the previously established calibrations by Armandroff & Da Costa (1991) and Rutledge, Hesser & Stetson (1997). We measured metallicities for 37 stars in Sculptor, 32 stars in Fornax, and 23 stars in NGC 6822, yie...

  6. SU Lyncis, a Hard X-Ray Bright M Giant: Clues Point to a Large Hidden Population of Symbiotic Stars

    Science.gov (United States)

    Mukai, K.; Luna, G. J. M.; Cusumano, G.; Segreto, A.; Munari, U.; Sokoloski, J. L.; Lucy, A. B.; Nelson, T.; Nunez, N. E.

    2016-01-01

    Symbiotic star surveys have traditionally relied almost exclusively on low resolution optical spectroscopy. However, we can obtain amore reliable estimate of their total Galactic population by using all available signatures of the symbiotic phenomenon. Here we report the discovery of a hard X-ray source, 4PBC J0642.9+5528, in the Swift hard X-ray all-sky survey, and identify it with a poorly studied red giant, SU Lyn, using pointed Swift observations and ground-based optical spectroscopy. The X-ray spectrum, the optical to UV spectrum, and the rapid UV variability of SU Lyn are all consistent with our interpretation that it is a symbiotic star containing an accreting white dwarf. The symbiotic nature of SU Lyn went unnoticed until now, because it does not exhibit emission lines strong enough to be obvious in low resolution spectra. We argue that symbiotic stars without shell-burning have weak emission lines, and that the current lists of symbiotic stars are biased in favour of shell-burning systems. We conclude that the true population of symbiotic stars has been underestimated, potentially by a large factor.

  7. VizieR Online Data Catalog: The SEGUE K giant survey. II. Distances of 6036 stars (Xue+, 2014)

    Science.gov (United States)

    Xue, X.-X.; Ma, Z.; Rix, H.-W.; Morrison, H. L.; Harding, P.; Beers, T. C.; Ivans, I. I.; Jacobson, H. R.; Johnson, J.; Lee, Y. S.; Lucatello, S.; Rockosi, C. M.; Sobeck, J. S.; Yanny, B.; Zhao, G.; Allende Prieto, C.

    2016-08-01

    SDSS and its extensions use a dedicated 2.5m telescope to obtain ugriz imaging and resolution (defined as R=λ/Δλ)~2000 spectra for 640 (SDSS spectrograph) or 1000 (BOSS spectrograph) objects over a 7deg2 field. Sloan Extension for Galactic Understanding and Exploration (SEGUE), one of the key projects executed during SDSS-II and SDSS-III, obtained some 360000 spectra of stars in the Galaxy, selected to explore the nature of stellar populations from 0.5kpc to 100kpc (Yanny et al. 2009, cat. J/AJ/137/4377; and C. M. Rockosi et al., in preparation). Data from SEGUE is a significant part of the ninth SDSS public data release (DR9; Ahn et al. 2012, cat. V/139). The SEGUE project obtained spectra for a large number of different stellar types: 18 for SEGUE-1 (see Yanny et al. 2009, cat. J/AJ/137/4377, for details) and 11 for SEGUE-2 (C. M. Rockosi et al. in preparation). Three of these target types were specifically designed to detect K giants: these are designated "l-color K giants", "red K giants", and "proper-motion K giants." The K-giant targets from these three categories all have 0.5heliocentric radial velocities plus SSPP atmospheric parameters. In addition, we provide the Bayesian estimates of the distance moduli, distances to the Sun, Galactocentric distances, the absolute magnitudes and their uncertainties, along with the distance moduli at (5%, 16%, 50%, 84%, 95%) confidence of L(DM). (2 data files).

  8. New model of relativistic slowly rotating neutron stars with surface layer crust: application to giant glitches of Vela Pulsar

    Energy Technology Data Exchange (ETDEWEB)

    Gonzalez-Romero, L M; Blazquez-Salcedo, J L, E-mail: mgromero@fis.ucm.es, E-mail: joseluis.blazquez@fis.ucm.es [Depto. Fisica Teorica II, Facultad de Ciencias Fisicas, Universidad Complutense de Madrid, 28040-Madrid (Spain)

    2011-09-22

    Introducing a surface layer of matter on the edge of a neutron star in slow rigid rotation, we analyze, from an intrinsic point of view, the junction conditions that must be satisfied between the interior and exterior solutions of the Einstein equations. In our model the core-crust transition pressure arise as an essential parameter in the description of a configuration. As an application of this formalism, we describe giant glitches of the Vela pulsar as a result of variations in the transition pressure, finding that these small changes are compatible with the expected temperature variations of the inner crust during glitch time

  9. Search for Exoplanets around Northern Circumpolar Stars. II. The Detection of Radial Velocity Variations in M Giant Stars HD 36384, HD 52030, and HD 208742

    Science.gov (United States)

    Lee, Byeong-Cheol; Jeong, Gwanghui; Park, Myeong-Gu; Han, Inwoo; Mkrtichian, David E.; Hatzes, Artie P.; Gu, Shenghong; Bai, Jinming; Lee, Sang-Min; Oh, Hyeong-Il; Kim, Kang-Min

    2017-07-01

    We present the detection of long-period RV variations in HD 36384, HD 52030, and HD 208742 by using the high-resolution, fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) for the precise radial velocity (RV) survey of about 200 northern circumpolar stars. Analyses of RV data, chromospheric activity indicators, and bisector variations spanning about five years suggest that the RV variations are compatible with planet or brown dwarf companions in Keplerian motion. However, HD 36384 shows photometric variations with a period very close to that of RV variations as well as amplitude variations in the weighted wavelet Z-transform (WWZ) analysis, which argues that the RV variations in HD 36384 are from the stellar pulsations. Assuming that the companion hypothesis is correct, HD 52030 hosts a companion with minimum mass 13.3 M Jup orbiting in 484 days at a distance of 1.2 au. HD 208742 hosts a companion of 14.0 M Jup at 1.5 au with a period of 602 days. All stars are located at the asymptotic giant branch (AGB) stage on the H-R diagram after undergoing the helium flash and leaving the giant clump.With stellar radii of 53.0 R ⊙ and 57.2 R ⊙ for HD 52030 and HD 208742, respectively, these stars may be the largest yet, in terms of stellar radius, found to host substellar companions. However, given possible RV amplitude variations and the fact that these are highly evolved stars, the planet hypothesis is not yet certain.

  10. Mass loss on the red giant branch: the value and metallicity dependence of Reimers' {\\eta} in globular clusters

    CERN Document Server

    McDonald, Iain

    2015-01-01

    The impact of metallicity on the mass-loss rate from red giant branch (RGB) stars is studied through its effect on the parameters of horizontal branch (HB) stars. The scaling factors from Reimers (1975) and Schroder & Cuntz (2005) are determined for 56 well-studied Galactic globular clusters (GCs). The median values among clusters are, respectively, {\\eta}_R = 0.477 +/- 0.070 (+0.050/-0.062) and {\\eta}_SC = 0.172 +/- 0.024 (+0.018/-0.023) (standard deviation and systematic uncertainties, respectively). Mass-loss mechanisms on the RGB have very little metallicity dependence: over a factor of 200 in iron abundance, {\\eta} varies by <~30 per cent, within the current systematic uncertainties on cluster ages and evolution models. Since {\\eta} incorporates cluster age, the low standard deviation of {\\eta} among clusters (~14 per cent) suggests that age can almost entirely account for the "second parameter problem". The remaining spread in {\\eta} correlates with cluster mass and density, suggesting helium enr...

  11. Bad prospects for the detection of giant stars' tidal disruption: effect of the ambient medium on bound debris

    CERN Document Server

    Bonnerot, Clément; Lodato, Giuseppe

    2015-01-01

    Most massive galaxies are thought to contain a supermassive black holes in their centre surrounded by a tenuous gas environment, leading to no significant emission. In these quiescent galaxies, tidal disruption events represent a powerful detection method for the central black hole. Following the disruption, the stellar debris evolve into an elongated gas stream, which partly falls back towards the disruption site and accrete onto the black hole producing a luminous flare. Using an analytical treatment, we investigate the interaction between the debris stream and the gas environment of quiescent galaxies. Although we find dynamical effects to be negligible, we demonstrate that Kelvin-Helmholtz instability can lead to the dissolution of the stream into the ambient medium before it reaches the black hole, likely dimming the associated flare. Furthermore, we find this effect to be enhanced for disruptions involving more massive black holes and/or giant stars. Consequently, although disruptions of evolved stars h...

  12. The Mass-Loss Return from Evolved Stars to the Large Magellanic Cloud II: Dust Properties for Oxygen-Rich Asymptotic Giant Branch Stars

    CERN Document Server

    Sargent, Benjamin A; Meixner, M; Kemper, F; Tielens, A G G M; Speck, A K; Matsuura, M; Bernard, J -Ph; Hony, S; Gordon, Karl D; Indebetouw, R; Marengo, M; Sloan, G C; Woods, Paul M

    2014-01-01

    We model multi-wavelength broadband UBVIJHKs and Spitzer IRAC and MIPS photometry and IRS spectra from the SAGE and SAGE-Spec observing programs of two oxygen-rich asymptotic giant branch (O-rich AGB) stars in the Large Magellanic Cloud (LMC) using radiative transfer models of dust shells around stars. We chose a star from each of the bright and faint O-rich AGB populations found by earlier studies of the SAGE sample in order to derive a baseline set of dust properties to be used in the construction of an extensive grid of radiative transfer models of the O-rich AGB stars found in the SAGE surveys. From the bright O-rich AGB population we chose HV 5715, and from the faint O-rich AGB population we chose SSTISAGE1C J052206.92-715017.6 (SSTSAGE052206). We found the complex indices of refraction of oxygen-deficient silicates from Ossenkopf et al (1992) and a "KMH"-like grain size distribution with gamma of -3.5, a_min of 0.01 microns, and a_0 of 0.1 microns to be reasonable dust properties for these models. There...

  13. Spike-triggered dendritic calcium transients depend on synaptic activity in the cricket giant interneurons.

    Science.gov (United States)

    Ogawa, Hiroto; Baba, Yoshichika; Oka, Kotaro

    2002-02-15

    The relationship between electrical activity and spike-induced Ca2+ increases in dendrites was investigated in the identified wind-sensitive giant interneurons in the cricket. We applied a high-speed Ca2+ imaging technique to the giant interneurons, and succeeded in recording the transient Ca2+ increases (Ca2+ transients) induced by a single action potential, which was evoked by presynaptic stimulus to the sensory neurons. The dendritic Ca2+ transients evoked by a pair of action potentials accumulated when spike intervals were shorter than 100 ms. The amplitude of the Ca2+ transients induced by a train of spikes depended on the number of action potentials. When stimulation pulses evoking the same numbers of action potentials were separately applied to the ipsi- or contra-lateral cercal sensory nerves, the dendritic Ca2+ transients induced by these presynaptic stimuli were different in their amplitude. Furthermore, the side of presynaptic stimulation that evoked larger Ca2+ transients depended on the location of the recorded dendritic regions. This result means that the spike-triggered Ca2+ transients in dendrites depend on postsynaptic activity. It is proposed that Ca2+ entry through voltage-dependent Ca2+ channels activated by the action potentials will be enhanced by excitatory synaptic inputs at the dendrites in the cricket giant interneurons.

  14. Modeling and Control for Giant Magnetostrictive Actuators with Rate-Dependent Hysteresis

    Directory of Open Access Journals (Sweden)

    Ping Liu

    2013-01-01

    Full Text Available The rate-dependent hysteresis in giant magnetostrictive materials is a major impediment to the application of such material in actuators. In this paper, a relevance vector machine (RVM model is proposed for describing the hysteresis nonlinearity under varying input current. It is possible to construct a unique dynamic model in a given rate range for a rate-dependent hysteresis system using the sinusoidal scanning signals as the training set input signal. Subsequently, a proportional integral derivative (PID control scheme combined with a feedforward compensation is implemented on a giant magnetostrictive actuator (GMA for real-time precise trajectory tracking. Simulations and experiments both verify the effectiveness and the practicality of the proposed modeling and control methods.

  15. Temperature dependence of a spreading width of giant dipole resonance in neutron-rich nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Vdovin, A.I.; Storozhenko, A.N

    2003-07-14

    A temperature dependence of the spreading width of a giant dipole resonance is studied in the framework of the Quasiparticle-Phonon Model extended to finite temperature using a formalism of the Thermo Field Dynamics. Numerical calculations are performed for {sup 120}Sn and the neutron-rich double-magic isotope {sup 132}Sn It is found that the dispersion of the E1 strength function {sigma} increases with temperature.

  16. Exploring wind-driving dust species in cool luminous giants III. Wind models for M-type AGB stars: dynamic and photometric properties

    CERN Document Server

    Bladh, S; Aringer, B; Eriksson, K

    2015-01-01

    Stellar winds observed in asymptotic giant branch (AGB) stars are usually attributed to a combination of stellar pulsations and radiation pressure on dust. Shock waves triggered by pulsations propagate through the atmosphere, compressing the gas and lifting it to cooler regions, which create favourable conditions for grain growth. If sufficient radiative acceleration is exerted on the newly formed grains through absorption or scattering of stellar photons, an outflow can be triggered. Strong candidates for wind-driving dust species in M-type AGB stars are magnesium silicates (Mg$_2$SiO$_4$ and MgSiO$_3$). Such grains can form close to the stellar surface, they consist of abundant materials and, if they grow to sizes comparable to the wavelength of the stellar flux maximum, they experience strong acceleration by photon scattering. We use a frequency-dependent radiation-hydrodynamics code with a detailed description for the growth of Mg$_2$SiO$_4$ grains to calculate the first extensive set of time-dependent wi...

  17. KIC 8410637: a 408-day period eclipsing binary containing a pulsating giant star

    NARCIS (Netherlands)

    S. Frandsen; H. Lehmann; S. Hekker; J. Southworth; J. Debosscher; P. Beck; M. Hartmann; A. Pigulski; G. Kopacki; Z. Kołaczkowski; M. Stȩślicki; A.O. Thygesen; K. Brogaard; Y. Elsworth

    2013-01-01

    Context. Detached eclipsing binaries (dEBs) are ideal targets for accurately measuring the masses and radii of their component stars. If at least one of the stars has evolved off the main sequence (MS), the masses and radii give a strict constraint on the age of the stars. Several dEBs containing a

  18. SU Lyncis, a hard X-ray bright M giant: Clues point to a large hidden population of symbiotic stars

    CERN Document Server

    Mukai, K; Cusumano, G; Segreto, A; Munari, U; Sokoloski, J L; Lucy, A B; Nelson, T; Nunez, N E

    2016-01-01

    Symbiotic star surveys have traditionally relied almost exclusively on low resolution optical spectroscopy. However, we can obtain a more reliable estimate of their total Galactic population by using all available signatures of the symbiotic phenomenon. Here we report the discovery of a hard X-ray source, 4PBC J0642.9+5528, in the Swift hard X-ray all-sky survey, and identify it with a poorly studied red giant, SU Lyn, using pointed Swift observations and ground-based optical spectroscopy. The X-ray spectrum, the optical to UV spectrum, and the rapid UV variability of SU Lyn are all consistent with our interpretation that it is a symbiotic star containing an accreting white dwarf. The symbiotic nature of SU Lyn went unnoticed until now, because it does not exhibit emission lines strong enough to be obvious in low resolution spectra. We argue that symbiotic stars without shell-burning have weak emission lines, and that the current lists of symbiotic stars are biased in favor of shell-burning systems. We conclu...

  19. Kepler-63b: A Giant Planet in a Polar Orbit around a Young Sun-like Star

    CERN Document Server

    Sanchis-Ojeda, Roberto; Marcy, Geoffrey W; Howard, Andrew W; Isaacson, Howard; Johnson, John Asher; Torres, Guillermo; Albrecht, Simon; Campante, Tiago L; Chaplin, William J; Davies, Guy R; Lund, Mikkel L; Carter, Joshua A; Dawson, Rebekah I; Buchhave, Lars A; Everett, Mark E; Fischer, Debra A; Geary, John C; Gilliland, Ronald L; Horch, Elliott P; Howell, Steve B; Latham, David W

    2013-01-01

    We present the discovery and characterization of a giant planet orbiting the young Sun-like star Kepler-63 (KOI-63, $m_{\\rm Kp} = 11.6$, $T_{\\rm eff} = 5576$ K, $M_\\star = 0.98\\, M_\\odot$). The planet transits every 9.43 days, with apparent depth variations and brightening anomalies caused by large starspots. The planet's radius is $6.1 \\pm 0.2 R_{\\earth}$, based on the transit light curve and the estimated stellar parameters. The planet's mass could not be measured with the existing radial-velocity data, due to the high level of stellar activity, but if we assume a circular orbit we can place a rough upper bound of $120 M_{\\earth}$ (3$\\sigma$). The host star has a high obliquity ($\\psi$ = $104^{\\circ}$), based on the Rossiter-McLaughlin effect and an analysis of starspot-crossing events. This result is valuable because almost all previous obliquity measurements are for stars with more massive planets and shorter-period orbits. In addition, the polar orbit of the planet combined with an analysis of spot-cross...

  20. Peak Bagging of red giant stars observed by Kepler: first results with a new method based on Bayesian nested sampling

    Directory of Open Access Journals (Sweden)

    Corsaro Enrico

    2015-01-01

    Full Text Available The peak bagging analysis, namely the fitting and identification of single oscillation modes in stars’ power spectra, coupled to the very high-quality light curves of red giant stars observed by Kepler, can play a crucial role for studying stellar oscillations of different flavor with an unprecedented level of detail. A thorough study of stellar oscillations would thus allow for deeper testing of stellar structure models and new insights in stellar evolution theory. However, peak bagging inferences are in general very challenging problems due to the large number of observed oscillation modes, hence of free parameters that can be involved in the fitting models. Efficiency and robustness in performing the analysis is what may be needed to proceed further. For this purpose, we developed a new code implementing the Nested Sampling Monte Carlo (NSMC algorithm, a powerful statistical method well suited for Bayesian analyses of complex problems. In this talk we show the peak bagging of a sample of high signal-to-noise red giant stars by exploiting recent Kepler datasets and a new criterion for the detection of an oscillation mode based on the computation of the Bayesian evidence. Preliminary results for frequencies and lifetimes for single oscillation modes, together with acoustic glitches, are therefore presented.

  1. Close-in planets around giant stars. Lack of hot-Jupiters and prevalence of multi-planetary systems

    CERN Document Server

    Lillo-Box, J; Correia, A C M

    2016-01-01

    Extrasolar planets abound in almost any possible configuration. However, until five years ago, there was a lack of planets orbiting closer than 0.5 au to giant or subgiant stars. Since then, recent detections have started to populated this regime by confirming 13 planetary systems. We discuss the properties of these systems in terms of their formation and evolution off the main sequence. Interestingly, we find that $70.0\\pm6.6$ % of the planets in this regime are inner components of multiplanetary systems. This value is 4.2$\\sigma$ higher than for main-sequence hosts, which we find to be $42.4\\pm0.1$ %. The properties of the known planets seem to indicate that the closest-in planets (a < 0.06 au) to main-sequence stars are massive (i.e., hot Jupiters) and isolated and that they are subsequently engulfed by their host as it evolves to the red giant branch, leaving only the predominant population of multiplanetary systems in orbits 0.06 < a < 0.5 au. We discuss the implications of this emerging observa...

  2. Bridging the Gap from Galactic to Extragalactic: Star Formation and Giant Molecular Clouds within the Nearby Spiral Galaxy NGC 300

    Science.gov (United States)

    Faesi, Christopher

    2017-01-01

    The questions surrounding the origins of stars are of key importance in astrophysics across a huge range in physical scales. However, until recently, investigations have been restricted to either detailed studies targeting a few nearby regions in the Milky Way, or kpc- or larger-scale studies of entire galaxies. Between these two scales lies a crucial gap in understanding. In this thesis work, I have taken steps in bridging this gap between Galactic and extragalactic star formation. I will present the results of a campaign of observations and modeling targeting the nearby spiral galaxy NGC 300. Using an extensive suite of multi-wavelength data I have characterized the star formation activity and molecular gas in a large sample of star-forming regions within this galaxy. Additionally, I have assembled an extensive (300 clouds) and high resolution (10 pc) catalog of Giant Molecular Clouds (GMCs) based on ALMA CO observations. This unprecedented look at the population of GMCs in a nearby spiral galaxy reveals an astonishing range of morphologies and properties in the Molecular Gas as well as providing a key testbed for comparison with GMCs in the Milky Way and other nearby galaxies. The GMCs in NGC 300 appear to have similar global properties and show scaling relations consistent with those seen in the Milky Way. Furthermore, the star formation rate appears to correlate with the mass of molecular gas with approximately 250 Gyr depletion time, extending the relation discovered in the Milky Way linearly to larger scales. These results suggest a level of universality in the star formation process within spiral galaxy disks like our own Milky Way.

  3. Amplitudes and lifetimes of solar-like oscillations observed by CoRoT* Red-giant versus main-sequence stars

    CERN Document Server

    Baudin, F; Belkacem, K; Hekker, S; Morel, T; Samadi, R; Benomar, O; Goupil, M -J; Carrier, F; Ballot, J; Deheuvels, S; De Ridder, J; Hatzes, A P; Kallinger, T; Weiss, W W

    2011-01-01

    Context. The advent of space-borne missions such as CoRoT or Kepler providing photometric data has brought new possibilities for asteroseismology across the H-R diagram. Solar-like oscillations are now observed in many stars, including red giants and main- sequence stars. Aims. Based on several hundred identified pulsating red giants, we aim to characterize their oscillation amplitudes and widths. These observables are compared with those of main-sequence stars in order to test trends and scaling laws for these parameters for both main-sequence stars and red giants. Methods. An automated fitting procedure is used to analyze several hundred Fourier spectra. For each star, a modeled spectrum is fitted to the observed oscillation spectrum, and mode parameters are derived. Results. Amplitudes and widths of red-giant solar-like oscillations are estimated for several hundred modes of oscillation. Amplitudes are relatively high (several hundred ppm) and widths relatively small (very few tenths of a {\\mu}Hz). Conclus...

  4. Amplitudes of solar-like oscillations in red-giant stars: Evidences for non-adiabatic effects using CoRoT observations

    CERN Document Server

    Samadi, R; Dupret, M -A; Ludwig, H -G; Baudin, F; Caffau, E; Goupil, M -J; Barban, C

    2012-01-01

    A growing number of solar-like oscillations has been detected in red-giant stars thanks to CoRoT and Kepler space-crafts. The seismic data gathered by CoRoT on red-giant stars allow us to test mode driving theory in different physical conditions than main-sequence stars. Using a set of 3D hydrodynamical models representative of the upper layers of sub- and red-giant stars, we compute the acoustic modes energy supply rate (Pmax). Assuming adiabatic pulsations and using global stellar models where the surface stratification comes from the 3D hydrodynamical models, mode amplitude is computed in terms of surface velocity. The latter is then converted into intensity fluctuations using either a simplified adiabatic scaling relation or a non-adiabatic one. Given L and M (the luminosity and mass respectively), the energy supply rate Pmax is found to scale as (L/M)^(2.6) for both main-sequence and red-giant stars, extending previous results by Samadi et al. (2007). The theoretical amplitudes in velocity under-estimate...

  5. The mass-loss return from evolved stars to the Large Magellanic Cloud III. Dust properties for carbon-rich asymptotic giant branch stars

    CERN Document Server

    Srinivasan, Sundar; Matsuura, M; Meixner, M; Kemper, F; Tielens, A G G M; Volk, K; Speck, A K; Woods, Paul M; Gordon, K; Marengo, M; Sloan, G C

    2010-01-01

    We present a 2Dust model for the dust shell around a LMC long-period variable (LPV) previously studied as part of the OGLE survey. OGLE LMC LPV 28579 (SAGE J051306.40-690946.3) is a carbon-rich asymptotic giant branch (AGB) star for which we have photometry and spectra from the Spitzer SAGE and SAGE-Spec programs along with UBVIJHK_s photometry. By modeling this source, we obtain a baseline set of dust properties to be used in the construction of a grid of models for carbon stars. We reproduce its spectral energy distribution using a mixture of AmC and SiC (15% by mass). The grain sizes are distributed according to the KMH model. The best-fit model has an optical depth of 0.28 for the shell at the peak of the SiC feature, with R_in~1430 R_sun or 4.4 R_star. The temperature at this inner radius is 1310 K. Assuming an expansion velocity of 10 km s^-1, we obtain a dust mass-loss rate of 2.5x10^-9 M_sun yr-1. We calculate a 15% variation in this rate by testing the fit sensitivity against variation in input param...

  6. The Pan-Pacific Planet Search III: Five companions orbiting giant stars

    CERN Document Server

    Wittenmyer, R A; Wang, L; Bergmann, C; Salter, G S; Tinney, C G; Johnson, John Asher

    2015-01-01

    We report a new giant planet orbiting the K giant HD 155233, as well as four stellar-mass companions from the Pan-Pacific Planet Search, a southern hemisphere radial velocity survey for planets orbiting nearby giants and subgiants. We also present updated velocities and a refined orbit for HD 47205b (7 CMa b), the first planet discovered by this survey. HD 155233b has a period of 885$\\pm$63 days, eccentricity e=0.03$\\pm$0.20, and m sin i=2.0$\\pm$0.5 M_jup. The stellar-mass companions range in m sin i from 0.066 M_sun to 0.33 M_sun. Whilst HD 104358B falls slightly below the traditional 0.08 M_sun hydrogen-burning mass limit, and is hence a brown dwarf candidate, we estimate only a 50% a priori probability of a truly substellar mass.

  7. A search for Li-rich giants in a sample of 12 open clusters: Li enhancement in two stars with substellar companions

    CERN Document Server

    Mena, E Delgado; Sousa, S G; Kunitomo, M; Adibekyan, V; Zaworska, P; Santos, N C; Israelian, G; Lovis, C

    2015-01-01

    The aim of this work is to search for Li-rich giants in a sample of clusters where planets have been searched, thus we can study the planet engulfment scenario to explain Li replenishment using a proper comparison sample of stars without detected giant planets. We derived Li abundances for a sample of 67 red giant stars in 12 different open clusters using standard spectral synthesis techniques and high resolution spectra (from HARPS and UVES). We also determined masses, ages and radius from PARSEC stellar isochrones to constrain the evolutionary stage of these stars. We find three stars in different clusters with clearly enhanced Li abundances compared to other stars within the cluster. Interestingly, the only two stars with a detected substellar companion in our sample belong to that group. One of the planet hosts, NGC2423No3, might lie close to the luminosity bump on the HR diagram, a phase where Li production by the Cameron-Fowler process is supported by extra-mixing to bring fresh Li up to the surface. On...

  8. THE INSIDIOUS BOOSTING OF THERMALLY PULSING ASYMPTOTIC GIANT BRANCH STARS IN INTERMEDIATE-AGE MAGELLANIC CLOUD CLUSTERS

    Energy Technology Data Exchange (ETDEWEB)

    Girardi, Léo [Osservatorio Astronomico di Padova-INAF, Vicolo dell' Osservatorio 5, I-35122 Padova (Italy); Marigo, Paola [Dipartimento di Fisica e Astronomia Galileo Galilei, Università di Padova, Vicolo dell' Osservatorio 3, I-35122 Padova (Italy); Bressan, Alessandro [SISSA, via Bonomea 365, I-34136 Trieste (Italy); Rosenfield, Philip [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)

    2013-11-10

    In the recent controversy about the role of thermally pulsing asymptotic giant branch (TP-AGB) stars in evolutionary population synthesis (EPS) models of galaxies, one particular aspect is puzzling: TP-AGB models aimed at reproducing the lifetimes and integrated fluxes of the TP-AGB phase in Magellanic Cloud (MC) clusters, when incorporated into EPS models, are found to overestimate, to various extents, the TP-AGB contribution in resolved star counts and integrated spectra of galaxies. In this paper, we call attention to a particular evolutionary aspect, linked to the physics of stellar interiors, that in all probability is the main cause of this conundrum. As soon as stellar populations intercept the ages at which red giant branch stars first appear, a sudden and abrupt change in the lifetime of the core He-burning phase causes a temporary 'boost' in the production rate of subsequent evolutionary phases, including the TP-AGB. For a timespan of about 0.1 Gyr, triple TP-AGB branches develop at slightly different initial masses, causing their frequency and contribution to the integrated luminosity of the stellar population to increase by a factor of ∼2. The boost occurs for turn-off masses of ∼1.75 M{sub ☉}, just in the proximity of the expected peak in the TP-AGB lifetimes (for MC metallicities), and for ages of ∼1.6 Gyr. Coincidently, this relatively narrow age interval happens to contain the few very massive MC clusters that host most of the TP-AGB stars used to constrain stellar evolution and EPS models. This concomitance makes the AGB-boosting particularly insidious in the context of present EPS models. As we discuss in this paper, the identification of this evolutionary effect brings about three main consequences. First, we claim that present estimates of the TP-AGB contribution to the integrated light of galaxies derived from MC clusters are biased toward too large values. Second, the relative TP-AGB contribution of single-burst populations

  9. The CRIRES Search for Planets Around the Lowest-Mass Stars. II. No Giant Planet Orbiting VB10

    CERN Document Server

    Bean, Jacob L; Hartman, Henrik; Nilsson, Hampus; Reiners, Ansgar; Dreizler, Stefan; Henry, Todd J; Wiedemann, Guenter

    2009-01-01

    We present radial velocities of the very low-mass star VB10 obtained over a time span of 0.61 yr as part of an ongoing search for planets around stars at the end of the main sequence. The radial velocities were measured from high-resolution near-infrared spectra obtained using the CRIRES instrument on the VLT with an ammonia gas cell. The typical internal precision of the measurements is 10 m/s. These data do not exhibit significant variability and are essentially constant at a level consistent with the measurement uncertainties. Therefore, we do not detect the radial velocity variations of VB10 expected due to the presence of an orbiting giant planet similar to that recently proposed by Pravdo and Shaklan based on apparent astrometric perturbations. In addition, we do not confirm the ~1 km/s radial velocity variability of the star tentatively detected by Zapatero Osorio and colleagues with lower precision measurements. Our measurements rule out planets with M > 3 M_Jup and the orbital period and inclination ...

  10. The chemical composition of red giant stars in four intermediate-age clusters of the Large Magellanic Cloud

    CERN Document Server

    Mucciarelli, A; Origlia, L; Ferraro, F R

    2008-01-01

    This paper presents the chemical abundance analysis of a sample of 27 red giant stars located in 4 popolous intermediate-age globular clusters in the Large Magellanic Cloud, namely NGC 1651, 1783, 1978 and 2173. This analysis is based on high-resolution (R ~ 47000) spectra obtained with the UVES@VLT spectrograph. For each cluster we derived up to 20 abundance ratios sampling the main chemical elemental groups, namely light odd-Z, alpha, iron-peak and neutron-capture elements. All the analysed abundance patterns behave similarly in the 4 clusters and also show negligible star-to-star scatter within each cluster. We find [Fe/H]=-0.30+-0.03, -0.35+-0.02, -0.38+-0.02 and -0.51+-0.03 dex for NGC 1651, 1783, 1978 and 2173, respectively. The measurement of light odd-Z nuclei gives slightly subsolar [Na/Fe] and a more significant [Al/Fe] depletion (~ -0.50 dex). The [alpha / Fe] abundance ratios are nearly solar, while the iron-peak elements well trace that one of the iron. s-process elements behave in a peculiar way...

  11. Exclusion of a luminous red giant as a companion star to the progenitor of supernova SN 2011fe.

    Science.gov (United States)

    Li, Weidong; Bloom, Joshua S; Podsiadlowski, Philipp; Miller, Adam A; Cenko, S Bradley; Jha, Saurabh W; Sullivan, Mark; Howell, D Andrew; Nugent, Peter E; Butler, Nathaniel R; Ofek, Eran O; Kasliwal, Mansi M; Richards, Joseph W; Stockton, Alan; Shih, Hsin-Yi; Bildsten, Lars; Shara, Michael M; Bibby, Joanne; Filippenko, Alexei V; Ganeshalingam, Mohan; Silverman, Jeffrey M; Kulkarni, S R; Law, Nicholas M; Poznanski, Dovi; Quimby, Robert M; McCully, Curtis; Patel, Brandon; Maguire, Kate; Shen, Ken J

    2011-12-14

    Type Ia supernovae are thought to result from a thermonuclear explosion of an accreting white dwarf in a binary system, but little is known of the precise nature of the companion star and the physical properties of the progenitor system. There are two classes of models: double-degenerate (involving two white dwarfs in a close binary system) and single-degenerate models. In the latter, the primary white dwarf accretes material from a secondary companion until conditions are such that carbon ignites, at a mass of 1.38 times the mass of the Sun. The type Ia supernova SN 2011fe was recently detected in a nearby galaxy. Here we report an analysis of archival images of the location of SN 2011fe. The luminosity of the progenitor system (especially the companion star) is 10-100 times fainter than previous limits on other type Ia supernova progenitor systems, allowing us to rule out luminous red giants and almost all helium stars as the mass-donating companion to the exploding white dwarf.

  12. Variations on Debris Disks III. Collisional Cascades and Giant Impacts in the Terrestrial Zones of Solar-type Stars

    CERN Document Server

    Kenyon, Scott J

    2015-01-01

    We analyze two new sets of coagulation calculations for solid particles orbiting within the terrestrial zone of a solar-type star. In models of collisional cascades, numerical simulations demonstrate that the total mass, the mass in 1 mm and smaller particles, and the dust luminosity decline with time more rapidly than predicted by analytic models, $\\propto t^{-n}$ with $n \\approx$ 1.1-1.2 instead of 1. Size distributions derived from the numerical calculations follow analytic predictions at radii less than 0.1 km but are shallower than predicted at larger sizes. In simulations of planet formation, the dust luminosity declines more slowly than in pure collisional cascades, with $n \\approx$ 0.5-0.8 instead of 1.1-1.2. Throughout this decline, giant impacts produce large, observable spikes in dust luminosity which last roughly 0.01-0.1 Myr and recur every 1-10 Myr. If most solar-type stars have Earth mass planets with $a \\lesssim$ 1-2 AU, observations of debris around 1-100 Myr stars allow interesting tests of ...

  13. Migration and Growth of Protoplanetary Embryos. III. Mass and Metallicity Dependence for FGKM Main-sequence Stars

    Science.gov (United States)

    Liu, Beibei; Zhang, Xiaojia; Lin, Douglas N. C.

    2016-06-01

    Radial velocity and transit surveys have found that the fraction of FGKM stars with close-in super-Earth(s) (η ⊕) is around 30%-50%, independent of the stellar mass M * and metallicity Z *. In contrast, the fraction of solar-type stars harboring one or more gas giants (η J) with masses M p > 100 M ⊕ is nearly 10%-15%, and it appears to increase with both M * and Z *. Regardless of the properties of their host stars, the total mass of some multiple super-Earths systems exceeds the core mass of Jupiter and Saturn. We suggest that both super-Earths and supercritical cores of gas giants were assembled from a population of embryos that underwent convergent type I migration from their birthplaces to a transition location between viscously heated and irradiation-heated disk regions. We attribute the cause for the η ⊕-η J dichotomy to conditions required for embryos to merge and to acquire supercritical core mass ({M}{{c}}˜ 10 {M}\\oplus ) for the onset of efficient gaseous envelope accretion. We translate this condition into a critical disk accretion rate, and our analysis and simulation results show that it weakly depends on M * and decreases with metallicity of disk gas Z d. We find that embryos are more likely to merge into supercritical cores around relatively massive and metal-rich stars. This dependence accounts for the observed η J-M *. We also consider the {Z}{{d}}{--}{Z}* dispersed relationship and reproduce the observed η J-Z * correlation.

  14. Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars. V. Oxygen abundance in the metal-poor giant HD 122563 from OH UV lines

    CERN Document Server

    Prakapavičius, D; Dobrovolskas, V; Klevas, J; Steffen, M; Bonifacio, P; Ludwig, H -G; Spite, M

    2016-01-01

    Although oxygen is an important tracer of the early Galactic evolution, its abundance trends with metallicity are still relatively poorly known at [Fe/H] < -2.5. This is in part due to a lack of reliable oxygen abundance indicators in the metal-poor stars, in part due to shortcomings in 1D LTE abundance analyses. In this study we determined the oxygen abundance in the metal-poor halo giant HD 122563 using a 3D hydrodynamical CO5BOLD model atmosphere. Our main goal was to understand whether a 3D LTE analysis may help to improve the reliability of oxygen abundances determined from OH UV lines in comparison to those obtained using standard 1D LTE methodology. The oxygen abundance in HD 122563 was determined using 71 OH UV lines located in the wavelength range between 308-330 nm. The analysis was done using a high-resolution VLT UVES spectrum with a 1D LTE spectral line synthesis performed using the SYNTHE package and classical ATLAS9 model atmosphere. Subsequently, a 3D hydrodynamical CO5BOLD, and 1D hydrosta...

  15. The Neuro Imaging Description of Giant Pituitary Adenomas Depending on Mechanical Factor

    Directory of Open Access Journals (Sweden)

    Yu.M. Urmanova

    2016-08-01

    Full Text Available The research aim is to analyze of magnetically-resonance tomography data depending on the mechanical factor of giant pituitary adenomas. Materials and methods. Twenty-two adult patients with giant pituitary adenomas were observed during the period from 2015 to 2016 (men 50 %, aged 48.5 years old. The duration of disease varied from 2 months to 25 years. Results. Patients with endo-suprasellar growth of pituitary tumour had signs of chiasmal syndrome with bitemporal hemianopsia, initial or complete homonym hemianopsia, scotomas and others. Such variant of pituitary tumour growth was observed in 7 cases (31.8 %. 4.5 % patients with retro-sellar growth of pituitary tumour typically had violations caused by the growth of tumour into brainstem, that stipulated both the lesion of craniocerebral nerves and vegetative disorders, and also pyramid symptomatology (pathological reflexes, symptoms of oral automatism. Patients with the endo-laterosellar growth of tumour suffered from decline of sharpness of sight on one eye, one-sided headaches, lesion of oculomotorius. For 4.5 % patients with the endo-infrasellar growth of tumour violations of the nasal breathing and swallowing (odynophagia were typical. Conclusions. The most expressed neuroendocrine, ophthalmology and pillar disorders were observed in patients with the total growth of tumor. The giant pituitary adenomas are often accompanied by an invasion growth into surrounding anatomic structures (69.2 % that is a basic factor limiting radical operative intervention and increasing the number of relapses.

  16. The Mass Loss Return from Evolved Stars to the Large Magellanic Cloud : Oxygen-Rich Asymptotic Giant Branch Stars

    NARCIS (Netherlands)

    Sargent, Benjamin A.; Srinivasan, S.; Meixner, M.; Kemper, F.; Tielens, X.; Speck, A.; Matsuura, M.; Bernard, J.; Hony, S.; Gordon, K.; Indebetouw, R.; Marengo, M.; Sloan, G.; Woods, P.; Vijh, U. P.

    2010-01-01

    The Spitzer Space Telescope Legacy program Surveying the Agents of a Galaxy's Evolution (SAGE; PI: M. Meixner) has observed over 6 million stars in the Large Magellanic Cloud with both the Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS) instruments to explore the lif

  17. The Mass Loss Return from Evolved Stars to the Large Magellanic Cloud: Oxygen-Rich Asymptotic Giant Branch Stars

    NARCIS (Netherlands)

    Sargent, Benjamin A.; Srinivasan, S.; Meixner, M.; Kemper, F.; Tielens, X.; Speck, A.; Matsuura, M.; Bernard, J.; Hony, S.; Gordon, K.; Indebetouw, R.; Marengo, M.; Sloan, G.; Woods, P.; Vijh, U. P.

    2010-01-01

    The Spitzer Space Telescope Legacy program Surveying the Agents of a Galaxy's Evolution (SAGE; PI: M. Meixner) has observed over 6 million stars in the Large Magellanic Cloud with both the Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS) instruments to explore the lif

  18. SIM PlanetQuest Key Project Precursor Observations to Detect Gas Giant Planets Around Young Stars

    Science.gov (United States)

    Tanner, Angelle; Beichman, Charles; Akeson, Rachel; Ghez, Andrea; Grankin, Konstantin N.; Herbst, William; Hillenbrand, Lynne; Huerta, Marcos; Konopacky, Quinn; Metchev, Stanimir; Mohanty, Subhanjoy; Prato, L.; Simon, Michal

    2008-01-01

    We present a review of precursor observing programs for the SIM PlanetQuest Key project devoted to detecting Jupiter mass planets around young stars. In order to ensure that the stars in the sample are free of various sources of astrometric noise that might impede the detection of planets, we have initiated programs to collect photometry, high contrast images, interferometric data and radial velocities for stars in both the Northern and Southern hemispheres. We have completed a high contrast imaging survey of target stars in Taurus and the Pleiades and found no definitive common proper motion companions within one arcsecond (140 AU) of the SIM targets. Our radial velocity surveys have shown that many of the target stars in Sco-Cen are fast rotators and a few stars in Taurus and the Pleiades may have sub-stellar companions. Interferometric data of a few stars in Taurus show no signs of stellar or sub-stellar companions with separations of 0.1 mag) that would degrade the astrometric accuracy achievable for that star. While the precursor programs are still a work in progress, we provide a comprehensive list of all targets ranked according to their viability as a result of the observations taken to date. By far, the observable that removes the most targets from the SIM-YSO program is photometric variability.

  19. Giant clumps in simulated high- z Galaxies: properties, evolution and dependence on feedback

    Science.gov (United States)

    Mandelker, Nir; Dekel, Avishai; Ceverino, Daniel; DeGraf, Colin; Guo, Yicheng; Primack, Joel

    2017-01-01

    We study the evolution and properties of giant clumps in high-z disc galaxies using adaptive mesh refinement cosmological simulations at redshifts z ˜ 6-1. Our sample consists of 34 galaxies, of halo masses 1011-1012 M⊙ at z = 2, run with and without radiation pressure (RP) feedback from young stars. While RP has little effect on the sizes and global stability of discs, it reduces the amount of star-forming gas by a factor of ˜2, leading to a similar decrease in stellar mass by z ˜ 2. Both samples undergo extended periods of violent disc instability continuously forming giant clumps of masses 107-109 M⊙ at a similar rate, though RP significantly reduces the number of long-lived clumps (LLCs). When RP is (not) included, clumps with circular velocity ≲ 40 (20) km s- 1, baryonic surface density ≲ 200 (100)M⊙ pc- 2 and baryonic mass ≲ 108.2 (107.3) M⊙ are short-lived, disrupted in a few free-fall times. More massive and dense clumps survive and migrate towards the disc centre over a few disc orbital times. In the RP simulations, the distribution of clump masses and star formation rates (SFRs) normalized to their host disc is similar at all redshifts, exhibiting a truncated power law with a slope slightly shallower than -2. The specific SFR (sSFR) of the LLCs declines with age as they migrate towards the disc centre, producing gradients in mass, stellar age, gas fraction, sSFR and metallicity that distinguish them from the short-lived clumps which tend to populate the outer disc. Ex situ mergers comprise ˜37 per cent of the mass in clumps and ˜29 per cent of the SFR. They are more massive and with older stellar ages than the in situ clumps, especially near the disc edge. Roughly half the galaxies at redshifts z = 4-1 are clumpy, with ˜3-30 per cent of their SFR and ˜0.1-3 per cent of their stellar mass in clumps.

  20. On Titanium Carbide Nanoparticles as the Origin of the 21 Micron Emission Feature in Post-Asymptotic Giant Branch Stars

    CERN Document Server

    Li, A

    2003-01-01

    Titanium carbide (TiC) nanocrystals were recently proposed as the carrier of the mysterious 21$\\mum$ emission feature observed in post-asymptotic giant branch stars, based on their close spectral match and the presolar nature of meteoritic TiC nanograins (which reveals their stellar ejecta origin). But we show in this {\\it Letter} that the Kramers-Kronig dispersion relations, which relate the wavelength-integrated extinction cross section to the total dust mass, would impose a lower bound on the TiC mass. This Kramers-Kronig lower limit exceeds the maximum available TiC mass by a factor of at least $\\simali$50, independent of the absolute value of the ultraviolet/visible absorptivity of nano TiC. The TiC model is therefore readily ruled out by the Kramers-Kronig physical principle.

  1. A grid of NLTE corrections for magnesium and calcium in late-type giant and supergiant stars: application to Gaia

    CERN Document Server

    Merle, Thibault; Pichon, Bernard; Bigot, Lionel

    2011-01-01

    We investigate NLTE effects for magnesium and calcium in the atmospheres of late-type giant and supergiant stars. The aim of this paper is to provide a grid of NLTE/LTE equivalent width ratios W/W* of Mg and Ca lines for the following range of stellar parameters: Teff in [3500, 5250] K, log g in [0.5, 2.0] dex and [Fe/H] in [-4.0, 0.5] dex. We use realistic model atoms with the best physics available and taking into account the fine structure. The Mg and Ca lines of interest are in optical and near IR ranges. A special interest concerns the lines in the Gaia spectrograph (RVS) wavelength domain [8470, 8740] A. The NLTE corrections are provided as function of stellar parameters in an electronic table as well as in a polynomial form for the Gaia/RVS lines.

  2. 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.

  3. Three-dimensional hydrodynamical simulations of red giant stars: semi-global models for the interpretation of interferometric observations

    CERN Document Server

    Chiavassa, A; Casagrande, L; Asplund, M

    2010-01-01

    Context. Theoretical predictions from models of red giant branch stars are a valuable tool for various applications in astrophysics ranging from galactic chemical evolution to studies of exoplanetary systems. Aims. We use the radiative transfer code OPTIM3D and realistic 3D radiative-hydrodynamical (RHD) surface convection simulations of red giants to explore the impact of granulation on interferometric observables. Methods. We compute intensity maps for the 3D simulation snapshots in two filters: in the optical at 5000 \\pm 300 {\\AA} and in the K band 2.14 $\\pm$ 0.26 {\\mu}m FLUOR filter, corresponding to the wavelength-range of instruments mounted on the CHARA interferometer. From the intensity maps, we construct images of the stellar disks, accounting for center-to-limb variations. We then derive interferometric visibility amplitudes and phases. We study their behavior with position angle and wavelength. Results. We provide average limb-darkening coefficients for different metallicities and wavelength-ranges...

  4. The Dense Filamentary Giant Molecular Cloud G23.0-0.4: Birthplace of Ongoing Massive Star Formation

    CERN Document Server

    Su, Yang; Shao, Xiangjun; Yang, Ji

    2015-01-01

    We present observations of 1.5 square degree maps of the 12CO, 13CO, and C18O (J=1-0) emission toward the complex region of the supernova remnant (SNR) W41 and SNR G22.7-0.2. A massive (~5E5Msun), large (~84x15 pc), and dense (~10E3 cm^-3) giant molecular cloud (GMC), G23.0-0.4 with VLSR~77 km/s, is found to be adjacent to the two SNRs. The GMC displays a filamentary structure approximately along the Galactic plane. The filamentary structure of the dense molecular gas, traced by C18O (J=1-0) emission, is also coincident well with the distribution of the dust-continuum emission in the direction. Two dense massive MC clumps, two 6.7 GHz methanol masers, and one HII/SNR complex, associated with the 77 km/s GMC G23.0-0.4, are aligned along the filamentary structure, indicating the star forming activity within the GMC. These sources have periodic projected spacing of 0.18-0.26degree along the giant filament, which is consistent well with the theoretical predictions of 0.22degree. It indicates that the turbulence s...

  5. Connecting the evolution of thermally pulsing asymptotic giant branch stars to the chemistry in their circumstellar envelopes - I. Hydrogen cyanide

    Science.gov (United States)

    Marigo, Paola; Ripamonti, Emanuele; Nanni, Ambra; Bressan, Alessandro; Girardi, Léo

    2016-02-01

    We investigate the formation of hydrogen cyanide (HCN) in the inner circumstellar envelopes of thermally pulsing asymptotic giant branch (TP-AGB) stars. A dynamic model for periodically shocked atmospheres, which includes an extended chemo-kinetic network, is for the first time coupled to detailed evolutionary tracks for the TP-AGB phase computed with the COLIBRI code. We carried out a calibration of the main shock parameters (the shock formation radius rs,0 and the effective adiabatic index γ _ad^eff) using the circumstellar HCN abundances recently measured for a populous sample of pulsating TP-AGB stars. Our models recover the range of the observed HCN concentrations as a function of the mass-loss rates, and successfully reproduce the systematic increase of HCN moving along the M-S-C chemical sequence of TP-AGB stars, which traces the increase of the surface C/O ratio. The chemical calibration brings along two important implications for the physical properties of the pulsation-induced shocks: (i) the first shock should emerge very close to the photosphere (rs,0 ≃ 1R), and (ii) shocks are expected to have a dominant isothermal character (γ _ad^eff˜eq 1) in the denser region close to the star (within ˜3-4R), implying that radiative processes should be quite efficient. Our analysis also suggests that the HCN concentrations in the inner circumstellar envelopes are critically affected by the H-H2 chemistry during the post-shock relaxation stages. Given the notable sensitiveness of the results to stellar parameters, this paper shows that such chemo-dynamic analyses may indeed provide a significant contribution to the broader goal of attaining a comprehensive calibration of the TP-AGB evolutionary phase.

  6. Investigating the origin of cyclical wind variability in hot massive stars - II. Hydrodynamical simulations of corotating interaction regions using realistic spot parameters for the O giant ξ Persei

    Science.gov (United States)

    David-Uraz, A.; Owocki, S. P.; Wade, G. A.; Sundqvist, J. O.; Kee, N. D.

    2017-09-01

    OB stars exhibit various types of spectral variability historically associated with wind structures, including the apparently ubiquitous discrete absorption components (DACs). These features have been proposed to be caused either by magnetic fields or non-radial pulsations. In this second paper of this series, we revisit the canonical phenomenological hydrodynamical modelling used to explain the formation of DACs by taking into account modern observations and more realistic theoretical predictions. Using constraints on putative bright spots located on the surface of the O giant ξ Persei derived from high precision space-based broad-band optical photometry obtained with the Microvariability and Oscillations of Stars (MOST) space telescope, we generate 2D hydrodynamical simulations of corotating interaction regions in its wind. We then compute synthetic ultraviolet (UV) resonance line profiles using Sobolev Exact Integration and compare them with historical timeseries obtained by the International Ultraviolet Explorer (IUE) to evaluate if the observed behaviour of ξ Persei's DACs is reproduced. Testing three different models of spot size and strength, we find that the classical pattern of variability can be successfully reproduced for two of them: the model with the smallest spots yields absorption features that are incompatible with observations. Furthermore, we test the effect of the radial dependence of ionization levels on line driving, but cannot conclusively assess the importance of this factor. In conclusion, this study self-consistently links optical photometry and UV spectroscopy, paving the way to a better understanding of cyclical wind variability in massive stars in the context of the bright spot paradigm.

  7. Giant coronal loops dominate the quiescent X-ray emission in rapidly rotating M stars

    CERN Document Server

    Cohen, O; Garraffo, C; Saar, S H; Wolk, S J; Kashyap, V L; Drake, J J; Pillitteri, I

    2016-01-01

    Observations indicate that magnetic fields in rapidly rotating stars are very strong, on both small and large scales. What is the nature of the resulting corona? Here we seek to shed some light on this question. We use the results of an anelastic dynamo simulation of a rapidly rotating fully-convective M-star to drive a physics-based model for the stellar corona. We find that due to the several kilo Gauss large-scale magnetic fields at high latitudes, the corona and its X-ray emission are dominated by star-size large hot loops, while the smaller, underlying colder loops are not visible much in the X-ray. Based on this result we propose that, in rapidly rotating stars, emission from such coronal structures dominates the quiescent, cooler but saturated X-ray emission.

  8. Binarity in Cool Asymptotic Giant Branch Stars: A Galex Search for Ultraviolet Excesse

    CERN Document Server

    Sahai, R; de Paz, A Gil; Contreras, C Sánchez

    2008-01-01

    The search for binarity in AGB stars is of critical importance for our understanding of how planetary nebulae acquire the dazzling variety of aspherical shapes which characterises this class. However, detecting binary companions in such stars has been severely hampered due to their extreme luminosities and pulsations. We have carried out a small imaging survey of AGB stars in ultraviolet light (using GALEX) where these cool objects are very faint, in order to search for hotter companions. We report the discovery of significant far-ultraviolet excesses towards nine of these stars. The far-ultraviolet excess most likely results either directly from the presence of a hot binary companion, or indirectly from a hot accretion disk around the companion.

  9. Mixing along the Red Giant Branch in Metal-poor Field Stars

    CERN Document Server

    Carretta, E; Sneden, C; Bragaglia, A; Carretta, Eugenio; Gratton, Raffaele; Sneden, Chris; Bragaglia, Angela

    1999-01-01

    We have determined Li, C, N, O, Na, and Fe abundances, and 12C/13C isotopic ratios for a sample of 62 field metal-poor stars (plus 43 taken from the literature). This large sample was used to show that small mass lower-RGB stars (i.e., fainter than the RGB bump) have abundances of light elements in agreement with theoretical predictions from classical evolutionary models. A second, distinct mixing episode occurs just after the RGB bump, reaching regions of incomplete CNO burning. No O-Na anticorrelation, as observed in globular cluster stars, is found in field stars. This means that the mixing episode is not deep enough to reach regions where ON-burning occurs.

  10. Star clusters and the structure of the ISM Tunnels and wakes in giant extragalactic HII regions

    CERN Document Server

    Tenorio-Tagle, G; Tenorio-Tagle, Guillermo; Tanco, Gustavo Medina

    1998-01-01

    Several structures have been discovered embedded in regions of recent or ongoing star formation, which point to the importance of the interaction between fast moving wind-blowing stars and their environment. Using hydrodynamic simulations, we investigate the passage through the interstellar medium of a supersonic stellar wind source, and show how it can naturally lead to the formation of tubes, channels and swamps of globules as interfaces are crossed. The results are in excellent agreement with observation of 30 Doradus.

  11. KELT-9b: A giant planet with the temperature of a red dwarf star transiting an unevolved A0 star

    Science.gov (United States)

    Gaudi, B. Scott; Stassun, Keivan G.; Collins, Karen A.; Beatty, Thomas G.; Zhou, George; Latham, David W.; Bieryla, Allyson; Eastman, Jason D.; Siverd, Robert; Crepp, Justin R.; Gonzales, Erica J.; Stevens, Daniel J.; Buchhave, Lars A.; Pepper, Joshua; Johnson, Marshall C.; Colon, Knicole D.; Jensen, Eric L. N.; Rodriguez, Joseph; KELT and KELT-FUN Collaborations

    2017-06-01

    We report the discovery of KELT-9b, the hottest, most irradiated known hot Jupiter, with a period of ~1.5 days, and radius and mass of ~1.8 Jupiter radii and ~2.7 Jupiter masses. The host is a massive (~2.3 solar masses), hot (effective temperature of ~9,600 K) rapidly-rotating (projected rotation velocity of ~100 km/s) A0 star. Given the implied planetary equilibrium temperature of ~3800 K and scale height of ~1000 km (assuming zero albedo and no heat redistribution), this system provides one of the best targets for detailed characterization of a hot Jupiter atmosphere under extreme irradiation. The planet has been confirmed via high-precision primary transit observations in multiple bands, a lack of companions in deep AO observations, radial velocity detection of the reflex motion of the star due to the companion, detection of the Doppler tomographic signal, and a detection of the secondary eclipse depth in the far-red optical (z) that implies a brightness temperature of ~4600 K, and thus exceptionally poor heat redistribution to the night side. We find that the planet is on a near-polar orbit, likely resulting in orbital precession that will be detectable within a few years. The brightness of the host, the extreme planet temperature, large planet-to-star radius ratio, large planetary atmospheric scale height, and short orbital period, make this an exceptional target for follow-up studies of the planet's atmosphere, which may exhibit unusual photochemistry due to the extreme amount of incident high-energy radiation.

  12. Bad prospects for the detection of giant stars' tidal disruption: effect of the ambient medium on bound debris

    Science.gov (United States)

    Bonnerot, Clément; Rossi, Elena M.; Lodato, Giuseppe

    2016-05-01

    Most massive galaxies are thought to contain a supermassive black hole in their centre surrounded by a tenuous gas environment, leading to no significant emission. In these quiescent galaxies, tidal disruption events represent a powerful detection method for the central black hole. Following the disruption, the stellar debris evolves into an elongated gas stream, which partly falls back towards the disruption site and accretes on to the black hole producing a luminous flare. Using an analytical treatment, we investigate the interaction between the debris stream and the gas environment of quiescent galaxies. Although we find dynamical effects to be negligible, we demonstrate that Kelvin-Helmholtz instability can lead to the dissolution of the stream into the ambient medium before it reaches the black hole, likely dimming the associated flare. This result is robust against the presence of a typical stellar magnetic field and fast cooling within the stream. Furthermore, we find this effect to be enhanced for disruptions involving more massive black holes and/or giant stars. Consequently, although disruptions of evolved stars have been proposed as a useful probe of black holes with masses ≳ 108 M⊙, we argue that the associated flares are likely less luminous than expected.

  13. The Identification of Extreme Asymptotic Giant Branch Stars and Red Supergiants in M33 by 24 {\\mu}m Variability

    CERN Document Server

    Montiel, Edward J; Clayton, Geoffrey C; Engelbracht, Charles W; Johnson, Christopher B

    2014-01-01

    We present the first detection of 24 {\\mu}m variability in 24 sources in the Local Group galaxy M33. These results are based on 4 epochs of MIPS observations, which are irregularly spaced over ~750 days. We find that these sources are constrained exclusively to the Holmberg radius of the galaxy, which increases their chances of being members of M33. We have constructed spectral energy distributions (SEDs) ranging from the optical to the sub-mm to investigate the nature of these objects. We find that 23 of our objects are most likely heavily self-obscured, evolved stars; while the remaining source is the Giant HII region, NGC 604. We believe that the observed variability is the intrinsic variability of the central star reprocessed through their circumstellar dust shells. Radiative transfer modeling was carried out to determine their likely chemical composition, luminosity, and dust production rate (DPR). As a sample, our modeling has determined an average luminosity of (3.8 $\\pm$ 0.9) x 10$^4$ L$_\\odot$ and a ...

  14. Disruption of a Red Giant Star by a Supermassive Black Hole and the Case of PS1-10jh

    CERN Document Server

    Bogdanovic, Tamara; Amaro-Seoane, Pau

    2013-01-01

    The development of a new generation of theoretical models for tidal disruptions is timely, as increasingly diverse events are being captured in surveys of the transient sky. Recently, Gezari et al. (2012) reported a discovery of a new class of tidal disruption events: the disruption of a helium-rich stellar core, thought to be a remnant of a red giant (RG) star. Motivated by this discovery and in anticipation of others, we consider tidal interaction of a RG star with a supermassive black hole (SMBH) which leads to the stripping of the stellar envelope and subsequent inspiral of the compact core towards the black hole. Once the stellar envelope is removed the inspiral of the core is driven by tidal heating as well as the emission of gravitational radiation until the core either falls into the SMBH or is tidally disrupted. In the case of tidal disruption candidate PS1-10jh we find that there is a set of orbital solutions at high eccentricities in which the tidally stripped hydrogen envelope is accreted by the S...

  15. The Chemical Composition of Red Giant Branch Stars in the Galactic Globular Clusters NGC 6342 and NGC 6366

    CERN Document Server

    Johnson, Christian I; Rich, R Michael; Pilachowski, Catherine A; Hsyu, Tiffany

    2016-01-01

    We present radial velocities and chemical abundances for red giant branch stars in the Galactic bulge globular clusters NGC 6342 and NGC 6366. The velocities and abundances are based on measurements of high resolution (R > 20,000) spectra obtained with the MMT-Hectochelle and WIYN-Hydra spectrographs. We find that NGC 6342 has a heliocentric radial velocity of +112.5 km/s (sigma = 8.6 km/s), NGC 6366 has a heliocentric radial velocity of -122.3 km/s (sigma = 1.5 km/s), and that both clusters have nearly identical metallicities ([Fe/H] ~ -0.55). NGC 6366 shows evidence of a moderately extended O-Na anti-correlation, but more data are needed for NGC 6342 to determine if this cluster also exhibits the typical O-Na relation likely found in all other Galactic globular clusters. The two clusters are distinguished from similar metallicity field stars as having larger [Na/Fe] spreads and enhanced [La/Fe] ratios, but we find that NGC 6342 and NGC 6366 display alpha and Fe-peak element abundance patterns that are typic...

  16. The Chemical Composition of Red Giant Branch Stars in the Galactic Globular Clusters NGC 6342 and NGC 6366

    Science.gov (United States)

    Johnson, Christian I.; Caldwell, Nelson; Rich, R. Michael; Pilachowski, Catherine A.; Hsyu, Tiffany

    2016-07-01

    We present radial velocities and chemical abundances for red giant branch stars in the Galactic bulge globular clusters NGC 6342 and NGC 6366. The velocities and abundances are based on measurements of high-resolution (R ≳ 20,000) spectra obtained with the MMT-Hectochelle and WIYN-Hydra spectrographs. We find that NGC 6342 has a heliocentric radial velocity of +112.5 km s-1 (σ = 8.6 km s-1), NGC 6366 has a heliocentric radial velocity of -122.3 km s-1 (σ = 1.5 km s-1), and both clusters have nearly identical metallicities ([Fe/H] ≈ -0.55). NGC 6366 shows evidence of a moderately extended O-Na anti-correlation, but more data are needed for NGC 6342 to determine if this cluster also exhibits the typical O-Na relation likely found in all other Galactic globular clusters. The two clusters are distinguished from similar metallicity field stars as having larger [Na/Fe] spreads and enhanced [La/Fe] ratios, but we find that NGC 6342 and NGC 6366 display α and Fe-peak element abundance patterns that are typical of other metal-rich ([Fe/H] > -1) inner Galaxy clusters. However, the median [La/Fe] abundance may vary from cluster-to-cluster.

  17. Constraints on the Magellanic Clouds' Interaction from the Distribution of OB Stars and the Kinematics of Giants

    CERN Document Server

    Casetti-Dinescu, Dana I; Girard, Terrence M; van Altena, William F

    2012-01-01

    Young, OB-type candidates are identified in a ~7900 sq-deg. region encompassing the Large and Small Magellanic Clouds (LMC/SMC) periphery, the Bridge, part of the Magellanic Stream (MS) and Leading Arm (LA). Selection is based on UV, optical and IR photometry from existing large-area surveys and proper motions from the Southern Proper Motion 4 catalog (SPM4). The spatial distribution of these young star candidates shows: 1) a well-populated SMC wing which continues westward with two branches partially surrounding the SMC, 2) a rather narrow path from the SMC wing eastward toward the LMC which is offset by 1 to 2 deg. from the high-density H I ridge in the Bridge, 3) a well-populated periphery of the LMC dominated by clumps of stars at the ends of the LMC bar and 4) a few scattered candidates in the MS and two overdensities in the LA regions above and below the Galactic plane. Additionally, a proper-motion analysis is made of a radial-velocity selected sample of red giants and supergiants in the LMC, previousl...

  18. Determining the forsterite abundance of the dust around Asymptotic Giant Branch stars

    CERN Document Server

    de Vries, B L; Waters, L B F M; Blommaert, J A D L; Kemper, F

    2010-01-01

    Aims. We present a diagnostic tool to determine the abundance of the crystalline silicate forsterite in AGB stars surrounded by a thick shell of silicate dust. Using six infrared spectra of high mass-loss oxygen rich AGB stars we obtain the forsterite abundance of their dust shells. Methods. We use a monte carlo radiative transfer code to calculate infrared spectra of dust enshrouded AGB stars. We vary the dust composition, mass-loss rate and outer radius. We focus on the strength of the 11.3 and the 33.6 \\mu m forsterite bands, that probe the most recent (11.3 \\mu m) and older (33.6 \\mu m) mass-loss history of the star. Simple diagnostic diagrams are derived, allowing direct comparison to observed band strengths. Results. Our analysis shows that the 11.3 \\mu m forsterite band is a robust indicator for the forsterite abundance of the current mass-loss period for AGB stars with an optically thick dust shell. The 33.6 \\mu m band of forsterite is sensitive to changes in the density and the geometry of the emitti...

  19. Searching for gas giant planets on Solar System scales - A NACO/APP L'-band survey of A- and F-type Main Sequence stars

    CERN Document Server

    Meshkat, T; Reggiani, M; Quanz, S P; Mamajek, E E; Meyer, M R

    2015-01-01

    We report the results of a direct imaging survey of A- and F-type main sequence stars searching for giant planets. A/F stars are often the targets of surveys, as they are thought to have more massive giant planets relative to solar-type stars. However, most imaging is only sensitive to orbital separations $>$30 AU, where it has been demonstrated that giant planets are rare. In this survey, we take advantage of the high-contrast capabilities of the Apodizing Phase Plate coronagraph on NACO at the Very Large Telescope. Combined with optimized principal component analysis post-processing, we are sensitive to planetary-mass companions (2 to 12 $M_{\\rm Jup}$) at Solar System scales ($\\leq$30 AU). We obtained data on 13 stars in L'-band and detected one new companion as part of this survey: an M$6.0\\pm0.5$ dwarf companion around HD 984. We re-detect low-mass companions around HD 12894 and HD 20385, both reported shortly after the completion of this survey. We use Monte Carlo simulations to determine new constraints...

  20. CONSTRAINTS ON THE MAGELLANIC CLOUDS' INTERACTION FROM THE DISTRIBUTION OF OB STARS AND THE KINEMATICS OF GIANTS

    Energy Technology Data Exchange (ETDEWEB)

    Casetti-Dinescu, Dana I.; Girard, Terrence M.; Van Altena, William F. [Astronomy Department, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Vieira, Katherine, E-mail: dana.casetti@yale.edu, E-mail: terry.girard@yale.edu, E-mail: william.vanaltena@yale.edu, E-mail: kvieira@cida.ve [Centro de Investigaciones de Astronomia, Apartado Postal 264, Merida 5101-A (Venezuela, Bolivarian Republic of)

    2012-07-10

    Young, OB-type candidates are identified in a {approx}7900 deg{sup 2} region encompassing the Large and Small Magellanic Clouds (LMC/SMC) periphery, the Bridge, part of the Magellanic Stream (MS), and Leading Arm (LA). Selection is based on UV, optical, and IR photometry from existing large-area surveys and proper motions from the Southern Proper Motion 4 (SPM4) catalog. The spatial distribution of these young star candidates shows (1) a well-populated SMC wing which continues westward with two branches partially surrounding the SMC, (2) a rather narrow path from the SMC wing eastward toward the LMC which is offset by 1 Degree-Sign -2 Degree-Sign from the high-density H I ridge in the Bridge, (3) a well-populated periphery of the LMC dominated by clumps of stars at the ends of the LMC bar, and (4) a few scattered candidates in the MS and two overdensities in the LA regions above and below the Galactic plane. Additionally, a proper-motion analysis is made of a radial-velocity-selected sample of red giants and supergiants in the LMC, previously shown to be a kinematically and chemically distinct subgroup, most likely captured from the SMC. SPM4 proper motions of these stars also indicate they are distinct from the LMC population. The observational results presented here, combined with the known orbits of the Clouds and other aspects of the LMC morphology, suggest an off-center, moderate to highly inclined collision between the SMC and the LMC's disk that took place between 100 and 200 Myr ago.

  1. The K2-ESPRINT Project V: a short-period giant planet orbiting a subgiant star

    CERN Document Server

    Van Eylen, Vincent; Gandolfi, Davide; Dai, Fei; Winn, Joshua N; Hirano, Teriyuki; Narita, Norio; Bruntt, Hans; Prieto-Arranz, Jorge; Bejar, Victor J S; Nowak, Grzegorz; Lund, Mikkel N; Palle, Enric; Ribas, Ignasi; Sanchis-Ojeda, Roberto; Yu, Liang; Arriagada, Pamela; Butler, R Paul; Crane, Jeffrey D; Handberg, Rasmus; Deeg, Hans; Jessen-Hansen, Jens; Johnson, John A; Nespral, David; Rogers, Leslie; Ryu, Tsuguru; Shectman, Stephen; Shrotriya, Tushar; Slumstrup, Ditte; Takeda, Yoichi; Teske, Johanna; Thompson, Ian; Vanderburg, Andrew; Wittenmyer, Robert

    2016-01-01

    We report on the discovery and characterization of the transiting planet K2-39b (EPIC 206247743b). With an orbital period of 4.6 days, it is the shortest-period planet orbiting a subgiant star known to date. Such planets are rare, with only a handful of known cases. The reason for this is poorly understood, but may reflect differences in planet occurrence around the relatively high-mass stars that have been surveyed, or may be the result of tidal destruction of such planets. K2-39 is an evolved star with a spectroscopically derived stellar radius and mass of $3.88^{+0.48}_{-0.42}~\\mathrm{R_\\odot}$ and $1.53^{+0.13}_{-0.12}~\\mathrm{M_\\odot}$, respectively, and a very close-in transiting planet, with $a/R_\\star = 3.4$. Radial velocity (RV) follow-up using the HARPS, FIES and PFS instruments leads to a planetary mass of $50.3^{+9.7}_{-9.4}~\\mathrm{M_\\oplus}$. In combination with a radius measurement of $8.3 \\pm 1.1~\\mathrm{R_\\oplus}$, this results in a mean planetary density of $0.50^{+0.29}_{-0.17}$ g~cm$^{-3}$...

  2. The K2-ESPRINT Project V: a short-period giant planet orbiting a subgiant star

    DEFF Research Database (Denmark)

    Van Eylen, Vincent; Albrecht, Simon; Gandolfi, Davide;

    2016-01-01

    {R_\\odot}$ and $1.53^{+0.13}_{-0.12}~\\mathrm{M_\\odot}$, respectively, and a very close-in transiting planet, with $a/R_\\star = 3.4$. Radial velocity (RV) follow-up using the HARPS, FIES and PFS instruments leads to a planetary mass of $50.3^{+9.7}_{-9.4}~\\mathrm{M_\\oplus}$. In combination with a radius measurement......We report on the discovery and characterization of the transiting planet K2-39b (EPIC 206247743b). With an orbital period of 4.6 days, it is the shortest-period planet orbiting a subgiant star known to date. Such planets are rare, with only a handful of known cases. The reason for this is poorly...... understood, but may reflect differences in planet occurrence around the relatively high-mass stars that have been surveyed, or may be the result of tidal destruction of such planets. K2-39 is an evolved star with a spectroscopically derived stellar radius and mass of $3.88^{+0.48}_{-0.42}~\\mathrm...

  3. A giant stream of metal-rich stars in the halo of the galaxy M31

    NARCIS (Netherlands)

    Ibata, R; Irwin, M; Lewis, G; Ferguson, AMN; Tanvir, N

    2001-01-01

    Recent observations have revealed streams of gas and stars in the halo of the Milky Way(1-3) that are the debris from interactions between our Galaxy and some of its dwarf companion galaxies; the Sagittarius dwarf galaxy and the Magellanic clouds. Analysis of the material has shown that much of the

  4. Energy dependence of the freeze out eccentricity from the azimuthal dependence of HBT at STAR

    CERN Document Server

    ,

    2011-01-01

    Non-central heavy ion collisions create an out-of-plane-extended participant zone that expands toward a more round state as the system evolves. The recent RHIC Beam Energy Scan at sqrt{s_{NN}} of 7.7, 11.5, and 39 GeV provide an opportunity to explore the energy dependence of the freeze out eccentricity. The new low energy data from STAR complements high statistics data sets at sqrt{s_{NN}} of 62.4 and 200 GeV. Hanbury-Brown-Twiss (HBT) interferometry allows to determine the size of pion emitting source regions. The dependence of the HBT radius parameters on azimuthal angle relative to the reaction plane have been extracted. These dependencies can be related to the freeze out eccentricity. The new results from STAR are consistent with a monotonically decreasing freeze out eccentricity and constrain any minimum, suggested by previously available data, to lie in the range between 11.5 and 39 GeV. Of several models UrQMD appears to best predict the STAR and AGS data.

  5. The K2-ESPRINT Project V: A Short-period Giant Planet Orbiting a Subgiant Star*

    Science.gov (United States)

    Van Eylen, Vincent; Albrecht, Simon; Gandolfi, Davide; Dai, Fei; Winn, Joshua N.; Hirano, Teriyuki; Narita, Norio; Bruntt, Hans; Prieto-Arranz, Jorge; Béjar, Víctor J. S.; Nowak, Grzegorz; Lund, Mikkel N.; Palle, Enric; Ribas, Ignasi; Sanchis-Ojeda, Roberto; Yu, Liang; Arriagada, Pamela; Butler, R. Paul; Crane, Jeffrey D.; Handberg, Rasmus; Deeg, Hans; Jessen-Hansen, Jens; Johnson, John A.; Nespral, David; Rogers, Leslie; Ryu, Tsuguru; Shectman, Stephen; Shrotriya, Tushar; Slumstrup, Ditte; Takeda, Yoichi; Teske, Johanna; Thompson, Ian; Vanderburg, Andrew; Wittenmyer, Robert

    2016-11-01

    We report on the discovery and characterization of the transiting planet K2-39b (EPIC 206247743b). With an orbital period of 4.6 days, it is the shortest-period planet orbiting a subgiant star known to date. Such planets are rare, with only a handful of known cases. The reason for this is poorly understood but may reflect differences in planet occurrence around the relatively high-mass stars that have been surveyed, or may be the result of tidal destruction of such planets. K2-39 (EPIC 206247743) is an evolved star with a spectroscopically derived stellar radius and mass of {3.88}-0.42+0.48 {R}ȯ and {1.53}-0.12+0.13 {M}ȯ , respectively, and a very close-in transiting planet, with a/{R}\\star =3.4. Radial velocity (RV) follow-up using the HARPS, FIES, and PFS instruments leads to a planetary mass of {50.3}-9.4+9.7 {M}\\oplus . In combination with a radius measurement of 8.3+/- 1.1 {R}\\oplus , this results in a mean planetary density of {0.50}-0.17+0.29 g cm‑3. We furthermore discover a long-term RV trend, which may be caused by a long-period planet or stellar companion. Because K2-39b has a short orbital period, its existence makes it seem unlikely that tidal destruction is wholly responsible for the differences in planet populations around subgiant and main-sequence stars. Future monitoring of the transits of this system may enable the detection of period decay and constrain the tidal dissipation rates of subgiant stars. Based on observations made with the NOT telescope under program ID. 50-022/51-503, 50-213(CAT), 52-201 (CAT), 52-108 (OPTICON), 51-211 (CAT), and ESOs 3.6 m telescope at the La Silla Paranal Observatory under program ID 095.C-0718(A).

  6. Analytical approximation to the dynamics of a binary stars system with time depending mass variation

    CERN Document Server

    López, Gustavo V

    2016-01-01

    We study the classical dynamics of a binary stars when there is an interchange of mass between them. Assuming that one of the star is more massive than the other, the dynamics of the lighter one is analyzed as a function of its time depending mass variation. Within our approximations and models for mass transference, we obtain a general result which establishes that if the lightest star looses mass, its period increases. If the lightest star win mass, its period decreases.

  7. Abundances in red giant stars - Nitrogen isotopes in carbon-rich molecular envelopes

    Science.gov (United States)

    Wannier, P. G.; Andersson, B.-G.; Olofsson, H.; Ukita, N.; Young, K.

    1991-01-01

    Results are presented of millimeter- and submillimeter-wave observations of HCN and HCCCN that were made of the circmustellar envelopes of eight carbon stars, including the two protoplanetary nebulae CRL 618 and CRL 2688. The observations yield a measure of the double ratio (N-14)(C-13)/(N-15)(C-12). Measured C-12/C-13 ratios are used to estimate the N-14/N-15 abundance ratio, with the resulting lower limits in all eight envelopes and possible direct determinations in two envelopes. The two determinations and four of the remaining six lower limits are found to be in excess of the terrestrial value of N-14/N-15 = 272, indicating an evolution of the nitrogen isotope ratio, which is consistent with stellar CNO processing. Observations of thermal SiO (v = 0, J = 2-1) emission show that the Si-29/Si-28 ratio can be determined in carbon stars, and further observations are indicated.

  8. Mass loss from late-type WN stars and its Z-dependence: very massive stars approaching the Eddington limit

    CERN Document Server

    Graefener, G

    2008-01-01

    The mass loss from Wolf-Rayet (WR) stars is of fundamental importance for the final fate of massive stars and their chemical yields. Its Z-dependence is discussed in relation to the formation of long-duration Gamma Ray Bursts (GRBs) and the yields from early stellar generations. However, the mechanism of formation of WR-type stellar winds is still under debate. We present the first fully self-consistent atmosphere/wind models for late-type WN stars. We investigate the mechanisms leading to their strong mass loss, and examine the dependence on stellar parameters, in particular on the metallicity Z. We identify WNL stars as very massive stars close to the Eddington limit, potentially still in the phase of central H-burning. Due to their high L/M ratios, these stars develop optically thick, radiatively driven winds. These winds show qualitatively different properties than the thin winds of OB stars. The resultant mass loss depends strongly on Z, but also on the Eddington factor, and the stellar temperature. We c...

  9. VLA Observations of HI in the Circumstellar Envelopes of Asymptotic Giant Branch Stars

    CERN Document Server

    Matthews, Lynn D; 10.1086/512613

    2008-01-01

    (Abridged) We have used the VLA to search for neutral atomic hydrogen in the circumstellar envelopes of five AGB stars. We have detected HI 21-cm emission coincident in both position and velocity with the semi-regular variable RS Cnc. The emission comprises a compact, slightly elongated feature centered on the star with a mean diameter ~82'' (1.5e17 cm), plus an additional filament extending ~6' to the NW. This filament suggests that a portion of the mass loss is highly asymmetric. We estimate MHI=1.5e-3 Msun and M_dot~1.7e-7 Msun/yr. Toward R Cas, we detect weak emission that peaks at the stellar systemic velocity and overlaps with the location of its circumstellar dust shell and thus is probably related to the star. In the case of IRC+10216, we were unable to confirm the detection of HI in absorption against the cosmic background previously reported by Le Bertre & Gerard. However, we detect arcs of emission at projected distances of r~14'-18' (~2e18 cm) to the NW. A large separation of the emission from...

  10. System and Energy Dependence of Strangeness Production with STAR

    CERN Document Server

    Salur, S

    2006-01-01

    The yields and spectra of strange hadrons have each been measured by STAR as a function of centrality in $\\rm \\sqrt{s_{NN}}=$ 200 GeV AuAu collisions. By comparison to measurements in pp and dAu at $\\rm \\sqrt{s_{NN}}=200$ GeV and in AuAu at $\\rm \\sqrt{s_{NN}}=62$ GeV the dependence on system size and energy is studied. Short-lived resonances, such as $\\Sigma (1385)$ and $\\Lambda (1520)$, that may decay and regenerate in the medium, are used to examine the dynamical evolution between production and freeze-out for these systems. Particle production is investigated by comparison to thermal models, which assume a simple scaling of the yield with $\\rm N_{part}$, in order to calculate the strangeness enhancement. Our hyperon measurements in AuAu indicate that $\\rm N_{bin}$ may be a more appropriate scale for the strangeness correlation volume. In this case canonical suppression can not be simply parameterized with the geometrical overlap volume but will depend on the individual quark content of each particle. This ...

  11. Band-structure-dependent nonlinear giant magnetoresistance in Ni1-xFex dual spin valves

    Science.gov (United States)

    Banerjee, N.; Robinson, J. W. A.; Aziz, A.; Ali, M.; Hickey, B. J.; Blamire, M. G.

    2012-10-01

    Conventional giant magnetoresistance (GMR) in spin valves is current-independent, so the resistance of a device depends only on the relative orientation of the magnetic layers. In dual spin valves consisting of three ferromagnetic (FM) layers separated by nonmagnetic (NM) spacers (i.e., a FM1/NM/FM2/NM/FM1), GMR can be current-dependent if spin can accumulate in FM2 when outer FM1 layers are aligned antiparallel. Currently the underlying physics is poorly understood, although spin accumulation in FM2 is likely to depend on the gradient in the density of states at the Fermi energy of the ferromagnet. To investigate this hypothesis, we have measured a series of dual spin valves with Ni1-xFex as FM2 layers of varying composition. We show that both the magnitude and sign of the nonlinear GMR depend strongly on the Fe content and thus on the band structure of the ferromagnet FM2.

  12. Evolution of low mass close binary systems with a neutron star: its dependence with the initial neutron star mass

    CERN Document Server

    De Vito, M A

    2012-01-01

    We construct a set of binary evolutionary sequences for systems composed by a normal, solar composition, donor star together with a neutron star. We consider a variety of masses for each star as well as for the initial orbital period corresponding to systems that evolve to ultra-compact or millisecond pulsar-helium white dwarf pairs. Specifically, we select a set of donor star masses of 0.50, 0.65, 0.80, 1.00, 1.25, 1.50, 1.75, 2.00, 2.25, 2.50, 3.00, and 3.50 solar masses, whereas for the accreting neutron star we consider initial masses values of 0.8, 1.0, 1.2, and 1.4 solar masses. The considered initial orbital period interval ranges from 0.5 to 12 days. It is found that the evolution of systems, with fixed initial values for the orbital period and the mass of the normal donor star, heavily depends upon the mass of the neutron star. In some cases, varying the initial value of the neutron star mass, we obtain evolved configurations ranging from ultra-compact to widely separated objects. We also analyse the...

  13. Solar-like oscillations from the depths of the red-giant star KIC 4351319 observed with Kepler

    CERN Document Server

    Di Mauro, M P; Catanzaro, G; Ventura, R; Barban, C; Bedding, T R; Christensen-Dalsgaard, J; De Ridder, J; Hekker, S; Huber, D; Kallinger, T; Miglio, A; Montalban, J; Mosser, B; Stello, D; Uytterhoeven, K; Kinemuchi, K; Kjeldsen, H; Mullally, F; Still, M

    2011-01-01

    We present the results of the asteroseismic analysis of the red-giant star KIC 4351319 (TYC 3124-914-1), observed for 30 days in short-cadence mode with the Kepler satellite. The analysis has allowed us to determine the large and small frequency separations, and the frequency of maximum oscillation power. The high signal-to-noise ratio of the observations allowed us to identify 25 independent pulsation modes whose frequencies range approximately from 300 to 500 muHz. The observed oscillation frequencies together with the accurate determination of the atmospheric parameters (effective temperature, gravity and metallicity), provided by additional ground-based spectroscopic observations, enabled us to theoretically interpret the observed oscillation spectrum. KIC 4351319 appears to oscillate with a well defined solar-type p-modes pattern due to radial acoustic modes and non-radial nearly pure p modes. In addition, several non-radial mixed modes have been identified. Theoretical models well reproduce the observed...

  14. Evolution of asymptotic giant branch stars II. Optical to far-infrared isochrones with improved TP-AGB models

    CERN Document Server

    Marigo, Paola; Bressan, Alessandro; Groenewegen, Martin A T; Silva, Laura; Granato, Gian Luigi

    2007-01-01

    We present a large set of theoretical isochrones, whose distinctive features mostly reside on the greatly improved treatment of the thermally pulsing asymptotic giant branch (TP-AGB) phase. Essentially, we have coupled the TP-AGB tracks described in Paper I, at their stages of pre-flash quiescent H-shell burning, with the evolutionary tracks for the previous evolutionary phases from Girardi et al. (2000). Theoretical isochrones for any intermediate value of age and metallicity are then derived by interpolation in the grids. We take care that the isochrones keep, to a good level of detail, the several peculiarities present in these TP-AGB tracks. Theoretical isochrones are then converted to about 20 different photometric systems -- including traditional ground-based systems, and those of recent major wide-field surveys such as SDSS, OGLE, DENIS, 2MASS, UKIDSS, etc., -- by means of synthetic photometry applied to an updated library of stellar spectra, suitably extended to include C-type stars. Finally, we corre...

  15. Swift, UVOT and Hot Stars

    CERN Document Server

    Siegel, Michael H; Hagen, Lea M Z; Hoversten, Erik A

    2015-01-01

    We present the results of our ongoing investigation into the properties of hot stars and young stellar populations using the Swift/UVOT telescope. We present UVOT photometry of open and globular clusters and show that UVOT is capable of characterizing a variety of rare hot stars, including Post-Asymptotic Giant Branch and Extreme Horizontal Branch Stars. We also present very early reults of our survey of stellar populations in the Small Magellanic Cloud. We find that the SMC has experienced recent bouts of star formation but constraining the exact star formation history will depend on finding an effective model of the reddening within the SMC.

  16. Evolution of Thermally Pulsing Asymptotic Giant Branch Stars I. The COLIBRI Code

    CERN Document Server

    Marigo, Paola; Nanni, Ambra; Girardi, Leo; Pumo, Maria Letizia

    2013-01-01

    We present the COLIBRI code for computing the evolution of stars along the TP-AGB phase. Compared to purely synthetic TP-AGB codes, COLIBRI relaxes a significant part of their analytic formalism in favour of a detailed physics applied to a complete envelope model, in which the stellar structure equations are integrated from the atmosphere down to the bottom of the hydrogen-burning shell. This allows to predict self-consistently: (i) the effective temperature, and more generally the convective envelope and atmosphere structures, correctly coupled to the changes in the surface chemical abundances and gas opacities; (ii) sphericity effects in the atmospheres; (iii) the core mass-luminosity relation and its break-down due to hot bottom burning (HBB) in the most massive AGB stars, (iv) the HBB nucleosynthesis via the solution of a complete nuclear network (pp chains, and the CNO, NeNa, MgAl cycles), including also the production of 7Li via the Cameron-Fowler beryllium transport mechanism; (v) the chemical composit...

  17. Giant molecular clouds and massive star formation in the southern milky way

    CERN Document Server

    Garcia, P; Nyman, L; Dame, T M

    2014-01-01

    The Columbia - U. de Chile CO Survey of the Southern Milky Way is used for separating the CO(1-0) emission of the fourth Galactic quadrant within the solar circle into its dominant components, giant molecular clouds (GMCs). After the subtraction of an axisymmetric model of the CO background emission in the inner Southern Galaxy, 92 GMCs are identified, and for 87 of them the two-fold distance ambiguity is solved. Their total molecular mass is M(H2) = 1.14 +/- 0.05 x 10^8 Msolar accounting for around 40% of the molecular mass estimated from an axisymmetric analysis of the H2 volume density in the Galactic disk (Bronfman et al. 1988b) M(H2) disk = 3.03 x 10^8 Msolar. The large scale spiral structure in the Southern Galaxy, within the solar circle, is traced by the GMCs in our catalog; 3 spiral arm segments: the Centaurus, Norma, and 3-kpc expanding arm are analyzed. After fitting a logarithmic spiral arm model to the arms, tangent directions at 310{\\deg}, 330{\\deg}, and 338{\\deg}, respectively, are found, consi...

  18. Ca II Triplet Spectroscopy of Small Magellanic Cloud Red Giants. IV. Abundances for a Large Sample of Field Stars and Comparison with the Cluster Sample

    Science.gov (United States)

    Parisi, M. C.; Geisler, D.; Carraro, G.; Clariá, J. J.; Villanova, S.; Gramajo, L. V.; Sarajedini, A.; Grocholski, A. J.

    2016-09-01

    This paper represents a major step forward in the systematic and homogeneous study of Small Magellanic Cloud (SMC) star clusters and field stars carried out by applying the calcium triplet technique. We present in this work the radial velocity and metallicity of approximately 400 red giant stars in 15 SMC fields, with typical errors of about 7 km s-1 and 0.16 dex, respectively. We added to this information our previously determined metallicity values for 29 clusters and approximately 350 field stars using the identical techniques. Using this enlarged sample, we analyze the metallicity distribution and gradient in this galaxy. We also compare the chemical properties of the clusters and of their surrounding fields. We find a number of surprising results. While the clusters, taken as a whole, show no strong evidence for a metallicity gradient (MG), the field stars exhibit a clear negative gradient in the inner region of the SMC, consistent with the recent results of Dobbie et al. For distances to the center of the galaxy less than 4°, field stars show a considerably smaller metallicity dispersion than that of the clusters. However, in the external SMC regions, clusters and field stars exhibit similar metallicity dispersions. Moreover, in the inner region of the SMC, clusters appear to be concentrated in two groups: one more metal-poor and another more metal-rich than field stars. Individually considered, neither cluster group presents an MG. Most surprisingly, the MG for both stellar populations (clusters and field stars) appears to reverse sign in the outer regions of the SMC. The difference between the cluster metallicity and the mean metallicity of the surrounding field stars turns out to be a strong function of the cluster metallicity. These results could be indicating different chemical evolution histories for these two SMC stellar populations. They could also indicate variations in the chemical behavior of the SMC in its internal and external regions.

  19. RADIAL VELOCITIES FROM VLT-KMOS SPECTRA OF GIANT STARS IN THE GLOBULAR CLUSTER NGC 6388

    Energy Technology Data Exchange (ETDEWEB)

    Lapenna, E.; Mucciarelli, A.; Lanzoni, B.; Ferraro, F. R.; Dalessandro, E. [Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Viale Berti Pichat 6/2, I-40127 Bologna (Italy); Origlia, L. [INAF-Osservatorio Astronomico di Bologna, Via Ranzani, 1, I-40127 Bologna (Italy); Valenti, E. [European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei München (Germany); Cirasuolo, M. [Institute for Astronomy, University of Edinburgh and STFC, UK Astronomy Technology Center Royal Observatory, Blackford Hill, EH9 3HJ, Edinburgh (United Kingdom)

    2015-01-01

    We present new radial velocity measurements for 82 stars, members of the Galactic globular cluster (GC) NGC 6388, obtained from ESO-VLT K-band Multi Object Spectrograph (KMOS) spectra acquired during the instrument Science Verification. The accuracy of the wavelength calibration is discussed and a number of tests of the KMOS response are presented. The cluster systemic velocity obtained (81.3 ± 1.5 km s{sup –1}) is in very good agreement with previous determinations. While a hint of ordered rotation is found between 9'' and 20'' from the cluster center, where the distribution of radial velocities is clearly bimodal, more data are needed before drawing any firm conclusions. The acquired sample of radial velocities has also been used to determine the cluster velocity dispersion (VD) profile between ∼9'' and 70'', supplementing previous measurements at r < 2'' and r > 60'' obtained with ESO-SINFONI and ESO-FLAMES spectroscopy, respectively. The new portion of the VD profile nicely matches the previous ones, better defining the knee of the distribution. The present work clearly shows the effectiveness of a deployable integral field unit in measuring the radial velocities of individual stars for determining the VD profile of Galactic GCs. It represents the pilot project for an ongoing large program with KMOS and FLAMES at the ESO-VLT, aimed at determining the next generation of VD and rotation profiles for a representative sample of GCs.

  20. Population synthesis to constrain Galactic and stellar physics. I. Determining age and mass of thin-disc red-giant stars

    Science.gov (United States)

    Lagarde, N.; Robin, A. C.; Reylé, C.; Nasello, G.

    2017-05-01

    Context. The cornerstone mission of the European Space Agency, Gaia, together with forthcoming complementary surveys (CoRoT, Kepler, K2, APOGEE, and Gaia-ESO), will revolutionize our understanding of the formation and history of our Galaxy, providing accurate stellar masses, radii, ages, distances, as well as chemical properties for a very large sample of stars across different Galactic stellar populations. Aims: Using an improved population synthesis approach and new stellar evolution models we attempt to evaluate the possibility of deriving ages and masses of clump stars from their chemical properties. Methods: A new version of the Besançon Galaxy models (BGM) is used in which new stellar evolutionary tracks are computed from the stellar evolution code STAREVOL. These provide global, chemical, and seismic properties of stars from the pre-main sequence to the early-AGB. For the first time, the BGM can explore the effects of an extra-mixing occurring in red-giant stars. In particular we focus on the effects of thermohaline instability on chemical properties as well as on the determination of stellar ages and masses using the surface [C/N] abundance ratio. Results: The impact of extra-mixing on 3He, 12C/13C, nitrogen, and [C/N] abundances along the giant branch is quantified. We underline the crucial contribution of asteroseismology to discriminate between evolutionary states of field giants belonging to the Galactic disc. The inclusion of thermohaline instability has a significant impact on 12C/13C, 3He as well as on the [C/N] values. We clearly show the efficiency of thermohaline mixing at different metallicities and its influence on the determined stellar mass and age from the observed [C/N] ratio. We then propose simple relations to determine ages and masses from chemical abundances according to these models. Conclusions: We emphasize the usefulness of population synthesis tools to test stellar models and transport processes inside stars. We show that transport

  1. RAVE stars in K2. I. Improving RAVE red giants spectroscopy using asteroseismology from K2 Campaign 1

    Science.gov (United States)

    Valentini, M.; Chiappini, C.; Davies, G. R.; Elsworth, Y. P.; Mosser, B.; Lund, M. N.; Miglio, A.; Chaplin, W. J.; Rodrigues, T. S.; Boeche, C.; Steinmetz, M.; Matijevič, G.; Kordopatis, G.; Bland-Hawthorn, J.; Munari, U.; Bienaymé, O.; Freeman, K. C.; Gibson, B. K.; Gilmore, G.; Grebel, E. K.; Helmi, A.; Kunder, A.; McMillan, P.; Navarro, J.; Parker, Q. A.; Reid, W.; Seabroke, G.; Sharma, S.; Siviero, A.; Watson, F.; Wyse, R. F. G.; Zwitter, T.; Mott, A.

    2017-04-01

    We present a set of 87 RAVE stars with detected solar like oscillations, observed during Campaign 1 of the K2 mission (RAVE K2-C1 sample). This data set provides a useful benchmark for testing the gravities provided in RAVE data release 4 (DR4), and is key for the calibration of the RAVE data release 5 (DR5). The RAVE survey collected medium-resolution spectra (R = 7500) centred in the Ca II triplet(8600 Å) wavelength interval, which although being very useful for determining radial velocity and metallicity, even at low S/N, is known be affected by a log (g)-Teff degeneracy. This degeneracy is the cause of the large spread in the RAVE DR4 gravities for giants. The understanding of the trends and offsets that affects RAVE atmospheric parameters, and in particular log (g), is a crucial step in obtaining not only improved abundance measurements, but also improved distances and ages. In the present work, we use two different pipelines, GAUFRE and Sp_Ace, to determine atmospheric parameters and abundances by fixing log (g) to the seismic one. Our strategy ensures highly consistent values among all stellar parameters, leading to more accurate chemical abundances. A comparison of the chemical abundances obtained here with and without the use of seismic log (g) information has shown that an underestimated (overestimated) gravity leads to an underestimated (overestimated) elemental abundance (e.g. [Mg/H] is underestimated by 0.25 dex when the gravity is underestimated by 0.5 dex). We then perform a comparison between the seismic gravities and the spectroscopic gravities presented in the RAVE DR4 catalogue, extracting a calibration for log (g) of RAVE giants in the colour interval 0.50 gravities differ by more than 0.5 dex. The method illustrated in this work will be used for analysing RAVE targets present in the other K2 campaigns, in the framework of Galactic Archaeology investigations. Data (atmospheric parameters, abundances, distances, ages and reddening) are only

  2. A light-dependent ammonia-assimilating mechanism in the ctenidia of a giant clam

    Science.gov (United States)

    Hiong, Kum C.; Choo, Celine Y. L.; Boo, Mel V.; Ching, Biyun; Wong, Wai P.; Chew, Shit F.; Ip, Yuen K.

    2017-03-01

    Giant clams harbor symbiotic zooxanthellae and manifest light-enhanced calcification. In light, they also increase the absorption and assimilation of exogenous ammonia, but the roles of the host and symbionts are unclear and the reason for light dependency remains enigmatic. Here, we report the complete coding cDNA sequence of a glutamine synthetase (GS), from the ctenidia (gill) of Tridacna squamosa. The deduced GS amino acid sequence was closely related to other animal GSs, indicating a host origin. The GS/GS transcript level and protein abundance increased significantly in the ctenidia after 12 h of light exposure. These results denote the ctenidia as the site of light-enhanced ammonia absorption with the absorbed ammonia being assimilated to glutamine by the host GS. Immunofluorescence microscopy confirmed that GS was expressed predominantly in the cytoplasm of the epithelial cells separating the tertiary water channels from the hemolymph inside the ctenidia. Hence, unlike symbiotic cnidarians, the host clam probably supplies exogenous nitrogen as glutamine from the ctenidia, through the hemolymph and tubular fluid, to the nitrogen-deficient zooxanthellae which reside extracellularly in the extensible outer mantle. This is the first report on light-dependent gene and protein expression of a host enzyme involved in nitrogen metabolism in an alga-invertebrate association.

  3. Radial velocities and metallicities of red giant stars in the old open cluster NGC 7762

    CERN Document Server

    Carraro, Giovanni; Villanova, Sandro

    2016-01-01

    We present and discuss radial velocity and the very first metallicity measurements for nine evolved stars in the poorly known old open cluster NGC 7762. We isolated eight radial velocity cluster members and one interloper. Radial velocities are in good agreement with previous studies. NGC 7762 turns out to be of solar metallicity within the uncertainties ([Fe/H]=0.04$\\pm$0.12). For this metallicity, the cluster age is 2.5$\\pm$0.2 Gyr, and falls in a age range where only a few old open clusters are known. With respect to previous studies, we find a larger distance, implying the cluster to be located at 900$^{+70}_{-50}$ pc from the Sun. For most of the elements we measure solar-scaled abundance ratios. We searched the literature for open clusters of similar age in the solar vicinity and found that NGC 7762 can be considered a twin of Ruprecht 147, a similar age cluster located at only 300 pc from the Sun. In fact, beside age, also metallicity and abundance ratios are very close to Ruprecht 147 values within th...

  4. On the Stellar Masses of Giant Clumps in Distant Star-forming Galaxies

    Science.gov (United States)

    Dessauges-Zavadsky, Miroslava; Schaerer, Daniel; Cava, Antonio; Mayer, Lucio; Tamburello, Valentina

    2017-02-01

    We analyze stellar masses of clumps drawn from a compilation of star-forming galaxies at 1.1 galaxies, we examine the effects of spatial resolution and sensitivity on the inferred stellar masses. Large differences are found, with median stellar masses ranging from ∼ {10}9 {M}ȯ for clumps in the often-referenced field galaxies to ∼ {10}7 {M}ȯ for fainter clumps selected in deep-field or lensed galaxies. We argue that the clump masses, observed in non-lensed galaxies with a limited spatial resolution of ∼1 kpc, are artificially increased due to the clustering of clumps of smaller mass. Furthermore, we show that the sensitivity threshold used for the clump selection affects the inferred masses even more strongly than resolution, biasing clumps at the low-mass end. Both improved spatial resolution and sensitivity appear to shift the clump stellar mass distribution to lower masses, qualitatively in agreement with clump masses found in recent high-resolution simulations of disk fragmentation. We discuss the nature of the most massive clumps, and we conclude that it is currently not possible to properly establish a meaningful clump stellar mass distribution from observations and to infer the existence and value of a characteristic clump mass scale.

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

    CERN Document Server

    Spite, M; Hill, V; Spite, F; François, P; Plez, B; Bonifacio, P; Molaro, P; Depagne, E; Andersen, J; Barbuy, B; Beers, T C; Nordström, B; Primas, F

    2006-01-01

    Extremely metal-poor (EMP) stars preserve a fossil record of the composition of the ISM when the Galaxy formed. It is crucial, however, to verify whether internal mixing has modified their surface. We aim to understand the CNO abundance variations found in some, but not all EMP field giants analysed earlier. Mixing beyond the first dredge-up of standard models is required, and its origin needs clarification.The 12C/13C ratio is the most robust diagnostic of deep mixing, because it is insensitive to the adopted stellar parameters and should be uniformly high in near-primordial gas. We have measured 12C and 13C abundances in 35 EMP giants from high-quality VLT/UVES spectra. Correlations with other abundance data are used to study the depth of mixing.The 12C/13C ratio is found to correlate with [C/Fe] (and Li/H), and clearly anti-correlate with [N/Fe]. Evidence for such deep mixing is observed in giants above log L/Lsolar = 2.6, brighter than in less metal-poor stars, but matching the bump in the luminosity func...

  6. The Penn State - Toruń Centre for Astronomy Planet Search stars. II. Lithium abundance analysis of the red giant clump sample

    Science.gov (United States)

    Adamów, M.; Niedzielski, A.; Villaver, E.; Wolszczan, A.; Nowak, G.

    2014-09-01

    Context. Standard stellar evolution theory does not predict existence of Li-rich giant stars. Several mechanisms for Li-enrichment have been proposed to operate at certain locations inside some stars. The actual mechanism operating in real stars is still unknown. Aims: Using the sample of 348 stars from the Penn State - Toruń Centre for Astronomy Planet Search, for which uniformly determined atmospheric parameters are available, with chemical abundances and rotational velocities presented here, we investigate various channels of Li enrichment in giants. We also study Li-overabundant giants in more detail in search for origin of their peculiarities. Methods: Our work is based on the Hobby-Eberly Telescope spectra obtained with the High Resolution Spectrograph, which we use for determination of abundances and rotational velocities. The Li abundance was determined from the 7Li λ670.8 nm line, while we use a more extended set of lines for α-elements abundances. In a series of Kolmogorov-Smirnov tests, we compare Li-overabundant giants with other stars in the sample. We also use available IR photometric and kinematical data in search for evidence of mass-loss. We investigate properties of the most Li-abundant giants in more detail by using multi-epoch precise radial velocities. Results: We present Li and α-elements abundances, as well as rotational velocities for 348 stars. We detected Li in 92 stars, of which 82 are giants. Eleven of them show significant Li abundance A(Li)NLTE> 1.4 and seven of them are Li-overabundant objects, according to common criterion of A(Li) > 1.5 and their location on HR diagram, including TYC 0684-00553-1 and TYC 3105-00152-1, which are two giants with Li abundances close to meteoritic level. For another 271 stars, upper limits of Li abundance are presented. We confirmed three objects with increased stellar rotation. We show that Li-overabundant giants are among the most massive stars from our sample and show larger than average

  7. The red giant branch phase transition: Implications for the RGB luminosity function bump and detections of Li-rich red clump stars

    CERN Document Server

    Cassisi, Santi; Pietrinferni, Adriano

    2015-01-01

    We performed a detailed study of the evolution of the luminosity of He-ignition stage and of the red giant branch bump luminosity during the red giant branch phase transition for various metallicities. To this purpose we calculated a grid of stellar models that sample the mass range of the transition with a fine mass step equal to ${\\rm 0.01M_\\odot}$. We find that for a stellar population with a given initial chemical composition, there is a critical age (of 1.1-1.2~Gyr) around which a decrease in age of just 20-30 million years causes a drastic drop in the red giant branch tip brightness. We also find a narrow age range (a few $10^7$ yr) around the transition, characterized by the luminosity of the red giant branch bump being brighter than the luminosity of He ignition. We discuss a possible link between this occurrence and observations of Li-rich core He-burning stars.

  8. Temperature dependence of the giant dipole resonance width in 152Gd

    Science.gov (United States)

    Ghosh, C.; Mishra, G.; Rhine Kumar, A. K.; Dokania, N.; Nanal, V.; Pillay, R. G.; Kumar, Suresh; Rout, P. C.; Joshi, Sandeep; Arumugam, P.

    2016-07-01

    To investigate the dependence of giant dipole resonance (GDR) width on temperature (T ) and angular momentum (J ), high energy γ -ray spectra were measured in the reaction 28Si+124Sn at E28Si=135 MeV. The J information was deduced from multiplicity of low-energy γ rays. The GDR parameters, namely, the centroid energy and width are extracted using statistical model analysis. The observed variation of the GDR width for T ˜1.2 -1.37 MeV and J ˜20 ℏ -40 ℏ is consistent with the universal scaling given by Kusnezov et al., which is applicable in the liquid-drop regime. The GDR input cross sections extracted from the statistical model best fits are compared with thermal shape fluctuation model (TSFM) calculations and are found to be in good agreement. The TSFM calculations predominantly favor the noncollective oblate shape, while the statistical model fit with both prolate and oblate shapes describes the data. The present data together with earlier measurements indicate a very slow variation of the GDR width for T ˜1.2 to 1.5 MeV. The observed trend is well explained by the TSFM calculations, although the calculated values are ˜4 %-13% higher than the data.

  9. Frequency-dependent electrodeformation of giant phospholipid vesicles in AC electric field

    CERN Document Server

    Peterlin, Primoz

    2010-01-01

    A model of vesicle electrodeformation is described which obtains a parametrized vesicle shape by minimizing the sum of the membrane bending energy and the energy due to the electric field. Both the vesicle membrane and the aqueous media inside and outside the vesicle are treated as leaky dielectrics, and the vesicle itself is modelled as a nearly spherical shape enclosed within a thin membrane. It is demonstrated (a) that the model achieves a good quantitative agreement with the experimentally determined prolate-to-oblate transition frequencies in the kHz range, and (b) that the model can explain a phase diagram of shapes of giant phospholipid vesicles with respect to two parameters: the frequency of the applied AC electric field and the ratio of the electrical conductivities of the aqueous media inside and outside the vesicle, explored in a recent paper (S. Aranda et al., Biophys. J. 95:L19--L21, 2008). A possible use of the frequency-dependent shape transitions of phospholipid vesicles in conductometry of m...

  10. Zinc-dependent action potentials in giant neurons of the snail, Euhadra quaestia.

    Science.gov (United States)

    Kawa, K

    1979-09-14

    In giant neurons of subesophageal ganglion of the Japanese land snail, Euhadra quaestia Deshayes, permeation of Zn ions through Ca channels were investigated with a conventional current clamp method. All-or-none action potentials of long duration (90 to 120 sec) were evoked in 24 mM Zn containing salines. The overshoots were about +10 mV and the maximum rate of rises (MRRs) was about 2.9 V/sec. The amplitudes and the MRRs of the action potentials depended on external Zn ion concentrations. The action potentials were suppressed by specific Ca-channel inhibitors such as Co2+, La3+ and Verapamil, but they were resistant to Na-channel inhibitor, tetrodotoxin, even at 30 microM. It is concluded that these action potentials are generated by Zn ions permeating Ca channels in snail neuronal membrane. On the basis of Hagiwara and Takahashi's (S. Hagiwara & K. Takahashi, 1967, J. Gen. Physiol. 50:583) model of Ca channels, it is inferred that Zn ions are 5 to 10 times stronger in affinity to Ca channels than Ca ions, but 10 to 20 times less permeable.

  11. The Stellar Spectral Features of Nearby Galaxies in the Near-Infrared: Tracers of Thermally-Pulsing Asymptotic Giant Branch Stars?

    CERN Document Server

    Riffel, Rogério; Martins, Lucimara P; Rodíguez-Ardila, Alberto; Ho, Luis C; Riffel, Rogemar A; Lira, Paulina; Martin, Omaira Gonzalez; Ruschel-Dutra, Daniel; Alonso-Herrero, Almudena; Flohic, Helene; McDermid, Richard M; Almeida, Cristina Ramos; Thanjavur, Karun; Winge, Claudia

    2015-01-01

    We analyze the stellar absorption features in high signal-to-noise ratio near-infrared (NIR) spectra of the nuclear region of 12 nearby galaxies, mostly spirals. The features detected in some or all of the galaxies in this sample are the TiO (0.843 $\\mu$m\\ and 0.886 $\\mu$m), VO (1.048 $\\mu$m), CN (1.1 $\\mu$m\\ and 1.4 $\\mu$m), H$\\rm _2$O (1.4 $\\mu$m\\ and 1.9 $\\mu$m) and CO (1.6 $\\mu$m\\ and 2.3 $\\mu$m) bands. The C$\\rm _2$ (1.17 $\\mu$m\\ and 1.76 $\\mu$m) bands are generally weak or absent, although C$\\rm _2$ (1.76 $\\mu$m) may be weakly present in the mean galaxy spectrum. A deep feature near 0.93 $\\mu$m, likely caused by CN, TiO and/or ZrO, is also detected in all objects. Fitting a combination of stellar spectra to the mean spectrum shows that the absorption features are produced by evolved stars: cool giants and supergiant stars in the early- or thermally-pulsing asymptotic giant branch (E-AGB or TP-AGB) phases. The high luminosity of TP-AGB stars, and the appearance of VO and ZrO features in the data, suggest...

  12. Spitzer SAGE-Spec: Near Infrared Spectroscopy, Dust Shells, and Cool Envelopes in Extreme Large Magellanic Cloud Asymptotic Giant Branch Stars

    Science.gov (United States)

    Blum, R. D.; Srinivasan, S.; Kemper, F.; Ling, B.; Volk, K.

    2014-11-01

    K-band spectra are presented for a sample of 39 Spitzer Infrared Spectrograph (IRS) SAGE-Spec sources in the Large Magellanic Cloud. The spectra exhibit characteristics in very good agreement with their positions in the near-infrared—Spitzer color-magnitude diagrams and their properties as deduced from the Spitzer IRS spectra. Specifically, the near-infrared spectra show strong atomic and molecular features representative of oxygen-rich and carbon-rich asymptotic giant branch stars, respectively. A small subset of stars was chosen from the luminous and red extreme ``tip" of the color-magnitude diagram. These objects have properties consistent with dusty envelopes but also cool, carbon-rich ``stellar" cores. Modest amounts of dust mass loss combine with the stellar spectral energy distribution to make these objects appear extreme in their near-infrared and mid-infrared colors. One object in our sample, HV 915, a known post-asymptotic giant branch star of the RV Tau type, exhibits CO 2.3 μm band head emission consistent with previous work that demonstrates that the object has a circumstellar disk. Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

  13. THE CALIFORNIA PLANET SURVEY IV: A PLANET ORBITING THE GIANT STAR HD 145934 AND UPDATES TO SEVEN SYSTEMS WITH LONG-PERIOD PLANETS

    Energy Technology Data Exchange (ETDEWEB)

    Katherina Feng, Y.; Wright, Jason T.; Nelson, Benjamin; Wang, Sharon X.; Ford, Eric B. [Center for Exoplanets and Habitable Worlds, Department of Astronomy and Astrophysics, 525 Davey Lab, The Pennsylvania State University, University Park, PA 16802 (United States); Marcy, Geoffrey W.; Isaacson, Howard [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); Howard, Andrew W., E-mail: astrowright@gmail.com [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)

    2015-02-10

    We present an update to seven stars with long-period planets or planetary candidates using new and archival radial velocities from Keck-HIRES and literature velocities from other telescopes. Our updated analysis better constrains orbital parameters for these planets, four of which are known multi-planet systems. HD 24040 b and HD 183263 c are super-Jupiters with circular orbits and periods longer than 8 yr. We present a previously unseen linear trend in the residuals of HD 66428 indicative of an additional planetary companion. We confirm that GJ 849 is a multi-planet system and find a good orbital solution for the c component: it is a 1 M {sub Jup} planet in a 15 yr orbit (the longest known for a planet orbiting an M dwarf). We update the HD 74156 double-planet system. We also announce the detection of HD 145934 b, a 2 M {sub Jup} planet in a 7.5 yr orbit around a giant star. Two of our stars, HD 187123 and HD 217107, at present host the only known examples of systems comprising a hot Jupiter and a planet with a well constrained period greater than 5 yr, and with no evidence of giant planets in between. Our enlargement and improvement of long-period planet parameters will aid future analysis of origins, diversity, and evolution of planetary systems.

  14. First stars VI - Abundances of C, N, O, Li, and mixing in extremely metal-poor giants. Galactic evolution of the light elements

    CERN Document Server

    Spite, M; Plez, B; Hill, V; Spite, F; Depagne, E; François, P; Bonifacio, P; Barbuy, B; Beers, T; Andersen, J; Molaro, P; Nordström, B; Primas, F

    2004-01-01

    We have investigated the poorly-understood origin of nitrogen in the early Galaxy by determining N abundances in 35 extremely metal-poor halo giants (22 stars have [Fe/H]<-3.0) using the C and O abundances determined in Paper V. Because any dredge-up of CNO processed material to the surface may complicate the interpretation of CNO abundances in giants, we have also measured the surface abundance of lithium. Our sample shows a clear dichotomy between two groups of stars. The first group shows evidence of C to N conversion through CN cycling and strong Li dilution, a signature of mixing. The second group shows no evidence for C to N conversion, and Li is only moderately diluted, and we conclude that their C and N abundances are very close to those of the gas from which they formed in the early Galaxy. These "unmixed" stars reflect the abundances in the early Galaxy: the [C/Fe] ratio is constant (about +0.2 dex) and the [C/Mg] ratio is close to solar at low metallicity, favouring a high C production by massiv...

  15. Spitzer SAGE-Spec: Near infrared spectroscopy, dust shells, and cool envelopes in extreme Large Magellanic Cloud asymptotic giant branch stars

    Energy Technology Data Exchange (ETDEWEB)

    Blum, R. D. [NOAO, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Srinivasan, S.; Kemper, F.; Ling, B. [Academia Sinica, Institute of Astronomy and Astrophysics, 11F of Astronomy-Mathematics Building, NTU/AS, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan (China); Volk, K. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2014-11-01

    K-band spectra are presented for a sample of 39 Spitzer Infrared Spectrograph (IRS) SAGE-Spec sources in the Large Magellanic Cloud. The spectra exhibit characteristics in very good agreement with their positions in the near-infrared—Spitzer color-magnitude diagrams and their properties as deduced from the Spitzer IRS spectra. Specifically, the near-infrared spectra show strong atomic and molecular features representative of oxygen-rich and carbon-rich asymptotic giant branch stars, respectively. A small subset of stars was chosen from the luminous and red extreme ''tip'' of the color-magnitude diagram. These objects have properties consistent with dusty envelopes but also cool, carbon-rich ''stellar'' cores. Modest amounts of dust mass loss combine with the stellar spectral energy distribution to make these objects appear extreme in their near-infrared and mid-infrared colors. One object in our sample, HV 915, a known post-asymptotic giant branch star of the RV Tau type, exhibits CO 2.3 μm band head emission consistent with previous work that demonstrates that the object has a circumstellar disk.

  16. Pygmies, Giants, and Skins

    CERN Document Server

    Piekarewicz, J

    2012-01-01

    Understanding the equation of state (EOS) of neutron-rich matter is a central goal of nuclear physics that cuts across a variety of disciplines. Indeed, the limits of nuclear existence, the collision of energetic heavy ions, the structure of neutron stars, and the dynamics of core-collapse supernova all depend critically on the nuclear-matter EOS. In this contribution I focus on the EOS of cold baryonic matter with special emphasis on its impact on the structure, dynamics, and composition of neutron stars. In particular, I discuss how laboratory experiments on neutron skins as well as on Pygmy and Giant resonances can help us elucidate the structure of these fascinating objects.

  17. The metallicity dependence of envelope inflation in massive stars

    CERN Document Server

    Sanyal, D; Szécsi, D; Yoon, S -C; Grassitelli, L

    2016-01-01

    Recently it has been found that models of massive stars reach the Eddington limit in their interior, which leads to dilute extended envelopes. We perform a comparative study of the envelope properties of massive stars at different metallicities, with the aim to establish the impact of the stellar metallicity on the effect of envelope inflation. We analyse published grids of core-hydrogen burning massive star models computed with metallicities appropriate for massive stars in the Milky Way, the LMC and the SMC, the very metal poor dwarf galaxy I Zwicky 18, and for metal-free chemical composition. Stellar models of all the investigated metallicities reach and exceed the Eddington limit in their interior, aided by the opacity peaks of iron, helium and hydrogen, and consequently develop inflated envelopes. Envelope inflation leads to a redward bending of the zero-age main sequence and a broadening of the main sequence band in the upper part of the Hertzsprung-Russell diagram. We derive the limiting L/M-values as ...

  18. Radial dependence of line profile variability in seven O9--B0.5 stars

    CERN Document Server

    Martins, F; Hillier, D J; Donati, J -F; Bouret, J -C

    2014-01-01

    Massive stars show a variety of spectral variability: presence of discrete absorption components in UV P-Cygni profiles, optical line profile variability, X-ray variability, radial velocity modulations. Our goal is to study the spectral variability of single OB stars to better understand the relation between photospheric and wind variability. For that, we rely on high spectral resolution, high signal-to-noise ratio optical spectra collected with the spectrograph NARVAL on the Telescope Bernard Lyot at Pic du Midi. We investigate the variability of twelve spectral lines by means of the Temporal Variance Spectrum (TVS). The selected lines probe the radial structure of the atmosphere, from the photosphere to the outer wind. We also perform a spectroscopic analysis with atmosphere models to derive the stellar and wind properties, and to constrain the formation region of the selected lines. We show that variability is observed in the wind lines of all bright giants and supergiants, on a daily timescale. Lines form...

  19. The galactocentric radius dependent upper mass limit of young star clusters: stochastic star formation ruled out

    CERN Document Server

    Pflamm-Altenburg, Jan; Kroupa, Pavel

    2013-01-01

    It is widely accepted that the distribution function of the masses of young star clusters is universal and can be purely interpreted as a probability density distribution function with a constant upper mass limit. As a result of this picture the masses of the most-massive objects are exclusively determined by the size of the sample. Here we show, with very high confidence, that the masses of the most-massive young star clusters in M33 decrease with increasing galactocentric radius in contradiction to the expectations from a model of a randomly sampled constant cluster mass function with a constant upper mass limit. Pure stochastic star formation is thereby ruled out. We use this example to elucidate how naive analysis of data can lead to unphysical conclusions.

  20. Radial oscillations of magnetized proto strange stars in temperature- and density-dependent quark mass model

    Indian Academy of Sciences (India)

    V K Gupta; Asha Gupta; S Singh; J D Anand

    2003-10-01

    We report on the study of the mass–radius (–) relation and the radial oscillations of magnetized proto strange stars. For the quark matter we have employed the very recent modification, the temperature- and density-dependent quark mass model of the well-known density-dependent quark mass model. We find that the effect of magnetic field, both on the maximum mass and radial frequencies, is rather small. Also a proto strange star, whether magnetized or otherwise, is more likely to evolve into a strange star rather than transform into a black hole.

  1. A non-LTE study of silicon abundances in giant stars from the Si I infrared lines in the zJ-band

    CERN Document Server

    Tan, Kefeng; Takada-Hidai, Masahide; Takeda, Yoichi; Zhao, Gang

    2016-01-01

    We investigate the feasibility of the Si I infrared (IR) lines as Si abundance indicators for giant stars. We find that Si abundances obtained from the Si I IR lines based on the local thermodynamic equilibrium (LTE) analysis show large line-to-line scatter (mean value of 0.13dex), and are higher than those from the optical lines. However, when the non-LTE effects are taken into account, the line-to-line scatter reduces significantly (mean value of 0.06dex), and the Si abundances are consistent with those from the optical lines. The typical average non-LTE correction of [Si/Fe] for our sample stars is about $-$0.35dex. Our results demonstrate that the Si I IR lines could be reliable abundance indicators provided that the non-LTE effects are properly taken into account.

  2. Star Clusters

    OpenAIRE

    Gieles, M.

    1993-01-01

    Star clusters are observed in almost every galaxy. In this thesis we address several fundamental problems concerning the formation, evolution and disruption of star clusters. From observations of (young) star clusters in the interacting galaxy M51, we found that clusters are formed in complexes of stars and star clusters. These complexes share similar properties with giant molecular clouds, from which they are formed. Many (70%) of the young clusters will not survive the fist 10 Myr, due to t...

  3. Migration of giant planets in a time-dependent planetesimal accretion disc

    CERN Document Server

    Popolo, A D

    2002-01-01

    In this paper, we further develop the model for the migration of planets introduced in Del Popolo et al. (2001). We first model the protoplanetary nebula as a time-dependent accretion disc and find self-similar solutions to the equations of the accretion disc that give to us explicit formulas for the spatial structure and the temporal evolution of the nebula. These equations are then used to obtain the migration rate of the planet in the planetesimal disc and to study how the migration rate depends on the disc mass, on its time evolution and on some values of the dimensionless viscosity parameter alpha. We find that planets that are embedded in planetesimal discs, having total mass of 10^{-4}-0.1 M_{\\odot}, can migrate inward a large distance for low values of alpha (e.g., alpha \\simeq 10^{-3}-10^{-2}) and/or large disc mass and can survive only if the inner disc is truncated or because of tidal interaction with the star. Orbits with larger $a$ are obtained for smaller value of the disc mass and/or for larger...

  4. The identification of extreme asymptotic giant branch stars and red supergiants in M33 with 24 μm variability

    Energy Technology Data Exchange (ETDEWEB)

    Montiel, Edward J.; Clayton, Geoffrey C.; Johnson, Christopher B. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Srinivasan, Sundar [Academica Sinica, Institute of Astronomy and Astrophysics, PO Box 23-141, Taipei 10617, Taiwan, R. O. C. (China); Engelbracht, Charles W., E-mail: emonti2@lsu.edu [Steward Observatory, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

    2015-02-01

    We present the first detection of 24 μm variability in 24 sources in the Local Group galaxy M33. These results are based on 4 epochs of Multiband Imaging Photometer for Spitzer observations, which are irregularly spaced over ∼750 days. We find that these sources are constrained exclusively to the Holmberg radius of the galaxy, which increases their chances of being members of M33. We have constructed spectral energy distributions (SEDs) ranging from the optical to the submillimeter to investigate the nature of these objects. We find that 23 of our objects are most likely heavily self-obscured, evolved stars, while the remaining source is the Giant H ii region, NGC 604. We believe that the observed variability is the intrinsic variability of the central star reprocessed through their circumstellar dust shells. Radiative transfer modeling was carried out to determine their likely chemical composition, luminosity, and dust production rate (DPR). As a sample, our modeling has determined an average luminosity of (3.8±0.9)×10{sup 4} L{sub ⊙} and a total DPR of (2.3±0.1)×10{sup −5} M{sub ⊙} yr{sup −1}. Most of the sources, given the high DPRs and short wavelength obscuration, are likely extreme asymptotic giant branch (XAGB) stars. Five of the sources are found to have luminosities above the classical AGB limit (M{sub bol} <−7.1 mag, L > 54,000 L{sub ⊙}), which classifies them as probable red supergiants (RSGs). Almost all of the sources are classified as oxygen-rich. As also seen in the LMC, a significant fraction of the dust in M33 is produced by a handful of XAGB and RSG stars.

  5. Luminosity dependence of the cyclotron line and the accretion regime transition in 2015 giant outburst of V 0332+53

    CERN Document Server

    Doroshenko, Victor; Mushtukov, Alexander A; Lutovinov, Alexander A; Santangelo, Andrea; Suleimanov, Valery F; Poutanen, Juri

    2016-01-01

    We report on the analysis of NuSTAR observations of the Be-transient X-ray pulsar V 0332+53 during the giant outburst in 2015. We confirm the cyclotron-line energy - luminosity correlation previously reported in the source, and for the first time observe a significant departure from this correlation below L$\\sim10^{37}$ erg/s. We interpret this finding as first observational evidence for the transition from super- to sub- critical accretion associated with the disappearance of the accretion column. We also discuss the discrepancy in cyclotron line energies corresponding to the same luminosities in rising and declining parts of the outburst and based on the spin evolution of the source conclude that it is likely caused by a change of the emission region geometry rather than the accretion-induced decay of the magnetic field as previously suggested.

  6. 1FGL J1417.7-4407: A Likely Gamma-Ray Bright Binary with A Massive Neutron Star and A Giant Secondary

    Science.gov (United States)

    Strader, Jay; Chomiuk, Laura; Cheung, C. C.; Sand, David J.; Donato, Davide; Corbet, Robin H. D.; Koeppe, Dana; Edwards, Philip G.; Stevens, Jamie; Petrov, Leonid

    2015-01-01

    We present multiwavelength observations of the persistent Fermi-Large Area Telescope unidentified gamma-ray source 1FGL J1417.7-4407, showing it is likely to be associated with a newly discovered X-ray binary containing a massive neutron star (nearly 2 solar mass) and a approximately 0.35 solar mass giant secondary with a 5.4 day period. SOAR optical spectroscopy at a range of orbital phases reveals variable double-peaked H alpha emission, consistent with the presence of an accretion disk. The lack of radio emission and evidence for a disk suggests the gamma-ray emission is unlikely to originate in a pulsar magnetosphere, but could instead be associated with a pulsar wind, relativistic jet, or could be due to synchrotron self-Compton at the disk-magnetosphere boundary. Assuming a wind or jet, the high ratio of gamma- ray to X-ray luminosity (approximately 20) suggests efficient production of gamma-rays, perhaps due to the giant companion. The system appears to be a low-mass X-ray binary that has not yet completed the pulsar recycling process. This system is a good candidate to monitor for a future transition between accretion-powered and rotational-powered states, but in the context of a giant secondary.

  7. The Unique Molecular Choreography of Giant Pore Formation by the Cholesterol-Dependent Cytolysins of Gram-Positive Bacteria.

    Science.gov (United States)

    Tweten, Rodney K; Hotze, Eileen M; Wade, Kristin R

    2015-01-01

    The mechanism by which the cholesterol-dependent cytolysins (CDCs) assemble their giant β-barrel pore in cholesterol-rich membranes has been the subject of intense study in the past two decades. A combination of structural, biophysical, and biochemical analyses has revealed deep insights into the series of complex and highly choreographed secondary and tertiary structural transitions that the CDCs undergo to assemble their β-barrel pore in eukaryotic membranes. Our knowledge of the molecular details of these dramatic structural changes in CDCs has transformed our understanding of how giant pore complexes are assembled and has been critical to our understanding of the mechanisms of other important classes of pore-forming toxins and proteins across the kingdoms of life. Finally, there are tantalizing hints that the CDC pore-forming mechanism is more sophisticated than previously imagined and that some CDCs are employed in pore-independent processes.

  8. Habitability of Super-Earth Planets around Main-Sequence Stars including Red Giant Branch Evolution: Models based on the Integrated System Approach

    CERN Document Server

    Cuntz, M; Schroeder, K -P; Bounama, C; Franck, S

    2011-01-01

    In a previous study published in Astrobiology, we focused on the evolution of habitability of a 10 M_E super-Earth planet orbiting a star akin to the Sun. This study was based on a concept of planetary habitability in accordance to the integrated system approach that describes the photosynthetic biomass production taking into account a variety of climatological, biogeochemical, and geodynamical processes. In the present study, we pursue a significant augmentation of our previous work by considering stars with zero-age main sequence masses between 0.5 and 2.0 M_sun with special emphasis on models of 0.8, 0.9, 1.2 and 1.5 M_sun. Our models of habitability consider again geodynamical processes during the main-sequence stage of these stars as well as during their red giant branch evolution. Pertaining to the different types of stars, we identify so-called photosynthesis-sustaining habitable zones (pHZ) determined by the limits of biological productivity on the planetary surface. We obtain various sets of solution...

  9. Kiloparsec-Scale Simulations of Star Formation in Disk Galaxies II. Structure and Dynamics of Filaments and Clumps in Giant Molecular Clouds

    CERN Document Server

    Butler, Michael J; Van Loo, Sven

    2014-01-01

    We present hydrodynamic simulations of self-gravitating dense gas in a galactic disk, exploring scales ranging from 1 kpc down to $\\sim 0.1$~pc. Our primary goal is to understand how dense filaments form in Giant Molecular Clouds (GMCs). These structures, often observed as Infrared Dark Clouds (IRDCs) in the Galactic plane, are thought to be the precursors to massive stars and star clusters, so their formation may be the rate limiting step controlling global star formation rates in galactic systems as described by the Kennicutt-Schmidt relation. Our study follows on from Van Loo et al. (2013, Paper I), which carried out simulations to 0.5~pc resolution and examined global aspects of the formation of dense gas clumps and the resulting star formation rate. Here, using our higher resolution, we examine the detailed structural, kinematic and dynamical properties of dense filaments and clumps, including mass surface density ($\\Sigma$) probability distribution functions, filament mass per unit length and its disper...

  10. Precise radial velocities of giant stars. IV. A correlation between surface gravity and radial velocity variation and a statistical investigation of companion properties

    CERN Document Server

    Hekker, S; Aerts, C; Quirrenbach, Andreas G; Reffert, S; Mitchell, D S

    2008-01-01

    Since 1999, we have been conducting a radial velocity survey of 179 K giants using the CAT at UCO/Lick observatory. At present ~20-100 measurements have been collected per star with a precision of 5 to 8 m/s. Of the stars monitored, 145 (80%) show radial velocity (RV) variations at a level >20 m/s, of which 43 exhibit significant periodicities. Our aim is to investigate possible mechanism(s) that cause these observed RV variations. We intend to test whether these variations are intrinsic in nature, or possibly induced by companions, or both. In addition, we aim to characterise the parameters of these companions. A relation between log g and the amplitude of the RV variations is investigated for all stars in the sample. Furthermore, the hypothesis that all periodic RV variations are caused by companions is investigated by comparing their inferred orbital statistics with the statistics of companions around main sequence stars. A strong relation is found between the amplitude of the RV variations and log g in K ...

  11. The Outer Halo of M31: A New Method for Isolating Red Giant Stars and a Measurement of the Brightness Profile and Metallicity Distribution

    CERN Document Server

    Gilbert, K M; Singh-Kalirai, J; Rich, R M; Majewski, S R; Ostheimer, J C; Reitzel, David B; Cenarro, A J; Cooper, M C; Luine, C; Patterson, R J; Gilbert, Karoline M.; Guhathakurta, Puragra; Kalirai, Jasonjot S.; Majewski, Steven R.; Ostheimer, James C.; Reitzel, David B.; Cooper, Michael C.; Luine, Carynn; Patterson, Richard J.

    2006-01-01

    We present a method for isolating a clean sample of red giant branch stars in the outer regions of the Andromeda spiral galaxy (M31) from an ongoing spectroscopic survey using the DEIMOS instrument on the Keck~II 10-m telescope. The survey aims to study the kinematics, global structure, substructure, and metallicity of M31's halo. Although most of our spectroscopic targets were photometrically screened to reject foreground Milky Way dwarf star contaminants, the latter class of objects still constitutes a substantial fraction of the observed spectra in the sparse outer halo. Our likelihood-based method for isolating M31 red giants uses multiple criteria: (1) radial velocity, (2) intermediate-width band photometry through the DDO51 filter centered on the surface-gravity sensitive MgH/Mg b absorption features, (3) strength of the Na I 8190 Angstrom absorption line doublet, (4) location within an (I, V-I) color-magnitude diagram, and (5) comparison of photometric versus spectroscopic metallicity estimates. Traini...

  12. Infrared spectral properties of M giants

    CERN Document Server

    Sloan, G C; Ramirez, R M; Kraemer, K E; Engelke, C W

    2015-01-01

    We observed a sample of 20 M giants with the Infrared Spectrograph on the Spitzer Space Telescope. Most show absorption structure at 6.6-6.8 um which we identify as water vapor, and in some cases, the absorption extends from 6.4 um into the SiO band at 7.5 um. Variable stars show stronger H2O absorption. While the strength of the SiO fundamental at 8 um increases monotonically from spectral class K0 to K5, the dependence on spectral class weakens in the M giants. As with previously studied samples, the M giants show considerable scatter in SiO band strength within a given spectral class. All of the stars in our sample also show OH band absorption, most noticeably in the 14-17 um region. The OH bands behave much like the SiO bands, increasing in strength in the K giants but showing weaker dependence on spectral class in the M giants, and with considerable scatter. An examination of the photometric properties reveals that the V-K color may be a better indicator of molecular band strength than the spectral class...

  13. Methylprednisolone prevents tumour necrosis factor-alpha-dependent multinucleated giant cell formation

    DEFF Research Database (Denmark)

    Maltesen, Henrik Rasmus; Nielsen, Claus H; Dalbøge, Christina Schjellerup

    2010-01-01

    Granulomas contain multinucleated giant cells (MGCs), the function of which remains largely unknown. In patients with autoimmune granulomatous disease, the granulomas can be resolved during treatment with glucocorticosteroid (GCS). However, little is known about the influence of GCSs on the forma...

  14. Study of Proto Strange Stars (PSS) in Temperature and Density Dependent Quark Mass Model

    CERN Document Server

    Gupta, V K; Singh, S; Anand, J D; Gupta, Asha

    2003-01-01

    We report on the study of the mass-radius (M-R) relation and the radial oscillations of proto strange stars. For the quark matter we have employed the well known density dependent quark mass model and its very recent modification, the temperature and density dependent quark mass model. We find that the maximum mass the star can support increases significantly with the temperature of the star in this model which implies that transition to a black hole at the early stage of formation of the star is inhibited. As for the neutrinos, we find, contrary to the expectation that the M-R and oscillation frequencies are almost independent of the neutrino chemical potentials.

  15. The GAPS programme with HARPS-N at TNG. II. No giant planets around the metal-poor star HIP 11952

    Science.gov (United States)

    Desidera, S.; Sozzetti, A.; Bonomo, A. S.; Gratton, R.; Poretti, E.; Claudi, R.; Latham, D. W.; Affer, L.; Cosentino, R.; Damasso, M.; Esposito, M.; Giacobbe, P.; Malavolta, L.; Nascimbeni, V.; Piotto, G.; Rainer, M.; Scardia, M.; Schmid, V. S.; Lanza, A. F.; Micela, G.; Pagano, I.; Bedin, L. R.; Biazzo, K.; Borsa, F.; Carolo, E.; Covino, E.; Faedi, F.; Hébrard, G.; Lovis, C.; Maggio, A.; Mancini, L.; Marzari, F.; Messina, S.; Molinari, E.; Munari, U.; Pepe, F.; Santos, N.; Scandariato, G.; Shkolnik, E.; Southworth, J.

    2013-06-01

    In the context of the programme Global Architecture of Planetary Systems (GAPS), we have performed radial velocity monitoring of the metal-poor star HIP 11952 on 35 nights during about 150 days using the newly installed high-resolution spectrograph HARPS-N at the TNG and HARPS at the ESO 3.6 m telescope. The radial velocities show a scatter of 7 m s-1, compatible with the measurement errors for such a moderately warm metal-poor star (Teff = 6040 ± 120 K; [Fe/H] = -1.9 ± 0.1). We exclude the presence of the two giant planets with periods of 6.95 ± 0.01 d and 290.0 ± 16.2 d and radial velocity semi-amplitudes of 100.3 ± 19.4 m s-1 and 105.2 ± 14.7 m s-1, respectively, which have recently been announced. This result is important because HIP 11952 was thought to be the most metal-poor star hosting a planetary systemwith giant planets, which challenged some models of planet formation. Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundacion Galileo Galilei of the INAF at the Spanish Observatorio del Roque de los Muchachos of the IAC in the frame of the programme Global Architecture of Planetary Systems (GAPS). Based on observations collected at the La Silla Observatory, ESO (Chile): Program 185.D-0056.Table 1 is available in electronic form at http://www.aanda.org

  16. EUROPIUM s-PROCESS SIGNATURE AT CLOSE-TO-SOLAR METALLICITY IN STARDUST SiC GRAINS FROM ASYMPTOTIC GIANT BRANCH STARS

    Energy Technology Data Exchange (ETDEWEB)

    Avila, Janaina N.; Ireland, Trevor R.; Holden, Peter [Research School of Earth Sciences, Australian National University, Canberra ACT 0200 (Australia); Lugaro, Maria [Monash Centre for Astrophysics, Monash University, Clayton, VIC 3800 (Australia); Gyngard, Frank; Zinner, Ernst [Laboratory for Space Sciences and the Department of Physics, Washington University, One Brookings Drive, St. Louis, MO 63130 (United States); Cristallo, Sergio [Osservatorio Astronomico di Collurania, INAF, via Maggini snc, Teramo I-64100 (Italy); Rauscher, Thomas, E-mail: janaina.avila@anu.edu.au [Centre for Astrophysics Research, School of Physics, Astronomy, and Mathematics, University of Hertfordshire, Hatfield AL10 9AB (United Kingdom)

    2013-05-01

    Individual mainstream stardust silicon carbide (SiC) grains and a SiC-enriched bulk sample from the Murchison carbonaceous meteorite have been analyzed by the Sensitive High Resolution Ion Microprobe-Reverse Geometry for Eu isotopes. The mainstream grains are believed to have condensed in the outflows of {approx}1.5-3 M{sub Sun} carbon-rich asymptotic giant branch (AGB) stars with close-to-solar metallicity. The {sup 151}Eu fractions [fr({sup 151}Eu) = {sup 151}Eu/({sup 151}Eu+{sup 153}Eu)] derived from our measurements are compared with previous astronomical observations of carbon-enhanced metal-poor stars enriched in elements made by slow neutron captures (the s-process). Despite the difference in metallicity between the parent stars of the grains and the metal-poor stars, the fr({sup 151}Eu) values derived from our measurements agree well with fr({sup 151}Eu) values derived from astronomical observations. We have also compared the SiC data with theoretical predictions of the evolution of Eu isotopic ratios in the envelope of AGB stars. Because of the low Eu abundances in the SiC grains, the fr({sup 151}Eu) values derived from our measurements show large uncertainties, in most cases being larger than the difference between solar and predicted fr({sup 151}Eu) values. The SiC aggregate yields a fr({sup 151}Eu) value within the range observed in the single grains and provides a more precise result (fr({sup 151}Eu) = 0.54 {+-} 0.03, 95% conf.), but is approximately 12% higher than current s-process predictions. The AGB models can match the SiC data if we use an improved formalism to evaluate the contribution of excited nuclear states in the calculation of the {sup 151}Sm(n, {gamma}) stellar reaction rate.

  17. Tracking Advanced Planetary Systems (TAPAS) with HARPS-N . I. A multiple planetary system around the red giant star TYC 1422-614-1

    Science.gov (United States)

    Niedzielski, A.; Villaver, E.; Wolszczan, A.; Adamów, M.; Kowalik, K.; Maciejewski, G.; Nowak, G.; García-Hernández, D. A.; Deka, B.; Adamczyk, M.

    2015-01-01

    Context. Stars that have evolved off the main sequence are crucial for expanding the frontiers of knowledge on exoplanets toward higher stellar masses and for constraining star-planet interaction mechanisms. These stars have an intrinsic activity, however, which complicates the interpretation of precise radial velocity (RV) measurements, and therefore they are often avoided in planet searches. Over the past ten years, we have monitored about 1000 evolved stars for RV variations in search for low-mass companions under the Penn State - Toruń Centre for Astronomy Planet Search program with the Hobby-Eberly Telescope. Selected prospective candidates that required higher RV precision measurements have been followed with HARPS-N at the 3.6 m Telescopio Nazionale Galileo. Aims: We aim to detect planetary systems around evolved stars, to be able to build sound statistics on the frequency and intrinsic nature of these systems, and to deliver in-depth studies of selected planetary systems with evidence of star-planet interaction processes. Methods: We obtained 69 epochs of precise RV measurements for TYC 1422-614-1 collected over 3651 days with the Hobby-Eberly Telescope, and 17 epochs of ultra-precise HARPS-N data collected over 408 days. We complemented these RV data with photometric time-series from the All Sky Automatic Survey archive. Results: We report the discovery of a multiple planetary system around the evolved K2 giant star TYC 1422-614-1. The system orbiting the 1.15 M⊙ star is composed of a planet with mass msini = 2.5 MJ in a 0.69 AU orbit, and a planet or brown dwarf with msini = 10 MJ in an orbit of 1.37 AU. The multiple planetary system orbiting TYC 1422-614-1 is the first finding of the TAPAS project, a HARPS-N monitoring of evolved planetary systems identified with the Hobby-Eberly Telescope. Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University

  18. Tracking Advanced Planetary Systems (TAPAS) with HARPS-N. IV. TYC 3667-1280-1: The most massive red giant star hosting a warm Jupiter

    Science.gov (United States)

    Niedzielski, A.; Villaver, E.; Nowak, G.; Adamów, M.; Maciejewski, G.; Kowalik, K.; Wolszczan, A.; Deka-Szymankiewicz, B.; Adamczyk, M.

    2016-05-01

    Context. We present the latest result of the TAPAS project that is devoted to intense monitoring of planetary candidates that are identified within the PennState-Toruń planet search. Aims: We aim to detect planetary systems around evolved stars to be able to build sound statistics on the frequency and intrinsic nature of these systems, and to deliver in-depth studies of selected planetary systems with evidence of star-planet interaction processes. Methods: The paper is based on precise radial velocity measurements: 13 epochs collected over 1920 days with the Hobby-Eberly Telescope and its High-Resolution Spectrograph, and 22 epochs of ultra-precise HARPS-N data collected over 961 days. Results: We present a warm-Jupiter (Teq = 1350 K, m2 sin i = 5.4 ± 0.4 MJ) companion with an orbital period of 26.468 days in a circular (e = 0.036) orbit around a giant evolved (log g = 3.11 ± 0.09, R = 6.26 ± 0.86 R⊙) star with M⋆ = 1.87 ± 0.17 M⊙. This is the most massive and oldest star found to be hosting a close-in giant planet. Its proximity to its host (a = 0.21 au) means that the planet has a 13.9 ± 2.0% probability of transits; this calls for photometric follow-up study. Conclusions: This massive warm Jupiter with a near circular orbit around an evolved massive star can help set constraints on general migration mechanisms for warm Jupiters and, given its high equilibrium temperature, can help test energy deposition models in hot Jupiters. Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto

  19. The extended molecular envelope of the asymptotic giant branch star π1 Gruis as seen by ALMA. I. Large-scale kinematic structure and CO excitation properties

    Science.gov (United States)

    Doan, L.; Ramstedt, S.; Vlemmings, W. H. T.; Höfner, S.; De Beck, E.; Kerschbaum, F.; Lindqvist, M.; Maercker, M.; Mohamed, S.; Paladini, C.; Wittkowski, M.

    2017-09-01

    Context. The S-type asymptotic giant branch (AGB) star π1 Gru has a known companion at a separation of 2.̋7 (≈400 AU). Previous observations of the circumstellar envelope (CSE) show strong deviations from spherical symmetry. The envelope structure, including an equatorial torus and a fast bipolar outflow, is rarely seen in the AGB phase and is particularly unexpected in such a wide binary system. Therefore a second, closer companion has been suggested, but the evidence is not conclusive. Aims: The aim is to make a 3D model of the CSE and to constrain the density and temperature distribution using new spatially resolved observations of the CO rotational lines. Methods: We have observed the J = 3-2 line emission from 12CO and 13CO using the compact arrays of the Atacama Large Millimeter/submillimeter Array (ALMA). The new ALMA data, together with previously published 12CO J = 2-1 data from the Submillimeter Array (SMA), and the 12CO J = 5-4 and J = 9-8 lines observed with Herschel/Heterodyne Instrument for the Far-Infrared (HIFI), is modeled with the 3D non-LTE radiative transfer code SHAPEMOL. Results: The data analysis clearly confirms the torus-bipolar structure. The 3D model of the CSE that satisfactorily reproduces the data consists of three kinematic components: a radially expanding torus with velocity slowly increasing from 8 to 13 km s-1 along the equator plane; a radially expanding component at the center with a constant velocity of 14 km s-1; and a fast, bipolar outflow with velocity proportionally increasing from 14 km s-1 at the base up to 100 km s-1 at the tip, following a linear radial dependence. The results are used to estimate an average mass-loss rate during the creation of the torus of 7.7 × 10-7 M⊙ yr-1. The total mass and linear momentum of the fast outflow are estimated at 7.3 × 10-4 M⊙ and 9.6 × 1037 g cm s-1, respectively. The momentum of the outflow is in excess (by a factor of about 20) of what could be generated by radiation

  20. Frequency and Field Dependences of Giant Magneto-Impedance Effect in Sandwiched FeCuCrVSiB Films

    Institute of Scientific and Technical Information of China (English)

    DAI You-Yong; XIAO Shu-Qin; LIU Yi-Hua; ZHANG Lin; WU Hou-Zheng; ZHANG Yan-Zhong

    2001-01-01

    The giant magneto-impedance (GMI) effect has been investigated in sandwiched FeCuCrVSiB films annealed at 300 ℃ for 1.5 h. The frequency and field dependences of the GMI have been observed in the frequency range from 50 kHz to 13 MHz. The GMI ratio increases at first with increasing frequency, and reaches its maximum value of 136% at a very low characteristic frequency of about 4 MHz, and then decreases with further increasing frequency. These superior properties are related to the special structure of the sandwiched films.

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

    CERN Document Server

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

    2015-01-01

    The tidal disruption of the Sagittarius dwarf Spheroidal galaxy (Sgr dSph) is producing the most prominent substructure in the Milky Way (MW) halo, the Sagittarius Stream. Aside from field stars, the Sgr dSph is suspected to have lost a number of globular clusters (GC). Many Galactic GC are suspected to have originated in the Sgr dSph. While for some candidates an origin in the Sgr dSph has been confirmed due to chemical similarities, others exist whose chemical composition has never been investigated. NGC 5053 and NGC 5634 are two among these scarcely studied Sgr dSph candidate-member clusters. To characterize their composition we analyzed one giant star in NGC 5053, and two in NGC 5634. We analize high-resolution and signal-to-noise spectra by means of the MyGIsFOS code, determining atmospheric parameters and abundances for up to 21 species between O and Eu. The abundances are compared with those of MW halo field stars, of "unassociated" MW halo globulars, and of the metal poor Sgr dSph main body population...

  2. The California Planet Survey IV: A Planet Orbiting the Giant Star HD 145934 and Updates to Seven Systems with Long-Period Planets

    CERN Document Server

    Feng, Y Katherina; Nelson, Benjamin; Wang, Sharon X; Ford, Eric B; Marcy, Geoffrey W; Isaacson, Howard; Howard, Andrew W

    2015-01-01

    We present an update to seven stars with long-period planets or planetary candidates using new and archival radial velocities from Keck-HIRES and literature velocities from other telescopes. Our updated analysis better constrains orbital parameters for these planets, four of which are known multi-planet systems. HD 24040 b and HD 183263 c are super-Jupiters with circular orbits and periods longer than 8 yr. We present a previously unseen linear trend in the residuals of HD 66428 indicative on an additional planetary companion. We confirm that GJ 849 is a multi-planet system and find a good orbital solution for the c component: it is a $1 M_{\\rm Jup}$ planet in a 15 yr orbit (the longest known for a planet orbiting an M dwarf). We update the HD 74156 double-planet system. We also announce the detection of HD 145934 b, a $2 M_{\\rm Jup}$ planet in a 7.5 yr orbit around a giant star. Two of our stars, HD 187123 and HD 217107, at present host the only known examples of systems comprising a hot Jupiter and a planet...

  3. The Carina Project VII: Towards the breaking of the age-metallicity degeneracy of red giant branch stars using the c_UBI index

    CERN Document Server

    Monelli, M; Fabrizio, M; Bono, G; Stetson, P B; Walker, A R; Cassisi, S; Gallart, C; Nonino, M; Aparicio, A; Buonanno, R; Dall'Ora, M; Ferraro, I; Iannicola, G; Pulone, L; Thévenin, F

    2014-01-01

    We present an analysis of photometric and spectroscopic data of the Carina dSph galaxy, testing a new approach similar to that used to disentangle multiple populations in Galactic globular clusters (GCs). We show that a proper colour combination is able to separate a significant fraction of the red giant branch (RGB) of the two main Carina populations (the old one, \\sim 12 Gyr, and the intermediate-age one, 4-8 Gyr). In particular, the c_UBI=(U-B)-(B-I) pseudo-colour allows us to follow the RGB of both populations along a relevant portion of the RGB. We find that the oldest stars have more negative c_UBI pseudo-colour than intermediate-age ones. We correlate the pseudo-colour of RGB stars with their chemical properties, finding a significant trend between the iron content and the c_UBI. Stars belonging to the old population are systematically more metal poor ([Fe/H]=-2.32\\pm0.08 dex) than the intermediate-age ones ([Fe/H]=-1.82\\pm0.03 dex). This gives solid evidence on the chemical evolution history of this g...

  4. Torsional Alfv\\xE9n resonances as an efficient damping mechanism for non-radial oscillations in red giant stars

    Science.gov (United States)

    Loi, Shyeh Tjing; Papaloizou, John C. B.

    2017-05-01

    Stars are self-gravitating fluids in which pressure, buoyancy, rotation and magnetic fields provide the restoring forces for global modes of oscillation. Pressure and buoyancy energetically dominate, while rotation and magnetism are generally assumed to be weak perturbations and often ignored. However, observations of anomalously weak dipole mode amplitudes in red giant stars suggest that a substantial fraction of these are subject to an additional source of damping localized to their core region, with indirect evidence pointing to the role of a deeply buried magnetic field. It is also known that in many instances, the gravity-mode character of affected modes is preserved, but so far, no effective damping mechanism has been proposed that accommodates this aspect. Here we present such a mechanism, which damps the oscillations of stars harbouring magnetised cores via resonant interactions with standing Alfvén modes of high harmonic index. The damping rates produced by this mechanism are quantitatively on par with those associated with turbulent convection, and in the range required to explain observations, for realistic stellar models and magnetic field strengths. Our results suggest that magnetic fields can provide an efficient means of damping stellar oscillations without needing to disrupt the internal structure of the modes, and lay the groundwork for an extension of the theory of global stellar oscillations that incorporates these effects.

  5. Connecting the evolution of thermally pulsing asymptotic giant branch stars to the chemistry in their circumstellar envelopes -- I. The case of hydrogen cyanide

    CERN Document Server

    Marigo, Paola; Nanni, Ambra; Bressan, Alessandro; Girardi, Leo

    2015-01-01

    We investigate the formation of hydrogen cyanide (HCN) in the inner circumstellar envelopes of thermally pulsing asymptotic giant branch (TP-AGB) stars. A dynamic model for periodically shocked atmospheres, which includes an extended chemo-kinetic network, is for the first time coupled to detailed evolutionary tracks for the TP-AGB phase computed with the COLIBRI code. We carried out a calibration of the main shock parameters (the shock formation radius and the effective adiabatic index) using the circumstellar HCN abundances recently measured for a populous sample of pulsating TP-AGB stars. Our models recover the range of the observed HCN concentrations as a function of the mass-loss rates, and successfully reproduce the systematic increase of HCN moving along the M-S-C chemical sequence of TP-AGB stars, that traces the increase of the surface C/O ratio. The chemical calibration brings along two important implications: i) the first shock should emerge very close to the photosphere, and ii) shocks are expecte...

  6. Origins of the Thick Disk as Traced by the Alpha Elements of Metal-poor Giant Stars Selected from Rave

    NARCIS (Netherlands)

    Ruchti, G. R.; Fulbright, J. P.; Wyse, R. F. G.; Gilmore, G. F.; Bienaymé, O.; Binney, J.; Bland-Hawthorn, J.; Campbell, R.; Freeman, K. C.; Gibson, B. K.; Grebel, E. K.; Helmi, A.; Munari, U.; Navarro, J. F.; Parker, Q. A.; Reid, W.; Seabroke, G. M.; Siebert, A.; Siviero, A.; Steinmetz, M.; Watson, F. G.; Williams, M.; Zwitter, T.

    2010-01-01

    Theories of thick-disk formation can be differentiated by measurements of stellar elemental abundances. We have undertaken a study of metal-poor stars selected from the RAVE spectroscopic survey of bright stars to establish whether or not there is a significant population of metal-poor thick-disk st

  7. VizieR Online Data Catalog: WISE and 2MASS photometry of M giant stars (Li+, 2016)

    Science.gov (United States)

    Li, J.; Smith, M. C.; Zhong, J.; Hou, J.; Carlin, J. L.; Newberg, H. J.; Liu, C.; Chen, L.; Li, L.; Shao, Z.; Small, E.; Tian, H.

    2016-08-01

    We cross-matched our LAMOST spectroscopically confirmed sample of M giants, M dwarfs, and QSOs (see section 2) to the ALLWISE Source Catalog in the NASA/IPAC Infrared Science Archive, using a search radius of 3". We also applied some cuts detailed in section 3. (1 data file).

  8. Analysis of strange-mode instability with time-dependent convection in hot massive stars

    CERN Document Server

    Sonoi, Takafumi

    2013-01-01

    We carry out nonadiabatic analysis of strange-modes in hot massive stars with time-dependent convection (TDC) for the first time. Although convective luminosity in envelopes of hot massive stars is not as dominative as in stars near the red edge of the classical Cepheid instability strip in the Hertzsprung-Russell (H-R) diagram, we have found that the strange-mode instability can be affected by the treatment of convection. However, existence of the instability around and over the Humphreys-Davidson (H-D) limit is independent of the treatment. This implies that the strange-mode instability could be responsible for the lack of observed stars over the H-D limit regardless of uncertainties on convection theories.

  9. Puzzling Origin of CEMP-r/s Stars: An Interpretation of Abundance and Enrichment of s- and r-Process Elements from Asymptotic Giant Branch Supernovae

    Indian Academy of Sciences (India)

    Jiang Zhang; Fang Zhao; Yanping Chen; Wenyuan Cui; Bo Zhang

    2013-12-01

    CEMP-r/s stars at low metallicity are known as double-enhanced stars that show enhancements of both r-process and s-process elements. The chemical abundances of these very metal-poor stars provide us a lot of information for putting new restraints on models of neutron-capture processes. In this article, we put forward an accreted scenario in which the double enrichment of r-process and s-process elements is caused by a former intermediate-mass Asymptotic Giant Branch (AGB) companion in a detached binary system. As the AGB superwind is only present at the ultimate phase of AGB stars, there is thus a lot of potential that the degenerate-core mass of an intermediate-mass AGB star reaches the Chandrasekhar limit before the AGB superwind. In these circumstances, both s-process elements produced in the AGB shell and r-process elements synthesized in the subsequent explosion would be sprayed contemporaneously and accreted by its companion. Despite similarity to physical conditions of a core-collapse supernova, a major focus in this scenario is the degenerate C–O core surrounded by an envelope of a former intermediate-mass AGB donor that may collapse and explode. Due to the existence of an outer envelope, r-process nucleosynthesis is expected to occur. Hypothesizing the material-rich europium (Eu) accreted by the secondary via the wind from the supernova to be in proportion to the geometric fraction of the companion with respect to the exploding donor star, we find that the estimated yield of Eu (as representative of r-process elements) per AGB supernova event is about 1 × 10-9⊙ ∼ 5 × 10-9⊙. Using the yields of Eu, the overabundance of r-process elements in CEMP-r/s stars can be accounted for. The calculated results show that the value of parameter , standing for efficiency of wind pollution from the AGB supernova, will reach about 104, which means that the enhanced factor is much larger than unity due to the impact of gravity of the donor and the result of the

  10. The Atmospheric Dynamics of Alpha Tau (K5 III) - Clues to Understanding the Magnetic Dynamo in Late-Type Giant Stars

    Science.gov (United States)

    Carpenter, Kenneth G.; Airapetian, Vladimir

    2008-01-01

    Using HST/GHRS, HST/STIS and FUSE archival data for a Tau and the CHIANTI spectroscopic code, we have derived line shifts, volumetric emission measures, and plasma density estimates, and calculated filling factors for a number of UV lines forming between 10,000 K and 300,000 K in the outer atmosphere of this red giant star. The data suggest the presence of low-temperature extended regions and high-temperature compact regions, associated with magnetically open and closed structures in the stellar atmosphere, respectively. The signatures of UV lines from a Tau can be consistently understood via a model of upward-traveling Alfv6n waves in a gravitationally stratified atmosphere. These waves cause nonthermal broadening in UV lines due to unresolved wave motions and downward plasma motions in compact magnetic loops heated by resonant Alfven wave heating.

  11. Giant temperature dependence of the spin reversal field in magnetoelectric chromia

    Science.gov (United States)

    Fallarino, Lorenzo; Berger, Andreas; Binek, Christian

    2014-01-01

    Magnetic field-induced reversal of surface spin polarization for the magnetoelectric antiferromagnet chromia is studied via magnetometry in (0001)-textured thin films of various thicknesses. Reversal solely by magnetic means has been experimentally evidenced in sufficiently thin films. It sets the field-response of chromia films apart from bulk behavior, where switching between time-reversed single domain states requires the simultaneous presence of electric and magnetic fields. In our detailed experiments, we furthermore observe a giant sensitivity of the coercive field on temperature, thus, indicating the potential of magnetoelectric antiferromagnets as promising candidates for energy assisted magnetic recording media.

  12. Giant temperature dependence of the spin reversal field in magnetoelectric chromia

    Energy Technology Data Exchange (ETDEWEB)

    Fallarino, Lorenzo; Berger, Andreas [CIC Nanogune Consolider, Tolosa Hiribidea 76, 20018 Donostia-San Sebastian (Spain); Binek, Christian [CIC Nanogune Consolider, Tolosa Hiribidea 76, 20018 Donostia-San Sebastian (Spain); IKERBASQUE, Basque Foundation for Science, 48011 Bilbao (Spain)

    2014-01-13

    Magnetic field-induced reversal of surface spin polarization for the magnetoelectric antiferromagnet chromia is studied via magnetometry in (0001)-textured thin films of various thicknesses. Reversal solely by magnetic means has been experimentally evidenced in sufficiently thin films. It sets the field-response of chromia films apart from bulk behavior, where switching between time-reversed single domain states requires the simultaneous presence of electric and magnetic fields. In our detailed experiments, we furthermore observe a giant sensitivity of the coercive field on temperature, thus, indicating the potential of magnetoelectric antiferromagnets as promising candidates for energy assisted magnetic recording media.

  13. 1FGL J1417.7-4407: A gamma-ray bright binary with a massive neutron star and a giant secondary

    CERN Document Server

    Strader, Jay; Cheung, C C; Sand, David J; Donato, Davide; Corbet, Robin; Koeppe, Dana; Edwards, Philip G; Stevens, Jamie; Petrov, Leonid; Salinas, Ricardo; Peacock, Mark; Finzell, Thomas; Reichart, Daniel; Haislip, Joshua

    2015-01-01

    We present multiwavelength observations of the persistent Fermi-LAT unidentified gamma-ray source 1FGL J1417.7-4407, showing it is likely to be associated with a newly discovered X-ray binary containing a massive neutron star (nearly 2 M_sun) and a ~ 0.4 M_sun giant secondary with a 5.4 day period. SOAR optical spectroscopy at a range of orbital phases reveals variable double-peaked H-alpha emission, consistent with the presence of an accretion disk. The lack of radio emission and evidence for a disk suggests the gamma-ray emission is unlikely to originate in a pulsar magnetosphere, but could instead be associated with a pulsar wind, relativistic jet, or could be due to synchrotron self-Compton at the disk/magnetosphere boundary. Assuming a wind or jet, the high ratio of gamma-ray to X-ray luminosity (~ 20) suggests efficient production of gamma-rays, perhaps due to the giant companion. The system appears to be a low-mass X-ray binary that has not yet completed the pulsar recycling process. This system is a g...

  14. The Carina project. VII. Toward the breaking of the age-metallicity degeneracy of red giant branch stars using the C {sub U,} {sub B,} {sub I} index

    Energy Technology Data Exchange (ETDEWEB)

    Monelli, M.; Milone, A. P.; Gallart, C.; Aparicio, A. [Instituto de Astrofísica de Canarias, Calle Via Lactea s/n, E-38205 La Laguna, Tenerife (Spain); Fabrizio, M.; Cassisi, S.; Buonanno, R. [Istituto Nazionale di Astrofisica-Osservatorio Astronomico Collurania, Via M. Maggini, I-64100 Teramo (Italy); Bono, G. [Dipartimento di Fisica, Universitá di Roma Tor Vergata, Via della Ricerca Scientifica 1, I-00133 Rome (Italy); Stetson, P. B. [Dominion Astrophysical Observatory, NRC-Herzberg, 5071 West Saanich Road, Victoria, BC, V9E 2E7 (Canada); Walker, A. R. [Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, Casilla 603, La Serena (Chile); Nonino, M. [Istituto Nazionale di Astrofisica-Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, I-40131 Trieste (Italy); Dall' Ora, M. [INAF—Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, I-80131 Napoli (Italy); Ferraro, I.; Iannicola, G.; Pulone, L. [Istituto Nazionale di Astrofisica-Osservatorio Astronomico di Roma, Via Frascati 33, Monte Porzio Catone, I-00044 Rome (Italy); Thévenin, F., E-mail: monelli@iac.es [Université de Nice Sophia-antipolis, CNRS, Observatoire de la Côte d' Azur, Laboratoire Lagrange, BP 4229, F-06304 Nice (France)

    2014-12-01

    We present an analysis of photometric and spectroscopic data of the Carina dSph galaxy, testing a new approach similar to that used to disentangle multiple populations in Galactic globular clusters (GCs). We show that a proper color combination is able to separate a significant fraction of the red giant branch (RGB) of the two main Carina populations (the old one, ∼12 Gyr, and the intermediate-age one, 4-8 Gyr). In particular, the c {sub U,} {sub B,} {sub I} = (U – B) – (B – I) pseudo-color allows us to follow the RGB of both populations along a relevant portion of the RGB. We find that the oldest stars have a more negative c {sub U,} {sub B,} {sub I} pseudo-color than intermediate-age ones. We correlate the pseudo-color of RGB stars with their chemical properties, finding a significant trend between the iron content and the c {sub U,} {sub B,} {sub I}. Stars belonging to the old population are systematically more metal-poor ([Fe/H] =–2.32 ± 0.08 dex) than the intermediate-age ones ([Fe/H] =–1.82 ± 0.03 dex). This gives solid evidence of the chemical evolution history of this galaxy, and we have a new diagnostic that can allow us to break the age-metallicity degeneracy of H-burning advanced evolutionary phases. We compared the distribution of stars in the c {sub U,} {sub B,} {sub I} plane with theoretical isochrones, finding that no satisfactory agreement can be reached with models developed in a theoretical framework based on standard heavy element distributions. Finally, we discuss possible systematic differences when compared with multiple populations in GCs.

  15. Hybrid stars Spin polarised nuclear matter and density dependent quark masses

    CERN Document Server

    Maheswari, V S U; Samaddar, S K

    1998-01-01

    The possibility of formation of a droplet phase (DP) inside a star and its consequences on the structural properties of the star are investigated. For nuclear matter (NM), an equation of state (EOS) based on finite range, momentum and density dependent interaction, and which predicts that neutron matter undergoes ferromagnetic transition at densities realisable inside the neutron star is employed. An EOS for quark matter (QM) with density dependent quark masses, the so-called effective mass model, is constructed by correctly treating the quark chemical potentials. It is then found that a droplet phase consisting of strange quark matter and unpolarised nuclear matter sandwiched between a core of polarised nuclear matter and a crust containing unpolarised nuclear matter exists. Moreover, we could explain the mass and surface magnetic field satisfactorily, and as well allow, due to the presence of a droplet phase, the direct URCA process to happen.

  16. Contamination from a nearby star cannot explain the anomalous transmission spectrum of the ultrashort period giant planet WASP-103 b

    Science.gov (United States)

    Southworth, John; Evans, Daniel F.

    2016-11-01

    The planet in the WASP-103 system is an excellent candidate for transmission spectroscopy because of its large radius and high temperature. Application of this technique found a variation of radius with wavelength which was far too strong to be explained by scattering processes in the planetary atmosphere. A faint nearby star was subsequently detected, whose contamination of the transit light curves might explain this anomaly. We present a reanalysis of published data in order to characterize the faint star and assess its effect on the measured transmission spectrum. The faint star has a mass of 0.72 ± 0.08 M⊙ and is almost certainly gravitationally bound to the planetary system. We find that its effect on the measured physical properties of the planet and host star is small, amounting to a planetary radius larger by 0.6σ and planetary density smaller by 0.8σ. Its influence on the measured transmission spectrum is much greater: the spectrum now has a minimum around 760 nm and opacity rises to both bluer and redder wavelengths. It is a poor match to theoretical spectra and the spectral slope remains too strong for Rayleigh scattering. The existence of the faint nearby star cannot therefore explain the measured spectral properties of this hot and inflated planet. We advocate further observations of the system, both with high spatial resolution in order to improve the measured properties of the faint star, and with higher spectral resolution to confirm the anomalous transmission spectrum of the planet.

  17. Intermediate-mass Asymptotic Giant Branch Stars and Sources of 26Al, 60Fe, 107Pd, and 182Hf in the Solar System

    Science.gov (United States)

    Wasserburg, G. J.; Karakas, Amanda I.; Lugaro, Maria

    2017-02-01

    We explore the possibility that the short-lived radionuclides {}26{{A}}l, {}60{{F}}e, {}107{{P}}d, and {}182{{H}}f inferred to be present in the proto-solar cloud originated from 3–8 {M}ȯ asymptotic giant branch (AGB) stars. Models of AGB stars with initial mass above 5 {M}ȯ are prolific producers of {}26{{A}}l owing to hot bottom burning (HBB). In contrast, {}60{{F}}e, {}107{{P}}d, and {}182{{H}}f are produced by neutron captures: {}107{{P}}d and {}182{{H}}f in models ≲ 5 {M}ȯ , and {}60{{F}}e in models with higher mass. We mix stellar yields from solar-metallicity AGB models into a cloud of solar mass and composition to investigate whether it is possible to explain the abundances of the four radioactive nuclides at the Sun’s birth using one single value of the mixing ratio between the AGB yields and the initial cloud material. We find that AGB stars that experience efficient HBB (≥slant 6 {M}ȯ ) cannot provide a solution because they produce too little {}182{{H}}f and {}107{{P}}d relative to {}26{{A}}l and {}60{{F}}e. Lower-mass AGB stars cannot provide a solution because they produce too little {}26{{A}}l relative to {}107{{P}}d and {}182{{H}}f. A self-consistent solution may be found for AGB stars with masses in between (4–5.5 {M}ȯ ), provided that HBB is stronger than in our models and the {}13{{C}}(α, n){}16{{O}} neutron source is mildly activated. If stars of {{M}}< 5.5 {M}ȯ are the source of the radioactive nuclides, then some basis for their existence in proto-solar clouds needs to be explored, given that the stellar lifetimes are longer than the molecular cloud lifetimes.

  18. Modeling the near-UV band of GK stars, Paper III: Dependence on abundance pattern

    CERN Document Server

    Short, C Ian

    2013-01-01

    We extend the grid of NLTE models presented in Paper II to explore variations in abundance pattern in two ways: 1) The adoption of the Asplund et al. (2009) (GASS10) abundances, 2) For stars of metallicity, [M/H], of -0.5, the adoption of a non-solar enhancement of alpha-elements by +0.3 dex. Moreover, our grid of synthetic spectral energy distributions (SEDs) is interpolated to a finer numerical resolution in both T_eff (Delta T_eff = 25 K) and log g (Delta log g = 0.25). We compare the values of T_eff and log g inferred from fitting LTE and Non-LTE SEDs to observed SEDs throughout the entire visible band, and in an ad hoc "blue" band. We compare our spectrophotometrically derived T_eff values to a variety of T_eff calibrations, including more empirical ones, drawn from the literature. For stars of solar metallicity, we find that the adoption of the GASS10 abundances lowers the inferred T_eff value by 25 - 50 K for late-type giants, and NLTE models computed with the GASS10 abundances give T_eff results that ...

  19. Giant exchange bias and its angular dependence in Co/CoO core-shell nanowire assemblies

    Energy Technology Data Exchange (ETDEWEB)

    Gandha, Kinjal; Chaudhary, Rakesh P.; Mohapatra, Jeotikanta; Koymen, Ali R.; Liu, J. Ping, E-mail: pliu@uta.edu

    2017-07-12

    The exchange-bias field (H{sub EB}) and its angular dependence are systematically investigated in Co/CoO core-shell nanowire assemblies (∼15 nm in diameter and ∼200 nm in length) consisting of single-crystalline Co core and polycrystalline CoO shell. Giant exchange-bias field (H{sub EB}) up to 2.4 kOe is observed below a blocking temperature (T{sub EB} ∼150 K) in the aligned Co/CoO nanowire assemblies. It is also found that there is an angular dependence between the H{sub EB} and the applied magnetization direction. The H{sub EB} showed a peak at 30° between the applied field and the nanowire aligned direction, which may be attributed to the noncollinear spin orientations at the interface between the ferromagnetic core and the antiferromagnetic shell. This behavior is quantitatively supported by an analytical calculation based on Stoner–Wohlfarth model. This study underlines the importance of the competing magnetic anisotropies at the interface of Co/CoO core-shell nanowires. - Highlights: • Giant exchange bias is observed in oriented Co/CoO core-shell nanowire assemblies. • Study of angular and temperature dependence of the exchange bias effect. • Competing magnetic anisotropies at the interface of Co/CoO core-shell nanowires. • Effect of misaligned spins in FM/AFM interface on angular dependence of exchange bias. • We explain the analytical model that accounts for experimental results.

  20. Maxwell equation violation by density dependent magnetic fields in neutron stars

    CERN Document Server

    Menezes, Débora P

    2016-01-01

    We show that the widely used density dependent magnetic field prescriptions, necessary to account for the variation of the field intensity from the crust to the core of neutron stars violate one of the Maxwell equations. We estimate how strong the violation is when different equations of state are used and check for which cases the pathological problem can be cured.

  1. Seismology of Giant Planets

    CERN Document Server

    Gaulme, Patrick; Schmider, Francois-Xavier; Guillot, Tristan

    2014-01-01

    Seismology applied to giant planets could drastically change our understanding of their deep interiors, as it has happened with the Earth, the Sun, and many main-sequence and evolved stars. The study of giant planets' composition is important for understanding both the mechanisms enabling their formation and the origins of planetary systems, in particular our own. Unfortunately, its determination is complicated by the fact that their interior is thought not to be homogeneous, so that spectroscopic determinations of atmospheric abundances are probably not representative of the planet as a whole. Instead, the determination of their composition and structure must rely on indirect measurements and interior models. Giant planets are mostly fluid and convective, which makes their seismology much closer to that of solar-like stars than that of terrestrial planets. Hence, helioseismology techniques naturally transfer to giant planets. In addition, two alternative methods can be used: photometry of the solar light ref...

  2. The PdBI arcsecond whirlpool survey (PAWS): Environmental dependence of giant molecular cloud properties in M51

    Energy Technology Data Exchange (ETDEWEB)

    Colombo, Dario; Hughes, Annie; Schinnerer, Eva; Meidt, Sharon E. [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Leroy, Adam K. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Pety, Jérôme; Dumas, Gaëlle; Schuster, Karl F. [Institut de Radioastronomie Millimétrique, 300 Rue de la Piscine, F-38406 Saint Martin d' Hères (France); Dobbs, Clare L. [School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); García-Burillo, Santiago [Observatorio Astronómico Nacional - OAN, Observatorio de Madrid Alfonso XII, 3, E-28014 Madrid (Spain); Thompson, Todd A. [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Kramer, Carsten [Instituto Radioastronomía Milimétrica, Av. Divina Pastora 7, Nucleo Central, E-18012 Granada (Spain)

    2014-03-20

    Using data from the PdBI Arcsecond Whirlpool Survey (PAWS), we have generated the largest extragalactic giant molecular cloud (GMC) catalog to date, containing 1507 individual objects. GMCs in the inner M51 disk account for only 54% of the total {sup 12}CO(1-0) luminosity of the survey, but on average they exhibit physical properties similar to Galactic GMCs. We do not find a strong correlation between the GMC size and velocity dispersion, and a simple virial analysis suggests that ∼30% of GMCs in M51 are unbound. We have analyzed the GMC properties within seven dynamically motivated galactic environments, finding that GMCs in the spiral arms and in the central region are brighter and have higher velocity dispersions than inter-arm clouds. Globally, the GMC mass distribution does not follow a simple power-law shape. Instead, we find that the shape of the mass distribution varies with galactic environment: the distribution is steeper in inter-arm region than in the spiral arms, and exhibits a sharp truncation at high masses for the nuclear bar region. We propose that the observed environmental variations in the GMC properties and mass distributions are a consequence of the combined action of large-scale dynamical processes and feedback from high-mass star formation. We describe some challenges of using existing GMC identification techniques for decomposing the {sup 12}CO(1-0) emission in molecule-rich environments, such as M51's inner disk.

  3. Dynamic acoustics for the STAR-100. [computer algorithms for time dependent sound waves in jet

    Science.gov (United States)

    Bayliss, A.; Turkel, E.

    1979-01-01

    An algorithm is described to compute time dependent acoustic waves in a jet. The method differs from previous methods in that no harmonic time dependence is assumed, thus permitting the study of nonharmonic acoustical behavior. Large grids are required to resolve the acoustic waves. Since the problem is nonstiff, explicit high order schemes can be used. These have been adapted to the STAR-100 with great efficiencies and permitted the efficient solution of problems which would not be feasible on a scalar machine.

  4. THE C+N+O ABUNDANCE OF {omega} CENTAURI GIANT STARS: IMPLICATIONS FOR THE CHEMICAL-ENRICHMENT SCENARIO AND THE RELATIVE AGES OF DIFFERENT STELLAR POPULATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Marino, A. F. [Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching bei Muenchen (Germany); Milone, A. P.; Aparicio, A. [Instituto de Astrofisica de Canarias, E-38200 La Laguna, Tenerife, Canary Islands (Spain); Piotto, G. [Dipartimento di Astronomia, Universita di Padova, Vicolo dell' Osservatorio 3, Padova, I-35122 (Italy); Cassisi, S. [INAF-Osservatorio Astronomico di Teramo, Via M. Maggini, 64100 Teramo (Italy); D' Antona, F. [INAF-Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monteporzio (Italy); Anderson, J. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Bedin, L. R.; Renzini, A. [INAF-Osservatorio Astronomico di Padova, Vicolo dellOsservatorio 5, 35122 Padova (Italy); Villanova, S., E-mail: amarino@MPA-Garching.MPG.DE, E-mail: milone@iac.es, E-mail: aparicio@iac.es, E-mail: giampaolo.piotto@unipd.it, E-mail: cassisi@oa-teramo.inaf.it, E-mail: dantona@oa-roma.inaf.it, E-mail: jayander@stsci.edu, E-mail: luigi.bedin@oapd.inaf.it, E-mail: alvio.renzini@oapd.inaf.it, E-mail: svillanova@astro-udec.cl [Departamento de Astronomia, Universidad de Concepcion, Casilla 160-C, Concepcion (Chile)

    2012-02-10

    We present a chemical-composition analysis of 77 red-giant stars in Omega Centauri. We have measured abundances for carbon and nitrogen, and combined our results with abundances of O, Na, La, and Fe that we determined in our previous work. Our aim is to better understand the peculiar chemical-enrichment history of this cluster by studying how the total C+N+O content varies among the different metallicity stellar groups, and among stars at different places along the Na-O anticorrelation. We find that the (anti)correlations among the light elements that would be expected on theoretical grounds for matter that has been nuclearly processed via high-temperature proton captures. The overall [(C+N+O)/Fe] increases by {approx}0.5 dex from [Fe/H] {approx}-2.0 to [Fe/H] {approx}-0.9. Our results provide insight into the chemical-enrichment history of the cluster, and the measured CNO variations provide important corrections for estimating the relative ages of the different stellar populations.

  5. A Two Micron All-Sky Survey View of the Sagittarius Dwarf Galaxy: II. Swope Telescope Spectroscopy of M Giant Stars in the Dynamically Cold Sagittarius Tidal Stream

    CERN Document Server

    Majewski, Steven R; Law, David R; Patterson, Richard J; Allyson A Polak; Rocha-Pinto, Helio J; Crane, Jeffrey D; Frinchaboy, Peter M; Hummels, Cameron B; Johnston, Kathryn V; Jaehyon, Rhee; Skrutskie, Michael F

    2004-01-01

    We present moderate resolution (~6 km/s) spectroscopy of 284 M giant candidates selected from the Two Micron All Sky Survey photometry. Radial velocities (RVs) are presented for stars mainly in the south, with a number having positions consistent with association to the trailing tidal tail of the Sagittarius (Sgr) dwarf galaxy. The latter show a clear RV trend with orbital longitude, as expected from models of the orbit and destruction of Sgr. A minimum 8 kpc width of the trailing stream about the Sgr orbital midplane is implied by verified RV members. The coldness of this stream (dispersion ~10 km/s) provides upper limits on the combined contributions of stream heating by a lumpy Galactic halo and the intrinsic dispersion of released stars, which is a function of the Sgr core mass. The Sgr trailing arm is consistent with a Galactic halo containing one dominant, LMC-like lump, however some lumpier halos are not ruled out. An upper limit to the total M/L of the Sgr core is 21 in solar units. A second structure...

  6. Angular momentum redistribution by mixed modes in evolved low-mass stars. II. Spin-down of the core of red giants induced by mixed modes

    CERN Document Server

    Belkacem, K; Goupil, M J; Mosser, B; Sonoi, T; Ouazzani, R M; Dupret, M A; Mathis, S; Grosjean, M

    2015-01-01

    The detection of mixed modes in subgiants and red giants by the CoRoT and \\emph{Kepler} space-borne missions allows us to investigate the internal structure of evolved low-mass stars. In particular, the measurement of the mean core rotation rate as a function of the evolution places stringent constraints on the physical mechanisms responsible for the angular momentum redistribution in stars. It showed that the current stellar evolution codes including the modelling of rotation fail to reproduce the observations. An additional physical process that efficiently extracts angular momentum from the core is thus necessary. Our aim is to assess the ability of mixed modes to do this. To this end, we developed a formalism that provides a modelling of the wave fluxes in both the mean angular momentum and the mean energy equations in a companion paper. In this article, mode amplitudes are modelled based on recent asteroseismic observations, and a quantitative estimate of the angular momentum transfer is obtained. This i...

  7. The C+N+O abundance of Omega Centauri giant stars: implications on the chemical enrichment scenario and the relative ages of different stellar populations

    CERN Document Server

    Marino, A F; Piotto, G; Cassisi, S; D'Antona, F; Anderson, J; Aparicio, A; Bedin, L R; Renzini, A; Villanova, S

    2011-01-01

    We present a chemical-composition analysis of 77 red-giant stars in Omega Centauri. We have measured abundances for carbon and nitrogen, and combined our results with abundances of O, Na, La, and Fe that we determined in our previous work. Our aim is to better understand the peculiar chemical-enrichment history of this cluster, by studying how the total C+N+O content varies among the different-metallicity stellar groups, and among stars at different places along the Na-O anticorrelation. We find the (anti)correlations among the light elements that would be expected on theoretical ground for matter that has been nuclearly processed via high-temperature proton captures. The overall [(C+N+O)/Fe] increases by 0.5 dex from [Fe/H] -2.0 to [Fe/H] -0.9. Our results provide insight into the chemical-enrichment history of the cluster, and the measured CNO variations provide important corrections for estimating the relative ages of the different stellar populations.

  8. A Non-LTE Study of Silicon Abundances in Giant Stars from the Si I Infrared Lines in the zJ-Band

    Science.gov (United States)

    Tan, Kefeng; Shi, Jianrong; Takada-Hidai, Masahide; Takeda, Yoichi; Zhao, Gang

    2016-05-01

    We investigate the feasibility of Si i infrared (IR) lines as Si abundance indicators for giant stars. We find that Si abundances obtained from the Si i IR lines based on the local thermodynamic equilibrium (LTE) analysis show large line-to-line scatter (mean value of 0.13 dex), and are higher than those from the optical lines. However, when non-LTE effects are taken into account, the line-to-line scatter reduces significantly (mean value of 0.06 dex), and the Si abundances are consistent with those from the optical lines. The typical average non-LTE correction of [Si/Fe] for our sample stars is about -0.35 dex. Our results demonstrate that the Si i IR lines could be reliable abundance indicators, provided that the non-LTE effects are properly taken into account. Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; based on observations made with ESO telescopes at the La Silla Paranal Observatory under programme IDs 266.D-5655(A) and 084.D-0912(A); based on observations carried out at the National Astronomical Observatories (Xinglong, China).

  9. Hubble Space Telescope study of resolved red giant stars in the outer halos of nearby dwarf starburst galaxies

    CERN Document Server

    Ryś, Agnieszka; van der Marel, Roeland P; Aloisi, Alessandra; Annibali, Francesca

    2011-01-01

    [abridged] Aims. We observed the outer parts of NGC 1569 and NGC 4449, two of the closest and strongest dwarf starburst galaxies in the local universe, to characterize their stellar density and populations, and obtain new insights into the structure, formation, and evolution of starburst galaxies and galaxy halos. Methods. We obtained HST/WFPC2 images between 5 and 8 scale radii from the center, along the intermediate and minor axes. We performed point-source photometry to determine color magnitude diagrams of I vs. V-I. We compared the results at different radii, including also our prior HST/ACS results for more centrally located fields. Results. We detect stars in the RGB and TP-AGB (carbon star) phases in all outer fields, but not younger stars such as those present at smaller radii. The RGB star density profile is well fit by either a de Vaucouleurs profile or a power-law profile, but has more stars at large radii than a single exponential. To within the uncertainties, there are no radial gradients in the...

  10. An analysis of the CoRoT-2 system: A young spotted star and its inflated giant planet

    CERN Document Server

    Guillot, Tristan

    2010-01-01

    Context: CoRoT-2b is one of the most anomalously large exoplanet known. Given its large mass, its large radius cannot be explained by standard evolution models. Interestingly, the planet's parent star is an active, rapidly rotating solar-like star with a large fraction (7 to 20%) of spots. Aims: We want to provide constraints on the properties of the star-planet system and understand whether the planet's inferred large size may be due to a systematic error on the inferred parameters, and if not, how it may be explained. Methods: We combine stellar and planetary evolution codes based on all available spectroscopic and photometric data to obtain self-consistent constraints on the system parameters. Results: We find no systematic error in the stellar modeling (including spots and stellar activity) that would yield the required ~10% reduction in size for the star and thus the planet. Two classes of solutions are found: the usual main sequence solution for the star yields for the planet a mass of 3.67+/-0.13 Mjup,...

  11. Monitoring survey of pulsating giant stars in the Local Group galaxies: survey description, science goals, target selection

    Science.gov (United States)

    Saremi, E.; Javadi, A.; van Loon, J. Th; Khosroshahi, H.; Abedi, A.; Bamber, J.; Hashemi, S. A.; Nikzat, F.; Molaei Nezhad, A.

    2017-06-01

    The population of nearby dwarf galaxies in the Local Group constitutes a complete galactic environment, perfect suited for studying the connection between stellar populations and galaxy evolution. In this study, we are conducting an optical monitoring survey of the majority of dwarf galaxies in the Local Group, with the Isaac Newton Telescope (INT), to identify long period variable stars (LPVs). These stars are at the end points of their evolution and therefore their luminosity can be directly translated into their birth masses; this enables us to reconstruct the star formation history. By the end of the monitoring survey, we will have performed observations over ten epochs, spaced approximately three months apart, and identified long-period, dust-producing AGB stars; five epochs of data have been obtained already. LPVs are also the main source of dust; in combination with Spitzer Space Telescope images at mid-IR wavelengths we will quantify the mass loss, and provide a detailed map of the mass feedback into the interstellar medium. We will also use the amplitudes in different optical passbands to determine the radius variations of the stars, and relate this to their mass loss.

  12. Slowly rotating superfluid neutron stars with isospin dependent entrainment in a two-fluid model

    CERN Document Server

    Kheto, Apurba

    2015-01-01

    We investigate the slowly rotating general relativistic superfluid neutron stars including the entrainment effect in a two-fluid model, where one fluid represents the superfluid neutrons and the other is the charge-neutral fluid called the proton fluid, made of protons and electrons. The equation of state and the entrainment effect between the superfluid neutrons and the proton fluid are computed using a relativistic mean field (RMF) model where baryon-baryon interaction is mediated by the exchange of $\\sigma$, $\\omega$, and $\\rho$ mesons and scalar self interactions are also included. The equations governing rotating neutron stars in the slow rotation approximation are second order in rotational velocities of neutron and proton fluids. We explore the effects of the isospin dependent entrainment and the relative rotation between two fluids on the global properties of rotating superfluid neutron stars such as mass, shape, and the mass shedding (Kepler) limit within the RMF model with different parameter sets. ...

  13. On the metallicity dependance of the [Y/Mg] - age relation for solar type stars

    CERN Document Server

    Feltzing, S; McMillan, P J; Stonkute, E

    2016-01-01

    Several recent studies of Solar twins in the Solar neighbourhood have shown a tight correlation between various elemental abundances and age, in particular [Y/Mg]. If this relation is real and valid for other types of stars as well as elsewhere in the Galaxy it would provide a very powerful tool to derive ages of stars without the need to resort to determining their masses (evolutionary stage) very precisely. The method would also likely work if the stellar parameters have relatively large errors. The studies presented in the recent literature span a narrow range of [Fe/H]. By studying a larger sample of Solar neighbourhood dwarfs with a much larger range in [Fe/H], we find that the relation between [Y/Mg] and age depends on the [Fe/H] of the stars. Hence, it appears that the [Y/Mg] - age relation is unique to Solar analogues.

  14. On the metallicity dependence of the [Y/Mg]-age relation for solar-type stars

    Science.gov (United States)

    Feltzing, Sofia; Howes, Louise M.; McMillan, Paul J.; Stonkutė, Edita

    2017-02-01

    Several recent studies of solar twins in the solar neighbourhood have shown a tight correlation between various elemental abundances and age, in particular [Y/Mg]. If this relation is real and valid for other types of stars as well as elsewhere in the Galaxy, it would provide a very powerful tool to derive ages of stars without the need to resort to determining their masses (evolutionary stage) very precisely. The method would also likely work if the stellar parameters have relatively large errors. The studies presented in the recent literature span a narrow range of [Fe/H]. By studying a larger sample of solar neighbourhood dwarfs with a much larger range of [Fe/H], we find that the relation between [Y/Mg] and age depends on the [Fe/H] of the stars. Hence, it appears that the [Y/Mg]-age relation is unique to solar analogues.

  15. A Multitransition CO and CS(2--1) Comparison of a Star-forming and a Non--Star-forming Giant Molecular Cloud

    Science.gov (United States)

    Williams, Jonathan P.; Blitz, Leo

    1998-02-01

    CO (3-2), CO (1-0), and CS (2-1) observations of clumps in the cold, low-luminosity cloud G216-2.5 discovered by Maddalena & Thaddeus are compared to the star-forming Rosette molecular cloud. The comparisons suggest that the clumps in a cloud may be characterized as being either dormant, incipient star forming, or star forming. In the Rosette molecular cloud, each set accounts for, respectively, 80%, 10%, and 10% of the total mass, but in G216-2.5, nearly 100% of the clumps are dormant. The physical conditions of the clumps in both clouds suggest a mass agglomeration evolutionary sequence from dormant to star-forming clumps. Detailed results for the clumps in both clouds are as follows. Clump excitation conditions are remarkably uniform in G216-2.5 but show wide variation in the Rosette. CO (3-2) integrated intensities and the ratio of (3-2) to (1-0) emission are significantly greater in the star-forming cloud and greatest of all in those clumps with embedded IRAS sources. The ratio of CO (3-2) to (1-0) line widths is also greater in the Rosette cloud. Peak clump CO (1-0) temperatures are greater in the Rosette than G216-2.5, implying higher gas kinetic temperatures, and are highest of all for those clumps associated with IRAS sources. The ratios of peak CO (3-2) to (1-0) temperatures, however, are comparable in the two clouds, which implies that the volume density of emitting gas in the clumps in each cloud is similar, nH2~=103 cm-3. The CS observations indicate the presence of denser gas, nH2~105 cm-3, in the clumps in each cloud. CS integrated intensities are generally an order of magnitude weaker than 13CO emission in each cloud, but the ratio of the two is a factor of 2 less in G216-2.5. CS to 13CO line width ratios are also lower in G216-2.5, which suggests that there is a deficiency of dense gas relative to the Rosette. Again, the star-forming clumps in the Rosette possess the highest ratios. In addition, CO (2-1) emission was mapped over the central region

  16. Dramatic impact of the giant local magnetic fields on spin-dependent recombination processes in gadolinium based garnets

    Energy Technology Data Exchange (ETDEWEB)

    Romanov, N. G., E-mail: nikolai.romanov@mail.ioffe.ru; Tolmachev, D. O.; Gurin, A. S.; Uspenskaya, Yu. A.; Asatryan, H. R.; Badalyan, A. G. [Ioffe Institute, St. Petersburg 194021 (Russian Federation); Baranov, P. G. [Ioffe Institute, St. Petersburg 194021 (Russian Federation); Peter the Great St. Petersburg Polytechnic University, St. Petersburg 195251 (Russian Federation); Wieczorek, H.; Ronda, C. [Philips Research, High Tech Campus 34, 5656 AE Eindhoven (Netherlands)

    2015-06-29

    A giant magnetic field effect on spin-dependent recombination of the radiation-induced defects has been found in cerium doped gadolinium based garnet crystals and ceramics, promising materials for scintillator applications. A sharp and strong increase in the afterglow intensity stimulated by external magnetic field and an evidence of the magnetic field memory have been discovered. The effect was ascribed to huge Gd-induced internal magnetic fields, which suppress the recombination, and cross-relaxation with Gd{sup 3+} ions leading to reorientation of the spins of the electron and hole centers. Thus, the spin system of radiation-induced defects in gadolinium garnet based scintillator materials was shown to accumulate significant energy which can be released in external magnetic fields.

  17. Dramatic impact of the giant local magnetic fields on spin-dependent recombination processes in gadolinium based garnets

    Science.gov (United States)

    Romanov, N. G.; Tolmachev, D. O.; Gurin, A. S.; Uspenskaya, Yu. A.; Asatryan, H. R.; Badalyan, A. G.; Baranov, P. G.; Wieczorek, H.; Ronda, C.

    2015-06-01

    A giant magnetic field effect on spin-dependent recombination of the radiation-induced defects has been found in cerium doped gadolinium based garnet crystals and ceramics, promising materials for scintillator applications. A sharp and strong increase in the afterglow intensity stimulated by external magnetic field and an evidence of the magnetic field memory have been discovered. The effect was ascribed to huge Gd-induced internal magnetic fields, which suppress the recombination, and cross-relaxation with Gd3+ ions leading to reorientation of the spins of the electron and hole centers. Thus, the spin system of radiation-induced defects in gadolinium garnet based scintillator materials was shown to accumulate significant energy which can be released in external magnetic fields.

  18. X-ray emission from the giant magnetosphere of the magnetic O-type star NGC 1624-2

    CERN Document Server

    Petit, V; Wade, G A; Nazé, Y; Owocki, S P; Sundqvist, J O; ud-Doula, A; Fullerton, A; Leutenegger, M; Gagné, M

    2015-01-01

    We observed NGC 1624-2, the O-type star with the largest known magnetic field Bp~20 kG), in X-rays with the ACIS-S camera onboard the Chandra X-ray Observatory. Our two observations were obtained at the minimum and maximum of the periodic Halpha emission cycle, corresponding to the rotational phases where the magnetic field is the closest to equator-on and pole-on, respectively. With these observations, we aim to characterise the star's magnetosphere via the X-ray emission produced by magnetically confined wind shocks. Our main findings are: (i) The observed spectrum of NGC 1624-2 is hard, similar to the magnetic O-type star Theta 1 Ori C, with only a few photons detected below 0.8 keV. The emergent X-ray flux is 30% lower at the Halpha minimum phase. (ii) Our modelling indicated that this seemingly hard spectrum is in fact a consequence of relatively soft intrinsic emission, similar to other magnetic Of?p stars, combined with a large amount of local absorption (~1-3 x 10^22 cm^-2). This combination is necess...

  19. Tests of the asymptotic large frequency separation of acoustic oscillations in solar-type and red-giant stars

    NARCIS (Netherlands)

    S. Hekker; Y. Elsworth; S. Basu; A. Mazumdar; V. Silva Aguirre; W.J. Chaplin

    2013-01-01

    Asteroseismology, i.e. the study of the internal structures of stars via their global oscillations, is a valuable tool to obtain stellar parameters such as mass, radius, surface gravity and mean density. These parameters can be obtained using certain scaling relations which are based on an asymptoti

  20. Abundance Differences Between Exoplanet Binary Host Stars XO-2N and XO-2S -- Dependence on Stellar Parameters

    CERN Document Server

    Teske, Johanna K; Cunha, Katia; Smith, Verne V; Schuler, Simon C; Bergemann, Maria

    2015-01-01

    The chemical composition of exoplanet host stars is an important factor in understanding the formation and characteristics of their orbiting planets. The best example of this to date is the planet-metallicity correlation. Other proposed correlations are thus far less robust, in part due to uncertainty in the chemical history of stars pre- and post-planet formation. Binary host stars of similar type present an opportunity to isolate the effects of planets on host star abundances. Here we present a differential elemental abundance analysis of the XO-2 stellar binary, in which both G9 stars host giant planets, one of which is transiting. Building on our previous work, we report 16 elemental abundances and compare the $\\Delta$(XO-2N-XO-S) values to elemental condensation temperatures. The $\\Delta$(N-S) values and slopes with condensation temperature resulting from four different pairs of stellar parameters are compared to explore the effects of changing the relative temperature and gravity of the stars. We find t...

  1. Debris disks as signposts of terrestrial planet formation. II Dependence of exoplanet architectures on giant planet and disk properties

    CERN Document Server

    Raymond, Sean N; Moro-Martin, Amaya; Booth, Mark; Wyatt, Mark C; Armstrong, John C; Mandell, Avi M; Selsis, Franck; West, Andrew A

    2012-01-01

    We present models for the formation of terrestrial planets, and the collisional evolution of debris disks, in planetary systems that contain multiple unstable gas giants. We previously showed that the dynamics of the giant planets introduces a correlation between the presence of terrestrial planets and debris disks. Here we present new simulations that show that this connection is qualitatively robust to changes in: the mass distribution of the giant planets, the width and mass distribution of the outer planetesimal disk, and the presence of gas in the disk. We discuss how variations in these parameters affect the evolution. Systems with equal-mass giant planets undergo the most violent instabilities, and these destroy both terrestrial planets and the outer planetesimal disks that produce debris disks. In contrast, systems with low-mass giant planets efficiently produce both terrestrial planets and debris disks. A large fraction of systems with low-mass outermost giant planets have stable gaps between these p...

  2. Constraining stellar physics from red-giant stars in binaries - stellar rotation, mixing processes and stellar activity

    CERN Document Server

    Beck, P G; Pavlovski, K; Palacios, A; Tkachenko, A; García, R A; Mathis, S; Corsaro, E; Johnston, C; Mosser, B; Ceillier, T; Nascimento, J -D do; Raskin, G

    2016-01-01

    The unparalleled photometric data obtained by NASA's Kepler Space Telescope has led to an improved understanding of stellar structure and evolution - in particular for solar-like oscillators in this context. Binary stars are fascinating objects. Because they were formed together, binary systems provide a set of two stars with very well constrained parameters. Those can be used to study properties and physical processes, such as the stellar rotation, dynamics and rotational mixing of elements and allows us to learn from the differences we find between the two components. In this work, we discussed a detailed study of the binary system KIC9163796, discovered through Kepler photometry. The ground-based follow-up spectroscopy showed that this system is a double-lined spectroscopic binary, with a mass ratio close to unity. However, the fundamental parameters of the components of this system as well as their lithium abundances differ substantially. Kepler photometry of this system allows to perform a detailed seism...

  3. Galactic planetary nebulae with precise nebular abundances as a tool to understand the evolution of asymptotic giant branch stars

    CERN Document Server

    Garcia-Hernandez, D A; Delgado-Inglada, G; Dell'Agli, F; Di Criscienzo, M; Yagüe, A

    2016-01-01

    We present nucleosynthesis predictions (HeCNOCl) from asymptotic giant branch (AGB) models, with diffusive overshooting from all the convective borders, in the metallicity range Z/4 3.5 Msun) solar/supersolar metallicity AGBs that experience hot bottom burning (HBB), but other formation channels in low-mass AGBs like extra mixing, stellar rotation, binary interaction, or He pre-enrichment cannot be disregarded until more accurate C/O ratios would be obtained. Two objects among the DC PNe show the imprint of advanced CNO processing and deep second dredge-up, suggesting progenitors masses close to the limit to evolve as core collapse supernovae (above 6 Msun). Their actual C/O ratio, if confirmed, indicate contamination from the third dredge-up, rejecting the hypothesis that the chemical composition of such high-metallicity massive AGBs is modified exclusively by HBB.

  4. The Mass of the Planet-hosting Giant Star Beta Geminorum Determined from its p-mode Oscillation Spectrum

    CERN Document Server

    Hatzes, A P; Matthews, J; Kuschnig, R; Walker, G A H; Doellinger, M; Guenther, D B; Moffat, A F J; Rucinski, S M; Sasselov, D

    2012-01-01

    We use precise radial velocity measurements and photometric data to derive the frequency spacing of the p-mode oscillation spectrum of the planet-hosting star Beta Gem. This spacing along with the interferometric radius for this star is used to derive an accurate stellar mass. A long time series of over 60 hours of precise stellar radial velocity measurements of Beta Gem were taken with an iodine absorption cell and the echelle spectrograph mounted on the 2m Alfred Jensch Telescope. Complementary photometric data for this star were also taken with the MOST microsatellite spanning 3.6 d. A Fourier analysis of the radial velocity data reveals the presence of up to 17 significant pulsation modes in the frequency interval 10-250 micro-Hz. Most of these fall on a grid of equally-spaced frequencies having a separation of 7.14 +/- 0.12 micro-Hz. An analysis of 3.6 days of high precision photometry taken with the MOST space telescope shows the presence of up to 16 modes, six of which are consistent with modes found i...

  5. Carbon in Red Giants in Globular Clusters and Dwarf Spheroidal Galaxies

    CERN Document Server

    Kirby, Evan N; Zhang, Andrew J; Deng, Michelle; Cohen, Judith G; Guhathakurta, Puragra; Shetrone, Matthew D; Lee, Young Sun; Rizzi, Luca

    2015-01-01

    We present carbon abundances of red giants in Milky Way globular clusters and dwarf spheroidal galaxies (dSphs). Our sample includes measurements of carbon abundances for 154 giants in the clusters NGC 2419, M68, and M15 and 398 giants in the dSphs Sculptor, Fornax, Ursa Minor, and Draco. This sample doubles the number of dSph stars with measurements of [C/Fe]. The [C/Fe] ratio in the clusters decreases with increasing luminosity above log(L/L_sun) ~= 1.6, which can be explained by deep mixing in evolved giants. The same decrease is observed in dSphs, but the initial [C/Fe] of the dSph giants is not uniform. Stars in dSphs at lower metallicities have larger [C/Fe] ratios. We hypothesize that [C/Fe] (corrected to the initial carbon abundance) declines with increasing [Fe/H] due to the metallicity dependence of the carbon yield of asymptotic giant branch stars and due to the increasing importance of Type Ia supernovae at higher metallicities. We also identified 11 very carbon-rich giants (8 previously known) in...

  6. Nonadiabatic analysis of strange-modes in hot massive stars with time-dependent convection

    Directory of Open Access Journals (Sweden)

    Sonoi Takafumi

    2015-01-01

    Full Text Available We carry out nonadiabatic analysis of strange-modes in hot massive stars with time-dependent convection (TDC. We find that the instability of the modes excited at the Fe bump is weaker with TDC than with frozen-in convection (FC. But the instability still remains with TDC, and could be a possible candidate for the trigger of luminous blue variable (LBV phenomena.

  7. Spectroscopic determination of masses (and implied ages) for red giants

    CERN Document Server

    Ness, M; Rix, H-W; Martig, M; Pinsonneault, Marc H; Ho, A Y Q

    2015-01-01

    The mass of a star is arguably its most fundamental parameter. For red giant stars, tracers luminous enough to be observed across the Galaxy, mass implies a stellar evolution age. It has proven to be extremely difficult to infer ages and masses directly from red giant spectra using existing methods. From the KEPLER and APOGEE surveys, samples of several thousand stars exist with high-quality spectra and asteroseismic masses. Here we show that from these data we can build a data-driven spectral model using The Cannon, which can determine stellar masses to $\\sim$ 0.07 dex from APOGEE DR12 spectra of red giants; these imply age estimates accurate to $\\sim$ 0.2 dex (40 percent). We show that The Cannon constrains these ages foremost from spectral regions with CN absorption lines, elements whose surface abundances reflect mass-dependent dredge-up. We deliver an unprecedented catalog of 80,000 giants (including 20,000 red-clump stars) with mass and age estimates, spanning the entire disk (from the Galactic center t...

  8. Migration and Growth of Protoplanetary Embryos III: Mass and Metallicity Dependence for FGKM main-sequence stars

    CERN Document Server

    Liu, Beibei; Lin, Doug

    2016-01-01

    Radial velocity and transit surveys have found that the fraction of FGKM stars with close-in super-Earth(s) ($\\eta_\\oplus$) is around $30 \\%- 50\\%$, independent of the stellar mass $M_\\ast$ and metallicity $Z_\\ast$. In contrast, the fraction of solar-type stars harboring one or more gas giants ($\\eta_J $) with masses $M_{\\rm p} > 100 \\ M_\\oplus $ is nearly $ 10\\%-15\\%$, and it appears to increase with both $M_\\ast$ and $Z_\\ast$. Regardless of the properties of their host stars, the total mass of some multiple super-Earth systems exceeds the core mass of Jupiter and Saturn. We suggest that both super-Earths and supercritical cores of gas giants were assembled from a population of embryos that underwent convergent type I migration from their birthplaces to a transition location between viscously heated and irradiation heated disk regions. We attribute the cause for the $\\eta_\\oplus$-$\\eta_{\\rm J}$ dichotomy to conditions required for embryos to merge and to acquire supercritical core mass ($M_c \\sim 10 \\ M_\\opl...

  9. Lifestyles of the Stars.

    Science.gov (United States)

    National Aeronautics and Space Administration, Cocoa Beach, FL. John F. Kennedy Space Center.

    Some general information on stars is provided in this National Aeronautics and Space Administration pamphlet. Topic areas briefly discussed are: (1) the birth of a star; (2) main sequence stars; (3) red giants; (4) white dwarfs; (5) neutron stars; (6) supernovae; (7) pulsars; and (8) black holes. (JN)

  10. Very Low-Mass Stellar and Substellar Companions to Solar-like Stars From MARVELS VI: A Giant Planet and a Brown Dwarf Candidate in a Close Binary System HD 87646

    CERN Document Server

    Ma, Bo; Wolszczan, Alex; Muterspaugh, Matthew W; Lee, Brian; Henry, Gregory W; Schneider, Donald P; Martin, Eduardo L; Niedzielski, Andrzej; Xie, Jiwei; Fleming, Scott W; Thomas, Neil; Williamson, Michael; Zhu, Zhaohuan; Agol, Eric; Bizyaev, Dmitry; da Costa, Luiz Nicolaci; Jiang, Peng; Fiorenzano, A F Martinez; Hernandez, Jonay I Gonzalez; Guo, Pengcheng; Grieves, Nolan; Li, Rui; Liu, Jane; Mahadevan, Suvrath; Mazeh, Tsevi; Nguyen, Duy Cuong; Paegert, Martin; Sithajan, Sirinrat; Stassun, Keivan; Thirupathi, Sivarani; van Eyken, Julian C; Wan, Xiaoke; Wang, Ji; Wisniewski, John P; Zhao, Bo; Zucker, Shay

    2016-01-01

    We report the detections of a giant planet (MARVELS-7b) and a brown dwarf candidate (MARVELS-7c) around the primary star in the close binary system, HD 87646. It is the first close binary system with more than one substellar circum-primary companion discovered to the best of our knowledge. The detection of this giant planet was accomplished using the first multi-object Doppler instrument (KeckET) at the Sloan Digital Sky Survey (SDSS) telescope. Subsequent radial velocity observations using ET at Kitt Peak National Observatory, HRS at HET, the "Classic" spectrograph at the Automatic Spectroscopic Telescope at Fairborn Observatory, and MARVELS from SDSS-III confirmed this giant planet discovery and revealed the existence of a long-period brown dwarf in this binary. HD 87646 is a close binary with a separation of $\\sim22$ AU between the two stars, estimated using the Hipparcos catalogue and our newly acquired AO image from PALAO on the 200-inch Hale Telescope at Palomar. The primary star in the binary, HD 87646...

  11. The Dependence of Star Formation Rates on Stellar Mass and Environment at z~0.8

    CERN Document Server

    Patel, Shannon G; Kelson, Daniel D; Illingworth, Garth D; Franx, Marijn

    2009-01-01

    We examine the star formation rates (SFRs) of galaxies in a redshift slice encompassing the z=0.834 cluster RX J0152.7-1357. We used a low-dispersion prism in the Inamori Magellan Areal Camera and Spectrograph (IMACS) to identify galaxies with z2x10^{10} M_sun) of 330 galaxies that were imaged by Spitzer MIPS at 24 micron to derive SFRs and study the dependence of specific SFR (SSFR) on stellar mass and environment. We find that the SFR and SSFR show a strong decrease with increasing local density, similar to the relation at z~0. Our result contrasts with other work at z~1 that find the SFR-density trend to reverse for luminosity-limited samples. These other results appear to be driven by star-formation in lower mass systems (M~10^{10} M_sun). Our results imply that the processes that shut down star-formation are present in groups and other dense regions in the field. Our data also suggest that the lower SFRs of galaxies in higher density environments may reflect a change in the ratio of star-forming to non-s...

  12. Improved angular momentum evolution model for solar-like stars II. Exploring the mass dependence

    CERN Document Server

    Gallet, Florian

    2015-01-01

    We developed angular momentum evolution models for 0.5 and 0.8 $M_{\\odot}$ stars. The parametric models include a new wind braking law based on recent numerical simulations of magnetised stellar winds, specific dynamo and mass-loss rate prescriptions, as well as core/envelope decoupling. We compare model predictions to the distributions of rotational periods measured for low mass stars belonging to star forming regions and young open clusters. Furthermore, we explore the mass dependence of model parameters by comparing these new models to the solar-mass models we developed earlier. Rotational evolution models are computed for slow, median, and fast rotators at each stellar mass. The models reproduce reasonably well the rotational behaviour of low-mass stars between 1~Myr and 8-10~Gyr, including pre-main sequence to zero-age main sequence spin up, prompt zero-age main sequence spin down, and early-main sequence convergence of the surface rotation rates. Fast rotators are found to have systematically shorter di...

  13. Stability Analysis of Strange-Modes in Hot Massive Stars with Time-Dependent Convection

    CERN Document Server

    Sonoi, Takafumi

    2014-01-01

    We carry out a nonadiabatic analysis of strange-modes in hot massive stars with time-dependent convection (TDC). In envelopes of such stars, convective luminosity is not so dominant as that in envelopes of stars in the redder side of the classical instability strip. Around the Fe opacity bump, however, convection non-negligibly contributes to energy transfer. Indeed, instability of modes excited at the Fe bump is likely to be suppressed with TDC compared with the case of adopting the frozen-in convection approximation. But we make sure that unstable strange-modes certainly appear in hot massive stars even by taking into account TDC. We also examine properties of the strange-mode instability, which is related to destabilization of strange-modes without adiabatic counterparts. In this type of instability, the phase lag between density and pressure varies from 0 to $180^{\\circ}$ in an excitation zone unlike the case of the $\\kappa$-mechanism. In addition, we confirm by comparing models with $Z=0$ and $Z=0.02$ th...

  14. DRAMATIC INFRARED VARIABILITY OF WISE J1810-3305: CATCHING EARLY-TIME DUST EJECTION DURING THE THERMAL PULSE OF AN ASYMPTOTIC GIANT BRANCH STAR?

    Energy Technology Data Exchange (ETDEWEB)

    Gandhi, Poshak; Yamamura, Issei; Takita, Satoshi [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan)

    2012-05-20

    We present the discovery of a source with broadband infrared photometric characteristics similar to Sakurai's object. WISE J180956.27-330500.2 (hereafter J1810-3305) shows very red WISE colors, but a very blue 2MASS [K] versus WISE [W1 (3.4 {mu}m)] color. It was not visible during the IRAS era, but now has a 12 {mu}m flux well above the IRAS point-source catalog detection limit. There are also indications of variability in historical optical photographic plates as well as in multi-epoch AKARI mid-infrared measurements. The broadband infrared spectral energy distribution (SED) shape, post-IRAS brightening, and multiwavelength variability are all characteristics also shared by Sakurai's object-a post-asymptotic giant branch (post-AGB) star which underwent a late thermal pulse and recently ejected massive envelopes of dust that are currently expanding and cooling. Optical progenitor colors suggest that J1810-3305 may have been of late spectral class. Its dramatic infrared brightening and the detection of a late-type optical counterpart are consistent with a scenario in which we have caught an extremely massive dust ejection event (in 1998 or shortly before) during the thermal pulse of an AGB star, thus providing a unique opportunity to observe stellar evolution in this phase. J1810-3305 is the only source in the entire WISE preliminary data release with similar infrared SED and variability, emphasizing the rarity of such sources. Confirmation of its nature is of great importance.

  15. Red giant seismology: Observations

    Directory of Open Access Journals (Sweden)

    Mosser B.

    2013-03-01

    Full Text Available The CoRoT and Kepler missions provide us with thousands of red-giant light curves that allow a very precise asteroseismic study of these objects. Before CoRoT and Kepler, the red-giant oscillation patterns remained obscure. Now, these spectra are much more clear and unveil many crucial interior structure properties. For thousands of red giants, we can derive from seismic data precise estimates of the stellar mass and radius, the evolutionary status of the giants (with a clear difference between clump and RGB stars, the internal differential rotation, the mass loss, the distance of the stars... Analyzing this amount of information is made easy by the identification of the largely homologous red-giant oscillation patterns. For the first time, both pressure and mixed mode oscillation patterns can be precisely depicted. The mixed-mode analysis allows us, for instance, to probe directly the stellar core. Fine details completing the red-giant oscillation pattern then provide further information on the interior structure, including differential rotation.

  16. Thickness dependence and the role of spin transfer torque in nonlinear giant magnetoresistance of permalloy dual spin valves

    Science.gov (United States)

    Banerjee, N.; Aziz, A.; Ali, M.; Robinson, J. W. A.; Hickey, B. J.; Blamire, M. G.

    2010-12-01

    The recent discovery of nonlinear current-dependent magnetoresistance in dual spin valve devices [A. Aziz, O. P. Wessely, M. Ali, D. M. Edwards, C. H. Marrows, B. J. Hickey, and M. G. Blamire, Phys. Rev. Lett. 103, 237203 (2009)10.1103/PhysRevLett.103.237203] opens up the possibility for distinct physics which extends the standard model of giant magnetoresistance. When the outer ferromagnetic layers of a dual spin valve are antiparallel, the resulting accumulation of spin in the middle ferromagnetic layer strongly modifies its bulk and interfacial spin asymmetry and resistance. Here, we report experimental evidence of the role of bulk spin accumulation in this nonlinear effect and show that interfacial spin accumulation alone cannot account for the observed dependence of the effect on the thickness of the middle ferromagnetic layer. It is also shown that spin torque acting on the middle ferromagnetic layer combined with the nonlinear effect might be useful in understanding the dynamical features associated with the nonlinear behavior.

  17. Spot evolution on the red giant star XX Triangulum. A starspot-decay analysis based on time-series Doppler imaging

    CERN Document Server

    Künstler, A; Strassmeier, K G

    2015-01-01

    Solar spots appear to decay linearly proportional to their size. The decay rate of solar spots is directly related to magnetic diffusivity, which itself is a key quantity for the length of a magnetic-activity cycle. Is a linear spot decay also seen on other stars, and is this in agreement with the large range of solar and stellar activity cycle lengths? We investigate the evolution of starspots on the rapidly-rotating ($P_{\\rm rot}$ $\\approx$ 24 d) K0 giant XX Tri, using consecutive time-series Doppler images. Our aim is to obtain a well-sampled movie of the stellar surface over many years, and thereby detect and quantify a starspot decay law for further comparison with the Sun. We obtained continuous high-resolution and phase-resolved spectroscopy with the 1.2-m robotic STELLA telescope on Tenerife over six years. For each observing season, we obtained between 5 to 7 independent Doppler images, one per stellar rotation, making up a total of 36 maps. To quantify starspot area decay and growth, we match the ob...

  18. Formation of SiC Grains in Pulsation-Enhanced Dust-Driven Wind Around Carbon Rich Asymptotic Giant Branch Stars

    CERN Document Server

    Yasuda, Yuki

    2011-01-01

    We investigate the formation of silicon carbide (SiC) grains in the framework of dust-driven wind around pulsating carbon-rich Asymptotic Giant Branch (C-rich AGB) stars in order to reveal not only the amount but also the size distribution. Two cases are considered for the nucleation process; one is the LTE case where the vibration temperature of SiC clusters $T_{\\rm v}$ is equal to the gas temperature as usual, and another is the non-LTE case in which $T_{\\rm v}$ is assumed to be the same as the temperature of small SiC grains. The results of hydrodynamical calculations for a model with stellar parameters of mass $M_{\\ast}$=1.0 $M_{\\odot}$, luminosity $L_{\\ast}$=10$^{4}$ $L_{\\odot}$, effective temperature $T_{\\rm eff}$=2600 K, C/O ratio=1.4, and pulsation period $P$=650 days show the followings: In the LTE case, SiC grains condense in accelerated outflowing gas after the formation of carbon grains and the resulting averaged mass ratio of SiC to carbon grains of $\\sim$ 10$^{-8}$ is too small to reproduce the ...

  19. A superconducting tunnel junction receiver for submillimeter astronomy, and analysis of observations of post-AGB star molecular envelopes. [AGB (asymptotic giant branch)

    Energy Technology Data Exchange (ETDEWEB)

    Jaminet, P.A.

    1992-01-01

    A heterodyne receiver designed for astronomical use between 450 and 520 GHz has been constructed. Very low capacitance (C [approximately] 5-10 fF) Superconductor-Insulator-Superconductor (SIS) junctions have been fabricated as the detectors; these junctions lie on the edges of niobium thin films and form Nb-Al-Al[sub 2]O[sub 3]-Al-Nb sandwiches. The double sideband (DSB) receiver noise temperature is between 400 K and 800 K throughout the 70 GHz band. In addition, detailed modelling and analysis of astronomical observations of two post-AGB (Asymptotic Giant Branch) stars was performed. The observations were made with an SIS receiver designed for 345 GHz. CO observations and modelling of the young planetary nebula NGC 7027 provided the best determination yet of its AGB mass loss rate, the first direct evidence for bipolarity in its AGB mass loss, evidence for close hydrodynamic coupling between the planetary nebula and the relic AGB wind, and evidence for evolution in the metallicity of the stellar wind. Observations of the proto-planetary nebula CRL 2688 found evidence for spatially extended fast wind emission with a non-bipolar morphology, and evidence for evolution is elemental abundances in the stellar wind.

  20. Library of medium-resolution fiber optic echelle spectra of F, G, K and M field dwarfs to giant stars

    CERN Document Server

    Montes, D; Welty, A D; Montes, David; Ramsey, Lawrence W.; Welty, Alan D.

    1999-01-01

    We present a library of Penn State Fiber Optic Echelle (FOE) observations of a sample of field stars with spectral types F to M and luminosity classes V to I. The spectral coverage is from 3800 AA to 10000 AA with nominal a resolving power 12000. These spectra include many of the spectral lines most widely used as optical and near-infrared indicators of chromospheric activity such as the Balmer lines (H_alpha, H_beta), Ca II H & K, Mg I b triplet, Na I D_{1} and D_{2}, He I D_{3}, and Ca II IRT lines. There are also a large number of photospheric lines, which can also be affected by chromospheric activity, and temperature sensitive photospheric features such as TiO bands. The spectra have been compiled with the goal of providing a set of standards observed at medium resolution. We have extensively used such data for the study of active chromosphere stars by applying a spectral subtraction technique. However, the data set presented here can also be utilized in a wide variety of ways ranging from radial vel...

  1. Faint-Source-Star Planetary Microlensing: The Discovery of the Cold Gas-Giant Planet OGLE-2014-BLG-0676Lb

    Science.gov (United States)

    Rattenbury, N. J.; Bennett, D. P.; Sumi, T.; Koshimoto, N.; Bond, I. A.; Udalski, A.; Shvartzvald, Y.; Maoz, D.; Jorgensen, U. G.; Barry, R.; hide

    2016-01-01

    We report the discovery of a planet OGLE-2014-BLG-0676Lb via gravitational microlensing. Observations for the lensing event were made by the following groups: Microlensing Observations in Astrophysics; Optical Gravitational Lensing Experiment; Wise Observatory; RoboNETLas Cumbres Observatory Global Telescope; Microlensing Network for the Detection of Small Terrestrial Exoplanets; and -FUN. All analyses of the light-curve data favoura lens system comprising a planetary mass orbiting a host star. The most-favoured binary lens model has a mass ratio between the two lens masses of (4.78 +/- 0.13) 10(exp -3). Subject to some important assumptions, a Bayesian probability density analysis suggests the lens system comprises a 3.09(+1.02/-1.12) MJ planet orbiting a 0.62(+0.20/-0.22) solar mass host star at a deprojected orbital separation of 4.40(+2.16/-1.46) au. The distance to the lens system is 2.22(+0.96/-0.83) kpc. Planet OGLE-2014-BLG-0676Lb provides additional data to the growing number of cool planets discover redusing gravitational microlensing against which planetary formation theories may be tested. Most of the light in the baseline of this event is expected to come from the lens and thus high-resolution imaging observations could confirm our planetary model interpretation.

  2. Can there be additional rocky planets in the Habitable Zone of tight binary stars with a known gas giant?

    CERN Document Server

    Funk, Barbara; Eggl, Siegfried

    2015-01-01

    Locating planets in HabitableZones (HZs) around other stars is a growing field in contemporary astronomy. Since a large percentage of all G-M stars in the solar neighbourhood are expected to be part of binary or multiple stellar systems, investigations of whether habitable planets are likely to be discovered in such environments are of prime interest to the scientific community. As current exoplanet statistics predicts that the chances are higher to find new worlds in systems that are already known to have planets, we examine four known extrasolar planetary systems in tight binaries in order to determine their capacity to host additional habitable terrestrial planets. Those systems are Gliese 86, gamma Cephei, HD 41004 and HD 196885. In the case of gamma Cephei, our results suggest that only the M dwarf companion could host additional potentially habitable worlds. Neither could we identify stable, potentially habitable regions around HD 196885 A. HD 196885 B can be considered a slightly more promising target ...

  3. Oxygen in the early Galaxy: OH lines as tracers of oxygen abundance in extremely metal-poor giant stars

    CERN Document Server

    Kucinskas, A; Bonifacio, P; Caffau, E; Ludwig, H -G; Steffen, M; Spite, M

    2014-01-01

    Oxygen is a powerful tracer element of Galactic chemical evolution. Unfortunately, only a few oxygen lines are available in the ultraviolet-infrared stellar spectra for the reliable determination of its abundance. Moreover, oxygen abundances obtained using different spectral lines often disagree significantly. In this contribution we therefore investigate whether the inadequate treatment of convection in 1D hydrostatic model atmospheres used in the abundance determinations may be responsible for this disagreement. For this purpose, we used VLT CRIRES spectra of three EMP giants, as well as 3D hydrodynamical CO$^5$BOLD and 1D hydrostatic LHD model atmospheres, to investigate the role of convection in the formation of infrared (IR) OH lines. Our results show that the presence of convection leads to significantly stronger IR OH lines. As a result, the difference in the oxygen abundance determined from IR OH lines with 3D hydrodynamical and classical 1D hydrostatic model atmospheres may reach -0.2 ... -0.3 dex. I...

  4. Galactic planetary nebulae with precise nebular abundances as a tool to understand the evolution of asymptotic giant branch stars

    Science.gov (United States)

    García-Hernández, D. A.; Ventura, P.; Delgado-Inglada, G.; Dell'Agli, F.; Di Criscienzo, M.; Yagüe, A.

    2016-09-01

    We present nucleosynthesis predictions (HeCNOCl) from asymptotic giant branch (AGB) models, with diffusive overshooting from all the convective borders, in the metallicity range Z⊙/4 chemical pattern similar to the DC PNe. In agreement with recent literature, the DC PNe mostly descend from high-mass (M ≥ 3.5 M⊙) solar/supersolar metallicity AGBs that experience hot bottom burning (HBB), but other formation channels in low-mass AGBs like extra mixing, stellar rotation, binary interaction, or He pre-enrichment cannot be disregarded until more accurate C/O ratios would be obtained. Two objects among the DC PNe show the imprint of advanced CNO processing and deep second dredge-up, suggesting progenitors masses close to the limit to evolve as core collapse supernovae (above 6M⊙). Their actual C/O ratio, if confirmed, indicate contamination from the third dredge-up, rejecting the hypothesis that the chemical composition of such high-metallicity massive AGBs is modified exclusively by HBB.

  5. Star Formation in Disk Galaxies. I. Formation and Evolution of Giant Molecular Clouds via Gravitational Instability and Cloud Collisions

    CERN Document Server

    Tasker, Elizabeth J

    2008-01-01

    We investigate the formation and evolution of giant molecular clouds (GMCs) in a Milky-Way-like disk galaxy with a flat rotation curve. We perform a series of 3D adaptive mesh refinement (AMR) numerical simulations that follow both the global evolution on scales of ~20kpc and resolve down to scales ~=100cm^-3 and track the evolution of individual clouds as they orbit through the galaxy from their birth to their eventual destruction via merger or via destructive collision with another cloud. After ~140Myr a large fraction of the gas in the disk has fragmented in clouds, with typical masses ~10^6Msun, similar to Galactic GMCs. The disk settles into a quasi steady state in which gravitational scattering of clouds keeps the disk near the threshold of global gravitational instability. The cloud collision time is found to be a small fraction, ~1/5, of the orbital time, and this is an efficient mechanism to inject turbulence into the clouds. This keeps the clouds only moderately gravitationally bound, with virial pa...

  6. Δ (1232 ) effects in density-dependent relativistic Hartree-Fock theory and neutron stars

    Science.gov (United States)

    Zhu, Zhen-Yu; Li, Ang; Hu, Jin-Niu; Sagawa, Hiroyuki

    2016-10-01

    The density-dependent relativistic Hartree-Fock (DDRHF) theory is extended to include Δ isobars for the study of dense nuclear matter and neutron stars. To this end, we solve the Rarita-Schwinger equation for spin-3/2 particle. Both the direct and exchange terms of the Δ isobars' self-energies are evaluated in detail. In comparison with the relativistic mean field theory (Hartree approximation), a weaker parameter dependence is found for DDRHF. An early appearance of Δ isobars is recognized at ρB˜0.28 fm-3, comparable with that of hyperons. Also, we find that the Δ isobars' softening of the equation of state is mainly due to the reduced Fock contributions from the coupling of the isoscalar mesons, while the pion contributions are negligibly small. We finally conclude that with typical parameter sets, neutron stars with Δ isobars in their interiors could be as heavy as the two massive pulsars whose masses are precisely measured, with slightly smaller radii than normal neutron stars.

  7. The statistical properties of stars and their dependence on metallicity: the effects of opacity

    CERN Document Server

    Bate, Matthew R

    2014-01-01

    We report the statistical properties of stars and brown dwarfs obtained from four radiation hydrodynamical simulations of star cluster formation that resolve masses down to the opacity limit for fragmentation. The calculations are identical except for their dust and gas opacities. Assuming dust opacity is proportional to metallicity, the calculations span a range of metallicities from 1/100 to 3 times solar, although we emphasise that changing the metallicity has other thermodynamic effects that the calculations do not capture (e.g. on the thermal coupling between gas and dust). All four calculations produce stellar populations whose statistical properties are difficult to distinguish from observed stellar systems, and we find no significant dependence of stellar properties on opacity. The mass functions and properties of multiple stellar systems are consistent with each other. However, we find protostellar mergers are more common with lower opacities. Combining the results from the three calculations with th...

  8. Consistent neutron star models with magnetic field dependent equations of state

    CERN Document Server

    Chatterjee, Debarati; Novak, Jerome; Oertel, Micaela

    2014-01-01

    We present a self-consistent model for the study of the structure of a neutron star in strong magnetic fields. Starting from a microscopic Lagrangian, this model includes the effect of the magnetic field on the equation of state, the interaction of the electromagnetic field with matter (magnetisation), and anisotropies in the energy-momentum tensor, as well as general relativistic aspects. We build numerical axisymmetric stationary models and show the applicability of the approach with one example quark matter equation of state (EoS) often employed in the recent literature for studies of strongly magnetised neutron stars. For this EoS, the effect of inclusion of magnetic field dependence or the magnetisation do not increase the maximum mass significantly in contrast to what has been claimed by previous studies.

  9. Tests of the asymptotic large frequency separation of acoustic oscillations in solar-type and red giant stars

    CERN Document Server

    Hekker, S; Basu, S; Mazumdar, A; Aguirre, V Silva; Chaplin, W J

    2013-01-01

    Asteroseismology, i.e. the study of the internal structures of stars via their global oscillations, is a valuable tool to obtain stellar parameters such as mass, radius, surface gravity and mean density. These parameters can be obtained using certain scaling relations which are based on an asymptotic approximation. Usually the observed oscillation parameters are assumed to follow these scaling relations. Recently, it has been questioned whether this is a valid approach, i.e., whether the order of the observed oscillation modes are high enough to be approximated with an asymptotic theory. In this work we use stellar models to investigate whether the differences between observable oscillation parameters and their asymptotic estimates are indeed significant. We compute the asymptotic values directly from the stellar models and derive the observable values from adiabatic pulsation calculations of the same models. We find that the extent to which the atmosphere is included in the models is a key parameter. Conside...

  10. Field-angle and DC-bias dependence of spin-torque diode in giant magnetoresistive microstripe

    Science.gov (United States)

    Li, X.; Zhou, Y.; Zheng, C.; Chan, P. H.; Chan, M.; Pong, Philip W. T.

    2016-11-01

    The spin torque diode effect in all metal spintronic devices has been proposed as a microwave detector with a high power limit and resistivity to breakdown. The previous works have revealed the field-angle dependence of the rectified DC voltage (VDC) in the ferromagnetic stripe. The giant magnetoresistive (GMR) microstripe exhibits higher sensitivity compared with the ferromagnetic stripe. However, the influence of the magnetic field direction and bias current in the spin rectification of GMR microstripe is not yet reported. In this work, the angular dependence and bias dependence of resonant frequency (fR) and VDC are investigated. A macrospin model concerning the contribution of magnetic field, shape anisotropy, and unidirectional anisotropy is engaged to interpret the experimental data. fR exhibits a |sin δH| dependence on the in-plane field angle (δH). VDC presents either |sin δH| or |sin2 δH cos δH | relation, depending on the magnitude of Hext. Optimized VDC of 24 μV is achieved under 4 mT magnetic field applied at δH = 170°. Under out-of-plane magnetic field, fR shows a cos 2θH reliance on the polar angle (θH), whereas VDC is sin θH dependent. The Oersted field of the DC bias current (IDC) modifies the effective field, resulting in shifted fR. Enhanced VDC with increasing IDC is attributed to the elevated contribution of spin-transfer torque. Maximum VDC of 35.2 μV is achieved, corresponding to 47% increase compared with the optimized value under zero bias. Higher IDC also results in enlarged damping parameter in the free layer, resulting in increased linewidth in the spin torque diode spectra. This work experimentally and analytically reveals the angular dependence of fR and VDC in the GMR microstripe. The results further demonstrate a highly tunable fR and optimized VDC by bias current without the external magnetic field. GMR microstripe holds promise for application as a high-power, frequency-tunable microwave detector that works under small

  11. How does the far-IR properties of star-forming galaxies depend on environment?

    Science.gov (United States)

    Guo, Qi

    2015-08-01

    Traditionally, most observational studies estimate SFRs using rest-frame UV luminosities or emission lines, which are subject to uncertain corrections for dust extinction. In star-forming regions, UV photons heat the dust, and their energy is re-emitted in the mid- and far-IR range. About half of the starlight is absorbed and re-emitted over the history of the Universe. Observations at IR wavelengths are thus an essential complement to UV and optical tracers of star formation. We use far-IR selected galaxies from the Herschel ATLAS (H-ATLAS) survey and optically selected galaxies from the Galaxy and Mass Assembly (GAMA) redshift survey to study the environmental effects on far-IR properties. It includes the following aspects. What is the typical halo mass of the low-redshift H-ATLAS sources? How does far-IR luminosity depend on host halo mass? How do the far-IR conditional luminosity functions depend on group masses and redshifts? How is the total far-IR light-to-mass ratio in groups of different masses at different redshifts? How much of the far-IR luminosity is contributed by galaxies in groups? Are there any environmental effects on the far-IR-to-optical colour? How does the far-IR properties depend on large-scale environments? Can we pose constrains on current galaxy formation models?

  12. RAVE stars in K2 - I. Improving RAVE red giants spectroscopy using asteroseismology from K2 Campaign 1

    CERN Document Server

    Valentini, M; Davies, G R; Elsworth, Y P; Mosser, B; Lund, M N; Miglio, A; Chaplin, W J; Rodrigues, T; Boeche, C; Steinmetz, M; Matijevic, G; Kordopatis, G; Bland-Hawthorn, J; Munari, U; Bienayme, O; Gibson, B K; Gilmore, G; Grebel, E K; Helmi, A; Kunder, A; McMillan, P; Navarro, J; Parker, Q A; Reid, W; Seabroke, G; Siviero, A; Watson, F; Wise, R M; Zwitter, T

    2016-01-01

    We present a set of 87 RAVE stars with detected solar like oscillations, observed during Campaign 1 of the K2 mission (RAVE K2-C1 sample). This dataset provides a useful benchmark for testing the gravities provided in RAVE Data Release 4 (DR4), and is key for the calibration of the RAVE Data Release 5 (DR5). In the present work, we use two different pipelines, GAUFRE (Valentini et al. 2013) and Sp_Ace (Boeche et al. 2015), to determine atmospheric parameters and abundances by fixing log(g) to the seismic one. Our strategy ensures highly consistent values among all stellar parameters, leading to more accurate chemical abundances. A comparison of the chemical abundances obtained here with and without the use of seismic log(g) information has shown that an underestimated (overestimated) gravity leads to an underestimated (overestimated) elemental abundance (e.g. [Mg/H] is underestimated by ~0.25 dex when the gravity is underestimated by 0.5 dex). We then perform a comparison between the seismic gravities and the...

  13. Evolution of asymptotic giant branch stars I. Updated synthetic TP-AGB models and their basic calibration

    CERN Document Server

    Marigo, P; Marigo, Paola; Girardi, Leo

    2007-01-01

    We present new synthetic models of the TP-AGB evolution. They are computed for 7 values of initial metal content (Z from 0.0001 to 0.03) and for initial masses between 0.5 and 5.0 Msun, thus extending the low- and intermediate-mass tracks of Girardi et al. (2000) until the beginning of the post-AGB phase. The calculations are performed by means of a synthetic code that incorporates many recent improvements, among which we mention: (1) the use of detailed and revised analytical relations to describe the evolution of quiescent luminosity, inter-pulse period, third dredge-up, hot bottom burning, pulse cycle luminosity variations, etc.; (2) the use of variable molecular opacities -- i.e. opacities consistent with the changing photospheric chemical composition -- in the integration of a complete envelope model, instead of the standard choice of scaled-solar opacities; (3) the use of formalisms for the mass-loss rates derived from pulsating dust-driven wind models of C- and O-rich AGB stars; and (4) the switching o...

  14. Two New Long-Period Giant Planets from the McDonald Observatory Planet Search and Two Stars with Long-Period Radial Velocity Signals Related to Stellar Activity Cycles

    CERN Document Server

    Endl, Michael; Cochran, William D; MacQueen, Phillip J; Robertson, Paul; Meschiari, Stefano; Ramirez, Ivan; Shetrone, Matthew; Gullikson, Kevin; Johnson, Marshall C; Wittenmyer, Robert; Horner, Jonathan; Ciardi, David R; Horch, Elliott; Simon, Attila E; Howell, Steve B; Everett, Mark; Caldwell, Caroline; Castanheira, Barbara G

    2015-01-01

    We report the detection of two new long-period giant planets orbiting the stars HD 95872 and HD 162004 (psi1 Draconis B) by the McDonald Observatory planet search. The planet HD 95872b has a minimum mass of 4.6 M_Jup and an orbital semi-major axis of 5.2 AU. The giant planet psi1 Dra Bb has a minimum mass of 1.5 M_Jup and an orbital semi-major axis of 4.4 AU. Both of these planets qualify as Jupiter analogs. These results are based on over one and a half decades of precise radial velocity measurements collected by our program using the McDonald Observatory Tull Coude spectrograph at the 2.7 m Harlan J. Smith telescope. In the case of psi1 Draconis B we also detect a long-term non-linear trend in our data that indicates the presence of an additional giant planet, similar to the Jupiter-Saturn pair. The primary of the binary star system, psi1 Dra A, exhibits a very large amplitude radial velocity variation due to another stellar companion. We detect this additional member using speckle imaging. We also report t...

  15. Rapidly rotating red giants

    CERN Document Server

    Gehan, Charlotte; Michel, Eric

    2016-01-01

    Stellar oscillations give seismic information on the internal properties of stars. Red giants are targets of interest since they present mixed modes, which behave as pressure modes in the convective envelope and as gravity modes in the radiative core. Mixed modes thus directly probe red giant cores, and allow in particular the study of their mean core rotation. The high-quality data obtained by CoRoT and Kepler satellites represent an unprecedented perspective to obtain thousands of measurements of red giant core rotation, in order to improve our understanding of stellar physics in deep stellar interiors. We developed an automated method to obtain such core rotation measurements and validated it for stars on the red giant branch. In this work, we particularly focus on the specific application of this method to red giants having a rapid core rotation. They show complex spectra where it is tricky to disentangle rotational splittings from mixed-mode period spacings. We demonstrate that the method based on the id...

  16. $\\Delta$ (1232) effects in density-dependent relativistic Hartree-Fock theory and neutron stars

    CERN Document Server

    Zhu, Zhen-Yu; Hu, Jin-Niu; Sagawa, Hiroyuki

    2016-01-01

    The density-dependent relativistic Hartree-Fock (DDRHF) theory is extended to include $\\Delta$-isobars for the study of dense nuclear matter and neutron stars. To this end, we solve the Rarita-Schwinger equation for spin-3/2 particle. Both the direct and exchange terms of the $\\Delta$-isobars' self-energies are evaluated in details. In comparison with the relativistic mean field theory (Hartree approximation), a weaker parameter dependence is found for DDRHF. An early appearance of $\\Delta$-isobars is recognized at $\\rho_B\\sim0.27$fm$^{-3}$, comparable with that of hyperons. Also, we find that the $\\Delta$-isobars' softening of the equation of state is found to be mainly due to the reduced Fock contributions from the coupling of the isoscalar mesons, while the pion contributions are found negligibly small. We finally conclude that with typical parameter sets, neutron stars with $\\Delta$-isobars in their interiors could be as heavy as the two massive pulsars whose masses are precisely measured, with slightly s...

  17. Star Formation in Irregular Galaxies.

    Science.gov (United States)

    Hunter, Deidre; Wolff, Sidney

    1985-01-01

    Examines mechanisms of how stars are formed in irregular galaxies. Formation in giant irregular galaxies, formation in dwarf irregular galaxies, and comparisons with larger star-forming regions found in spiral galaxies are considered separately. (JN)

  18. The Star-Formation Main Sequence: The Dependence of Specific Star Formation Rate and Its Dispersion on Galaxy Stellar Mass

    CERN Document Server

    Guo, Kexin; Wang, Tao; Fu, Hai

    2015-01-01

    The dispersion of the star-formation main sequence (SFMS) reflects the diversity of star formation histories and variation in star formation rates (SFRs) in star-forming galaxies (SFGs) with similar stellar masses ($M^\\ast$). We examine the dispersion of local SFMS using a complete sample of Sloan Digital Sky Survey galaxies at 0.01$$8.8. The SFRs are estimated from H$\\alpha$ in combination with 22$\\mu m$ observation from WISE. The catalog of bulge+disk decomposition from Simard et al. (2011) is available for the sample galaxies. We measure the dispersion of specific SFR (SSFR) as a function of $M^*$. We confirm that the dispersion increases with $M^*$ from 0.37$\\pm0.01$dex at $\\log(M^\\ast/M_\\odot)$10.2. Despite star formation is mostly associated with disks, the dispersion of disk SSFR still increases with $M^*$. We conclude that the presence of bulges/bars is likely responsible for the large dispersion of SSFR in massive SFGs while low-mass SFGs are mostly disk-dominated and thus with small dispersion. Our ...

  19. Evolution of Exoplanets and their Parent Stars

    CERN Document Server

    Guillot, Tristan; Morel, Pierre; Havel, Mathieu; Parmentier, Vivien

    2014-01-01

    Studying exoplanets with their parent stars is crucial to understand their population, formation and history. We review some of the key questions regarding their evolution with particular emphasis on giant gaseous exoplanets orbiting close to solar-type stars. For masses above that of Saturn, transiting exoplanets have large radii indicative of the presence of a massive hydrogen-helium envelope. Theoretical models show that this envelope progressively cools and contracts with a rate of energy loss inversely proportional to the planetary age. The combined measurement of planetary mass, radius and a constraint on the (stellar) age enables a global determination of the amount of heavy elements present in the planet interior. The comparison with stellar metallicity shows a correlation between the two, indicating that accretion played a crucial role in the formation of planets. The dynamical evolution of exoplanets also depends on the properties of the central star. We show that the lack of massive giant planets a...

  20. Dynamic atmospheres and winds of cool luminous giants, I. Al$_2$O$_3$ and silicate dust in the close vicinity of M-type AGB stars

    CERN Document Server

    Höfner, Susanne; Aringer, Bernhard; Ahuja, Rajeev

    2016-01-01

    High spatial resolution techniques have given valuable insights into the mass loss mechanism of AGB stars, which presumably involves a combination of atmospheric levitation by pulsation-induced shock waves and radiation pressure on dust. Observations indicate that Al$_2$O$_3$ condenses at distances of about 2 stellar radii or less, prior to the formation of silicates. Al$_2$O$_3$ grains are therefore prime candidates for producing the scattered light observed in the close vicinity of several M-type AGB stars, and they may be seed particles for the condensation of silicates at lower temperatures. We have constructed a new generation of Dynamic Atmosphere & Radiation-driven Wind models based on Implicit Numerics (DARWIN), including a time-dependent treatment of grain growth & evaporation for both Al$_2$O$_3$ and Fe-free silicates (Mg$_2$SiO$_4$). The equations describing these dust species are solved in the framework of a frequency-dependent radiation-hydrodynamical model for the atmosphere & wind s...

  1. Very Low-mass Stellar and Substellar Companions to Solar-like Stars from MARVELS. VI. A Giant Planet and a Brown Dwarf Candidate in a Close Binary System HD 87646

    Science.gov (United States)

    Ma, Bo; Ge, Jian; Wolszczan, Alex; Muterspaugh, Matthew W.; Lee, Brian; Henry, Gregory W.; Schneider, Donald P.; Martín, Eduardo L.; Niedzielski, Andrzej; Xie, Jiwei; Fleming, Scott W.; Thomas, Neil; Williamson, Michael; Zhu, Zhaohuan; Agol, Eric; Bizyaev, Dmitry; Nicolaci da Costa, Luiz; Jiang, Peng; Martinez Fiorenzano, A. F.; González Hernández, Jonay I.; Guo, Pengcheng; Grieves, Nolan; Li, Rui; Liu, Jane; Mahadevan, Suvrath; Mazeh, Tsevi; Nguyen, Duy Cuong; Paegert, Martin; Sithajan, Sirinrat; Stassun, Keivan; Thirupathi, Sivarani; van Eyken, Julian C.; Wan, Xiaoke; Wang, Ji; Wisniewski, John P.; Zhao, Bo; Zucker, Shay

    2016-11-01

    We report the detections of a giant planet (MARVELS-7b) and a brown dwarf (BD) candidate (MARVELS-7c) around the primary star in the close binary system, HD 87646. To the best of our knowledge, it is the first close binary system with more than one substellar circumprimary companion that has been discovered. The detection of this giant planet was accomplished using the first multi-object Doppler instrument (KeckET) at the Sloan Digital Sky Survey (SDSS) telescope. Subsequent radial velocity observations using the Exoplanet Tracker at the Kitt Peak National Observatory, the High Resolution Spectrograph at the Hobby Eberley telescope, the “Classic” spectrograph at the Automatic Spectroscopic Telescope at the Fairborn Observatory, and MARVELS from SDSS-III confirmed this giant planet discovery and revealed the existence of a long-period BD in this binary. HD 87646 is a close binary with a separation of ˜22 au between the two stars, estimated using the Hipparcos catalog and our newly acquired AO image from PALAO on the 200 inch Hale Telescope at Palomar. The primary star in the binary, HD 87646A, has {T}{eff} = 5770 ± 80 K, log g = 4.1 ± 0.1, and [Fe/H] = -0.17 ± 0.08. The derived minimum masses of the two substellar companions of HD 87646A are 12.4 ± 0.7 {M}{Jup} and 57.0 ± 3.7 {M}{Jup}. The periods are 13.481 ± 0.001 days and 674 ± 4 days and the measured eccentricities are 0.05 ± 0.02 and 0.50 ± 0.02 respectively. Our dynamical simulations show that the system is stable if the binary orbit has a large semimajor axis and a low eccentricity, which can be verified with future astrometry observations.

  2. The empirical metallicity dependence of the mass-loss rate of O- and early B-type stars

    NARCIS (Netherlands)

    Mokiem, M.R.; de Koter, A.; Vink, J.S.; Puls, J.; Evans, C.J.; Smartt, S.J.; Crowther, P.A.; Herrero, A.; Langer, N.; Lennon, D.J.; Najarro, F.; Villamariz, M.R.

    2007-01-01

    Abridged] We present a comprehensive study of the metallicity dependence of the mass-loss rates in stationary stellar winds of hot massive stars. Assuming a power-law dependence of mass loss on metallicity, Mdot \\propto Z^{m}, and adopting a theoretical relation between the terminal velocity and met

  3. A proposed direct measurement of cross section at Gamow window for key reaction $^{19}$F($p$,$\\alpha$)$^{16}$O in Asymptotic Giant Branch stars with a planned accelerator in CJPL

    CERN Document Server

    He, J J; Ma, S B; Hu, J; Zhang, L Y; Fu, C B; Zhang, N T; Lian, G; Su, J; Li, Y J; Yan, S Q; Shen, Y P; Hou, S Q; Jia, B L; Zhang, T; Zhang, X P; Guo, B; Kubono, S; Liu, W P

    2016-01-01

    In 2014, the National Natural Science Foundation of China (NSFC) approved the Jinping Underground Nuclear Astrophysics laboratory (JUNA) project, which aims at direct cross-section measurements of four key stellar nuclear reactions right down to the Gamow windows. In order to solve the observed fluorine overabundances in Asymptotic Giant Branch (AGB) stars, measuring the key $^{19}$F($p$,$\\alpha$)$^{16}$O reaction at effective burning energies (i.e., at Gamow window) is established as one of the scientific research sub-projects. The present paper describes this sub-project in details, including motivation, status, experimental setup, yield and background estimation, aboveground test, as well as other relevant reactions.

  4. Time-dependent, compositionally driven convection in the oceans of accreting neutron stars

    CERN Document Server

    Medin, Zach

    2014-01-01

    We discuss the effect of chemical separation as matter freezes at the base of the ocean of an accreting neutron star, and the subsequent enrichment of the ocean in light elements and inward transport of heat through convective mixing. We extend the steady-state results of Medin & Cumming 2011 to transiently accreting neutron stars, by considering the time-dependent cases of heating during accretion outbursts and cooling during quiescence. Convective mixing is extremely efficient, flattening the composition profile in about one convective turnover time (weeks to months at the base of the ocean). During accretion outbursts, inward heat transport has only a small effect on the temperature profile in the outer layers until the ocean is strongly enriched in light elements, a process that takes hundreds of years to complete. During quiescence, however, inward heat transport rapidly cools the outer layers of the ocean while keeping the inner layers hot. We find that this leads to a sharp drop in surface emission...

  5. The Energy Dependence of Neutron Star Surface Modes and X-ray Burst Oscillations

    CERN Document Server

    Piro, A L; Piro, Anthony L.; Bildsten, Lars

    2006-01-01

    We calculate the photon energy dependence of the pulsed amplitude of neutron star (NS) surface modes. Simple approximations demonstrate that it depends most strongly on the bursting NS surface temperature. This result compares well with full integrations that include Doppler shifts from rotation and general relativistic corrections to photon propagation. We show that the energy dependence of type I X-ray burst oscillations agrees with that of a surface mode, lending further support to the hypothesis that they originate from surface waves. The energy dependence of the pulsed emission is rather insensitive to the NS inclination, mass and radius, or type of mode, thus hindering constraints on these parameters. We also show that, for this energy-amplitude relation, the majority of the signal (relative to the noise) comes in the 2-25 keV band, so that the current burst oscillation searches with the Rossi X-Ray Timing Explorer are close to optimal. The critical test of the mode hypothesis for X-ray burst oscillatio...

  6. System size, energy and centrality dependence of strange hadron elliptic flow at STAR

    Energy Technology Data Exchange (ETDEWEB)

    Masui, Hiroshi

    2008-12-21

    The elliptic flow (v{sub 2}) pattern in terms of hadron mass and transverse momentum p{sub T} is qualitatively described for p{sub T} < 2 GeV/c by ideal hydrodynamics in Au + Au collisions at RHIC. In addition, for p{sub T} = 2-6 GeV/c the measured v{sub 2} follow a universal scaling by the number of quarks explained by quark coalescence/recombination models. These observations suggest that a partonic collectivity develops in the matter in early stage of heavy ion collisions. Centrality as well as system size and energy dependence of the v{sub 2} is important to shed light on the underlying collision dynamics in heavy ion collisions. We present the measurements of centrality dependence of v{sub 2} at {radical}s{sub NN} = 200 and 62.4 GeV in Au + Au and Cu + Cu collisions for K{sub S}{sup 0}, {phi}, {Lambda}, {Xi} and {Omega} at STAR experiment. We focus on the recent Cu + Cu results and discuss the centrality dependence of v{sub 2} as well as the number of quark scaling as a function of transverse kinetic energy at different system size and energies. We also discuss the eccentricity scaled v{sub 2} for identified hadrons and implications that ideal hydrodynamical limit has not been reached at RHIC.

  7. Looks like a duck, moves like a duck, but does it quack like a duck? Asteroseismology of red-giant stars in clusters

    DEFF Research Database (Denmark)

    Miglio, Andrea; Brogaard, Karsten Frank; Handberg, Rasmus

    .g. radius, mass, evolutionary state, age) on a star-by-star basis.These constraints give us a “new pair of eyes” to look at clusters, and they open several exciting opportunities. Based on a detailed analysis of the complete set of 4-years-long Kepler data, we present clear evidence for stars that have...

  8. Shielding effects in polymer-polymer reactions. V. Concentration dependence of contact formation between star-branched and linear chains.

    Science.gov (United States)

    Nardai, Michael M; Zifferer, Gerhard

    2013-07-19

    By use of the Dissipative Particle Dynamics (DPD) simulation technique mixtures of star-branched (arm number F = 4) and linear chains in athermal (good) solvent are analyzed regarding probabilities for intermolecular contacts of various reactive sites within different polymer coils. The accompanying sterical hindrances are described in the framework of shielding factors in order to investigate reactions and side reactions in radical polymerization and other techniques that involve polymer-polymer coupling. The shielding factors are studied as a function of total concentration from high dilution up to the bulk for different chain lengths of star-shaped and linear chains. Results indicate that their concentration dependence can be described by a power law for systems above the overlap concentration, whereas the chain length dependence vanishes when extrapolating to infinite chain lengths in that concentration range. Also the influence of the ratio of star chains and linear chains is studied for various concentrations.

  9. Rapid Formation of Ice Giant Planets

    CERN Document Server

    Boss, A P; Haghighipour, N; Boss, Alan P.; Wetherill, George W.; Haghighipour, Nader

    2002-01-01

    The existence of Uranus and Neptune presents severe difficulties for the core accretion model for the formation of ice giant planets. We suggest an alternative mechanism, namely disk instability leading to the formation of gas giant protoplanets, coagulation and settling of dust grains to form ice/rock cores at their centers, and photoevaporation of their gaseous envelopes by a nearby OB star, as a possible means of forming ice giant planets.

  10. A GALA lipopeptide mediates pH- and membrane charge dependent fusion with stable giant unilamellar vesicles

    DEFF Research Database (Denmark)

    Etzerodt, Thomas P.; Trier, Sofie; Henriksen, Jonas R.

    2012-01-01

    ,2-diamino propanoic acid (Dap) moiety, yielding the lipopeptide dimyristoyl-Dap-GALA (DMDGALA). We have investigated DMDGALA as a component in large unilamellar vesicles (LUVs) and demonstrate pH-triggered fusion of peptide containing LUVs with stable target giant unilamellar vesicles (GUVs), which were...... used as simple mimics of cell membranes. The number of fusion events was large at pH 5.0, which is a physiologically relevant pH-range for a drug delivery system....

  11. Ultra-faint dwarf galaxies as a test of early enrichment and metallicity-dependent star formation

    CERN Document Server

    Tassis, Konstantinos; Kravtsov, Andrey V

    2011-01-01

    The tight relation of star formation with molecular gas indicated by observations and assumed in recent models implies that the efficiency with which galaxies convert their gas into stars depends on gas metallicity. This is because the abundance of molecular hydrogen is sensitive to the abundance of dust, which catalyzes the formation of H_2 and helps to shield it from dissociating radiation. In this study we point out that in the absence of significant pre-enrichment by Population III stars forming out of zero metallicity gas, such H_2-based star formation is expected to leave an imprint in the form of bi-modality in the metallicity distribution among dwarf galaxies and in the metallicity distribution of stars within individual galaxies. The bi-modality arises because when gas metallicity (and dust abundance) is low, formation of molecular gas is inefficient, the gas consumption time scale is long, and star formation and metal enrichment proceed slowly. When metallicity reaches a critical threshold value sta...

  12. The Role of Galaxy Interaction in Environmental Dependence of the Star Formation Activity at z~1.2

    CERN Document Server

    Ideue, Yuko; Nagao, Tohru; Shioya, Yasuhiro; Kajisawa, Masaru; Trump, Jonathan R; Vergani, Daniela; Iovino, Angela; Koekemoer, Anton M; Fevre, Olivier Le; Ilbert, Olivier; Scoville, Nick

    2011-01-01

    In order to understand environmental effects on star formation in high-redshift galaxies, we investigate the physical relationships between the star formation activity, stellar mass, and environment for z ~1.2 galaxies in the 2 deg^2 COSMOS field. We estimate star formation using the [OII] emission line and environment from the local galaxy density. Our analysis shows that for massive galaxies M_*>10^10 M_sun, the fraction of [OII] emitters in high-density environments is 1.7 times higher than in low-density environments, while the [OII] emitter fraction does not depend on environment for low-mass M_* 10^10 M_sun. In addition, massive galaxies are more likely to have companions in high-density environments. However, although the "number" of star forming galaxies increases for massive galaxies with close companions and in dense environments, the "average" star formation rate of star forming galaxies at a given mass is independent of environment and the presence/absence of a close companion. These results sugg...

  13. The effect of sublimation temperature dependencies on disk walls around T Tauri stars

    CERN Document Server

    Nagel, Erick; Calvet, Nuria; Espaillat, Catherine; Trinidad, Miguel Angel

    2012-01-01

    The dust cannot survive closer to the star from the point where a grain reaches a temperature equal to the sublimation temperature. The boundary between a dust-free and a dusty region defines the sublimation wall. In the literature two models for the structure of the wall are used: a wall with a fixed sublimation temperature and a wall with a density-dependent sublimation temperature. In the former, the wall is vertical and in the latter, the wall is curved. We find important differences between these models SEDs in the wavelength range from 3 to 8\\mu m, being the emission of the former larger than that of the latter model. We quantify the differences in IRAC colors when these models are used to explain the observations. In the IRAC color-color diagram ([3.6]-[4.5] vs. [5.8]-[8.0]), the models are located in specific regions, either depending on the inclination, the mass accretion rate, or which model is used.

  14. Environmental Dependence of Star Formation Law in the Disk and Center of IC 342

    CERN Document Server

    Pan, Hsi-An; Hirota, Akihiko

    2013-01-01

    The Kennicutt-Schmidt (K--S) law in IC 342 is examined using the 12CO-to-H2 conversion factor (Xco,v), which depends on the metallicity and CO intensity. Additionally, an optically thin 13CO (1-0) is also independently used to analyze the K--S law. Xco,v is two to three times lower than the Galactic standard Xco in the galactic center and approximately two times higher than Xco at the disk. The surface densities of molecular gas (Sigma_H2) derived from 12CO and 13CO are consistent at the environment in a high-Sigma_H2 region. By comparing the K-S law in the disk and the central regions of IC 342, we found that the power law index of K-S law (N) increases toward the central region. Furthermore, the dependence of N on Sigma_H2 is observed. Specifically, N increases with Sigma_H2. The derived N in this work and previous observations are consistent with the implication that star formation is likely triggered by gravitational instability in the disk (low-Sigma_H2 region) of IC 342 and both gravitational instabilit...

  15. Determining Ages of APOGEE Giants with Known Distances

    Science.gov (United States)

    Feuillet, Diane K.; Bovy, Jo; Holtzman, Jon; Girardi, Léo; MacDonald, Nick; Majewski, Steven R.; Nidever, David L.

    2016-01-01

    We present a sample of 705 local giant stars observed using the New Mexico State University 1 m telescope with the Sloan Digital Sky Survey-III/Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectrograph, for which we estimate stellar ages and the local star formation history (SFH). The high-resolution (R ˜ 22,500), near infrared (1.51-1.7 μm) APOGEE spectra provide measurements of stellar atmospheric parameters (temperature, surface gravity, [M/H], and [α/M]). Due to the smaller uncertainties in surface gravity possible with high-resolution spectra and accurate Hipparcos distance measurements, we are able to calculate the stellar masses to within 30%. For giants, the relatively rapid evolution up the red giant branch allows the age to be constrained by the mass. We examine methods of estimating age using both the mass-age relation directly and a Bayesian isochrone matching of measured parameters, assuming a constant SFH. To improve the SFH prior, we use a hierarchical modeling approach to constrain the parameters of the model SFH using the age probability distribution functions of the data. The results of an α-dependent Gaussian SFH model show a clear age-[α/M] relation at all ages. Using this SFH model as the prior for an empirical Bayesian analysis, we determine ages for individual stars. The resulting age-metallicity relation is flat, with a slight decrease in [M/H] at the oldest ages and a ˜0.5 dex spread in metallicity across most ages. For stars with ages ≲1 Gyr we find a smaller spread, consistent with radial migration having a smaller effect on these young stars than on the older stars.

  16. DETERMINING AGES OF APOGEE GIANTS WITH KNOWN DISTANCES

    Energy Technology Data Exchange (ETDEWEB)

    Feuillet, Diane K.; Holtzman, Jon [Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States); Bovy, Jo [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada); Girardi, Léo [Osservatorio Astronomico di Padova—INAF, Vicolo dell’Osservatorio 5, I-35122 Padova (Italy); MacDonald, Nick [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States); Majewski, Steven R. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); Nidever, David L., E-mail: feuilldk@nmsu.edu [Large Synoptic Survey Telescope, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)

    2016-01-20

    We present a sample of 705 local giant stars observed using the New Mexico State University 1 m telescope with the Sloan Digital Sky Survey-III/Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectrograph, for which we estimate stellar ages and the local star formation history (SFH). The high-resolution (R ∼ 22,500), near infrared (1.51–1.7 μm) APOGEE spectra provide measurements of stellar atmospheric parameters (temperature, surface gravity, [M/H], and [α/M]). Due to the smaller uncertainties in surface gravity possible with high-resolution spectra and accurate Hipparcos distance measurements, we are able to calculate the stellar masses to within 30%. For giants, the relatively rapid evolution up the red giant branch allows the age to be constrained by the mass. We examine methods of estimating age using both the mass–age relation directly and a Bayesian isochrone matching of measured parameters, assuming a constant SFH. To improve the SFH prior, we use a hierarchical modeling approach to constrain the parameters of the model SFH using the age probability distribution functions of the data. The results of an α-dependent Gaussian SFH model show a clear age–[α/M] relation at all ages. Using this SFH model as the prior for an empirical Bayesian analysis, we determine ages for individual stars. The resulting age–metallicity relation is flat, with a slight decrease in [M/H] at the oldest ages and a ∼0.5 dex spread in metallicity across most ages. For stars with ages ≲1 Gyr we find a smaller spread, consistent with radial migration having a smaller effect on these young stars than on the older stars.

  17. Internal rotation of red giants by asteroseismology

    CERN Document Server

    Di Mauro, M P; Ventura, R; Stello, D; Beck, P G; Davies, G; Elsworth, Y; Garcıa, R A; Hekker, S; Mosser, B; Christensen-Dalsgaard, J; Bloemen, S; Catanzaro, G; De Smedt, K; Tkachenko, A

    2012-01-01

    We present an asteroseismic approach to study the dynamics of the stellar interior in red-giant stars by asteroseismic inversion of the splittings induced by the stellar rotation on the oscillation frequencies. We show preliminary results obtained for the red giant KIC4448777 observed by the space mission Kepler.

  18. An Evolutionary Model for Collapsing Molecular Clouds and Their Star Formation Activity. II. Mass Dependence of the Star Formation Rate

    CERN Document Server

    Zamora-Avilés, Manuel

    2013-01-01

    In a previous study, we presented a semi-analytical model for the regulation of the star formation rate (SFR) and efficiency (SFE) in which the molecular clouds (MCs) were assumed to be in gravitational collapse, and the SFR was instantaneously controlled by evaporation of the cloud material by massive-star ionization feedback. In this model, the main parameter controlling the evolution of the clouds was found to be the gas mass involved in the process and here we discuss various properties of the SFR and SFE as a function of the cloud masses, that can be compared with observations and implemented in numerical models of galactic evolution. Because the model neglects magnetic fields, supernova explosions, and radiation pressure, the results presented are upper limits. We find that $\\SFRavg$ and $\\SFEavg$ are well represented as functions of the maximum cloud mass by the fits $\\SFRavg \\approx 100 (1+\\Mmax/2 \\times 10^5 ~ \\Msun)^{2} ~ \\Msun \\Myr^{-1}$ and $\\SFEavg \\approx 0.024 (\\Mmax/10^5 ~ \\Msun)^{0.28}$, resp...

  19. On the asymptotic acoustic-mode phase in red giant stars and its dependence on evolutionary state

    DEFF Research Database (Denmark)

    Christensen-Dalsgaard, Jørgen; Silva Aguirre, Victor; Elsworth, Yvonne;

    2014-01-01

    Asteroseismic investigations based on the wealth of data now available, in particular from the CoRoT and Kepler missions, require a good understanding of the relation between the observed quantities and the properties of the underlying stellar structure. Kallinger et al. found a relation between ...

  20. Simulating radiative feedback and star cluster formation in GMCs - II. Mass dependence of cloud destruction and cluster properties

    Science.gov (United States)

    Howard, Corey S.; Pudritz, Ralph E.; Harris, William E.

    2017-09-01

    The process of radiative feedback in giant molecular clouds (GMCs) is an important mechanism for limiting star cluster formation through the heating and ionization of the surrounding gas. We explore the degree to which radiative feedback affects early (≲5 Myr) cluster formation in GMCs having masses that range from 104 to 106 M⊙ using the flash code. The inclusion of radiative feedback lowers the efficiency of cluster formation by 20-50 per cent relative to hydrodynamic simulations. Two models in particular - 5 × 104 and 105 M⊙ - show the largest suppression of the cluster formation efficiency, corresponding to a factor of ∼2. For these clouds only, the internal energy, a measure of the energy injected by radiative feedback, exceeds the gravitational potential for a significant amount of time. We find a clear relation between the maximum cluster mass, Mc,max, formed in a GMC and the mass of the GMC itself, MGMC: Mc,max ∝ M_{GMC}^{0.81}. This scaling result suggests that young globular clusters at the necessary scale of 106 M⊙ form within host GMCs of masses near ∼5 × 107 M⊙. We compare simulated cluster mass distributions to the observed embedded cluster mass function [d log (N)/dlog (M) ∝ Mβ where β = -1] and find good agreement (β = -0.99 ± 0.14) only for simulations including radiative feedback, indicating this process is important in controlling the growth of young clusters. However, the high star formation efficiencies, which range from 16 to 21 per cent, and high star formation rates compared to locally observed regions suggest other feedback mechanisms are also important during the formation and growth of stellar clusters.