- ID:
- ivo://CDS.VizieR/J/A+AS/141/141
- Title:
- 8500-8750{AA} high resolution spectroscopy. II.
- Short Name:
- J/A+AS/141/141
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a library of synthetic spectra characterized by -2.5<=[Z/Z_{sun}_]<=+0.5, 4.5<=logg<=1.0, and T_eff_<=7500K computed at the same {lambda}/{Delta}{lambda}=20000 resolving power of the observed spectra given in Paper I (Munari, 1999, Cat. <J/A+AS/137/521>) for 131 standard stars mapping the MKK spectral classification system. This range of parameters includes the majority of the galactic stars expected to dominate the GAIA target population, i.e. F-G-K-M type stars with metallicity ranging from that of the galactic globular clusters to Population I objects. Extension to T_eff_>7500K will be given later on in this series. The 254 synthetic spectra presented here are based on Kurucz's codes and line data and have been computed over a more extended wavelength interval (7650-8750{AA}) than that currently baselined for implementation on GAIA, i.e. the 8500-8750{AA}. This last range is dominated by the near-IR Ca II triplet and the head of the Paschen series. The more extended wavelength range allows us to investigate the behaviour of other strong near-IR spectral features (severely contaminated by telluric absorptions in ground-based observed spectra) as the K I doublet (7664, 7699{AA}), the Na I doublet (8183, 8194{AA}) and the lines of Fe I multiplet N.60 at 8327 and 8388{AA}. The synthetic spectra support our previous conclusions about the superior performance of the Paschen/Ca II 8500-8750{AA} region in meeting the GAIA requirements when compared to other near-IR intervals of similar {Delta}{lambda}=250{AA}.
« Previous |
1 - 10 of 728
|
Next »
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/366/1003
- Title:
- 8500-8750{AA} high resolution spectroscopy. III.
- Short Name:
- J/A+A/366/1003
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we complete the library of synthetic spectra for the range 7650-8750{AA}, which includes the 8500-8750{AA} interval currently base-lined for the spectroscopic observations by GAIA, candidate ESA Cornerstone 5 mission. As for Paper II (Munari & Castelli, Cat. <J/A+AS/141/141>), the spectra are based on Kurucz's codes and line data. The explored metallicity, gravity and temperature ranges are -2.5<=[Z/Z_{sun}_]<=+0.5, 4.5<=logg<=2.0 and 7750<=T_eff_<=50000K, respectively. The 698 new spectra are computed at the same {lambda}/{Delta}{lambda}=20000 resolving power of the observed spectra given in Paper I (Munari & Castelli, Cat. <J/A+AS/137/521>) (131 standard stars mapping the MKK spectral classification system) and the 254 synthetic spectra of Paper II (characterized by T_eff_<=7500K).
- ID:
- ivo://CDS.VizieR/J/ApJ/774/148
- Title:
- Ab initio EOS for hydrogen-helium mixtures
- Short Name:
- J/ApJ/774/148
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using density functional molecular dynamics simulations, we determine the equation of state (EOS) for hydrogen-helium mixtures spanning density-temperature conditions typical of giant-planet interiors, ~0.2-9g/cm3 and 1000-80000K for a typical helium mass fraction of 0.245. In addition to computing internal energy and pressure, we determine the entropy using an ab initio thermodynamic integration technique. A comprehensive EOS table with 391 density-temperature points is constructed and the results are presented in the form of a two-dimensional free energy fit for interpolation. Deviations between our ab initio EOS and the semi-analytical EOS model by Saumon and Chabrier (1992PhRvA..46.2084S, 1995ApJS...99..713S) are analyzed in detail, and we use the results for initial revision of the inferred thermal state of giant planets with known values for mass and radius. Changes are most pronounced for planets in the Jupiter mass range and below. We present a revision to the mass-radius relationship that makes the hottest exoplanets increase in radius by ~0.2 Jupiter radii at fixed entropy and for masses greater than ~0.5 Jupiter mass. This change is large enough to have possible implications for some discrepant "inflated giant exoplanets."
- ID:
- ivo://CDS.VizieR/J/ApJ/806/228
- Title:
- Ab initio EOS for water-hydrogen mixtures
- Short Name:
- J/ApJ/806/228
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from ab initio simulations of liquid water-hydrogen mixtures in the range from 2 to 70GPa and from 1000 to 6000K, covering conditions in the interiors of ice giant planets and parts of the outer envelope of gas giant planets. In addition to computing the pressure and the internal energy, we derive the Gibbs free energy by performing a thermodynamic integration. For all conditions under consideration, our simulations predict hydrogen and water to mix in all proportions. The thermodynamic behavior of the mixture can be well described with an ideal mixing approximation. We suggest that a substantial fraction of water and hydrogen in giant planets may occur in homogeneously mixed form rather than in separate layers. The extent of mixing depends on the planet's interior dynamics and its conditions of formation, in particular on how much hydrogen was present when icy planetesimals were delivered. Based on our results, we do not predict water-hydrogen mixtures to phase separate during any stage of the evolution of giant planets. We also show that the hydrogen content of an exoplanet is much higher if the mixed interior is assumed.
- ID:
- ivo://CDS.VizieR/J/ApJ/795/64
- Title:
- A catalog of exoplanet physical parameters
- Short Name:
- J/ApJ/795/64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- No true extrasolar Earth analog is known. Hundreds of planets have been found around Sun-like stars that are either Earth-sized but on shorter periods, or else on year-long orbits but somewhat larger. Under strong assumptions, exoplanet catalogs have been used to make an extrapolated estimate of the rate at which Sun-like stars host Earth analogs. These studies are complicated by the fact that every catalog is censored by non-trivial selection effects and detection efficiencies, and every property (period, radius, etc.) is measured noisily. Here we present a general hierarchical probabilistic framework for making justified inferences about the population of exoplanets, taking into account survey completeness and, for the first time, observational uncertainties. We are able to make fewer assumptions about the distribution than previous studies; we only require that the occurrence rate density be a smooth function of period and radius (employing a Gaussian process). By applying our method to synthetic catalogs, we demonstrate that it produces more accurate estimates of the whole population than standard procedures based on weighting by inverse detection efficiency. We apply the method to an existing catalog of small planet candidates around G dwarf stars. We confirm a previous result that the radius distribution changes slope near Earth's radius. We find that the rate density of Earth analogs is about 0.02 (per star per natural logarithmic bin in period and radius) with large uncertainty. This number is much smaller than previous estimates made with the same data but stronger assumptions.
- ID:
- ivo://CDS.VizieR/J/AJ/156/121
- Title:
- A catalog of 518 likely open cluster NGC 6405 members
- Short Name:
- J/AJ/156/121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents a combined method of Gaussian mixture model and random forest to compute membership probabilities of stars by using large, high-dimensional data sets. A significant advantage of this method is that it allows us to easily identify likely cluster members in large data sets starting from small training samples. As a benchmark, we select 40318 stars in the field of the open cluster NGC 6405 from the Gaia Data Release 2 (Gaia-DR2, Cat. I/345) by means of all five astrometric (positions, proper motions, and parallax) and photometric parameters. We use this combined method to determine likely cluster members in an eleven-dimensional parameter space. A total number of 518 high-probability (>=0.6) memberships are obtained, and the mean parallax and proper motion of the cluster are determined to be 2.171+/-0.005 mas (461+/-1 pc) and (<{mu}_{alpha}_cos{delta}>, <{mu}_{delta}_>)=(-1.357+/-0.023, -5.823+/-0.020) mas/yr, respectively. In addition, we quantitatively evaluate the relative importance of the parameters for membership determination and find that colors and magnitudes cannot be ignored in membership determination when using the RF method. Our results show that this combined method exhibits good performance in handling arbitrary high-dimensional and large data sets, such as Gaia-DR2, and it can also be used to investigate other open clusters.
- ID:
- ivo://CDS.VizieR/J/ApJS/185/1
- Title:
- A catalog of star formation and metallicity
- Short Name:
- J/ApJS/185/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We applied the VESPA algorithm to the Sloan Digital Sky Survey (DR7) of the Main Galaxies and Luminous Red Galaxies samples. The result is a catalog of stellar masses, detailed star formation and metallicity histories and dust content of nearly 800000 galaxies. We make the catalog public via a T-SQL database. We present the results using a range of stellar population and dust models, and will continue to update the catalog as new and improved models are made public. We also present a brief exploration of the catalog, and show that the quantities derived are robust: luminous red galaxies can be described by one to three populations, whereas a main galaxy sample galaxy needs on average two to five; red galaxies are older and less dusty; the dust values we recover are well correlated with measured Balmer decrements and star formation rates are also in agreement with previous measurements. We find that whereas some derived quantities are robust to the choice of modelling, many are still not.
- ID:
- ivo://CDS.VizieR/J/ApJ/850/207
- Title:
- Action dynamics of the Local Supercluster
- Short Name:
- J/ApJ/850/207
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The fully nonlinear gravitationally induced trajectories of a nearly complete set of galaxies, groups, and clusters in the Local Supercluster are constructed in a numerical action method model constrained by data from the CosmicFlows survey and various distance indicators. We add the gravity field due to inhomogeneities external to the sample sphere by making use of larger-scale peculiar flow measurements. Assignments of total masses were made to find the best overall set of mutual attractions, as determined by a goodness criterion based on present-day radial velocities, individually for the Virgo Cluster, M31, and the Milky Way (MW), and via a mass-to-light ratio relationship for other masses. The low median chi-square found indicates that the model fits the present-day velocity flow well, but a slightly high mean chi-square may indicate that some masses underwent complex orbits. The best fit, when setting the value of H_0_ to the CosmicFlows value of 75km/s/Mpc and the WMAP value for {Omega}_m_=0.244 consistent with that H_0_, occurs with the following parameters: {Omega}_orphan_=0.077+/-0.016, M/L_K_=40+/-2L_10_^0.15^M_{sun}_/L_{sun}_ (L_10_ is the K-band luminosity in units of 10^10^L_{sun}_), a Virgo mass of 6.3+/-0.8x10^14^M_{sun}_ (M/L_K_=113+/-15M_{sun}_/L_{sun}_), and a mass for the MW plus M31 of 5.15+/-0.35x10^12^M_{sun}_. The best constant mass-to-light ratio is M/L_K_=58+/-3M_{sun}_/L_{sun}_. The Virgocentric turnaround radius is 7.3+/-0.3Mpc. We explain several interesting trends in peculiar motions for various regions now that we can construct the 3D orbital histories.
- ID:
- ivo://CDS.VizieR/J/ApJ/812/40
- Title:
- Adiabatic mass loss in binary stars. II.
- Short Name:
- J/ApJ/812/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the limit of extremely rapid mass transfer, the response of a donor star in an interacting binary becomes asymptotically one of adiabatic expansion. We survey here adiabatic mass loss from Population I stars (Z=0.02) of mass 0.10M_{sun}_-100M_{sun}_ from the zero-age main sequence to the base of the giant branch, or to central hydrogen exhaustion for lower main sequence stars. The logarithmic derivatives of radius with respect to mass along adiabatic mass-loss sequences translate into critical mass ratios for runaway (dynamical timescale) mass transfer, evaluated here under the assumption of conservative mass transfer. For intermediate- and high-mass stars, dynamical mass transfer is preceded by an extended phase of thermal timescale mass transfer as the star is stripped of most of its envelope mass. The critical mass ratio q_ad_ (throughout this paper, we follow the convention of defining the binary mass ratio as q{equiv}M_donor_/M_accretor_) above which this delayed dynamical instability occurs increases with advancing evolutionary age of the donor star, by ever-increasing factors for more massive donors. Most intermediate- or high-mass binaries with nondegenerate accretors probably evolve into contact before manifesting this instability. As they approach the base of the giant branch, however, and begin developing a convective envelope, q_ad_ plummets dramatically among intermediate-mass stars, to values of order unity, and a prompt dynamical instability occurs. Among low-mass stars, the prompt instability prevails throughout main sequence evolution, with q_ad_ declining with decreasing mass, and asymptotically approaching q_ad_=2/3, appropriate to a classical isentropic n=3/2 polytrope. Our calculated q_ad_ values agree well with the behavior of time-dependent models by Chen & Han (2003MNRAS.341..662C) of intermediate-mass stars initiating mass transfer in the Hertzsprung gap. Application of our results to cataclysmic variables, as systems that must be stable against rapid mass transfer, nicely circumscribes the range in q_ad_ as a function of the orbital period in which they are found. These results are intended to advance the verisimilitude of population synthesis models of close binary evolution.
- ID:
- ivo://CDS.VizieR/J/ApJ/899/132
- Title:
- Adiabatic Mass Loss in Binary Stars. III.
- Short Name:
- J/ApJ/899/132
- Date:
- 14 Mar 2022 07:06:32
- Publisher:
- CDS
- Description:
- The distinguishing feature of the evolution of close binary stars is the role played by the mass exchange between the component stars. Whether or not the mass transfer is dynamically stable is one of the essential questions in binary evolution. In the limit of extremely rapid mass transfer, the response of a donor star in an interacting binary becomes asymptotically one of adiabatic expansion. We use the adiabatic mass-loss model to systematically survey the thresholds for dynamical timescale mass transfer over the entire span of possible donor star evolutionary states. We also simulate mass-loss process with isentropic envelopes, the specific entropy of which is fixed to be that at the base of the convective envelope, to artificially mimic the effect of such mass loss in superadiabatic surface convection regions, where the adiabatic approximation fails. We illustrate the general adiabatic response of 3.2M{odot} donor stars at different evolutionary stages. We extend our study to a grid of donor stars with different masses (from 0.1 to 100 M{sun} with Z=0.02) and at different evolutionary stages. We proceed to present our criteria for dynamically unstable mass transfer in both tabular and graphical forms. For red giant branch (RGB) and asymptotic giant branch (AGB) donors in systems with such mass ratios, they may have convective envelopes deep enough to evolve into common envelopes on a thermal timescale, if the donor star overfills its outer Lagrangian radius. Our results show that the RGB and AGB stars tend to be more stable than previously believed, and this may be helpful to explain the abundance of observed post-AGB binary stars with an orbital period of around 1000 days.
