- ID:
- ivo://CDS.VizieR/J/ApJS/220/2
- Title:
- Rosseland opacities with the OPAS model
- Short Name:
- J/ApJS/220/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The OPAS opacity model has been used to calculate the radiative opacity of stellar plasmas in local thermodynamic equilibrium. According to the recent chemical composition revision of the solar photosphere, opacities have been computed for various hydrogen and metallic element mass fractions. Calculations have been performed toward solar interior modeling for temperatures between log[T(K)]=6 and log[T(K)]=7.2, and for electron densities between 10^20^ and 10^26^cm^-3^. We discuss possible sources of uncertainty in the calculations. We also compare Rosseland opacities to OPAL and OP data.
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- ID:
- ivo://CDS.VizieR/J/ApJS/214/25
- Title:
- Rosseland & Planck gaseous mean opacities
- Short Name:
- J/ApJS/214/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new calculations of Rosseland and Planck gaseous mean opacities relevant to the atmospheres of giant planets and ultracool dwarfs. Such calculations are used in modeling the atmospheres, interiors, formation, and evolution of these objects. Our calculations are an expansion of those presented in Freedman (2008ApJS..174..504F) to include lower pressures, finer temperature resolution, and also the higher metallicities most relevant for giant planet atmospheres. Calculations span 1{mu}bar to 300bar, and 75-4000K, in a nearly square grid. Opacities at metallicities from solar to 50 times solar abundances are calculated. We also provide an analytic fit to the Rosseland mean opacities over the grid in pressure, temperature, and metallicity. In addition to computing mean opacities at these local temperatures, we also calculate them with weighting functions up to 7000K, to simulate the mean opacities for incident stellar intensities, rather than locally thermally emitted intensities. The chemical equilibrium calculations account for the settling of condensates in a gravitational field and are applicable to cloud-free giant planet and ultracool dwarf atmospheres, but not circumstellar disks. We provide our extensive opacity tables for public use.
- ID:
- ivo://CDS.VizieR/J/A+A/530/A115
- Title:
- Rotating massive MS stars evolutionary models
- Short Name:
- J/A+A/530/A115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a dense grid of evolutionary tracks and isochrones of rotating massive main-sequence stars. We provide three grids with different initial compositions tailored to compare with early OB stars in the Small and Large Magellanic Clouds and in the Galaxy. Each grid covers masses ranging from 5 to 60M_{sun}_ and initial rotation rates between 0 and about 600km/s. To calibrate our models we used the results of the VLT-FLAMES Survey of Massive Stars. We determine the amount of convective overshooting by using the observed drop in rotation rates for stars with surface gravities logg<3.2 to determine the width of the main sequence. We calibrate the efficiency of rotationally induced mixing using the nitrogen abundance determinations for B stars in the Large Magellanic cloud. We describe and provide evolutionary tracks and the evolution of the central and surface abundances.
- ID:
- ivo://CDS.VizieR/J/A+A/346/586
- Title:
- Rotating models of A and F stars
- Short Name:
- J/A+A/346/586
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Magnitude differences between rotating and non-rotating copartners for a grid of models with solar metallicity are tabulated here. The results are expressed in terms of the dimensionless angular velocity w-bar- defined in Eq.(1) of the paper, the angle of inclination i and the atmospheric parameters T_e_ and g_e_ defined in Eqs.(22) and (21), respectively. To obtain the absolute magnitudes for a given rotating model, the magnitudes of a non-rotating model with T_eff_=T_e_, g=g_e_ and the same intrinsic luminosity must be added. Results are given for the filters in the Geneva, Johnson and Stroemgren systems. Eq (1): w-bar = {Omega}/{Omega}_c_, where {Omega} is the angular velocity of the star, and {Omega}_c_^2^=8GM/(27R^3^_p_), where M is the mass and R_p_ the polar radius.
- ID:
- ivo://CDS.VizieR/J/A+A/291/155
- Title:
- Rotating neutron stars models. I.
- Short Name:
- J/A+A/291/155
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/A+AS/108/455
- Title:
- Rotating neutron stars models. II.
- Short Name:
- J/A+AS/108/455
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/A+A/606/A55
- Title:
- Rotational mixing in CEMP-s stars
- Short Name:
- J/A+A/606/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Carbon-enhanced metal-poor (CEMP) stars with s-process enrichment (CEMP-s) are believed to be the products of mass transfer from an asymptotic giant branch (AGB) companion, which has long since become a white dwarf. The surface abundances of CEMP-s stars are thus commonly assumed to reflect the nucleosynthesis output of the first AGB stars. We have previously shown that, for this to be the case, some physical mechanism must counter atomic diffusion (gravitational settling and radiative levitation) in these nearly fully radiative stars, which otherwise leads to surface abundance anomalies clearly inconsistent with observations. Here we take into account angular momentum accretion by these stars. We compute in detail the evolution of typical CEMP-s stars from the zero-age main sequence, through the mass accretion, and up the red giant branch for a wide range of specific angular momentum ja of the accreted material, corresponding to surface rotation velocities, v_rot_, between about 0.3 and 300km/s. We find that only for j_a_>~10^17^cm^2^/s (v_rot_>20km/s, depending on mass accreted) angular momentum accretion directly causes chemical dilution of the accreted material. This could nevertheless be relevant to CEMP-s stars, which are observed to rotate more slowly, if they undergo continuous angular momentum loss akin to solar-like stars. In models with rotation velocities characteristic of CEMP-s stars, rotational mixing primarily serves to inhibit atomic diffusion, such that the maximal surface abundance variations (with respect to the composition of the accreted material) prior to first dredge-up remain within about 0.4dex without thermohaline mixing or about 0.5-1.5dex with thermohaline mixing. Even in models with the lowest rotation velocities (v_rot_<~1km/s), rotational mixing is able to severely inhibit atomic diffusion, compared to non-rotating models. We thus conclude that it offers a natural solution to the problem posed by atomic diffusion and cannot be neglected in models of CEMP-s stars.
548. Rotational tracks
- ID:
- ivo://CDS.VizieR/J/ApJ/776/67
- Title:
- Rotational tracks
- Short Name:
- J/ApJ/776/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stellar rotation is a strong function of both mass and evolutionary state. Missions such as Kepler and CoRoT provide tens of thousands of rotation periods, drawn from stellar populations that contain objects at a range of masses, ages, and evolutionary states. Given a set of reasonable starting conditions and a prescription for angular momentum loss, we address the expected range of rotation periods for cool field stellar populations (~0.4-2.0M_{sun}_). We find that cool stars fall into three distinct regimes in rotation. Rapid rotators with surface periods less than 10 days are either young low-mass main sequence (MS) stars, or higher mass subgiants which leave the MS with high rotation rates. Intermediate rotators (10-40 days) can be either cool MS dwarfs, suitable for gyrochronology, or crossing subgiants at a range of masses. Gyrochronology relations must therefore be applied cautiously, since there is an abundant population of subgiant contaminants. The slowest rotators, at periods greater than 40 days, are lower mass subgiants undergoing envelope expansion. We identify additional diagnostic uses of rotation periods. There exists a period-age relation for subgiants distinct from the MS period-age relations. There is also a period-radius relation that can be used as a constraint on the stellar radius, particularly in the interesting case of planet host stars. The high-mass/low-mass break in the rotation distribution on the MS persists onto the subgiant branch, and has potential as a diagnostic of stellar mass. Finally, this set of theoretical predictions can be compared to extensive datasets to motivate improved modeling.
- ID:
- ivo://CDS.VizieR/J/ApJ/746/15
- Title:
- Runaway massive stars from R136
- Short Name:
- J/ApJ/746/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We conduct a theoretical study on the ejection of runaway massive stars from R136 -the central massive, starburst cluster in the 30 Doradus complex of the Large Magellanic Cloud. Specifically, we investigate the possibility of the very massive star (VMS) VFTS 682 being a runaway member of R136. Recent observations of the above VMS, by virtue of its isolated location and its moderate peculiar motion, have raised the fundamental question of whether isolated massive star formation is indeed possible. We perform the first realistic N-body computations of fully mass-segregated R136-type star clusters in which all the massive stars are in primordial binary systems. These calculations confirm that the dynamical ejection of a VMS from an R136-like cluster, with kinematic properties similar to those of VFTS 682, is common. Hence, the conjecture of isolated massive star formation is unnecessary to account for this VMS. Our results are also quite consistent with the ejection of 30 Dor 016, another suspected runaway VMS from R136. We further note that during the clusters' evolution, mergers of massive binaries produce a few single stars per cluster with masses significantly exceeding the canonical upper limit of 150 M_{sun}_. The observations of such single super-canonical stars in R136, therefore, do not imply an initial mass function with an upper limit greatly exceeding the accepted canonical 150M_{sun}_limit, as has been suggested recently, and they are consistent with the canonical upper limit.
- ID:
- ivo://CDS.VizieR/J/AJ/156/89
- Title:
- RVs & predicted transit-times for the K2-24 system
- Short Name:
- J/AJ/156/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- While planets between the size of Uranus and Saturn are absent within the solar system, the star K2-24 hosts two such planets, K2-24b and c, with radii equal to 5.4 R_{Earth}_ and 7.5 R_{Earth}_, respectively. The two planets have orbital periods of 20.9 days and 42.4 days, residing only 1% outside the nominal 2:1 mean-motion resonance. In this work, we present results from a coordinated observing campaign to measure planet masses and eccentricities that combines radial velocity measurements from Keck/HIRES and transit-timing measurements from K2 and Spitzer. K2-24b and c have low, but nonzero, eccentricities of e_1_~e_2_~0.08. The low observed eccentricities provide clues to the formation and dynamical evolution of K2-24b and K2-24c, suggesting that they could be the result of stochastic gravitational interactions with a turbulent protoplanetary disk, among other mechanisms. K2-24b and c are 19.0_-2.1_^+2.2^ M_{Earth}_ and 15.4_-1.8_^+1.9^ M_{Earth}_, respectively; K2-24c is 20% less massive than K2-24b, despite being 40% larger. Their large sizes and low masses imply large envelope fractions, which we estimate at 26_-3_^+3^ % and 52_-3_^+5^ %. In particular, K2-24c's large envelope presents an intriguing challenge to the standard model of core-nucleated accretion that predicts the onset of runaway accretion when f_env_~50%.
