- ID:
- ivo://CDS.VizieR/J/MNRAS/371/879
- Title:
- Effective temperatures of 215 FGK giants
- Short Name:
- J/MNRAS/371/879
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present precise effective temperatures (Teff) of 215 FGK giants determined using the method of line-depth ratios. For each star, we have measured the line depths and equivalent widths of a large number of spectral lines of low and high excitation potentials and established ~100 relations between Teff and their ratios. Starting with an initial value Teff, the relations are then self-calibrated by an iterative process. Our final estimates have been compared with very accurate (1 per cent) published temperatures and show a good agreement. Using our calibrations, we derive precise temperatures for 215 giants with near-solar metallicity, from high-resolution (R=42000) and high signal-to-noise ratio (S/N=100250) echelle spectra, obtained with the ELODIE spectrometer at the Observatoire de Haute Provence (OHP).
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- ID:
- ivo://CDS.VizieR/J/AN/321/277
- Title:
- Effective temperatures of K-M giants
- Short Name:
- J/AN/321/277
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A high-resolution spectroscopic survey in the 6380-6460{AA} region of 224 slowly-rotating M-K class III giants is presented. Spectral line-depth ratio are calibrated against effective temperature obtained from B-V and V-I color indices in the range 3200-7500K (M6-A9). A table of polynomial coefficients for 12 line-ratio-Teff relations can be used to derive Teff of F-M stars to within 33K (rms), and of early-F and mid-to-late M stars to within 77-106K (rms).
- ID:
- ivo://CDS.VizieR/J/ApJ/879/105
- Title:
- Effective temperatures of low-mass stars
- Short Name:
- J/ApJ/879/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-resolution, near-infrared spectra will be the primary tool for finding and characterizing Earth-like planets around low-mass stars. Yet, the properties of exoplanets cannot be precisely determined without accurate and precise measurements of the host star. Spectra obtained with the Immersion Grating Infrared Spectrometer simultaneously provide diagnostics for most stellar parameters, but the first step in any analysis is the determination of the effective temperature. Here we report the calibration of high-resolution H-band spectra to accurately determine the effective temperature for stars between 4000 and 3000K (~K8-M5) using absorption line-depths of FeI, OH, and Al I. The field star sample used here contains 254 K and M stars with temperatures derived using BT-Settl synthetic spectra. We use 106 stars with precise temperatures in the literature to calibrate our method, with typical errors of about 140K, and systematic uncertainties less than ~120K. For the broadest applicability, we present Teff-line-depth-ratio relationships, which we test on 12 members of the TW Hydrae Association and at spectral resolving powers between ~10000 and 120000. These ratios offer a simple but accurate measure of effective temperatures in cool stars that are distance and reddening independent.
- ID:
- ivo://CDS.VizieR/J/AJ/156/292
- Title:
- Effect of close companions on exoplanetary radii
- Short Name:
- J/AJ/156/292
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Understanding the distribution and occurrence rate of small planets was a fundamental goal of the Kepler transiting exoplanet mission, and could be improved with K2 and Transiting Exoplanet Survey Satellite (TESS). Deriving accurate exoplanetary radii requires accurate measurements of the host star radii and the planetary transit depths, including accounting for any "third light" in the system due to nearby bound companions or background stars. High-resolution imaging of Kepler and K2 planet candidate hosts to detect very close (within ~0.5") background or bound stellar companions has been crucial for both confirming the planetary nature of candidates, and the determination of accurate planetary radii and mean densities. Here we present an investigation of the effect of close companions, both detected and undetected, on the observed (raw count) exoplanet radius distribution. We demonstrate that the recently detected "gap" in the observed radius distribution (also seen in the completeness-corrected distribution) is fairly robust to undetected stellar companions, given that all of the systems in the sample have undergone some kind of vetting with high-resolution imaging. However, while the gap in the observed sample is not erased or shifted, it is partially filled in after accounting for possible undetected stellar companions. These findings have implications for the most likely core composition, and thus formation location, of super-Earth and sub-Neptune planets. Furthermore, we show that without high-resolution imaging of planet candidate host stars, the shape of the observed exoplanet radius distribution will be incorrectly inferred, for both Kepler- and TESS-detected systems.
- ID:
- ivo://CDS.VizieR/J/AJ/156/83
- Title:
- Effect of stellar companions on planetary systems
- Short Name:
- J/AJ/156/83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Kepler light curves used to detect thousands of planetary candidates are susceptible to dilution due to blending with previously unknown nearby stars. With the automated laser adaptive optics instrument, Robo-AO, we have observed 620 nearby stars around 3857 planetary candidates host stars. Many of the nearby stars, however, are not bound to the KOI. We use galactic stellar models and the observed stellar density to estimate the number and properties of unbound stars. We estimate the spectral type and distance to 145 KOIs with nearby stars using multi-band observations from Robo-AO and Keck-AO. Most stars within 1" of a Kepler planetary candidate are likely bound, in agreement with past studies. We use likely bound stars and the precise stellar parameters from the California Kepler Survey to search for correlations between stellar binarity and planetary properties. No significant difference between the binarity fraction of single and multiple-planet systems is found, and planet hosting stars follow similar binarity trends as field stars, many of which likely host their own non-aligned planets. We find that hot Jupiters are ~4x more likely than other planets to reside in a binary star system. We correct the radius estimates of the planet candidates in characterized systems and find that for likely bound systems, the estimated planetary radii will increase on average by a factor of 1.77, if either star is equally likely to host the planet. Lastly, we find the planetary radius gap is robust to the impact of dilution.
- ID:
- ivo://CDS.VizieR/J/ApJS/208/10
- Title:
- Effects of a {kappa}-distribution in HII regions
- Short Name:
- J/ApJS/208/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recently, Nicholls et al. (2012ApJ...752..148N), inspired by in situ observations of solar system astrophysical plasmas, suggested that the electrons in H II regions are characterized by a {kappa}-distribution of energies rather than a simple Maxwell-Boltzmann distribution. Here, we have collected together new atomic data within a modified photoionization code to explore the effects of both the new atomic data and the {kappa}-distribution on the strong-line techniques used to determine chemical abundances in H II regions. By comparing the recombination temperatures (T_rec_) with the forbidden line temperatures (T_FL_), we conclude that {kappa}~20. While representing only a mild deviation from equilibrium, this result is sufficient to strongly influence abundances determined using methods that depend on measurements of the electron temperature from forbidden lines. We present a number of new emission line ratio diagnostics that cleanly separate the two parameters determining the optical spectrum of H II regions--the ionization parameter q or {} and the chemical abundance, 12+log(O/H). An automated code to extract these parameters is presented. Using the homogeneous data set from van Zee et al. 1998, Cat. J/AJ/116/2805, we find self-consistent results between all of these different diagnostics. The systematic errors between different line ratio diagnostics are much smaller than those found in the earlier strong-line work. Overall, the effect of the {kappa}-distribution on the strong-line abundances derived solely on the basis of theoretical models is rather small.
- ID:
- ivo://CDS.VizieR/J/A+A/623/A126
- Title:
- Effects of a revised ^7^Be e^-^-capture rate
- Short Name:
- J/A+A/623/A126
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The electron-capture rate on ^7^Be is the main production channel for ^7^Li in several astrophysical environments. Theoretical evaluations have to account for not only the nuclear interaction, but also the processes in the plasma where ^7^Be ions and electrons interact. In the past decades several estimates were presented, pointing out that the theoretical uncertainty in the rate is in general of few percents. In the framework of fundamental solar physics, we consider here a recent evaluation for the ^7^Be+e^-^ rate, not used up to now in the estimate of neutrino fluxes. We analysed the effects of the new assumptions on Standard Solar Models (SSMs) and compared the results obtained by adopting the revised ^7^Be+e^-^ rate to those obtained by the one reported in a widely used compilation of reaction rates (ADE11). We found that new SSMs yield a maximum difference in the efficiency of the ^7^Be channel of about -4% with respect to what is obtained with the previously adopted rate. This fact affects the production of neutrinos from ^8^B, increasing the relative flux up to a maximum of 2.7%. Negligible variations are found for the physical and chemical properties of the computed solar models. The agreement with the SNO measurements of the neutral current component of the ^8^B neutrino flux is improved
- ID:
- ivo://CDS.VizieR/J/ApJ/719/996
- Title:
- Effects of binarity in SEGUE pipeline
- Short Name:
- J/ApJ/719/996
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the effects that unresolved binaries have on the determination of various stellar atmospheric parameters for targets from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) using numerical modeling, a grid of synthetic spectra, and the SEGUE Stellar Parameter Pipeline (SSPP). The SEGUE survey, a component of the Sloan Digital Sky Survey-II (SDSS-II) project focusing on Galactic structure, provides medium resolution spectroscopy for over 200000 stars of various spectral types over a large area on the sky. To model undetected binaries that may be in this sample, we use a variety of mass distributions for the primary and secondary stars in conjunction with empirically determined relationships for orbital parameters to determine the fraction of G-K dwarf stars, defined by SDSS color cuts as having 0.48<=(g-r)_0_<=0.75, that will be blended with a secondary companion. We focus on the G-K dwarf sample in SEGUE as it records the history of chemical enrichment in our galaxy. To determine the effect of the secondary on the spectroscopic parameters, specifically effective temperature, surface gravity, metallicity, and [{alpha}/Fe], we synthesize a grid of model spectra from 3275 to 7850K and [Fe/H]=-0.5 to -2.5 from MARCS model atmospheres using TurboSpectrum. These temperature and metallicity ranges roughly correspond to a stellar mass range of 0.1-1.0M_{sun}_. We assume that both stars in the pair have the same metallicity. We analyze both "infinite" signal-to-noise ratio (S/N) models and degraded versions of the spectra, at median S/N of 50, 25, and 10.
- ID:
- ivo://CDS.VizieR/J/A+A/650/A203
- Title:
- Effects of IMG on Galactic chemical enrichment
- Short Name:
- J/A+A/650/A203
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We have been seeing mounting evidence that the stellar initial mass function (IMF) might extend far beyond the canonical Mi~100M_{sun}_ limit, but the impact of such a hypothesis on the chemical enrichment of galaxies is yet to be clarified. We aim to address this question by analysing the observed abundances of thin- and thick-disc stars in the Milky Way with chemical evolution models that account for the contribution of very massive stars dying as pair instability supernovae. We built new sets of chemical yields from massive and very massive stars up to Mi~350M_{sun}_ by combining the wind ejecta extracted from our hydrostatic stellar evolution models with explosion ejecta from the literature. Using a simple chemical evolution code, we analysed the effects of adopting different yield tables by comparing predictions against observations of stars in the solar vicinity. After several tests, we set our focus on the [O/Fe] ratio that best separates the chemical patterns of the two Milky Way components. We nd that with a standard IMF, truncated at Mi~100M_{sun}_, we can reproduce various observational constraints for thin-disc stars; however, the same IMF fails to account for the [O/Fe] ratios of thick-disc stars. The best results are obtained by extending the IMF up to Mi=350M_{sun}_; while including the chemical ejecta of very massive stars in the form of winds and pair instability supernova (PISN) explosions. Our study indicates that PISN may have played a significant role in shaping the chemical evolution of the thick disc of the Milky Way. Including their chemical yields makes it easier to reproduce not only the level of the a-enhancement, but also the observed slope of thick-disc stars in the [O/Fe] versus [Fe/H] diagram. The bottom line is that the contribution of very massive stars to the chemical enrichment of galaxies is potentially quite important and should not be neglected in models of chemical evolution.
- ID:
- ivo://CDS.VizieR/J/ApJS/229/34
- Title:
- Effects of preionization in radiative shocks
- Short Name:
- J/ApJS/229/34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we treat the preionization problem in shocks over the velocity range 10<v_s_<1500km/s in a self-consistent manner. We identify four distinct classes of solutions controlled by the value of the shock-precursor parameter, {Psi}=Q/v_s_, where Q is the ionization parameter of the UV photons escaping upstream. This parameter determines both the temperature and the degree of ionization of the gas entering the shock. In increasing velocity, the shock solution regimes are cold neutral precursors (v_s_<~40km/s), warm neutral precursors (40<~v_s_<~75km/s), warm partly ionized precursors (75<~v_s_<~120km/s), and fast shocks in which the preshock gas is in photoionization equilibrium and is fully ionized. The main effect of a magnetic field is to push these velocity ranges to higher values and to limit the postshock compression. In order to facilitate comparison with observations of shocks, we provide a number of convenient scaling relationships for parameters, such as postshock temperature, compression factors, cooling lengths, and H{beta} and X-ray luminosity.