- ID:
- ivo://CDS.VizieR/J/AJ/161/71
- Title:
- Paramaters for 40 LITTLE THINGS galaxies
- Short Name:
- J/AJ/161/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The stellar, gaseous and young stellar disks in the LITTLE THINGS sample of nearby dwarf irregular galaxies are fitted with functions to search for correlations between the parameters. We find that the HI radial profiles are generally flatter in the center and fall faster in the outer regions than the V-band profiles, while young stars are more centrally concentrated, especially if the HI is more centrally flat. This pattern suggests that the HI is turning into molecules in the center, and the molecular clouds are forming stars and FUV. A model that assumes the molecular surface density is proportional to the total gas surface density to a power of 1.5 or 2, in analogy with the Kennicutt-Schmidt relation, reproduces the relationship between the ratio of the visible to the HI scale length and the HI Sersic index. The molecular fraction is estimated as a function of radius for each galaxy by converting the FUV to a molecular surface density using conventional calibrations. The average molecular fraction inside 3RD is 23%{+/-}17%. However, the break in the stellar surface brightness profile has no unified tracer related to star formation.
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- ID:
- ivo://CDS.VizieR/J/AJ/159/174
- Title:
- Parameters & abundances for Hyades/Field G-K dwarfs
- Short Name:
- J/AJ/159/174
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It has been suggested that Fe abundances of K dwarfs derived from FeI and FeII lines show considerable discrepancies, and oxygen abundances determined from high-excitation OI-7771-5 triplet lines are appreciably overestimated (the problem becoming more serious toward lower Teff), which, however, has not yet been widely confirmed. With the aim of clarifying this issue, we spectroscopically determined the atmospheric parameters of 148 G-K dwarfs (Hyades cluster stars and field stars) by assuming the classical FeI/FeII ionization equilibrium as usual, and determined their oxygen abundances by applying the non-local thermal equilibrium spectrum fitting analysis to OI-7771-5 lines. It turned out that the resulting parameters did not show any significant inconsistency with those determined by other methods (for example, the mean differences in Teff and logg from the well-determined solutions of Hyades dwarfs are mostly <~100K and <~0.1dex). Likewise, the oxygen abundances of Hyades stars are around [O/H]~+0.2dex (consistent with the metallicity of this cluster) without exhibiting any systematic Teff-dependence. Accordingly, we conclude that parameters can be spectroscopically evaluated to a sufficient precision in the conventional manner (based on the Saha-Boltzmann equation for FeI/FeII) and oxygen abundances can be reliably determined from the OI-7771-5 triplet for K dwarfs as far as stars of Teff>~4500K are concerned. We suspect that previously reported strongly Teff-dependent discrepancies may have stemmed mainly from overestimation of weak-line strengths and/or improper Teff scale.
- ID:
- ivo://CDS.VizieR/J/AJ/133/2464
- Title:
- Parameters and abundances of nearby giants
- Short Name:
- J/AJ/133/2464
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present parameter and abundance data for a sample of 298 nearby giants. The spectroscopic data for this work have a resolution of R~60000S/N>150, and spectral coverage from 475 to 685nm. Overall trends in the Z>10 abundances are dominated by Galactic chemical evolution, while the light-element abundances are influenced by stellar evolution, as well as Galactic evolution. We find several super-Li stars in our sample and confirm that Li abundances in the first giant branch are related to mixing depths.
- ID:
- ivo://CDS.VizieR/J/AJ/159/254
- Title:
- Parameters for 453 metal-poor stars in NGC5139
- Short Name:
- J/AJ/159/254
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The most massive and complex globular clusters in the Galaxy are thought to have originated as the nuclear cores of now tidally disrupted dwarf galaxies, but the connection between globular clusters and dwarf galaxies is tenuous with the M54/Sagittarius system representing the only unambiguous link. The globular cluster Omega Centauri ({omega}Cen) is more massive and chemically diverse than M54, and is thought to have been the nuclear star cluster of either the Sequoia or Gaia-Enceladus galaxy. Local Group dwarf galaxies with masses equivalent to these systems often host significant populations of very metal-poor stars ([Fe/H]<-2.5), and one might expect to find such objects in {omega}Cen. Using high-resolution spectra from Magellan-M2FS, we detected 11 stars in a targeted sample of 395 that have [Fe/H] ranging from -2.30 to -2.52. These are the most metal-poor stars discovered in the cluster, and are five times more metal-poor than {omega}Cen's dominant population. However, these stars are not so metal-poor as to be unambiguously linked to a dwarf galaxy origin. The cluster's metal-poor tail appears to contain two populations near [Fe/H]~-2.1 and -2.4, which are very centrally concentrated but do not exhibit any peculiar kinematic signatures. Several possible origins for these stars are discussed.
- ID:
- ivo://CDS.VizieR/J/A+A/618/A15
- Title:
- Parameters of EHB stars in {omega} Cen
- Short Name:
- J/A+A/618/A15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The presence of extreme horizontal branch (EHB) and blue hook stars in some Galactic globular clusters (GGCs) constitutes one of the remaining mysteries of stellar evolution. While several evolutionary scenarios have been proposed to explain the characteristics of this peculiar population of evolved stars, their observational verification has been limited by the availability of spectroscopic data for a statistically significant sample of such objects in any single GGC. In this first paper, we focus on {omega} Centauri, a peculiar, massive GGC that hosts multiple stellar populations. We use non-LTE model atmospheres to derive atmospheric parameters (Teff, log g and N(He)/N(H)) and spectroscopic masses for 152 EHB stars in the cluster. We also search for close binaries among these stars based on radial velocity variations. The majority of our sample consists of sdOB stars that have roughly solar or super-solar atmospheric helium abundances. It is these objects that constitute the blue hook at V>18.5mag in the {omega} Cen colour-magnitude diagram.
- ID:
- ivo://CDS.VizieR/J/AJ/152/6
- Title:
- Parameters of Kepler stars using LAMOST & seismic data
- Short Name:
- J/AJ/152/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Asteroseismology is a powerful tool to precisely determine the evolutionary status and fundamental properties of stars. With the unprecedented precision and nearly continuous photometric data acquired by the NASA Kepler mission, parameters of more than 10^4^ stars have been determined nearly consistently. However, most studies still use photometric effective temperatures (Teff) and metallicities ([Fe/H]) as inputs, which are not sufficiently accurate as suggested by previous studies. We adopted the spectroscopic Teff and [Fe/H] values based on the LAMOST low-resolution spectra (R~1,800), and combined them with the global oscillation parameters to derive the physical parameters of a large sample of stars. Clear trends were found between {Delta}logg(LAMOST-seismic) and spectroscopic Teff as well as logg, which may result in an overestimation of up to 0.5dex for the logg of giants in the LAMOST catalog. We established empirical calibration relations for the logg values of dwarfs and giants. These results can be used for determining the precise distances to these stars based on their spectroscopic parameters.
- ID:
- ivo://CDS.VizieR/J/AJ/158/73
- Title:
- Parameters of OB stars & their bow shock nebulae
- Short Name:
- J/AJ/158/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Second only to initial mass, the rate of wind-driven mass loss determines the final mass of a massive star and the nature of its remnant. Motivated by the need to reconcile observational values and theory, we use a recently vetted technique to analyze the mass-loss rates in a sample of OB stars that generate bow shock nebulae. We measure peculiar velocities from new Gaia parallax and proper motion data and their spectral types from new optical and infrared spectroscopy. For our sample of 70 central stars in morphologically selected bow shock nebulae, 67 are OB stars. The median peculiar velocity is 11 km/s, significantly smaller than classical "runaway star" velocities. Mass-loss rates for these O and early B stars agree with recently lowered theoretical predictions, ranging from ~10^-7^ M_{sun}_/yr for mid-O dwarfs to 10^-9^ M_{sun}_/yr for late O dwarfs - a factor of about 2.7 lower than the often-used Vink et al. (2000A&A...362..295V, 2001A&A...369..574V) formulation. Our results provide the first observational mass-loss rates for B0-B3 dwarfs and giants - 10^-9^ to 10^-8^ M_{sun}_/yr. We find evidence for an increase in the mass-loss rates below a critical effective temperature, consistent with predictions of the bistability phenomenon in the range T_eff_=19000-27000 K. The sample exhibits a correlation between modified wind momentum and luminosity, consistent in slope but lower by 0.43 dex in magnitude compared to canonical wind-luminosity relations. We identify a small subset of objects deviating most significantly from theoretical expectations as probable radiation-driven bow wave nebulae by virtue of their low stellar-to-nebular luminosity ratios. For these, the inferred mass-loss rates must be regarded as upper limits.
- ID:
- ivo://CDS.VizieR/J/ApJS/207/20
- Title:
- Parity-forbidden [Co II] and [V II] lines
- Short Name:
- J/ApJS/207/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report a comprehensive list of accurate Ritz wavelengths for parity-forbidden [Co II] and [V II] lines obtained from the analysis of energy levels measured in the laboratory with Fourier transform emission spectroscopy. Such lines, particularly those in the infrared, are in demand for the analysis of low-density astrophysical plasmas in and around objects such as planetary nebulae, star-forming regions, and active galactic nuclei. Transitions between all known metastable levels of Co II and V II are included in our analysis, producing wavelengths for 1477 [V II] lines and 782 [Co II] lines. Of these, 170 [V II] lines and 171 [Co II] lines arise from transitions with calculated transition probabilities greater than 1x10^-2^/s and upper level excitations of less than 5 eV, and thus are likely to be observed in astrophysical spectra.
- ID:
- ivo://CDS.VizieR/J/A+A/553/A95
- Title:
- PCA approach to stellar effective temperatures
- Short Name:
- J/A+A/553/A95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The derivation of the effective temperature of a star is a critical first step in order to perform a detailed spectroscopic analysis. Spectroscopic methods suffer from systematic errors related to model simplifications. Photometric methods may be more robust, but are exposed to distortions caused by interstellar reddening. Direct methods are difficult to apply, since fundamental data of high accuracy are hard to obtain. We explore a new approach in which the spectrum is used to characterize a star's effective temperature based on a calibration established by a small set of standard stars. We perform Principal Component Analysis on homogeneous libraries of stellar spectra, then calibrate a relationship between the principal components and the effective temperature using a set of stars with reliable effective temperatures. We find that our procedure gives excellent consistency when spectra from a homogeneous set of observations are used. Systematic offsets may appear when combining observations from different sources. Using as reference the spectra of stars with high-quality spectroscopic temperatures in the Elodie library, we define a temperature scale for FG-type disk dwarfs with an internal consistency of about 50K, in excellent agreement with temperatures from direct determinations, but distinct from widely-used scales based in the infrared flux method.
- ID:
- ivo://CDS.VizieR/J/AJ/141/120
- Title:
- P Cygni H{alpha} measurements
- Short Name:
- J/AJ/141/120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- P Cygni is a prototype of the luminous blue variables (or S Doradus variables), and the star displays photometric and emission line variability on a timescale of years (known as the "short S Doradus-phase" variations). Here we present new high-resolution H{alpha} spectroscopy of P Cyg that we combine with earlier spectra and concurrent V-band photometry to document the emission and continuum flux variations over a 24 year time span.
