- ID:
- ivo://CDS.VizieR/J/ApJ/817/40
- Title:
- High-resolution NIR spectra of local giants
- Short Name:
- J/ApJ/817/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of 705 local giant stars observed using the New Mexico State University 1m 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~22500), near infrared (1.51-1.7{mu}m) APOGEE spectra provide measurements of stellar atmospheric parameters (temperature, surface gravity, [M/H], and [{alpha}/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 {alpha}-dependent Gaussian SFH model show a clear age-[{alpha}/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 <~1Gyr we find a smaller spread, consistent with radial migration having a smaller effect on these young stars than on the older stars.
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- ID:
- ivo://CDS.VizieR/J/ApJS/248/19
- Title:
- High-resolution spectroscopy of TESS stars
- Short Name:
- J/ApJS/248/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Accurate atmospheric parameters and chemical composition of stars play a vital role in characterizing physical parameters of exoplanetary systems and understanding of their formation. A full asteroseismic characterization of a star is also possible if its main atmospheric parameters are known. The NASA Transiting Exoplanet Survey Satellite (TESS) space telescope will play a very important role in searching of exoplanets around bright stars and stellar asteroseismic variability research. We have observed all 302 bright (V<8mag) and cooler than F5 spectral class stars in the northern TESS continuous viewing zone with a 1.65m telescope at the Moletai Astronomical Observatory of Vilnius University and the high-resolution Vilnius University Echelle Spectrograph. We uniformly determined the main atmospheric parameters, ages, orbital parameters, velocity components, and precise abundances of 24 chemical species (C(C2), N(CN), [OI], NaI, MgI, AlI, SiI, SiII, CaI, CaII, ScI, ScII, TiI, TiII, VI, CrI, CrII, MnI, FeI, FeII, CoI, NiI, CuI, and ZnI) for 277 slowly rotating single stars in the field. About 83% of the sample stars exhibit the Mg/Si ratios greater than 1.0 and may potentially harbor rocky planets in their systems.
- ID:
- ivo://CDS.VizieR/J/ApJ/877/104
- Title:
- High-res. spectroscopy of LAMOST Li-rich giants
- Short Name:
- J/ApJ/877/104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The discovery of Li-rich giants has introduced a new challenge for standard stellar evolution models. To resolve this issue, the number of this type of object has been rapidly increased through the development of worldwide surveys. Taking advantage of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope survey, 44 new Li-rich giants are reported, which are confirmed with high-resolution observations. Based on the high-resolution and high signal-to-noise spectra, we derived the atmospheric parameters and elemental abundances with the spectral synthesis method. We performed a detailed analysis of their evolutionary stages, infrared excess, projected rotational velocity (vsini), and stellar population. We find that (1) the Li-rich giants concentrate at the evolutionary status of the red giant branch bump, red clump, and asymptotic giant branch; (2) three of them are fast rotators and none exhibit infrared excess. Our results imply that the origins of Li enrichment are most likely to be associated with the extra mixing in the stellar interior, and the external sources might only make a minor contribution. Moreover, various Li-rich episodes take place at different evolutionary stages.
- ID:
- ivo://CDS.VizieR/J/AJ/132/242
- Title:
- H II absorption regions at 74MHz
- Short Name:
- J/AJ/132/242
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work we present 74MHz observations in the region 26{deg}>l>-15{deg}, -5{deg}<b<5{deg} report the detection of 92 absorption features associated with known HII regions; and derive the brightness temperature of the Galactic cosmic-ray electron synchrotron emission emanating from the column behind these regions. For the 42 HII regions with known distances, the average emissivity of the column behind the HII region is derived. The 74MHz emissivity values range between 0.3 and 1.0K/pc for a model assuming uniform distribution of emissivity. Methods for using this type of data to model the three-dimensional distribution of cosmic-ray emissivity and the possibility of using this method to break the HII region kinematic distance degeneracy are discussed.
- ID:
- ivo://CDS.VizieR/J/A+A/621/A127
- Title:
- HII regions synchrotron radiation
- Short Name:
- J/A+A/621/A127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Cosmic rays (CRs) and magnetic fields are dynamically important components in the Galaxy, and their energy densities are comparable to that of the turbulent interstellar gas. The interaction of CRs and Galactic magnetic fields (GMF) produces synchrotron radiation clearly visible in the radio regime. Detailed measurements of synchrotron radiation averaged over the line-of-sight (LOS), so-called synchrotron emissivities, can be used as a tracer of the CR density and GMF strength. Our aim is to model the synchrotron emissivity in the Milky Way using a three-dimensional dataset instead of LOS-integrated intensity maps on the sky. Using absorbed HII regions, we measured the synchrotron emissivity over a part of the LOS through the Galaxy, changing from a two-dimensional to a three-dimensional view. Performing these measurements on a large scale is one of the new applications of the window opened by current low-frequency arrays. Using various simple axisymmetric emissivity models and a number of GMF-based emissivity models, we were able to simulate the synchrotron emissivities and compare them to the observed values in the catalog. We present a catalog of low-frequency absorption measurements of HII regions, their distances and electron temperatures, compiled from literature. These data show that the axisymmetric emissivity models are not complex enough, but the GMF-based emissivity models deliver a reasonable fit. These models suggest that the fit can be improved by either an enhanced synchrotron emissivity in the outer reaches of the Milky Way or an emissivity drop near the Galactic center. Current GMF models plus a constant CR density model cannot explain low-frequency absorption measurements, but the fits improved with slight (ad hoc) adaptations. It is clear that more detailed models are needed, but the current results are very promising.
- ID:
- ivo://CDS.VizieR/J/BaltA/20/89
- Title:
- Homegenized effective temperatures of 800 stars
- Short Name:
- J/BaltA/20/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Some selected catalogs of the effective temperatures (Teff) for F, G and K stars are analyzed. By an improved technique we estimate the external errors of these catalogs from data intercomparisons. The Teff values are then averaged with the appropriate weights to produce a mean homogeneous catalog based on the selected data. This catalog, containing 800 stars, is compared with some other independent catalogs for estimating their external errors. The data may be used as a source of reliable homogeneous values of Teff, together with their errors.
- ID:
- ivo://CDS.VizieR/J/A+A/650/A182
- Title:
- Homogeneous study of Herbig Ae/Be stars
- Short Name:
- J/A+A/650/A182
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Herbig Ae/Be stars (HAeBes) have so far been studied based on relatively small samples that are scattered throughout the sky. Their fundamental stellar and circumstellar parameters and statistical properties were derived with heterogeneous approaches before Gaia. Our main goal is to contribute to the study of HAeBes from the largest sample of such sources to date, for which stellar and circumstellar properties have been determined homogeneously from the analysis of the spectral energy distributions (SEDs) and Gaia EDR3 parallaxes and photometry. Multiwavelength photometry was compiled for 209 bona fide HAeBes for which Gaia EDR3 distances were estimated. Using the Virtual Observatory SED Analyser (VOSA), photospheric models were fit to the optical SEDs to derive stellar parameters, and the excesses at infrared (IR) and longer wavelengths were characterized to derive several circumstellar properties. A statistical analysis was carried out to show the potential use of such a large dataset. The stellar temperature, luminosity, radius, mass, and age were derived for each star based on optical photometry. In addition, their IR SEDs were classified according to two different schemes, and their mass accretion rates, disk masses, and the sizes of the inner dust holes were also estimated uniformly. The initial mass function fits the stellar mass distribution of the sample within 2<M_star_/M_{sun}_<12. In this aspect, the sample is therefore representative of the HAeBe regime and can be used for statistical purposes when it is taken into account that the boundaries are not well probed. Our statistical study does not reveal any connection between the SED shape from the Meeus et al., 2001A&A...365..476M classification and the presence of transitional disks, which are identified here based on the SEDs that show an IR excess starting at the K band or longer wavelengths. In contrast, only ~28% of the HAeBes have transitional disks, and the related dust disk holes are more frequent in HBes than in HAes (~34% vs 15%). The relatively small inner disk holes and old stellar ages estimated for most transitional HAes indicate that photoevaporation cannot be the main mechanism driving disk dissipation in these sources. In contrast, the inner disk holes and ages of most transitional HBes are consistent with the photoevaporation scenario, although these results alone do not unambiguously discard other disk dissipation mechanisms. The complete dataset is available online through a Virtual Observatory- compliant archive, representing the most recent reference for statistical studies on the HAeBe regime. VOSA is a complementary tool for the future characterization of newly identified HAeBes.
- ID:
- ivo://CDS.VizieR/J/AJ/162/188
- Title:
- Hot degenerates in the MCT survey. III.
- Short Name:
- J/AJ/162/188
- Date:
- 21 Mar 2022 00:13:43
- Publisher:
- CDS
- Description:
- We present optical spectra of 144 white dwarfs detected in the Montreal-Cambridge-Tololo colorimetric survey, including 120 DA, 12 DB, 4 DO, 1 DQ, and 7 DC stars. We also perform a model atmosphere analysis of all objects in our sample using the so-called spectroscopic technique, or the photometric technique in the case of DC white dwarfs. The main objective of this paper is to contribute to the ongoing effort of confirming spectroscopically all white dwarf candidates in the Gaia survey, in particular in the southern hemisphere. All our spectra are made available in the Montreal White Dwarf Database.
- ID:
- ivo://CDS.VizieR/J/A+A/526/A136
- Title:
- Hot HB stars in {omega} Cen
- Short Name:
- J/A+A/526/A136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- UV observations of some massive globular clusters have revealed a significant population of stars hotter and fainter than the hot end of the horizontal branch (HB), the so-called blue hook stars. This feature might be explained either by the late hot flasher scenario where stars experience the helium flash while on the white dwarf cooling curve or by the progeny of the helium-enriched sub-population postulated to exist in some clusters. Previous spectroscopic analyses of blue hook stars in omega Cen and NGC 2808 support the late hot flasher scenario, but the stars contain much less helium than expected and the predicted C and N enrichment cannot be verified. We compare the observed effective temperatures, surface gravities, helium abundances, and carbon line strengths (where detectable) of our targets stars with the predictions of the two aforementioned scenarios.
- ID:
- ivo://CDS.VizieR/J/A+A/576/A44
- Title:
- Hot subdwarf binaries from MUCHFUSS
- Short Name:
- J/A+A/576/A44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims at finding hot subdwarf stars with massive compact companions like massive white dwarfs (M>1.0M_{sun}_), neutron stars, or stellar-mass black holes. The existence of such systems is predicted by binary evolution theory, and recent discoveries indicate that they exist in our Galaxy. We present orbital and atmospheric parameters and put constraints on the nature of the companions of 12 close hot subdwarf B star (sdB) binaries found in the course of the MUCHFUSS project. The systems show periods between 0.14 and 7.4days. In nine cases the nature of the companions cannot be constrained unambiguously whereas three systems most likely have white dwarf companions. We find that the companion to SDSSJ083006.17+475150.3 is likely to be a rare example of a low-mass helium-core white dwarf. SDSSJ095101.28+034757.0 shows an excess in the infrared that probably originates from a third companion in a wide orbit, which makes this system the second candidate hierarchical triple system containing an sdB star. SDSSJ113241.58-063652.8 is the first helium deficient sdO star with a confirmed close companion. This study brings to 142 the number of sdB binaries with orbital periods of less than 30 days and with measured mass functions. We present an analysis of the minimum companion mass distribution and show that it is bimodal. One peak around 0.1M_{sun}_ corresponds to the low-mass main sequence (dM) and substellar companions. The other peak around 0.4M_{sun}_ corresponds to the white dwarf companions. The derived masses for the white dwarf companions are significantly lower than the average mass for single carbon-oxygen white dwarfs. In a T_eff_-logg diagram of sdB+dM companions, we find signs that the sdB components are more massive than the rest of the sample. The full sample was compared to the known population of extremely low-mass white dwarf binaries as well as short-period white dwarfs with main sequence companions. Both samples show a significantly different companion mass distribution indicating either different selection effects or different evolutionary paths. We identified 16 systems where the dM companion will fill its Roche Lobe within a Hubble time and will evolve into a cataclysmic variable; two of them will have a brown dwarf as donor star. Twelve systems with confirmed white dwarf companions will merge within a Hubble time, two of them having a mass ratio to evolve into a stable AMCVn-type binary and another two which are potential supernova Ia progenitor systems. The remaining eight systems will most likely merge and form RCrB stars or massive C/O white dwarfs depending on the structure of the white dwarf companion.
