- 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/ApJ/846/23
- Title:
- High-resolution spectra of 9 RGB stars in NGC6681
- Short Name:
- J/ApJ/846/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtain high-resolution spectra of nine red giant branch stars in NGC 6681 and perform the first detailed abundance analysis of stars in this cluster. We confirm cluster membership for these stars based on consistent radial velocities of 214.5+/-3.7km/s and find a mean [Fe/H]=-1.63+/-0.07dex and [{alpha}/Fe]=0.42+/-0.11dex. Additionally, we confirm the existence of a Na-O anti-correlation in NGC 6681 and identify two populations of stars with unique abundance trends. With the use of HST photometry from Sarajedini+ (2007AJ....133.1658S) and Piotto+ (2015AJ....149...91P) we are able to identify these two populations as discrete sequences in the cluster CMD. Although we cannot confirm the nature of the polluter stars responsible for the abundance differences in these populations, these results do help put constraints on possible polluter candidates.
- 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/A+A/638/A122
- Title:
- High-speed stars. Galactic hitchhikers
- Short Name:
- J/A+A/638/A122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The search for stars born in the very early stages of the Milky Way star formation history is of paramount importance in the study of the early Universe since their chemistry carries irreplaceable information on the conditions in which early star formation and galaxy buildup took place. The search for these objects has generally taken the form of expensive surveys for faint extremely metal-poor stars, the most obvious but not the only candidates to a very early formation. Thanks to Gaia DR2 radial velocities and proper motions, we identified 72 bright cool stars displaying heliocentric transverse velocities in excess of 500km/s. These objects are most likely members of extreme outer-halo populations, either formed in the early Milky Way build-up or accreted from since-destroyed self-gravitating stellar systems. We analysed low-resolution FORS spectra of the 72 stars in the sample and derived the abundances of a few elements. Despite the large uncertainties on the radial velocity determination, we derived reliable orbital parameters for these objects. The stars analysed are mainly slightly metal poor, with a few very metal-poor stars. Their chemical composition is much more homogeneous than expected. All the stars have very eccentric halo orbits, some extending well beyond the expected dimension of the Milky Way. These stars can be the result of a disrupted small galaxy or they could have been globular cluster members. Age estimates suggest that some of them are evolved blue stragglers, now on the subgiant or asymptotic giant branches.
- ID:
- ivo://CDS.VizieR/J/ApJS/252/3
- Title:
- High-velocity stars in the Gal. halo from LAMOST & Gaia
- Short Name:
- J/ApJS/252/3
- Date:
- 03 Mar 2022 11:59:54
- Publisher:
- CDS
- Description:
- In this paper, we report 591 high-velocity star candidates (HiVelSCs) selected from over 10 million spectra of Data Release 7 (DR7) of the Large Sky Area Multi-object Fiber Spectroscopic Telescope and the second Gaia data release, with three-dimensional velocities in the Galactic rest frame larger than 445km/s. We show that at least 43 HiVelSCs are unbound to the Galaxy with escape probabilities larger than 50%, and this number decreases to eight if the possible parallax zero-point error is corrected. Most of these HiVelSCs are metal-poor and slightly {alpha}-enhanced inner halo stars. Only 14% of them have [Fe/H]>-1, which may be the metal-rich "in situ" stars in the halo formed in the initial collapse of the Milky Way or metal-rich stars formed in the disk or bulge but kinematically heated. The low ratio of 14% implies that the bulk of the stellar halo was formed from the accretion and tidal disruption of satellite galaxies. In addition, HiVelSCs on retrograde orbits have slightly lower metallicities on average compared with those on prograde orbits; meanwhile, metal-poor HiVelSCs with [Fe/H]{<}-1 have an even faster mean retrograde velocity compared with metal-rich HiVelSCs. To investigate the origins of HiVelSCs, we perform orbit integrations and divide them into four types, i.e., hypervelocity stars, hyper-runaway stars, runaway stars and fast halo stars.
- ID:
- ivo://CDS.VizieR/J/AJ/103/514
- Title:
- High-velocity stars toward South Galactic Cap
- Short Name:
- J/AJ/103/514
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present spectroscopic observations of stars identified in Murray's (1986) astrometric survey of the South Galactic Cap
- ID:
- ivo://CDS.VizieR/J/A+A/652/A23
- Title:
- HII-chi-mistry-IR. Abundances
- Short Name:
- J/A+A/652/A23
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We provide a new method to derive heavy element abundances based on the unique suite of nebular lines in the mid- to far-infrared (IR) range. Using grids of photo-ionisation models that cover a wide range in O/H and N/O abundances, and ionisation parameter, our code HII-CHI-MISTRY-IR (HCm-IR) provides model-based abundances based on extinction free and temperature insensitive tracers, two significant advantages over optical diagnostics. The code is probed using a sample of 56 galaxies observed with Spitzer and Herschel covering a wide range in metallicity, 7.2~<12+log(O/H)~<8.9. The IR model-based metallicities obtained are robust within a scatter of 0.03dex when the hydrogen recombination lines, which are typically faint transitions in the IR range, are not available. When compared to the optical abundances obtained with the direct method,model- based methods, and strong-line calibrations, HCm-IR estimates show a typical dispersion of ~0.2dex, in line with previous studies comparing IR and optical abundances, a do not introduce a noticeable systematic above 12+log(O/H)>7.6. This accuracy can be achieved using the lines [SIV]10.5um, [SIII]18.7,33.5um, [NeIII]15.6um and [NeII]12.8um. Additionally, HCm-IR provides an independent N/O measurement when the [OIII]52,88um and [NIII]57um transitions are measured, and therefore the derived abundances in this case do not rely on particular assumptions in the N/O ratio. Large uncertainties (~0.4dex) may affect the abundance determinations of galaxies at sub- or over-solar metallicities when a solar-like N/O ratio is adopted. Finally, the code has been applied to 8 galaxies located at 1.8<z<7.5 with ground-based detections of far-IR lines redshifted in the submm range, revealing solar-like N/O and O/H abundances in agreement with recent studies.
- ID:
- ivo://CDS.VizieR/J/ApJ/830/4
- Title:
- HII region abundances in NGC 5457 (M101)
- Short Name:
- J/ApJ/830/4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Large Binocular Telescope observations of 109 HII regions in NGC 5457 (M101) obtained with the Multi-Object Double Spectrograph. We have robust measurements of one or more temperature-sensitive auroral emission lines for 74 HII regions, permitting the measurement of "direct" gas-phase abundances. Comparing the temperatures derived from the different ionic species, we find: (1) strong correlations of T[NII] with T[SIII] and T[OIII], consistent with little or no intrinsic scatter; (2) a correlation of T[SIII] with T[OIII], but with significant intrinsic dispersion; (3) overall agreement between T[NII], T[SII], and T[OII], as expected, but with significant outliers; (4) the correlations of T[NII] with T[SIII] and T[OIII] match the predictions of photoionization modeling while the correlation of T[SIII] with T[OIII] is offset from the prediction of photoionization modeling. Based on these observations, which include significantly more observations of lower excitation HII regions, missing in many analyses, we inspect the commonly used ionization correction factors (ICFs) for unobserved ionic species and propose new empirical ICFs for S and Ar. We have discovered an unexpected population of HII regions with a significant offset to low values in Ne/O, which defies explanation. We derive radial gradients in O/H and N/O which agree with previous studies. Our large observational database allows us to examine the dispersion in abundances, and we find intrinsic dispersions of 0.074+/-0.009 in O/H and 0.095+/-0.009 in N/O (at a given radius). We stress that this measurement of the intrinsic dispersion comes exclusively from direct abundance measurements of HII regions in NGC 5457.
- ID:
- ivo://CDS.VizieR/J/MNRAS/477/4152
- Title:
- H II region candidates in NGC628
- Short Name:
- J/MNRAS/477/4152
- Date:
- 17 Jan 2022 00:25:45
- Publisher:
- CDS
- Description:
- This is the first paper of a series dedicated to nebular physics and the chemical evolution of nearby galaxies by investigating large samples of H II regions with the Canada-France-Hawaii Telescope imaging spectrograph SITELLE (Spectro-Imageur a Transformee de Fourier pour l'Etude en Long et en Large des raies d'Emission). We present a technique adapted to imaging spectroscopy to identify and extract parameters from 4285 H II region candidates found in the disc of NGC 628. Using both the spatial and spectral capabilities of SITELLE, our technique enables the extraction of the position, dust extinction, velocity, H{alpha} profile, diffuse ionized gas (DIG) background, luminosity, size, morphological type, and the emission-line fluxes for individual spaxels and the integrated spectrum for each region. We have produced a well-sampled H II region luminosity function and studied its variation with galactocentric radius and level of the DIG background. We found a slope {alpha} of -1.12+/-0.03 with no evidence of a break at high luminosity. Based on the width of the region profile, bright regions are rather compact, while faint regions are seen over a wide range of sizes. The radius function reveals a slope of -1.81+/-0.02. BPT diagrams of the individual spaxels and integrated line ratios confirm that most detections are H II regions. Also, maps of the line ratios show complex variations of the ionization conditions within HII regions. All this information is compiled in a new catalogue for HII regions. The objective of this data base is to provide a complete sample which will be used to study the whole parameter space covered by the physical conditions in active star-forming regions.
