- ID:
- ivo://CDS.VizieR/J/ApJ/850/34
- Title:
- 3000-25000{AA} spectroscopy of nearby M dwarfs
- Short Name:
- J/ApJ/850/34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent studies of the stellar population in the solar neighborhood (<20pc) suggest that there are undetected white dwarfs (WDs) in multiple systems with main-sequence companions. Detecting these hidden stars and obtaining a more complete census of nearby WDs is important for our understanding of stellar and galactic evolution, as well as the study of explosive phenomena. In an attempt to uncover these hidden WDs, we present intermediate resolution spectroscopy over the wavelength range of 3000-25000{AA} of 101 nearby M dwarfs (dMs), observed with the Very Large Telescope X-Shooter spectrograph. For each star we search for a hot component superimposed on the dM spectrum. X-Shooter has excellent blue sensitivity and thus can reveal a faint hot WD despite the brightness of its red companion. Visual examination shows no clear evidence of a WD in any of the spectra. We place upper limits on the effective temperatures of WDs that may still be hiding by fitting dM templates to the spectra and modeling the WD spectra. On average our survey is sensitive to WDs hotter than about 5300K. This suggests that the frequency of WD companions of Teff>~5300K with separation of the order of <~50 au among the local dM population is <3% at the 95% confidence level.
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- ID:
- ivo://CDS.VizieR/J/ApJS/162/346
- Title:
- Abundance gradients in the Galaxy
- Short Name:
- J/ApJS/162/346
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Six HII regions at galactocentric distances of R=10-15kpc have been observed in the far-IR emission lines of [OIII] (52{mu}m, 88{mu}m), [NIII] (57{mu}m), and [SIII] (19{mu}m) using the Kuiper Airborne Observatory. These observations have been combined with Very Large Array radio continuum observations of these sources to determine the abundances of O++, N++, and S++ relative to hydrogen. In addition, eight of the most recent sets of measurements of ionic line strengths in HII regions have been reanalyzed in order to attempt to reconcile differences in optical versus far-IR abundance determinations. We have in total 168 sets of observations of 117 HII regions in our analysis.
- ID:
- ivo://CDS.VizieR/J/ApJ/900/4
- Title:
- Abundances and ages of stars in the Milky Way bulge
- Short Name:
- J/ApJ/900/4
- Date:
- 14 Mar 2022 07:37:10
- Publisher:
- CDS
- Description:
- The age and chemical characteristics of the Galactic bulge link to the formation and evolutionary history of the Galaxy. Data-driven methods and large surveys enable stellar ages and precision chemical abundances to be determined for vast regions of the Milky Way, including the bulge. Here, we use the data-driven approach of The Cannon, to infer the ages and abundances for 125367 stars in the Milky Way, using spectra from Apache Point Observatory Galaxy Evolution Experiment (apogee) DR14. We examine the ages and metallicities of 1654 bulge stars within R_GAL_<3.5kpc. We focus on fields with b<12{deg}, and out to longitudes of l<15{deg}. We see that stars in the bulge are about twice as old ({tau}=8Gyr), on average, compared to those in the solar neighborhood ({tau}=4Gyr), with a larger dispersion in [Fe/H] (~0.38 compared to 0.23dex). This age gradient comes primarily from the low-{alpha} stars. Looking along the Galactic plane, the very central field in the bulge shows by far the largest dispersion in [Fe/H] ({sigma}[Fe/H]~0.4dex) and line-of- sight velocity ({sigma}vr~90km/s), and simultaneously the smallest dispersion in age. Moving out in longitude, the stars become kinematically colder and less dispersed in [Fe/H], but show a much broader range of ages. We see a signature of the X-shape within the bulge at a latitude of b=8{deg}, but not at b=12{deg}. Future apogee and other survey data, with larger sampling, affords the opportunity to extend our approach and study in more detail, to place stronger constraints on models of the Milky Way.
- ID:
- ivo://CDS.VizieR/J/ApJ/900/146
- Title:
- Abundances in 2 metal-poor GCs, M53 & NGC5053
- Short Name:
- J/ApJ/900/146
- Date:
- 02 Feb 2022 13:00:59
- Publisher:
- CDS
- Description:
- We search for extratidal stars around two metal-poor Galactic globular clusters, M53 and NGC 5053, using the near-infrared APOGEE spectra. Applying the t-distributed stochastic neighbor embedding (t-SNE) algorithm on the chemical abundances and radial velocities results in identification of two isolated stellar groups composed of cluster member stars in the t-SNE projection plane. With additional selection criteria of radial velocity, location in the color-magnitude diagram, and abundances from a manual chemical analysis, we find a total of 73 cluster member candidates; seven extratidal stars are found beyond the tidal radii of the two clusters. The extratidal stars around the clusters tend to be located along the leading direction of the cluster proper motion, and the individual proper motion of these stars also seems to be compatible to those of clusters. Interestingly, we find that one extratidal star of NGC 5053 is located on the southern outskirts of M53, which is part of common stellar envelope by the tidal interaction between two clusters. We discuss the nature of this star in the context of the tidal interaction between two clusters. We find apparent Mg-Al anticorrelations with a clear gap and spread (~0.9dex) in Al abundances for both clusters, and a light Si abundance spread (~0.3dex) for NGC 5053. Since all extratidal stars have Mg-enhanced and Al-depleted features, they could be first-generation stars of two globular clusters. Our results support that M53 and NGC5053 originated in dwarf galaxies and are surrounded by extended stellar substructures of more numerous populations of clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/865/44
- Title:
- Abundances of evolved stars from IGRINS. I.
- Short Name:
- J/ApJ/865/44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have derived elemental abundances of three field red horizontal branch stars using high-resolution (R~45000), high signal-to-noise ratio (S/N>~200) H- and K-band spectra obtained with the Immersion Grating Infrared Spectrograph (IGRINS). We have determined the abundances of 21 elements, including {alpha} (Mg, Si, Ca, S), odd-Z (Na, Al, P, K), Fe-group (Sc, Ti, Cr, Co, Ni), neutron-capture (Ce, Nd, Yb), CNO-group elements. S, P, and K are determined for the first time in these stars. H- and K-band spectra provide a substantial number of S I lines, which potentially can lead to a more robust exploration of the role of sulfur in the cosmochemical evolution of the Galaxy. We have also derived ^12^C/^13^C ratios from synthetic spectra of the first-overtone ^12^CO (2-0) and (3-1) and ^13^CO (2-0) lines near 23440{AA} and ^13^CO (3-1) lines at about 23730{AA}. Comparison of our results with the ones obtained from the optical region suggests that the IGRINS high-resolution H- and K-band spectra offer more internally self-consistent line abundances of the same species for several elements, especially the {alpha}-elements. This in turn provides more reliable abundances for the elements with analytical difficulties in the optical spectral range.
- ID:
- ivo://CDS.VizieR/J/ApJ/872/137
- Title:
- Abundances of red clump & RGB stars with APOGEE
- Short Name:
- J/ApJ/872/137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Internal mixing on the giant branch is an important process which affects the evolution of stars and the chemical evolution of the galaxy. While several mechanisms have been proposed to explain this mixing, better empirical constraints are necessary. Here, we use [C/N] abundances in 26097 evolved stars from the SDSS-IV/APOGEE-2 DR14 to trace mixing and extra mixing in old field giants with -1.7<[Fe/H]<0.1. We show that the APOGEE [C/N] ratios before any dredge-up occurs are metallicity dependent, but that the change in [C/N] at the first dredge-up is metallicity independent for stars above [Fe/H]~-1. We identify the position of the red giant branch (RGB) bump as a function of metallicity, note that a metallicity-dependent extra mixing episode takes place for low-metallicity stars ([Fe/H]{<}-0.4) 0.14dex in logg above the bump, and confirm that this extra mixing is stronger at low metallicity, reaching {Delta}[C/N]=0.58dex at [Fe/H]=-1.4. We show evidence for further extra mixing on the upper giant branch, well above the bump, among the stars with [Fe/H]{<}-1.0. This upper giant branch mixing is stronger in the more metal-poor stars, reaching 0.38 dex in [C/N] for each 1.0dex in logg. The APOGEE [C/N] ratios for red clump (RC) stars are significantly higher than for stars at the tip of the RGB, suggesting additional mixing processes occur during the helium flash or that unknown abundance zero points for C and N may exist among the RC sample. Finally, because of extra mixing, we note that current empirical calibrations between [C/N] ratios and ages cannot be naively extrapolated for use in low-metallicity stars specifically for those above the bump in the luminosity function.
- ID:
- ivo://CDS.VizieR/J/ApJ/819/103
- Title:
- Abundances of two very metal-poor stars
- Short Name:
- J/ApJ/819/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From high resolution (R~=45000), high signal-to-noise ratio (S/N>400) spectra gathered with the Immersion Grating Infrared Spectrograph (IGRINS) in the H and K photometric bands, we have derived elemental abundances of two bright, well-known metal-poor halo stars: the red giant HD 122563 and the subgiant HD 140283. Since these stars have metallicities approaching [Fe/H]=-3, their absorption features are generally very weak. Neutral-species lines of Mg, Si, S and Ca are detectable, as well as those of the light odd-Z elements Na and Al. The derived IR-based abundances agree with those obtained from optical-wavelength spectra. For Mg and Si the abundances from the infrared transitions are improvements to those derived from shorter wavelength data. Many useful OH and CO lines can be detected in the IGRINS HD 122563 spectrum, from which derived O and C abundances are consistent to those obtained from the traditional [OI] and CH features. IGRINS high resolutions H- and K-band spectroscopy offers promising ways to determine more reliable abundances for additional metal-poor stars whose optical features are either not detectable, or too weak, or are based on lines with analytical difficulties.
- ID:
- ivo://CDS.VizieR/J/AJ/139/1542
- Title:
- A catalog of MIPSGAL disk and ring sources
- Short Name:
- J/AJ/139/1542
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 416 extended, resolved, disk and ringlike objects as detected in the MIPSGAL 24um survey of the Galactic plane. This catalog is the result of a search in the MIPSGAL image data for generally circularly symmetric, extended "bubbles" without prior knowledge or expectation of their physical nature. Most of the objects have no extended counterpart at 8um or 70um, with less than 20% detections at each wavelength. For the 54 objects with central point sources, the sources are nearly always seen in all Infrared Array Camera bands. About 70 objects (16%) have been previously identified, with another 35 listed as Infrared Astronomical Satellite sources.
- ID:
- ivo://CDS.VizieR/V/138
- Title:
- A catalogue of cross-matched radio/infrared/X-ray sources
- Short Name:
- V/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of cross-correlated radio, infrared and X-ray sources using a very restrictive selection criteria with an IDL-based code developed by us. The significance of the observed coincidences was evaluated through Monte Carlo simulations of synthetic sources following a well-tested protocol. We found 3320 coincident radio/X-ray sources with a high statistical significance characterized by the sum of error-weighted coordinate differences. For 997 of them, 2MASS counterparts were found. The percentage of chance coincidences is less than 1%. X-ray hardness ratios of well-known populations of objects were used to provide a crude representation of their X-ray spectrum and to make a preliminary diagnosis of the possible nature of unidentified X-ray sources. The results support the fact that the X-ray sky is largely dominated by Active Galactic Nuclei at high galactic latitudes (|b|>=10deg). At low galactic latitudes (|b|<=10deg) most of unidentified X-ray sources (~94%) lie at |b|>=2deg. This result suggests that most of the unidentified sources found toward the Milky Way plane are galactic objects. Well-known and unidentified sources were classified in different tables with their corresponding radio/infrared and X-ray properties. These tables are intended as a useful tool for researchers interested in particular identifications.
- ID:
- ivo://CDS.VizieR/J/A+A/505/405
- Title:
- A catalogue of Spitzer dark clouds
- Short Name:
- J/A+A/505/405
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The majority of stars form in clusters. Therefore a comprehensive view of star formation requires understanding the initial conditions for cluster formation. The goal of our study is to shed light on the physical properties of infrared dark clouds (IRDCs) and the role they play in the formation of stellar clusters. This article, the first of a series dedicated to the study of IRDCs, describes techniques developed to establish a complete catalogue of Spitzer IRDCs in the Galaxy. We have analysed Spitzer GLIMPSE and MIPSGAL data to identify a complete sample of IRDCs in the region of Galactic longitude and latitude 10{deg}<|l|<65{deg} and |b|<1{deg}. From the 8um observations we have constructed opacity maps and used a newly developed extraction algorithm to identify structures above a column density of N_H2_=1x10^22^cm^-2^. The 24um data are then used to characterize the star formation activity of each extracted cloud. A total of 11303 clouds have been extracted. A comparison with the existing MSX based catalogue of IRDCs shows that 80% of these Spitzer dark clouds were previously unknown. The algorithm also extracts ~20000 to 50000 fragments within these clouds, depending on detection threshold used.A first look at the MIPSGAL data indicates that between 20% and 68% of these IRDCs show 24um point-like association. This new database provides an important resource for future studies aiming to understand the initial conditions of star formation in the Galaxy.
