- ID:
- ivo://CDS.VizieR/J/ApJ/894/5
- Title:
- APOGEE2-N NIR spectra of B-type stars
- Short Name:
- J/ApJ/894/5
- Date:
- 19 Jan 2022 00:59:33
- Publisher:
- CDS
- Description:
- We present a semi-empirical spectral classification scheme for normal B-type stars using near-infrared (NIR) spectra (1.5-1.7{mu}m) from the Sloan Digital Sky Survey Apache Point Observatory Galaxy Evolution Experiment (APOGEE2)-N data release 14 (DR14) database. The main motivation for working with B-type stars is their importance in the evolution of young stellar clusters; however, we also take advantage of having a numerous sample (316 stars) of B-type star candidates in APOGEE2-N, for which we also have optical (3600-9100{AA}) counterparts from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey. By first obtaining an accurate spectral classification of the sources using the LAMOST DR3 spectra and the canonical spectral classification scheme, we found a linear relation between optical spectral types and the equivalent widths of the hydrogen lines of the Brackett series in the APOGEE2-N NIR spectra. This relation extends smoothly from a similar relation for O and early B stars found by Roman-Lopes+ (2018, J/ApJ/855/68). This way, we obtain a catalog of B-type sources with features in both the optical and NIR and a classification scheme refined down to one spectral subclass.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/501
- Title:
- APOGEE N-rich stars in inner Galaxy
- Short Name:
- J/MNRAS/465/501
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Formation of globular clusters (GCs), the Galactic bulge, or galaxy bulges in general is an important unsolved problem in Galactic astronomy. Homogeneous infrared observations of large samples of stars belonging to GCs and the Galactic bulge field are one of the best ways to study these problems. We report the discovery by APOGEE (Apache Point Observatory Galactic Evolution Experiment) of a population of field stars in the inner Galaxy with abundances of N, C, and Al that are typically found in GC stars. The newly discovered stars have high [N/Fe], which is correlated with [Al/Fe] and anticorrelated with [C/Fe]. They are homogeneously distributed across, and kinematically indistinguishable from, other field stars within the same volume. Their metallicity distribution is seemingly unimodal, peaking at [Fe/H]~-1, thus being in disagreement with that of the Galactic GC system. Our results can be understood in terms of different scenarios. N-rich stars could be former members of dissolved GCs, in which case the mass in destroyed GCs exceeds that of the surviving GC system by a factor of ~8. In that scenario, the total mass contained in so-called 'first-generation' stars cannot be larger than that in 'second-generation' stars by more than a factor of ~9 and was certainly smaller. Conversely, our results may imply the absence of a mandatory genetic link between 'second-generation' stars and GCs. Last, but not least, N-rich stars could be the oldest stars in the Galaxy, the by-products of chemical enrichment by the first stellar generations formed in the heart of the Galaxy.
- ID:
- ivo://CDS.VizieR/J/ApJ/903/55
- Title:
- APOGEE parameters through 83 open clusters
- Short Name:
- J/ApJ/903/55
- Date:
- 15 Mar 2022
- Publisher:
- CDS
- Description:
- The chemical homogeneity of surviving stellar clusters contains important clues about interstellar medium (ISM) mixing efficiency, star formation, and the enrichment history of the Galaxy. Existing measurements in a handful of open clusters suggest homogeneity in several elements at the 0.03dex level. Here we present (I) a new cluster member catalog based only on APOGEE radial velocities and Gaia-DR2 proper motions, (II) improved abundance uncertainties for APOGEE cluster members, and (III) the dependence of cluster homogeneity on Galactic and cluster properties, using abundances of eight elements from the APOGEE survey for 10 high-quality clusters. We find that cluster homogeneity is uncorrelated with Galactocentric distance, |Z|, age, and metallicity. However, velocity dispersion, which is a proxy for cluster mass, is positively correlated with intrinsic scatter at relatively high levels of significance for [Ca/Fe] and [Mg/Fe]. We also see a possible positive correlation at a low level of significance for [Ni/Fe], [Si/Fe], [Al/Fe], and [Fe/H], while [Cr/Fe] and [Mn/Fe] are uncorrelated. The elements that show a correlation with velocity dispersion are those that are predominantly produced by core-collapse supernovae (CCSNe). However, the small sample size and relatively low correlation significance highlight the need for follow-up studies. If borne out by future studies, these findings would suggest a quantitative difference between the correlation lengths of elements produced predominantly by Type Ia SNe versus CCSNe, which would have implications for Galactic chemical evolution models and the feasibility of chemical tagging.
- ID:
- ivo://CDS.VizieR/J/MNRAS/460/3179
- Title:
- APOGEE stars distance and extinction
- Short Name:
- J/MNRAS/460/3179
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using a Bayesian technology, we derived distances and extinctions for over 100000 red giant stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey by taking into account spectroscopic constraints from the APOGEE stellar parameters and photometric constraints from Two Micron All-Sky Survey, as well as a prior knowledge on the Milky Way. Derived distances are compared with those from four other independent methods, the Hipparcos parallaxes, star clusters, APOGEE red clump stars, and asteroseismic distances from APOKASC and Stromgren survey for Asteroseismology and Galactic Archaeology catalogues. These comparisons covers four orders of magnitude in the distance scale from 0.02 to 20kpc. The results show that our distances agree very well with those from other methods: the mean relative difference between our Bayesian distances and those derived from other methods ranges from -4.2 per cent to +3.6 per cent, and the dispersion ranges from 15 per cent to 25 per cent. The extinctions towards all stars are also derived and compared with those from several other independent methods: the Rayleigh-Jeans Colour Excess (RJCE) method, Gonzalez's 2D extinction map, as well as 3D extinction maps and models. The comparisons reveal that, overall, estimated extinctions agree very well, but RJCE tends to overestimate extinctions for cool stars and objects with low logg.
- ID:
- ivo://CDS.VizieR/J/A+A/629/A34
- Title:
- APOGEE stars members of 35 star clusters
- Short Name:
- J/A+A/629/A34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The vast volume of data generated by modern astronomical surveys offer test beds for the application of machine learning. In these exploratory applications, it is important to evaluate potential existing tools and determine which ones are optimal to extract scientific knowledge from the available observations. This work aims to explore the possibility of using unsupervised clustering algorithms to separate stellar populations with distinct chemical patterns. Star clusters are likely the most chemically homogeneous populations in the Galaxy, and therefore any practical approach to identify distinct stellar populations should at least be able to separate clusters from each other. We have applied eight clustering algorithms combined with four dimensionality reduction strategies to discriminate automatically stellar clusters using chemical abundances of 13 elements. Our test-bed sample includes 18 stellar clusters with a total of 453 stars. We have applied statistical tests showing that some pairs of clusters (e.g., NGC 2458-NGC 2420) are indistinguishable from each other when using the Apache Point Galactic Evolution Experiment (APOGEE) chemical abundances. However, for most clusters we are able to automatically assign membership with metric scores similar to previous works. The confusion level of the automatically selected clusters is consistent with statistical tests that demonstrate the impossibility of perfectly discriminating all the clusters from each other. These statistical tests, and confusion levels establish a limit for the prospect of blindly identifying stars born in the same cluster based solely on chemical abundances. We find that some of the algorithms explored are capable of blindly identify stellar populations with similar ages and chemical distributions in the APOGEE data. Even though we are not able to fully separate the clusters from each other, the main confusion arises from clusters with similar ages. Since there are stellar clusters that are chemically indistinguishable, our study supports the notion of extending weak chemical tagging involving families of clusters instead of individual clusters.
1086. APOGEE strings
- ID:
- ivo://CDS.VizieR/J/A+A/589/A80
- Title:
- APOGEE strings
- Short Name:
- J/A+A/589/A80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compare APOGEE radial velocities (RVs) of young stars in the Orion A cloud with CO line gas emission and find a correlation between the two at large scales in agreement with previous studies. However, at smaller scales we find evidence for the presence of a substructure in the stellar velocity field. Using a friends-of-friends approach we identify 37 stellar groups with almost identical RVs. These groups are not randomly distributed, but form elongated chains or strings of stars with five or more members with low velocity dispersion across lengths of 1-1.5pc. The similarity between the kinematic properties of the APOGEE strings and the internal velocity field of the chains of dense cores and fibers recently identified in the dense interstellar medium is striking and suggests that for most of the Orion A cloud, young stars keep memory of the parental gas substructure where they originated.
- ID:
- ivo://CDS.VizieR/J/AJ/156/84
- Title:
- APOGEE-2 survey of Orion Complex. II.
- Short Name:
- J/AJ/156/84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of spectroscopic and astrometric data from APOGEE-2 and Gaia DR2 (Cat. I/345) to identify structures toward the Orion Complex. By applying a hierarchical clustering algorithm to the six-dimensional stellar data, we identify spatially and/or kinematically distinct groups of young stellar objects with ages ranging from 1 to 12 Myr. We also investigate the star-forming history within the Orion Complex and identify peculiar subclusters. With this method we reconstruct the older populations in the regions that are currently largely devoid of molecular gas, such as Orion C (which includes the {sigma} Ori cluster) and Orion D (the population that traces Ori OB1a, OB1b, and Orion X). We report on the distances, kinematics, and ages of the groups within the Complex. The Orion D group is in the process of expanding. On the other hand, Orion B is still in the process of contraction. In {lambda} Ori the proper motions are consistent with a radial expansion due to an explosion from a supernova; the traceback age from the expansion exceeds the age of the youngest stars formed near the outer edges of the region, and their formation would have been triggered when they were halfway from the cluster center to their current positions. We also present a comparison between the parallax and proper-motion solutions obtained by Gaia DR2 and those obtained toward star-forming regions by the Very Long Baseline Array.
- ID:
- ivo://CDS.VizieR/J/ApJS/236/27
- Title:
- APOGEE-2 survey of Orion Complex (OSFC). I.
- Short Name:
- J/ApJS/236/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Orion Star-forming Complex (OSFC) is a central target for the APOGEE-2 Young Cluster Survey. Existing membership catalogs span limited portions of the OSFC, reflecting the difficulty of selecting targets homogeneously across this extended, highly structured region. We have used data from wide-field photometric surveys to produce a less biased parent sample of young stellar objects (YSOs) with infrared (IR) excesses indicative of warm circumstellar material or photometric variability at optical wavelengths across the full 420deg^2^ extent of the OSFC. When restricted to YSO candidates with H<12.4, to ensure S/N~100 for a six-visit source, this uniformly selected sample includes 1307 IR excess sources selected using criteria vetted by Koenig & Leisawitz (2014ApJ...791..131K) and 990 optical variables identified in the Pan-STARRS1 3{pi} survey: 319 sources exhibit both optical variability and evidence of circumstellar disks through IR excess. Objects from this uniformly selected sample received the highest priority for targeting, but required fewer than half of the fibers on each APOGEE-2 plate. We filled the remaining fibers with previously confirmed and new color-magnitude selected candidate OSFC members. Radial velocity measurements from APOGEE-1 and new APOGEE-2 observations taken in the survey's first year indicate that ~90% of the uniformly selected targets have radial velocities consistent with Orion membership. The APOGEE-2 Orion survey will include >1100 bona fide YSOs whose uniform selection function will provide a robust sample for comparative analyses of the stellar populations and properties across all sub-regions of Orion.
1089. APOGLIMPSE Archive
- ID:
- ivo://irsa.ipac/Spitzer/Catalog/GLIMPSE/APOGLMA
- Title:
- APOGLIMPSE Archive
- Short Name:
- APOGLMA
- Date:
- 26 Oct 2019 00:02:11
- Publisher:
- NASA/IPAC Infrared Science Archive
- Description:
- The APOGLIMPSE project re-images 53 square degrees of the inner Galactic plane that have also been targeted by the APOGEE/APOGEE-2 surveys - Sloan III and IV programs to obtain high resolution H band spectroscopy for hundreds of thousands of red giants. The data will be combined with the original GLIMPSE observations of the Galactic plane in 2004-2005 to measure the proper motions of the sources along the Galactic plane over the past decade.
1090. APOGLIMPSE Catalog
- ID:
- ivo://irsa.ipac/Spitzer/Catalog/GLIMPSE/APOGLMC
- Title:
- APOGLIMPSE Catalog
- Short Name:
- APOGLMC
- Date:
- 26 Oct 2019 00:02:11
- Publisher:
- NASA/IPAC Infrared Science Archive
- Description:
- The APOGLIMPSE project re-images 53 square degrees of the inner Galactic plane that have also been targeted by the APOGEE/APOGEE-2 surveys - Sloan III and IV programs to obtain high resolution H band spectroscopy for hundreds of thousands of red giants. The data will be combined with the original GLIMPSE observations of the Galactic plane in 2004-2005 to measure the proper motions of the sources along the Galactic plane over the past decade.
