7 research outputs found
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New families in our Solar neighborhood: applying Gaussian Mixture models for objective classification of structures in the Milky Way and in simulations
No full textThe standard picture of galaxy formation motivates the decomposition of the
Milky Way into 3--4 stellar populations with distinct kinematic and elemental
abundance distributions: the thin disk, thick disk, bulge, and stellar halo. To
test this idea, we construct a Gaussian mixture model (GMM) for both simulated
and observed stars in the Solar neighborhood, using measured velocities and
iron abundances (i.e., an augmented Toomre diagram) as the distributions to be
decomposed. We compare results for the Gaia-APOGEE DR16 crossmatch catalog of
the Solar neighborhood with those from a suite of synthetic Gaia-APOGEE
crossmatches constructed from FIRE-2 cosmological simulations of Milky Way-mass
galaxies. We find that in both the synthetic and real data, the best-fit GMM
uses five independent components, some of whose properties resemble the
standard populations predicted by galaxy formation theory. Two components can
be identified unambiguously as the thin disk and another as the halo. However,
instead of a single counterpart to the thick disk, there are three intermediate
components with different age and alpha abundance distributions (although these
data are not used to construct the model). We use decompositions of the
synthetic data to show that the classified components indeed correspond to
stars with different origins. By analogy with the simulated data, we show that
our mixture model of the real Gaia-APOGEE crossmatch distinguishes the
following components: (1) a classic thin disk of young stars on circular orbits
(46%), (2) thin disk stars heated by interactions with satellites (22%), (3, 4)
two components representing the velocity asymmetry of the alpha-enhanced thick
disk (27%), and (5) a stellar halo consistent with early, massive accretion
(4%)
Catalog of Integrated-Light Star Cluster Light Curves in TESS
No full textWe present the first integrated light, TESS-based light curves for star
clusters in the Milky Way, Small Magellanic Cloud, and Large Magellanic Cloud.
We explore the information encoded in these light curves, with particular
emphasis on variability. We describe our publicly available package ELK, which
is designed to extract the light curves by applying principal component
analysis to perform background light correction, and incorporating corrections
for TESS systematics, allowing us to detect variability on time scales shorter
than ~10 days. We perform a series of checks to ensure the quality of our light
curves, removing observations where systematics are identified as dominant
features, and deliver light curves for 348 previously-cataloged open and
globular clusters. Where TESS has observed a cluster in more than one observing
sectors, we provide separate light curves for each sector (for a total of 2204
light curves). We explore in detail the light curves of star clusters known to
contain high-amplitude Cepheid and RR Lyrae variable stars, and confirm that
the variability of these known variables is still detectable when summed
together with the light from thousands of other stars. We also demonstrate that
even some low-amplitude stellar variability is preserved when integrating over
a stellar population.Comment: 17 pages, 9 Figures, 3 Tables, Accepted to AAS Journal
New families in our Solar neighborhood: applying Gaussian Mixture models for objective classification of structures in the Milky Way and in simulations
No full textRecommended from our members
Open Cluster Chemical Homogeneity throughout the Milky Way
No full textThe 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 0.03.dex 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.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
APOGEE Data and Spectral Analysis from SDSS Data Release 16 : Seven Years of Observations including First Results from APOGEE-South
No full textThe spectral analysis and data products in Data Release 16 (DR16; 2019 December) from the high-resolution near-infrared Apache Point Observatory Galactic Evolution Experiment (APOGEE)-2/Sloan Digital Sky Survey (SDSS)-IV survey are described. Compared to the previous APOGEE data release (DR14; 2017 July), APOGEE DR16 includes about 200,000 new stellar spectra, of which 100,000 are from a new southern APOGEE instrument mounted on the 2.5 m du Pont telescope at Las Campanas Observatory in Chile. DR16 includes all data taken up to 2018 August, including data released in previous data releases. All of the data have been re-reduced and re-analyzed using the latest pipelines, resulting in a total of 473,307 spectra of 437,445 stars. Changes to the analysis methods for this release include, but are not limited to, the use of MARCS model atmospheres for calculation of the entire main grid of synthetic spectra used in the analysis, a new method for filling "holes"in the grids due to unconverged model atmospheres, and a new scheme for continuum normalization. Abundances of the neutron-capture element Ce are included for the first time. A new scheme for estimating uncertainties of the derived quantities using stars with multiple observations has been applied, and calibrated values of surface gravities for dwarf stars are now supplied. Compared to DR14, the radial velocities derived for this release more closely match those in the Gaia DR2 database, and a clear improvement in the spectral analysis of the coolest giants can be seen. The reduced spectra as well as the result of the analysis can be downloaded using links provided on the SDSS DR16 web page
The Seventeenth Data Release of the Sloan Digital Sky Surveys: Complete Release of MaNGA, MaStar and APOGEE-2 Data
No full textThis paper documents the seventeenth data release (DR17) from the Sloan Digital Sky Surveys; the fifth and final release from the fourth phase (SDSS-IV). DR17 contains the complete release of the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, which reached its goal of surveying over 10,000 nearby galaxies. The complete release of the MaNGA Stellar Library (MaStar) accompanies this data, providing observations of almost 30,000 stars through the MaNGA instrument during bright time. DR17 also contains the complete release of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) survey which publicly releases infra-red spectra of over 650,000 stars. The main sample from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), as well as the sub-survey Time Domain Spectroscopic Survey (TDSS) data were fully released in DR16. New single-fiber optical spectroscopy released in DR17 is from the SPectroscipic IDentification of ERosita Survey (SPIDERS) sub-survey and the eBOSS-RM program. Along with the primary data sets, DR17 includes 25 new or updated Value Added Catalogs (VACs). This paper concludes the release of SDSS-IV survey data. SDSS continues into its fifth phase with observations already underway for the Milky Way Mapper (MWM), Local Volume Mapper (LVM) and Black Hole Mapper (BHM) surveys.40 pages, 8 figures, 6 tables. In press at ApJSS (arxiv v2 corrects some minor typos and updates references
The 16th data release of the Sloan Digital Sky Surveys:first release from the APOGEE-2 Southern Survey and full release of eBOSS Spectra
No full textInternational audienceThis paper documents the sixteenth data release (DR16) from the Sloan Digital Sky Surveys; the fourth and penultimate from the fourth phase (SDSS-IV). This is the first release of data from the southern hemisphere survey of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from APOGEE-2 North are also included. DR16 is also notable as the final data release for the main cosmological program of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project are released here. DR16 also includes all the data from the Time Domain Spectroscopic Survey (TDSS) and new data from the SPectroscopic IDentification of ERosita Survey (SPIDERS) programs, both of which were co-observed on eBOSS plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey (or the MaNGA Stellar Library "MaStar"). We also preview future SDSS-V operations (due to start in 2020), and summarize plans for the final SDSS-IV data release (DR17)
