21 research outputs found
Spectroscopic distance, mass, and age estimations for APOGEE DR17
We derive distances and masses of stars from the Sloan Digital Sky Survey
(SDSS) Apache Point Observatory Galactic Evolution Experiment (APOGEE) Data
Release 17 (DR17) using simple neural networks. Training data for distances
comes from Gaia EDR3, supplemented by literature distances for star clusters.
For masses, the network is trained using asteroseismic masses for evolved stars
and isochrone masses for main sequence stars. The models are trained on
effective temperature, surface gravity, metallicity and carbon and nitrogen
abundances. We found that our distance predictions have median fractional
errors that range from at low log g and at higher
log g with a standard deviation of . The mass predictions have a
standard deviation of . Using the masses, we derive ages for evolved
stars based on the correspondence between mass and age for giant stars given by
isochrones. The results are compiled into a Value Added Catalog (VAC) called
DistMass that contains distances and masses for 733901 independent spectra,
plus ages for 396548 evolved stars.Comment: 23 pages, 18 figure
Hubble Space Telescope Near-Ultraviolet Spectroscopy of Bright CEMP-s Stars
We present an elemental-abundance analysis, in the near-ultraviolet (NUV)
spectral range, for the bright carbon-enhanced metal-poor (CEMP) stars HD196944
(V = 8.40, [Fe/H] = -2.41) and HD201626 (V = 8.16, [Fe/H] = -1.51), based on
data acquired with the Space Telescope Imaging Spectrograph (STIS) on the
Hubble Space Telescope. Both of these stars belong to the sub-class CEMP-s, and
exhibit clear over-abundances of heavy elements associated with production by
the slow neutron-capture process. HD196944 has been well-studied in the optical
region, but we are able to add abundance results for six species (Ge, Nb, Mo,
Lu, Pt, and Au) that are only accessible in the NUV. In addition, we provide
the first determination of its orbital period, P=1325 days. HD201626 has only a
limited number of abundance results based on previous optical work -- here we
add five new species from the NUV, including Pb. We compare these results with
models of binary-system evolution and s-process element production in stars on
the asymptotic giant branch, aiming to explain their origin and evolution. Our
best-fitting models for HD 196944 (M1,i = 0.9Mo, M2,i = 0.86Mo, for
[Fe/H]=-2.2), and HD 201626 (M1,i = 0.9Mo , M2,i = 0.76Mo , for [Fe/H]=-2.2;
M1,i = 1.6Mo , M2,i = 0.59Mo, for [Fe/H]=-1.5) are consistent with the current
accepted scenario for the formation of CEMP-s stars.Comment: 25 pages, 13 figures; accepted for publication in Ap
A Tale of Two Disks: Mapping the Milky Way with the Final Data Release of APOGEE
We present new maps of the Milky Way disk showing the distribution of
metallicity ([Fe/H]), -element abundances ([Mg/Fe]), and stellar age,
using a sample of 66,496 red giant stars from the final data release (DR17) of
the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. We
measure radial and vertical gradients, quantify the distribution functions for
age and metallicity, and explore chemical clock relations across the Milky Way
for the low- disk, high- disk, and total population
independently. The low- disk exhibits a negative radial metallicity
gradient of dex kpc, which flattens with distance from
the midplane. The high- disk shows a flat radial gradient in
metallicity and age across nearly all locations of the disk. The age and
metallicity distribution functions shift from negatively skewed in the inner
Galaxy to positively skewed at large radius. Significant bimodality in the
[Mg/Fe]-[Fe/H] plane and in the [Mg/Fe]-age relation persist across the entire
disk. The age estimates have typical uncertainties of in (age)
and may be subject to additional systematic errors, which impose limitations on
conclusions drawn from this sample. Nevertheless, these results act as critical
constraints on galactic evolution models, constraining which physical processes
played a dominant role in the formation of the Milky Way disk. We discuss how
radial migration predicts many of the observed trends near the solar
neighborhood and in the outer disk, but an additional more dramatic evolution
history, such as the multi-infall model or a merger event, is needed to explain
the chemical and age bimodality elsewhere in the Galaxy.Comment: 41 pages, 32 figures, accepted to Ap
SDSS-IV MaStar: theoretical atmospheric parameters for the MaNGA stellar library
We calculate the fundamental stellar parameters effective temperature, surface gravity, and iron abundance â Teff, log g, [Fe/H] â for the final release of the Mapping Nearby Galaxies at APO (MaNGA) Stellar Library (MaStar), containing 59â266 per-visit-spectra for 24â290 unique stars at intermediate resolution (R ⌠1800) and high S/N (median = 96). We fit theoretical spectra from model atmospheres by both MARCS and BOSZ-ATLAS9 to the observed MaStar spectra, using the full spectral fitting code pPXF. We further employ a Bayesian approach, using a Markov Chain Monte Carlo (MCMC) technique to map the parameter space and obtain uncertainties. Originally in this paper, we cross match MaStar observations with Gaia photometry, which enable us to set reliable priors and identify outliers according to stellar evolution. In parallel to the parameter determination, we calculate corresponding stellar population models to test the reliability of the parameters for each stellar evolutionary phase. We further assess our procedure by determining parameters for standard stars such as the Sun and Vega and by comparing our parameters with those determined in the literature from high-resolution spectroscopy (APOGEE and SEGUE) and from lower resolution matching template (LAMOST). The comparisons, considering the different methodologies and S/N of the literature surveys, are favourable in all cases. Our final parameter catalogue for MaStar cover the following ranges: 2592 †Teff †32â983âK; â0.7 †log g †5.4âdex; â2.9 †[Fe/H] †1.0âdex and will be available with the last SDSS-IV Data Release, in 2021 December
The 16th Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra
This paper documents the 16th data release (DR16) from the Sloan Digital Sky Surveys (SDSS), 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 and new data from the SPectroscopic IDentification of ERosita Survey 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)
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The 16th Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra
This paper documents the 16th data release (DR16) from the Sloan Digital Sky Surveys (SDSS), 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 and new data from the SPectroscopic IDentification of ERosita Survey 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)
The 16th Data Release of the Sloan Digital Sky Surveys : First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra
This paper documents the 16th data release (DR16) from the Sloan Digital Sky Surveys (SDSS), 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 and new data from the SPectroscopic IDentification of ERosita Survey 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).Peer reviewe
The Seventeenth Data Release of the Sloan Digital Sky Surveys: Complete Release of MaNGA, MaStar and APOGEE-2 Data
This 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
SDSS-IV MaStar : a large and comprehensive empirical stellar spectral libraryâfirst release
We present the first release of the MaNGA Stellar Library (MaStar), which is a large, well-calibrated, high-quality empirical library covering the wavelength range 3622â10354 Ă
at a resolving power of R ~ 1800. The spectra were obtained using the same instrument as used by the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) project, by piggybacking on the Sloan Digital Sky Survey (SDSS-IV)/Apache Point Observatory Galaxy Evolution Experiment 2-N (APOGEE-2N) observations. Compared to previous empirical libraries, the MaStar library will have a higher number of stars and a more comprehensive stellar-parameter coverage, especially of cool dwarfs, low-metallicity stars, and stars with different [α/Fe], achieved by a sophisticated target-selection strategy that takes advantage of stellar-parameter catalogs from the literature. This empirical library will provide a new basis for stellar-population synthesis and is particularly well suited for stellar-population analysis of MaNGA galaxies. The first version of the library contains 8646 high-quality per-visit spectra for 3321 unique stars. Compared to photometry, the relative flux calibration of the library is accurate to 3.9% in g â r, 2.7% in r â i, and 2.2% in i â z. The data are released as part of SDSS Data Release 15. We expect the final release of the library to contain more than 10,000 stars.Publisher PDFPeer reviewe
The Milky Way tomography with APOGEE: intrinsic density distribution and structure of mono-abundance populations
The spatial distribution of mono-abundance populations (MAPs, selected in
[Fe/H] and [Mg/Fe]) reflect the chemical and structural evolution in a galaxy
and impose strong constraints on galaxy formation models. In this paper, we use
APOGEE data to derive the intrinsic density distribution of MAPs in the Milky
Way, after carefully considering the survey selection function. We find that a
single exponential profile is not a sufficient description of the Milky Way's
disc. Both the individual MAPs and the integrated disc exhibit a broken radial
density distribution; densities are relatively constant with radius in the
inner Galaxy and rapidly decrease beyond the break radius. We fit the intrinsic
density distribution as a function of radius and vertical height with a 2D
density model that considers both a broken radial profile and radial variation
of scale height (i.e., flaring). There is a large variety of structural
parameters between different MAPs, indicative of strong structure evolution of
the Milky Way. One surprising result is that high- MAPs show the
strongest flaring. The young, solar-abundance MAPs present the shortest scale
height and least flaring, suggesting recent and ongoing star formation confined
to the disc plane. Finally we derive the intrinsic density distribution and
corresponding structural parameters of the chemically defined thin and thick
discs. The chemical thick and thin discs have local surface mass densities of
5.620.08 and 15.690.32 , respectively,
suggesting a massive thick disc with a local surface mass density ratio between
thick to thin disc of 36%.Comment: 25 pages, 17 figures, accepted to publish in MNRA