ASPCAP: THE APOGEE STELLAR PARAMETER AND CHEMICAL ABUNDANCES PIPELINE

Context. The Gaia-ESO Survey has taken high-quality spectra of a subset of 100 000 stars observed with the Gaia spacecraft. The goal for this subset is to derive chemical abundances for these stars that will complement the astrometric data collected by Gaia. Deriving the chemical abundances requires that the stellar parameters be determined. Aims. We present a pipeline for deriving stellar parameters from spectra observed with the FLAMES-UVES spectrograph in its standard fibre-fed mode centred on 580 nm, as used in the Gaia-ESO Survey. We quantify the performance of the pipeline in terms of systematic offsets and scatter. In doing so, we present a general method for benchmarking stellar parameter determination pipelines. Methods. Assuming a general model of the errors in stellar parameter pipelines, together with a sample of spectra of stars whose stellar parameters are known from fundamental measurements and relations, we use a Markov chain Monte Carlo method to quantitatively test the pipeline. Results. We find that the pipeline provides parameter estimates with systematic errors on effective temperature below 100 K, on surface gravity below 0.1 dex, and on metallicity below 0.05 dex for the main spectral types of star observed in the Gaia-ESO Survey and tested here. The performance on red giants is somewhat lower. Conclusions. The pipeline performs well enough to fulfil its intended purpose within the Gaia-ESO Survey. It is also general enough that it can be put to use on spectra from other surveys or other spectrographs similar to FLAMES-UVES.

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Derivation of parameters for 3748 FGK stars using H-band spectra from APOGEE Data Release 14

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936296 ◽

2020 ◽

Vol 636 ◽

pp. A85

Author(s):

Pedro Sarmento ◽

Elisa Delgado Mena ◽

Bárbara Rojas-Ayala ◽

Sergi Blanco-Cuaresma

Keyword(s):

Main Sequence ◽

Near Infrared ◽

High Accuracy ◽

Chemical Abundances ◽

Stellar Spectrum ◽

Stellar Parameter ◽

Evolution Experiment ◽

Line Selection ◽

Selection For ◽

Band Spectra

Context. The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has observed the H-band spectra of over 200 000 stars with R ∼ 22 000. Aims. The main motivation for this work is to test an alternative method to the standard APOGEE pipeline (APOGEE Stellar Parameter and Chemical Abundances Pipeline, ASPCAP) to derive parameters in the near-infrared for FGK dwarfs. Methods. iSpec and Turbospectrum are used to generate synthetic spectra matching APOGEE observations and to determine the parameters through χ2 minimization. Results. We present spectroscopic parameters (Teff, [M/H], log g, vmic) for a sample of 3748 main-sequence and subgiant FGK stars, obtained from their APOGEE H-band spectra. Conclusions. We compare our output parameters with the ones obtained with ASPCAP for the same stellar spectrum, and find that the values agree within the expected uncertainties. A comparison with the optical samples California Planet Survey, High Accuracy Radial Velocity Planet Searcher – Guaranteed Time Observations, and PASTEL is also available, and median differences below 10 K for Teff and 0.2 dex for [M/H] are found. Reasons for these differences are explored. The full H-band line list, the line selection for the synthesis, and the synthesized spectra are available at the CDS, as are the calculated parameters and their estimated uncertainties.

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SSPP: SEGUE Stellar Parameter Pipeline

10.22323/1.146.0094 ◽

2013 ◽

Author(s):

Tim Beers ◽

Young Sun Lee

Keyword(s):

Stellar Parameter

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Bidimensional Spectroscopic Mapping and Chemical Abundances of the Star‐forming Dwarf Galaxy I Zw 18

The Astrophysical Journal ◽

10.1086/306374 ◽

1998 ◽

Vol 508 (1) ◽

pp. 248-261 ◽

Cited By ~ 44

Author(s):

José M. Vílchez ◽

Jorge Iglesias‐Páramo

Keyword(s):

Dwarf Galaxy ◽

Chemical Abundances ◽

Star Forming

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H2-Bearing Damped Lyman-α Systems as Tracers of Cosmological Chemical Evolution

Symposium - International Astronomical Union ◽

10.1017/s0074180900197669 ◽

2004 ◽

Vol 217 ◽

pp. 252-257

Author(s):

M. T. Murphy ◽

S. J. Curran ◽

J. K. Webb

Keyword(s):

Chemical Evolution ◽

Selection Effects ◽

Host Galaxies ◽

Chemical Abundances ◽

Physical Conditions ◽

Observational Selection ◽

Host Type ◽

Molecular Fraction ◽

Magnitude Variation

The chemical abundances in damped Lyman-α systems (DLAs) show more than 2 orders of magnitude variation at a given epoch, possibly because DLAs arise in a wide variety of host galaxies. This could significantly bias estimates of chemical evolution. We explore the possibility that DLAs in which H2 absorption is detected may trace cosmological chemical evolution more reliably since they may comprise a narrower set of physical conditions. The 9 known H2 absorption systems support this hypothesis: metallicity exhibits a faster, more well-defined evolution with redshift than in the general DLA population. The dust-depletion factor and, particularly, H2 molecular fraction also show rapid increases with decreasing redshift. We comment on possible observational selection effects which may bias this evolution. Larger samples of H2-bearing DLAs are clearly required and may constrain evolution of the UV background and DLA galaxy host type with redshift.

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Photometric methods for stellar parameter determinations

Physica Scripta ◽

10.1088/0031-8949/2008/t133/014019 ◽

2008 ◽

Vol T133 ◽

pp. 014019

Author(s):

M S Bessell

Keyword(s):

Stellar Parameter

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Chemical Abundances of Early Type Stars

Symposium - International Astronomical Union ◽

10.1017/s007418090011486x ◽

1998 ◽

Vol 188 ◽

pp. 224-225

Author(s):

S. Tanaka ◽

S. Kitamoto ◽

T. Suzuki ◽

K. Torii ◽

M.F. Corcoran ◽

...

Keyword(s):

Surface Layer ◽

Stellar Wind ◽

Nuclear Reactions ◽

X Rays ◽

Early Type ◽

Chemical Abundances ◽

X Ray ◽

Low Metallicity ◽

Early Type Stars

X-rays from early-type stars are emitted by the corona or the stellar wind. The materials in the surface layer of early-type stars are not contaminated by nuclear reactions in the stellar inside. Therefore, abundance study of the early-type stars provides us an information of the abundances of the original gas. However, the X-ray observations indicate low-metallicity, which is about 0.3 times of cosmic abundances. This fact raises the problem on the cosmic abundances.

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Chemical Enrichment and Central Star Properties

Symposium - International Astronomical Union ◽

10.1017/s0074180900172468 ◽

1993 ◽

Vol 155 ◽

pp. 572-572

Author(s):

C.Y. Zhang

Keyword(s):

Planetary Nebulae ◽

Central Star ◽

Agb Stars ◽

Physical Processes ◽

Chemical Abundances ◽

Core Mass ◽

Chemical Enrichment ◽

The Core ◽

Stellar Temperature ◽

Independent Parameters

We have selected a sample of planetary nebulae, for which the core masses are determined using distance-independent parameters (Zhang and Kwok 1992). The chemical abundances of He, N, O, and C are taken from the literature for them. Relationships of the ratios of He/H, N/O, and C/O with various stellar parameters of planetary nebulae (PN), such as the core mass, the mass of the core plus the ionized nebular gas, the stellar age and temperature, are examined. It is found that the N/O increases with increasing mass, while the C/O first increases and then decreases with the core mass. No strong correlation seems to exist between the He/H and the core mass. A correlation of the N/O and He/H with the stellar temperature exists. The current dredge-up theory for the progenitor AGB stars cannot satisfactorily account for these patterns of chemical enrichment in PN. Furthermore, the correlations of the N/O and He/H with the stellar age and temperature indicate that besides the dredge-ups in the RG and AGB stages, physical processes that happen in the planetary nebula stage may also play a role in forming the observed patterns of chemical enrichment in the planetary nebulae.

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Are “realistic” model atmospheres realistic enough?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310000529 ◽

2009 ◽

Vol 5 (S265) ◽

pp. 187-196 ◽

Cited By ~ 1

Author(s):

Bengt Gustafsson

Keyword(s):

Realistic Model ◽

Considerable Progress ◽

Observational Methods ◽

Construction Technology ◽

Mixing Length ◽

Late Type ◽

Chemical Abundances ◽

Stellar Spectra ◽

Analysis Methods ◽

Major Break

AbstractDuring the latest decades the number of papers on stellar chemical abundances has increased dramatically. This is basically reflecting the very great achievements in telescope- and spectrometer-construction technology. The analysis of the resulting stellar spectra, however, is still not up to the standard that is offered by the observational methods. Recent significant advances in the analysis methods (i.e., in constructing model atmospheres and model spectra to compare with the observed ones) is reviewed with the emphasis on the application to abundance analysis of late-type stars. It is found that the very considerable progress that have been made beyond mixing-length convection and LTE is a major break-through for physically consistent modeling. Still, however, further steps must be taken, in particular for the cooler stars, before the situation is fully satisifactory.

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Structure and dynamics of the Milky Way disk as revealed from the radial velocity distributions of APOGEE red clump stars

Proceedings of the International Astronomical Union ◽

10.1017/s174392131601173x ◽

2016 ◽

Vol 11 (S321) ◽

pp. 50-50

Author(s):

Daisuke Toyouchi ◽

Masashi Chiba

Keyword(s):

Near Infrared ◽

Milky Way ◽

Radial Velocities ◽

Galactocentric Distance ◽

Chemical Abundances ◽

Structure And Dynamics ◽

Evolution Experiment ◽

Dynamical Properties ◽

Red Clump ◽

Independent Work

AbstractWe investigate the structure and dynamics of the Milky Way (MW) disk stars based on the analysis of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) data, to infer the past evolution histories of the MW disk component(s) possibly affected by radial migration and/or satellite accretions. APOGEE is the first near-infrared spectroscopic survey for a large number of the MW disk stars, providing their radial velocities and chemical abundances without significant dust extinction effects. We here adopt red-clump (RC) stars (Bovy et al. 2014), for which the distances from the Sun are determined precisely, and analyze their radial velocities and chemical abundances in the MW disk regions covering from the Galactocentric distance, R, of 5 kpc to 14 kpc. We investigate their dynamical properties, such as mean rotational velocities, 〈Vφ〉 and velocity dispersions, as a function of R, based on the MCMC Bayesian method. We find that at all radii, the dynamics of alpha-poor stars, which are candidates of young disk stars, is much different from that of alpha-rich stars, which are candidates of old disk stars. We find that our Jeans analysis for our sample stars reveals characteristic spatial and dynamical properties of the MW disk, which are generally in agreement with the recent independent work by Bovy et al. (2015) but with a different method from ours.

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