TY - JOUR
T1 - Bayesian analysis of resolved stellar spectra
T2 - Application to MMT/Hectochelle observations of the Draco dwarf spheroidal
AU - Walker, Matthew G.
AU - Olszewski, Edward W.
AU - Mateo, Mario
N1 - Funding Information:
We acknowledge helpful discussions with Sergey Koposov, Alan McConnachie, Jorge Pe?arrubia, Nelson Caldwell, Evan Kirby and Alwin Mao. We further thank Evan Kirby for making available the velocities measured from Keck/DEIMOS spectra. We thank Andy Szentgyorgyi, Gabor Furesz and Dan Fabricant for building and maintaining Hectochelle. We thank the MMT and SAO staff, particularly Perry Berlind, Mike Calkins, Marc Lacasse, John McAfee, Ale Milone, Ricardo Ortiz, Dennis Smith, Bill Wyatt and all the observers who participated in the Hectochelle queue. Finally, we thank an anonymous referee for helpful suggestions. MGW is supported by National Science Foundation grants AST-1313045, AST-1412999 and in part by National Science Foundation Grant No. PHYS-1066293 and the hospitality of the Aspen Center for Physics, where portions of this work were completed. EO is supported by NSF grant AST-0807498 and AST-1313006. MM is supported by NSF grants AST-0808043 and AST-1312997. Table 5 include g-and i-band magnitudes from the ninth data release of SDSS. SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, NewMexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington and Yale University.
Funding Information:
We acknowledge helpful discussions with Sergey Koposov, Alan McConnachie, Jorge Peñarrubia, Nelson Caldwell, Evan Kirby and Alwin Mao. We further thank Evan Kirby for making available the velocities measured from Keck/DEIMOS spectra. We thank Andy Szentgyorgyi, Gabor Furesz and Dan Fabricant for building and maintaining Hectochelle. We thank the MMT and SAO staff, particularly Perry Berlind, Mike Calkins, Marc Lacasse, John McAfee, Ale Milone, Ricardo Ortiz, Dennis Smith, Bill Wyatt and all the observers who participated in the Hectochelle queue. Finally, we thank an anonymous referee for helpful suggestions. MGW is supported by National Science Foundation grants AST-1313045, AST-1412999 and in part by National Science Foundation Grant No. PHYS-1066293 and the hospitality of the Aspen Center for Physics, where portions of this work were completed. EO is supported by NSF grant AST-0807498 and AST-1313006. MM is supported by NSF grants AST-0808043 and AST-1312997.
Publisher Copyright:
© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.
PY - 2015/4/11
Y1 - 2015/4/11
N2 - We introduce a Bayesian method for fitting faint, resolved stellar spectra in order to obtain simultaneous estimates of redshift and stellar-atmospheric parameters. We apply the method to thousands of spectra - covering 5160-5280 Å at resolution R ~ 20 000 - that we have acquired with the MMT/Hectochelle fibre spectrograph for red giant and horizontal branch candidates along the line of sight to the Milky Way's dwarf spheroidal satellite in Draco. The observed stars subtend an area of ~4 deg2, extending ~3 times beyond Draco's nominal 'tidal' radius. For each spectrum, we tabulate the first four moments - central value, variance, skewness and kurtosis - of posterior probability distribution functions representing estimates of the following physical parameters: line-of-sight velocity (vlos), effective temperature (Teff), surface gravity (log g) and metallicity ([Fe/H]). After rejecting low-quality measurements, we retain a new sample consisting of 2813 independent observations of 1565 unique stars, including 1879 observations for 631 stars with (as many as 13) repeat observations. Parameter estimates have median random errors of σvlos = 0.88 km s-1, σTeff = 162 K, σlog g = 0.37 dex and σ[Fe/H] = 0.20 dex. Our estimates of physical parameters distinguish ~470 likely Draco members from interlopers in the Galactic foreground.
AB - We introduce a Bayesian method for fitting faint, resolved stellar spectra in order to obtain simultaneous estimates of redshift and stellar-atmospheric parameters. We apply the method to thousands of spectra - covering 5160-5280 Å at resolution R ~ 20 000 - that we have acquired with the MMT/Hectochelle fibre spectrograph for red giant and horizontal branch candidates along the line of sight to the Milky Way's dwarf spheroidal satellite in Draco. The observed stars subtend an area of ~4 deg2, extending ~3 times beyond Draco's nominal 'tidal' radius. For each spectrum, we tabulate the first four moments - central value, variance, skewness and kurtosis - of posterior probability distribution functions representing estimates of the following physical parameters: line-of-sight velocity (vlos), effective temperature (Teff), surface gravity (log g) and metallicity ([Fe/H]). After rejecting low-quality measurements, we retain a new sample consisting of 2813 independent observations of 1565 unique stars, including 1879 observations for 631 stars with (as many as 13) repeat observations. Parameter estimates have median random errors of σvlos = 0.88 km s-1, σTeff = 162 K, σlog g = 0.37 dex and σ[Fe/H] = 0.20 dex. Our estimates of physical parameters distinguish ~470 likely Draco members from interlopers in the Galactic foreground.
KW - Galaxies: dwarf
KW - Galaxies: individual: Draco
KW - Galaxies: kinematics and dynamics
KW - Local Group
KW - Methods: data analysis
KW - Techniques: spectroscopic
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U2 - 10.1093/mnras/stv099
DO - 10.1093/mnras/stv099
M3 - Article
AN - SCOPUS:85015660175
VL - 448
SP - 2717
EP - 2732
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 3
ER -