J/MNRAS/448/2717 Bayesian analysis of resolved stellar spectra (Walker+, 2015)
Bayesian analysis of resolved stellar spectra: application to MMT/Hectochelle
observations of the Draco dwarf spheroidal.
Walker M.G., Olszewski E.W., Mateo M.
<Mon. Not. R. Astron. Soc., 448, 2717-2732 (2015)>
=2015MNRAS.448.2717W 2015MNRAS.448.2717W (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Stars, giant ; Stars, horizontal branch ;
Spectroscopy ; Photometry, SDSS
Keywords: methods: data analysis - techniques: spectroscopic - galaxies: dwarf -
galaxies: individual: Draco - galaxies: kinematics and dynamics -
Local Group
Abstract:
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 5160-5280Å at resolution R∼20000 - 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 ∼4deg2, 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 (logg) 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
vlos=0.88km/s, Teff=162K, σlogg=0.37dex and
σ[Fe/H]=0.20dex. Our estimates of physical parameters
distinguish ∼470 likely Draco members from interlopers in the Galactic
foreground.
Description:
Our MMT/Hectochelle observations took place between April 2006 and May
2011, during which we observed 33 unique fibre configurations for
Draco. We observed nine of these fields on two separate occasions, and
henceforth we treat these repeat observations independently.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 117 2295 Hectochelle data from individual observations
table5.dat 78 1565 Hectochelle data with weighted means for stars
with multiple observations
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See also:
J/ApJS/145/245 : SDSS stars in Draco dwarf spheroidal galaxy (Rave+, 2003)
J/MNRAS/375/831 : Draco MegaCam, INT and HST photometry (Segall+, 2007)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right ascension (J2000)
4- 5 I2 min RAm Right ascension (J2000)
7- 11 F5.2 s RAs Right ascension (J2000)
13 A1 --- DE- Declination sign (J2000)
14- 15 I2 deg DEd Declination (J2000)
17- 18 I2 arcmin DEm Declination (J2000)
20- 23 F4.1 arcsec DEs Declination (J2000)
25- 34 F10.2 d HJD Heliocentric Julian date
36- 39 F4.1 --- S/N median signal-to-noise ratio per pixel
41- 46 F6.1 km/s vlos Model line-of-sight velocity in the
heliocentric rest frame (1)
48- 50 F3.1 km/s e_vlos rms uncertainty on vlos (2)
52- 55 F4.1 --- vlossk Third (skewness) moment for vlos
57- 59 F3.1 --- vlosku Fourth (kurtosis) moment for vlos
61- 64 I4 K Teff Model effective temperature (1)
66- 69 I4 K e_Teff rms uncertainty on Teff (2)
71- 74 F4.1 --- Teffsk Third (skewness) moment for Teff
76- 79 F4.1 --- Teffku Fourth (kurtosis) moment for Teff
81- 83 F3.1 [cm/s2] logg Model surface gravity (1)
85- 87 F3.1 [cm/s2] e_logg rms uncertainty on logg (2)
89- 92 F4.1 --- loggsk Third (skewness) moment for logg
94- 96 F3.1 --- loggku Fourth (kurtosis) moment for logg
98-102 F5.2 [-] [Fe/H] Model metallicity (1)
104-107 F4.2 [-] e_[Fe/H] rms uncertainty on [Fe/H] (2)
109-112 F4.1 [-] [Fe/H]sk Third (skewness) moment for [Fe/H]
114-116 F3.1 [-] [Fe/H]ku Fourth (kurtosis) moment for [Fe/H]
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Note (1): central value, i.e. first moment (mean) of the posterior probability
distribution function (PDF).
Note (2): square root of the second moment (square root of the variance).
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Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 h RAh Right ascension (J2000)
4- 5 I2 min RAm Right ascension (J2000)
7- 11 F5.2 s RAs Right ascension (J2000)
13 A1 --- DE- Declination sign (J2000)
14- 15 I2 deg DEd Declination (J2000)
17- 18 I2 arcmin DEm Declination (J2000)
20- 23 F4.1 arcsec DEs Declination (J2000)
25- 29 F5.2 mag gmag ?=0 SDSS g magnitude, corrected for extinction
31- 35 F5.2 mag imag ?=0 SDSS i magnitude, corrected for extinction
37- 42 F6.1 km/s vlos Estimates line-of-sight velocity in the
heliocentric rest frame
44- 46 F3.1 km/s e_vlos rms uncertainty on vlos
48- 51 I4 K Teff Estimates effective temperature
53- 56 I4 K e_Teff rms uncertainty on Teff
58- 60 F3.1 [cm/s2] logg Estimates surface gravity
62- 64 F3.1 [cm/s2] e_logg rms uncertainty on logg
66- 70 F5.2 [-] [Fe/H] Estimates metallicity
72- 75 F4.2 [-] e_[Fe/H] rms uncertainty on [Fe/H]
77- 78 I2 --- Nobs Number of observations
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 10-Sep-2015