J/ApJ/736/146 Radial velocities of stars in Bootes I (Koposov+, 2011)
Accurate stellar kinematics at faint magnitudes: application to the Bootes I
dwarf spheroidal galaxy.
Koposov S.E., Gilmore G., Walker M.G., Belokurov V., Evans N.W.,
Fellhauer M., Gieren W., Geisler D., Monaco L., Norris J.E., Okamoto S.,
Penarrubia J., Wilkinson M., Wyse R.F.G., Zucker D.B.
<Astrophys. J., 736, 146 (2011)>
=2011ApJ...736..146K 2011ApJ...736..146K
ADC_Keywords: Galaxies, nearby ; Radial velocities ; Photometry, SDSS ;
Abundances, [Fe/H] ; Stars, fundamental
Keywords: galaxies: dwarf - galaxies: individual (Bootes I) -
galaxies: kinematics and dynamics - methods: data analysis -
techniques: radial velocities
Abstract:
We develop, implement, and characterize an enhanced data reduction
approach which delivers precise, accurate, radial velocities from
moderate resolution spectroscopy with the fiber-fed VLT/FLAMES+GIRAFFE
facility. This facility, with appropriate care, delivers radial
velocities adequate to resolve the intrinsic velocity dispersions of
the very faint dwarf spheroidal (dSph) galaxies. Importantly, repeated
measurements let us reliably calibrate our individual velocity errors
(0.2km/s≤δV≤5km/s) and directly detect stars with variable
radial velocities. We show, by application to the Bootes I dSph, that
the intrinsic velocity dispersion of this system is significantly
below 6.5km/s reported by previous studies. Our data favor a
two-population model of Bootes I, consisting of a majority "cold"
stellar component, with velocity dispersion 2.4+0.9-0.5km/s, and a
minority "hot" stellar component, with velocity dispersion ∼9km/s,
although we cannot completely rule out a single component distribution
with velocity dispersion 4.60.8-0.6km/s. We speculate that this
complex velocity distribution actually reflects the distribution of
velocity anisotropy in Bootes I, which is a measure of its formation
processes.
Description:
We used the FLAMES spectrograph at the 8.2m Kueyen (VLT/UT2) telescope
at Cerro Paranal, Chile, to acquire spectra of individual stellar
targets in Bootes I. Observations took place in service mode during
2009 February to March in fulfillment of ESO Programme 182.B-0372A
(PI: Gilmore). The Giraffe spectra sample the region 8180-9375Å, in
LR08 setup, including the prominent CaII-triplet (CaT) absorption
feature, with resolving power R∼6500.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 84 118 Observational data for all stars observed
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See also:
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
J/ApJ/723/1632 : Abundance spreads in Bootes I and Segue 1 (Norris+, 2010)
J/ApJ/711/350 : Metal-poor giant Boo-1137 abundances (Norris+, 2010)
J/AJ/136/2321 : Washington photometry of Bootes I stars (Hughes+, 2008)
J/MNRAS/380/281 : Galactic satellites spectroscopic survey (Martin+, 2007)
J/A+A/407/1157 : UVES sky atlas (Hanuschik+, 2003)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [0/117] Running sequence number
5- 23 A19 --- SDSS Star name (JHHMMSS.ss+DDMMSS.s)
25- 32 F8.4 deg RAdeg [209.8/210.3] Right ascension in decimal
degrees (J2000)
34- 40 F7.4 deg DEdeg [14.3/14.8] Declination in decimal degrees (J2000)
42- 45 F4.1 mag gmag [16.6/22.4] SDSS g-band magnitude
47- 50 F4.1 mag rmag SDSS r-band magnitude
52- 58 F7.2 km/s RV [-236/225]?=- Radial velocity
60- 63 F4.2 km/s e_RV [0.05/9.14]?=- RV uncertainty
65- 68 F4.2 --- Pvar [0/1]?=- Probability of detected radial
velocity variability
70- 73 I4 K Teff [4000/9000]?=- Effective temperature
75- 78 F4.1 [Sun] [Fe/H] [-2.5/0]?=- Fe/H abundance
80- 82 F3.1 [cm/s2] logg [1/4.5]?=- Surface gravity
84 A1 --- Mm [B] Best flag (1)
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Note (1): B marks the 37 stars which are highly probable Bootes I members,
i.e., those with log(g)<3.5, [Fe/H]←1.5, not showing any variability
according to our Bayes factor criterion and with small errors of their
radial velocity measurement σv<2.5km/s. See section 8 for
further explanations.
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 04-Jan-2013