J/MNRAS/456/4315 RGB stars in NGC 6822, Ca II triplet (Swan+, 2016)
Ca II triplet spectroscopy of RGB stars in NGC 6822:
kinematics and metallicities.
Swan J., Cole A.A., Tolstoy E., Irwin M.J.
<Mon. Not. R. Astron. Soc., 456, 4315-4327 (2016)>
=2016MNRAS.456.4315S 2016MNRAS.456.4315S (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Stars, giant ; Radial velocities ;
Equivalent widths ; Abundances, [Fe/H]
Keywords: galaxies: abundances - galaxies: dwarf - galaxies: irregular -
galaxies: kinematics and dynamics - galaxies: stellar content
Abstract:
We present a detailed analysis of the chemistry and kinematics of red
giants in the dwarf irregular galaxy NGC 6822. Spectroscopy at
∼8500Å was acquired for 72 red giant stars across two fields using
FORS2 at the VLT. Line-of-sight extinction was individually estimated
for each target star to accommodate the variable reddening across NGC
6822. The mean radial velocity was found to be
<vrad≥-52.8±2.2km/s with dispersion σv=24.1km/s, in
agreement with other studies. Ca ii triplet equivalent widths were
converted into [Fe/H] metallicities using a V magnitude proxy for
surface gravity. The average metallicity was <[Fe/H]≥-0.84±0.04
with dispersion σ=0.31dex and interquartile range 0.48. Our
assignment of individual reddening values makes our analysis more
sensitive to spatial variations in metallicity than previous studies.
We divide our sample into metal-rich and metal-poor stars; the former
were found to cluster towards small radii with the metal-poor stars
more evenly distributed across the galaxy. The velocity dispersion of
the metal-poor stars was found to be higher than that of the
metal-rich stars σvMP=27.4km/s; σvMR=21.1km/s);
combined with the age-metallicity relation this indicates that the
older populations have either been dynamically heated during their
lifetimes or were born in a less disc-like distribution than the
younger stars.. The low ratio vrot/σv suggests that within
the inner 10-arcmin, NGC 6822's stars are dynamically decoupled from
the HI gas, and possibly distributed in a thick disc or spheroid
structure.
Description:
The observations of NGC 6822 were made over several nights in late
2003 July and early August using the FORS2 instrument mounted on the
Yepun UT4 8m telescope of the ESO VLT in Chile.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea2.dat 90 72 Amalgamation of important parameters for our
72 NGC 6822 RGB stars
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See also:
J/ApJ/501/153 : VRB photometry of red supergiants (Massey 1998)
J/A+A/454/717 : C and AGB stars in NGC 6822 near-IR photometry (Kang+, 2006)
J/A+A/537/A108 : NGC 6822 AGB spectroscopic catalogue (Kacharov+, 2012)
J/MNRAS/428/2216 : JHKs photometry of AGB stars in NGC 6822 (Whitelock+, 2013)
Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- Star Star ID
6- 12 F7.3 deg RAdeg Right ascension (J2000)
14- 20 F7.3 deg DEdeg Declination (J2000)
22- 26 F5.2 mag Vmag V magnitude
28- 31 F4.2 mag e_Vmag rms uncertainty on Vmag
33- 38 F6.1 km/s RV Radial velocity
40- 42 F3.1 km/s e_RV rms uncertainty on RV
44- 48 F5.2 mag ITRGB Tip of the red giant branch (TRGB) I magnitude
50- 53 F4.2 mag e_ITRGB rms uncertainty on ITRGB
55- 58 F4.2 0.1nm SWCa Unweighted sum of the equivalent width of all
three lines (W8498+W8542+W8662)
60- 63 F4.2 0.1nm e_SWCa rms uncertainty on SWCa
65- 69 F5.2 mag VHB Horizonthal branch V magnitude
71- 74 F4.2 mag e_VHB rms uncertainty on VHB
76- 80 F5.2 [-] [Fe/H] Metallicity
82- 85 F4.2 [-] e_[Fe/H] rms uncertainty on [Fe/H]
87- 90 F4.2 0.1nm WMg Magnesium line width
(error is ∼0.1 for most cases)
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 07-Oct-2016