J/MNRAS/327/918 CaII in extragalactic red giants (Tolstoy+, 2001)
Using the Ca II triplet to trace abundance variations in individual red giant
branch stars in three nearby galaxies.
Tolstoy E., Irwin M.J., Cole A.A., Pasquini L., Gilmozzi R., Gallagher J.S.
<Mon. Not. R. Astron. Soc. 327, 918 (2001)>
=2001MNRAS.327..918T 2001MNRAS.327..918T
ADC_Keywords: Galaxies, nearby ; Stars, giant ; Radial velocities ; Abundances
Keywords: galaxies: individual: Sculptor - galaxies: individual: Fornax -
galaxies: individual: NGC 6822 galaxies: kinematics and dynamics -
Local Group - infrared: galaxies
Abstract:
Spectroscopic abundance determinations for stars spanning a Hubble
time in age are necessary in order to determine unambiguously the
evolutionary histories of galaxies. Using FORS1 in multi-object
spectroscopy mode on ANTU (UT1) at the ESO VLT on Paranal, we have
obtained near-infrared spectra from which we have measured the
equivalent widths of the two strongest Ca II triplet lines to
determine metal abundances for a sample of red giant branch stars,
selected from ESO NTT optical (I, V-I) photometry of three nearby
Local Group galaxies: the Sculptor dwarf spheroidal, the Fornax dwarf
spheroidal and the dwarf irregular NGC 6822. The summed equivalent
width of the two strongest lines in the Ca II triplet absorption-line
feature, centred at 8500Å, can be readily converted into an [Fe/H]
abundance using the previously established calibrations by Armandroff
& Da Costa (1991AJ....101.1329A 1991AJ....101.1329A) and Rutledge, Hesser & Stetson (1997,
Cat. J/PASP/109/883). We have measured metallicities for 37 stars in
Sculptor, 32 stars in Fornax and 23 stars in NGC 6822, yielding more
precise estimates of the metallicity distribution functions for these
galaxies than it is possible to obtain photometrically. In the case of
NGC 6822, this is the first direct measurement of the abundances of
the intermediate-age and old stellar populations. We find metallicity
spreads in each galaxy which are broadly consistent with the
photometric width of the red giant branch, although the abundances of
individual stars do not always appear to correspond to their colour.
This is almost certainly predominantly due to a highly variable star
formation rate with time in these galaxies, which results in a
non-uniform, non-globular-cluster-like evolution of the Ca/Fe ratio.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table5.dat 63 44 Sculptor results
table6.dat 63 33 Fornax result
table7.dat 63 26 NGC 6822 results
tablea1.dat 28 44 Sculptor positions
tablea2.dat 28 33 Fornax positions
tablea3.dat 28 26 NGC 6822 Positions
--------------------------------------------------------------------------------
See also:
I/185 : Giant branch of the Fornax dwarf spheroidal galaxy (Sagar+, 1990)
J/AJ/116/1922 : CaII H and K filter photometry. III. (Anthony-Twarog+, 1998)
J/PASP/109/883 : Globular metallicity scale. I. (Rutledge+ 1997)
Byte-by-byte Description of file: table5.dat table6.dat table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Name Star designation (G1)
8 A1 --- n_Name [*$p+|] Note (1)
10- 13 F4.1 mag Imag I magnitude
15- 18 F4.2 mag V-I V-I colour index
20- 23 F4.2 0.1nm EWCaII Summed equivalent width of the two strongest
lines in the Ca II triplet absorption-line
feature, 8542Å+8662Å
25- 28 F4.2 0.1nm e_EWCaII rms uncertainty on EWCaII
30- 34 F5.2 Sun [Fe/H] ? Metallicity
36- 39 F4.2 Sun e_[Fe/H] ? rms uncertainty on [Fe/H]
41- 46 F6.1 km/s RV Measured radial velocity
48- 51 F4.1 km/s e_RV rms uncertainty on RV
53- 56 I4 km/s Offset Offset of the star position in a through-slit
image to correct the radial velocity
58- 63 F6.1 km/s RVc Corrected radial velocity (RV + Offset)
--------------------------------------------------------------------------------
Note (1): Notes as follows:
* = Too blue to be an RGB star;
not included in Fig. 12. (table5) or Fig. 15 (table6)
$ = Probably not a Sculptor member, from radial velocity;
not included in Fig. 12.
p = Probably a horizontal branch star in Sculptor;
not included in Fig. 12.
+ = This could be a Galactic M star, certainly not a Sculptor member;
not included in Fig. 12
| = Large error bars on equivalent width measurements;
plotted as crosses in Fig. 15. (table6) or Fig. 18 (table7)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea1.dat tablea2.dat tablea3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Name Star name (G1)
9- 10 I2 h RAh Right ascension (J2000.0)
12- 13 I2 min RAm Right ascension (J2000.0)
15- 18 F4.1 s RAs Right ascension (J2000.0)
20 A1 --- DE- Declination sign (J2000.0)
21- 22 I2 deg DEd Declination (J2000.0)
24- 25 I2 arcmin DEm Declination (J2000.0)
27- 28 I2 arcsec DEs Declination (J2000.0)
--------------------------------------------------------------------------------
Global notes:
Note (G1): Nomenclature:
-- In tables 5 and a1: The nomenclature for the stars is that stars
with c1 or c2 before a number are taken from the central field
[a distinction is made between the two susi2 chips, i.e. c1 (east)
and c2 (west)]. The north-eastern field is o1 and the south-western
one is o2. These stars are identified as
[TIC2001] Sculptor aN-NNN in Simbad.
-- In tables 6 and a2: These stars are identified as
[TIC2001] Fornax aN-NNN in Simbad.
-- In tables 7 and a3: The nomenclature for the stars is that stars
with the prefix s1 are from the eastern half of the NTT field, and
those with the prefix s2 are from the western half of the field.
Those stars with prefix s1b refer to a second series of observations
on the eastern field, but for some reason they were of much poorer
signal-to-noise ratio than the s1 data. These stars are identified as
[TIC2001] NGC 6822 aN-NNN in Simbad.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) James Marcout, Patricia Bauer [CDS] 30-Jan-2002