Issue |
A&A
Volume 375, Number 3, September 2001
|
|
---|---|---|
Page(s) | 909 - 921 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20010863 | |
Published online | 15 September 2001 |
RR Lyrae stars in the Sagittarius dwarf galaxy: Period analysis*,**
1
DASGAL, Observatoire de Paris, 61 avenue de l'Observatoire, 75014 Paris, France
2
Centre d'Analyse des Images -INSU, France
Received:
19
April
2001
Accepted:
1
June
2001
We carried out a period analysis on ~3700 RR Lyrae stars on two Schmidt fields centred on , -7.1°)
and (6.6°, -10.8°) respectively, covering an area of ~50 deg2. These stars are distributed almost evenly between
the Sagittarius dwarf galaxy (Sgr) and the Milky Way. For Sgr members, the average periods are
and
for RRab and RRc stars respectively. This places Sgr in the long-period tail of the
Oosterhoff I group. We report the detection of 53 double-mode RR Lyrae stars (RRd) within
our sample. The magnitude of 40 of these stars
is consistent with membership in Sgr whereas 13 RRds are located within our Galaxy.
We also found 13 RR Lyraes (5 in Sgr and 8 in the Galaxy) exhibiting two closely spaced frequencies, most probably related to
non-radial pulsations.
The period distribution of the RR Lyrae
variables in Sgr is compared to those of other Milky Way satellites. We find a remarkable similarity between the RR Lyrae
populations in Sgr and the Large Magellanic Cloud (LMC), suggesting that these galaxies have similar horizontal branch morphologies.
This may indicate that Sgr
and the LMC started their formation under similar conditions.
Using various photometric indicators, we estimate the metallicity of the RR Lyrae stars in Sgr and find
dex with a dispersion of
0.5 dex around this value and a minor but significant population at ≲-2.0 dex.
We do not find evidence for a spatial metallicity
gradient in the RR Lyrae population of Sgr. From the spatial distribution of RR Lyraes, we find that the main body of Sgr contains
~4200 RRab stars. Assuming that population gradients are negligible in Sgr, we find
13.9
mag for the main body. If Sgr has been stripped of 50% of its mass through Galactic tides, as assumed by some models, it would imply
a total absolute magnitude of ~-14.7 mag for this galaxy. Such a luminosity would be consistent with the empirical
metallicity/luminosity relation for dwarf spheroidal galaxies.
Key words: stars: horizontal-branch / stars: population II / stars: variables: RR Lyr / galaxies: dwarf / galaxies: individual: Sagittarius dwarf / local group
© ESO, 2001
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