| Issue |
A&A
Volume 468, Number 3, June IV 2007
Extended baselines for the IRAM Plateau de Bure interferometer: First results
|
|
|---|---|---|
| Page(s) | 973 - 978 | |
| Section | Extragalactic astronomy | |
| DOI | https://doi.org/10.1051/0004-6361:20067024 | |
| Published online | 11 April 2007 | |
The blue plume population in dwarf spheroidal galaxies*
Genuine blue stragglers or young stellar population?
1
INAF: Osservatorio Astronomico di Padova, vicolo dell'Osservatorio 5, 35122 Padova, Italy e-mail: [yazan.almomany;enrico.held;marco.gullieuszik;simone.zaggia]@oapd.inaf.it
2
European Southern Observatory, A. de Cordova 3107, Santiago, Chile e-mail: isaviane@eso.org
3
Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822, USA e-mail: rizzi@ifa.hawaii.edu
Received:
22
December
2006
Accepted:
3
April
2007
Aims.Blue stragglers (BSS) in the Milky Way field and globular/open
clusters are thought to be the product of either primordial or
collisional binary systems. In the context of dwarf spheroidal
galaxies it is hard to firmly disentangle a genuine BSS population
from young main sequence (MS) stars tracing a ∼
Gyr old star
forming episode.
Methods. Assuming that their blue plume populations are made of BSS,
we estimate the BSS frequency (
; as normalized
to the horizontal branch star counts) for 8 Local Group non
star-forming dwarf galaxies, using a compilation of ground and space
based photometry.
Results. (i) The BSS frequency in dwarf galaxies, at any given 
, is always higher than that in globular clusters of similar
luminosities; (ii) the BSS frequency for the lowest luminosity dwarf
galaxies is in excellent agreement with that observed in the Milky Way
halo and open clusters; and most interestingly (iii) derive a
statistically significant 
anti-correlation for dwarf galaxies, similar to that observed in
globular clusters.
Conclusions.The low density, almost collision-less, environments of our dwarf
galaxy sample allow us to infer (i) their very low dynamical
evolution; (ii) a negligible production of collisional BSS; and
consequently (iii) that their blue plumes are mainly made of
primordial binaries.
The dwarf galaxies 
anti-correlation
can be used as a discriminator: galaxies obeying the anti-correlation
are more likely to possess genuine primordial BSS rather than young
main sequence stars.
Key words: stars: galaxies: dwarf / blue stragglers / galaxies: stellar content / stars: Hertzspring-Russell (HR) and C-M diagrams / galaxies: Local Group / galaxies: photometry
© ESO, 2007
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