| Issue |
A&A
Volume 400, Number 1, March II 2003
|
|
|---|---|---|
| Page(s) | 137 - 143 | |
| Section | Extragalactic astronomy | |
| DOI | https://doi.org/10.1051/0004-6361:20021909 | |
| Published online | 24 February 2003 | |
A bright early-type star in the halo of NGC 253: Runaway or in situ formation? *
1
European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei Muenchen, Germany e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
2
Observatoire de Paris-Meudon, GEPI, UMR 8111 du CNRS, 92195 Meudon Cedex, France e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
3
Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Av. Diagonal 647, 08028 Barcelona, Spain e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Corresponding author: F. Comerón, This email address is being protected from spambots. You need JavaScript enabled to view it.
Received:
13
November
2002
Accepted:
19
December
2002
Abstract
We present observations of J004804.8-251749, a blue
object in the direction of the halo of NGC 253 with 
, 
and a stellar spectrum showing the
Balmer lines redshifted to a velocity of 
km s-1.
These data are consistent with a B5/B8 supergiant star with a mass
and a maximum age 
Myr in the
halo of NGC 253. Based on its position, radial velocity, and
inferred maximum age, we consider the possibility that
J004804.8-251749 may be a runaway star ejected from the disk of
NGC 253. We derive a lower limit of 172 km s-1 for the
ejection velocity, or 148 km s-1 if the lower limit of the
distance fork to NGC 253 is adopted. While being within the range
of velocities accessible to runaway stars through the dynamical
ejection mechanism, such high velocities are rather unlikely,
especially since the inferred value is only a lower limit. This
leads us to consider in situ formation as a possible
alternative scenario, in which the formation of J004804.8-251749
would have been triggered by the interaction between the
starburst-driven superwind stemming from the center of NGC 253 and
a cloud of cold hydrogen in the halo. Such a formation mechanism
would be consistent with our previous finding of an excess of blue
point sources in the direction of the halo of NGC 253, which we
interpreted as indicating the existence of superwind-triggered
star formation.
Key words: stars: early-type / stars: formation / stars: kinematics / galaxies: starburst / galaxies: individual: NGC 253
Based on observations obtained at the European Southern Observatory using the Very Large Telescope in Cerro Paranal (programme 69.D-0109(A)).
© ESO, 2003
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