Bibcode
Hünsch, M.; Weidner, C.; Schmitt, J. H. M. M.
Referencia bibliográfica
Astronomy and Astrophysics, v.402, p.571-586 (2003)
Fecha de publicación:
5
2003
Revista
Número de citas
15
Número de citas referidas
14
Descripción
We have conducted a detailed study of the object NGC 2451, which
actually consists of two different open clusters A and B along the same
line of sight at 206 pc and 370 pc distance, respectively. Although
belonging to the nearest clusters, they have not been much investigated
until present due to strong contamination by field stars. ROSAT X-ray
observations and optical UBVR photometry are used to identify cluster
members by means of X-ray emission and colour-magnitude diagrams. The
identified stars concentrate nicely around the expected main sequences
in the colour-magnitude diagram at the distances derived from
astrometric investigations. Altogether, 39 stars are identified as
member candidates of the nearer cluster A, 49 stars as member candidates
of the more distant cluster B, and 22 faint stars are probably members
of either of the two clusters, but due to large errors it is not clear
to which one they belong. Further 40 stars identified with X-ray sources
are probably non-members. For the first time, the range of known
probable cluster members of NGC 2451 A and B has been extended downwards
the main sequence to stars of spectral class M. Isochrone fitting yields
an age of 50 to 80 Myrs for NGC 2451 A and ~50 Myrs for NGC 2451 B,
consistent with the X-ray luminosity distribution functions, which are
comparable to other clusters in the same age range. Except from the
occurence of four flares, the stars of both clusters do not show strong
long-term X-ray variability exceeding a factor 5 over a time span of 1
to 3 years.
Based on observations performed by the ROSAT X-ray observatory and the
European Southern Observatory.
Tables 3-6 are only available in electronic form at
http://www.edpsciences.org