8 research outputs found
Contact Binary Variables as X-ray Sources
We present cross-identification of archived X-ray point sources with W UMa
variable stars found in the All-Sky Automated Survey (ASAS). In a surveyed sky
area of 300 square degrees of ASAS, 36 W UMa stars have been found associated
with X-ray emission. We compute the distances of these W UMa systems and hence
their X-ray luminosities. Our data support the "supersaturation" phenomenon
seen in these fast rotators, namely that the faster a W UMa star rotates, the
weaker its X-ray luminosity.Comment: 10 pages, 2 figures, 1 table; submitted to A
Near-infrared Study of the Carina Nebula
We have carried out near-infrared (NIR) imaging observations of the Carina
Nebula for an area of ~400 sq. arcmin. including the star clusters Trumpler 14
(Tr 14) and Trumpler 16 (Tr 16). With 10 sigma limiting magnitudes of J ~ 18.5,
H ~ 17.5 and K_s ~ 16.5, we identified 544 Class II and 11 Class I young star
candidates. We find some 40 previously unknown very red sources with H-K_s > 2,
most of which remain undetected at the J band. The red NIR sources are found to
be concentrated to the south-east of Tr 16, along the `V' shaped dust lane,
where the next generation of stars seems to be forming. In addition, we find
indications of ongoing star formation near the three MSX point sources,
G287.51-0.49, G287.47-0.54, and G287.63-0.72. A handful of red NIR sources are
seen to populate around each of these MSX sources. Apart from this, we
identified two hard Chandra X-ray sources near G287.47-0.54, one of which does
not have an NIR counterpart and may be associated with a Class I/Class 0
object. The majority of the Class II candidates, on the other hand, are seen to
be distributed in the directions of the clusters, demarcating different
evolutionary stages in this massive star-forming region. A comparison of the
color-magnitude diagrams of the clusters with pre-main sequence model tracks
shows that the stellar population of these clusters is very young (< 3 Myr).
The K_s band luminosity function (KLF) of Tr 14 shows structure at the faint
end, including a sharp peak due to the onset of deuterium burning, implying an
age of 1-2 Myr for the cluster. The KLF of Tr 16, in contrast, is found to rise
smoothly until it turns over. The slopes of the mass functions derived for the
clusters are found to be in agreement with the canonical value of the field
star initial mass function derived by Salpeter.Comment: Accepted for publication in ApJ; 45 pages, 18 figures, and 3 tables.
The manuscript with higher resolution figures can be downloaded from
http://cepheus.astro.ncu.edu.tw/~kaushar/download/ms.pd
A Smoking Gun in the Carina Nebula
The Carina Nebula is one of the youngest, most active sites of massive star
formation in our Galaxy. In this nebula, we have discovered a bright X-ray
source that has persisted for ~30 years. The soft X-ray spectrum, consistent
with kT ~128 eV blackbody radiation with mild extinction, and no counterpart in
the near- and mid-infrared wavelengths indicate that it is a ~1e6-year-old
neutron star housed in the Carina Nebula. Current star formation theory does
not suggest that the progenitor of the neutron star and massive stars in the
Carina Nebula, in particular Eta Carinae, are coeval. This result suggests that
the Carina Nebula experienced at least two major episodes of massive star
formation. The neutron star may be responsible for remnants of high energy
activity seen in multiple wavelengths.Comment: 9 pages, 3 figures, accepted for publication to ApJ