442 research outputs found
X-Ray Emission from Pre-Main-Sequence Stars - Testing the Solar Analogy
This LTSA award funds my research on the origin of stellar X-ray emission and the solar-stellar analogy. The focus during most of this reporting period continued to be on the reduction and analysis of data acquired with the ASCA observatory (Advanced Satellite for Cosmology and Astrophysics). During the last few months of this reporting period, considerable time and effort was also devoted to the submission of AXAF observing proposals in preparation for the upcoming AXAF launch. During this reporting period, five papers appeared in refereed journals for which I was either author or co-author, and two additional papers have recently been submitted to ApJ. Also, three conference proceedings papers were submitted. These publications are listed in the attached bibliography
Chandra Reveals Variable Multi-Component X-ray Emission from FU Orionis
FU Orionis is the prototype of a class of eruptive young stars (``FUors'')
characterized by strong optical outbursts. We recently completed an exploratory
survey of FUors using XMM-Newton to determine their X-ray properties, about
which little was previously known. The prototype FU Ori and V1735 Cyg were
detected. The X-ray spectrum of FU Ori was found to be unusual, consisting of a
cool moderately-absorbed component plus a hotter component viewed through an
absorption column density that is an order of magnitude higher. We present here
a sensitive (99 ks) follow-up X-ray observation of FU Ori obtained at higher
angular resolution with Chandra ACIS-S. The unusual multi-component spectrum is
confirmed. The hot component is centered on FU Ori and dominates the emission
above 2 keV. It is variable (a signature of magnetic activity) and is probably
coronal emission originating close to FU Ori's surface viewed through cool gas
in FU Ori's strong wind or accretion stream. In contrast, the X-ray centroid of
the soft emission below 2 keV is offset 0.20 arcsec to the southeast of FU Ori,
toward the near-IR companion (FU Ori S). This offset amounts to slightly less
than half the separation between the two stars. The most likely explanation for
the offset is that the companion contributes significantly to the softer X-ray
emission below 2 keV (and weakly above 2 keV). The superimposed X-ray
contributions from FU Ori and the companion resolve the paradox posed by
XMM-Newton of an apparently single X-ray source viewed through two different
absorption columns.Comment: 21 pages, 3 tables, 6 figure
Observations of Binary and Single Wolf-Rayet Stars with XMM-Newton and Chandra
We present an overview of recent X-ray observations of Wolf-Rayet (WR) stars
with XMM-Newton and Chandra. A new XMM spectrum of the nearby WN8 + OB binary
WR 147 shows hard absorbed X-ray emission, including the Fe K-alpha line
complex, characteristic of colliding wind shock sources. In contrast, sensitive
observations of four of the closest known single WC (carbon-rich) WR stars have
yielded only non-detections. These results tentatively suggest that single WC
stars are X-ray quiet. The presence of a companion may thus be an essential
factor in elevating the X-ray emission of WC + OB stars to detectable levels.Comment: To appear in conf. proceedings: Close Binaries in the 21st Century -
New Opportunities and Challenges, eds. A. Gimenez, E. Guinan, P. Niarchos, S.
Rucinski; Astrophys. and Space Sci. (special issue), 2006. 4 pages, 2 figure
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