6 research outputs found
Continuous heating of a giant X-ray flare on Algol
Giant flares can release large amounts of energy within a few days: X-ray
emission alone can be up to ten percent of the star's bolometric luminosity.
These flares exceed the luminosities of the largest solar flares by many orders
of magnitude, which suggests that the underlying physical mechanisms supplying
the energy are different from those on the Sun. Magnetic coupling between the
components in a binary system or between a young star and an accretion disk has
been proposed as a prerequisite for giant flares. Here we report X-ray
observations of a giant flare on Algol B, a giant star in an eclipsing binary
system. We observed a total X-ray eclipse of the flare, which demonstrates that
the plasma was confined to Algol B, and reached a maximum height of 0.6 stellar
radii above its surface. The flare occurred around the south pole of Algol B,
and energy must have been released continously throughout its life. We conclude
that a specific extrastellar environment is not required for the presence of a
flare, and that the processes at work are therefore similar to those on the
Sun.Comment: Nature, Sept. 2 199
Open Clusters IC 4665 and Cr 359 and a Probable Birthplace of the Pulsar PSR B1929+10
Based on the epicyclic approximation, we have simulated the motion of the
young open star clusters IC 4665 and Collinder 359. The separation between the
cluster centers is shown to have been minimal 7 Myr ago, 36 pc. We have
established a close evolutionary connection between IC 4665 and the
Scorpius-Centaurus association -- the separation between the centers of these
structures was pc 15 Myr ago. In addition, the center of IC 4665
at this time was near two well-known regions of coronal gas: the Local Bubble
and the North Polar Spur. The star HIP 86768 is shown to be one of the
candidates for a binary (in the past) with the pulsar PSR B1929+10. At the
model radial velocity of the pulsar km s, a close
encounter of this pair occurs in the vicinity of IC 4665 at a time of -1.1 Myr.
At the same time, using currently available data for the pulsar B1929+10 at its
model radial velocity km s, we show that the hypothesis
of Hoogerwerf et al. (2001) about the breakup of the Oph--B1929+10
binary in the vicinity of Upper Scorpius (US) about 0.9 Myr ago is more
plausible.Comment: 19 pages, 8 figure
The formation of planetary disks and winds: an ultraviolet view
Planetary systems are angular momentum reservoirs generated during star
formation. This accretion process produces very powerful engines able to drive
the optical jets and the molecular outflows. A fraction of the engine energy is
released into heating thus the temperature of the engine ranges from the 3000K
of the inner disk material to the 10MK in the areas where magnetic reconnection
occurs. There are important unsolved problems concerning the nature of the
engine, its evolution and the impact of the engine in the chemical evolution of
the inner disk. Of special relevance is the understanding of the shear layer
between the stellar photosphere and the disk; this layer controls a significant
fraction of the magnetic field building up and the subsequent dissipative
processes ougth to be studied in the UV.
This contribution focus on describing the connections between 1 Myr old suns
and the Sun and the requirements for new UV instrumentation to address their
evolution during this period. Two types of observations are shown to be needed:
monitoring programmes and high resolution imaging down to, at least,
milliarsecond scales.Comment: Accepted for publication in Astrophysics and Space Science 9 figure