From: LARRY KLAES (ljk4_at_msn.com)
Date: Wed Jun 08 2005 - 14:12:48 PDT
Paper: astro-ph/0506132
Date: Tue, 7 Jun 2005 07:23:20 GMT (260kb)
Title: Where Are The M Dwarf Disks Older Than 10 Million Years?
Authors: Peter Plavchan, M. Jura, & S. J. Lipscy
Comments: 24 pages, 2 figures, accepted to ApJ
\\
We present 11.7-micron observations of nine late-type dwarfs obtained at the
Keck I 10-meter telescope in December 2002 and April 2003. Our targets were
selected for their youth or apparent IRAS 12-micron excess. For all nine
sources, excess infrared emission is not detected. We find that stellar wind
drag can dominate the circumstellar grain removal and plausibly explain the
dearth of M Dwarf systems older than 10 Myr with currently detected infrared
excesses. We predict M dwarfs possess fractional infrared excess on the
order
of L_{IR}/L_{*}\sim10^{-6} and this may be detectable with future efforts.
\\ ( http://arXiv.org/abs/astro-ph/0506132 , 260kb)
Paper: astro-ph/0506134
Date: Tue, 7 Jun 2005 08:33:35 GMT (344kb)
Title: Bright X-ray flares in Orion young stars from COUP: evidence for
star-disk magnetic fields?
Authors: F. Favata, E. Flaccomio, F. Reale, G. Micela, S. Sciortino, H.
Shang,
K. Stassun, E.D. Feigelson
Comments: Accepted to ApJS, COUP special issue
\\
We have analyzed a number of intense X-ray flares observed in the Chandra
Orion Ultradeep Project (COUP), a 13 days observation of the Orion Nebula
Cluster (ONC). Analysis of the flare decay allows to determine the size,
peak
density and magnetic field of the flaring structure. A total of 32 events
(the
most powerful 1% of COUP flares), have sufficient statistics for the
analysis.
A broad range of decay times (from 10 to 400 ks) are present in the sample.
Peak flare temperatures are often very high, with half of the flares in the
sample showing temperatures in excess of 100 MK. Significant sustained
heating
is present in the majority of the flares. The magnetic structures which are
found, are in a number of cases very long, with semi-lengths up to 10^12 cm,
implying the presence of magnetic fields of hundreds of G extending to
comparable distance from the stellar photosphere. These very large sizes for
the flaring structures ($ >> R_*) are not found in more evolved stars,
where,
almost invariably, the same type of analysis results in structures with L <=
R_*. As the majority of young stars in the ONC are surrounded by disks, we
speculate that the large magnetic structures which confine the flaring
plasma
are actually the same type of structures which channel the plasma in the
magnetospheric accretion paradigm, connecting the star's photosphere with
the
accretion disk.
\\ ( http://arXiv.org/abs/astro-ph/0506134 , 344kb)
Paper: astro-ph/0506147
Date: Tue, 7 Jun 2005 18:00:28 GMT (19kb)
Title: Jupiter's Obliquity and a Long-lived Circumplanetary Disk
Authors: I. Mosqueira and P. R. Estrada
Comments: 8 pages, 1 figure. Submitted note to Icarus
\\
It has been claimed (Canup and Ward 2002; Ward 2003) that a long-lived
massive (compared to the mass of the Galilean satellites) circumplanetary
gas
disk is inconsistent with Jupiter's low obliquity. Such a constraint could
be
downplayed on the basis that it deals with a single observation. Here we
argue
that this argument is flawed because it assumes a solar system much like
that
of the present day with the one exception of a circumjovian disk which is
then
allowed to dissipate on a long timescale (10^6-10^7 yrs). Given that the
sequence of events in solar-system history that fit known constraints is
non-unique, we choose for the sake of clarity of exposition the orbital
architecture framework of Tsiganis et al. (2005), in which Jupiter and
Saturn
were once in closer, less inclined orbits than they are at present, and show
that Jupiter's low obliquity is consistent with the SEMM (solids-enhanced
minimum mass) satellite formation model of Mosqueira and Estrada (2003a,b).
\\ ( http://arXiv.org/abs/astro-ph/0506147 , 19kb)
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