38,864 research outputs found
VLA Observations of H I in the Helix Nebula (NGC 7293)
We report the detection of 21-cm line emission from H I in the planetary
nebula NGC 7293 (the Helix). The observations, made with the Very Large Array,
show the presence of a ring of atomic hydrogen that is associated with the
outer portion of the ionized nebula. This ring is most probably gas ejected in
the AGB phase that has been subsequently photodissociated by radiation from the
central star. The H I emission spreads over about 50 km/s in radial velocity.
The mass in H I is approximately 0.07 solar masses, about three times larger
than the mass in molecular hydrogen and comparable with the mass in ionized
hydrogen.Comment: 19 pages, 9 figure
Optical and near-infrared observations of the microquasar V4641 Sagittarii during the 1999 September outburst
We present photometric and spectroscopic optical and near-infrared (NIR)
observations (Based on observations collected at the European Southern
Observatory, Chile (ESO ID 63.H-0493 and 64.H-0382)) taken during the outburst
of the microquasar V4641 Sgr = SAX J1819.3-2525 (in'tzand et al., 2000) in
September 1999. We observed an increase in the J-Ks colour between 5 and 8 days
after the outburst, which we interpret as likely evidence for the presence of
dust around the source. We also observed an extraordinarily strong, broad and
variable H_alpha line, with a velocity width of 4560 km/s suggesting the
presence of a high-velocity outflow component. We constrain the distance of the
system between 3 and 8 kpc, locating it further away than previously derived
from radio observations (Hjellming et al., 2000), but consistent with Orosz et
al. (2001). We then discuss the nature of this system, showing that the
companion star is either a B3-A2 main sequence star, or a B3-A2 sub-giant
crossing the Hertzsprung gap. The system is therefore an Intermediate or High
Mass X-ray Binary System (IMXB or HMXB). The distance derived by these
optical/NIR observations implies that the jets observed by Hjellming et al.
(2000) would then exhibit apparent velocities of ~ 10 c. We finally discuss the
possibility of an interaction between the jets and surroundings of the source,
and also of this source being a ``microblazar''.Comment: 7 pages, 6 figures, accepted for publication in MNRA
Euler Chern Simons Gravity from Lovelock Born Infeld Gravity
In the context of a gauge theoretical formulation, higher dimensional gravity
invariant under the AdS group is dimensionally reduced to Euler-Chern-Simons
gravity. The dimensional reduction procedure of Grignani-Nardelli [Phys. Lett.
B 300, 38 (1993)] is generalized so as to permit reducing D-dimensional Lanczos
Lovelock gravity to d=D-1 dimensions.Comment: 6 pages, no figures, accepted for publication in Phys. Lett.
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