48 research outputs found
Star Formation in Dwarf Galaxies
We explore mechanisms for the regulation of star formation in dwarf galaxies.
We concentrate primarily on a sample in the Virgo cluster, which has HI and
blue total photometry, for which we collected H data at the Wise
Observatory. We find that dwarf galaxies do not show the tight correlation of
the surface brightness of H (a star formation indicator) with the HI
surface density, or with the ratio of this density to a dynamical timescale, as
found for large disk or starburst galaxies. On the other hand, we find the
strongest correlation to be with the average blue surface brightness,
indicating the presence of a mechanism regulating the star formation by the
older (up to 1 Gyr) stellar population if present, or by the stellar population
already formed in the present burst.Comment: 15 pages (LATEX aasms4 style) and three postscript figures, accepted
for publication in the Astrophysical Journa
TAUVEX: status in 2011
We present a short history of the TAUVEX instrument, conceived to provide
multi-band wide-field imaging in the ultraviolet, emphasizing the lack of
sufficient and aggressive support on the part of the different space agencies
that dealt with this basic science mission. First conceived in 1985 and
selected by the Israel Space Agency in 1989 as its first priority payload,
TAUVEX is fast becoming one of the longest-living space project of space
astronomy. After being denied a launch on a national Israeli satellite, and
then not flying on the Spectrum X-Gamma (SRG) international observatory, it was
manifested since 2003 as part of ISRO's GSAT-4 Indian satellite to be launched
in the late 2000s. However, two months before the launch, in February 2010, it
was dismounted from its agreed-upon platform. This proved to be beneficial,
since GSAT-4 and its launcher were lost on April 15 2010 due to the failure of
the carrier rocket's 3rd stage. TAUVEX is now stored in ISRO's clean room in
Bangalore with no firm indications when or on what platform it might be
launched.Comment: Invited contribution presented at the "UV Universe 2010". Accepted
for publication in Astrophysics & Space Scienc
Meteor light curves: the relevant parameters
We investigate a uniform sample of 113 light curves (LCs) of meteors
collected at the Wise Observatory in November 2002 while observing the Leonid
meteor shower. We use previously defined descriptors such as the skewness F and
a recently defined pointedness parameter along with a number of other
measurable or derived quantities to explore the parameter space in search of
meaningful LC descriptors. We make extensive use of statistical techniques to
reveal links among the variables and to understand their relative importance.
In particular, we show that meteors with long-duration trails rise slowly to
their maximal brightness and also decay slowly from there while showing milder
flaring than other meteors. Early skewed LCs show a fast rise to the peak. We
show that the duration of te luminous phase of the meteor is th emost important
variable differentiating among the 2002 LCs. The skewness parameter F appears
only as the 2nd or 3rd in explaining the LC variance. We suggest that the
pointedness parameter P could possibly be useful to discriminate among meteors
from different showers, or to compare observations and model predictions.Comment: 10 pages (2 figures) in press with MNRA