4,501 research outputs found
Characterizing Supernova Progenitors via the Metallicities of their Host Galaxies, from Poor Dwarfs to Rich Spirals
We investigate how the different types of supernovae are relatively affected
by the metallicity of their host galaxy. We match the SAI Supernova Catalog to
the SDSS-DR4 catalog of star-forming galaxies with measured metallicities.
These supernova host galaxies span a range of oxygen abundance from 12 +
log(O/H) = 7.9 to 9.3 (~ 0.1 to 2.7 solar) and a range in absolute magnitude
from MB = -15.2 to -22.2. To reduce the various observational biases, we select
a subsample of well-characterized supernovae in the redshift range from 0.01 to
0.04, which leaves us with 58 SN II, 19 Ib/c, and 38 Ia. We find strong
evidence that SN Ib/c are occurring in higher-metallicity host galaxies than SN
II, while we see no effect for SN Ia relative to SN II. We note some extreme
and interesting supernova-host pairs, including the metal-poor (~ 1/4 solar)
host of the recent SN Ia 2007bk, where the supernova was found well outside of
this dwarf galaxy. To extend the luminosity range of supernova hosts to even
fainter galaxies, we also match all the historical supernovae with z < 0.3 to
the SDSS-DR6 sky images, resulting in 1225 matches. This allows us to identify
some even more extreme cases, such as the recent SN Ic 2007bg, where the likely
host of this hypernova-like event has an absolute magnitude MB ~ -12, making it
one of the least-luminous supernova hosts ever observed. This low-luminosity
host is certain to be very metal poor (~ 1/20 solar), and therefore this
supernova is an excellent candidate for association with an off-axis GRB. The
two catalogs that we have constructed are available online and will be updated
regularly. Finally, we discuss various implications of our findings for
understanding supernova progenitors and their host galaxies.Comment: ApJ accepted, 26 pages, 5 figures, 1 table. Updated catalogs are
available at http://www.astronomy.ohio-state.edu/~prieto/snhosts
An Unexpectedly Swift Rise in the Gamma-ray Burst Rate
The association of long gamma-ray bursts with supernovae naturally suggests
that the cosmic GRB rate should trace the star formation history. Finding
otherwise would provide important clues concerning these rare, curious
phenomena. Using a new estimate of Swift GRB energetics to construct a sample
of 36 luminous GRBs with redshifts in the range z=0-4, we find evidence of
enhanced evolution in the GRB rate, with ~4 times as many GRBs observed at z~4
than expected from star formation measurements. This direct and empirical
demonstration of needed additional evolution is a new result. It is consistent
with theoretical expectations from metallicity effects, but other causes remain
possible, and we consider them systematically.Comment: 4 pages, 4 figures; minor changes to agree with published versio
The Host Galaxy of GRB 060505: Host ISM Properties
We investigate the ISM environment of GRB 060505. Using optical emission-line
diagnostic ratios, we compare the ISM properties of the GRB 060505 host region
with the hosts of unambiguous long- and short-duration GRBs. We show that the
metallicity, ionization state, and star formation rate of the GRB 060505
environment are more consistent with short-duration GRBs than with
long-duration GRBs. We compare the metallicity and star formation rates of the
GRB 060505 region with four other star-forming regions within the GRB 060505
host galaxy. We find no significant change in metallicity or star formation
rate between the GRB 060505 region and the other four host regions. Our results
are consistent with a compact-object-merger progenitor for GRB 060505.Comment: 7 pages, two figures; accepted for publication in ApJ
Long-term variability survey of the old open cluster NGC 6791
We present the results of a long-term variability survey of the old open
cluster NGC 6791. The BVI observations, collected over a time span of 6 years,
were analyzed using the ISIS image subtraction package. The main target of our
observations were two cataclysmic variables B7 and B8. We have identified
possible cycle lenghts of about 25 and 18 days for B7 and B8, respectively. We
tentatively classify B7 as a VY Scl type nova-like variable or a Z Cam type
dwarf nova. B8 is most likely an SS Cygni type dwarf nova. We have also
extracted the light curves of 42 other previously reported variable stars and
discovered seven new ones. The new variables show long-period or non-periodic
variability. The long baseline of our observations has also allowed us to
derive more precise periods for the variables, especially for the short period
eclipsing binaries.Comment: 13 pages LaTeX, including 8 PostScript figures and 4 tables. To
appear in June 2003 issue of The Astronomical Journa
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