9 research outputs found
Early Spectral Evolution of the Rapidly Expanding Type Ia SN 2006X
We present optical spectroscopic and photometric observations of Type Ia
supernova (SN) 2006X from --10 to +91 days after the -band maximum. This SN
exhibits one of the highest expansion velocity ever published for SNe Ia. At
premaximum phases, the spectra show strong and broad features of
intermediate-mass elements such as Si, S, Ca, and Mg, while the O{\sc
i}7773 line is weak. The extremely high velocities of Si{\sc ii} and
S{\sc ii} lines and the weak O{\sc i} line suggest that an intense
nucleosynthesis might take place in the outer layers, favoring a delayed
detonation model. Interestingly, Si{\sc ii}5972 feature is quite
shallow, resulting in an unusually low depth ratio of Si{\sc ii}5972
to 6355, (Si{\sc ii}). The low (Si{\sc ii}) is usually
interpreted as a high photospheric temperature. However, the weak Si{\sc
iii}4560 line suggests a low temperature, in contradiction to the low
(Si{\sc ii}). This could imply that the Si{\sc ii}5972 line
might be contaminated by underlying emission. We propose that (Si{\sc
ii}) may not be a good temperature indicator for rapidly expanding SNe Ia at
premaximum phases.Comment: 20 pages, 7 figures, (Received 2008 August 17; Accepted 2009 April
13
Spectroscopic Observations of the WZ Sge-Type Dwarf Nova GW Librae during the 2007 Superoutburst
We carried out an international spectroscopic observation campaign of the
dwarf nova GW Librae (GW Lib) during the 2007 superoutburst. Our observation
period covered the rising phase of the superoutburst, maximum, slowly decaying
phase (plateau), and long fading tail after the rapid decline from the plateau.
The spectral features dramatically changed during the observations. In the
rising phase, only absorption lines of H, H, and H were
present. Around the maximum, the spectrum showed singly-peaked emission lines
of H, He I 5876, He I 6678, He II 4686, and C III/N III as well as
absorption lines of Balmer components and He I. These emission lines
significantly weakened in the latter part of the plateau phase. In the fading
tail, all the Balmer lines and He I 6678 were in emission, as observed in
quiescence. We find that the center of the H emission component was
mostly stable over the whole orbital phase, being consistent with the low
inclination of the system. Comparing with the observational results of WZ Sge
during the 2001 superoutburst, the same type of stars as GW Lib seen with a
high inclination angle, we interpret that the change of the H profile
before the fading tail phase is attributed to a photoionized region formed at
the outer edge of the accretion disk, irradiated from the white dwarf and inner
disk.Comment: 10 pages, 9 figures, accepted for publication in PAS
COMET 17P/HOLMES: CONTRAST IN ACTIVITY BETWEEN BEFORE AND AFTER THE 2007 OUTBURST
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