38 research outputs found
Period Measurement of AGB Stars in the Outer Galactic Disk
Light variation of the 47 AGB star candidates in the outer Galactic disk has
been monitored at I-band for 5 years. Periods were determined well for 18 of
them and less reliably for the other 25. The average period of the objects is
then 500 days. According to the period-luminosity relation, the mean luminosity
of the sample stars is 10000 \LO. Based on the absolute luminosity derived
from the period-luminosity relation and the apparent luminosity from the
observation, the distances to the objects are determined. The distances
calculated are slightly greater than those obtained previously on the
assumption of constant luminosity of 8000 \LO. In addition, SiO maser
emission was detected for most of the observed objects so that their radial
velocities were known accurately. With the assumption of circular rotation in
the Galactic disk, the rotation curve and Oort's constants were derived.Comment: 13 pages including 4 tables, and 13 postscript figures. Accepted for
PASJ (Publication of the Astronomical Society of Japan
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
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