23 research outputs found
Variable Stars in the Magellanic Clouds: Results from OGLE and SIRIUS
We have performed a cross-identification between OGLE-II data and
single-epoch SIRIUS JHK survey data in the LMC and SMC. After eliminating
obvious spurious variables, we determined the pulsation periods for 9,681 and
2,927 variables in the LMC and SMC, respectively. Based on these homogeneous
data, we studied the pulsation properties and metallicity effects on period-K
magnitude (PK) relations by comparing the variable stars in the LMC and SMC.
The sample analyzed here is much larger, and we found the following new
features: (1) variable red giants in the SMC form parallel sequences on the PK
plane, just like those found by Wood (2000) in the LMC; (2) both of the
sequences A and B of Wood (2000) have discontinuities, and they occur at the
K-band luminosity of the TRGB; (3) the sequence B of Wood (2000) separates into
three independent sequences B+- and C'; (4) comparison between the theoretical
pulsation models (Wood et al. 1996) and observational data suggests that the
variable red giants on sequences C and newly discovered C' are pulsating in the
fundamental and first overtone mode, respectively; (5) the theory can not
explain the pulsation mode of sequences A+- and B+-, and they are unlikely to
be the sequences for the first and second overtone pulsators, as was previously
suggested; (6) the zero points of PK relations of Cepheids in the metal
deficient SMC are fainter than those of LMC ones by ~0.1 mag but those of SMC
Miras are brighter than those of LMC ones by ~0.13 mag, which are probably due
to metallicity effects.Comment: 9 pages, 10 figures, accepted for publication in MNRAS. High
resolution version is available at:
http://www.ioa.s.u-tokyo.ac.jp/~yita/scr/astro/papers/RefereedPaper/yitaMD250
.pd
The Infrared Counterpart of the X-Ray Nova XTE J1720-318
We report on the discovery of an infrared counterpart to the X-ray transient
XTE J1720-318 on 2003 January 18, nine days after an X-ray outburst, and the
infrared light curve during the first 130 days after the outburst. The infrared
light curve shows a decline of about 1.2 mag from the peak magnitude of Ks
about 15.3 over the observation period, and a secondary maximum, about 40 days
after the outburst. Another small increase in the flux was also recorded about
20 days after the outburst. These increases were also detected in the X-ray
light curve. The J H Ks colors are consistent with an X-ray irradiated
accretion disk suffering an extinction of Av about 8, which is also inferred
from its X-ray spectrum and the extinction map constructed from far-infrared
dust emission of this line of sight. These J, H, and Ks observations
demonstrate that useful data can be obtained even for such an object, which
suffers heavy optical extinction, possibly located beyond the Galactic center.Comment: 5 pages, 2 figures, to appear in PAS
Sequential star formation in a cometary globule (BRC37) of IC1396
We have carried out near-IR/optical observations to examine star formation
toward a bright-rimmed cometary globule (BRC37) facing the exciting star(s) of
an HII region (IC1396) containing an IRAS source, which is considered to be an
intermediate-mass protostar. With slit-less spectroscopy we detected ten
H_alpha emission stars around the globule, six of which are near the tip of the
globule and are aligned along the direction to the exciting stars. There is
evidence that this alignment was originally towards an O9.5 star, but has
evolved to align towards a younger O6 star when that formed. Near-IR and
optical photometry suggests that four of these six stars are low-mass young
stellar objects (YSOs) with masses of ~0.4 M_sun. Their estimated ages of ~1
Myr indicate that they were formed at the tip in advance of the formation of
the IRAS source. Therefore, it is likely that sequential star formation has
been taking place along the direction from the exciting stars towards the IRAS
source, due to the UV impact of the exciting star(s). Interestingly, one faint,
H_alpha emission star, which is the closest to the exciting star(s), seems to
be a young brown dwarf that was formed by the UV impact in advance of the
formation of other YSOs at the tip.Comment: main text (30 pages) + online material, 14 figures, published in A
A Distinct Structure Inside the Galactic Bar
We present the result of a near-infrared (J H Ks) survey along the Galactic
plane, -10.5deg < l < +10.5deg and b=+1.0deg, with the IRSF 1.4m telescope and
the SIRIUS camera. Ks vs. H-Ks color-magnitude diagrams reveal a well-defined
population of red clump (RC) stars whose apparent magnitude peak changes
continuously along the Galactic plane, from Ks=13.4 at l=-10deg to Ks=12.2 at
l=+10deg after dereddening. This variation can be explained by the bar-like
structure found in previous studies, but we find an additional inner structure
at |l| < 4deg, where the longitude - apparent magnitude relation is distinct
from the outer bar, and the apparent magnitude peak changes by only 0.1 mag
over the central 8deg. The exact nature of this inner structure is as yet
uncertain.Comment: 8 pages, 4 figures. accepted by ApJ
Variable stars in the Magellanic Clouds: II. The data and infrared properties
The data of 8,852 and 2,927 variable stars detected by OGLE survey in the
Large and Small Magellanic Clouds are presented. They are cross-identified with
the SIRIUS JHK survey data, and their infrared properties are discussed.
Variable red giants are well separated on the period-J - K plane, suggesting
that it could be a good tool to distinguish their pulsation mode and type.Comment: Accepted for publication in MNRAS. High resolution version is
available at:
http://www.ir.isas.jaxa.jp/%7Eyita/scr/astro/papers/Refereed/yitaMD1266.ps.g
Near Infrared Imaging Survey of Bok Globules: Density Structure
On the basis of near-infrared imaging observations, we derived visual
extinction (Av) distribution toward ten Bok globules through measurements of
both the color excess (E_{H-K}) and the stellar density at J, H, and Ks (star
count). Radial column density profiles for each globule were analyzed with the
Bonnor-Ebert sphere model. Using the data of our ten globules and four globules
in the literature, we investigated the stability of globules on the basis of
xi_max, which characterizes the Bonnor-Ebert sphere as well as the stability of
the equilibrium state against the gravitational collapse. We found that more
than half of starless globules are located near the critical state (xi_max =
6.5 +/- 2). Thus, we suggest that a nearly critical Bonnor-Ebert sphere
characterizes the typical density structure of starless globules. Remaining
starless globules show clearly unstable states (xi_max > 10). Since unstable
equilibrium states are not long maintained, we expect that these globules are
on the way to gravitational collapse or that they are stabilized by non-thermal
support. It was also found that all the star-forming globules show unstable
solutions of xi_max >10, which is consistent with the fact that they have
started gravitational collapse. We investigated the evolution of a collapsing
gas sphere whose initial condition is a nearly critical Bonnor-Ebert sphere. We
found that the column density profiles of the collapsing sphere mimic those of
the static Bonnor-Ebert spheres in unstable equilibrium. The collapsing gas
sphere resembles marginally unstable Bonnor-Ebert spheres for a long time. We
found that the frequency distribution of xi_max for the observed starless
globules is consistent with that from model calculations of the collapsing
sphere.Comment: Accepted for publication in the Astronomical Journal. 39 pages in
preprint format, including 10 figures. The version with higher resolution
figures can be obtained at the following site
(http://alma.mtk.nao.ac.jp/~kandori/preprint/