77 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
The Brightest AGB Stars in the Leo I Dwarf Spheroidal Galaxy
The first results of a study of the the dwarf spheroidal galaxy, Leo I, using
the new Japanese-South African Infrared Survey Facility (IRSF) are presented.
J,H,K_{s} observations show that most, if not all, of at least the top one
magnitude of the AGB is populated by carbon stars. These objects form a tight
sequence in the K_{s} - (J-K_{s}) plane. In addition there are five very red
objects which are believed to be dust enshrouded AGB stars. They have Mbol near
-5.0 and are at the AGB tip. Comparison with carbon Miras in Magellanic Cloud
clusters and taking into account other evidence on the ages and metallicities
of Leo I populations suggests that these obscured stars belong to the youngest
significant population of Leo I and have ages of ~2 Gyr. Some of them can be
shown to be variable.Comment: 5 pages, 2 figures, accepted for publication in MNRA
SiO Maser Survey of the Inner Bar of the Galactic Bulge
We surveyed 291 MSX/2MASS infrared objects in the 7 x 2 deg area of the
galactic center in the 43 GHz SiO J=1--0 v=1 and 2 maser lines, obtaining
accurate radial velocities of 163 detected objects. The surveyed area is the
region where the IRAS catalog is incomplete due to contamination by high source
density. The objects in the present MSX/2MASS sample were chosen to have
similar infrared characteristics to those of the previous SiO-maser-survey
samples based on the color selected IRAS sources. The sampling based on the
2MASS catalog causes a bias to the foreside objects of the bulge due to heavy
obscuration by interstellar dust; the detections are considerably leaned on the
V_{lsr}<0 side. The l--v diagram reveals two conspicuous features, which were
not present or tenuous in the previous studies: one feature indicating a linear
velocity increase with longitude with |l|<1.5 deg, which is likely associated
with the inner bar, and the other feature having considerably eccentric
velocities more than those of the normal x_1-orbit family feature. The
extinction-corrected K magnitudes (if used as a distance modulus) tend to show
a sequential deposition of these objects along the line of sight toward the
Galactic center depending on their radial velocities. The tendency that
appeared in the distance measures is consistent with the bulge-bar dynamical
model utilizing the periodic orbit families in the bar potential.Comment: Full high resolution figures available as NRO report No.638 at
http://www.nro.nao.ac.jp/library/report/list.html. PASJ 58, No. 3 (June 25
issue in press
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
AKARI/FIS Mapping of the ISM-Wind Bow Shock around Alpha Ori
We present 10' x 50' scan maps around an M supergiant Alpha Ori at 65, 90,
140 and 160 microns obtained with the AKARI Infrared Astronomy Satellite.
Higher spatial resolution data with the exact analytic solution permit us to
fit the de-projected shape of the stellar wind bow shock around Alpha Ori to
have the stand-off distance of 4.8', position angle of 55 degrees and
inclination angle of 56 degrees. The shape of the bow shock suggests that the
peculiar velocity of Alpha Ori with respect to the local medium is v_* = 40
(n_H)^(-1/2), where n_H is the hydrogen nucleus density at Alpha Ori. We find
that the local medium is of n_H = 1.5 to 1.9 cm^(-3) and the velocity of the
local flow is at 11 km s^(-1) by using the most recent astrometric solutions
for Alpha Ori under the assumption that the local medium is moving away from
the Orion OB 1 association. AKARI images may also reveal a vortex ring due to
instabilities on the surface of the bow shock as demonstrated by numerical
models. This research exemplifies the potential of AKARI All-Sky data as well
as follow-up observations with Herschel Space Telescope and Stratospheric
Observatory for Infrared Astronomy for this avenue of research in revealing the
nature of interaction between the stellar wind and interstellar medium.Comment: 8 pages, 2 figures, to be published in PASJ Vol. 60 Special Issue on
Recent Results from AKAR
SiO Maser Sources toward Globular Clusters
We report on the detection of SiO masers in Asymptotic Giant Branch variables
toward bulge/disk globular clusters. In five out of six cases, the radial
velocities are compatible with the optically measured radial velocities of
globular clusters in the assessed uncertainty. Two sources, toward Terzan~5 and
Terzan~12, lie very close to the cluster centers. The objects toward Pal~6 and
Terzan~12 have luminosities appropriate to the AGB tip in globular clusters,
while those toward NGC 6171, Pal~10, and Terzan~5 are brighter than expected.
It is suggested that the latter three may have evolved from merged binaries,
offering a test for binary-evolution scenarios in globular clusters, if the
membership is approved.Comment: 6 pages 1 figure PASJ, 57 No. 1 (in press
Papillo-Choledochectomy in the Operative Management of Mucosal Neoplasms of the Periampullary Region
Two patients with mucosal cancer of the periampullary region were treated with papillocholedochectomy,
which entails removal of the papilla of Vater and the whole length of the common bile duct. The neoplasm is dissected out through the plane between the duodenal circular and longitudinal muscles, deep to the sphincter of Oddi and the fibromuscular layer of the bile duct. Pathological examination showed that cancer was confined to the mucosal layer without stromal invasion, and that the operation achieved radical cure. For mucosal cancer, papillo-choledochectomy is
an alternative to pancreatoduodenectomy, provided that repeated frozen-section studies confirm the
completeness of excision
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