45 research outputs found
Probable association of T Tauri stars with the L1014 dense core
Using the Wide Field Grism Spectrograph 2 (WFGS2), we have carried out
slit-less spectroscopy, g'r'i' photometry, and slit spectroscopy on the L1014
dense core. We detected three Halpha emission line stars. We interpret one as
weak-line T Tauri star (WTTS) and the others as classical T Tauri stars (CTTS).
Since their g'-i' colors and/or classified spectral types are consistent with
those of T Tauri stars and two of them show less extinction than the cloud,
these three stars are likely to be T Tauri stars associated with L1014.
Adopting an age range for T Tauri stars, 1-10 Myr, the color-magnitude diagram
suggests a distance of ~400-900 pc, rather than the previously assumed
distance, 200 pc. This could strongly affect on the mass estimate of L1014-IRS,
which is thought to be either a very young protostar or proto-brown dwarf.Comment: 5 pages, 5 figures, to be published in Vol.58, No.5, October 25, 200
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
Interstellar Extinction Law in the J, H, and Ks Bands toward the Galactic Center
We have determined the ratios of total to selective extinction in the
near-infrared bands (J, H, Ks) toward the Galactic center from the observations
of the region |l| < 2.0deg and 0.5deg < |b| < 1.0deg with the IRSF telescope
and the SIRIUS camera. Using the positions of red clump stars in
color-magnitude diagrams as a tracer of the extinction and reddening, we
determine the average of the ratios of total to selective extinction to be
A(Ks)/E(H-Ks) = 1.44+-0.01, A(Ks)/E(J-Ks) = 0.494+-0.006, and A(H)/E(J-H) =
1.42+-0.02, which are significantly smaller than those obtained in previous
studies. From these ratios, we estimate that A(J) : A(H) : A(Ks) = 1 :
0.573+-0.009 : 0.331+-0.004 and E(J-H)/E(H-Ks) = 1.72+-0.04, and we find that
the power law A(lambda) \propto lambda^{-1.99+-0.02} is a good approximation
over these wavelengths. Moreover, we find a small variation in A(Ks)/E(H-Ks)
across our survey. This suggests that the infrared extinction law changes from
one line of sight to another, and the so-called ``universality'' does not
necessarily hold in the infrared wavelengths.Comment: 18 pages, 9 figures, Accepted for publication in the Ap
Near-Infrared Imaging Polarimetry of the NGC 2071 Star Forming Region with SIRPOL
We have conducted deep JHKs imaging polarimetry of a ~8' x 8' area of the NGC
2071 star forming region. Our polarization data have revealed various infrared
reflection nebulae (IRNe) associated with the central IR young star cluster
NGC2071IR and identified their illuminating sources. There are at least 4 IRNe
in NGC2071IR and several additional IRNe are identified around nearby young
stars in the same field-of-view. Each illuminating source coincides with a
known near-IR source except for IRS3, which is only a part of IRN2 and is
illuminated by the radio source 1c. Aperture polarimetry of each cluster source
is used to detect unresolved circumstellar disk/outflow systems. Aperture
polarimetry of the other point-like sources within the field is made in this
region for the first time. The magnetic field structures (from ~1 pc down to
\~0.1 pc) are derived using both aperture polarimetry of the point-like sources
and imaging polarimetry of the shocked H2 emission that is seen as the dominant
knotty nebulae in the Ks band image; they are both of dichroic origin and the
derived field directions are consistent with each other. The magnetic field
direction projected on the sky is also consistent with that inferred from the
850 micron thermal continuum emission polarimetry of the central 0.2 pc region,
but running roughly perpendicular (~75 degrees) to the direction of the large
scale outflow. We argue that the field strength is too weak to align the
outflow in the large scale field direction via magnetic braking.Comment: o appear in PASJ, 9 pages, 11 Postscript figure
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
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
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