200 research outputs found
Large Scale CO Observations of a Far-Infrared Loop in Pegasus; Detection of a Large Number of Very Small Molecular Clouds Possibly Formed via Shocks
We have carried out large scale 12CO and 13CO observations with a mm/sub-mm
telescope NANTEN toward a loop-like structure in far infrared whose angular
extent is about 20x20 degrees around (l, b) ~ (109, -45) in Pegasus. The 12CO
distribution is found to consist of 78 small clumpy clouds whose masses range
from 0.04 Mo to 11 Mo. About 83% of the 12CO clouds have very small masses less
than 1.0 Mo. 13CO emission shown in the 19 of the 78 12CO clouds was detected
in the region where the column density of H2 derived from 12CO is greater than
5x10(20) cm(-2), corresponding to Av of ~ 1 mag, which takes into account that
of HI. We find no indication of star formation in these clouds in IRAS and
2MASS Point Source Catalogs. The very low mass clouds, M < 1 Mo, identified are
unusual in the sense that they have very weak 12CO peak temperature of 0.5 K to
2.7 K and that they aggregate in a region of a few pc with no main massive
clouds of ~ 100 Mo. A comparison with a theoretical work on molecular cloud
formation (Koyama & Inutsuka 2002) suggests that the very low-mass clouds may
have been formed in the shocked layer through the thermal instability. The star
HD886 (B2IV) may be the source of the mechanical luminosity via stellar winds
to create shocks, forming the loop-like structure where the very low-mass
clouds are embedded.Comment: Accepted by ApJ, 35pages including 14 figure
Interstellar Gas and X-rays toward the Young Supernova Remnant RCW 86; Pursuit of the Origin of the Thermal and Non-Thermal X-ray
We have analyzed the atomic and molecular gas using the 21 cm HI and 2.6/1.3
mm CO emissions toward the young supernova remnant (SNR) RCW 86 in order to
identify the interstellar medium with which the shock waves of the SNR
interact. We have found an HI intensity depression in the velocity range
between and km s toward the SNR, suggesting a cavity in the
interstellar medium. The HI cavity coincides with the thermal and non-thermal
emitting X-ray shell. The thermal X-rays are coincident with the edge of the HI
distribution, which indicates a strong density gradient, while the non-thermal
X-rays are found toward the less dense, inner part of the HI cavity. The most
significant non-thermal X-rays are seen toward the southwestern part of the
shell where the HI gas traces the dense and cold component. We also identified
CO clouds which are likely interacting with the SNR shock waves in the same
velocity range as the HI, although the CO clouds are distributed only in a
limited part of the SNR shell. The most massive cloud is located in the
southeastern part of the shell, showing detailed correspondence with the
thermal X-rays. These CO clouds show an enhanced CO = 2-1/1-0 intensity
ratio, suggesting heating/compression by the shock front. We interpret that the
shock-cloud interaction enhances non-thermal X-rays in the southwest and the
thermal X-rays are emitted by the shock-heated gas of density 10-100 cm.
Moreover, we can clearly see an HI envelope around the CO cloud, suggesting
that the progenitor had a weaker wind than the massive progenitor of the
core-collapse SNR RX J1713.73949. It seems likely that the progenitor of RCW
86 was a system consisting of a white dwarf and a low-mass star with
low-velocity accretion winds.Comment: 19 pages, 15 figures, 4 tables, accepted for publication in Journal
of High Energy Astrophysics (JHEAp
New Low-Mass Stars and Brown Dwarfs with Disks in Lupus
Using the Infrared Array Camera and the Multiband Imaging Photometer aboard
the {\it Spitzer Space Telescope}, we have obtained images of the Lupus 3
star-forming cloud at 3.6, 4.5, 5.8, 8.0, and 24 \micron. We present photometry
in these bands for the 41 previously known members that are within our images.
In addition, we have identified 19 possible new members of the cloud based on
red 3.6-8.0 \micron colors that are indicative of circumstellar disks. We have
performed optical spectroscopy on 6 of these candidates, all of which are
confirmed as young low-mass members of Lupus 3. The spectral types of these new
members range from M4.75 to M8, corresponding to masses of 0.2-0.03
for ages of Myr according to theoretical evolutionary models. We also
present optical spectroscopy of a candidate disk-bearing object in the vicinity
of the Lupus 1 cloud, 2M 1541-3345, which Jayawardhana & Ivanov recently
classified as a young brown dwarf ( ) with a spectral type
of M8. In contrast to their results, we measure an earlier spectral type of
M5.750.25 for this object, indicating that it is probably a low-mass star
( ). In fact, according to its gravity-sensitive absorption
lines and its luminosity, 2M 1541-3345 is older than members of the Lupus
clouds ( Myr) and instead is probably a more evolved
pre-main-sequence star that is not directly related to the current generation
of star formation in Lupus.Comment: 18 pages, 3 tables, 6 figure
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