5,594 research outputs found
Study of the Bipolar Nebula IRAS 19312+1950. I. Mapping Observations
IRAS 19312+1950 is an SiO maser source that exhibits a prominent bipolar
nebulosity. Mapping observations of this object were made in the CO J=1--0,
13CO J=1--0, C18O J=1--0, CS J=2--1, and HCN J=1--0 lines and in the 150 GHz
continuum band. Near-infrared imaging observations were also made in the J, H,
and K-bands. The line profiles of the 12CO and HCN spectra consist of a weak
broad component with a line width of about 50 km/s and a strong narrow
component of the width of about 3 km/s. The profiles of the 13CO, C18O, and CS
lines have only the narrow component. Both of the components have an intensity
peak at the IRAS position. The narrow component was clearly resolved with a
15'' telescope beam. The spectral energy distribution of this object exhibits a
doubly peaked profile between 1 and 25 micron. The 150 GHz continuum flux
density was found to be 0.07 Jy, which is consistent with the flux density
predicted by the expanding envelope model with a mass loss rate of ~10^{-4}
M_sun/y at a distance of 2.5 kpc. We argue that the broad component originates
from the expanding envelope of this object, and that the hot dust cloud, which
is the source of the narrow component, is also physically associated with this
object. Though the present observations do not preclude the possibility of a
young stellar object, we argue that it is less plausible. We conclude that IRAS
19312+1950 is an AGB/post-AGB star that is evolved from a massive progenitor.Comment: 13 pages, 6 figures (jpg), high resolution figures available as no598
in http://www.nro.nao.ac.jp/library/report/list.html. PASJ, 56 No. 1 in pres
The Crystallography of Aluminum and its Alloys
This chapter begins with pure aluminium and a discussion of the form of the
crystal structure and different unit cells that can be used to describe the
crystal structure. Measurements of the face-centred cubic lattice parameter and
thermal expansion coefficient in pure aluminium are reviewed and
parametrisations given that allow the reader to evaluate them across the full
range of temperatures where aluminium is a solid. A new concept called the
vacancy triangle is introduced and demonstrated as an effective means for
determining vacancy concentrations near the melting point of aluminium. The
Debye-Waller factor, quantifying the thermal vibration of aluminium atoms in
pure aluminium, is reviewed and parametrised over the full range of
temperatures where aluminium is a solid. The nature of interatomic bonding and
the history of its characterisation in pure aluminium is reviewed with the
unequivocal conclusion that it is purely tetrahedral in nature. The
crystallography of aluminium alloys is then discussed in terms of all of the
concepts covered for pure aluminium, using prominent alloy examples. The
electron density domain theory of solid-state nucleation and precipitate growth
is introduced and discussed as a new means of rationalising phase
transformations in alloys from a crystallographic point of view.Comment: 93 pages, 21 figures, 4 tables and 4 tabular appendices, 465
reference
SiO and H2O Maser Observations of Red Supergiants in Star Clusters Embedded in the Galactic Disk
We present the result of radio observations of red supergiants in the star
cluster, Stephenson's #2, and candidates for red supergiants in the star
clusters, Mercer et al. (2005)'s #4, #8, and #13, in the SiO and HO maser
lines.The Stephenson's #2 cluster and nearby aggregation at the South-West
contain more than 15 red supergiants. We detected one at the center of
Stephenson's #2 and three in the south-west aggregation in the SiO maser line,
and three of these 4 were also detected in the H2O maser line. The average
radial velocity of the 4 detected objects is 96 km s^{-1}, giving a kinematic
distance of 5.5 kpc, which locates this cluster near the base of the
Scutum-Crux spiral arm. We also detected 6 SiO emitting objects associated with
the other star clusters. In addition, mapping observations in the CO J=1--0
line toward these clusters revealed that an appreciable amount of molecular gas
still remains around Stephenson's #2 cluster in contrast to the prototypical
red-supergiant cluster, Bica et al.'s #122. It indicates that a time scale of
gas expulsion differs considerably in individual clusters.Comment: high res. figures available at
http://www.nro.nao.ac.jp/~lib_pub/report/data/no674.pdf. PASJ 62, No.2 (2010,
April 25 issue) in pres
Submillimeter Array Observation of the Proto-Planetary Nebula CRL 618 in the CO J=6-5 Line
We report on the results of a Submillimeter Array interferometric observation
of the proto-planetary nebula CRL 618 in the 12CO J=6-5 line. With the new
capability of SMA enabling us to use two receivers at a time, we also observed
simultaneously in the 12CO J=2-1 and 13CO J=2-1 lines. The 12CO J=6-5 and 13CO
J=2-1 lines were first interferometrically observed toward CRL 618. The flux of
the high velocity component of the 12CO J=6-5 line is almost fully recovered,
while roughly 80% of the flux of the low velocity component is resolved out.
The low recovery rate suggests that the emission region of the low velocity
component of the 12CO J=6-5 line is largely extended. Continuum emission is
detected both at 230 and 690 GHz. The flux of the 690 GHz continuum emission
seems to be partially resolved out, suggesting dust emission partly
contaminates the 690 GHz continuum flux. The cavity structure, which has been
confirmed in a previous observation in the 12CO J=2-1 line, is not clearly
detected in the 12CO J=6-5 line, and only the south wall of the cavity is
detected. This result suggests that the physical condition of the molecular
envelope of CRL 618 is not exactly axial symmetric.Comment: 24 pages, 9 figures, 1 table, accepted for publication in AJ. Full
resolution version available at
http://www.asiaa.sinica.edu.tw/~junichi/paper
Physisorption of Nucleobases on Graphene
We report the results of our first-principles investigation on the
interaction of the nucleobases adenine (A), cytosine (C), guanine (G), thymine
(T), and uracil (U) with graphene, carried out within the density functional
theory framework, with additional calculations utilizing Hartree--Fock plus
second-order Moeller-Plesset perturbation theory. The calculated binding energy
of the nucleobases shows the following hierarchy: G > T ~ C ~ A > U, with the
equilibrium configuration being very similar for all five of them. Our results
clearly demonstrate that the nucleobases exhibit significantly different
interaction strengths when physisorbed on graphene. The stabilizing factor in
the interaction between the base molecule and graphene sheet is dominated by
the molecular polarizability that allows a weakly attractive dispersion force
to be induced between them. The present study represents a significant step
towards a first-principles understanding of how the base sequence of DNA can
affect its interaction with carbon nanotubes, as observed experimentally.Comment: 7 pages, 3 figure
Morphokinematic properties of the 21 micron source IRAS 22272+5435
We obtained a high-resolution CO map of IRAS 22272+5435 in the CO J=2-1 line using CARMA. The target exhibits a second biggest angular size of the circumstellar molecular envelope among known 21 μm sources. In the preliminary results, we found that the CO properties of IRAS 22272+5435 is clearly different from those of IRAS 07134+1005, which is another well-investigated 21 μm source. For example, elongations seen in the mid-infrared and CO images are extended in mutually perpendicular directions, although in case of IRAS 07134+1005 the CO feature coincides well with the mid-infrared structure. © 2012 International Astronomical Union.published_or_final_versio
Planetary nebulae detected in the Spitzer Space Telescope GLIMPSE 3D Legacy Survey
Due to interstellar extinction, optical census of Galactic planetary nebulae (PNs) is highly incomplete, and some compact H ii regions might have been mis-classified as PNs. The problem is particularly severe in the Galactic plane where the extinction in the optical is significant and hampers the detections of PNs. Unlike optical observations, infrared (IR) observations are hardly affected by interstellar extinction, and provide a good opportunity to study highly obscured PNs. In this study, we use the data from the Spitzer Legacy Infrared Mid-Plane Survey Extraordinaire 3D (GLIMPSE 3D) to investigate the mid-infrared (MIR) properties of PNs and PN candidates. © 2012 International Astronomical Union.published_or_final_versionThe IAU Symposium No. 283: 'Planetary Nebulae: an Eye to the Future', Puerto de la Cruz, Tenerife, Spain, 25-29 July 2011. In International Astronomical Union Proceedings, 2011, v. 7 n. S283, p. 528-52
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