21,907 research outputs found
Star formation activity in the southern Galactic HII region G351.63-1.25
The southern Galactic high mass star-forming region, G351.6-1.3, is a HII
region-molecular cloud complex with a luminosity of 2.0 x 10^5 L_sun, located
at a distance of 2.4 kpc. In this paper, we focus on the investigation of the
associated HII region, embedded cluster and the interstellar medium in the
vicinity of G351.6-1.3. We address the identification of exciting source(s) as
well as the census of stellar populations. The ionised gas distribution has
been mapped using the Giant Metrewave Radio Telescope (GMRT), India at three
continuum frequencies: 1280, 610 and 325 MHz. The HII region shows an elongated
morphology and the 1280 MHz map comprises six resolved high density regions
encompassed by diffuse emission spanning 1.4 pc x 1.0 pc. The zero age
main-sequence (ZAMS) spectral type of the brightest radio core is O7.5. We have
carried out near-infrared observations in the JHKs bands using the SIRIUS
instrument on the 1.4 m Infrared Survey Facility (IRSF) telescope. The
near-infrared images reveal the presence of a cluster embedded in nebulous
fan-shaped emission. The log-normal slope of the K-band luminosity function of
the embedded cluster is found to be 0.27 +- 0.03 and the fraction of the
near-infrared excess stars is estimated to be 43%. These indicate that the age
of the cluster is consistent with 1 Myr. The champagne flow model from a flat,
thin molecular cloud is used to explain the morphology of radio emission with
respect to the millimetre cloud and infrared brightness.Comment: 18 pages, 8 figures, To be published in MNRA
Bound states in two spatial dimensions in the non-central case
We derive a bound on the total number of negative energy bound states in a
potential in two spatial dimensions by using an adaptation of the Schwinger
method to derive the Birman-Schwinger bound in three dimensions. Specifically,
counting the number of bound states in a potential gV for g=1 is replaced by
counting the number of g_i's for which zero energy bound states exist, and then
the kernel of the integral equation for the zero-energy wave functon is
symmetrized. One of the keys of the solution is the replacement of an
inhomogeneous integral equation by a homogeneous integral equation.Comment: Work supported in part by the U.S. Department of Energy under Grant
No. DE-FG02-84-ER4015
NGC 7538 : Multiwavelength Study of Stellar Cluster Regions associated with IRS 1-3 and IRS 9 sources
We present deep and high-resolution (FWHM ~ 0.4 arcsec) near-infrared (NIR)
imaging observations of the NGC 7538 IRS 1-3 region (in JHK bands), and IRS 9
region (in HK bands) using the 8.2m Subaru telescope. The NIR analysis is
complemented with GMRT low-frequency observations at 325, 610, and 1280 MHz,
molecular line observations of H13CO+ (J=1-0), and archival Chandra X-ray
observations. Using the 'J-H/H-K' diagram, 144 Class II and 24 Class I young
stellar object (YSO) candidates are identified in the IRS 1-3 region. Further
analysis using 'K/H-K' diagram yields 145 and 96 red sources in the IRS 1-3 and
IRS 9 regions, respectively. A total of 27 sources are found to have X-ray
counterparts. The YSO mass function (MF), constructed using a theoretical
mass-luminosity relation, shows peaks at substellar (~0.08-0.18 Msolar) and
intermediate (~1-1.78 Msolar) mass ranges for the IRS 1-3 region. The MF can be
fitted by a power law in the low mass regime with a slope of Gamma ~ 0.54-0.75,
which is much shallower than the Salpeter value of 1.35. An upper limit of 10.2
is obtained for the star to brown dwarf ratio in the IRS 1-3 region. GMRT maps
show a compact HII region associated with the IRS 1-3 sources, whose spectral
index of 0.87+-0.11 suggests optical thickness. This compact region is resolved
into three separate peaks in higher resolution 1280 MHz map, and the 'East'
sub-peak coincides with the IRS 2 source. H13CO+ (J=1-0) emission reveals peaks
in both IRS 1-3 and IRS 9 regions, none of which are coincident with visible
nebular emission, suggesting the presence of dense cloud nearby. The virial
masses are approximately of the order of 1000 Msolar and 500 Msolar for the
clumps in IRS 1-3 and IRS 9 regions, respectively.Comment: 27 pages, 18 figures, 5 tables. Accepted for publication in MNRA
The ASCA Spectrum of the Vela Pulsar Jet
ROSAT observations of the Vela pulsar and its surroundings revealed a
collimated X-ray feature almost 45' in length (Markwardt & Ogelman 1995),
interpreted as the signature ``cocoon'' of a one-sided jet from the Vela
pulsar. We report on a new ASCA observation of the Vela pulsar jet at its head,
the point where the jet is believed to interact with the supernova remnant. The
head is clearly detected, and its X-ray spectrum is remarkably similar to the
surrounding supernova remnant spectrum, extending to X-ray energies of at least
7 keV. A ROSAT+ASCA spectrum can be fit by two-component emission models but
not standard one-component models. The lower energy component is thermal and
has a temperature of 0.29+/-0.03 keV (1 sigma); the higher energy component can
be fit by either a thermal component of temperature ~4 keV or a power law with
photon index ~2.0. Compared to the ROSAT-only results, the mechanical
properties of the jet and its cocoon do not change much. If the observed
spectrum is that of a hot jet cocoon, then the speed of the jet is at least 800
km s^-1, depending on the angle of inclination. The mechanical power driving
the jet is >10^36 erg s^-1, and the mass flow rate at the head is > 10^-6 M_sun
yr^-1. We conclude that the jet must be entraining material all along its
length in order to generate such a large mass flow rate. We also explore the
possibility that the cocoon emission is synchrotron radiation instead of
thermal.Comment: 12 pages, LaTeX in AAS v4.0 preprint style, two PS figures, accepted
for publication in the ApJ Letter
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