204 research outputs found
VLBA imaging of a periodic 12.2 GHz methanol maser flare in G9.62+0.20E
The class II methanol maser source G9.62+0.20E undergoes periodic flares at
both 6.7 and 12.2 GHz. The flare starting in 2001 October was observed at seven
epochs over three months using the VLBA at 12.2 GHz. High angular resolution
images (beam size 1.7 x 0.6 mas) were obtained, enabling us to observe
changes in 16 individual maser components. It was found that while existing
maser spots increased in flux density, no new spots developed and no changes in
morphology were observed. This rules out any mechanism which disturbs the
masing region itself, implying that the flares are caused by a change in either
the seed or pump photon levels. A time delay of 1--2 weeks was observed between
groups of maser features. These delays can be explained by light travel time
between maser groups. The regularity of the flares can possibly be explained by
a binary system.Comment: 11 pages, accepted for publication in MNRA
X-Ray Emission from Young Stars in the Massive Star Forming Region IRAS 20126+4104
We present a ks Chandra observation of the IRAS20126+4104 core
region. In the inner two X-ray sources were detected, which
are coincident with the radio jet source I20S and the variable radio source
I20Var. No X-ray emission was detected from the nearby massive protostar I20N.
The spectra of both detected sources are hard and highly absorbed, with no
emission below keV.
For I20S, the measured keV count rate was ctsks.
The X-ray spectrum was fit with an absorbed 1T APEC model with an energy of
kTkeV and an absorbing column of Ncm.
An unabsorbed X-ray luminosity of about ergs
was estimated. The spectrum shows broad line emission between 6.4 and 6.7\,
keV, indicative of emission from both neutral and highly ionized iron. The
X-ray lightcurve indicates that I20S is marginally variable; however, no flare
emission was observed.
The variable radio source I20Var was detected with a count rate of
ctsks but there was no evidence of X-ray variability. The
best fit spectral model is a 1T APEC model with an absorbing hydrogen column of
Ncm and a plasma energy of kT = 6.0keV.
The unabsorbed X-ray luminosity is about ergs.Comment: 17pages, 4 figures to appear in Astronomical Journa
High Resolution Observations of the Massive Protostar in IRAS18566+0408
We report 3 mm continuum, CH3CN(5-4) and 13CS(2-1) line observations with
CARMA, in conjunction with 6 and 1.3 cm continuum VLA data, and 12 and 25
micron broadband data from the Subaru Telescope toward the massive proto-star
IRAS18566+0408. The VLA data resolve the ionized jet into 4 components aligned
in the E-W direction. Radio components A, C, and D have flat cm SEDs indicative
of optically thin emission from ionized gas, and component B has a spectral
index alpha = 1.0, and a decreasing size with frequency proportional to
frequency to the -0.5 power. Emission from the CARMA 3 mm continuum, and from
the 13CS(2-1), and CH3CN(5-4) spectral lines is compact (i.e. < 6700 AU), and
peaks near the position of VLA cm source, component B. Analysis of these lines
indicates hot, and dense molecular gas, typical for HMCs. Our Subaru telescope
observations detect a single compact source, coincident with radio component B,
demonstrating that most of the energy in IRAS18566+0408 originates from a
region of size < 2400 AU. We also present UKIRT near-infrared archival data for
IRAS18566+0408 which show extended K-band emission along the jet direction. We
detect an E-W velocity shift of about 10 km/sec over the HMC in the CH3CN lines
possibly tracing the interface of the ionized jet with the surrounding core
gas. Our data demonstrate the presence of an ionized jet at the base of the
molecular outflow, and support the hypothesis that massive protostars with
O-type luminosity form with a mechanism similar to lower mass stars
Long-term Variability of HCO Masers in Star-forming Regions
We present results of a multi-epoch monitoring program on variability of
6cm formaldehyde (HCO) masers in the massive star forming region
NGC7538IRS1 from 2008 to 2015 conducted with the GBT, WSRT, and
VLA. We found that the similar variability behaviors of the two formaldehyde
maser velocity components in NGC7538IRS1 (which was pointed out by
Araya and collaborators in 2007) have continued. The possibility that the
variability is caused by changes in the maser amplification path in regions
with similar morphology and kinematics is discussed. We also observed
12.2GHz methanol and 22.2GHz water masers toward
NGC7538IRS1. The brightest maser components of CHOH and HO
species show a decrease in flux density as a function of time. The brightest
HCO maser component also shows a decrease in flux density and has a similar
LSR velocity to the brightest HO and 12.2GHz CHOH masers. The line
parameters of radio recombination lines and the 20.17 and 20.97GHz CHOH
transitions in NGC7538IRS1 are also reported. In addition, we
observed five other 6cm formaldehyde maser regions. We found no evidence of
significant variability of the 6cm masers in these regions with respect to
previous observations, the only possible exception being the maser in
G29.960.02. All six sources were also observed in the HCO
isotopologue transition of the 6cm HCO line; HCO absorption
was detected in five of the sources. Estimated column density ratios
[HCO]/[HCO] are reported.Comment: 29 pages, 9 figure
Broadband VLA Spectral Line Survey of a Sample of Ionized Jet Candidates
The study of the interaction between ionized jets, molecular outflows and
their environments is critical to understanding high-mass star formation,
especially because jets and outflows are thought to be key in the transfer of
angular momentum outwards from accretion disks. We report a low-spectral
resolution VLA survey for hydrogen radio recombination lines, OH, NH, and
CHOH lines toward a sample of 58 high-mass star forming regions that
contain numerous ionized jet candidates. The observations are from a survey
designed to detect radio continuum; the novel aspect of this work is to search
for spectral lines in broadband VLA data (we provide the script developed in
this work to facilitate exploration of other datasets). We report detection of
25GHz CHOH transitions toward ten sources; five of them also show
NH emission. We found that most of the sources detected in CHOH and
NH have been classified as ionized jets or jet candidates and that the
emission lines are coincident with, or very near ( pc) these
sources, hence, these molecular lines could be used as probes of the
environment near the launching site of jets/outflows. No radio recombination
lines were detected, but we found that the RMS noise of stacked spectra
decreases following the radiometer equation. Therefore, detecting radio
recombination lines in a sample of brighter free-free continuum sources should
be possible. This work demonstrates the potential of broadband VLA continuum
observations as low-resolution spectral line scans.Comment: 38 pages, 19 figures. Accepted for publication in The Astrophysical
Journal Supplement Serie
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