1,089 research outputs found
A High-Mass Protobinary System in the Hot Core W3(H2O)
We have observed a high-mass protobinary system in the hot core W3(H2O) with
the BIMA Array. Our continuum maps at wavelengths of 1.4mm and 2.8mm both
achieve sub-arcsecond angular resolutions and show a double-peaked morphology.
The angular separation of the two sources is 1.19" corresponding to 2.43X10^3
AU at the source distance of 2.04 kpc. The flux densities of the two sources at
1.4mm and 2.8mm have a spectral index of 3, translating to an opacity law of
kappa ~ nu. The small spectral indices suggest that grain growth has begun in
the hot core. We have also observed 5 K components of the CH3CN (12-11)
transitions. A radial velocity difference of 2.81 km/s is found towards the two
continuum peaks. Interpreting these two sources as binary components in orbit
about one another, we find a minimum mass of 22 Msun for the system. Radiative
transfer models are constructed to explain both the continuum and methyl
cyanide line observations of each source. Power-law distributions of both
density and temperature are derived. Density distributions close to the
free-fall value, r^-1.5, are found for both components, suggesting continuing
accretion. The derived luminosities suggest the two sources have equivalent
zero-age main sequence (ZAMS) spectral type B0.5 - B0. The nebular masses
derived from the continuum observations are about 5 Msun for source A and 4
Msun for source C. A velocity gradient previously detected may be explained by
unresolved binary rotation with a small velocity difference.Comment: 38 pages, 9 figures, accepted by The Astrophysical Journa
VLA observations of candidate high-mass protostellar objects at 7 mm
We present radio continuum observations at 7 mm made using the Very Large
Array towards three massive star forming regions thought to be in very early
stages of evolution selected from the sample of Sridharan et al. (2002).
Emission was detected towards all three sources (IRAS 18470-0044, IRAS
19217+1651 and IRAS 23151+5912). We find that in all cases the 7 mm emission
corresponds to thermal emission from ionized gas. The regions of ionized gas
associated with IRAS 19217+1651 and IRAS 23151+5912 are hypercompact with
diameters of 0.009 and 0.0006 pc, and emission measures of 7.0 x 10^8 and 2.3 x
10^9 pc cm^(-6), respectively.Comment: 17 pages, 5 figures, accepted by The Astronomical Journa
Comparison between various indices of exposure to traffic-related air pollution and their impact on respiratory health in adults
IRAS 23385+6053: a candidate protostellar massive object
We present the results of a multi-line and continuum study towards the source
IRAS 23385+6053,performed with the IRAM-30m telescope, the Plateau de Bure
Interferometer, the Very Large Array Interferometer and the James Clerk Maxwell
Telescope. The new results confirm our earlier findings, namely that IRAS
23385+6053 is a good candidate high-mass protostellar object, precursor of an
ultracompact H region. The source is roughly composed of two regions: a
molecular core pc in size, with a temperature of K
and an H volume density of the order of 10 cm, and an
extended halo of diameter 0.4 pc, with an average kinetic temperature of
K and H volume density of the order of 10 cm. The
core temperature is much smaller than what is typically found in molecular
cores of the same diameter surrounding massive ZAMS stars. We deduce that the
core luminosity is between 150 and , and we believe
that the upper limit is near the ``true'' source luminosity. Moreover, by
comparing the H volume density obtained at different radii from the IRAS
source, we find that the halo has a density profile of the type . This suggests that the source is gravitationally
unstable. Finally, we demonstrate that the temperature at the core surface is
consistent with a core luminosity of and conclude that we
might be observing a protostar still accreting material from its parental
cloud, whose mass at present is .Comment: 18 pages, 20 figure
Molecular CO outflows in the L1641-N cluster: kneading a cloud core
We present results of 1.3mm interferometric and single-dish observations of
the center of the L1641-N cluster in Orion. Single-dish wide-field continuum
and CO(2-1) observations reveal the presence of several molecular outflows
driven by deeply embedded protostellar sources. At higher angular resolution,
the dominant millimeter source in the cluster center is resolved into a pair of
protostars (L1641-N-MM1 and MM3), each driving a collimated outflow, and a more
extended, clumpy core. Low-velocity CO line-wing emission is widely spread over
much of the cluster area. We detect and map the distribution of several other
molecular transitions (13CO, C18O, 13CS, SO, CH3OH, CH3CN, and OCS). CH3CN and
OCS may indicate the presence of a hot corino around L1641-N-MM1. We
tentatively identify a velocity gradient over L1641-N-MM1 in CH3CN and OCS,
oriented roughly perpendicular to the outflow direction, perhaps indicative of
a circumstellar disk. An analysis of the energy and momentum load of the CO
outflows, along with the notion that apparently a large volume fraction is
affected by the multiple outflow activity, suggests that outflows from a
population of low-mass stars might have a significant impact on clustered (and
potentially high-mass) star formation.Comment: 16 pages plus 10 figures accepted by AJ, full resolution version
available at http://www.eso.org/~tstanke/preprints.htm
Search for massive protostellar candidates in the southern hemisphere: I. Association with dense gas
(Abridged) We have observed CS and C17O lines, and 1.2 mm cont. emission
towards a sample of 130 high-mass protostellar candidates with DEC<-30 deg.
This is the first step of the southern extension of a project started more than
a decade ago aimed at the identification of massive protostellar candidates. We
selected from the IRAS PSC 429 sources which potentially are compact molecular
clouds. The sample is divided into two groups: the 298 sources with
[25-12]>0.57 and [60-12]>1.30 we call 'High' sources, the remaining 131 we call
'Low' sources. In this paper, we check the association with dense gas and dust
in 130 'Low' sources. We find a detection rate of ca. 85% in CS, demonstrating
a tight association with dense molecular clumps. Among the sources detected in
CS, ca. 76% have also been detected in C17O and ca. 93% in the 1.2 mm cont.
Mm-cont. maps show the presence of clumps with diameters 0.2-2 pc and masses
from a few Msun to 10^5 Msun; H2 volume densities lie between ca. 10^{4.5} and
10^{5.5} cm^{-3}. The L(bol) are 10^3-10^6 Lsun, consistent with embedded
high-mass objects. Based on our results and those found in the literature for
other samples, we conclude that our sources are massive objects probably in a
stage prior to the formation of an HII region. We propose a scenario in which
'High' and 'Low' sources are both made of a massive clump hosting a high-mass
protostellar candidate and a nearby stellar cluster. The difference might be
due to the fact that the IRAS 12mu flux, the best discriminant between the two
groups, is dominated by the emission from the cluster in 'Lows' and from the
massive protostellar object in 'Highs'.Comment: Accepted for publication in Astron. & Astroph.; 34 pages (incl. 14
figures and 8 tables
Weak and Compact Radio Emission in Early High-Mass Star Forming Regions: II. The Nature of the Radio Sources
In this study we analyze 70 radio continuum sources associated with dust
clumps and considered to be candidates for the earliest stages of high-mass
star formation. The detection of these sources was reported by Rosero et al.
(2016), who found most of them to show weak (1 mJy) and
compact (0.6) radio emission. Herein, we
used the observed parameters of these sources to investigate the origin of the
radio continuum emission. We found that at least of these radio
detections are most likely ionized jets associated with high-mass protostars,
but for the most compact sources we cannot discard the scenario that they
represent pressure-confined HII regions. This result is highly relevant for
recent theoretical models based on core accretion that predict the first stages
of ionization from high-mass stars to be in the form of jets. Additionally, we
found that properties such as the radio luminosity as a function of the
bolometric luminosity of ionized jets from low and high-mass stars are
extremely well-correlated. Our data improve upon previous studies by providing
further evidence of a common origin for jets independently of luminosity.Comment: Accepted for publication in the Ap
Weak and Compact Radio Emission in Early High-Mass Star Forming Regions: I. VLA Observations
We present a high sensitivity radio continuum survey at 6 and 1.3cm using
the Karl G. Jansky Very Large Array towards a sample of 58 high-mass star
forming regions. Our sample was chosen from dust clumps within infrared dark
clouds with and without IR sources (CMC-IRs, CMCs, respectively), and hot
molecular cores (HMCs), with no previous, or relatively weak radio continuum
detection at the mJy level. Due to the improvement in the continuum
sensitivity of the VLA, this survey achieved map rms levels of 3-10
Jy beam at sub-arcsecond angular resolution. We extracted 70
centimeter continuum sources associated with 1.2mm dust clumps. Most
sources are weak, compact, and are prime candidates for high-mass protostars.
Detection rates of radio sources associated with the mm dust clumps for CMCs,
CMC-IRs and HMCs are 6, 53 and 100, respectively. This result is
consistent with increasing high-mass star formation activity from CMCs to HMCs.
The radio sources located within HMCs and CMC-IRs occur close to the dust clump
centers with a median offset from it of 12,000AU and 4,000AU,
respectively. We calculated 5 - 25GHz spectral indices using power law fits
and obtain a median value of 0.5 (i.e., flux increasing with frequency),
suggestive of thermal emission from ionized jets. In this paper we describe the
sample, observations, and detections. The analysis and discussion will be
presented in Paper II.Comment: Accepted for publication in the ApJ
A New Galactic 6cm Formaldehyde Maser
We report the detection of a new H2CO maser in the massive star forming
region G23.71-0.20 (IRAS 18324-0820), i.e., the fifth region in the Galaxy
where H2CO maser emission has been found. The new H2CO maser is located toward
a compact HII region, and is coincident in velocity and position with 6.7 GHz
methanol masers and with an IR source as revealed by Spitzer/IRAC GLIMPSE data.
The coincidence with an IR source and 6.7 GHz methanol masers suggests that the
maser is in close proximity to an embedded massive protostar. Thus, the
detection of H2CO maser emission toward G23.71-0.20 supports the trend that
H2CO 6cm masers trace molecular material very near young massive stellar
objects.Comment: Accepted for publication in The Astrophysical Journal Letter
A highly-collimated SiO jet in the HH212 protostellar outflow
We mapped the HH212 Class 0 outflow in SiO(2--1, 5--4) and continuum using
the PdBI in its extended configurations. The unprecedented angular resolution
(down to 0.34") allows accurate comparison with a new, deep H2 image obtained
at the VLT. The SiO emission is confined to a highly-collimated bipolar jet
(width 0.35") along the outflow axis. The jet can be traced down to within 500
AU of the protostar, in a region that is heavily obscured in H2 images. Where
both species are detected, SiO shows the same overall kinematics and structure
as H2, indicating that both molecules are tracing the same material. We find
that the high-velocity SiO gas near the protostar is not tracing a wide-angle
wind but is already confined to a flow inside a narrow cone of half-opening
angle < 6 deg.Comment: Astronomy and Astrophysics Letter, in pres
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