525 research outputs found
Radio emission from the high-mass X-ray binary BP Cru: first detection
BP Cru is a well known high-mass X-ray binary composed of a late B hypergiant
(Wray 977) and a neutron star, also observed as the X-ray pulsar GX 301-2. No
information about emission from BP Cru in other bands than X-rays and optical
has been reported to date in the literature, though massive X-ray binaries
containing black holes can have radio emission from a jet. In order to assess
the presence of a radio jet, we searched for radio emission towards BP Cru
using the Australia Compact Array Telescope during a survey for radio emission
from Be/X-ray transients. We probed the 41.5d orbit of BP Cru with the
Australia Telescope Compact Array not only close to periastron but also close
to apastron. BP Cru was clearly detected in our data on 4, possibly 6, of 12
occasions at 4.8 and 8.6 GHz. Our data suggest that the spectral index of the
radio emission is modulated either by the X-ray flux or the orbital phase of
the system. We propose that the radio emission of BP Cru probably arises from
two components: a persistent component, coming from the mass donor Wray 977,
and a periodic component connected to the accretion onto the neutron star,
possibly coming from a (weak and short lived) jet.Comment: 2 figures, accepted for publication in A+A letter
Bipolar HII regions - Morphology and star formation in their vicinity - I - G319.8800.79 and G010.3200.15
Our goal is to identify bipolar HII regions and to understand their
morphology, their evolution, and the role they play in the formation of new
generations of stars. We use the Spitzer and Herschel Hi-GAL surveys to
identify bipolar HII regions. We search for their exciting star(s) and estimate
their distances using near-IR data. Dense clumps are detected using
Herschel-SPIRE data. MALT90 observations allow us to ascertain their
association with the central HII region. We identify Class 0/I YSOs using their
Spitzer and Herschel-PACS emissions. These methods will be applied to the
entire sample of candidate bipolar HII regions. This paper focuses on two
bipolar HII regions, one interesting in terms of its morphology,
G319.8800.79, and one in terms of its star formation, G010.3200.15. Their
exciting clusters are identified and their photometric distances estimated to
be 2.6 kpc and 1.75 kpc, respectively. We suggest that these regions formed in
dense and flat structures that contain filaments. They have a central ionized
region and ionized lobes perpendicular to the parental cloud. The remains of
the parental cloud appear as dense (more than 10^4 per cm^3) and cold (14-17 K)
condensations. The dust in the PDR is warm (19-25 K). Dense massive clumps are
present around the central ionized region. G010.32-00.14 is especially
remarkable because five clumps of several hundred solar masses surround the
central HII region; their peak column density is a few 10^23 per cm^2, and the
mean density in their central regions reaches several 10^5 per cm^3. Four of
them contain at least one massive YSO; these clumps also contain extended green
objects and Class II methanol masers. This morphology suggests that the
formation of a second generation of massive stars has been triggered by the
central bipolar HII region. It occurs in the compressed material of the
parental cloud.Comment: 32 pages, 28 figures, to be published in A&
The value of PET, CT and in-line PET/CT in patients with gastrointestinal stromal tumours: long-term outcome of treatment with imatinib mesylate
Purpose: Gastrointestinal stromal tumours (GIST) are mesenchymal neoplasms of the gastrointestinal tract that are unresponsive to standard sarcoma chemotherapy. Imaging of GIST patients is done with structural and functional methods such as contrast-enhanced helical computed tomography (ceCT) and positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG). The aim of this study was to compare the prognostic power of PET and ceCT and to evaluate the clinical role of PET/CT imaging. Methods: All patients with GIST undergoing PET or PET/CT examinations were prospectively included in this study, and the median overall survival, time to progression and treatment duration were documented. The prognostic significance of PET and ceCT criteria of treatment response was assessed and PET/CT was compared with PET and ceCT imaging. Data for 34 patients (19 male, 15 female, 21-76 years) undergoing PET or PET/CT for staging or restaging were analysed. Results: In 28 patients, PET/CT and ceCT were available after introduction of treatment with the tyrosine kinase inhibitor imatinib mesylate (Gleevec; Novartis, Basel, Switzerland). Patients without FDG uptake after the start of treatment had a better prognosis than patients with residual activity. In contrast, ceCT criteria provided insufficient prognostic power. However, more lesions were found on ceCT images than on PET images, and FDG uptake was sometimes very variable. PET/CT delineated active lesions better than did the combination of PET and ceCT imaging. Conclusion: Both PET and PET/CT provide important prognostic information and have an impact on clinical decision-making in GIST patients. PET/CT precisely delineates lesions and thus allows for the correct planning of surgical intervention
The Bolocam Galactic Plane Survey. XIV. Physical Properties of Massive Starless and Star Forming Clumps
We sort molecular clouds between from the
Bolocam Galactic Plane Survey based on observational diagnostics of star
formation activity: compact sources, mid-IR color-selected
YSOs, and masers, and UCHII regions. We also
present a combined -derived gas kinetic temperature and maser catalog for clumps from our own GBT 100m observations and
from the literature. We identify a subsample of () starless
clump candidates, the largest and most robust sample identified from a blind
survey to date. Distributions of flux density, flux concentration, solid angle,
kinetic temperature, column density, radius, and mass show strong ( dex)
progressions when sorted by star formation indicator. The median starless clump
candidate is marginally sub-virial () with of clumps
with known distance being gravitationally bound (). These samples
show a statistically significant increase in the median clump mass of M from the starless candidates to clumps associated with
protostars. This trend could be due to (i) mass growth of the clumps at
Msun Myr for an average free-fall Myr
time-scale, (ii) a systematic factor of two increase in dust opacity from
starless to protostellar phases, (iii) and/or a variation in the ratio of
starless to protostellar clump lifetime that scales as . By
comparing to the observed number of maser containing clumps we
estimate the phase-lifetime of massive ( M) starless clumps to
be ; the majority
( M) have phase-lifetimes longer than their average free-fall
time.Comment: Accepted for publication in ApJ; 33 pages; 22 figures; 7 table
NG7538 IRS1 N: modeling a circumstellar maser disk
We present an edge-on Keplerian disk model to explain the main component of
the 12.2 and 6.7 GHz methanol maser emission detected toward NGC7538-IRS1 N.
The brightness distribution and spectrum of the line of bright masers are
successfully modeled with high amplification of background radio continuum
emission along velocity coherent paths through a maser disk. The bend seen in
the position-velocity diagram is a characteristic signature of differentially
rotating disks. For a central mass of 30 solar masses, suggested by other
observations, our model fixes the masing disk to have inner and outer radii of
about 270 AU and 750 AU.Comment: To appear in The Proceedings of the 2004 European Workshop: "Dense
Molecular Gas around Protostars and in Galatic Nuclei", Eds. Y. Hagiwara,
W.A. Baan, H.J. van Langevelde, 2004, a special issue of ApSS, Kluwe
Methanol masers probing the ordered magnetic field of W75N
The role of magnetic fields during the protostellar phase of high-mass
star-formation is a debated topic. In particular, it is still unclear how
magnetic fields influence the formation and dynamic of disks and outflows. Most
current information on magnetic fields close to high-mass protostars comes from
H2O and OH maser observations. Recently, the first 6.7 GHz methanol maser
polarization observations were made, and they reveal strong and ordered
magnetic fields. The morphology of the magnetic field during high-mass
star-formation needs to be investigated on small scales, which can only be done
using very long baseline interferometry observations. The massive star-forming
regionW75N contains three radio sources and associated masers, while a
large-scale molecular bipolar outflow is also present. Polarization
observations of the 6.7 GHz methanol masers at high angular resolution probe
the strength and structure of the magnetic field and determine its relation to
the outflow. Eight of the European VLBI network antennas were used to measure
the linear polarization and Zeeman-splitting of the 6.7 GHz methanol masers in
the star-forming region W75N. We detected 10 methanol maser features, 4 of
which were undetected in previous work. All arise near the source VLA1 of W75N.
The linear polarization of the masers reveals a tightly ordered magnetic field
over more than 2000 AU around VLA1 that is exactly aligned with the large-scale
molecular outflow. This is consistent with the twisted magnetic field model
proposed for explaining dust polarization observations. The Zeeman-splitting
measured on 3 of the maser features indicates a dynamically important magnetic
field in the maser region of the order of 50mG. We suggest VLA1 is the powering
sources of the bipolar outflow.Comment: 5 pages, 3 figures, accepted by Astronomy and Astrophysic
The RMS Survey: 13CO observations of candidate massive YSOs in the southern hemisphere
Abridged: The Red MSX Source (RMS) survey is an ongoing multi-wavelength
observational programme designed to return a large, well-selected sample of
massive young stellar objects (MYSOs). Here we present 13CO observations made
towards 854 MYSOs candidates located in the 3rd and 4th quadrants. We detected
13CO emission towards a total of 751 of the 854 RMS sources observed (~88%). In
total 2185 emission components are detected above 3 level. Multiple
emission profiles are observed towards the majority of these sources - 455
sources (~60%) - with an average of ~4 molecular clouds along the line of
sight. These multiple emission features make it difficult to assign a kinematic
velocity to many of our sample. We have used archival CS (J=2-1) and maser
velocities to resolved the component multiplicity towards 82 sources and have
derived a criterion which is used to identify the most likely component for a
further 202 multiple component sources. Combined with the single component
detections we have obtained unambiguous kinematic velocities towards 580
sources (~80% of the detections). The 171 sources for which we have not been
able to determine the kinematic velocity will require additional line data.
Using the rotation curve of Brand and Blitz (1993) and their radial velocities
we calculate kinematic distances for all components detected.Comment: Summitted to A&A, the resolution of figure 1 has been reduced,
samples of Table 3 and Figure 11 are now included but the full version will
only be available in the online version of the journa
Physical characterisation of southern massive star-forming regions using Parkes NH observations
We have undertaken a Parkes ammonia spectral line study, in the lowest two
inversion transitions, of southern massive star formation regions, including
young massive candidate protostars, with the aim of characterising the earliest
stages of massive star formation. 138 sources from the submillimetre continuum
emission studies of Hill et al., were found to have robust (1,1) detections,
including two sources with two velocity components, and 102 in the (2,2)
transition.
We determine the ammonia line properties of the sources: linewidth, flux
density, kinetic temperature, NH column density and opacity, and revisit
our SED modelling procedure to derive the mass for 52 of the sources. By
combining the continuum emission information with ammonia observations we
substantially constrain the physical properties of the high-mass clumps. There
is clear complementarity between ammonia and continuum observations for
derivations of physical parameters.
The MM-only class, identified in the continuum studies of Hill et al.,
display smaller sizes, mass and velocity dispersion and/or turbulence than
star-forming clumps, suggesting a quiescent prestellar stage and/or the
formation of less massive stars.Comment: 20 pages, 9 Figures, 1 appendix (to appear in full online only, a
sample appendix in the paper); 7 tables. Accepted by MNRA
<i>Herschel</i> observations of B1-bS and B1-bN: two first hydrostatic core candidates in the Perseus star-forming cloud
We report far-infrared Herschel observations obtained between 70 μm and 500 μm of two star-forming dusty condensations, [HKM99] B1-bS and [HKM99] B1-bN, in the B1 region of the Perseus star-forming cloud. In the western part of the Perseus cloud, B1-bS is the only source detected in all six PACS and SPIRE photometric bands, but it is not visible in the Spitzer map at 24 μm. B1-bN is clearly detected between 100 μm and 250 μm. We have fitted the spectral energy distributions of these sources to derive their physical properties, and find that a simple greybody model fails to reproduce the observed spectral energy distributions. At least a two-component model is required, consisting of a central source surrounded by a dusty envelope. The properties derived from the fit, however, suggest that the central source is not a Class 0 object. We then conclude that while B1-bS and B1-bN appear to be more evolved than a pre-stellar core, the best-fit models suggest that their central objects are younger than a Class 0 source. Hence, they may be good candidates to be examples of the first hydrostatic core phase. The projected distance between B1-bS and B1-bN is a few Jeans lengths. If their physical separation is close to this value, this pair would allow studying the mutual interactions between two forming stars at a very early stage of their evolution
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