14 research outputs found
Infrared emission from interstellar dust cloud with two embedded sources: IRAS 19181+1349
Mid and far infrared maps of many Galactic star forming regions show multiple
peaks in close proximity, implying more than one embedded energy sources. With
the aim of understanding such interstellar clouds better, the present study
models the case of two embedded sources. A radiative transfer scheme has been
developed to deal with an uniform density dust cloud in a cylindrical geometry,
which includes isotropic scattering in addition to the emission and absorption
processes. This scheme has been applied to the Galactic star forming region
associated with IRAS 19181+1349, which shows observational evidence for two
embedded energy sources. Two independent modelling approaches have been
adopted, viz., to fit the observed spectral energy distribution (SED) best; or
to fit the various radial profiles best, as a function of wavelength. Both the
models imply remarkably similar physical parameters.Comment: 17 pages, 6 Figures, uses epsf.sty. To appear in Journal of
Astronophysics & Astronom
Recent star formation in the inner Galactic Bulge seen by ISOGAL. I - Classification of bright mid-IR sources in a test field
Context: The stellar populations in the central region of the Galaxy are
poorly known because of the high visual extinction and very great source
density in this direction.
Aims: To use recent infrared surveys for studying the dusty stellar objects
in this region.
Methods: We analyse the content of a 20x20 arcmin^2 field centred at
(l,b)=(-0.27,-0.06) observed at 7 and 15 microns as part of the ISOGAL survey.
These ISO observations are more than an order of magnitude better in
sensitivity and spatial resolution than the IRAS observations. The sources are
cross-associated with other catalogues to identify various types of objects. We
then derive criteria to distinguish young objects from post-main sequence
stars.
Results: We find that a sample of about 50 young stellar objects and
ultra-compact HII regions emerges, out of a population of evolved AGB stars. We
demonstrate that the sources colours and spatial extents, as they appear in the
ISOGAL catalogue, possibly complemented with MSX photometry at 21 microns, can
be used to determine whether the ISOGAL sources brighter than 300 mJy at 15
microns (or [15] < 4.5 mag) are young objects or late-type evolved stars.Comment: 15 pages, 12 figures. Accepted for publication in Astronomy and
Astrophysic
Far and mid infrared observations of two ultracompact H II regions and one compact CO clump
Two ultracompact H II regions (IRAS 19181+1349 and 20178+4046) and one
compact molecular clump (20286+4105) have been observed at far infrared
wavelengths using the TIFR 1 m balloon-borne telescope and at mid infrared
wavelengths using ISO. Far infrared observations have been made simultaneously
in two bands with effective wavelengths of ~ 150 and ~ 210 micron, using liquid
3He cooled bolometer arrays. ISO observations have been made in seven spectral
bands using the ISOCAM instrument; four of these bands cover the emission from
Polycyclic Aromatic Hydrocarbon (PAH) molecules. In addition, IRAS survey data
for these sources in the four IRAS bands have been processed using the HIRES
routine. In the high resolution mid infrared maps as well as far infrared maps
multiple embedded energy sources have been resolved. There are structural
similarities between the images in the mid infrared and the large scale maps in
the far infrared bands, despite very different angular resolutions of the two.
Dust temperature and optical depth (tau_150 um) maps have also been generated
using the data from balloon-borne observations. Spectral energy distributions
(SEDs) for these sources have been constructed by combining the data from all
these observations. Radiation transfer calculations have been made to
understand these SEDs. Parameters for the dust envelopes in these sources have
been derived by fitting the observed SEDs. In particular, it has been found
that radial density distribution for three sources is diffrent. Whereas in the
case of IRAS 20178+4046, a steep distribution of the form r^-2 is favoured, for
IRAS 20286+4105 it is r^-1 and for IRAS 19181+1349 it the uniform distribution
(r^0). Line ratios for PAH bands have generally been found to be similar to
those for other compact H II regions but different from general H II regions.Comment: To appear in Astronomy & Astrophysics; (19 pages including 14 Figures
and 6 Tables
Radio sources at low Galactic latitudes
We present high-resolution radio observations of a sample of 65 radio sources
at low Galactic latitudes. The sources were all observed at 5 GHz with the Very
Large Array A-array. MERLIN observations at 5 GHz of the ultracompact HII
region G34.26+0.15 and one of the extragalactic sources, B1857-000, are also
presented, as are GMRT observations of HI in the direction of three sources,
B1801-203, B1802-196 and B1938+229. These observations were made with the
objectives of (i) finding compact components suitable for studying the effects
of interstellar scattering at lower frequencies, (ii) identifying high
surface-brightness lobes of background radio sources to probe the Galactic
magnetic field on different scales via polarization observations, and (iii)
searching for young supernova remnants. We discuss the nature of the sources
found to have shell or shell-like structure and exhibiting both thermal and
non-thermal spectra. Of the remaining sources, B1749-281 is coincident within
the positional errors of a known pulsar, not detected earlier at 5 GHz. The
rest are likely to be background extragalactic objects.Comment: 12 pages, 6 figures (most with multiple images), 1 table. Accepted
for publicaton in MNRA
Understanding the Spectral Energy Distributions of the Galactic Star Forming Regions IRAS 18314-0720, 18355-0532 & 18316-0602
Embedded Young Stellar Objects (YSO) in dense interstellar clouds is treated
self-consistently to understand their spectral energy distributions (SED).
Radiative transfer calculations in spherical geometry involving the dust as
well as the gas component, have been carried out to explain observations
covering a wide spectral range encompassing near-infrared to radio continuum
wavelengths. Various geometric and physical details of the YSOs are determined
from this modelling scheme. In order to assess the effectiveness of this
self-consistent scheme, three young Galactic star forming regions associated
with IRAS 18314-0720, 18355-0532 and 18316-0602 have been modelled as test
cases. They cover a large range of luminosity ( 40). The modelling of
their SEDs has led to information about various details of these sources, e.g.
embedded energy source, cloud structure & size, density distribution,
composition & abundance of dust grains etc. In all three cases, the best fit
model corresponds to the uniform density distribution.Comment: AAMS style manuscript with 3 tables (in a separate file) and 4
figures. To appear in Journal of Astronophysics & Astronom
The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X
We have made an extensive 1.2mm continuum mosaicing study of the Cygnus X
molecular cloud complex using the MAMBO cameras at the IRAM 30 m telescope. We
then compared our mm maps with mid-IR images, and have made SiO(2-1) follow-up
observations of the best candidate progenitors of high-mass stars. Our complete
study of Cygnus X provides, for the first time, an unbiased census of massive
young stellar objects. We discover 129 massive dense cores, among which 42 are
probable precursors of high-mass stars. Our study qualifies 17 cores as good
candidates for hosting massive IR-quiet protostars, while up to 25 cores
potentially host high-luminosity IR protostars. We fail to discover the
high-mass analogs of pre-stellar dense cores in CygnusX, but find several
massive starless clumps that might be gravitationally bound. Since our sample
is derived from a single molecular complex and covers every embedded phase of
high-mass star formation, it gives the first statistical estimates of their
lifetime. In contrast to what is found for low-mass class 0 and class I phases,
the IR-quiet protostellar phase of high-mass stars may last as long as their
better-known high-luminosity IR phase. The statistical lifetimes of high-mass
protostars and pre-stellar cores (~ 3 x 10^4 yr and < 10^3 yr) in Cygnus X are
one and two order(s) of magnitude smaller, respectively, than what is found in
nearby, low-mass star-forming regions. We therefore propose that high-mass
pre-stellar and protostellar cores are in a highly dynamic state, as expected
in a molecular cloud where turbulent processes dominate.Comment: 32 pages, 62 figures to be published in Astronomy & Astrophysics
journa
The SPECFIND V2.0 catalogue of radio cross-identifications and spectra. SPECFIND meets the Virtual Observatory
The new release of the SPECFIND radio cross-identification catalogue,
SPECFIND V2.0, is presented. It contains 107488 cross-identified objects with
at least three radio sources observed at three independent frequencies.
Compared to the previous release the number of entry radio catalogues is
increased from 20 to 97 containing 115 tables. This large increase was only
made possible by the development of four tools at CDS which use the standards
and infrastructure of the Virtual Observatory (VO). This was done in the
framework of the VO-TECH European Design Study of the Sixth Framework Program.
We give an overview of the different classes of radio sources that a user can
encounter. Due to the increase of frequency coverage of the input radio
catalogues, this release demonstrates that the SPECFIND algorithm is able to
detect spectral breaks around a frequency of ~1 GHz.Comment: 11 pages, 10 figures, accepted for publication in A&
Excited-state hydroxyl maser catalogue from the methanol multibeam survey -- I. Positions and Variability
We present the results of the first complete unbaised survey of the Galactic Plane for 6035-MHz excited-state hydroxyl masers undertaken as part of the Methanol Multibeam Survey. These observations cover the Galactic longitude ranges $186^{\circ}Peer reviewedFinal Published versio
HESS VHE Gamma-Ray Sources Without Identified Counterparts
The detection of gamma rays in the very-high-energy (VHE) energy range (100
GeV--100 TeV) provides a direct view of the parent population of
ultra-relativistic particles found in astrophysical sources. For this reason,
VHE gamma rays are useful for understanding the underlying astrophysical
processes in non-thermal sources. We investigate unidentified VHE gamma-ray
sources that have been discovered with HESS in the most sensitive blind survey
of the Galactic plane at VHE energies conducted so far. The HESS array of
imaging atmospheric Cherenkov telescopes (IACTs) has a high sensitivity
compared with previous instruments(~ 0.01 Crab) in 25 hours observation time
for a 5 sigma point-source detection), and with its large field of view, is
well suited for scan-based observations. The on-going HESS survey of the inner
Galaxy has revealed a large number of new VHE sources, and for each we attempt
to associate the VHE emission with multi-wavelength data in the radio through
X-ray wavebands. For each of the eight unidentified VHE sources considered
here, we present the energy spectra and sky maps of the sources and their
environment. The VHE morphology is compared with available multi-wavelength
data (mainly radio and X-rays). No plausible counterparts are found
ATLASGAL-selected massive clumps in the inner Galaxy IV. Millimeter hydrogen recombination lines from associated HII regions
Aims: Observations of millimeter wavelength radio recombination lines (mm-RRLs) are used to search for H ii regions in an unbiased way that is complementary to many of the more traditional methods previously used (e.g., radio continuum, far-infrared colors, maser emission). The mm-RRLs can be used to derive physical properties of H ii regions and to provide velocity information of ionized gas.
Methods: We carried out targeted mm-RRL observations (39 ≤ principal quantum number (n) ≤ 65 and Δn = 1, 2, 3, and 4, named Hnα, Hnβ, Hnγ, and Hnδ) using the IRAM 30 m and Mopra 22 m telescopes. In total, we observed 976 compact dust clumps selected from a catalog of ~10 000 sources identified by the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL). The sample was selected to ensure a representative mix of star-forming and quiescent clumps such that a variety of different evolutionary stages is represented. Approximately half of the clumps are mid-infrared quiet while the other half are mid-infrared bright.
Results: We detected Hnα mm-RRL emission toward 178 clumps; Hnβ, Hnγ, and Hnδ were also detected toward 65, 23, and 22 clumps, respectively. This is the largest sample of mm-RRLs detections published to date. Comparing the positions of these clumps with radio continuum surveys we identified compact radio counterparts for 134 clumps, confirming their association with known H ii regions. The nature of the other 44 detections is unclear, but 8 detections are thought to be potentially new H ii regions while the mm-RRL emission from the others may be due to contamination from nearby evolved H ii regions. Broad linewidths are seen toward nine clumps (linewidth > 40 km s-1) revealing significant turbulent motions within the ionized gas; in the past, such wide linewidths were found toward very compact and dense H ii regions. We find that the systemic velocity of the associated dense molecular gas, traced by H13CO+(1−0), is consistent with the mm-RRL velocities and confirms them as embedded H ii regions. We also find that the linewidth of the H13CO+(1−0) emission is significantly wider than those without mm-RRL detection, indicating a physical connection between the embedded H ii region and their natal environments. We also find a correlation between the integrated fluxes of the mm-RRLs and the 6 cm continuum flux densities of their radio counterparts (the correlation coefficient, ρ, is 0.70). By calculating the electron densities we find that the mm-RRL emission is associated with H ii regions with ne 0.03 pc.
Conclusions: We detected mm-RRLs toward 178 clumps and identified eight new H ii region candidates. The broad mm-RRL from nine clumps may indicate that they arise in very young hyper-compact H ii regions. The mm-RRLs trace the radio continuum sources detected by high-resolution observations and their line parameters show associations with the embedded radio sources and their parental molecular clumps