241 research outputs found
[CI], [CII] and CO emission lines as a probe for alpha variations at low and high redshifts
The offsets between the radial velocities of the rotational transitions of
carbon monoxide and the fine structure transitions of neutral and singly
ionized carbon are used to test the hypothetical variation of the fine
structure constant, alpha. From the analysis of the [CI] and [CII] fine
structure lines and low J rotational lines of 12CO and 13CO, emitted by the
dark cloud L1599B in the Milky Way disk, we find no evidence for fractional
changes in alpha at the level of || < 3*10^-7. For the
neighbour galaxy M33 a stringent limit on Delta alpha/alpha is set from
observations of three HII zones in [CII] and CO emission lines: || < 4*10^-7. Five systems over the redshift interval z = 5.7-6.4,
showing CO J=6-5, J=7-6 and [CII] emission, yield a limit on || < 1.3*10^-5. Thus, a combination of the [CI], [CII], and CO
emission lines turns out to be a powerful tool for probing the stability of the
fundamental physical constants over a wide range of redshifts not accessible to
optical spectral measurements.Comment: 10 pages, 3 figures, 5 tables. Accepted for publication 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
The Carbon content in the Galactic CygnusX/DR21 star forming region
Observations of Carbon bearing species are among the most important
diagnostic probes of ongoing star formation. CO is a surrogate for H and is
found in the vicinity of star formation sites. There, [CI] emission is thought
to outline the dense molecular cores and extend into the lower density regions,
where the impinging interstellar UV radiation field plays a critical role for
the dissociation and ionization processes. Emission of ionized carbon ([CII])
is found to be even more extended than [CI] and is linking up with the ionized
medium. These different tracers emphasize the importance of multi-wavelength
studies to draw a coherent picture of the processes driving and driven by high
mass star formation. Until now, large scale surveys were only done with low
resolution, such as the COBE full sky survey, or were biased to a few selected
bright sources (e.g. Yamamoto et al. 2001, Schneider et al. 2003). A broader
basis of unbiased, high-resolution observations of [CI], CO, and [CII] may play
a key role to probe the material processed by UV radiation.Comment: 4 pages, 4 figure, to appear in "Proceedings of the 4th
Cologne-Bonn-Zermatt-Symposium", ed. S. Pfalzner, C. Kramer, C. Straubmeier,
and A. Heithausen (Springer Verlag
Spatial distribution of emission in Unidentified Infrared Bands from Midcourse Space Experiment Survey
Recently the Midcourse Space Experiment (MSX) has surveyed the Galactic plane
in mainly four infrared bands between 6 and 25 micron. Two of these bands cover
several Unidentified Infrared emission Bands (UIBs). With the aim of extracting
the spatial distribution of the UIB emission on a large scale, a scheme has
been developed to model the MSX data with emission in the UIBs alongwith the
underlying thermal continuum from the interstellar dust. In order to test this
scheme, a sample of five Galactic compact H II regions (Sh-61, Sh-138, Sh-152,
Sh-156, Sh-186; Zavagno & Ducci 2001) for which imaging study in some
individual UIBs is available from ISOCAM measurements, has been studied. The
results of this comparative study on small angular scale are as follows : (i)
the morphological details extracted from our scheme agree very well with those
from the superior ISOCAM measurements; (ii) the integrated strength of UIBs
extracted from the MSX database correlates extremely well with the sum of the
strengths of individual UIBs measured from ISOCAM. This tight correlation is
very encouraging and promises the potential of MSX database for study of large
scale spatial distribution of UIB emission (and the carriers of UIBs) in the
entire Galactic plane.Comment: to be published in Astronomy & Astrophysics; (9 pages including 2
tables & 11 figures
Probing the massive star forming environment - a multiwavelength investigation of the filamentary IRDC G333.73+0.37
We present a multiwavelength study of the filamentary infrared dark cloud
(IRDC) G333.73+0.37. The region contains two distinct mid-infrared sources S1
and S2 connected by dark lanes of gas and dust. Cold dust emission from the
IRDC is detected at seven wavelength bands and we have identified 10 high
density clumps in the region. The physical properties of the clumps such as
temperature: 14.3-22.3 K and mass: 87-1530 M_sun are determined by fitting a
modified blackbody to the spectral energy distribution of each clump between
160 micron and 1.2 mm. The total mass of the IRDC is estimated to be $~4700
M_sun. The molecular line emission towards S1 reveals signatures of
protostellar activity. Low frequency radio emission at 1300 and 610 MHz is
detected towards S1 (shell-like) and S2 (compact morphology), confirming the
presence of newly formed massive stars in the IRDC. Photometric analysis of
near and mid-infrared point sources unveil the young stellar object population
associated with the cloud. Fragmentation analysis indicates that the filament
is supercritical. We observe a velocity gradient along the filament, that is
likely to be associated with accretion flows within the filament rather than
rotation. Based on various age estimates obtained for objects in different
evolutionary stages, we attempt to set a limit to the current age of this
cloud.Comment: 26 pages, 20 figures, accepted by Ap
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
Efficient absolute aspect determination of a balloon borne far infrared telescope using a solid state optical photometer
The observational and operational efficiency of the TIFR 1 meter balloon
borne far infrared telescope has been improved by incorporating a multielement
solid state optical photometer (SSOP) at the Cassegrain focus of the telescope.
The SSOP is based on a 1-D linear photo diode array (PDA). The online and
offline processing schemes of the PDA signals which have been developed, lead
to improvement in the determination of absolute telescope aspect (
0\farcm8), which is very crucial for carrying out the observations as well as
offline analysis. The SSOP and its performance during a recent balloon flight
are presented here.Comment: To appear in the February 2000 issue of the PAS
Far infrared mapping of three Galactic star forming regions : W3(OH), S 209 & S 187
Three Galactic star forming regions associated with W3(OH), S209 and S187
have been simultaneously mapped in two trans-IRAS far infrared (FIR) bands
centered at ~ 140 and 200 micron using the TIFR 100 cm balloon borne FIR
telescope. These maps show extended FIR emission with structures. The HIRES
processed IRAS maps of these regions at 12, 25, 60 & 100 micron have also been
presented for comparison. Point-like sources have been extracted from the
longest waveband TIFR maps and searched for associations in the other five
bands. The diffuse emission from these regions have been quantified, which
turns out to be a significant fraction of the total emission. The spatial
distribution of cold dust (T < 30 K) for two of these sources (W3(OH) & S209),
has been determined reliably from the maps in TIFR bands. The dust temperature
and optical depth maps show complex morphology. In general the dust around S209
has been found to be warmer than that in W3(OH) region.Comment: Accepted for publication in Journal of Astrophysics and Astronomy (20
pages including 8 figures & 3 tables
Temperatures of dust and gas in S~140
In dense parts of interstellar clouds (> 10^5 cm^-3), dust & gas are expected
to be in thermal equilibrium, being coupled via collisions. However, previous
studies have shown that the temperatures of the dust & gas may remain decoupled
even at higher densities. We study in detail the temperatures of dust & gas in
the photon-dominated region S 140, especially around the deeply embedded
infrared sources IRS 1-3 and at the ionization front. We derive the dust
temperature and column density by combining Herschel PACS continuum
observations with SOFIA observations at 37 m and SCUBA at 450 m. We
model these observations using greybody fits and the DUSTY radiative transfer
code. For the gas part we use RADEX to model the CO 1-0, CO 2-1, 13CO 1-0 and
C18O 1-0 emission lines mapped with the IRAM-30m over a 4' field. Around IRS
1-3, we use HIFI observations of single-points and cuts in CO 9-8, 13CO 10-9
and C18O 9-8 to constrain the amount of warm gas, using the best fitting dust
model derived with DUSTY as input to the non-local radiative transfer model
RATRAN. We find that the gas temperature around the infrared sources varies
between 35 and 55K and that the gas is systematically warmer than the dust by
~5-15K despite the high gas density. In addition we observe an increase of the
gas temperature from 30-35K in the surrounding up to 40-45K towards the
ionization front, most likely due to the UV radiation from the external star.
Furthermore, detailed models of the temperature structure close to IRS 1 show
that the gas is warmer and/or denser than what we model. Finally, modelling of
the dust emission from the sub-mm peak SMM 1 constrains its luminosity to a few
~10^2 Lo. We conclude that the gas heating in the S 140 region is very
efficient even at high densities, most likely due to the deep UV penetration
from the embedded sources in a clumpy medium and/or oblique shocks.Comment: 15 pages, 23 figures, 4 tables, accepted for publication in A&
- …