R. P. Verma

Distribution of Cold Dust in Orion A and B

Large-scale far-infrared (FIR) observations of the Orion complex at 205 and 138 μm are presented with the aim of studying the distribution of cold (<25 K) dust. The maps in these FIR bands extend over ~3600 arcmin2 and cover regions around OMC-1, 2, and 3 in Orion A and NGC 2023 and NGC 2024 in Orion B. Some limited regions have also been mapped at 57 μm. A total of 15 sources in Orion A and 14 in Orion B (south) have been identified from our FIR maps. Dust temperature distribution in both Orion A and Orion B (south) have been determined reliably using the maps at 205 and 138 μm obtained from simultaneous observations using almost identical beams (16 diameter). These temperatures have been used to generate the map of τ150, the optical depth at 150 μm, for the Orion B region. The coldest source detected is in OMC-3 and has temperature ~15 K. The diffuse FIR emission in the different subregions is found to vary between 25% and 50% of the total FIR emission from that subregion.

Far-infrared and radio observations of the W31 star-forming region

New 150 micron mapping of the W31 star-forming region with a resolution of 1.5 arcmin has resolved 12 sources, including eight new ones. About 35 percent of the emission is of diffuse origin. The IRAS two-dimensional COADD data of the same region at 60 and 100 microns have been deconvolved using a maximum-entropy algorithm. The dust temperature, dust optical depth, far-IR luminosity, and so on, have been derived for individual sources in the star-forming complex; several of these seem to be excited by embedded young stars. One young stellar object with an optically thick ionized envelope has been identified. New high-resolution maps of selected regions around the two most prominent H II regions in the W31 complex, G10.2-0.3 and G10.3-0.1, have been obtained at 5 and 15 GHz using the VLA. The initial mass function for G10.2-0.3 is quite steep. An energetic bipolar outflow source candidate has been found which is proposed to be the mid-IR source in the G10.2-0.3 complex. 41 refs.

Far-Infrared Observations of the Galactic Star-forming Regions Associated with IRAS 00338+6312 and RAFGL 5111

Two Galactic star-forming regions, one in a very early phase of evolution and another evolved one, associated with the IRAS sources 00338)6312 and 03595)5110 (RAFGL 5111), respectively, have been studied in detail. These sources have been mapped simultaneously in two far-infrared bands (j eff \ 143 and 185 km), with angular resolution, using the Tata Institute of Fundamental Research (TIFR) D1@ 100 cm balloon-borne telescope. The HIRES-processed IRAS maps at 12, 25, 60, and 100 km have been used for comparison. Whereas IRAS 00338)6312 is resolved only in the TIFR bands, RAFGL 5111 is very well resolved in both the TIFR bands as well as in at least three IRAS bands. The neighboring fainter source IRAS 04004)5114 has also been resolved in the TIFR bands. Taking advantage of the identical beams in the two TIFR bands at 143 and 185 km, dust color temperature, T (143/185), and optical depth, maps have been generated for RAFGL 5111. These maps show interesting structural q 150 , details. Radiative-transfer modeling in spherical geometry has been carried out for individual sources to extract information about the cloud size, the type of the embedded source, the radial density distribu- tion, the optical depth, the gas-to-dust ratio, and the dust grain composition. The best-—t models are in good agreement with the observed spectral energy distribution (SED), radio continuum data, and so on. Another scheme of radiative transfer through the interstellar dust-gas cloud including the heavier ele- ments has been used to predict ionic nebular line emission, which is in reasonable agreement with the measurements for RAFGL 5111. An important conclusion from the present study is that, for all three sources (IRAS 00338)6312, 03595)5110, and 04004)5114, a faint source in the neighborhood of RAFGL 5111), the best —t to the observed SED is obtained for a uniform density (n(r) D r0) cloud. Subject headings: H II regionsinfrared: ISM: continuum ¨ ISM: individual (IRAS 00338)6312, IRAS 03595)5110)

Study of star formation in RCW 106 using far‐infrared observations

High resolution far-infrared observations of a large area of the star forming complex RCW 106 obtained using the TIFR 1-metre balloon-borne telescope are presented. Intensity maps have been obtained simultaneously in two bands centred around 150&210 micron. Intensity maps have also been obtained at the 4 IRAS bands using HIRES processed IRAS data. From the 150&210 micron maps, reliable maps of dust temperature and optical depth have been generated. The star formation in this complex has occured in five linear subclumps. Using the map at 210 micron, which has a spatial resolution superior to that of the IRAS at 100 micron, 23 sources have been identified. The SED and luminosity of these sources have been determined using the associations wit hthe IRAS maps. Luminosity distribution of these sources has been obtained. Assuming these embedded sources to be ZAMS stars and using the mass-luminosity relation, the power law slope of the Initial Mass Function is found to be -1.73+-0.5. This index for this very young complex is about the same as that for more evolved complexes and clusters. Radiation transfer calculations in spherical geometry have been undertaken to fit the SEDs of 13 sources with fluxes in both the TIFR and IRAS bands. From this, the r^-2 density distribution in the envelopes is ruled out. Finally, a correlation is seen between the luminosity of embedded sources and the computed dust masses of the envelopes.

Far-infrared observations of NGC 4945 and the Circinus galaxy

Results of observations of NGC 4945 and the Circinus galaxy carried out with a 1 m balloon-borne far-infrared telescope are reported. While only an upper limit (5 σ) of 150 Jy for the 150 μm flux density is obtained for Circinus, the central region of NGC 4945 has been mapped in two bands with effective wavelengths of ∼58 and ∼150 μm. Pointed observations of IRAS, using survey detectors, have been deconvolved to get higher angular resolution intensity maps at 12, 25, 60, and 100 μm, respectively, for both of these galaxies

Star formation activity in the southern Galactic H ii region G351.63−1.25

The southern Galactic high-mass star-forming region, G351.63−1.25, is an H ii region–molecular cloud complex with a luminosity of ∼2.0 × 10 5 L ⊙ , located at a distance of 2.4 kpc from the Sun. In this paper, we focus on the investigation of the associated H ii region, embedded cluster and the interstellar medium in the vicinity of G351.63−1.25. We address the identification of exciting source(s) as well as the census of the stellar populations, in an attempt to unfold star formation activity in this region. The ionized gas distribution has been mapped using the Giant Metrewave Radio Telescope, India, at three frequencies: 1280, 610 and 325 MHz. The H ii region shows an elongated morphology and the 1280 MHz map comprises six resolved high-density regions encompassed by diffuse emission spanning 1.4 × 1.0 pc 2 . Based on the measurements of flux densities at multiple radio frequencies, the brightest ultracompact core has electron temperature T e ∼7647 ±153 K and emission measure, EM∼2.0 ± 0.8×10 7 cm −6 pc. The zero-age main-sequence spectral type of the brightest radio core is O7.5. We have carried out near-infrared observations in the JHK s bands using the SIRIUS camera on the 1.4 m Infrared Survey Facility telescope. The near-infrared images reveal the presence of a cluster embedded in nebulous fan-shaped emission. The log-normal slope of the K -band luminosity function of the embedded cluster is found to be ∼0.27 ± 0.03, and the fraction of the near-infrared excess stars is estimated to be 43 per cent. These indicate that the age of the cluster is consistent with ∼1 Myr. Other available data of this region show that the warm (mid-infrared) and cold (millimetre) dust emission peak at different locations indicating progressive stages of star formation process. The champagne flow model from a flat, thin molecular cloud is used to explain the morphology of radio emission with respect to the millimetre cloud and infrared brightness.

Far-infrared study of IRAS 00494+5617 and IRAS 05327-0457

High angular resolution far-infrared observations at 143 and 185 μm, using the Tata Institute of Fundamental Research 1 m balloon-borne telescope, are presented for two Galactic star-forming complexes associated with IRAS 00494+5617 and IRAS 05327-0457. The latter map also reveals the cold dust in OMC-3. Both these regions are illuminated at the edges by high-mass stars with substantial UV flux. The HIRES (High-Resolution processing using Maximum Correlation Method) processed IRAS maps at 12, 25, 60, and 100 μm have also been presented for comparison. The present study is aimed at quantifying the role of the nearby stars vis-a-vis embedded young stellar objects in the overall heating of these sources. Based on the FIR observations at 143 and 185 μm carried out simultaneously with almost identical angular resolution, reliable dust temperature and optical depth maps have been generated for the brighter regions of these sources. Radiative transfer modeling in spherical geometry has been carried out to extract physical parameters of these sources by considering the observational constraints, such as spectral energy distribution, angular size at different wavelengths, dust temperature distribution, etc. It is concluded that for both IRAS 00494+5617 and IRAS 05327-0457, the embedded energy sources play the major role in heating them with finite contribution from the nearby stars. The best-fit model for IRAS 00494+5617 is consistent with a simple two-phase clump-interclump picture with ~5% volume filling factor (of clumps) and a density contrast of ≈80.

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.

Far-infrared observations of G351. 6 - 1. 3/G351. 7 - 1. 2 region

An area of about 20 arcmin x 25 arcmin around the H II region-molecular cloud complexes G351.6 - 1.3 and G351.7 - 1.2 has been mapped in a 120 - 300 micron far-infrared band with a spatial resolution of about 1.5 arcmin. Besides the two main sources, five weaker sources have been seen. The IRAS two-dimensional COADD data of the same region at 60 microns and 100 microns have been deconvolved for comparison with the 150 micron intensity map. Combining all the available far-infrared measurements, dust temperature, optical depth, far-infrared luminosity, etc, have been derived for the individual sources in this complex. Spectra have been constructed for the two main sources using all available data. These have been compared with the results of radiation transfer calculations for a spherically symmetric model. Information has been derived on the nature of the dust and its distribution in the main source in G351.6 - 1.3. A mixture of graphite and silicate grains gives a good fit to the observed spectrum. The favored radial dust density distribution is uniform. 30 refs.

Far-infrared brightness temperature of Saturn's disk and rings

Abstract We present far-infrared observations of Saturn in the wavelength band 76–116 μm, using a balloon-borne 75-cm telescope launched on 10 December 1980 from Hyderabad, India, when B′, the Saturnicentric latitude of the Sun, was 4°.3. Normalizing with respect to Jupiter, we find the average brightness temperature of the disk-ring system to be 90 ± 3° K. Correcting for the contribution from rings using experimental information on the brightness temperature of rings at 20 μm, we find TD, the brightness temperature of the disk, to be 96.9 ± 3.5° K. The systematic errors and the correction for the ring contribution are small for our observations. We, therefore, make use of our estimate of TD and earlier observations of Saturn when contribution from the rings was large and find that for wavelengths greater than 50 μm, there is a small reduction in the ring brightness temperature as compared to that at 20 μm.