R. P. Verma
Articles written in Journal of Astrophysics and Astronomy
Volume 14 Issue 3-4 December 1993 pp 131-134
The observed infrared excess in Be stars is usually interpreted as free-free and free-bound emission from a hot gas envelope around the Be star. This hot gas should also emit H-alpha line radiation. Earlier observations had suggested that the infrared excess and Hα radiation were not consistent with models in which they arise from the same ionized region; however the observations were made at different times. We have made simultaneous observation of infrared and H-alpha line radiation. Our observations imply that either both these radiations cannot arise from the same hot gas or additional processes have to be invoked to account for the observed excess infrared radiation.
Volume 21 Issue 1-2 June 2000 pp 61-76
A new scheme of radiation transfer for understanding the infrared spectra of HII regions, has been developed. This scheme considers non-equilibrium processes (e.g. transient heating of the very small grains, VSG; and the polycyclic aromatic hydrocarbon, PAH) also, in addition to the equilibrium thermal emission from normal dust grains (BG). The spherically symmetric interstellar dust cloud is segmented into a large number of “onion skin” shells in order to implement the non-equilibrium processes. The scheme attempts to fit the observed SED originating from the dust component, by exploring the following parameters: (i) geometrical details of the dust cloud, (ii) PAH size and abundance, (iii) composition of normal grains (BG), (iv) radial distribution of all dust (BG, VSG & PAH).
The scheme has been applied to a set of five compact H II regions (IRAS 18116 − 1646, 18162 − 2048, 19442 + 2427, 22308 + 5812, and 18434 - 0242) whose spectra are available with adequate spectral resolution. The best fit models and inferences about the parameters for these sources are presented.
Volume 22 Issue 2-3 June 2001 pp 173-185
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 200μm 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 ìm 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.
Volume 42, 2021
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