Amit Pathak | Tezpur University (original) (raw)

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Papers by Amit Pathak

We have used Far Ultraviolet Spectroscopic Explorer (FUSE) observations of the Large Magellanic C... more We have used Far Ultraviolet Spectroscopic Explorer (FUSE) observations of the Large Magellanic Cloud (LMC) to determine the O VI column densities in the Milky Way (MW) towards 6 LMC lines of sight. The mean column density of O VI in the MW is found to be log N(O VI)=14.257 +0.096 −0.084 . The results confirm the patchiness of O VI absorption in the MW and the column densities are higher or comparable to the LMC.

We report the first results of Time-dependent Density Functional Theory calculations of electroni... more We report the first results of Time-dependent Density Functional Theory calculations of electronic transitions of protonated stable neutral polycyclic aromatic hydrocarbon (PAH) molecules. Unlike most neutral closed-shell PAHs which generally absorb strongly in the ultraviolet (UV) or near-UV, the corresponding isoelectronic protonated forms of PAH molecules such as coronene and ovalene are predicted to have absorptions in the visible spectral region. Combining this with other astrophysical, chemical and physical aspects, it is concluded that the protonated forms of PAHs represent a strong class of candidate carriers of diffuse interstellar bands.

We present a survey of interstellar O vi absorption in the Large Magellanic Cloud (LMC) towards 7... more We present a survey of interstellar O vi absorption in the Large Magellanic Cloud (LMC) towards 70 lines of sight based on Far Ultraviolet Spectroscopic Explorer (FUSE) observations. The survey covers O vi absorption in a large number of objects in different environmental conditions of the LMC. Overall, a high abundance of O vi is present in active and inactive regions of the LMC with mean log N(O vi) = 14.23 atoms cm−2. There is no correlation observed between O vi absorption and emissions from the hot gas (X-ray surface brightness) or the warm gas (Hα surface brightness). O vi absorption in the LMC is patchy and the properties are similar to that of the Milky Way (MW). In comparison to the Small Magellanic Cloud (SMC), O vi is lower in abundance even though SMC has a lower metallicity compared to the LMC and the MW. We present observations in 10 superbubbles of the LMC of which we detect O vi absorption in five superbubbles for the first time and the superbubbles show an excess O vi absorption of about 40 per cent compared to non-superbubble lines of sight. We have also studied the properties of O vi absorption in the 30 Doradus region. Even though O vi does not show any correlation with X-ray emission for the LMC, a good correlation between log N(O vi) and X-ray surface brightness for 30 Doradus region is present. We also find that O vi abundance decreases with increasing distance from the star cluster R136.

Phys. Chem. Chem. Phys., Jan 1, 2009