Dr Sujatha N V
@stxaviersaluva.ac.in
Assistant Professor, Department of Physics
St. Xavier's College for Women, Aluva
RESEARCH, TEACHING, or OTHER INTERESTS
Physics and Astronomy
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Nimmi Narayanan, Shivashankar S. Menon, and N. V. Sujatha
IOP Publishing
Abstract The study of diffuse ultraviolet (UV) background radiation is vital in the investigation of stellar and galactic evolution. Space-based UV observations are comprised of both foreground and background radiations. The foreground emission in an observation is a result of solar contamination in the direction of observation. In our previous work, we modeled airglow (one of the major constituents of the foreground emission) as a function of 10.7 cm Solar Flux and Sun Angle with great accuracy using GALEX deep observations. We adopt a similar methodology to validate the obtained model and run equivalent experiments here using far-UV (FUV) and near-UV (NUV) GALEX medium imaging surveys (MIS) with a total exposure time greater than 3300 s. We obtained a predictive model having excellent compatibility with the earlier model. Our analysis shows that the total foreground emission varies between 59 and 295 photon units in FUV whereas in NUV, it varies between 671 and 1195 photon units depending upon the date and time of observation. We also noticed a strong correlation between the background emission and optical depth both in FUV and NUV, especially in the low density regions. This clearly indicates that the major contributor in diffuse background radiation is the starlight scattered by interstellar dust grains.
Nimmi Narayanan, Shivashankar S. Menon, and Sujatha N.V.
Elsevier BV
S. N. Jyothy, N. V. Sujatha, and Narayanankutty Karuppath
Springer Science and Business Media LLC
S. N. Jyothy, Jayant Murthy, Narayanankutty Karuppath, and N. V. Sujatha
Oxford University Press (OUP)
We present an analysis of the diffuse ultraviolet (UV) background in a low latitude region near the Aquila Rift based on observations made by the Galaxy Evolution Explorer (GALEX). The UV background is at a level of about 2000 ph cm^-2 s^-1 sr^-1 \\AA^-1 with no correlation with either the Galactic latitude or the 100 micron infrared (IR) emission. Rather, the UV emission falls off with distance from the bright B2 star HIP 88149, which is in the centre of the field. We have used a Monte Carlo model to derive an albedo of 0.6 - 0.7 in the UV with a phase function asymmetry factor (g) of 0.2 - 0.4. The value for the albedo is dependent on the dust distribution while g is determined by the extent of the halo.
Lakshmi S. Bose, N. V. Sujatha, K. Narayanankutty, and Jayant Murthy
Pleiades Publishing Ltd
A. Pathak, A. C. Pradhan, N. V. Sujatha, and J. Murthy
Oxford University Press (OUP)
We present a survey of interstellar O VI absorption in the Large Magellanic Cloud (LMC) towards 70 lines of sight based onFarUltravioletSpectroscopicExplorer(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 logN(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 logN(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.
Jayant Murthy, R. C. Henry, and N. V. Sujatha
American Astronomical Society
We present a map of the diffuse ultraviolet cosmic background in two wavelength bands (FUV: 1530 Å and NUV: 2310 Å) over almost 75% of the sky using archival data from the Galaxy Evolution Explorer (GALEX) mission. Most of the diffuse flux is due to dust-scattered starlight and follows a cosecant law with slopes of 545 photons cm−2 s−1 sr−1 Å−1 and 433 photons cm−2 s−1 sr−1 Å−1 in the FUV and NUV bands, respectively. There is a strong correlation with the 100 μm Infrared Astronomy Satellite (IRAS) flux with an average UV/IR ratio of 300 photons cm−2 s−1 sr−1 Å−1 (MJy sr−1)−1 in the FUV band and that of 220 photons cm−2 s−1 sr−1 Å−1 (MJy sr−1)−1 in the NUV band but with significant variations over the sky. In addition to the large-scale distribution of the diffuse light, we note a number of individual features including bright spots around the hot stars Spica and Achernar.
N. V. Sujatha, Jayant Murthy, Rahul Suresh, Richard Conn Henry, and Luciana Bianchi
American Astronomical Society
We have studied small-scale (2′) spatial variation of the diffuse ultraviolet (UV) radiation using a set of 11 Galaxy Evolution Explorer deep observations in the constellation of Draco. We find a good correlation between the observed UV background and the infrared (IR) 100 μm flux, indicating that the dominant contributor of the diffuse background in the field is scattered starlight from the interstellar dust grains. We also find strong evidence of additional emission in the far-ultraviolet (FUV) band which is absent in the near-ultraviolet (NUV) band. This is most likely due to Lyman band emission from molecular hydrogen in a ridge of dust running through the field and to line emissions from species such as C iv (1550 Å) and Si ii (1533 Å) in the rest of the field. A strong correlation exists between the FUV/NUV ratio and the FUV intensity in the excess emission regions in the FUV band irrespective of the optical depth of the region. The optical depth increases more rapidly in the UV than the IR and we find that the UV/IR ratio drops off exponentially with increasing IR due to saturation effects in the UV. Using the positional details of Spitzer extragalactic objects, we find that the contribution of extragalactic light in the diffuse NUV background is 49 ± 13 photons cm−2 sr−1 s−1 Å−1 and is 30 ± 10 photons cm−2 sr−1 s−1 Å−1 in the FUV band.
N. V. Sujatha, Jayant Murthy, Abhay Karnataki, Richard Conn Henry, and Luciana Bianchi
American Astronomical Society
We have observed a region of nebulosity first identified as starlight scattered by interstellar dust by Sandage using the Galaxy Evolution Explorer (GALEX) ultraviolet imaging telescope. Apart from airglow and zodiacal emission, we have found a diffuse UV background of between 500 and 800 photons cm−2 sr−1 s−1 Å−1 in both the GALEX far-ultraviolet (FUV) (1350–1750 Å) and NUV (1750–2850 Å) bands. Of this emission, up to 250 photons cm−2 sr−1 s−1 Å−1 is due to H2 fluorescent emission in the FUV band. The remainder is consistent with scattering from interstellar dust with forward scattering grains of albedo about 0.4. These are the highest spatial resolution observations of the diffuse UV background to date and show an intrinsic scatter beyond that expected from instrumental noise alone. Further modeling is required to understand the nature of this scatter and its implications for the ISM.
N. V. Sujatha, Jayant Murthy, P. Shalima, and Richard Conn Henry
American Astronomical Society
We have used FUSE and Voyager observations of dust-scattered starlight in the neighborhood of the Coalsack Nebula to derive the optical constants of the dust grains. The albedo is consistent with a value of 0.28 ± 0.04, and the phase function asymmetry factor with a value of 0.61 ± 0.07, throughout the spectral range from 900-1200 Å, in agreement with previous determinations as well as theoretical predictions. We have now observed two regions (Ophiuchus and Coalsack) with intense diffuse background radiation and in both cases have found that the emission is due to light from nearby hot stars scattered by a relatively thin foreground cloud, with negligible contribution from the background molecular cloud.
P. Shalima, N. V. Sujatha, J. Murthy, R. C. Henry, and D. J. Sahnow
Oxford University Press (OUP)
We have modelled diffuse far-ultraviolet (FUV) spectrum observed by the Far Ultraviolet Spectroscopic Explorer (FUSE) near M42 as the scattering of the starlight from the Trapezium stars by dust in front of the nebula. The dust grains are known to be anomalous in Orion with R V = 5.5 and these are the first measurements of the FUV optical properties of the grains outside of 'normal' Milky Way dust. We find an albedo varying from 0.3 ± 0.1 at 912 A to 0.5 ± 0.2 at 1020 A which is consistent with theoretical predictions.
N. V. Sujatha, P. Shalima, Jayant Murthy, and Richard Conn Henry
American Astronomical Society
We have derived the albedo (a) and phase function asymmetry factor (g) of interstellar dust grains at 1100 Å using archival Voyager observations of diffuse radiation in Ophiuchus. We have found that the grains are highly forward-scattering, with g = 0.55 ± 0.25 and a = 0.40 ± 0.10. Even though most of the gas in this direction is in the Ophiuchus molecular cloud, the diffuse FUV radiation is almost entirely due to scattering in a relatively thin foreground cloud. This suggests that one cannot assume that the UV background is directly correlated with the total amount of gas in any direction.
G Ambika, N V Sujatha, and K P Harikrishnan
Springer Science and Business Media LLC
G Ambika and N V Sujatha
Springer Science and Business Media LLC
G Ambika and N V Sujatha
Springer Science and Business Media LLC