Divya Oberoi

Reader - F
Email: div [at] ncra.tifr.res.in
Phone: +91 - 20 - 25719245
Extn: 9245
Office: F222
National Centre for Radio Astrophysics
Tata Institute of Fundamental Research
Savitribai Phule Pune University Campus,
Pune 411 007
Maharashtra, INDIA


Main Research Areas: Solar Physics, Interplanetary Scintillations, Interferometry.

Biography:

Divya Oberoi completed his B.Sc and M.Sc. from University of Delhi in 1991 and 1993 respectively. He then joined the Joint Astronomy Program (JAP) for his Ph.D. As a part of this program, he spent a year at the Indian Institute of Science (IISc) to complete the graduate school and then joined the National Centre for Radio Astrophysics for his doctoral research, which he completed in 2000. He held postdoctoral fellowships at the "Laboratoire de Physique et Chimie de l'Environnement et de l'Espace in Orleans, France and MIT Haystack Observatory, Westford, MA, USA. In 2005 he joined MIT Haystack Observatory as a Research Scientist and In February 2012 he took up the position of a Reader at the National Centre for Radio Astrophysics.

Research description:

The bulk of my research work tends to be at the intersection of science and numerical analysis or techniques, or is about harnessing the recent developments in technology and computing for meeting science goals which have remained elusive using the earlier generation of instrumentation and computing resources. Trying to extract the most information from the available data has been an enduring theme of my work. Along the frequency axis, my research interests have so far typically been at the low radio frequency end.
Solar Physics
The radio Sun is very dynamic, especially at metre wavelengths. Its emission can not only change rapidly in time, it also has very strong spectral features and the morphology of emission changes with both time and frequency. So, to study the radio Sun, one essentially needs a video camera which can simultaneously make independent movies at multiple different radio frequencies. This has been a tough challenge for traditional interferometers. Recently with a new generation of instruments, like the Murchison Widefield Array (MWA), now becoming available (2013) this is changing. The MWA offers unprecedented capabilities for high dynamic range, high fidelity spectroscopic imaging with good time and frequency resolution over a wide band, and useful angular resolution to explore many interesting problems in solar physics which could be addressed only in a limited manner earlier due to lack of suitable data. These include: 1. Imaging studies of origin and evolution of different types of solar bursts, especially type II and type III bursts. 2. Reliable studies of low radio frequency solar flux, spectral index and its variations over small and long time scales. These will in turn help understand scattering processes and micro turbulence in the corona. 3. A truly exciting possibility is about looking for missing contributions to the famous and long standing coronal heating problem. I have been a part of the design, construction and commissioning team of the MWA from its inception, and play a leading role for solar science with the instrument.
Heliospheric Physics
The region around the Sun dominated by plasma of solar origin, the solar wind, is termed the Heliosphere. During solar eclipse times, the base of the solar wind is visible as the corona. The corona is very hot plasma which is constantly flowing out of the Sun, and Earth and all other planets are immersed in it. The solar wind serves as the medium which propagates the impact of the dynamics on the solar surface to the Earth and its neighbourhood, and gives rise to Space Weather. As one moves farther away from the Sun, the density of the solar wind drops as inverse squared and it becomes much harder to observe and study directly, though there are some spacecraft which try to do exactly this. An alternative way to study the solar wind is by using propagation effects of the solar wind plasma at low radio frequencies using the technique of Interplanetary Scintillation (see below). My own research in this field was an attempt to build a 3D model of the density and velocity distribution of the solar wind in the entire inner heliosphere by using a very large number of individual observations using IPS observations from the Ooty Radio Telescope (ORT). These observations were designed to sample the entire heliosphere and the analysis used a technique functionally similar to tomography. The ORT is currently undergoing a major upgrade. With its new multi-beaming capability over wide fields of view and improved sensitivity, it can potentially become the most capable IPS instrument on the planet.
Interplanetary Scintillation
(IPS) is a remote sensing technique which has been used effectively for many decades. IPS is most easily described as the radio analogue of optical twinkling of stars. As the plane wavefronts from a distant compact radio source travels through the solar wind, the structures in the solar wind plasma leave their imprint on the passing waves, leading to corrugations in the wavefronts. By the time these wavefronts arrive at the telescope, the phase fluctuations develop into amplitude scintillation. The motion of the solar wind drags this interference pattern across the telescope aperture leading to observations of IPS. IPS can then be studied to estimate a variety of parameters of the solar wind, the most important of them are: plasma density, fluctuations in plasma density and the speed of solar wind plasma. One of the most important uses of IPS is for studies of Coronal Mass Ejections (CMEs), the most important driver of Space Weather events in the terrestrial neighbourhood. IPS allows us to trace the path and evolution of energetic CME plasma through the vast heliosphere even when it can no longer be studied by most other techniques.

Selected publications:

1. Science with the Murchison Widefield Array. (Bowman, J. D., Cairns, I. H., Kaplan, D., Murphy, T., Oberoi, D. et al. 2013, Pub. of the Astr. Soc. of Aus., 30, 31)

2. Media Responsible for Faraday Rotation - A Review. (Oberoi, D. and Lonsdale, C. J., 2012, Radio Science, 47, RS0K08)

3. First Spectroscopic Imaging Observations of the Sun at Low Radio Frequencies with the Murchison Widefield Array Prototype. (Oberoi, D. et al. 2011, Astrophysical Journal Letters, 728, L27)

4. Remote Sensing of the Heliosphere with the Murchison Widefield Array. (Oberoi, D. and Benkevitch, L., 2010, Solar Physics, 265, 2930)

5. High Temporal and Spectral Resolution Interferometric Observations of Unusual Solar Radio Bursts. (Oberoi, D., Evarts, E. R. and Rogers, A. E. E., 2009, Solar Physics, 260, 389)

6. New Design for a Very Low Frequency Space Borne Radio Interferometer. (Oberoi, D. and Pincon, J.-L., 2005, Radio Science, 40, 4004)

7. Imaging Strategies and Postprocessing Computing Costs for Large-N SKA Designs. (Lonsdale, C. J., Doeleman S. S. and Oberoi, D., 2004, Experimental Astronomy, 17, 345)

8. LOFAR: The potential for solar and space weather studies. (Oberoi, D. and Kasper, J. C., 2004, Planetary and Space Science, 52, 1415)




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