Professional Interests

• Data Pipeline, analysis and archive Software for TAUVEX and UVIT
• Automated Source Classification schemes for TAUVEX data
• Ultraviolet imaging of environments around evolved stars
• HI 21cm line studies of gaseous shells around evolved stars
• Observation Planning Tools and Simulations
• Software Utilities for Astronomical Data Analysis

Subject vice breakup and details of the various projects in which I am involved in are listed below

Space Missions

At Indian Institute of Astrophysics, we are involved in two upcoming space astronomical missions. First of them, the TAUVEX space observatory is a set of three co-aligned 20cm UV telescopes, which will scan large areas of the sky from geostationary orbit. Second is the UV imaging telescopes (UVIT) on board ASTROSAT, India's first dedicated astronomical satellite scheduled for a 2010 launch. Our work is mainly centered around the development of automated data pipeline software and data archival for both these missions.

Further Reading: TAUVEX Project Wiki

Automated Source Classification Schemes

In order to develop a pipeline for automated classification of stars to be observed by the TAUVEX, we are working on an artificial neural network (ANN) technique for classifying stars. Preliminary studies are being carried out using simulated UV spectra as the training set and International Ultraviolet Explorer (IUE) low resolution spectra as the test set. TAUVEX filter response is applied on both the datasets to obtain the source count rates, as seen by TAUVEX. We have successfully classified 229 stars from the IUE low resolution catalog to within 3-4 spectral sub-class using two different simulated training spectra,IUE spectra of 286 spectral types and UVBLUE spectra of 277 spectral types. Further, we have also been able to obtain the colour excess (i.e. E(B-V) in magnitude units) or the interstellar reddening for those IUE spectra which have known reddening to an accuracy of better than 0.1 magnitudes. Our results indicate that even with a limitation of data from just photometric bands, ANNs have not only classified the stars, but also provided satisfactory estimates for interstellar extinction. The ANN based classification scheme has been successfully tested on the simulated TAUVEX data pipeline. It is expected that the same technique can be employed for data validation in the ultraviolet from the virtual observatories. Finally, the interstellar extinction estimated by applying the ANNs on the TAUVEX data base would provide an extensive extinction map for our galaxy and which could in turn be modeled for the dust distribution in the galaxy.

Further Reading: Archana Bora et al. 2007

Astronomy Tools

There is an enormous range of products and tools to assist astronomers. However, every now and then we face the need for a little extra functionality. We are trying to cover such small gaps with these tools. They are meant to compliment existing softwares. Some of these programs are listed below. You may find more of them in the TAUVEX Online Tools page

Gaseous Shells around Evolved Stars: HI 21cm line Imaging

Observations of atomic resonance lines, infrared emission from circumstellar dust grains, molecular absorption and emission lines, have established the fact that most, if not all, red giants are loosing mass at a substantial rate. Information gathered from these observations have been used to derive values of stellar radial velocity, chemical composition and mass-loss rate from many evolved stars (See for eg. Zuckerman & Dyck, 1986).

Recent results suggest that at least part of the material in the circumstellar envelopes of many evolved stars is atomic, and that it is feasible to use HI 21cm emission as a diagnostic probe of the late stages of stellar evolution. HI content of the circumstellar envelope provide vital information on the circumstellar and interstellar chemistry. In addition, it can provide reliable values for mass-loss rate, total mass of the envelope and its age. Mass loss is an important parameter in deciding the course of evolution of stars. Molecular line studies can provide only a lower limit to the radius of the envelope, because the extent of molecular emission is likely to be determined by photodissociation due to interstellar ultraviolet radiation. HI does not suffer from this problem.

We are carrying out high resolution imaging using GMRT towards a selected subset of these stars, to study the distribution of HI within the envelope and its expansion rate.

Gaseous Shells around Evolved Stars: UV Studies

Recent GALEX discovery of hot UV emitting gas tail of Mira shows the kind of surprises in the shells around evolved stars. Mira's tail is visible only in the ultraviolet, which might explain why other observatories have missed it. Such targets are ideal for TAUVEX observatory, with its wide field of view and scanning observations. These observations will complement the ongoing radio observations of the same using GMRT (see above).