Professional Interests

Space Missions Astronomy Software ISM Past Life

Current Projects

  • 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.

UVS Data Pipeline Software

Raw data acquired by the space based observatories require considerable amount of processing before it can be presented to the user community. The data pipeline software does most of the required data reduction. Written in java, this software is a set of independent, fully configurable and platform independent modules, each representing a distinct logical operation/step in data reduction. These modules will be governed by parameter files and may be called from a control script. These collection of programs, invoked and managed by a smart script constitute the UVS data pipeline software. We begin with the first mission in hand, the TAUVEX observatory and keep building on the collection of modules for future missions. Preliminary version of the data pipeline software is available for download from the TAUVEX Download Area. Documentation is available in the TAUVEX Project Wiki.

UVS Data Archival and Dissemination Software

This project is currently under active development. Once completed, it will provide a web based search and download interface for TAUVEX data. We will also provide web based data analysis options, so that experienced users may run customized instances of the entire data pipeline system. At a later stage, this will be extended to other observatories operated by Indian Institute of Astrophysics.

Further Reading: TAUVEX Project Wiki

Role: Project Management, Design, Documentation, some Coding and Testing
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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

Role: Co-Investigator, in collaboration with Ranjan Gupta & Archana Bora (IUCAA), H.P Singh (Delhi Univ.) and J. Murthy (IIA)

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

  • Fits Utils: A set of java programs for visualization & analysis of fits images, fits header and extension editors, coordinate conversion applet, point source extractor etc. You can find initial releases in TAUVEX Download Area
  • TAUVEX ETC: Exposure time calculator for TAUVEX Mission
  • UV Sky Simulation: Simulates the sky as seen from a photon counting instrument. Can be configured for scanning or targetted observation. Integration time, instrument aperture, efficiency, dark count, jitter, input catalog etc. are user defined. Web interface is also available.
  • Stellar Flux Calculator: Kurucz model based stellar spectrum generator. Web interface to this tool is also available.
  • fits2jpeg: Converts fits images to jpeg. Features include a image scaling options (linear/square/square-root/log) and batch conversion (several fits files at once).
  • Zodiacal Light Calculator: Estimates the zodiacal light intensity for a given location and time of year. We interface is also available
  • Planet Position Calculator: perl/cgi program to calculate positions, visual magnitude and distance to solar system objects for a given date, time and geographical location.
  • Javascript Utils: A set of javscript routines to calculate distance between two points in sky (name resolver included), distance conversion, magnitude to/from flux conversion, julian date to/from calender date etc.
Role: Varies with project. Includes Management, architect, documentation, lead & solo developer, testing. etc.
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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.

Role: Co-Investigator, in collaboration with N.K. Rao (IIA) and D.L. Lambert, Univ. Texas, Austin
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).

Role: Principal Investigator, in collaboration with N.K. Rao (IIA)
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Past Life: Kinematics of Galaxy

That was my PhD. thesis topic. Never got time to get back to it, though we got several open questions. More observations in various wavelengths are required to address these issues, but now I have dropped the baggage and moved on in life. Might as well return to it at some later stage. A brief summary is given below:

My PhD thesis entitled ``Kinematics of Diffuse Interstellar Clouds in the Galaxy'' chiefly pertains to the HI 21cm line studies of the Interstellar medium, with emphasis on the search and properties of large velocity clouds. Sensitive HI absorption and emission data from our observations provide credible evidence for a higher velocity tail in the HI absorption line velocities from the Galactic ISM, hitherto observed only in the optical absorption lines. These higher velocity lines are of lower optical depth, probably arising in shock heated gas. These investigations were based on observational programs carried out using the Giant Meterwave Radio Telescope (GMRT) and other international facilities like the Westerbork Synthesis Radio Telescope (WSRT) and the Australia Telescope Compact Array (ATCA).

Perhaps my shift of interest from Galactic kinematics to present day musings is due (and many thanks) to the following advice:

If you are (or intend to be) an active observational, enterprising astronomer, not shy of building software that's required to do the science you wish to do, it will be generally useful to know how to use tools like RCS, C/C++, lex/bision, and be able to handle compilation of programs which are beyond "Hello World" level. Good luck!
-- S.Bhatnagar (May 18, 1999)

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