The study of stars begins with the knowledge of its spectral type. In the early 1900s, E. C. Pickering, Annie Cannon and their colleagues at the Harward Observatory set up th spectral classification scheme, which we use today. According to this scheme, the stars are classified into O B A F G K M types depending mainly upon their surface temperatures and also their chemical compositions. The different types of stars have been studied for quite a long time. Among them the study of A type stars has been somewhat unique as some stars of this type have been found to show anomalous overabundances of certain elements like the Si, Sr, Cr and rare earths as compared to the normal stars of the same kind. The A type stars with the above mentioned anomalies are termed as “peculiar A type stars” and denoted as Ap stars. The other observed anomalies of the Ap stars are under abundance of the helium in most of the star, small deficit in the light elements C, O, Mg, Si in some stars, Ca deficit in most stars, 10 to 100 fold excess of the elements like Sc, Ti, Cr, Mn, Fe in many stars, excess of elements like Sr, Y, Zr up to 1000 times, excess of rare-earths like La, Eu, Gd, Dy by factors of 300 to 1000 and more.
Many of the Ap stars have been found to show photometric and spectroscopic variations in addition to the variation in magnetic field strengths. The need for the knowledge of physical parameters of Ap stars has been strongly felt and hence studies have been carried out at MPBIFR in different lines like photometric, spectroscopic and study of magnetic field strengths.
Papers Published in Refereed Journals:
- “Search for rapid spectral feature variations in chemically peculiar star HR4330”
Sriraghavan, S. M.; Babu, G. S. D., MNRAS, 396, 2061, 2009.
- “On the behaviour of chemically peculiar star HR 2095”
Sriraghavan, S. M.; Jayakumar, K.; Babu, G. S. D.; Sujatha, S., Bulletin of Astronomical Society of India, 33, 373, 2005.
- “Variation of the Si II features in the chemically peculiar star – HD 115735”
Sriraghavan, S. M., Jayakumar, K., Babu, G. S. D., and Sujatha, S., Bulletin of Astronomical Society of India, 32, 113-119, 2004.
- “Spectral Line Variations in the Ap Star HD42536”
Babu, G. S. D., Jayakumar, K. J., Velu, C., and Sujatha, S., Bulletin of Astronomical Society of India, 31, 337-339, 2003.
Publications in Conference Proceedings:
- “Search for rapid spectral feature variations in HR4330”
Sriraghavan, S. M.; Babu, G. S. D., Bulletin of Astronomical Society of India, 2008, 25, 62 (abstract only).
- “On the behaviour of the Si II features in the chemically peculiar star HR2095”
Sriraghavan S.M., Jayakumar K., Sujatha S. and Babu G. S. D., Bulletin of Astronomical Society of India, 2005, 33, 373 – 373 (abstract only)