Research activities



SUPERNOVAE


My research activities are currently focused mostly on observations of Type Ia supernovae (SNe Ia). SNe Ia are believed to result from termonuclear explosion of C/O white dwarf with mass close to the Chandrasakhar limit.  SNe Ia are very luminous with peak absolute magnitude MB=-19.3. The peak luminosity correlates well with the decline rate after maximum, which allows SNe Ia to be turned into standard candles. These two properties make SNe Ia very important tools for estimation distances on cosmological scales. Observations of SNe Ia at high redshift of z~0.3-1 have led to one of the most important discoveries in cosmology - the accelerating expansion of the Universe. This fundamental discovery indicates that ~2/3 of the Universe is made of constituent with largely unknown properties called dark energy.
    
Nearby SNe Ia

I am involved in  The Europen Supernova Collaboration and EU Research Training Network (ESC/RTN) "The Physics of Type Ia Supernova Explosions". In ESC we are observing in a coordinated way a set of bright nearby SNe Ia. Our goal is to obtain optical and near infrared photometric and spectral observations with exceptionally good temporal coverage. To do that with use a number of telescopes at European Southern Observatory, La Palma, Calar Alto, Asiago, Australia and UKIRT. The collected data will be used to constrain state-of-the-art theoretical models with the ultimate goal to make brakethrough in our understanding of the physics of the SNe Ia  explosions.

I cooredinated, and/or reduced and analysed the data for a number of SNe Ia:

             1. SN 2003du (ESC/RTN page, restricted access)
             2. SN 2003gs (ESC/RTN page, restricted access)
             3. SN 2005hk (ESC/RTN page, restricted access)
       

I also manage the ESC observations at the Nordic Optical Telescope. Besides the follow-up obsrvations we have also obtained a number of classification spectra. They can be seen here.
High-redshift SNe Ia

With the Supernova Cosmology Project (SCP) I am involved in studies of high-redshift SNe Ia. In 2004 SCP undertook a campaign to discover and follow very high-redshift SNe Ia in GOODS-N filed using HST. ACS/grism spectra were also obtained in order to confirm that the SNe were of Type I. I reduced the ACS/grism spectra and the results can be seen here (SCP limited access).
          There are two ACS/grism pointings with fairly long exposure time. Becuase it is slitless spectroscopy the spectra of all sources in the field were also observed. Besides the suspected SNe I also extracted all possible spectra in search of very high-redshift (z>3) objects, specifically QSOs and Lyman break galaxies at z~6.  No such objects were unambigiously deteced, but nevertheless several interesting sources were identified. Some of the spectra can be seen here.



CATACLYSMIC VARIABLES


During my PhD I have studied interactining binary stars called cataclysmic variables. They are close binaries consisting of a white dwarf and a main sequence star orbiting each other for a typical period of 1-16 hours. The white dwarf accretes mass from the main sequence star, which leads to interesting accretion phenomena like formation of an accretion disc if the white dwarf has low magnetic field. I am still trying to work on cataclysmic with my collegues back in Institute of Astronomy in Bulgaria, but supernovae now take almost all my time. A nice introdution to cataclysmic variables with key references can be found here.