Bodhisattva Sen

 

Applications in Astronomy and High Energy Physics

In collaboration with Mario Mateo and Matthew Walker in the Astronomy department at the University of Michigan, Ann Arbor, I investigate numerous properties of the dwarf spheroidal (dSph) galaxies in the Local group from data obtained on the position and velocity of a sample stars in these galaxies. These galaxies are the smallest systems that are supposed to contain dark matter and thus have important astronomical implications. The collaboration has been quite fruitful, with numerous applications arising at various stages of the project, ranging from data collection to the final analysis. The data we observe is usually a contaminated sample, containing foreground (Milky Way) stars that are in the field of view of the telescope. We develop variants (and extensions) of the EM algorithm to address this data contamination (see e.g., [8], [7]). We develop statistical methods to investigate whether a dSph galaxy is in equilibrium or being tidally disrupted by the Milky Way (see [8]).


A serious limitation in the study of many globular clusters -- especially those located near the Galactic center -- has been the existence of large and differential extinction by foreground dust. In a series of papers (see e.g., [9, 10]), in collaboration with Javier Alonso, we intend to map the differential extinction and remove its effects, using a new dereddening technique, in a sample of clusters in the direction of the inner Galaxy, observed using the Magellan 6.5 m telescope and the Hubble Space Telescope.



References


  1. 1.Walker, M.G., Mateo, M., Olszewski, E.W., Pal, J.K., Sen, B., and Woodroofe, M. (2006). On Kinematic Substructure in the Sextans Dwarf Spheroidal Galaxy. Astrophysical Journal, 642, L41-L44.


  1. 2.Walker, M.G., Mateo, M., Olszewski, E.W., Bernstein, R., Sen, B. and Woodroofe, M. (2007). The Michigan/MIKE Fiber System Survey of Stellar Radial Velocities in Dwarf Spheroidal Galaxies: Acquisition and Reduction of Data. Astrophysical Journal Supplement Series, 171, 389-418.


  1. 3.Sen, B., Walker, M. and Woodroofe, M. (2007). On the Unified Method with Nuisance Parameters. Statist. Sinica, 19, 301-314.


  1. 4.Walker, M.G., Mateo, M., Olszewski, E.W., Gnedin, O.Y., Wang, X., Sen, B. and Woodroofe, M. (2007). Velocity Dispersion Profiles of Seven Dwarf Spheroidal Galaxies. Astrophysical Journal, 667, L53-L56.


  1. 5.Alonso, J., Mateo, M. and Sen, B. (2008). Uncloaking globular clusters of the inner Galaxy. Proceedings IAU Symposium 245: Formation and Evolution of Galaxy Bulges, 359-360.


  1. 6.Woodroofe, M. and Sen, B. (2007). Discussion of 'The small-n problem in High Energy Physics' by Glen Cowan and 'Bayesian Methods in Particle Physics From Small- N to Large' by Harrison Prosper. Statistical Challenges in Modern Astronomy (SCMA) IV, (Eds. G.J.Babu and E.D.Feigelson), ASP Conference Series, 371, 98-100.


  1. 7.Walker, M.G., Mateo, M., Olszewski, E.W., Sen, B. and Woodroofe, M. (2008). Clean Kinematic Samples in Dwarf Spheroidals: An Algorithm for Evaluating Membership and Estimating Distribution Parameters When Contamination is present. Astronomical Journal , 137, 3109-3138.


  1. 8.Sen, B., Banerjee, M., Woodroofe, M., Walker, M.G. and Mateo, M. (2009). Streaming Motion in Leo I.  Ann. Appl. Statis., 3, 96-116.


  1. 9.Alonso, J., Mateo, M., Sen, B., Banerjee, M. and Braun, K. (2011). Mapping differential reddening in the inner Galactic globular cluster system. Astronomical Journal, 141, 146.


  1. 10. Alonso, J., Mateo, M., Sen, B., Banerjee, M., Catelan, M., and Minniti, D. (2011). Uncloking globular clusters in the inner Galaxy. (submitted)