Date: Wednesday 12th December, 3:30PM, 3rd floor

Speaker:  ZengHua Zhang (张曾华)

Institution:  University of Hertfordshire

Talk Title:  Discovery and characterization of ultracool dwarfs in large scale surveys

Abstract: 
　 I will present some works I did during my PhD at the University of Hertfordshire. Ultracool dwarfs are a mixture of low mass stars and brown dwarfs, they form the low mass end of mass function. They provide valuable insights into the efficiency of star formation. They represent fossilized records of star formation at all Galactic epochs. They also show what low-temperature atmospheres look like, could help us to understand atmospheres of gaseous planets. I used SDSS and UKIDSS to search for ultracool dwarfs and their binaries and have found hundreds of ultracool dwarfs and tens of their binaries. Halo ultracool mass function and metal-poor ultracool atmospheres have not been studied well due to the leak of known ultracool subdwarsf. Only one possible halo brown dwarf been discovered so far. In the last two years, I focused on the identification of ultracool subdwarfs in the Galactic halo. I will present some of my latest results, including discoveries of M and L subdwarfs and their binary systems. Then discuss a few scientific topics related to ultracool subdwarfs, e.g. halo substellar mass function, metal-poor ultracool atmospheres, Galactic kinematics. Then finish the presentation with my future research plan.