Postdoc Colloquium

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Postdoc Colloquium

Tuesday, September 03, 2019, 03:30pm - 04:30pm

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Speakers:

Will Best, The University of Texas at Austin
Probing the Low-Mass End of the Initial Mass Function

Abstract

As the lowest-mass objects created by star formation processes, brown dwarfs are essential to a complete understanding of star formation in our galaxy. The Initial Mass Function (IMF) for brown dwarfs remains poorly constrained due to incomplete samples of these faint objects in the Solar neighborhood and nearby star-forming regions. I will describe two of my projects that take different approaches to probe the low-mass IMF. One, we are using deep HST image maps of five benchmark Milky Way star-forming regions to comprehensively identify members down to planetary masses and explore variations of the IMF with star-forming environment. Two, we have built a parallax-defined volume-limited sample of brown dwarfs within 25 pc of the Sun, and we are using population synthesis to constrain the IMF and birth history that gave rise to the local brown dwarf population

Hope Chen, The University of Texas at Austin
Core Evolution through a Coherent Phase: An Updated Core Evolution Theory Told by Machine Learning

Abstract

The conventional core formation theory usually focuses on the gravitational boundedness of a core. A core is assumed to form out of a gravitationally bound density structure in a molecular cloud. In this talk, I will present the latest effort to examine the evolution of density structures found in a MHD simulation, in order to better understand the formation and evolution of star forming cores. By applying a principal component analysis (PCA) on the density and velocity distributions, we find that there exists a prolonged coherent phase in the evolution of density structures preceding the gravitational collapse and star formation in dense cores. We find that the coherent phase lasts ~ 3x10^5 to 4x10^5 years and is essential in the formation of star forming cores. By tracking the density structures in the simulation and comparing them to structures identified in observations, we characterize an evolutionary track in the parameter space and try to provide an updated theory of core formation and evolution.

Chenxu Liu, The University of Texas at Austin
Searching for “Naked” Supermassive Black Hole Candidates with HETDEX

Abstract

As the largest blind spectroscopic survey ever undertaken, HETDEX offers the possibility to explore unique, rare and important objects in the universe. I will focus on discovery of (nearly) naked black holes. There is a supermassive black hole (SMBH) in the nucleus of every galaxy, with their properties often correlated with the bulges of their hosts. The hierarchical merging of small galaxies thereby cause their black holes to merger. If a merger is tidally disrupted before the event is completed, one or both BHs could recoil and remain without a galaxy (i.e., naked) for a few gigayears. These naked SMBHs will be optically faint, making them unlikely to be targeted by almost all of the sky surveys. I will start from the introduction of the current status of the HETDEX survey, through our efforts to identify the real lines, to the selection of the naked BH candidates with HDR1.

Yifan Zhou, The University of Texas at Austin
Time-Resolved Observations of Directly-imaged Planetary-Mass Companions and Exoplanets

Abstract

Condensate clouds pose a central challenge in the atmospheric characterization of brown dwarfs and exoplanets. For variable brown dwarfs, it has been demonstrated that time-resolved observations place unique and strong constraints on their clouds. I will present my research on extending this technique to high-contrast observations of directly-imaged planetary-mass companions and exoplanets. We have achieved sub-percent level precisions in high-contrast HST/WFC3/IR light curves. With such precisions, we find the likelihood of detecting variability on planetary-mass companions is high. We also find tentative evidence for similar cloud structures shared between planetary-mass companions and brown dwarfs. There is substantial synergy between my studies and ongoing research at UT. I am looking forward to exciting collaborations on these topics.

Location: RLM 15.216B