Colloquium

graduating students' colloquium

Sarah Pearson:
Title: Stellar streams and the galaxies they reside in
Abstract: As galaxies collide, as smaller galaxies are disrupted by larger galaxies, or as clusters of stars orbit a galaxy, a gravitational tidal interaction unfolds and the systems tear apart into distinct morphological and kinematic structures. In this talk, I will focus on my thesis work related to the stellar stream emerging from the old, globular cluster, Palomar 5 (Pal 5). As the stellar stream members were once closely tied together in energy and angular momentum space, we can use their distribution in phase space to trace back where they were once located and what affected them along their paths. In particular, I will show that the mere existence of Pal 5’s thin stream can rule out a moderately triaxial potential model of our Galaxy and that the debris of Pal 5-like streams will spread much further in space in a triaxial potential (a mechanism which I dubbed “stream fanning”) . Additionally, I will show that the Milky Way's Galactic bar, can punch holes in stellar streams and explain the recently discovered length asymmetry between Pal 5’s leading and trailing arm.

Aleksey Generozov:
Title: How to capture stars and form X-ray binaries
Abstract: Observations have revealed the presence of a large population of X-ray binaries (XRBs) in the central parsec of the Galactic Center, including ~10 black hole XRBs discovered recently by Hailey et al. 2018. This population is likely just the tip of the iceberg, signifying the presence of hundreds of less luminous XRBs. I will describe how tidal capture of low mass stars by black holes can account for this population.

David Hendel:
Title: Dynamics and detection of tidal debris
Abstract: Faint tidal features in stellar halos retain information about galaxies' merger histories for many Gyr and therefore hold clues to their growth and assembly. I will describe how this information is encoded in the debris morphology and share progress on a new machine vision classifier that will provide a crucial step in its extraction.

Yong Zheng:
Title: Finding the Milky Way's Hidden Circumgalactic Medium (CGM)
Abstract: Extragalactic studies of galaxies at z~1 and in the local Universe have shown that galaxies are surrounded by massive and multiphase CGM. The detection of such massive CGM alleviates the missing baryon problem which says that the total baryonic mass found in stars and ISM of galaxies is only 10-20% of the amount predicted by the Lambda CDM cosmology. Searching for the MW's extended CGM has been a notoriously difficult task, as we reside inside the Galactic disk and our lines of sight are blocked by nearby gas in both position and velocity spaces. In my talk, I will discuss these difficulties and present two novel methods of finding the MW's hidden CGM.

Alejandro Nunez
Title:The Relation Between Stellar Rotation and Magnetic Activity in Open Clusters
Abstract:In low-mass stars, the strength of the magnetic dynamo decreases over time as stars spin down through the loss of angular momentum via magnetized winds. Both coronal X-ray emission and chromospheric H-alpha emission trace the strength of the changing dynamo and, when combined with rotation periods in a single-aged population, can therefore be used to examine the dependence of magnetic activity on rotation across a range of masses. We observed two open clusters, the 60 Myr-old Alpha Persei and the 500 Myr-old M37 clusters, to obtain X-ray fluxes, H-alpha equivalent widths, and rotation periods of their stars. We explore how X-ray and H-alpha luminosity depend on rotation and how the different tracers of activity differ from each other in the same set of stars.

Jingjing Chen:
Title:On the Rate of Abiogenesis from a Bayesian Informatics Perspective
Abstract: Life appears to have emerged relatively quickly on the Earth, a fact sometimes used to justify a high rate of spontaneous abiogene (lambda) among Earthlike worlds. Conditioned upon a single datum - the time of earliest evidence for life - previous Bayesian formalisms for the posterior distribution of lambda have demonstrated how inferences are highly sensitive to the priors. Rather than attempt to infer the true lambda posterior, we here compute the relative change to lambda when new experimental/observational evidence is introduced. By simulating posterior distributions and resulting entropic information gains, we compare three experimental pressures on lambda : 1) evidence for an earlier start to life; 2) constraints on spontaneous abiogenesis from the lab; and 3) an exoplanet survey for biosignatures.

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