Jan. 17

"Searching for Clues to the Black Hole-Galaxy Relationship Through Nearby AGN Surveys"

abstract

Lisa M. Winter

University of Colorado at Boulder

host: Shardha Jogee

Jan. 24

Tinsley Visiting Scholar (Stars Group)

"Heavy Element Nucleosynthesis in the Brightest Asymptotic Giant Branch Stars"

abstract

Amanda Karakas

Mt. Stromlo Observatory, Canberra, Australia

host: Harriet Dinerstein

Jan. 31

"Probing the Cosmic History of Star Formation in Galaxies with the Herschel Space Observatory and CCAT"

abstract

Jason Glenn

University of Colorado at Boulder

host: Shardha Jogee

Feb. 7

"New Observational Insights into Cosmic Reionization"

abstract

George Becker

University of Cambridge, Kavli Institute for Cosmology, UK

host: Milos Milosavljevic

Thurs
Feb. 9

"Early Star Forming Galaxies and Reionization"

abstract

Daniel Stark

Steward Observatory, Arizona

hosts: Sally Dodson-Robinson & Shardha Jogee

Feb. 14

"Fueling Cosmic Star Formation: The Molecular Gas Mass Density of the Universe"

abstract

Dominik Riechers

California Institute of Technology

hosts: Shardha Jogee & Milos Milosavljevic

Feb. 21

"Direct Imaging of Exoplanets: Prospects for Comparative Exoplanetology"

abstract

Beth Biller

Max-Planck Institute for Astronomy, Heidelberg, Germany

host: Anita Cochran

Thurs
Feb. 23

"Understanding Galaxy Evolution in the Early Universe"

abstract

Steven Finkelstein

University of Texas at Austin

host: Shardha Jogee

Feb. 28

"Giant Planets Caught at Formation"

abstract

Adam L. Kraus

University of Hawaii, Institute for Astronomy

host: Chris Sneden

Thurs
Mar. 1

"The Dark Art of Detecting and Characterizing Planets by Direct Imaging"

abstract

Thayne Currie

NASA, Goddard Space Flight Center

host: Chris Sneden

Mar. 6

"Molecular spectroscopy of planet-forming regions: A quest to understand the diversity of planets and planetary systems"

abstract

Colette Salyk

National Optical Astronomy Observatory (NOAO)

host: Sally Dodson-Robinson

Mar. 13

Spring Break: 12 - 16 March. No Colloquium scheduled.

Mar. 20

No talk scheduled.

Mar 27

"Dark Matter Properties from the Faintest Galaxies"

abstract

Louis Strigari

Stanford University / Kavli Institute for Particle Astrophysics and Cosmology

host: Karl Gebhardt

Apr. 3
RLM 15.216B
3:30 PM

Antoinette de Vaucouleurs Medalist and Lecturer

"The Carnegie Supernova and Hubble Constant Projects"

abstract

Wendy Freedman

Director, Observatories of the Carnegie Institution for Science

host: Dan Jaffe

Apr. 4
ETC 2.136
4:30 PM

Antoinette de Vaucouleurs Medalist and Lecturer (visiting: 4/2-4/8)

Public Talk: "A Journey of Discovery: Our Expanding Universe"

abstract

Wendy Freedman

Director, Observatories of the Carnegie Institution for Science

host: Dan Jaffe

Apr. 10

"The ABCs of Low-Mass Stars"

abstract

Andrew West

Boston University

host: TBD

Apr. 17

"The History of Massive Galaxy Formation as a Cosmological Tool"

abstract

Christopher J. Conselice

University of Nottingham, UK

host: Shardha Jogee

Apr. 24

"Black Holes and Neutron Stars in the Local Universe"

abstract

Krzysztof Belczynski

University of Warsaw and University of Texas, Brownsville

host: Milos Milosavljevic

Wed
Apr. 25

Tinsley Visiting Professor (visiting: 4/23-5/17)

"The First Billion Years of our Universe"

abstract

Andrea Ferrara

Scuola Normale Superiore, Pisa, Italy

host: Volker Bromm

May 1

Texas Cosmology Center Distinguished Visitor

"Constraining Cosmology through the Growth of Structure: New Results from the South Pole Telescope"

abstract

John Carlstrom

University of Chicago

host: Eiichiro Komatsu

Mon
June 18
10 AM

PhD Defense Presentation

"Dark Matter Halos and Stellar Kinematics of Elliptical Galaxies"

abstract

Jeremy Murphy

University of Texas at Austin

Tue
July 24
1 PM

PhD Defense Presentation

"An Experiment in Integrated, Guided-Inquiry Science Classes and Implications for Teaching Astronomy"

abstract

Randi Ludwig

University of Texas at Austin

Tue
Aug 21
2 PM

PhD Defense Presentation

"Tests of the Episodic Mass Accretion Model for Low-Mass Star Formation"

A wide range of observed luminosities of young forming stars conflicts with predictions of the standard star formation model, which features a constant accretion rate. To resolve this discrepancy, an episodic accretion model has been suggested. The focus of this dissertation is to test this model in low mass star formation.

I used CARMA to observe a sample of embedded protostars, especially lower luminosity sources. The standard model predicts the disk mass increases steadily while the episodic accretion model predicts no clear relationship between disk mass and bolometric temperature. Masses of six detected disks spread out regardless of bolometric temperature. With the pure CO2 ice detection, I can explain disk masses of the source in the context of episodic mass accretion.

I present CO2 ice observations toward 19 low luminosity embedded protostars. About half of the sources have evidence for pure CO2 ice, and six have significant double-peaked features, which are strong evidence of pure CO2 ice. The presence of detectable amounts of pure CO2 ice signify a higher past luminosity, consistent with the past high accretion.

I present new observations of the CB130 region along with detailed chemo-dynamical modeling. The observed photometric data from Spitzer and ground-based telescopes are used to determine the luminosity, and radiative transfer modeling of dust and gas are used to characterize the envelope and disk. I compare molecular line observations to models to constrain the chemical characteristics and abundance variations. Based on the chemical model result and molecular line observations, the low luminosity of the embedded protostar is explained better as a quiescent stage between episodic accretion bursts rather than as the first hydrostatic core stage.

Using chemical evolution modeling, the episodic accretion scenario, in which mixed CO-CO2 ice is converted to pure CO2 ice during each high luminosity phase, explains the presence of pure CO2 ice, the total amount of CO2 ice, and the observed residual C18O gas.

close

Hyo Jeong Kim

University of Texas at Austin