Calendar

Mar
28
Wed
Colloquium PhD Thesis Defense: Ethan Dederick
Mar 28 @ 3:15 pm – 4:15 pm
Colloquium PhD Thesis Defense: Ethan Dederick @ Science Hall 109

Seismic Inferences of Gas Giant Planets: Excitation & Interiors

Ethan Dederick, NMSU

Seismology has been the premier tool of study for understanding the interior structure of the Earth, the Sun, and even other stars. In this thesis we develop the framework for the first ever seismic inversion of a rapidly rotating gas giant planet. We extensively test this framework to ensure that the inversions are robust and operate within a linear regime. This framework is then applied to Saturn to solve for its interior density and sound speed profiles to better constrain its interior structure. This is done by incorporating observations of its mode frequencies derived from Linblad and Vertical Resonances in Saturn’s C-ring. We find that although the accuracy of the inversions is mitigated by the limited number of observed modes, we find that Saturn’s core density must be at least 8.97 +/- 0.01 g cm^{-3} below r/R_S = 0.3352 and its sound speed must be greater than 54.09 +/- 0.01 km s^{-1} below r/R_S = 0.2237. These new constraints can aid the development of accurate equations of state and thus help determine the composition in Saturn’s core. In addition, we investigate mode excitation and whether the \kappa-Mechanism can excite modes on Jupiter. While we find that the \kappa-Mechanism does not play a role in Jovian mode excitation, we discover a different opacity driven mechanism, The Radiative Suppression Mechanism, that can excite modes in hot giant planets orbiting extremely close to their host stars if they receive a stellar flux greater than 10^9~erg cm^{-2} s^{-1}. Finally, we investigate whether moist convection is responsible for exciting Jovian modes. Mode driving can occur if, on average, one cloud column with a 1-km radius exists per 6423 km^2 or if ~43 storms with 200 columns, each with a radius of 25 km, erupt per day. While this seems unlikely given current observations, moist convection does have enough thermal energy to drive Jovian oscillations, should it be available to them.

Sep
21
Fri
Colloquium: Dave Thilker (Host: Rene Walterbos)
Sep 21 @ 3:15 pm – 4:15 pm
Colloquium: Dave Thilker (Host: Rene Walterbos) @ BX102

Fresh Perspectives on Star Formation from LEGUS, the Legacy ExtraGalactic Ultraviolet Survey

David Thilker, Johns Hopkins University

The Legacy ExtraGalactic Ultraviolet Survey (LEGUS) was a Cycle 21 Large Treasury HST program which obtained ~parsec resolution NUV- to I-band WFC3 imaging for 50 nearby, representative star-forming Local Volume galaxies, with a primary goal of linking the scales of star formation from the limit of individual stars, to clusters and associations, eventually up through the hierarchy to giant star forming complexes and galaxy-scale morphological features.

I will review the basics of the survey, public data products and science team results pertaining to clusters and the field star hierarchy.  I will then describe work to optimize photometric selection methods for massive main sequence O star candidates and LBV candidates, in the former case establishing a means to statistically constrain the fraction of O stars in very isolated locales.  I will introduce new ideas on how to quantify the complex spatio-temporal nature of hierarchical star formation using multi-scale clustering methods. The first steps of this work have yielded a landmark OB association database for 36 LEGUS target fields (in 28 of the nearest available galaxies), with tracer stellar populations selected and interpreted uniformly.  I will finish with discussion of a pilot HST program to demonstrate remarkably increased survey efficiency of WFC3 UV imaging enabled by use of extra-wide (X) filter bandpasses.  Such efficiency is required as we move beyond LEGUS and begin to rigorously explore low surface brightness star-forming environments where canonical results for the IMF and cluster formation efficiency are increasingly called into question.

 

Feb
20
Wed
Special Colloquium: Stella Kafka (Host: Karen Kinemuchi)
Feb 20 @ 3:15 pm – 4:15 pm
Special Colloquium: Stella Kafka (Host: Karen Kinemuchi) @ Domenici Hall

The AAVSO Program: A Resource for Variable Star Research

Stella Kafka, AAVSO

The AAVSO was formed in 1911 as a group of US-based amateur observers obtaining data in support of professional astronomy projects. Now, it has evolved into an International Organization with members and observers from both the professional and non-professional astronomical community, contributing photometry to a public photometric database of about 25,000 variable objects, and using it for research projects. As such, the AAVSO’s main claim to fame is that it successfully engages backyard Astronomers, educators, students and professional astronomers in astronomical research. I will present the main aspects of the association and how it has evolved with time to become a premium resource for variable star researchers. I will also discuss the various means that the AAVSO is using to support cutting-edge variable star science, and how it engages its members in projects building a stronger international astronomical community.

 

Dr. Stella Kafka, is the Director of the AAVSO (American Association of Variable Star Observers). Before her tenure at the AAVSO, Dr Kafka held positions at CTIO, Spitzer Science center/Caltech, Carnegie Institution of Washington/DTM and AIP Publishing. The AAVSO is an international non-profit organization of variable star observers whose mission is to enable anyone, anywhere, to participate in scientific discovery through variable star astronomy.