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.

Colloquium (Joint with Physics): Jim Fuller (Host: Ethan Dederick)
Mar 29 @ 4:00 pm – 5:00 pm
Colloquium (Joint with Physics): Jim Fuller (Host: Ethan Dederick) @ Gardiner Hall 230

Surprising Impacts of Gravity Waves

Jim Fuller, Caltech

Gravity waves are low frequency fluid oscillations restored by buoyancy forces in planetary and stellar interiors. Despite their ubiquity, the importance of gravity waves in evolutionary processes and asteroseismology has only recently been appreciated. For instance, Kepler asteroseismic data has revealed gravity modes in thousands of red giant stars, providing unprecedented measurements of core structure and rotation. I will show how gravity modes (or lack thereof) can also reveal strong magnetic fields in the cores of red giants, and I will demonstrate that strong fields appear to be common within “retired” A stars but are absent in their lower-mass counterparts. In the late phase evolution of massive stars approaching core-collapse, vigorous convection excites gravity waves that can redistribute huge amounts of energy within the star. I will present preliminary models of this process, showing how wave energy redistribution can drive outbursts and enhanced mass loss in the final years of massive star evolution, with important consequences for the appearance of subsequent supernovae.
Colloquium PhD Thesis Defense: Sten Hasselquist
Apr 6 @ 3:15 pm – 4:15 pm
Colloquium PhD Thesis Defense: Sten Hasselquist @ BX102

Colloquium Title

Sten Hasselquist, NMSU


Colloquium Thesis Proposal: Emma Dahl
Apr 13 @ 3:15 pm – 4:15 pm
Colloquium Thesis Proposal: Emma Dahl @ BX102

Colloquium Title

Emma Dahl, NMSU

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Colloquium: Kat Barger (Host: Moire Prescott)
Apr 20 @ 3:15 pm – 4:15 pm
Colloquium: Kat Barger (Host: Moire Prescott) @ BX102

Colloquium Title

Kat Barger, Texas Christian University

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Colloquium Thesis Proposal: Caitlin Doughty
May 9 @ 2:15 pm – 3:15 pm
Colloquium Thesis Proposal: Caitlin Doughty @ Science Hall 107

Metal Absorption in the Circumgalactic Medium During the Epoch of Reionization

Caitlin Doughty, NMSU

The characteristics of metal absorption arising from the circumgalactic medium of galaxies have been demonstrated to be related to conditions in the galaxy which sourced them, as well as to the ambient ultraviolet background. I propose a three- pronged thesis in order to better understand and utilize these relationships. First, I will explore whether the spectral energy distributions of binary stars, incorporated into a custom version of GADGET-3, can explain the discrepancy between observed and simulated absorber statistics. Second, I will study the relationship between neu- tral oxygen absorbers and the neutral hydrogen fraction in simulated quasar sight- lines and relate the results to observations of neutral oxygen at z ≥ 4.0. Third, I will study the relationships between the emissive properties of galaxies, stemming from their nebular gas, and the metal absorbers which they source. Taken as a whole, this thesis will improve the ability of cosmological simulations to reproduce realistic metal absorption, probe the local progress and topology of reionization, and under- stand what emissive galaxy traits we expect at z > 5 based on observations of metal absorbers.

Colloquium PhD Thesis Defense: Kathryn Steakley
May 11 @ 2:15 pm – 3:30 pm
Colloquium PhD Thesis Defense: Kathryn Steakley @ BX102

Impact heating of the early Martian climate

Kathryn Steakley, NMSU Astronomy

The nature of Mars’ ancient climate has been the subject of debate for decades. Abundant geologic evidence suggests that liquid water flowed on the surface of Mars during the late Noachian and early Hesperian eras (~3.5 – 3.8 billion years ago), but climate models struggle to reproduce such warm and wet conditions. Characterizing the climate that supported this aqueous activity and constraining the duration and intensity of warm and wet periods is crucial to understanding whether Mars was habitable in the past. 1-D climate modeling studies suggest that asteroid impacts are capable of inducing greenhouse warming on early Mars due to the substantial amounts of energy and water that are injected into the atmosphere (Segura et al., 2008). We use a 3-D global climate model (GCM) to simulate the post-impact climate conditions presented in Segura et al. (2008) (30-, 50-, and 100-km impactors in 150 mbar, 1 bar, and 2 bar atmospheres) and examine the resulting global distributions of surface temperatures and precipitation to assess whether these post-impact climates can facilitate valley network formation in Mars’ southern highlands. We find that these post-impact scenarios do result in above-freezing temperatures and 10s of cm of rainfall in the southern highlands, but that ultimately these warm and wet periods are short lived (on the order of years) and do not support the sustained warm and wet conditions that facilitate valley network formation. We find that scenarios with high surface pressures and scenarios with radiatively active clouds experience longer periods of above-freezing temperatures and result in higher final mean annual temperatures (up to 272.8K in our warmest scenario). In future work, we will investigate other greenhouse gases delivered by impacts in addition to water, including hydrogen and/or methane, to test whether this prolongs the warm and wet periods following impacts.

Colloquium: Dawn Gelino (Host: Tom Harrison)
Aug 24 @ 3:15 pm – 4:15 pm
Colloquium: Dawn Gelino (Host: Tom Harrison) @ BX102

NASA, Exoplanets, and Life After NMSU

Dawn Gelino, NASA Exoplanet Science Institute, CalTech

Abstract:  Are you interested in learning more about the search for life in the Universe? Or perhaps you may be interested in being awarded time on 10 m telescopes for your science? Or maybe you are ready to learn more about prestigious NASA Postdoctoral Fellowships? This talk will touch on some recent and exciting results in the exoplanet field, as well as the different NASA HQ programs that I currently run for all of astrophysics (many of which may be helpful and applicable to YOU), and the path I took from NMSU to where I am now.

Colloquium: Don Terndrup (Host: Nancy Chanover)
Aug 31 @ 3:15 pm – 4:15 pm
Colloquium: Don Terndrup (Host: Nancy Chanover) @ BX102

Stellar Winds and Stellar Rotation

Don Terndrup, Ohio State University

For more than 50 years, we have known that stars rotate quickly when they are young and slow down as they age.  This process gives us important clues about magnetic field strength and geometry, as well as the nature of stellar winds, in solar-like stars.  We have been working to put the analysis of stellar rotation on a modern statistical footing, and in this talk I will give you an update on our efforts.  There are a number of critical observational problems that must be considered in calibrating models of angular momentum loss, especially problems of data censorship (older or less active stars are not detected in studies of rotation).  I will conclude by evaluating the prospects for using stellar rotation as an age indicator, and demonstrate that such ages are far less precise – though still useful – than our group and others have previously claimed.



Colloquium PhD Thesis Defense: Alexander Thelen (Host: Nancy Chanover)
Sep 12 @ 3:00 pm – 4:00 pm
Colloquium PhD Thesis Defense: Alexander Thelen (Host: Nancy Chanover) @ Domenici Hall Room 102

The Chemical Composition and Dynamics of Titan’s Atmosphere as Revealed by ALMA

Alexander Thelen, NMSU

Over the last century, remarkable advances in our understanding of Titan’s atmosphere have been accomplished by a campaign of ground- and space-based observations revealing a wealth of complex, organic species in the moon’s upper atmosphere. Many of Titan’s atmospheric constituents produced through the photochemistry and ionospheric interactions of N2 and CH4 exhibit significant variations with latitude and time, particularly towards the poles and within the winter circumpolar vortex. The measurement of spatial and temporal variations in Titan’s atmosphere enables us to elucidate connections between its dynamics, photochemistry, and the influence of seasonal changes. At the end of the Cassini mission in 2017, we can employ the Atacama Large Millimeter/submillimeter Array (ALMA) for future observations of Titan’s atmosphere. Here we detail the analysis of numerous short integration (~3 minute) ALMA observations from 2012 to 2015 to investigate Titan’s stratospheric composition, temporal variations, and search for new molecular species. Using the Non-linear optimal Estimator for MultivariatE spectral analySIS (NEMESIS) radiative transfer code, we retrieved vertical profiles of temperature and abundance in Titan’s lower stratosphere through mesosphere (~50–550 km) from three spatially independent regions. We modeled CO emission lines to obtain temperature measurements, and retrieved abundance profiles for HCN, HC3N, C3H4, and CH3CN. The combination of integrated flux maps and vertical atmospheric profiles from spatially resolved observations allowed us to study the circulation of Titan’s middle atmosphere during northern spring. We observed increased temperatures in Titan’s stratopause at high northern latitudes and a persistent northern enrichment of HCN, C3H4, and CH3CN during this epoch; however, increased abundances of all molecules in the southern mesosphere, particularly HCN, and spatial maps of HC3N also show evidence for subsidence at the south pole. We validated these measurements through direct comparisons with contemporaneous Cassini data, previous ground-based observations, and photochemical model results. While no new trace species were detected, ALMA has proven to be a highly capable asset to enhance the data from the final few years of the Cassini mission, and for the continued study of Titan’s atmospheric dynamics, composition, and chemistry into Titan’s northern summer.