Calendar

Oct
9
Fri
Colloquium: Ben Weiner
Oct 9 @ 3:15 pm – 4:15 pm
Colloquium:  Ben Weiner @ BX102

Searching for Dwarf Satellites around Milky Way – Analog Galaxies with the SAGA survey

Ben Weiner, Steward Observatory

Dwarf satellites of massive galaxies are a probe of many issues in galaxy evolution and cosmology, including the nature of low-mass galaxies, star formation at early times, accretion into halos, and the abundance of low-mass dark matter halos. Much attention has been devoted to the number and nature of Milky Way and M31 dwarf satellites, especially the “missing satellites problem.” However, we know very little about dwarf satellites outside the Local Group below the mass of the LMC, and we don’t know if the MW and M31 satellite systems are typical. The SAGA (Satellites Around Galactic Analogs) survey collaboration aims to address this with both observational and theoretical studies of satellite abundances and properties around Milky Way analog central galaxies. I will present results from our MMT/Hectospec wide field spectroscopic surveys for satellites. We have surveyed the fields of several nearby galaxies that are similar to the Milky Way to detect and spectroscopically confirm dwarf satellites.  We find a range of numbers of satellites, suggesting that there is a significant variance in halo histories.  We also find that not all dwarf systems resemble the Milky Way and M31 systems. I will discuss these results and some of the implications on the life cycle of satellites that we can infer from satellite abundances and properties, including their images and spectra.

 

Apr
8
Fri
Colloquium PhD Defense: Meredith Rawls
Apr 8 @ 3:00 pm – 4:00 pm
Colloquium PhD Defense: Meredith Rawls @ BX102

Red Giants in Eclipsing Binaries as a Benchmark for Asteroseismology

Meredith Rawls, NMSU

Aug
26
Fri
Colloquium PhD Defense: Kyle Uckert
Aug 26 @ 3:15 pm – 4:15 pm
Colloquium PhD Defense: Kyle Uckert @ BX102

Characterization of Biosignatures within Geologic Samples Analyzed using a Suite of in situ Techniques

Kyle Uckert, NMSU   

Abstract:
I investigated the biosignature detection capabilities of several in situ techniques to evaluate their potential to
detect the presence of extant or extinct life on other planetary surfaces. These instruments included: a laser desorption
time-of- flight mass spectrometer (LD-TOF-MS), an acousto-optic tunable filter (AOTF) infrared (IR) point spectrometer, a
laser-induced breakdown spectrometer (LIBS), X-ray diffraction (XRD)/X-ray fluorescence (XRF), and scanning electron
microscopy (SEM)/energy dispersive X-Ray spectroscopy (EDS). I measured the IR reflectance spectra of several speleothems
in caves in situ to detect the presence of biomineralization. Microorganisms (such as those that may exist on other solar
system bodies) mediate redox reactions to obtain energy for growth and reproduction, producing minerals such as
carbonates, metal oxides, and sulfates as waste products. Microbes occasionally become entombed in their mineral
excrement, essentially acting as a nucleation site for further crystal growth. This process produces minerals with a
crystal lattice distinct from geologic precipitation, detectable with IR reflectance spectroscopy. Using a suite of
samples collected from three subterranean environments, along with statistical analyses including principal component
analysis, I measured subsurface biosignatures associated with these biomineralization effects, including the presence of
trace elements, morphological characteristics, organic molecules, and amorphous crystal structures.

I also explored the optimization of a two-step LD-TOF-MS (L2MS) for the detection of organic molecules and other
biosignatures. I focused my efforts on characterizing the L2MS desorption IR laser wavelength dependence on organic
detection sensitivity in an effort to optimize the detection of high mass (≤100 Da) organic peaks. I analyzed samples
with an IR reflectance spectrometer and an L2MS with a tunable desorption IR laser whose wavelength range (2.7 – 3.45
microns) overlaps that of our IR spectrometer (1.6 – 3.6 microns), and discovered a IR resonance enhancement effect. A
correlation between the maximum IR absorption of organic functional group and mineral vibrational transitions – inferred
from the IR spectrum – and the optimal IR laser configuration for organic detection using L2MS indicates that IR
spectroscopy may be used to inform the optimal L2MS IR laser wavelength for organic detection. This work suggests that a
suite of instruments, particularly LD-TOF-MS and AOTF IR spectroscopy, has strong biosignature detection potential on a
future robotic platform for investigations of other planetary surfaces or subsurfaces.

Oct
10
Mon
Pizza Lunch: Laura Mayorga
Oct 10 @ 12:30 pm – 1:30 pm
Pizza Lunch: Laura Mayorga @ AY 119

Title: Proto-BD disks and the Kavli Summer Program in Astrophysics

Laura Mayorga

 

Oct
28
Fri
Colloquium: Mark Wardle
Oct 28 @ 3:15 pm – 4:15 pm
Colloquium: Mark Wardle @ Biology Annex 102

Star formation in the vicinity of the supermassive black hole at the Galactic Centre

Dr. Mark Wardle, Macquarie University

The disruptive tidal field near supermassive black holes overcomes the self-gravity of objects that are less dense than the Roche density.  This was once expected to suppress star formation within several parsecs of  Sgr A*, the four million solar mass black hole at the centre of the Galaxy.   It has since become apparent that things are not this simple:  Sgr A* is surrounded by a sub-parsec-scale orbiting disk of massive stars, indicating a star formation event occurred a few million years ago.    And on parsec scales,  star formation seems to be happening now:  there are proplyd candidates and protostellar outflow candidates,  as well as methanol and water masers that in the galactic disk would be regarded as sure-fire signatures of star formation.  In this talk, I shall consider how star formation can occur so close to Sgr A*.

The stellar disk may be created through the partial capture of a molecular cloud as it swept through the inner few parsecs of the galaxy and temporarily engulfed Sgr A*.  This rather naturally creates a disk of gas with the steep surface density profile of the present stellar disk.  The inner 0.04 pc  is so optically thick that it cannot fragment, instead accreting onto Sgr A* in a few million years; meanwhile the outer disk fragments and creates the observed stellar disk.   The isolated young stellar objects found at larger distances, on the other hand,  can be explained by stabilisation of clouds or cloud cores by the high external pressure that permeates the inner Galaxy.   A virial analysis shows that clouds are indeed tidally disrupted within 0.5 pc of Sgr A*, but outside this the external pressure allows self-gravitating clouds to survive, providing the raw material for ongoing star formation.

 

Mar
13
Mon
Pizza Lunch: Jean McKeever
Mar 13 @ 12:30 pm – 1:30 pm
Pizza Lunch: Jean McKeever @ AY 119

Red Giants in Eclipsing Binary Systems

Jean McKeever

 

Sep
20
Wed
Colloquium PhD Defense: Jean McKeever
Sep 20 @ 3:00 pm – 4:15 pm
Colloquium PhD Defense: Jean McKeever @ Business College 103

Asteroseismology of Red Giants: The Detailed Modeling of Red Giants in Eclipsing Binary Systems

Jean McKeever, NMSU

Asteroseismology is an invaluable tool that allows one to peer into the inside of a star and know its fundamental stellar properties with relative ease. There has been much exploration of solar-like oscillations within red giants with recent advances in technology, leading to new innovations in observing. The Kepler mission, with its 4-year observations of a single patch of sky, has opened the floodgates on asteroseismic studies. Binary star systems are also an invaluable tool for their ability to provide independent constraints on fundamental stellar parameters such as mass and radius. The asteroseismic scaling laws link observables in the light curves of stars to the physical parameters in the star, providing a unique tool to study large populations of stars quite easily. In this work we present our 4-year radial velocity observing program to provide accurate dynamical masses for 16 red giants in eclipsing binary systems. From this we find that asteroseismology overestimates the mass and radius of red giants by 15% and 5% respectively. We further attempt to model the pulsations of a few of these stars using stellar evolution and oscillation codes. The goal is to determine which masses are correct and if there is a physical cause for the discrepancy in asteroseismic masses. We find there are many challenges to modeling evolved stars such as red giants and we address a few of the major concerns. These systems are some of the best studied systems to date and further exploration of their asteroseismic mysteries is inevitable.