Abstracts
The Predicted Range of Observable Pulsation Periods in Extremely Low-mass White Dwarf Stars
Jesús Aguilar-Landaverde, UT Austin
White dwarf stars are the expected final evolutionary states for approximately 97% of all stars. A subclass of these stars exhibits non-radial oscillations in a well-known instability strip in the log g - Teff plane. These pulsators contain a Carbon-Oxygen core with a thin hydrogen or helium-dominated atmosphere and have been studied closely for decades. A new class of white dwarfs of extremely low mass (~0.17-0.3 Msun), discovered in recent years, has motivated theoretical calculations for possible oscillations in these objects. In this work, we focus on the star NLTT 11748 and calculate a set of expected periods in this object; furthermore, we calculate how these periods vary with effective temperature in order to determine if such periods are detectable. We find for this system that the fundamental p-mode periods are greater than 80 s in its allowed range of Teff; these same periods can be as large as 150 s at higher temperatures (12, 000 K), thus placing these theoretical periods in the observable range of modern technology. Not only have pulsations not been found in these extremely low mass white dwarfs, but p-mode oscillations have never been detected in any class of white dwarf pulsator.
Observations of Suspected RR Lyrae Variable Stars
Hans Amende & Caleb Bahr, Texas Lutheran University
Our group is working on confirming variability of suspected RR Lyrae variables we have identified, and making follow-up observations of confirmed new variables. We developed a new method of detecting RR Lyrae variable stars using only a single epoch of both photometry and spectroscopy taken from the Sloan Digital Sky Survey (SDSS). The method takes advantage of clear departures from the template norm for stars that have photometry and spectroscopy taken out of phase. Over 1,000 stars have been identified as probable RR Lyrae stars, scattered across the halo and ranging from 14th to 20th magnitude. This paper describes observations taken at McDonald Observatory by undergraduate students as part of this project. We will discuss how and why the method works, and our McDonald observations to confirm variability and obtain full lightcurves.
How Useful Is U-band Photometry of Type Ia Supernova?
Deepak Bastola, Texas A&M
The optical photometry of Type Ia Supernova 2003hv was studied in detail, especially focusing on the U-band. U-band photometry of supernova is of special importance as the red shifted photon emitted from the supernova as seen by us is actually in the U-band in its rest frame. We had the photometry of several supernovae from CTIO 1.3m, CTIO-0.9m, and Las Campanas Observatory in Chile, and after reducing them with standard IRAF scripts, we derived their U-band light curves. The light curves of supernova need to undergo specific correction to be fit for cosmology. The discrepancies in the photometry can be remedied by using S-corrections. The S-corrected photometry of 36 objects was used to get a U-band decline rate relation.
Sigmoid: A Twisted Tale of Flux and Fields
Tyler Behm, Texas A&M
The high resolution of space-based solar telescopes like the Hinode X-Ray Telescope has allowed astronomers to see fine S-shaped filaments in active regions. These S-shaped filaments are known as sigmoids and are of great interest to solar astronomy because 68% of coronal mass ejections come from sigmoids. In this talk, we detail methods of studying sigmoids by using magnetograms to make field models and by comparing these models to the visible fluxes in image data. Through our research, we find the best fit models of two different sigmoids.
Caroline Caldwell, UT Austin
McDonald Observatory's Planet Search has recorded twelve years of high precision radial velocity measurements. Since Jupiter's period is approximately 12 years, it is possible to test the frequency of Jupiter analogues in the database. From the initial sample we selected 84 stars with the required time line of observations and no known companions. Our criteria for a Jupiter analogue are a planetary companion of a sun-like star with a mass between 1 to 4 Jupiter masses, at a distance ranging from 4 to 5 AU. A true Jupiter signal is at the limit of our observations at a distance of 5AU with a period of 4330 days, or 11.9 years. We performed simulations to test our sensitivity to detect radial velocity signals of Jupiter analogues. We present the results of these simulations and show the database's sensitivity to Jupiter analogues and the frequency of Jupiter analogues. The results demonstrate that the McDonald Observatory Planet Search is a valuable source of high precision radial velocity measurements, and that the continuation of the program is beneficial to the discovery and study of exoplanets.
The Morphology of Dual Active Galactic Nuclei
James Diekmann, UT Austin
We report the morphologies of double-peaked active galactic nuclei (DPAGN) in the Sloan Digital Sky Survey (SDSS) obtained with Galaxy Zoo, a citizen scientist project that visually classifies galaxies from SDSS. DPAGN are active galaxies that have double-peaked, AGN-fueled [O III] emission lines that indicate they are good candidates for dual AGN. Dual AGN are produced when two galaxies merge, and each galaxy has a central supermassive black hole (SMBH) powering an AGN.The results from the Galaxy Zoo catalog suggest that the morphologies of DPAGN favor elliptical galaxies. In the DPAGN population, 57% are classified as ellipticals, 41% as spirals, and 2% as mergers. In contrast, spiral galaxies are the dominant morphology of a comparison sample of active galaxies, with ∼55% of active galaxies classified as spirals and ∼45% as ellipticals. These results suggest that DPAGN occur preferentially in elliptical galaxies, which is consistent with expectations that dual AGN are produced in merger-remnant galaxies with elliptical morphologies. Overall, understanding the structure of a galaxy containing DPAGN can be used to probe formation scenarios of dual AGN and dynamics of SMBHs in mergers.
The Temperature Gradient of Diffuse X-Ray Emissions of Edge-on Galaxies
David Durke, UT San Antonio
Galaxies diffuse x-ray emissions. The Chandra X-ray observatory is equipped with an ACIS (Advanced CCD[Charged Coupled Device] Imaging Spectrometer) which detects x-ray photons. The ACIS has FI (Front Illuminated) and BI (Back Illuminated) chips through which the structure of the chips filter out certain energies of x-rays. The FI chips block lower energy photons, while the BI chips have a better coverage of low energy photons, but a lower energy resolution as well. For this project we have observed the temperature gradient of diffuse x-ray emissions of NGC891 through the S3 BI chip on the Chandra (the BI chip that provides the best resolution). By observing a detailed temperature gradient along the galaxy, we can get a stepping stone to a better understanding on whether the temperature emissions of a galaxy are caused mainly by supernovas or star clusters.
Understanding Stellar Birth through the Photometric and Spectroscopic Variability of T Tauri Stars
Michael Eastwood, Rice University
T Tauri stars are protostellar objects currently evolving toward the main sequence. These stars, which have not started nuclear fusion at their core, are powered by gravitational contraction. Accretion events from a surrounding disk and magnetically generated cool spots coupled with the rotation of the star contribute to the highly variable nature of these stars. We use a time series of BVR photometry measurements and spectroscopy obtained from the McDonald Observatory to search for the presence of hot and cool spots on the surface of three classical T Tauri stars: BP Tau, DN Tau and DG Tau. The erratic variability of these stars can lead to false positive results in radial-velocity searches for low-mass companions, making it important to understand the sources of variability in these objects. Future work will focus on using the radial-velocity technique to search for low-mass companions around these young stars in order to constrain the timescale for planetary formation.
Ionized Gas in the Inner 2 pc of the Milky Way
Wesley Irons, UT Austin
Like most galaxies, the center of the Milky Way contains a supermassive black hole (SMBH), Sgr A*. Because it is the closest of these phenomena, it is an important laboratory for obtaining a better understanding of galaxy evolution and active galaxies. The galactic center consists of many components, all of which are important in the study of this region. We present new observations of the ionized gas in the central two parsecs of the Milky Way, using [NeII] as a tracer. The observations were made using TEXES, a high-resolution mid-infrared spectrograph, on the NASA IRTF in June 2003. With the high spectral and spatial resolution datacube, we compare two kinematic models for the ‘mini-spiral’ at the galactic center. For the first model, it has been widely suggested that the gas streamers are tidally stretched clouds with motion along the streamers (Serabyn et al., Zhao et al.). Here, we analyze the Doppler pattern along three ellipses derived by Zhao et al. that fit the filaments as separate keplerian orbits in the gravitational potential of Sgr A*. The second model, taken from Lacy et al. (1991), consists of a one-armed spiral structure. It is suggested that rather than flowing along the filaments, the gas in the spiral follows circular keplerian orbits that cross them. We can report that the spiral model with circular velocities is a better fit kinematically than the ellipse models. The physics behind these observations is not entirely clear, and more theoretical work is needed to adequately interpret them.
Is This Really a Cluster?: SDSS-III/APOGEE Cluster Target Selection
Kelly Jackson, Texas Christian University
Which of the stellar overdensities from within the inner Milky Way are actual star clusters? Using data collected from the Two Micron All-Sky Survey (2MASS) and Spitzer Space Telescope/GLIMPSE-I, II, 3D, and 360 surveys, we have developed a new technique which utilizes each star’s extinction (AK) value in order to isolate nearby open stars clusters. Once a cluster is confirmed, we use the "cleaned" color magnitude diagram to measure the cluster age, metallicity, and distance. In addition to acquiring a new catalog of clusters, this process also serves as an important step in the target selection process for the Sloan Digital Sky Survey III / Apache Point Observatory Galactic Evolution Experiment (SDSS-III/APOGEE) as likely cluster members identified by this technique are then targeted for APOGEE.
AGB Dust and Evolution of the ISM in the Early Universe
Andy Liao, UT Austin
Stars are known to form out of clouds of molecular hydrogen (H2). However, hydrogen atoms do not readily combine in interstellar space by themselves. In order for H2 to form, dust must be present as a catalyst. Dust is created and released into the interstellar medium (ISM) by either massive dying stars undergoing supernovae (SN) or low mass stars in their final stage of life on the asymptotic giant branch (AGB). Most research on star formation in the early universe has focused on SN as the production mechanism of dust. However, recent research indicates that low mass stars are expected to be able to form in the early universe, and thus AGB dust production may be relevant. Our research examines whether if AGB produced dust is sufficient in quantity to catalyze the formation of molecular clouds in the first galaxies. For a crude simulation, we use the FLASH hydrodynamic code to generate a 1 pc box filled with primordial gas (hydrogen and helium) as well as an AGB star as a source of dust, metals, and radiation. The box is then 'stirred' to simulate the dominating effect of random supersonic turbulence expected to be present in these first galaxies. The first results of our simulation are presented here.
Production and Alignment of the Visible Integral-Field Replicable Unit Spectrograph (VIRUS)
Emily Martin, Texas A&M
The Visible Integral-Field Replicable Unit Spectrograph (VIRUS) spectrographs are being built at Texas A&M University and are being designed in collaboration with The University of Texas at Austin. As many as 192 units of this instrument will be employed by the Hobby Eberly Telescope Dark Energy Experiment (HETDEX) to search for answers regarding Dark Energy. Texas A&M is currently assembling the spectrographs for VIRUS and designing alignment fixtures to aid in the construction. My research this summer was to help with the planning and optical alignment process for various parts of VIRUS. Using ZEMAX, optical design software, I took models of VIRUS optics designed by UT engineers and used them to analyze the functionality of various tests that we will perform to ensure that the spectrographs are properly aligned.
Stellar Kinematics in the Bar of the Milky Way
Connor McKeel, Texas Christian University
In 2005 the Galactic Legacy Mid-Plane Survey Extraordinaire (GLIMPSE) found the Milky Way to contain a long bar within its structure, the results of this survey were unclear though of the full size, structure, and dynamics of the bar. Studying the bar is difficult due to the large extinction in the inner mid-plane of the Galaxy. Using the Two Micron All Sky Survey (2MASS) and GLIMPSE I & II a large number of evolved stars, bright in the infrared can be identified in the area of the long bar. To explore the kinematics of the long bar, spectra of candidate long bar stars have been obtained to measure radial velocities, to measure the extent and kinematics of the long bar. Here we present preliminary results from 100 stars at |b| ≈ 3◦
Using the MONET Telescope to Study White Dwarf Pulsations
George Miller, UT Austin
Pulsating white dwarf stars provide vast amounts of information in nearly every field of astronomy. Using precision asteroseismology, we can explore, for example, a star's mass, rotation rate, equation of state, and nuclear reaction rates. By studying the rate of change of WD pulsations we can explore galactic time measurements, orbiting planets, dark matter theories, or interior crystallization. Yet, to obtain accurate pulsation measurements, astronomers require long stretches of time-resolved data often spanning years. Thus, telescope time and travel funds often are the greatest constraint placed on WD pulsation studies. I believe the MONET telescope can help alleviate this problem. The MONET telescope is a remotely controlled 1.2m telescope operated by the Georg-August-Universität Göttingen and McDonald Observatory. By adapting the high-speed reduction packages developed by Antonio Kanaan for the 82’’ Otto-Struve telescope, I have successfully created a pipeline for producing accurate Fourier transforms of known WD pulsators using the MONET telescope. By comparing similar runs in similar weather conditions, the 82’’ telescope produces only roughly twice the signal-to-noise as the MONET. The accessibility of the MONET creates a number of scientific advantages. For example, time critical data can be obtained quickly without waiting for scheduled 82’’ observing runs. Moreover, data can be obtained evenly throughout the year rather than every few months. Finally, the MONET allows for telescope use by undergraduate astronomy students.
Observations of the 2010 January Outburst of the Recurrent Nova U Scorpius using NASA's Swift
Marilyn Moore, UT San Antonio
X-ray observations from the recurrent nova U Scorpius were obtained with NASA's Swift telescope in January 2010. This cataclysmic variable (CV) system contains a white dwarf (WD) and a low-mass star, and is the shortest known recurrent nova (RN) which erupts on a ~10 year cycle; average RNe have outbursts that may take centuries or millennia to recur. Spectra from this system were recorded in the super soft X-ray band, and several characteristics were obtained, including a pseudo-temperature, an integrated X-ray luminosity, and an interstellar absorption column. The analysis included determining abundance values of elements in the burst using NASA’s Heasoft software. During our analysis, we discovered that the optical eclipses were apparent, but X-ray eclipses were not. This raises more questions about the emitting area of X-ray radiation around a binary companion near directly in our line of sight. Our findings create a substantial basis for understanding of CV systems, and bring us closer to determining the ultimate fate of these stars. If we find that the WD is gaining mass, this may determine the origins of Type Ia supernovae.
Composition of the Orion Nebula from Hubble Space Telescope Spectra
Kathryn Powell, Rice University
The Orion Nebula (M42, NGC 1976) is the nearest H II region, a cloud of ionized gas that contains regions of recent star formation. We analyzed two areas of the Orion Nebula using spectra from the Hubble Space Telescope Faint Object Spectrograph. This instrument is unique in that it observed the ultraviolet and optical spectra of the nebula at the same exact location permitting accurate comparisons between emission lines in the two wavelength regions for the first time. We measured the emission line intensities using IRAF, determined the appropriate interstellar reddening corrections to the line intensities, and calculated improved abundances for carbon relative to oxygen and other elements. We present the ionic and elemental abundances of C, N, O, Ne, and S. Finally, we compare these measurements to previous studies of the Orion Nebula, other Galactic H II regions, as well as solar abundances.
Bolometric Temperature and Luminosity of Embedded Young Stellar Objects
Michelle Rascati, UT Austin
The study of young stellar objects (YSOs) gives insight to how stars and planets form. Currently YSOs are divided into classes based on the shape of the object’s Spectral Energy Distribution (SED). These classifications are not necessarily accurate in describing the physical evolution of the object and there are many other unknowns in the entire process of YSO evolution. I have used data from the Herschel Space Observatory PACS Spectrometer to study the SEDs of Class 0 and I embedded YSOs. From this I found a single temperature and luminosity to characterize the entire spectrum, referred to as the bolometric temperature, Tbol and bolometric luminosity, Lbol, respectively. Herschel-PACS covers a wavelength range from 50-200 microns, which generally corresponds to the peak of these objects and has yet to be observed with a high resolution of \delta\lambda/\lambda\sim1000-3000. Using ancillary data ranging from the UV to sub-millimeter along with Herschel-PACS spectra I was able to compare the effect of including PACS in the SEDs to determine the Tbol and Lbol I have found that for sources with a well-sampled range of data points the SED is minimally affected. The analysis with the Herschel-PACS spectrum confirms that these embedded objects have been previously characterized accurately.
The Fate of Metals Synthesized in Population III Stars
Jeremy Ritter, UT Austin
Even the most metal poor stars observed today contain certain amounts of elements heavier than hydrogen and helium, and some of the most iron-poor stars have enhanced α-element abundances. This suggests that an earlier generation of core-collapse supernovae should have enriched the medium from which these metal-poor stars formed. A goal of this research is to study the fate of metals synthesized in the explosions of the first ”Population III” supernovae as they are injected into the primordial medium and then become subject to bulk transport and mixing during the recollapse of larger cosmological structures. Our simulations begin with cosmological initial conditions within a 1 Mpc comoving domain at redshift z = 145.5 and proceed until the baryons have undergone central collapse in a dark matter mini-halo at a redshift of approximately z = 20. Assuming that the collapse leads to the formation of a star or a small cluster of stars, we utilize a direction-dependent Str ̈omgren-type radiative transfer algorithm to create a physically consistent HII region surrounding the collapsed baryons. After allowing the HII region to undergo pressure-driven expansion for several million years, the approximate lifetime of a massive star, we introduce metal ejecta in the free expansion phase of a supernova explosion within the HII region. We track the ionization state and cooling rate of the metal gas through metallicity- and temperature-dependent table lookup. The chemistry of primordial gas and molecules is solved by an iterative chemical network. The supernova remnant expands within its progenitor mini-halo and may be mixed with other baryonic gas or ejected into the surrounding intergalactic medium. The metal enriched gas will eventually cool and recollapse to form the next generation of metal-poor stars.
Exploration of Mass-Radius Relation for Low-mass White Dwarfs
Arina Rostopchina, UT Austin
White dwarf (WD) stars are believed to be the final evolutionary state for approximately 98% of all stars – including our own Sun. Since they have exhausted their fuel and are now simply cooling off, they are in many ways easier to study than main-sequence stars. Our group has recently discovered a binary WD system with the shortest known binary period. This is a double-eclipsing system, giving us extremely accurate estimates for the radii of the two stars. Future spectroscopic observations may lead to accurate mass determinations, allowing us to test the Mass-Radius relation for low-mass WD stars. In an effort to establish the accuracy with which the mass of the star would need to be known for this test, I have used the MESA stellar evolution code to examine theoretically the Mass-Radius relationship of the 0.25Msun WD in the binary. I have also included the uncertainties associated with the thickness of the hydrogen layer and residual nuclear reactions as part of this work.
Optimal Resolutions for Optical and IR Spectroscopy through Atmospheric Emission Lines
Steven Villanueva, Texas A&M
We study the effects of atmospheric emission lines in the 0.4-2.4 micron range at resolutions ranging from 10-10,000 on a pixel-by-pixel basis. After taking an atmospheric emission model from ESO, we define and calculate the fraction of pixels free of emission lines in 7 different band passes. We then discuss the effect of the background emission on the SNR of targets of various magnitudes to determine a ‘best’ resolution at which to observe.
MOSAIC Reductions for z~2.1 Lyman Alpha Emitting Galaxies
Patrick Williams, Texas A&M
Lyman Alpha Emitting Galaxies (LAEs) are extremely important in the study of galaxy evolution as they are considered to be the progenitors of the galaxies observed in the local Universe due to their compact size and starburst nature. Although observations of LAEs corresponding to redshifts of 3.1 < z < 6 indicate very little evolution of the luminosity function (LF), separate observations at z~0.3 indicate a rarer and fainter sample of LAEs. We use narrow-band imaging to select LAEs at an intermediate redshift z~2.1 to search for evolution in the range of 0.3 < z < 3.1. The data sets consisted of images gathered from three separate observing runs spanning three years at the Kitt Peak National Observatory (KPNO) and Cerro Tololo Inter-American Observatory (CTIO). In addition to standard reductions, we used specifically designed reduction techniques outlined for the MOSAIC camera at KPNO and CTIO in order to combine our final reduced images into a single stacked image. This deep, stacked image will aid us in detecting LAEs at our chosen redshift of z~2.1. Using this sample at z~2.1, we hope to investigate certain evolutionary properties of LAEs including age, stellar mass, dust and dark matter halo mass.
Automation of Calibration System for Dark Energy Survey
Jason Wise, Texas A&M
DECal is a spectrophotometric calibration system for the DECam camera that will be used for the Dark Energy Survey. The calibration system uses a monochromator to produce a light source with a narrow bandpass (2nm) that is then projected onto a dome flat screen. The reflection off the screen is measured by the camera and a NIST calibrated photodiode, and the results are compared to measure the throughput of the telescope vs wavelength. We present our efforts to automate this system using LabVIEW software to integrate it into the telescope control system.