Honoring the Contributions of Dr. Harry Shipman

Transcription

1 Program Information White dwarfs have been mysterious objects since the discovery that faint 40 Eri B was much hotter than expected, meaning that it must be very small and dense. We now know that white dwarfs represent the endpoint of stellar evolution for the majority of stars. They hold clues about physical processes that take place during earlier stages of stellar evolution. White dwarf masses, atmospheres, rotation rates, and internal composition are all important clues linked to fundamental questions of astrophysics. We have learned much since the discovery of 40 Eri B, Sirius B, and Procyon B. This workshop is being organized to honor the contributions of Dr. Harry Shipman to the fields of white dwarfs and science education. We plan to highlight recent results, and discuss the possibilities of future projects in this age of high quality data and large surveys. This workshop will provide an opportunity to discuss the latest results by leading scientists at the forefront of their fields. The SOC welcomes applications for contributed talks and posters. The workshop program will cover a wide range of topics related to all aspects of white dwarfs, including structure, evolution, atmospheres, asteroseismology, and science education. ************************************************************************************************************************ June 2 9:00 AM Welcome Session 1: Astronomy Education Chair: Barbara Castanheira Endl 9:15 General Astronomy Education Harry Shipman 9:40 The Successes and Failures of On-line Introductory Astronomy Courses Kurtis Williams Abstract: Many universities strongly encourage faculty to develop on-line courses, ostensibly to increase the geographic footprint of a university, though supposed cost savings are also cited. I will present anecdotes and (where possible) statistics from an online section of Introductory Stars and Galaxies I have developed over the past several semesters. Generally, I find that true distance learners have a higher rate of completion compared to on-campus students enrolled in an online section, that learning gains are smaller or comparable to face-to-face instruction, and that active instructor involvement is appreciated but not necessary for student success. This project is sponsored in part by a Texas Space Grant Consortium Higher Education Program award. 10:05 Python Scripts for Teaching Astronomy Mike Montgomery Abstract: Python has become an important tool in astronomy. I will demonstrate how python can be used to aid in astronomy education. 10:15-10:50 Discussion Session Astronomy Education Chair: Tim Lawlor 10:50-11:00 Coffee Break Page 1 of 7

2 Session 2: White Dwarf Atmospheres Chair: Agnes Kim 11:00 On the Extreme Ultraviolet Spectrum of White Dwarfs Stephane Vennes Abstract: In 1976, Harry offered the first correct explanation for the detection of hot white dwarfs in the early EUV/soft-Xray missions. The year 2016 will mark 40 years since Harry made that fundamental contribution. I will summarize the progress made since the dawn of EUV astronomy and, in particular, I will revisit key results obtained from the analysis of spectroscopic surveys conducted with NASA's Extreme Ultraviolet Explorer that still influence our understanding of the spectral evolution of white dwarfs. 11:25 New Opacity Models for Hydrogen in Dense Plasmas for White Dwarf Photospheres Thomas Gomez Abstract: White dwarf masses are important in many astrophysical contexts including asteroseismology and cosmochronology. These masses are most commonly determined by fitting a model to an observed spectrum; this is known as the spectroscopic method. However, there are well known discrepancies between the spectroscopic method and those of other methods, such as astrometric, dynamical, and gravitational redshift methods. We are developing a new model of hydrogen in a dense plasma that is a significant departure from previously models. We have developed two approaches to this problem, a simulation and semi-analytic approach. The simulation approach treats the perturbing influences of the protons and electrons classically, and then solves the time-dependent Schrodinger equation numerically to get the broadened profile. The semi-analytic approach treats the perturbing electrons quantum mechanically. Near the Inglis-Teller limit, perturbation theory is not sufficient to accurately capture the changes in atomic structure due to the nearby protons, we have therefore developed a way to directly solve the time-independent Schrodinger equation for the hydrogen atom with several nearby protons. Preliminary results for the proton-dependent energy-level structure show that discrete states exist beyond the Inglis-Teller limit, but, due to the averaging of the different proton configurations and the electron broadening, the spectrum appears featureless above this threshold. The resulting changes produce different opacities compared to the standard treatment, and should result in systematically different inferred masses for white dwarf stars. Experiments at Sandia National Laboratories are currently underway to validate these new models, and we have begun modifications to incorporate these models into the stellar atmosphere code TLUSTY. 11:50 Ultraviolet Spectroscopy of Helium Atmosphere White Dwarfs Judi Provencal Abstract: I came to Delaware in 1994 as Harry Shipman's post-doc to work on UV spectroscopy of Procyon B. I warned Harry that I didn't have much experience with spectroscopy, but he hired me anyway! I will outline the story of Procyon B, and provide an overview of recent investigations into the UV spectra of helium atmosphere white dwarfs. 12:10 1:10 Lunch 1:10 2:10 Discussion Session - Stellar Atmospheres Chair: John Gizis 2:10 2:20 Coffee Break Page 2 of 7

3 Session 3: White Dwarf Structure and Evolution Chair: Jim MacDonald 2:20 White Dwarfs in Cataclysmic Variables Ed Sion 2:45 Variability of Planetary Nebula Central Stars: Binarity, Rotation, Winds, and Pulsation Gerald Handler 3:05 Hot DQ White Dwarfs Bart Dunlap End of Day 1 4:00 Meet at Iron Hill Brewery Page 3 of 7

4 June 3 9:00 10:30 Discussion Session - White Dwarf Structure and Evolution Chair: Mike Montgomery 10:30-10:45 Coffee Break Session 4 White Dwarf Pulsations Chair: Ed Sion 10:45 Lessons Learned from Fitting GD358 Agnes Kim Abstract: The analysis of 33 years worth of data on GD358 allowed us to assemble a spectrum of 15 ell=1 modes, 13 of which constitute a consecutive sequence. This is the longest consecutive sequence of modes we fit formally so far, with high resolution grids. There were some hints before that some periods may be highly sensitive to some parameters in certain areas of parameter space. With the long consecutive sequence of same ell modes in GD358 s pulsation spectrum, we can study the effect such behaviors can have on asteroseismic fitting. We show some examples of sudden changes in the calculated period spectra and discuss the implications on pipeline fitting of white dwarfs. 11:10 Calibrating White Dwarf Asteroseismic Fitting Techniques Barbara Castanheira Endl 11:35 1:30 Lunch 1:30 Rogue Waves on Pulsating White Dwarfs JJ Hermes Abstract: While it has been an efficient planet-discovery machine, the unblinking photometry of the Kepler space telescope has also revolutionized the way we look at pulsating stars. I will discuss some of the rapid advances Kepler has enabled in our understanding of white dwarf stars, including a completely unexpected new physical phenomenon: large-amplitude outbursts in the coolest pulsating white dwarfs. These outbursts are essentially rogue waves, sporadically increases the overall stellar brightness by up to 15%. The outbursts have provided fresh insight into how pulsation energy can be transferred through nonlinear resonances, as well as the eventual cessation of pulsations in cool white dwarfs. 1:55 Kepler Observations of EC Judi Provencal 2:20-2:40 Coffee Break 3:00 4:30 Discussion Session - White Dwarf Pulsations Chair: Gerald Handler Page 4 of 7

5 4:30 Workshop Summary Stephane Vennes Page 5 of 7

6 Posters: Late Thermal Pulse Models and the Central Star of the Stingray Nebula Tim Lawlor Abstract: For the first time, it is believed a post-agb object is being observed to be undergoing a Late Thermal Pulse (LTP) which is a helium pulse that occurs shortly following the AGB and causes a rapid and wide looping evolution in temperature between the AGB and PN phase. It is a short lived phase that is related to, but different than, Very Late Thermal Pulse (VLTP) objects such as Sakurai s Object, FG Sge, and V605 Aql. These observed objects are believed to have experienced a similar thermal pulse, but later on the white dwarf cooling track. The potential observed LTP object is the central star of the Stingray Nebula, SAO or V838 Ara. This star has been observed to be rapidly evolving and heating over more than 50 years and is in the youngest known planetary nebula. These characteristics are similar to what is expected during the early stages of evolution for LTP models. In this work, we present evolution calculations from the Asymptotic Giant Branch (AGB) to the Planetary Nebula (PNe) phase for low Z models of mass 0.9 M and for solar Z models of mass 1.2 M. In order to bracket the behavior of V838 Ara, we adjust the mass of helium in both just prior to AGB departure to create a grid of LTP models. We focus here on models that experience a so called Late Thermal Pulse, though some undergo a VLTP and an AGB final Thermal Pulse (AFTP). For our LTP models, we compare our evolution tracks in the log(g)-t plane to V838 Ara and also compare our model surface abundances. Pulsation Frequencies of the ELM WDJ1518 Taran Copenhaver Participants Affiliation James Dalessio University of Delaware dalessio.james.at.gmail.com Bart Dunlap University of North Carolina, Chapel Hill bhdunlap.at.physics.unc.edu Barbara Castanheira Endl University of Texas barbara.at.astro.as.utexas.edu John Gizis University of Delaware gizis.at.udel.ed Thomas Gomez University of Texas Gerald Handler Nicolaus Copernicus Astronomical Center Warsaw gerald.at.camk.edu.pl JJ Hermes University of North Carolina, Chapel Hill jjhermes.at.unc.edu Budd Howard Mt. Cuba Observatory astroflight.at.comcast.net Agnes Kim Penn State Worthington Scranton axk55.at.psu.edu Tim Lawlor Penn State University Brandywine tlawlor.at.psu.edu Mike Montgomery University of Texas mikemon.at.astro.as.utexas.edu Jim MacDonald University of Delaware jimmacd.at.udel.edu Judith Provencal University of Delaware jlp.at.udel.edu Harry Shipman University of Delaware harrys.at.udel.edu Edward M. Sion Villanova University edward.sion.at.villanova.edu Stephane Vennes Czech Academy of Sciences vennes.at.asu.cas.cz Kurtis Williams Texas A&M University-Commerce kurtis.williams.at.tamuc.edu Page 6 of 7

7 Page 7 of 7