A5011125777- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astronomical Observations and Instrumentation
- Astro and Planetary Science
- Astrophysics and Star Formation Studies
- Gamma-ray bursts and supernovae
- Pulsars and Gravitational Waves Research
- Adaptive optics and wavefront sensing
- Astrophysical Phenomena and Observations
- High-pressure geophysics and materials
- Optical Coatings and Gratings
- Geophysics and Gravity Measurements
- Solar and Space Plasma Dynamics
- Geophysics and Sensor Technology
- SAS software applications and methods
- Photonic and Optical Devices
- Astrophysics and Cosmic Phenomena
- History and Developments in Astronomy
- Advanced Optical Sensing Technologies
- Radio Astronomy Observations and Technology
- Magnetic confinement fusion research
- solar cell performance optimization
- Optical Systems and Laser Technology
- Composite Structure Analysis and Optimization
- Anorectal Disease Treatments and Outcomes
University of North Carolina at Chapel Hill
2013-2023
The University of Texas at Austin
1990-2008
Iowa State University
1993-2008
Association of Universities For Research In Astronomy
2008
Cerro Tololo Inter-American Observatory
2008
U.S. National Science Foundation
2008
Alfred P. Sloan Foundation
2003-2004
California Institute of Technology
1997-2000
Canada–France–Hawaii Telescope
1998
University of Hawaii System
1998
Abstract We present optical and ultraviolet spectra of the first electromagnetic counterpart to a gravitational-wave (GW) source, binary neutron star merger GW170817. Spectra were obtained nightly between 1.5 9.5 days post-merger, using Southern Astrophysical Research Magellan telescopes; UV spectrum was with Hubble Space Telescope at 5.5 days. Our data reveal rapidly fading blue component ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>T</mml:mi>...
view Abstract Citations (320) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Whole Earth Telescope: A New Astronomical Instrument Nather, R. E. ; Winget, D. Clemens, J. C. Hansen, Hine, B. P. new multimirror ground-based telescope for time-series photometry of rapid variable stars, designed to minimize or eliminate gaps in the brightness record caused by rotation earth, is described. sequence existing telescopes distributed longitude,...
The Goodman Spectrograph is an imaging, multi-object spectrograph for the SOuthern Astrophysical Research telescope (SOAR). It one of first designed to take advantage Volume Phase Holographic (VPH) gratings by employing articulated camera. This aspect mechanical design has had complicating effects on a number usually simple systems, and led some unorthodox solutions. also highly optimized efficiency from 320 850 nm, rapid configuration changes, so that its throughput makes it competitive...
view Abstract Citations (332) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Asteroseismology of the DOV Star PG 1159-035 with Whole Earth Telescope Winget, D. E. ; Nather, R. Clemens, J. C. Provencal, Kleinman, S. Bradley, P. A. Wood, M. Claver, F. Frueh, L. Grauer, Hine, B. Hansen, Fontaine, G. Achilleos, N. Wickramasinghe, T. Marar, K. Seetha, Ashoka, O'Donoghue, Warner, Kurtz, W. Buckley, Brickhill, Vauclair, Dolez, Chevreton, Barstow,...
view Abstract Citations (255) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Whole Earth Telescope Observations of the DBV White Dwarf GD 358 Winget, D. E. ; Nather, R. Clemens, J. C. Provencal, L. Kleinman, S. Bradley, P. A. Claver, F. Dixson, Montgomery, M. H. Hansen, Hine, B. Birch, Candy, Marar, T. K. Seetha, Ashoka, N. Leibowitz, O'Donoghue, Warner, Buckley, Tripe, Vauclair, G. Dolez, Chevreton, Serre, Garrido, Kepler, O. Kanaan,...
We present photometry and spectroscopy for 27 pulsating hydrogen-atmosphere white dwarfs (DAVs; a.k.a. ZZ Ceti stars) observed by the Kepler space telescope up to K2 Campaign 8, an extensive compilation of observations with unprecedented duration (>75 days) duty cycle (>90%). The space-based reveals pulsation properties previously inaccessible ground-based observations. observe a sharp dichotomy in oscillation mode line widths at roughly 800 s, such that dwarf pulsations periods exceeding s...
We validate the discovery of a 2 Earth radii sub-Neptune-size planet around nearby high proper motion M2.5-dwarf G 9-40 (EPIC 212048748), using high-precision near-infrared (NIR) radial velocity (RV) observations with Habitable-zone Planet Finder (HPF), precision diffuser-assisted ground-based photometry custom narrow-band photometric filter, and adaptive optics imaging. At distance $d=27.9\mathrm{pc}$, 9-40b is second closest transiting discovered by K2 to date. The planet's large transit...
The white dwarfs are promising laboratories for the study of cosmochronology and stellar evolution. Through observations pulsating dwarfs, we can measure their internal structures compositions, critical to understanding post main sequence evolution, along with cooling rates, allowing us calibrate ages directly. most important set dwarf variables oldest pulsators, cool DAVs, which have not previously been explored through asteroseismology due complexity instability. a time-series photometry...
Tidal disruption and subsequent accretion of planetesimals by white dwarfs can reveal the elemental abundances rocky bodies in exoplanetary systems. Those provide information on composition nebula from which systems formed, is analogous to how meteorite inform our understanding early Solar System. We report detection lithium, sodium, potassium, calcium atmosphere dwarf Gaia DR2 4353607450860305024, we ascribe a planetesimal. Using model atmospheres, determine abundance ratios these elements,...
Abstract Observations of debris disks, the products collisional evolution rocky planetesimals, can be used to trace planetary activity across a wide range stellar types. The most common end points are no exception, as disks have been observed around several dozen white dwarf stars. But instead formation, post-main-sequence signpost destruction, resulting in compact from tidal disruption remnant planetesimals. In this work, we present discovery five new stars with gaseous emission. All...
view Abstract Citations (95) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Detection of the Evolutionary Time Scale DA White Dwarf G117-B15A with Whole Earth Telescope Kepler, S. O. ; Winget, D. E. Nather, R. Bradley, P. A. Grauer, Fontaine, G. Bergeron, Vauclair, Claver, C. F. Marar, T. M. K. Seetha, Ashoka, B. N. Mazeh, Leibowitz, Dolez, Chevreton, Barstow, Clemens, J. Kleinman, Sansom, Tweedy, W. Kanaan, Hine, Provencal, L. Wesemael,...
92 h of new Whole Earth Telescope observations have been acquired for the δ Scuti star CD-24 7599. All seven pulsation modes reported by Handler et al. are confirmed. However, significant amplitude variations which not caused beating closely spaced frequencies occurred within two years. Analysing combined data both WET runs, we detect six further modes, bringing total number up to 13. We also examine our high-frequency pulsations similar those exhibited rapidly oscillating Ap stars, but do...
We present the observed pulsation spectra of all known noninteracting ZZ Ceti stars (hydrogen atmosphere white dwarf variables [DAVs]) and examine changes in their properties across instability strip. confirm well-established trend increasing period with decreasing effective temperature do not find a dramatic order-of-magnitude increase number independent modes stars, traversing from hot to cool edge strip; we that DAVs have one more mode on average than DAVs. initial amplitude at blue...
We report on analysis of 308.3 hrs high speed photometry targeting the pulsating DA white dwarf EC14012-1446. The data were acquired with Whole Earth Telescope (WET) during 2008 international observing run XCOV26. Fourier transform light curve contains 19 independent frequencies and numerous combination frequencies. dominant peaks are 1633.907, 1887.404, 2504.897 microHz. Our amplitudes reveals that parent consistent modes spherical degree l=1. also provide m identifications for largest...
We present observations of a new phenomenon in pulsating white dwarf stars: large-amplitude outbursts at timescales much longer than the pulsation periods. The cool (Teff = 11,010 K), hydrogen-atmosphere PG 1149+057 was observed nearly continuously for more 78.8 d by extended Kepler mission K2 Campaign 1. target showed 10 outburst events, recurring roughly every 8 and lasting 15 hr, with maximum flux excursions up to 45% bandpass. demonstrate that affect pulsations therefore must come from...
Observations of heavy metal pollution in white dwarf stars indicate that metal-rich planetesimals are frequently scattered into star-grazing orbits, tidally disrupted, and accreted onto the surface, offering direct insight dynamical evolution post-main-sequence exoplanetary systems. Emission lines from gaseous debris accretion disks some these systems show variations on timescales decades, have been interpreted as general relativistic precession recently formed, elliptical disk. Here we...
We report the discovery of short-period photometric variability and modulated Zeeman-split hydrogen emission in SDSSJ125230.93-023417.72 (EPIC 228939929), a variable white dwarf star observed at long cadence \textit{K2} Campaign 10. The behavior is associated with magnetic ($B=5.0$ MG) spot on stellar surface, making $317.278$-second period direct measurement rotation rate. This object therefore fastest-rotating apparently isolated (without companion) yet discovered, second found to exhibit...
We introduce a model for pulsars in which non-radial oscillations of high spherical degree (l) aligned to the magnetic axis spinning neutron star reproduce morphological features pulsar beams. In our model, rotation carries pattern pulsation nodes underneath sightline, reproducing longitude stationary structure seen average pulse profiles, while associated time-like "drifting subpulses"--features that change their between successive spins. will show presence nodal lines can account observed...
We announce the discovery of a new eclipsing hot subdwarf B + M dwarf binary, EC 10246−2707, and present multicolour photometric spectroscopic observations this system. Similar to other HW Vir-type binaries, light curve shows both primary secondary eclipses, along with strong reflection effect from dwarf; no intrinsic contribution is detected cool companion. The orbital period 0.118 507 9936 ± 0.000 000 0009 d, or about 3 h. Analysis our time series spectroscopy reveals velocity...
ABSTRACT We report the discovery of two apparently isolated stellar remnants that exhibit rotationally modulated magnetic Balmer emission, adding to emerging DAHe class white dwarf stars. While previously discovered members this show Zeeman-split triplet emission features corresponding single field strengths, these new objects significant fluctuations in their apparent strengths with variability phase. The hydrogen lines LP 705−64 broaden from 9.4 22.2 MG over an spin period 72.629 min....
We have used time-resolved spectroscopy to measure the colour dependence of pulsation amplitudes in DAV white dwarf G29-38. Model atmospheres predict that mode should change with wavelength a manner depends on spherical harmonic degree ℓ mode. This arises from convolution geometry wavelength-dependent limb darkening. Our analysis six largest normal modes detected Keck observations G29-38 reveals one different other five, permitting us identify ℓ-value all and test model predictions. The also...
view Abstract Citations (71) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Whole Earth Telescope Observations and Seismological Analysis of the Pre--White Dwarf PG 2131+066 Kawaler, S. D. ; O'Brien, M. Clemens, J. C. Nather, R. E. Winget, Watson, T. K. Yanagida, Dixson, Bradley, P. A. Wood, Sullivan, Kleinman, Meistas, Leibowitz, Moskalik, Zola, Pajdosz, G. Krzesinski, Solheim, -E. Bruvold, O'Donoghue, Katz, Vauclair, Dolez, N. Chevreton,...
PG 1159-035, a pre-white dwarf with T_eff=140,000 K, is the prototype of both two classes: PG1159 spectroscopic class and DOV pulsating class. Previous studies 1159-035 photometric data obtained Whole Earth Telescope (WET) showed rich frequency spectrum allowing identification 122 pulsation modes. In this work, we used all available WET from 1983, 1985, 1989, 1993 2002 to identify periods identified 76 additional modes, increasing 198 number known modes in largest detected any star besides...
Abstract Using patterns in the oscillation frequencies of a white dwarf observed by K2 , we have measured fastest rotation rate (1.13 ± 0.02 hr) any isolated pulsating known to date. Balmer-line fits follow-up spectroscopy from SOAR telescope show that star (SDSSJ0837+1856, EPIC 211914185) is K, 0.87 0.03 M ⊙ dwarf. This highest mass for with rotation, suggesting possible link between high and fast rotation. If it product single-star evolution, its progenitor was roughly 4.0 main-sequence B...