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Full-Text Articles in Physical Sciences and Mathematics
Whole Earth Telescope Discovery Of A Strongly Distorted Quadrupole Pulsation In The Largest Amplitude Rapidly Oscillating Ap Star, Daniel L. Holdsworth, Donald W. Kurtz, Hideyuki Saio, Judith L. Provençal, Bruno Letarte, Ramotholo R. Sefako, Véronique Petit, Barry Smalley, H. Thomsen, C. L. Fletcher
Whole Earth Telescope Discovery Of A Strongly Distorted Quadrupole Pulsation In The Largest Amplitude Rapidly Oscillating Ap Star, Daniel L. Holdsworth, Donald W. Kurtz, Hideyuki Saio, Judith L. Provençal, Bruno Letarte, Ramotholo R. Sefako, Véronique Petit, Barry Smalley, H. Thomsen, C. L. Fletcher
Aerospace, Physics, and Space Science Faculty Publications
We present a new analysis of the rapidly oscillating Ap (roAp) star, 2MASS J19400781 - 4420093 (J1940; V = 13.1). The star was discovered using SuperWASP broad-band photometry to have a frequency of 176.39 d-1 (2041.55 μHz; P = 8.2min; Holdsworth et al. 2014a) and is shown here to have a peak-to-peak amplitude of 34 mmag. J1940 has been observed during three seasons at the South African Astronomical Observatory, and has been the target of a Whole Earth Telescope campaign. The observations reveal that J1940 pulsates in a distorted quadrupole mode with unusual pulsational phase variations. A higher signal-to-noise ratio …
Studying The Photometric And Spectroscopic Variability Of The Magnetic Hot Supergiant Ζ Orionis Aa, Bram Buysschaert, Alexandre David-Uraz
Studying The Photometric And Spectroscopic Variability Of The Magnetic Hot Supergiant Ζ Orionis Aa, Bram Buysschaert, Alexandre David-Uraz
Aerospace, Physics, and Space Science Faculty Publications
Massive stars play a significant role in the chemical and dynamical evolution of galaxies. However, much of their variability, particularly during their evolved supergiant stage, is poorly understood. To understand the variability of evolved massive stars in more detail, we present a study of the O9.2Ib supergiant ζ Ori Aa, the only currently confirmed supergiant to host a magnetic field. We have obtained two-color space-based BRIght Target Explorer photometry (BRITE) for ζ Ori Aa during two observing campaigns, as well as simultaneous ground-based, high-resolution optical CHIRON spectroscopy. We perform a detailed frequency analysis to detect and characterize the star's periodic …
An Ancient Extrasolar System With Five Sub-Earth-Size Planets, Tiago L. Campante, Darin Ragozzine
An Ancient Extrasolar System With Five Sub-Earth-Size Planets, Tiago L. Campante, Darin Ragozzine
Aerospace, Physics, and Space Science Faculty Publications
The chemical composition of stars hosting small exoplanets (with radii less than four Earth radii) appears to be more diverse than that of gas-giant hosts, which tend to be metal-rich. This implies that small, including Earth-size, planets may have readily formed at earlier epochs in the universe's history when metals were more scarce. We report Kepler spacecraft observations of Kepler-444, a metal-poor Sun-like star from the old population of the Galactic thick disk and the host to a compact system of five transiting planets with sizes between those of Mercury and Venus. We validate this system as a true five-planet …
Empirical Determination Of Convection Parameters In White Dwarfs. I. Whole Earth Telescope Observations Of Ec14012-1446, Judith L. Provençal, Matt A. Wood, Stéphane Vennes, Péter Németh
Empirical Determination Of Convection Parameters In White Dwarfs. I. Whole Earth Telescope Observations Of Ec14012-1446, Judith L. Provençal, Matt A. Wood, Stéphane Vennes, Péter Németh
Aerospace, Physics, and Space Science Faculty Publications
We report on an analysis of 308.3 hr of high-speed photometry targeting the pulsating DA white dwarf EC14012-1446. The data were acquired with the Whole Earth Telescope during the 2008 international observing run XCOV26. The Fourier transform of the light curve contains 19 independent frequencies and numerous combination frequencies. The dominant peaks are 1633.907, 1887.404, and 2504.897μHz. Our analysis of the combination amplitudes reveals that the parent frequencies are consistent with modes of spherical degree l = 1. The combination amplitudes also provide m identifications for the largest amplitude parent frequencies. Our seismology analysis, which includes 2004–2007 archival data, confirms …
The Period And Amplitude Changes In The Coolest Gw Virginis Variable Star (Pg 1159-Type) Pg 0122+200, Gérard P. Vauclair, Jianning Fu, Jan Erik Solheim, Seunglee Kim, Noël Dolez, M Chevreton, Li Chen, Matt A. Wood, Isaac M. Silver, Zs Bognár, Margit Paparó, Alejandro H. Córsico
The Period And Amplitude Changes In The Coolest Gw Virginis Variable Star (Pg 1159-Type) Pg 0122+200, Gérard P. Vauclair, Jianning Fu, Jan Erik Solheim, Seunglee Kim, Noël Dolez, M Chevreton, Li Chen, Matt A. Wood, Isaac M. Silver, Zs Bognár, Margit Paparó, Alejandro H. Córsico
Aerospace, Physics, and Space Science Faculty Publications
Context: The PG 1159 pre-white dwarf stars experiment a rapidly cooling phase with a time scale of a few 106 years. Theoretical models predict that the neutrinos produced in their core should play a dominant role in the cooling, mainly at the cool end of the PG 1159 sequence. Measuring the evolutionary time scale of the coolest PG 1159 stars could offer a unique opportunity to empirically constrain the neutrino emission rate. Aims. A subgroup of the PG 1159 stars are nonradial pulsators, the GW Vir type of variable stars. They exhibit g-mode pulsations with periods of a few hundred …
Multi-Site Photometry Of The Pulsating Herbig Ae Star V346 Ori, S Bernabei, T D. Oswalt
Multi-Site Photometry Of The Pulsating Herbig Ae Star V346 Ori, S Bernabei, T D. Oswalt
Aerospace, Physics, and Space Science Faculty Publications
Context. The study of pulsation in pre-main-sequence intermediate-mass stars represents an important tool for deriving information about fundamental stellar parameters and internal structure, as well as testing theoretical models. Interest in this class of variable stars has increased significantly during the last decade and about 30 members are presently known in the literature. Aims. After constructing the frequency spectrum of oscillations in V346 Ori, we apply asteroseismic tools to these data to estimate the intrinsic parameters (mass, luminosity, effective temperature) of V346 Ori and obtain information about its internal structure. Methods. CCD time-series photometry in the Johnson V filter was …
The Pulsation Modes Of The Pre-White Dwarf Pg 1159-035, Jörge E.S. Costa, Matt A. Wood, Thomas J. Ahrens
The Pulsation Modes Of The Pre-White Dwarf Pg 1159-035, Jörge E.S. Costa, Matt A. Wood, Thomas J. Ahrens
Aerospace, Physics, and Space Science Faculty Publications
Context. PG 1159-035 , a pre-white dwarf with Teff ≃ 140 000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to measure the stellar mass, the rotational period and the inclination of the rotation axis, to estimate an upper limit for the magnetic field, and even to obtain information about the inner stratification of the star. …
Asteroseismology Of The Pg 1159 Star Pg 0122+200, Jianning Fu, Matt A. Wood
Asteroseismology Of The Pg 1159 Star Pg 0122+200, Jianning Fu, Matt A. Wood
Aerospace, Physics, and Space Science Faculty Publications
Context. The variable pre-white dwarf PG 1159 stars (GW Vir) are g-mode non-radial pulsators. Asteroseismology puts strong constraints on their global parameters and internal structure. PG 0122+200 defines the red edge of the instability strip and its evolutionary timescale is predicted to be dominated by neutrino emission. Its study offers the opportunity to better understand the instability mechanism and to validate the physics of the neutrino production in dense plasma. Aims. To achieve such a goal requires determining precisely its fundamental parameters. This is the goal of this paper. Methods. We present new multi-site photometric observations obtained in 2001 and …
Whole Earth Telescope Observations Of The Pulsating Subdwarf B Star Pg 0014+067, Maja Vučković, Matt A. Wood, V. Wilkat
Whole Earth Telescope Observations Of The Pulsating Subdwarf B Star Pg 0014+067, Maja Vučković, Matt A. Wood, V. Wilkat
Aerospace, Physics, and Space Science Faculty Publications
PG 0014+067 is one of the most promising pulsating subdwarf B stars for seismic analysis, as it has a rich pulsation spectrum. The richness of its pulsations, however, poses a fundamental challenge to understanding the pulsations of these stars, as the mode density is too complex to be explained only with radial and nonradial low-degree (l < 3) p-modes without rotational splittings. One proposed solution, suggested by Brassard et al. in 2001 for the case of PG 0014+067 in particular, assigns some modes with high degree (l - 3). On the other hand, theoretical models of sdB stars suggest that they may retain rapidly rotating cores, and so the high mode density may result from the presence of a few rotationally split triplet (l = 1) and quintuplet (l = 2) modes, along with radial (l = 0)p-modes. To examine alternative theoretical models for these stars, we need better frequency resolution and denser longitude coverage. Therefore, we observed this star with the Whole Earth Telescope for two weeks in 2004 October. In this paper we report the results of Whole Earth Telescope observations of the pulsating subdwarf B star PG 0014+067. We find that the frequencies seen in PG 0014+067 do not appear to fit any theoretical model currently available; however, we find a simple empirical relation that is able to match all of the well-determined frequencies in this star.
The Rapidly Pulsating Subdwarf B Star Pg 1325+101 I. Oscillation Modes From Multisite Observations, R Silvotti, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston
The Rapidly Pulsating Subdwarf B Star Pg 1325+101 I. Oscillation Modes From Multisite Observations, R Silvotti, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston
Aerospace, Physics, and Space Science Faculty Publications
In this article we present the results of 215 h of time-series photometry on the rapidly pulsating subdwarf B star PG 1325+101 (Teff - 35 000 K, log g = 5.8, log N(Hs)/N(H) = -1.7), obtained during 25 days of observation in Spring 2003 from nine different sites. As in previous observations, the temporal spectrum is dominated by the main peak at 7255.55 μHz, with an amplitude of about 2.7% which, however, is dropped to about 1.7% in February 2005. No secondary peaks close to the dominant pulsation mode are clearly detected. In addition, at least fourteen more pulsation frequencies …
The Rapidly Pulsating Subdwarf B Star Pg 1325+101 Ii. Structural Parameters From Asteroseismology, Stéphane Charpinet, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston
The Rapidly Pulsating Subdwarf B Star Pg 1325+101 Ii. Structural Parameters From Asteroseismology, Stéphane Charpinet, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston
Aerospace, Physics, and Space Science Faculty Publications
We present a detailed analysis of the rapidly pulsating subdwarf B star (or EC14026 star) PG 1325+101. This analysis exploits the outcome of dedicated multisite observations using time-series photometry that revealed the presence of (at least) 15 periodicities in the luminosity modulation of this star (Silvotti et al. 2006, A&A, 459, 557, Paper I). Based on high-S/N, medium-resolution spectra obtained at the Steward Observatory's 2.3 m Telescope and at the 6.5 m MMT Telescope, new NLTE spectroscopic derivations of the atmospheric parameters of PG 1325+101 are presented. The mean values of T eff = 35 050 ± 220 K, log …
A Multisite Photometric Campaign On The Pre-Main-Sequence Δ Scuti Pulsator Ip Persei, Vincenzo Ripepi, T D. Oswalt
A Multisite Photometric Campaign On The Pre-Main-Sequence Δ Scuti Pulsator Ip Persei, Vincenzo Ripepi, T D. Oswalt
Aerospace, Physics, and Space Science Faculty Publications
We present the results of a photometric multisite campaign on the δ Scuti Pre-Main-Sequence star IP Per. Nine telescopes have been involved in the observations, with a total of about 190 h of observations over 38 nights. Present data confirms the multiperiodic nature of this star and leads to the identification of at least nine pulsational frequencies. Comparison with the predictions of linear non-adiabatic radial pulsation models allowed us to identify only five of the nine observed frequencies, and to constrain the position of IP Per in the HR diagram. The latter is in good agreement with the empirical determination …
Whole Earth Telescope Observations Of The Zz Ceti Star Hl Tau 76, Noël Dolez, Matt A. Wood, Thomas J. Ahrens, Nicole Silvestri
Whole Earth Telescope Observations Of The Zz Ceti Star Hl Tau 76, Noël Dolez, Matt A. Wood, Thomas J. Ahrens, Nicole Silvestri
Aerospace, Physics, and Space Science Faculty Publications
This paper analyses the Whole Earth Telescope observations of HL Tau 76, the first discovered pulsating DA white dwarf. The star was observed during two Whole Earth Telescope campaigns. It was a second priority target during the XCOV13 campaign in 1996 and the first priority one during the XCOV18 campaign in 1999. The 1999 campaign reached 66.5% duty cycle. With a total duration of 18 days, the frequency resolution achieved is 0.68 μHz. With such a frequency resolution, we were able to find as many as 78 significant frequencies in the power spectrum, of which 34 are independent frequencies after …
Observations Of The Pulsating White Dwarf G 185-32, Bárbara Garcia Castanheira, Matt A. Wood
Observations Of The Pulsating White Dwarf G 185-32, Bárbara Garcia Castanheira, Matt A. Wood
Aerospace, Physics, and Space Science Faculty Publications
We observed the pulsating hydrogen atmosphere white dwarf G 185-32 with the Whole Earth Telescope in 1992. We report on a weighted Fourier transform of the data detecting 18 periodicities in its light curve. Using the Hubble Space Telescope Faint Object Spectrograph time resolved spectroscopy, and the wavelength dependence of the relative amplitudes, we identify the spherical harmonic degree (ℓ) for 14 pulsation signals. We also compare the determinations of effective temperature and surface gravity using the excited modes and atmospheric methods, obtaining Teff = 11960 ± 80 K, log g = 8.02 ± 0.04 and M = 0.617 ± …
Constraining The Evolution Of Zz Ceti, Anjum S. Mukadam, Matt A. Wood, Nicole M. Silvestri
Constraining The Evolution Of Zz Ceti, Anjum S. Mukadam, Matt A. Wood, Nicole M. Silvestri
Aerospace, Physics, and Space Science Faculty Publications
We report our analysis of the stability of pulsation periods in the DAV star (pulsating hydrogen atmosphere white dwarf) ZZ Ceti, also called R548. On the basis of observations that span 31 years, we conclude that the period 213. 13 s observed in ZZ Ceti drifts at a rate dP/dt ≤ (5.5 ± 1.9) × 10ˉ¹⁵ s sˉ¹, after correcting for proper motion. Our results are consistent with previous Ṗ values for this mode and an improvement over them because of the larger time base. The characteristic stability timescale implied for the pulsation period is | Ṗ / |≥ 1.2 …
Multisite Observations Of The Pms Δ Scuti Star V351 Ori, Vincenzo Ripepi, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston
Multisite Observations Of The Pms Δ Scuti Star V351 Ori, Vincenzo Ripepi, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston
Aerospace, Physics, and Space Science Faculty Publications
We present the results of multisite observations spanning two years on the pre-main-sequence (PMS) star V351 Ori. A total of around 180 hours of observations over 29 nights have been collected, allowing us to measure five different periodicities, most likely related to the δ Scuti variability of V351 Ori. Comparison with the predictions of linear nonadiabatic radial pulsation models put stringent constraints on the stellar parameters and indicate that the distance to V351 Ori is intermediate between the lower limit measured by Hipparcos (210 pc) and that of the Orion Nebula (450 pc). However, radial pulsation models are unable to …
The Everchanging Pulsating White Dwarf Gd358, Souza Oliveira Kepler, Matt A. Wood, Nicole M. Silvestri, Thomas J. Ahrens
The Everchanging Pulsating White Dwarf Gd358, Souza Oliveira Kepler, Matt A. Wood, Nicole M. Silvestri, Thomas J. Ahrens
Aerospace, Physics, and Space Science Faculty Publications
We report 323 hours of nearly uninterrupted time series photometric observations of the DBV star GD 358 acquired with the Whole Earth Telescope (WET) during May 23rd to June 8th, 2000. We acquired more than 232 000 independent measurements. We also report on 48 hours of time-series photometric observations in Aug 1996. We detected the non-radial g-modes consistent with degree ℓ = 1 and radial order 8 to 20 and their linear combinations up to 6th order. We also detect, for the first time, a high amplitude ℓ = 2 mode, with a period of 796 s. In the 2000 …
The Temporal Spectrum Of The Sdb Pulsating Star Hs 2201+2610 At 2 Ms Resolution, R Silvotti, T D. Oswalt, Nicole M. Silvestri, Glenn Carlson
The Temporal Spectrum Of The Sdb Pulsating Star Hs 2201+2610 At 2 Ms Resolution, R Silvotti, T D. Oswalt, Nicole M. Silvestri, Glenn Carlson
Aerospace, Physics, and Space Science Faculty Publications
In this article we present the results of more than 180 hours of time-series photometry on the low gravity (log g = 5.4, Teff = 29 300 K, log He/H = -3.0 by number) sdB pulsating star HS 2201+2610, obtained between September 2000 and August 2001. The temporal spectrum is resolved and shows 5 close frequencies: three main signals at 2860.94, 2824.10 and 2880.69 μHz, with amplitudes of about 1%, 0.5% and 0.1% respectively, are detected from single run observations; two further peaks with very low amplitude (<0.07%) at 2738.01 and 2921.82 μHz are confirmed by phase analysis on several independent runs. Due to the small number of detected frequencies, it is not possible to obtain a univocal identification of the excited modes and perform a detailed seismological analysis of the star. No clear signatures of rotational splitting are seen. Nevertheless, the observed period spectrum is well inside the excited period window obtained from pulsation calculations with nonadiabatic models having effective temperature and surface gravity close to the spectroscopic estimates. Due to its relatively simple temporal spectrum, HS 2201+2610 is a very good candidate for trying to measure the secular variation of the pulsation periods in time. With this purpose a long-term monitoring of the star was started. The results of the first 11 months show amplitude variations up to ∼20% on time-scales of months, which are probably real, and allow us to measure the pulsation frequencies with an unprecedented 0.02 μHz resolution.
Asteroseismology Of Rxj 2117+3412, The Hottest Pulsating Pg 1159 Star, G Vauclair, Matt A. Wood
Asteroseismology Of Rxj 2117+3412, The Hottest Pulsating Pg 1159 Star, G Vauclair, Matt A. Wood
Aerospace, Physics, and Space Science Faculty Publications
The pulsating PG 1159 planetary nebula central star RXJ 2117+3412 has been observed over three successive seasons of a multisite photometric campaign. The asteroseismological analysis of the data, based on the 37 identified ℓ = 1 modes among the 48 independent pulsation frequencies detected in the power spectrum, leads to the derivation of the rotational splitting, the period spacing and the mode trapping cycle and amplitude, from which a number of fundamental parameters can be deduced. The average rotation period is 1.16 ± 0.05 days. The trend for the rotational splitting to decrease with increasing periods is incompatible with a …
Understanding The Cool Da White Dwarf Pulsator, G29-38, Scot J. Kleinman, Matt A. Wood
Understanding The Cool Da White Dwarf Pulsator, G29-38, Scot J. Kleinman, Matt A. Wood
Aerospace, Physics, and Space Science Faculty Publications
The white dwarfs are promising laboratories for the study of cosmochronology and stellar evolution. Through observations of the pulsating white dwarfs, we can measure their internal structures and compositions, critical to understanding post-main-sequence evolution, along with their cooling rates, which will allow us to calibrate their ages directly. The most important set of white dwarf variables to measure are the oldest of the pulsators, the cool DA variables (DAVs), which have not been explored previously through asteroseismology due to their complexity and instability. Through a time-series photometry data set spanning 10 yr, we explore the pulsation spectrum of the cool …
Whole Earth Telescope Observations Of The Helium Interacting Binary Pg 1346+082 (Cr Bootis), Judith L. Provençal, Matt A. Wood
Whole Earth Telescope Observations Of The Helium Interacting Binary Pg 1346+082 (Cr Bootis), Judith L. Provençal, Matt A. Wood
Aerospace, Physics, and Space Science Faculty Publications
We present our analysis of 240 hr of white-light, high-speed photometry of the dwarf nova-like helium variable PG 1346+082 (CR Boo). We identify two frequencies in the low-state power spectrum, at 679.670 ± 0.004 μHz and 669.887 ± 0.008 μHz. The 679.670 μHz variation is coherent over at least a 2 week time span, the first demonstration of a phase-coherent photometric variation in any dwarf nova-like interacting binary white dwarf system. The high-state power spectrum contains a complex fundamental with a frequency similar, but not identical, to the low-state spectrum, and a series of harmonics not detected in low state. …
The Δ Scuti Star Fg Virginis Ii. A Search For High Pulsation Frequencies, Michel Breger, Matt A. Wood
The Δ Scuti Star Fg Virginis Ii. A Search For High Pulsation Frequencies, Michel Breger, Matt A. Wood
Aerospace, Physics, and Space Science Faculty Publications
Although the δ Scuti and roAp variables occupy similar positions on and near the main sequence, δ Scuti variables pulsate with lower radial and nonradial overtones and lower frequencies. To test whether high frequencies (as found in the roAp stars) are also present in δ Scuti stars, a multisite campaign with the Whole Earth Telescope (WET) was carried out for the star FG Vir. The 96.7 hours of WET photometry were supplemented by measurements made with the Delta Scuti Network (DSN), because the DSN technique includes regular measurements of comparison stars and is better suited to monitoring the low frequencies …