scholarly journals High-speed photometric observations of the pulsating DA white dwarf GD 165

1993 ◽  
Vol 106 ◽  
pp. 1987 ◽  
Author(s):  
P. Bergeron ◽  
G. Fontaine ◽  
P. Brassard ◽  
R. Lamontagne ◽  
F. Wesemael ◽  
...  
Keyword(s):  
White Dwarf ◽  
High Speed ◽  
Photometric Observations

scholarly journals Probing the Extraordinary Ends of Ordinary Stars: White Dwarf Seismology with the Whole Earth Telescope

1995 ◽  
Vol 155 ◽  
pp. 81-91
Author(s):  
Steven D. Kawaler
Keyword(s):  
White Dwarf ◽  
High Speed ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Dense Cores ◽  
Photometric Observations ◽  
Nuclear Burning ◽  
Stellar Seismology ◽  
Composition Changes ◽  
Whole Earth

AbstractDuring the final evolution of most stars, they shed their outer skin and expose their core of the hot ashes of nuclear burning. As these hot and very dense cores cool into white dwarf stars, they go through episodes of multiperiodic, nonradial g-mode pulsation. The tools of stellar seismology allow us to use the pulsation spectra as powerful probes into the deep interiors of these stars. Progress in white dwarf seismology has required significant international cooperation, since another consequence of the complex pulsations of these stars is decoding the true pulsation frequencies requires a coordinated global effort involving high-speed photometric observations. Through one such effort, the Whole Earth Telescope project, we have located subsurface composition changes, detected differential rotation and magnetic fields, and measured fundamental quantities such as stellar mass, luminosity, and distance to extraordinary accuracy.

Radial Velocities for the Pulsating Subdwarf B Star PG 1605+072

2002 ◽  
Vol 185 ◽  
pp. 376-377
Author(s):  
V.M. Woolf ◽  
C.S. Jeffery ◽  
D.L. Pollacco
Keyword(s):  
Radial Velocity ◽  
Line Shape ◽  
High Speed ◽  
Radial Velocities ◽  
Peak Amplitude ◽  
Amplitude Ratios ◽  
Time Line ◽  
Photometric Observations ◽  
Velocity Variations ◽  
Over Time

AbstractWe have performed high-speed spectroscopy of the pulsating subdwarf B star PG 1605+072. Its radial velocity variations have frequencies similar to those reported from photometric observations. Peak amplitude ratios are different, probably as a result of power shifting between modes over time. Line-shape variations have also been detected.

scholarly journals Searching for optical companions to four binary millisecond pulsars with the Gran Telescopio Canarias

2020 ◽  
Vol 492 (2) ◽  
pp. 3032-3040 ◽  
Author(s):  
A Yu Kirichenko ◽  
A V Karpova ◽  
D A Zyuzin ◽  
S V Zharikov ◽  
E A López ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Optical Data ◽  
Pure Hydrogen ◽  
Millisecond Pulsars ◽  
Upper Limit ◽  
Photometric Observations ◽  
Low Mass

ABSTRACT We report on multiband photometric observations of four binary millisecond pulsars with the Gran Telescopio Canarias. The observations led to detection of binary companions to PSRs J1630+3734, J1741+1351, and J2042+0246 in the Sloan g′, r′, and i′ bands. Their magnitudes in the r′ band are ≈24.4, 24.4, and 24.0, respectively. We also set a 3σ upper limit on the brightness of the PSR J0557+1550 companion in the r′ band of ≈25.6 mag. Combining the optical data with the radio timing measurements and white dwarf cooling models, we show that the detected companions are cool low-mass white dwarfs with temperatures and ages in the respective ranges of (4–7) × 103 K and 2–5 Gyr. All the detected white dwarfs are found to likely have either pure hydrogen or mixed helium–hydrogen atmospheres.

Study of Pulsations in the Nova-like Variable KR Aur and the Intermediate Polar BG CMi

1991 ◽  
Vol 9 (2) ◽  
pp. 279-280
Author(s):  
J. Singh ◽  
P. C. Agrawal ◽  
M. V. K. Apparao ◽  
R. K. Manchanda ◽  
P. Vivekananda Rao ◽  
...  
Keyword(s):  
Neutron Star ◽  
White Dwarf ◽  
Accretion Disc ◽  
Light Curves ◽  
Pulsation Period ◽  
Variable Amplitude ◽  
X Ray ◽  
Photometric Observations ◽  
The Times ◽  
Made In

AbstractFast photometric observations of a nova-like variable KR Aurigae and the intermediate polar BG CMi (3A0729+103) were made in the B and U bands during 1984–89 to study pulsations in them. The light curves of KR Aur show large amplitude quasi-periodic pulsations with periods in the range 500–800s which can be ascribed to inhomogeneities in the accretion disc. The light curves of the X-ray emitting intermediate polar BG CMi show variable amplitude pulsations with 913s period. From the times of maxima of the pulsations obtained from observations over the period 1984–1989, the pulsation period is derived to be 0.010572966 ± 8 days and the spin-up rate to be (−5.7 ± 0.5) × 10−11 ss−1. The spin-up rate is consistent with the pulsating source being a white dwarf and not a neutron star.

scholarly journals An Isolated White Dwarf with a 70 s Spin Period

2021 ◽  
Vol 923 (1) ◽  
pp. L6
Author(s):  
Mukremin Kilic ◽  
Alekzander Kosakowski ◽  
Adam G. Moss ◽  
P. Bergeron ◽  
Annamarie A. Conly
Keyword(s):  
White Dwarf ◽  
High Speed ◽  
White Dwarfs ◽  
Tangential Velocity ◽  
Large Mass ◽  
Atmospheric Composition ◽  
Instability Strip ◽  
Detailed Model ◽  
Helium Atmosphere ◽  
Spin Period

Abstract We report the discovery of an isolated white dwarf with a spin period of 70 s. We obtained high-speed photometry of three ultramassive white dwarfs within 100 pc and discovered significant variability in one. SDSS J221141.80+113604.4 is a 1.27 M ⊙ (assuming a CO core) magnetic white dwarf that shows 2.9% brightness variations in the BG40 filter with a 70.32 ± 0.04 s period, becoming the fastest spinning isolated white dwarf currently known. A detailed model atmosphere analysis shows that it has a mixed hydrogen and helium atmosphere with a dipole field strength of B d = 15 MG. Given its large mass, fast rotation, strong magnetic field, unusual atmospheric composition, and relatively large tangential velocity for its cooling age, J2211+1136 displays all of the signatures of a double white dwarf merger remnant. Long-term monitoring of the spin evolution of J2211+1136 and other fast-spinning isolated white dwarfs opens a new discovery space for substellar and planetary mass companions around white dwarfs. In addition, the discovery of such fast rotators outside of the ZZ Ceti instability strip suggests that some should also exist within the strip. Hence, some of the monoperiodic variables found within the instability strip may be fast-spinning white dwarfs impersonating ZZ Ceti pulsators.

scholarly journals Asteroseismology of the DOV star PG 1159−035

2019 ◽  
Vol 488 (2) ◽  
pp. 2253-2262
Author(s):  
Y H Chen
Keyword(s):  
Kinetic Energy ◽  
White Dwarf ◽  
Period Change ◽  
Photometric Data ◽  
Optimal Model ◽  
Frequency Splitting ◽  
The Core ◽  
Star Models ◽  
Photometric Observations ◽  
Atmospheric Constituent

ABSTRACT Grids of DOV star models are evolved by wdec with fixed atmospheric constituent to the spectral values of XC/XHe/XO = 50/33/17. The core compositions are from white dwarf models at highest Teff evolved by mesa. The eigenfrequencies are calculated and used to fit the observed modes. Based on 264.1 h of photometric observations on PG 1159−035, Winget et al. identified 125 individual frequencies. Costa et al. identified 198 pulsation modes for PG 1159−035 according to the WET photometric data from 1983, 1985, 1989, and 2002. Both of them derived frequency splitting values of δσl = 1 ∼ 4.2 $\mu$Hz and δσl = 2 ∼ 6.9 $\mu$Hz. According to the values of δσl = 1 and δσl = 2, 20 triplets and 9 quintuplets are selected and used to constrain the fitting models. Our optimal model has Teff = 129 000 K, M* = 0.63 M⊙, log g = 7.59, log(Menv/M*) = −5.0, and σRMS = 1.97 s. The values of Teff and log g are consistent with that values of Córsico et al. The calculated modes of minimum rate of period change correspond to modes with maximum kinetic energy distributed in the envelope. The observed rates of period change with positive and negative values can also be partially reproduced. In particular, there are negative rates of period change for the calculated modes from our optimal model, which is not found in previous work.

High-Speed Photometry of Bright roAp Stars With Small Telescopes

2001 ◽  
Vol 183 ◽  
pp. 187-196
Author(s):  
D.W. Kurtz
Keyword(s):  
Magnetic Field ◽  
High Speed ◽  
Frequency Spectra ◽  
Photometric Observations ◽  
High Speed Photometry ◽  
Effective Temperatures ◽  
Ap Stars ◽  
The Magnetic Field ◽  
Theoretical Developments

AbstractThe rapidly oscillating Ap stars are magnetic peculiar A stars which pulsate in multiple p modes with periods in the range of about 6 to 16 minutes with their oscillation axes aligned with the oblique magnetic axes of the stars. Some of these stars have the richest frequency spectra of any non-degenerate stars other than the sun. This paper shows how photometric observations using small telescopes can be used to work on several astrophysically interesting problems posed by these stars. An example of high precision photometry is shown. The proof of oblique dipole pulsation, the distortion of pulsation modes (probably by the magnetic field), and the determination of asteroseismic luminosities are all discussed. The latter, especially when combined with new theoretical developments concerning magnetic field-pulsation interaction, suggests that Ap stars have lower effective temperatures and/or smaller radii than has been previously thought. It is pointed out that this may be related to the recently discovered extreme discrepancy in effective temperature determined from the wings and cores of the Hα line.

scholarly journals RADIUS CONSTRAINTS FROM HIGH-SPEED PHOTOMETRY OF 20 LOW-MASS WHITE DWARF BINARIES

2014 ◽  
Vol 792 (1) ◽  
pp. 39 ◽  
Author(s):  
J. J. Hermes ◽  
Warren R. Brown ◽  
Mukremin Kilic ◽  
A. Gianninas ◽  
Paul Chote ◽  
...  
Keyword(s):  
White Dwarf ◽  
High Speed ◽  
High Speed Photometry ◽  
Low Mass

scholarly journals Radio and optical observations of the possible AE Aqr twin, LAMOST J024048.51+195226.9

2021 ◽  
Vol 503 (3) ◽  
pp. 3692-3697
Author(s):  
M L Pretorius ◽  
D M Hewitt ◽  
P A Woudt ◽  
R P Fender ◽  
I Heywood ◽  
...  
Keyword(s):  
White Dwarf ◽  
High Speed ◽  
Good Evidence ◽  
Optical Observations ◽  
Cataclysmic Variable ◽  
Radio Luminosity ◽  
Spin Modulation ◽  
Short Period ◽  
High Speed Photometry

ABSTRACT It was recently proposed that the cataclysmic variable (CV) LAMOST J024048.51+195226.9 may be a twin to the unique magnetic propeller system AE Aqr. If this is the case, two predictions are that it should display a short period white dwarf spin modulation, and that it should be a bright radio source. We obtained follow-up optical and radio observations of this CV, in order to see if this holds true. Our optical high-speed photometry does not reveal a white dwarf spin signal, but lacks the sensitivity to detect a modulation similar to the 33 s spin signal seen in AE Aqr. We detect the source in the radio, and measure a radio luminosity similar to that of AE Aqr and close to the highest so far reported for a CV. We also find good evidence for radio variability on a time-scale of tens of minutes. Optical polarimetric observations produce no detection of linear or circular polarization. While we are not able to provide compelling evidence, our observations are all consistent with this object being a propeller system.

scholarly journals CCD Time-Series Photometry of White Dwarf Stars

2021 ◽  
Author(s):  
◽  
Paul Robin Brian Chote
Keyword(s):  
Data Reduction ◽  
White Dwarf ◽  
High Speed ◽  
Energy Transport ◽  
Hydrogen Atmosphere ◽  
Rate Of Change ◽  
Ccd Photometry ◽  
Helium Atmosphere ◽  
Convection Layer ◽  
Radial Pulsations

<p>This thesis describes a practical programme that focused on CCD photometry of pulsating white dwarf (WD) stars. The first part of this thesis describes the development of two high-speed CCD photometer instruments and their data reduction pipeline, while the remainder describes the observation and analysis of several pulsating WDs and other targets. The two photometers (Puoko-nui North and South) share a common hardware design that is optimized for acquiring efficient photometry with integration periods of milliseconds through to minutes. The design integrates a commercial CCD (Charge-Coupled Device) camera and GPS (Global Positioning System) receiver with custom timing electronics and control software. The reduction and visualization software developed for these instruments provide detailed real-time information to the observer, and a streamlined data reduction pipeline. EC04207-4748 is a pulsating helium atmosphere WD that shows significant non-sinusoidal intensity variations. We show that the pulsation spectrum of this WD can be described by four independent pulsation eigenmodes plus linear combinations that arise from non-linear energy transport through a sub-surface convection layer. Our results are consistent with similar analyses that have been made for similar stars, and add an additional data point to the growing catalogue of these convection measurements. We argue that the convection layer depth may form a useful substitute for the effective temperatures of these WDs. GWLibrae is the class prototype of the accreting WD pulsators. These stars exist in cataclysmic variable (CV) systems, and show a mix of CV and pulsating WD-related phenomena. Our observations of GW Librae four - six years after its 2007 outburst show signs of quasi-stable intensity modulations that we believe may be caused by non-radial pulsations, but these are not convincingly explained by existing WD or CV models. L19-2 is a hydrogen atmosphere WD pulsator that shows extremely stable pulsation behaviour. We combine new observations with archival observations dating back to the mid 1970's, and derive a preliminary estimate of the period rate of change Ṗ for two of the pulsation modes in this target. We show a clear result for the main 192 s pulsation mode Ṗf₂ ≾ 10⁻¹⁴ s s-¹, and discuss the improvements that we plan to make in order to convincingly improve this constraint by an additional order of magnitude. Observations of other rapidly variable targets include two extremely low mass (ELM) WDs, which exhibit variability due to their orbital motion (J0751) as well as non-radial pulsations (J1518); the 33 ms optical period of the Crab Pulsar; the helium atmosphere WD pulsators EC05221-4725 and EC20058-5234; the stable hydrogen atmosphere pulsator G117–B15A; and the eclipsing sdB binary system PG1336-018.</p>

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