scholarly journals Observational Proof of the ZZ Ceti Red Edge

2000 ◽  
Vol 176 ◽  
pp. 518-518
Author(s):  
A. Kanaan ◽  
D. E. Winget ◽  
S. O. Kepler ◽  
M. H. Montgomery
Keyword(s):  
High Speed ◽  
Selection Effect ◽  
Hydrogen Atmosphere ◽  
Color Filter ◽  
Instability Strip ◽  
Ccd Photometry ◽  
Red Edge ◽  
High Speed Photometry ◽  
Comparison Stars ◽  
Sky Brightness

With a time-series CCD photometry survey, we have demonstrated clearly that the observed red edge for the ZZ Ceti stars instability strip at 11,000 K is not an observational selection effect. Previous surveys for variability among hydrogen atmosphere white dwarfs at around 11,000 K have been carried out using high speed photometry which suffers from variable extinction effects that start becoming important at periods of 15 minutes. In our survey we constantly monitor the sky brightness as well as one or more comparison stars. This is done through the same color filter, therefore minimizing adverse effects of differential extinction. The fact that the theoretical red edge should be around 8,000 K remains, but effects not included in the theory, especially convection-aulsation interaction, could explain it.

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>

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>

On the Red Edge of the δ Scuti Instability Strip

2002 ◽  
Vol 2 (5) ◽  
pp. 441-448 ◽  
Author(s):  
Yan Xu ◽  
Zhi-Ping Li ◽  
Li-Cai Deng ◽  
Da-Run Xiong
Keyword(s):  
Instability Strip ◽  
Red Edge

scholarly journals HIGH-SPEED PHOTOMETRY OF THE DISINTEGRATING PLANETESIMALS AT WD1145+017: EVIDENCE FOR RAPID DYNAMICAL EVOLUTION

2016 ◽  
Vol 818 (1) ◽  
pp. L7 ◽  
Author(s):  
B. T. Gänsicke ◽  
A. Aungwerojwit ◽  
T. R. Marsh ◽  
V. S. Dhillon ◽  
D. I. Sahman ◽  
...  
Keyword(s):  
High Speed ◽  
Dynamical Evolution ◽  
High Speed Photometry

BVRI CCD-Photometry of comparison stars in the fields of galaxies with active nuclei. V

Astrophysics ◽  
2013 ◽  
Vol 56 (3) ◽  
pp. 343-358 ◽  
Author(s):  
V. T. Doroshenko ◽  
S. G. Sergeev ◽  
Yu. S. Efimov ◽  
G. A. Borman ◽  
D. N. Okhmat ◽  
...  
Keyword(s):  
Ccd Photometry ◽  
Comparison Stars

The Moderate and High-Speed Photometry of the Black Hole Candidate XTE J1118+480

Microquasars ◽  
2001 ◽  
pp. 63-64
Author(s):  
Elena P. Pavlenko ◽  
Elena S. Dmitrienko ◽  
Nikolai M. Shakhovskoi ◽  
Sergei Yu. Shugarov ◽  
Nataly A. Katysheva ◽  
...  
Keyword(s):  
Black Hole ◽  
High Speed ◽  
Black Hole Candidate ◽  
High Speed Photometry

scholarly journals High-Speed Photometry of Cluster Flare Stars

1975 ◽  
Vol 67 ◽  
pp. 69-73
Author(s):  
M. Rodonò
Keyword(s):  
High Speed ◽  
Activity Level ◽  
Flare Star ◽  
Solar Neighbourhood ◽  
High Occurrence ◽  
High Speed Photometry ◽  
Flare Stars ◽  
Photoelectric Observations ◽  
Absolute Luminosity

Recent photoelectric observations made at Catania Observatory show a high occurrence of short-lived faint flares on the Hyades member II Tau (H II 2411). Its activity level turns out to be higher than for UV Cet-type stars of equal absolute luminosity.II Tau could represent a transition prototype between UV Cet-type flare star in the solar neighbourhood and cluster ones.The importance of coordinated photoelectric patrol of properly selected flare stars in clusters of different age is emphasized.

scholarly journals Convective effects and the RR lyrae instability strip

1984 ◽  
Vol 105 ◽  
pp. 461-463
Author(s):  
R. F. Stellingwerf
Keyword(s):  
Nonlinear Behavior ◽  
Instability Strip ◽  
Unstable Region ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Red Edge ◽  
Diffusive Convection ◽  
Structure Equations ◽  
Lyrae Stars

The effects of nonlinear, nonlocal, diffusive convection have been included in the structure equations of pulsational hydrodynamic analyses of a series of RR Lyrae models. We find a well-defined red edge of the unstable region that depends on mode of pulsation. It is shown that this result has strong implications for the nonlinear behavior of RR Lyrae stars.

scholarly journals High-speed photometry of faint cataclysmic variables – VIII. Targets from the Catalina Real-Time Transient Survey

2013 ◽  
Vol 437 (1) ◽  
pp. 510-523 ◽  
Author(s):  
Deanne L. Coppejans ◽  
Patrick A. Woudt ◽  
Brian Warner ◽  
Elmar Körding ◽  
Sally A. Macfarlane ◽  
...  
Keyword(s):  
Real Time ◽  
High Speed ◽  
Cataclysmic Variables ◽  
High Speed Photometry
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