Photometric variability of the unique magnetic white dwarf GD 356

Brinkworth, Carolyn; Burleigh, M. R.; Wynn, G. A.; Marsh, T. R.

doi:10.1111/j.1365-2966.2004.07538.x

Cited by 45 publications

(50 citation statements)

References 20 publications

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“…The shorter rotation periods observed in white dwarfs are of the order of few hours. This is the case, for example, for the DBV EC20058-5234 (P rot 2 h, Sullivan et al 2008) and of the magnetic GD 356 (P rot = 2.6 h, Brinkworth et al 2004). If the PG 1159-035 rotation period changed from its current value to P rot = 2 h during the DOV phase (∼10 6 yr), the variation rate would beṖ rot −0.1 s/yr.…”

Section: Summary and Discussionmentioning

confidence: 96%

The temporal changes of the pulsational periods of the pre-white dwarf PG 1159-035

Costa¹,

Kepler²

2008

A&A

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Context. PG 1159-035, a pre-white dwarf with T eff ≃ 140 000 K, is the prototype of the PG 1159 spectroscopic class and the DOV pulsating class. Pulsating pre-white dwarf stars evolve rapidly: the effective surface temperature decreases rapidly, the envelope contracts and the inner structure experiences stratification due to gravitational settling. These changes in the star generate variations in its oscillation periods. The measurement of temporal change in the oscillation periods, Ṗ, allows us to estimate directly rates of stellar evolutionary changes, such as the cooling rate and the envelope contraction rate, providing a way to test and refine evolutionary models for pre-white dwarf pulsating stars. Aims. Previously, only two pulsation modes of the highest amplitudes for PG 1159-035 have had their Ṗ measured: the 516.0 s and the 539.3 s modes. We measured the Ṗ of a larger number of pulsation modes, increasing the number of constraints for evolutionary studies of PG 1159-035. We attempted to use the secular variations in the periods of multiplets to calculate the variation in the rotational period, the envelope contraction rate, and the cooling rate of the star. Methods. The period variations were measured directly from the PG 1159-035 observational data and refined by the (O-C) method. Results. We measured 27 pulsation mode period changes. The periods varied at rates of between 1 and 100 ms/yr, and several can be directly measured with a relative standard uncertainty below 10%. For the 516.0 s mode (the highest in amplitude) in particular, not only the value of Ṗ can be measured directly with a relative standard uncertainty of 2%, but the second order period change, P, can also be calculated reliably. By using the (O-C) method, we refined the Ṗs and estimated the Ps for six other pulsation periods. As a first application, we calculated the change in the PG 1559-035 rotation period, Ṗrot = (−2.13 ± 0.05) × 10 −6 ss −1 , the envelope contraction rate Ṙ = (−2.2 ± 0.5) × 10 −13 R ⊙ s −1 , and the cooling rate Ṫ = −1.42 × 10 −3 Ks −1 .

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Section: Summary and Discussionmentioning

confidence: 96%

The temporal changes of the pulsational periods of the pre-white dwarf PG 1159-035

Costa¹,

Kepler²

2008

A&A

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“…However, planets of sub-Jupiter to Jupiter size, if they are abundant at these orbits around WDs, could explain three or four cases. Figure 8 shows the seven periods and amplitudes we have measured, along with the ground-based measurements by Brinkworth et al (2004Brinkworth et al ( , 2005Brinkworth et al ( , 2013, for 10 magnetic WDs with fairly precise rotation periods (out of 23 WDs monitored by them, 14 of them with sensitivity to periods of up to a week). Also plotted is a point for the T = 34, 000 K DA WD BOKS53856, for which Holberg & Howell (2011) have measured, using Kepler, amplitude A = 2.5% variations with a period P = 0.255 day.…”

Section: Discussionmentioning

confidence: 99%

“…Variation amplitude vs. period for white dwarfs with measured periods. Red filled circles are from this study, blue empty circles are from the sample of magnetic WDs studied by Brinkworth et al (2004Brinkworth et al ( , 2005Brinkworth et al ( , 2013 plus the WD from Holberg & Howell (2011). Curves are the maximum possible amplitudes in several models.…”

Section: Discussionmentioning

confidence: 99%

Kepler and the seven dwarfs: detection of low-level day-time-scale periodic photometric variations in white dwarfs

Maoz

Mazeh

McQuillan

2014

Monthly Notices of the Royal Astronomical Society

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We make use of the high photometric precision of Kepler to search for periodic modulations among 14 normal (DA-and DB-type, likely non-magnetic) hot white dwarfs (WDs). In five, and possibly up to seven of the WDs, we detect periodic, ∼ 2 hr to 10 d, variations, with semi-amplitudes of 60-2000 ppm, lower than ever seen in WDs. We consider various explanations: WD rotation combined with magnetic cool spots; rotation combined with magnetic dichroism; rotation combined with hot spots from an interstellar-medium accretion flow; transits by size ∼ 50-200 km objects; relativistic beaming due to reflex motion caused by a cool companion WD; or reflection/reradiation of the primary WD light by a brown-dwarf or giant-planet companion, undergoing illumination phases as it orbits the WD. Each mechanism could be behind some of the variable WDs, but could not be responsible for all five to seven variable cases. Alternatively, the periodicity may arise from UV metal-line opacity, associated with accretion of rocky material, a phenomenon seen in ∼ 50% of hot WDs. Nonuniform UV opacity, combined with WD rotation and fluorescent optical re-emission of the absorbed UV energy, could perhaps explain our findings. Even if reflection by a planet is the cause in only a few of the seven cases, it would imply that hot Jupiters are very common around WDs. If some of the rotation-related mechanisms are at work, then normal WDs rotate as slowly as do peculiar WDs, the only kind for which precise rotation measurements have been possible to date.

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“…"Our" candidate, GD 356, at least has a star spot (Brinkworth et al 2004, who are kind enough to cite us), but even Zheleznyakov et al (2004), who probably started the whole thing, no longer expect much in the way of X-rays. The few ROSAT candidates for X-ray emitting white dwarfs include three dMe stars, one BL Lac active galaxy, and one or two hot photospheres (Chu et al 2004a).…”

Section: White Dwarf Pulsation Masses and Activitymentioning

confidence: 97%