HST observations of the pulsating white dwarf GD 358

Castanheira, B. G.; Nitta, A.; Winget, D. E.; Koester, D.

doi:10.1051/0004-6361:20041573

Cited by 20 publications

(12 citation statements)

References 38 publications

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“…V777 Her itself is also known to shift the distribution of amplitudes significantly among its excited modes (Provencal et al 2009). In extreme cases, the pulsation spectrum can undergo a dramatic change known as an sforzando, where it suddenly acquires a single large amplitude pulsation mode (Castanheira et al 2005), which subsequently fades. There is a good chance that KIC 8626021 will show similar behavior, so extended Kepler observations will not just bring down the noise level in the amplitude spectrum and reveal further low-level excited modes, but will also have a unique opportunity to monitor the processes that lead up to sforzando events and other types of variabilities that characterize these pulsators.…”

Section: Discussionmentioning

confidence: 99%

AT LAST—A V777 HER PULSATOR IN THE KEPLER FIELD

Østensen

Bloemen

Vučković

et al. 2011

ApJ

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We present the discovery of the first-and so far the only-pulsating white dwarf star located in the field of view of the Kepler spacecraft. During our ongoing effort to search for compact pulsator candidates that can benefit from the near-continuous coverage of Kepler, we recently identified a faint DB star from spectroscopy obtained with the William Herschel Telescope. After establishing its physical parameters to be T eff = 24,950 K and log g = 7.91 dex, placing it right in the middle of the V777 Her instability strip, we immediately submitted the target for follow-up space observations. The Kepler light curve reveals a pulsation spectrum consisting of five modes that follow a sequence roughly equally spaced in period with a mean spacing of 37 s. The three strongest modes show a triplet structure with a mean splitting of 3.3 μHz. We conclude that this object is a V777 Her pulsator with a mass of ∼0.56 M , and very similar to the class prototype.

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Section: Discussionmentioning

confidence: 99%

AT LAST—A V777 HER PULSATOR IN THE KEPLER FIELD

Østensen

Bloemen

Vučković

et al. 2011

ApJ

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“…At this stage we cannot identify the reason for these changes and need to keep observing PG 1351+489 to determine whether the star reverts to the original set of pulsation modes or maintains this new pulsation spectrum. Another star has shown changes in its periodicities: GD 358, the first DBV detected, showed a remarkable change in its pulsation spectrum in 1996 (Kepler et al 2003; Castanheira et al 2005). During that year, the amplitude of all modes changed, the dominant mode changed and even the shape of its light curve went from non‐sinusoidal to sinusoidal.…”

Section: Rotation Periodmentioning

confidence: 99%

The pulsations of PG 1351+489

Redaelli¹,

Costa

Winget

et al. 2011

Monthly Notices of the Royal Astronomical Society

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PG 1351+489 is one of the 20 DBVs -pulsating helium-atmosphere white dwarf stars -known and has the simplest power spectrum for this class of star, making it a good candidate to study cooling rates. We report accurate period determinations for the main peak at 489.334 48 s and two other normal modes using data from the Whole Earth Telescope (WET) observations of 1995 and 2009. In 2009, we detected a new pulsation mode and the main pulsation mode exhibited substantial change in its amplitude compared to all previous observations. We were able to estimate the star's rotation period, of 8.9 h, and discuss a possible determination of the rate of period change of (2.0 ± 0.9) × 10 −13 s s −1 , the first such estimate for a DBV.

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“…They determined that these modes all share the same l value, which is probably l=1. Castanheira et al (2005) use HST UV time resolved spectroscopy to determine that k=9 and 8 are best explained as l=1.…”

Section: Gd358 In 2006 41 Independent Modesmentioning

confidence: 99%

“…The following discussion requires that we draw into the mix a remarkable sequence of events that occurred over ≈30 days in 1996. We follow Castanheira et al (2005) in calling the event the sforzando. In classical music, sforzando is an abrupt change in the character of music, usually accompanied by an increase in volume.…”

Section: Multiplet Structure Change Andmentioning

confidence: 99%

2006 Whole Earth Telescope Observations of Gd358: A New Look at the Prototype DBV

Provençal

Montgomery

Kanaan

et al. 2009

ApJ

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We report on the analysis of 436.1 hrs of nearly continuous high-speed photometry on the pulsating DB white dwarf GD358 acquired with the Whole Earth Telescope (WET) during the 2006 international observing run, designated XCOV25. The Fourier transform (FT) of the light curve contains power between 1000 to 4000 µHz, with the dominant peak at 1234 µHz. We find 27 independent frequencies distributed in 10 modes, as well as numerous combination frequencies. Our discussion focuses on a new asteroseismological analysis of GD358, incorporating the 2006 data set and drawing on 24 years of archival observations. Our results reveal that, while the general frequency locations of the identified modes are consistent throughout the years, the multiplet structure is complex and cannot be interpreted simply as l=1 modes in the limit of slow rotation. The high k multiplets exhibit significant variability in structure, amplitude and frequency. Any identification of the m components for the high k multiplets is highly suspect. The k=9 and 8 modes typically do show triplet structure more consistent with theoretical expectations. The frequencies and amplitudes exhibit some variability, but much less than the high k modes. Analysis of the k=9 and 8 multiplet splittings from 1990 to 2008 reveal a long-term change in multiplet splittings coinciding with the 1996 sforzando event, where GD358 dramatically altered its pulsation characteristics on a timescale of hours. We explore potential implications, including the possible connections between convection and/or magnetic fields and pulsations. We suggest future investigations, including theoretical investigations of the relationship between magnetic fields, pulsation, growth rates, and convection.

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HST observations of the pulsating white dwarf GD 358

Cited by 20 publications

References 38 publications

AT LAST—A V777 HER PULSATOR IN THE KEPLER FIELD

AT LAST—A V777 HER PULSATOR IN THE KEPLER FIELD

The pulsations of PG 1351+489

2006 Whole Earth Telescope Observations of Gd358: A New Look at the Prototype DBV

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