The pulsating DA white dwarf star EC 14012−1446: results from four epochs of time-resolved photometry

Handler, G.; Romero-Colmenero, E.; Provençal, J. L.; Sanchawala, K.; Wood, M. A.; Silver, Isaac M.; Chen, W. P.

doi:10.1111/j.1365-2966.2008.13509.x

Cited by 11 publications

(28 citation statements)

References 38 publications

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“…The challenges of comparing multi-season pulsation measurements for ZZ Ceti variables that have cooled significantly beyond the hot edge of the instability strip are well established in the literature, particularly from Whole Earth Telescope (Nather et al 1990) campaigns. GD 154 (Pfeiffer et al 1996), G29-38 (Kleinman et al 1998), HL Tau 76 (Dolez et al 2006), and EC14012-1446 (Handler et al 2008;Provencal et al 2012), for example, show such dramatic amplitude changes that significant modes from one year can be completely absent the next. With nine and seven month gaps between space-and ground-based campaigns on EPIC 210377280 and EPIC 220274129, we have no expectation that the same eigenmodes will be excited to similar amplitudes in both data sets.…”

Section: Spectral Windowmentioning

confidence: 99%

Destroying Aliases from the Ground and Space: Super-Nyquist ZZ Cetis in K2 Long Cadence Data

Bell

Hermes

Vanderbosch

et al. 2017

ApJ

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With typical periods of order 10 minutes, the pulsation signatures of ZZ Ceti variables (pulsating hydrogen-atmosphere white dwarf stars) are severely undersampled by long-cadence (29.42 minutes per exposure) K2 observations. Nyquist aliasing renders the intrinsic frequencies ambiguous, stifling precision asteroseismology. We report the discovery of two new ZZ Cetis in long-cadence K2 data: EPIC 210377280 and EPIC 220274129. Guided by 3-4 nights of follow-up, high-speed (≤ 30 s) photometry from McDonald Observatory, we recover accurate pulsation frequencies for K2 signals that reflected 4-5 times off the Nyquist with the full precision of over 70 days of monitoring (∼0.01 µHz). In turn, the K2 observations enable us to select the correct peaks from the alias structure of the ground-based signals caused by gaps in the observations. We identify at least seven independent pulsation modes in the light curves of each of these stars. For EPIC 220274129, we detect three complete sets of rotationally split = 1 (dipole mode) triplets, which we use to asteroseismically infer the stellar rotation period of 12.7 ± 1.3 hr. We also detect two sub-Nyquist K2 signals that are likely combination (difference) frequencies. We attribute our inability to match some of the K2 signals to the ground-based data to changes in pulsation amplitudes between epochs of observation. Model fits to SOAR spectroscopy place both EPIC 210377280 and EPIC 220274129 near the middle of the ZZ Ceti instability strip, with T eff = 11590 ± 200 K and 11810 ± 210 K, and masses 0.57 ± 0.03 M and 0.62 ± 0.03 M , respectively.

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Section: Spectral Windowmentioning

confidence: 99%

Destroying Aliases from the Ground and Space: Super-Nyquist ZZ Cetis in K2 Long Cadence Data

Bell

Hermes

Vanderbosch

et al. 2017

ApJ

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“…They observed it for four nights, and then derived five independent frequencies from the obtained light curves. Subsequently, Handler et al observed it several times in 2004April and June, 2005May, and 2007 April, and obtained 19 independent frequencies (Handler et al 2008). Recently, Provencal et al observed EC14012−1446 again in the WET run XCOV26 in 2008 and obtained 19 independent frequencies (Provencal et al 2012).…”

Section: Introductionmentioning

confidence: 97%

“…Later, based on those independent frequencies they had obtained, Handler et al (2008) declared the discovery of two triplets with an average frequency splitting of 9.55 μHz. However, Provencal et al (2012) did not confirm the discovery of Handler et al (2008). Instead, they identified a new triplet with an average frequency splitting of 3.79 μHz, which was in disagreement with result of Handler et al (2008).…”

Section: Introductionmentioning

confidence: 99%

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, and by Provencal et al in 2008. We review the observations together and obtain 34 independent frequencies.

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mentioning

confidence: 99%

“…For EC14012−1446, Stobie et al (1995) did not find any rotational splitting phenomenon. Later, based on those independent frequencies they had obtained, Handler et al (2008) declared the discovery of two triplets with an average frequency splitting of 9.55 μHz. However, Provencal et al (2012) did not confirm the discovery of Handler et al…”

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confidence: 99%

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Asteroseismology of DAV star EC14012−1446, mode identification and model fittings

Chen

2014

Monthly Notices of the Royal Astronomical Society

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, and by Provencal et al. in 2008. We review the observations together and obtain 34 independent frequencies. According to the frequency splitting and the asymptotic period spacing law, we identify 6 l = 1 modes, 4 l = 2 modes, 5 l = 3 modes, 10 l = 1 or 2 modes. Grids of white dwarf models are generated by WDEC with H, He, C, O diffusion in a four-parameter space. The core compositions are directly from white dwarf models generated by MESA. The best-fitting model has M * = 0.710 M , T eff = 12 200 K, log(M He /M * ) = −2.5, log(M H /M * ) = −7.0, log g = 8.261, and φ = 3.185 s. There are four, two, and one modes identified as trapped in H envelope for observed l = 1, 2, and 3 modes, respectively. Trapped modes jump the queue of uniform period spacing.Key words: asteroseismology -stars: individual: EC14012−1446 -white dwarfs. I N T RO D U C T I O NAbout 80 per cent of white dwarfs show DA spectral class. A DA white dwarf star consists of a hydrogen atmosphere covering an intermediate helium layer and a carbon/oxygen core. According to existence of partial hydrogen ionization and subsurface convection zone, a DA star will pulsate when its effective temperature (T eff ) is between 10 850 and 12 270 K (Castanheira, Kepler & Costa 2007). With buoyancy acting as the restoring force, DAV stars are pulsating in g modes. Asteroseismology is a unique tool to detect the inner structure of DAV stars, which requires enough observed frequencies, reliable mode identifications, and realistic stellar models.EC14012−1446, also called WD1401−147, was first identified as a DAV star by Stobie et al. (1995). They observed it for four nights, and then derived five independent frequencies from the ob- Mode identification is an important task for asteroseismological studies. An eigenmode can be characterized by three indices (k, l, m), which are, respectively, the radial order, the spherical harmonic degree, and the azimuthal number. Frequencies of pulsation modes with definite spherical harmonic degrees play a role as tick marks on a ruler for theoretical modelling of pulsating white dwarfs. In particular, stellar rotation can split a pulsation frequency into several ones. The approximate formula between frequency splitting (δν n, l ) and rotational period (P rot ) is derived by Brickhill (1975) aswhere m can be taken from −l to l, leading to totally 2l+1 different values. According to equation (1), modes with l = 1 form a triplet and modes with l = 2 form a quintuplet. Therefore, if triplets or quintuplets are derived from observations of a pulsating star, they can be reliably identified as rotational splitting of l = 1 or l = 2 modes, respectively. For EC14012−1446, Stobie et al. (1995) did not find any rotational splitting phenomenon. Later, based on those independent frequencies they had obtained, Handler et al. (2008) declared the discovery of two triplets with an average frequency splitting of 9.55 μHz. However, Provencal et al. (2012) did not confirm the discovery of Handler et al.

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Study of short period variables and small amplitude periodic variables

Váradi

Eyer

Jordan

et al. 2010

EAS Publications Series

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Abstract. Our goal is to assess Gaia's performance on the period recovery of short period (p < 2 hours) and small amplitude variability. To reach this goal first we collected the properties of variable stars that fit the requirements described above. Then we built a database of synthetic light-curves with short period and low amplitude variability with time sampling that follows the Gaia nominal scanning law and with noise level corresponding to the expected photometric precision of Gaia. Finally we performed period search on the synthetic light-curves to obtain period recovery statistics. This work extends our previous period recovery studies to short period variable stars which have nonstationary Fourier spectra.

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The pulsating DA white dwarf star EC 14012−1446: results from four epochs of time-resolved photometry

Cited by 11 publications

References 38 publications

Destroying Aliases from the Ground and Space: Super-Nyquist ZZ Cetis in K2 Long Cadence Data

Destroying Aliases from the Ground and Space: Super-Nyquist ZZ Cetis in K2 Long Cadence Data

Asteroseismology of DAV star EC14012−1446, mode identification and model fittings

Study of short period variables and small amplitude periodic variables

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