Timing by Stellar Pulsations as an Exoplanet Discovery Method

Hermes, J. J.

doi:10.1007/978-3-319-55333-7_6

Cited by 10 publications

(6 citation statements)

References 19 publications

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“…However, the O−C observations are hardly constraining in terms of orbital modulation. A maximum amplitude in the phase variation can be calculated for a potential companion (Hermes 2018). As shown in Fig.…”

Section: Photometric Variabilitymentioning

confidence: 99%

A test of the planet–star unipolar inductor for magnetic white dwarfs

Walters

Farihi

Marsh

et al. 2021

Monthly Notices of the Royal Astronomical Society

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Despite thousands of spectroscopic detections, only four isolated white dwarfs exhibit Balmer emission lines. The temperature inversion mechanism is a puzzle over 30 years old that has defied conventional explanations. One hypothesis is a unipolar inductor that achieves surface heating via ohmic dissipation of a current loop between a conducting planet and a magnetic white dwarf. To investigate this model, new time-resolved spectroscopy, spectropolarimetry, and photometry of the prototype GD 356 are studied. The emission features vary in strength on the rotational period, but in anti-phase with the light curve, consistent with a cool surface spot beneath an optically thin chromosphere. Possible changes in the line profiles are observed at the same photometric phase, potentially suggesting modest evolution of the emission region, while the magnetic field varies by 10 per cent over a full rotation. These comprehensive data reveal neither changes to the photometric period, nor additional signals such as might be expected from an orbiting body. A closer examination of the unipolar inductor model finds points of potential failure: the observed rapid stellar rotation will inhibit current carriers due to the centrifugal force, there may be no supply of magnetospheric ions, and no anti-phase flux changes are expected from ohmic surface heating. Together with the highly similar properties of the four cool, emission-line white dwarfs, these facts indicate that the chromospheric emission is intrinsic. A tantalizing possibility is that intrinsic chromospheres may manifest in (magnetic) white dwarfs, and in distinct parts of the HR diagram based on structure and composition.

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Section: Photometric Variabilitymentioning

confidence: 99%

A test of the planet–star unipolar inductor for magnetic white dwarfs

Walters

Farihi

Marsh

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…This is, of course, assuming that the observations allow us to achieve the limits of the method, which for longcadence Kepler data occurs when the time-delay amplitude is about 5 s (or a 1 sin(i) ≈ 0.01 AU, Balona 2014). However, only a few of the claimed substellar mass candidates have been based on pulsation timings applied to δ Scuti stars (Hermes 2018).…”

Section: Technique Of Analysis and Time Series Datamentioning

confidence: 99%

The quest for planets around subdwarfs and white dwarfs from Kepler space telescope fields: Part I. Techniques and tests of the methods

Krzesinski,

Blokesz,

Siwak

et al. 2020

Preprint

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Context. In this study, we independently test the presence of an exoplanet around the binary KIC 9472174, which is composed of a red dwarf and a pulsating type B subdwarf. We also present the results of our search for Jupiter-mass objects orbiting near to the eclipsing binary KIC 7975824, which is composed of a white dwarf and type B subdwarf, and the pulsating white dwarf KIC 8626021. Aims. The goal is to test analytical techniques and prepare the ground for a larger search for possible substellar survivors on tight orbits around post-common envelope binaries and stars at the end of their evolution, that is, extended horizontal branch stars and white dwarfs. We, therefore, mainly focus on substellar bodies orbiting these stars within the range of the host's former red-giant or asymptotic-giant phase envelopes. Due to the methods we use, the quest is restricted to single-pulsating type B subdwarf and white dwarf stars and short-period eclipsing binaries containing a white dwarf or a subdwarf component. Methods. Our methods rely on the detection of exoplanetary signals hidden in photometric time series data from the Kepler space telescope, and they are based on natural clocks within the data itself, such as stellar pulsations and eclipse times. The light curves are analyzed using Fourier transforms, time-delays, and eclipse timing variations. Results. Based on the three objects studied in this paper, we demonstrate that these methods can be used to detect giant exoplanets orbiting around pulsating white dwarf or type B subdwarf stars as well as short-period binary systems, at distances which fall within the range of the former red-giant envelope of a single star or the common envelope of a binary. Using our analysis techniques, we reject the existence of a Jupiter-mass exoplanet around the binary KIC 9472174 at the distance and orbital period previously suggested in the literature. We also found that the eclipse timing variations observed in the binary might depend on the reduction and processing of the Kepler data. The other two objects analyzed in this work do not have Jupiter mass exoplanets orbiting within 0.7 -1.4 AU from them, or larger-mass objects on closer orbits (the given mass limits are minimum masses). Conclusions. Depending on the detection threshold of the time-delay method and the inclination of the exoplanet orbit toward the observer, data from the primary Kepler mission allows for the detection of bodies with a minimum of ∼ 1 Jupiter-mass orbiting these stars at ∼1 AU, while data from the K2 mission extends the detection of objects with a minimum mass of ∼ 7 Jupiter-mass on ∼ 0.1 AU orbits. The exoplanet mass and orbital distance limits depend on the length of the available photometric time series.

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“…The same modulation should be seen in all modes if the source is binary motion. Only one pulsation-timing exoplanet discovery remains plausible (Hermes, 2017), which comes from the two-mode analysis of a δ Sct star (Murphy et al, 2016a), though it should be noted that the planet mass is close to the brown-dwarf mass range.…”

Section: Hot Subdwarfsmentioning

confidence: 99%

“…However, intrinsic phase variability once again foils attempts to exploit this sensitivity (Hermes et al, 2013b;Dalessio et al, 2013). Hermes (2017) provided an overview of pulsation timing attempts on WDs, including the discovery and subsequent refutation of a possible substellar companion to the ZZ Ceti star GG 66 (Mullally et al 2008;cf. Dalessio 2013).…”

Section: White Dwarfsmentioning

confidence: 99%

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Pulsating stars in binary systems: a review

Murphy

2018

Preprint

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Binary systems anchor many of the fundamental relations relied upon in asteroseismology. Masses and radii are rarely constrained better than when measured via orbital dynamics and eclipse depths. Pulsating binaries have much to o er. They are clocks, moving in space, that encode orbital motion in the Doppler-shifted pulsation frequencies. They o er twice the opportunity to obtain an asteroseismic age, which is then applicable to both stars. They enable comparative asteroseismology -the study of two stars by their pulsation properties, whose only fundamental di erences are the mass and rotation rates with which they were born. In eccentric binaries, oscillations can be excited tidally, informing our knowledge of tidal dissipation and resonant frequency locking. Eclipsing binaries o er benchmarks against which the asteroseismic scaling relations can be tested. We review these themes in light of both observational and theoretical developments recently made possible by space-based photometry.

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Timing by Stellar Pulsations as an Exoplanet Discovery Method

Cited by 10 publications

References 19 publications

A test of the planet–star unipolar inductor for magnetic white dwarfs

A test of the planet–star unipolar inductor for magnetic white dwarfs

The quest for planets around subdwarfs and white dwarfs from Kepler space telescope fields: Part I. Techniques and tests of the methods

Pulsating stars in binary systems: a review

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