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

Bell, Keaton J.; Hermes, J. J.; Vanderbosch, Zachary P.; Montgomery, M. H.; Winget, D. E.; Dennihy, E.; Fuchs, J.; Tremblay, Pier-Emmanuel

doi:10.3847/1538-4357/aa9702

Cited by 23 publications

(27 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, we note that if any of these stars are indeed oscillating in these regions, or even above the Nyquist frequency, the measured amplitude will be highly diminished as a result of the non-zero duration of Kepler integration times, a phenomenon referred to as apodization (Murphy 2015a;Hekker & Christensen-Dalsgaard 2017) or phase smearing (Bell et al 2017). The amplitudes measured from the data (A measured ) are smaller than their intrinsic amplitudes in the Kepler filter by a factor of η,…”

Section: Apodizationmentioning

confidence: 89%

“…c) shows the aliased signal at 406.2 µHz of the true oscillation at d), 972.6 µHz, distinguishable by both the Kepler orbital separation frequency (dashed blue lines) and maximum amplitudes. The Python code Pyquist has been used to plot the apodization (Bell et al 2017).…”

Section: Target Selectionmentioning

confidence: 99%

“…Since their discovery by Kurtz (1978Kurtz ( , 1982, only 70 rapidly oscillating Ap (roAp) stars have been found (Smalley et al 2015;Joshi et al 2016;Cunha et al 2019;Balona et al 2019). Progress in understanding their pulsation mechanism, abundance, and the origin of their magnetic fields has been hindered by the relatively small number of known roAp stars.…”

Section: Introductionmentioning

confidence: 99%

“…This technique, known as super-Nyquist asteroseismology, has previously been used with red giants and solar-like oscillators on a case-by-case basis (Chaplin et al 2014;Yu et al 2016;Mathur et al 2016), as well as in combinations of LC data with ground-based observations for compact pulsators (Bell et al 2017). Applications in the context of roAp stars have been limited only to frequency verification of SC or other data (Holdsworth et al 2014b;Smalley et al 2015).…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Six new rapidly oscillating Ap stars in the Kepler long-cadence data using super-Nyquist asteroseismology

Hey

Holdsworth

Bedding

et al. 2019

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

We perform a search for rapidly oscillating Ap stars in the Kepler long-cadence data, where true oscillations above the Nyquist limit of 283.21 µHz can be reliably distinguished from aliases as a consequence of the barycentric time corrections applied to the Kepler data. We find evidence for rapid oscillations in six stars: KIC 6631188, KIC 7018170, KIC 10685175, KIC 11031749, KIC 11296437 and KIC 11409673, and identify each star as chemically peculiar through either pre-existing classifications or spectroscopic measurements. For each star, we identify the principal pulsation mode, and are able to observe several additional pulsation modes in KIC 7018170. We find that KIC 7018170 and KIC 11409673 both oscillate above their theoretical acoustic cutoff frequency, whilst KIC 11031749 oscillates at the cutoff frequency within uncertainty. All but KIC 11031749 exhibit strong amplitude modulation consistent with the oblique pulsator model, confirming their mode geometry and periods of rotation.

show abstract

Section: Apodizationmentioning

confidence: 89%

Section: Target Selectionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Six new rapidly oscillating Ap stars in the Kepler long-cadence data using super-Nyquist asteroseismology

Hey

Holdsworth

Bedding

et al. 2019

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

show abstract

“…Without a physical argument for choosing one of these candidates over the others, analyses of TESS data are ambiguous at best and inaccurate at worst. In these cases, it is typically necessary to obtain follow-up observations with a different cadence to resolve which peaks correspond to intrinsic frequencies (e.g., Bell et al 2017). This strains observing resources, limits results to researchers with abundant telescope access, and is impractical for the millions of stars that TESS is observing.…”

mentioning

confidence: 99%

TESS Extended Mission 10 Minute Cadence Retains Nyquist Aliases

Bell

2020

Res. Notes AAS

Self Cite

View full text Add to dashboard Cite

During its two-year prime mission, the Transiting Exoplanet Survey Satellite (TESS;Ricker et al. 2014) is obtaining full-frame images with a regular 30-minute cadence in a sequence of 26 sectors that cover a combined 85% of the sky. While its primary science case is to discover new exoplanets transiting nearby stars, TESS data are superb for studying many types of stellar variability, with the number of publications using TESS data for other areas of astrophysics keeping pace with exoplanet papers. 1 Following the conclusion of its prime mission in July 2020, TESS will revisit the sky in an extended mission that records full-frame images at a faster ten-minute cadence. In this note, I demonstrate that choosing a large submultiple of the original exposure times for the new cadence limits the synergy between prime and extended TESS mission data since both sampling rates produce many of the same Nyquist aliases. Adjusting the extended mission exposure time by as little as one second would largely resolve Nyquist ambiguities in the combined TESS data set.Recording any periodic signal with a regular time sampling of ∆t will produce an infinite number of identical alias peaks in a periodogram that are reflected off of the Nyquist frequency, f Nyq = (2∆t) −1 . This means that there are an infinite number of candidate frequency solutions that do an equally good job of explaining the regularly sampled signal. Without a physical argument for choosing one of these candidates over the others, analyses of TESS data are ambiguous at best and inaccurate at worst. In these cases, it is typically necessary to obtain follow-up observations with a different cadence to resolve which peaks correspond to intrinsic frequencies (e.g., Bell et al. 2017). This strains observing resources, limits results to researchers with abundant telescope access, and is impractical for the millions of stars that TESS is observing. TESS itself could eliminate the need for such follow-up if it were to carry out its extended mission observations with a sample spacing that is not precisely a small submultiple of the original cadence. Figure 1 depicts the Lomb-Scargle periodograms of simulated light curves sampled at three rates: (a) once every 30 minutes; (b) once every 10 minutes; and (c) once every 11 minutes. The underlying source exhibits a single signal with an intrinsic frequency of 1000 µHz, resulting in an infinite set of aliases in each periodogram. Because the spacing between samples in (b) is a submultiple of the sampling of (a), all aliases in periodogram (b) are exactly coincident with aliases in (a), and the solution from the combined data set remains ambiguous. However, since the sampling of (c) is not so simply related to (a), the peak at the intrinsic frequency is easily identified as the only one that appears at the same location in both periodograms (a) and (c).The same conclusion holds for periodic signals that are not strictly sinusoidal, since all harmonics in the periodogram are also aliased to the same frequencies for 30-and 10-minu...

show abstract

Pulsating white dwarfs: new insights

Córsico

Althaus

Bertolami

et al. 2019

Astron Astrophys Rev

194

224

View full text Add to dashboard Cite

Stars are extremely important astronomical objects that constitute the pillars on which the Universe is built, and as such, their study has gained increasing interest over the years. White dwarf stars are not the exception. Indeed, these stars constitute the final evolutionary stage for more than 95 per cent of all stars. The Galactic population of white dwarfs conveys a wealth of information about several fundamental issues and are of vital importance to study the structure, evolution and chemical enrichment of our Galaxy and its components -including the star formation history of the Milky Way. Several important studies have emphasized the advantage of using white dwarfs as reliable clocks to date a variety of stellar populations in the solar neighborhood and in the nearest stellar clusters, including the thin and thick disks, the Galactic spheroid and the system of globular and open clusters. In addition, white dwarfs are tracers of the evolution of planetary systems along several phases of stellar evolution. Not less relevant than these applications, the study of matter at high densities has benefited from our detailed knowledge about evolutionary and observational properties of white dwarfs. In this sense, white dwarfs are used as laboratories for astro-particle physics, being their interest focused on physics beyond the standard model, that is, neutrino physics, axion physics and also radiation from "extra dimensions", and even crystallization.The last decade has witnessed a great progress in the study of white dwarfs. In particular, a wealth of information of these stars from different surveys has

show abstract

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

Cited by 23 publications

References 40 publications

Six new rapidly oscillating Ap stars in the Kepler long-cadence data using super-Nyquist asteroseismology

Six new rapidly oscillating Ap stars in the Kepler long-cadence data using super-Nyquist asteroseismology

TESS Extended Mission 10 Minute Cadence Retains Nyquist Aliases

Pulsating white dwarfs: new insights

Contact Info

Product

Resources

About