arXiv subjects

D. Kurtz

Publications and source records attributed to D. Kurtz.

5 recordsLinked to original sources

arXiv2026

Discovery of the First Octupole Pulsation Mode in a delta Scuti Star: A Stationary l = 3 Sectoral Mode

Aims. We are attempting to better understand how stellar pulsations in close binary systems are affected, and possibly induced, by tidal, Coriolis, and centrifugal forces. Methods. We analyzed TESS data for some 50,000 potential eclipsing binaries selected by machine learning algorithms in order to search for pulsation multiplets split by integer multiples of the orbital frequency. Results. We report on the discovery of an octupole pulsation mode in the binary star system TIC 287869463, which contains a delta Scuti star. This mode is actually a combination of Y3+3 and Y3-3 modes that are perturbed into a new eigenmode of the star via tidal, Coriolis, and centrifugal forces, which we call a Y33+ mode. The mode is stationary on the star. To our knowledge, this is the first time that such an l = 3 mode identification has been securely made in any delta Scuti star, and the first stationary l = 3 sectoral mode of this type seen in any star, including the Sun. The l = 3 pulsations appear as a combination of two components at 34.94617 per day and 39.31127 per day, split by exactly six times the frequency of the orbital motion to within better than 1 part in 100,000. We extract the pulsation frequencies from the TESS data spanning more than three years, and model the system to gain a better understanding of this novel asteroseismic discovery. The pulsation frequencies are found to be steadily increasing with time, but always maintaining a split equal to six times the orbital frequency. Conclusions. We discuss the implications for the broader class of "tidally tilted pulsators" and "tri-axial pulsators" that have been discovered to date. We conclude that these previous categories can all be interpreted as linear combinations of spherical harmonics whose axes coincide with the orbital axis and form new eigenmodes of the star via tidal, Coriolis, and centrifugal perturbations

astro-ph.SR↗

arXiv2020

Pulsation in the white dwarf HE 1017-1352: confirmation of the class of hot DAV stars

We report the detection of periodic variations on the T_eff ~32 000 K DA white dwarf star HE 1017-1352. We obtained time series photometry using the 4.1 m SOAR telescope on three separate nights for a total of 16.8 h. From the frequency analysis we found four periods of 605 s, 556 s, 508 s and 869 s with significant amplitudes above the 1/1000 false alarm probability detection limit. The detected modes are compatible with low harmonic degree g-mode non-radial pulsations with radial order higher than ~ 9. This detection confirms the pulsation nature of HE 1017-1352 and thus the existence of the new pulsating class of hot DA white dwarf stars. In addition, we detect a long period of 1.52 h, compatible with a rotation period of DA white dwarf stars.

astro-ph.SR↗

arXiv2014

Subaru and Swift observations of V652 Herculis: resolving the photospheric pulsation

High resolution spectroscopy with the Subaru High Dispersion Spectrograph, and Swift ultraviolet photometry are presented for the pulsating extreme helium star V652\,Her. Swift provides the best relative ultraviolet photometry obtained to date, but shows no direct evidence for a shock at ultraviolet or X-ray wavelengths. Subaru has provided high spectral and high temporal resolution spectroscopy over 6 pulsation cycles (and eight radius minima). These data have enabled a line-by-line analysis of the entire pulsation cycle and provided a description of the pulsating photosphere as a function of optical depth. They show that the photosphere is compressed radially by a factor of at least two at minimum radius, that the phase of radius minimum is a function of optical depth and the pulse speed through the photosphere is between 141 and 239 km/s (depending how measured) and at least ten times the local sound speed. The strong acceleration at minimum radius is demonstrated in individual line profiles; those formed deepest in the photosphere show a jump discontinuity of over 70 km/s on a timescale of 150 s. The pulse speed and line profile jumps imply a shock is present at minimum radius. These empirical results provide input for hydrodynamical modelling of the pulsation and hydrodynamical plus radiative transfer modelling of the dynamical spectra.

astro-ph.SR↗

arXiv2013

KIC 11285625: a double-lined spectroscopic binary with a gamma Dor pulsator discovered from Kepler space photometry

We present the first binary modelling results for the pulsating eclipsing binary KIC 11285625, discovered by the Kepler mission. An automated method to disentangle the pulsation spectrum and the orbital variability in high quality light curves, was developed and applied. The goal was to obtain accurate orbital and component properties, in combination with essential information derived from spectroscopy. A binary model for KIC 11285625 was obtained, using a combined analysis of high-quality space-based Kepler light curves and ground-based high-resolution HERMES echelle spectra. The binary model was used to separate the pulsation characteristics from the orbital variability in the Kepler light curve in an iterative way. We used an automated procedure to perform this task, based on the JKTEBOP binary modelling code, and adapted codes for frequency analysis and prewhitening of periodic signals. Using a disentangling technique applied to the composite HERMES spectra, we obtained a higher signal-to-noise mean component spectrum for both the primary and the secondary. A model grid search method for fitting synthetic spectra was used for fundamental parameter determination for both components. Accurate orbital and component properties of KIC 11285625 were derived, and we have obtained the pulsation spectrum of the gamma Dor pulsator in the system. Detailed analysis of the pulsation spectrum revealed amplitude modulation on a time scale of a hundred days, and strong indications of frequency splittings at both the orbital frequency, and the rotational frequency derived from spectroscopy.

astro-ph.SR↗

arXiv2011

Observational Constraints, Stellar Models, and Kepler Data for theta Cyg, the Brightest Star Observable by Kepler

The V=4.48 F4 main-sequence star theta Cyg is the brightest star observable in the Kepler spacecraft field-of-view. Short-cadence (58.8 s) photometric data were obtained by Kepler during 2010 June-September. Preliminary analysis shows solar-like oscillations in the frequency range 1200- 2500 microHz. To interpret these data and to motivate further observations, we use observational constraints from the literature to construct stellar evolution and pulsation models for this star. We compare the observed large frequency separation of the solar-like oscillations with the model predictions, and discuss the prospects for gamma Doradus-like g-mode pulsations, given the observational constraints. We discuss the value of angular diameter measurements from optical interferometry for constraining stellar properties and the implications for asteroseismology.

astro-ph.SR↗