The first evidence for multiple pulsation axes: a new roAp star in the Kepler field, KIC 10195926
D. W. Kurtz, M. S. Cunha, H. Saio, L. Bigot, L. A. Balona, V. G. Elkin, H. Shibahashi, I. M. Brandao, K. Uytterhoeven, S. Frandsen, S. Frimann, A. Hatzes, T. Lu… 展开作者
D. W. Kurtz, M. S. Cunha, H. Saio, L. Bigot, L. A. Balona, V. G. Elkin, H. Shibahashi, I. M. Brandao, K. Uytterhoeven, S. Frandsen, S. Frimann, A. Hatzes, T. Lueftinger, M. Gruberbauer, H. Kjeldsen, J. Christensen-Dalsgaard, S. D. Kawaler
We have discovered a new rapidly oscillating Ap star among the Kepler Mission target stars, KIC 10195926. This star shows two pulsation modes with periods that are amongst the longest known for roAp stars at 17.1 min and 18.1 min, indicating that the star is near the terminal age main sequence. The principal pulsation mode is an oblique dipole mode that shows a rotationally split frequency septuplet that provides information on the geometry of the mode. The secondary mode also appears to be a dipole mode with a rotationally split triplet, but we are able to show within the improved oblique pulsator model that these two modes cannot have the same axis of pulsation. This is the first time for any pulsating star that evidence has been found for separate pulsation axes for different modes. The two modes are separated in frequency by 55 microHz, which we model as the large separation. The star is an alpha^2 CVn spotted magnetic variable that shows a complex rotational light variation with a period of Prot = 5.68459 d. For the first time for any spotted magnetic star of the upper main sequence, we find clear evidence of light variation with a period of twice the rotation period; i.e. a subharmonic frequency of $ν_{\rm rot}/2$. We propose that this and other subharmonics are the first observed manifestation of torsional modes in an roAp star. From high resolution spectra we determine Teff = 7400 K, log g = 3.6 and v sin i = 21 km/s. We have found a magnetic pulsation model with fundamental parameters close to these values that reproduces the rotational variations of the two obliquely pulsating modes with different pulsation axes. The star shows overabundances of the rare earth elements, but these are not as extreme as most other roAp stars. The spectrum is variable with rotation, indicating surface abundance patches.
Time-resolved spectroscopic observations of rapidly oscillating Ap (roAp) stars show a complex picture of propagating magneto-acoustic pulsation waves, with amplitude and phase strongly changing as a function of atmospheric height. We have recently conducted numerical, non-linear MHD simulations to get an insight into the complex atmospheric dynamics of magnetic pulsators. Here we use the resulting time-dependent atmospheric structure and velocity field to predict line profile variations for roAp stars. These calculations use realistic atmospheric structure, account for vertical chemical strat…
Observations of the A5p star KIC 8677585 obtained during the Kepler 10-d commissioning run with 1-min time resolution show that it is a roAp star with several frequencies with periods near 10 min. In addition, a low frequency at 3.142 cycles/day is also clearly present. Multiperiodic gamma Doradus and delta Scuti pulsations, never before seen in any Ap star, are present in Kepler observations of at least three other Ap stars. Since gamma Doradus pulsations are seen in Ap stars, it is likely that the low-frequency in KIC 8677585 is also a gamma Doradus pulsation. The simultaneous presence of bo…
We have carried out a survey of short-period pulsations among a sample of carefully chosen cool Ap stars using time-resolved observations with the UVES spectrometer at the ESO 8-m VLT telescope. Here we report the discovery of pulsations with amplitudes 50-100 m/s and periods 7-12 min in HD132205, HD148593 and HD151860. These objects are therefore established as new rapidly oscillating Ap (roAp) stars. In addition, we independently confirm the presence of pulsations in HD69013, HD96237 and HD143487 and detect, for the first time, radial velocity oscillations in two previously known photometric…
Spectroscopy is a powerful tool for detecting variability in the rapidly oscillating Ap (roAp) stars. The technique requires short integrations times and high resolution, and so is limited to only a few telescopes and instruments. To test the capabilities of the High Resolution Spectrograph (HRS) at the Southern African Large Telescope (SALT) for the study of pulsations in roAp stars, we collected 2.45 hr of high-resolution data of the well studied roAp star $α$ Cir in a previously unused instrument configuration. We extracted radial velocity measurements using different rare earth elements, a…
We present a multi-instrument analysis of the rapidly oscillating Ap (roAp) star HD 42659. We have obtained $B$ photometric data for this star and use these data, in conjunction with TESS observations, to analyse the high-frequency pulsation in detail. We find a triplet which is split by the rotation frequency of the star ($ν_{\rm rot}=0.3756$ d$^{-1}$; $P_{\rm rot}=2.66$ d) and present both distorted dipole and distorted quadrupole mode models. We show that the pulsation frequency, $150.9898$ d$^{-1}$ ($P_{\rm puls}=9.54$ min) is greater than the acoustic cutoff frequency. We utilise 27 high-…
We report the frequency analysis of a known roAp star, HD 86181 (TIC 469246567), with new inferences from TESS data. We derive the rotation frequency to be $ν_{rot}$ = 0.48753 $\pm$ 0.00001d$^{-1}$. The pulsation frequency spectrum is rich, consisting of two doublets and one quintuplet, which we interpret to be oblique pulsation multiplets from consecutive, high-overtone dipole, quadrupole and dipole modes. The central frequency of the quintuplet is 232.7701d$^{-1}$ (2.694 mHz). The phases of the sidelobes, the pulsation phase modulation, and a spherical harmonic decomposition all show that th…
Photometric observations of HD~217522 in 1981 revealed only one pulsation frequency $ν_1=1.21529$~mHz. Subsequent observations in 1989 showed the presence of an additional frequency $ν_2=2.0174$~mHz. New observations in 2008 confirm the presence of the mode with $ν_2=2.0174$~mHz. Examination of the 1989 data shows amplitude modulation over a time scale of the order of a day, much shorter than what has been observed in other roAp stars. High spectral and time resolution data obtained using the VLT in 2008 confirm the presence of $ν_2$ and short term modulations in the radial velocity amplitudes…
We report the results of a 60-hr photometric campaign of a rapidly oscillating Ap star, J0855 (TYC 2488-1241-1). We have utilised the multi-site Las Cumbres Observatory's (LCO) 0.4-m telescopes to obtain short cadence B-band observations of an roAp star previously lacking detailed study. Our observations confirm the rotation period presented in the discovery paper of this star ($P_{\rm rot}=3.0918$ d), and reveal the star to be pulsating in a distorted mode. The B data show this star to be among the highest amplitude roAp stars, with a peak-to-peak amplitude of 24 mmag. Modelling of the pulsat…
Precise time-series photometry with the MOST satellite has led to identification of 10 pulsation frequencies in the rapidly oscillating Ap (roAp) star HD 134214. We have fitted the observed frequencies with theoretical frequencies of axisymmetric modes in a grid of stellar models with dipole magnetic fields. We find that, among models with a standard composition of $(X,Z) = (0.70,0.02)$ and with suppressed convection, eigenfrequencies of a $1.65\,{\rm M}_\odot$ model with $\log T_{\rm eff} = 3.858$ and a polar magnetic field strength of 4.1kG agree best with the observed frequencies. We identi…
Studies based on high-resolution spectroscopic data of rapidly oscillating Ap stars show a surprising diversity of pulsation behavior in the atmospheric layers, pointing, in particular, to the co-existence of running and standing waves. The correct interpretation of these data requires a careful modelling of pulsations in these magnetic stars. In light of this, in this work we present a theoretical analysis of pulsations in roAp stars, taking into account the direct influence of the magnetic field. We derive approximate analytical solutions for the displacement components parallel and perpendi…
We analyse the fifth roAp star reported in the Kepler field, KIC 7582608, discovered with the SuperWASP project. The object shows a high frequency pulsation at 181.7324 d$^{-1}$ (P=7.9 min) with an amplitude of 1.45 mmag, and low frequency rotational modulation corresponding to a period of 20.4339 d with an amplitude of 7.64 mmag. Spectral analysis confirms the Ap nature of the target, with characteristic lines of Eu II, Nd III and Pr III present. The spectra are not greatly affected by broadening, which is consistent with the long rotational period found from photometry. From our spectral obs…
We present the first results from the Transiting Exoplanet Survey Satellite (TESS) on the rotational and pulsational variability of magnetic chemically peculiar A-type stars. We analyse TESS 2-min cadence data from sectors 1 and 2 on a sample of 83 stars. Five new rapidly oscillating Ap (roAp) stars are announced. One of these pulsates with periods around 4.7 min, making it the shortest period roAp star known to date. Four out of the five new roAp stars are multiperiodic. Three of these, and the singly-periodic one show the presence of rotational mode splitting. Individual frequencies are prov…
KIC 10685175 (TIC 264509538) was discovered to be a rapidly oscillating Ap star from {\it Kepler} long cadence data using super-Nyquist frequency analysis. It was re-observed by TESS with 2-min cadence data in Sectors 14 and 15. We analyzed the TESS light curves, finding that the previously determined frequency is a Nyquist alias. The revised pulsation frequency is $191.5151 \pm 0.0005$d$^{-1}$ ($P = 7.52$min) and the rotation frequency is $0.32229 \pm 0.00005$d$^{-1}$ ($P_{\rm rot} = 3.1028$d). The star is an oblique pulsator with pulsation amplitude modulated by the rotation, reaching pulsat…
We present the first short time scale observations of the roAp star gamma Equ in linear polarized light obtained with the PEPSI polarimeter installed at the LBT. These observations are used to search for pulsation variability in Stokes Q and U line profiles belonging to different elements. The atmospheres of roAp stars are significantly stratified with spectral lines of different elements probing different atmospheric depths. roAp stars with strong magnetic fields, such as gamma Equ with a magnetic field modulus of 4kG and a pulsation period of 12.21min, are of special interest because the eff…
We report the identification of 61.45 d^-1 (711.2 mu Hz) oscillations, with amplitudes of 62.6-mu mag, in KIC 4768731 (HD 225914) using Kepler photometry. This relatively bright (V=9.17) chemically peculiar star with spectral type A5 Vp SrCr(Eu) has previously been found to exhibit rotational modulation with a period of 5.21 d. Fourier analysis reveals a simple dipole pulsator with an amplitude that has remained stable over a 4-yr time span, but with a frequency that is variable. Analysis of high-resolution spectra yields stellar parameters of T_eff = 8100 +/- 200 K, log g = 4.0 +/- 0.2, [Fe/H…
Some Ap stars with strong magnetic fields pulsate in high order p-modes; they are called roAp (rapidly oscillating Ap) stars. The p-mode frequencies are modified by the magnetic fields. Although the large frequency separations are hardly affected, small separations are modified considerably. The magnetic field also affects the latitudinal amplitude distribution on the surface. We discuss the property of axisymmetric p-mode oscillations in roAp stars.
We have used high-speed spectroscopy of the rapidly oscillating Ap (roAp) star HD99563 to study the pulsation amplitude and phase behaviour of elements in its stratified atmosphere over one 2.91-d rotation cycle. We identify spectral features related to patches in the surface distribution of chemical elements and study the pulsation amplitudes and phases as the patches move across the stellar disk. The variations are consistent with a distorted nonradial dipole pulsation mode. We measure a 1.6 km/s rotational variation in the mean radial velocities of H-alpha and argue that this is the first o…
The 60 known rapidly oscillating Ap (roAp) stars are excellent laboratories to test pulsation models in the presence of stellar magnetic fields. Our survey is dedicated to search for new group members in the Northern Hemisphere. We attempt to increase the number of known chemically peculiar stars that are known to be pulsationally unstable. About 40 h of new CCD photometric data of 21 roAp candidates, observed at the 1m Austrian-Croatian Telescope (Hvar Observatory) are presented. We carefully analysed these to search for pulsations in the frequency range of up to 10mHz. No new roAp star was d…
We present two new rapidly oscillating Ap (roAp) stars, TIC 198781841 and TIC 229960986, discovered in TESS photometric data. The periodogram of TIC 198781841 has a large peak at 166.506 d$^{-1}$ (1.93 mHz), with two nearby peaks at 163.412 d$^{-1}$ (1.89 mHz) and 169.600 d$^{-1}$ (1.96 mHz). These correspond to three independent high-overtone pressure modes, with alternating even and odd $\ell$ values. TIC 229960986 has a high-frequency triplet centered at 191.641 d$^{-1}$ (2.218 mHz), with sidebands at 191.164 d$^{-1}$ (2.213 mHz) and 192.119 d$^{-1}$ (2.224 mHz). This pulsation appears to b…
We discuss pulsations of the rapidly oscillating Ap (roAp) star HD 24712 (HR 1217) based on nonadiabatic analyses taking into account the effect of dipole magnetic fields. We have found that all the pulsation modes appropriate for HD 24712 are damped; i.e., the kappa-mechanism excitation in the hydrogen ionization layers is not strong enough to excite high-order p-modes with periods consistent with observed ones, all of which are found to be above the acoustic cut-off frequencies of our models. The main (2.721 mHz) and the highest (2.806 mHz) frequencies are matched with modified $l=2$ and $l=…
Rapidly oscillating Ap stars exhibit an astrophysically interesting combination of strong, dipolar-like magnetic fields and high-overtone p-mode pulsations similar to the Sun. Recent time-resolved spectroscopy of these stars unravelled a complex picture of propagating magneto-acoustic pulsation waves, with amplitude and phase strongly changing as a function of atmospheric height. To interpret these observations and gain a new insight into the atmospheric dynamics of roAp stars we have carried out 2-D time-dependent, non-linear magneto-hydrodynamical simulations of waves for a realistic atmosph…
The rapidly oscillating Ap (roAp) stars exhibit pulsational photometric and/or radial velocity variations on time scales of several minutes, which are essential to test current pulsation models as well as our assumptions of atmospheric structure characteristics. In addition, their chemical peculiarity makes them very interesting for probing stellar formation and evolution in the presence of a global magnetic field. To date, a limited number of only 61 roAp stars are known to show photometric variability. On the other hand, a literature survey yields 619 unique stars that have unsuccessfully be…
Context. The dipole modes are the most common geometry of oscillations in roAp stars inferred from photometric measurements and are therefore of special interest for asteroseismic purposes. Aims. We present a theoretical and analytical study of the light curves associated with dipole (l = 1) pulsations of roAp stars in the framework of the revisited oblique pulsator model. Methods. We describe the light curves in terms of the inclination and polarization of the elliptical displacement vector of the dipole modes. We study the influence of the magnetic field and rotation on the shape of these li…
Context: Chemically peculiar A type (Ap) stars are a subgroup of the CP2 stars which exhibit anomalous overabundances of numerous elements, e.g. Fe, Cr, Sr and rare earth elements. The pulsating subgroup of the Ap stars, the roAp stars, present ideal laboratories to observe and model pulsational signatures as well as the interplay of the pulsations with strong magnetic fields and vertical abundance gradients. Aims: Based on high resolution spectroscopic observations and observed stellar energy distributions we construct a self consistent model atmosphere, that accounts for modulations of the t…
We report on the analysis of high-precision space-based photometry of the roAp (rapidly oscillating Ap) stars HD 9289, HD 99563, and HD134214. All three stars were observed by the MOST satellite for more than 25 days, allowing unprecedented views of their pulsation. We find previously unknown candidate frequencies in all three stars. We establish the rotation period of HD 9289 (8.5 d) for the first time and show that the star is pulsating in two modes that show different mode geometries. We present a detailed analysis of HD 99563's mode multiplet and find a new candidate frequency which appear…
We present the results of a systematic search for new rapidly oscillating Ap (roAp) stars using the 2-min cadence data collected by the Transiting Exoplanet Survey Satellite (TESS) during its Cycle 1 observations. We identify 12 new roAp stars. Amongst these stars we discover the roAp star with the longest pulsation period, another with the shortest rotation period, and six with multiperiodic variability. In addition to these new roAp stars, we present an analysis of 44 known roAp stars observed by TESS during Cycle 1, providing the first high-precision and homogeneous sample of a significant …
We present the discovery of a long-period, rapidly oscillating Ap star, HD177765. Using high-resolution time-series observations obtained with UVES at the ESO VLT telescope, we found radial velocity variations with amplitudes 7-150 m/s and a period of 23.6 min, exceeding that of any previously known roAp star. The largest pulsation amplitudes are observed for Eu III, Ce III and for the narrow core of Halpha. We derived the atmospheric parameters and chemical composition of HD177765, showing this star to be similar to other long-period roAp stars. Comparison with theoretical pulsational models …
Over the last decade significant amounts of high-spectral and time-resolution spectroscopic data have been acquired for a number of rapidly oscillating Ap stars. Progress in the understanding of the information held by these data requires the development of theoretical models that can be directly compared with them. In this work we present a theoretical model for the radial velocities of roAp stars that takes full account of the coupling between the pulsations and the magnetic field. We explore the impact on the radial velocities of changing the position of the observer, the mode frequency and…
We report on an analysis of high-precision, multi-colour photometric observations of the rapidly-oscillating Ap (roAp) star $α$ Cir. These observations were obtained with the BRITE-Constellation, which is a coordinated mission of five nanosatellites that collects continuous millimagnitude-precision photometry of dozens of bright stars for up to 180 days at a time in two colours (Johnson B and R). BRITE stands for BRight Target Explorer. The object $α$ Cir is the brightest roAp star and an ideal target for such investigations, facilitating the determination of oscillation frequencies with high …
Chemically peculiar (CP) stars with a measurable magnetic field comprise the group of mCP stars. The pulsating members define the subgroup of rapidly oscillating Ap (roAp) stars, of which Alpha Circini is the brightest member. Hence, Alpha Circini allows the application of challenging techniques, such as interferometry, very high temporal and spectral resolution photometry, and spectroscopy in a wide wavelength range, that have the potential to provide unique information about the structure and evolution of a star. Based on new photometry from BRITE-Constellation, obtained with blue and red fi…
We present the results of a multisite photometric observing campaign on the rapidly oscillating Ap (roAp) star 2MASS 16400299-0737293 (J1640; $V=12.7$). We analyse photometric $B$ data to show the star pulsates at a frequency of $151.93$ d$^{-1}$ ($1758.45 μ$Hz; $P=9.5$ min) with a peak-to-peak amplitude of 20.68 mmag, making it one of the highest amplitude roAp stars. No further pulsation modes are detected. The stellar rotation period is measured at $3.6747\pm0.0005$ d, and we show that rotational modulation due to spots is in anti-phase between broadband and $B$ observations. Analysis and m…
We present a new analysis of the rapidly oscillating Ap (roAp) star, 2MASS J$19400781-4420093$ (J1940; $V=13.1$). The star was discovered using SuperWASP broadband photometry to have a frequency of 176.39 d$^{-1}$ (2041.55 $μ$Hz; $P = 8.2$ min; Holdsworth et al. 2014a) and is shown here to have a peak-to-peak amplitude of 34 mmag. J1940 has been observed during three seasons at the South African Astronomical Observatory, and has been the target of a Whole Earth Telescope campaign. The observations reveal that J1940 pulsates in a distorted quadrupole mode with unusual pulsational phase variatio…
We present an analysis of the first Kepler K2 mission observations of a rapidly oscillating Ap (roAp) star, HD 24355 ($V=9.65$). The star was discovered in SuperWASP broadband photometry with a frequency of 224.31 d$^{-1}$, (2596.18 $μ$Hz; $P = 6.4$ min) and an amplitude of 1.51 mmag, with later spectroscopic analysis of low-resolution spectra showing HD 24355 to be an A5 Vp SrEu star. The high precision K2 data allow us to identify 13 rotationally split sidelobes to the main pulsation frequency of HD 24355. This number of sidelobes combined with an unusual rotational phase variation show this…
KIC 3429637 (HD 178875) is a delta Sct star whose light-curve shows continuous pulsational amplitude growth in Kepler Mission photometry. Analysis of the three largest amplitude peaks in the Fourier transform indicates different growth rates for all three. We have ruled out instrumental causes, and determine the amplitude growth to be intrinsic to the star. We calculate time-dependent convection models and compare them with the observations. We confirm earlier characterisations that KIC 3429637 is a marginal Am star through the analysis of new spectroscopic data. With the data presently availa…
Strong magnetic fields in chemically peculiar A-type (Ap) stars typically suppress low-overtone pressure modes (p modes) but allow high-overtone p modes to be driven. KIC 11296437 is the first star to show both. We obtained and analysed a Subaru spectrum, from which we show that KIC 11296437 has abundances similar to other magnetic Ap stars, and we estimate a mean magnetic field modulus of $2.8\pm0.5$ kG. The same spectrum rules out a double-lined spectroscopic binary, and we use other techniques to rule out binarity over a wide parameter space, so the two pulsation types originate in one $δ$ …
We present both binarity and pulsation of KIC 6220497 from the {\it Kepler} observations. The light curve synthesis shows that the eclipsing system is a semi-detached Algol with parameters of $q$ = 0.243$\pm$0.001, $i$ = 77.3$\pm$0.3 deg, and $ΔT$ = 3,372$\pm$58 K, in which the detached primary component fills its Roche lobe by $\sim$87\%. A multiple frequency analysis of the eclipse-subtracted light residuals reveals 33 frequencies in the range of 0.75$-$20.22 d$^{-1}$ with amplitudes between 0.27 and 4.56 mmag. Among these, four are pulsation frequencies in fundamental ($f_1$, $f_5$) and $p$…
Among A-type main-sequence variables, pulsations of $δ$ Sct and $γ$ Dor variables are driven in the He II ionization zone, while H-ionization zone and strong magnetic fields seem to play roles in the excitation of high-order p-modes in rapidly oscillating Ap (roAp) stars. Pulsations in B-type variables, $β$ Cephei and slowly pulsating B (SPB) stars are excited by the $κ$-mechanism at the Fe-opacity bump at $T\approx 2\times10^5$K. In addition, the strange-mode instability seems responsible for the excitation of pulsations in luminous AB-supergiants ($α$ Cygni variables). We discuss excitation …
We present the ${\it Kepler}$ photometry of KIC 6048106 exhibiting O'Connell effect and multiperiodic pulsations. Including a starspot on either of the components, light-curve synthesis indicates that this system is a semi-detached Algol with a mass ratio of 0.211, an orbital inclination of 73.9 deg, and a large temperature difference of 2,534 K. To examine in detail both spot variations and pulsations, we separately analyzed the {\it Kepler} time-series data at the interval of an orbital period by an iterative way. The results reveal that the variable asymmetries of the light maxima can be in…
The physics of magnetic hot stars and how a large-scale magnetic field affects their interior properties is largely unknown. Few studies have combined high-quality observations and modelling of magnetic pulsating stars, known as magneto-asteroseismology, primarily because of the dearth of detected pulsations in stars with a confirmed and well-characterised large-scale magnetic field. We aim to characterise observational signatures of rotation and pulsation in chemically peculiar candidate magnetic stars using photometry from the K2 space mission. Thus, we identify the best candidate targets fo…
We present Kepler satellite photometry of KIC 10661783, a short-period binary star system which shows total eclipses and multi-periodic delta Scuti pulsations. A frequency analysis of the eclipse-subtracted light curve reveals at least 68 frequencies of which 55 or more can be attributed to pulsation modes. The main limitation on this analysis is the frequency resolution within the 27-day short-cadence light curve. Most of the variability signal lies in the frequency range 18 to 31 c/d, with amplitudes between 0.1 and 4 mmag. One harmonic term (2.f) and a few combination frequencies (f_i+f_j) …
KIC 3230227 is a short period ($P\approx 7.0$ days) eclipsing binary with a very eccentric orbit ($e=0.6$). From combined analysis of radial velocities and {\it Kepler} light curves, this system is found to be composed of two A-type stars, with masses of $M_1=1.84\pm 0.18M_{\odot}$, $M_2=1.73\pm 0.17M_{\odot}$ and radii of $R_1=2.01\pm 0.09R_{\odot}$, $R_2=1.68\pm 0.08 R_{\odot}$ for the primary and secondary, respectively. In addition to an eclipse, the binary light curve shows a brightening and dimming near periastron, making this a somewhat rare eclipsing heartbeat star system. After removi…
We present the analysis of KIC 8164262, a heartbeat star with a high-amplitude (~1 mmag), tidally resonant pulsation (a mode in resonance with the orbit) at 229 times the orbital frequency and a plethora of tidally induced g-mode pulsations (modes excited by the orbit). The analysis combines Kepler light curves with follow-up spectroscopic data from the Keck telescope, KPNO (Kitt Peak National Observatory) 4-m Mayal telescope and the 2.7-m telescope at the McDonald observatory. We apply the binary modelling software, PHOEBE, to the Kepler light curve and radial velocity data to determine a det…
Analysis of the \textit{Kepler} $δ$\,Sct star KIC\,7106205 showed amplitude modulation in a single pressure mode, whilst all other pressure and gravity modes remained stable in amplitude and phase over the 1470\,d length of the dataset. The \textit{Kepler} dataset was divided into a series with time bins of equal length for which consecutive Fourier transforms were calculated. An optimum fixed frequency, calculated from a least-squares fit of all data, allowed amplitude and phase of each pulsation mode for each time bin to be tracked. The single pressure mode at $ν$\,=\,13.3942\,d$^{-1}$ chang…
We report the discovery of a new Kepler first-overtone RR Lyrae pulsator, KIC 2831097. The pulsation shows large, 0.1 d amplitude, systematic phase variations that can be interpreted as light travel-time effect caused by orbital motion in a binary system, superimposed on a linear pulsation-period decrease. The assumed eccentric (e=0.47) orbit with the period of approximately 2 yr is the shortest among the non-eclipsing RR Lyrae binary candidates. The binary model gives a lowest estimate for the mass of the companion of 8.4 M_Sun, that places it among black hole candidates. Beside the first-ove…
We report the ${\it Kepler}$ photometry of KIC 11401845 displaying multiperiodic pulsations, superimposed on binary effects. Light-curve synthesis represents that the binary star is a short-period detached system with a very low mass ratio of $q$ = 0.070 and filling factors of $F_1$ = 45 % and $F_2$ = 99 %. Multiple frequency analyses were applied to the light residuals after subtracting the synthetic eclipsing curve from the observed data. We detected 23 frequencies with signal to noise amplitude ratios larger than 4.0, of which the orbital harmonics ($f_4$, $f_6$, $f_9$, $f_{15}$) in the low…
We present the absolute properties of the double-lined eclipsing binary KIC 6206751 exhibiting multiperiodic pulsations. The ${\it Kepler}$ light curve of this system was simultaneously solved with the radial-velocity data given by Matson et al. (2017). The results indicate that the binary star is a short-period semi-detached system with fundamental parameters of $M_1$ = 1.66$\pm$0.04 M$_\odot$, $M_2$ = 0.215$\pm$0.006 M$_\odot$, $R_1$ = 1.53$\pm$0.02 R$_\odot$, $R_2$ = 1.33$\pm$0.02 R$_\odot$, $L_1$ = 5.0$\pm$0.6 L$_\odot$, and $L_2$ = 0.96$\pm$ 0.09 L$_\odot$. We applied multiple frequency a…
We present the first preliminary results on the analysis of ground-based time series of the γ Dor star KIC 6462033 (TYC 3144-646-1, V = 10.83, P = 0.69686 d) as well as Kepler photometry in order to study pulsational behaviour in this star.γ Dor variables, which exhibit g-mode pulsations, are promising asteroseismic targets to understand their rich complexity of pulsational characteristics in detail. In order to achieve this goal, intensive and numerous multicolour and high resolution spectroscopic observations are also required, to complete space-based data aimed at the determination of their…
We present an analysis of high time resolution spectra of the chemically peculiar Ap star HD 213637. The star shows rapid radial velocity variations with a period close to the photometric pulsation period. Radial velocity pulsation amplitudes vary significantly for different rare earth elements. The highest pulsation amplitudes belong to lines of TbIII ~360 m/s, PrII ~250 m/s and PrIII ~230 m/s . We did not detect any pulsations from spectral lines of EuII and in Halpha, in contrast to many other roAp stars. We also did not find radial velocity pulsations using spectral lines of other chemical…
We present a comprehensive study of the eclipsing binary system KIC 10661783. The analysis of the whole Kepler light curve, corrected for the binary effects, reveals a rich oscillation spectrum with 590 significant frequency peaks, 207 of which are independent. In addition to typical $δ$ Sct frequencies, we find small-amplitude signals in the low-frequency range that, most probably, are a manifestation of gravity-mode pulsations. We perform binary-evolution computations for this system in order to find an acceptable model describing its current stage. Our models show that the binary KIC 106617…
Learned et. al. proposed that a sufficiently advanced extra-terrestrial civilization may tickle Cepheid and RR Lyrae variable stars with a neutrino beam at the right time, thus causing them to trigger early and jogging the otherwise very regular phase of their expansion and contraction. This would turn these stars into beacons to transmit information throughout the galaxy and beyond. The idea is to search for signs of phase modulation (in the regime of short pulse duration) and patterns, which could be indicative of intentional, omnidirectional signaling. We have performed such a search among …
The present work concerns the Asteroseismology of the Kepler detached eclipsing binary KIC 8504570. Particularly, it focuses on the pulsational behaviour of the oscillating component of this system and the estimation of its physical parameters in order to enrich the so far poor sample of this kind of systems. Using spectroscopic observations, the spectral type of the primary component was determined and used to create accurate light curves models and estimate its absolute parameters. The light curve residuals were subsequently analysed using Fourier transformation techniques to obtain the puls…
Context. Thanks to the high-precision photometry from space missions such as Kepler and TESS, tidal perturbations and tilting of pulsations have been detected in more than a dozen binary systems. However, only two of these were g-mode pulsators. Aims. We aim to detect tidally perturbed g modes in additional binary systems and characterise them observationally. Methods. We perform a custom data reduction of the available Kepler and TESS photometry of a well-studied sample of 35 binary systems with gamma Doradus pulsators. For each target, we model the binary signal using a sum of 100 sine waves…
We present a detailed study of the pulsation of alpha Circini, the brightest of the rapidly oscillating Ap stars. We have obtained 84 days of high-precision photometry from four runs with the star tracker on the WIRE satellite. Simultaneously, we collected ground-based Johnson B observations on 16 nights at the South African Astronomical Observatory. In addition to the dominant oscillation mode at 2442 microHz, we detect two new modes that lie symmetrically around the principal mode to form a triplet. The average separation between these modes is 30.173+-0.004 microHz and they are nearly equid…
