Results of analysis of 60010 data photometric observations from the AAVSO international database are presented, which span 120 years of monitoring. The periodogram analysis shows the best fit period of 70.74d, a half of typically published periods for smaller intervals. Contrary to expectation for deep/shallow minima, the changes between them are not so regular. There may be series of deep (or shallow) minima without alternations. There may be two acting periods of 138.5 days and 70.74, so the beat modulation may be expected. The dependence of the phases of deep minima argue for two alternating periods with a characteristic life-time of a mode of 30years. These phenomenological results better explain the variability than the model of chaos.
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…
Under the Nainital-Cape Survey, eight $δ\,$Scuti type pulsators have been discovered with the pulsation periods in the range of several minutes to few hours. In order to understand these observed pulsational variabilities, we have performed non-adiabatic linear stability analyses in models of these stars having mass in the range of 1 to 3 M$_{\odot}$. Several low order p-modes are found to be unstable where the pulsation periods associated with these unstable modes are in good agreement with the observed periods. Particularly for HD$\,$118660, HD$\,$113878, HD$\,$102480, HD$\,$98851, and HD$\,…
HD 187547 was the first candidate that led to the suggestion that solar-like oscillations are present in delta Scuti stars. Longer observations, however, show that the modes interpreted as solar-like oscillations have either very long mode lifetimes, longer than 960 days, or are coherent. These results are incompatible with the nature of `pure' stochastic excitation as observed in solar-like stars. Nonetheless, one point is certain: the opacity mechanism alone cannot explain the oscillation spectrum of HD 187547. Here we present new theoretical investigations showing that convection dynamics c…
Time-series photometric observations were made for the High Amplitude $δ$ Scuti star CW Ser between 2011 and 2012 at the Xinglong Station of National Astronomical Observatories of China. After the frequency analysis of the light curves, we confirmed the fundamental frequency of $f = 5.28677\ cd^{-1}$, together with 8 harmonics of the fundamental frequency, 7 of which are newly detected. No additional frequencies were detected. The O-C diagram, produced with the 21 newly determined times of maximum light combined with those provided in the literature, helps to obtain a new ephemeris formula of …
A photometric variability study of a sample of northern field stars, which previously classified as either PMS or Herbig Ae/Be objects, has been undertaken with the purpose of detecting δ Scuti-type pulsations. Determination of physical parameters for these stars has also been carried out to locate them on the HR diagram and check the instability strip for this type of pulsators. Multichannel photomultiplier and CCD time series photometry in the uvby Strömgren and BVI Johnson bands were obtained during four consecutive years from 2007 to 2010. The light curves have been analysed, and a variabi…
Several Delta Sct stars were photometrically monitored with the satellite CoRoT and observed in high-resolution spectroscopy from ground. We present here the preliminary analysis of the abundance analysis of several potential CoRoT targets. Moreover, new insights are given about the problem of the huge number of detected frequencies by comparing Delta Sct stars with normal A-stars.
The Antartica Search for Transiting Extrasolar Planets (ASTEP), an automatized 400 mm telescope located at Concordia station in Antarctica, monitored beta Pictoris continuously to detect any variability linked to the transit of the Hill sphere of its planet beta Pictoris b. The long observation sequence, from March to September 2017, combined with the quality and high level duty cycle of our data, enables us to detect and analyse the delta Scuti pulsations of the star. Time series photometric data were obtained using aperture photometry by telescope defocussing. The 66 418 data points were ana…
We announce the discovery of pulsations in HD 23642, the only bright eclipsing system in the Pleiades, based on light curves from the Transiting Exoplanet Survey Satellite (TESS). We measure 46 pulsation frequencies and attribute them to delta Scuti pulsations in the secondary component. We find four l=1 doublets, three of which have frequency splittings consistent with the rotation rate of the star. The dipole mode amplitude ratios are consistent with a high stellar inclination angle and the stellar rotation period agrees with the orbital period. Together, these suggest that the spin axis of …
Unveiling $δ$ Scuti and $γ$ Doradus Hybrid Pulsation of HD 53166 and HD 53349 Plus Rich Frequencies in HD 52788 -- Catalogs of 70552 $δ$ Sct and 8080 $γ$ Dor
RR Lyn is a detached eclipsing binary with a 9.95 d orbit containing two A-stars: one metallic-lined and one possibly metal-poor. We use the light curve from the TESS satellite and two sets of published radial velocity measurements to determine the properties of the system to high precision. We find masses of 1.939 +/- 0.007 and 1.510 +/- 0.003 Msun, and radii of 2.564 +/- 0.019 and 1.613 +/- 0.013 Rsun. After adjusting published effective temperatures upwards by 200 K we find a good agreement with theoretical models for a solar chemical composition and an age of 1 Gyr, and a distance slightly…
We study the frequency distributions of Delta Scuti stars observed by the Kepler satellite in short-cadence mode. To minimize errors in the estimated stellar parameters, we divided the instability strip into ten regions and determined the mean frequency distribution in each region. We confirm that the presence of low frequencies is a property of all Delta Scuti stars, rendering meaningless the concept of Delta Sct/Gamma Dor hybrids. We obtained the true distribution of equatorial rotational velocities in each region and calculated the frequency distributions predicted by pulsation models, taki…
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) …
Pulsating stars are remarkable objects for stellar astrophysics. Their pulsation frequencies allow us to probe the internal structure of stars. One of the most known groups of pulsating stars is $δ$ Scuti variables which could be used to understand the energy transfer mechanism in A-F type stars. Therefore, in the current study, we focused on the discovery of $δ$ Scuti stars. For this investigation, we followed some criteria. First, we inspected TESS database by eye and discovered some single stars that exhibit pulsation-like behaviour. Our second criterion is $T_{\rm eff}$ and $\log g$ range.…
Discovery of new magnetic δ Scuti stars and impact of magnetism on pulsation excitation
Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université（巴黎天文台，巴黎文理研究大学，法国国家科学研究中心，索邦大学，巴黎西岱大学，塞吉-巴黎大学）；Newcastle University（纽卡斯尔大学）；DTU Space, Technical University of Denmark（丹麦技术大学空间研究所）；Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM（巴黎萨克雷大学，巴黎西岱大学，法国原子能和替代能源委员会，法国国家科学研究中心，天体物理、仪器与方法实验室）
The physics of early stellar evolution (e.g. accretion processes) is often not properly included in the calculations of pre-main-sequence models, leading to insufficient model grids and hence systematic errors in the results. We aim to investigate current and improved approaches for the asteroseismic modelling of pre-main-sequence delta Scuti stars. We calculated an extensive grid of pre-main-sequence models including the early accretion phase and used the resulting equilibrium models as input to calculate theoretical frequency spectra. These spectra were used to investigate different approach…
A series of spectra of the RV Tauri star R Scuti taken as it rose from a deep minimum to a bright maximum during 2013 October and November reveals major changes taking place in the photosphere and outer atmosphere of the star. This may be the first such series of spectra and demonstrates the capability of amateur spectroscopy for studying these complex stars.
Although pulsations of $δ$ Scuti type are not expected among Ap stars from a theoretical point of view, previous observations of the known $δ$ Scuti star HD21190 indicated a spectral classification F2 III SrEuSi:, making it the most evolved Ap star known. Our atmospheric chemical analysis based on recent HARPS observations confirms the presence of chemical peculiarities in HD21190. This star is also the only target known to host a magnetic field along with its $δ$ Scuti pulsation properties. Using an astrometric analysis, we show that HD21190 forms a physical binary system with the companion C…
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…
Modelling $δ$ Scuti pulsations: A new grid of p, g, and f modes across pre-main-sequence to post-main-sequence evolution
Centre for Astrophysics, University of Southern Queensland（南昆士兰大学天体物理中心）；Sydney Institute for Astronomy, School of Physics, University of Sydney（悉尼大学物理学院悉尼天文研究所）
The preliminary results of a multisite photometric campaign on the Pleiades Delta Scuti variable V650 Tauri are reported. The star was observed photometrically for 14 days during 2008 November from three observatories distributed in Longitude around the Earth. As a result of the preliminary analysis we have detected in V650 Tauri at least nine oscillation frequencies above a 99% confidence level.
The preliminary results of a three-site CCD photometric campaign are reported. The $δ$ Scuti variable V650 Tauri belonging to the Pleiades cluster was observed photometrically for 14 days on three continents during 2008 November. An overall run of 164 hr of data was collected. At least five significant frequencies for V650 Tauri have been detected.
We have searched for photometric variability in 95 Vir, a fast rotating, chromospherically active early F-type star, which was observed in the framework of Campaign 6 of the Kepler K2 mission. Available literature information on 95 Vir were procured, and well-established calibrations were employed to verify the derived astrophysical parameters. We have investigated the location of our target star in the M(Bol) versus log T(eff) diagram, which provides information on evolutionary status. We have discussed our results in detail, drawing on literature information and the theoretical predictions o…
Stellar components in binaries are subject to tidal forces which influence asteroseismic properties. Tidally pertubed pulsations have been reported for different objects but none of these are in their pre-main sequence phase of evolution. This makes RS Cha, consisting of two $δ$ Scuti stars and with pulsational characteristics influenced by tidal effects , the first such object observed. We aim to investigate the pulsational properties of the eclipsing binary RS Cha in terms of the theory of tidally perturbed pulsations. Based on photometric time series obtained from the TESS satellite, we per…
In some delta Scuti stars, only one or two radial modes are excited (usually the fundamental mode and/or first overtone mode) and the observed peak-to-peak amplitudes exceed 0.3 mag (V). These stars are known as High Amplitude Delta Scuti (HADS) variables. We here present a detailed photometric and spectroscopic analysis of the HADS star TYC 3637-1152-1. We have derived a metallicity close to solar, a spectral type of F4V and an age of log t = 9.1. Employing archival time series data from different sources, two frequencies f0 =10.034 c/d and f1 =12.681 c/d and their harmonics and linear combin…
Based on 2-minute cadence TESS data from sectors 1-50, we report the results of the systematic extraction of $δ$ Scuti-type pulsations in the 6431 eclipsing binaries with orbital periods shorter than 13 days. A total number of 242 pulsators were found in those systems, including 143 new discoveries. We examined their pulsation properties based on the H-R diagram and the relationships between the dominant pulsation period $P_{\rm dom}$, orbital period $P_{\rm orb}$, and effective temperature $T_{\rm eff}$. As a consequence, 216 targets are likely $δ$ Scuti stars (123 new), 11 likely $γ$ Doradus…
delta Scuti variables are stars which exhibit periodic changes in their luminosity through radial and non-radial pulsations. Internally, these stars have relatively small convective cores, and convective overshoot can significantly affect the size. Recently, models of radial pulsation in delta Scuti stars found a strong correlation between the pulsation constant (Q) as a function of effective temperature and the amount of convective overshoot within the star. However, only models with metallicities of Z = 0.02 were examined, leaving the dependence of this relationship on chemical composition u…
By using a non-local and time-dependent convection theory, we have calculated radial and low-degree non-radial oscillations for stellar evolutionary models with $M=1.4$--3.0\,$\mathrm{M}_\odot$. The results of our study predict theoretical instability strips for $δ$ Scuti and $γ$ Doradus stars, which overlap with each other. The strip of $γ$ Doradus is slightly redder in colour than that of $δ$ Scuti. We have paid great attention to the excitation and stabilization mechanisms for these two types of oscillations, and we conclude that radiative $κ$ mechanism plays a major role in the excitation …
Many stars exhibit stellar pulsations, favoring them for asteroseismic analyses. Interpreting the oscillations requires some knowledge of the oscillation mode geometry (spherical degree, radial and azimuthal orders). The delta Scuti stars (1.5 - 2.5 M_sol) often show just one or few pulsation frequencies. Although this may promise a successful seismological analysis, we may not know enough about either the mode or the star to use the oscillation frequency to improve the determination of the stellar model, or probe the star's structure. For the observed frequencies to be used successfully as se…
This paper presents a large amount of observations for the $δ$ Scuti star AN Lyncis carried out in 2001--2012. The extensive observations include two tri-continent campaigns coordinated in 2002 and 2011, respectively, and several single-site contributions throughout the period. The data in total have more than 104100 raw CCD frames and photoelectric records, which consist of 165 nights (about 816 hours) spanning over 3778 days. The final reduced light curves have more than 26500 data points (including those 3462 unpublished BYU data), from which we determined 306 new timings of maximum light. …
Identifying 850 delta Scuti pulsators in a narrow Gaia colour range with TESS 10-minute full-frame images
Sydney Institute for Astronomy, School of Physics, University of Sydney（悉尼大学物理学院天体物理研究所）；School of Physics, University of New South Wales（新南威尔士大学物理学院）；UNSW Data Science Hub, University of New South Wales（新南威尔士大学数据科学中心）；Institute for Astronomy, University of Hawai‘i（夏威夷大学天体物理研究所）；Centre for Astrophysics, University of Southern Queensland（南昆士兰大学天体物理学中心）
We present a study on the pulsations of the high-amplitude $δ$ Scuti star YZ Boo based on photometric observations in Johnson $V$ and $R$ bands with both the Nanshan 1-m telescope of Xinjiang Astronomical Observatory (XAO) and the Xinglong 85-cm telescope of National Astronomical Observatories, Chinese Academy of Sciences (NAOC). The Fourier analysis of the light curves reveals the fundamental radial mode and its five harmonics, with the fourth and the fifth newly detected. 39 new times of light maximum are determined from the light curves, and combined with those in the literature, we constru…
We investigate the pulsation properties of stellar models representative of $δ$ Scuti and $γ$ Doradus variables. We have calculated a grid of stellar models from 1.2 to 2.2 M$_{\odot}$, including the effects of both rotation and convective overshoot using MESA, and we investigate the pulsation properties of these models using GYRE. We discuss observable patterns in the frequency spacing for $p$ modes and the period spacings for g modes. Using the observable patterns in g mode period spacings, it may be possible to observationally constrain the convective overshoot and rotation of a model. We a…
The bRing robotic observatory network was built to search for circumplanetary material within the transiting Hill sphere of the exoplanet $β$ Pic b across its bright host star $β$ Pic. During the bRing survey of $β$ Pic, it simultaneously monitored the brightnesses of thousands of bright stars in the southern sky ($V$ $\simeq$ 4-8, $δ$ $\lesssim$ -30$^{\circ}$). In this work, we announce the discovery of $δ$ Scuti pulsations in the A-type star HD 156623 using bRing data. HD 156623 is notable as it is a well-studied young star with a dusty and gas-rich debris disk, previously detected using ALM…
The primary target in the seismo-field of CoRoT, HD 49434, known to be a bona fide hybrid gamma Doradus/delta Scuti, shows excited intermediate-order g modes. Time-Dependent Convection models, however, predict a range in frequency that is stable to pulsations, between the simultaneously excited high-order g modes (gamma Dor) and low-order p and g modes (delta Sct). Furthermore, theoretical studies based on model computations of delta Sct stars suggest that stochastically excited modes are likely to be observed. A pertinent question would then be to ask: Might those observed intermediate-order …
$δ$ Scuti stars are remarkable objects for asteroseismology. In spite of decades of investigations, there are still important questions about these pulsating stars to be answered, such as their positions in $\log$$T_{\rm eff}$ $-$ $\log g$ diagram, or the dependence of the pulsation modes on atmospheric parameters and rotation. Therefore, we performed a detailed spectroscopic study of $41$ $δ$ Scuti stars. The selected objects are located near the $γ$ Doradus instability strip to make a reliable comparison between both types of variables. Spectral classification, stellar atmospheric parameters…
F type stars are characterised by several physical processes such as different pulsation mechanisms, rotation, convection, diffusion, and magnetic fields. The rapidly rotating delta Scuti star beta Cas can be considered as a benchmark star to study the interaction of several of these effects. We investigate the pulsational and magnetic field properties of beta Cas. We also determine the star's apparent fundamental parameters and chemical abundances. Based on photometric time series obtained from three different space missions (BRITE-Constellation, SMEI, and TESS), we conduct a frequency analys…
Revisiting bright delta Scuti stars and their period-luminosity relation with TESS and Gaia DR3
University of Pennsylvania（宾夕法尼亚大学）；Sydney Institute for Astronomy, School of Physics, University of Sydney（悉尼大学物理学院天体物理研究所）；Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University（奥胡斯大学物理与天文系恒星天体物理中心）；Centre for Astrophysics, University of Southern Queensland（昆士兰南部大学天体物理中心）；Institute for Astronomy, University of Hawai‘i（夏威夷大学天体物理研究所）
The 76 frequencies determined from Kepler measurements of the A-type star KIC 9700322 can be understood in a rather simple way as the radial fundamental and first overtone radial modes, a nonradial \ell = 2 quintuplet, stellar rotation and combinations of all of these. Two low-frequency peaks are found: f=0.160 c/d and a 2f peak. We show from a variety of arguments that the low-frequency peak, f, (rather than the 2f peak) is the rotational frequency. The corresponding prediction of slow rotation is confirmed by a spectrum from which v sin i = 19 \pm 1 km/s is obtained. During rotation, the bri…
MOST observations and model analysis of the Herbig Ae star HD 34282 (V1366 Ori) reveal δ-Scuti pulsations. 22 frequencies are observed, 10 of which confirm those previously identified by Amado et al. (2006), and 12 of which are newly discovered in this work. We show that the weighted-average frequency in each group fits the radial p-mode frequencies of viable models. We argue that the observed pulsation spectrum extends just to the edge to the acoustic cut-off frequency and show that this also is consistent with our best-fitting models.
Hybrid $δ$ Scuti-$γ$ Doradus pulsating stars show acoustic ($p$) oscillation modes typical of $δ$ Scuti variable stars, and gravity ($g$) pulsation modes characteristic of $γ$ Doradus variable stars simultaneously excited. Observations from space missions like MOST, CoRoT, and \emph{Kepler} have revealed a large number of hybrid $δ$ Scuti-$γ$ Doradus pulsators, thus paving the way for a exciting new channel for asteroseismic studies. We perform a detailed asteroseismological modeling of five hybrid $δ$ Scuti-$γ$ Doradus stars. We employ a grid-based modeling approach to sound the internal stru…
As part of the NASA Kepler Guest Observer program, we requested and obtained long-cadence data on about 2700 faint (magnitude 14-16) Kepler stars with effective temperatures and surface gravities that lie near or within the pulsation instability region for main-sequence gamma Doradus and delta Scuti pulsating variables. These variables are of spectral type A-F with masses of 1.4 to 2.5 solar masses. The delta Scuti stars pulsate in radial and non-radial acoustic modes, with periods of a few hours (frequencies around 10 cycles/day), while gamma Doradus variables pulsate in nonradial gravity mod…
Pulsating extremely low-mass pre-white dwarf stars (pre-ELMV), with masses between ~0.15 Msun and ~0.30 Msun, constitute a new class of variable stars showing g- and possibly p-mode pulsations with periods between 320 and 6000 s, while main sequence delta Scuti stars, with masses between 1.2-2.5 Msun, pulsate in low-order g and p modes with periods in the range [700-28800] s. Interestingly enough, the instability strips of pre-ELM white dwarf and delta Scuti stars nearly overlap in the Teff vs. log g diagram, leading to a degeneracy when spectroscopy is the only tool to classify the stars and …
Hybrid stars of the γ Doradus and δ Scuti pulsation types have great potential for asteroseismic analysis to explore their interior structure. To achieve this, mode identi- fications of pulsational frequencies observed in the stars must be made, a task which is far from simple. In this work we begin the analysis by scrutinizing the frequencies found in the CoRoT photometric satellite measurements and ground-based high-resolution spectroscopy of the hybrid star HD 49434. The results show almost no consistency between the frequencies found using the two techniques and no characteristic period sp…
Thanks to relatively firm mode identification, possible based on period ratios only, High Amplitude Delta Scuti Stars pulsating in at least three radial modes are promising targets for asteroseismic inference. In this study we used the most numerous sample of HADS from the OGLE inner bulge fields that likely pulsate in either three or four radial modes simultaneously. We have computed a grid of pulsation models along evolutionary tracks and determined the physical parameters of stars by matching their pulsation periods and period ratios. For 176 HADS we determined physical parameters, i.e. mas…
The catalogue contains 199 confirmed cases of binary systems containing at least one pulsating component of δ Scuti type. The sample is divided into subgroups in order to describe the properties and characteristics of the δ Sct type stars in binaries according to their Roche geometry. Demographics describing quantitatively our knowledge for these systems as well as the distributions of their pulsating components in the Mass-Radius, Colour-Magnitude and Evolutionary Status-Temperature diagrams are presented and discussed. It is shown that a threshold of ~13 days of the orbital period regarding …
The preliminary results of new photometric observations of the $δ$ Scuti stars 7 Aql and 8 Aql are reported. 51 hr of $uvby-β$ photoelectric photometric data were obtained over the period June and July 2007 at the San Pedro Mártir Observatory, Mexico. Period analyses confirm the three pulsation modes discovered in 8 Aql in the framework of the STEPHI 2003 multisite campaign. For the star 7 Aql we were able to detect only the main pulsation modes. The standard magnitudes of both stars are obtained. The frequency, amplitude and phases of the frequency modes in different filters are presented.
IM Per is a triple star system whose eclipsing pair masses and radii are accurate to within 1 \%. The TESS light curve of the program target exhibits partial eclipses and multiple oscillations with mmag-level amplitudes. It is found that the oscillations affect eclipse timing measurements. Binary modeling of the high-quality TESS data indicates that the eclipsing components of the triple system are twin dwarfs with parameters of $M_2$/$M_1$ = 0.995, $R_2$/$R_1$ = 0.901, and $Δ$($T_{\rm eff,1}$--$T_{\rm eff,2}$) = 12 K in an eccentric ($e$ = 0.049), detached configuration. The third light of $l…
The present work contains light curve, spectroscopic and asteroseismic analyses for KIC 04851217 and KIC 10686876. These systems are detached eclipsing binaries hosting a pulsating component of delta Scuti type and have been observed with the unprecedented accuracy of the Kepler space telescope. Using ground based spectroscopic observations, the spectral types of the primary components of the systems were estimated as A6V and A5V for KIC 04851217 and KIC 10686876, respectively, with an uncertainty of one subclass. The present spectral classification together with literature radial velocities c…
Existence of pulsating stars in eclipsing binaries has been known for decades. These types of objects are extremely valuable systems for astronomical studies as they exhibit both eclipsing and pulsation variations. The eclipsing binaries are the only way to directly measure the mass and radius of stars with a good accuracy ($\leq$1\%), while the pulsations are a unique way to probe the stellar interior via oscillation frequencies. There are different types of pulsating stars existing in eclipsing binaries. One of them is the Delta Scuti variables. Currently, the known number of Delta Scuti sta…
BRITE-Constellation has obtained data for a few delta Scuti and gamma Doradus type stars. A short overview of the pulsational content found in five stars - beta Cassiopeiae, epsilon Cephei, M Velorum, beta Pictoris and QW Puppis - is given and the potential of BRITE-Constellation observations of delta Scuti and gamma Doradus pulsators is discussed.
