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 effect of the magnetic field on the structure of their atmospheres can be studied with greatest detail and accuracy. Our results show that we may detect changes in the transversal field component in Fe I and rare-earth lines possessing large second-order Lande factors. Such variability can be due to the impact of pulsation on the transverse magnetic field, causing changes in the obliquity angles of the magnetic force lines. Further studies of roAp stars in linear polarized light and subsequent detailed modelling are necessary to improve our understanding of the involved physics.
We report results from the TESS photometric data and new high-resolution spectra of the Algol system X Tri showing short-period pulsations. From the echelle spectra, the radial velocities of the eclipsing pair were measured, and the rotational rate and effective temperature of the primary star were obtained to be $v_1$$\sin$$i=84\pm6$ km s$^{-1}$ and $T_{\rm eff,1}=7900 \pm 110$ K, respectively. The synthetic modeling of these observations implies that X Tri is in synchronous rotation and is physically linked to a visual companion TIC 28391715 at a separation of about 6.5 arcsec. The absolute …
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 study the $δ$ Scuti -- red giant binary KIC9773821, the first double-pulsator binary of its kind. It was observed by \textit{Kepler} during its four-year mission. Our aims are to ascertain whether the system is bound, rather than a chance alignment, and to identify the evolutionary state of the red giant via asteroseismology. An extension of these aims is to determine a dynamical mass and an age prior for a $δ$ Sct star, which may permit mode identification via further asteroseismic modelling. We determine spectroscopic parameters and radial velocities (RVs) for the red giant component usin…
Tidally tilted pulsators (TTPs) are an intriguing new class of oscillating stars in binary systems; in such stars, the pulsation axis coincides with the line of apsides, or semi-major axis, of the binary. All three TTPs discovered so far have been $δ$~Scuti stars. In this Letter, we report the first conclusive discovery of tidally tilted pulsations in a subdwarf B (sdB) star. HD 265435 is an sdB--white dwarf binary with a 1.65-hr period that has been identified and characterized as the nearest potential Type Ia supernova progenitor. Using TESS 20-s cadence data from Sectors 44 and 45, we show …
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…
Wildly Oscillating Stars -- Unexplained dense ridge-like frequency agglomerations in A and F type pulsators
DTU Space, Technical University of Denmark（丹麦技术大学空间中心）；Centre for Astrophysics, University of Southern Queensland（南昆士兰大学天体物理中心）；Centre for Space Research, North-West University（西北大学太空研究中心）；Jeremiah Horrocks Institute, University of Lancashire（兰开夏大学杰里米·霍罗克斯研究所）；Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney（悉尼大学物理学院悉尼天文研究所）；Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文学中心）；TAPIR, Mailcode 350-17, California Institute of Technology（加州理工学院TAPIR）；LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris（巴黎天文台LESIA实验室（隶属巴黎文理研究大学、法国国家科学研究中心、索邦大学、巴黎大学））；Instutute for Physics and Astronomy, Aarhus University（奥胡斯大学物理与天文学研究所）；STAR Institute, University of Liège（列日大学STAR研究所）
Rapidly varying A-type stars in the SuperWASP archive
对凌日系外行星的搜索已经产生了数百万颗恒星的大量时间分辨光度数据。其中一个主要的地面调查是SuperWASP项目。我们目前的调查超过150万的A型星在寻找高频脉动使用SuperWASP测光的初步结果。在宽波段测光中，我们能够探测到低至0.5毫磁级的脉动。这使得发现了几个快速振荡的Ap星和超过200个频率超过50 d $^{-1}$的盾牌座δ星，以及至少一个脉动sdB星。如此大量的结果使我们能够统计研究roAp和delta Scuti星之间的频率重叠，并利用现有数据探索更高的频率区域。
Context: Rapid rotation is a common feature of early-type stars but which remains a challenge for the models. The understanding of its effect on stellar evolution is however imperative to interpret the observed properties of numerous stars. Aims: We wish to bring more observational constraints on the properties of fast rotating stars, especially on their oscillation modes. Methods: We focus on the nearby star Altair which is known as a very rapidly rotating star with an equatorial velocity estimated recently at 313 km/s. We observed this star with the high-resolution spectropolarimeter Neo-Nar…
IZ Tel and UW Vir: Southern oscillating eclipsing Algol systems with active mass transfer
Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens（雅典国家天文台天文学、天体物理学、空间应用与遥感研究所）；The University of Queensland（昆士兰大学）；Astronomical Association of Queensland（昆士兰天文协会）；Çanakkale Onsekiz Mart University（恰纳卡莱18马月大学）
This work presents an extensive analysis of the properties of three southern semi-detached eclipsing binaries hosting a pulsating component, namely HM Pup, V632 Sco, and TT Vel. Systematic multi-filtered photometric observations were obtained using telescopes located in Australia and Chile mostly between 2018-2021. These observations were combined with data from the Transiting Exoplanet Survey Satellite (TESS) mission for a detailed analysis of pulsations. Spectral types and radial velocities were determined from spectra obtained with the Australian National University's 2.3 m telescope and Wi…
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…
The contour method is a new approach to calculating the non-adiabatic pulsation frequencies of stars. These frequencies can be found by solving for the complex roots of a characteristic equation constructed from the linear non-adiabatic stellar pulsation equations. A complex-root solver requires an initial trial frequency for each non adiabatic root. A standard method for obtaining initial trial frequencies is to use a star's adiabatic pulsation frequencies, but this method can fail to converge to non-adiabatic roots, especially as the growth and/or damping rate of the pulsations becomes large…
We report about HD 213258, an Ap star that we recently identified as presenting a unique combination of rare, remarkable properties. Our study of this star is based on ESPaDOnS Stokes I and V data obtained at 7 epochs spanning a time interval slightly shorter than 2 years, on TESS data, and on radial velocity measurements from the CORAVEL data base. We confirm that HD 213258 is definitely an Ap star. We found that, in its spectrum, the Fe II λ6149.2 Å line is resolved into its two magnetically split components. The mean magnetic field modulus of HD 213258, <B> ~ 3.8 kG does not show significan…
