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-resolution ($R\simeq65\,000$), high signal-to-noise ($\sim120$) spectra to provide new orbital parameters for this, the only known roAp star to be in a short period binary ($P_{\rm orb}=93.266$ d). We find the system to be more eccentric than previously thought, with $e=0.317$, and suggest the companion is a mid-F to early-K star. We find no significant trend in the average pulsation mode amplitude with time, as measured by TESS, implying that the companion does not have an affect on the pulsation in this roAp star. We suggest further photometric observations of this star, and further studies to find more roAp stars in close binaries to characterise how binarity may affect the detection of roAp pulsations.
From sector 1--44 {\em TESS} observations, 19 new roAp stars, 103 ostensibly non-peculiar stars with roAp-like frequencies and 617 $δ$~Scuti stars with independent frequencies typical of roAp stars were found. Examination of all chemically peculiar stars observed by {\em TESS} resulted in the discovery of 199 Ap stars which pulsate as $δ$~Sct or $γ$~Dor variables. The fraction of pulsating Ap stars is the same as the fraction of pulsating chemically normal stars. There is no distinct separation in frequency or radial order between chemically peculiar $δ$~Sct stars and roAp stars. In fact, all …
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 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 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 …
Rapidly oscillating Ap stars observed with TESS. The LAMOST Ap sample and 49 Cam
Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto（波尔图大学空间与天体物理研究所）；Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto（波尔图大学理学院物理与天文学系）；South African Astronomical Observatory（南非天文台）；School of Physics, Engineering and Technology, University of York（约克大学物理、工程与技术学院）；DTU Space, Technical University of Denmark（丹麦技术大学空间中心）；Centre for Space Research, North-West University（西北大学太空研究中心）；Jeremiah Horrocks Institute, University of Lancashire（兰开夏大学杰里米亚·霍罗克斯研究所）；Department of Astronomy, Cornell University（康奈尔大学天文学系）；Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM（巴黎萨克雷大学、巴黎西岱大学、法国原子能与替代能源委员会、法国国家科学研究中心、天体物理学与信息分子研究所）
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…
Before the launch of the Kepler Space Telescope, most studies of the rapidly oscillating Ap (roAp) stars were conducted with ground-based photometric $B$ observations, supplemented with high-resolution time-resolved spectroscopy and some space observations with the WIRE, MOST and BRITE satellites. These modes of observation often only provided information on a single star at a time, however, Kepler provided the opportunity to observe hundreds of thousands of stars simultaneously. Over the duration of the primary 4-yr Kepler mission, and its 4-yr reconfigured K2 mission, the telescope observed …
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 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…
The TESS space mission is producing superb data for asteroseismology, eclipsing binary stars, gyrochronology, and other fields of stellar astronomy where the data are variable light curves. We show that TESS data are excellent for astrophysical inference from peculiar stars that show variability. The Ap stars have the strongest magnetic fields of any main-sequence stars. Some have been shown to have rotation periods of months to centuries. The astrophysical cause of their slow rotation -- the braking mechanism -- is not known with certainty. These stars are rare: there are currently about 3 do…
Classification of over 50000 TESS stars in sectors 1-18 has resulted in the detection of 766 pulsating main sequence B stars as well as over 5000 $δ$ Scuti, 2300 $γ$ Doradus and 114 roAp candidates. It is found that a distinct group of $β$ Cephei stars, defined as B stars with frequencies greater than 2.5 d$^{-1}$ and predicted by models, does not exist. Instead, high frequencies are to be found over the whole B-star range, eventually merging with $δ$ Scuti stars. The cool B stars pulsating in high frequencies are the Maia variables. It is shown that Maia variables are not rapidly-rotating $β$…
The rotation periods of the magnetic Ap stars span five to six orders of magnitude. Period differentiation must have taken place at the pre-main sequence stage, but the physical processes that lead to it remain elusive. The study of Ap stars that have rotation periods of tens to hundreds of years represents a promising avenue to gain additional insight into the origin and evolution of rotation in Ap stars. Historically, almost all the longest period Ap stars known have been found to be strongly magnetic; very few weakly magnetic Ap stars with very long periods have been identified and studied.…
We present a sample of 2700 Ap stars in LAMOST DR9. The candidates are first selected to be in a temperature range typical of Ap stars by using the $BP$-$RP$ color index from Gaia DR3. Then the 5200\,Å flux depression features characteristic of Ap stars are visually checked in LAMOST DR9 spectra. The detailed spectral features are given by applying a modified spectral classification program, MKCLASS. Stellar parameters of these Ap stars such as $T_{\rm eff}$, $\log g$, [Fe/H], [Si/H], and $v{\sin}i$ are either extracted from a hot star catalog or derived through empirical relations and then a …
We present photometric and spectroscopic observations of the unusual Type Ia supernova ASASSN-18tb, including a series of SALT spectra obtained over the course of nearly six months and the first observations of a supernova by the Transiting Exoplanet Survey Satellite (TESS). We confirm a previous observation by Kollmeier et al. (2019) showing that ASASSN-18tb is the first relatively normal Type Ia supernova to exhibit clear broad ($\sim1000$ km s$^{-1}$) H$α$ emission in its nebular phase spectra. We find that this event is best explained as a sub-Chandrasekhar mass explosion with $M_{Ni} \app…
We report the detection and characterization of a new magnetospheric star, HD 135348, based on photometric and spectropolarimetric observations. The TESS light curve of this star exhibited variations consistent with stars known to possess rigidly rotating magnetospheres (RRMs), so we obtained spectropolarimetric observations using the Robert Stobie Spectrograph (RSS) on the Southern African Large Telescope (SALT) at four different rotational phases. From these observations, we calculated the longitudinal magnetic field of the star $\langle B_z \rangle$, as well as the Alfvén and Kepler radii, …
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…
Asteroseismic analysis of RY Leporis: the post-main sequence HADS in a binary system
University of Wroclaw（弗罗茨瓦夫大学）；Instituto de Astrofísica de Andalucía, CSIC（安达卢西亚天体物理研究所，西班牙国家研究委员会）；STAR Institute, University of Liège（列日大学STAR研究所）；ELTE Eötvös Lòrànd University（罗兰大学）
Young exoplanets are snapshots of the planetary evolution process. Planets that orbit stars in young associations are particularly important because the age of the planetary system is well constrained. We present the discovery of a transiting planet larger than Neptune but smaller than Saturn in the 45 Myr Tucana-Horologium young moving group. The host star is a visual binary, and our follow-up observations demonstrate that the planet orbits the G6V primary component, DS Tuc A (HD 222259A, TIC 410214986). We first identified transits using photometry from the Transiting Exoplanet Survey Satell…
We report the detection of radio emission from the known X-ray flaring star EXO 040830$-$7134.7 during MeerKAT observations of the nearby cataclysmic variable VW Hydri. We have three epochs of MeerKAT observations, where the star is not detected in the first epoch, is detected in the second epoch, and is marginally detected in the third epoch. We cannot distinguish whether the detection is quiescent emission or a transient radio burst. If we assume the radio detection is quiescent emission the source lies somewhat to the right of the Güdel-Benz relation; however, if we assume the upper-limit o…
