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 performed a systematic search based on TESS data to identify super-slowly rotating Ap (ssrAp) stars independently of the strengths of their magnetic fields, with the intention to characterise the distribution of the longest Ap star rotation periods in an unbiased manner. We find 67 Ap stars with no rotational variability in the northern ecliptic hemisphere TESS data. Among them, 46 are newly identified ssrAp star candidates, which is double the number previously found in the southern ecliptic hemisphere.
We confirm that super-slow rotation tends to occur less frequently in weakly magnetic Ap stars than in strongly magnetic stars. We present new evidence of the existence of a gap between ~2 kG and ~3 kG in the distribution of the magnetic field strengths of long period Ap stars. We also confirm that the incidence of roAp stars is higher than average in slowly rotating Ap stars. We report the unexpected discovery of nine definite and five candidate δ Sct stars, and of two eclipsing binaries. This work paves the way for a systematic, unbiased study of the longest period Ap stars, with a view to characterise the correlations between their rotational, magnetic, and pulsational properties.
Context. We present our findings on 18 formerly known ZZ Ceti stars observed by the TESS space telescope in 120s cadence mode during the survey observation of the southern ecliptic hemisphere. Aims. We focus on the frequency analysis of the space-based observations, comparing the results with the findings of the previous ground-based measurements. The frequencies detected by the TESS observations can serve as inputs for future asteroseismic analyses. Methods. We performed standard pre-whitening of the data sets to derive the possible pulsation frequencies of the different targets. In some case…
We report the results of our search for pulsating subdwarf B stars in Full Frame Images collected during Year 2 of the TESS mission and covering the northern ecliptic hemisphere. This is a continuation of our effort we presented in Paper I. We found 13 likely new pulsating subdwarf B stars, 10 pulsating candidates that are identified as other hot subdwarfs, and 30 spectroscopically unclassified objects that show amplitude spectra typical of pulsating subdwarf B stars. We found 506 variable objects, most of them spectroscopically unclassified, hence their specific variability class yet to be co…
We present an update on the variable star survey performed on the TESS 30 min Full Frame Image (FFI) data reported by our first two papers in this series. This update includes a contamination analysis in order to identify false positives and analysis of the TESS 10 min FFI data collected during Years 3 and 4 of the mission. We clarify the variability status of 2 995 targets identifying 1 403 variable stars. In addition, we spectroscopically classify 24 pre-filtered targets sampled with the 10 min FFI data and discover 11 new sdB pulsators. Future follow-up space- and/or ground-based data of va…
We present results of a Transiting Exoplanet Survey Satellite (TESS) search for short-period pulsations in compact stellar objects observed in years 1 and 3 of the TESS mission, during which the southern ecliptic hemisphere was targeted. We describe the TESS data used and the details of the search method. For many of the targets, we use unpublished spectroscopic observations to classify the objects. From the TESS photometry, we clearly identify 43 short-period hot-subdwarf pulsators, including 32 sdB stars, eight sdOB stars, two sdO stars, and, significantly, one He-sdOB star, which is the fir…
We report the results of our search for pulsating subdwarf B stars in Full Frame Images, sampled at 30 min cadence and collected during Year 1 of the TESS mission. Year 1 covers most of the southern ecliptic hemisphere. The sample of objects we checked for pulsations was selected from a subdwarf B stars database available to public. Only two positive detections have been achieved, however, as a by-product of our search we found 1807 variable objects, most of them not classified, hence their specific variability class cannot be confirmed at this stage. Our preliminary discoveries include: two n…
TESS photometry is analyzed for 432 classical Be stars observed in the first year of the mission. The often complex and diverse variability of each object in this sample is classified to obtain an understanding of the behavior of this class as a population. 98\% of the systems are variable above the noise level, with timescales spanning nearly the entire range of what is accessible with TESS, from tens of minutes to tens of days. The variability seen with TESS is summarized as follows. Nearly every system contains multiple periodic signals in the frequency regime between about 0.5 -- 4 d$^{-1}…
Although the Transiting Exoplanet Survey Satellite (TESS) primary mission observed the northern and southern ecliptic hemispheres, generally avoiding the ecliptic, and the Kepler space telescope during the K2 mission could only observe near the ecliptic, many of the K2 fields extend far enough from the ecliptic plane that sections overlap with TESS fields. Using photometric observations from both K2 and TESS, combined with archival spectroscopic observations, we globally modeled four known planetary systems discovered by K2 that were observed in the first year of the primary TESS mission. Spec…
Superflares on solar-type stars has been a rapidly developing field ever since the launch of $\it Kepler$. Over the years, there have been several studies investigating the statistics of these explosive events. In this study, we present a statistical analysis of stellar flares on solar-type stars made using photometric data in 2-min cadence from $\it TESS$ of the whole southern hemisphere (sectors 1 - 13). We derive rotational periods for all stars in our sample from rotational modulations present in the lightcurve as a result of large starspot(s) on the surface. We identify 1980 stellar flare…
In this work, we present the analysis of 976 814 FGKM dwarf and sub-giant stars in the TESS Full Frame Images (FFIs) of the Southern ecliptic hemisphere. We present a new pipeline, DIAmante, developed to extract optimized, multi-sector photometry from TESS FFIs and a classifier, based on the Random Forest technique, trained to discriminate plausible transiting planetary candidates from common false positives. A new statistical model was developed to provide the probability of correct identification of the source of variability. We restricted the planet search to the stars located in the least …
The scope of the project "A PSF-based Approach to TESS High Quality data Of Stellar clusters" (PATHOS) is the extraction and analysis of high-precision light curves of stars in stellar clusters and young associations for the identification of candidate exoplanets and variable stars. The cutting-edge tools used in this project allow us to measure the real flux of stars in dense fields, minimising the effects due to contamination by neighbour sources. We extracted about 200 000 light curves of stars in 645 open clusters located in the southern ecliptic hemisphere and observed by TESS during the …
We embarked on a high-resolution optical spectroscopic survey of bright Transiting Exoplanet Survey Satellite (TESS) stars around the Northern Ecliptic Pole (NEP), dubbed the Vatican-Potsdam-NEP (VPNEP) survey. Our NEP coverage comprises 1067 stars, of which 352 are bona fide dwarf stars and 715 are giant stars, all cooler than spectral type F0 and brighter than V=8. m 5. Our aim is to characterize these stars for the benefit of future studies in the community. We analyzed the spectra via comparisons with synthetic spectra. Particular line profiles were analyzed by means of eigen-profiles, equ…
The Kepler spacecraft provided the first long-baseline, high-precision photometry for large numbers of stars. This enabled the discovery of thousands of new exoplanets, and the characterization of myriad astrophysical phenomena. However, one of the challenges with interpreting Kepler data has been that no instrument has provided a comparison dataset. Therefore, the replication of Kepler time-series data has remained elusive. The Transiting Exoplanet Survey Satellite (TESS) launched in April 2018 and began science operations in July 2018. During the TESS primary mission, it will survey 85% of t…
Tidal forces are important for understanding how close binary stars and compact exoplanetary systems form and evolve. However, tides are difficult to model and significant uncertainties exist about the strength of tides. Here, we investigate tidal circularization in close binaries using a large sample of well-characterised eclipsing systems. We searched TESS photometry from the southern hemisphere for eclipsing binaries. We derive best-fit orbital and stellar parameters by jointly modelling light curves and spectral energy distributions. To determine the eccentricity distribution of eclipsing …
It has long been suspected that tidal forces in close binary stars could modify the orientation of the pulsation axis of the constituent stars. Such stars have been searched for, but until now never detected. Here we report the discovery of tidally trapped pulsations in the ellipsoidal variable HD 74423 in TESS space photometry data. The system contains a Delta Scuti pulsator in a 1.6-d orbit, whose pulsation mode amplitude is strongly modulated at the orbital frequency, which can be explained if the pulsations have a much larger amplitude in one hemisphere of the star. We interpret this as an…
The long-term, high precision photometry delivered by the Transiting Exoplanet Survey Satellite (TESS) enables us to gain new insight into known and hitherto well-studied stars. In this paper, we present the result of our TESS study of the photospheric activity of the rapid rotator AB Doradus. Due to its favorable position near the southern ecliptic pole, the TESS satellite recorded almost 600 rotations of AB Doradus with high cadence, allowing us to study starspots and flares on this ultra-active star. The observed peak-to-peak variation of the rotational modulations reaches almost 11 %, and …
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…
We present simultaneous multiwavelength observations of the ultra-active star AB~Doradus obtained in the X-ray range with the eROSITA instrument on board the Russian--German Spectrum-Roentgen-Gamma mission (SRG), and in the optical range obtained with the Transiting Exoplanet Survey Satellite (TESS). Thanks to its fortuitous location in the vicinity of the southern ecliptic pole, AB~Dor was observed by these missions simultaneously for almost 20 days. With the hitherto obtained data we study the long-term evolution of the X-ray flux from AB~Dor and the relation between this observable and the …
The All-Sky Automated Survey for Supernovae (ASAS-SN) provides long baseline (${\sim}4$ yrs) light curves for sources brighter than V$\lesssim17$ mag across the whole sky. The Transiting Exoplanet Survey Satellite (TESS) has started to produce high-quality light curves with a baseline of at least 27 days, eventually for most of the sky. The combination of ASAS-SN and TESS light curves probes both long and short term variability in great detail, especially towards the TESS continuous viewing zones (CVZ) at the ecliptic poles. We have produced ${\sim}1.3$ million V-band light curves covering a t…
We report the discovery of 74 new pulsating DA white dwarf stars, or ZZ Cetis, from the data obtained by the Transiting Exoplanet Survey Satellite (TESS) mission, from Sectors 1 to 39, corresponding to the first 3 cycles. This includes objects from the Southern Hemisphere (Sectors 1-13 and 27-39) and the Northern Hemisphere (Sectors 14-26), observed with 120 s- and 20 s-cadence. Our sample likely includes 13 low-mass and one extremely low-mass white dwarf candidate, considering the mass determinations from fitting Gaia magnitudes and parallax. In addition, we present follow-up time series phot…
Alpha Cygni Variables as Seen from the Transiting Exoplanet Survey Satellite
Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）；University of New Mexico（新墨西哥大学）；New Mexico Institute of Mining and Technology（新墨西哥矿业与技术学院）；New Mexico State University（新墨西哥州立大学）
The Transiting Exoplanet Survey Satellite (TESS) is the first high-precision full-sky photometry survey in space. We present light curves from a magnitude limited set of stars and other stationary luminous objects from the TESS Full Frame Images, as reduced by the MIT Quick Look Pipeline (QLP). Our light curves cover the full two-year TESS Primary Mission and include $\sim$ 14,770,000 and $\sim$ 9,600,000 individual light curve segments in the Southern and Northern ecliptic hemispheres, respectively. We describe the photometry and detrending techniques we used to create the light curves, and c…
In our previous study of low mass stars using TESS, we found a handful which show a periodic modulation on a period <1 d but also displayed no flaring activity. Here we present the results of a systematic search for Ultra Fast Rotators (UFRs) in the southern ecliptic hemisphere which were observed in 2 min cadence with TESS. Using data from Gaia DR2, we obtain a sample of over 13,000 stars close to the lower main sequence. Of these, we identify 609 stars which lie on the lower main sequence and have a periodic modulation <1 d. The fraction of stars which show flares appears to drop significant…
The Transiting Exoplanet Survey Satellite (TESS) is NASA's latest space telescope dedicated to the discovery of transiting exoplanets around nearby stars. Besides the main goal of the mission, asteroseismology is an important secondary goal and very relevant for the high-quality time series that TESS will make during its two year all-sky survey. Using TESS for asteroseismology introduces strong timing requirements, especially for coherent oscillators. Although the internal clock on board TESS is precise in its own time, it might have a constant drift and will thus need calibration, or offsets …
The symphony of pulsations and binarity among massive stars using HERMES spectroscopy and TESS photometry
Newcastle University（纽卡斯尔大学）；KU Leuven（荷语鲁汶大学）；University of Amsterdam（阿姆斯特丹大学）；Tel Aviv University（特拉维夫大学）；Royal Observatory of Belgium（比利时皇家天文台）；Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文学中心）
Investigating Gaia EDR3 parallax systematics using asteroseismology of Cool Giant Stars observed by Kepler, K2, and TESS I. Asteroseismic distances to 12,500 red-giant stars
The solar-like latitudinal distribution of flaring activities revealed by TESS, APOGEE and GALAH
Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台光学天文重点实验室）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学天文与前沿科学研究院）；School of Astronomy and Space Sciences, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）
Doppler imaging combined with high-cadence photometry. I. Revisiting the surface of a pre-main-sequence flare star
Kyoto University（京都大学）；Ankara University（安卡拉大学）；Max-Planck-Institut für Sonnensystemforschung（马克斯·普朗克太阳系研究所）；Hitotsubashi University（一桥大学）；The Hakubi Center for Advanced Research, Kyoto University（京都大学哈库比高级研究中心）；NASA Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）；The Catholic University of America（美利坚天主教大学）；National Astronomical Observatory of Japan（日本国立天文台）；Nishi-Harima Astronomical Observatory, University of Hyogo（兵库县立西播磨天文台）
We report the delivery to the Mikulski Archive for Space Telescopes of target pixel and light curve files for up to 160,000 targets selected from full-frame images (FFI) for each TESS Northern hemisphere observing sector. The data include calibrated target pixels, simple aperture photometry flux time series, and presearch data conditioning corrected flux time series. These data provide TESS users with high quality, uniform pipeline products for a selection of FFI targets, that would otherwise not be readily available. Additionally, we deliver cotrending basis vectors derived from the FFI targe…
Context: the theory of stellar evolution presents shortcomings when confronted with asteroseismic probes of interior physical properties. The differences between observations and theory are often great because stellar models have mainly been calibrated from observables connected to the surface of stars. Period-spacing patterns caused by gravity modes are a particularly powerful asteroseismic tool that are useful for probing the near-core rotation and mixing of chemical elements in main-sequence stars with convective cores. Aims: we aim to compose a catalog of intermediate-mass stars in the TES…
In fulfilling the aims of the planetary and asteroseismic research missions, such as that of the NASA Transiting Exoplanet Survey Satellite (TESS) space telescope, accurate stellar atmospheric parameters and a detailed chemical composition are required as input. We have observed high-resolution spectra for all 848 bright (V<8 mag) stars that are cooler than F5 spectral class in the area up to 12 deg surrounding the northern TESS continuous viewing zone and uniformly determined the main atmospheric parameters, ages, orbital parameters, velocity components, and precise abundances of up to 24 che…
Apache Point Observatory follow-up of ACcelerating Candidate ExopLanet host Stars (APO ACCELS): Ages for 166 Accelerating Stars in the Northern Hemisphere
The Transiting Exoplanet Survey Satellite (TESS) will provide high precision time-series photometry for millions of stars with at least a half-hour cadence. Of particular interest are the circular regions of 12-degree radius centered around the ecliptic poles that will be observed continuously for a full year. Spectroscopic stellar parameters are desirable to characterize and select suitable targets for TESS, whether they are focused on exploring exoplanets, stellar astrophysics, or Galactic archaeology. Here, we present spectroscopic stellar parameters ($T_{\rm eff}$, $\log g$, [Fe/H], $v \si…
We present a comprehensive catalog of the dippers---young stellar objects that exhibit episodic dimming---derived from the one year's worth of data of Transiting Exoplanet Survey Satellite ($ TESS$) full-frame images. In the survey, we found 35 dippers using the convolutional neural network, most of them newly discovered. Although these dippers are widely distributed over the first half-hemisphere that $TESS$ surveyed, we identified the majority's membership with the nearest association Scorpius--Centaurus, Velorum OB2, and nearby Orion molecular cloud complex. However, several dippers are lik…
Superflares, as strong explosions on stars, have been well studied with the progress of space time-domain astronomy. In this work, we present the study of superflares on solar-type stars using Transiting Exoplanet Survey Satellite ({\em{TESS}}) data. 13 sectors of observations during the first year of the {\em TESS} mission have covered the southern hemisphere of the sky, containing 25,734 solar-type stars. We verified 1,216 superflares on 400 solar-type stars through automatic search and visual inspection with 2-minute cadence data. Our result suggests a higher superflare frequency distributi…
In this work, 1272 superflares on 311 stars are collected from 22,539 solar-type stars from the second-year observation of Transiting Exoplanet Survey Satellite (TESS), which almost covered the northern hemisphere of the sky. Three superflare stars contain hot Jupiter candidates or ultrashort-period planet candidates. We obtain $γ= -1.76\pm 0.11$ of the correlation between flare frequency and flare energy ($dN/dE\propto E^{-γ}$) for all superflares and get $β=0.42\pm0.01$ of the correlation between superflare duration and energy ($T_{\text {duration }} \propto E^β$), which supports that a simi…
The knowledge of the ages of stars hosting exoplanets allows us to obtain an overview on the evolution of exoplanets and understand the mechanisms affecting their life. The measurement of the ages of stars in the Galaxy is usually affected by large uncertainties. An exception are the stellar clusters: for their coeval members, born from the same molecular cloud, ages can be measured with extreme accuracy. In this context, the project PATHOS is providing candidate exoplanets orbiting members of stellar clusters and associations through the analysis of high-precision light curves obtained with c…
Driven largely by multiple ground-based radial-velocity (RV) surveys and photometric space missions such as Kepler and K2, the discovery of new exoplanets has increased rapidly since the early 2000s. However, due to a target selection bias in favor of main-sequence stars, only a handful of transiting planets have been found orbiting evolved hosts. These planets, most of which are giants, hold important information regarding the formation and evolution of planetary systems. In this thesis, I sought to increase the sample of known giant planets orbiting red-giant stars, focusing on data from NAS…
We present the discovery and validation of a three-planet system orbiting the nearby (31.1 pc) M2 dwarf star TOI-700 (TIC 150428135). TOI-700 lies in the TESS continuous viewing zone in the Southern Ecliptic Hemisphere; observations spanning 11 sectors reveal three planets with radii ranging from 1 R$_\oplus$ to 2.6 R$_\oplus$ and orbital periods ranging from 9.98 to 37.43 days. Ground-based follow-up combined with diagnostic vetting and validation tests enable us to rule out common astrophysical false-positive scenarios and validate the system of planets. The outermost planet, TOI-700 d, has …
We measure rotation periods and sinusoidal amplitudes in Evryscope light curves for 122 two-minute K5-M4 TESS targets selected for strong flaring. The Evryscope array of telescopes has observed all bright nearby stars in the South, producing two-minute cadence light curves since 2016. Long-term, high-cadence observations of rotating flare stars probe the complex relationship between stellar rotation, starspots, and superflares. We detect periods from 0.3487 to 104 d, and observe amplitudes from 0.008 to 0.216 g' mag. We find the Evryscope amplitudes are larger than those in TESS with the effec…
Chromospheric activity cycles are common in late-type stars; however, only a handful of coronal activity cycles have been discovered. \ihor\ is the most active and youngest star with known coronal cycles. It is also a young solar analog, and we are likely facing the earliest cycles in the evolution of solar-like stars, at an age (~600 Myr) when life appeared on Earth. Our aim is to confirm the ~1.6 yr coronal cycle and characterize its stability over time. We use X-ray observations of iota Hor to study the corona of a star representing the solar past through variability, thermal structure, and…
We search for superflares from 4,068 cool stars in 2+ years of Evryscope photometry, focusing on those with high-cadence data from both Evryscope and TESS. The Evryscope array of small telescopes observed 575 flares from 284 stars, with a median energy of 10^34.0 erg. Since 2016, Evryscope has enabled the detection of rare events from all stars observed by TESS through multi-year, high-cadence continuous observing. We report ~2X the previous largest number of 10^34 erg high-cadence flares from nearby cool stars. We find 8 flares with amplitudes of 3+ g' magnitudes, with the largest reaching 5.…
CO~Cam (TIC 160268882) is the second ``single-sided pulsator'' to be discovered. These are stars where one hemisphere pulsates with a significantly higher amplitude than the other side of the star. CO~Cam is a binary star comprised of an Am $δ$~Sct primary star with $T_{\rm eff} = 7070 \pm 150$\,K, and a spectroscopically undetected G main-sequence secondary star. The dominant pulsating side of the primary star is centred on the L$_1$ point. We have modelled the spectral energy distribution combined with radial velocities, and independently the {\em TESS} light curve combined with radial veloc…
Since 2011, the SOPHIE spectrograph has been used to search for Neptunes and super-Earths in the Northern Hemisphere. As part of this observational program, 290 radial velocity measurements of the 6.4 V magnitude star HD 158259 were obtained. Additionally, TESS photometric measurements of this target are available. We present an analysis of the SOPHIE data and compare our results with the output of the TESS pipeline. The radial velocity data, ancillary spectroscopic indices, and ground-based photometric measurements were analyzed with classical and $\ell_1$ periodograms. The stellar activity w…
