TESS Light Curve Research Articles

PHOTOMETRIC ANALYSIS OF ECLIPSING BINARIES: VY UMI, RU UMI AND GSC 04364-00648

We present the photometric analysis of BVR and TESS light curves of three eclipsing binaries, together with their period changes considering archival data and new minima times from our and TESS observations. For the first time we detected wave-like variations with low-amplitude in O − C residua of RU UMi, which can be interpreted as a consequence of the light-time effect caused by the 3rd component with period 7370 days. The period increase detected in the VY UMi system corresponds to mass transfer from the secondary to the primary component. For the GSC 04364-00648 binary system we find quadratic changes on the O − C diagram, which correspond to a period decrease. We cannot make assumptions about their nature, mainly due to short time of observation and uneven coverage of O − C diagram. We also determined the absolute parameter of their components using the photometric solution and GAIA distances.

TOI-2525 b and c: A Pair of Massive Warm Giant Planets with Strong Transit Timing Variations Revealed by TESS* ∗ Based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere under MPG program 0104.A-9007. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

The K-type star TOI-2525 has an estimated mass of M = M ⊙ and radius of R = R ⊙ observed by the TESS mission in 22 sectors (within sectors 1 and 39). The TESS light curves yield significant transit events of two companions, which show strong transit timing variations (TTVs) with a semiamplitude of ∼6 hr. We performed TTV dynamical and photodynamical light-curve analysis of the TESS data combined with radial velocity measurements from FEROS and PFS, and we confirmed the planetary nature of these companions. The TOI-2525 system consists of a transiting pair of planets comparable to Neptune and Jupiter with estimated dynamical masses of m b = and m c = M Jup, radii of r b = and r c = R Jup, and orbital periods of P b = and P c = days for the inner and outer planet, respectively. The period ratio is close to the 2:1 period commensurability, but the dynamical simulations of the system suggest that it is outside the mean-motion resonance (MMR) dynamical configuration. Object TOI-2525 b is among the lowest-density Neptune-mass planets known to date, with an estimated median density of ρ b = g cm−3. The TOI-2525 system is very similar to the other K dwarf systems discovered by TESS, TOI-2202 and TOI-216, which are composed of almost identical K dwarf primaries and two warm giant planets near the 2:1 MMR.

A puffy polar planet

TOI-640 b is a hot, puffy Jupiter with a mass of 0.57 ± 0.02 MJ and radius of 1.72 ± 0.05 RJ, orbiting a slightly evolved F-type star with a separation of 6.33−0.06+0.07 R⋆. Through spectroscopic in-transit observations made with the HARPS spectrograph, we measured the Rossiter-McLaughlin effect, analysing both in-transit radial velocities and the distortion of the stellar spectral lines. From these observations, we find the host star to have a projected obliquity of λ = 184 ± 3°. From the TESS light curve, we measured the stellar rotation period, allowing us to determine the stellar inclination, i⋆ = 23−2+3°, meaning we are viewing the star pole-on. Combining this with the orbital inclination allowed us to calculate the host star obliquity, ψ = 104 ± 2°. TOI-640 b joins a group of planets orbiting over stellar poles within the range 80°–125°. The origin of this orbital configuration is not well understood.

Examining the Rotation Period Distribution of the 40 Myr Tucana–Horologium Association with TESS

The Tucana–Horologium association (Tuc-Hor) is a 40 Myr old moving group in the southern sky. In this work, we measure the rotation periods of 313 Tuc-Hor objects with TESS light curves derived from TESS full-frame images and membership lists driven by Gaia EDR3 kinematics and known youth indicators. We recover a period for 81.4% of the sample and report 255 rotation periods for Tuc-Hor objects. From these objects we identify 11 candidate binaries based on multiple periodic signals or outlier Gaia DR2 and EDR3 renormalized unit weight error values. We also identify three new complex rotators (rapidly rotating M dwarf objects with intricate light-curve morphology) within our sample. Along with the six previously known complex rotators that belong to Tuc-Hor, we compare their light-curve morphology between TESS Cycle 1 and Cycle 3 and find that they change substantially. Furthermore, we provide context for the entire Tuc-Hor rotation sample by describing the rotation period distributions alongside other youth indicators such as Hα and Li equivalent width, as well as near-ultraviolet and X-ray flux. We find that measuring rotation periods with TESS is a fast and effective means to confirm members in young moving groups.

Six Newly Discovered Eclipsing Binary Systems in the TESS field

We present the first detailed investigation of six eclipsing binary systems in the TESS field. The TESS light curves of the targets are analyzed by determining the initial effective temperatures via SED fits. The absolute parameters are derived and the systems are compared to well-known binaries of the same type. Results show that CD-58791, CD-621257 and TYC 9356-355-1 are detached binary systems. CD-54942 and UCAC4 136-007295 are contact binaries while TYC 8508-1413-1 is a semidetached system.

Occurrence rate of hot Jupiters orbiting red giant stars

Context. Hot Jupiters form an enigmatic class of object whose formation pathways are not yet clear. Determining their occurrence rates as a function of orbit, planet and stellar mass, and system age can be an important ingredient for understanding how they form. To date, various hot Jupiters have been discovered orbiting red giant stars, and deriving their incidence would be highly interesting. Aims. In this study our aim is to determine the number of hot Jupiters in a well-defined sample of red giants, estimate their occurrence rate, and compare it with that for A-, F-, and G-type stars. Methods. A sample of 14474 red giant stars, with estimated radii between 2 and 5 R⊙, was selected using Gaia to coincide with observations by the NASA TESS mission. Subsequently, the TESS light curves were searched for transits from hot Jupiters. The detection efficiency was determined using injected signals, and the results further corrected for the geometric transit probability to estimate the occurrence rate. Results. Three previously confirmed hot Jupiters were found in the TESS data, in addition to one other TESS object of interest, and two M-dwarf companions. This results in an occurrence rate of 0.37−0.09+0.29%. Due to the still large uncertainties, this cannot be distinguished from that of A-, F-, and G-type stars. We argue that it is unlikely that planet engulfment in expanding red giants plays an important role in this sample.

An Ap Star Catalog Based on LAMOST DR9

We present a sample of 2700 Ap stars in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) DR9 catalog. 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. The stellar parameters of these Ap stars, such as the T eff, , [Fe/H], [Si/H], and , are either extracted from a hot star catalog or derived through empirical relations and then a statistical analysis is carried out. The evolutionary stages are also discussed. Finally, we discuss the rotation and pulsation features of those that have TESS or Kepler light curves. Among these Ap stars, we find seven new rotation variables, one new roAp star, and a new δ Scuti pulsation of a previously known roAp star.

The Behavior of HgMn Stars in the Far UV—Paper 27: HD 1909

The analysis of two spectra of the spectroscopic binary B9 Hg star HD 1909 recorded by the SWP camera on board the International Ultraviolet Explorer reveals one instance of variations of the far-ultraviolet flux of this star from 1300 up to 2000 Å. The first TESS lightcurve of HD 1909 on the MAST website is periodic with a period close to 7 days which is very close to an earlier period found for the variations of the Strömgren index u. The FUV variations, which occur over about 5 yr, could be caused by the motion of the lower mass companion.

False Alarms Revealed in a Planet Search of TESS Light Curves

In this paper, we investigate the impact of false alarms on planet searches of TESS data by performing a search of a large number of stars. We examine the period distribution of transit-like signatures uncovered in a Box-Least Squares transit search of TESS light curves, and show significant pileups at periods related to instrumental and astrophysical noise sources. Signatures uncovered in a search of inverted light curves feature similar structures in the period distribution. Automated vetting methods will need to remove these excess detections, and light curve inversion appears to be a suitable method for simulating false alarms and designing new vetting metrics. Automated vetting will be a significant step toward making TESS data useful for demographic studies.

A photometric study of NSVS 7453183: a probable quadruple system with long-term surface activity

ABSTRACT The VRC light curves were regularly measured for the eclipsing binary NSVS 7453183 as a part of our long-term observational project for studying of low-mass eclipsing binaries with a short orbital period and surface activity. The TESS light curve solution in phoebe results to the detached configuration, where the temperature of primary component was adopted to T1 = 4300 K according to the SED approximation. It gives us T2 = 4080 ± 100 K for the secondary component. The spectral type of the primary component was estimated to be K6, and the photometric mass ratio was derived q = 0.86. We confirm presence of the third body in this system, a stellar companion with a minimal mass 0.33 M⊙ orbiting the eclipsing pair with a short period about 425 days, and propose the next, fourth body with a longer orbiting period of about 12 years, probably a brown dwarf with the minimal mass of 50 MJup. The hierarchical structure ((1+1)+1) + 1 of this quadruple system is assumed. Characteristics and temporal variations of the dark region on the surface of the primary component were estimated. The average migration speed of about 10° per month was found during years 2020–2022.

Photometric variable stars in the young open cluster NGC 6823

ABSTRACT We present stellar variability towards the young open cluster NGC 6823. Time series V- and I-band CCD photometry led to identification and characterization of 88 variable stars, of which only 14 have been previously recognized. We ascertain the membership of each variable with optical UBVI and infrared photometry, and with Gaia EDR3 parallax and proper motion data. Seventy two variable stars are found to be cluster members, of which 25 are main sequence stars and 48 are pre-main-sequence stars. The probable cluster members collectively suggest an isochrone age of the cluster to be about 2 Myrs based on the GAIA photometry. With the colour and magnitude, as well as the shape of the light curve, we have classified the main sequence variables into β Cep, δ Scuti, slowly pulsating B type, and new class variables. Among the pre-main-sequence variables, eight are classical T Tauri variables, and four are Herbig Ae/Be objects, whereas the remaining belong to the weak-lined T Tauri population. The variable nature of 32 stars is validated with TESS light curves. Our work provides refined classification of variability of pre-main-sequence and main-sequence cluster members of the active star-forming complex, Sharpless 86. Despite no strong evidence of the disc-locking mechanism in the present sample of TTSs, one TTS with larger Δ(I − K) is found to be a slow rotator.

Magnetic Activity and Parameters of 43 Flare Stars in the GWAC Archive

In the archive of the Ground Wide Angle Camera (GWAC), we found 43 white light flares from 43 stars, among which, three are sympathetic or homologous flares, and one of them also has a quasi-periodic pulsation with a period of 13.0 ± 1.5 minutes. Among these 43 flare stars, there are 19 new active stars and 41 stars that have available TESS and/or K2 light curves, from which we found 931 stellar flares. We also obtained rotational or orbital periods of 34 GWAC flare stars, of which 33 are less than 5.4 days, and ephemerides of three eclipsing binaries from these light curves. Combining with low resolution spectra from LAMOST and the Xinglong 2.16 m telescope, we found that L Hα /L bol are in the saturation region in the rotation-activity diagram. From the LAMOST medium-resolution spectrum, we found that Star #3 (HAT 178–02667) has double Hα emissions which imply it is a binary, and two components are both active stars. Thirteen stars have flare frequency distributions (FFDs) from TESS and/or K2 light curves. These FFDs show that the flares detected by GWAC can occur at a frequency of 0.5 to 9.5 yr−1. The impact of flares on habitable planets was also studied based on these FFDs, and flares from some GWAC flare stars may produce enough energetic flares to destroy ozone layers, but none can trigger prebiotic chemistry on their habitable planets.

The Behavior of HgMn Stars in the Far UV—Paper 22: HD 37752

The analysis of three spectra of the He-weak Hg star HD 37752 recorded by the SWP camera on board the International Ultraviolet Explorer does not reveal variations of the far-ultraviolet flux of this star over one set of observations on 1982 September 19th. The IUE spectra cover only a very small fraction (10%) of the rotational period derived from the TESS lightcurve which precludes any conclusion on the far-ultraviolet variability of HD 37752.

The Behavior of HgMn Stars in the Far UV—Paper 21: HD 29589

The analysis of two spectra of the Mn Hg star HD 29589 recorded by the SWP camera on board the International Ultraviolet Explorer does not reveal variations of the far-ultraviolet flux over a thirteen years time interval. The TESS lightcurve of HD 29589 shows a complex pattern of oscillations with variable amplitudes and probably several periods. A very strong resonance line of Ga ii is present at 1414.40 Å and confirms the Hg Mn status of HD 29589. A P Cygni profile at 1793.20 Å on SWP04948 could correspond to the resonance line of Sr ii at 1793.09 Å and indicate transient mass loss.

The Behavior of HgMn Stars in the Far UV—Paper 20: HD 14228

Abstract The analysis of three spectra of the Mn Hg Sr star HD 14228 recorded by the SWP camera on board the International Ultraviolet Explorer does not reveal variations of the far-ultraviolet flux over a nine years time interval. The analysis of the TESS lightcurve of HD 14228 confirms a very short period of 0.34 day already reported in the literature. This periodicity, attributed to rotation, could be a mode of radial pulsation too.

A Low-mass Pre-main-sequence Eclipsing Binary in Lower Centaurus Crux Discovered with TESS

We report the discovery of 2M1222−57 as a low-mass, pre-main-sequence (PMS) eclipsing binary (EB) in the Lower Centaurus Crux (LCC) association for which, using Gaia parallaxes and proper motions with a neural net age estimator, we determine an age of 16.2 ± 2.2 Myr. The broadband spectral energy distribution (SED) shows clear excess at ≳10 μm indicative of a circumbinary disk, and new speckle imaging observations reveal a faint, tertiary companion separated by ∼100 au. Hα emission is modulated on the orbital period, consistent with theoretical models of orbitally pulsed accretion streams reaching from the inner disk edge to the central stars. From a joint analysis of spectroscopically determined radial velocities and TESS light curves, together with additional tight constraints provided by the SED and the Gaia parallax, we measure masses for the eclipsing stars of 0.74 M ⊙ and 0.67 M ⊙; radii of 0.98 R ⊙ and 0.94 R ⊙; and effective temperatures of 3750 K and 3645 K. The masses and radii of both stars are measured to an accuracy of ∼1%. The measured radii are inflated, and the temperatures suppressed, relative to predictions of standard PMS evolutionary models at the age of LCC; also, the Li abundances are ∼2 dex less depleted than predicted by those models. However, models that account for the global and internal effects of surface magnetic fields are able to simultaneously reproduce the measured radii, temperatures, and Li abundances at an age of 17.0 ± 0.5 Myr. Altogether, the 2M1222−57 system presents very strong evidence that magnetic activity in young stars alters both their global properties and the physics of their interiors.

Accretion Variability of the Multiple T Tauri System VW Cha

Classical T Tauri stars are low-mass objects that are still accreting material from the surrounding circumstellar disk. The accretion process is essential in the formation of Sun-like stars and in setting the properties of the disk at the time when planet formation occurs. We constructed a complex data set in order to examine the accretion process of VW Cha, a classical T Tauri multiple system, with the aim of studying the physical origin of the photometric and spectroscopic variability of the system. The TESS space telescope observed VW Cha between 2019 April 22 and June 19, and we complemented these data with contemporaneous ground-based I CJHK-band photometric measurements. In addition, we obtained high-resolution optical spectra with the VLT/ESPRESSO and the 2.2 m/FEROS instruments. Analyzing these data, we found that the TESS light curve shows photometric variations on timescales from minutes to weeks with a peak-to-peak amplitude of ∼0.8 mag. The near-infrared light curves follow the shape of the optical measurements; however, the peak-to-peak amplitudes are slightly increasing toward the longer wavelengths. We took spectra in both fainter and brighter photometric states of the system, allowing us to examine the origin of a photometric brightening event. Our results show that this brightening event can be explained by increased accretion. In addition, our spectroscopic data also suggest that the primary component of VW Cha is a spectroscopic binary, as was proposed in earlier works.

Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS

Context. The TESS space mission has recently demonstrated its great potential to discover new pulsating white dwarf and pre-white dwarf stars, and to detect periodicities with high precision in already known white-dwarf pulsators. Aims. We report the discovery of two new pulsating He-rich atmosphere white dwarfs (DBVs) and present a detailed asteroseismological analysis of three already known DBV stars employing observations collected by the TESS mission along with ground-based data. Methods. We processed and analyzed TESS observations of the three already known DBV stars PG 1351+489 (TIC 471015205), EC 20058−5234 (TIC 101622737), and EC 04207−4748 (TIC 153708460), and the two new DBV pulsators WDJ152738.4−50207.4 (TIC 150808542) and WD 1708−871 (TIC 451533898), whose variability is reported for the first time in this paper. We also carried out a detailed asteroseismological analysis using fully evolutionary DB white-dwarf models built considering the complete evolution of the progenitor stars. We constrained the stellar mass of three of these target stars by means of the observed period spacing, and derived a representative asteroseismological model using the individual periods, when possible. Results. We extracted frequencies from the TESS light curves of these DBV stars using a standard pre-whitening procedure to derive the potential pulsation frequencies. All the oscillation frequencies that we found are associated with g-mode pulsations with periods spanning from ∼190 s to ∼936 s. We find hints of rotation from frequency triplets in some of the targets, including the two new DBVs. For three targets, we find constant period spacings, which allowed us to infer their stellar masses and constrain the harmonic degree ℓ of the modes. We also performed period-to-period fit analyses and found an asteroseismological model for three targets, with stellar masses generally compatible with the spectroscopic masses. Obtaining seismological models allowed us to estimate the seismological distances and compare them with the precise astrometric distances measured with Gaia. We find a good agreement between the seismic and the astrometric distances for three stars (PG 1351+489, EC 20058-5234, and WD 1708-871); although, for the other two stars (EC 04207-4748 and WD J152738.4-50207), the discrepancies are substantial. Conclusions. The high-quality data from the TESS mission continue to provide important clues which can be used to help determine the internal structure of pulsating pre-white dwarf and white dwarf stars through the tools of asteroseismology.

TESS light curves of cataclysmic variables – II – Superhumps in old novae and novalike variables

ABSTRACT Superhumps are among the abundant variable phenomena observed in the light curves of cataclysmic variables (CVs). They come in two flavours as positive and negative superhumps, distinguished by periods slightly longer or shorter, respectively, than the orbital periods of these interacting binary systems. Positive superhumps are ubiquitous in superoutbursting short-period dwarf novae of the SU UMa type but are less common in longer period systems with accretion discs in a permanent bright state, such as novalike variables and most old novae. Negative superhumps do not seem to have a preference for a particular type of CV. Here, I take advantage of the long high-cadence light curves provided by TESS for huge number of stars, selecting all old novae and novalike variables with past reported superhumps for which TESSlight curves are available and have not yet been analysed in previous publications in order to study their superhump behaviour. In combination with information taken from the literature, the results enable to compile the most complete census of superhumps in these stars so far. As a corollary, for the eclipsing systems in the present sample of objects, eclipse epochs derived from the TESS light curves and in some cases from archival light curves are listed and used to update orbital ephemeris and to discuss period changes.

A Population of Dipper Stars from the Transiting Exoplanet Survey Satellite Mission

Dipper stars are a classification of young stellar objects that exhibit dimming variability in their light curves, dropping in brightness by 10%–50%, likely induced by occultations due to circumstellar disk material. This variability can be periodic, quasiperiodic, or aperiodic. Dipper stars have been discovered in young stellar associations via ground-based and space-based photometric surveys. We present the detection and characterization of the largest collection of dipper stars to date: 293 dipper stars, including 234 new dipper candidates. We have produced a catalog of these targets, which also includes young stellar variables that exhibit predominately burst-like variability and symmetric variability (equal parts bursting and dipping). The total number of catalog sources is 414. These variable sources were found in a visual survey of TESS light curves, where dip-like variability was observed. We found a typical age among our dipper sources of <5 Myr, with the age distribution peaking at ≈2 Myr, and a tail of the distribution extending to ages older than 20 Myr. Regardless of the age, our dipper candidates tend to exhibit infrared excess, which is indicative of the presence of disks. TESS is now observing the ecliptic plane, which is rich in young stellar associations, so we anticipate many more discoveries in the TESS data set. A larger sample of dipper stars would enhance the census statistics of light-curve morphologies and dipper ages.