Transiting Exoplanet Survey Satellite Observations Research Articles

A study of two young multipolar planetary nebulae: Hen 2-73 and Hen 2-96

We perform an infrared (IR) spectral and visible morphological study of two young planetary nebulae (YPNe) Hen 2-73 and Hen 2-96 using archival Spitzer Space Telescope and Hubble Space Telescope (HST) observations to understand their dust properties and nebular structures. High-resolution HST images of these nebulae show several bipolar lobes and ionised tori in the central regions of both objects. The presence of these multi-lobe structures suggests that the formation process of these nebulae is complex. To search for a possible link between the central sources and multipolar appearances of these objects, the Transiting Exoplanet Survey Satellite (TESS) observations are used to examine whether their central stars (CSs) exhibit periodic photometric variations. In the TESS observations, the CS light curve of Hen 2-96 shows a photometric variation with a period of 2.23 hr. The IR spectra of these two YPNe suggest that the nebulae have mixed dust environments, which are associated with the presence of dense tori created by central binary interactions in these objects. Two three-dimensional models are constructed to study the complex nebular structures of the YPNe. These simulations suggest that the number of multipolar YPNe may be larger than observed. In addition, we analyse the spectral energy distributions of these nebulae to study their gas, dust, and photospheric components.

A Perfect Tidal Storm: HD 104067 Planetary Architecture Creating an Incandescent World

The discovery of planetary systems beyond the solar system has revealed a diversity of architectures, most of which differ significantly from our system. The initial detection of an exoplanet is often followed by subsequent discoveries within the same system as observations continue, measurement precision is improved, or additional techniques are employed. The HD 104067 system is known to consist of a bright K-dwarf host star and a giant planet in a ∼55 days period eccentric orbit. Here we report the discovery of an additional planet within the HD 104067 system, detected through the combined analysis of radial velocity (RV) data from the High Resolution Echelle Spectrometer and High Accuracy Radial velocity Planet Searcher instruments. The new planet has a mass similar to Uranus and is in an eccentric ∼14 days orbit. Our injection-recovery analysis of the RV data exclude Saturn-mass and Jupiter-mass planets out to 3 au and 8 au, respectively. We further present Transiting Exoplanet Survey Satellite observations that reveal a terrestrial planet candidate (R p = 1.30 ± 0.12 R ⊕) in a ∼2.2 days period orbit. Our dynamical analysis of the three planet model shows that the two outer planets produce significant eccentricity excitation of the inner planet, resulting in tidally induced surface temperatures as high as ∼2600 K for an emissivity of unity. The terrestrial planet candidate may therefore be caught in a tidal storm, potentially resulting in its surface radiating at optical wavelengths.

Discovery of a new IW And-type dwarf nova with both tilted disc and tidal instability

ABSTRACT IW And-type dwarf novae are anomalous Z Cam stars featured with outbursts happening during standstill states, which are not expected in the standard disc instability model. The physical mechanisms for these variations remain unclear. In this study, we report the discovery of a new candidate IW And-type dwarf nova J0652+2436, identified with its frequent outbursts from the slowly rising standstill states. Luckily, the Transiting Exoplanet Survey Satellite observations during a long standstill state and the earlier K2 observations give a chance to find the orbital and negative superhump period in the light curve of J0652+2436, allowing the measurement of its mass ratio of 0.366. This mass ratio is marginally possible for the tidal instability to set in according to previous smoothed particle hydrodynamics simulations. Thus, we propose that the outbursts in J0652+2436 are likely to be caused by the growing accretion disc during standstills, in favour of the previous hypothesis of the mechanisms lying in all IW And stars. We conclude that J0652+2436 might be the first IW And star with both a precessing tilted disc and tidal instability, which will be an important laboratory for studying the accretion disc dynamics and help understand the IW And phenomenon.

Statistical analysis of asteroseismic indices and stellar parameters of TESS-observed delta Scuti stars

Over the last few years stars have been at the center of the attention of the asteroseismology community thanks to the derivation of seismic indices connected to stellar parameters. The statistical analysis of the wealth of data offered by a large space survey such as the Transiting Exoplanet Survey Satellite (TESS), the identification of new stars, and the correlation between asteroseismic indices and stellar parameters in the resulting sample are therefore of utmost interest. The goal of our study is to analyze the statistical properties of stellar parameters and characterize the asteroseismic indices of stars observed in TESS cycle 4. We used TESS 2 min cadence photometric data and the corresponding Fourier transform to identify stars. The asteroseismic indices for these stars were determined using an empirical relation and a 2D autocorrelation method. We discovered 765 stars from the data obtained by the TESS mission, from Sectors 40 to 55, corresponding to cycle 4 and observed with a 2 min cadence. Of these stars, 179 stars have low-resolution spectral parameters from LAMOST. We first analyzed the relation between pulsation and stellar parameters from TESS observations and the distribution of stars with two different stellar parameters, TESS Input Catalog (TIC) and Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), within the classical instability strip. Most of the stars lie within the instability strip and follow the period-luminosity relation of stars. Additionally, the majority of the stars exhibit pulsation properties consistent with those expected for stars, including periods falling within the typical range, amplitudes at the millimagnitude level, and fundamental parameters such as spectral type, effective temperature, log g, and luminosity that match the characteristics of stars. This confirms the reliability of the stars we have identified. We subsequently obtained the large frequency separation ($ max $, and $ Amax )$ for 179 stars with LAMOST parameters by using an empirical relation and a 2D autocorrelation method, and obtained the relations between these asteroseismic indices. These stars will provide significant support for a deeper study of the internal structure and evolution of stars.

Identifying reliable periods in 2MASS J09213414–5939068, IGR J16167–4957, and V667 Pup

Detailed timing analyses of three cataclysmic variables, namely 2MASS J09213414−5939068, IGR J16167−4957, and V667 Pup are carried out using the long-baseline and high-cadence optical photometric data from the Transiting Exoplanet Survey Satellite (TESS). Periods of 908.12 ± 0.05 s and 990.10 ± 0.06 s are observed in the optical variation of 2MASS J09213414−5939068 that were not found in earlier studies and appear to be probable spin and beat periods of the system, respectively. The presence of multiple periods at spin, beat, and other sidebands indicates that 2MASS J09213414−5939068 likely belongs to an intermediate polar class of magnetic cataclysmic variables that seems to be accreted via a disc-overflow mechanism. Clear evidence of a period of 582.45 ± 0.04 s is found during the TESS observations of IGR J16167−4957, which can be interpreted as the spin period of the system. Strong modulation at this frequency supports its classification as an intermediate polar, where accretion may primarily be governed by a disc. The dominance of the spin pulse unveils the disc-fed dominance accretion in V667 Pup, but the detection of the previously unknown beat period of 525.77 ± 0.03 s suggests that a portion of the material is also accreted through a stream. Moreover, the double-peaked structure observed in the optical spin pulse profile of V667 Pup suggests the possibility of a two-pole accretion geometry, where each pole accretes at a different rate and is separated by 180°.

The First TESS Self-lensing Pulses: Revisiting KIC 12254688

We report the observations of two self-lensing pulses from KIC 12254688 in Transiting Exoplanet Survey Satellite (TESS) light curves. This system, containing an F2V star and white-dwarf companion, was among the first self-lensing binary systems discovered by the Kepler Space Telescope over the past decade. Each observed pulse occurs when the white dwarf transits in front of its companion star, gravitationally lensing the star’s surface, thus making it appear brighter to a distant observer. These two pulses are the very first self-lensing events discovered in TESS observations. We describe the methods by which the data were acquired and detrended, as well as the best-fit binary parameters deduced from our self-lensing+radial velocity model. We highlight the difficulties of finding new self-lensing systems with TESS, and we discuss the types of self-lensing systems that TESS may be more likely to discover in the future.

The TESS-Keck Survey. XVII. Precise Mass Measurements in a Young, High-multiplicity Transiting Planet System Using Radial Velocities and Transit Timing Variations

We present a radial velocity (RV) analysis of TOI-1136, a bright Transiting Exoplanet Survey Satellite (TESS) system with six confirmed transiting planets, and a seventh single-transiting planet candidate. All planets in the system are amenable to transmission spectroscopy, making TOI-1136 one of the best targets for intra-system comparison of exoplanet atmospheres. TOI-1136 is young (∼700 Myr), and the system exhibits transit timing variations (TTVs). The youth of the system contributes to high stellar variability on the order of 50 m s−1, much larger than the likely RV amplitude of any of the transiting exoplanets. Utilizing 359 High Resolution Echelle Spectrometer and Automated Planet Finder RVs collected as part of the TESS-Keck Survey, and 51 High-Accuracy Radial velocity Planetary Searcher North RVs, we experiment with a joint TTV-RV fit. With seven possible transiting planets, TTVs, more than 400 RVs, and a stellar activity model, we posit that we may be presenting the most complex mass recovery of an exoplanet system in the literature to date. By combining TTVs and RVs, we minimized Gaussian process overfitting and retrieved new masses for this system: (m b−g = 3.50−0.7+0.8 , 6.32−1.3+1.1 , 8.35−1.6+1.8 , 6.07−1.01+1.09 , 9.7−3.7+3.9 , 5.6−3.2+4.1 M ⊕). We are unable to significantly detect the mass of the seventh planet candidate in the RVs, but we are able to loosely constrain a possible orbital period near 80 days. Future TESS observations might confirm the existence of a seventh planet in the system, better constrain the masses and orbital properties of the known exoplanets, and generally shine light on this scientifically interesting system.

TESS duotransit candidates from the Southern Ecliptic Hemisphere

ABSTRACT Discovering transiting exoplanets with long orbital periods allows us to study warm and cool planetary systems with temperatures similar to the planets in our own Solar system. The Transiting Exoplanet Survey Satellite (TESS) mission has photometrically surveyed the entire Southern Ecliptic Hemisphere in Cycle 1 (2018 August–2019 July), Cycle 3 (2020 July–2021 June), and Cycle 5 (2022 September–2023 September). We use the observations from Cycle 1 and Cycle 3 to search for exoplanet systems that show a single transit event in each year, which we call duotransits. The periods of these planet candidates are typically in excess of 20 d, with the lower limit determined by the duration of individual TESS observations. We find 85 duotransit candidates, which span a range of host star brightnesses: 8 < Tmag < 14, transit depths between 0.1 per cent and 1.8 per cent, and transit durations between 2 and 10 h with the upper limit determined by our normalization function. Of these candidates, 25 are already known, and 60 are new. We present these candidates along with the status of photometric and spectroscopic follow-up.

Update on WASP-19

Tidal interaction between a star and a close-in massive exoplanet causes the planetary orbit to shrink and eventually leads to tidal disruption. Understanding orbital decay in exoplanetary systems is crucial for advancing our knowledge of planetary formation and evolution. Moreover, it sheds light on the broader question of the long-term stability of planetary orbits and the intricate interplay of gravitational forces within stellar systems. Analyzing Transiting Exoplanet Survey Satellite (TESS) data for the ultra-short period gas giant WASP-19, we aim to measure orbital period variations and constrain the stellar tidal quality parameter. For this, we fitted the TESS observations together with two WASP-19 transits observed using the Las Cumbres Observatory Global Telescope (LCOGT) and searched for orbital decay in combination with previously published transit times. As a result, we find a deviation from the constant orbital period at the 7σ level. The orbital period changes at a rate of P˙=−3.7±0.5msyear−1, which translates into a tidal quality factor of Q★′=(7±1)×105. We additionally modeled WASP-19 b’s phase curve using the new TESS photometry and obtained updated values for the planet’s eclipse depth, dayside temperature, and geometric albedo. We estimate an eclipse depth of 520±60 ppm, which is slightly higher than previous estimates and corresponds to a dayside brightness temperature of 2400±60 K and geometric albedo of 0.20±0.04.

A Possible Mechanism for the “Late Phase” in Stellar White-light Flares

M dwarf flares observed by the Transiting Exoplanet Survey Satellite (TESS) sometimes exhibit a peak-bump light-curve morphology, characterized by a secondary, gradual peak well after the main, impulsive peak. A similar late phase is frequently detected in solar flares observed in the extreme ultraviolet from longer hot coronal loops distinct from the impulsive flare structures. White-light emission has also been observed in off-limb solar flare loops. Here, we perform a suite of one-dimensional hydrodynamic loop simulations for M dwarf flares inspired by these solar examples. Our results suggest that coronal plasma condensation following impulsive flare heating can yield high electron number density in the loop, allowing it to contribute significantly to the optical light curves via free-bound and free–free emission mechanisms. Our simulation results qualitatively agree with TESS observations: the longer evolutionary timescale of coronal loops produces a distinct, secondary emission peak; its intensity increases with the injected flare energy. We argue that coronal plasma condensation is a possible mechanism for the TESS late-phase flares.

HST/WFC3 Light Curve Supports a Terrestrial Composition for the Closest Exoplanet to Transit an M Dwarf

Previous studies of the exoplanet LTT 1445Ac concluded that the light curve from the Transiting Exoplanet Survey Satellite (TESS) was consistent with both grazing and nongrazing geometries. As a result, the radius and hence density of the planet remained unknown. To resolve this ambiguity, we observed the LTT 1445 system for six spacecraft orbits of the Hubble Space Telescope (HST) using WFC3/UVIS imaging in spatial scan mode, including one partial transit of LTT 1445Ac. This imaging produces resolved light curves of each of the three stars in the LTT 1445 system. We confirm that the planet transits LTT 1445A and that LTT 1445C is the source of the rotational modulation seen in the TESS light curve, and we refine the estimate of the dilution factor for the TESS data. We perform a joint fit to the TESS and HST observations, finding that the transit of LTT 1445Ac is not grazing with 97% confidence. We measure a planetary radius of . Combined with previous radial velocity observations, our analysis yields a planetary mass of 1.37 ± 0.19 M ⊕ and a planetary density of g cm−3. LTT 1445Ac is likely an Earth analog with respect to its mass and radius, albeit with a higher instellation, and is therefore an exciting target for future atmospheric studies.

Precise Transit Photometry Using TESS: Updated Physical Properties for 28 Exoplanets around Bright Stars

The Transiting Exoplanet Survey Satellite (TESS) follow-up of a large number of known transiting exoplanets provides a unique opportunity to study their physical properties more precisely. Being a space-based telescope, the TESS observations are devoid of any noise component resulting from the interference of Earth’s atmosphere. TESS also provides a greater probability to observe subsequent transit events owing to its longer uninterrupted time-series observations compared to ground-based telescopes. For the exoplanets around bright host stars in particular, TESS time-series observations provide high signal-to-noise ratio (S/N) lightcurves, which can be used for higher-precision studies for these exoplanets. In this work, I have studied the TESS transit photometric follow-up observations of 28 exoplanets around bright stars with V mag ≤ 10. The already high-S/N lightcurves from TESS have been further processed with a critical noise-treatment algorithm, using the wavelet-denoising and the Gaussian-process regression techniques, to effectively reduce the noise components, both correlated and uncorrelated in time, which were then used to estimate the physical properties of these exoplanets. The study has resulted in very precise values for the physical properties of the target exoplanets, with the improvements in precision being significant for most of the cases compared to the previous studies. Also, since a comparatively large number of transit lightcurves from TESS observations were used to estimate these physical properties for each of the target exoplanets, which removes any bias due to the lack of sufficient data sets, these updated physical properties can be considered extremely accurate and reliable for future studies.

Refined parameters of the HD 22946 planetary system and the true orbital period of planet d

Context. Multi-planet systems are important sources of information regarding the evolution of planets. However, the long-period planets in these systems often escape detection. These objects in particular may retain more of their primordial characteristics compared to close-in counterparts because of their increased distance from the host star. HD 22946 is a bright (G = 8.13 mag) late F-type star around which three transiting planets were identified via Transiting Exoplanet Survey Satellite (TESS) photometry, but the true orbital period of the outermost planet d was unknown until now. Aims. We aim to use the Characterising Exoplanet Satellite (CHEOPS) space telescope to uncover the true orbital period of HD 22946d and to refine the orbital and planetary properties of the system, especially the radii of the planets. Methods. We used the available TESS photometry of HD 22946 and observed several transits of the planets b, c, and d using CHEOPS. We identified two transits of planet d in the TESS photometry, calculated the most probable period aliases based on these data, and then scheduled CHEOPS observations. The photometric data were supplemented with ESPRESSO (Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations) radial velocity data. Finally, a combined model was fitted to the entire dataset in order to obtain final planetary and system parameters. Results. Based on the combined TESS and CHEOPS observations, we successfully determined the true orbital period of the planet d to be 47.42489 ± 0.00011 days, and derived precise radii of the planets in the system, namely 1.362 ± 0.040 R⊕, 2.328 ± 0.039 R⊕, and 2.607 ± 0.060 R⊕ for planets b, c, and d, respectively. Due to the low number of radial velocities, we were only able to determine 3σ upper limits for these respective planet masses, which are 13.71 M⊕, 9.72 M⊕, and 26.57 M⊕. We estimated that another 48 ESPRESSO radial velocities are needed to measure the predicted masses of all planets in HD 22946. We also derived stellar parameters for the host star. Conclusions. Planet c around HD 22946 appears to be a promising target for future atmospheric characterisation via transmission spectroscopy. We can also conclude that planet d, as a warm sub-Neptune, is very interesting because there are only a few similar confirmed exoplanets to date. Such objects are worth investigating in the near future, for example in terms of their composition and internal structure.

TESS shines light on the origin of the ambiguous nuclear transient ASASSN-18el

ABSTRACT We analyse high-cadence data from the Transiting Exoplanet Survey Satellite (TESS) of the ambiguous nuclear transient (ANT) ASASSN-18el. The optical changing-look phenomenon in ASASSN-18el has been argued to be due to either a drastic change in the accretion rate of the existing active galactic nucleus (AGN) or the result of a tidal disruption event (TDE). Throughout the TESS observations, short-time-scale stochastic variability is seen, consistent with an AGN. We are able to fit the TESS light curve with a damped-random-walk (DRW) model and recover a rest-frame variability amplitude of $\hat{\sigma } = 0.93 \pm 0.02$ mJy and a rest-frame time-scale of $\tau _{DRW} = 20^{+15}_{-6}$ d. We find that the estimated τDRW for ASASSN-18el is broadly consistent with an apparent relationship between the DRW time-scale and central supermassive black hole mass. The large-amplitude stochastic variability of ASASSN-18el, particularly during late stages of the flare, suggests that the origin of this ANT is likely due to extreme AGN activity rather than a TDE.

Circumstellar Medium Interaction in SN 2018lab, A Low-luminosity Type IIP Supernova Observed with TESS

We present photometric and spectroscopic data of SN 2018lab, a low-luminosity Type IIP supernova (LLSN) with a V-band peak luminosity of −15.1 ± 0.1 mag. SN 2018lab was discovered by the Distance Less Than 40 Mpc (DLT40) SN survey only 0.73 days post-explosion, as determined by observations from the Transiting Exoplanet Survey Satellite (TESS). TESS observations of SN 2018lab yield a densely sampled, fast-rising, early-time light curve likely powered by ejecta–circumstellar medium (CSM) interaction. The blueshifted, broadened flash feature in the earliest spectra (<2 days) of SN 2018lab provides further evidence for ejecta–CSM interaction. The early emission features in the spectra of SN 2018lab are well described by models of a red supergiant progenitor with an extended envelope and a close-in CSM. As one of the few LLSNe with observed flash features, SN 2018lab highlights the need for more early spectra to explain the diversity of the flash feature morphology of Type II SNe.

V907 Sco Switched to the Eclipsing Mode Again

V907 Scorpii is a unique triple system in which the inner binary component has been reported to have switched on and off eclipses several times in modern history. In spite of its peculiarity, observational data on this system are surprisingly scarce. Here we make use of the recent Transiting Exoplanet Survey Satellite observations, as well as our own photometric and spectroscopic data, to expand the overall data set and study the V907 Sco system in more detail. Our analysis provides both new and improved values for several of its fundamental parameters: (i) the masses of the stars in the eclipsing binary are 2.74 ± 0.02 M ⊙ and 2.56 ± 0.02 M ⊙; and (ii) the third component is a solar-type star with mass M ⊙ (90% C.L.), orbiting the binary on an elongated orbit with an eccentricity of 0.47 ± 0.02 and a period of 142.01 ± 0.05 days. The intermittent intervals of time when eclipses of the inner binary are switched on and off are caused by a mutual inclination of the inner- and outer-orbit planes, and a favorable inclination of about 71° of the total angular momentum of the system. The nodal precession period is yr. The inner binary will remain eclipsing for another ≃26 yr, offering an opportunity to significantly improve the parameters of the model. This is especially true during the next decade when the inner-orbit inclination will increase to nearly 90°. Further spectroscopic observations are also desirable, as they can help to improve constraints on the system’s orbital architecture and its physical parameters.

Measuring the orbit shrinkage rate of hot Jupiters due to tides

Context. A tidal interaction between a star and a close-in exoplanet leads to shrinkage of the planetary orbit and eventual tidal dis- ruption of the planet. Measuring the shrinkage of the orbits will allow for the tidal quality parameter of the star (Q★′) to be measured, which is an important parameter to obtain information about stellar interiors. Aims. We analyse data from the Transiting Exoplanet Survey Satellite (TESS) for two targets known to host close-in hot Jupiters, which have significant data available and are expected to have a fast decay: WASP-18 and WASP-19. We aim to measure the current limits on orbital period variation and provide new constrains on Q★′ for our targets. Methods. We modelled the transit shape using all the available TESS observations and fitted the individual transit times of each tran- sit. We used previously published transit times together with our results to fit two models, a constant period model, and a quadratic orbital decay model, using Markov chain Monte Carlo (MCMC) algorithms. Results. We obtain new constrains on Q★′ for both targets and improve the precision of the known planet parameters with the newest observations from TESS. We find period change rates of (−0.11 ± 0.21) × 10−10 for WASP-18b and (−0.35 ± 0.22) × 10−10 for WASP-19b and we do not find significant evidence of orbital decay in these targets. We obtain new lower limits for Q★′ of (1.42 ± 0.34) × 107 in WASP-18 and (1.26 ± 0.10) × 106 in WASP-19, corresponding to upper limits of the orbital decay rate of −0.45 × 10−10 and −0.71 × 10−10, respectively, with a 95% confidence level. We compare our results with other relevant targets for tidal decay studies. Conclusions. We find that the orbital decay rate in both WASP-18b and WASP-19b appears to be smaller than the measured orbital decay of WASP-12b. We show that the minimum value of Q★′ in WASP-18 is two orders of magnitude higher than that of WASP-12, while WASP-19 has a minimum value one order of magnitude higher, which is consistent with other similar targets. Further observations are required to constrain the orbital decay of WASP-18 and WASP-19.

CHEOPS finds KELT-1b darker than expected in visible light

Recent studies based on photometry from the Transiting Exoplanet Survey Satellite (TESS) have suggested that the dayside of KELT-1b, a strongly irradiated brown dwarf, is significantly brighter in visible light than what would be expected based on Spitzer observations in the infrared. We observed eight eclipses of KELT-1b with CHaracterising ExOPlanet Satellite (CHEOPS) to measure its dayside brightness temperature in the bluest passband observed so far, and we jointly modelled the CHEOPS photometry with the existing optical and near-infrared photometry from TESS, LBT, CFHT, and Spitzer. Our modelling has led to a self-consistent dayside spectrum for KELT-1b covering the CHEOPS, TESS, H, Ks, and Spitzer IRAC 3.6 and 4.5 µm bands, where our TESS, H, Ks, and Spitzer band estimates largely agree with the previous studies. However, we discovered a strong discrepancy between the CHEOPS and TESS bands. The CHEOPS observations yield a higher photometric precision than the TESS observations, but they do not show a significant eclipse signal, while a deep eclipse is detected in the TESS band. The derived TESS geometric albedo of 0.36−0.13+0.12 is difficult to reconcile with a CHEOPS geometric albedo that is consistent with zero because the two passbands have considerable overlap. Variability in cloud cover caused by the transport of transient nightside clouds to the dayside could provide an explanation for reconciling the TESS and CHEOPS geometric albedos, but this hypothesis needs to be tested by future observations.

Exploring short-term optical variability of blazars using TESS

ABSTRACT We present a first systematic time series study of a sample of blazars observed by the Transiting Exoplanet Survey Satellite (TESS). By cross matching the positions of the sources in the TESS observations with those from Roma-BZCAT, 29 blazars including both BL Lacerate objects and flat-spectrum radio quasars were identified. The observation lengths of the 79 light curves of the sources, across all sectors on which the targets of interest have been observed by TESS, range between 21.25 and 28.2 d. The light curves were analysed using various methods of time series analysis. The results show that the sources exhibit significant variability with fractional variability spanning between 1.41 per cent and 53.84 per cent. The blazar flux distributions were studied by applying normal and log-normal probability density function models. The results indicate that optical flux histogram of the sources are consistent with normal probability density function with most of them following bimodal distribution as opposed to unimodal distribution. This suggests that the days-time-scale optical variability is contributed either by two different emission zones or two distinct states of short-term activity in blazars. Power spectral density analysis was performed by using the power spectral response method and the true power spectra of unevenly sampled light curves were estimated. The power spectral slopes of the light curves ranged from 1.7 to 3.2.

Stars on the Verge: From Days to Decades, Studying the Photometric Variations of the Red Supergiant W Persei

W Persei is a massive, luminous and large red supergiant located relatively nearby. W Persei is a probable SN-II progenitor. We analyzed ∼120 yr of photometry from the AAVSO database. The analysis was conducted in the period analysis software Peranso where the CLEANest power spectrum and WWZ-wavelet programs were utilized. Two dominant periods of P = 532 ± 68 days and P = 2922 ± 140 days are found. Intermediate and transitory periods are also uncovered along with period events such as a significant increase in the long-period, period-merging and period-splitting. Using Transiting Exoplanet Survey Satellite observations, stochastic ∼0.3–0.8 mmag light variability on timescales of ∼0.3 day appears present. The physical causes of these variations is discussed.