Chemically peculiar stars investigated by the BRITE mission

Despite the thousands of planets in orbit around stars known to date, the mechanisms of planetary formation, migration, and atmospheric loss remain unresolved. In this work, we confirm the planetary nature of a young Saturn-size planet transiting a solar-type star every 8.03 d, TOI-1135 b. The age of the parent star is estimated to be in the interval of 125-1000 Myr based on various activity and age indicators, including its stellar rotation period of 5.13 ± 0.27 days and the intensity of photospheric lithium. We obtained follow-up photometry and spectroscopy, including precise radial velocity measurements using the CARMENES spectrograph, which together with the TESS data allowed us to fully characterise the parent star and its planet. As expected for its youth, the star is rather active and shows strong photometric and spectroscopic variability correlating with its rotation period. We modelled the stellar variability using Gaussian process regression. We measured the planetary radius at 9.02 ± 0.23 R⊕ (0.81 ± 0.02 RJup) and determined a 3σ upper limit of < 51.4 M⊕ (< 0.16 MJup) on the planetary mass by adopting a circular orbit. Our results indicate that TOI-1135 b is an inflated planet less massive than Saturn or Jupiter but with a similar radius, which could be in the process of losing its atmosphere by photoevaporation. This new young planet occupies a region of the mass-radius diagram where older planets are scarse, and it could be very helpful to understanding the lower frequency of planets with sizes between Neptune and Saturn.

We go on paving the way for the study of Earth-like exoplanets around M-type dwarfs stars by measuring the rotation periods of stars observed by the CARMENES survey using TESS data. This study will help to distinguish exoplanet radial-velocity signals from the ones produced by features on the rotating features in the stellar atmosphere. We looked for signals in the photometric time series of 352 CARMENES M dwarfs of the guaranteed time observations GTO sample covered by the first 26 TESS sectors. We collected either SAP (Simple Aperture Photometry) or PDCSAP (Pre-search Data Conditioning SAP) time series for 210 stars, and custom extracted the light curves for a further 32 stars from the FFI (Full Frame Images). We measured 69 rotational periods between 0.12 d and 13.20 d of which 23 are new. With those periods in hand, we studied the distribution of angular momenta of stellar systems with and without planets.

Context. The occurrence rate and period distribution of (giant) planets around young stars is still not as well constrained as for older main-sequence stars. This is mostly due to the intrinsic activity-related complications and the avoidance of young stars in many large planet search programmes. Yet, dynamical restructuring processes in planetary systems may last significantly longer than the actual planet formation phase and may well extend long into the debris disc phase, such that the planet populations around young stars may differ from those observed around main-sequence stars. Aims. We introduce our Radial Velocity Survey for Planets around Young stars (RVSPY), which is closely related to the NaCo-ISPY direct imaging survey, characterise our target stars, and search for substellar companions at orbital separations smaller than a few au from the host star. Methods. We used the FEROS spectrograph, mounted to the MPG/ESO 2.2 m telescope in Chile, to obtain high signal-to-noise spectra and time series of precise radial velocities (RVs) of 111 stars, most of which are surrounded by debris discs. Our target stars have spectral types between early F and late K, a median age of 400 Myr, and a median distance of 45 pc. During the initial reconnaissance phase of our survey, we determined stellar parameters and used high-cadence observations to characterise the intrinsic stellar activity, searched for hot companions with orbital periods of up to 10 days, and derived the detection thresholds for longer-period companions. In our analysis we, have included archival spectroscopic data, spectral energy distribution, and data for photometric time series from the TESS mission. Results. For all target stars we determined their basic stellar parameters and present the results of the high-cadence RV survey and activity characterisation. We have achieved a median single-measurement RV precision of 6 m s−1 and derived the short-term intrinsic RV scatter of our targets (median 23 m s−1), which is mostly caused by stellar activity and decays with an age from >100 m s−1 at <20 Myr to <20 m s−1 at >500 Myr. We analysed time series periodograms of the high-cadence RV data and the shape of the individual cross-correlation functions. We discovered six previously unknown close companions with orbital periods between 10 and 100 days, three of which are low-mass stars, and three are in the brown dwarf mass regime. We detected no hot companion with an orbital period <10 days down to a median mass limit of ~1 MJup for stars younger than 500 Myr, which is still compatible with the established occurrence rate of such companions around main-sequence stars. We found significant RV periodicities between 1.3 and 4.5 days for 14 stars, which are, however, all caused by rotational modulation due to starspots. We also analysed the data for TESS photometric time series and found significant periodicities for most of the stars. For 11 stars, the photometric periods are also clearly detected in the RV data. We also derived stellar rotation periods ranging from 1 to 10 days for 91 stars, mostly from the TESS data. From the intrinsic activity-related short-term RV jitter, we derived the expected mass-detection thresholds for longer-period companions, and selected 84 targets for the longer-term RV monitoring.

We perform a study of stellar flares for the 24,809 stars observed with 2 minute cadence during the first two months of the TESS mission. Flares may erode exoplanets’ atmospheres and impact their habitability, but might also trigger the genesis of life around small stars. TESS provides a new sample of bright dwarf stars in our galactic neighborhood, collecting data for thousands of M dwarfs that might host habitable exoplanets. Here, we use an automated search for flares accompanied by visual inspection. Then, our public allesfitter code robustly selects the appropriate model for potentially complex flares via Bayesian evidence. We identify 1228 flaring stars, 673 of which are M dwarfs. Among 8695 flares in total, the largest superflare increased the stellar brightness by a factor of 16.1. Bolometric flare energies range from 1031.0 to 1036.9 erg, with a median of 1033.1 erg. Furthermore, we study the flare rate and energy as a function of stellar type and rotation period. We solidify past findings that fast rotating M dwarfs are the most likely to flare and that their flare amplitude is independent of the rotation period. Finally, we link our results to criteria for prebiotic chemistry, atmospheric loss through coronal mass ejections, and ozone sterilization. Four of our flaring M dwarfs host exoplanet candidates alerted on by TESS, for which we discuss how these effects can impact life. With upcoming TESS data releases, our flare analysis can be expanded to almost all bright small stars, aiding in defining criteria for exoplanet habitability.

Tidal interactions influence the orbital motions of binary star systems and extrasolar planets alike. Tides also affect stellar and planetary rotation rates. We demonstrate that in addition to altering spin synchronization and pseudosynchronization, tidally driven inertial waves in the convective envelopes of low-mass stars and gas-giant planets can enhance tidal eccentricity damping. Analytically, we find that eccentricity damping by inertial waves can be orders of magnitude faster than equilibrium tides, independent of any eddy viscosity prescription. We use simplified numerical experiments to demonstrate this enhancement and to explore the effects of different mixing-length treatments of convective turbulence, as well as a spindown torque from magnetic braking. These calculations demonstrate that tidally driven inertial waves can produce an extended cool core of nearly circular binaries, helping to reconcile a longstanding discrepancy between observed and predicted main-sequence binary circularization. Our calculations additionally suggest that tidally driven inertial waves may leave identifiable signatures in the ratios of the orbital to rotation periods for stellar binaries, including synchronous and subsynchronous rotation periods reminiscent of populations identified in Kepler, TESS, and Gaia data.

We report the validation of a third terrestrial exoplanet in the nearby (22 pc) TOI-2267 system. TOI-2267 is a binary system with stellar components TOI-2267A (M5, 3030 K) and TOI-2267B (M6, 2930 K), with an on-sky separation of 0 . ″ 384 (8 au projected separation). TOI-2267 hosts two Earth-sized planets (TOI-2267 b, 1.00 ± 0.11 R ⊕ , and TOI-2267 c, 1.14 ± 0.13 R ⊕ , if orbiting the primary star; or 1.22 ± 0.29 R ⊕ and 1.36 ± 0.33 R ⊕ , respectively, if orbiting the secondary star) with orbital periods of 2.3 and 3.5 days. This system also contains a third Earth-sized planet candidate with an orbital period of 2.0 days that was previously identified as a likely planet with a low false-positive probability, but could not be firmly validated due to the lack of independent observations beyond TESS data. We combine two new transit observations from the 5.1 m Hale Telescope at Palomar Observatory with archival TESS data and high-resolution imaging to statistically validate the planetary nature of TOI-2267 d (0.98 ± 0.09 R ⊕ if orbiting the primary star, or 1.77 ± 0.43 R ⊕ if orbiting the secondary star) using the updated TRICERATOPS+ pipeline. We attempt to determine the host star for TOI-2267 d using a transit shape stellar density analysis, but are unable to conclusively assign a host. Our validation of TOI-2267 d suggests that TOI-2267 either is the first known double-transiting M-dwarf binary system or hosts three planets in an extremely compact orbital configuration.

We present the results from the discovery and study of ∼3000 chromospherically active giant and subgiant stars toward the Galactic bulge. We find that these stars are predominantly RS CVn binaries with rotation periods between 10 and 100 days. We discover that the average rotational period of these stars decreases with their distance from the Galactic plane. We find that the primary stars in the RS CVn systems are predominantly first-ascent giants. Our research also suggests that if these stars have spot cycles like the Sun, then the cycle period must be longer than 10 yr on average. We confirm that the amplitude of the spot-induced modulations observed in the light curves of these objects is generally larger at minimum light than at maximum. Furthermore, we confirm that the amplitudes of the modulations due to stellar spots generally increase as the observed change in average brightness increases. We find no evidence for a relationship between a chromospherically active star's brightness and its rotational period. However, the average period does increase with color for stars with periods ≲30 days.

A curious rotation period distribution in the colour–magnitude–period diagram (CMPD) of the Kepler field was recently revealed, thanks to data from Gaia and Kepler spacecraft. It was found that redder and brighter stars are spinning slower than the rest of the main sequence. On the theoretical side, it was demonstrated that metallicity should affect the rotational evolution of stars as well as their evolution in the Hertzprung–Rüssel or colour–magnitude diagram. In this work, we combine this data set with medium- and high-resolution spectroscopic metallicities and carefully select main-sequence single stars in a given mass range. We show that the structure seen in the CMPD also corresponds to a broad correlation between metallicity and rotation, such that stars with higher metallicity rotate, on average, more slowly than those with low metallicity. We compare this sample to theoretical rotational evolution models that include a range of different metallicities. They predict a correlation between rotation rate and metallicity that is in the same direction and of about the same magnitude as that observed. Therefore, metallicity appears to be a key parameter to explain the observed rotation period distributions. We also discuss a few different ways in which metallicity can affect the observed distribution of rotation period, due to observational biases and age distributions, as well as the effect on stellar wind torques.

We report the results of a comprehensive study of the spectroscopic binary (SB2) system HD 34736 hosting two chemically peculiar (CP) late B-type stars. Using new and archival observational data, we characterize the system and its components, including their rotation and magnetic fields. Fitting of the radial velocities yields $P_\mathrm{orb}=83\rm{.\!\!^{ {\rm{d}}}}219(3)$ and $e=0.8103(3)$. The primary component is a CP He-wk star with $T_{{\rm eff}A}$$\,\,=13000\pm 500$ K and $\upsilon _{\rm e}\sin i\,$$\,\,=75\pm 3$ km s$^{-1}\,$, while the secondary exhibits variability of Mg and Si lines, and has $T_{{\rm eff}B}$$\,\,=11500\pm 1000$ K and $\upsilon _{\rm e}\sin i\,$$\,\,=110$–180 km s$^{-1}\,$. Transiting Exoplanet Survey Satellite and Kilodegree Extremely Little Telescope photometry reveal clear variability of the primary component with a rotational period $P_{\mathrm{rot}A}=1\rm{.\!\!^{ {\rm{d}}}}279\, 988\, 5(11)$, which is lengthening at a rate of 1.26(6) s yr$^{-1}$. For the secondary, $P_{\mathrm{rot}B}=0\rm{.\!\!^{ {\rm{d}}}}522\, 693\, 8(5)$, reducing at a rate of $-0.14(3)$ s yr$^{-1}$. The longitudinal component $\langle B_{\rm z}\rangle$ of the primary’s strongly asymmetric global magnetic field varies from $-6$ to +5 kG. Weak spectropolarimetric evidence of a magnetic field is found for the secondary star. The observed X-ray and radio emission of HD 34736 may equally be linked to a suspected T Tau-like companion or magnetospheric emission from the principal components. Given the presence of a possible third magnetically active body, one can propose that the magnetic characteristics of the protostellar environment may be connected to the formation of such systems.

view Abstract Citations (83) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photometric Variations of Orion Population Stars. V. A Search for Periodicities Herbst, W. ; Booth, J. F. ; Koret, D. L. ; Zajtseva, G. V. ; Kholotilov, E. ; Shakhovskaya, H. I. ; Vrba, F. J. ; Covino, E. ; Terranegra, L. ; Vittone, A. ; Hoff, D. ; Kelsey, L. ; Lines, R. ; Barksdale, W. Abstract An intensive monitoring campaign aimed at detecting rotation periods in a set of bright T Tauri and Herbig Ae/Be stars was undertaken during the 1985/86 Milky Way season. Between 85 and 200 V magnitude measurements were made for each star on the program. In addition to the rotation period found for T Tau, on the basis of these data (Herbst et al. 1986) we find a probable period for SU Aur of 1.55 or 2.73 ± 0.03 days, the ambiguity arising because of a sampling frequency of (1 day)-1, and a possible period for RY Tau of 5.6 days. Z CMa displayed a remarkably regular variation of peculiar form on a time scale of 60 days, which could be its rotation period. Our study suggests that periodicity due to rotational modulation may be present in all T Tauri light curves, but that it will often be difficult to find due to masking by large-amplitude, irregular variations. Significant peaks in the periodograms of all the large-amplitude variables in our sample are seen at periods of 30-70 days. RY Tau has shown a persistent periodicity of about 65 days during the last three seasons. This cannot be its rotation period. Other aspects of the variability of these stars are discussed, and absolute photometry given for comparison and check stars. Publication: The Astronomical Journal Pub Date: July 1987 DOI: 10.1086/114456 Bibcode: 1987AJ.....94..137H Keywords: A Stars; Orion Constellation; Stellar Rotation; Stellar Spectrophotometry; T Tauri Stars; Variable Stars; Astronomical Catalogs; B Stars; Periodic Variations; Stellar Magnitude; Astronomy; STARS: PRE-MAIN-SEQUENCE full text sources ADS | data products SIMBAD (34) Related Materials (4) Part 1: 1982AJ.....87.1710H Part 2: 1983AJ.....88.1648H Part 3: 1984AJ.....89.1716H Part 4: 1986AJ.....92.1387H

Uranus and Neptune: Shape and rotation

<p>The recently developed Unistellar’s eVscope/eVscope2 and eQuinox telescopes have been delivered to more than 5,000 customers around the globe. These telescope owners already represent the largest worldwide network of potential citizen astronomers. Due to the unified design and user-friendly operation via a smartphone app, several types of useful scientific observations are enabled and supported by Unistellar.</p> <p>Each individual frame is stored in the telescope and can be accessed in 12-bit TIFF format by the user for the following data processing and analysis. Moreover, the user can upload the data to Unistellar for further processing, which is the main concept of the campaign mode: Any owner of an eVscope can receive notifications on their smartphone of transient events visible in the sky, such as comets, supernovae, asteroid flybys, stellar occultations by asteroids, or other targets of interest, perform the observations and upload the data to Unistellar’s server.</p> <p>In this contribution, we focus on</p> <p>(i) light curve observations of asteroids, and</p> <p>(ii) stellar occultations by asteroids.</p> <p>Light curves represent the temporal changes of asteroids' brightness within the typical night observational window, which takes usually several hours. Light curve observations allow us to study asteroidal physical properties - rotation period, rotation axis, and the 3D shape model.</p> <p>During the stellar occultation, the asteroid is passing in front of a bright star, which is occulted, the duration of this event is directly related to the asteroid's dimension. Various observers distributed on the ground can sample different parts of the asteroid, which can lead to an accurate size estimate, and possibly even to a shape model refinement.</p> <p>In 2021 and 2022, we initiated several observing campaigns aiming at obtaining light curve data of several near-Earth asteroids (NEA) that were having close approaches to the Earth - e.g., NEAs 1999 AP10 and 2000 PQ9. Dozens of citizen scientists provided their observations. Here we show the initial results obtained by analyzing these optical data. We will also discuss the quality of the photometric data and the significance and potential of the eVscope network for the study of the physical properties of asteroids.</p> <p>We selected asteroids that get bright enough for at least one month, which provides a sufficiently wide window of opportunity for the eVscope users that are often limited by the weather conditions. Also, these targets have unknown or poorly constrained physical properties, which results in the opportunity to contribute to the better characterization and understanding of the population of asteroids.</p> <p>Within the Unistellar's eVscope network of citizen astronomers, we are targeting stellar occultations in order to estimate their dimensions with an accuracy non-achievable by commonly used techniques such as thermal modeling. This task is quite challenging, however, we will report the first successful observations of these events.</p> <p><strong><span dir="ltr" role="presentation">Acknowledgments</span></strong></p> <p><span dir="ltr" role="presentation">The work of JH and JD has been supported by the Czech </span><span dir="ltr" role="presentation">Science Foundation through grant 22-17783S.<br /></span></p>

Directly imaging temperate rocky planets orbiting nearby, Sun-like stars with a 6 m class IR/O/UV space telescope, recently dubbed the Habitable Worlds Observatory, is a high-priority goal of the Astro2020 Decadal Survey. To prepare for future direct imaging (DI) surveys, the list of potential targets should be thoroughly vetted to maximize efficiency and scientific yield. We present an analysis of archival radial velocity data for southern stars from the NASA/NSF Extreme Precision Radial Velocity (EPRV) Working Group’s list of high-priority target stars for future DI missions (drawn from the HabEx, LUVOIR, and Starshade Rendezvous studies). For each star, we constrain the region of companion mass and period parameter space we are already sensitive to based on the observational baseline, sampling, and precision of the archival radial velocity (RV) data. Additionally, for some of the targets, we report new estimates of magnetic activity cycle periods, rotation periods, improved orbital parameters for previously known exoplanets, and new candidate planet signals that require further vetting or observations to confirm. Our results show that for many of these stars we are not yet sensitive to even Saturn-mass planets in the habitable zone, let alone smaller planets, highlighting the need for future EPRV vetting efforts before the launch of a DI mission. We present evidence that the candidate temperate super-Earth exoplanet HD 85512b is most likely due to the star’s rotation, and report an RV acceleration for δ Pav that supports the existence of a distant giant planet previously inferred from astrometry.

Calvera is an unusual, isolated neutron star with a pure thermal X-ray spectrum typical of central compact objects in supernova remnants. On the other hand, its rotation period and spin-down rate are typical of ordinary rotation-powered pulsars. It was discovered and studied through X-rays, and has not yet been detected in other spectral domains. We present deep optical imaging of the Calvera field, obtained with the Gran Telescopio Canarias, in the and bands. Within the vicinity of of Calvera, we detected two point-like objects that were invisible at previous shallow observations. However, accurate astrometry showed that neither of them can be identified with the pulsar. We put new upper limits of and on its optical brightness. We also reanalyzed all available archival X-ray data on Calvera. Comparison of the Calvera thermal emission parameters and upper limits on optical and non-thermal X-ray emission with respective data on rotation-powered pulsars shows that Calvera might belong to the class of ordinary middle-aged pulsars, if we assume that its distance is in the range of 1.5–5 kpc.

We study the relation between stellar rotation and magnetic activity for a sample of 134 bright, nearby M dwarfs observed in the Kepler Two-Wheel (K2) mission during campaigns C0 to C4. The K2 lightcurves yield photometrically derived rotation periods for 97 stars (79 of which without previous period measurement), as well as various measures for activity related to cool spots and flares. We find a clear difference between fast and slow rotators with a dividing line at a period of ~10d at which the activity level changes abruptly. All photometric diagnostics of activity (spot cycle amplitude, flare peak amplitude and residual variability after subtraction of spot and flare variations) display the same dichotomy, pointing to a quick transition between a high-activity mode for fast rotators and a low-activity mode for slow rotators. This unexplained behavior is reminiscent of a dynamo mode-change seen in numerical simulations that separates a dipolar from a multipolar regime. A substantial number of the fast rotators are visual binaries. A tentative explanation is accelerated disk evolution in binaries leading to higher initial rotation rates on the main-sequence and associated longer spin-down and activity lifetimes. We combine the K2 rotation periods with archival X-ray and UV data. X-ray, FUV and NUV detections are found for 26, 41, and 11 stars from our sample, respectively. Separating the fast from the slow rotators, we determine for the first time the X-ray saturation level separately for early- and for mid-M stars.