The FUor Star V2493 Cyg (HBC 722)—Eleven Years at Maximum Brightness

At the time of stellar evolution, young stellar objects go through processes of increased activity and instability. Star formation takes place in several stages during which the star accumulates enough mass to initiate thermonuclear reactions in the nucleus. A significant percentage of the mass of Sun-like stars accumulates during periods of increased accretion known as FUor outbursts. Since we know only about two dozen stars of this type, the study of each new object is very important for our knowledge. In this paper, we present data from photometric monitoring on a FUor object V2493 Cyg discovered in 2010. Our data were obtained in the optical region with BVRI Johnson–Cousins set of filters during the period from November 2016 to February 2021. The results of our observations show that during this period no significant changes in the brightness of the star were registered. We only detect variations with a small amplitude around the maximum brightness value. Thus, since 2013 V2493 Cyg remains at its maximum brightness, without a decrease in brightness. Such photometric behavior is not typical of other stars from FUor type. Usually, the light curves of FUors are asymmetrical, with a very rapid rise and gradual decline of the brightness. V2493 Cyg remains unique in this respect with a very rapid rise in brightness and prolonged retention in maximum light. Our period analysis made for the interval February 2013–February 2021 reveals a well-defined period of 914 ± 10 days. Such periodicity can be explained by dust structures remaining from star formation in orbit around the star.

V899 Mon: A Peculiar Eruptive Young Star Close to the End of Its Outburst

The eruptive young star V899 Mon shows characteristics of both FUors and EXors. It reached a peak brightness in 2010, then briefly faded in 2011, followed by a second outburst. We conducted multifilter optical photometric monitoring, as well as optical and near-infrared spectroscopic observations, of V899 Mon. The light curves and color–magnitude diagrams show that V899 Mon has been gradually fading after its second outburst peak in 2018, but smaller accretion bursts are still happening. Our spectroscopic observations taken with Gemini/IGRINS and VLT/MUSE show a number of emission lines, unlike during the outbursting stage. We used the emission line fluxes to estimate the accretion rate and found that it has significantly decreased compared to the outbursting stage. The mass-loss rate is also weakening. Our 2D spectroastrometric analysis of emission lines recovered jet and disk emission of V899 Mon. We found that the emission from permitted metallic lines and the CO bandheads can be modeled well with a disk in Keplerian rotation, which also gives a tight constraint for the dynamical stellar mass of 2 M ⊙. After a discussion of the physical changes that led to the changes in the observed properties of V899 Mon, we suggest that this object is finishing its second outburst.

CHEOPS precision phase curve of the Super-Earth 55 Cancri e

Context. 55 Cnc e is a transiting super-Earth (radius 1.88 R⊕ and mass 8 M⊕) orbiting a G8V host star on a 17-h orbit. Spitzer observations of the planet’s phase curve at 4.5 μm revealed a time-varying occultation depth, and MOST optical observations are consistent with a time-varying phase curve amplitude and phase offset of maximum light. Both broadband and high-resolution spectroscopic analyses are consistent with either a high mean molecular weight atmosphere or no atmosphere for planet e. A long-term photometric monitoring campaign on an independent optical telescope is needed to probe the variability in this system. Aims. We seek to measure the phase variations of 55 Cnc e with a broadband optical filter with the 30 cm effective aperture space telescope CHEOPS and explore how the precision photometry narrows down the range of possible scenarios. Methods. We observed 55 Cnc for 1.6 orbital phases in March of 2020. We designed a phase curve detrending toolkit for CHEOPS photometry which allowed us to study the underlying flux variations in the 55 Cnc system. Results. We detected a phase variation with a full-amplitude of 72 ± 7 ppm, but did not detect a significant secondary eclipse of the planet. The shape of the phase variation resembles that of a piecewise-Lambertian; however, the non-detection of the planetary secondary eclipse, and the large amplitude of the variations exclude reflection from the planetary surface as a possible origin of the observed phase variations. They are also likely incompatible with magnetospheric interactions between the star and planet, but may imply that circumplanetary or circumstellar material modulate the flux of the system. Conclusions. This year, further precision photometry of 55 Cnc from CHEOPS will measure variations in the phase curve amplitude and shape over time.

The PLATO mission: Overview and status

<p>PLATO is an ESA mission dedicated to the study of exoplanets and stars, with a planned launch date in 2026. By performing photometric monitoring of about 250 000 bright stars (m<sub>V</sub> < 13), PLATO will be able to discover and characterise hundreds of exoplanets, including small planets orbiting up to the habitable zone of solar-like stars. PLATO’s precision will also allow for a precise characterisation of the host stars through asteroseismology. These objectives require both a wide field of view and high sensitivity, which are achieved with a payload comprising 24 cameras with partially overlapping fields of view. They are complemented by 2 more cameras optimised for brighter stars that will also be used as fine guidance sensor. The PLATO development phase started after the mission adoption in July 2017. The Mission Preliminary Design Review (PDR) was declared successful in October 2020. The implementation and delivery to ESA of the flight model CCDs for all cameras (4 CCDs per camera) has been completed. Currently the Structural Thermal Model (STM) of the payload optical bench is being manufactured, while the STM of a single camera has already been successfully tested. In parallel, a first engineering model of a complete, fully functional camera is being integrated, to verify its performance under operational conditions, and the qualification models of the different payload units are being built.</p> <p>We will present the status of the PLATO payload implementation in the context of the satellite development. In particular, we will describe the payload manufacturing, integration, and tests that will be reviewed at the Critical Milestone in the second half of 2021. We will also summarise the progress made in the science preparation activities, as well as on the ground segment.</p>

Space Photometry with Brite-Constellation

BRITE-Constellation is devoted to high-precision optical photometric monitoring of bright stars, distributed all over the Milky Way, in red and/or blue passbands. Photometry from space avoids the turbulent and absorbing terrestrial atmosphere and allows for very long and continuous observing runs with high time resolution and thus provides the data necessary for understanding various processes inside stars (e.g., asteroseismology) and in their immediate environment. While the first astronomical observations from space focused on the spectral regions not accessible from the ground it soon became obvious around 1970 that avoiding the turbulent terrestrial atmosphere significantly improved the accuracy of photometry and satellites explicitly dedicated to high-quality photometry were launched. A perfect example is BRITE-Constellation, which is the result of a very successful cooperation between Austria, Canada and Poland. Research highlights for targets distributed nearly over the entire HRD are presented, but focus primarily on massive and hot stars.

A planetary system with two transiting mini-Neptunes near the radius valley transition around the bright M dwarf TOI-776

We report the discovery and characterization of two transiting planets around the bright M1 V star LP 961-53 (TOI-776, J = 8.5 mag, M = 0.54 ± 0.03 M ⊙) detected during Sector 10 observations of the Transiting Exoplanet Survey Satellite (TESS). Combining the TESS photometry with HARPS radial velocities, as well as ground-based follow-up transit observations from the MEarth and LCOGT telescopes, for the inner planet, TOI-776 b, we measured a period of P b = 8.25 d, a radius of R b = 1.85 ± 0.13 R ⊕, and a mass of M b = 4.0 ± 0.9 M ⊕; and for the outer planet, TOI-776 c, a period of P c = 15.66 d, a radius of R c = 2.02 ± 0.14 R ⊕, and a mass of M c = 5.3 ± 1.8 M ⊕. The Doppler data shows one additional signal, with a period of ~34 d, associated with the rotational period of the star. The analysis of fifteen years of ground-based photometric monitoring data and the inspection of different spectral line indicators confirm this assumption. The bulk densities of TOI-776 b and c allow for a wide range of possible interior and atmospheric compositions. However, both planets have retained a significant atmosphere, with slightly different envelope mass fractions. Thanks to their location near the radius gap for M dwarfs, we can start to explore the mechanism(s) responsible for the radius valley emergence around low-mass stars as compared to solar-like stars. While a larger sample of well-characterized planets in this parameter space is still needed to draw firm conclusions, we tentatively estimate that the stellar mass below which thermally-driven mass loss is no longer the main formation pathway for sculpting the radius valley is between 0.63 and 0.54 M ⊙. Due to the brightness of the star, the TOI-776 system is also an excellent target for the James Webb Space Telescope, providing a remarkable laboratory in which to break the degeneracy in planetary interior models and to test formation and evolution theories of small planets around low-mass stars.

Long-term optical photometric monitoring of the FUor star V900 Mon

We present results from photometric monitoring of V900 Mon, one of the newly discovered and still under-studied object from the FU Orionis type. The FUor phenomenon is very rarely observed, but it is essential for stellar evolution. Since we only know about twenty stars of this type, the study of each new object is very important for our knowledge. Our data were obtained in optical spectral region with the BVRI Johnson-Cousins set of filters during the period from September 2011 to April 2021. In order to follow the photometric history of the object, we measured its stellar magnitudes on available plates from the Mikulski Archive for Space Telescopes. The collected archival data suggest that the rise in brightness of V900 Mon began after January 1989 and the outburst goes on so far. In November 2009, when the outburst was registered, the star had already reached the level of brightness close to the current one. Our observations indicate that during the period 2011-2017 the stellar magnitude increased gradually in each pass band. The observed amplitude of the outburst is about 4 magnitudes (R). During the last three years, the increase in brightness has stopped and there has even been a slight decline. The comparison of light curves of the known FUor objects shows that they are very diverse and are rarely repeated. However, the photometric data we have so far show that V900 Mon's light curve is somewhat similar to those of V1515 Cyg and V733 Cep.