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HL Draconis (HL Dra) is an oscillating eclipsing binary with an orbital period of 0.944276 d. By analysing the light curves observed with the Transiting Exoplanet Survey Satellite (TESS), it has been detected that HL Dra is an Algol-like binary system with a mass ratio of 0.361, where the radius filling factor (=r/RL) of the primary and secondary component is $87\, {{\ \rm per\ cent}}$ and $98\, {{\ \rm per\ cent}}$, respectively. The secondary component is almost filling its critical Roche lobe, but not entirely. The absolute parameters of the component are estimated in this paper. Both the variable O’Connell effect and the existence of superflares indicate that the secondary should have strong magnetic activities. It is discovered that the O − C curve shows a sinusoidal variation with a period of 129.88 yr. This cyclic change might be caused by the effects of the light travel time as a result of the presence of a cool red dwarf third body. The correlations between the changes of the O − C diagrams and the variable O’Connell effect during TESS observations might be caused by the magnetic activity of the secondary (i.e. the Applegate mechanism). After removal of the binary model, a total of 252 pulsation frequencies are detected from the high-precision photometric data of TESS, including 28 multiplets of tidally split frequencies. We identify two radial modes, 21 non-radial p-modes and three non-radial f-modes from the possible independent frequencies. All of these features reveal that HL Dra is a very interesting system for further investigations of binary formation and evolution, and for tidal interactions on stellar pulsations and on magnetic activities.

We have performed a model analysis of the optical radiation from the young pre-cataclysmic variable Lan 30 and determined the set of its fundamental characteristics. Spectroscopic and multiband photometric observations have been carried out with the BTA and Zeiss-1000 telescopes at the Special Astrophysical Observatory of the Russian Academy of Sciences. The technique for modeling irradiated atmospheres of stars in close binary systems has been used for the computations of synthetic spectra and light curves. We have established the dominance of the radiation from an sdB subdwarf with atmospheric parameters $$T_{\textrm{eff}}=30\,500\pm 1100$$ K and $$\log g=5.60\pm 0.10$$ in the optical band under moderate influence of reflection effects on the light curves and HI line profiles. We have analyzed the measured sets of radial velocities of the primary component by taking into account the possible influence of reflection effects on them and refined their semi-amplitude $$K_{1}=56.3\pm 2.0$$ km s $${}^{-1}$$ . We have found that the nearly sinusoidal shape of the light curves of Lan 30 allows only an upper limit on the orbital inclination to be set. Based on agreement between the model and observed light curves, we have estimated the radii of the components at various inclinations. To determine their lower limit, we have used evolutionary estimates of the radii of low-mass main-sequence stars. The mass of the primary component has been taken to be equal to the normal mass of single sdB subdwarfs, $$M_{1}=0.47M_{\odot}$$ . As a result, we have determined the ranges of possible variations of the orbital inclination $$i=33^{\circ}{-}45^{\circ}$$ and semimajor axis, the radii of the components, and the mass $$M_{2}=0.127{-}0.175M_{\odot}$$ of the red dwarf.

The closet exoplanets to the Sun provide opportunities for detailed characterization of planets outside the Solar System. We report the discovery, using radial velocity measurements, of a compact multiplanet system of super-Earth exoplanets orbiting the nearby red dwarf star GJ 887. The two planets have orbital periods of 9.3 and 21.8 days. Assuming an Earth-like albedo, the equilibrium temperature of the 21.8-day planet is ~350 kelvin. The planets are interior to, but close to the inner edge of, the liquid-water habitable zone. We also detect an unconfirmed signal with a period of ~50 days, which could correspond to a third super-Earth in a more temperate orbit. Our observations show that GJ 887 has photometric variability below 500 parts per million, which is unusually quiet for a red dwarf. © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works, S.V.J. acknowledges the support of the German Science Foundation (DFG) Research Unit FOR2544 "Blue Planets around Red Stars" project (JE 701/3-1) and DFG priority program SPP 1992 "Exploring the Diversity of Extrasolar Planets" JE 701/5-1. J.R.Ba.nd CA.H. acknowledge support from STFC Consolidated Grants ST/P000584/1 and ST/T000295/1. R.PN. was supported by STFC Consolidated Grant ST/P000592/1. E.R. M.J.L.-G. N,M., and P.J.A. acknowledge support from the Spanish Agencia Estatal de Investigacion through projects AYA2017-89637R, AYA2016-79425-C3-3-S, ESP2017-87676-C5-2-R, and ESP2017-87143R and the Centre of Excellence "Severo Ochoa" Instituto de Astrofisica de Andalucia (SEV-2017-0709). E.P. acknowledges support from the Spanish Agencia Estatal de Investigacion PGC2018-098153-B-C31 and ESP2016-80435-C2-2-R. Z.M.B. acknowledges funds from CONICYT/FONDECYT Postdoctorado 3180405. G.A.L.C. acknowledges support from the Swiss National Science Foundation. M.R.D.acknowledges support of CONICYT/PFCHA-Doctorado Nacional 21140646, Chile. I.R. acknowledges support from the Spanish Ministry of Science and Innovation and the European Regional Development Fund through grants ESP2016-80435-C2-1-R and PGC2018-098153-B-C33 and the Generalitat de Catalunya/CERCA program. H.R.A.J. acknowledges support from the U.K.Science and Technology Facilities Council grant ST/M001008/1. C.G.T. is supported by Australian Research Council grants DP0774000, DP130102695, and DP170103491. J.T. wassupported by NASA through Hubble Fellowship grant HST-HF2-51399.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. G.A.-E is supported by the Ministerio de Ciencia, Innovacion y Universidades Ramon y Cajal fellowship RYC-2017-22489 and by the Science and Technology Facilities Council grant number ST/P000592/1.

The envelopes accreted by white dwarf stars from their hydrogen-rich companions1 experience thermonuclear-powered runaways2,3 observed as classical nova eruptions4,5 peaking at 105–106 solar luminosities6–9. Virtually all nova progenitors—‘nova-like variables’—exhibit high mass transfer rates to their white dwarfs before and after an eruption10. Surprisingly, 10–1,000 times lower mass transfer rate11 binaries, exhibiting accretion-powered ‘dwarf nova’ outbursts12, exist at identical orbital periods. Nova shells surrounding dwarf novae13–16 demonstrate that at least some novae metamorphize into dwarf novae17,18, though the mechanisms and timescales governing mass transfer rate variations are poorly understood. Here, we report simulations of the multi-Gyr evolution of novae modelling every eruption’s thermonuclear runaway, mass and angular momentum losses, feedback due to irradiation and variable mass transfer rate, and orbital size and period changes. These feedback-dominated simulations reproduce the observed range of mass transfer rates at a given orbital period, with large and cyclic kyr–Myr timescale changes. They also demonstrate Myr-long deep hibernation (complete stoppage of mass transfer), but only in short-period binaries; that initially different binaries converge to become nearly identical systems; low-mass-transfer-rate dwarf novae occasionally generate novae; and that the masses of white dwarfs decrease monotonically, but only slightly while their red dwarf companions are consumed. Cataclysmic variables—a binary pairing of a white dwarf and a hydrogen-rich donor star—experience mass transfer and other complex interactions. This numerical simulation by Hillman et al. models in particular the feedback between the stellar pair, and succeeds in reproducing many of the observed characteristics of cataclysmic variables.

В работе представлен краткий обзор исследований EXO 040830-7134.7 с момента открытия рентгеновского транзиента. Анализируются данные его наблюдений в рентгеновском и оптическом диапазонах спектра. В результате обработки кривых блеска и путем визуального контроля обнаружено более 30 значительных вспышек. Зафиксирована максимальная энергия вспышки 1034 эрг. Публикация проиллюстрирована изображениями с наиболее характерными вспышками., This paper provides a brief overview of the research on EXO 040830-7134.7 since the discoveryof the X-ray transient. The data of its observations in the X-ray and optical ranges of the spectrum areanalyzed. As a result of processing the light curves and by means of visual control, more than 30 significantflares have been detected. The maximum flare energy is recorded at 1034 erg. Images with the most typicalflares are presented in this publication., Известия Крымской астрофизической обсерватории, Выпуск 118 (2) 2022, Pages 28-33

Ultra-short-period (USP) exoplanets have orbital periods shorter than one day. Precise masses and radii of USPs could provide constraints on their unknown formation and evolution processes. We report the detection and characterization of the USP planet GJ 367b using high precision photometry and radial velocity observations. GJ 367b orbits a bright (V-band magnitude = 10.2), nearby, red (M-type) dwarf star every 7.7 hours. GJ 367b has a radius of $0.718 \pm 0.054$ Earth-radii, a mass of $0.546 \pm 0.078$ Earth-masses, making it a sub-Earth. The corresponding bulk density is $8.106 \pm 2.165$ g cm$^-3$, close to that of iron. An interior structure model predicts the planet has an iron core radius fraction of $86 \pm 5\%$, similar to Mercury's interior., Comment: Note: "This is the author's version of the work. It is posted here by permission of the AAAS for personal use, not for redistribution. The definitive version was published in Science , (2021-12-03), doi: 10.1126/science.aay3253"

The orbital period of Nova-like variable RW Tri is expected to experience a long-term evolution due to a stable mass transfer from the red dwarf to the white dwarf. By adding 297 new eclipse timings obtained from our own observations and a cross-identification of many databases, we fully reinvestigated the variations in orbital period of RW Tri, based on a total of 658 data points spanning over 80 years. The new O-C diagram demonstrates a more complicate pattern than a pure sinusoidal modulation shown in the previous O-C analyses. The best fit of the O-C variations is a quadratic-plus-sinusoidal curve with a period of 22.66 (2) years and a typical decrease rate of P˙ = −2d.32(4) × 10−9 yr−1. To explain secular orbital period decrease, the magnetic braking effect is required to cause the orbital angular moment loss in RW Tri with a mass ratio less than unity, while a conserved mass transfer is also enough for RW Tri with a mass ratio larger than unity. No matter what the mass ratio is, a slightly enhanced mass transfer rate, 2.4–5.3 × 10−9 M⊙ yr−1, derived from our O-C diagram, providing an evidence supporting the disk instability model and the standard/revised models of cataclysmic variable evolution, is almost the same as that obtained from the light-curve modeling. This further confirms our observed orbital period decrease and the controversial system parameter, mass transfer rate. Our updated O-C analysis further verifies the claimed cyclical changes of orbital period with a period range of 21–24 years, which is approximately one half of the results in the literature. In accordance with the light-travel time effect, this periodical variation shown in our new O-C diagram indicates a brown dwarf hidden in RW Tri at a coplanar orbit. Note that the large scatter in the data range of 0–3 × 104 cycles requires the high-precision photometry in the longer base line in the future.

A modern paradigm on the sources of galactic cosmic rays includes supernovae and supernova remnants as the powerful ones to accelerate particles up to ∼ 10 17 eV. Meanwhile, the recent experimental data obtained by PAMELA, AMS-02, Fermi-LAT, CALET, and DAMPE require the existence of other cosmic-ray sources located nearby the solar system, at the distances less than 1 kpc. Presence of such local sources could explain the unexpected rise of the positron fraction in cosmic rays, the observed electron fluxes with the energies more than one TeV, complex shapes of the proton and helium spectra, and anomalous low-energy cosmic rays. Here we consider active dwarf stars as possible sources of Galactic cosmic rays in the energy range up to 10 14 eV. These stars are producing powerful stellar flares sometimes with energy release more than 10 36 erg. Meanwhile, the generation of high-energy cosmic rays should be accompanied by the high-energy γ -ray emission, which may be observed. Here we present the results of the SHALON long-term observations of generation of γ -ray emission above 800 GeV from the active red dwarf stars.

The Kepler data show that habitable small planets orbiting Red Dwarf stars (RDs) are abundant, and hence might be promising targets to look at for biomarkers and life. Planets orbiting within the Habitable Zone of RDs are close enough to be tidally locked. Some recent works have cast doubt on the ability of planets orbiting RDs to support life. In contrast, it is shown that temperatures suitable for liquid water and even for organic molecules may exist on tidally locked planets of RDs for a wide range of atmospheres. We chart the surface temperature distribution as a function of the irradiation, greenhouse factor and heat circulation. The habitability boundaries and their dependence on the atmospheric properties are derived. Extending our previous analyses of tidally locked planets, we find that tidally locked as well as synchronous (not completely locked) planets of RDs and K-type stars may support life, for a wider range of orbital distance and atmospheric conditions than previously thought. In particular, it is argued that life clement environments may be possible on tidally locked and synchronously orbiting planets of RDs and K-type stars, with conditions supporting Oxygenic Photosynthesis, which on Earth was a key to Complex life. Different climate projections and the biological significance of tidal locking on putative complex life are reviewed. We show that when the effect of continuous radiation is taken into account, the Photo-synthetically Active Radiation (PAR) available on tidally locked planets, even of RDs, could produce a high Potential Plant Productivity, in analogy to mid-summer growth at high latitudes on Earth. Awaiting the findings of TESS and JWST, we discuss the implications of the above arguments to the detection of biomarkers such as liquid water and oxygen, as well as to the abundance of biotic planets and life., Comment: 23 pages, 5 figures, accepted for publication in the International Journal of Astrobiology. arXiv admin note: text overlap with arXiv:1802.00141

The results of a long-term photometric observations of the cataclysmic variable EX Dra acquired between 2014 and 2016 at the Crimean Station of the Sternberg Astronomical Institute (24 nights, more than 10 500 measurements) are presented. The observations were performed using CCD photometers mounted on 50-cm and 60-cm telescopes in the visible and red, during both quiescence and the active state. For completeness, photometric observations obtained at the Ondrejov Observatory in 2010 in the V and R Johnson filters are also used in the analysis. The new observations of EX Dra are used to derive the orbital period of the system, which agrees well with earlier determinations. A combined model that takes into account the radiation fluxes from the gaseous stream and a hot spot on the lateral surface of the accretion disk is used to determine the parameters of the system components (white dwarf, red dwarf, accretion disk and hot spot, and gaseous stream). Variations of the parameters when the system changes from one activity state to the other are considered. Six light curves displaying unsatisfactory agreement between the observed and theoretical light curves can be successfully fitted using a version of the combined model that includes hot spots on the secondary’s surface. This model is able to qualitatively reproduce a secondary minima in the light curves that exhibits shifts of this minimum from phase 0.5. The parameters of dark spots on the red-dwarf surface were determined. The data obtained indicate that the outbursts in the EX Dra system are related to instability of the matter outflow from the secondary.

We present the discovery of a unique object, a chemically peculiar Ap-type star showing $\delta$ Scuti pulsations which is bound in an eclipsing binary system with an orbital period shorter than 3 days. HD 99458 is, therefore, a complex astrophysical laboratory opening doors for studying various, often contradictory, physical phenomena at the same time. It is the first Ap star ever discovered in an eclipsing binary. The orbital period of 2.722 days is the second shortest among all known chemically peculiar (CP2) binary stars. Pulsations of $\delta$ Scuti type are also extremely rare among CP2 stars and no unambiguously proven candidate has been reported. HD 99458 was formerly thought to be a star hosting an exoplanet, but we definitely reject this hypothesis by using photometric observations from the K2 mission and new radial velocity measurements. The companion is a low-mass red dwarf star ($M_{2}=0.45(2)$ M$_{\odot}$) on an inclined orbit ($i=73.2(6)$ degrees) that shows only grazing eclipses. The rotation and orbital periods are synchronized, while the rotation and orbital axes are misaligned. HD 99458 is an interesting system deserving of more intense investigations., Comment: 8 pages, 4 figures, 4 tables, accepted in MNRAS

While most of the exoplanets have been found orbiting around solar-type stars, low-mass stars have recently been recognized as ideal exo-life laboratory. Currently, stellar activity is one of the limiting factors for the characterization of Earth-twins and for assessing their habitability: understanding the activity of M dwarfs is thus crucial. In this contribution I present the spectroscopic analysis of the quiet early-M dwarfs monitored within the HADES (HArps-n red Dwarf Exoplanet Survey) radial velocity survey. The spectra allow us to analyze simultaneously the Ca ii H&K doublet and the Hydrogen Balmer series, while the intensive follow up gives us a large number of spectra ( 100) for each target. We complement this dataset with ground-based follow-up photometry and archival X-ray data. I present our results on the activity-rotation-stellar parameters and flux-flux relationships, and discuss the correlation of emission fluxes at low activity levels and the evolution timescales of active regions.

We present the results of a radial velocity survey of 20 white dwarf plus M dwarf binaries selected as a follow up to a \textit{Hubble Space Telescope} study that aimed to spatially resolve suspected binaries. Our candidates are taken from the list of targets that were spatially unresolved with \textit{Hubble}. We have determined the orbital periods for 16 of these compact binary candidates. The period distribution ranges from 0.14 to 9.16\,d and peaks near 0.6\,d. The original sample therefore contains two sets of binaries, wide orbits ($\approx100-1000$\,au) and close orbits ($\lesssim1-10$\,au), with no systems found in the $\approx10-100$\,au range. This observational evidence confirms the bimodal distribution predicted by population models and is also similar to results obtained in previous studies. We find no binary periods in the months to years range, supporting the post common envelope evolution scenario. One of our targets, WD\,1504+546, was discovered to be an eclipsing binary with a period of 0.93\,d.

This study is the direct continuation of the work performed in Hillman et al. (2020) where they used their feedback dominated numerical simulations to model the evolution of four initial models with white dwarf (WD) masses of 0.7 and 1.0M_Solar and red dwarf (RD) masses of 0.45 and 0.7M_Solar from first Roche-lobe contact of the donor RD, over a few times 10^9 years, until the RD was eroded down to below 0.1M_Solar. This study presents an in-depth analysis of their four models complimented by three models with a higher WD mass of 1.25M_Solar, one of which comprises an oxygen-neon (ONe) core. Common features were found for all seven models on a secular time scale as well as on a cyclic time scale. On the other hand, certain features were found that are strongly dependent either on the WD or the RD mass but are indifferent to the other of the two. Additionally, a model with a WD composed of an ONe core was compared with its corresponding carbon oxygen (CO) core WD model and found to have a significant impact on the heavy element abundances in the ejecta composition., Accepted for publication in the MNRAS

Spectroscopy of transiting exoplanets can be used to investigate their atmospheric properties and habitability. Combining radial velocity (RV) and transit data provides additional information on exoplanet physical properties. We detect a transiting rocky planet with an orbital period of 1.467 days around the nearby red dwarf star Gliese 486. The planet Gliese 486 b is 2.81 Earth masses and 1.31 Earth radii, with uncertainties of 5%, as determined from RV data and photometric light curves. The host star is at a distance of ~8.1 parsecs, has a J-band magnitude of ~7.2, and is observable from both hemispheres of Earth. On the basis of these properties and the planet's short orbital period and high equilibrium temperature, we show that this terrestrial planet is suitable for emission and transit spectroscopy. © 2021 American Association for the Advancement of Science. All rights reserved., Funding was provided by Deutsche Forschungsgemeinschaft through research unit FOR2544 "Blue Planets around Red Stars" and priority program SPP1992 "Exploring the Diversity of Extrasolar Planets"; Agencia Estatal de Investigacion of the Ministerio de Ciencia e Innovacion and the European Regional Development Fund through projects PID2019-109522GB-C51/2/3/4, PGC2018-098153-B-C33, SEV-2017-0709, MDM-2017-0737, AYA2016-79425-C3-1/2/3-P, ESP2016-80435-C2-1-R, and SEV-2015-0548; Klaus Tschira Stiftung; European Union's Horizon 2020 through Marie Sklodowska Curie grant 713673; "la Caixa" through INPhINT grant LCF/BQ/IN17/1162033; NASA through grants NNX17AG24G, 80NSSC19K0533, 80NSSC19K1721, and 80NSSC18K158 and the NASA Science Mission Directorate; Japan Society for the Promotion of Science KAKENHI through grants JP17H04574, JP18H01265, and JP18H05439; and Japan Science and Technology Agency PRESTO through grant JPMJPR1775.

We scrutinize the red dwarf component in the eclipsing binary system V471 Tau in order to unravel relations between different activity layers from the stellar surface through the chromosphere up to the corona. We aim at studying how the magnetic dynamo in the late-type component is affected by the close white dwarf companion. We use space photometry, high resolution spectroscopy and X-ray observations from different space instruments to explore the main characteristics of magnetic activity. From K2 photomery we find that 5-10 per cent of the apparent surface of the red dwarf is covered by cool starspots. From seasonal photometric period changes we estimate a weak differential rotation. From the flare activity we derive a cumulative flare frequency diagram which suggests that frequent flaring could have a significant role in heating the corona. Using high resolution spectroscopy we reconstruct four Doppler images for different epochs which reveal an active longitude, that is, a permanent dominant spot facing the white dwarf. From short term changes in the consecutive Doppler images we derive a weak solar-type surface differential rotation with 0.0026 shear coefficient, similar to that provided by photometry. The long-term evolution of X-ray luminosity reveals a possible activity cycle length of 12.7 ys, traces of which were discovered also in the H$\alpha$ spectra. We conclude that the magnetic activity of the red dwarf component in V471 Tau is strongly influenced by the close white dwarf companion. We confirm the presence of a permanent dominant spot (active longitude) on the red dwarf facing the white dwarf. The weak differential rotation of the red dwarf is very likely the result of tidal confinement by the companion. We find that the periodic appearance of the inter-binary H$\alpha$ emission from the vicinity of the inner Lagrangian point is correlated with the activity cycle., Comment: 21 pages, 18 figures, 5 tables, submitted to Astronomy and Astrophysics

Spherical asymmetries are prevalent within the outflows of AGB stars. Since binary interaction with a stellar or planetary companion is thought to be the underlying mechanism behind large-scale structures, we included the effects of UV radiation originating from a stellar companion in our chemical kinetics model. The one-dimensional model provides a first approximation of its effects on the chemistry throughout the outflow. The presence of a close-by stellar companion can strongly influence the chemistry within the entire outflow. Its impact depends on the intensity of the radiation (set by the stellar radius and blackbody temperature) and on the extinction the UV radiation experiences (set by the outflow density, density structure, and assumed radius of dust formation). Parent species can be photodissociated by the companion, initiating a rich photon-driven chemistry in the inner parts of the outflow. The outcome depends on the balance between two-body reactions and photoreactions. If two-body reactions dominate, chemical complexity within the outflow increases. This can make the abundance profiles of daughters appear like those of parents, with a larger inner abundance and a gaussian decline. If photoreactions dominate, the outflow can appear molecule-poor. We model three stellar companions. The impact of a red dwarf companion is limited. Solar-like companions show the largest effect, followed by a white dwarf. A stellar companion can also lead to the formation of unexpected species. The outflow's molecular content, especially combined with abundance profiles, can indicate a stellar companion's presence. Our results pave the way for further outflow-specific (three-dimensional) model development., Comment: Accepted for publication in the Monthly Notices of the Royal Astronomical Society. Main paper: 20 pages, 12 figures, 4 tables. Supplementary material: 42 pages, 66 figures, 2 tables. Revision: corrections to legibility of the label of Fig. A2

Most stars in the Universe are red dwarfs. They outnumber stars like our Sun by a factor of 5 and outlive them by another factor of 20 (population-weighted mean). When combined with recent observations uncovering an abundance of temperate, rocky planets around these diminutive stars, we're faced with an apparent logical contradiction - why don't we see a red dwarf in our sky? To address this "Red Sky paradox", we formulate a Bayesian probability function concerning the odds of finding oneself around a F/G/K-spectral type (Sun-like) star. If the development of intelligent life from prebiotic chemistry is a universally rapid and ensured process, the temporal advantage of red dwarfs dissolves softening the Red Sky paradox, but exacerbating the classic Fermi paradox. Otherwise, we find that humanity appears to be a 1-in-100 outlier. Whilst this could be random chance (resolution I), we outline three other non-mutually exclusive resolutions (II-IV) that broadly act as filters to attenuate the suitability of red dwarfs for complex life. Future observations may be able to provide support for some of these. Notably, if surveys reveal a paucity temperate rocky planets around the smallest (and most numerous) red dwarfs then this would support resolution II. As another example, if future characterization efforts were to find that red dwarf worlds have limited windows for complex life due to stellar evolution, this would support resolution III. Solving this paradox would reveal guidance for the targeting of future remote life sensing experiments and the limits of life in the cosmos., Comment: Published in PNAS

Theory suggests that the orbits of a large fraction of binary systems, including planet-star binary systems, shrink by few orders of magnitude after formation. But so far, only one hot Jupiter with tidally-driven orbital decay has been found by transit timing variations. We propose to search for orbital decay companions in heartbeat star systems because the orbital angular momentum is effectively transferred to the host star causing tidal dissipation. KIC 3766353 is one of the heartbeat stars with tidally excited oscillations. We acquired the primary and the secondary eclipse time variations from the \textit{Kepler} photometric light curves. Timing analysis shows that KIC 3766353 is a hierarchical triple system with a hidden third body and a red dwarf (mass $0.35\ M_{\odot}$, radius $0.34\ R_{\odot}$) in its inner orbit. The minimum mass of the third body is $\sim 0.26 \ M_{\odot}$, and the distance from the inner orbital is $\sim 111.4 \ R_{\odot}$. The period decay rate of the red dwarf is approximately 358 ms yr$^{-1}$. The combined effects of the light-travel time and the orbital decay lead to the observed timing variations. Future monitoring with a long time base-line observations is required to delve into the contributions of these two effects., Comment: 10 pages, 7 figures, and 2 tables. Accepted for publication in MNRAS

Full list of authors: Soto, M. G.; Anglada-Escudé, G.; Dreizler, S.; Molaverdikhani, K.; Kemmer, J.; Rodríguez-López, C.; Lillo-Box, J.; Pallé, E.; Espinoza, N.; Caballero, J. A.; Quirrenbach, A.; Ribas, I.; Reiners, A.; Narita, N.; Hirano, T.; Amado, P. J.; Béjar, V. J. S.; Bluhm, P.; Burke, C. J.; Caldwell, D. A.; Charbonneau, D.; Cloutier, R.; Collins, K. A.; Cortés-Contreras, M.; Girardin, E.; Guerra, P.; Harakawa, H.; Hatzes, A. P.; Irwin, J.; Jenkins, J. M.; Jensen, E.; Kawauchi, K.; Kotani, T.; Kudo, T.; Kunimoto, M.; Kuzuhara, M.; Latham, D. W.; Montes, D.; Morales, J. C.; Mori, M.; Nelson, R. P.; Omiya, M.; Pedraz, S.; Passegger, V. M.; Rackham, B. V.; Rudat, A.; Schlieder, J. E.; Schöfer, P.; Schweitzer, A.; Selezneva, A.; Stockdale, C.; Tamura, M.; Trifonov, T.; Vanderspek, R.; Watanabe, D., One of the main objectives of the Transiting Exoplanet Survey Satellite (TESS) mission is the discovery of small rocky planets around relatively bright nearby stars. Here, we report the discovery and characterization of the transiting super-Earth planet orbiting LHS 1478 (TOI-1640). The star is an inactive red dwarf (J ∼ 9.6 mag and spectral type m3 V) with mass and radius estimates of 0.20 ± 0.01M· and 0.25 ± 0.01R· , respectively, and an effective temperature of 3381 ± 54 K. It was observed by TESS in four sectors. These data revealed a transit-like feature with a period of 1.949 days. We combined the TESS data with three ground-based transit measurements, 57 radial velocity (RV) measurements from CARMENES, and 13 RV measurements from IRD, determining that the signal is produced by a planet with a mass of 2.33-0.20+0.20 Mâ• and a radius of 1.24-0.05+0.05 Ra• . The resulting bulk density of this planet is 6.67 g cm-3, which is consistent with a rocky planet with an Fe-and MgSiO3-dominated composition. Although the planet would be too hot to sustain liquid water on its surface (its equilibrium temperature is about ∼595 K, suggesting aVenus-like atmosphere), spectroscopic metrics based on the capabilities of the forthcoming James Webb Space Telescope and the fact that the host star is rather inactive indicate that this is one of the most favorable known rocky exoplanets for atmospheric characterization. © 2021 ESO., CARMENES is an instrument at the Centro Astronómico Hispano-Alemán (CAHA) at Calar Alto (Almería, Spain), operated jointly by the Junta de Andalucía and the Instituto de Astrofísica de Andalucía (CSIC). CARMENES was funded by the Max-Planck-Gesellschaft (MPG), the Consejo Superior de Investigaciones Científicas (CSIC), the Ministerio de Economía y Competitividad (MINECO) and the European Regional Development Fund (ERDF) through projects FICTS-2011-02, ICTS-2017-07-CAHA-4, and CAHA16-CE-3978, and the members of the CARMENES Consortium (Max-Planck-Institut für Astronomie, Instituto de Astrofísica de Andalucía, Landessternwarte Königstuhl, Institut de Ciències de l’Espai, Institut für Astrophysik Göttingen, Universidad Complutense de Madrid, Thüringer Landessternwarte Tautenburg, Instituto de Astrofísica de Canarias, Hamburger Sternwarte, Centro de Astrobiología and Centro Astronómico Hispano-Alemán), with additional contributions by the MINECO, the Deutsche Forschungsgemeinschaft through the Major Research Instrumentation Programme and Research Unit FOR2544 “Blue Planets around Red Stars”, the Klaus Tschira Stiftung, the states of Baden-Württemberg and iedersachsen, and by the Junta de Andalucía. This paper included data collected by the TESS mission. Funding for the TESS mission is provided by the NASA’s Science Mission Directorate. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. This work made use of observations from the LCOGT network. LCOGT telescope time was granted by NOIRLab through the Mid-Scale Innovations Program (MSIP), which is funded by the National Science Foundation. We acknowledge financial support from STFC grants ST/P000592/1 and ST/T000341/1, NASA grant NNX17AG24G, the Agencia Estatal de Investigación of the Ministerio de Ciencia, Innovación y Universidades and the ERDF through projects PID2019-109522GB-C5[1:4]/AEI/10.13039/501100011033, PGC2018-098153-B-C3[1,3] and the Centre of Excellence “Severo Ochoa” and “María de Maeztu” awards to the Instituto de Astrofísica de Canarias (SEV-2015-0548), Instituto de Astrofísica de Andalucía (SEV-2017-0709), and Centro de Astrobiología (MDM-2017-0737), the Generalitat de Catalunya/CERCA programme, Grant-in-Aid for JSPS Fellows Grant (JP20J21872), JSPS KAKENHI Grant (22000005, JP15H02063,JP18H01265, JP18H05439, JP18H05442, JP19K14783), JST PRESTO Grant (JPMJPR1775), and University Research Support Grant from the National Astronomical Observatory of Japan.

A nearby red dwarf doesn’t emit flares or harmful radiation — so its planets might have atmospheres. A nearby red dwarf doesn’t emit flares or harmful radiation — so its planets might have atmospheres.

ASAS J174406+2446.8 was originally found as a $\delta$ Scuti-type pulsating star with the period P=0.189068 $days$ by ASAS survey. However, the LAMOST stellar parameters reveal that it is far beyond the red edge of pulsational instability strip on the $\log g-T$ diagram of $\delta$ Scuti pulsating stars. To understand the physical properties of the variable star, we observed it by the 1.0-m Cassegrain reflecting telescope at Yunnan Observatories. Multi-color light curves in B, V, R$_{c}$ and I$_{c}$ bands were obtained and are analyzed by using the W-D program. It is found that this variable star is a shallow-contact binary with an EB-type light curve and an orbital period of 0.3781\,days rather than a $\delta$ Scuti star. It is a W-subtype contact binary with a mass ratio of $1.135(\pm0.019)$ and a fill-out factor of $10.4(\pm5.6)\,\%$. The situation of ASAS J174406+2446.8 resembles those of other EB-type marginal-contact binaries such as UU Lyn, II Per and GW Tau. All of them are at a key evolutionary phase from a semi-detached configuration to a contact system predicted by the thermal relaxation oscillation theory. The linear ephemeris was corrected by using 303 new determined times of light minimum. It is detected that the O - C curve shows a sinusoidal variationthat could be explained by the light-travel-time effect via the presence of a cool red dwarf. The present investigation reveals that some of the $\delta$ Scuti-type stars beyond the red edge of pulsating instability strip on the $\log g-T$ diagram are misclassified eclipsing binaries. To understand their structures and evolutionary states, more studies are required in the future., Comment: 12 pages, 9 figures

We use 20 years of astrometric data from the RECONS program on the CTIO/SMARTS 0.9-m to provide new insight into multiple star systems in the solar neighborhood. We provide new and updated parallaxes for 210 systems and derive nine high-quality astrometric orbits with periods of 2.49 - 16.63 years. Using a total of 542 systems' parallaxes from RECONS, we compare systems within 25 parsecs to Gaia DR2 to define criteria for selecting unresolved astrometric multiples from the DR2 results. We find that three out of four unresolved multi-star red dwarf systems within 25 pc in DR2 have parallax_error $\geq 0.32$ mas, astrometric_gof_al $\geq 56$, astrometric_excess_noise_sig $\geq 108.0$, ruwe $\geq 2.0$, and parallaxes more than $\sim$10% different than the long-term RECONS results. These criteria have broad applications to any work targeting nearby stars, from studies seeking binary systems to efforts targeting single stars for planet searches., Comment: Accepted for publication in The Astronomical Journal. 23 pages, 7 figures, 3 tables. Contact corresponding author for full electronic tables

We present the results of our new photometric observations of the chromospherically active star FR Cnc performed with a robotic telescope at the Zvenigorod Observatory of INASAN in March 2019. The observations were carried out from March 2 to 13, 2019, in the period of time that coincided most closely in time interval with the observations of this star with the Astrosat space telescope. A total of 450 magnitude estimates were obtained in each of the B, V, and R photometric bands over 12 days (from HJD 2458545.2 to HJD 2458556.5). Based on the V-band photometric variability of the star, we have constructed a map of surface temperature inhomogeneities. According to our estimate, the spot area on the surface of the star was ~12% of its total surface area in early 2019. On March 3, 2019, a flare on FR Cnc was detected during our observations at a time corresponding to HJD = 2458554.25891447 or rotation phase 0.8. The data for the flare suggest a rapid brightening of the star by 0.19m in the B band and by 0.09m in the V band; the flare lasted for about 60 min. The energy radiated in the flare was ITEB = 2.17 × 1033 erg and Ey = 1.40 × 1033 erg in the B and V bands, respectively.

The results of a spottedness study for twelve red dwarf stars covering several decades and based on a vast amount of photometric observations are presented. The analysis makes use of multicolor (UBV RI) photometric monitoring of ten of these stars since 1991 at the Crimean Astrophysical Observatory, as well as data from the literature. The spottedness parameters for selected active BY Dra red dwarfs have been refined using an improved zonal model for the spotted stellar atmospheres to allow for the possible presence of two active longitudes on the stars. Time variations in the spot activity of these systems are analyzed in order to look for possible cycles. Three of the stars show a drift of their spots in the latitude towards the stellar poles; however, the magnitude of this latitude drift is a factor of two to three lower than the analogous value for sunspots. All the stars except for YZ CMi display relationships between the area of the spots and their latitude, with correlation coefficients R from 0.67 to 0.97. Evidence for the presence of activity cycles with durations from 25 to 40 years is found for six stars, which are characterized by synchronous variations in the areas and latitudes of their spots, as well as of the overall photometric brightness.

A radio detection of an old red dwarf might reveal the presence of a planetary system, and open up the search for exoplanets to a new technique.

1SWASP J161335.80$-$284722.2 (hereafter J161335) is an eclipsing red-dwarf binary with an orbital period of $0.229778\:$d, which is around the short-period limit for contact binaries. Three sets of multi-color light curves of J161335 were obtained from different telescopes in 2015 and 2016 and are analyzed using the Wilson–Devinney method. We discovered that the system is a W-type contact system with a contact degree of 19% and a high mass ratio of 0.91. By using all available eclipse times, we found that the observed $-$ calculated $(O-C)$ diagram displays a cyclic oscillation with an amplitude of 0.00196($\pm 0.00006)\:$d and a period of 4.79($\pm 0.14)\:$yr while it undergoes a downward parabolic change. This downward variation corresponds to a continuous decrease in the orbital period at a rate of $dP/dt = -4.26(\pm$0.01) $\times$ 10$^{-7}\:$d$\:$yr$^{-1}$. The small-amplitude oscillation is explained as the light travel-time effect from the gravitational influence of a third body with a lowest mass of $M _{3}$ = 0.15($\pm 0.01)M_{\,\odot }$. In solving the light curves, we found that the third light is increasing, with the wavelength suggesting that the third body may be a cool red dwarf. This is in agreement with the results obtained by analyzing the $O-C$ diagram. The tertiary red dwarf is orbiting the central red-dwarf binary at an orbital separation of 2.8($\pm 0.2$) au. These results suggest that the J161335 system may be formed through early dynamical interaction where the original low-mass component was replaced by a higher-mass third body and the lower-mass component was kicked out to a wider orbit. In this way, a hierarchical triple system similar to J161335 with a high-mass-ratio binary and a small close-in third body is formed.

The closest potentially habitable worlds outside our Solar system orbit a different kind of star than our Sun: smaller red dwarf stars. Such stars can flare frequently, bombarding their planets with biologically damaging high-energy UV radiation, placing planetary atmospheres at risk of erosion and bringing the habitability of these worlds into question. However, the surface UV flux on these worlds is unknown. Here we show the first models of the surface UV environments of the four closest potentially habitable exoplanets: Proxima-b, TRAPPIST-1e, Ross-128b, and LHS-1140b assuming different atmospheric compositions, spanning Earth-analogue to eroded and anoxic atmospheres and compare them to levels for Earth throughout its geological evolution. Even for planet models with eroded and anoxic atmospheres, surface UV radiation remains below early Earth levels, even during flares. Given that the early Earth was inhabited, we show that UV radiation should not be a limiting factor for the habitability of planets orbiting M stars. Our closest neighbouring worlds remain intriguing targets for the search for life beyond our Solar system., This article has been accepted for publication in MNRAS, published by Oxford University Press on behalf of the Royal Astronomical Society

The HArps-n red Dwarf Exoplanet Survey is providing a major contribution to the widening of the current statistics of low-mass planets, through the in-depth analysis of precise radial velocity measurements in a narrow range of spectral sub-types. As part of that program, we obtained radial velocity measurements of Gl 686, an M1 dwarf at d = 8.2 pc. The analysis of data obtained within an intensive observing campaign demonstrates that the excess dispersion is due to a coherent signal, with a period of 15.53 d. Almost simultaneous photometric observations were carried out within the APACHE and EXORAP programs to characterize the stellar activity and to distinguish periodic variations related to activity from signals due to the presence of planetary companions, complemented also with ASAS photometric data. We took advantage of the available radial velocity measurements for this target from other observing campaigns. The analysis of the radial velocity composite time series from the HIRES, HARPS and HARPS-N spectrographs, consisting of 198 measurements taken over 20 years, enabled us to address the nature of periodic signals and also to characterize stellar physical parameters (mass, temperature, and rotation). We report the discovery of a super-Earth orbiting at a distance of 0.092 AU from the host star Gl 686. Gl 686 b has a minimum mass of 7.1 +/- 0.9 MEarth and an orbital period of 15.532 +/- 0.002 d. The analysis of the activity indexes, correlated noise through a Gaussian process framework and photometry, provides an estimate of the stellar rotation period at 37 d, and highlights the variability of the spot configuration during the long timespan covering 20 yrs. The observed periodicities around 2000 d likely point to the existence of an activity cycle., Comment: 21 pages, 17 figures, changed paper numbering from X to IX, added a co-author. arXiv admin note: text overlap with arXiv:1607.03632

Magnetic cataclysmic variables are close binaries which consist of a compact object - a white dwarf - and a red dwarf filling its Roche Lobe. Such systems are physical laboratories which enable study of the influence of magnetic fields on matter flows. They often exhibit spin-up or spin-down of the white dwarf, while some systems exhibit more complex behaviour of the spin period change. We monitor changes of the spin periods of white dwarfs in a sample of close binary systems to study interaction of the magnetic field and accretion processes as well as evolution of intermediate polars. Within the framework of our intermediate polar monitoring program, we obtained photometric CCD observations at several observatories. Two-period trigonometric polynomial fitting was used for determination of extrema timings. The (O-C) analysis was performed to study the variability of the orbital and spin periods of the systems. Using data taken during 9 years of observations of the magnetic cataclysmic variable V2306 Cygni (formerly known as 1WGA J1958.2+3232), we detected the spin period variability which shows a spin-up of the white dwarf with a characteristic time of $(53\pm5)\cdot10^4$ years. The value of the spin period was $733.33976$ seconds with the formal accuracy of $0.00015$ seconds. We derived an improved value of the orbital period of the system to be $4.371523\pm0.000009$ hours.

In recent years, several close post-common-envelope eclipsing binaries have been found to show cyclic eclipse timing variations (ETVs). This effect is usually interpreted either as the gravitational interaction among circumbinary bodies and the host binary -- known as the light travel time (LTT) effect -- or as the quadrupole moment variations in one magnetic active component -- known as Applegate mechanism. In this study, we present an analysis of the ETV and the magnetic cycle of the close binary KIC 10544976. This system is composed of a white dwarf and a red dwarf in a short orbital period (0.35 days) and was monitored by ground-based telescopes between 2005 and 2017 and by the Kepler satellite between 2009 and 2013. Using the Kepler data, we derived the magnetic cycle of the red dwarf by two ways: the rate and energy of flares and the variability due to spots. Both methods resulted in a cycle of ~600 days, which is in agreement with magnetic cycles measured for single low-mass stars. The orbital period of KIC 10544976 shows only one long-term variation which can be fitted by an LTT effect with period of ~16.8 yr. Hence, one possible explanation for the ETVs is the presence of a circumbinary body with minimal mass of ~13.4 M_Jup. In the particular scenario of coplanarity between the external body and the inner binary, the third body mass is also ~13.4 M_Jup. In this case, the circumbinary planet must either have survived the evolution of the host binary or have been formed as a consequence of its evolution., 8 pages, 5 figures, 2 tables, Accepted to AJ

As above, so below. Although the fervor of research builds over the impact of the geosphere on planetary habitability, considerably more research is going into understanding how planetary atmospheres may influence the same property. This chapter expands upon, improves the accuracy of, and produces viable models of atmospheres for planets with different orbital distances from red dwarf stars.

Exoplanets Most exoplanets have been detected using either the radial velocity (RV) method or the transit method, which provide only limited information on the planet's physical properties. In the rare cases in which both methods detect the same planet, the combination determines the planet's mass, radius, and density. Trifonov et al. identified a planet, Gliese 486 b, using both RV and transit data. The host star is a red dwarf only 8 parsecs away, making this one of the closest exoplanet systems known. A rocky super-Earth, Gliese 486 b has an equilibrium surface temperature of 700 kelvin. The authors say that it is observationally favorable for searches for an atmosphere. Science , this issue p. [1038][1] [1]: /lookup/doi/10.1126/science.abd7645

There are 88 stars which lack colors, but have measured parallaxes in Gaia EDR3 that place them within 20 pc from the Sun. Among them we found two new common parallax and proper motion (CPPM) companions separated from their primaries by about 3″. The CPPM companion of a nearby (d = 14.98 pc) F1 star, HD 105452 B, was already imaged with the Hubble Space Telescope and is now confirmed with Gaia data and photometrically classified by us as M4 dwarf. The other CPPM companion, SCR J1214-2345 B orbiting an M4.5 dwarf at d = 10.77 pc, represents the faintest brown dwarf discovery made by Gaia so far. It was also imaged by the VISTA Hemisphere Survey and partly detected in the near-infrared. Our photometric classification led to an uncertain spectral type of T1 ± 3 and needs to be confirmed by spectroscopic follow-up.

IO Cnc was classified to be a new G-type (G0) W UMa-type eclipsing binary system. Our first multicolor photometric solutions show that IO Cnc is a new W-subtype shallow contact binary with a fill-out factor of f = 16.1% and a low mass ratio of q = 3.12 (or 1/q = 0.32). During orbital period investigations, a cyclic variation and a downward parabolic variation with a rate of (−1.28 ± 0.43) × 10−7 d yr−1 was discovered in the observed–calculated (O − C) curve. The cyclic variation was analyzed by the light travel time effect (LTTE) via a potential red dwarf companion star, an orbital semi-major axis shorter than 4.88 ± 0.82 AU was obtained. Finally, we collect physical parameters of a sample of 50 G-type shallow contact binaries (f ≤ 20%), it is suggested that most of the G-type shallow contact binaries are undergoing a long-term and periodic orbital period changes, especially more systems show long-term decreases. The long-term orbital period decrease indicates that IO Cnc is in a mass transferring from the more massive component to the less massive one. With the long-term decrease of the orbital period, this shallow contact binary will evolve into a deeper contact one.

We study the possible origin of long-lasting soft X-ray flares on the AD Leo star, which were observed onboard the Extreme Ultraviolet Explorer (EUVE) spacecraft for the period of 1993-2000 [1]. These flares have relatively long rise and decay times of the radiation intensity (τ R ≈ 104 s and τ d ≈ 5 · 103, respectively), as well as a relatively large emission measure EM ≈ 1051cm−3, which exceeds by 1–3 orders of magnitude the emission measure of soft X-ray flares on the Sun. Assuming that the radiation appears in magnetic loops and basing on the observed values of the emission measure and radiation decay time, the authors of [1] determined the typical length $$ \overline{l}\approx 1.5\cdot {10}^{10} cm $$ , electron number density $$ \overline{n}\approx 3\cdot {10}^{11}c{m}^{-3} $$ , and plasma temperature $$ \overline{T}\approx 2.5\cdot 107 $$ K of the loops. This paper considers plasma heating due to dissipation of the electric currents in the coronal magnetic loops of the star induced by the photospheric convection. The large inductance of the loop as an equivalent electric circuit determines the long time of the current rise in the source and explains the observed time of plasma heating and the rise time of the X-ray radiation intensity. It is shown that the parameters of the X-ray sources in the AD Leo atmosphere agree with the parameters calculated under the assumption of simultaneous emission of a great number of loops (about 50) with electric currents greater than 1013 A, which exceeds the electric currents in the solar coronal magnetic loops by 1–3 orders of magnitude. Such an exceeding can be related to the higher photospheric convection velocities on the late-type stars compared with the Sun.