Search

The intensities of the hydrogen Balmer lines of solar-like stars are investigated for stellar chromospheric activity by using the co-source spectral data of the LAMOST Low-Resolution Spectroscopic Survey (LRS) and Medium-Resolution Spectroscopic Survey (MRS). The Balmer H α , H β , H γ , and H δ lines in the LRS data and the H α line in the MRS data are analyzed. The absolute flux indexes, defined as the ratios of the absolute fluxes at the centers of the Balmer lines to the stellar bolometric flux, are employed to indicate the intensity magnitudes of the Balmer lines in response to stellar activity. The H α indexes derived from the LRS data and the MRS data, respectively, are calibrated to be quantitatively consistent with each other. It is found that, as the H α index increases, the H β , H γ , and H δ indexes first present trend of increasing and then decreasing, and finally increase synchronously with the H α index. The distributions of the Balmer line indexes also reveal the three distinct stages of stellar activity (normal stage, intense stage, and extremely intense stage), in which the extremely intense stage is characterized by the synchronous growth of the indexes of the four Balmer lines. The different behaviors of the H β , H γ , and H δ lines from that of the H α line can be interpreted by the different mechanisms by which the line-core intensities are formed, and the three distinct activity stages imply the very different magnetic field environments and physical conditions of solar-like stars. [ABSTRACT FROM AUTHOR]

The article presents an interview with Dave Charbonneau, an astronomer at the Harvard-Smithsonian Center for Astrophysics. He discusses his shift from studying cosmology to focusing on exoplanets, the difficulties he faced in detecting exoplanet reflected light, and the evolution of exoplanet research. Topics discussed include their early academic connection, the technical challenges of using spectrographs, and the significant contributions of early exoplanet discoveries to the field.

Context. Stellar variability strongly impacts the search for low-mass exoplanets with radial velocity techniques. Two types of planet-free time series can be used to quantify this impact: models and direct solar observations after a subtraction of the Solar System planetary contribution. Making a comparison among these approaches is necessary to improve the models, which can then be used for blind tests across a broad range of conditions. Aims. Our objective is therefore to validate the amplitude of the convective blueshift in plages used in our previous works, particularly in blind tests, with HARPS-N solar data. Methods. We applied our model to the structures observed at the time of HARPS-N observations and established a direct comparison between the radial velocity time series. To complete our diagnosis, we also studied the observed radial velocities separately for each diffraction order derived from the individual cross-correlation functions, as well as our line-by-line radial velocities. Results. We find that our previous model had been underestimating the amplitude of the convective blueshift inhibition by a factor of about 2. A direct estimation of the convective blueshift in the spectra, which is shown to be correlated with the plage filling factor, allows us to explain the difference with previous estimations obtained with MDI/SOHO Dopplergrams, based on the specific properties of the Ni line used in this mission. In addition, we identified several instrumental systematics, in particular, the presence of a 2 m s−1 peak-to-peak signal with a period of about 200 days in radial velocity and bisector. This signal could be due to periodic detector warmups, a systematic dependence of the long-term trend on wavelength that is possibly related to the variability of the continuum over time, and/or an offset in radial velocity after the interruption of several months in October 2017. Conclusions. A large amplitude in the convective blueshift inhibition of (360 ms−1, namely twice more than in our previous works) must be used when building synthetic times series for blind tests. The presence of instrumental systematics should also be taken into account when using sophisticated methods based on line properties to mitigate stellar activity when searching for very weak signals. [ABSTRACT FROM AUTHOR]

The morphology of galaxies is shaped by stellar activity, feedback, gas and dust properties, and interactions with surroundings, and can therefore provide insight into these processes. In this paper, we study the spatial offsets between stellar and interstellar medium emission in a sample of 54 main-sequence star-forming galaxies at z ∼ 4–6 observed with the Atacama Large Millimeter/submillimeter Array (ALMA), and drawn from the ALMA Large Program to INvestigate C+ at Early times (ALPINE). We find no significant spatial offset for the majority (∼70 per cent) of galaxies in the sample among any combination of [C  ii ], far-infrared continuum, optical, and ultraviolet emission. However, a fraction of the sample (∼30 per cent) shows offsets larger than the median by more than 3σ significance (compared to the uncertainty on the offsets), especially between [C  ii ] and ultraviolet emission. We find that these significant offsets are of the order of ∼0.5–0.7 arcsec, corresponding to ∼3.5–4.5 kiloparsecs. The offsets could be caused by a complex dust geometry, strong feedback from stars and active galactic nuclei, large-scale gas inflow and outflow, or a combination of these phenomena. However, our current analysis does not definitively constrain the origin. Future, higher resolution ALMA and JWST observations may help resolve the ambiguity. Regardless, since there exist at least some galaxies that display such large offsets, galaxy models and spectral energy distribution fitting codes cannot assume co-spatial emission in all main-sequence galaxies, and must take into account that the observed emission across wavelengths may be spatially segregated. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Aims. Our aim in this paper is to refine the orbital and physical parameters of the HATS-2 planetary system and study transit timing variations and atmospheric composition thanks to transit observations that span more than 10 yr and that were collected using different instruments and pass-band filters. We also investigate the orbital alignment of the system by studying the anomalies in the transit light curves induced by starspots on the photosphere of the parent star. Methods. We analysed new transit events from both ground-based telescopes and NASA's TESS mission. Anomalies were detected in most of the light curves and modelled as starspots occulted by the planet during transit events. We fitted the clean and symmetric light curves with the JKTEBOP code and those affected by anomalies with the PRISM+GEMC codes to simultaneously model the photometric parameters of the transits and the position, size, and contrast of each starspot. Results. We found consistency between the values we found for the physical and orbital parameters and those from the discovery paper and ATLAS9 stellar atmospherical models. We identified different sets of consecutive starspot-crossing events that temporally occurred in less than five days. Under the hypothesis that we are dealing with the same starspots, occulted twice by the planet during two consecutive transits, we estimated the rotational period of the parent star and, in turn the projected and the true orbital obliquity of the planet. We find that the system is well aligned. We identified the possible presence of transit timing variations in the system, which can be caused by tidal orbital decay, and we derived a low-resolution transmission spectrum. [ABSTRACT FROM AUTHOR]

EUV radiation is primarily responsible for driving hydrodynamic mass loss and thus determining whether an exoplanet can retain its atmosphere and water. The Lyman- α flux is primarily responsible for photo-dissociating water and methane, and therefore plays a major role in determining the chemistry in the upper atmospheres of exoplanets. Since interstellar hydrogen absorbs much of the EUV and Lyman- α radiation, reconstruction and theoretical techniques are needed to determine the intrinsic flux levels received by exoplanets. We describe the techniques and their limitations for estimating the extreme ultraviolet (EUV) spectral energy distribution (10–91.2 nm) and hydrogen Lyman- α flux (121.6 nm) emitted by host stars and incident on exoplanet atmospheres. We evaluate how each reconstruction technique can match the observed solar EUV spectral energy distribution and Lyman- α flux. Each technique has its limitations, but the techniques that can reconstruct the observed solar emission and are based on stellar activity observables that are not affected by interstellar absorption should best explain the intrinsic EUV and Lyman- α stellar emission. [ABSTRACT FROM AUTHOR]

While the mission's primary goal was focused on exoplanet detection and characterization, Kepler made and continues to make extraordinary advances in stellar physics. Stellar rotation and magnetic activity are no exceptions. Kepler allowed for these properties to be determined for tens of thousands of stars from the main sequence up to the red giant branch. From photometry, this can be achieved by investigating the brightness fluctuations due to active regions, which cause surface inhomogeneities, or through asteroseismology as oscillation modes are sensitive to rotation and magnetic fields. This review summarizes the rotation and magnetic activity properties of the single main-sequence solar-like stars within the Kepler field. We contextualize the Kepler sample by comparing it to known transitions in the stellar rotation and magnetic-activity evolution, such as the convergence to the rotation sequence (from the saturated to the unsaturated regime of magnetic activity) and the Vaughan-Preston gap. While reviewing the publicly available data, we also uncover one interesting finding related to the intermediate-rotation gap seen in Kepler and other surveys. We find evidence for this rotation gap in previous ground-based data for the X-ray luminosity. Understanding the complex evolution and interplay between rotation and magnetic activity in solar-like stars is crucial, as it sheds light on fundamental processes governing stellar evolution, including the evolution of our own Sun. [ABSTRACT FROM AUTHOR]

We outline the impact of a small two-band UV-photometry satellite mission on the field of stellar physics, magnetospheres of stars, binaries, stellar clusters, interstellar matter, and exoplanets. On specific examples of different types of stars and stellar systems, we discuss particular requirements for such a satellite mission in terms of specific mission parameters such as bandpass, precision, cadence, and mission duration. We show that such a mission may provide crucial data not only for hot stars that emit most of their light in UV, but also for cool stars, where UV traces their activity. This is important, for instance, for exoplanetary studies, because the level of stellar activity influences habitability. While the main asset of the two-band UV mission rests in time-domain astronomy, an example of open clusters proves that such a mission would be important also for the study of stellar populations. Properties of the interstellar dust are best explored when combining optical and IR information with observations in UV. It is well known that dust absorbs UV radiation efficiently. Consequently, we outline how such a UV mission can be used to detect eclipses of sufficiently hot stars by various dusty objects and study disks, rings, clouds, disintegrating exoplanets or exoasteroids. Furthermore, UV radiation can be used to study the cooling of neutron stars providing information about the extreme states of matter in the interiors of neutron stars and used for mapping heated spots on their surfaces. [ABSTRACT FROM AUTHOR]

The emergence of active regions on the Sun is an integral feature of the solar dynamo mechanism. However, details about the generation of active-region-scale magnetism and the journey of this magnetic flux from the interior to the photosphere are still in question. Shifting paradigms are now developing for the source depth of the Sun's large-scale magnetism, the organization of this magnetism into fibril flux tubes, and the role of convection in shaping active-region observables. Here we review the landscape of flux emergence theories and simulations, highlight the role flux emergence plays in the global dynamo process, and make connections between flux emergence on the Sun and other cool stars. As longer-term and higher fidelity observations of both solar active regions and their associated flows are amassed, it is now possible to place new constraints on models of emerging flux. We discuss the outcomes of statistical studies which provide observational evidence that flux emergence may be a more passive process (at least in the upper convection zone); dominated to a greater extent by the influence of convection and to a lesser extent by buoyancy and the Coriolis force acting on rising magnetic flux tubes than previously thought. We also discuss how the relationship between stellar rotation, fractional convection zone depth, and magnetic activity on other stars can help us better understand the flux emergence processes. Looking forward, we identify open questions regarding magnetic flux emergence that we anticipate can be addressed in the next decade with further observations and simulations. [ABSTRACT FROM AUTHOR]

In this study, we revisit 32 planetary systems around evolved stars observed within the framework of the Okayama Planet Search Program (OPSP) and its collaborative framework of the East Asian Planet Search Network to search for additional companions and investigate the properties of stars and giant planets in multiple-planet systems. With our latest radial velocities obtained from Okayama Astrophysical Observatory, we confirm an additional giant planet in the wide orbit of the 75 Cet system (⁠|$P_{\rm {c}} = 2051.62_{-40.47}^{+45.98}\ \rm {d}$|⁠ , |$M_{\rm {c}}\sin i=0.912_{-0.090}^{+0.088}\,\,M_{\rm {J}}$|⁠ , and |$a_{\rm {c}}=3.929_{-0.058}^{+0.052}\ \rm {au}$|⁠), along with five stars exhibiting long-term radial velocity accelerations, which indicates massive companions in the wide orbits. We also find that the radial velocity variations of several planet-harboring stars may indicate additional planet candidates, stellar activities, or other understudied sources. These stars include ϵ Tau, 11 Com, 24 Boo, 41 Lyn, 14 And, HD 32518, and ω Ser. We further constrain the orbital configuration of the HD 5608, HD 14067, HD 120084, and HD 175679 systems by combining radial velocities with astrometry, as their host central stars exhibit significant astrometric accelerations. For other systems, we simply refine their orbital parameters. Moreover, our study indicates that the OPSP planet-harboring stars are more metal poor compared to the currently known planet-harboring stars, and this is likely due to the B − V color upper limit at 1.0 for star selection in the beginning of the survey. Finally, by investigating the less massive giant planets (<5  M J) around currently known planet-harboring evolved stars, we find that metallicity positively correlates with the multiplicity and total planet mass of the system, which can be evidence for the core-accretion planet formation model. [ABSTRACT FROM AUTHOR]

We present the results of our analysis of the manifestations of activity in the young solar analog HD 109833 and estimate the mass loss rate from the atmospheres of its two planets. HD 109833 probably belongs to the Lower Centaurus Crux (LCC) association with an age of 27 3 Myr, but it is not inconceivable that the star is only spatially associated with the association and may be older, although in any case its age does not exceed 100–200 Myr. Based on data from the TESS archive for HD 109833, we have determined the stellar rotation period days and the photometric variability amplitude (about 0.6 of the mean stellar brightness) and estimated the spot areas on its surface, which exceed the maximum sunspot area and are 15 200–17 700 m.s.h. Based on data from the All-Sky Automated Survey archive, we have revealed a stellar activity cycle with a duration days (5.3 years). Both planets in the HD 109833 system are characterized as sub-Neptunes with radii of 2.9 and 2.6 and periods of 9.2 and 13.9 days. The mass loss rates by the planetary atmospheres have been found using an approximate formula corresponding to the energy-limited atmospheric escape model. To estimate the flux, we have applied analytical dependences relating the flux and the parameter and information about the distribution of these quantities for G-type stars, suggesting that there are two pronounced peaks with maxima for values and dex in low-activity and active stars, respectively. In addition, we have used the relation between the X-ray flux from the star and . The value found is comparable to the estimate obtained by applying the parameter for active stars and exceeds it by a factor of 4. Both exoplanets HD 109833 b and c being considered by us fall into the region on the diagram in which the populations of rocky and volatile-rich exoplanets overlap and do not allow their masses to be estimated unambiguously. Our calculations were performed for two cases—rocky exoplanets and volatile-rich exoplanets. The masses of the exoplanets HD 109833 b and c are, respectively, 34.9 and 24 for rocky exoplanets and 9.3 and 7.8 for volatile-rich exoplanets. We present the results of our calculations of the atmospheric mass loss rates by the planets HD 109833 b and c while varying the parameters related to the estimates of the planetary masses and the UV flux incident on the planets. The parameter for HD 109833 b and c varies in the ranges from to g s and from to g s , respectively. The high mass loss rates found can be a consequence of a fairly high flux from the solar-type star (an analog of the young active Sun) and a fairly close location of the planets from the host star. [ABSTRACT FROM AUTHOR]

We present our analysis of many-year photometry for several dozens of chromospherically active stars that exhibit solar-type activity (from our own observations as well as from data in the literature). Modeling of the distribution of cool photospheric spots, based on the zonal model, was performed, with several hundred models constructed. We find that, for most stars, their spots are located at intermediate and moderate latitudes and that the largest spotted areas can cover from 7 to 58% of the star's surface. We demonstrate that a latitude drift of spots can be suspected for a number of stars, towards the equator as well as towards the pole; however, the rate of this drift is several times lower than for solar spots. For 15 stars, we detected the presence of activity cycles from 3 to 28 years long that reveal themselves in variations of the system's brightness as well as in variations of the total spot coverage of the star. This paper is based on a talk presented at the memorial astrophysical workshop "Novelties in Understanding the Evolution of Binary Stars" dedicated to the 90th birthday of Prof. M.A. Svechnikov. [ABSTRACT FROM AUTHOR]

Flare stars are a type of variable star that change in brightness. They are characterized by intense, localized releases of electromagnetic radiation in their atmospheres, similar to solar flares. Flare stars are common, especially among cool, red stars. They have been observed since the 1950s and can be detected through their hot emission lines and ultraviolet emission. Recent satellite missions have provided valuable data on flare stars and their statistics, shedding light on their behavior and potential effects on planets. The study of flare stars is important for understanding the diversity of stars and the potential for life on other planets. [Extracted from the article]

The document titled "Exoplanet Division Meeting, 2023 September 30: Variations on an exoplanet theme" provides an update on the Asteroids & Remote Planets Section Exoplanet Division Meeting held on September 30, 2023. The meeting aimed to review the variations in exoplanet transits and demonstrate how these variations can be measured to infer possible causes. Presentations were given on topics such as the effects of stellar activity on transit timings, the causes of transit-timing variations, and the potential habitability of transiting exoplanets. Various software packages for analyzing exoplanet data were also discussed. The document concludes with a list of new members welcomed by the British Astronomical Association. [Extracted from the article]

This article provides a comprehensive overview of the study of exoplanets, planets outside of our solar system. It traces the historical development of this field and highlights the technological advancements that have enabled the detection and study of exoplanets. The article explores the diversity of exoplanets in terms of their physical and orbital properties, as well as their atmospheres. It emphasizes the need for further exploration and the development of new instruments and infrastructures to expand our understanding of exoplanets. The article also discusses the challenges in detecting and studying different types of exoplanets, and the ongoing search for life on Earth-like planets. Overall, it presents the study of exoplanets as a fascinating and ongoing endeavor for humanity. [Extracted from the article]

Radio emission has been detected for all types of stars in the Hertzsprung Russell diagram. Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) low and medium-resolution spectroscopic surveys provide a good opportunity to obtain the spectroscopic properties of radio stars. We cross-matched big data from the LAMOST DR7 low resolution spectral survey with a catalogue of radio stars, and obtained 449 stellar spectra of 258 stars. We detected 185 spectra with H α emission. There are a total of 108 objects with repeated low resolution spectral observations, of which 63 show variations in the H α line over a long time, about several months. We cross-matched LAMOST DR7 medium resolution spectra with the radio star catalogue. We obtained 1319 LAMOST medium-resolution spectra of the 156 radio stars and then calculated their equivalent widths ( E W s ) of the H α line. Among them, 93 radio stars with H α emission were found from the LAMOST medium resolution spectra, and 63 objects showed short and long-term variabilities, especially on a short time scale of approximately 20 min. Finally, we estimated the minimal detectable radio flux of the FAST telescope and provided a scientific plan for studying radio stars. [ABSTRACT FROM AUTHOR]

The review presents the results of a wide range of studies on modeling the atmospheres and shells of exoplanets and studying the processes associated with the activity of the parent star, performed at the Institute of Astronomy of the Russian Academy of Sciences in recent years. The developed methods of analyzing superflares in solar-type stars are applied to stars with planetary systems and the obtained estimates are used to detail the conditions of extreme stellar activity in the study of atmospheric losses for Earth-type planets in low orbits—super-Earths and sub-Neptunes. The results of calculations of the rate of atmospheric loss for exoplanets in orbits close to the parent star (close-in exoplanets) are presented and it is shown that under conditions of a high level of stellar radiation rigidity, and even more so under conditions of a stellar flare, the contribution of exothermic photochemistry processes to the formation of a flow of supra-thermal hydrogen atoms escaping from the atmosphere becomes significant and comparable to the flow of hydrodynamic outflow. Accordingly, this source of supra-thermalhydrogen atoms should be included in modern aeronomic models of physical and chemical processes in the upper atmospheres of hot exoplanets. Taking into account the contribution of supra-thermal particles in the aeronomic model made it possible to clarify the heating rates of atmospheric gas due to the absorption of hard radiation from the parent star. This, in turn, made it possible to more accurately calculate the values of the rate of mass loss by atmospheres and, accordingly, to study the evolutionary properties of the atmospheres of hot exoplanets. It is also important to note that the kinetic and aeronomic models presented in the review, developed in recent years at the Institute of Astronomy of the Russian Academy of Sciences, will be used to analyze and interpret existing and expected observations of the atmospheres of Earth-type exoplanets. Such work will allow to impose additional restrictions on the models and thereby make them more reliable. [ABSTRACT FROM AUTHOR]

Radio emission has been detected for all types of stars in the Hertzsprung Russell diagram. Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) low and medium-resolution spectroscopic surveys provide a good opportunity to obtain the spectroscopic properties of radio stars. We cross-matched big data from the LAMOST DR7 low resolution spectral survey with a catalogue of radio stars, and obtained 449 stellar spectra of 258 stars. We detected 185 spectra with Hα emission. There are a total of 108 objects with repeated low resolution spectral observations, of which 63 show variations in the Hα line over a long time, about several months. We cross-matched LAMOST DR7 medium resolution spectra with the radio star catalogue. We obtained 1319 LAMOST medium-resolution spectra of the 156 radio stars and then calculated their equivalent widths (EWs) of the Hα line. Among them, 93 radio stars with Hα emission were found from the LAMOST medium resolution spectra, and 63 objects showed short and long-term variabilities, especially on a short time scale of approximately 20 min. Finally, we estimated the minimal detectable radio flux of the FAST telescope and provided a scientific plan for studying radio stars.

We report on the progress of our survey on ancient solar-type stars down to main-sequence effective temperatures T eff ≥ 5300 K and within 42 pc of the Sun. High signal-to-noise, high-resolution spectroscopy is presented for a second major subset of the Population II (τ ≥ 12 Gyr) and the intermediate-disc stars (τ ≃ 10 Gyr) within that volume. In conjunction with updates and the analyses of the single and composite sample spectra, we discuss evidence for new companions or candidates from their radial velocities, chromospheric activities, lithium and barium enrichments, and we also draw attention to related sources in the Gaia DR2 data. Among the Population II stars we note a substantial fraction of degenerates, mass transfer, and merger systems that possibly amount to about 20 per cent of that population, with inherently important consequences on the involved stellar ages and the baryonic mass budget. At the present stage, the survey has reached a two-thirds level of local volume-completeness. Key to that objective will be the forthcoming Gaia data, in terms of new companions, companion masses, and precision parallaxes from orbital solutions, in particular at the sample periphery, where many of the sources inevitably reside. In an appendix we describe a subset of about fifty a priori survey candidates, whose analyses discard them as Population I stars. [ABSTRACT FROM AUTHOR]

Rossby waves are a pervasive feature of the large-scale motions of the Earth's atmosphere and oceans. These waves (also known as planetary waves and r-modes) also play an important role in the large-scale dynamics of different astrophysical objects such as the solar atmosphere and interior, astrophysical discs, rapidly rotating stars, planetary and exoplanetary atmospheres. This paper provides a review of theoretical and observational aspects of Rossby waves on different spatial and temporal scales in various astrophysical settings. The physical role played by Rossby-type waves and associated instabilities is discussed in the context of solar and stellar magnetic activity, angular momentum transport in astrophysical discs, planet formation, and other astrophysical processes. Possible directions of future research in theoretical and observational aspects of astrophysical Rossby waves are outlined. [ABSTRACT FROM AUTHOR]

We report the discovery of a planetary system orbiting TOI-763(aka CD-39 7945), a V  = 10.2, high proper motion G-type dwarf star that was photometrically monitored by the TESS space mission in Sector 10. We obtain and model the stellar spectrum and find an object slightly smaller than the Sun, and somewhat older, but with a similar metallicity. Two planet candidates were found in the light curve to be transiting the star. Combining TESS transit photometry with HARPS high-precision radial velocity (RV) follow-up measurements confirm the planetary nature of these transit signals. We determine masses, radii, and bulk densities of these two planets. A third planet candidate was discovered serendipitously in the RV data. The inner transiting planet, TOI-763 b, has an orbital period of P b  =  5.6 d, a mass of M b  =  9.8 ± 0.8 M⊕, and a radius of R b  =  2.37 ± 0.10  R ⊕. The second transiting planet, TOI-763 c, has an orbital period of P c  =  12.3 d, a mass of M c  =  9.3 ± 1.0 M⊕, and a radius of R c  =  2.87 ± 0.11  R ⊕. We find the outermost planet candidate to orbit the star with a period of ∼48 d. If confirmed as a planet, it would have a minimum mass of M d  =  9.5 ± 1.6 M⊕. We investigated the TESS light curve in order to search for a mono transit by planet d without success. We discuss the importance and implications of this planetary system in terms of the geometrical arrangements of planets orbiting G-type stars. [ABSTRACT FROM AUTHOR]

Using photometric data collected by Evryscope-South, we search for nearby young variable systems on the upper main sequence (UMS) and pre-main sequence (PMS). The Evryscopes are all-sky high-cadence telescope arrays operating in the Northern and Southern hemispheres. We base our search on a Gaia-selected catalog of young neighborhood upper- and pre-main sequence stars which were chosen through both astrometric and photometric criteria. We analyze 44,971 Evryscope-South light curves in search of variability. We recover 615 variables, with 378 previously known, and 237 new discoveries including 84 young eclipsing binaries (EB) candidates. We discover a new highly eccentric binary system and recover a further four previously known systems, with periods ranging from 299 to 674 hr. We find 158 long-period (>50 hr) candidate EB systems, 9 from the PMS and 149 from the UMS, which will allow constraints on the mass/radius/age relation. These long-period EBs include a 179.3 hr PMS system and a 867.8 hr system from the UMS. For PMS variable candidates we estimate system ages, which range from 1 to 23 Myr for non-EBs and from 2 to 17 Myr for EBs. Other non-EB discoveries that show intrinsic variability will allow relationships between stellar rotation rates, ages, activity, and mass to be characterized. [ABSTRACT FROM AUTHOR]

Context. Gaia benchmark stars are selected to be calibration stars for different spectroscopic surveys. Very high-quality and homogeneous spectroscopic data for these stars are therefore required. We collected ultrahigh-resolution ESPRESSO spectra for 30 of the 34 Gaia benchmark stars and made them public. Aims. We quantify the consistency of the results that are obtained with different high- (R ~ 115 000), and ultrahigh- (R ~ 220 000) resolution spectrographs. We also comprehensively studied the effect of using different spectral reduction products of ESPRESSO on the final spectroscopic results. Methods. We used ultrahigh- and high-resolution spectra obtained with the ESPRESSO, PEPSI, and HARPS spectrographs to measure spectral line characteristics (line depth; line width; and equivalent width, EW) and determined stellar parameters and abundances for a subset of 11 Gaia benchmark stars. We used the ARES code for automatic measurements of the spectral line parameters. Results. Our measurements reveal that the same individual spectral lines measured from adjacent 2D (spectrum in the wavelength-order space) echelle orders of ESPRESSO spectra differ slightly in line depth and line width. When a long list of spectral lines is considered, the EW measurements based on the 2D and 1D (the final spectral product) ESPRESSO spectra agree very well. The EW spectral line measurements based on the ESPRESSO, PEPSI, and HARPS spectra also agree to within a few percent. However, we note that the lines appear deeper in the ESPRESSO spectra than in PEPSI and HARPS. The stellar parameters derived from each spectrograph by combining the several available spectra agree well overall. Conclusions. We conclude that the ESPRESSO, PEPSI, and HARPS spectrographs can deliver spectroscopic results that are sufficiently consistent for most of the science cases in stellar spectroscopy. However, we found small but important differences in the performance of the three spectrographs that can be crucial for specific science cases. [ABSTRACT FROM AUTHOR]

SPIRou is the newest spectropolarimeter and high-precision velocimeter that has recently been installed at the Canada-France-Hawaii Telescope on Maunakea, Hawaii. It operates in the near-infrared and simultaneously covers the 0.98–2.35 μm domain at high spectral resolution. SPIRou is optimized for exoplanet search and characterization with the radial-velocity technique, and for polarization measurements in stellar lines and subsequent magnetic field studies. The host of the transiting hot Jupiter HD 189733 b has been observed during early science runs. We present the first near-infrared spectropolarimetric observations of the planet-hosting star as well as the stellar radial velocities as measured by SPIRou throughout the planetary orbit and two transit sequences. The planetary orbit and Rossiter-McLaughlin anomaly are both investigated and modeled. The orbital parameters and obliquity are all compatible with the values found in the optical. The obtained radial-velocity precision is compatible with about twice the photon-noise estimates for a K2 star under these conditions. The additional scatter around the orbit, of about 8 m s−1, agrees with previous results that showed that the activity-induced scatter is the dominant factor. We analyzed the polarimetric signal, Zeeman broadening, and chromospheric activity tracers such as the 1083nm HeI and the 1282nm Paβ lines to investigate stellar activity. First estimates of the average unsigned magnetic flux from the Zeeman broadening of the FeI lines give a magnetic flux of 290 ± 58 G, and the large-scale longitudinal field shows typical values of a few Gauss. These observations illustrate the potential of SPIRou for exoplanet characterization and magnetic and stellar activity studies. [ABSTRACT FROM AUTHOR]

Context. Understanding stellar activity in M dwarfs is fundamental to improving our knowledge of the physics of stellar atmospheres and for planet search programmes. High levels of stellar activity (also frequently associated with flare events) can cause additional variations in the stellar emission that contaminate the signal induced by a planet and that need to be corrected. The study of activity indicators in active stars can improve our capability of modelling the signal generated by magnetic activity. Aims. In this work we present measurements of activity indicators at visible wavelength for a star with a high activity level, AD Leonis, observed with HARPS in 2006, and HARPS-N in 2018. Our aim is to understand the behaviour of stellar chromospheres of M stars, studying the more sensitive chromospheric activity indicators. We also focus on characterising their variability and on finding the correlations among these indicators to obtain information on the origin of the magnetic activity in low-mass stars. Methods. We performed a study of the main optical activity indicators (Ca II H&K, Balmer lines, Na I D1,2 doublet, He I D3, and other helium lines) measured for AD Leonis using the data provided by the HARPS-N high-resolution spectrograph at the Telescopio Nazionale Galileo in 2018, and by the HARPS instrument at La Silla observatory in 2006. Spectra were flux-calibrated in units of flux at the stellar surface. We measured excess flux of the selected activity indicators. The correlations between the different activity indicators as well as the temporal evolution of fluxes were analysed. A stellar flare was identified during the 2018 observing run and the Hα, Hβ, He I 4471 Å, and He I 5876 Å lines were analysed in detail by fitting the line profiles with two Gaussian components. Results. We found that the Ca II H&K flux excesses are strongly correlated with each other, but the Ca II H&K doublet is generally less correlated with the other indicators. Moreover, Hα is correlated with Na I doublet and helium lines. Analysing the time variability of flux of the studied lines, we found a higher level of activity of the star during the observations in 2018 than in 2006, while Ca II H&K showed more intense emission on spectra obtained during the observations in 2006. Thanks to a detailed analysis of selected line profiles, we investigated the flare evaluating the mass motion during the event. [ABSTRACT FROM AUTHOR]

We report the detection of a transiting, dense Neptune planet candidate orbiting the bright (V  = 8.6) K0.5V star HD 95338. Detection of the 55-d periodic signal comes from the analysis of precision radial velocities from the Planet Finder Spectrograph on the Magellan II Telescope. Follow-up observations with HARPS also confirm the presence of the periodic signal in the combined data. HD 95338 was also observed by the Transiting Exoplanet Survey Satellite (TESS) where we identify a clear single transit in the photometry. A Markov chain Monte Carlo period search on the velocities allows strong constraints on the expected transit time, matching well the epoch calculated from TESS data, confirming both signals describe the same companion. A joint fit model yields an absolute mass of 42.44 |$^{+2.22}_{-2.08}\,{\rm M}_{\oplus }$| and a radius of 3.89 |$^{+0.19}_{-0.20}$| R ⊕, which translates into a density of 3.98 |$^{+0.62}_{-0.64}$|  g cm−3 for the planet. Given the planet mass and radius, structure models suggest it is composed of a mixture of ammonia, water, and methane. HD 95338 b is one of the most dense Neptune planets yet detected, indicating a heavy element enrichment of ∼90 per cent (⁠|$\sim 38\, {\rm M}_{\oplus }$|⁠). This system presents a unique opportunity for future follow-up observations that can further constrain structure models of cool gas giant planets. [ABSTRACT FROM AUTHOR]

We present the results from a systematic study of temporal variation of stellar activity in young late-type stars. We used multi-epoch LAMOST (Large sky Area Multi-Object fiber Spectroscopic Telescope) low-resolution spectra of over 300 member candidates in three young open clusters: Pleiades, Praesepe, and Hyades. The spectral measurements of TiO band strength near 7050 Å (TiO2) and equivalent width of H α line (EWH α) are used as the tracers of cool spot coverage and chromospheric emission strength, respectively. The analysis of time-variation patterns of these two tracers suggested that there exist detectable variabilities in TiO2 and EWH α, and their time-scales are in the wide range from days to years. Results showed that more active stars, younger and fast rotators, tend to have larger activity variations. There is a tendency of anticorrelation between temporal variations in TiO2 and EWH α. Also, appreciable anticorrelation in the rotational phase between H α emission and K2 brightness is detected in some M dwarfs, indicating spatial co-location of the plages with cool star-spots; however, cool stars do not always show such co-location features. Furthermore, spot coverage and H α emission were evident at all rotational phases of several M dwarfs, indicating a basal level of activity, perhaps due to many small and randomly located active regions in the atmosphere. [ABSTRACT FROM AUTHOR]

It was recently claimed that the magnetic O-type star HD 54879 exhibits important radial velocity variability indicative of its presence in a spectroscopic binary. More remarkably, it was furthermore reported that the star underwent a short, sudden variation in spectral type and magnetic field. In this letter, we examine new Narval and ESPaDOnS data of this star in addition to the previously published FORS2 data and conclude that both the reported velocity variations and the sudden spectral and magnetic changes are spurious. [ABSTRACT FROM AUTHOR]

In this study, an analysis of spectral line bisector variations for HD 199719 which was examined as a part of the exoplanet studies that carried on the TÜBİTAK National Observatory (TUG). Cross-correlation functions (CCF) were implemented to the observed spectra using some template spectra to determine mean line profile. Line bisectors were derived from mean line profiles. In order to quantify asymmetries on the line profiles, some bisectors criteria were used. The velocity spans were calculated in the profiles with these criteria and correlation between the star's radial velocity measurements were investigated. In addition, equivalent width measurements of the Hα and Hβ were performed to check other variability due to nature of star (granulation, pulsation, magnetic cycle and stellar spots due to activity). No correlation has been found between the radial velocity and line bisectors measurements. Period analysis for bisectors (BIS and BVC) show that significant periodicity appearing around 4.88 and 10.36 days. Although there was a long-term variation for the equivalent width measurements of Hα, a similar change was not obtained for equivalent width measurements of Hβ. [ABSTRACT FROM AUTHOR]

The results of many-year infrared observations of the Herbig AeBe star AB Aur at 1-5 μm (JHKLM bands) are presented. The duration of the photometric series, together with observations published earlier, is about 18 years. The observations demonstrate that, in contrast to the optical, the star is quite active in the studied infrared range. The variability amplitude increases with wavelength, reaching ΔM = 0.72m. Modeling shows that both the amount of IR radiation from the inner part of the disk and its temperature increase when the star becomes brighter. A periodogram analysis demonstrates that variations of the IR flux from AB Aur display significant evidence for periodic changes, whose stability is uncertain. This behavior is most probably associated with transient quasi-oscillations related to instability processes in the inner disk. The estimated correlation timescale, τ = 130 ± 40d, can be considered as an approximate characteristic of the duration of such processes. The analysis results provide no certain grounds to believe that the inner disk contains any massive objects in permanent orbits, such as protoplanets. The existing trend in the variations of the IR flux, most clearly expressed in the KLM bands, provides evidence for the presence of large-scale perturbations in the disk. Conditions that could bring about a cyclic character in the accretion of gas from the circumstellar disk onto the young star are briefly discussed. [ABSTRACT FROM AUTHOR]

Context. A number of high-precision time series have recently become available for many stars as a result of data from CoRoT, Kepler, and TESS. These data have been widely used to study stellar activity. Photometry provides information that is integrated over the stellar disk. Therefore, there are many degeneracies between spots and plages or sizes and contrasts. In addition, it is important to relate activity indicators, derived from photometric light curves, to other indicators (Log R′HK $R'_{\rm{HK}}$ R HK ′ and radial velocities). Aims. Our aim is to understand how to relate photometric variability to physical parameters in order to help the interpretation of these observations. Methods. We used a large number of synthetic time series of brightness variations for old main sequence stars within the F6-K4 range. Simultaneously, we computed using consistent modeling for radial velocity, astrometry, and chromospheric emission. We analyzed these time series to study the effect of the star spectral type on brightness variability, the relationship between brightness variability and chromospheric emission, and the interpretation of brightness variability as a function of spot and plage properties. We then studied spot-dominated or plage-dominated regimes. Results. We find that within our range of activity levels, the brightness variability increases toward low-mass stars, as suggested by Kepler results. However, many elements can create an interpretation bias. Brightness variability roughly correlates to Log R′HK $R'_{\rm{HK}}$ R HK ′ level. There is, however, a large dispersion in this relationship, mostly caused by spot contrast and inclination. It is also directly related to the number of structures, and we show that it can not be interpreted solely in terms of spot sizes. Finally, a detailed analysis of its relation with Log R′HK $R'_{\rm{HK}}$ R HK ′ shows that in the activity range of old main-sequence stars, we can obtain both spot or plage dominated regimes, as was shown by observations in previous works. The same star can also be observed in both regimes depending on inclination. Furthermore, only strong correlations between chromospheric emission and brightness variability are significant. Conclusions. Our realistic time series proves to be extremely useful when interpreting observations and understanding their limitations, most notably in terms of activity interpretation. Inclination is crucial and affects many properties, such as amplitudes and the respective role of spots and plages. [ABSTRACT FROM AUTHOR]

The variability of the components A and B of the visual binary system 61 Cyg is analyzed. The observations were made on the normal astrograph of the Pulkovo Observatory from 1956 through 1982 (a total of 296 brightness estimates). A search was undertaken for the periods of the variability of both components of the system with independent application of two periodogram analysis techniques: a sinusoidal approximation and the traditional Scargle method. As a comparison, the complete photometric series including all 296 values of the stellar magnitude and the yearly averages (27 values) were analyzed. This yielded a reliable value of about 15 years for the period of both components and a period of 8.5-9 years for the component 61 Cyg B that coincides with the 9.1-year period of the coronal and chromospheric activity discovered in 1978 by Wilson. 61 Cyg A was also found to have a less significant period of about 6 years, which coincides, to within the limits of accuracy, with a period of 7.5±1.7 years of the coronal and chromospheric activity previously noted by Hempelmann. Yet another less significant period of about 4 years of unknown origin was observed for 61 Cyg B. This may be the second harmonic of the fundamental period. We assume that the low accuracy of the estimated periods may be related to their instability owing to the complicated multicomponent character of the observed variability. A period of about 15 years detected for both components A and B may be related to astroclimatic or instrumental effects. [ABSTRACT FROM AUTHOR]

The internal structures and properties of oscillating red-giant stars can be accurately inferred through their global oscillation modes (asteroseismology). Based on 1460 d of Kepler observations we perform a thorough asteroseismic study to probe the stellar parameters and evolutionary stages of three red giants in eclipsing binary systems. We present the first detailed analysis of individual oscillation modes of the red-giant components of KIC 8410637, KIC 5640750, and KIC 9540226. We obtain estimates of their asteroseismic masses, radii, mean densities, and logarithmic surface gravities by using the asteroseismic scaling relations as well as grid-based modelling. As these red giants are in double-lined eclipsing binaries, it is possible to derive their independent dynamical masses and radii from the orbital solution and compare it with the seismically inferred values. For KIC 5640750 we compute the first spectroscopic orbit based on both components of this system. We use high-resolution spectroscopic data and light curves of the three systems to determine up-to-date values of the dynamical stellar parameters. With our comprehensive set of stellar parameters we explore consistencies between binary analysis and asteroseismic methods, and test the reliability of the well-known scaling relations. For the three red giants under study, we find agreement between dynamical and asteroseismic stellar parameters in cases where the asteroseismic methods account for metallicity, temperature, and mass dependence as well as surface effects. We are able to attain agreement from the scaling laws in all three systems if we use $$\Delta \nu _{\rm ref,emp} = 130.8 \pm 0.9 \,\mu$$ Hz instead of the usual solar reference value. [ABSTRACT FROM AUTHOR]

The δ Sct stars are a diverse group of intermediate-mass pulsating stars located on and near the main sequence within the classical instability strip in the Hertzsprung–Russell diagram. Many of these stars are hybrid stars pulsating simultaneously with pressure and gravity modes that probe the physics at different depths within a star's interior. Using two large ensembles of δ Sct stars observed by the Kepler Space Telescope, the instrumental biases inherent to Kepler mission data and the statistical properties of these stars are investigated. An important focus of this work is an analysis of the relationships between the pulsational and stellar parameters, and their distribution within the classical instability strip. It is found that a non-negligible fraction of main-sequence δ Sct stars exist outside theoretical predictions of the classical instability boundaries, which indicates the necessity of a mass-dependent mixing length parameter to simultaneously explain low and high radial order pressure modes in δ Sct stars within the Hertzsprung–Russell diagram. Furthermore, a search for regularities in the amplitude spectra of these stars is also presented, specifically the frequency difference between pressure modes of consecutive radial order. In this work, it is demonstrated that an ensemble-based approach using space photometry from the Kepler mission is not only plausible for δ Sct stars, but that it is a valuable method for identifying the most promising stars for mode identification and asteroseismic modelling. The full scientific potential of studying δ Sct stars is as yet unrealized. The ensembles discussed in this paper represent a high-quality data set for future studies of rotation and angular momentum transport inside A and F stars using asteroseismology. [ABSTRACT FROM AUTHOR]

The BOKZ-M60 star sensor (Unit for Measuring Star Coordinates) is intended for determining the parameters of the orientation of the axes of the intrinsic coordinate system relative to the axes of the inertial system by observations of the regions of the stellar sky. It is convenient to characterize an error of the single determination of the orientation of the intrinsic coordinate system of the sensor by the vector of an infinitesimal turn of this system relative to its found position. Full-scale ground-based tests have shown that, for a resting sensor the root-mean-square values of the components of this vector along the axes of the intrinsic coordinate system lying in the plane of the sensor CCD matrix are less than 2″ and the component along the axis perpendicular to the matrix plane is characterized by the root-mean-square value of 15″. The joint processing of one-stage readings of several sensors installed on the same platform allows us to improve the indicated accuracy characteristics. In this paper, estimates of the accuracy of systems from BOKZ-M60 with two and four sensors performed from measurements carried out during the normal operation of these sensors on the Resurs-P satellite are given. Processing the measurements of the sensor system allowed us to increase the accuracy of determining the each of their orientations and to study random and systematic errors in these measurements. [ABSTRACT FROM AUTHOR]