Search

To understand the uniqueness of our solar system, we must assess the system architectures and demographic features existing in the known planet population, but such a task requires a homogeneous set of candidates. Fortunately, the Kepler spacecraft continuously collected photometry from a single patch of the sky, which in turn produced a well characterized catalog of transiting exoplanets. However, previous studies assumed multi-planet systems were subject to the same selection effects as their single-planet counterparts. I investigate this assumption, finding that a proper completeness accounting significantly increases the underlying occurrence of multi-planet systems to 5.86 planets per FGK dwarf and only requires a 1.5 degree average system mutual inclination. Using this correction I provide an updated extrapolation of the occurrence of Earth analogs and find that 5.9% of GK dwarfs have more than one planet within their habitable zone.Additionally, the K2 mission collected photometry from 18 fields along the ecliptic plane, providing a unique opportunity to understand how exoplanet formation may be affected by galactic latitude, stellar metallicity, and stellar age. For my thesis, I developed a fully automated pipeline able to detect and vet transit signals in K2 photometry, enabling assessment of sample completeness and reliability. This catalog contains 768 planets, with 235 newly identified candidates. Correspondingly, I present the first uniform analysis of small transiting exoplanet occurrence outside of the Kepler field, finding a metallicity dependence in small planet occurrence.I also discuss how the Sun’s late stage evolution and the existing solar system architecture will capture Jupiter and Saturn into a mean-motion resonance. Eventually perturbations from passing stars will trigger large-scale instability, culminating in the disassociation of all outer planets. Extrapolating this result to other systems indicates a temporal dependence on bound planet occurrence in the Galaxy.

The existence of super-massive (> 10^4M⊙) Pop III stars has been theorized, but never observed. If such stars were to have existed during early galaxy formation, it has long been thought that in absence of heavy metals (A > 4), they would have collapsed due to instabilities caused by general relativity. Such a collapse would have resulted in the creation of a super- massive black hole, possibly emitting gravitational waves if accompanied by an anisotropic neutrino burst. Super-massive black holes have been detected very early on in galaxy formation (red shift: z ≈ 7), and their origin remains unknown. Gravitational waves created by such a collapse may be detectable by next generation gravitational wave detectors.Recent simulations have suggested that a narrow range of super-massive stars with masses around 5 × 10^4M⊙ may have exploded due to simultaneously reaching the general relativistic instability and the ignition of triple-α fusion. If such explosions were to have occurred, depending on their frequency of occurrence, they may have left behind a measurable elemental signature of heavy elements in an otherwise primordial elemental composition during early galaxy formation.This dissertation details the investigation of post-instability energetics, both from a theoretical stand point as well as via simulations using the KEPLER stellar evolution code. Previous research has found that for a small range of stars with masses around 5 × 10^4M⊙, due to the extreme temperature sensitivity of the triple-α process at its ignition point (~2 × 10^8 K), there is a theoretical basis for accelerated nuclear energy production to possibly reverse the collapse before too much energy is lost in electron-positron pair annihilation neutrinos combined with in-falling kinetic energy. However, complimentary findings via simulations were not found to be satisfactory. Future three dimensional simulations with high precision accounting of nuclear energy production as well as energy losses and kinematics would be necessary to definitively conclude whether such explosions are energetically possible.

Asteroseismology, the study of intrinsic oscillations in stars, can reveal fundamental properties of cool stars critical in our understanding of stellar rotational evolution. Through space missions such as Kepler and TESS, asteroseismology has seen a surge of new data and research in the past decade. These data have contributed to important results in the field of stellar braking particularly for F, G and K stars, thanks to estimates of stellar age for rotating field stars, and the measurement of stellar rotation through oscillation spectra as important comparisons for estimates from star-spots. In this talk, I will provide an introduction to asteroseismology how it can provide important results for your research. This will be followed by a breakdown of how asteroseismologists have used these techniques to establish the presence of weakened magnetic braking on the main sequence using asteroseismic data, and what we should be looking forward to from these techniques with the TESS mission., {"references":["Hall, Oliver et al. (2021), Nature Astronomy, Volume 5, p. 707-714","Nielsen, Martin et al. (2015), Astronomy & Astrophysics, Volume 582, id.A10, 5 pp.","Davies, Guy et al. (2015), Monthly Notices of the Royal Astronomical Society, Volume 446, Issue 3, p.2959-2966","Benomar, Othman et al. (2018), Science, Volume 361, Issue 6408, pp. 1231-1234","Silva Aguirre, Victor et al. (2015), Monthly Notices of the Royal Astronomical Society, Volume 452, Issue 2, p.2127-2148","Davies, Guy et al. (2016), Monthly Notices of the Royal Astronomical Society, Volume 456, Issue 2, p.2183-2195","Lund, Mikkel et al. (2017), The Astrophysical Journal, Volume 835, Issue 2, article id. 172, 31 pp.","Silva Aguirre, Victor et al. (2017), The Astrophysical Journal, Volume 835, Issue 2, article id. 173, 18 pp.","Lund, Mikkel et al. (2014), The Astrophysical Journal, Volume 790, Issue 2, article id. 121, 28 pp.","David, Trevor et al. (2022), The Astrophysical Journal, Volume 933, Issue 1, id.114, 22 pp."]}

The study of detached eclipsing binaries in open clusters can provide powerful tests of theoretical stellar evolutionary models. These models must simultaneously fit the masses, radii, and radiative properties of the eclipsing stars with essentially the same distance, age, and initial composition. In this way, clusters are ideal test benches for verification of the stellar evolution theory. To fully exploit this potential, we present a detailed analysis of three spectroscopic binaries that are members of NGC 6791. Measurements of the radial velocities were combined with Kepler photometry, to provide a full set of orbital and physical parameters. We applied a standard analysis to disentangle the spectra of each binary system and to determine the temperatures and metallicities for each component in binaries. High-precision analysis affords us the opportunity to define the evolutionary status of the components. We also derived the distances to the systems. Finally, we report on the detection of solar-like oscillation signals in a member in data from the Kepler mission., Scientific and Technological Research Council of Turkey [119F216]; ESO [091.D0125(A), 081.D-0091(A)]; NASA's Science Mission Directorate; National Aeronautics and Space Administration; National Science Foundation, We are grateful to the anonymous referee for her/his valuable suggestions. This study is supported by Scientific and Technological Research Council of Turkey under project number 119F216. This research made use of data collected at ESO under programmes 091.D0125(A) (PI: Brogaard, K.) and 081.D-0091(A) (PI: Grundahl, F.). The following internet-based resources were used in research for this paper: the NASA Astrophysics Data System and the SIMBAD data base operated at CDS, Strasbourg, France. This work is based on data from the Kepler mission. Kepler was competitively selected as the tenth Discovery mission. Funding for this mission is provided by NASA's Science Mission Directorate. The photometric data were obtained from the Mikulski Archive for Space Telescopes. This work has also made use of data from the European Space Agency mission Gaia (http://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (http://www.cosmos.esa.int/web/gaia/dpac/consortium).This research made use of LIGHTKURVE, a Python package for Kepler and TESS data analysis (Lightkurve Collaboration et al. 2018). This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.

We present the findings for the magnetic activities seen on V1130 Cyg and V461 Lyr. In the case of V1130 Cyg, the secondary component's temperature was found to be 3891 +/- 50 K, while the mass ratio was computed as 0.689 +/- 0.001, and the orbital inclination as 90 degrees.00 +/- 0 degrees.01. The temperature of V461 Lyr's secondary component was found to be 4206 +/- 50 K, and the mass ratio was calculated as 0.999 +/- 0.001 with 89 degrees.58 +/- 0 degrees.01 of orbital inclination. The analyses exhibit the effects of the stellar spots on the light curves. The models indicate that there are two types of flares in the case of V1130 Cyg, and three types of flares for V461 Lyr. The Plateau parameters have been found as 2.1997 s for Group 1 and 1.0068 s for Group 2 in the case of V1130 Lyr. They have been computed as 1.9015 s for Group 1, 2.7943 s for Group 2, and 3.4324 s for Group 3 of V461 Lyr., Turkish Scientific and Tech-nical Research Council (TdUBITAK) [116F213], We thank the referee for useful comments that contributed to the improvement of the paper. We also wish to thank the Turkish Scientific and Tech-nical Research Council (TdUBITAK) for supporting this work through Grant No. 116F213.

We present the results of a search for stellar flares from stars neighbouring the target sources in the Kepler short cadence data. These flares have been discarded as contaminants in previous surveys and therefore provide an unexplored resource of flare events, in particular high energy events from faint stars. We have measured M dwarf flare energies up to 1.5$\times$10^35 erg, pushing the limit for flare energies measured using Kepler data. We have used our sample to study theflaring activity of wide binaries, finding that the lower mass counterpart in a wide binary flares more often at a given energy. Of the 4430 flares detected in our original search, 298 came from a neighbouring star, a rate of 6.7$\pm$0.4 per cent for the Kepler short cadence lightcurves. We have used our sample to estimate a 5.8$\pm$0.1 per cent rate of false positive flare events in studies using TESS short cadence data., 10 pages, 2 figures, 2 tables. Accepted for publication in the Monthly Notices of the Royal Astronomical Society

Dedicated transiting surveys, such as the Kepler space telescope, have provided the astronomy community with a rich data set resulting in many new discoveries. In this paper, we look at eight Kepler objects identified by Wheeler & Kipping with a periodic, broad increase in flux, that look distinctly different from intrinsic star variability. We consider two physical phenomena as explanations for these observed Kepler light curves; the first being the classical explanation while the second being an alternative scenario: (i) tidal interactions in a binary star system, and (ii) forward scattering from an optically thin cloud around an exoplanet. We investigate the likelihood of each model by modelling and fitting to the observed data. The binary system qualitatively does a good job of reproducing the shape of the observed light curves due to the tidal interaction of the two stars. We do, however, see a mismatch in flux right before or after the peak brightness. We find that six out of the eight systems require an F-type primary star with a K-type companion with large eccentricities. At the same time, we find that optically thin discs, modelled using a Henyey–Greenstein phase function are also able to generate these broad brightening events. Five of the eight observed objects can be described with this new hypothesis in the absence of RV observations. As the other three are not well-described by the disc model, we conclude that they are indeed heartbeat stars.

Approximately half of the planets discovered by NASA's Kepler mission are in systems where just a single planet transits its host star, and the remaining planets are observed to be in multi-planet systems. Recent analyses have reported a dichotomy in the eccentricity distribution displayed by systems where a single planet transits compared with that displayed by the multi-planet systems. Using $N$-body simulations, we examine the hypothesis that this dichotomy has arisen because inner systems of super-Earths are frequently accompanied by outer systems of giant planets that can become dynamically unstable and perturb the inner systems. Our initial conditions are constructed using a subset of the known Kepler five-planet systems as templates for the inner systems, and systems of outer giant planets with masses between those of Neptune and Saturn that are centred on orbital radii $2 \le a_{\rm p} \le 10$ au. The parameters of the outer systems are chosen so that they are always below an assumed radial velocity detection threshold of 3 ms$^{-1}$. The results show an inverse relation between the mean eccentricities and the multiplicites of the systems. Performing synthetic transit observation of the final systems reveals dichotomies in both the eccentricity and multiplicity distributions that are close to being in agreement with the Kepler data. Hence, understanding the observed orbital and physical properties of the compact systems of super-Earths discovered by Kepler may require holistic modelling that couples the dynamics of both inner and outer systems of planets during and after the epoch of formation., 19 pages, 24 figures, accepted to MNRAS

The ratio of small-to-large separations r010 has been widely used in helioseismology and asteroseismology to investigate the internal structure of a star, as it is approximately independent of the structure of the outer layers. Several studies have used this tool to constrain the convective-core overshooting of main-sequence stars (i.e. 0.0 ≤ δov ≤ 0.2). This is consistent with the generally accepted values. However, Yang et al. have proposed that there is large convective-core overshooting in the Kepler targets KIC 2837475 and 11081729: 1.2 ≤ δov ≤ 1.6 and 1.7 ≤ δov ≤ 1.8, respectively. These are much larger than the normal values. Thus, the aim of this study is to re-investigate the ratios of the two stars using a model-independent method with the latest p-mode observations. Our results indicate that there is no robustness for including such a large convective-core overshooting while modelling these two stars. In fact, this leads to over-fitting, and the observational constraints of r010 prefer models with a normal convective-core overshooting (i.e. 0.0 ≤ δov ≤ 0.2) as the candidates for the best-fitting model of KIC 2837475 and 11081729.

According to statistics of planetary period ratios in multi-planet extrasolar systems, evident excesses appear just over the exact integral ratios 2 : 1 and 3 : 2 , while deficits exist on the near left side. There are various dynamical explanations for the phenomenon. For three observed planets in Kepler-9 system, the period ratio of the planet b and c approximately equals to 2.03, which cause this planet pair as a typical sample close to the 2:1 resonance. For two situations where secular interactions are considered only and resonance perturbations are added in, we applied Hamiltonian functions with second-order eccentricity terms to provide positions of current orbital configurations located in the level curves of energy as well as surfaces of section, then discussed the probable near resonance configurations of the two planets.

International audience; We present the analysis of the multi-planetary system Kepler-117, which is part of our program of observations of Kepler planets. This system is composed of a ~ 30 MEarth planet in a ~ 19 days orbit and a ~ 2 MJ planet orbiting in ~ 51 days. Both the orbits have low eccentricity. The planets are not close to an exact low-order mean motion resonance, but exhibit significant transit timing variations (TTVs) nevertheless. We perform a combined Markov Chain Monte Carlo fit on all the available data: the Kepler photometry, the TTVs, the radial velocities we obtained with SOPHIE/OHP and the stellar parameters. The prime result is that the modelling of the TTVs allows to increase the precision on the system parameters which are not constrained by the radial velocities alone.

The anomalously large radii of highly-irradiated gaseous exoplanets has long been a mystery. One mechanism suggested as a solution for hot Jupiters is the heating of the deep atmosphere via the vertical advection of potential temperature resulting in an increased internal entropy. Here we intend to explore if this mechanism can also explain the observed brown dwarf radii trend: a general increase in radius with irradiation, with an exception for highly-irradiated brown dwarfs orbiting white dwarfs. We use a 3D GCM, DYNAMICO, to run a series of long-timescale models of the atmospheres of Kepler-13Ab, KELT-1b, and SDSS1411B. These models allow us to explore not only if a stable advective adiabat can develop, but also the associated dynamics. We find that our models fall into two distinct regimes: Kepler-13Ab and KELT-1b both show signs of significant deep heating and hence maintain adiabats that are hotter than 1D models predict. On the other hand, SDSS1411B exhibits a much weaker downward heating profile which not only struggles to heat the interior under ideal conditions, but is highly sensitive to the presence of deep radiative dynamics. We find that the vertical advection of potential temperature by large-scale atmospheric circulations represents a robust mechanism to explain the trend of increasing inflation with irradiation, including the exception for highly irradiated brown dwarfs orbiting white dwarfs. This can be understood as occurring due to the role that increasing rotational influence plays on mid- to-high latitude advective dynamics. Furthermore, when paired with a suitable parametrisation of the outer atmosphere irradiation profile, this mechanism alone could potentially provide a complete explanation for the observed levels of inflation in our brown dwarfs., 20 pages, 11 figures. Accepted for publication in A&A. Updated version with a fixed typo in the vertical enthalpy flux equation

Many fundamental physical processes regarding planetary formation in protoplanetary disks are still imperfectly understood, with an elusive phenomenon being turbulence in such disks. Observations are available of planetary systems and of some protoplanetary disks, which can serve as a starting point for these investigations. Detected systems reveal different architectures of planets. One particularly interesting case to consider is the Kepler-223 system, which contains a rare configuration of four planets in a resonance chain, implying a certain migration history. We aim to use the orbital configuration of Kepler-223's planets to constrain the parameters of the protoplanetary disk that allow for the formation of a chain of mean-motion resonances that resembles the one of Kepler-223. The parameters we aim to investigate are primarily the disk viscosity and surface density. We use the swift_symba N-body integrator with additional dissipative forces to mimic planet-disk interactions. We constrain the surface densities and viscosities that allow the formation of a resonant chain like that of Kepler-223. We find that surface densities of up to a few minimum mass solar nebula (MMSN) surface densities and disk viscosity parameters $\alpha$ of a few $10^{-3}$ up to $10^{-2}$ are most successful at reproducing the architecture of this particular planetary system. We describe how these two quantities are linked to each other considering the success of reproducing the chain and find that higher disk surface densities in turn require lower viscosities to build the chain. Our results show that well characterized observed planetary systems hold information about their formation conditions in the protoplanetary disks and that it is possible to extract this information, namely the initial disk surface density and viscosity, helping to constrain planet formation., Comment: 12 pages, 7 figues, accepted for publication in A&A

The spectroscopic class of subdwarf A-type (sdA) stars has come into focus in recent years because of their possible link to extremely low-mass white dwarfs, a rare class of objects resulting from binary evolution. Although most sdA stars are consistent with metal-poor halo main-sequence stars, the formation and evolution of a fraction of these stars are still matters of debate. The identification of photometric variability can help to put further constraints on the evolutionary status of sdA stars, in particular through the analysis of pulsations. Moreover, the binary ratio, which can be deduced from eclipsing binaries and ellipsoidal variables, is important as input for stellar models. In order to search for variability due to either binarity or pulsations in objects of the spectroscopic sdA class, we have extracted all available high precision light curves from the Kepler K2 mission. We have performed a thorough time series analysis on all available light curves, employing three different methods. Frequencies with a signal-to-noise ratio higher than four have been used for further analysis. From the 25 targets, 13 turned out to be variables of different kinds (i.e. classical pulsating stars, ellipsoidal and cataclysmic variables, eclipsing binaries, and rotationally induced variables). For the remaining 12 objects, a variability threshold was determined., 11 pages, 11 figures, 3 tables, accepted for publication in Astronomy & Astrophysics

We report on precise Doppler measurements of L231-32 (TOI-270), a nearby M dwarf ($d=22$ pc, $M_\star = 0.39$ M$_\odot$, $R_\star = 0.38$ R$_\odot$), which hosts three transiting planets that were recently discovered using data from the Transiting Exoplanet Survey Satellite (TESS). The three planets are 1.2, 2.4, and 2.1 times the size of Earth and have orbital periods of 3.4, 5.7, and 11.4 days. We obtained 29 high-resolution optical spectra with the newly commissioned Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) and 58 spectra using the High Accuracy Radial velocity Planet Searcher (HARPS). From these observations, we find the masses of the planets to be $1.58 \pm 0.26$, $6.15 \pm 0.37$, and $4.78 \pm 0.43$ M$_\oplus$, respectively. The combination of radius and mass measurements suggests that the innermost planet has a rocky composition similar to that of Earth, while the outer two planets have lower densities. Thus, the inner planet and the outer planets are on opposite sides of the `radius valley' -- a region in the radius-period diagram with relatively few members, which has been interpreted as a consequence of atmospheric photo-evaporation. We place these findings into the context of other small close-in planets orbiting M dwarf stars, and use support vector machines to determine the location and slope of the M dwarf ($T_\mathrm{eff} < 4000$ K) radius valley as a function of orbital period. We compare the location of the M dwarf radius valley to the radius valley observed for FGK stars, and find that its location is a good match to photo-evaporation and core-powered mass loss models. Finally, we show that planets below the M dwarf radius valley have compositions consistent with stripped rocky cores, whereas most planets above have a lower density consistent with the presence of a H-He atmosphere., Accepted for publication in MNRAS

During the survey phase of the Kepler mission, several thousands of stars were observed in short cadence, allowing the detection of solar-like oscillations in more than 500 main-sequence and sub-giant stars. Later, the Kepler Science Office discovered an issue in the calibration that affected half of the short-cadence data, leading to a new data release (DR25) with improved corrections. We re-analyze the one-month time series of the Kepler survey phase to search for new solar-like oscillations. We study the seismic parameters of 99 stars (46 targets with new reported solar-like oscillations) increasing by around 8% the known sample of solar-like stars with asteroseismic analysis of the short-cadence data from Kepler. We compute the masses and radii using seismic scaling relations and find that this new sample populates the massive stars (above 1.2Ms and up to 2Ms) and subgiant phase. We determine the granulation parameters and amplitude of the modes, which agree with previously derived scaling relations. The stars studied here are slightly fainter than the previously known sample of main-sequence and subgiants with asteroseismic detections. We also study the surface rotation and magnetic activity levels of those stars. Our sample of has similar levels of activity compared to the previously known sample and in the same range as the Sun between the minimum and maximum of its activity cycle. We find that for 7 stars, a possible blend could be the reason for the previous non detection. We compare the radii obtained from the scaling relations with the Gaia ones and find that the Gaia radii are overestimated by 4.4% on average compared to the seismic radii and a decreasing trend with evolutionary stage. We re-analyze the DR25 of the main-sequence and sub-giant stars with solar-like oscillations previously detected and provide their global seismic parameters for a total of 526 stars., 18 pages, 21 figures. Accepted for publication in A&A

We present the second results of an ensemble and systematic survey of oscillation mode variability in compact pulsators observed with the original {\sl Kepler} mission. Two types of flux calibrations, raw and corrected, collected on two hot B subdwarf stars, KIC\,2438324 and KIC\,11179657, are thoroughly examined with the goal to evaluate the difference of patterns when oscillation modes modulate in amplitude (AM) and frequency (FM). We concentrate on AMs and FMs occurring in seven multiplet components in each star as representative frequencies. The analysis shows that FM measurements are independent of the flux calibration we choose. However, if flux contamination by nearby stars is large, AMs may be significantly different between raw and corrected flux. In addition, AMs suffer, to some extent, from systematic modulation pattern which is most likely induced by instrumental effects {and} differs from one star to another. Our results indicate that stars with no contamination are better candidates to quantitatively compare modulation patterns with theory and should be given a higher priority for such studies, since light contamination will destroy real amplitude modulation patterns., 17 pages, 12 figures, 3 tables, ApJ in press

The planetary systems detected so far already exhibit a wide diversity of architectures, and various methods are proposed to study quantitatively this diversity. Straightforward ways to quantify the difference between two systems and more generally, two sets of multiplanetary systems, are useful tools in the study of this diversity. In this work we present a novel approach, using a Weighted extension of the Energy Distance (WED) metric, to quantify the difference between planetary systems on the logarithmic period-radius plane. We demonstrate the use of this metric and its relation to previously introduced descriptive measures to characterise the arrangements of Kepler planetary systems. By applying exploratory machine learning tools, we attempt to find whether there is some order that can be ascribed to the set of Kepler multiplanet system architectures. Based on WED, the 'Sequencer', which is such an automatic tool, identifies a progression from small and compact planetary systems to systems with distant giant planets. It is reassuring to see that a WED-based tool indeed identifies this progression. Next, we extend WED to define the Inter-Catalogue Energy Distance (ICED) - a distance metric between sets of multiplanetary systems. We have made the specific implementation presented in the paper available to the community through a public repository. We suggest to use these metrics as complementary tools in attempting to compare between architectures of planetary system, and in general, catalogues of planetary systems., Comment: 8 pages, 5 figures, accepted for publication in A&A, usage examples at: https://github.com/dolevbas/PASSta

Over the course of the last two decades, traditional models of planet formation have been repeatedly challenged by the emerging census of extrasolar planets. Key among them is the orbital architecture problem: while standard models of orbital migration predict resonant orbits for short-period objects, most planets do not appear to lie in orbital resonances. Here, we show that the four-planet system Kepler-221, not previously recognized to have active orbital resonances, has a three-body commensurability relation unique within the Kepler sample. Using a suite of numerical experiments as well as a perturbative analysis, we demonstrate that this system likely began as a resonant chain and proceeded to undergo large-scale divergence away from resonance, under the action of tidal dissipation. Our results further indicate that obliquity tides, driven by a secular spin–orbit resonance and mutual inclination, are an excellent candidate for driving this orbital divergence, and that the high tidal luminosity may also explain the anomalous size of planet b, which lies within the Fulton radius gap.

We have identified a star, EPIC 249706694 (HD 139139), that was observed during K2 Campaign 15 with the Kepler extended mission that appears to exhibit 28 transit-like events over the course of the 87-day observation. The unusual aspect of these dips, all but two of which have depths of $200 \pm 80$ ppm, is that they exhibit no periodicity, and their arrival times could just as well have been produced by a random number generator. We show that no more than four of the events can be part of a periodic sequence. We have done a number of data quality tests to ascertain that these dips are of astrophysical origin, and while we cannot be absolutely certain that this is so, they have all the hallmarks of astrophysical variability on one of two possible host stars (a likely bound pair) in the photometric aperture. We explore a number of ideas for the origin of these dips, including actual planet transits due to multiple or dust emitting planets, anomalously large TTVs, S- and P-type transits in binary systems, a collection of dust-emitting asteroids, `dipper-star' activity, and short-lived starspots. All transit scenarios that we have been able to conjure up appear to fail, while the intrinsic stellar variability hypothesis would be novel and untested., Comment: 12 pages, 6 figures, and 7 tables; Accepted for publication in MNRAS

We perform a search for rapidly oscillating Ap stars in the Kepler long-cadence data, where true oscillations above the Nyquist limit of 283.21 {\mu}Hz can be reliably distinguished from aliases as a consequence of the barycentric time corrections applied to the Kepler data. We find evidence for rapid oscillations in six stars: KIC 6631188, KIC 7018170, KIC 10685175, KIC 11031749, KIC 11296437 and KIC 11409673, and identify each star as chemically peculiar through either pre-existing classifications or spectroscopic measurements. For each star, we identify the principal pulsation mode, and are able to observe several additional pulsation modes in KIC 7018170. We find that KIC 7018170 and KIC 11409673 both oscillate above their theoretical acoustic cutoff frequency, whilst KIC 11031749 oscillates at the cutoff frequency within uncertainty. All but KIC 11031749 exhibit strong amplitude modulation consistent with the oblique pulsator model, confirming their mode geometry and periods of rotation., Comment: 20 pages, 14 figures, accepted for publication in MNRAS

KOI-3890 is a highly eccentric, 153-day period eclipsing, single-lined spectroscopic binary system containing a red-giant star showing solar-like oscillations alongside tidal interactions. The combination of transit photometry, radial velocity observations, and asteroseismology have enabled the detailed characterisation of both the red-giant primary and the M-dwarf companion, along with the tidal interaction and the geometry of the system. The stellar parameters of the red-giant primary are determined through the use of asteroseismology and grid-based modelling to give a mass and radius of $M_{\star}=1.04\pm0.06\;\textrm{M}_{\odot}$ and $R_{\star}=5.8\pm0.2\;\textrm{R}_{\odot}$ respectively. When combined with transit photometry the M-dwarf companion is found to have a mass and radius of $M_{\mathrm{c}}=0.23\pm0.01\;\textrm{M}_{\odot}$ and $R_{\mathrm{c}}=0.256\pm0.007\;\textrm{R}_{\odot}$. Moreover, through asteroseismology we constrain the age of the system through the red-giant primary to be $9.1^{+2.4}_{-1.7}\;\mathrm{Gyr}$. This provides a constraint on the age of the M-dwarf secondary, which is difficult to do for other M-dwarf binary systems. In addition, the asteroseismic analysis yields an estimate of the inclination angle of the rotation axis of the red-giant star of $i=87.6^{+2.4}_{-1.2}$ degrees. The obliquity of the system\textemdash the angle between the stellar rotation axis and the angle normal to the orbital plane\textemdash is also derived to give $\psi=4.2^{+2.1}_{-4.2}$ degrees showing that the system is consistent with alignment. We observe no radius inflation in the M-dwarf companion when compared to current low-mass stellar models., Comment: 11 pages, 5 figures, accepted for publication in MNRAS

KIC 10684673 (TYC 3562-805-1) was observed by the Kepler mission, which obtained nearly 50,000 data points in the short cadence mode from May through June of 2009 for a total of about 33 days. It has been added to the Kepler Eclipsing Binary Catalog as an eclipsing binary. However it is flagged as uncertain in nature. Upon visual inspection, it is found the light curve is not consistent with features present in light curves from typical eclipsing binary systems. Instead, it shows features more consistent with pulsation. In the present study, it is shown the light curve can be satisfactorily modeled by considering the target as single, multi-modal δ Scuti pulsator.

Period–eccentricity distribution of eccentric eclipsing binaries (eEB) has inevitable importance in the study of the different kinds of tidal circularization (and synchronization) processes. Recent space missions provide a large amount of continuous and precise light curves, which enable us to determine several accurate stellar and dynamical parameters for thousands of freshly discovered eEBs. For statistical analysis we developed a fast, automated, although approximating method for determining eccentricity and argument of periastron from the displacement of the secondary minima and the difference of primary and secondary eclipse durations for large samples of eclipsing lightcurves. Applying this method to several hundreds of recently discovered eEBs in the fields of the primordial and secondary Kepler and also the CoRoT missions, we present a comprehensive statistical analysis of the period–eccentricity relation for different subgroups of these double star systems.

We investigate the role that planet detection order plays in the Kepler planet detection pipeline. The Kepler pipeline typically detects planets in order of descending signal strength (MES). We find that the detectability of transits experiences an additional $5.5\%$ and $15.9\%$ efficiency loss, for periods $200$ days respectively, when detected after the strongest signal transit in a multiple-planet system. We provide a method for determining the transit probability for multiple-planet systems by marginalizing over the empirical Kepler dataset. Furthermore, because detection efficiency appears to be a function of detection order, we discuss the sorting statistics that affect the radius and period distributions of each detection order. Our occurrence rate dataset includes radius measurement updates from the California Kepler Survey (CKS), Gaia DR2, and asteroseismology. Our population model is consistent with the results of Burke et al. (2015), but now includes an improved estimate of the multiplicity distribution. From our obtained model parameters, we find that only $4.0\pm4.6\%$ of solar-like GK dwarfs harbor one planet. This excess is smaller than prior studies and can be well modeled with a modified Poisson distribution, suggesting that the Kepler Dichotomy can be accounted for by including the effects of multiplicity on detection efficiency. Using our modified Poisson model we expect the average number of planets is $5.86\pm0.18$ planets per GK dwarf within the radius and period parameter space of Kepler., 17 pages, 8 figures, and 4 tables; accepted for publishing in MNRAS

Studies using asteroseismic ages and rotation rates from star-spot rotation have indicated that standard age-rotation relations may break down roughly half-way through the main sequence lifetime, a phenomenon referred to as weakened magnetic braking. While rotation rates from spots can be difficult to determine for older, less active stars, rotational splitting of asteroseismic oscillation frequencies can provide rotation rates for both active and quiescent stars, and so can confirm whether this effect really takes place on the main sequence. We obtained asteroseismic rotation rates of 91 main sequence stars showing high signal-to-noise modes of oscillation. Using these new rotation rates, along with effective temperatures, metallicities and seismic masses and ages, we built a hierarchical Bayesian mixture model to determine whether the ensemble more closely agreed with a standard rotational evolution scenario, or one where weakened magnetic braking takes place. The weakened magnetic braking scenario was found to be 98.4% more likely for our stellar ensemble, adding to the growing body of evidence for this stage of stellar rotational evolution. This work represents the largest catalogue of seismic rotation on the main sequence to date, opening up possibilities for more detailed ensemble analysis of rotational evolution with Kepler., 48 pages, 10 figures, 1 table. Published in Nature Astronomy

Measuring phase modulation in pulsating stars has proved to be a highly successful way of finding binary systems. The class of pulsating main-sequence A and F variables known as delta Scuti stars are particularly good targets for this, and the \textit{Kepler} sample of these has been almost fully exploited. However, some \textit{Kepler} $\delta$ Scuti stars have incorrect temperatures in stellar properties catalogues, and were missed in previous analyses. We used an automated pulsation classification algorithm to find 93 new $\delta$ Scuti pulsators among tens of thousands of F-type stars, which we then searched for phase modulation attributable to binarity. We discovered 10 new binary systems and calculated their orbital parameters, which we compared with those of binaries previously discovered in the same way. The results suggest that some of the new companions may be white dwarfs., Comment: 8 pages, 6 figures that make liberal use of colour

The NASA Kepler and follow-on K2 missions (2009-2018) left a legacy of data and discoveries, finding thousands of exoplanets, and also obtaining high-precision long time-series data for hundreds of thousands of stars, including many types of pulsating variables. Here we highlight a few of the ongoing discoveries from Kepler data on $\delta$ Scuti pulsating variables, which are core hydrogen-burning stars of about twice the mass of the Sun. We discuss many unsolved problems surrounding the properties of the variability in these stars, and the progress enabled by Kepler data in using pulsations to infer their interior structure, a field of research known as asteroseismology., Comment: 15 figures. Review paper submitted to Frontiers in Astronomy and Space Sciences, published in April 2021. Part of research topic Asteroseismology in the Kepler Era

About 22,000 Kepler stars, 7,000 K2 stars, and nearly 60,000 TESS stars from sectors 1–24 have been classified according to variability type. A large proportion of stars of all spectral types appear to have periods in their light curves consistent with the expected rotation periods. A previous analysis of A- and late B-type stars suggests that these stars are indeed rotational variables. In this paper we have accumulated data to show that rotational modulation is present in about 30–40% of A- and B-type stars. A search for flares in TESS A- and B-type stars resulted in the detection of 102 flares in 57 stars. Analysis of flare energies show that the source of the flares cannot be a cool dwarf companion nor a F/G giant. The realization that a considerable fraction of A- and B-type stars are active indicates that a revision of current concepts regarding hot star envelopes is required.

37th International Cosmic Ray Conference, ICRC 2021, Berlin, online, Germany, 12 Jul 2021 - 23 Jul 2021; Proceedings of Science / International School for Advanced Studies (ICRC2021), 805 (2021). doi:10.22323/1.395.0805, Kepler���s supernova remnant (SNR) which is produced by the most recent naked-eye supernova in our Galaxy is one of the best studied SNRs, but its gamma-ray detection has eluded us so far. Observations with modern imaging atmospheric Cherenkov telescopes (IACT) have enlarged the knowledge about nearby SNRs with ages younger than 500 years by establishing Cassiopeia A and Tycho���s SNRs as very high energy (VHE) gamma-ray sources and setting a lower limit on the distance to Kepler���s SNR. This SNR is significantly more distant than the other two and expected to be one of the faintest gamma-ray sources within reach of the IACT arrays of this generation. We report strong evidence for a VHE signal from Kepler���s SNR based on deep observations of the High Energy Stereoscopic System (H.E.S.S.) with an exposure of 152 hours, including 122 hours accumulated in 2017-2020. We further discuss implications of this result for cosmic-ray acceleration in young SNRs., Published by SISSA, Trieste

(abridged) Observations of exoplanets indicate the existence of several correlations in the architecture of planetary systems. Exoplanets within a system tend to be of similar size and mass, evenly spaced, and are often ordered in size and mass. Small planets are frequently packed in tight configurations, while large planets often have wider orbital spacing. Together, these correlations are called the peas in a pod trends in the architecture of planetary systems. In this paper these trends are investigated in theoretically simulated planetary systems and compared with observations. Whether these correlations emerge from astrophysical processes or the detection biases of the transit method is examined. Synthetic planetary system were simulated using the Generation III Bern Model. KOBE, a new computer code, simulates the geometrical limitations of the transit method and applies the detection biases and completeness of the Kepler survey. This allows simulated planetary systems to be compared with observations. The architecture of synthetic planetary systems, observed via KOBE, show the peas in a pod trends in good agreement with observations. These correlations are also present in the theoretical underlying population, from the Bern Model, indicating that these trends are probably of astrophysical origin. The physical processes involved in planet formation are responsible for the emergence of evenly spaced planets with similar sizes and masses. The size--mass similarity trends are primordial and originate from the oligarchic growth of protoplanetary embryos and the uniform growth of planets at early times. Later stages in planet formation allows planets within a system to grow at different rates, thereby decreasing these correlations. The spacing and packing correlations are absent at early times and arise from dynamical interactions., Comment: Accepted in A&A. Main body: 18 pages, 13 figures. Appendices: 7 pages, 3 figures. Code: https://github.com/exomishra/kobe

Kepler high cadence data are used to measure the orbital periods and to determine the orbital waveforms of five dwarf novae. A significant improvement of the period of V1504 Cyg is achieved, while for the other systems periods are derived which are compatible with previous determinations. The orbital waveforms of the short period systems V1504 Cyg, V344 Lyr and V516 Lyr are very nearly sinusoidal, while the longer period dwarf nova V447 Lyr appears almost to be a twin of U Gem. The unusual system KIC 9202990 exhibits distinct variations of its waveform as a function of brightness during its outburst cycle.

Holczer, Mazeh, and collaborators (HM+16) used the Kepler four-year observations to derive a transit-timing catalog, identifying 260 Kepler objects of interest (KOI) with significant transit timing variations (TTV). For KOIs with high enough SNRs, HM+16 also derived the duration and depth of their transits. In the present work, we use the duration measurements of HM+16 to systematically study the duration changes of 561 KOIs and identify 15 KOIs with a significant long-term linear change of transit durations and another 16 KOIs with an intermediate significance. We show that the observed linear trend is probably caused by a precession of the orbital plane of the transiting planet, induced in most cases by another planet. The leading term of the precession rate depends on the mass and relative inclination of the perturber, and the period ratio between the two orbits, but not on the mass and period of the transiting planet itself. Interestingly, our findings indicate that, as a sample, the detected time derivatives of the durations get larger as a function of the planetary orbital period, probably because short-period planetary systems display small relative inclinations. The results might indicate that short-period planets reside in relatively flattened planetary systems, suggesting these systems experienced stronger dissipation either when formed or when migrated to short orbits. This should be used as a possible clue for the formation of such systems., Comment: 19 pages, 14 figures. Accepted for publication in MNRAS

Asteroseismology using space-based telescopes is vital to our understanding of stellar structure and evolution. {\textit{CoRoT}}, {\textit{Kepler}}, and {\textit{TESS}} space telescopes have detected large numbers of solar-like oscillating evolved stars. %(kaynaklar, Kallinger, vb ). Solar-like oscillation frequencies have an important role in the determination of fundamental stellar parameters; in the literature, the relations between the two is established by the so-called scaling relations. % These scaling relations are in better agreement with mass and radius of main-sequence stars with large separation ($\Delta\nu$) and frequency of maximum amplitude (${\nu_{\rm max}}$). In this study, we analyse data obtained from the observation of 15 evolved solar-like oscillating stars using the {\textit{Kepler}} and ground-based %\textit{CoRoT} telescopes. The main purpose of the study is to determine very precisely the fundamental parameters of evolved stars by constructing interior models using asteroseismic parameters. We also fit the reference frequencies of models to the observational reference frequencies caused by the He {\scriptsize II} ionization zone. The 15 evolved stars are found to have masses and radii within ranges of $0.79$-$1.47$ $M_{\rm sun}$ and $1.60$-$3.15$ $R_{\rm sun}$, respectively. Their model ages range from $2.19$ to $12.75$ Gyr. %Using a number of methods based on conventional and modified scaling relations and evolutionary models constructed with using the {\small {MESA}} code, we determine stellar radii, masses and ages. It is revealed that fitting reference frequencies typically increase the accuracy of asteroseismic radius, mass, and age. The typical uncertainties of mass and radius are $\sim$ 3-6 and $\sim$ 1-2 per cent, respectively. Accordingly, the differences between the model and literature ages are generally only a few Gyr.

Light echoes of flares on active stars offer the opportunity for direct detection of circumstellar dust. We revisit the problem of identifying faint echoes in post-flare light curves, focusing on debris disks from on-going planet formation. Starting with simulations, we develop an algorithm for estimating the radial extent and total mass from disk echo profiles. We apply this algorithm to light curves from over 2,100 stars observed by NASA's Kepler mission, selected for multiple, short-lived flares in either the long-cadence or short-cadence data sets. While flux uncertainties in light curves from individual stars preclude useful mass limits on circumstellar disks, catalog-averaged light curves yield constraints on disk mass that are comparable to estimates from known debris disks. The average mass in micron- to millimeter-sized dust around the Kepler stars cannot exceed 10% of an Earth mass in exo-Kuiper belts or 10% of a Lunar mass in the terrestrial zone. We group stars according to IR excess, based on WISE W1-W3 color, as an indicator for the presence of circumstellar dust. The mass limits are greater for stars with strong IR excess, a hint that echoes are lurking not far beneath the noise in post-flare light curves. With increased sensitivity, echo detection will let time-domain astronomy complement spectroscopic and direct-imaging studies in mapping how, when, and where planets form., Comment: AJ in press, 35 pages with 14 figures and 2 tables

Context: Being part of the brightest solar-like stars, and close solar analogues, the 16 Cygni system is of great interest to the scientific community and may provide insight into the past and future evolution of our Sun. It has been observed thoroughly by the Kepler satellite, which provided us with data of an unprecedented quality. Aims: This paper is the first of a series aiming to extensively characterise the system. We test several choices of micro- and macro-physics to highlight their effects on optimal stellar parameters and provide realistic stellar parameter ranges. Methods: We used a recently developed method, WhoSGlAd, that takes the utmost advantage of the whole oscillation spectrum of solar-like stars by simultaneously adjusting the acoustic glitches and the smoothly varying trend. For each choice of input physics, we computed models which account, at best, for a set of seismic indicators that are representative of the stellar structure and are as uncorrelated as possible. The search for optimal models was carried out through a Levenberg-Marquardt minimisation. First, we found individual optimal models for both stars. We then selected the best candidates to fit both stars while imposing a common age and composition. Results: We computed realistic ranges of stellar parameters for individual stars. We also provide two models of the system regarded as a whole. We were not able to build binary models with the whole set of choices of input physics considered for individual stars as our constraints seem too stringent. We may need to include additional parameters to the optimal model search or invoke non-standard physical processes., 25 pages, Accepted for publication in Astronomy and Astrophysics

In this work we empirically measure the detection efficiency of Kepler pipeline used to create the final Kepler Threshold Crossing Event (TCE; Twicken et al. 2016) and planet candidate catalogs (Thompson et al. 2018), a necessary ingredient for occurrence rate calculations using these lists. By injecting simulated signals into the calibrated pixel data and processing those pixels through the pipeline as normal, we quantify the detection probability of signals as a function of their signal strength and orbital period. In addition we investigate the dependence of the detection efficiency on parameters of the target stars and their location in the Kepler field of view. We find that the end-of-mission version of the Kepler pipeline returns to a high overall detection efficiency, averaging a 90-95% rate of detection for strong signals across a wide variety of parameter space. We find a weak dependence of the detection efficiency on the number of transits contributing to the signal and the orbital period of the signal, and a stronger dependence on the stellar effective temperature and correlated noise properties. We also find a weak dependence of the detection efficiency on the position within the field of view. By restricting the Kepler stellar sample to stars with well-behaved correlated noise properties, we can define a set of stars with high detection efficiency for future occurrence rate calculations., 13 pages, 9 figure. This paper presents work that was previously presented in a Kepler technical document (KSCI-19110-001; Christiansen 2017), as well as new analysis, in a peer-reviewed journal article. Please update citations from Christiansen 2017 to this work

With the observations of an unprecedented number of oscillating subgiant stars expected from NASA's TESS mission, the asteroseismic characterization of subgiant stars will be a vital task for stellar population studies and for testing our theories of stellar evolution. To determine the fundamental properties of a large sample of subgiant stars efficiently, we developed a deep learning method that estimates distributions of fundamental parameters like age and mass over a wide range of input physics by learning from a grid of stellar models varied in eight physical parameters. We applied our method to four Kepler subgiant stars and compare our results with previously determined estimates. Our results show good agreement with previous estimates for three of them (KIC 11026764, KIC 10920273, KIC 11395018). With the ability to explore a vast range of stellar parameters, we determine that the remaining star, KIC 10005473, is likely to have an age 1 Gyr younger than its previously determined estimate. Our method also estimates the efficiency of overshooting, undershooting, and microscopic diffusion processes, from which we determined that the parameters governing such processes are generally poorly-constrained in subgiant models. We further demonstrate our method's utility for ensemble asteroseismology by characterizing a sample of 30 Kepler subgiant stars, where we find a majority of our age, mass, and radius estimates agree within uncertainties from more computationally expensive grid-based modelling techniques., 18 pages, 15 figures. Published in MNRAS. Updated citations and amendments to Figure 2 reference in V2

High-precision space-based photometry obtained by the \emph{Kepler} and \emph{TESS} missions has revealed evidence of rotational modulation associated with main sequence (MS) A and late-B type stars. Generally, such variability in these objects is attributed to inhomogeneous surface structures (e.g. chemical spots), which are typically linked to strong magnetic fields ($B\gtrsim100\,{\rm G}$) visible at the surface. It has been reported that $\approx44$~per~cent of all A-type stars observed during the \emph{Kepler} mission exhibit rotationally modulated light curves. This is surprising considering that $\lesssim10$~per~cent of all MS A-type stars are known to be strongly magnetic (i.e. they are Ap/Bp stars). We present a spectroscopic monitoring survey of 44 A and late-B type stars reported to exhibit rotational modulation in their \emph{Kepler} light curves. The primary goal of this survey is to test the hypothesis that the variability is rotational modulation by comparing each star's rotational broadening ($v\sin{i}$) with the equatorial velocities ($v_{\rm eq}$) inferred from the photometric periods. We searched for chemical peculiarities and binary companions in order to provide insight into the origin of the apparent rotational modulation. We find that 14 stars in our sample have $v\sin{i}>v_{\rm eq}$ and/or have low-mass companions that may contribute to or be responsible for the observed variability. Our results suggest that more than $10$~per~cent of all MS A and late-B type stars may exhibit inhomogeneous surface structures; however, the incidence rate is likely $\lesssim30$~per~cent., 18 pages, 12 figures. Accepted for publication in MNRAS

The NASA $Kepler$ mission obtained long-term high-quality photometric observations for a large number of stars in its original field of view from 2009 to 2013. In order to provide reliable stellar parameters in a homogeneous way, the LAMOST telescope began to carry out low-resolution spectroscopic observations for as many stars as possible in the $Kepler$ field in 2012. By September 2018, 238,386 low-resolution spectra with SNR$_g \geq 6$ had been collected for 155,623 stars in the $Kepler$ field, enabling the determination of atmospheric parameters and radial velocities, as well as spectral classification of the target stars. This information has been used by astronomers to carry out research in various fields, including stellar pulsations and asteroseismology, exoplanets, stellar magnetic activity and flares, peculiar stars and the Milky Way, binary stars, etc. We summarize the research progress in these fields where the usage of data from the LAMOST-$Kepler$ (LK) project has played a role. In addition, time-domain medium-resolution spectroscopic observations have been carried out for about 12,000 stars in four central plates of the $Kepler$ field since 2018. The currently available results show that the LAMOST-$Kepler$ medium resolution (LK-MRS) observations provide qualified data suitable for research in additional science projects including binaries, high-amplitude pulsating stars, etc. As LAMOST is continuing to collect both low- and medium-resolution spectra of stars in the $Kepler$ field, we expect more data to be released continuously and new scientific results to appear based on the LK project data., 15 pages, 9 figures, 1 table, RAA accepted

The Kepler space mission has detected a large number of exoplanets in multiple transiting planet systems. Previous studies found that these Kepler multiple planet systems exhibit an intra-system uniformity, namely planets in the same system have similar sizes and correlated orbital spacings. However, it is important to consider the possible role of selection effects due to observational biases. In this paper, we revisit the orbital spacing aspect of the pattern after taking observational biases into account using a forward modeling method. We find that orbital spacings, in terms of period ratios, of Kepler multiple planet systems are significantly correlated only for those tightly packed systems, and the transition from correlation to non-correlation is abrupt with a boundary at mean period ratio $\overline{PR}$ $\sim 1.5 - 1.7$. In this regard, the pattern of orbital spacing is more like a dichotomy rather than a global correlation. Furthermore, we find that such an apparent orbital spacing dichotomy could be essentially a projection of a dichotomy that related to mean motion resonance (MMR), which we dub as MMR dichotomy, and itself could be a natural result of planet migration and dynamical evolution., Accepted for publication in Astronomical Journal. 11 figures

Long, high-quality time-series data provided by previous space-missions such as CoRoT and $\mathit{Kepler}$ have made it possible to derive the evolutionary state of red-giant stars, i.e. whether the stars are hydrogen-shell burning around an inert helium core or helium-core burning, from their individual oscillation modes. We utilise data from the $\mathit{Kepler}$ mission to develop a tool to classify the evolutionary state for the large number of stars being observed in the current era of K2, TESS and for the future PLATO mission. These missions provide new challenges for evolutionary state classification given the large number of stars being observed and the shorter observing duration of the data. We propose a new method, $\mathtt{Clumpiness}$, based upon a supervised classification scheme that uses "summary statistics" of the time series, combined with distance information from the Gaia mission to predict the evolutionary state. Applying this to red giants in the APOKASC catalogue, we obtain a classification accuracy of ~91% for the full 4 years of $\mathit{Kepler}$ data, for those stars that are either only hydrogen-shell burning or also helium-core burning. We also applied the method to shorter $\mathit{Kepler}$ datasets, mimicking CoRoT, K2 and TESS achieving an accuracy >91% even for the 27 day time series. This work paves the way towards fast, reliable classification of vast amounts of relatively short-time-span data with a few, well-engineered features., 16 pages, 8 figures, accepted for publication in MNRAS

Detailed modelling of stellar oscillations is able to give precise estimates for stellar ages, but the inferred results typically depend on the adopted model parameters used for the age inference. High-quality asteroseismic data with precise measurements of mixed modes are available for 36 Kepler subgiants. To obtain a handle on the robustness of the ages for these stars, we first study the dependencies of seismic ages on three model input parameters. We find that inferred ages do not change systematically with the helium fraction (Y) or the mixing-length parameter but depend strongly on the metallicity ([M/H]) of the model. The results indicate that age estimates of subgiants have less model dependence and hence are more reliable than those of main-sequence stars or red giants. We then model individual oscillation frequencies of the same 36 Kepler subgiants, using observed metallicities, and obtain their ages with an average precision of ~15%. The comparison with previous age estimates with different stellar codes or input physics shows good agreement (mostly within 2#). We hence suggest that seismology-determined ages of subgiants are not greatly model-dependent., MNRAS Accepted

One of the key methods for determining the unknown nature of Type Ia supernovae (SNe Ia) is the search for traces of interaction between the SN ejecta and the circumstellar structures at the resulting supernova remnants (SNRs Ia). So far, the observables that we receive from well-studied SNRs Ia cannot be explained self-consistently by any model presented in the literature. In this study, we suggest that the circumstellar medium (CSM) being observed to surround several SNRs Ia was mainly shaped by planetary nebulae (PNe) that originated from one or both progenitor stars. Performing two-dimensional hydrodynamic simulations, we show that the ambient medium shaped by PNe can account for several properties of the CSM that have been found to surround SNe Ia and their remnants. Finally, we model Kepler&rsquo, s SNR considering that the SN explosion occurred inside a bipolar PN. Our simulations show good agreement with the observed morphological and kinematic properties of Kepler&rsquo, s SNR. In particular, our model reproduces the current expansion parameter of Kepler&rsquo, s SNR, the partial interaction of the remnant with a dense CSM at its northern region and finally the existence of two opposite protrusions (&lsquo, ears&rsquo, ) at the equatorial plane of the SNR.

We present the discovery of Kepler-88 d ($P_d = 1403\pm14$ days, $M\mathrm{sin}i_d = 965\pm44\,M_\oplus = 3.04\pm0.14\,M_J$, $e_d = 0.41\pm0.03$) based on six years of radial velocity (RV) follow-up from the W. M. Keck Observatory HIRES spectrograph. Kepler-88 has two previously identified planets. Kepler-88 b (KOI-142.01) transits in the NASA \Kepler\ photometry and has very large transit timing variations. \citet{Nesvorny2013} perfomed a dynamical analysis of the TTVs to uniquely identify the orbital period and mass of the perturbing planet (Kepler-88 c), which was later was confirmed with RVs from the Observatoire de Haute-Provence (OHP, Barros et al. 2014). To fully explore the architecture of this system, we performed photodynamical modeling on the \Kepler\ photometry combined with the RVs from Keck and OHP and stellar parameters from spectroscopy and Gaia. Planet d is not detectable in the photometry, and long-baseline RVs are needed to ascertain its presence. A photodynamical model simultaneously optimized to fit the RVs and \Kepler\ photometry yields the most precise planet masses and orbital properties yet for b and c: $P_b = 10.91647\pm0.00014\,\mathrm{days}$, $M_b=9.5\pm1.2\,M_\oplus$, $P_c=22.2649\pm0.0007\,\mathrm{days}$, and $M_c=214.1\pm5.3\,M_\oplus$. The photodynamical solution also finds that planets b and c have low eccentricites and low mutual inclination, are apsidally anti-aligned, and have conjunctions on the same hemisphere of the star. Continued RV follow-up of systems with small planets will improve our understanding of the link between inner planetary system architectures and giant planets., 25 pages, 14 figures, published in AJ

An accurate and precise Kepler Stellar Properties Catalog is essential for the interpretation of the Kepler exoplanet survey results. Previous Kepler Stellar Properties Catalogs have focused on reporting the best-available parameters for each star, but this has required combining data from a variety of heterogeneous sources. We present the Gaia-Kepler Stellar Properties Catalog, a set of stellar properties of 186,301 Kepler stars, homogeneously derived from isochrones and broadband photometry, Gaia Data Release 2 parallaxes, and spectroscopic metallicities, where available. Our photometric effective temperatures, derived from $g-K_s$ colors, are calibrated on stars with interferometric angular diameters. Median catalog uncertainties are 112 K for $T_{\mathrm{eff}}$, 0.05 dex for $\log g$, 4% for $R_\star$, 7% for $M_\star$, 13% for $\rho_\star$, 10% for $L_\star$, and 56% for stellar age. These precise constraints on stellar properties for this sample of stars will allow unprecedented investigations into trends in stellar and exoplanet properties as a function of stellar mass and age. In addition, our homogeneous parameter determinations will permit more accurate calculations of planet occurrence and trends with stellar properties., Comment: 22 pages, 13 figures, 2 tables. Published in AJ. Electronic versions of Tables 1 & 2 are now, in this submission, included as ancillary files (sidebar on the right)

In this study, investigation of two double-lined binary stars KIC 5113146 and KIC 5111815 in NGC 6819 is presented based on both photometric and spectroscopic data. Simultaneous analysis of light and radial velocity curves was made and the absolute parameters of the systems' components were determined for the first time. We find that both systems have F-type main-sequence components. The masses and radii were found to be $M_1=1.29\pm0.02 M_{\odot}$, $R_{1}=1.47\pm0.03 R_{\odot}$ and $M_{2}=1.19\pm0.02 M_{\odot}$, $R_{2}=1.13\pm0.02 R_{\odot}$ for the primary and secondary components of KIC 5113146; $M_{1}=1.51\pm0.08 M_{\odot}$, $R_{1}=2.02\pm0.05 R_{\odot}$ and $M_{2}=1.19\pm0.07 M_{\odot}$, $R_{2}=1.32\pm0.04 R_{\odot}$ for components of KIC 5111815, respectively. Evolutionary status of the components was evaluated based on the MESA evolutionary tracks and isochrones. The ages of the KIC 5111815 and KIC 5113146 were derived to be about $2.50\pm0.35$ Gyr and $1.95\pm0.40$ Gyr, respectively. Photometric distances were calculated to be $2850\pm 185$ pc for KIC 5113146 and $3120\pm 260$ pc for KIC 5111815. The results obtained in this study, astrometric data and researches in the literature reveal that both KIC 5113146 and KIC 5111815 systems are the most likely member of NGC 6819., Comment: 26 pages, including 7 figures and 4 tables, accepted for publication in Astronomical Journal