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Here, we report an ensemble study of 214 A- and F-type stars observed by Kepler , exhibiting the so-called hump and spike periodic signal, explained by Rossby modes (r modes) – the hump – and magnetic stellar spots or overstable convective (OsC) modes – the spike , respectively. We determine the power confined in the non-resolved hump features and find additional gravity-mode (g-mode) humps always occurring at higher frequencies than the spike. Furthermore, we derive projected rotational velocities from FIES, SONG, and HERMES spectra for 28 stars and the stellar inclination angle for 89 stars. We find a strong correlation between the spike amplitude and the power in the r and g modes, which suggests that both types of oscillations are mechanically excited by either stellar spots or OsC modes. Our analysis suggests that stars with a higher power in m  = 1 r-mode humps are more likely to also exhibit humps at higher azimuthal orders (m = 2, 3, or 4). Interestingly, all stars that show g-mode humps are hotter and more luminous than the observed red edge of the δ Scuti instability strip, suggesting that either magnetic fields or convection in the outer layers could play an important role. [ABSTRACT FROM AUTHOR]

We report the analysis of high-precision space-based photometric and high-resolution spectroscopic observations of HD 180347. The high-quality light curves from the Transiting Exoplanet Survey Satellite (TESS) under sectors 14, 15, and 26 were used. By visual inspection of the light curves and the Fourier transforms, only low-frequency signals (less than 1 d−1) were detected. After using wavelet, autocorrelation, and composite spectrum analyses, HD 180347 is classified as a rotational variable with a period of about 4.1 ± 0.2 d. In reference to the observation limit of TESS , no pulsations were detected. For the spectroscopic analysis, we used data collected with the High Efficiency and Resolution Mercator Échelle Spectrograph (HERMES). We determined the spectral type of this star and obtained atmospheric parameters such as the effective temperature, the surface gravity, and the projected rotational, microturbulent, and radial velocities. We performed a detailed chemical abundance analysis. The LTE abundances were derived for 25 chemical elements. For 13 of them, including Ca, Sc, Sr, Zr, and Ba, which are important for the characterization of chemical peculiarities, we also present the non-local thermodynamic equilibrium (NLTE) abundances. NLTE improves the accuracy of the derived abundances and confirms that Ca and Sc are depleted in HD 180347 relative to their solar abundances, while the heavy elements beyond Sr are enhanced, by more than 0.7 dex. Based on the spectral class and the element abundance pattern, we classify this star as Am (kA1hA8mA8). [ABSTRACT FROM AUTHOR]

The K2 eclipsing binary (EB) candidates EPIC 211982753 (hereinafter called EPIC2753) and EPIC 211915147 (hereinafter called EPIC5147) are characterized with the help of photometric and high-resolution spectroscopic data. The light curve analysis uses the Rc -band photometric data from the 1.3-m Devasthal Fast Optical Telescope (DFOT , India), ASAS-3, and K2 observations. High-resolution échelle spectra are collected using the HERMES spectrograph at the 1.2-m MERCATOR telescope (La Palma, Spain). The synthetic light and radial velocity curves are generated with the help of the modeling package phoebe 1.0. The orbital period analysis based on the ∼3.2 yr of K2 observations does not show any change in the orbital period of both targets. The component masses M 1, 2 are estimated as 1.69(0.02) and 1.59(0.02) M⊙ for EPIC2753, and 1.48(0.01) and 1.27(0.01) M⊙ for EPIC5147. Both systems are high mass-ratio EBs with q>0.85. The component radii R 1, 2 are found to be 1.66(0.02) and 1.53(0.02) R ⊙ for EPIC2753, and 1.80(0.05) and 1.42(0.05) R ⊙ for EPIC5147. The distances of EPIC2753 and EPIC5147 are determined as 238(4) and 199(5) pc, respectively. MESA Isochrones and Stellar Tracks are used to understand the evolutionary status of both systems. [ABSTRACT FROM AUTHOR]

We summarize the results of the completed first round of the LAMOST-Kepler project, and describe the status of its on-going second round. As a result of the first round of this project, the atmospheric parameters (Teff, log g, and [Fe/H]), the spectral classification (spectral type and luminosity class), and the radial velocities (RV) have been measured for 51,385 stars. For 4031 stars, we were able to measure the projected rotational velocity, while the minimum detectable v sin i was 120 km s−1. For 8821 stars with more than one observation, we computed the χ-square probability that the detected RV variations have a random occurrence. Finally, we classified 442 stars as chromospherically active on the basis of the analysis of their Hα and Ca II-IRT fluxes. All our results have been obtained from the low-resolution (R ∼ 1800) spectroscopic observations acquired with the LAMOST instrument.

The predicted width of the upper main sequence in stellar evolution models depends on the empirical calibration of the convective overshooting parameter. Despite decades of discussions, its precise value is still unknown and further observational constraints are required to gauge it. Irrgang et al. ([1]) showed that the B3 III giant 18 Peg is one of the most evolved members of the class of slowly pulsating B (SPB) stars and, thus, bears tremendous potential to derive a tight lower limit for the width of the upper main sequence. In addition, 18 Peg turns out to be part of a single-lined spectroscopic binary system with an eccentric, more than 6-year orbit. The orbital solution, in combination with the absence of additional signatures of the secondary component in the spectroscopic data and the spectral energy distribution, lead to the conclusion that all the observations of 18 Peg are fully compatible with the assumption that the secondary component is either a main-sequence star with a mass of 1-4 M⊙ or a neutron star.

In the past decade, the research of pulsating variable stars has taken a giant leap forward thanks to the photometric measurements provided by space missions like Most, CoRoT, Kepler/K2, and Brite. These missions have provided quasi uninterrupted photometric time-series with an ultra-high quality and a total length that is not achievable from Earth. However, many of the success stories could not have been told without ground-based spectroscopic follow-up observations. Indeed, spectroscopy has some important assets as it can provide (more) accurate information about stellar parameters (like the effective temperature, surface gravity, metallicity, and abundances that are mandatory parameters for an in-depth asteroseismic study), the radial velocity (that is important for the detection of binaries and for the confirmation of cluster membership, if applicable), and the projected rotational velocity (that allows the study of the effects of rotation on pulsations). Fortunately, several large spectroscopic surveys are (becoming) available that can be used for these purposes. For some of these surveys, sub-projects have been initiated with the specific goal to complement space-based photometry. In this review, several spectroscopic surveys are introduced and compared with each other. We show that a large amount of spectroscopic data is (becoming) available for a large variety of objects.

A photometric and spectroscopic investigation is performed on five W Ursae Majoris eclipsing binaries J015818.6+260247 (hereinafter as J0158b), J073248.4+405538 (hereinafter as J0732), J101330.8+494846 (hereinafter as J1013), J132439.8+130747 (hereinafter as J1324), and J152450.7+245943 (hereinafter as J1524). The photometric data are collected with the help of the 1.3 m Devasthal Fast Optical Telescope, the 1.04 m Sampurnanand Telescope, and the Transiting Exoplanet Survey Satellite space mission. The low-resolution spectra of the 4 m Large Sky Area Multi-Object Fiber Spectroscopic Telescope are used for spectroscopic analysis. The orbital period change of these systems is determined using our photometric data and previously available photometric data from different surveys. The orbital period of J1013 and J1524 is changing at a rate of âˆ'2.552 (±0.249) Ă— 10âˆ'7 days yrâˆ'1 and âˆ'6.792(±0.952) Ă— 10âˆ'8 days yrâˆ'1, respectively, while others do not show any orbital period change. The orbital period change of J1013 and J1524 corresponds to a mass transfer rate of 2.199 Ă— 10âˆ'7 and 6.151 Ă— 10âˆ'8 M ⊙ yrâˆ'1 from the primary to the secondary component in these systems. It is likely that angular momentum loss via magnetic braking may also be responsible for the observed orbital period change in the case of J1524. All systems have a mass ratio lower than 0.5, except J0158b with a mass ratio of 0.71. All the systems are shallow-type contact binaries. J0158b and J1524 are subtype A while others are subtype W. The H α emission line region is compared with template spectra prepared using two inactive stars with the help of the STARMOD program. The J0158, J1324, and J1524 systems show excess emission in the residual spectra after subtraction of the template. [ABSTRACT FROM AUTHOR]

The nominal Kepler mission provided very high precision photometric data. Using these data, interesting phenomena such as spots, and 'hump and spike' features were observed in the light curves of some normal A and metallic lined A stars (Am stars). However, the connection between such phenomena and the chemical peculiarity of the Am stars is still unclear. In order to make progress on these issues, it's important to collect high-resolution spectroscopic data to determine their fundamental parameters and individual chemical abundances. In this paper, we present a spectroscopic study of a sample of 'hump and spike' stars in the nominal Kepler field. We used data collected with the High Efficiency and Resolution Mercator Échelle Spectrograph (HERMES). We determined the spectral types of these stars and obtained the atmospheric stellar parameters such as effective temperatures, surface gravities, projected rotational, microturbulent, and radial velocities. We also performed a detailed individual chemical abundance analysis for each target. We confirmed KIC 3459226 and KIC 6266219 as Am stars, KIC 9349245 as a marginal Am star, while KIC 4567097, KIC 4818496, KIC 5524045, KIC 5650229, KIC 7667560, and KIC 9272082 are non-Am stars. To estimate their evolutionary phases, all the stars were placed in the Hertzsprung–Russell diagram. Based on their spectral classification and chemical abundance pattern, we reclassified KIC 6266219 (previously treated as chemically normal) as an Am star (kA3hA7mF1) and KIC 9272082 (previously treated as Am) as non-Am. [ABSTRACT FROM AUTHOR]

Frequency analysis of long-term ultraprecise photometry can lead to precise values of rotation frequencies of rotating stars with 'hump and spike' features in their periodograms. Using these features, we computed the rotation frequencies and amplitudes. The corresponding equatorial rotational velocity (⁠|$V_{\rm{rot}}$|⁠) and spot size were estimated. On fitting the autocorrelation functions of the light curves with the appropriate model, we determined the star-spot decay time-scale. The |$\rm \mathit{ V}_{rot}$| agrees well with the projected rotational velocity (⁠|$\rm \nu ~sin$|   i) in the literature. Considering a single circular and black spot, we estimate its radius from the amplitude of the 'spike'. No evidence for a significant difference in the average 'spike' amplitude and spot radius was found for Am/Fm and normal A stars. Indeed, we derived an average value of |$\rm \sim\! 21\pm 2$| and |$\rm \sim\! 19\pm 2$|  ppm for the photometric amplitude and of |$\rm 1.01\, \pm \, 0.13$| and |$\rm 1.16\, \pm \, 0.12$|   |$R_\mathrm{ E}$| for the spot radius (where |$\rm \mathit{ R}_E$| is the Earth radius), respectively. We do find a significant difference for the average spot decay time-scale, which amounts to 3.6 ± 0.2 and 1.5 ± 0.2 d for Am/Fm and normal A stars, respectively. In general, spots on normal A stars are similar in size to those on Am/Fm stars, and both are weaker than previously estimated. The existence of the 'spikes' in the frequency spectra may not be strongly dependent on the appearance of star-spots on the stellar surface. In comparison with G, K, and M stars, spots in normal A and Am/Fm stars are weak, which may indicate the presence of a weak magnetic field. [ABSTRACT FROM AUTHOR]

The nearly circular (mean eccentricity e0.06) and coplanar (mean mutual inclination (i ≈3°) orbits of the solar system planets motivated Kant and Laplace to hypothesize that planets are formed in disks, which has developed into the widely accepted theory of planet formation. The first several hundred extrasolar planets (mostly Jovian) discovered using the radial velocity (RV) technique are commonly on eccentric orbits (e≈0.3). This raises a fundamental question: Are the solar system and its formation special? The Kepler mission has found thousands of transiting planets dominated by sub-Neptunes, but most of their orbital eccentricities remain unknown. By using the precise spectroscopic host star parameters from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) observations, we measure the eccentricity distributions for a large (698) and homogeneous Kepler planet sample with transit duration statistics. Nearly half of the planets are in systems with single transiting planets (singles), whereas the other half are multiple transiting planets (multiples). We find an eccentricity dichotomy: on average, Kepler singles are on eccentric orbits with e≈ 0.3, whereas the multiples are on nearly circular (e=0.04-0.04+0.03) and coplanar (i =1.4-1.1+0.8 degree) orbits similar to those of the solar system planets. Our results are consistent with previous studies of smaller samples and individual systems. We also show that Kepler multiples and solar system objects follow a common relation [e≈(1-2)?i] between mean eccentricities and mutual inclinations. The prevalence of circular orbits and the common relation may imply that the solar system is not so atypical in the galaxy after all. [ABSTRACT FROM AUTHOR]

The NASA Kepler satellite has provided unprecedented high duty-cycle, high-precision light curves for a large number of stars by continuously monitoring a field of view in Cygnus-Lyra region, leading to great progress in both discovering exoplanets and characterizing planet-hosting stars by means of asteroseismic methods. The asteroseismic survey allows the investigation of stars covering the whole H-R diagram. However, the low precision of effective temperatures and surface gravities in the KIC catalogue and the lack of information on chemical composition, metallicity and rotation rate prevent asteroseismic modeling, requiring spectroscopic observations for thousands of asteroseismic targets in the Kepler field in a homogeneous way. [ABSTRACT FROM PUBLISHER]

The seismology and physics of localized structures beneath the surface of the Sun takes on a special significance with the completion in 2006 of a solar cycle of observations by the ground-based Global Oscillation Network Group (GONG) and by the instruments on board the Solar and Heliospheric Observatory (SOHO). Of course, the spatially unresolved Birmingham Solar Oscillation Network (BiSON) has been observing for even longer. At the same time, the testing of models of stellar structure moves into high gear with the extension of deep probes from the Sun to other solar-like stars and other multi-mode pulsators, with ever-improving observations made from the ground, the success of the MOST satellite, and the recently launched CoRoT satellite. Here we report the current state of the two closely related and rapidly developing fields of helio- and asteroseimology. [ABSTRACT FROM PUBLISHER]

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) at the Xinglong observatory in China is a 4-m telescope equipped with 4,000 optical fibres. In 2010, we initiated the LAMOST-Kepler project which aimed at collecting low-resolution spectra of stars from the Kepler Input Catalog covering uniformly the Kepler field of view. The first round of the LAMOST-Kepler project has been completed in September 2014 resulting in more than 100,000 low-resolution spectra. We used those data to derive the effective temperature, the surface gravity, and the mean metallicity of our targets, as well as to detect fast rotators, and to identify emission-line stars. Our results are consistent with those reported in the literature and derived from high-resolution spectroscopy. The second round of the LAMOST-Kepler project will allow to improve the coverage of the Kepler field and to repeat observations of selected targets. [ABSTRACT FROM PUBLISHER]

We present the results of time-series photometric analysis of 15106 A-K type stars observed by the Kepler space mission. We identified 513 new rotational variables and measured their starspot rotation periods as a function of spectral type and discuss the distribution of their amplitudes. We examined the well-established period-color relationship that applies to stars of spectral types F5-K for all of these rotational variables and, interestingly, found that a similar period-color relationship appears to extend to stars of spectral types A7 to early-F too. This result is not consistent with the very foundation of the period-color relationship. We have characterized 350 new non-radial pulsating variables such as A- and F-type candidate δ Scuti, γ Doradus and hybrid stars, which increases the known candidate non-radial pulsators in the Kepler field significantly, by ∼20%. The relationship between two recently constructed observables, Energy and Efficiency, was also studied for the large sample of non-radial pulsators, which shows that the distribution in the logarithm of Energy (log(En)) can be used as a potential tool to distinguish between the non-radial pulsators, to some extent. Through visual inspection of the light curves and their corresponding frequency spectra, we found 23 new candidate red giant solar-like oscillators not previously reported in the literature. The basic physical parameters such as masses, radii and luminosities of these solar-like oscillators were also derived using asteroseismic relations. [ABSTRACT FROM AUTHOR]

We present results of observations of 22 664 stars in the Kepler field of view acquired with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) in the years 2011 – 2012, and provide a database of the atmospheric parameters derived from those data. [ABSTRACT FROM PUBLISHER]