KIC 4768731: a bright long-period roAp star in theKeplerfield

We report the identification of 61.45 d−1 (711.2 μHz) oscillations, with amplitudes of 62.6 μmag, in KIC 4768731 (HD 225914) using Kepler photometry. This relatively bright (V = 9.17) chemically peculiar star with spectral type A5 Vp SrCr(Eu) has previously been found to exhibit rotational modulation with a period of 5.21 d. Fourier analysis reveals a simple dipole pulsator with an amplitude that has remained stable over a 4-yr time span, but with a frequency that is variable. Analysis of high-resolution spectra yields stellar parameters of Teff = 8100 ± 200 K, log g = 4.0 ± 0.2, [Fe/H] = +0.31 ± 0.24 and v sin i = 14.8 ± 1.6 km s−1. Line profile variations caused by rotation are also evident. Lines of Sr, Cr, Eu, Mg and Si are strongest when the star is brightest, while Y and Ba vary in antiphase with the other elements. The abundances of rare earth elements are only modestly enhanced compared to other roAp stars of similar Teff and log g. Radial velocities in the literature suggest a significant change over the past 30 yr, but the radial velocities presented here show no significant change over a period of 4 yr

Spectral analysis of Kepler SPB and Beta Cep candidate stars

We determine the fundamental parameters of SPB and Beta Cep candidate stars observed by the Kepler satellite mission and estimate the expected types of non-radial pulsators by comparing newly obtained high-resolution spectra with synthetic spectra computed on a grid of stellar parameters assuming LTE and check for NLTE effects for the hottest stars. For comparison, we determine Teff independently from fitting the spectral energy distribution of the stars obtained from the available photometry. We determine Teff, log(g), micro-turbulent velocity, vsin(i), metallicity, and elemental abundance for 14 of the 16 candidate stars, two of the stars are spectroscopic binaries. No significant influence of NLTE effects on the results could be found. For hot stars, we find systematic deviations of the determined effective temperatures from those given in the Kepler Input Catalogue. The deviations are confirmed by the results obtained from ground-based photometry. Five stars show reduced metallicity, two stars are He-strong, one is He-weak, and one is Si-strong. Two of the stars could be Beta Cep/SPB hybrid pulsators, four SPB pulsators, and five more stars are located close to the borders of the SPB instability region.Comment: 10 pages, 10 figures, 10 table

Affecting surface chirality via multicomponent adsorption of chiral and achiral molecules

Here we report on the apparent reduction in surface chirality upon co-assembling a chiral and achiral molecule into a physisorbed self-assembled monolayer at the liquid/solid interface as revealed by scanning tunneling microscopy (STM). Chiral OPV with achiral thymine gives rise to surface-confined supramolecular diastereomers

The orbits of subdwarf B + main-sequence binaries. I: The sdB+G0 system PG 1104+243

The predicted orbital period histogram of an sdB population is bimodal with a peak at short ( 250 days) periods. Observationally, there are many short-period sdB systems known, but only very few long-period sdB binaries are identified. As these predictions are based on poorly understood binary interaction processes, it is of prime importance to confront the predictions to observational data. In this contribution we aim to determine the absolute dimensions of the long-period sdB+MS binary system PG1104+243. High-resolution spectroscopy time-series were obtained with HERMES at the Mercator telescope at La Palma, and analyzed to obtain radial velocities of both components. Photometry from the literature was used to construct the spectral energy distribution (SED) of the binary. Atmosphere models were used to fit this SED and determine the surface gravity and temperature of both components. The gravitational redshift provided an independent confirmation of the surface gravity of the sdB component. An orbital period of 753 +- 3 d and a mass ratio of q = 0.637 +- 0.015 were found from the RV-curves. The sdB component has an effective temperature of Teff = 33500 +- 1200 K and a surface gravity of logg = 5.84 +- 0.08 dex, while the cool companion is found to be a G-type star with Teff = 5930 +- 160 K and logg = 4.29 +- 0.05 dex. Assuming a canonical mass of Msdb = 0.47 Msun, the MS component has a mass of 0.74 +- 0.07 Msun, and its Teff corresponds to what is expected for a terminal age main-sequence star with sub-solar metalicity. PG1104+243 is the first long-period sdB binary in which accurate physical parameters of both components could be determined, and the first sdB binary in which the gravitational redshift is measured. Furthermore, PG1104+243 is the first sdB+MS system that shows consistent evidence for being formed through stable Roche-lobe overflow.Comment: Accepted by A&A on 05-10-201

MOST light-curve analysis of the gamma Dor pulsator HR 8799, showing resonances and amplitude variations

Context: The central star of the HR 8799 system is a gamma Doradus-type pulsator. The system harbours four planetary-mass companions detected by direct imaging, and is a good solar system analogue. The masses of the companions are not known accurately, because the estimation depends strongly on the age of the system, which is also not known with sufficient accuracy. Asteroseismic studies of the star might help to better constrain the age of HR 8799. We organized an extensive photometric and multi-site spectroscopic observing campaign for studying the pulsations of the central star. Aims: The aim of the present study is to investigate the pulsation properties of HR 8799 in detail via the ultra-precise 47-d-long nearly continuous photometry obtained with the MOST space telescope, and to find as many independent pulsation modes as possible, which is the prerequisite of an asteroseismic age determination. Methods: We carried out Fourier analysis of the wide-band photometric time series. Results: We find that resonance and sudden amplitude changes characterize the pulsation of HR 8799. The dominant frequency is always at f1 = 1.978 c/d. Many multiples of one ninth of the dominant frequency appear in the Fourier spectrum of the MOST data: n/9 f1, where n={1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14, 17, 18}. Our analysis also reveals that many of these peaks show strong amplitude decrease and phase variations even on the 47-d time-scale. The dependencies between the pulsation frequencies of HR 8799 make the planned subsequent asteroseismic analysis rather difficult. We point out some resemblance between the light curve of HR 8799 and the modulated pulsation light curves of Blazhko RR Lyrae stars.Comment: Accepted for publication in Astronomy and Astrophysics. 8 pages, 4 figure

Spectrum Analysis of Bright Kepler Gamma Doradus Candidate Stars

Ground-based spectroscopic follow-up observations of the pulsating stars observed by the Kepler satellite mission are needed for their asteroseismic modelling. We aim to derive the fundamental parameters for a sample of 26 Gamma Doradus candidate stars observed by the Kepler satellite mission to accomplish one of the required preconditions for their asteroseismic modelling and to compare our results with the types of pulsators expected from the existing light curve analysis. We use the spectrum synthesis method to derive the fundamental parameters like Teff, logg, [M/H], and vsini from newly obtained spectra and compute the spectral energy distribution from literature photometry to get an independent measure of Teff. We find that most of the derived Teff values agree with the values given in the Kepler Input Catalogue. According to their positions in the HR-diagram three stars are expected Gamma Dor stars, ten stars are expected Delta Sct stars, and seven stars are possibly Delta Sct stars at the hot border of the instability strip. Four stars in our sample are found to be spectroscopic binary candidates and four stars have very low metallicity where two show about solar C abundance. Six of the 10 stars located in the Delta Sct instability region of the HR-diagram show both Delta Sct and Gamma Dor-type oscillations in their light curves implying that Gamma Dor-like oscillations are much more common among the Delta Sct stars than predicted by theory. Moreover, seven stars showing periods in the Delta Sct and the Delta Sct-Gamma Dor range in their light curves are located in the HR-diagram left of the blue edge of the theoretical Delta Sct instability strip. The consistency of these findings with recent investigations based on high-quality Kepler data implies the need for a revision of the theoretical Gamma Dor and Delta Sct instability strips.Comment: 10 pages, 3 figures, 7 tables; accepted for publication in MNRA

Long-term photometric monitoring with the Mercator telescope. Frequencies and multicolour amplitudes of γ\gamma Doradus stars

Gamma Doradus stars are excellent targets for asteroseismology since the gravity modes present in these stars probe the deep stellar interiors. Mode identification will improve the knowledge of these stars considerably. A selected group of Gamma Doradus stars and some candidates were observed with the Mercator telescope to find and/or confirm the periodicities in the light variations and to derive reliable amplitude ratios in different pass bands. A frequency analysis was performed on all new data obtained in the Geneva photometric system. In order to have more reliable and accurate frequencies, the new data were combined with similar data from the literature and with Hipparcos observations. A set of frequencies that minimized the the residuals in a harmonic fit was searched for while allowing means and amplitudes to vary from one observation set to another. Frequencies and amplitudes in the photometric passbands of the Geneva system are given for 21 Gamma Doradus stars. We report the discovery of HD 74504 as a newly found Gamma Doradus star. Our study provides the first extensive multicolour database for the understanding of gravity modes in F-type stars.Comment: Electronic tables (5 to 25) not included in this versio

Tidally induced radial-velocity variations in close binaries

A theoretical framework for the determination of tidally induced radial-velocity variations in a component of a close binary is presented. Both the free and the forced oscillations of the component are treated as linear, isentropic perturbations of a spherically symmetric star. Resonances between dynamic tides and free oscillation modes are taken into account by means of the formalism developed by Smeyers et al. (1998). The amplitude of the tidally induced radial-velocity variations seen by the observer depends on the orbital eccentricity and on the orbital inclination. The amplitude increases with increasing orbital eccentricity and is most sensitive to the value of the orbital inclination when 20 < i < 70. In the case of a 5 solar mass ZAMS star with a 1.4 solar mass compact companion, it is shown that resonant dynamic tides can lead to radial-velocity variations with amplitudes large enough to be detected in observations. The shape of the tidally induced radial-velocity curves varies from very irregular for orbital periods away from any resonances with free oscillation modes to sinusoidal for orbital periods close to a resonance with a free oscillation mode. Our investigation is concluded with an application to the slowly pulsating B star HD 177863 showing the possibility of resonant excitation of a high-order second-degree g-mode in this star.Comment: 11 pages, Accepted for publication in Astronomy and Astrophysic

New Beta Cephei Stars from the KELT Project

We present the results of a search for Galactic β Cephei stars, which are massive pulsating stars with both pressure modes and mixed modes. Thus, these stars can serve as benchmarks for seismological studies of the interiors of massive stars. We conducted the search by performing a frequency analysis on the optical light curves of known O- and B-type stars with data from the Kilodegree Extremely Little Telescope exoplanet survey. We identify 113 β Cephei stars, of which 86 are new discoveries, which altogether represent a 70% increase in the number currently known. An additional 97 candidates are identified. Among our targets, we find five new eclipsing binaries and 22 stars with equal frequency spacings suggestive of rotational splitting of nonradial pulsation modes. Candidates for runaway stars among our targets and a number of interesting individual objects are discussed. Most of the known and newly discovered β Cephei stars will be observed by the Transiting Exoplanet Survey Satellite mission, providing by far the most comprehensive observational data set of massive main-sequence pulsating stars of sufficient quality for detailed asteroseismic studies. Future analysis of these light curves has the potential to dramatically increase our understanding of the structure of stellar interiors and the physical processes taking place therein