Search

Context. Our knowledge of populations and occurrence of planets orbiting evolved intermediate-mass stars is still incomplete. In 2010 we started a planet-search program among 95 giant stars observed by the Kepler mission to increase the sample of giant stars with planets and with reliable estimates of stellar masses and radii. Aims. We present the two systems KIC 3526061 and HD 187878 from our planet-search program for which we could characterise their companions. Methods. We used precise stellar radial velocity measurements taken with four different echelle spectrographs to derive an orbital solution. We used Gaia astrometric measurements to obtain the inclination of the HD 187878 system and Kepler photometric observations to estimate the stellar mass and radius. Results. We report the discovery of a sub-stellar and a stellar companion around two intermediate-mass red giant branch stars. KIC 3526061 b is most likely a brown dwarf with a minimum mass of 18.15 Jupiter masses in a long-period eccentric orbit, with the orbital period 3552 d and orbital eccentricity 0.85. It is the most evolved system found having a sub-stellar companion with such a large eccentricity and wide separation. HD 187878 B has a minimum mass of 78.4 Jupiter masses. Combining the spectroscopic orbital parameters with the astrometric proper motion anomaly we derived an orbital inclination 9.8 deg, which corresponds to the companion's mass in the stellar regime of 0.51 Sun mass. Conclusions. A sub-stellar companion of KIC 3526061 extends the sample of known red giant branch stars with sub-stellar companions on very eccentric wide orbits and might provide a probe of the dynamical evolution of such systems over time., Comment: 14 pages, 11 figures. Accepted to A&A

The analysis of the wavelength-dependent albedo of exoplanets represents a direct way to provide insight of their atmospheric composition and to constrain theoretical planetary atmosphere modelling. Wavelength-dependent albedo can be inferred from the exoplanet's reflected light of the host star, but this is not a trivial task. In fact, the planetary signal may be several orders of magnitude lower ($10^{-4}$ or below) than the flux of the host star, thus making its extraction very challenging. Successful detection of the planetary signature of 51~Peg\,b has been recently obtained by using cross-correlation function (CCF) or autocorrelation function (ACF) techniques. In this paper we present an alternative method based on the use of Independent Component Analysis (ICA). In comparison to the above-mentioned techniques, the main advantages of ICA are that the extraction is \textit{"blind"} i.e. it does not require any \textit{a priori} knowledge of the underlying signals, and that our method allows us not only to detect the planet signal but also to estimate its wavelength dependence. To show and quantify the effectiveness of our method we successfully applied it to both simulated data and real data of an eclipsing binary star system. Eventually, when applied to real 51~Peg~+~51~Peg\,b data, our method extracts the signal of 51~Peg but we could not soundly detect the reflected spectrum of 51~Peg\,b mainly due to the insufficient $SNR$ of the input composite spectra. Nevertheless, our results show that with "ad-hoc" scheduled observations an ICA approach will be, in perspective, a very valid tool for studying exoplanetary atmospheres., Comment: 25 pages, 12 figures. Accepted to AJ

We present an analysis of the first Kepler K2 mission observations of a rapidly oscillating Ap (roAp) star, HD 24355 ($V=9.65$). The star was discovered in SuperWASP broadband photometry with a frequency of 224.31 d$^{-1}$, (2596.18 $\mu$Hz; $P = 6.4$ min) and an amplitude of 1.51 mmag, with later spectroscopic analysis of low-resolution spectra showing HD 24355 to be an A5 Vp SrEu star. The high precision K2 data allow us to identify 13 rotationally split sidelobes to the main pulsation frequency of HD 24355. This number of sidelobes combined with an unusual rotational phase variation show this star to be the most distorted quadrupole roAp pulsator yet observed. In modelling this star, we are able to reproduce well the amplitude modulation of the pulsation, and find a close match to the unusual phase variations. We show this star to have a pulsation frequency higher than the critical cut-off frequency. This is currently the only roAp star observed with the Kepler spacecraft in Short Cadence mode that has a photometric amplitude detectable from the ground, thus allowing comparison between the mmag amplitude ground-based targets and the $\mu$mag spaced-based discoveries. No further pulsation modes are identified in the K2 data, showing this star to be a single-mode pulsator., Comment: 18 pages, accepted for publication in MNRAS

Eclipsing binary systems with pulsating components allow the determination of several physical parameters of the stars, such as mass and radius, that, when combined with the pulsation properties, can be used to constrain the modeling of stellar interiors and evolution. Hereby, we present the results of the study of CoRoT 105906206, an eclipsing binary system with a pulsating component located in the CoRoT LRc02 field. The analysis of the CoRoT light curve was complemented by high-resolution spectra from the Sandiford at McDonald Observatory and FEROS at ESO spectrographs, which revealed a double-lined spectroscopic binary. We used an iterative procedure to separate the pulsation-induced photometric variations from the eclipse signals. First, a Fourier analysis was used to identify the significant frequencies and amplitudes due to pulsations. Second, after removing the contribution of the pulsations from the light curve we applied the PIKAIA genetic-algorithm approach to derive the best parameters that describe the orbital properties of the system. The light curve cleaned for pulsations contains the partial eclipse of the primary and the total eclipse of the secondary. The system has an orbital period of about 3.694 days and is formed by a primary star with mass M1 = 2.25 +/- 0.04 solar masses, radius R1 = 4.24 +/- 0.02 solar radii, and effective temperature Teff1 = 6750 +/- 150 K, and a secondary with M2 = 1.29 +/- 0.03 solar masses, R2 = 1.34 +/- 0.01 solar radii, and Teff2 = 6152 +/- 162 K. The best solution for the parameters was obtained by taking into account the asymmetric modulation observed in the light curve, known as the O'Connell effect, presumably caused by Doppler beaming. The analysis of the Fourier spectrum revealed that the primary component has p-mode pulsations in the range 5-13 c/d, which are typical of Delta Scuti type stars., Comment: 11 pages, 8 figures, 3 tables

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 MNRAS

Context: Miras are long-period variables thought to be in the asymptotic giant branch (AGB) phase of evolution. In about one percent of known Miras, the pulsation period is changing. It has been speculated that this changing period is the consequence of a recent thermal pulse in these stars. Aims: We aim to clarify the evolutionary state of these stars, and to determine in particular whether or not they are in the thermally-pulsing (TP-)AGB phase. Methods: One important piece of information that has been neglected so far when determining the evolutionary state is the presence of the radio-active s-process element technetium (Tc). We obtained high-resolution, high signal-to-noise-ratio optical spectra of a dozen prominent Mira variables with changing pulsation period to search for this indicator of TPs and dredge-up. We also use the spectra to measure lithium (Li) abundances. Furthermore, we establish the evolutionary states of our sample stars by means of their present-day periods and luminosities. Results: Among the twelve sample stars observed in this programme, five were found to show absorption lines of Tc. BH Cru is found to be a carbon-star, its period increase in the past decades possibly having stopped by now. We report a possible switch in the pulsation mode of T UMi from Mira-like to semi-regular variability in the past two years. R Nor, on the other hand, is probably a fairly massive AGB star, which could be true for all meandering Miras. Finally, we assign RU Vul to the metal-poor thick disk with properties very similar to the short-period, metal-poor Miras. Conclusions: We conclude that there is no clear correlation between period change class and Tc presence. The stars that are most likely to have experienced a recent TP are BH Cru and R Hya, although their rates of period change are quite different., Comment: 11 pages, 7 figures, 2 tables; accepted for publication in A&A

Direct imaging of the HR8799 system was a major achievement in the study of exoplanets. HR8799 is a $\gamma$\,Doradus variable and asteroseismology can provide an independent constraint on the inclination. Using 650 high signal-to-noise, high resolution, full visual wavelength spectroscopic observations obtained over two weeks at Observatoire de Haute Provence (OHP) with the SOPHIE spectrograph we find that the main frequency in the radial velocity data is 1.9875 d$^{-1}$. This frequency corresponds to the main frequency as found in previous photometric observations. Using the FAMIAS software to identify the pulsation modes, we find this frequency is a prograde $\ell$=1 sectoral mode and obtain the constraint that inclination $i\gtrsim$40$^{\circ}$., Comment: 12 pages, 3 figures, 2 tables, accepted in ApJ Letters

The HERMES high-resolution spectrograph project aims at exploiting the specific potential of small but flexible telescopes in observational astrophysics. The optimised optical design of the spectrograph is based on the well-proven concept of white-pupil beam folding for high-resolution spectroscopy. In this contribution we present the complete project, including the spectrograph design and procurement details, the telescope adaptor and calibration unit, the detector system, as well as the optimised data-reduction pipeline. We present a detailed performance analysis to show that the spectrograph performs as specified both in optical quality and in total efficiency. With a spectral resolution of 85000 (63000 for the low-resolution fibre), a spectral coverage from 377 to 900nm in a single exposure and a peak efficiency of 28%, HERMES proves to be an ideal instrument for building up time series of high-quality data of variable (stellar) phenomena., Comment: 13 pages