RAT J0455+1305: A rare hybrid pulsating subdwarf B star

We present results on the second-faintest pulsating subdwarf B (sdB) star known, RAT J0455+1305, derived from photometric data obtained in 2009. It shows both short and long periods oscillations, theoretically assigned as pressure and gravity modes. We identify six short-period frequencies (with one being a combination) and six long-period frequencies. This star is the fourth hybrid sdB star discovered so far which makes it of special interest as each type of mode probes a different part of the star. This star is similar to the sdB hybrid pulsator Balloon 090100001 in that it exhibits short-period mode groupings, which can be used to identify pulsation parameters and constrain theoretical models.Comment: published in MNRA

The orbit of the close spectroscopic binary epsilon Lupi and the intrinsic variability of its early B-type components

We subjected 106 new high-resolution spectra of the double-lined spectroscopic close binary epsilon Lupi, obtained in a time-span of 17 days from two different observatories, to a detailed study of orbital and intrinsic variations. We derived accurate values of the orbital parameters. We refined the sidereal orbital period to 4.55970 days and the eccentricity to e=0.277. By adding old radial velocities, we discovered the presence of apsidal motion with a period of the rotation of apses of about 430 years. Such a value agrees with theoretical expectations. Additional data is needed to confirm and refine this value. Our dataset did not allow us to derive the orbit of the third body, which is known to orbit the close system in approximately 64 years. We present the secondary of epsilon Lupi as a new beta Cephei variable, while the primary is a beta Cephei suspect. A first detailed analysis of line-profile variations of both primary and secondary led to detection of one pulsation frequency near 10.36 c/d in the variability of the secondary, while no clear periodicity was found in the primary, although low-amplitude periodicities are still suspected. The limited accuracy and extent of our dataset did not allow any further analysis, such as mode-identification.Comment: 13+3 pages, 20 figures. Astronomy and Astrophysics, accepte

A new method for the spectroscopic identification of stellar non-radial pulsation modes. I. The method and numerical tests

We present the Fourier parameter fit method, a new method for spectroscopically identifying stellar radial and non-radial pulsation modes based on the high-resolution time-series spectroscopy of absorption-line profiles. In contrast to previous methods this one permits a quantification of the statistical significance of the computed solutions. The application of genetic algorithms in seeking solutions makes it possible to search through a large parameter space. The mode identification is carried out by minimizing chi-square, using the observed amplitude and phase across the line profile and their modeled counterparts. Computations of the theoretical line profiles are based on a stellar displacement field, which is described as superposition of spherical harmonics and that includes the first order effects of the Coriolis force. We made numerical tests of the method on a grid of different mono- and multi-mode models for 0 <= l <= 4 in order to explore its capabilities and limitations. Our results show that whereas the azimuthal order m can be unambiguously identified for low-order modes, the error of l is in the range of pm 1. The value of m can be determined with higher precision than with other spectroscopic mode identification methods. Improved values for the inclination can be obtained from the analysis of non-axisymmetric pulsation modes. The new method is ideally suited to intermediatley rotating Delta Scuti and Beta Cephei stars.Comment: 12 pages, 14 figure

On the Hα\alpha emission from the β\beta Cephei system

Be stars, which are characterised by intermittent emission in their hydrogen lines, are known to be fast rotators. This fast rotation is a requirement for the formation of a Keplerian disk, which in turn gives rise to the emission. However, the pulsating, magnetic B1IV star $\beta$ Cephei is a very slow rotator that still shows H$\alpha$ emission episodes like in other Be stars, contradicting current theories. We investigate the hypothesis that the H$\alpha$ emission stems from the spectroscopically unresolved companion of $\beta$ Cep. Spectra of the two unresolved components have been separated in the 6350-6850\AA range with spectro-astrometric techniques, using 11 longslit spectra obtained with ALFOSC at the Nordic Optical Telescope, La Palma. We find that the H$\alpha$ emission is not related to the primary in $\beta$ Cep, but is due to its 3.4 magnitudes fainter companion. This companion has been resolved by speckle techniques, but it remains unresolved by traditional spectroscopy. The emission extends from about $-$400 to +400 km s$^{-1}$. The companion star in its 90-year orbit is likely to be a classical Be star with a spectral type around B6-8. By identifying its Be-star companion as the origin of the H$\alpha$ emission behaviour, the enigma behind the Be status of the slow rotator $\beta$ Cep has been resolved.Comment: 4 pages, 3 figures. Accepted by A&A Letter

Interpretation of the variability of the <i>β</i> Cephei star <i>λ</i> Scorpii. I. The multiple character

We derive accurate values of the orbital parameters of the close binary β Cephei star λ Scorpii. Moreover, we present the first determination of the properties of the triple system to which λ Scorpii belongs. Our analysis is based on a time series of 815 high-resolution spectra, covering a timespan of 14 years. We find a close orbit of 5d.9525days (e=0.26) and a wide orbit of approximately 1082d days (e=0.23). The orbital parameters of the triple star and a spectrum synthesis lead us to conclude that the system is composed of two early-type B stars and a low-mass pre-main-sequence star rather than containing an ultra-massive white dwarf as claimed before. Our proposed configuration is compatible with population synthesis. The radial velocity variations of the primary allow us to confirm the presence of at least one pulsation mode with frequency 4.679410 c d-1 which is subject to the light-time effect in the triple system. A detailed analysis of the complex line-profile variations is described in a subsequent paper

Mode identification from monochromatic amplitude and phase variations for the rapidly pulsating subdwarf B star EC 20338-1925

We obtain time-series spectrophotometry observations at the VLT with the aim of partially identifying the dominant oscillation modes in the rapidly pulsating subdwarf B star EC 20338-1925 on the basis of monochromatic amplitude and phase variations. From the data gathered, we detect four previously known pulsations with periods near 147, 168, 126 and 140 s and amplitudes between 0.2 and 2.3 % of the star's mean brightness. We also determine the atmospheric parameters of EC 20338-1925 by fitting our non-LTE model atmospheres to an averaged combined spectrum. The inferred parameters are Teff = 34,153+-94 K, log g =5.966+-0.017 and log[N(He)/N(H)] = - 1.642+-0.022, where the uncertainty estimates quoted refer to the formal fitting errors. Finally, we calculate the observed monochromatic amplitudes and phases for the periodicities extracted using least-squares fitting to the light curves obtained for each wavelength bin. These observed quantities are then compared to the corresponding theoretical values computed on the basis of dedicated model atmosphere codes and also taking into account non-adiabatic effects. We find that the quality of the data is sufficient to identify the dominant pulsation at 146.9 s as a radial mode, while two of the lower amplitude periodicities must be low-degree modes with l=0-2. This is the first time that monochromatic amplitudes and phases have been used for mode identification in a subdwarf B star, and the results are highly encouraging.Comment: 11 pages. Accepted for publication in Astronomy & Astrophysic

Constraining the degree of the dominant mode in QQ Vir

We present early results of the application of a method which uses multicolor photometry and spectroscopy for \ell discrimination. This method has been successfully applied to the pulsating hot subdwarf Balloon 090100001. Here we apply the method to QQ Vir (PG1325+101). This star was observed spectroscopically and photometrically in 2008. Details on spectroscopy can be found in Telting et al. (2010) while photometry and preliminary results on \ell discrimination are provided here. The main aim of this work was to compare the value of the \ell parameter derived for the main mode in QQ Vir to previously published values derived by using different methods.Comment: Proceedings of The Fourth Meeting on Hot Subdwarf Stars and Related Objects held in China, 20-24 July 2009. Accepted for publication in Astrophysics and Space Scienc

Finding non-eclipsing binaries through pulsational phase modulation

We present a method for finding binaries among pulsating stars that were observed by the Kepler Mission. We use entire four-year light curves to accurately mea- sure the frequencies of the strongest pulsation modes, then track the pulsation phases at those frequencies in 10-d segments. This produces a series of time-delay measurements in which binarity is apparent as a periodic modulation whose amplitude gives the projected light travel time across the orbit. Fourier analysis of this time-delay curve provides the pa- rameters of the orbit, including the period, eccentricity, angle of ascending node and time of periastron passage. Differentiating the time-delay curve yields the full radial-velocity curve directly from the Kepler photometry, without the need for spectroscopy. We show examples with delta Scuti stars having large numbers of pulsation modes, including one system in which both components of the binary are pulsating. The method is straightfor- ward to automate, thus radial velocity curves can be derived for hundreds of non-eclipsing binary stars from Kepler photometry alone. This contribution is based largely upon the work by Murphy et al. [1], describing the phase-modulation method in detail