We present an analysis of high time resolution spectra of the chemically peculiar Ap star HD 213637. The star shows rapid radial velocity variations with a period close to the photometric pulsation period. Radial velocity pulsation amplitudes vary si
gnificantly for different rare earth elements. The highest pulsation amplitudes belong to lines of TbIII ~360 m/s, PrII ~250 m/s and PrIII ~230 m/s . We did not detect any pulsations from spectral lines of EuII and in Halpha, in contrast to many other roAp stars. We also did not find radial velocity pulsations using spectral lines of other chemical elements, including Mg, Si, Ca, Sc, Cr, Fe, Ni, Y and Ba. There are phase shifts between the maxima of pulsation amplitudes of different rare earth elements and ions, which is evidence of an outwardly running magneto-acoustic wave propagating through the upper stellar atmosphere.
The candidate SX Phe star KIC 11754974 shows a remarkably high number of combination frequencies in the Fourier amplitude spectrum: 123 of the 166 frequencies in our multi-frequency fit are linear combinations of independent modes. Predictable patter
ns in frequency spacings are seen in the Fourier transform of the light curve. We present an analysis of 180 d of short-cadence Kepler photometry and of new spectroscopic data for this evolved, late A-type star. We infer from the 1150-d, long-cadence light curve, and in two different ways, that our target is the primary of a 343-d, non-eclipsing binary system. According to both methods, the mass function is similar, f(M)=0.0207 +/- 0.0003 Msun. The observed pulsations are modelled extensively, using separate, state-of-the-art, time-dependent convection (TDC) and rotating models. The models match the observed temperature and low metallicity, finding a mass of 1.50-1.56 Msun. The models suggest the whole star is metal-poor, and that the low metallicity is not just a surface abundance peculiarity. This is the best frequency analysis of an SX Phe star, and the only Kepler delta Sct star to be modelled with both TDC and rotating models.
We have studied over 1600 Am stars at a photometric precision of 1 mmag with SuperWASP photometric data. Contrary to previous belief, we find that around 200 Am stars are pulsating delta Sct and gamma Dor stars, with low amplitudes that have been mis
sed in previous, less extensive studies. While the amplitudes are generally low, the presence of pulsation in Am stars places a strong constraint on atmospheric convection, and may require the pulsation to be laminar. While some pulsating Am stars have been previously found to be delta Sct stars, the vast majority of Am stars known to pulsate are presented in this paper. They will form the basis of future statistical studies of pulsation in the presence of atomic diffusion.
We have discovered a new rapidly oscillating Ap star among the Kepler Mission target stars, KIC 10195926. This star shows two pulsation modes with periods that are amongst the longest known for roAp stars at 17.1 min and 18.1 min, indicating that the
star is near the terminal age main sequence. The principal pulsation mode is an oblique dipole mode that shows a rotationally split frequency septuplet that provides information on the geometry of the mode. The secondary mode also appears to be a dipole mode with a rotationally split triplet, but we are able to show within the improved oblique pulsator model that these two modes cannot have the same axis of pulsation. This is the first time for any pulsating star that evidence has been found for separate pulsation axes for different modes. The two modes are separated in frequency by 55 microHz, which we model as the large separation. The star is an alpha^2 CVn spotted magnetic variable that shows a complex rotational light variation with a period of Prot = 5.68459 d. For the first time for any spotted magnetic star of the upper main sequence, we find clear evidence of light variation with a period of twice the rotation period; i.e. a subharmonic frequency of $ u_{rm rot}/2$. We propose that this and other subharmonics are the first observed manifestation of torsional modes in an roAp star. From high resolution spectra we determine Teff = 7400 K, log g = 3.6 and v sin i = 21 km/s. We have found a magnetic pulsation model with fundamental parameters close to these values that reproduces the rotational variations of the two obliquely pulsating modes with different pulsation axes. The star shows overabundances of the rare earth elements, but these are not as extreme as most other roAp stars. The spectrum is variable with rotation, indicating surface abundance patches.
We report the detection of short period variations in the stars HD69013 and HD96237. These stars possess large overabundances of rare earth elements and global magnetic fields, thus belong to the class of chemically peculiar Ap stars of the main sequ
ence. Pulsations were found from analysis of high time resolution spectra obtained with the ESO Very Large Telescope using a cross correlation method for wide spectral bands, from lines belonging to rare earth elements and from the H alpha core. Pulsation amplitudes reach more than 200 m/s for some lines in HD69013 with a period of 11.4 min and about 100m/s in HD96237 with periods near 13.6 min. The pulsations have also been detected in photometric observations obtained at the South African Astronomical Observatory.
We obtained thirteen spectropolarimetric observations of the strongly magnetic rapidly oscillating Ap star HD154708 over three months with the multi-mode instrument FORS1, installed at the 8-m Kueyen telescope of the VLT. These observations have been
used for the determination of the rotation period of P=5.3666+-0.0007d. Using stellar fundamental parameters and the longitudinal magnetic field phase curve, we briefly discuss the magnetic field geometry. The star is observed nearly pole-on and the magnetic field geometry can be described by a centred dipole with a surface polar magnetic field strength B_d between 26.1 and 28.8kG and an inclination of the magnetic axis to the rotation axis in the range 22.5deg to 35.5deg.
The Ap star HD3980 appears to be a promising roAp candidate based on its fundamental parameters, leading us to search for rapid pulsations with the VLT UV-Visual Echelle Spectrograph (UVES). A precise Hipparcos parallax and estimated temperature of 8
100K place HD3980 in the middle of the theoretical instability strip for rapidly oscillating Ap stars, about halfway through its main sequence evolution stage. The star has a strong, variable magnetic field, as is typical of the cool magnetic Ap stars. Dipole model parameters were determined from VLT observations using FORS1. From Doppler shift measurements for individual spectral lines of rare earth elements and the H-alpha line core, we find no pulsations above 20-30 m/s. This result is corroborated by inspection of lines of several other chemical elements, as well as with crosscorrelation for long spectral regions with the average spectrum as a template. Abundances of chemical elements were determined and show larger than solar abundances of rare earth elements. Further, ionisation disequilibria for the first two ionised states of Nd and Pr are detected. We also find that the star has a strong overabundance of manganese, which is typical for much hotter HgMn and other Bp stars. Line profile variability with the rotation period was detected for the majority of chemical species.
Recently, Tiwari, Chaubey, & Pandey (2007) detected the bright component of the visual binary HD151878 to exhibit rapid photometric oscillations through a Johnson B filter with a period of 6 min (2.78 mHz) and a high, modulated amplitude up to 22 mma
g peak-to-peak, making this star by far the highest amplitude roAp star known. As a new roAp star, HD151878 is of additional particular interest as a scarce example of the class in the northern sky, and only the second known case of an evolved roAp star - the other being HD 116114. We used the FIES spectrograph at the Nordic Optical Telescope to obtain high time resolution spectra at high dispersion to attempt to verify the rapid oscillations. We show here that the star at this epoch is spectroscopically stable to rapid oscillations of no more than a few tens of m/s. The high-resolution spectra furthermore show the star to be of type Am rather than Ap and we show the star lacks most of the known characteristics for rapidly oscillating Ap stars. We conclude that this is an Am star that does not pulsate with a 6-min period. The original discovery of pulsation is likely to be an instrumental artefact.
Chemically peculiar A stars (Ap) are extreme examples of the interaction of atomic element diffusion processes with magnetic fields in stellar atmospheres. The rapidly oscillating Ap stars provide a means for studying these processes in 3D and are at
the same time important for studying the pulsation excitation mechanism in A stars. As part of the first comprehensive, uniform, high resolution spectroscopic survey of Ap stars, which we are conducting in the southern hemisphere with the Michigan Spectral Catalogues as the basis of target selection, we report here the discovery of 17 new magnetic Ap stars having spectroscopically resolved Zeeman components from which we derive magnetic field moduli in the range 3 - 30 kG. Among these are 1) the current second-strongest known magnetic A star, 2) a double-lined Ap binary with a magnetic component and 3) an A star with particularly peculiar and variable abundances. Polarimetry of these stars is needed to constrain their field geometries and to determine their rotation periods. We have also obtained an additional measurement of the magnetic field of the Ap star HD 92499.
