Discovery of Rapid oscillations in HD 218994

Asteroseismology has the potential to provide new insights into the physics of stellar interiors. Among the most promising objects that can be studied through this technique are the rapidly oscillating Ap (roAp) stars. These pulsate in high-overtone, low-degree, nonradial p-modes, with periods in the range 6-21 min. Our previous study (Hubrig et al., 2000) discussed the relationship between the roAp stars and the non-oscillating Ap (noAp) stars and concluded that the noAp stars are, in general, slightly more evolved than the roAp stars. The Ap Sr star HD 218994 was checked photometrically for the presence of rapid oscillations in the Cape Survey, but no oscillations have been detected by Martinez & Kurtz. This star was previously included in the sample of non-pulsating binary Ap stars studied by Hubrig et al. (2000). We have been granted one hour of UVES high time resolution observations of this star at ESO VLT on Cierro Paranal on November 15, 2006 and were able to obtain 15 spectra with exposure times of 3 min and a sampling of 3.7 min, taking into account the CCD readout time. To search for pulsational line variability, we calculated the average spectrum of the observed 15 spectra and subtracted it from the original spectra. In Fig. 1 we present the behaviour of the spectral profile of the Nd III line at {lambda} 6327 and its standard deviations. Similar variations were also found for the Pr III lines at {lambda} 6053 and {lambda} 6090. It was already shown in numerous studies that rare elements have higher amplitudes in roAp stars compared to lines of Fe-peak elements (e.g. Kurtz, Elkin & Mathys 2005). We also note that the mean RV for different elements is different, indicating the presence of chemical inhomogeneities on the stellar surface. Our analysis of RV variations of the Nd III line indicates two pulsation periods: one period of 5.1 min with an amplitude of 516 m/s and another one of 13.9 min and an amplitude of 497 m/s. It is very likely that one of these peaks is an alias. The amplitude spectrum of the radial velocity variations is presented in Fig. 2. We note that a longer time series with better temporal resolution is needed for a careful identification of the principal frequency and a search for the presence of other pulsation frequencies. To confirm the detected spectroscopic variation period, we searched for a periodicity in the photometric data using Hipparcos and ASAS photometric databases. Indeed, also the photometric data show a sinusoidal variation with a period identical to the spectroscopic period, P=5.1 min, and an amplitude of 0.005 mag. In Fig. 3 we present both the RV variations of the Nd III line and the ASAS light curve. The star HD 218994 becomes now the 36th star known to be a roAp star.Fil: Gonzalez, Jorge Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Hubrig, S.. European Southern Observatory; EspañaFil: Savanov, I.. College Hill; Irland

Discovery of Rapid oscillations in HD 218994

Asteroseismology has the potential to provide new insights into the physics of stellar interiors. Among the most promising objects that can be studied through this technique are the rapidly oscillating Ap (roAp) stars. These pulsate in high-overtone, low-degree, nonradial p-modes, with periods in the range 6-21 min. Our previous study (Hubrig et al., 2000) discussed the relationship between the roAp stars and the non-oscillating Ap (noAp) stars and concluded that the noAp stars are, in general, slightly more evolved than the roAp stars. The Ap Sr star HD 218994 was checked photometrically for the presence of rapid oscillations in the Cape Survey, but no oscillations have been detected by Martinez & Kurtz. This star was previously included in the sample of non-pulsating binary Ap stars studied by Hubrig et al. (2000). We have been granted one hour of UVES high time resolution observations of this star at ESO VLT on Cierro Paranal on November 15, 2006 and were able to obtain 15 spectra with exposure times of 3 min and a sampling of 3.7 min, taking into account the CCD readout time. To search for pulsational line variability, we calculated the average spectrum of the observed 15 spectra and subtracted it from the original spectra. In Fig. 1 we present the behaviour of the spectral profile of the Nd III line at {lambda} 6327 and its standard deviations. Similar variations were also found for the Pr III lines at {lambda} 6053 and {lambda} 6090. It was already shown in numerous studies that rare elements have higher amplitudes in roAp stars compared to lines of Fe-peak elements (e.g. Kurtz, Elkin & Mathys 2005). We also note that the mean RV for different elements is different, indicating the presence of chemical inhomogeneities on the stellar surface. Our analysis of RV variations of the Nd III line indicates two pulsation periods: one period of 5.1 min with an amplitude of 516 m/s and another one of 13.9 min and an amplitude of 497 m/s. It is very likely that one of these peaks is an alias. The amplitude spectrum of the radial velocity variations is presented in Fig. 2. We note that a longer time series with better temporal resolution is needed for a careful identification of the principal frequency and a search for the presence of other pulsation frequencies. To confirm the detected spectroscopic variation period, we searched for a periodicity in the photometric data using Hipparcos and ASAS photometric databases. Indeed, also the photometric data show a sinusoidal variation with a period identical to the spectroscopic period, P=5.1 min, and an amplitude of 0.005 mag. In Fig. 3 we present both the RV variations of the Nd III line and the ASAS light curve. The star HD 218994 becomes now the 36th star known to be a roAp star.Fil: Gonzalez, Jorge Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Hubrig, S.. European Southern Observatory; EspañaFil: Savanov, I.. College Hill; Irland

Vertical distribution of chromium in the atmospheres of HgMn stars

We use multiplet 30 Cr II lines in the wings of H_beta to test the hypothesis of an anomalous concentration of Cr in the upper layers of the atmospheres of a sample of 10 HgMn stars. These lines are at different distances from the H_beta line center and are therefore formed at different depths in the stellar atmosphere. Except for HD49606, all HgMn stars show an increase of Cr abundance with height in the stellar atmosphere. A similar vertical distribution of Cr, but less pronounced, has been previously found in Am stars. In contrast, no variation of Cr abundance with the depth has been found for the normal late B-type star HD196426 and the weak magnetic late B-type star HD168733. It is possible that in HgMn stars the vertical stratification parameter, a, depends on T_eff, with the strongest vertical gradient being found in the hotter stars. No correlation was found between $a$ and the average stellar abundance log epsilon(Cr/H).Comment: 7 pages, 3 figures, accepted for publication in A&

Dynamical Spot Evolution in HD 11753

Our recent studies of HD 11753, a late B-type star showing a HgMn peculiarity for the first time revealed the presence of a fast dynamical evolution of chemical spots on the surface of this chemically peculiar early-type star. These observations suggest a hitherto unknown physical process operating in stars with outer radiative envelopes. Furthermore, we have also discovered existence of magnetic fields on HgMn stars that were up to now considered non-magnetic. Here we will discuss the dynamical spot evolution in HD 11753 in detail, and also summarize our new results on the magnetic fields of the AR Aur binary system

The exceptional Herbig Ae star HD101412: The first detection of resolved magnetically split lines and the presence of chemical spots in a Herbig star

We obtained high-resolution, high signal-to-noise UVES and a few lower quality HARPS spectra revealing the presence of resolved magnetically split lines. HD101412 is the first Herbig Ae star for which the rotational Doppler effect was found to be small in comparison to the magnetic splitting. The measured mean magnetic field modulus varies from 2.5 to 3.5kG, while the mean quadratic field was found to vary in the range of 3.5 to 4.8kG. To determine the period of variations, we used radial velocity, equivalent width, line width, and line asymmetry measurements of variable spectral lines of several elements, as well as magnetic field measurements. The most pronounced variability was detected for spectral lines of He I and the iron peak elements, whereas the spectral lines of CNO elements are only slightly variable. From spectral variations and magnetic field measurements we derived a potential rotation period P_rot=13.86d, which has to be proven in future studies with a larger number of observations. It is the first time that the presence of element spots is detected on the surface of a Herbig Ae/Be star. Our previous study of Herbig Ae stars revealed a trend towards stronger magnetic fields for younger Herbig Ae stars, confirmed by statistical tests. This is in contrast to a few other (non-statistical) studies claiming that magnetic Herbig Ae stars are progenitors of the magnetic Ap stars. New developments in MHD theory show that the measured magnetic field strengths are compatible with a current-driven instability of toroidal fields generated by differential rotation in the stellar interior. This explanation for magnetic intermediate-mass stars could be an alternative to a frozen-in fossil field.Comment: 7 pages, 6 figures, 1 table, to appear in Astronomische Nachrichte

Discovery of pulsational line profile variations in the delta Scuti star HD21190 and in the Ap Sr star HD218994

Asteroseismology has the potential to provide new insights into the physics of stellar interiors. We have obtained UVES high time resolution observations of the delta Scuti star HD21190 and of the Ap Sr star HD218994 to search for pulsational line profile variations. We report the discovery of a new roAp star, HD218994, with a pulsation period of 14.2 min. This is one of the most evolved roAp stars. No rapid pulsations have been found in the spectra of the cool Ap star - delta Scuti star HD21190. However, we detect with unprecedented clarity for a delta Sct star moving peaks in the cores of spectral lines that indicate the presence of high degree non-radial pulsations in this star.Comment: 5 pages, 4 figures, 1 table, accepted for publication in MNRA