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Ap Stars (ap + star)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Discovery of 17 new sharp-lined Ap stars with magnetically resolved lines,

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
L. M. Freyhammer
ABSTRACT 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 three dimensions 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. [source]

Discovery of rapid radial velocity variations in the roAp star 10 Aql and possible pulsations of , CrB

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002
O Kochukhov
ABSTRACT We report discovery of radial velocity variations in rare earth spectral lines of the roAp star 10 Aql with amplitudes of between 30 and 130 m s,1 and periods of about 11 min. Radial velocity variations with amplitude 70 m s,1 may also have been detected in one spectral line of Fe i in , CrB. If confirmed, our results may indicate that all Ap stars in a certain temperature range pulsate, which means that roAp stars do not exist as a separate class but are only distinguished by higher pulsational amplitudes. [source]

The exceptional Herbig Ae star HD 101412: The first detection of resolved magnetically split lines and the presence of chemical spots in a Herbig star,

ASTRONOMISCHE NACHRICHTEN, Issue 4 2010
S. Hubrig
Abstract In our previous search for magnetic fields in Herbig Ae stars, we pointed out that HD 101412 possesses the strongest magnetic field among the Herbig Ae stars and hence is of special interest for follow-up studies of magnetism among young pre-main-sequence stars. We obtained high-resolution, high signal-to-noise UVES and a few lower quality HARPS spectra revealing the presence of resolved magnetically split lines. HD 101412 is the first Herbig Ae star for which the rotational Doppler effect was found to be small in comparison to the magnetic splitting and several spectral lines observed in unpolarized light at high dispersion are resolved into magnetically split components. 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 4.8 kG. 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 period determination was done using the Lomb-Scargle method. 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 Prot = 13.86 d, 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 (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]