We report the detection of a strong, reversing magnetic field and variable H-alpha emission in the bright helium-weak star HD 176582 (HR 7185). Spectrum, magnetic and photometric variability of the star are all consistent with a precisely determined
period of 1.5819840 +/- 0.0000030 days which we assume to be the rotation period of the star. From the magnetic field curve, and assuming a simple dipolar field geometry, we derive a polar field strength of approximately 7 kG and a lower limit of 52 degrees for the inclination of the rotation axis. However, based on the behaviour of the H-alpha emission we adopt a large inclination angle of 85 degrees and this leads to a large magnetic obliquity of 77 degrees. The H-alpha emission arises from two distinct regions located at the intersections of the magnetic and rotation equators and which corotate with the star at a distance of about 3.5 R* above its surface. We estimate that the emitting regions have radial and meridional sizes on the order of 2 R* and azimuthal extents (perpendicular to the magnetic equator) of less than approximately 0.6 R*. HD 176582 therefore appears to show many of the cool magnetospheric phenomena as that displayed by other magnetic helium-weak and helium-strong stars such as the prototypical helium-strong star sigma Ori E. The observations are consistent with current models of magnetically confined winds and rigidly-rotating magnetospheres for magnetic Bp stars.
The helium-peculiar star a Cen exhibits line profile variations of elements such as iron, nitrogen and oxygen in addition to its well-known extreme helium variability. New high S/N, high-resolution spectra are used to perform a quantitative measureme
nt of the abundances of the star and determine the relation of the concentrations of the heavier elements on the surface of the star to the helium concentration and the magnetic field orientation. Doppler images have been created using programs described in earlier papers by Rice and others. An alternative surface abundance mapping code has been used to model the helium line variations after our Doppler imaging of certain individual helium lines produced mediocre results. We confirm the long-known existence of helium-rich and helium-poor hemispheres on a Cen and we measure a difference of more than two orders of magnitude in helium abundance from one side of the star to the other. Helium is overabundant by a factor of about 5 over much of the helium-rich hemisphere. Of particular note is our discovery that the helium-poor hemisphere has a very high abundance of helium-3, approximately equal to the helium-4 abundance. a Cen is therefore a new member of the small group of helium-3 stars and the first well-established magnetic member of the class. For the three metals investigated here, there are two strong concentrations of abundance near the equator consistent with the positive magnetic maximum and two somewhat weaker concentrations of abundance where the helium concentration is centered and roughly where the negative peak of the magnetic field would be found. Another strong concentration is found near the equator and this is not explainable in terms of any simple symmetry with the helium abundance or the apparent magnetic field main polar locations.
Evidence suggesting an observable magnetic interaction between a star and its hot Jupiter appears as a cyclic variation of stellar activity synchronized to the planets orbit. In this study, we monitored the chromospheric activity of 7 stars with hot
Jupiters using new high-resolution echelle spectra collected with ESPaDOnS over a few nights in 2005 and 2006 from the CFHT. We searched for variability in several stellar activity indicators (Ca II H, K, the Ca II infrared triplet, Halpha, and He I). HD 179949 has been observed almost every year since 2001. Synchronicity of the Ca II H & K emission with the orbit is clearly seen in four out of six epochs, while rotational modulation with P_rot=7 days is apparent in the other two seasons. We observe a similar phenomenon on upsilon And, which displays rotational modulation (P_rot=12 days) in September 2005, in 2002 and 2003 variations appear to correlate with the planets orbital period. This on/off nature of star-planet interaction (SPI) in the two systems is likely a function of the changing stellar magnetic field structure throughout its activity cycle. Variability in the transiting system HD 189733 is likely associated with an active region rotating with the star, however, the flaring in excess of the rotational modulation may be associated with its hot Jupiter. As for HD 179949, the peak variability as measured by the mean absolute deviation for both HD 189733 and tau Boo leads the sub-planetary longitude by 70 degrees. The tentative correlation between this activity and the ratio of Mpsini to the planets rotation period, a quantity proportional to the hot Jupiters magnetic moment, first presented in Shkolnik et al. 2005 remains viable. This work furthers the characterization of SPI, improving its potential as a probe of extrasolar planetary magnetic fields.
