Nikolai E. Piskunov

Transiting extrasolar planetary candidates in the Galactic bulge

More than 200 extrasolar planets have been discovered around relatively nearby stars, primarily through the Doppler line shifts owing to reflex motions of their host stars, and more recently through transits of some planets across the faces of the host stars. The detection of planets with the shortest known periods, 1.2–2.5 days, has mainly resulted from transit surveys which have generally targeted stars more massive than 0.75 M[circdot], where M[circdot] is the mass of the Sun. Here we report the results from a planetary transit search performed in a rich stellar field towards the Galactic bulge. We discovered 16 candidates with orbital periods between 0.4 and 4.2 days, five of which orbit stars of masses in the range 0.44–0.75 M[circdot]. In two cases, radial-velocity measurements support the planetary nature of the companions. Five candidates have orbital periods below 1.0 day, constituting a new class of ultra-short-period planets, which occur only around stars of less than 0.88 M[circdot]. This indicates that those orbiting very close to more-luminous stars might be evaporatively destroyed or that jovian planets around stars of lower mass might migrate to smaller radii.

DIVISIONS IV-V / WORKING GROUP Ap & RELATED STARS

The purpose of the Working Group on Ap and Related Stars (ApWG) is to promote and facilitate research about stars in the spectral type range from B to early F that exhibit surface chemical peculiarities and related phenomena. This is a very active field of research, in which a wide variety of new developments have taken place since 2009, as illustrated by the following selected highlights. The evolutionary context of the large-scale organised magnetic fields of Ap stars, which have been known for more than 60 years to be one of their most salient features, is starting to be outlined with the recent detection and study of rotationally modulated magnetic fields in their progenitors, the Herbig Ae/Be stars (Alecian et al. 2009; Hubrig et al. 2011a) and the identification and characterisation of magnetic late-type supergiants that are their potential descendants (Grunhut et al. 2010; Aurière et al. 2011). On the other hand, the sequence of hotter early-type magnetic stars is becoming increasingly populated through the works of the MiMeS (Magnetism in Massive Stars) collaboration (e.g., Wade et al. 2011) and of other teams (e.g., Hubrig et al. 2011b), putting the magnetism of Ap stars in a new perspective. The discovery of sub-Gauss magnetic fields with large-scale structure in the A0V star Vega (Lignières et al. 2009; Alina et al. 2011) and in the hot Am star Sirius (Petit et al. 2011) raises the possibility that all tepid main-sequence stars may be magnetic to a certain level. However, unprecedented stringent limits have been set on the mean longitudinal magnetic fields of Am and HgMn stars (e.g., Aurière et al. 2010; Makaganiuk et al. 2011), indicating that they must be at least one order of magnitude weaker than those of magnetic Ap stars. Arlt & Rüdiger (2010) have proposed Tayler instability as a possible mechanism of generation of magnetic fields in A stars while Ferrario et al. (2009) have suggested that magnetic Ap stars could have formed from the merging of two protostars. Kepler observations have allowed the non-radial pulsation modes of hundreds of A-F stars to be classified, revealing the existence of a class of “hybrid” stars showing both

Magnetic Doppler imaging of II Peg

Rotational modulation of the intensity and polarization spectra of magnetic stars offers a unique possibility to reconstruct the structure of surface magnetic fields and to investigate their relation to cool starspots. We have developed a new magnetic Doppler imaging code which aims at self-consistent temperature and magnetic mapping of cool active stars. Here we present magnetic Doppler imaging analysis of high-resolution circular polarization observations of the active star II Peg. We demonstrate that a self-consistent approach to magnetic inversion unveils stronger magnetic fields than found previously through disjoint analyses of polarization and intensity observations of active stars.