PHASES Differential Astrometry and Iodine Cell Radial Velocities of the kappa Pegasi Triple Star System

kappa Pegasi is a well-known, nearby triple star system. It consists of a ``wide'' pair with semi-major axis 235 milli-arcseconds, one component of which is a single-line spectroscopic binary (semi-major axis 2.5 milli-arcseconds). Using high-precision differential astrometry and radial velocity observations, the masses for all three components are determined and the relative inclinations between the wide and narrow pairs' orbits is found to be 43.8 +/- 3.0 degrees, just over the threshold for the three body Kozai resonance. The system distance is determined to 34.60 +/- 0.21 parsec, and is consistent with trigonometric parallax measurements.Comment: Accepted for publication in ApJ, complete versions of tables 2 and 4 can be found at http://stuff.mit.edu/~matthew1/kapPegTables

Direct detection of a magnetic field at the surface of V390 Aurigae - an effectively single active giant

International audienceAims.We have studied the active giant V390 Aur using spectropolarimetry to obtain direct and simultaneous measurements of the magnetic field and the activity indicators in order to infer the origin of the activity. Methods: We used the new spectropolarimeter NARVAL at the Bernard Lyot Telescope (Observatoire du Pic du Midi, France) to obtain a series of Stokes I and Stokes V profiles. Using the LSD technique we were able to detect the Zeeman signature of the magnetic field in each of our 5 observations and to measure its longitudinal component. Using the wide wavelength range of the spectra we could monitor the CaII K&H and IR triplet, as well as the H? lines which are activity indicators. The Stokes I LSD profiles enabled us to detect and measure the profiles of two weak stellar companions. Results: From five observations obtained from November 2006 to March 2007, we deduce that the magnetic field has a complex structure which evolves with time and is reminiscent of a dynamo-induced magnetic field. The activity indicators also present day to day variations, but their behaviour does not completely follow the magnetic field variations, because their longitudinal component can cancel the contribution of complex magnetic features. There is a significant difference between the magnetic field observed on November 27, 2006 and on March 15, 2007, at the same rotational phase, but with an interval of 10 rotations. The behaviour of the activity indicators together with the measured enhanced magnetic field on March 15, 2007 support the idea of a change in the field topology. Analysis (RV and EW) of the absorption components of the Stokes I LSD profile shows that the secondary of the visual wide orbit binary ADS 3812 is itself a spectroscopic binary, and suggests that the synchronization effect does not play role for V390 Aur (the primary), and that the giant should be considered as effectively single with regard to its fast rotation and activity. Based on data obtained using the Télescope Bernard Lyot at Observatoire du Pic du Midi, CNRS and Université Paul Sabatier, France