ALBERT

Description: We obtained 128 high signal-to-noise ratio Stokes V spectra of the B3V star Her on five consecutive nights in 2012 with the ESPaDOnS spectropolarimeter at the Canada–France–Hawaii Telescope, with the aim of searching for the presence of weak and/or complex magnetic fields. Least-squares deconvolution (LSD) mean profiles were computed from individual spectra, averaged over individual nights and over the entire run. No Zeeman signatures are detected in any of the profiles. The longitudinal magnetic field in the grand average profile was measured to be –0.24 ± 0.32 G, as compared to –0.22 ± 0.32 G in the null profile. Our observations therefore provide no evidence for the presence of Zeeman signatures analogous to those observed in the A0V star Vega by Lignières et al. We interpret these observations in three ways. First, we compare the LSD profiles with synthetic Stokes V profiles corresponding to organized (dipolar) magnetic fields, for which we find an upper limit of about 8 G on the polar strength of any surface dipole present. Secondly, we compare the grand average profile with calculations corresponding to the random magnetic spot topologies of Kochukhov & Sudnik, inferring that spots, if present, of 2° radius with strengths of 2–4 G and a filling factor of 50 per cent should have been detected in our data. Finally, we compare the observations with synthetic V profiles corresponding to the surface magnetic maps of Vega (Petit et al.) computed for the spectral characteristics of Her. We conclude that while it is unlikely we would have detected a magnetic field identical to Vega's, we would have likely detected one with a peak strength of about 30 G, i.e. approximately four times as strong as that of Vega.

Description: Over the last 40 years variations in the systemic velocity and the observed minus computed time of first conjunction have been observed in the RS Cha binary system. Our goal is to determine the probability for the existence of a third body in this system, and to calculate an orbital solution for this component. A total of 381 high-resolution echelle spectra were obtained at Mount John University Observatory using the 1.0-m McLellan telescope and High Efficiency and Resolution Canterbury University Large Echelle Spectrograph (HERCULES; echelle spectrograph). The spectra were collected during three observing runs occurring over a 15 month period spanning from 2005 November 18 to 2007 February 17, and the data were reduced using the HERCULES reduction software package 2.3. Radial velocities for the 46 echelle orders were generated using Two-Dimensional Correlation, and the velocities from the best 15 orders were selected and used in the calculation of a weighted mean. The weight for each order was determined by generating a preliminary orbital solution for that particular order, using Stern's method, with the rms of the orbital fit used to calculate the associated weight on the order. Systemic velocities for each of the three observing runs were computed by applying a linear regression to the radial velocities of one star against its companion (i.e. V 1 versus V 2 ). The value of the slope and intercept of the regression line are required for calculating the systemic velocity. Analysis of the 381 spectra confirmed the suspected variation of the system velocity during the time-span over which these data were collected. The systemic velocity for each observing run differs significantly (12.13 ± 0.26, 11.41 ± 0.22 and 9.68 ± 0.78 km s –1 ) and combined with four historical (previously published) values they failed the 2 test, and imply a 99.9 per cent confidence that a third body exists. Three possible orbital solutions for the third body, with respect to the close binary, were generated using the historical and current systemic velocity values ( P  = 12.69 ± 0.01 or 24.17 ± 0.01 or 74.45 ± 0.02 d). The orbital solution for the binary was calculated after the effects of the shift in systemic velocity during the course of our data were removed. Values for the period and masses are P  = 1.66988 ± 0.00002 d, M 1  = 1.823 ± 0.012 M and M 2  = 1.764 ± 0.012 M , with the lowest possible mass range obtained from the orbital solutions of the third body ranging from M 3  = 0.30 to 0.52 M .