A BCool magnetic snapshot survey of solar-type stars

Abstract

Stellar magnetic field measurements obtained from spectropolarimetry offer key data for activity and dynamo studies, and we present the results of a major high-resolution spectropolarimetric Bcool project magnetic snapshot survey of 170 solar-type stars from observations with the Telescope Bernard Lyot and the Canada-France-Hawaii Telescope. For each target star a high signal-to-noise circularly polarised Stokes V profile has been obtained using Least-Squares Deconvolution, and used to detect surface magnetic fields and measure the corresponding mean surface longitudinal magnetic field (B l ). Chromospheric activity indicators were also measured.Surface magnetic fields were detected for 67 stars, with 21 of these stars classified as mature solar-type stars, a result that increases by a factor of four the number of mature solar-type stars on which magnetic fields have been observed. In addition, a magnetic field was detected for 3 out of 18 of the subgiant stars surveyed. For the population of K-dwarfs the mean value of |B l | (|B l | mean ) was also found to be higher (5.7 G) than |B l | mean measured for the G-dwarfs (3.2 G) and the F-dwarfs (3.3 G). For the sample as a whole |B l | mean increases with rotation rate and decreases with age, and the upper envelope for |B l | correlates well with the observed chromospheric emission. Stars with a chromospheric S-index greater than about 0.2 show a high magnetic field detection rate and so offer optimal targets for future studies.This survey constitutes the most extensive spectropolarimetric survey of cool stars undertaken to date, and suggests that it is feasible to pursue magnetic mapping of a wide range of moderately active solar-type stars to improve understanding of their surface fields and dynamos.

Analysis of combined radial velocities and activity of BD+20 1790: evidence supporting the existence of a planetary companion

“…Applying the centre-of-gravity technique to estimate the line-of-sight projection of the stellar magnetic field (Rees & Semel 1979), we derive values of −19.6 ± 2.3 G and −67.8 ± 2.5 G for April 22 and May 04, respectively. These field values are in global agreement with measurements reported by Marsden et al (2014) for stars of similar R HK levels, and show that BD+20 1790 is an excellent possible target for magnetic mapping through Zeeman-Doppler Imaging methods.…”

“…Each observation provides us with both intensity (Stokes I) and circularly polarized (Stokes V) measurements, in a search for Zeeman signatures of surface magnetic fields. The data reduction and analysis was a strict duplicate of the one proposed by Marsden et al (2014) for other cool active stars. The least-squares-deconvolution (LSD) cross-correlation technique (Donati et al 1997) was applied to both Stokes I and V spectra, using a line-mask computed for stellar atmospheric parameters close to those of the star.…”

The effects of stellar winds on the magnetospheres and potential habitability of exoplanets

“…In contrast, the ram pressure dominates in the HZ of solar-type stars (Zarka et al 2001;Zarka 2007;Jardine & Collier Cameron 2008) and so we limit ourselves to studying the stellar wind ram pressure term in this paper. A&A 570, A99 (2014) In order to study the interaction between stellar winds and exoplanets, we use a survey of 167 stars observed by the Bcool Collaboration (Marsden et al 2014). We excluded the subgiants and any stars that did not have all the data required for our wind models.…”

Bayesian least squares deconvolution

“…Meanwhile, the spectral line itself presents correlations that will make it appear above the noise after adding many spectral lines. This idea was later improved with the introduction of the least squares deconvolution technique (LSD; Donati et al 1997), which has facilitated the detection of polarimetric signals in a wide variety of stars and the generation of a set of interesting surveys for the detection of magnetic fields in different stellar types (e.g., Wade et al 2012;Marsden et al 2014;Martins et al 2015).…”