Evidence of a massive planet candidate orbiting the young active K5V star BD+20 1790

Abstract

Context. BD+20 1790 is a young active, metal-rich, late-type K5Ve star. We have undertaken a study of stellar activity and kinematics for this star over the past few years. Previous results show a high level of stellar activity, with the presence of prominence-like structures, spots on the surface and strong flare events, despite the moderate rotational velocity of the star. In addition, radial velocity variations with a semi-amplitude of up to 1 km s −1 were detected. Aims. We investigated the nature of these radial velocity variations, in order to determine whether they are due to stellar activity or the reflex motion of the star induced by a companion. Methods. We have analysed high-resolution echelle spectra, by measuring stellar activity indicators, and computing radial velocity (RV) and bisector velocity spans. Also two-band photometry was obtained to produce the light curve and determine the photometric period.Results. Based upon the analysis of the bisector velocity span, as well as spectroscopic indices of chromospheric indicators, like e.g. Ca II H & K, Hα, and taking into account the photometric analysis, we report that the best explanation for the RV variation is the presence of a sub-stellar companion. The Keplerian fit of the RV data yields a solution for a close-in massive planet with an orbital period of 7.78 days. The presence of the close-in massive planet could also be an interpretation for the high level of stellar activity detected. Since the RV data are not part of a planet search program, we can consider our results as a serendipitous evidence of a planetary companion. To date, this is the youngest main sequence star for which a planetary candidate has been reported.

A High-Precision Near-Infrared Survey for Radial Velocity Variable Low-Mass Stars Using Cshell and a Methane Gas Cell

“…Our RV curve is consistent with variations at an amplitude of ≈1 km s −1 (see Figure 3(g)), thus providing further indication that the RV variability might not be explained by chromospheric activity alone. However, our data are inconsistent with any of the orbital solutions presented by Hernán-Obispo et al (2010) (e.g., see Figure 15). …”

“…They furthermore suggest that the bisector span-RV correlation reported by Figueira et al (2010) was due to flare events and that the correlation disappears in flare-free data. They present new orbital parameters for the candidate BD+201790b that are similar to those reported by Hernán-Obispo et al (2010), except that they find a more eccentric solution (e≈0.1 to e≈0.2).…”

“…Hernán-Obispo et al (2010) identified RV variability at an amplitude of ≈1.8 km s −1 in the optical. Based on its photometric variability as well as analyses of its bisector and spectroscopic indices of chromospheric activity, they interpret the RV signal as the probable signature of a close-in (0.07 au), massive (6-7 M Jup ) planet on a 7.8 day orbit rather than the effect of chromospheric activity.…”

“…Using any combination of our data set or the data of Hernán-Obispo et al (2010) and Figueira et al (2010), we cannot identify any statistically significant periodicity. More follow-up observations will thus be needed to assess whether the RV variations could be caused by a companion or not.…”

Hiding in the Shadows. Ii. Collisional Dust as Exoplanet Markers

“…However, due to the chaotic nature of planetary dynamics, many formation models produce end results that are indistinguishable. Observations of young exoplanets would discriminate between formation models, as suggested by Setiawan et al (2007) and Hernán-Obispo et al (2010).…”