A search for star-planet interactions in theυAndromedae system at X-ray and optical wavelengths

Abstract

Context. Close-in, giant planets are expected to influence their host stars via tidal or magnetic interaction. But are these effects in X-rays strong enough in suitable targets known so far to be observed with today's instrumentation? Aims. The υ And system, an F8V star with a Hot Jupiter, was observed to undergo cyclic changes in chromospheric activity indicators with its innermost planet's period. We aim to investigate the stellar chromospheric and coronal activity over several months. Methods. We therefore monitored the star in X-rays as well as at optical wavelengths to test coronal and chromospheric activity indicators for planet-induced variability, making use of the Chandra X-ray Observatory as well as the echelle spectrographs FOCES and HRS at Calar Alto (Spain) and the Hobby-Eberly Telescope (Texas, US). Results. The stellar activity level is low, as seen both in X-rays as in Ca ii line fluxes; the chromospheric data show variability with the stellar rotation period. We do not find activity variations in X-rays or in the optical that can be traced back to the planet. Conclusions. Gaining observational evidence of star-planet interactions in X-rays remains challenging.

Solar wind charge exchange X-ray emission from Mars

“…Wargelin & Drake (2001) advanced this CX X-ray based approach to study the mass-loss rate of late-type dwarfs through the CX interaction of their winds with neutral material of the IS medium (in the same context as heliospheric SWCX emission), but did not detect any significant CX halo in the cases of Proxima Centauri and the M dwarf Ross 154 studied (Wargelin & Drake 2002;Wargelin et al 2008). Recent studies of star-planet interactions in X-rays have mainly focused on the star's X-ray environment to determine the irradiation-driven mass loss of superEarths or the effects of giant planets on the chromospheric and coronal activity (Poppenhaeger et al 2011(Poppenhaeger et al , 2012, concluding that "observational evidence of star-planet interaction in X-rays remains challenging". Hopefully, the next-generation X-ray observatories proposed (e.g., ATHENA) will be able to shed more light in star-planet interactions in extrasolar systems.…”

A Comprehensive Statistical Assessment of Star-Planet Interaction

“…The focus of this work is a study of solar analogs, with the sample constructed to mitigate many of the selection biases that affected previous work (e.g., Poppenhaeger & Schmitt 2011). Finally, we use a variety of statistical tests to assess whether hot Jupiter systems display enhanced activity, including the Bayesian linear regression tool of Kelly (2007) that handles both measurement errors and censoring.…”

“…Single-pointing X-ray observations of planet-bearing stars have been utilized to search for systematic enhancements in L X in hot Jupiter systems, with mixed results (e.g., Kashyap et al 2008;Poppenhaeger et al 2010;Scharf 2010;Poppenhaeger & Schmitt 2011). Such investigations typically statistically average over orbital phase, trading decreased sensitivity to a phase-restricted effect in a given system for a much larger sample size and increased comparative sensitivity to phase-independent or full-surface activity increases; these X-ray surveys probe magnetic or tidal star-planet interaction (presumed one-sided or two-sided, respectively) as well as the potential cumulative tidal influence of hot Jupiters upon their hosts (e.g., stellar spin-up and associated activity rejuvenation; Schröter et al 2011;).…”

“…16 Approximate L X upper limits were estimated for undetected stars from the typical RASS faint source catalog limit of 10 −13 erg s −1 cm −2 . In two cases we use literature values for L X that are based on the median of multiple high-quality observations: υ And has Chandra coverage described in Poppenhaeger et al (2011), while HD 179949 has XMM-Newton coverage described in Scandariato et al (2013).…”

Magnetism and activity of planet hosting stars

“…Shkolnik et al (2008) found the detections of these signals difficult to reproduce, leading them to speculate that the effect has an "on/off nature" (see Figure 2). Indeed, Poppenhaeger et al (2011) found no variability in the υ And system at the orbital period of its close-in planet in Ca ii H & K or in X-rays, nor did Scandariato et al (2013) in their observing campaign on HD 179949. The difficulty in confirming this mode of interaction since its putative discovery casts doubt on the interpretation that the variations were necessarily due to planetary perturbations.…”