Chromospheric Activity of HAT-P-11: An Unusually Active Planet-hosting K Star

Abstract

Kepler photometry of the hot Neptune host star HAT-P-11 suggests that its spot latitude distribution is comparable to the Sun's near solar maximum. We search for evidence of an activity cycle in the Ca II H & K chromospheric emission S-index with archival Keck/HIRES spectra and observations from the echelle spectrograph on the Astrophysical Research Consortium 3.5 m Telescope at Apache Point Observatory. The chromospheric emission of HAT-P-11 is consistent with an 10 year activity cycle, which plateaued near maximum during the Kepler mission. In the cycle that we observed, the star seemed to spend more time near active maximum than minimum. We compare the ¢ R log HK normalized chromospheric emission index of HAT-P-11 with other stars. HAT-P-11 has unusually strong chromospheric emission compared to planet-hosting stars of similar effective temperature and rotation period, perhaps due to tides raised by its planet.

Ca II H&K stellar activity parameter: a proxy for extreme ultraviolet stellar fluxes

“…For each star in the France et al ( 2018) sample, we collected measurements of the log R HK activity parameter from the literature and retained only the stars for which we found at least one measurement (Isaacson & Fischer 2010;Boro Saikia et al 2018;Jenkins et al 2011Jenkins et al , 2006Caillault et al 1991;Mamajek & Hillenbrand 2008;Gray et al 2006Gray et al , 2003Moutou et al 2014;Arriagada 2011;Robertson et al 2012;Anderson et al 2014;Wittenmyer et al 2009;Laws et al 2003;Henry et al 1996;Canto Martins et al 2011;Pace 2013;Astudillo-Defru et al 2017;Hinkel et al 2017;Ment et al 2018;Wright et al 2004;Hall et al 2009;Morris et al 2017). The total number of collected log R HK measurements is 498.…”

Three short-period Jupiters from TESS

“…In order to get a life span of the system that is consistent with the MIST age one must use Q s > 10 8 . Other systems with short period planets, such as HAT-P-11b (Bakos et al 2010), show evidence of tidal spin which induces increased stellar activity (Morris et al 2017b). Figure 12 shows the orbital separation of known exoplanets normalised with the Roche limit as a function of planet-to-star mass ratio.…”

How to Characterize the Atmosphere of a Transiting Exoplanet

“…Spot crossings cause the flux to increase, because the spots are dark, so the planet is not blocking as many photons. The crossing of large spots can be readily identified in transit photometry (Morris et al 2017), but small spot-crossings may go unnoticed. The cumulative effect of small spot crossings will be to make the planet appear smaller, especially at shorter wavelengths.…”