Hot Jupiters and Hot Spots: The Short- and Long-Term Chromospheric Activity on Stars with Giant Planets

By E. Shkolnik, G. Walker, D. Bohlender, Pin-Gao Gu, M. Kürster. 2004

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We monitored the chromospheric activity in the Ca II H and K lines of 13 solar-type stars (including the Sun): 8 of them over 3 years at the Canada-France-Hawaii Telescope (CFHT) and 5 in a single run at the Very Large Telescope (VLT). A total of 10 of the 13 targets have close planetary companions. All of the stars observed at the CFHT show long-term (months to years) changes in H and K intensity levels. Four stars display short-term (days) cyclical activity. For two, HD 73256 and κ1 Cet, the activity is likely associated with an active region rotating with the star; however, the flaring in excess of the rotational modulation may be associated with a hot Jupiter. A planetary companion remains a possibility for κ1 Cet. For the other two, HD 179949 and υ And, the cyclic variation is synchronized to the hot Jupiter's orbit. For both stars this synchronicity with the orbit is clearly seen in two out of three epochs. The effect is only marginal in the third epoch at which the seasonal level of chromospheric activity had changed for both stars. Short-term chromospheric activity appears weakly dependent on the mean K line reversal intensities for the sample of 13 stars. In addition, a suggestive correlation exists between this activity and the Mp sin i of the star's hot Jupiter. Because of their small separation (≤0.1 AU), many of the hot Jupiters lie within the Alfvén radius of their host stars, which allows a direct magnetic interaction with the stellar surface. We discuss the conditions under which a planet's magnetic field might induce activity on the stellar surface and why no such effect was seen for the prime candidate, τ Boo. This work opens up the possibility of characterizing planet-star interactions, with implications for extrasolar planet magnetic fields and the energy contribution to stellar atmospheres.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/dc3e6cd85ce266f51511cd70b045ef4d1d33128e

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Citations in the corpus

• Predicting low-frequency radio fluxes of known extrasolar planets (2007, methodology): “The lead angles observed by Shkolnik et al. (2003) and Shkolnik et al. (2005) were recently explained with an Alfvén-wing model using realistic stellar wind parameters obtained from the stellar wind model by Weber and Davis (Preusse, 2006; Preusse et al., 2006).”
• The On/Off Nature of Star-Planet Interactions (2007, methodology): “…evidence of tidal and magnetic interactions exists in the exaggerated case of the RS Canum Venaticorum (RS CVn) stars, which are tightly-orbiting binary systems consisting of two chromospherically active late-type stars (e.g. Glebocki et al. 1986, Catalano et al. 1996, Shkolnik et al. 2005b ).”
• THE MUSCLES TREASURY SURVEY. I. MOTIVATION AND OVERVIEW (2016, background): “…a general trend of enhanced energy dissi- pation, which could be observed as enhanced emission from the stellar corona (X-rays; Kashyap et al. 2008) or chromosphere (Ca II; Shkolnik et al. 2005), should correlate with Mplan/aplan, where Mplan is the planetary mass and aplan is the semi-major axis.”
• Magnetic cycles of the planet-hosting star τ Bootis (2008, background): “…of the planet rather than with the rotation phase of the star, arguing that this increased activity is induced by the presence of the planet (e.g., Shkolnik et al. 2003, 2005); recent observations even suggest that these star-planet interactions could be cyclic in nature and oscillate between…”
• Hot nights on extrasolar planets: mid‐infrared phase variations of hot Jupiters (2007, background): “…believe that chromospheric activity is responsible for the phase function we observe in HD 179949, however, as the cycle in chromospheric activity Shkolnik et al. (2005) observed in this system was 60◦ out of phase with the planetary orbit, and this pattern persisted for at least the year they…”
• Magnetic cycles of the planet-hosting star τ Bootis – II. A second magnetic polarity reversal (2009, background): “Observations suggest that some HJ systems undergo episodes of enhanced variability in their activity (e.g. central emission in Ca II H & K or Balmer lines) (Shkolnik et al. (2003), Shkolnik et al. (2005)) or in their mean optical brightness (Walker et al. 2008).”
• The HARPS search for southern extra-solar planets. X. A m sin i = 11 M_â planet around the nearby spotted M dwarf GJ 674 (2007, background): “Planet-induced activity through magnetic coupling (e.g. Shkolnik et al. 2005) should be an alternative explanation of the correlation, but here it is not a very attractive one: the inner planet is at least as massive as the hypothetical 35-day planet and would, at least naively, be expected to have…”
• Magnetic energy fluxes in sub-Alfvénic planet star and moon planet interactions (2013, background): “Shkolnik et al. (2005) measure the excess energy flux in the chromospheric emission ascribed to magnetic planet star coupling for HD 179949 b to be ∼1020 W.”
• Searching for star–planet interactions within the magnetosphere of HD 189733 (2010, background): “Studying the activity of HJ hosting stars, Shkolnik et al. (2003, 2005, 2008) concluded that not all the observed systems show hints”