NASA Astrobiology Institute (NAI)

1. Spectropolarimetric studies of stars with hot jupiters

   Project Investigators: David Bohlender, Claire Moutou, Evgenya Shkolnik

   Summary

   Several independent studies have recently converged on the same scenario: that a short-period planet can induce stellar activity on the photosphere and upper atmosphere of its host star. As part of a collaborative proposal with both Canada and France, we will continue our very successful program to understand SPI. We are expanding the range of properties of hot-Jupiter systems which will bring constraints of unprecedented quality and completeness to the models of tidal and magnetic interactions and derive quantitative models of SPI to measure extrasolar planetary magnetic fields.

   Astrobiology Roadmap Objectives:

   • Objective 1.2: Indirect and direct astronomical observations of extrasolar habitable planets

   Project Progress

   Several independent studies have recently converged on the same scenario: that a short-period planet can induce stellar activity on the photosphere and upper atmosphere of its host star. For example, tau Boo’s massive planet has seemingly synchronized the stellar rotation, or at least its outer layer though tidal interactions, and HD 179949’s cyclic variations of spectroscopic activity tracers with the planet’s orbital period is evidence for magnetic reconnections of the planetary field with the stellar magnetosphere (Shkolnik et al. 2003, 2005, 2008b).
   The magnetic interaction between the star and its hot Jupiter provides a useful tool to explore the planetary magnetic field. Measuring the magnetic field strength of a hot Jupiter would 1) provide a constraint on the rapid hydrodynamic escape of its atmosphere, which could affect the planet’s formation and evolution, and 2) present implications for the planet’s internal structure (i.e., as inferred for Jupiter, an electrically conducting and differentially rotating layer could exist above a metallic hydrogen region.

   Mapping the stellar magnetic field with Zeeman Doppler Imaging (ZDI) is important for determining the 3-D magnetic structure of the coronal or wind environment in which the planet is orbiting. In addition to the polarimetric analysis, the study of activity tracers and their evolution with respect to the stellar and planetary periods are key to our understanding of SPI. With the proposed spectropolarimetric observations, we will span a range of properties of hot-Jupiter systems; this will bring constraints of unprecedented quality and completeness to the models of tidal and magnetic interactions and derive quantitative models of SPI to measure extrasolar planetary magnetic fields.

   We seek to address the following questions: a) What is the exact planet impact on the star? b) What are the rates of tidal energy dissipation in the star and planet? c) What are the energetics of the magnetic SPI? d) What are the impacts of these interactions on the planet in terms of orbital evolution and planetary magnetic activity? e) Do hot-Jupiter planets have measurable magnetic fields?

   
   

   Integrated flux of the K-line residuals from a normalized mean spectrum of HD 179949 as a function of orbital phase for the 2001 and 2002 data (open circles) published in Shkolnik et al. (2003) and 2005 data (filled circles). The grey line is a best-fit spot model to the earlier data whose thickness reflects the error in the phase shift. The black line is the same fit slightly shifted in phase by -0.07 to better fit the 2005 data. This small shift relative to the earlier data is not significant. Error bars in the integrated residual K flux are the intranight residual RMS. Note that the data points are repeated for two cycles.

Publications

Catala, C., Donati, J.-F., Shkolnik, E., Bohlender, D. & Alecian, E.  (2007).  The Magnetic Field of the Planet-hosting Star t Bootis.  Monthly Notices of the Royal Astronomical Society-Letters, 374:42.

Donati, J.F., Moutou, C., Farés, R., Bohlender, D.A., Catala, C., Deleuil, M., Shkolnik, E., Collier Cameron, A., Jardine, M.J. & Walker, G.A.H.  (2008).  Magnetic Cycles of the Planet-hosting star t Bootis.  Monthly Notices of the Royal Astronomical Society, 385:1179.

Gu, P.-G., Li, S.L., Shkolnik, E., Nishioka, H. & Liu, X.-W.  (2008).  The Correlation Between Stellar Metallicity and Rotation for Early-G and Late-F Dwarfs.  The Astrophysical Journal, submitted.

Shkolnik, E., Bohlender, D.A., Walker, G.A.H. & Collier Cameron, A.  (2008).  The On/Off Nature of Star-Planet Interactions.  The Astrophysical Journal, 676:628.

Walker, G.A.H., Croll, B., Matthews, J., Kuchnig, R., Huber, D., Weiss, W.W., Shkolnik, E., Rucinski, S.M., Guenther, D.B., Moffat, A. & Sasselov, D.  (2008).  MOST Detects an Active Spot on ? Bootis Induced by its Planetary Companion.  Astronomy & Astrophysics, 482:691.