1,348 research outputs found
The Impact of Hot Jupiters on the Spin-down of their Host Stars
We present a numerical Magnetohydrodynamic (MHD) study of the dependence of
stellar mass and angular momentum- loss rates on the orbital distance to
close-in giant planets. We find that the mass loss rate drops by a factor of
1.5-2, while the angular momentum loss rate drops by a factor of
4 as the distance decreases past the Alfv\'en surface. This reduction
in angular momentum loss is due to the interaction between the stellar and
planetary Alfv\'en surfaces, which modifies the global structure of the stellar
corona and stellar wind on the hemisphere facing the planet, as well as the
opposite hemisphere. The simulation also shows that the magnitude of change in
angular momentum loss rate depends mostly on the strength of the planetary
magnetic field and not on its polarity. The interaction however, begins at
greater separation if the overall field topology of the star and the planet are
of anti-aligned. Our results are consistent with evidence for excess angular
momentum in stars harboring close-in giant planets, and show that the reduction
in wind-driven angular momentum loss can compete with, and perhaps dominate,
spin-up due to tidal interaction.Comment: 6 pages, 3 figure
Transiting the Sun: The impact of stellar activity on X-ray and ultraviolet transits
Transits of hot Jupiters in X-rays and the ultraviolet have been shown to be
both deeper and more variable than the corresponding optical transits. This
variability has been attributed to hot Jupiters having extended atmospheres at
these wavelengths. Using resolved images of the Sun from NASA's Solar Dynamics
Observatory spanning 3.5 years of Solar Cycle 24 we simulate transit light
curves of a hot Jupiter to investigate the impact of Solar like activity on our
ability to reliably recover properties of the planet's atmosphere in soft
X-rays (94 {\AA}), the UV (131-1700 {\AA}), and the optical (4500 {\AA}). We
find that for stars with similar activity levels to the Sun, the impact of
stellar activity results in the derived radius of the planet in soft X-ray/EUV
to be underestimated by up-to 25% or overestimated by up-to 50% depending on
whether the planet occults active regions. We also find that in up-to 70% of
the X-ray light curves the planet transits over bright star spots. In the far
ultraviolet (1600 & 1700 {\AA}), we find the mean recovered value of the
planet-to-star radius ratio to be over-estimated by up-to 20%. For optical
transits we are able to consistently recover the correct planetary radius. We
also address the implications of our results for transits of WASP-12b and HD
189733b at short wavelengths.Comment: Accepted for publication in Ap
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