Do we know of any hot jupiters that could be orbiting a red dwarf (or, more probably, orbiting a barycenter between the two)? Is this scenario even physically possible?
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2$\begingroup$ Rare but not unknown arxiv.org/abs/1112.0017 $\endgroup$– James KMar 10, 2016 at 22:16
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2$\begingroup$ "or, more probably, orbiting a barycenter between the two" I'd say 100% probable since that is how it always works. $\endgroup$– zephyrMar 11, 2016 at 1:52
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$\begingroup$ Yes, they are known. $\endgroup$– ProfRobMar 11, 2016 at 7:52
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$\begingroup$ @zephyr I mean a barycenter external to the star. $\endgroup$– Breaking BioinformaticsMar 11, 2016 at 14:33
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$\begingroup$ @BreakingBioinformatics The barycenter point is interesting. The larger red dwarfs have a luminosity of only about 4% of the sun. A "hot" Jupiter would need to be some 1/5 of an AU away from such a star to approach being hot. (receive earth level solar energy). I would think all hot jupiters around red dwarfs would have a barycenter inside the dwarf, unless it was a very massive Jupiter. My calculations were done rather quickly though, but I think in most cases, the barycenter would be in the red dwarf. $\endgroup$– userLTKMar 11, 2016 at 21:52
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1 Answer
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I found one "hot Jupiter" in the Kepler data (Kepler 45b). The star is a M dwarf with an effective temperature of 3820K. The planet has an estimated mass of 160.5 M(Earth) and radius of 10.76 R(Earth). This gives a density of about 0.8 g/cm2 which is consistent. The planet is located at approximately 0.03 AU from the star with an orbital eccentricity of 0.11. Also, it may be interesting that the star has a very high metallicity of Fe/H = 0.28. (This data is from http://kepler.nasa.gov/Mission/discoveries/ ).
It must be said, however, that M dwarfs only made up about 4.3% of the initial Kepler study which found 82 "Jupiter size" planets (as of my tally in April of 2015). Thus, there is an indication that there are less "hot Jupiters" around M dwarfs, but sample size is way too small. There does seem to be a correlation between stars hosting "hot Jupiters" and their metallicity (more common around higher Fe/H stars).
My gut feeling is that "hot Jupiters" in general are uncommon. They are just the easiest thing to find.
answered Mar 16, 2016 at 15:17
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$\begingroup$ I need to make the comment that the numbers in the answer above are not from the entire Kepler study, but just the listing of confirmed exoplanets from the Kepler 1 mission as of April 1, 2015. Also, I just looked at James Kilfiger's link and it's the same star/ "hot Jupiter" that I mentioned. $\endgroup$ Mar 16, 2016 at 15:30
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$\begingroup$ I wouldn't call them "uncommon", because during planetary formation, large planets migrating inwards seems fairly common. Jupiter is thought to have done this, but fortunately, it stopped somewhere outside of Mars and then migrated back outwards. (I think) hot jupiters are fairly common, but I agree with you on being the easiest to discover. $\endgroup$– userLTKMar 16, 2016 at 17:31
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1$\begingroup$ @userLTK Too bad we're not famous like Hawking and Thorne or I'd bet you a Penthouse subscription. Hopefully, we will have a good idea within the next decade or so. $\endgroup$ Mar 17, 2016 at 3:02
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1$\begingroup$ @userLTK Hot Jupiter's are uncommon (found around only ~1% of stars). Hot Jupiter's around M dwarfs are even less common. No gut feelings required. This has been answered on Astro SE before I'm sure. $\endgroup$– ProfRobMar 17, 2016 at 10:28
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1$\begingroup$ Indeed. astronomy.stackexchange.com/questions/107/… However, Jack's answer, presenting a single example, fully answers the question as asked... $\endgroup$– ProfRobMar 17, 2016 at 10:30