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Post Info TOPIC: WASP-91b, WASP-105b and WASP-107b


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WASP-107b
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Title: The Oblique Orbit of WASP-107b from K2 Photometry
Author: Fei Dai, Joshua N. Winn

Observations of nine transits of WASP-107 during the {\it K2} mission reveal three separate occasions when the planet crossed in front of a starspot. The data confirm the stellar rotation period to be 17 days --- approximately three times the planet's orbital period --- and suggest that large spots persist for at least one full rotation. If the star had a low obliquity, at least two additional spot crossings should have been observed. They were not observed, giving evidence for a high obliquity. We use a simple geometric model to show that the obliquity is likely in the range 40-140°, i.e., both spin-orbit alignment and anti-alignment can be ruled out. WASP-107 thereby joins the small collection of relatively low-mass stars hosting a giant planet with a high obliquity. Most such stars have been observed to have low obliquities; all the exceptions, including WASP-107, involve planets with relatively wide orbits ("warm Jupiters", with a_min/R_star \gtrsim 8). This demonstrates a connection between stellar obliquity and planet properties, in contradiction to some theories for obliquity excitation.

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Date:
WASP-91b, WASP-105b and WASP-107b
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Title: The discoveries of WASP-91b, WASP-105b and WASP-107b: two warm Jupiters and a planet in the transition region between ice giants and gas giants
Author: D. R. Anderson, A. Collier Cameron, L. Delrez, A. P. Doyle, M. Gillon, C. Hellier, E. Jehin, M. Lendl, P. F. L. Maxted, N. Madhusudhan, F. Pepe, D. Pollacco, D. Queloz, D. Ségransan, B. Smalley, A. M. S. Smith, A. H. M. J. Triaud, O. D. Turner, S. Udry, R. G. West

We report the discoveries of three transiting exoplanets. WASP-91b is a warm Jupiter (1.34 M_Jup, 1.03 R_Jup) in a 2.8-day orbit around a metal-rich K3 star. WASP-105b is a warm Jupiter (1.8 M_Jup, 0.96 R_Jup) in a 7.9-day orbit around a metal-rich K2 star. WASP-107b is a warm super-Neptune/sub-Saturn (0.12 M_Jup, 0.94 R_Jup) in a 5.7-day orbit around a solar-metallicity K6 star. Considering that giant planets seem to be more common around stars of higher metallicity and stars of higher mass, it is notable that the hosts are all metal-rich, late-type stars. With orbital separations that place both WASP-105b and WASP-107b in the weak-tide regime, measurements of the alignment between the planets' orbital axes and their stars' spin axes may help us to understand the inward migration of short-period, giant planets. The mass of WASP-107b (2.2 M_Nep, 0.40 M_Sat) places it in the transition region between the ice giants and gas giants of the Solar System. Its radius of 0.94 R_Jup suggests that it is a low-mass gas giant with a H/He-dominated composition. The planet thus sets a lower limit of 2.2 M_Nep on the planetary mass above which large gaseous envelopes can be accreted and retained by proto-planets on their way to becoming gas giants. We may discover whether WASP-107b more closely resembles an ice giant or a gas giant by measuring its atmospheric metallicity via transmission spectroscopy, for which WASP-107b is a very good target.

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