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Register a new userTwo Upper Limits on the Rossiter-McLaughlin Effect, with Differing Implications: WASP-1 has a High Obliquity and WASP-2 is Indeterminate
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We present precise radial-velocity measurements of WASP-1 and WASP-2 throughout transits of their giant planets. Our goal was to detect the Rossiter-McLaughlin (RM) effect, the anomalous radial velocity observed during eclipses of rotating stars, which can be used to study the obliquities of planet-hosting stars. For WASP-1 a weak signal of a prograde orbit was detected with ~2sigma confidence, and for WASP-2 no signal was detected. The resulting upper bounds on the RM amplitude have different implications for these two systems, because of the contrasting transit geometries and the stellar types. Because WASP-1 is an F7V star, and such stars are typically rapid rotators, the most probable reason for the suppression of the RM effect is that the star is viewed nearly pole-on. This implies the WASP-1 star has a high obliquity with respect to the edge-on planetary orbit. Because WASP-2 is a K1V star, and is expected to be a slow rotator, no firm conclusion can be drawn about the stellar obliquity. Our data and our analysis contradict an earlier claim that WASP-2b has a retrograde orbit, thereby revoking this systems status as an exception to the pattern that cool stars have low obliquities.
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We present new measurements of the Rossiter-McLaughlin (RM) effect for three WASP planetary systems, WASP-16, WASP-25 and WASP-31, from a combined analysis of their complete sets of photometric and spectroscopic data. We find a low amplitude RM effect for WASP-16 (Teff = 5700 pm 150K), suggesting that the star is a slow rotator and thus of an advanced age, and obtain a projected alignment angle of lambda = -4.2 degrees +11.0 -13.9. For WASP-25 (Teff = 5750pm100K) we detect a projected spin-orbit angle of lambda = 14.6 degrees pm6.7. WASP-31 (Teff = 6300pm100K) is found to be well-aligned, with a projected spin-orbit angle of lambda = 2.8degrees pm3.1. A circular orbit is consistent with the data for all three systems, in agreement with their respective discovery papers. We consider the results for these systems in the context of the ensemble of RM measurements made to date. We find that whilst WASP-16 fits the hypothesis of Winn et al. (2010) that cool stars (Teff < 6250K) are preferentially aligned, WASP-31 has little impact on the proposed trend. We bring the total distribution of the true spin-orbit alignment angle, psi, up to date, noting that recent results have improved the agreement with the theory of Fabrycky & Tremaine (2007) at mid-range angles. We also suggest a new test for judging misalignment using the Bayesian Information Criterion, according to which WASP-25 bs orbit should be considered to be aligned.
WASP-121b is one of the most studied Ultra-hot Jupiters: many recent analyses of its atmosphere report interesting features at different wavelength ranges. In this paper we analyze one transit of WASP-121b acquired with the high-resolution spectrograph ESPRESSO at VLT in 1-telescope mode, and one partial transit taken during the commissioning of the instrument in 4-telescope mode. We investigate the anomalous in-transit radial velocity curve and study the transmission spectrum of the planet. By analysing the in-transit radial velocities we were able to infer the presence of the atmospheric Rossiter-McLaughlin effect. We measured the height of the planetary atmospheric layer that correlates with the stellar mask (mainly Fe) to be 1.052$pm$0.015 Rp and we also confirmed the blueshift of the planetary atmosphere. By examining the planetary absorption signal on the stellar cross-correlation functions we confirmed the presence of a temporal variation of its blueshift during transit, which could be investigated spectrum-by-spectrum. We detected significant absorption in the transmission spectrum for Na, H, K, Li, CaII, Mg, and we certified their planetary nature by using the 2D tomographic technique. Particularly remarkable is the detection of Li, with a line contrast of $sim$0.2% detected at the 6$sigma$ level. With the cross-correlation technique we confirmed the presence of FeI, FeII, CrI and VI. H$alpha$ and CaII are present up to very high altitudes in the atmosphere ($sim$1.44 Rp and $sim$2 Rp, respectively), and also extend beyond the transit-equivalent Roche lobe radius of the planet. These layers of the atmosphere have a large line broadening that is not compatible with being caused by the tidally-locked rotation of the planet alone, and could arise from vertical winds or high-altitude jets in the evaporating atmosphere.
We present Rossiter-McLaughlin observations of WASP-13b and WASP-32b and determine the sky-projected angle between the normal of the planetary orbit and the stellar rotation axis ($lambda$). WASP-13b and WASP-32b both have prograde orbits and are consistent with alignment with measured sky-projected angles of $lambda={8^{circ}}^{+13}_{-12}$ and $lambda={-2^{circ}}^{+17}_{-19}$, respectively. Both WASP-13 and WASP-32 have $T_{mathrm{eff}}<6250$K and therefore these systems support the general trend that aligned planetary systems are preferentially found orbiting cool host stars. A Lomb-Scargle periodogram analysis was carried out on archival SuperWASP data for both systems. A statistically significant stellar rotation period detection (above 99.9% confidence) was identified for the WASP-32 system with $P_{mathrm{rot}}=11.6 pm 1.0 $ days. This rotation period is in agreement with the predicted stellar rotation period calculated from the stellar radius, $R_{star}$, and $v sin i$ if a stellar inclination of $i_{star}=90^{circ}$ is assumed. With the determined rotation period, the true 3D angle between the stellar rotation axis and the planetary orbit, $psi$, was found to be $psi=11^{circ} pm 14$. We conclude with a discussion on the alignment of systems around cool host stars with $T_{mathrm{eff}}<6150$K by calculating the tidal dissipation timescale. We find that systems with short tidal dissipation timescales are preferentially aligned and systems with long tidal dissipation timescales have a broad range of obliquities.
We measure a tilt of 86+-6 deg between the sky projections of the rotation axis of the WASP-7 star, and the orbital axis of its close-in giant planet. This measurement is based on observations of the Rossiter-McLaughlin (RM) effect with the Planet Finder Spectrograph on the Magellan II telescope. The result conforms with the previously noted pattern among hot-Jupiter hosts, namely, that the hosts lacking thick convective envelopes have high obliquities. Because the planets trajectory crosses a wide range of stellar latitudes, observations of the RM effect can in principle reveal the stellar differential rotation profile; however, with the present data the signal of differential rotation could not be detected. The host star is found to exhibit radial-velocity noise (``stellar jitter) with an amplitude of ~30m/s over a timescale of days.
We present new measurements of the projected spin--orbit angle $lambda$ for six WASP hot Jupiters, four of which are new to the literature (WASP-61, -62, -76, and -78), and two of which are new analyses of previously measured systems using new data (WASP-71, and -79). We use three different models based on two different techniques: radial velocity measurements of the Rossiter--McLaughlin effect, and Doppler tomography. Our comparison of the different models reveals that they produce projected stellar rotation velocities ($v sin I_{rm s}$) measurements often in disagreement with each other and with estimates obtained from spectral line broadening. The Boue model for the Rossiter--McLaughlin effect consistently underestimates the value of $vsin I_{rm s}$ compared to the Hirano model. Although $v sin I_s$ differed, the effect on $lambda$ was small for our sample, with all three methods producing values in agreement with each other. Using Doppler tomography, we find that WASP-61,b ($lambda=4^circ.0^{+17.1}_{-18.4}$), WASP-71,b ($lambda=-1^circ.9^{+7.1}_{-7.5}$), and WASP-78,b ($lambda=-6^circ.4pm5.9$) are aligned. WASP-62,b ($lambda=19^circ.4^{+5.1}_{-4.9}$) is found to be slightly misaligned, while WASP-79,b ($lambda=-95^circ.2^{+0.9}_{-1.0}$) is confirmed to be strongly misaligned and has a retrograde orbit. We explore a range of possibilities for the orbit of WASP-76,b, finding that the orbit is likely to be strongly misaligned in the positive $lambda$ direction.
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