Physical properties, star-spot activity, orbital obliquity and transmission spectrum of the Qatar-2 planetary system from multicolour photometry★

Mancini, L.; Southworth, J.; Ciceri, S.; Tregloan-Reed, J.; Crossfield, Ian J. M.; Nikolov, Nikolay; Bruni, I.; Zambelli, Roberto; Henning, Th.

doi:10.1093/mnras/stu1286

Cited by 79 publications

(57 citation statements)

References 60 publications

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“…According to Eq. (1) of Mancini et al (2014), the same starspot can be observed after consecutive transits or after some orbital cycles, presuming that in the latter case, the star performs one or more rotations around its axis. Since the projected obliquity measured by the RM effect (see Sect.…”

Section: Hat-p-36 Starspotsmentioning

confidence: 74%

The GAPS Programme with HARPS-N at TNG

Mancini

Esposito

Covino

et al. 2015

A&A

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Context. Orbital obliquity is thought to be a fundamental parameter in tracing the physical mechanisms that cause the migration of giant planets from the snow line down to roughly 10 −2 au from their host stars. We are carrying out a large programme to estimate the spin-orbit alignment of a sample of transiting planetary systems to study what the possible configurations of orbital obliquity are and whether they correlate with other stellar or planetary properties. Aims. We determine the true and the projected obliquity of HAT-P-36 and WASP-11/HAT-P-10 systems, respectively, which are both composed of a relatively cool star (with effective temperature T eff < 6100 K) and a hot-Jupiter planet. Methods. Thanks to the high-resolution spectrograph HARPS-N, we observed the Rossiter-McLaughlin effect for both systems by acquiring precise (3−8 m s −1 ) radial-velocity measurements during planetary transit events. We also present photometric observations comprising six light curves that cover five transit events, which were obtained using three medium-class telescopes. One transit of WASP-11/HAT-P-10 was followed simultaneously from two observatories. The three transit light curves of HAT-P-36 b show anomalies that are attributable to starspot complexes on the surface of the parent star, in agreement with the analysis of its spectra that indicates moderate activity (log R HK = −4.65 dex). By analysing the complete HATNet data set of HAT-P-36, we estimated the stellar rotation period by detecting a periodic photometric modulation in the light curve caused by star spots, obtaining P rot = 15.3± 0.4 days, which implies that the inclination of the stellar rotational axis with respect to the line of sight is i = 65• ± 34 • . Results. We used the new spectroscopic and photometric data to revise the main physical parameters and measure the sky-projected misalignment angle of the two systems. We found λ = −14• ± 18• for HAT-P-36 and λ = 7 • ± 5 • for WASP-11/HAT-P-10, indicating in both cases a good spin-orbit alignment. In the case of HAT-P-36, we were also able to estimate an upper limit of its real obliquity, which turned out to be ψ < 63 degrees.

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Section: Hat-p-36 Starspotsmentioning

confidence: 74%

The GAPS Programme with HARPS-N at TNG

Mancini

Esposito

Covino

et al. 2015

A&A

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“…Particularly for stars rotating significantly slower than the planet's orbital period, the spot will have moved a little by the time the planet returns in transit. An inclined planet will more easily miss the spot as it rotates out of the transit chord, but an aligned planet is likely to encounter the spot on a few occasions Sanchis-Ojeda and Winn 2011;Nutzman et al 2011;Mancini et al 2014;Močnik et al 2016;Dai et al 2017). The timing of starspot crossings can also be combined with out-of-transit variations to estimate the spin-orbit angle (Sanchis-Ojeda et al 2012).…”

Section: Alternate Means To Measure the Spin-orbit Angle Of Exoplanetsmentioning

confidence: 99%

The Rossiter–McLaughlin Effect in Exoplanet Research

Triaud

2017

Handbook of Exoplanets

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The Rossiter-McLaughlin effect occurs during a planet's transit. It provides the main means of measuring the sky-projected spin-orbit angle between a planet's orbital plane, and its host star's equatorial plane. Observing the Rossiter-McLaughlin effect is now a near routine procedure. It is an important element in the orbital characterisation of transiting exoplanets. Measurements of the spin-orbit angle have revealed a surprising diversity, far from the placid, Kantian and Laplacian ideals, whereby planets form, and remain, on orbital planes coincident with their star's equator. This chapter will review a short history of the Rossiter-McLaughlin effect, how it is modelled, and will summarise the current state of the field before describing other uses for a spectroscopic transit, and alternative methods of measuring the spin-orbit angle.

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“…This weakness is especially serious when the technique is applied to ground-based data, for which quasi-continuous monitoring is very difficult to achieve. For example, Mancini et al (2014) did not have the stellar rotation period as an independent check for their model of Qatar-2b. By assuming that two particular spot-crossing anomalies they observed were associated with a single spot, they derived a stellar rotation period of 14.8±0.3 days (as later revised by Mancini et al 2016).…”

Section: Anomaly Identification and Timingmentioning

confidence: 99%

The Stellar Obliquity, Planet Mass, and Very Low Albedo of Qatar-2 From K2 Photometry

Dai

Winn

et al. 2017

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The Qatar-2 transiting exoplanet system was recently observed in short-cadence mode by Kepler as part of K2 Campaign 6. We identify dozens of starspot-crossing events, when the planet eclipses a relatively dark region of the stellar photosphere. The observed patterns of these events demonstrate that the planet always transits over the same range of stellar latitudes and, therefore, that the stellar obliquity is less than about 10°. We support this conclusion with two different modeling approaches: one based on explicit identification and timing of the events and the other based on fitting the light curves with a spotted-star model. We refine the transit parameters and measure the stellar rotation period (18.5 ± 1.9 days), which corresponds to a "gyrochronological" age of 1.4±0.3 Gyr. Coherent flux variations with the same period as the transits are well modeled as the combined effects of ellipsoidal light variations (15.4 ± 4.8 ppm) and Doppler boosting (14.6 ± 5.1 ppm). The magnitudes of these effects correspond to a planetary mass of  M 2.6 0.9 Jup and  M 3.9 1.5 Jup , respectively. Both of these independent mass estimates agree with the mass determined by the spectroscopic Doppler technique (  M 2.487 0.086 Jup ). No occultations are detected, giving a 2σ upper limit of 0.06 on the planet's visual geometric albedo. We find no evidence for orbital decay, although we are only able to place a weak lower bound on the relevant tidal quality factor:  ¢ >Q 1.5 10 4 (95% confidence).

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Physical properties, star-spot activity, orbital obliquity and transmission spectrum of the Qatar-2 planetary system from multicolour photometry★

Cited by 79 publications

References 60 publications

The GAPS Programme with HARPS-N at TNG

The GAPS Programme with HARPS-N at TNG

The Rossiter–McLaughlin Effect in Exoplanet Research

The Stellar Obliquity, Planet Mass, and Very Low Albedo of Qatar-2 From K2 Photometry

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