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Register a new userSpi-OPS: Spitzer and CHEOPS confirm the near-polar orbit of MASCARA-1 b and reveal a hint of dayside reflection
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The light curves of tidally-locked hot Jupiters transiting fast-rotating, early type stars are a rich source of information about both planet and star, with full-phase coverage enabling a detailed atmospheric characterisation of the planet. Although it is possible to determine the true spin-orbit angle $Psi$, a notoriously difficult parameter to measure, from any transit asymmetry resulting from gravity darkening induced by the stellar rotation, the correlations that exist between the transit parameters have led to large disagreements in published values of $Psi$ for some systems. We aimed to study these phenomena in the light curves of the ultra-hot Jupiter MASCARA-1 b. We obtained optical CHEOPS transit and occultation light curves of MASCARA-1 b, and analysed them jointly with a Spitzer/IRAC 4.5 $mu$m full-phase curve. When fitting the CHEOPS and Spitzer transits together, the degeneracies are greatly diminished and return results consistent with previously published Doppler tomography. Placing priors informed by the tomography achieves even better precision, allowing a determination of $Psi=72.1^{+2.5}_{-2.4}$ deg. From the occultations and phase variations we derived dayside and nightside temperatures of $3062^{+66}_{-68}$ K and $1720pm330$ K, respectively. In addition, we can separately derive geometric albedo $A_g=0.171^{+0.066}_{-0.068}$ and spherical albedo $A_s=0.266^{+0.097}_{-0.100}$ from the CHEOPS data, and Bond albedo $A_B=0.057^{+0.083}_{-0.101}$ from the Spitzer phase curve. Where possible, priors informed by Doppler tomography should be used when fitting transits of fast-rotating stars, though multi-colour photometry may also unlock an accurate measurement of $Psi$. Our approach to modelling the phase variations at different wavelengths provides a template for how to separate thermal emission from reflected light in spectrally-resolved JWST phase curve data.
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The CHEOPS space mission dedicated to exoplanet follow-up was launched in December 2019, equipped with the capacity to perform photometric measurements at the 20 ppm level. As CHEOPS carries out its observations in a broad optical passband, it can provide insights into the reflected light from exoplanets and constrain the short-wavelength thermal emission for the hottest of planets by observing occultations and phase curves. Here, we report the first CHEOPS observation of an occultation, namely, that of the hot Jupiter WASP-189b, a $M_P approx 2 M_J$ planet orbiting an A-type star. We detected the occultation of WASP-189 b at high significance in individual measurements and derived an occultation depth of $dF = 87.9 pm 4.3$ppm based on four occultations. We compared these measurements to model predictions and we find that they are consistent with an unreflective atmosphere heated to a temperature of $3435 pm 27$K, when assuming inefficient heat redistribution. Furthermore, we present two transits of WASP-189b observed by CHEOPS. These transits have an asymmetric shape that we attribute to gravity darkening of the host star caused by its high rotation rate. We used these measurements to refine the planetary parameters, finding a $sim25%$ deeper transit compared to the discovery paper and updating the radius of WASP-189b to $1.619pm0.021 R_J$. We further measured the projected orbital obliquity to be $lambda = 86.4^{+2.9}_{-4.4}$deg, a value that is in good agreement with a previous measurement from spectroscopic observations, and derived a true obliquity of $Psi = 85.4pm4.3$deg. Finally, we provide reference values for the photometric precision attained by the CHEOPS satellite: for the V=6.6 mag star, and using a one-hour binning, we obtain a residual RMS between 10 and 17ppm on the individual light curves, and 5.7ppm when combining the four visits.
We report detections of atomic species in the atmosphere of MASCARA-2 b, using the first transit observations obtained with the newly commissioned EXPRES spectrograph. EXPRES is a highly stabilised optical echelle spectrograph, designed to detect stellar reflex motions with amplitudes down to 30 cm/s, and was recently deployed at the Lowell Discovery Telescope. By analysing the transmission spectrum of the ultra-hot Jupiter MASCARA-2 b using the cross-correlation method, we confirm previous detections of Fe I, Fe II and Na I, which likely originate in the upper regions of the inflated atmosphere. In addition, we report significant detections of Mg I and Cr II. The absorption strengths change slightly with time, possibly indicating different temperatures and chemistry in the day-side and night-side terminators. Using the effective stellar line-shape variation induced by the transiting planet, we constrain the projected spin-orbit misalignment of the system to $1.6pm3.1$ degrees, consistent with an aligned orbit. We demonstrate that EXPRES joins a suite of instruments capable of phase-resolved spectroscopy of exoplanet atmospheres.
We report the discovery of MASCARA-1 b, the first exoplanet discovered with the Multi-site All-Sky CAmeRA (MASCARA). It is a hot Jupiter orbiting a bright $m_V=8.3$, rapidly rotating ($vsin i_star > 100~rm{km~s}^{-1}$) A8 star with a period of $2.148780pm8times10^{-6} ~rm{days}$. The planet has a mass and radius of $3.7pm0.9~rm{M}_{rm{Jup}}$ and $1.5pm0.3~rm{R}_{rm{Jup}}$, respectively. As with most hot Jupiters transiting early-type stars we find a misalignment between the planet orbital axis and the stellar spin axis, which may be signature of the formation and migration histories of this family of planets. MASCARA-1 b has a mean density of $1.5pm0.9~rm{g~cm^{-3}}$ and an equilibrium temperature of $2570^{+50}_{-30}~rm{K}$, one of the highest temperatures known for a hot Jupiter to date. The system is reminiscent of WASP-33, but the host star lacks apparent delta-scuti variations, making the planet an ideal target for atmospheric characterization. We expect this to be the first of a series of hot Jupiters transiting bright early-type stars that will be discovered by MASCARA.
We analyzed two eclipse observations of the low-density transiting, likely grazing, exoplanet WASP-34b with the Spitzer Space Telescopes InfraRed Array Camera (IRAC) using two techniques to correct for intrapixel sensitivity variation: Pixel-Level Decorrelation (PLD) and BiLinearly Interpolated Subpixel Sensitivity (BLISS). When jointly fitting both light curves, timing results are consistent within 0.7$sigma$ between the two models and eclipse depths are consistent within 1.1$sigma$, where the difference is due to photometry methods, not the models themselves. By combining published radial velocity data, amateur and professional transit observations, and our eclipse timings, we improved upon measurements of orbital parameters and found an eccentricity consistent with zero (0.0). Atmospheric retrieval, using our Bayesian Atmospheric Radiative Transfer code (BART), shows that the planetary spectrum most resembles a blackbody, with no constraint on molecular abundances or vertical temperature variation. WASP-34b is redder than other warm Jupiters with a similar temperature, hinting at unique chemistry, although further observations are necessary to confirm this.
Aims: MASCARA and bRing are photometric surveys designed to detect variability caused by exoplanets in stars with $m_V < 8.4$. Such variability signals are typically small and require an accurate calibration algorithm, tailored to the survey, in order to be detected. This paper presents the methods developed to calibrate the raw photometry of the MASCARA and bRing stations and characterizes the performance of the methods and instruments. Methods: For the primary calibration a modified version of the coarse decorrelation algorithm is used, which corrects for the extinction due to the earths atmosphere, the camera transmission, and intrapixel variations. Residual trends are removed from the light curves of individual stars using empirical secondary calibration methods. In order to optimize these methods, as well as characterize the performance of the instruments, transit signals were injected in the data. Results: After optimal calibration an RMS scatter of 10 mmag at $m_V sim 7.5$ is achieved in the light curves. By injecting transit signals with periods between one and five days in the MASCARA data obtained by the La Palma station over the course of one year, we demonstrate that MASCARA La Palma is able to recover 84.0, 60.5 and 20.7% of signals with depths of 2, 1 and 0.5% respectively, with a strong dependency on the observed declination, recovering 65.4% of all transit signals at $delta > 0^circ$ versus 35.8% at $delta < 0^circ$. Using the full three years of data obtained by MASCARA La Palma to date, similar recovery rates are extended to periods up to ten days. We derive a preliminary occurrence rate for hot Jupiters around A-stars of ${>} 0.4 %$, knowing that many hot Jupiters are still overlooked. In the era of TESS, MASCARA and bRing will provide an interesting synergy for finding long-period (${>} 13.5$ days) transiting gas-giant planets around the brightest stars.
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