Theoretical gravity and limb-darkening coefficients for the MOST satellite photometric system

Claret, A.; Dragomir, Diana; Matthews, J. M.

doi:10.1051/0004-6361/201423515

Cited by 14 publications

(11 citation statements)

References 25 publications

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“…We assume a polar temperature of T pole = 8000 K and the above equation inherently assumes a gravity darkening exponent of 1.0, which is appropriate for hot stars Claret et al (2014). The local surface gravitational potential (V) is calculated by assuming a two-axial ellipsoidal shape of the host star and given as 3…”

Section: Transitmentioning

confidence: 99%

The hot dayside and asymmetric transit of WASP-189 b seen by CHEOPS

Lendl

Csizmadia

Deline

et al. 2020

A&A

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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-189 b, a M P ≈ 2M 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 ± 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 ± 27 K, when assuming inefficient heat redistribution. Furthermore, we present two transits of WASP-189 b 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 ∼ 25% deeper transit compared to the discovery paper and updating the radius of WASP-189 b to 1.619 ± 0.021R J. We further measured the projected orbital obliquity to be λ = 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 Ψ = 85.4 ± 4.3 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 17 ppm on the individual light curves, and 5.7 ppm when combining the four visits.

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Section: Transitmentioning

confidence: 99%

The hot dayside and asymmetric transit of WASP-189 b seen by CHEOPS

Lendl

Csizmadia

Deline

et al. 2020

A&A

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“…Limb darkened transits are generated using the Mandel & Agol (2002) algorithm. Two quadratic limb darkening coefficients are kept fixed at u 1 = 0.7948 and u 2 = 0.0825, estimated by finding nearest neighbor in-terpolation of the PHOENIX model grids for MOST generated in Claret et al (2014) (using log g = 5.25 and T eff = 3050 K). Eccentricity is kept fixed at zero, since Proxima b has a low eccentricity (Anglada-Escudé et al 2016).…”

Section: Models Considered and Associated Priorsmentioning

confidence: 99%

No Conclusive Evidence for Transits of Proxima b in MOST Photometry

Kipping¹,

Cameron²,

Hartman³

et al. 2017

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The analysis of Proxima Centauri's radial velocities recently led Anglada-Escudé et al. (2016) to claim the presence of a low mass planet orbiting the Sun's nearest star once every 11.2 days. Although the a-priori probability that Proxima b transits its parent star is just 1.5%, the potential impact of such a discovery would be considerable. Independent of recent radial velocity efforts, we observed Proxima Centauri for 12.5 days in 2014 and 31 days in 2015 with the MOST space telescope. We report here that we cannot make a compelling case that Proxima b transits in our precise photometric time series. Imposing an informative prior on the period and phase, we do detect a candidate signal with the expected depth. However, perturbing the phase prior across 100 evenly spaced intervals reveals one strong false-positive and one weaker instance. We estimate a false-positive rate of at least a few percent and a much higher false-negative rate of 20-40%, likely caused by the very high flare rate of Proxima Centauri. Comparing our candidate signal to HATSouth ground-based photometry reveals that the signal is somewhat, but not conclusively, disfavored (1-2 σ) leading us to argue that the signal is most likely spurious. We expect that infrared photometric follow-up could more conclusively test the existence of this candidate signal, owing to the suppression of flare activity and the impressive infrared brightness of the parent star.

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“…Limb darkening is treated by applying the Claret et al (2013Claret et al ( , 2014 four parameter nonlinear limb darkening models. For the photometric modeling, this corresponds to where S is the number of spots, and the term in parentheses is the Claret four-parameter limb darkening model as a function of the spot position angle, μ.…”

Section: Modelmentioning

confidence: 99%

A Combined Spectroscopic and Photometric Stellar Activity Study of Epsilon Eridani

Giguere

Fischer

Zhang

et al. 2016

ApJ

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We present simultaneous ground-based radial velocity (RV) measurements and space-based photometric measurements of the young and active K dwarf Epsilon Eridani. These measurements provide a data set for exploring methods of identifying and ultimately distinguishing stellar photospheric velocities from Keplerian motion. We compare three methods we have used in exploring this data set: Dalmatian, an MCMC spot modeling code that fits photometric and RV measurements simultaneously; the FF′ method, which uses photometric measurements to predict the stellar activity signal in simultaneous RV measurements; and Hα analysis. We show that our Hα measurements are strongly correlated with the Microvariability and Oscillations of STars telescope (MOST) photometry, which led to a promising new method based solely on the spectroscopic observations. This new method, which we refer to as the HH′ method, uses Hα measurements as input into the FF′ model. While the Dalmatian spot modeling analysis and the FF′ method with MOST space-based photometry are currently more robust, the HH′ method only makes use of one of the thousands of stellar lines in the visible spectrum. By leveraging additional spectral activity indicators, we believe the HH′ method may prove quite useful in disentangling stellar signals.

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Theoretical gravity and limb-darkening coefficients for the MOST satellite photometric system

Cited by 14 publications

References 25 publications

The hot dayside and asymmetric transit of WASP-189 b seen by CHEOPS

The hot dayside and asymmetric transit of WASP-189 b seen by CHEOPS

No Conclusive Evidence for Transits of Proxima b in MOST Photometry

A Combined Spectroscopic and Photometric Stellar Activity Study of Epsilon Eridani

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