How stellar activity affects the size estimates of extrasolar planets

Czesla, S.; Huber, K. F.; Wolter, Uwe; Schröter, Sebastian; Schmitt, J. H. M. M.

doi:10.1051/0004-6361/200912454

Cited by 143 publications

(189 citation statements)

References 11 publications

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“…The presence of stellar activity and star-spots on the stellar surface can produce variations in the observed transit depth when measured at different times (e.g. Czesla et al 2009;Oshagh et al 2013;Oshagh et al 2014; Zellem et al Variation of R p /R * versus wavelength for CoRoT-1b, GJ 436b, HAT-P-1b, HAT-P-13b, HAT-P-16b, and TrES-2b. Overplotted in red are atmospheric models by Fortney et al (2010) for planets with a 1 M Jup , g p = 25m s −1 , base radius of 1.25 R Jup at 10 bar, and T eq (specified on plot).…”

Section: Variability Due To the Host Starsmentioning

confidence: 99%

Ground-based near-UV observations of 15 transiting exoplanets: constraints on their atmospheres and no evidence for asymmetrical transits

Turner

Pearson

Biddle

et al. 2016

Mon. Not. R. Astron. Soc.

109

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Transits of exoplanets observed in the near-UV have been used to study the scattering properties of their atmospheres and possible star-planet interactions. We observed the primary transits of 15 exoplanets (CoRoT-1b, GJ436b, HAT-P-1b, HAT-P-13b, HAT-P-16b, HAT-P-22b, TrES2b, in the near-UV and several optical photometric bands to update their planetary parameters, ephemerides, search for a wavelength dependence in their transit depths to constrain their atmospheres, and determine if asymmetries are visible in their light curves. Here, we present the first ground-based near-UV light curves for 12 of the targets (CoRoT1b, GJ436b, HAT-P-1b, HAT-P-13b, HAT-P-22b, TrES-2b, TrES-4b, WASP-1b, WASP-33b, WASP-36b, WASP-48b, and WASP-77Ab). We find that none of the near-UV transits exhibit any non-spherical asymmetries, this result is consistent with recent theoretical predictions by Ben-Jaffel et al. and Turner et al. The multiwavelength photometry indicates a constant transit depth from near-UV to optical wavelengths in 10 targets (suggestive of clouds), and a varying transit depth with wavelength in 5 targets (hinting at Rayleigh or aerosol scattering in their atmospheres). We also present the first detection of a smaller near-UV transit depth than that measured in the optical in WASP-1b and a possible opacity source that can cause such radius variations is currently unknown. WASP-36b also exhibits a smaller near-UV transit depth at

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Section: Variability Due To the Host Starsmentioning

confidence: 99%

Ground-based near-UV observations of 15 transiting exoplanets: constraints on their atmospheres and no evidence for asymmetrical transits

Turner

Pearson

Biddle

et al. 2016

Mon. Not. R. Astron. Soc.

109

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“…2.2). The effect of the wavelength dependence of the limb darkening is shown in the case of CoRoT-2 by Czesla et al (2009) using optical light curves at different wavelengths. The LDCs decrease from the U band to the infrared giving a more flat-bottomed transit at longer wavelengths with shorter ingress and egress profiles (see discussion in Sect.…”

Section: Modelling Stellar Activitymentioning

confidence: 99%

“…On the other hand, they found no significant correction in the inclination i of the orbital plane of the planet to the plane of the sky. A limitation of the approach by Czesla et al (2009) is that by fixing the ratio a/R , the duration of the transit t T fixes the inclination because t T = √ 1 − b 2 P orb /(πa/R ), where b = a/R cos i is the impact parameter and P orb the orbital period. Since the effects of the spots on the duration of the transit are generally small, the inclination is not changed by fitting their unperturbed transit profile.…”

Section: Effects Of Starspots On the Determination Of The Orbital Parmentioning

confidence: 99%

Multiwavelength flux variations induced by stellar magnetic activity: effects on planetary transits

Ballerini

Micela

Lanza

et al. 2012

A&A

102

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Stellar magnetic activity is a source of noise in the study of the transits of extrasolar planets. It induces flux variations that significantly affect the transit depth determination and the derivations of planetary and stellar parameters. Furthermore, the colour dependence of stellar activity may significantly influence the characterization of planetary atmospheres. Here we present a systematic approach to quantify the corresponding stellar flux variations as a function of wavelength bands. We consider a star with spots covering a given fraction of its disc and model the variability in both the UBVRIJHK photometric system and the Spitzer/IRAC wavebands for dwarf stars from G to M spectral types. We compare activity-induced flux variations in different passbands with planetary transits and quantify how they affect the determination of the planetary radius and the analysis of the transmission spectroscopy in the study of planetary atmospheres. We suggest that the monitoring of the systems by using broad-band photometry, from visible to infrared, helps us to constrain activity effects. The ratio of the relative variations in the stellar fluxes at short wavelength optical bands (e.g., U or B) to near-infrared ones (e.g., J or K) can be used to distinguish starspot brightness dips from planetary transits in a stellar light curve. In addition to the perturbations in the measurement of the planetary radius, we find that starspots can affect the determinations of both the relative semimajor axis and the inclination of the planetary orbit, which have a significant impact on the derivation of the stellar density from the transit light curves.

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“…The impact of these features on the light curve depends on their location relative to the planetary path across the stellar disk. Unlike occulted starspots, activity features, located in the non-eclipsed area of the stellar surface, do not cause distinct anomalies in a TLC, but have an impact on the overall level of the light curve (Czesla et al 2009). …”

Section: Introductionmentioning

confidence: 99%

“…The improper treatment of starspots in a TLC fitting process can thus lead to an incorrect determination of the depth, duration and timing of the transit. Additional effects can be introduced by unocculted spots or bright features of stellar activity such as faculae or plages (e.g., Czesla et al 2009;Désert et al 2011b;Kipping 2012). The impact of these features on the light curve depends on their location relative to the planetary path across the stellar disk.…”

Section: Introductionmentioning

confidence: 99%

PyTranSpot: A tool for multiband light curve modeling of planetary transits and stellar spots

Juvan

Lendl

Cubillos

et al. 2018

A&A

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Several studies have shown that stellar activity features, such as occulted and non-occulted starspots, can affect the measurement of transit parameters biasing studies of transit timing variations and transmission spectra. We present PyTranSpot, which we designed to model multiband transit light curves showing starspot anomalies, inferring both transit and spot parameters. The code follows a pixellation approach to model the star with its corresponding limb darkening, spots, and transiting planet on a two dimensional Cartesian coordinate grid. We combine PyTranSpot with an MCMC framework to study and derive exoplanet transmission spectra, which provides statistically robust values for the physical properties and uncertainties of a transiting star-planet system. We validate PyTranSpot's performance by analyzing eleven synthetic light curves of four different star-planet systems and 20 transit light curves of the well-studied WASP-41b system. We also investigate the impact of starspots on transit parameters and derive wavelength dependent transit depth values for WASP-41b covering a range of 6200-9200 Å, indicating a flat transmission spectrum.

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How stellar activity affects the size estimates of extrasolar planets

Cited by 143 publications

References 11 publications

Ground-based near-UV observations of 15 transiting exoplanets: constraints on their atmospheres and no evidence for asymmetrical transits

Ground-based near-UV observations of 15 transiting exoplanets: constraints on their atmospheres and no evidence for asymmetrical transits

Multiwavelength flux variations induced by stellar magnetic activity: effects on planetary transits

PyTranSpot: A tool for multiband light curve modeling of planetary transits and stellar spots

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