Multiband modelling of the Sun as a variable star from VIRGO/SoHO data

Lanza, A. F.; Rodonò, M.; Pagano, I.

doi:10.1051/0004-6361:20047028

Cited by 59 publications

(77 citation statements)

References 45 publications

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“…The situation is more complex for plages. We can either use a shape such as the one used by Lanza et al (2004Lanza et al ( , 2007 and in Paper I, i.e. a temperature excess as a function of 1-μ (where μ = cos θ).…”

Section: Spot and Plage Observed Contrastsmentioning

confidence: 99%

Using the Sun to estimate Earth-like planets detection capabilities

Meunier¹,

Desort²,

Lagrange³

2010

A&A

276

394

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Aims. Stellar activity produced by spots and plages affects the radial velocity (RV) signatures. Because even low activity stars would produce such a signal, it is crucial to determine how it influences our ability to detect small planetary signals such as those produced by Earth-mass planets in the habitable zone (HZ). In a recent paper, we investigated the impact of sunlike spots. We aim here to investigate the additional impact of plages. Methods. We used the spot and plage properties over a solar cycle to derive the RV that would be observed if the Sun was seen edgeon. The RV signal comes from the photometric contribution of spots and plages and from the attenuation of the convective blueshift in plages. We analyzed the properties of the RV signal at different activity levels and compared it with commonly used activity indicators such as photometry and the Ca index. We also compared it with the signal that would be produced by an Earth-mass planet in the HZ. Results. We find that the photometric contributions of spots and plages to the RV signal partially balance each other out, so that the residual signal is comparable to the spot signal. However, the plage contribution due to the convective blueshift attenuation dominates the total signal, with an amplitude over the solar cycle of about 8-10 m/s. Short-term variations are also significantly greater than the spot and plage photometric contribution. This contribution is very strongly correlated with the Ca index on the long term, which may be a way to distinguish between stellar activity and a planet. Conclusions. Providing a very good temporal sampling and signal-to-noise ratio, the photometric contribution of plages and spots should not prevent detection of Earth-mass planets in the HZ. However, the convection contribution makes such a direct detection impossible, unless its effect can be corrected for by methods that still need to be found. We show that it is possible to identify the convection contribution if the sensitivity is good enough, for example, by using activity indicators.

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Section: Spot and Plage Observed Contrastsmentioning

confidence: 99%

Using the Sun to estimate Earth-like planets detection capabilities

Meunier¹,

Desort²,

Lagrange³

2010

A&A

276

394

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“…For the Sun as a star, ΔT 500-600 K because sunspot irradiance is dominated by the penumbral regions (cf., e.g., Lanza et al 2004, and references therein). For a star with T = 3750 K, a spot temperature deficit ΔT ≥ 1500 K is required to produce a R s that is comparable to that of a planetary transit, which is also unlikely for such a cool star (see, e.g., Berdyugina 2005;Zboril 2003).…”

Section: Influence Of Stellar Activity On Stellar Colours and The Chamentioning

confidence: 99%

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

Ballerini

Micela

Lanza

et al. 2012

A&A

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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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“…Moreover, the spot and facular contrasts depend on the wavelength (Lanza et al 2004), leading to a difference of ≈10 percent in the RV variations as derived from different orders of an echelle spectrum (cf., e.g., Desort et al 2007). The simultaneous presence of several active regions gives rise to a complex line profile distortion in the case of a slowly rotating star because the perturbation of each active region is not separated from the other by the rotational broadening.…”

Section: Modelling the Line Distortion Induced By Activitymentioning

confidence: 99%

“…In the models computed with a facular contribution, the facular contrast is assumed to be solar-like with c f = 0.115 (Lanza et al 2004). The best value of the area ratio Q between the faculae and the spots in each active region has been estimated by means of the three-spot model by Lanza et al (2003, cf.…”

Section: Model Parametersmentioning

confidence: 99%

Deriving the radial-velocity variations induced by stellar activity from high-precision photometry

Lanza

Boisse

Bouchy

et al. 2011

A&A

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Context. Stellar activity induces apparent radial velocity (RV) variations in late-type main-sequence stars that may hamper the detection of low-mass planets and the measurement of their mass. Aims. We use simultaneous measurements of the active planet host star HD 189733 with high-precision optical photometry by the MOST satellite and high-resolution spectra by SOPHIE. We apply on this unique dataset a spot model to predict the activity-induced RV variations and compare them with the observed ones. Methods. The model is based on the rotational modulation of the stellar flux. A maximum entropy regularization is applied to find a unique and stable solution for the distribution of the active regions versus stellar longitude. The RV variations are synthesized considering the effects on the line profiles of the brightness perturbations due to dark spots and bright faculae and the reduction of the convective blueshifts in the active regions. Results. The synthesized RV time series shows a remarkably good agreement with the observed one although variations on timescales shorter than 4-5 days cannot be reproduced by our model. Persistent active longitudes are revealed by the spot modelling. They rotate with slightly different periods yielding a minimum relative amplitude of the differential rotation of ΔΩ/Ω = 0.23 ± 0.10. Moreover, several active regions with an evolution timescale of 2-5 days and an area of 0.1-0.3 percent of the stellar disc are detected. Conclusions. The method proves capable of reducing the power of the activity-induced RV variations by a factor from 2 to 10 at the rotation frequency and its harmonics up to the third. Thanks to the high-precision space-borne photometry delivered by CoRoT, Kepler, or later PLATO, it is possible to map the longitudinal distribution of active regions in late-type stars and apply the method presented in this paper to reduce remarkably the impact of stellar activity on their RV jitter allowing us to confirm the detection of low-mass planets or refine the measurement of their mass.

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Multiband modelling of the Sun as a variable star from VIRGO/SoHO data

Cited by 59 publications

References 45 publications

Using the Sun to estimate Earth-like planets detection capabilities

Using the Sun to estimate Earth-like planets detection capabilities

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

Deriving the radial-velocity variations induced by stellar activity from high-precision photometry

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