Modelling solar irradiance variability on time scales from minutes to months

Seleznyov, A. D.; Solanki, S. K.; Krivova, N. A.

doi:10.1051/0004-6361/200811138

Cited by 20 publications

(37 citation statements)

References 27 publications

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“…The cause of this inhomogeneity is the magnetic field on the solar surface, which gives rise to sunspots and facuale, convection (granulation), and oscillations (p-modes). Whereas convection and oscillations are the dominant contributors to solar irradiance variability on timescales shorter than a day (Seleznyov et al 2011), the surface magnetic field is currently believed to be the main source of the solar irradiance variability over timescales ranging from days to decades and centuries (Domingo et al 2009;Ermolli et al 2013;). Modern models (e.g., Lean et al 2005;Krivova & Solanki 2008;Shapiro et al 2011;Fontenla et al 2011) attribute the variability of the solar irradiance to the imbalance between the contributions from dark (e.g., sunspots or pores) and bright (e.g., faculae or network) magnetic features in the solar atmosphere.…”

Section: Solar Irradiance Variabilitymentioning

confidence: 99%

Variability of Sun-like stars: reproducing observed photometric trends

Шапиро

Solanki

Krivova

et al. 2014

A&A

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161

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Context. The Sun and stars with low magnetic activity levels become photometrically brighter when their activity increases. Magnetically more active stars display the opposite behavior and become fainter when their activity increases. Aims. We reproduce the observed photometric trends in stellar variations with a model that treats stars as hypothetical suns with coverage by magnetic features different from that of the Sun. Methods. The model attributes the variability of stellar spectra to the imbalance between the contributions from different components of the solar atmosphere, such as dark starspots and bright faculae. A stellar spectrum is calculated from spectra of the individual components by weighting them with corresponding disk-area coverages. The latter are obtained by extrapolating the solar dependences of spot and facular disk-area coverages on chromospheric activity to stars with different levels of mean chromospheric activity. Results. We find that the contribution by starspots to the variability increases faster with chromospheric activity than the facular contribution. This causes the transition from faculae-dominated variability and direct activity-brightness correlation to spot-dominated variability and inverse activity-brightness correlation with increasing chromospheric activity level. We show that the regime of the variability also depends on the angle between the stellar rotation axis and the line-of-sight and on the latitudinal distribution of active regions on the stellar surface. Our model can be used as a tool for extrapolating the observed photometric variability of the Sun to Sun-like stars at different activity levels, which makes a direct comparison between solar and stellar irradiance data possible.

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Section: Solar Irradiance Variabilitymentioning

confidence: 99%

Variability of Sun-like stars: reproducing observed photometric trends

Шапиро

Solanki

Krivova

et al. 2014

A&A

Self Cite

161

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“…Seleznyov et al (2011) have simulated photometric time series due to granulation by considering a collection of granules evolving in time and by studying the resulting power spectrum. In this work, we follow a similar approach; we simulate photometric and RV variations due to a collection of cells.…”

Section: Introductionmentioning

confidence: 99%

“…In this work, we follow a similar approach; we simulate photometric and RV variations due to a collection of cells. Contrary to the work of Seleznyov et al (2011), however, we do not consider a fixed number of granules, but a fixed surface covered by the granules, because it allows us to consider the proper number of granules. We also take projection effects into account, which is necessary when dealing with RV, and simulate a full hemisphere, hence our simulation is more realistic.…”

Section: Introductionmentioning

confidence: 99%

Using the Sun to estimate Earth-like planet detection capabilities

Meunier

Lagrange

Borgniet

et al. 2015

A&A

125

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Context. Stellar variability, at a variety of timescales, can strongly affect the ability to detect exoplanets, in particular when using radial velocity (RV) techniques. Accurately characterized solar variations are precious in this context to study the impact of stellar variations on planet detectability. Here we focus on the impact of small timescale variability. Aims. The objective of this paper is to model realistic RV time series due to granulation and supergranulation and to study in greater detail the impact of granulation and supergranulation on RV times series in the solar case. Methods. We have simulated a collection of granules and supergranules evolving in time to reproduce solar photometric and RV time series. Synthetic time series are built over the full hemisphere over one solar cycle. Results. We obtain intensity and RV rms due to solar granulation of respectively 0.8 m/s and 67 ppm, with a strong variability at timescales up to more than 1 h. The rms RV due to supergranulation is between 0.28 and 1.12 m/s. Conclusions. To minimize the effect of granulation, the best strategy is to split the observing time during the night into several periods instead of observing over a consecutive duration. However, the best strategy depends on the precise nature of the signal. The granulation RV remains large after even an hour of smoothing (about 0.4 m/s) while the supergranulation signal cannot be significantly reduced on such timescales: a reduction of a factor 2 in rms RV can for example be obtained over 7 nights (with 26 min/night). The activity RV variability dominates at larger timescales. Detection limits can easily be as high as 1 M Earth or above for periods of tens or hundreds of days. The impact on detection limits is therefore important and may prevent the detection of 1 M Earth planets for long orbital periods, while the impact is much smaller at small orbital periods. These results do not take the presence of pulsations into account.

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“…For periods less than an hour the power decreases with frequency due to the increasing coherence between granulation patterns. Since the period corresponding to the transition between the flat and decreasing parts of the power spectrum depends on the mean granule lifetime 24 , the power spectra of stellar variations, observed with the Kepler and CoRoT (and in future TESS and PLATO) missions, could provide a sensitive tool for determining lifetimes of stellar granules.…”

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confidence: 99%