Comparing different approaches to model the rotational modulation of the Sun as a star

Free access article

Issue		A&A Volume 464, Number 2, March III 2007


Page(s)		741 - 751
Section		The Sun
DOI		http://dx.doi.org/10.1051/0004-6361:20066575

A&A 464, 741-751 (2007)
DOI: 10.1051/0004-6361:20066575

Comparing different approaches to model the rotational modulation of the Sun as a star

A. F. Lanza¹, A. S. Bonomo^{1, 2}, and M. Rodonò^{1, 2}

¹ INAF - Osservatorio Astrofisico di Catania, Italy
e-mail: nlanza@oact.inaf.it
² Dipartimento di Fisica e Astronomia, Università degli Studi di Catania, via S. Sofia 78, 95123 Catania, Italy
e-mail: aldo.bonomo@oact.inaf.it

(Received 16 October 2006 / Accepted 5 December 2006)

Abstract
Context.The space missions MOST, COROT and Kepler are going to provide us with high-precision optical photometry of solar-like stars with time series extending from tens of days to several years. They can be modelled to obtain information on stellar magnetic activity by fitting the rotational modulation of the stellar flux produced by the brightness inhomogeneities associated with photospheric active regions.
Aims.The variation of the total solar irradiance provides a good proxy for those photometric time series and can be used to test the performance of different spot modelling approaches.
Methods.We test discrete spot models as well as maximum entropy and Tikhonov regularized spot models by comparing the reconstructed total sunspot area variation and longitudinal distributions of sunspot groups with those actually observed in the Sun along activity cycle 23. Appropriate statistical methods are introduced to measure model performance versus the timescale of variation.
Results.The maximum entropy regularized spot models show the best agreement with solar observations reproducing the total sunspot area variation on time scales ranging from a few months to the activity cycle, although the model amplitudes are affected by systematic errors during the minimum and the maximum activity phases. The longitudinal distributions derived from the models compare well with the observed sunspot group distributions except during the minimum of activity, when faculae dominate the rotational modulation. The resolution in longitude attainable through the spot modelling is ~ $60^{\circ}$ , on average.
Conclusions.The application of the maximum entropy modelling to solar analogues will provide us with a quite detailed picture of their photospheric magnetic activity that can be the base for comparative and evolutionary studies of solar-like magnetic activity and irradiance variations.

Key words: Sun: activity -- Sun: rotation -- stars: activity -- stars: rotation -- stars: starspots -- stars: planetary systems

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.