EDP Sciences
Free access
Volume 397, Number 3, January III 2003
Page(s) 1075 - 1081
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20021603

A&A 397, 1075-1081 (2003)
DOI: 10.1051/0004-6361:20021603

Centre-to-limb variation of solar granulation in the infrared

M. Sánchez Cuberes1, M. Vázquez1, J. A. Bonet1 and M. Sobotka2

1  Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
    e-mail: msanchez@ll.iac.es; mva@ll.iac.es; jab@ll.iac.es
2  Astronomical Institute, Academy of Sciences of the Czech Republic, 25165 Ondrejov, The Czech Republic
    e-mail: msobotka@asu.cas.cz

(Received 25 January 2002 / Accepted 22 October 2002)

Broad-band images have been obtained at the extremes of the continuum absorption coefficient of the solar atmosphere, at $\lambda$0.8  $\mu$m and $\lambda$1.55  $\mu$m. Quiet regions have been observed for different heliocentric angles. The centre-to-limb variation of granulation contrast has been computed in both wavelength ranges and a steeper decrease in the contrast is obtained for $\lambda$0.8  $\mu$m than for $\lambda$1.55  $\mu$m. For positions near the solar limb the granulation contrast shows a tendency to increase at both wavelengths. Mean granular sizes vary from 1.25 arcsec 2 at the disc centre to 2 arcsec 2 at $\mu=0.6$ in the $\lambda$0.8  $\mu$m images and from 1.24 arcsec 2 to 1.85 arcsec 2 at $\lambda$1.55  $\mu$m. Observations close to the limb detect granular structures of 0. ´´96 or even smaller at a distance from the limb of d= 0. ´´32, equal to the diffraction limit of the telescope at $\lambda$8000 Å. Using an Eddington-Barbier approximation this implies a penetration of the temperature fluctuations associated with granulation up to approximately $z \approx$ 220 km, although the calculation of response functions defines a broader interval.

Key words: Sun: granulation -- Sun: photosphere

Offprint request: M. Sanchez Cuberes, msanchez@ll.iac.es

© ESO 2003