On the Sun's absolute disk-center and mean disk intensities, its limb darkening, and its 'limb temperature' (λλ330 to 1099 nm)

The coefficients A(0) of the limb-darkening functions I (mu)/I-center=P-5(mu)=SigmaA(i)mu(i) (i=0,... 5, mu=cos theta), published by Neckel and Labs (1994), and the corresponding disk-center intensities I-center=I (mu=1), which were taken from the absolutely calibrated Kitt Peak FTS Atlas of the disk center (Brault et al., see Neckel and Labs, 1984, and Neckel 1999), are used to derive 'limb intensities' I-limb=I (mu=0)=A(0)I(center). The corresponding 'limb temperatures' T-limb vary only slightly with wavelength; the mean value (similar or equal to4750 K) and the wavelength of maximum intensity (similar or equal to605 nm) conform to Wien's law (lambda(max)T=0.288 cm K). Further, T-limb agrees closely with that temperature, which follows from Avrett's (2000) model of the photosphere for tau(500)similar or equal to0.006; for this layer the optical thickness along the line of sight is close to 1 ('the limb'; compare Unsold, 1968). The slight variation of T-limb with wavelength is presumably due to systematic errors in the Neckel and Labs intensity data: it corresponds almost precisely to the differences between their data and the more recent ones provided by, e. g., Burlov-Vasiljev, Gurtovenko, and Matvejev (1995), and Burlov-Vasiljev, Matvejev, and Vasiljeva (1998). Two simple correction functions (for lambdaless than or equal to550 nm and lambdagreater than or equal to550 nm) are proposed, which apply to all Neckel and Labs intensity data (disk center and full disk, line spectrum and (quasi) continuum), and to the absolutely calibrated Kitt-Peak FTS Atlas (spectra of disk center and full disk) as well.