* Astronomy

Title: The UBV(RI)c colours of the Sun
Authors: I. Ramirez, R. Michel, R. Sefako, M. Tucci Maia, W. J. Schuster, F. van Wyk, J. Melendez, L. Casagrande, B. V. Castilho

Photometric data in the UBV(RI)c system have been acquired for 80 solar analogue stars for which we have previously derived highly precise atmospheric parameters Teff, log g, and [Fe/H] using high resolution, high signal-to-noise ratio spectra. UBV and (RI)c data for 46 and 76 of these stars, respectively, are published for the first time. Combining our data with those from the literature, colours in the UBV(RI)c system, with ~0.01 mag precision, are now available for 112 solar analogues. Multiple linear regression is used to derive the solar colours from these photometric data and the spectroscopically derived Teff, log g, and [Fe/H] values. To minimise the impact of systematic errors in the model-dependent atmospheric parameters, we use only the data for the ten stars that most closely resemble our Sun, i.e., the solar twins, and derive the following solar colours: (B-V)=0.653±0.005, (U-B)=0.166±0.022, (V-R)=0.352±0.007, and (V-I)=0.702±0.010. These colours are consistent, within the 1 sigma errors, with those derived using the entire sample of 112 solar analogues. We also derive the solar colours using the relation between spectral line-depth ratios and observed stellar colours, i.e., with a completely model-independent approach, and without restricting the analysis to solar twins. We find: (B-V)=0.653±0.003, (U-B)=0.158±0.009, (V-R)=0.356±0.003, and (V-I)=0.701±0.003, in excellent agreement with the model-dependent analysis.

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