Another forbidden solar oxygen abundance: the [OI] 5577 Å line

Context. Recent works with improved model atmospheres, line formation, atomic and molecular data, and detailed treatment of blends have resulted in a significant downward revision of the solar oxygen abundance. Aims. Considering the importance of the Sun as an astrophysical standard and the current conflict of standard solar models using the new solar abundances with helioseismological observations we have performed a new study of the solar oxygen abundance based on the forbidden [Oi] line at 5577.34 angstrom, not previously considered. Methods. High-resolution (R > 500 000), high signal-to-noise (S/N > 1000) solar spectra of the [OI] 5577.34 angstrom line have been analyzed employing both three-dimensional (3D) and a variety of 1D (spatially and temporally averaged 3D, Holweger & Muller, MARCS and Kurucz models with and without convective overshooting) model atmospheres. Results. The oxygen abundance obtained from the [OI] 5577.3 angstrom forbidden line is almost insensitive to the input model atmosphere and has a mean value of log epsilon(O) = 8.71 +/- 0.02 (sigma from using the different model atmospheres). The total error (0.07 dex) is dominated by uncertainties in the log gf value (0.03 dex), apparent line variation (0.04 dex) and uncertainties in the continuum and line positions (0.05 dex). Conclusions. The oxygen abundance derived here is close to the 3D-based estimates from the two other [OI] lines at 6300 and 6363 angstrom, the permitted Oi lines and vibrational and rotational OH transitions in the infrared. Our study thus supports a low solar oxygen abundance (log epsilon(O) approximate to 8.7), independent of the adopted model atmosphere.