Astronomical Observatory of Odessa National University and Isaac Newton Institute of Chile, Shevchenko Park, 65014, Odessa, Ukraine e-mail: email@example.com
2 Observatoire Aquitain des Sciences de l'Univers, CNRS UMR 5804, BP 89, 33270 Floirac, France
Accepted: 20 July 2004
Highly precise temperatures ( K) have been determined from line depth ratios for a set of 248 F-K field dwarfs of about solar metallicity (), based on high resolution (), high echelle spectra. A new gap has been discovered in the distribution of stars on the Main Sequence in the temperature range 5560 to 5610 K. This gap coincides with a jump in the microturbulent velocity and the well-known Li depression near 5600 K in field dwarfs and open clusters. As the principal cause of the observed discontinuities in stellar properties we propose the penetration of the convective zone into the inner layers of stars slightly less massive than the Sun and related to it, a change in the temperature gradient.
Key words: stars: fundamental parameters / convection / stars: Hertzsprung-Russell (HR) and C-M diagrams / stars: abundances
© ESO, 2004