THE ABSOLUTE PARAMETERS FOR NSVS 11868841 AND THE OVERSIZED STARS IN LOW-MASS ECLIPSING BINARIES

WOS: 000282596800015Spectroscopic observations of the low-mass eclipsing binary NSVS 11868841 have been obtained and the radial velocities were derived for both components. The masses and radii determined for the components are M(1) = 0.870 +/- 0.074 M(circle dot), M(2) = 0.607 +/- 0.053 M(circle dot) and R(1) = 0.983 +/- 0.030 R(circle dot) R(2) = 0.901 +/- 0.026 R(circle dot). Both the primary and secondary stars' radii are 10% and 57% larger than those of zeroage-main-sequence stars with the same masses. This discrepancy may arise from the large spot coverage of both stars. We collected absolute parameters of 21 low mass double-lined eclipsing binaries arid compared their positions in the mass-radius and mass-effective temperature panels. The large radii and lower effective temperatures found for NSV 11868841 are solved neither with differences in metallicity nor in mixing length parameters. These discrepancies for low mass stars may be due to magnetic fields inhibiting the convective energy transport, which lead to a large magnetic spot coverage of the surface of such low mass stars.Turkish Scientific and Technical Research CouncilTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [108T210]; EBILTEM Ege University Science FoundationEge University [08/BIL/027]The authors acknowledge generous allotments of observing time at TUBITAK National Observatory (TUG) of Turkey. We also wish to thank the Turkish Scientific and Technical Research Council for supporting this work through grant Nr. 108T210 and EBILTEM Ege University Science Foundation Project No:08/BIL/027. Dr. Esin Sipahi is acknowledged for the aid during the computation. We would like express our sincere gratitude to the anonymous referee, whose suggestions made the paper much clearer