The Absolute Parameters for NSVS11868841 and the Oversized Stars in Low–Mass Eclipsing Binaries¹

 

Ö. Çakirh,^2,3 C. Ibanoglu,² and A. Dervisoglu²

 

² Ege University, Science Faculty, Astronomy and Space Sciences Dept., 35100 Bornova, Izmir, Turkey (omur.cakirli@ege.edu.tr).

³ Tübitak National Observatory, Akdeniz University Campus, Turkey.

 

Received 2010 April 12
Accepted 2010 July 29

 

RESUMEN

Se han realizado observaciones espectroscópicas de la binaria eclipsante de baja masa NSV11868841, y se han derivado las velocidades radiales de ambas componentes. Las masas y radios dererminados son Los radios de ambas componentes son, respectivamente, 10% y 57% mayores que los que corresponden a estrellas de la secuencia principal de edad cero y de las mismas masas. Esta discrepancia puede deberse a que ambas estrellas tienen una gran cobertura por manchas. Hemos reunido parámetros absolutos para 21 binarias eclipsantes de doble línea y de baja masa, para comparar sus posiciones en los diagramas masa–radio y masa–temperatura efectiva. Los valores altos de los radios y las bajas temperaturas efectivas encontradas no son debidos a diferencias en metalicidad o en longitud de mezcla. Las discrepancias encontradas para estrellas de baja masa pueden deberse a campos magnéticos que inhiben el transporte convectivo, lo cual propicia una gran cobertura de la superficie estelar por manchas magnéticas.

 

ABSTRACT

Spectroscopic 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 Both the primary and secondary stars' radii are 10% and 57% larger than those of zero–age–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 and 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 ñor 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.

Key Words: binaries: eclipsing — stars: activity — stars: fundamental parameters — stars: low–mass.

 

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ACKNOWLEDGMENTS

The authors acknowledge generous allotments of observing time at TÜBITAK 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.

 

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NOTE

¹ NSVS11868841 Based on spectroscopic observations collected at TÜBÍTAK National Observatory, Turkey.