NSVS 06507557: a low-mass double-lined eclipsing binary

In this paper, we present the results of a detailed spectroscopic and photometric analysis of the V = 13.4 mag low-mass eclipsing binary NSVS 06507557 with an orbital period of 0.515 d. We have obtained a series of mid-resolution spectra covering nearly the entire orbit of the system. In addition, we have obtained simultaneous VRI broad-band photometry using a small aperture telescope. From these spectroscopic and photometric data, we have derived the system's orbital parameters and we have determined the fundamental stellar parameters of the two components. Our results indicate that NSVS 06507557 consists of a K9 pre-main-sequence star and an M3 pre-main-sequence star. These have masses of 0.66 +/- 0.09 M-circle dot and 0.28 +/- 0.05 M-circle dot and radii of 0.60 +/- 0.03 and 0.44 +/- 0.02 R-circle dot, respectively, and are located at a distance of 111 +/- 9 pc. The radius of the less massive secondary component is larger than that of a zero-age main-sequence (ZAMS) star having the same mass. While the radius of the primary component is in agreement with ZAMS, the secondary component appears to be larger by about 35 per cent with respect to its ZAMS counterpart. Night-to-night intrinsic light variations up to 0.2 mag have been observed. In addition, the H-alpha and H-beta lines and the forbidden line of [O i] are seen in emission. The Li i 6708 A absorption line is seen in most of the spectra. These features are taken to be signs of the characteristics of classic T Tauri stars. The parameters we have derived are consistent with an age of about 20 Myr, according to stellar evolutionary models. The spectroscopic and photometric results are in agreement with those obtained using theoretical predictions.