SPECTRAL CLASSIFICATION OF CHS7797: A 17.8 D PERIODIC VARIABLE IN THE STELLAR/SUBSTELLAR MASS BOUNDARY

RODRIGUEZ LEDESMA, M.V.; MUNDT, R,; PINTADO, O. I.; BOUDREAULT, S; HESSMAN, F.; HERBST, E

San Francisco

Congreso; Gemini Science Meeting 2012; 2012

Gemini Observatory

CHS 7797, an unusual very low mass high amplitude periodic variable in the Orion Nebula Cluster.  It  has a variation amplitude of ≈ 1.7 mag in the R, I, and z bands, and this amplitude decreases only slightly at longer wavelengths). The star is faint during ≈ 2/3 of the period and the shape of the phased light-curves for the seven different observing seasons shows minor changes and small-amplitude variations. Interestingly, there are no significant colour-flux correlations for λ ≲ 2 µm, while the object gets redder when fainter at longer wavelengths, which indicates that CHS 7797 is occulted by circumstellar matter in which grains have grown from typical interstellar medium sizes to 1-2 µm . The photometric information of CHS 7797 alone is not enough to characterize the system, and the spectral classification is then crucial to confirm its very low mass and possible binary character.We present the spectral classification of the system..  We derived slightly different spectral types at the two phases observed, namely M6.1 and M5.75, for the bright and the faint phase, respectively. The derived spectral types confirm the very low mass of CHS 7797, which is  in the stellar-substellar mass boundary. The different spectral types derived are additional hint towards the binarity of the system. Two possible scenarios are proposed, in which CHS 7797 is periodically eclipsed by structures in a disc, namely that CHS 7797 is a single object with a circumstellar disc, or that CHS 7797 is a 17.8 d binary in which an inclined circumbinary disc is responsible of the variability, and in which one component of the binary system is seen through the outer and less obscuring part of the disc.