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Title: An unusual very low-mass high-amplitude pre-main sequence periodic variable
Authors: Rodríguez-Ledesma, M. V
Mundt, R
Ibrahimov, M
Messina, S
Parihar, P. S
Hessman, F. V
Alves de Oliveira, C
Herbst, W
Keywords: Techniques: photometric;Stars: variables: T Tauri, Herbig Ae;Circumstellar matter;Stars: pre-main sequence;Starspots;Binaries: general
Issue Date: Aug-2012
Publisher: EDP Sciences
Citation: Astronomy & Astrophysics, Vol. 544, A112
Abstract: Aims. We have investigated the nature of the variability of CHS 7797, an unusual periodic variable in the Orion Nebula Cluster. Methods. An extensive I-band photometric data set of CHS 7797 was compiled between 2004−2010 using various telescopes. Further optical data have been collected in R and z′ bands. In addition, simultaneous observations of the ONC region including CHS 7797 were performed in the I,J,Ks & IRAC 3.6 and 4.5 μm bands over a time interval of ≈40 d. Results. CHS 7797 shows an unusual large-amplitude variation of ≈1.7 mag in the R,I, and z′ bands with a period 17.786  ± 0.03 d (FAP = 1  × 10-15%). The amplitude of the brightness modulation 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 becomes redder when fainter at longer wavelengths. CHS 7797 has a spectral type of M 6 and an estimated mass between 0.04−0.1 M⊙. Conclusions. The analysis of the data suggests that the periodic variability of CHS 7797 is most probably caused by an orbital motion. Variability as a result of rotational brightness modulation by a hot spot is excluded by the lack of any colour-brightness correlation in the optical. The latter indicates that CHS 7797 is most probably occulted by circumstellar matter in which grains have grown from typical 0.1 μm to ≈1−2 μm sizes. We discuss two possible scenarios 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 binary system, similar to KH 15D, in which an inclined circumbinary disc is responsible of the variability. Possible reasons for the typical 0.3 mag variations in I-band at a given phase are discussed.
ISSN: 0004-6361
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