The spectral type of CHS7797 - an intriguing very low mass periodic variable in the Orion Nebula Cluster

TL;DR

This paper spectroscopically characterizes CHS7797, a very low mass periodic variable in the Orion Nebula, suggesting it may be a binary system with a circumbinary disk based on spectral type variations.

Contribution

It provides the first detailed spectroscopic analysis of CHS7797, revealing its spectral type, youth, and potential binary nature, which was not previously known.

Findings

Spectral type of M6.05 at maximum light

Spectral type of M5.75 four days before maximum

Indications of a binary system with a circumbinary disk

Abstract

We present the spectroscopic characterization of the unusual high-amplitude very low mass pre-main-sequence periodic variable CHS7797. This study is based on optical medium-resolution (R=2200) spectroscopy in the 6450-8600 A range, carried out with GMOS-GEMINI-S in March 2011. Observations of CHS7797 have been carried out at two distinct phases of the 17.8d period, namely at maximum and four days before maximum. Four different spectral indices were used for the spectral classification at these two phases, all of them well-suited for spectral classification of young and obscured late M dwarfs. In addition, the gravity-sensitive NaI (8183/8195 A) and KI (7665/7699 A) doublet lines were used to confirm the young age of CHS7797. From the spectrum obtained at maximum light we derived a spectral type (SpT) of M6.05, while for the spectrum taken four days before maximum the derived SpT is M5.75. The derived SpTs confirm that CHS7797 has a mass in the stellar-substellar boundary mass range. In addition, the small differences in the derived SpTs at the two observed phases may provide indirect hints that CHS7797 is a binary system of similar mass components surrounded by a tilted circumbinary disk, a system similar to KH15D.