The eclipsing binary TY CrA revisited: What near-IR light curves tell us

TL;DR

This study provides new near-IR and optical observations of TY CrA, enabling detailed analysis of its eclipsing binary components, refining their physical parameters, and examining the system's orbital variations over two decades.

Contribution

First combined optical and near-IR light curve analysis of TY CrA's eclipsing binary, improving parameter accuracy and constraining third light contributions.

Findings

Confirmed the secondary eclipse in near-IR for the first time.

Refined absolute dimensions and masses of the binary components.

Discovered the primary is smaller and less luminous than previous estimates.

Abstract

New photometric observations of the hierarchical eclipsing TY CrA system were taken in the optical with VYSOS6 and in the near-IR with SOFI and REMIR. They are the first observations showing the deep eclipse minimum of the pre-main sequence secondary in the near-IR. For the first time, the secondary minimum can be reliably used in the calculation of the O-C diagram of TY CrA. By now, the O-C diagram can be studied on a time basis of about two decades. We confirm, that the O-C diagram cannot be explained by the spectroscopic tertiary. For the first time, the light curve of the inner eclipsing binary is analysed in both optical and near-IR bands simultaneously. In combination with already published spectroscopic elements, precise absolute dimensions and masses of the primary and the secondary component are obtained using the ROCHE code. The inclusion of the near-IR data puts strong constraints on the third light which is composed of the reflection nebula, the spectroscopic tertiary and a visual fourth component. The absolute parameters of the inner eclipsing binary agree very well with previous work except of the primary radius (1.46+/-0.15 Rsun) and luminosity (40+/-10 Lsun) which are clearly smaller. While the parameters of the secondary are well understood when assuming an age of about 3-5 Myrs, the primary seems considerably undersized. Low metallicity cannot explain the parameters of the primary.