HARPS-N contributes to discover the first low-mass totally eclipsing binary system in the young open cluster NGC2232

An international team of researchers lead by Antonio Frasca (INAF - Catania Astrophysical Observatory, OACT) has discovered the first low-mass totally eclipsing system in the young open cluster NGC2232.

Different set of data have been collected to reach this result. First of all a scrutiny of TESS light curves of candidate members were combined with light curves by the M. G. Fracastoro station (Mt. Etna – OACT, Italy). Radial velocity curves have then been obtained with HARPS-N, the ultra-precise and ultra-stable spectrograph mounted at TNG. HARPS-N data combined with data from literature (HERMES - Anglo Australian Observatory) and with the light curves allowed: i. to confirm this binary as a member of the cluster on the basis of the radial velocity of the center of mass and of the lithium abundance of the system components; ii. to provide the orbital elements and fundamental stellar parameters for the two stars.

The lower-mass secondary component of the system named TIC 43152097 results to be a late K-type star (Teff = 4130 K) that is still in the pre-main-sequence phase. The precise measurements of radius, mass, and effective temperature indicate a radius 7-11 % larger than predicted by standard evolutionary models. More sophisticated models incorporating the effect of magnetic fields and cool starspots covering a substantial fraction of the stellar surface (30-60 %) allow for a precise location of the star in the Hertzsprung-Russell and Mass-Radius diagrams.

TIC 43152097. The first eclipsing binary in NGC 2232 - A. Frasca, J. Alonso-Santiago, G. Catanzaro, A. Bragaglia, V. D’Orazi, X. Fu, A. Vallenari, G. Andreuzzi

Primary (top panel) and secondary (bottom panel) eclipse in the phased KSPSAP TESS light curve of sector 33 (black dots). The red solid lines represent the solution and the blue dots at nearly zero level are the residuals (observed−model). The magenta dots are those used to calculate the χ2 of the fit. Credits A&A.

Barycentric radial velocity curve (circles = HARPS-N, squares = HERMES) of TIC 43152097. Filled and open symbols have been used for the primary (more massive) and secondary component, respectively. The blue and red lines represent the orbital solution for the primary and secondary component, respectively. Credits A&A.