PZ Mon is a new synchronous binary with low mass ratio

TL;DR

This paper presents new radial velocity measurements of the active giant PZ Mon, establishing it as a synchronous binary with a very low mass ratio, contributing to understanding RS CVn systems.

Contribution

It provides the first detailed orbital parameters of PZ Mon, including its low mass ratio and synchronous rotation, based on extensive radial velocity data.

Findings

PZ Mon has a period of 34.15 days.

The mass ratio q is 0.09, the smallest among RS CVn giants.

The system exhibits a large cool spotted area on the surface.

Abstract

Analysis of new radial velocity measurements of the active giant PZ Mon is presented. Only in 2015 was reported that PZ Mon may be classified as RS CVn giant. At the same time was discovered the variability of radial velocity. However, lack of the data is not allowed to determine parameters of the system. The measurements of radial velocity were performed using Radial Velocity Meter installed at the Simeiz 1-m telescope of the Crimean Astrophysical Observatory and using echelle spectrographs installed at the 2-m Zeiss telescope of the Terskol Observatory and the 6-m telescope BTA of the Special Astrophysical Observatory of the Russian Academy of Sciences. We estimated parameters of this binary system including the $\gamma$-velocity 25.5$\pm$0.3 kms, the period on the circular orbit $P=34.15\pm0.02$ days, the mass of the secondary component $M_2$=0.14 \Mo, and the mass ratio $q=0.09$ The mass ratio is a smallest value among known RS CVn type giants. Combined with photometric data we conclude that PZ Mon is a system with synchronous rotation, and there is a big cool spotted area on the stellar surface towards to the secondary component that provides the optical variability.