Photometric study of HD 155555 C in the $\beta$ Pictoris Association

TL;DR

This study measures the rotation period of HD 155555C, a young star in the $eta$ Pictoris Association, confirming its membership and estimating its age as approximately 20 million years through photometric monitoring and comparison with stellar models.

Contribution

First measurement of the rotation period of HD 155555C, supporting its membership in the $eta$ Pictoris Association and its physical association with V824 Ara.

Findings

Rotation period of 4.43 days determined

Star is nearly equator-on with inclination ~90°

Estimated age of the system is 20±15 Myr

Abstract

We are carrying out a series of photometric monitoring to measure the rotation periods of members in the young $\beta$ Pictoris Association, as part of the RACE-OC project (Rotation and ACtivity Evolution in Open Clusters). In this paper, we present the results for HD 155555C which is believed to be physically associated to the spectroscopic binary V824 Ara (HD155555) and thus constituting a triple system. We collected B, V, and R-band photometric data timeseries and discovered from periodogram analysis the rotation period P = 4.43d. Combined with stellar radius and projected rotational velocity, we find this star almost equator-on with an inclination $i$ $\simeq$ 90$^{\circ}$. The rotational properties of HD155555C fit well into the period distribution of other $\beta$ Pic members, giving further support to the suggested membership to the association and to its physical association to V824 Ara. A comparison with Pre-Main-Sequence isochrones from various models allows us to estimate an age of 20$\pm$15 Myr for this triple system.