The multiplicity of \phi\ Phe revisited

TL;DR

This study revises the orbital parameters of the  Phe system using combined spectroscopic and astrometric data, confirming the primary's mass and predicting a potential eclipse, with recommendations for future observations.

Contribution

It provides a refined orbital solution for  Phe, combining spectroscopic and astrometric data to accurately determine system parameters and predict eclipses.

Findings

Confirmed primary mass of 3 Mot

Derived companion mass of 0.9 Mot

Predicted potential eclipse and next conjunction time

Abstract

The chemically peculiar B star $\phi$ Phe was, until very recently, considered a triple system, even though the data were not conclusive and the orbits rather uncertain. Very recent results by Korhonen et al. (2013) provided a revised orbit, different from the then available astrometric Hipparcos orbit. Additional spectroscopic data, obtained with the BESO spectrograph at Cerro Armazones, confirm the newly found orbit, even though the resulting radial velocities do not allow to improve on the recent orbit. We combine the latter with the Hipparcos measurements to secure the astrometric orbit, and derive the inclination of the system. Using evolutionary tracks, we can finally constrain all the parameters of the two components in this system. We confirm the mass of the primary, 3 M$_\odot$, and find that the companion has a mass of 0.9 M$_\odot$. The inclination of the system is $i=93^{\circ} \pm 4.7^{\circ}$, and is potentially eclipsing; we predict the time of the next conjunction. Given that the eccentricity of the orbit and the exact value of the semi-amplitude of the radial velocity relies on just one set of points, we also urge observers to measure radial velocities at the next periastron passage in April 2015.