The quadruple pre-main sequence system LkCa3: Implications for stellar evolution models

TL;DR

This study reveals that LkCa3 is a hierarchical quadruple system of M stars, providing new constraints on pre-main sequence stellar evolution models by combining orbital, photometric, and spectroscopic data.

Contribution

It is the first detailed characterization of LkCa3 as a quadruple system, offering empirical data to test and compare stellar evolution models, especially favoring Dartmouth models over Lyon series.

Findings

LkCa3 is a quadruple system of M stars with well-determined orbital parameters.

The system's age is estimated at 1.4 million years, consistent with Taurus region.

Dartmouth models better match the observed properties than Lyon models.

Abstract

We report the discovery that the pre-main sequence object LkCa3 in the Taurus-Auriga star-forming region is a hierarchical quadruple system of M stars. It was previously known to be a close (~0.5 arc sec) visual pair, with one component being a moderately eccentric 12.94-day single-lined spectroscopic binary. A re-analysis of archival optical spectra complemented with new near-infrared spectroscopy shows both visual components to be double-lined, the second one having a period of 4.06 days and a circular orbit. In addition to the orbital elements, we determine optical and near-infrared flux ratios, effective temperatures, and projected rotational velocities for all four stars. Using existing photometric monitoring observations of the system that had previously revealed the rotational period of the primary in the longer-period binary, we detect also the rotational signal of the primary in the 4.06-day binary, which is synchronized with the orbital motion. With only the assumption of coevality, a comparison of all of these constraints with current stellar evolution models from the Dartmouth series points to an age of 1.4 Myr and a distance of 133 pc, consistent with previous estimates for the region and suggesting the system is on the near side of the Taurus complex. Similar comparisons of the properties of LkCa3 and of the well-known quadruple pre-main sequence system GG Tau with the widely used models from the Lyon series for a mixing length parameter of alpha_ML = 1.0 strongly favor the Dartmouth models.