VLBA determination of the distance to nearby star-forming regions VII. Monoceros R2

TL;DR

This paper uses VLBA radio observations to measure the distance to the Monoceros R2 star-forming region with high precision, revealing a distance of approximately 893 parsecs and suggesting possible orbital motion of a magnetically active star.

Contribution

First direct VLBA parallax measurement of Monoceros R2, improving distance accuracy and indicating potential binary motion of a young star.

Findings

Measured parallax of 1.12 ± 0.05 mas for VLA 1*

Distance to Monoceros R2 is approximately 893 parsecs

Detected possible orbital motion of the radio source

Abstract

We present a series of sixteen Very Long Baseline Array (VLBA) high angular resolution observations of a cluster of suspected low-mass young stars in the Monoceros R2 region. Four compact and highly variable radio sources are detected; three of them in only one epoch, the fourth one a total of seven times. This latter source is seen in the direction to the previously known \UCHII\ region VLA~1, and has radio properties that resemble those of magnetically active stars; we shall call it VLA~1$^\star$. We model its displacement on the celestial sphere as a combination of proper motion and trigonometric parallax. The fit obtained using a uniform proper motion yields a parallax $\varpi$ = 1.10 $\pm$ 0.18 mas, but with a fairly high post-fit dispersion. If acceleration terms (probably due to an undetected companion) are included, the quality of the fit improves dramatically, and the best estimate of the parallax becomes $\varpi$ = 1.12 $\pm$ 0.05 mas. The magnitude of the fitted acceleration suggest an orbital period of order a decade. The measured parallax corresponds to a distance $d$ = 893$^{+44}_{-40}$ pc, in very good agreement with previous, indirect, determinations.