VLBI Astrometry of the Semiregular Variable RX Bootis

TL;DR

This paper reports a precise VLBI astrometry measurement of RX Bootis, determining its distance and properties more accurately, and discusses its position in the Period-Luminosity relation and evolutionary status.

Contribution

First VLBI astrometric measurement of RX Bootis's distance using VERA, reducing uncertainty and enabling detailed stellar property analysis.

Findings

Measured parallax of 7.31 mas, distance of 136 pc

RX Boo is on the Mira sequence of PL relation

Reduced distance uncertainty by a factor of two

Abstract

We present distance measurement of the semiregular variable RX Bootis (RX Boo) with its annual parallax. Using the unique dual-beam system of the VLBI Exploration of Radio Astrometry (VERA) telescope, we conducted astrometric observations of a water maser spot accompanying RX Boo referred to the quasar J1419+2706 separated by 1.69 degrees from RX Boo. We have measured the annual parallax of RX Boo to be 7.31 +/- 0.50 mas, corresponding to a distance of 136 +10/-9 pc, from the one-year monitoring observation data of one maser spot at VLSR = 3.2 km/s. The distance itself is consistent with the one obtained with Hipparcos. The distance uncertainty is reduced by a factor of two, allowing us to determine the stellar properties more accurately. Using our distance, we discuss the location of RX Boo in various sequences of Period-Luminosity (PL) relations. We found RX Boo is located in the Mira sequence of PL relation. In addition, we calculated the radius of photosphere and the mass limitation of RX Boo and discussed its evolutionary status.