Annual parallax measurements of a semi-regular variable star, RW Leporis

We have measured the annual parallax of water masers around the semi-regular variable star RW Leporis (RW Lep) from observations with VLBI Exploration of Radio Astrometry (VERA). The measured parallax is 1.62 ± 0.16 mas, corresponding to a distance of $617^{+68}_{-55}\:$pc. This is the first VLBI annual parallax of RW Lep, whose previously measured parallax is a negative value. Using the estimated distance we plot RW Lep on the period–luminosity plane. RW Lep is reported to have two different periods, the longer period shows that the star is located between the sequences C and C′. The shorter period shows that it is located on the sequence B+. We estimated the luminosity, radius, and mass of RW Lep to be 15400 L ⊙ , 428 R ⊙ , and 4.7 M ⊙ , respectively. We found 13 maser spots around the star, with a distribution ∼ 11 times larger than the star's radius.