Time Variation of SiO Masers in VX Sagittarii over an Optically Quiescent Phase

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  • Ryuichi Kamohara
    1VERA Project Office, National Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588
  • Shuji Deguchi
    3Nobeyama Radio Observatory, National Astronomical Observatory, Minamimaki, Minamisaku, Nagano 384-1305 deguchi@nro.nao.ac.jp
  • Makoto Miyoshi
    4Division of Radio Astronomy, National Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 makoto.miyoshi@nao.ac.jp
  • Zhi-Qiang Shen
    5Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, P.R. China

Abstract

<jats:title>Abstract</jats:title> <jats:p>The time variation of SiO masers in a semi-regular variable, VX Sgr, was investigated in the period between 1994 and 2004 when the optical light curve exhibited an $\sim 6$-yr quiescent phase intercepting a regularly pulsating era. The quiescent period occurred with a delay of several years after a decrease in the SiO maser flux. VLBA observations of SiO masers made during this period showed no drastic spatial variation except for emission features being shifted from south-west to north-east. The SiO maser flux decrease, and a succeeding optical quiescent phase, may indicate that the stellar mass-loss rate diminished over a few years around 1994. A SiO maser flare occurring in 1999 may be a reminiscence of a final gas blow, which resulted in the optically quiescent period.</jats:p>

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