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[vsolj-alert 660] V915 Sgr

V915 Sgr

> ミラ型と言うより、
> (1) RCB型−平常光度11等で、4月に入って減光。
>        (→ 平常光度で0.9等も変動があるので違うかも?)

 まったく同じ推論と文献チェックを行い、以下の alert を出しました。
 (分光やればすぐにわかるはず。水素が異常に弱い、C_2 が見える、減光中の
 phase によっては希土類の輝線などが見えることがある、など)。

V915 Sgr sudden fading

   Katsumi Haseda (Aichi, Japan) reports the sudden fading of V915 Sgr,
which is designated in GCVS as a Mira-type variable with a period of
281.8 d.  The observed variability is inconsitent with the suggested
classification.  Other data by Kanatsu are also included in the table.

  YYYYMMDD(UT)   mag  observer
  19960318.776  112p  (K. Haseda)
  19960522.707  112p  (K. Haseda)
  19960525.633  112p  (K. Haseda)
  19960815.592  112p  (K. Haseda)
  19961029.392  112p  (K. Haseda)
  19970317.817  111p  (K. Haseda)
  19970517.728  112p  (K. Haseda)
  19970606.681  112p  (K. Haseda)
  19970629.635  118p  (K. Haseda)
  19971019.413  109p  (K. Haseda)
  19980228.828  116p  (K. Haseda)
  19980307.812  112p  (K. Haseda)
  19980328.817  111p  (K. Haseda)
  19980402.778  109p  (K. Haseda)
  19980425.728  112p  (K. Haseda)
  19980429.733  111p  (K. Haseda)
  19980503.742  112p  (K. Haseda)
  19980522.705  116p  (K. Haseda)
  19980615.550  117p  (K. Haseda)
  19980629.635  111p  (K. Haseda)
  19980814.533  111p  (K. Haseda)
  19981009.438  112p  (K. Haseda)
  19990313.803  112p  (K. Haseda)
  19990614.601   105  (K. Kanatsu)
  19990706.589   108  (K. Kanatsu)
  19990831.478  109p  (K. Haseda)
  20000212.851  112p  (K. Haseda)
  20000313.826  113p  (K. Haseda)
  20000401.806  <130p  (K. Haseda)

   The object is identical with GSC 6870.90 = Tycho 6870.90.1, whose B-V
has been reported to be +0.71 (Tycho) to +0.65 (Tycho-2).  Pena et al.
1994 (Rev. Mex. Astron. Assoc. 28, 105) also reported variability inconsitent
with the Mira-type.  From the ubvy photometry and photographic records, Pena
et al. suggested that V915 Sgr may be an eclipsing variable.  Their ubvy
data V=10.588 b-y=1.001 m1=0.811 c1=0.156 beta=2.556 at maximum are consistent
with Tycho photometry.  However, the presumable IRAS identification
(IRAS18383-2906, FSC18383-2907), presumed spectral type from the ubvy data,
and the present light variation may be more signatures of a previously
unrecognized R CrB-type variable star currently entering a decline.
Further observations, including spectroscopy, are urgently requested to
clarify the nature of the object.

Taichi Kato

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