Central Bureau for Astronomical Telegrams
IAUC 5852: RX J1940.2-1025; V Hya
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Circular No. 5852
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
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MARSDEN@CFA or GREEN@CFA (.SPAN, .BITNET or .HARVARD.EDU)
RX J1940.2-1025
J. Patterson and J. Halpern, Columbia University, write: "
Photometry by D. R. Skillman shows variations from V = 16.9 to 16.0,
with a strict period of 12 150 s, equal within the 0.1-percent
measurement error to the x-ray period previously attributed to NGC
6814. The measurements were made over a 12-day baseline with the
0.32-m CBA reflector (Skillman 1993, Sky Tel. 85, No. 5, 83), and
maximum light followed the ephemeris HJD 2449199.608 + 0.14062E."
Corrigendum. On IAUC 5850, line 7, for count rate of 1.4
counts/s. read count rate of 0.2 counts/s.
V HYDRAE
T. L. Evans, South African Astronomical Observatory, reports:
"V Hya is a semiregular variable, of spectral type N, with a period
of 531 days superimposed on a large amplitude variation with a
period of 17-18 yr. Spectroscopic exposure times indicate a decline
of 2 mag in visible light between April and July, which may indicate
the start of the deep minimum that was expected about 1994.
Infrared photometry by B. S. Carter on Aug. 8 gives J = 4.0, H =
2.0, K = 0.5, and L = -1.3. This is 2 mag fainter in J and 1.1 mag
redder in J-K than in mid-1975 but agrees well with an observation
in early 1978, when V Hya would have been in its last deep minimum.
Spectroscopic monitoring every few months since 1986 December shows
that spectroscopic changes started in 1992 July: NaD absorption
weakened and became net emission in 1992 December and 1993 April,
reverting to absorption with emission cores in 1993 July. The C2
emission at 473.7 nm strengthened considerably in this period and
strong emission appeared for the first time in the 516.5-nm
bandhead of C2. H-alpha emission showed its usual variation in the
531-day period throughout. This suggests that V Hya ejected gas,
which then shone in NaD and C2 by resonance emission from the middle
of 1992, and that dust condensation a year later has caused the
fading of the star. The jet and accretion disk have also faded,
ruling out an explanation in terms of an eclipse by dust associated
with the latter. Observations in the far-infrared and microwave
regions of the spectrum are needed to search for other
manifestations of mass-loss."
1993 September 2 (5852) Daniel W. E. Green
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