COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                   Number 2281

                                     Konkoly Observatory
                                     Budapest
                                     1983 February 21

                                     HU ISSN 0374-0676

         NGC 2346 DOES NOT SHOW ECLIPSES BEFORE 1981


   Kohoutek (1982) and Mendez, Gathier, and Niemela (1982) discuss the
recently discovered eclipsing behavior of the central star of the planetary
nebula NGC 2346. They conclude that no eclipses were visible in the recent
past (i.e. the 1970's). This conclusion is primarily based on the exposure
of 52 spectrograms recorded between December 1976 and February 1981. If
large amplitude eclipses had occurred during this span of time, then the
spectrograms taken during the phase of the eclipse would be substantially
under exposed. This rapid onset of eclipses is a unique phenomenon and
should be confirmed by more direct methods.

   The collection of archival photographic plates at Harvard College
Observatory can be used to search for old eclipses. Briefly, I find that
NGC 2346 did not exhibit large amplitude eclipses before 1981. In the
table, I have tabulated 21 magnitudes, based on plates taken since January


                            Table I

                   Magnitudes for NGC 2346

             JD minus
DATE         2440000 COLOR  PHASE    m

Apr 15 '82   5074.544 B      0.85   13.2
Mar 20 '82   5048.876 R      0.25   bright
Mar 18 '82   5046.560 B      0.10   11.5
Feb 15 '82   5015.586 V      0.17   11.3
Jan 22 '82   4991.590 B      0.66   12.4
Dec 26 '81   4965.092 R      0.01   bright
Dec 26 '81   4965.056 B      0.01   11.5
Dec 20 '81   4958.793 B      0.61   12.3
Nov  3 '81   4911.887 B      0.68   11.3
Apr  2 '81   4696.874 B      0.23   11.1
Mar 28 '81   4691.540 B      0.90   11.2
Mar  9 '81   4672.943 B      0.74   11.1
Feb 28 '81   4663.581 B      0.15   11.4
Jan 31 '81   4635.657 B      0.41   11.3
Jan  6 '81   4610.679 B      0.84   11.2
Dec 15 '80   4588.759 R      0.47   bright
Nov  6 '80   4549.899 B      0.04   11.1
Mar 11 '80   4309.523 B      0.01   11.2
Feb  6 '80   4275.617 B      0.89   11.4
Jan 10 '80   4248.710 B      0.21   11.2
Jan 10 '80   4248.690 R      0.21   bright



1980. The magnitudes have a one sigma error of 0.2mag and the phase is based
on a period of 15.991d and an epoch of 2443126.0. Note that the December
1981 observation shows an eclipse, however the November 1981 observation
(at a similar phase) shows the star at its normal brightness. This could
indicate that either the period is incorrect or that the deep eclipses
started with a time scale similar to an orbital period. Spectroscopic and
photometric observations published elsewhere provide ample evidence that
the period is well known.
   I have also examined 37 plates taken between 1968 and 1979 and 155
plates taken between 1899 and 1953. On no plate exposed before December
1981 was the central star fainter than its normal magnitude. If eclipses
had occurred during any substantial fraction of the epoch when observations
are available, then it would be highly unlikely for them to have been
missed.
   My conclusion is that NGC 2346 probably experienced a sudden turn on
of deep eclipses in November 1981. Neither the nebular eclipse hypothesis
(Mendez, Gathier, and Niemela 1982) nor the nodal motion hypothesis (cf.
Schaefer 1981) can allow for such a short eclipse turn on time scale.




                BRADLEY E. SCHAEFER
                MIT, Room 37-576
                77 Massachusetts Ave
                Cambridge, MA 02139
                USA




References:
Kohoutek, L. 1982, I.B.V.S. no. 2113.
Mendez, R., Gathier, R., and Niemela, V. 1982, Astron. Astrophys. 116, L1. [BIBCODE 1982A&A...116L...1M ]
Schaefer, B.E. 1981, Pub. Astron. Soc. Pacific 93, 225. [BIBCODE 1981PASP...93..225S ]