One of the most exciting times of my life followed after I realized that a reddish star easily visible on the cover of the June 1990 issue of Astronomy was completely lacking on the cover of the Autumn 1990 issue of Deep Sky which, by a remarkable coincidence, showed apparently the same Dumbbell nebula (M27, NGC 6853). Reproduced by permission. Copyright © 1990, Kalmbach Publishing Company.
To put it lenghtily, all that began a long time ago, well before the Internet entered my life. Getting acquitanced with the fascinating world of planetary nebulae, I found, much to my surprise, that many of them had their stellar nucleus double. A popular book on astronomy (I can't recall its title now) even said that also the brightest planetary, the Dumbbell nebula (M27, NGC 6853) belonged to the class. Unfortunately, as it is often with similar sources, no reference or authority was given, and I forgot the episode.
A couple of years later I used to make regular trips to the library of the Astronomical Institute in Ondrejov, a quiet village in a nice hilly landscape some 30 kilometers from Prague, with forests all around and great beer in local pubs. By that time I had already learned to read technical papers and now I got access to the large library full of goodies! Browsing through bibliography of planetary nebulae in hefty volumes of Astronomy and Astrophysics Abstracts, I came across a paper "A probable binary central star in the planetary nebula NGC 6853" (PASP 89, 139, 1977) by Kyle M. Cudworth of the Yerkes Observatory. Comparing positions of a 17th magnitude star next to the nebula's nucleus (separation 6.5", position angle 214deg) measured at Lick and Yerkes plates in the 1960s and 1970s, he found that both the stars moved together and suggested they could be physically related to each other.
|Finding chart for Goldilocks' variable (arrowed). The common-proper-motion companion of the stellar nucleus is a small star next to (and southwest of) the latter.|
I knew that binarity of some other planetary nebulae was much more
dramatic (as it is with
When I emerged from books and journals heaped up during the search,
I was sure that the star was really a variable, not an artifact due
to some misprint, different magnitude limit or color sensitivity.
I was looking forward to add to my chart a detail completely
forgotten by authors of deep-sky guidebooks, but first I had to find its
coordinates to check them against variable star lists. First aid was
given by the image of M27 reproduced in Perek &
Kohoutek's Catalogue of Galactic Planetary Nebulae, the only
source at my disposal with clear orientation, angular scale and
coordinates of the stellar nucleus. During my next visit at the
Department of Theoretical Physics and Astrophysics, Masaryk
University, Brno, I went through the General Catalogue of Variable
stars (GCVS) that listed variable stars known in early 1980's, as
well as its more recent supplements. But none of those authoritative sources
mentioned the star of the Astronomy cover! I determined the
position again allowing for a pessimistically large error, checked
the latest numbers of
(Information Bulletin of Variable
Stars), but the result was the same. Finally, I admitted
the star was a discovery, and sent a short announcement
to IBVS through Attila Mizser
An enjoyable response - a small card saying that the
contribution was accepted and would appear
|It required 24 individual exposures of six fields to create this CCD mosaic of the Dumbbell Nebula. Daniel Del Rio (Fort Lauderdale, Florida) took them on November 23, 1994, with a ST-5 camera attached at his 14.5-inch reflector.|
That happened in the spring of 1991. What is known about the variable
today, six years later? The most precise piece of information is its position.
Soon after the discovery, Jan Manek (Stefanik Observatory, Prague) found that
my original coordinates were erroneous. Applying standard astrometric procedures to
a pair of photographs of the Dumbbell which appeared in print, he derived
new declination and right ascension:
Unfortunately, situation with the variable's photometry is much worse. It seems most likely that it belongs to the class of long-term variables of which Mira (Omicron Ceti) is the most popular representative. This is indicated by the red color of the star, the reason it's so bright on frames taken by common CCD cameras and on the near-infrared image of the Dumbbell nebula reproduced in the September 1996 issue of the Sky & Telescope, page 16. More importantly, the classification is supported by character of light changes documented by a series of CCD frames made by Daniel Del Rio (Fort Lauderdale, Florida) during the fall of 1994. Using the ST-5 camera attached at his 14.5-inch Newtonian, he got so far the best brightness measurements. Alhough relative and unfiltered, Daniel's photometry show that the variable has brightened by some two magnitudes between the early October and the late November of that year (the check star nearby was constant within a few hundredths of magnitude). This is too much for other sorts of red variables (those various semiregular and irregular beasts). In addition, the real range may be even greater, because the images of the variable and comparison star turned out to be saturated.
But that all isn't enough for giving the star (which I privately
named Goldilocks' variable after a ravishing young lady) the
While the comet mentioned above is finally gone, Goldilocks' variable is still out there, and what is most important, you can enjoy a preliminary light curve prepared by Rudolf "Karel" Novak (Nicholas Copernicus Observatory and Planetarium, Brno).
Between April and early July 1997, he took several frames with a ST-7 CCD
camera (R-band Kron-Cousins filter) attached at the Brno Observatory
Rudolf's most recent measurements (not included in the diagram yet) indicate that Goldilocks' variable has already reached its minimum and is brightnening.
To Attila Mizser (Konkoly Observatory) who arranged publication of my discovery report in IBVS. To Petr Pravec (Astronomical Institute, Ondrejov) and Jan Manek (Stefanik Observatory, Prague) for their careful positional measurements. To Daniel Del Rio for an envelope full of goodies related to the Dumbbell Nebula and nice CCD images. To Dave Bruning and Terry Conley (Astronomy) for permission to reproduce the discovery images. And to Rudolf Novak for his present and future photometry of my favorite variable star.
Leos Ondra (leo at sky.cz)
October 16, 1998
Last Modification: February 19, 1999