Friday, July 19, 2002
In May 1985 several astronomers decided to conduct a research survey deep in the teeming dense star fields of Sagittarius. In most areas near the galactic center of our barred spiral, distant stars and objects are hidden from view or deeply obscured by countless dust molecules. These astronomers did a search for RR Lyrae stars by taking advantage of a small area of clarity that is free from gas and dust called Baade's Window. Their idea was to search Baades' Window and find RR Lyrae stars for use as distance probes.
Using a 1.5-meter telescope at Cerro Tololo, Chile, survey plates were taken of these RR Lyrae stars in the galactic bulge. On one survey plate Arturo Gomez found a tiny extended object. This was unexpected, since Baade's Window was known to the professional astronomers to be clear of emission nebulae and dark clouds. They initially thought the object might be a background galaxy according to Andrew Phillips, a team member.
The object's glowing gas lobes (the buns) are cut in two by a dark equatorial absorption band resembling a hamburger patty. It was promptly named appropriately, Gomez's Hamburger. It is an unusual looking object. It is about .08pc by .05 pc in physical size, the size of a planetary nebula. At an estimated distance of 2.9 kiloparsecs, Gomez' Hamburger is only 3.5 by 5.5 arc seconds, and fairly dim at magnitude 14.4.
the journal article (Maria Teresa Ruiz et al., Astrophysical Journal,
316, L21 (1 May 1987), the discoverers point out that Gomez' Hamburger
could be a proto-planetary nebula. It was described as a torus of hot
dust encircling an A0III evolved giant central star. The giant star illuminates
the dust. The hot circular dust ring is also buried within an outer cloud
of colder dust. The light from the nebula is increasingly polarized away
from the center. Gomez's Hamburger was detected and catalogued previously
with IRAS (Infrared Astronomical Satellite) and designated as IRAS 18059
-3211. Its alternate designation is: PK 359-6.2.
Any object with such a delightful name has to be fair game at the eyepiece for an amateur astronomer. Sky and Telescope had a news note "Chewing on Gomez' Hamburger" (Sky and Telescope, Nov 1987, pg 462.) on its discovery. The photograph in the magazine showed a strange object unlike any seen before. It resembled a hamburger patty viewed edge on and the news item referred to the discovery article. I found the discovery article at the Rice University Library and photocopied it. As a bonus, the discovery article contained a finder photograph with the proverbial arrow (like the one you see on photographs of Pluto) pointing to tiny Gomez' Hamburger.
spectra in the article showed no emission lines, so led me to believe
that this object should behave like a reflection nebula (unlike a classical
planetary nebula) at the eyepiece.
At the April 1992 Texas Star Party, searching on consecutive nights, nothing was visible at the exact precessed position at powers ranging from 220x to 450X with my 20 inch f/4 Newtonian mounted on an equatorial platform. One complication was that I could never reconcile the ESO chart with the real sky. It seemed the Hamburger stand was closed for business!
I drew the field carefully noting all the stars visible at high power at what was to be our last clear night at the 1992 TSP. Back in Houston, I could not reconcile the eyepiece drawing with the ESO survey plate. Was the position wrong? Using another precession program, with a more precise algorithm, it appeared that the previous program had placed the elusive chiliburger 1 minute in declination too far south. To come so far, and miss by so little! Now everything became clear. I could now correlate my eyepiece drawing with the ESO chart's brighter stars. Replotting the position in MegaStar, the star fields now matched the ESO stars. The realization came that I had definitely been observing the correct field, but studying the wrong position. The J2000 position for Gomez' Hamburger is 18 hours 9 minutes 13.3 seconds - 32 degrees declination 10 minutes 47 seconds.
next attempt on May 23rd, a hazy humid southeast Texas night, I examined
the field carefully at high power, and was confident of having the correct
field using the ESO chart. No Hamburger!
On Saturday June 20th, the moon would rise at midnight, and the weather forecast predicted a front would arrive at 11 p.m. The observing window to search out this elusive object was only an hour, if the forecast was correct, and Sagittarius would not yet have reached the meridian. I took the chance anyway, going 80 miles to the Houston Astronomical Society's observing site.
The Sky was gloriously clear all evening as we waited for Sagittarius to rise. Finally I could wait no longer despite that the object was still east of the meridian. Just before 11 pm as the predicted clouds started slowly moving in from the northwest, I meticulously studied each star I could see in the eyepiece to the stars plotted on the ESO finder chart in order to positively identify the position of the protoplanetary nebula.
Using extreme averted vision, finally I saw the faintly glowing barely above stellar Gomez's Hamburger! It did not respond to a nebula filter, which was expected. The polarizing filter did not help. The best view came at 750 power, where the tiny object showed the most contrast. Gomez's object was visually fainter that I imagined. It never responded to direct vision. It could be seen at 220 power, however, not even a hint of its unusual structure was visible.
Wilson, Matt Delevoryas, Paula and Ken Drake, and Paul Sventek all observed
this protoplantary nebula with me that night, and I relished our stop
at the Hamburger Stand.
Epilogue: Gomez's Hamburger has been barely detected in telescopes as small as 8 inches, by a very experienced amateur since that date 10 years ago when I first tried to see it.