|
Gyulbudaghian's
Nebula is a little-known variable reflection nebula, similar to
Hubble's variable nebula. This nebula changes brightness and
shape over many months or years. In years past it has been a
challenge for an 18-inch scope under dark skies, but this month
Gyulbudaghian's Nebula is much brighter, making this the perfect
time to try to detect it in smaller instruments.
Armen
Gyulbudaghian is an Armenian astronomer at Byurakan Observatory.
He discovered this nebula in 1977, apparently during a
survey for new Herbig-Haro objects. The object as a whole is
known as HH 215; the reflection nebula is officially cataloged as
GM 1-29 (Magakyan -- the "M" -- was co-author on the
discovery paper).
At the heart of
the Herbig-Haro object lies the variable Herbig AbBe pre-main
sequence star PV Cep. This is a newly formed star that is
surrounded by a rotating disk of material. At right angles
to this disk are two jets of material, streaming away from the
star at high speeds. We see the effects of one of these jets
on the north side of PV Cep as the stream of material meets the
surrounding gas in the interstellar medium. The jet to the
south is obscured by a dark nebula (producing an absorption of
over 3 magnitudes). It can be seen faintly on the red POSS 2
image (right) as a string of tiny knots. The northern jet
appears on long-exposure photographs as a long chain of knots some
90" long. This chain was more visible in the 1950's
than it is today.
Today, a bright
fan-shaped reflection nebula appears immediately to the northeast
of the star. This reflection nebula appears to be the outer
edges of a hollow shell that has been carved out of the
interstellar medium surrounding the gas stream. The dust on
the outskirts of the shell is illuminated by the star. As
the light passes through the dusty cloud it is absorbed and
scattered. The blue light is most easily scattered so the
nebula appears blue. As the star varies in brightness so
does the nebula.
Stars form
together in groups, so there are at least 10 other HH objects in
the vicinity, but none are as visible as HH 215. The
distance to the Herbig-Haro object has been estimated to be about
1600 light years. At that distance the reflection nebula is
about 0.2 ly in diameter. The distance to the end of the
southern jet is about 0.7 ly.
I have made an annual visit to Gyulbudaghian's
Nebula with my 18-inch every fall for the last several years.
In 2001 the nebula was very difficult: it wasn't visible at all at
97x and I was able to detect it at 170x only with great effort and
averted vision.
In October of 2002 it appeared much
brighter. At 94x a definite irregularly-shaped fuzz-knot was
seen with averted vision. At 270x it appeared as an obvious
fuzzball -- very comet-like except for the color (slight off
blue-green?). There was a hint of a fan shape. This was the
best magnification. At 430x is was still obvious: quite
large in the field, much easier and larger than in the past.
At the end of September 2003
I once again turned my scope north to Cepheus. I was
surprised to see the nebula appear obvious at 97x. It looked
very much like the comet (29P) I had just viewed, only brighter.
At 270x it was quite easy. My crude drawing shows a
fan-shaped nebula with PV Cep at one end. PV Cep was quite
bright as well, perhaps as bright as 13.5 magnitude.
In 2008 Dave Mitsky reported
that in a 20-inch the nebula, "was extremely difficult
to see at the time and resembled the streak seen in the 1952
photo...". The photo he refers to is the second from
the top above. More recently, in
August 2009 I had a look but failed to spot the nebula at
all. Although conditions were not perfect I expected to have
seen something had it been as bright as earlier in the decade.
It's a pretty easy star hop
to the nebula. I usually start from 4 Cep. From there
the 7th magnitude star HD 198737 is in the same finder field.
Just to the west of this star lies a very distinctive quartile of
stars. Gyulbudaghian's Nebula
lies just beyond. If you don't see it at low magnification
try something between 100-200x. Look for a faint comet-like
smudge of light near a faint star. I have tried both
an H-Beta and OIII filter, but both kill it completely.
Lastly, just in case you are wondering,
Brian Skiff of Lowell Observatory suggest the following for the
correct pronunciation of the nebula: "gyool-bu-dah-ghee-an"
-- the first syllable sounds like "ghool" with a y sound
and "dah" sounds like "father."
|
