Galaxy in Triangulum
This pair of images should
satiate both camps: Those purists that insist on genuine G2V
calibrated colors (Left), and those who would like to see a more
complete picture of the stellar dynamics in process (Right).
First, let's give a brief description of the galaxy in the images
above, and then we will go into some of the details of the pair
M33 - Local
Group Face on Spiral
Known also as
NGC598, this 6th magnitude object is spread over a huge 70 x
40 arcminute field which we are looking at about half of it here
in these images. Classed as a SA(s)cd spiral, it is inclined
only 4 degrees to our line of sight. Its fairly neutral in color
overall, with a B-V index of .55, which makes it somewhat "tawny".
The core is very unconcentrated, and in fact we can see the bare
nucleus near the center, surrounded by a dim yellowish disk with
dark brownish dust lanes traceable all the way into the core.
This galaxy has more free hydrogen than any other Local Group
galaxy in the northern sky, and produces some very enlightening
comparisons when additional exposures are added that enhances
the hydrogen lines.
Images of Local
Group galaxies tend to share a common characteristic with CCD
images and my 12.5" - They almost always appear very granular
or grainy looking. This is because we are resolving the galaxies
individual stars, and even on the largest images here, the galaxy
will show tiny blue and yellow stars down to the magnitude limit
in huge numbers. There is not a piece of this image that does
not show this granular appearance in fact. On the left standard
RGB image, the yellow core is surrounded by blue highlights in
the arms. These are clusters of star clusters, known also as
OB associations. They consist of dominantly blue supergiant stars
with a maximum brightness of magnitude 17.5 and down to the images
estimated limit of 22.5 magnitude. Only hinted at here is the
amazingly complex interaction between the hydrogen and the OB
associations. For this, we turn to the right image, that has
been Halpha/Hbeta hydrogen enhanced.
The right image
has been produced in a special way which can combine every
shred of hydrogen alpha nebulosity in a deep (4h) dedicated
set of images of the same field as the RGB frame. The entire
galaxy is filled with an enormous amount of pink glowing hydrogen.
From concentrations along the edges of the arms, to small linear
wisps all the way into the very core. Also huge numbers of very
dim red filaments are in the spaces between the major regions
in the arms, yielding a soft general hydrogen glow to the entire
disk. If you look at the larger image, you can see the fine hair
like wisps everywhere. Now lets take a look more closely at some
of the details that can only be seen by this type of image.
Below are some
blowups of small areas of the original frame to illustrate the
unique processes in this galaxy that can be visualized by hydrogen
top row shows how the OB associations with their hot fierce stellar
winds will blow bubbles in the hydrogen, forming dark areas around
the O/B stars in the cores. These three bubbles show this process
very well and are all but invisible in the standard RGB image.|
Instrument: 12.5" f/5 Home made Newtonian
Platform: Astrophysics 1200 QMD
CCD Camera: SBIG 10XME NABG with Enhanced Water Cooling
Guider: SBIG ST4
Exposure: Ha+LRGB = 240:60:60:60
RGB Combine Ratio: 1: 1.05: 1.11
Filters: AstroDon RGB Tricolor
Location: Payson, Arizona
Elevation: 5150 ft.
Sky: Seeing FWHM = 5 arcsec (Maxim DL - 10min subframe), Transparency 9/10
Outside Temperature: 40F
CCD Temperature: -20 C
Processing Tools: Maxim DL, Gralaks Sigma, Photoshop, PixInsight, Starizona Debloomer.
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closeups of OB associations. (O and B are hot blue spectral types
that emit large amounts of ultraviolet radiation) You can still
see the areas immediately adjacent to the stars has been cleared
out, and some of the fantastic shapes and structures of nebulosities
are seen here. The huge NGC604 on the right is blown out a bit
in its core, but is the largest bright nebula in M33.
I must admit
to you that I belong to both camps - I enjoy the purity of the
precise G2V calibrated RGB images very much, because it transports
my mind to that galaxy and I can see it as the eye might if I
could make it big and bright enough. On the other hand, I want
all the information and details across the entire spectrum to
view and contemplate. I love to see the amazing intricate interactions
between nebulosity and stellar groupings. Mix in swirls of dust,
a black hole or two in the core, and I'm happy!
A standard RGB
non binned image with 10 minute subframes totaling 3h total was
produced in the normal way: Calibrate, curves, and cosmic ray
cleanup. On two other nights 4h of Ha data was taken, combined
with Gralaks Sigma Reject using standard deviation masking to
minimize artifacts, and cosmic ray hits. The two were combined
in Photoshop CS2 by first adjusting the Ha image to range from
complete black to nearly pure white - but NOT white clipped anywhere.
The RGB data was split again into its components and the Hydrogen
data was projected onto first the R channel at 100% using "Screen"
and then onto the B channel at 15% the same way to fill in the
Hbeta information. The results were recombined into RGB again.
The final result is the correct pink coloration, with
the stars and the remainder of the galaxy very close to G2V in