2012's M33, at last

Sometimes I think M33 is my Great White Whale. I'll probably keep shooting this thing every autumn - or nearly so - for as long as I can operate a CCD camera and telescope. I don't have the same vengeful feelings toward it that Ahab had towards Moby-Dick, but I am somewhat obsessed with it. In fact, it wouldn't surprise me if a lot of amateur imagers are, too.

M33, the Triangulum galaxy, distance about 2.5 - 3 million light years.

(You can click on the image for a larger version, or click here for Flickr.)

Why? I think it's because M33, the Triangulum galaxy, looks like a `logical next step' after M31, the great Andromeda Galaxy. Getting a decent M31 image isn't trivial, but it's bright enough that one can get something presentable without too much exposure time, and without having to work too hard at processing the data. M33 is different, however. Its surface brightness is lower, and consequently one has a significantly harder time getting the dimmer, outer portions of the galaxy to look good. Even when using a sensitive CCD camera, and when calibrating one's light frames with darks, flats, and biases, much of M33 can easily come out looking noisy and ugly. (I haven't totally overcome those issues in this image, but I think I've imaged the outer regions a bit better than before.) Unless you've got a very `fast' (i.e. numerically small f-ratio) imaging system, and/or a great deal of time, it's hard to get much out of M33. All of this results in M33 being a rather harder thing to acquire and process than M31.

I shot the data for this image at Calstar 2012. Calstar is a yearly get-together of Bay Area and SoCal amateur astronomers, at Lake San Antonio in inland Monterey County. This event is near and dear to many of our hearts, mostly due to its no-frills nature. The sky at LSA can get very dark, dark enough to see not only the gegenschein, but even a nearly horizon-to-horizon zodiacal `band'. I've spent many hours picking out individual objects in M31 and M33, through an 18" Dobsonian telescope. It's a great site for imaging and visual observing.

Although I shot these data in September 2012, it's taken until February 2013 to get them processed and posted on the blog. What an epic it's been! The main thing that ate up all this time was a seemingly-endless series of attempts to properly deconvolve (i.e. sharpen) the image, as described below.

Get the L out

The most unexpected thing about my processing workflow was how much data I ended up throwing away. I'd shot unbinned luminance in 2011, along with 2x2 binned color (and used those data to produce a previous version of M33.) I also shot additional unbinned L and binned color in December 2011, and my 2012 data set included a lot of unbinned L, too.

In the end, I chucked all the binned R, G, and B, and all the unbinned L. In the former case, I never found a good way to combine the binned and unbinned color images. Maybe I should work that problem more, someday, but for now I've given up on it. And when I tried to make an LRGB image from all-unbinned data, it never looked any good. I have two ideas on why this was so:

1) I don't think my L image was any sharper than my RGB image, nor sharper than any of the individual (stacked) color images. It's certainly true that if one is shooting unbinned L and binned R,G,B, the former will have more detail than the latter. That's the whole idea behind that trick. But if the data are all unbinned, then it comes down to a matter of optics. The optical system had better make a Luminance image that's sharper than (or at least as sharp as) the RGB image. And with a refractor (like the Orion ED80 refractor I used), that's a tall order. Even the best refractors will have a tiny bit of chromatic aberration, which means that the R, G, and B components of the Luminance won't all be focused the same. So, I've come to suspect that the Luminance image will, in fact, be a tiny bit blurrier than the RGB image, and I think that's so in my case. I'm just better off shooting straight R, G, and B, unbinned.

2) The uselessness of unbinned LRGB is described by Juan Conejero, author of Pixinsight software, in a thread on the Pixinsight forum. Juan points out that adding luminance to an image reduces chrominance, and so it really doesn't do any good to try unbinned LRGB. As far as I'm concerned, goodbye Luminance. I think I'll mostly use my L filter for focusing, drift alignment, and framing. (I might use the unbinned-L-and-binned-RGB trick if I was shooting a large, diffuse nebula that doesn't have much small-scale detail, though.)

After all this, I think I'll try to acquire image data by means of simple, unbinned R, G, and B. This may require some sort of automated acquisition workflow, however, in order to get some data through each filter, during each imaging session. There's a lot of focusing, slewing, and framing involved!

Pixinsight processing workflow

I followed a fairly `basic' workflow in Pixinsight. I suppose you might call this the `non-multiscale' approach, because I didn't try the RBA-like processing steps I used in the previous M33 image. Maybe next time! (I'm particularly intrigued by Emanuele Todini's recent post about his `multi-scale-layer' workflow.) Here's what I did (the abbreviations will probably be familiar to PI enthusiasts):

1. Calibration using the Batch Preprocessing script
2. Cropping off the outermost part of the image
3. Deconvolution of high-SNR areas (this took forever...)
4. MMT-based noise reduction of low-SNR areas (not too hard, thankfully)
5. Nonlinear stretch with HT
6. Dim the brightest regions a tiny bit with HDRMT
7. A little bit of contrast boost with LHE
8. Increase overall color saturation with Curves (Lum mask in place)
9. Increase color saturation in HII regions, blue spiral arms, and orange galaxy core with ColorSaturation tool (Lum mask in place)
10. Small amount of denoising the 1- and 2- pixel-scale layers with ATWT
11. Dimming stars a little bit with StarMask and MT
12. Making a mask for the largest stars with ATWT, HT, MT, and Convolution
13. Desaturating (and slightly dimming) the biggest stars with Curves and MT
14. Tiny tweak to the black point with HT
15. Color-space conversion, resampling, and saving as JPEG for web publishing

The Agony of Deconvolution - and a savior!

I spent the entire winter beating my head against Deconvolution. Whether it was on the RGB image, or on the (ultimately-not-used) Luminance image, I could not keep the stars from showing subtle dark `ringing' artifacts. I've successfully applied Deconvolution before, with results that pleased me, but this image just wouldn't deconvolve, for some reason. It drove me nuts for months.

In the end, it was something simple. It turned out to be the point-spread function I was using in the Deconvolution module. I knew that the parameters of the PSF were important, but I had no idea how important. I'd used Mike Schuster's excellent PSF evaluation script, but somehow that must have produced an averaged PSF that wasn't quite what Deconvolution wanted.

I came to realize this when I watched the Deconvolution videos in the new Pixinsight series by Warren Keller and Rogelio Bernal Andreo. There's some simple information in there, concerning how to measure one's PSF, and it did the trick! I don't want to give it away here, because I think Warren and RBA deserve to be rewarded for making the videos and helping people learn PI. I don't make any money off their videos, but I will say this... after feeling my months-long `Deconvolution Frustration' go away, I consider the money well spent! If, at any point during my long winter of frustration, someone had said to me "Your problem will go away if you spend an amount of money equivalent to Warren/RBA's "PI Part-1", I'd have said "Where do I sign??"

The Phoenix Butterfly

I spent last week on an imaging trip near Lassen Peak, in northern California. It's a minor miracle that I got an image of the Butterfly Nebula (IC 1318), given how much forest-fire smoke was in the air. The last several years of Lassen trips have been blessed with clear, blue, gorgeous skies, for the most part. Forest fires are par for the course in the area, however, and it was only a matter of time before the dice came up snake-eyes, smoke-wise. In other words, I was bound to lose a Lassen trip to forest fires, someday. That someday was the August 2012 dark-moon cycle... almost. Despite all the smoke (and clouds), there was enough clear sky to image some of the nebulosity around the star Gamma Cygni. I like to think of this as `a butterfly rising like a phoenix from the ashes of a fire-plagued season'.

IC 1318 d and e and LDN 889, a.k.a. the Butterfly Nebula, imaged from Lassen Peak.
Click on the image for a larger version, or click here for full size.

Only a couple of nights in my week-long trip had worthwhile skies, so I had to abandon my plans to image the Swan nebula (M17) and the Triangulum galaxy (M33), and concentrate on a single object that would be near the zenith for most of the night. An object that appears near the overhead point in the sky (the zenith) is seen through the least possible atmosphere. In this case that meant through the least possible smoke, depending on how the smoke was being blown around by the wind.

During northern-hemisphere summer nights, the region of the zenith is dominated by Cygnus, the Swan. Also known as the `Northern Cross', Cygnus is a grand constellation, one of the few that really looks like its namesake. Right at the heart of the swan is the star Gamma Cygni (a.k.a. Sadr). A good deal of bright emission nebulosity and dark dust can be seen around Gamma Cygni, making it a popular target for imagers. I happened to pick up the September 2012 issue of Sky and Telescope right before my trip, and when I had to pick an imaging target in Cygnus, I thought of the Gamma Cygni area. Sue French and Steve Gottlieb had covered this region in two very nice articles in the September S&T, and Rob Gendler's image, accompanying Steve's article, really got me excited about this area.

According to Steve's article, the `butterfly' is formed by two portions of the IC 1318 emission-nebula complex (IC 1318 d and e), in front of which lies the Lynds dark nebula 889, a mass of dark absorbing dust. The bright emission nebulosity forms the wings of the butterfly, and LDN 889 forms the body, complete with a head that sports two antennae! Like other `emission' nebulae, the bright material glows because of the excitation of the hydrogen atoms of which it's made. IC 1318 is a star-forming region, and ultraviolet light from hot, massive, young stars causes the hydrogen atoms to glow, a little like a fluorescent light tube or a fluorescent mineral. LDN 889 consists of microscope grains of interstellar dust, which absorb the light from the nebula. (The sky over the Lassen Peak region often contained clouds of smoke that dimmed the stars in much the same way.)

The Reading fire, one of the fires that turned the blue sky brown for much of this year's trip.
(Image credit: National Park Service, Lassen Volcanic National Park)

Data Acquisition

On two nights, the sky was acceptably transparent for imaging, and I managed to acquire three hours of data through a clear (`Luminance') filter, in 5-minute subexposures. The last night of the trip yielded a very nice sky, thanks to some fortuitous wind patterns, with the Milky blazing bright and `sugary' overhead. Two of my three hours of data were acquired under that sky.

I would have liked to shoot some color data, but equipment issues put an end to that idea.  Perhaps foolishly, I decided to try and `drive' my mount from my laptop. Maxim DL was able to talk to the mount and order it to slew around the sky, but I kept having a problem with `backwards slews' in the western part of the sky. I'd have shot an additional 3 or 4 hours of data on the final, clear night if I hadn't been trying to debug this problem. Oh well, I'll get it sorted eventually, and at least I got three hours of luminance.

Pixinsight processing:

The data for this image followed my standard Pixinsight processing routine for a luminance-only image:

1. Calibrate subexposures with the BatchPreprocessing script
2. Register and stack the calibrated subexposures
3. Deconvolution to sharpen the bright, high-signal-to-noise-ratio (high SNR) areas
4. Multiscale Median Transform to smooth the dark (low SNR) areas
5. Stretch the brightness values of the pixels with Histogram Transformation and Local Histogram Equalization
6. Shrinking (actually more like dimming) stars with StarMask and Morphological Transformation)
7. Cropping, conversion to standard ICC color profile for web publishing, and saving as JPEG.

Room for Improvement

(Pixinsight geekery ahead...)

Naturally, I would have liked to acquire more data, including color data. Processing-wise, I noticed that some small-scale, `salt-and-pepper-like' noise was introduced somewhere in the processing. This probably happened during the Histogram Transformation or the Local Histogram Equalization, despite my use of a luminance mask. The luminance mask was made in the usual way, by applying an auto-STF to a copy of the image (via HT). I wonder if I should have done a more elaborate intensity transformation when I made the luminance mask, so as to protect the dark areas better, and to get a more effective deconvolution in the bright areas.

After the initial star-shrinking, which worked mostly on the small stars, I tried to build a  new star mask for the larger, more bloated stars, but after a lot of experimentation, I hadn't gotten much of a result. I decided to post the image as-is, but I still dream of dealing with the large stars someday.

Globular Star Cluster M3

Harbinger of Summer - that's how I always think of the globular star cluster M3.

A little less than a hundred years ago, Harlow Shapley measured the distances to the globular clusters, and realized they form a spherical halo around a point that lies in the direction of the constellation Sagittarius. That was the beginning of the realization that our solar system is not at the center of the Milky Way galaxy. Globular clusters like M3 are classic summer objects; I've lost count of the number of times I've passed the short summer nights looking at them, through any number of different telescopes. Constellations like Sagittarius itself are rich hunting grounds for `globs' large and small, bright and dim. A trip to the southern hemisphere has, as one of its many treats, views of the huge, blazing Omega Centauri and 47 Tucanae globulars. Simply put, globular clusters are classic summer `eye candy'. Here's an image of M3 that I shot during the  June 2012 dark-moon cycle:

Globular star cluster M3
8-1/3 hours total exposure time
Evenly split between unbinned R, G, and B, shot in 4-minute subexposures.
Click the image for larger version, or click here for full size.

M3 will always have a special place in my astro-heart, since it was the first object I ever saw through a large amateur telescope. It occurred just over 10 years ago, in April of 2002. I went to one of my first Bay Area observing events, at a local hilltop site. I had my little 5" Meade ETX-125, and I was ready and excited to see some deep-sky objects! To my amazement, Bruce Jensen set up an 18" Starmaster dobsonian next to me. I'd never even looked at a telescope that big, at such close range, let alone looked through one. Bruce showed me M3, which was still rising in the east, and I was blown away. There was no going back - aperture fever took hold of me for good! (I'm lucky enough to be able to enjoy my own views through an 18" scope these days, something for which I'm very grateful, even if I'm mostly using my imaging rig these days.)

M3 is one of the farther-west of the bright globulars, so we see it in the (northern-hemisphere) spring, before the other globs are well-placed for viewing in the summer sky. I'll always associate M3 with April, May, and June, when we're enjoying the galaxies of Coma Berenices and Virgo, taking peeks at globs like M3 and M5, and dreaming of the summer Milky Way...

Acquisition and Processing

I shot the data for this image on three nights during the June 2012 dark-moon period, from the same site where Bruce Jensen showed me M3 through his Starmaster all those years ago. I decided to shoot unbinned R, G, and B images, to try and maximize the resolution of the image, and to avoid having to match the histogram of a luminance image to that of an RGB image. In the end, over the three sessions, I got about 36 four-minute subexposures through each filter. As with my other recent images, I used my Orion ED80 f/7.5 refractor on a Losmandy G-11 mount, with a short-tube 80 refractor and StarShoot camera for autoguiding. My trusty SBIG ST-8300 monochrome CCD camera gathered the photons, with a chip cooled to -15C.

Pixinsight processing followed my usual workflow, with deconvolution (i.e. sharpening) of the innermost core of the cluster, as well as smoothing of the background, done while the image was still linear. A wee touch of HDR Multiscale Transform helped to `un-blow-out' the cluster's core. I pumped up the color saturation in the brightest part of the cluster, so as to bring out the differences between the blue and orange stars.

Pixinsight geekery: The main thing I learned while processing this image was the usefulness of the `Amount' slider in Multiscale Medium Transform's noise-reduction routine. As with many of PI's tools, MMT is powerful yet somewhat hard to understand. I don't really know how to set the parameters for its noise-reduction routines, and I've always wanted to be able to increase the amount of noise reduction ever-so-slowly. Well, I should have guessed that the `Amount' sliders in the noise-reduction settings for each wavelet layer will do exactly that. I guessed at some Threshold values, starting with 4 for the first (1-pixel-scale) layer and decreasing roughly by half as I went from layer to layer. Then, having set those Threshold values, I set all of the Amount sliders to 0.1, and ran MMT. There was just the tiniest little bit of noise reduction in the background sky. (I used a luminance mask to protect the globular's stars.) By moving up the Amount sliders
one little increment at a time, I could get what I wanted: A nice, moderate amount of noise reduction.

Room for Improvement

I could have set the black point a little lower, to suppress the remaining background noise a little better. I could also have tried to dim/shrink the bright, burned-out-looking foreground stars. They're a little distracting. But, since the deep-sky object in question is a star cluster, I couldn't find a good way to make a star mask that didn't include stars from the cluster. So, I just left the stars alone and decided to post what I had. I think the thing I like the best about this image is the halo of very faint stars that makes up the outermost part of the cluster. I doubt I can see those visually, even through a large telescope. That's one of the joys of imaging, going deeper than the eye can see!

The (Leo) Luminance Triplet

For such a dry winter, California didn't have a lot of imaging-quality skies in early 2012. We had some late-season rain and mountain snow, which was good for our hydro balance, but not so good for the spring galaxy season. I finally got out in mid-May, and spent a couple of nights shooting M65, M66, and NGC 3628, otherwise known as the Leo Triplet. Here's the result, sized for a 15" MacBook Pro screen:

This is what's known as a `luminance' image, which means it was shot with a black-and-white (or `monochrome') CCD camera, through a clear (or `luminance') filter. In order to make a color image, I'll need to shoot it through 2 or 3 color filters. If all goes well, I hope to shoot it through Red, Green, and Blue filters before the spring season slips away. The subexposures for this image were each 5 minutes long, and I shot about 50 of them over two nights, for a total exposure time of about 4 hours. As always, the imaging scope was an Orion ED80 f/7.5 semi-apo refractor.

This was also the inaugural imaging run for my new (to me) Losmandy G-11 mount. I got a great deal on it from a fellow Bay Area imager, and I spent the April dark-moon period learning some of the ins and outs. I feel like I can polar align, acquire targets with the Gemini 1 (Level 4) goto system, and I can get pretty good autoguiding. During the nights when I shot these luminance frames, the RMS error on my guider corrections was running about 1/2 pixel in both RA and Dec.

I processed this image in Pixinsight, making use of the new Batch Preprocessing script. Very handy! Many thanks to the folks who wrote that script. Also many thanks to Mike Schuster for writing the PSF Estimation script, which auto-picked hundreds of stars and gave me the parameters of the point-spread function, which I used for Richardson-Lucy deconvolution. (Deconvolution is a sharpening routine that I used to bring out some of the details in the galaxies.) The hardest part of the whole processing workflow was the noise reduction, which I did with Multiscale Median Transform. Once I had the noise somewhat beaten down, I could get a halfway-decent stretched image from the Histogram Transformation. I did a bit of HDR Median Transform, but not nearly as much as I might use on, say, a large bright nebula.

I hope to be able to get out and shoot some RGB color data if I'm lucky; it would be nice to add color to these galaxies!

M33: Two nights at Dino

Here's M33, the Triangulum galaxy:

(There's probably an issue with orientation or `flipping' of the image, but since I've stared at it for so long in this orientation, this is becoming `how it looks to me'.)

This image has me thinking about two `themes':

1) The pleasures of imaging from a nice dark site, like Dinosaur Point.

2) The difficulties of getting good data on M33, the Triangulum Galaxy.

I shot these data on two successive Saturday evenings, October 22 and 29, 2011, from an observing site called Dinosaur Point. It's a boat ramp on the San Luis Reservoir. The reservoir is part of California's enormous system of water projects, which control floods, supply water, and supply electricity. One function of the San Luis reservoir is, essentially, as a giant electrical storage battery. Water gets pumped uphill into the reservoir at night, when electric rates are low, and the water is drained downhill (through generators) during the day.

Dinosaur Point has long been a favorite winter dark-sky site for Bay Area observers. It tends to be too windy during the warm months. But in the late fall and winter, if the `tule fog' from the nearby Central Valley hasn't covered it, Dino can be a very dark site. I really enjoyed setting up there and imaging M33; the sky was nice and dark. One night, in the wee hours of the morning, we even saw the adaptive-optics laser beam from Lick Observatory, shooting towards some object in the south.

It's very important to note, though, that observing access to Dino is subject to some very specific conditions. If you're a Bay Area observer who hasn't been there, make quite sure that you've read and understood the `gatekeeper' access protocol! You can also check the TAC list and the TAC Observing Intents page to see if a gatekeeper is going. Don't just go there without checking all of these details first!

I acquired these data with the same rig as the last couple of shots - my Orion ED80 refractor (80mm f/7.5) with the SBIG ST-8300M CCD camera. I shot unbinned luminance data, and 2x2 binned color data through R, G, and B filters. If I recall correctly, I think I have a couple of hours from each filter. That would make for 8 or so hours of total exposure time, give or take.

I think that M33 has some potential to be a frustrating object for beginning astro-imagers. Typically, I think a lot of us undergo a pattern like this: a) We get a CCD camera during the summer, and by autumn we have a basic understanding of how to use it. b) During the fall, we shoot M31, which is so bright that we can get a decent signal-to-noise ratio over most parts of the galaxy, without too much trouble. c) Next, we say to ourselves `Aha, look what's nearby - M33! There's another big bright galaxy just waiting to be shot!' As it turns out, however, M33 has a lower surface brightness than most of M31, and it's tough to build enough SNR to get a good image. Unless you're using an optical system with a very fast focal ratio, M33 is going to take a long time to build a decent dataset.

This dataset really isn't long enough, but I decided to go ahead and try to process it anyway. I probably won't be able to shoot M33 again until summer or fall 2012, so here's what I've got, so far. With a considerable amount of time invested in Pixinsight, I was able to get something semi-presentable.

Processing in Pixinsight:

I started with the usual calibration routine, using light, dark, bias, and flat-field frames, and I extracted the small amount of light-pollution gradient that one gets at Dino. This gave me linear (i.e. unstretched) luminance (L) and color (RGB) images. These images had the usual background-neutralization and color-calibration corrections applied to them. Then it was time to get a little more from the linear images. First, a bit of noise reduction using the Multiscale Median Transform tool. Then I used the new DynamicPSF module to build a model point-spread function for each image, and fed that PSF into a gentle application of regularized Richardson-Lucy deconvolution. This helped to bring out a bit more detail in the central part of the galaxy.

Then it was time to go non-linear with each image. I did this the easy way: For each image, I did an auto-STF (Screen Transfer Function), and applied each of those auto-STFs to instances of the Histogram Transformation tool. This gave me stretched images that had very similar histograms - and that's just what the LRGB combination tool wants.

If I recall correctly, I did a bit of SCNR (Selective Color Noise Reduction) to take out some of the `galaxy green' in the RGB image, before performing the LRGB combination. I increased the saturation a bit when making the LRGB image, and used Pixinsight's magic Chrominance Noise Reduction routine.

With the LRGB image in hand, it was time to perform two parallel lines of attack, which would later be combined:

1) Compress the dynamic range a bit with HDR wavelets, so as to take away some of the `over-bright dominance' (for lack of a better term) of the central part of the galaxy, and then punch up the contrast with Local Histogram Equalization.

2) Try my hand at the mystical `multiscale processing', a la Rogelio. I split a copy of the LRGB image into large-scale and small-scale components, following the general method of Rogelio's and Vicent's multiscale tutorials. I didn't to anything extra to the smallscale image; I just didn't have the mental energy. But I did some Histogram Transformation (and possibly HDRWT, IIRC) to the large-scale image, brightening the midtones and re-setting the black point. Then I combined everything back together with PixelMath:

a) The LRGB image
b) The LRGB image that had been HDRWavelets-ed and LHE-ed
c) The smallscale image
d) 0.25 * the stretched-even-more largescale image.

Following this recombination, I made a Star Mask (with default parameters), and used Morphological Transformation to dim/shrink the small and medium-sized stars. At that point, I said `Stick a fork in this sucker, it's done. Put it on the blog.'

Room for Improvement:

When I look at this image, it seems to me like it's still afflicted with a bit of `galaxy green', but when I applied an additional round of SCNR to it, it didn't seem to change. Some of the stars also wound up looking a bit pink, but at this point, I'm too tired to fight about it.

Next, there are the big, bloaty stars. These are the bane of all my images. My temptation is to blame them on the small aperture of my telescope. An 80mm scope will have a big, fat point-spread function, and if I want tiny stars, I'll need a bigger scope. That's probably true, to some extent, but I'll bet it's not the whole story. I am beginning to suspect that the big, halo-y stars are a consequence of the fairly severe stretching that the image has undergone. M33's dim, and it takes a lot of stretching. This probably brings the outer parts of the PSFs up to an objectionable brightness. With a longer total exposure time, I could probably get the faint parts of M33 to show up without as much stretching. (Of course, this raises the question of whether those outer portions of the PSFs would show up, too... hmm...) I'd love to figure out how to shrink those stars, so that it looks like I used a bigger scope. After a lot of fiddling around with Star Mask and Morphological Transformation, however, I haven't found a way. It remains a dream.

With more integration time, I think I could show more of the faint outer portions of M33. I'd love to get in night after night on this object, and really punch out every part of this galaxy. M33 is full of resolved stars and HII regions like NGC 604. I often think of M31 and M33 as the closest thing we've got the Magellanic Clouds up here in the NoHem, and it would be nice to make the deepest, sharpest images of them that I can.

Naturally, many people have gotten some very nice, very deep images of M33. One of my favorites is this one by Stephane Guisard, because he shot it from the Atacama region of Chile - exactly the `wrong' place to get a good image of M33. Shows you how good places like Paranal are! And of course, there's a nice Hubble image of NGC 604, the most prominent star-forming region in M33. (In my image, the way I've got it oriented, NGC 604 is down and to the right of the galaxy's center, above two prominent, bloated orange field stars.)

M31 2011

A major event for California observers is the yearly California Star Party, or `Calstar'. My Bay Area buddies and I look forward to it each year. In 2011, I worked on M31, the Andromeda galaxy. M31 is a classic autumn object, rising in the evening and riding high for much of the night. I'd spent previous Calstars observing it in detail visually, and this year I wanted to get the best possible RGB imaging data that I could.

Happily, I'd just taken delivery of a new SBIG ST-8300M CCD camera, and I was eager to try it out. (Many thanks to Sam Sweiss at Scope City for helping me get it! This also meant that I could give the QSI 583 back to my Cilice friend, enabling him to image at Calstar.)

SBIG ST-8300M and Orion 2" LRGB filter wheel

Like the Lassen run in which I imaged the Eagle nebula, this year's Calstar was blessed with good weather. I got in a solid 3 nights of clear, dark skies, and managed to get several hours each of unbinned R, G, and B images. Calibration, integration, and processing in Pixinsight gave me this image:

The Andromeda galaxy (M31), approx. 15 hours total exposure time

After talking about star shrinking in yesterday's blog entry, I went back to RBA's M31 star-shrinking tutorial, and worked the problem some more. The image above has had its `medium-sized' stars dimmed, following Rogelio's tutorial. As he pointed out, M31 is not in the plane of the Milky Way, and thus doesn't need a lot of star reduction, but I think it helps the overall appearance of the image.


Room for Improvement:

I'm fairly pleased with the star shrinking / reduction / whatever you want to call it, but I need to double-check that I haven't affected the starlike nuclei of M31, M32, and NGC 205 too much. I also really want to figure out how to reduce the brightest and most bloated stars, like the blue one that appears to the lower left of M32, and the orange one that appears to the upper left of M32. As I stretched the image, these got so big, their halos make them look like `candidate satellite galaxies'. I still haven't figured out how to make a star mask that isolates only the brightest stars.