Sunday, January 26, 2014

 

More Stellar Fingerprints


Unk doesn't always live up to his New Year’s resolutions. At least not right away. The one about giving up the dadburned cigarettes took dern near a decade to implement way back when. I am off to a pretty good start with 2014’s Big Resolution, though, “Get out and observe at least once a week, weather permitting.”

As y’all may know, I can do very little amateur astronomy of any kind from home. An occasional look at the Moon from the porch or my annual Christmas Eve peep at M42 is about it. Too many lights, and, worse, too many trees, huge old oak trees that block the sky in every direction. If I want to see pea turkey, I have to get to the club dark site.

When I was working 12 hours a day five (or more) days a week, that was a problem. The best I could do was a couple of nights a month. I worked a lot of weekends toward the end of my engineering gig, and by the time I got home I was often too tired to think about loading up a mess of gear and battling traffic, even for some blessed hours under the stars. That’s over, now. Since I am retired (well, semi-retired), there is nothing to keep me from visiting the Possum Swamp Astronomical Society dark site at least weekly. Other than the cotton-picking weather, that is.

So it was that I decided to head out last Saturday evening. The weather was perfect. Only buzzing bug in the butter? There would be a near full Moon in the sky a couple of hours after sundown. That was OK, I’d find something to do. I could shoot Jupiter, of course, but I didn't think the seeing would cooperate enough for that to be worth fooling with. Well, then, it sounded like an RSpec night.

As I wrote a couple of weeks back, I’ve begun playing around with spectroscopy using Tom Field's RSpec software and Robin Leadbeater's Star Analyser diffraction grating. The grating turns my humble little ZWO planet cam into a spectrograph. A low-resolution one, sure, but one capable of showing a surprising amount of detail in stellar spectra, nevertheless. The Moon wouldn’t do a thing to prevent me from imaging stellar spectra, but seeing was another matter. The consarned Clear Sky Clock (Chart) forecast seeing to be putrid at best. Still, I figgered giving it a go would be more fun than sitting home watching reruns of Wonder Woman on the cable TV.

According to The Cat, he did all the work...
At 3:45 p.m. it was time to load up the good, old Toyota, Miss Van Pelt, for the journey west. What was different from last week? The telescope. Last time, the goal was lunar and planetary imaging, and I thought my older C8, Celeste, an Ultima 8 OTA, was a better bet than the Edge 800. The reason being the older scope is set up for a JMI Motofocus, which I figgered might make it easier to focus the Moon and Jupiter. Turned out not to be the case. In the eight months I’ve had the new SCT, I’ve become proficient at manual focusing again. I may set the Edge 800 up for Motofocus one of these days, but I am not missing it too much yet.

I did miss having Mrs. Peel on the observing field with me last week, no denying it. One big reason for that, I must admit, is that she is just so doggone pretty and all with her slightly greenish Takahashi-white tube. I’ve loved orange C8s and black C8s and silver C8s, but for me white is still the color a telescope tube ought to be. Guess I’ve never forgot the look of the Cave and Unitron tubes of my youth. Appearance ain’t everything, of course, and there’s more to Emma than just that. Optically this is the best C8 I have ever owned with the best star test.

“What makes an Edge different from a regular C8, anyhow, Unk? And how is it different from Meade’s ACF? I’m confused.” Well, of course you are enthused, Skeezix. Oh, you’re cornfused are you? Well I can edumacate you about the new SCTs in short order.

Meade’s ACF optics got there first, coming ‘round about eight years ago in the form of the RCX SCTs. The RCXs’ optics were different. In addition to having focal ratios of f/8, the basic optical design was changed. Instead of using a spherical or near spherical secondary mirror, the RCX used one that was a parabola. The goal was to reduce coma, which is one of the two things that make stars at the edge of an SCT’s field look more like comets than stars. An f/10 SCT has coma equivalent to an f/6 Newtonian. Not bad, in other words, but there.

Mrs. Peel...
As you may know, the RCX was plagued by Meade missteps, starting with spurious claims, including that the telescope was some kind of Ritchey Chretien design and that the secondary was a hyperbola, and ending with horrendous quality control problems. Still, the idea of a reduced coma SCT was a good one, and the basic design, an aplantic SCT, not an r/c, was a sound one. It has lived on at Meade in the form of the f/10 ACF (“Advanced Coma Free”) SCTs and the new f/8 LX850s and 600s.

As has been the case for over 30 years, when one SCT maker does something, the other follows suit; that is the telescope arms race. Celestron was at this time probably better positioned to respond than Meade would have been if the situation were reversed. While Meade (who was bought out by the Chinese last year) was struggling financially, Celestron, who’ve been owned by the Chinese firm Synta for almost a decade, seemed to be doing well.

They were certainly doing well enough to one-up the Meadesters. It wasn’t long before Celestron announced the Edge series of Schmidt Cassegrains. Not only would these telescopes, which included 8, 9.25, 11, and 14-inch OTAs, correct for coma, they would, additionally, flatten the naturally curved SCT field, taking the final step to fix Schmidt Cassegrain edge-of-field performance.

Celestron took an entirely different path to an improved SCT than Meade. The Edge’s basic design is almost unchanged. The back-focus distance, the distance from the rear port to the focal plane been altered slightly, but that is it. To fix coma and curvature, Celestron incorporated a two-element optical corrector in the baffle tube. And, though it took them a while to do it, the company also introduced sophisticated add-on focal reducers for the Edges to bring the f/10 scopes down to f/7 (but we are still waiting for one designed for the Edge 9.25).

So what is the Real Deal on these telescopes? The Edges’ images are noticeably better at the eyepiece field stop than those of the ACFs, but it is not like night and day. The images in the Meades are very good indeed, with the 10-inch ACF of my friend Mike Harvey having some of the best SCT optics I’ve seen. Any advantages the Celestron has may be masked (for visual observing) by aberrations in your eyes or your eyepieces. In fact, you may find you don’t need either the Edge or the ACF, that you don’t need the More Better Gooder.

.
I will be the first to tell you that visually the Edge 800 is a dream. You may have heard that using one is like looking through a superbly corrected 8-inch refractor. That is true, but what if, like Unk, you don’t do much visual looking? And when you image, you often use cameras with small chips like planetary cameras or the Mallincam deep sky video cams? The Edge (or ACF) improvements are at the field edge, and a small chip camera doesn’t see that. Same goes if you are mainly a planetary observer. You are concerned with the field center and don’t give a hoot ‘n holler about the periphery.

And yet, and yet… While I don’t always take advantage of the innovations inherent in Mrs. Peel’s optical design, I still love her and have a hard time making myself use any other telescope. I’ve always loved C8s and she is the best C8 I have ever loved. She’s the best in part because of the care that was obviously exercised in her construction. Her finish is beautiful and flawless, and so are her optical coatings. As above, she shows a terrific star test. And I haven’t even mentioned her vents that speed cool-down or the mirror locks that eliminate mirror flop. In my opinion, if you are after a new SCT you owe it to yourself to at least consider the Edge.

Hokay, glad we got that out of the way. Where was we? Oh, yeah. I’d just loaded Mrs. Peel and the VX mount into the 4Runner, shut the tailgate, and made tracks for the PSAS’ little patch of dark sky heaven. I’d put out an announcement on the club's Facebook page (no more Yahoogroup for we-uns) that I’d be doing spectroscopy and would be  happy to have company. I didn't think I’d get any, though, it being a near full Moon. Unlike Unk, I would guess most of our members who want to observe Jupiter can do so from home.

And, indeed, not a soul other than my favorite yellow tomcat, the airfield’s mascot, greeted me upon my arrival. He was eager to “help” me,  and we soon had Mrs. Peel on the VX, the camera and the flip mirror on her rear port, and the computer fired up. As was the case last week, there was not a chance of clouds, obviously. Was it cold? Unk thought it was, the temperature having PLUMMETED into the mid 40s shortly after sunset. Luckily, this time I was prepared with a good sweater, a leather jacket, and a bunch of chemical hand-warmer packs.

As far as the observing run itself, ain’t much to tell. I was using the ZWO color cam at f/10 through the flip mirror. I mashed the buttons to go to the first star, fine tuned the aim a mite with the reticle eyepiece so the star and its spectra would be centered on the ZWO’s 1/3rd inch chip, flipped the mirror down, and headed to the computer.

At the computer, I fired up RSpec, clicked the “live camera” tab, positioned the star and its spectra so the star was on the left and the spectra on the right (the program has an image rotation tool to make that easy), and, voila!, there was a live spectrum on the program display. I did one thing differently this time. I thought the spectra I got on my initial outing looked a little thin, so I upped the exposure a wee bit. Not much. Even at 80 milliseconds the ZWO is sensitive enough that I was on the verge of overexposing bright stars.

Sirius...
Then it was just a matter of getting stars in the can. Since I am still just getting started with this stuff, I stuck to bright suns, the same stars I shot on my previous RSpec run: Rigel, Capella, Betelgeuse, and Sirius. The seeing wasn’t perfect, but it was at least a little better than on the previous RSpec run. Sirius was a little low and twinkling madly, but its spectrum seemed at least close to “good enough” to me.

“So, everything went smooth, no hiccups, no disasters, eh, Unk?” Hey! This was an Uncle Rod observing run. It wouldn’t be normal if something didn't go wrong. The culprit this time was the hand control extension cable I bought years ago for the CG5. Its flat telephone style cord gave up the ghost completely yielding lots of “No Response” errors. I ordered a new and better one from Jim Henson at Scopestuff as soon as I got back to the Old Manse, since the cords on Celestron’s current hand controls are so absurdly short that you really cannot get by without an extension.

Anyhoo, I persevered despite the HC cable problems, got at least two sequences of each star, and took a break. My four-footed friend had trotted back to his home in the nearby hangar. It was dark and it was lonely and it was cold. Did I get spooked? No, not really. The reason I decided to throw the big switch was because I didn't really have an agenda left. The old Moon was on the rise, which limited my options. Given the way Sirius looked onscreen, trying for Jupiter would have been an exercise in frustration.

If I’d had a buddy or two on the field with me, I’d no doubt have hung out shooting the breeze and messing with the scopes a while longer, but I doubt the run would have lasted much longer even then. By the time I’d finished packing, Luna was up over the horizon looking in on me, lighting the field like a searchlight. I made tracks for the Old Manse.

I was back home in plenty of time for Svengoolie, who was showing yet another 1950s SciFi “masterpiece,” The Mole People. I watched it, but it is really almost on the too freaky side today. It is just freaking odd, with its introductory lecture by a nervous English professor and an anti-Shangri-La plot that involves albino Sumerian mole people and a pretty girl. The film’s ill-concealed viewpoint, that the underground civilization is just another inferior non-western culture, tends to make us a little uneasy today, too.

Rigel...
During the commercials, I must admit I had a peep at my spectra. Just looking at the .avi files with Windows Media Player, I was somewhat encouraged. There seemed to be detail in the spectra, more than there was in the ones from my first attempt, I thought. Also, when I’d been shooting the video, the real time spectrum display seemed to indicate I was picking up absorption lines. But I was really too distracted by the task of operating the scope to pay close attention. I’d only know for sure how good or bad they were on the morrow when I ran ‘em through RSpec.

After my customary Sunday morning bowl of porridge, I pulled out the laptop and got down to work. Why did I choose to process the files on the laptop rather than on Chaos Manor South’s famous kitchen workstation, a high-powered Toshiba wide-screen desktop? Using what is essentially a video camera yields large .avi video files. At the ZWO’s highest resolution, which is what I habitually use, a short sequence is a gigabyte in size and transferring a dozen or more of those files to the desktop is a pain in the you-know-what.

Maybe it’s a good time to talk about what you can use with the Star Analyser grating other than a planetary webcam-style camera like Unk’s. If you’ve got a still camera of some kind you can somehow hook to the grating, that’s it. RSpec seems to be very good regarding the file types it will accept. You can even use that new DSLR you got for Christmas. Adapters are available for purchase through Tom’s website that allow you to use the grating, which comes in a standard, threaded, 1.25-inch cell, with your camera either by screwing it onto the lens, or directly to the camera in a T-mount set up.

Another popular option is Meade’s no longer produced DSI series of camera. While they've been gone for a while, many were made and it’s easy to find one of these basic CCD cams for sale in used venues. Certainly, you can use a big-boy camera like an SBIG with RSpec, too. RSpec can be configured to work in conjunction with CCD camera control programs like CCDsoft.

For me, though, the ZWO is easier to use. With video coming straight into the program, I can see the spectrum live on the computer display (remember, this program’s subtitle is “Real Time Spectroscopy”) and it’s obvious whether or not I’ve got everything working more or less correctly. Also, being able to take many frames and stack them with RSpec’s “Average” function makes it easier to deal with the punk seeing we get this time of year. Yes, even way down in the Swamp, seeing can be a problem in the depth of winter, especially a nasty winter like this one has been.

The ZWO...recommended!
I could see how just how bad the seeing had been when I began looking at my Rigel and Sirius sequences on RSpec. Their graphs moved up and down in “amplitude” like crazy. Not to worry. I clicked the Average button and their spectra, their graphs, settled right down. OK, time to calibrate, to change the pixel scale of the graph to angstroms (or nanometers if’n you prefer) so it would mean something. I’d just…I’d just… Suddenly Unk realized he was in over his head. I had absolutely no idea where the hydrogen beta line was and couldn’t click on it to complete the calibration process.

The more I looked at my spectra, the more confused I became. They looked different from the examples in Tom’s videos, and attempting to calibrate by guessing at the h-beta line led to crazy results. There was only one thing to do, run crying and screaming to Mr. Field and see if he could make heads or tails of my .avi files.

Indeed he could, and far more quickly than I could have dreamed of or asked for. In short order, Tom got me going again. Part of my problem was seeing. It was, if not as poor as on my initial RSpec outing, bad enough to complicate things. What was also confusing me was that I was seeing the second order spectrum peeking in on the right. Once Tom educated me about these things and a few other factors and I was back on track. Next time I will try to work under better seeing and see if I can eliminate that intrusive and confusing second order spectra.

Anyhoo, after Mr. Field got me calmed down, seeing straight, and thinking right I was able to successfully calibrate my spectra and pick out the Balmer Series lines and other things. Again, what I mostly think will help is better seeing—and more experience, of course. I’ve still got a lot to learn, but I sure am having fun doing it.

Though my results were a little indifferent this time, muchachos, they weren't that bad, I thought. MOst importantly, I’d had fun, learned a lot, and, wonder of wonders, found something I could do on a winter’s night with the full Moon in the sky and the jet stream overhead. You cannot beat that with a stick, muchachos, you cannot beat that with a stick.

Nota Bene:  One of the things I love about being an astronomy writer is that I get to do a lot of traveling to clubs and star parties to give talks. I know, however, that some clubs just can't afford to fly me in and put me up. I would much rather address your club in person, but if that is just not possible, I have a DVD video of my Herschel Project presentation I can send your way. It's not Cecil B. Demille quality, and I can do a better job live, but y'all may like it anyhow. Just ask...

Next Time: Atlas Rides Again…

Comments:
Great to see some articles on spectroscopy from you...amazing to see how you can do some real science with not too much gear or expense. Something I have been interested in for many years and your articles may just be the boost I need to get into it seriously here in New Zealand.

 
Uncle Rod, (how) does RSpec take into account the spectral sensitivity curve of the camera?
 
Hi Ivan... If I am understanding your question correctly, it's taken into account because of the calibration you do...
 
It appears that the calibration based on the user's identification of a known wavelength calibrates the camera pixels into wavelength units. And from what I have seen (I don't have the program), this calibration seems to do only that. If the user wants to identify absorption or emission lines, this is all that's needed. But the camera's spectral sensitivity curve affects, and largely determines, artifactually, the shape of the star's spectrum displayed by the program as a plot (intensity vs. wavelength).
 
Ivan, seeing as how I am very new to the program, I think you'd be better off asking the author, Tom Field. He can be contacted through the RSpec website, or on the RSpec Yahoogroup.
 
Thank you, Uncle Rod.
 
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