The Starry Night, 39
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01/03/2011. Happy New Year to you, too. "Son of Tom Swift's Amazing Telescopic Suitcase" made its debut tonight, replacing the huge inverted Tupperware bin that had been serving as dew, frost and cold air protector for the notebook computer. This new case is the cheap, lightweight ABS case I found tucked into the end of the Losmandy leg-shipping box while packing things up in Tennessee last October. I removed its single layer of pluckable foam in favor of a heating pad, used a couple of Forstner bits to make openings for power, USB, ethernet, and phone lines, determined how far closed the Aspire One can be without hibernating, cut foam chocks to keep it from closing farther than that, tucked everything inside (a cozy, appropriate fit) and voila: I think this smaller, warmer space is probably good to -20°F or lower, wind or no wind. I am more concerned about the little netbook baking in the waste heat of its own circuitry than freezing, which is part of the point: in anything but really cold weather, it should be able to stay warm on its own.
Desktop of the early 21st Century
This evening, I took aim at IC 342, the third largest
(in apparent size) galaxy in the northern half of the sky and the nearest galaxy
outside the local group. Note that despite its size and proximity, Messier
overlooked it. The stars and dust of the Milky Way hid
it from discovery until 1895. I remember reading about this galaxy in S&T
many years ago (in a column that also featured Kemble's Cascade, I believe).
I remember looking for it in small glass. It
did not look at all like this:
IC 342, a spiral galaxy in Camelopardalis
When I started, I thought I'd do a simple 45 minute RGB run, then opted to add luminosity, then opted to add more. Actually, when I started I calibrated on Deneb, then let the telescope do a meridian flip en route to the night's first target, lined up on what I thought was IC 342, and wasted the first couple of frames trying to make sense of what I was seeing. I was seeing a field a couple of degrees away. Also, I need a fresh dark and will grab one while I get lined up on the next target and recalibrate the guider. In processing the images, I had to compensate for a good bit of field rotation. So despite doing a fresh polar alignment, I was still off by some distance. Guiding was on the 10.7 magnitude star just left of the nucleus, near the lower end of a straight chain of stars.
Before beginning tonight, I neglected to reset the meridian in anticipation of the telescope's motion, and though the target was still high and the sky clear, I needed to end the series of luminosity frames to avoid bumping the camera into the pier.
For the second target, I reset the meridian east by 3 hours before slewing to IC443. I missed by the usual pier-flipped, unaligned, bugger-all distance and walked the camera over to the target. I shot RGB triplets (900s and 300s), then H-a until dawn.
There's more good h-a data in tonight's collection, so consider that a quick look. Eventually, I need lots of color data on the supernova remnant itself. There might be some rainbow-hued shock fronts in there. Tonight's short color frames were mostly for the stars.
CCD Inspector reports a lot of misalignment but relatively little tilt of the detector with respect to the optical axis. It's irritating, but I'm not sure what to try to address this. I'm also not sure that the reported miscollimation is a significant problem at my current level of expertise, using the relatively small chip in the ST2000XM. Anyway, I'm not touching anything until the next cloudy spell since I'm expecting to do multi-night exposures and can do without the need for extra flats. Let's see what happens overnight.
Clouds are what happened overnight. I woke to an altostratus overcast, with some breaks. I shot sky flats in h-a and L, then T-shirt flats in both as well. In each case, I shot sequences of 10 frames to average. There may be some genuine sky flats to use, too, judging from the appearance of some of the overnight frames. I'll use what I can from the overnight take, and if the forecast is correct, shoot more of both targets tomorrow. Here's a version with 15 H-a frames, some of which are pretty weak owing to the clouds, but all of which help:
IC 443, a Supernova
remnant in Gemini
Keeping the netbook warm. I installed Speedfan on the notebook which lets me monitor the HDD and core temperatures. What I'm more concerned about is the screen temperature, but there's little chance of monitoring that. FWIW, with the air at 30°F, the heating pad on medium, the case halfway closed, the notebook's HDD is running 31°C and cores (why plural, there is only one, no?) are 36°C. A little later, 30°C and 36°C, with the case freshly closed after being open for a while and the air down to 27°F. After ten minutes with the case all but latched, the HDD has warmed to 31° and the cores to 38°. Within 20 minutes of starting the overnight run on IC 443, the HDD heated up to 34°C and the cores to 41°C. A few minutes after that, I saw 35°C and 43°C. The air temperature by then was down to 21°F. I squinted at the trends, considered the possible problems, then turned the heating pad to "low" and let the box spring a little farther open. I'd rather run the computer a little cool than too hot, and it doesn't look like there's any danger of it getting too cold tonight. Ten minutes later: 34°C and 41°C. Twenty minutes after that: 33°C and 39°C. And seven hours later, in the morning: 34°C and 38°C with the air at 21°F. No wind last night, much frost.
This is all very interesting, but I don't know what my HDD and Atom CPU run under normal, room temperature conditions. I see online references to Atom CPUs running as hot as 80-90°C without concern, so the CPU temps I'm seeing are certainly not a problem. The netbook's CPU load is only 2-15% when guiding, controlling the SBIG CCD, and being operated remotely via wifi. (Just now: 34°C and 40°C under ordinary duty indoors.)
01/04/2011. Adding h-a data to IC 342 lights up the many star-forming regions in its spiral arms. Robert Gendler's description (never mind his deep, smooth, sharp image) of IC 342 as the nearest starburst galaxy moved me to take a look with the narrowband filter. Fine inner structure near the core is more clearly seen, including a vertical dark lane and an inner ring of star formation. My images are not smooth enough, sharp enough, or large enough to show it in detail, but it's satisfying to record such fine structure at all. Tonight is twenty Fahrenheit degrees warmer than last night (mid 40's vs mid 20's). The Peltier cooler is having some trouble holding the -40° setpoint. The chip temperature fluctuates between -37° and -40°.
I've started another long series of IC 443 because I know from experience that it rewards every additional hour of h-a exposure. I'm pretty sure that as midnight turns to morning, the temperature will fall a bit. It did: at 2:30AM, the cooler was holding -40° with "only" 94% power. This time, the sky stayed clear until the target dropped too low in the west:
IC 443, Supernova Remnant in Gemini
01/06/2011. The bulky aluminum counterweight — ever heard that phrase before? "Aluminum counterweight"? I mean except maybe here? You can imagine why not — threatened to get in the way during slews and tracking. After my misadventure trying to replace it with steel, I tried brass. Third time's the charm. The chop saw made quick work of that metal. The bar is 1.5 inches closer to the optical axis than the aluminum version, and c'mon, it's brass. Everybody knows that official astronomical equipment uses brass.
Later that same day... The connector between the CFW-8a and the ST2000XM body has always seemed vulnerable to me. It's a big piece of plastic held in place by two small screws. Bump it in the dark or steer it into the pier, and there's a good chance that you're out of business. Tonight I extended the idea of the counterweight and its bracketry to include a metal sheath around this connection. You can still get to the guider output port (which I have not used in ages). I won't say you can't hurt the data connection now, but I do think you'd have to work at it some.
Handwaving is free; more pix to follow. There on the left is the SBIG catalog shot of the filter wheel. See the cumbersome connector at the end of the cable? Mine's actually a little longer and less solid than the one shown. It's held sticking out from the side of the camera by two small screws, the same sort off attachment that you'd expect to use to attach a serial printer to a computer port (yes, Virginia, there were printers before there was USB). It's a long way from "robust," and even further from "sturdy." What I've done is encased it in a metal tube and bolted the tube to a piece of flat bar stock which is, in turn, bolted to the side of the camera. To damage the connector, you'd have to hit it hard enough to bend or loosen the bracket. The critical bits are not indestructbale, but they're safer than they were:
The connector in the former photo (mine's black) is at left, inside the aluminum cylinder; the CCD detector is behind the fan, and since the CCD chip is on the optical axis, you can see that the center of mass for the case, circuit boards, and connections is considerably off-center. The brass counterweight greatly reduces the (admittedly slight) tendancy of the camera to rotate about the optical axis. The bracket also makes a good place to wrap cables when toting the OTA with camera attached.
For the record, my CCD is an ST2000XM with serial number 20405677XM. Here's what SBIG has to say about its chip: "The KAI-2001M CCD is used in all ST-2000XM cameras produced in 1993, up until July, 2004 (serial numbers beginning with 20301xxx and ending with 20406xxx). The KAI-2020M CCD is used in cameras beginning with serial numbers 20407xxx. " So it's the KAI-2001M chip, whose quantum efficiency is shown in red in this SBIG graphic:
Not to say that there aren't some much more sensitive cameras out there, but I'm relieved. I'd thought I had the earliest chip rather than the chip of the middle-path. At 650nm, for example, my camera is about 50% more sensitive than I had believed (34% vs 22%). Overall, that red curve isn't bad, so luminance, blue, and green frames especially shouldn't suffer much at all compared to "hotter" cameras. And since I'm wedded to adding red anyway... it'll do unless several thousand bucks fall unexpectedly from the sky.
It's true that the noise is higher than the latest chip — de nada, just run it a few degrees cooler and keep your darks up to date.
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