Sunday, January 12, 2014
The Colors of the Stars
If nothing
else, muchachos, last Friday night’s expedition to the Possum Swamp
Astronomical Society dark site proved two things. First, that Unk is practicing
what he preaches. Second, that my little ZWO camera really does seem to be a jack-of-all-trades.
Is there anything the inexpensive ASI120MC can’t
do?
Let us begin
with Thing One. If you’ve been reading the Little Old Blog from Chaos Manor
South for long, you will recall my dark site expeditions have usually been on
Saturday nights. In the past, that was because of my heavy work schedule.
Saturday was the only evening where I could be sure I wouldn’t be too dog-tired
to lug all the gear out to the dark site.
In retirement,
I continued with Saturday as dark site night because, well, because it always
had been. So, I was distressed to see the last weekend of the current New Moon
cycle was forecast to be cloudy. On the other hand, Friday night was supposed
to be clear until 11 p.m., at least, if cold. That’s what the new version of my
most used weather app, Scope Nights said,
anyhow. Friday night, huh? Well, why not? It would be icy, sure, but I’ve
observed in upper 20s weather before and it had been a long dry spell, since early
November, since I’d got much astronomical work done. And there was that pledge
of mine, that aphorism, I’ve been trying to live up to: “If it ain’t raining, head to the dark site.”
Friday
dawned, as predicted, clear and cold. Miss Dorothy and I had a little running
around to do, including picking up Unk’s
new glasses. Yep, after years of denial, Unk had to admit the time had come
for him to start wearing glasses full time. On my first visit to an eye doc in
my life, I learned I now had considerable astigmatism. Hearing that, I wondered
whether that’s what had made visual observing seem not as good as it used to be
the last five years or so. We will see.
 |
| Four-eyed Unk... |
In the
course of picking up Unk’s specs, visiting Waffle House (cheesy eggs, raisin
toast, grits, bacon), and doing a couple of errands, Unk’s resolve about Friday
night began to falter. If it was in the dadgummed 40s at noon, what would it be
like after sundown? And there were some clouds, mares’ tails, scudding across
the sky in advance of Saturday’s front. Maybe it was shaping up as more of a Rebel
Yell and cable TV night than a dark site evening? Nope. At three p.m. the
clouds had left. No excuses. Load up the Toyota and get ready to go.
With it as
chilly as it was, dipping into the low 40s as the Sun began to sink, I was
happy the loadout for Miss Van Pelt, the 4Runner, was relatively light: Edge
800 C8, VX mount and tripod, camera case, one big gear box, Toshiba laptop,
small case of 1.25-inch eyepieces, three jump start batteries and that was
purty much it.
What was in
the camera case? My ZWO planet cam.
Despite Jupiter being high in the sky reasonably early, and a pretty, if
slim, crescent Moon in the west, I didn't plan to shoot any Solar System
objects on this run. Nope, I was out to do spectroscopy
with the ZWO and a new (to me, anyhow) computer program RSpec.
Spectroscopy
is not something I’ve talked about much—if at all—here, but it is something Unk
has been interested in for a long time. I’ve taught spectral classification,
figuring out the types and compositions of stars from their absorption spectra,
and spectrometry for years and years, but I’d never taken a spectrogram (an
image of a spectrum) with my own camera and my own telescope, though I used to
dream of doing that as a sprout.
Way back in
the vaunted day, in the 1960s, Edmund Scientific sold a stellar spectroscope, a
widget you inserted into your focuser, which would let you see the spectra of
stars. Presumably with enough resolution on bright stars to let you make out
their absorption lines, the dark lines that represent the elements in the
stellar atmosphere. How well did the Edmund
work? I have no earthly idea. I was fascinated by the idea that you could use
the thing to figure out what stars were made of, but at a price of $42.50 (at least 250 bucks in today’s small dollars),
I sure couldn’t pay the fare to find out, nor could any of my mates in our Backyard
Astronomy Society.
I didn't
think much about spectroscopy as an amateur pursuit much over the intervening
decades. That was part of my work as an astronomy educator, not as an amateur
astronomer. Sure, there’d been some growth of interest in decoding the
signatures of stars, but the “inexpensive” spectroscopes a few outfits began
offering were still in the 3K and up range. Too much for me when I wasn’t
convinced one could work well enough with small scopes to show much in even the
 |
| Edmund Scientific circa 1966... |
There things
stood till a few months ago when I got an email from Tom Field. His name was familiar to me as one of the folks leading the
charge in the spectroscopy area of the “scientific contribution” side of
amateur astronomy. Tom offered to let me try his program RSpec and a diffraction grating (used to produce spectra with your
camera), a 100mm grating called the Star Analyser SA-100. I was a little skeptical about my ability to make it all work,
but Tom insisted I could, so I said “yes,” though I had my doubts.
Naturally, we
had unrelievedly cloudy skies for months after I got RSpec. I was able to play with it indoors thanks to a picture of
Vega and its spectrum Tom sent me, and I was encouraged. The program installed
easily, was professional looking, and seemed completely bug-free. I could produce
a spectrum (in the form of an X-Y graph as per normal for electronic imagers in
these latter days) from the image of Vega without much hassle. I still wasn’t
sure about making it go in the field, however.
Before I
could think about doing that, I needed to pick a camera to use with the grating
and RSpec. What I had on hand was an SBIG
ST2000 CCD, a Mallincam Xtreme, a Canon DSLR, the ZWO, and my old Meade DSI.
Tom suggested the Mallincam might be a good place to start, but I demurred.
That would mean I’d have to involve a frame grabber and software to convert the
Xtreme’s composite video to digital form. As for the still CCDs and the DSLR? I
thought any of them might be a bit of a handful for this application. Well,
what about that new ZWO? People were using them for everything from the Moon
and planets, to hydrogen alpha imaging of the Sun, to deep sky imaging. Why
wouldn’t it work as a spectrograph?
It appeared
it would work with RSpec--the program recognized the camera/driver, at least. As
soon as I plugged the camera into the PC, RSpec’s video module picked it up,
began displaying its video, and indicated it was ready to record. I got out
under the stars shortly thereafter, and was again encouraged to believe RSpec and the ZWO would be a great
combo. Only fly in that there ointment was that clouds intervened before I
could really get everything sorted out and start taking spectra.
And so, back
to last Friday night. All loaded up, off we went. As me and Miss Van Pelt
navigated past the shopping malls, I was reminded why Saturday night is a
better choice than Friday this time of year. I needed to set out by 4 p.m. to
get to the site before sundown, and the Friday after-work traffic was just
freaking nuts by then, with my normal 45-minute trip to the dark site taking well over
an hour. On the way west, the cloud patches I was seeing began to concern me, but the
closer I got to the private airfield we use for observing, the clearer it got.
 |
| Pretty little Moon... |
The sky was
almost 100% cloud-free when I pulled onto the field, which was a good thing for
observing, if not such a good thing for comfort. I glanced down at the
temperature display on the dashboard of the truck. 39F already and the Sun
wasn’t even down yet. When I got out, it became abundantly clear this was not a
night for slowly layering on clothing. I grabbed my big red coat, the one that
helped me survive Bath, Maine one cold winter, put it on, and zipped it up.
As I was setting
up, I was all by myself except for the airstrip’s mascot, a great big yellow
tomcat. I wasn’t overly surprised. It would be below freezing shortly, which is
awful cold for us Southrons. Quite a few of my PSAS buddies were still doing
holiday trips and recovering from New Year’s Eve, too. The saving grace
temperature-wise? Absolutely no wind. Not at ground level, anyhow. The upper
atmosphere (and thus the seeing) was a different story, as Unk was to find out
before long.
Got Mrs.
Peel, the C8, on the VX. Not much to report there. Given the cold and the
weather forecast, which called for clouds before midnight, I didn't think I’d make it much beyond ten or eleven o’clock,
and so didn't go to the trouble of setting up NexRemote.
One thing I did do was connect the NexStar Plus hand control to the mount via
an extension cable. Why Celestron makes its current hand control cords so fraking
short I have no idea. But take it from moi,
they are short enough to be nearly unusable. I’d had some errors (No Response
16 and 17) the last time I’d used the extension, so I’d given its contacts a
good cleaning with alcohol before I’d left home. Aside from a momentary glitch
at start-up, the extension worked well, and it sure was nice to have the HC
right at the computer.
As for the
scope itself, the setup on the rear cell was the same as what I use for lunar
imaging: Meade flip mirror screwed onto the rear port, Meade 12mm reticle
eyepiece in its focuser, and the ZWO in the camera port. The only difference
this time was that the camera went directly into the flip mirror without a
Barlow. I figgered a smidge over 2000mm would be enough focal length.
 |
| Junior Telescope Operator... |
Why did I
use the flip mirror? The ZWO’s chip is small, 1/3-inch, and even without a
Barlow and with accurate go-to, I thought the flipper would make object finding
a lot easier. With the flip mirror in place, I flip the mirror down, center the
target in its eyepiece, flip the mirror up, and it is in the field of the
camera. In addition, the flip mirror is set so what’s in focus in its eyepiece
is in focus in the camera, with maybe just a little fine-tuning required.
I was in the
process of doing my go-to alignment when my former student and Escambia Amateur
Astronomers Association President, Jon Ellard, drove up. That was cool. I
wasn’t jittery on this night, as I sometimes am when I am alone at the site—the
cold was taking my mind off the spooks and haints—but it would be nice to have
some company. The friendly tomcat had headed for the hangar where he lives some
time before, giving me a look that seemed to say “Silly human! Don’t you know it’s cold?”
Mrs. Peel
was goto aligned and polar aligned without much fuss. Ran the six stars of the normal
go-to alignment procedure, and then did an AllStar polar alignment using Fomalhaut.
While there was not too much fuss,
there was some, as there always is with your silly old Uncle. Jon had forgot
one of his batteries, so I gave him one of my jumpstarters. I’d run the scope
and dew heaters off a single battery with a cigarette lighter splitter. That
would have worked fine, but I was too cold to feel like rummaging around in the
case for my good splitter, and used one that doesn't make very good contact.
Naturally, just after I finished the alignment, I bumped it, causing a
momentary power loss and the loss of my alignment.
Turned out
that was not such a big thing. I’d had to move the mount a fair distance in
altitude and azimuth to do the polar alignment, and my gotos were a little off
as a consequence. In the field of the 12mm eyepiece, but at the edge. After I
redid the alignment following the power glitch, my targets began falling near
the center of the eyepiece at 160x.
Alright,
time to get to work. Tom suggests starting with Vega or another bright A-type
star when you are new to RSpec. The
hydrogen beta line used to calibrate RSpec
is strong and obvious in A stars. Alas, Vega was now within 10-degrees of the
horizon, and given the seeing—even higher stars were twinkling like mad—was a
no-go. What then? Rigel was perfectly placed in the east. He’s not an A, he’s a
B, and the Balmer lines are weaker in his spectrum, but I reckoned he would do.
 |
| Flip mirror and ZWO... |
The most
surprising thing? Despite the cold and my relative inexperience with RSpec, I had no trouble getting the
star’s spectra onscreen. Centered Rigel precisely in the reticle eyepiece.
Flipped the mirror up. Lit-off RSpec,
hit the Live Video tab, and there was Rigel and its spectrum. What was really
cool, y’all? In the main display area of the program, I was seeing the graph of
the star’s spectrum—live. So, that’s
why Tom calls his program “Real Time Spectroscopy.”
It was far
too cold to make me want to play with the spectrum out on the field, though, so
I would record it for later processing. One thing was obvious without
processing of any kind; the graph was showing plenty of the dips that represent
absorption lines. It was clear the simple rig was picking up a fair amount of
detail in Rigel’s spectrum.
Before
mashing the record button, I centered the star a little better on the program’s
video display and placed it within the two movable bars that are used to bin
the image for the best image scale. I also rotated Rigel and its rainbow using
the tool provided in RSpec till the
star was on the left and the spectra on the right (the traditional way of doing
things) and I was set to record. Actually, I didn't have to rotate the star and spectra. The program only records the
raw video coming out of the camera, but I wanted to be sure Rigel was in a good
spot in the frame so I could adjust its position correctly during processing of
the recording later.
I fired off
about 15-seconds of video of Rigel, took another sequence as insurance, and
began pondering what else to shoot. Alnitak was nearby, and while it’s even
hotter than Rigel and has even less prominent Balmer lines, I went for it
anyway. I followed up with a cooler star, Capella, since it was bright and
nearby, and finally got an A star with Sirius, a natural, though he was hopping
around like crazy in the poor seeing.
I figgered
that ought to be enough to start with, but I wasn’t sure how good my exposures
were. Focus was OK given the seeing, and the little stripes of star spectra
looked sharp enough, but I wasn’t sure if I was exposing them properly. I did
note that the graph of the star’s spectrum was moving around a lot due to
seeing, but I hoped RSpec’s
image-averaging feature would fix that.
What then?
It was now truly, no fooling, honest-to-god c-o-l-d. I’d chugged about half a
Monster Energy Drink earlier, and had set it aside while I was doing my
spectroscopy. I went back to it now and was not exactly surprised to find what
was in the can was a Monster slushy.
Chaos Manor South’s warm den was sounding better and better, but it was early,
and I really wasn’t uncomfortable. I wouldn’t have been uncomfortable at all if
I’d a-had the good sense to rustle up a pack of chemical hand warmers and put
on my thermal socks before I left the Old Manse. But I didn't, and my hands as
well as my feet were turning into Achilles’ heels (I had a nice fuzzy watch-cap
on my noggin).
 |
| RSpec display... |
Jon was
finished with his picture taking, and like me, he wasn’t quite ready to go, so
we spent a half hour or so doing relaxing visual astronomy. What did I look at
(with the humble 20mm and 15mm Orion Expanse eyepieces I’d brought along)? M1, M37,
M35, M42, and a few other purties. Mostly, though, I got in my yearly
eyeballing of my old friend Uranus, the mysterious Seventh Planet. I also hit his buddy Neptune while I was at it. In
truth, they were not much; the seeing was not good enough to support
magnifications higher than about 150x, so they were both barely resolved.
Still, I’d paid my yearly call on these distant worlds.
Shortly
thereafter, Jon and I became aware of several things: the sky was beginning to degrade as
Saturday’s front began to push in, ice was forming on our equipment cases and
scopes, and our feet were danged cold. Time to load up and skedaddle. Which was
easy enough since I’d packed up camera and laptop once I’d got the last of my
spectral data.
Back at home
at Chaos Manor South with the gear unloaded, I was purty happy to be out of the
cold and sipping “sarsaparilla.” I was also momentarily put out. The dadburned
cable channel, ME TV, didn't have Svengoolie on. I had been looking forward to
watching King Kong Escapes. Then I
realized it was Friday, not Saturday. One of the hazards of being
retired is you tend to lose track of which day it is, campers.
Come
Saturday morning I was ready to start on what I figgered would be the real work
of spectrometry with RSpec, processing
the sequences I’d taken. First up was instructions. RSpec really doesn't have any yet. Mr. Field has written
instructions on his to-do list, but tells Unk that thus far he’s been too busy
getting the program working as well as possible to put together a manual. In
lieu of that, there is a series of excellent instructional videos on the web
you can access from within the program. That is cool enough, I reckon, but your old-fashioned Unk likes the “what to dos” set out in black and white in
writing. I watched the videos and made up my own shorthand list of instructions
on how to calibrate spectra.
 |
| Rigel's "profile"... |
Once the
program is running, you open your chosen video, and rotate the image with the
slider control as mentioned previously till the star is on the left and the
spectrum on the right. If the graph isn't moving around too much, you can just
pause it, scroll through it to pick out a particularly nice frame with another
slider, and proceed to calibration. If it is jumping around due to seeing, you
want to click the “average” box to steady it down a bit before beginning
calibration.
Calibration
is the heart of your task. You've got a spectrogram of your star, a graph
showing dips that represent absorption lines. However, the X axis of the graph
is in pixels, not angstroms, and is useless for figuring
out which lines are which, which represent what elements. You fix that by
calibrating your spectrogram, changing those pixels to angstroms.
Despite my
fears, calibration turned out to be fairly easy. Step one is to open the
calibration window, natch. You then click on the peak of the star’s image, the
big spike on the graph on its extreme left. Next, and a little trickier, you
have to click on the low point of the dip of the hydrogen beta line on the
graph. That in itself is not difficult—if
your star shows a prominent dip at the h beta wavelength. While Rigel didn't
show as prominent a line as Vega would have, it wasn’t too hard to pick out the
“line.” I looked at the spectrogram from Sirius, but its h-beta wasn’t any more
prominent. How do you know what’s the h beta dip? It should be the first big
valley to the left of the spectrum’s peak. Calibration done, click “apply” to
get to the moment of truth.
To find out
if you did good nor not, you click the “elements” button in the toolbar up top
(three vertical lines). In the window that appears, click “Hydrogen Balmer
series.” That makes vertical lines representing the good old Balmer lines
appear overlaid on your spectrogram (the graph). Does the hydrogen beta line
(you can run your mouse over the lines to identify them) pass through the dip
you identified as the hydrogen beta line on the graph? Do the other Balmer Series
lines coincide with dips on the graph? If so, you are in like Flynn.
My results?
Purty good. Maybe not perfect, but purty good, though some of my dips didn't
quite line up perfectly with the superimposed lines. I suspect that was mostly
due to me not quite getting my mouse on the lowest portion of the hydrogen beta
dip. Seeing may also have had some effect. And so might have exposure.
 |
| Capella... |
What do you
do next? Once you’re calibrated, you can go on to identify the other lines in
your spectrogram. RSpec provides
libraries of professional spectra for comparison purposes as well as a library
of elements (the vertical overlaid lines) in addition to the Balmer Series. Your
finished spectra, which RSpec calls
“Profiles” can be saved, exported, and printed. For me, though, what’s next is
another spectrographic run, one done under steadier seeing I hope, now that I
am more confident with the program and with using ZWO as a spectrograph. One
thing I’ll probably work on is exposure, since I think some of my spectra were
underexposed.
Nevertheless,
to say I was thrilled with my results with this incredible program would be an
understatement, muchachos. I was frankly dumbfounded by how well and easily RSpec worked. I was finally decoding the
fingerprints of the stars as I’d dreamed of doing as a sprout all those long
years ago.
Next Time: Destination Moon Night 4…
Comments:
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Thanks for your review. I've been interested in RSpec since I first ran into Tom Field's booth a few years ago at NEAF. Your article is fanning the flames again. What are your thoughts about using it with a DSLR?
Just as a follow up to my last post - my DSLR camera is a Hutech modified Canon 60D with video capability.
"On my first visit to an eye doc in my life".
Well at least you finally went. Two moons are not better than one even if it does cost an arm and a leg.
The spectroscope write-up is interesting but of limited appeal to the average enthusiast.
All hobbyists hit a wall sooner or later Rod.
Well at least you finally went. Two moons are not better than one even if it does cost an arm and a leg.
The spectroscope write-up is interesting but of limited appeal to the average enthusiast.
All hobbyists hit a wall sooner or later Rod.
Not at all sure what you mean by "hitting a wall." I certainly haven't and don't forsee doing so. ;-)
HI Jim: What I gather from Tom is that a DSLR will work very well. I happened to have the ZWO on hand, and it was ready to go with a grating without any additional accessories, so that is what I used...
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