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CCD Views Vol. 3 No. 1
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THE AMERICAN ASSOCIATION OF VARIABLE STAR OBSERVERS
25 Birch Street, Cambridge, MA 02138 USA
Tel. 617-354-0484 Fax 617-354-0665
http://www.aavso.org
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C C D V I E W S
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February, 2002 Vol 3 No 1
Table of Contents
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1. Introduction: Quite a Sky
2. SN 2002ap Illustrated
3. Lightcurve of an Active V1028 Cyg
4. Starting Out in CCD Photometry Part Two: Flat Frames
5. High Precision CCD Photometry Workshop MP3s and PowerPoint
Presentations
6. A Cautionary Tale of PEP to CCD Transition
7. FU ORI: A Flickering Sensation
8. CCD Observations In Online Light Curve Generator
9. Linux CCD Driver Support
10. CCD Points
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1. INTRODUCTION: QUITE A SKY
Sunday, January 27th was an interesting day. In one day a nova (N
OPH 02), supernova (2002ao), and a GRB (020127) were discovered. Think
about the majesty of it. Events that likely took place thousands
of years ago, millions of years ago, and billions of years ago
respectively all sent photons that converged with the Earth on the same
day. Quite a way to look at the distance scale! For one event, mankind
was in the stone ages, for another mankind was just an evolutionary
option, for the earliest the Earth wasn't even around!
Then came January 28th and the discovery of SN2002ap followed by the
weekend of February 2nd when V838 Mon decided to make a splash on the
night sky. We're half expecting Las Vegas to begin taking bets on
astronomical phenomenon.
Don't forget to get your applications for the 2nd High Energy
Astrophysics Workshop in by March 15. Do it now before it gets lost in
your INBOX!: http://www.aavso.org/meetings/heaapp.stm
Also, we are about to place the final order for CCD filters. If you
need a filter please fill out the form in the last issue of CCD Views
(http://www.aavso.org/ccdviews/ccdviewsvol2no4.shtml). It is vital
that CCD observations be made with a proper filter.
Clear skies!
Aaron Price Gary Walker
AAVSO Technical Assistant Chairman, CCD Committee
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2. SN 2002ap Illustrated
Thanks to all the observers who have taken up the challenge to build
a complete light curve of SN 2002ap. As of February 22, we have
received 102 CCD observations. Special thanks to UMB, MLF, VWA, WJL,
CRI, RGY, HOU, COO, SBS, WJD, KZX, VWA, GBL, GKA, BVJ, MMN, KDA, PCH,
and ZRE for their observations.
At the URL below we have placed online a few light curves of the data
to illustrate the observations. Remember that all this data is
preliminary and our goal is to build a complete light curve, this means
to follow it as it fades. This data is just as valuable because any
"breaks" in the decay rate can have profound implications for the model
of this object.
http://www.aavso.org/ccdviews/sn2002ap.shtml
Current results in the scientific community of SN 2002ap currently
suggest that it is very similar to SN 1998bw, which is widely believed
to be a Type Ib/c-pec a.k.a Hypernova. SN 1998bw has also been
associated with GRB 980425, a peculiar GRB in its intensity and gamma
ray peak. Data collected on Feb 11 suggest SN2002ap looked very similar
to SN 1998bw 2 weeks after "explosion" (IAUC 7825) which implies that
discovery of the supernova 12 days earlier was very close to its birth.
The progenitor has been estimated to be around 40 times the mass of the
sun (GCN 1240), close to the theoretical upper limit of star mass. It
is well located far from the nucleus of M74 and so suffers very little
dust extinction (GCN 1248) making observations of it even more valuable
compared to regular supernovae due to this rare clean line of sight we
have.
Please continue to observe SN 2002ap as much as possible using the
AAVSO f-scale chart linked at the URL above. Everyone needs to be using
the same chart. Much of the scatter in the light curve can be
attributed to using earlier (or non) AAVSO charts. If you have
submitted data with an earlier chart, feel free to recalibrate your
photometry with the new chart and send us the new data. Just send a
note to aaronp@aavso.org with the new data and telling us what data to
replace. Also remember to SAVE YOUR IMAGES as the AAVSO will be asking
for them soon.
Remember our goal for this object is to create an as accurate as
possible lightcurve. We would like to use this to show the professional
community what AAVSO CCD observers can do. This is also a terrific
learning experience and - hey, believe it or not, it's quite fun to
boot!
For the next issue of CCD Views we should have some serious results
to publish. So please keep sending the data and stay tuned!
Read the AAVSO GRB Discussion Group for more information, advice, and
updates about this object.
http://mailman.McMaster.CA/mailman/listinfo/aavso-grb-list
References: IAUC 7811, 7816, 7817, 7820, 7821, 7822, 7825, 7826
GCN 1237, 1238, 1240, 1242, 1243, 1244, 1247, 1248
More info at: http://www.supernovae.net/sn2002/sn2002ap.html
(P/S: Many people have asked me who I bribed to get my initials on the
hypernova, sorry but my confidentialty agreement with the AAVSO
prevents me from revealing trade secrets. - Aaron )
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3. LIGHTCURVE OF AN ACTIVE V1028 CYG
Around the beginning of the new year Gary Billings (BGW) by chance
caught V1028 Cyg in outburst. Braving the Canadian cold he got four
days of good photometry and what appear to be clear superhumps. You can
see the results at the URL below.
http://www.aavso.org/ccdviews/v1028-gwb.gif
Thanks to Gary for allowing us to share the data. If you have any
lightcurves you are especially proud of, data, or other interesting
results you'd like to share please feel free to contact aaronp@aavso.org.
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4. STARTING OUT IN CCD PHOTOMETRY PART TWO: FLAT FRAMES
By Keith Graham (GKA)
The following is the second installment in a series of contributions
written by Keith Graham (GKA), who is in his 20th year as an AAVSO
observer. The series will be continued in the next few issues of CCD
Views and previous installments are in prior issues available at
http://www.aavso.org/ccdviews/ .
Please note that all views here are views of the author. No
specific makes or models of equipment are officially advocated by the
AAVSO. The hardware mentioned in this article is here to illustrate
issues that apply to all CCD equipment.
- - - - - - - - -
Part Two: Flat Frames
Now that you have your equipment in order, it's time to use it. If
you have done any CCD imaging, you are familiar with such terms as
dark frame and flat field. Whereas most CCD users realize the
importance of subtracting a dark frame from the raw image, some will
shy away from taking a flat frame. I know I tried to weasel my way
around them, and I hoped someone in the know would placate me by
telling me I could easily get by without them in photometry.
NO SUCH LUCK.
Flat frames are essential. It took me hours of experimentation to
figure out the best way for me to take flats that are conducive to
good photometry. Different enthusiasts will give your their
impressions as to the best way to take flats. Professional
astronomers will have elaborate set ups with illumination at certain
wavelengths. But we are amateurs, and we must do the best we can with
what we have. There are advantages and disadvantages to the various
methods, but I found that simplicity pays off.
I have an observatory, so I have set up a piece of white board that
I bought at Menard's. I mounted this board on a wall and aim my scope
at this board. I also bought a small halogen work lamp (25 watts) for
illumination and set it up behind the scope and aimed at the board.
The light from this lamp that makes its way through the telescope's
optical train and lands ultimately on the CCD chip must be very
evenly diffused. To achieve this, I made a diffusion screen from a
piece of Styrofoam poster board and a sheet of milk plastic. I cannot
tell you how much searching I did for that piece of milk plastic, but
I found one by accident one day while accompanying my wife to her
favorite quilt shop. Quilters use this stuff to make stencils and it
is cheap. I paid $1.50 for a sheet large enough for my purposes. I
cut a circle in the Styrofoam poster board large enough to fit snugly
over the front end of the telescope, and I then mounted the milk
plastic sheet over the hole. The end result is the light from the
lamp is bounced from the white board on the observatory, diffusing it
once. This diffused light must enter the scope through the milk
plastic sheet causing it to further diffuse. This makes for a nice
evenly dispersed light across the CCD chip. It is important that
your scope is focused for a star, not for the board. I simply leave
my camera on the scope and leave it in focus from the previous nights
viewing.
I should mention that cleanliness is pretty important here. It
is true that the flat will remove dust donuts and other imperfections
in the optical path. But the fewer obstructions there are in the
first place, the better. So if you have removed your camera from the
scope, it might be a good idea to blow off any dust (using a squeeze
bulb) from the camera chip cover, the v filter, and the focal reducer
(if used).
Now, here is the important part. Does it matter how long you expose
your flat?? You bet it does. I had read many opinions on CCD imaging
which stated that the flat should be exposed to within 50%-75%
saturation. For my ST6 with a full well ADU of about 65000, that
would mean an average flat reading of between 32500 and 45000 ADU. I
used this as my basis for my photometry flats, and found that I was
not getting consistent readings in my photometric magnitude
estimates. What I found was that this 50%-75% saturation might be
good for "pretty picture" imaging, but it was too much for
photometry. I learned from the photometry gurus that the flats ADUs
should not be any more that 50% saturation. So I keep my flats to
around 30000 ADU. With my setup, this means a 4.6 second exposure.
To make a long story short, I found that taking flats is really no
pain at all. Once I got a system going, it became a snap. Now, the
first thing I do when I set up and get the camera thermally
stabilized is take a flat. Now here again, there are different
schools of thought. Some say you should take many flats and average
them. Others say 1 flat is sufficient. I have tried both ways, and I
have found that I can get by with one flat for the evening. I have
found my results to be rather consistent with the observations of
others and are repeatable. Both of these checks tell me that my data
is reliable.
Another way to take flats is with a light box. They are quite easy
to make, and can be used in the field if you do not have an
observatory. I will not go into their construction here, but you can
find them on the web sites of other CCD enthusiasts. In fact, if you
ask on the MAPUG (http://www.mapug.com/) or SBIG users list
(http://www.sbig.com/sbwhtmls/sbiglist.html), the people there are
very helpful in offering their plans on their own websites.
So, in summary, while the taking of flat frames might seem
impossible (or just a royal pain) at the outset, they are worth your
effort to perfecting them. Once you find a method that works for you,
stick with it. In your photometry, you want to do things the same way
each time so your results are consistent. The only reason to change
what you are doing is if you find you can do it better a different
way that will give you better results. But keep your exposures of
flats to below 50% saturation of your CCD chip.
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5. HIGH PRECISION CCD PHOTOMETRY WORKSHOP MP3s AND POWERPOINT
PRESENTATIONS
Audio from Arne Henden's workshop held at the 90th AAVSO Annual
Meeting last November has been placed online at the AAVSO web site
along with the slide show that went along with the presentation. They
can be downloaded in MP3 and PowerPoint format, respectively, at the
URL below.
http://www.aavso.org/meetings/fall01sounds.shtml
Many thanks to Arne Henden (USNO) for both holding the workshop and
allowing us to place this material online.
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6. A CAUTIONARY TALE OF PEP TO CCD TRANSITION
By Dan Kaiser (KDA), AAVSO President
This is aimed at the amateur. For the purpose of this discussion my
definition of an amateur will be one who supplies his own equipment. My
point is that when an amateur thinks of upgrading his/her equipment to
PEP or CCD, they must not only consider the program stars they wish to
observe, ie the limiting magnitude of the pep/CCD equipment is capable
of reaching, but assure themselves that the remaining hardware is up to
the job. I will use my experience as an example.
Photoelectric photometers generally have 1mm apertures. Your mount is
required to keep the target star inside the aperture during an
integration. Generally 10 seconds. In 1991 my mount/drive had a total
periodic error of 20 arc seconds, or +/- 10 seconds. My telescope focal
length gave a field of view of 30 arc seconds for the 1mm photometer
aperture. What that meant is that most of the time the target star
would stay in the 1mm aperture. It would occasionally wander out and
that particular integration would have to be discarded. Not a show
stopper. If the error had been larger it could have been a show
stopper.
But then I decided I wanted to observe stars much fainter than my pep
equipment was capable of doing. In 1995 a CCD was purchased. Now
instead of a keeping the target star in a 30 second fov, the CCD
required I keep the target on a few pixels covering 1/5 that or about 6
arc seconds. True the +/-10 arc second error was such I could integrate
for about 30 seconds and thus go fainter then the photometer, due to the
incredible sensitivity of the CCD. But for the cost of the upgrade the
gain in limiting magnitude was disappointing.
(Yes I know one can stack several 30 second images and sort of get the
same quality and longer integration. However for photometry that is not
recommended.)
So the solution was to track more accurately. This could be done by
either a better drive or guiding, or both. First I tried guiding. A
second CCD as an auto-guider on a guide scope. This improved the
tracking tremendously. I was able to track for 120 seconds. However I
also learned that the drive had a nasty spike in it. The auto-guider
could not keep up with the error in the spike and so integrations were
done during the part of the 4 minute worm cycle that did not contain the
spike.
In 1996 the drive was upgraded to an 11 5/16" from a 7 1/2". This was
another great improvement allowing 120 second _unguided_ images. With
the auto-guider a target could be followed for much longer. However
differential flexure between the imaging and the guiding scopes raised
it's ugly head. Continual tweaking of the hardware reduced the problem,
but it always remained.
All is good, correct? Well I wanted to set the equipment on a eclipsing
binary and let it gather data while I slept. After all I do have to
work during the day so that I can pay for all this equipment and still
afford to have food on the table. The differential flexure issue
allowed following a target for a few hours before one of the stars of
interest drifted out of the fov. So it required re-centering from time
to time. Unattended all nighter's were out of the question.
So, the guiding CCD and the imaging CCD were sold to help finance a self
guiding CCD. This has worked out very well. The self guiding CCD will
stay on a target for as long as it is visible. In fact the only
tracking errors are due to polar misalignment causing field rotation,
which requires several hours before it is detectable, and then it is in
the order of 2 arc seconds.
Sorry to be so long winded. But you do see my point? When thinking of
upgrading to pep or CCD, remember it is not only the detector that
requires consideration. If the ancillary equipment is inadequate you
will be disappointed. (We have not discussed matching the
photometer/CCD to the telescope, filters, acquisition and reduction
software, etc, etc. Let's leave that for another time.)
I have forgotten who the speaker was at the first AAVSO CCD workshop who
said, "Calculate the expense of all the required equipment, multiply
that by 3, and that is what the final cost will be." He did not mention
all the time it will require as well. I don't mean to sound negative or
to discourage. I just want you to be realistic in your expectations.
Once it all comes together the results are well worth the effort.
Dan Kaiser (KDA)
Current AAVSO President
(This article was adapted with permission from a post made to the
AAVSO Discussion Group. It was part of a larger discussion about the
differences between PEP and CCD observing.)
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7. FU ORI: A FLICKERING SENSATION
A new e-scale CCD chart has been published for FU ORI. This chart
uses a new CCDV sequence by Doug West and include V-Rc and Tycho B-V
values.
FU ORI is the subject of the February, 2002 Variable Star of the
Month written by Kerri Malatesta. FU ORI is normally around 9th
magnitude but the AAVSO International Database shows flickering by as
much as .03 mag. However, similar stars of the same type (of which FU
ORI is the prototype) have sometimes shown variations of as much as .1
mag so you can never predict what you will find.
Observations in V and I are encouraged on a nightly basis. If
flickering is detected, make an observation every 15 minutes and
reduce your data as carefully as possible. Notify aavso@aavso.org
after you have submitted the observations through the usual channels.
The complete VSOTM article and charts are available at the URLs
below:
http://www.aavso.org/vstar/vsotm/
http://www.aavso.org/charts/catalog/ORI/FU_ORI/
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8. CCD OBSERVATIONS VIA ONLINE LIGHT CURVE GENERATOR
The AAVSO Online Light Curve Generator has recently been upgraded to
distinguish between CCD observations and visual observations. CCD
observations will show up as the symbol "x" on a light curve while
visual observations continue to show up as an asterix (*). The color of
the "x" provides the band the data was taken in: Green for V, Blue for
B, Red for R, and orange for I. CCD "fainter than" observations are
unaffected.
http://www.aavso.org/adata/curvegenerator.shtml
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9. LINUX CCD DRIVER SUPPORT
Many consumer CCDs are now supported under Linux. Below is a list of
URLs where you can find drivers and software for various CCDs.
Linux Astronomy CCD Imaging
http://home.earthlink.net/~dschmenk
This site has kernel drivers for QuickCam, Audine, and the entire
line of Starlight Xpress cameras, including support for the
autoguider interface, new USB adapters and the TrueTech Custom
Filter Wheel. It also includes patches to use Xephem for CCD
control. The source code is available under the GNU license.
CCD Astronomy on Linux
http://www.dimensional.com/~ashe/ccd-astro.html
This site does pretty much the same for the SBIG ST7/8/5C/237 cameras,
CFW filter wheels, and the AO7 adaptic optics unit. Source code is
not available.
Linux Apogee Instruments CCD Camera Drivers
http://randomfactory.com/apogee-lfa.html
http://sourceforge.net/projects/apogee-driver/
This site has drivers, GUI, and a developer's kit for the Apogee line
of cameras. The source code is available under the GNU license.
FLI Software Page
http://www.moronski.com/fli/
You can download a Finger Lakes Instruments Linux SDK from this page.
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10. CCD POINTS
We decided to go with both totals this time: CCD Points and raw
number of observations submitted. However, I cutoff the total
observation column at 100 CCD Points because it would be too easy to
figure out the formula(e)! In the next issue we'll add a running point
total.
As always, remember that CCD Points are for *fun only* and serve
no official AAVSO purpose and are not recorded anywhere other than CCD
Views. In fact, I spend more time checking the locations of observers
in the list than I do checking the point totals! :)
CCD Points includes data from Dec - Jan.
Pts Obs Observer Location
3817 916 ARJ ARNOLD, JAMES AL, HUNTSVILLE
960 211 DRG DIETHELM, ROGER SWITZERLAND, RODERSDORF
549 154 WGR WALKER, GARY MA, SHERBORN
546 321 ZRE ZISSELL, RONALD E. MA, SOUTH HADLEY
541 471 BGW BILLINGS, GARY W. CANADA, CALGARY
313 26 MDW MACDONALD II, WALTER J. CANADA, OSHAWA ONT.
309 38 GKA GRAHAM, KEITH A. IL, MANHATTEN
291 46 NMI NICHOLAS, MIKE AZ, GLENDALE
220 66 SFK SCHEDER, FRANK L. MD, LEONARDTOWN
219 98 WJD WEST, JERRY DOUG KS, MULVANE
178 58 RSE ROBINSON, STEPHEN E. MD, ROCKVILLE
145 54 KDM KLINGLESMITH, DANIEL A. NM, SOCORRO
143 23 OAR OKSANEN, ARTO FINLAND, MUURAME
139 86 SYZ SANCHEZ, CRISTINA SPAIN, GIJON-ASTURIAS
129 18 PAH PRICE, AARON (C.AARON) MA, WATERTOWN
117 60 MTK MICHALIK, TOM VA, LYNCHBURG
104 17 HDU HURDIS, DAVE RI, NARRAGANSETT
69 COO COOK, LEWIS M. CA, CONCORD
62 MTM MATTEI, MICHAEL MA, LITTLETON
55 BJS BEDIENT, JAMES R. HI, HONOLULU
53 PMH PHELPS, MATT MA, ARLINGTON
46 RZD RODRIGUEZ, DIEGO SPAIN, VILLALBA,
42 RGY RUBRIGHT, GARY PA, LANCASTER
36 OCN O'CONNOR, STEPHEN D. CANADA, NORTH MONTREAL
35 WRX WILLIAMS, ROGER MI, KALAMAZOO
33 SDY SCHARNHORST, DANNY GERMANY, ERFURT
33 MLF MONARD,LIBERT A.G.(BERTO)SOUTH AFRICA, PRETORI
28 GBL GARY, BRUCE L. CA, SANTA BARBARA
23 LIW LILLER, WILLIAM CHILE, VINA DEL MAR
20 NLX NELSON, PETER AUSTRALIA, ELLINBANK,
18 CLF COHEN, LOUIS MA, CAMBRIDGE
14 UMB01TITTLEY, ERIC BALTIMORE, MD (UMBC)
12 CJI COLOMA, JOSEP MARIA SPAIN, BARCELONA
11 RGY RUBRIGHT, GARY PA, LANCASTER
10 LIW LILLER, WILLIAM CHILE, VINA DEL MAR
10 CML CURE, MICHEL CHILE, VALPARAISO
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CCD Views is published bimonthly and when circumstances warrant
via e-mail. An archive is available at http://www.aavso.org/ccdviews/ .
Please send comments and suggestions to aaronp@aavso.org.
To receive CCD Views via e-mail send a message to
majordomo@aavso.org with "subscribe ccdviews" in the body of the
e-mail. To unsubscribe, place "unsubscribe ccdviews" in the e-mail.
The AAVSO has many free online publications including "Eyepiece
Views", a similar newsletter intended for visual observers. To learn
more and subscribe visit: http://www.aavso.org/mailinglists.stm
Good observing!
Aaron Price, AAVSO Technical Assistant (PAH)
Gary Walker, Chairman of the AAVSO CCD Committee (WGR)
Copyright 2002, American Association of Variable Star Observers
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THE AMERICAN ASSOCIATION OF VARIABLE STAR OBSERVERS
25 Birch Street, Cambridge, MA 02138 USA
Tel. 617-354-0484 Fax 617-354-0665
http://www.aavso.org
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