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CCD Views #314
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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 #314
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April 2, 2003
Table of Contents
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1. Introduction
2. GRB Afterglow Discovered by AAVSO International GRB Network!
3. A New Blazar Observing Program: GLAST Telescope Network
4. Reporting CCD Error Magnitudes
5. Calculating CCD Error Ranges
6. Daytime CCD Observing
7. LONEOS Update
8. Using Automated Domes
9. CCD Manual Feedback Request
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1. Introduction
It has been a few months since our last CCD Views. But don't take
absence as meaning silence! Much has been going on behind the scenes to
create plans for the future. With this and future issues we will be
introducing some of those new plans. So dust off any cobwebs that may
have built up in the last few months of poor weather. Not all of us can
observe from Hawaii all the time. ( Lou ). :)
This issue of CCD Views is full of important information and
announcements. Please read it carefully. From the GRB afterglow
discovery to the preliminary announcement about an AAVSO collaboration
with GTN to a *very* important introduction to calculating error
magnitudes, all of this has the potential to affect us for years to
come.
Since we started putting this issue together GRB030329 has become the most
observed GRB to date. Sixteen members of the AAVSO International GRB
Network from seven countries have observed the afterglow as of this writing.
Two GCNs have been published with AAVSO data. To read them go here:
http://lheawww.gsfc.nasa.gov/docs/gamcosray/legr/bacodine/gcn3_archive.html
And click on GCNs 2058 and 2071.
We have put to bed the CCD Points feature. It may return at some date
but for now it creates some headaches to calculate and with the
inevitable segmenting of the CCD observing population its usefulness
deteriorated. In a future issue I'll publish the
super-secret-no-one-ever-guessed-it point formula.
As always, feedback and contributions are appreciated.
Aaron Price (PAH)
On behalf of Janet Mattei (MTT) and Gary Walker (WGR)
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2. GRB AFTERGLOW DISCOVERED BY THE AAVSO INTERNATIONAL GRB NETWORK!
The optical afterglow to GRB030323 was discovered by members of the
AAVSO International GRB Network. Alan Gilmore and Pam Kilmartin, working
at the Mt. John Observatory for the University of Canterbury in New
Zealand discovered the GRB using an ST-9E camera on loan from the AAVSO
and funded by a grant from the Curry Foundation. The afterglow was
later confirmed by ROTSE-III imaging of the field and later found by the
ESO's VLT telescopes to have a redshift of z=3.37. That is 12.4 billion
light years away (assuming a Hubble constant of 71.4 as described by
recent Wilkinson Microwave Anisotropy Probe [WMAP] results). Quite a
distance for photons to travel before dieing on the South Island of New
Zealand!
Their discovery was important because it gave a specific object
that could be studied by large telescopes (such as the VLT) that were
not able to image the entire original error circle. Indeed, an
observation published immediately after Gilmore et. al's announcement
covered a much smaller part of the error circle and missed the
afterglow. Without this timely announcement, even telescopes like
the VLT would not have been able to obtain a redshift for the burst.
Below is a personal note from Pam about their experience:
"We had the happy conjunction of the telescope available, good
seeing and fine autumn weather, and a GRB field south of the
celestial equator. Plus a possible GRB suspect in the fourth of the
nine fields we were observing to cover the error circle. Couldn't
have been better..."
This is the first _discovery_ of an afterglow by a member of the
AAVSO International GRB Network and the 7th afterglow imaged.
Congratulations to Alan & Pam for their wonderful discovery and quick
work!
URLs for more information:
Discovery announcement:
http://lheawww.gsfc.nasa.gov/docs/gamcosray/legr/bacodine/gcn3/1949.gcn3
Observation report & discussion of GRB030324:
http://www.aavso.org/grb/archive/030323-msglog.txt
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3. A NEW BLAZAR OBSERVING PROGRAM: GLAST TELESCOPE NETWORK
The AAVSO has partnered with the GLAST Telescope Network (GTN) to
optically observe blazars and other related high energy objects in
support of the Gamma Ray Large Area Space Telescope (GLAST), Swift, and
XMM-Newton space-based observatories. The details of this new program
will be coming forward within the next month. A paper will be presented
at the AAVSO Spring Meeting in Tucson and a new section of the AAVSO web
site will be setup for this collaboration.
In general, the program calls for AAVSO observers to monitor
blazars and certain polars for the next few years leading up to the
launch of GLAST in 2006. After launch, observers will support GLAST
operations by reporting blazar outbursts and observing all levels of
activity.
In a preliminary program to get some practice, we are asking
observers to monitor the blazar PKS0716+71 for the next several
months. Several telescopes in the GTN program will be monitoring
PKS0716+71 at the same time and our information will be shared with
those scientists. Lowell Observatory and Mount Laguna Observatory are
among the other GTN members observing this object.
A new chart with B,V,R,I photometry has been published on our web
site and is available at this URL:
/observing/charts/CAM/PKS0716/
Please observe this object a couple of times per week with a V
filter. If you have time, additional colors will be appreciated in
this order: I, R, B. The blazar models predict different things for
different wavelengths and GTN scientists are hoping to ultimately get
some data to beat against the models.
If you have room in your observing program (and you do, right?? :)
consider other blazars once a week in V and I. The AAVSO has V charts
for BL Lac, Mark 421, and 3C66A And. More multicolor CCD charts for
these and other blazar objects will be published in the future.
Thanks to Arto Oksanen and the Nyrola Observatory for already
supplying data and sky checking the new chart.
For more information on the GTN & GLAST visit:
http://www-glast.sonoma.edu/gtn/index.html
(Note the GTN web site is about to be redesigned soon)
http://www-glast.stanford.edu/
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4. REPORTING CCD ERROR MAGNITUDES
It is becoming increasingly important to submit error magnitudes
with your CCD observations. It will go a long way in making your data
more valuable to the professionals who use it.
Please submit your error estimate of your magnitude measurements in
the "COMMENTS EXPLAINED" field of your observation report. Use the
format "Error: X" where X is the error, omitting a +/- or any other
nomenclature. It can be anywhere in the field.
Examples:
2039+37 DR CYG 2452129.5694 14.51 CCDV 137,142,135PE1979 TST01 Error: 0.03
2039+37 DR CYG 2452129.7694 14.01 CCDVU 137,142,135PE1979 TST01 Clouds, Error: 0.6
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5. CALCULATING CCD ERROR RANGES
Calculating error doesn't have to be a tough job. Doug West (WJD)
contributed a section to the CCD Observing Manual about how to
calculate error. Dr. Gordon Spear (our mentor for the GTN project -
see above) and CCD Committee Chairman Gary Walker has also provided
some new information which we have incorporated into the manual.
Here is a summary to get you started.
*Simple* error ranges can be computed with this easy formula:
error(mag) = 1.0857 / sqrt(net_counts*gain)
...where net_counts is the count of electrons which you can get from
your software. This provides a first order approximation. This is usually available
in your photometry software. So basically divide 1.0857 by the square
root of the counts of the star as reported by your photometry
software. Tada!
IMPORTANT NOTE: This method only works for bright sources with a
relatively dim sky background and a CCD with low readout noise.
Basically, this is a good way to get started and if this is all you
do, it will be *much* better than nothing. But when you start imaging
dim targets there are more detailed error determination techniques
that must be followed Read the CCD Manual for more information if
that is the case.
Also, remember this does not take into account comp star error.
We'll address that at a later time.
MaximCCD and Mira both currently have error determination tools
built in. AIP4Win and Pinpoint have both committed to having it
available in future releases. CCDSoft does not display formal errors
but we hope future releases will.
For more details on error determination, visit the AAVSO CCD
Observing Manual at this URL:
http://www.aavso.org/ccd/manual/4.shtml#6
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6. DAYTIME CCD OBSERVING
By Arne Henden (HQA)
It always seems, with long period variables, that minimum or
maximum occurs just after the object disappears into evening
twilight. With shorter period variables, you can usually get
multiple cycles in a given observing season, but long period
variables can be pretty inconvenient.
At the same time, however, most of the long-period variables on
the AAVSO program are quite bright at maximum. It is entirely
possible to observe them during the daytime and therefore not have
that multi-month gap.
I do quite a bit of daytime observing in the near-infrared (JHKL).
There, exposure times have to be in the 0.10 second range to keep the
sky background down, but you just coadd many frames to improve the
signal/noise in the sky and object, and to improve the dynamic range.
During the 1978 occultation of SAO 85009 (V=10.8) by Pallas, we
observed with a 16" telescope at Indiana University, using a PEP
photometer in the Ic band during daylight. The Harvard-CFA Micro
Observatory project uses custom 6" telescopes as a teaching tool for
schools; its URL is http://mo-www.harvard.edu/Micro
Observatory/index.html They have included a neutral-density filter on
the telescope for daytime viewing. Surveyors use Polaris for north
determination because it is an easy daytime target.
It is quite easy to observe the brighter stars during the daytime,
as long as your CCD is capable of very short exposures or else
through the use of a neutral density filter. The Sony interline
CCDs, as used by Starlight Xpress, are capable of millisecond
exposures, far shorter than necessary. Many frame-transfer CCDs can
also give exposures with a few millisecond duration. Probably with
the typical amateur telescope, exposures in the 0.01sec range will be
necessary to not saturate your detector, but you should experiment
and see. As with the Micro Observatory, you can add a neutral density
filter in front of your usual photometric filter to decrease the
amount of light and thereby be able to use longer exposure times,
perhaps long enough to use a conventional shutter. You should avoid
having sunlight hit the telescope, as you will get thermal currents
in the tube, differential expansion of the mirrors, etc. We
typically avoid the 4-hour interval centered on local noon. Daytime
observing also usually has worse seeing than nighttime, but these
LPVs are typically bright objects and spreading the light over more
pixels will not hurt as much.
With LPVs, moving to Rc or Ic for daytime observations is a wise
choice. You have less scattered sunlight in those passbands, and the
variable may be several magnitudes brighter. The only bad feature is
that the longer wavelength passbands have more molecular features,
making transformations more difficult, but if the object is to
measure the time of maximum or minimum, magnitude differences between
observers is less important.
When taking flats, if you are using a neutral density filter for
your observations, you should take flats with that neutral density
filter in place. You may have increased scattered light during
daytime observations, but you should take your flats at night. The
scattered light can be removed by moving the telescope a field-width
off of the variable and taking "sky" frames that are then subtracted
from the variable frames.
You should give daytime observing a try!
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7. LONEOS Update
Brian Skiff has updated his LONEOS photometry reference file. It
is available at the Lowell ftp area:
ASCII: ftp://ftp.lowell.edu/pub/bas/starcats/loneos.phot (2.8Mb)
GZIP: ftp://ftp.lowell.edu/pub/bas/starcats/loneos.phot.gz (700Kb)
Reference: ftp://ftp.lowell.edu/pub/bas/starcats/loneos.ref (128Kb)
This is a good catalog to look for comp stars if an AAVSO chart does
not already exist for the object. Do not use this or any other
photometry in place of an already existing AAVSO chart. Particularly
useful is its photometry in bands other than V which may normally be
difficult to find. Below is reproduced from his post to the AAVSO
Discussion Group on March 13. Used with permission:
"There are not a lot of new additions, only minor changes. The
file contains BVRI photometry as available for some 33800 stars all
over the sky with V > 10; most of the stars are between 12th and 18th
magnitude. It is thus suitable for calibration of wide-field images
and other tasks. Most of the stars are in sequences near variable
stars and supernovae, active galaxies, on the periphery of star
clusters, etc. Though some bona-fide standard stars are included, in
general the intention is to provide local zero-point stars reliable
at the ~0.05 mag. level or better."
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8. USING AUTOMATED DOMES
By Gary Walker, CCD Committee Chair (WGR)
These days, it seems there is a never ending supply of technology
being offered the amateur astronomer. I know that I am always taken
in by this new technology, but then have to temper my enthusiasm.
Sometimes, additional technology and complexity offers an apparent
advantage, but in practice the advantage does not work out well.
For this reason, I subscribe to "KISS"--(Keep it Simple Stupid).
When observing late at night, after a day's work, the last thing that
I enjoy is wrestling with the setup.
For this reason, I was reluctant to add GoTo to my CCD Photometry
setup. I was concerned that to take full advantage, I would have to
add robotic dome control--another complexity. My normal setup is
that I have a small dome in my backyard, and I observe from the
comfort of the family room. At times like this, when the nighttime
temperature is 10 degrees below zero, this makes observing possible.
I am sure that the automatic dome control technology works very well,
but I took it as a challenge to keep things simple. I did upgrade my
mount to GoTo, and now let me tell you how I worked around the dome
automation--and no, I did not convert to a roll off observatory.
There were actually two keys. First, the slit on my 8 foot
diameter dome was designed to be nearly 4 feet wide. This gives a
wide view. By orienting the slit north-south, the scope was able to
acquire fields from decs of -20 degrees to +70 degrees. This range
covers all of the BVRI Stars and many of the CV's which I like to
observe.
The second key was to plan the order of the stars in my program.
I sorted my stars of interest by RA. I start with a target nearly
overhead, and then move to the East (increasing RA). This means that
I ignore all objects that are West of zenith. Another reason that I
do this is that my mount is a German Mount, and this avoids a
declination flip. The reason to avoid the dec flip is that the
camera, filter wheel, focuser and cooling cables and lines can get
snagged during this operation. With this mode of observations, the
scope stays between the Zenith and 3 hours of RA east of the Zenith.
If an object West of the Zenith is really important I perform a dec
flip while standing by making sure that the cables do not get
snagged.
So this system means that I never worry about the dome position.
In fact, I have even thought about building a future observatory that
does not rotate, but just has a slit that opens.
Clear Skies
Gary
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9. CCD MANUAL FEEDBACK REQUEST
Last summer we published online the "CCD Observing Manual" in HTML
and PDF formats. The goal of the manual was to be a guide and FAQ for
beginners in CCD photometry of variable stars. We've had good
response and the manual has become a popular section of our web site.
One sign of its success: the number of introductory CCD questions we
get at AAVSO HQ has greatly dropped since its publication!
One of the reasons we chose HTML as the format of the manual was
for its flexibility. We envisioned the manual to be updated and
expanded with the times. We'd like to ask our CCD observers to please
take a look at the manual and send us feedback on sections you would
like to see added or improved. In particular, we would like
volunteers willing to write those new sections, improve the graphics
and diagrams and/or rewrite existing sections that may need
improvement.
The CCD Observing Manual is available at this URL:
http://www.aavso.org/ccd/manual/
Send feedback to aaronp@aavso.org .
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CCD Views is published 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
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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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