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CCD Views #324

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                           C C D   V I E W S   #324
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                               August 17, 2004
 
Table of Contents
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1. INTRODUCTION
 
 The AAVSO-Photometry Discussion Group has really come into its own the
last two months. In July it was a great tool for coordination of the Var
Her 04 campaign and posting of preliminary results and daily updates. In
August it has been a great place for discussion of photometric issues
ranging from error reporting to transformation coefficients.
 
Please consider joining the AAVSO-photometry Discussion Group. If
you are worried about being deluged with e-mails then choose the Daily
Digest version, which sends you one e-mail per day with all the posts
included in it. Or you can avoid subscribing and just read the discussion
group via our online archives. Just remember to come back every few days
to stay up on the latest and greatest in variable star photometry.
 
Archive viewing is available at this URL:
        http://www.aavso.org/pipermail/aavso-photometry/
 
 Aaron Price (PAH), AAVSO HQ
Gary Walker (WGR), CCD Committee Chairperson
 
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2. VAR HER 04 UPDATE
 
Var Her 04 seems to be happily hovering around V=16-16.5.
AUG 15.2033 16.6 JM CCDV
AUG 14.8990 16.20 RZD CCD Err: 0.05
AUG 12.3298 16.11 JM CCDV
AUG 12.2948 17.79 HQA CCDI Err: 0.071
AUG 12.2803 16.59 HQA CCDV Err: 0.106
AUG 12.2589 16.77 HQA CCDB Err: 0.047
AUG 10.2038 16.5 JM CCDV
AUG 10.0672 15.96 RSE CCDV Err: 0.162 Transformed
AUG 10.0517 16.21 BKL CCDV Err: 0.0462
AUG 08.3015 16.25 CTX CCDV Err: .009
AUG 06.1215 15.97 CDV CCD
AUG 05.1965 16.22 HDF CCDV Err 0.07
 
JM Robert James HDF Dennis Hohman
CTX Tim Crawford BKL John Blackwell
HQA Arne A. Henden RSE Steve Robinson
RZD Diego Rodriguez
 
Our intensive campaign in June and July has been most interesting and rewarding. Those who did not follow the action on the photometry discussion group can go here for a link to the archives and the raw data: [link removed]
 
At the AAVSO Spring Meeting in Berkely I gave a short talk on both BZ UMa and Var Her 04 detailing our observing strategies and a quick look at analysis of the results. It is available online at: [link removed]
 
 We received a little over 7,500 CCD measurements of Var Her 04 from 23 observers over 16 days. The light curve is characterized by a steady decline of 0.017 magnitudes per day until June 24.5 . An inflection in the light curve gives rise to a gentle hump that spans 0.1 magnitudes over 2 days. Then the light curve resumes a slow decline until June 30.053 when a rapid decline began. The decline was terminated after 0.5062 days and a drop in ~1.1 magnitudes. The star remained steady at ~V=16 through the end of observations on July 16.237.
 *Very* preliminary analysis at this point is supporting the UGSU type. However, there are some questions that need to be answered before we are sure. There are also lots of complicating factors such as a companion ~1 arc second away which may be variable in itself. It is still possible that this is a unique class of CV and could end up being one of the oldest CV systems detected. We are investigating all these possibilities.
 A brief report of your observations was issued as IAUC #8734. We have assembled a team to work on a paper for this object. We hope to have something prepared and submitted by October, which of course means it will likely be after that! Those who contributed significant observations will be listed as co-authors and were e-mailed more details last week.
 We will continue making public updates via CCD Views and the Discussion Group.
 
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3. BZ UMA UPDATE
 
We haven't forgotten our friend in the belly of the great bear. BZ UMa has proven to be very difficult beast to tame. Our data is noisy because it was faint and, lets face it, for many of us this was our first attempt at high speed, faint photometry. Careful analysis of the data reveals the orbital period and a 0.033d period that comes and goes in the light curve, but is not consistent (a wavelet plot of this can be seen in the PowerPoint presentation listed in the previous article). Other than that, the light curve is dominated by heavy flickering and the power spectrum dominated by its associated red noise. What we really need is X-Ray observations to determine the spin period. There are a number of opportunities for just that in the coming months and we are pursuing them. We'll keep you updated via CCD Views and the coauthors via e-mail updates.
 
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4. BRIGHT STAR PHOTOMETRY
 
[Thanks to Arne Henden for much of the advice below.]
 
A good discussion of short exposure photometry occured on the AAVSO_Photometry Discussion Group in July. It can be read via the archives here: http://www.aavso.org/pipermail/aavso-photometry/2004-July/subject.html
 
As previously announced, the AAVSO is in the process of creating a program to detect exoplanet transits. The project will involve the monitoring of many bright stars with known planets but of unknown inclination (thus we're not sure if they transit or not). With all this emphasis on faint objects recently we wanted to summarize the results of this discussion of bright objects.
 
There are two main problems with high-precision short-exposure photometry (SEP from here on out). First, bright sources tend to get overexposed, especially if any nearby comparison star is fainter than the target. Antiblooming gate (ABG) CCDs typically saturate at about 50% of their full well depth, and many non-ABG chips saturate before the limit of their Analog/Digital Converters (ADCs). Second, the atmosphere itself conspires to degrade the photometry through a phenomenon called scintillation, where the turbulent bubbles of gas act like lenses, increasing or decreasing the amount of flux entering the front of your telescope. The twinkling of naked eye stars is caused by scintillation.
 
To counteract saturation, first test your CCD camera to find out the limits of its linearity and where full well occurs in the dynamic range of your ADC. Then keep the signal level within the linear range and below the full well. For very bright sources, you may reach a limit where you cannot take a short enough exposure to prevent saturation. Techniques to go even brighter include:
1. Stopping down the aperture of your telescope by using a mask with a cutout hole. You can often place the cutout so that the incoming light avoids the central obstruction and spiders.
2. Using a photometric filter, especially a blue one. The filter decreases the bandwidth and therefore decreases the amount of light reaching the CCD, enabling longer exposures. Using a blue filter further moves the incoming light to a wavelength regime where the CCD is less sensitive, enabling longer exposures.
3. Defocussing. While you don't want images with "donuts", you can often increase the image profile by a factor of two or more, thereby decreasing the central peak intensity.
4. Using a Barlow lens. Increasing the image scale spreads the starlight over more pixels, decreasing the peak intensity.
5. Wait for a night of poor seeing!
6. Often a night with uniform cirrus can be used, since such clouds decrease the incoming flux.
 
Scintillation can be tricky. It is stronger nearer the horizon where you are looking through more atmosphere. It is also stronger for smaller telescope apertures, where each blob of atmospheric gas is closer to the telescope aperture size (bigger telescopes average many blobs). It is also a function of wavelength (redder is better) and exposure time (longer is better). Tips to avoid scintillation:
1. Use relatively long exposures (10 seconds or longer). Use the techniques listed above to increase exposure time if necessary.
2. Don't work close to the horizon. We usually recommend staying above airmass 2.5 if possible.
3. Take multiple exposures and average to beat down the effects of scintillation.
 
Here is a formula posted By Radu Corlan (CXR) for estimating scintillation without taking altitude into consideration:
scint = (0.09 * A ^ 1.75) / (D ^ 0.66 * sqrt(2 * t))
Where A is the airmass, D is the aperture in cm and t is the integration time in seconds.
It is taken from a series of papers by Dravins et al. that begin with "Atmospheric Intensity Scintillation of Stars, I. Statistical Distributions and Temporal Properties" 1997, PASP. 109, 173.
 
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5. SWIFT STATUS & GRB AFTERGLOW ACTIVITY REPORT
 
There has not been much activity in the past four months. However, SWIFT is scheduled to be launched in early October. Good localizations are expected in mid November with their quality gradually increasing afterward. SWIFT is planning to follow an afterglow for at least 5.5 hours after detection.
 
SWIFT is expected to detect one GRB about every other day. Of these, we expect one GRB afterglow should be viewable from each observer's location every other week after accounting for daylight, weather and lunar interference. That is a lot of work! Remember, the race will no longer be about identifying and localizing a GRB from SWIFT. It will be about building high quality lightcurves. If each member of the High Energy Network observes one afterglow per month we would quickly build a substantial database of afterglow light curves which could be very popular among the researchers.
 
It is important to note that amateur observations of GRBs are still needed! In fact, NASA recognizes that and has given the AAVSO a nearly $50,000 grant to continue and expand operations of the High Energy Network in direct support of the SWIFT mission. Amateurs will be needed to build light curves after SWIFT stops monitoring the burst. In addition, the SWIFT monitoring telescope (UVOT) is a near UV-optical hybrid. It has a detector with a response range of 170-650nm. It peaks in the Johnson B band, has a little V sensitivity and no R or Ic coverage. Ground based observations in VRI will still be needed to complement the near-UV observations of SWIFT. In fact, SWIFT is planning to distribute the first UVOT image of the field for use as a finder chart for observers on the ground. The SWIFT team recognizes that they are part of a collaborative effort with ground based astronomers.
 
More information, including the SWIFT observing policy in Word and PDF format, can be found at this URL:
 
Below is a listing of the AAVSO International High Energy Network GRB observation reports since the last issue of CCD Views:
GRB040717: Zsolt Kereszty (KZX) imaged the field and did not detect anything down to R=17.95. To date, no optical transient has been reported by anyone else via GCN.
GRB040730: Berto Monard (MLF) imaged the field and did not detect anything down to CR=19.5 . To date, no optical transient has been reported by anyone else via GCN.
GRB040810: Berto Monard (MLF) imaged the center 22x20 arc minutes of the field and did not detect anything down to CR=17.5 under deteriorating weather conditions. To date, no optical transient has been reported by anyone else via GCN.
 
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6. ZEN OF IRAF
 
Chuck Pullen (PCH) has written "Zen Of Iraf: A Spiritual User's Guide to the 'Image Reduction and Analysis Facility' for the Linux Novice." It is a 53-page PDF treatise on achieving enlightment and the quenching of thirst through the use of the photometry package everyone loves to hate. Note, this is a work in progress. It can be downloaded at the following URL:
 
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7. THANKS TO SPECIAL EDITION OBSERVERS
 
Thanks to all those who have responded to the recent CCD Views Special Edition's we've been publishing in the last few months. Lots of professional observatories and satellites requested your help.
 
QS Tel (Chandra - CCD Views #323) MLF - Berto Monard
 
V4641 Sgr (Chandra and VLA - CCD Views #322) JM - Robert James (excellent time series coincident with the VLA run)
 
VW Hyi (FUSE - CCD Views #322, #309) MLF - Berto Monard
 
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8. ONLINE LIST OF AAVSO CCD CHARTS
 
Tim Crawford (CTX) recently assembled a list of AAVSO charts that have extended photometric information for CCD observers. Most of these charts have the data listed in a chart table in the lower righthand corner of the charts. The listing here includes the star designation, name, type, period, range and the filters for which photometric data is available (UBRI). AAVSO HQ is now maintaining this list on a web page and will update it when a new chart is issued with extended photometric information.
 
This is a good place to go when looking for new objects to add to your program. Currently we only add CCD tables to charts when there is a specific need for CCD observations of the object.
 
All charts can be found at http://www.aavso.org/vsp.
 
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9. CCD POINTS
 
The following totals are for April 1, 2004 (last issue of CCD Views) - August 1, 2004.
 
REMINDER: CCD Points are *not* an official AAVSO report and carry no weight at HQ. They are provided purely for fun and to start barroom brawls at AAVSO meetings.
 
Points Obs. Observer
18421 16779 COO COOK, LEWIS M. (CONCORD,CA,USA)
15049 9649 VMT VANMUNSTER, TONNY (B-3401 LANDEN,BELGIUM)
9856 2327 JM JAMES, ROBERT A. (LAS CRUCES,NM,USA)
5833 1226 MXD MESSIER, DAVID (LISBON,CT,USA)
5712 958 HQA HENDEN, ARNE ANTHON (FLAGSTAFF,AZ,USA)
5330 1120 BDG BOYD, DAVID (OXON OX12 9TX,ENGLAND)
4298 976 SDB STARKEY, DONN RAY (AUBURN,IN,USA)
3762 664 KMP KOPPELMAN, MICHAEL (GOLDEN VALLEY,MN,USA)
3409 614 GKA GRAHAM, KEITH A. (MANHATTEN,IL,USA)
3150 652 PCH PULLEN, A. CHARLES (WILTON,CA,USA)
3023 598 GBL GARY, BRUCE L. (HEREFORD,AZ,USA)
2988 593 NMI NICHOLAS, MICHAEL (GLENDALE,AZ,USA)
2722 480 NFD NIEUWENHOUT, FRANS D.J. (,NETHERLANDS)
2660 675 OAR OKSANEN, ARTO (FIN-40950 MUURAME,FINLAND)
2635 556 AWJ AQUINO, WILLIAM J. (NIAGARA FALLS,NY,USA)
2307 428 CTX CRAWFORD, TIMOTHY R. (ARCH CAPE,OR,USA)
2193 461 WGR WALKER, GARY (SHERBORN,MA,USA)
1991 402 QNK QUINN, NICK (WEST SUSSEX BN44 3LR,ENGLAND)
1730 336 FJQ FOSTER, JAMES (LOS ANGELES,CA,USA)
1530 397 MMU MUNKACSY, MARK J. (PORTSMOUTH,RI,USA)
1331 277 RSE ROBINSON, STEPHEN E. (ROCKVILLE,MD,USA)
1260 218 BKL BLACKWELL, JOHN A. (NORTHWOOD,NH,USA)
1254 249 TPE TIKKANEN, PETRI (FI-40320 JYVASKYLA,FINLAND)
1150 367 HBD HEATHCOTE, BERNARD DAVID (3141 SOUTH YARRA, VICTORIA,AUSTRALIA)
1141 214 DKS DVORAK, SHAWN W. (CLERMONT,FL,USA)
1080 1708 NLX NELSON, PETER ROBERT (VICTORIA 3820,AUSTRALIA)
1024 199 ITM ITKONEN, TOMMI (FIN-80160 JOENSUU,FINLAND)
957 1183 RIX RICHARDS, THOMAS JOSEPH (ELTHAM, VICTORIA 3095,AUSTRALIA)
932 82 CXR CORLAN, RADU (71206 BUCHAREST 1,ROMANIA)
889 146 KZX KERESZTY, ZSOLT (9081 GYORUJBARAT,HUNGARY)
837 99 CJS CASE, JAMES A. (KANSAS CITY,MO,USA)
820 143 SGE SARTY, GORDON ERIC (SASKATOON, SASKATCHEWAN S7H 4H2,CANADA)
813 66 CUA CORLAN, ALEXANDRU (71206 BUCHAREST 1,ROMANIA)
812 243 PPK PAAKKONEN, PERTTI (FIN-80160 JOENSUU,FINLAND)
793 136 HUZ HUZIAK, RICHARD (SASKATOON SASKATCHEWAN S7J 0A2,CANADA)
784 178 MDW MACDONALD II, WALTER J. (WINCHESTER, ONTARIO K0C 2K0,CANADA)
569 66 WDZ WELLS, DON (MISSOURI CITY,TX,USA)
539 103 HBB HARRIS, BARBARA (NEW SMYRNA BEACH,FL,USA)
529 104 KTC KRAJCI, TOM (DULLES,VA,USA)
492 93 KCH KNAPP, CHARLES (RENICK,WV,USA)
454 32 ARJ ARNOLD, JAMES E. (HUNTSVILLE,AL,USA)
398 58 RZD RODRIGUEZ, DIEGO (28400 VILLALBA, MADRID,SPAIN)
380 78 MVD MAIS, DALE (VALLEY CENTER,CA,USA)
368 52 GMZ GRAZIANI, MAURO (FUSIGNANO 48010 (RA),ITALY)
338 53 DPP DE PONTHIERE, PIERRE (5170 LESVE,BELGIUM)
335 29 CGY CLIMENT GARCIA, TONI (ALGINET-VALENCIA 46230,SPAIN)
326 43 CHG CHANTEGROS, HERVE (87200 SAINT-JUNIEN,FRANCE)
288 50 HDF HOHMAN, DENNIS G. (ORCHARD PARK,NY,USA)
252 100 MTK MICHALIK, TOM (LYNCHBURG,VA,USA)
250 34 RR ROYER, RONALD E. (SPRINGVILLE,CA,USA)
215 43 RWA RAUSCHER, WALTER (JENKINTOWN,PA,USA)
210 40 MXY MCCLUSKY, JOHN V. (SEGUIN,TX,USA)
190 36 SDY SCHARNHORST, DANNY (99084 ERFURT,GERMANY)
173 44 VST VALENTINI, STEFANO (CRESPADORO,ITALY)
172 19 DIL DILLON, WILLIAM G. (MISSOURI CITY,TX,USA)
162 15 CDV CORNELL, DAVID (ELSAH,IL,USA)
139 13 MXM MIFSUD, MARTIN (PIETA,MALTA)
133 21 WJD WEST, JERRY DOUG (MULVANE,KS,USA)
128 22 PAH PRICE, AARON (WATERTOWN,MA,USA)
123 111 MAV MATSNEV, DMITRY V. (MOSCOW,RUSSIA)
122 22 FMG FUGMAN, GARY C. (LYONS,NE,USA)
116 15 LJJ LAURENT, JEAN-LUC (91530 LE VAL SAINT GERMAIN,FRANCE)
115 21 WBY WALTER, BRADLEY (LOCKHART,TX,USA)
89 15 HJZ HORNE, JERRY D. (SAN JOSE,CA,USA)
86 11 ZFL ZATTERA, FLAVIO (36073 CORNEDO VICENTINO (VI),ITALY)
49 13 MMG MARTINENGO, MAURIZIO (10060 CANTALUPA (TURIN),ITALY)
43 13 SUQ SUCKER, ACHIM (D-31139 HILDESHEIM,GERMANY)
41 44 LVY LEVY, DAVID H. (VAIL,AZ,USA)
 
A description of the CCD Points algorithm is available in CCD Views #316.
 
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An archive of "CCD Views is available at http://www.aavso.org/ccd-views.
 
An archive of "Eyepiece Views," a similar newsletter intended for visual observers, is available at http://www.aavso.org/eyepiece-views.
 
Good observing!
 
Aaron Price, AAVSO Technical Assistant (PAH)
Gary Walker, Chairman of the AAVSO CCD Committee (WGR)
 
Copyright 2004, American Association of Variable Star Observers
Keywords:
AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484