Jerry Horne San Jose, California USA Automated Extraction of Photometric Data: A demonstration project using MaximDL on CV Images AAVSO Spring Meeting 5-6 May 2006 AAVSO Spring Meeting, Rockford, IL. Jerry Horne San Jose, California USA

Contents Abstract Background Concept Design The Software Some Results Conclusions Table of Contents - Abstract - Background - Concept - Design - The Software - Results and Tests - Conclusions AAVSO Spring Meeting 06 Automated Extraction

Abstract Automated Extraction of Photometric Data: A demonstration project using MaximDL on CV images The intrinsic photometric functions and scripting capability of the image processing software MaximDL is used to automate the extraction of photometric data from images of Cataclysmic Variable stars using standard AAVSO comparison stars. The resulting photometric data is then formatted for inclusion in the AAVSO variable star database. This automated technique is compared with manual data extraction methods and other photometric software. Automated Extraction of Photometric Data: A demonstration project using MaximDL on CV images The intrinsic photometric functions and scripting capability of the image processing software MaximDL is used to automate the extraction of photometric data from images of Cataclysmic Variable stars using standard AAVSO comparison stars. The resulting photometric data is then formatted for inclusion in the AAVSO variable star database. This automated technique is compared with manual data extraction methods and other photometric software CV = Cataclysmic Variables such as CY and AY Lyra AAVSO Spring Meeting 06 Automated Extraction

Background Multiple Image Processing and Photometry programs available: MaxIm DL, AIP4Win, Mira, Astro Art, IRAF, Canopus, AstroMB, xPhot… All have varying ability to process single or multiple images, then extract photometric data, and: Produce light curves Output data files that can be further analyzed by other programs MaxImDL and IRAF have a programmable interface. AAVSO Spring Meeting 06 Automated Extraction

Background No single program or tool that Computes the magnitude of AAVSO program stars Using data on comparison stars on AAVSO charts To produce formatted output ready for inclusion in the data base, via Web Obs or PC Obs Problem: How to reduce the labor required to extract data from images taken the night before and send the data off to AAVSO Hq. Various tools and spreadsheets can be used to obtain the data that can be inserted into PC Obs AAVSO Spring Meeting 06 Automated Extraction

Need a Specialized Software Tool Fill the Gap between: The current PC Obs program will be changing this summer. And: AAVSO Spring Meeting 06 Automated Extraction

Concept How to go from: (with data from): To: By clicking on: 1848+26 CY LYR 2453613.6688 13.32 CCDV 125,139,1561848+26FHJZ Err: 0.03 By clicking on: AAVSO Spring Meeting 06 Automated Extraction

Software Design Main Requirements: A programmable interface to an existing Image Processing Software program Ability to load and align images Find & Store Magnitude and stellar position data AAVSO Spring Meeting 06 Automated Extraction

Software Design Main Requirements (continued): Ability to Identify specific stars on an image Ability to measure intensities and SNR Perform calculations and format data AAVSO Spring Meeting 06 Automated Extraction

Design (continued) Programmable interface possibilities for MaximDL Windows Scripting Language (VBS) Visual Basic or Visual C++ stand-alone program VB or Visual C++ plug-in VB stand-alone program chosen Ease and speed of development MaximDL data structure reasons AAVSO Spring Meeting 06 Automated Extraction

Design (continued) Ability to Load and Align Images MaximDL provides software access to standard FITS load functions and image align routines Find/Store Magnitude and Position Data MaximDL contains intrinsic tools to obtain X & Y position data for stars in the image Input magnitude data from AAVSO Charts AAVSO Spring Meeting 06 Automated Extraction

Design (continued) Ability to Identify Specific Stars Two possible methods: Astrometrically solve a new image using a large star catalog such as GSC Align a new image to a reference image of the star field where the positions of stars of interest have already been identified. #2 is easier and faster AAVSO Spring Meeting 06 Automated Extraction

Design (continued) Align New Image to Reference Image: Reference New AAVSO Spring Meeting 06 Automated Extraction

Design (continued) Ability to measure intensities and SNR Internal MaximDL functions: Document.CalcInformation( X, Y[, Rings ]) Integrated intensity of star image in aperture Signal to Noise ratio of star image with respect to the background Rings settings (Aperture, Gap, Annulus) AAVSO Spring Meeting 06 Automated Extraction

Design (continued) Perform calculations and format data Multiple calculation methods for differential photometry: Basic V-C: the magnitude of the variable found by using a single comparison star: V = (v – c)o + C {e.g. V = 3.7 + 12.5 } Also use of a check star to gauge accuracy: (K – C)o =? (K – C)s This method is straightforward and available in MaxIm DL and AIP4Win AAVSO Spring Meeting 06 Automated Extraction

Design (continued) Methods of calculation - continued Average = Mean of variable magnitudes found using each comparison star: Vi = (v – c)i + Ci {e.g. Vi = 3.7 + 12.5 } Then: n V = ( Vi )/ i {e.g. V = (16.2 + 16.3 + 16.4) / 3 } i=1 AAVSO Spring Meeting 06 Automated Extraction

Design (continued) Methods of calculation - continued Biased Mean = Mean of variable magnitude using the results from selected comparison stars - using comparison stars closest in magnitude to the variable: a) Perform V-C Calculation, for example, using C1 (12.5) {16.3 = 3.7 + 12.5} b) Since variable’s magnitude is faint, go back and use the fainter comparison stars (C3 = 15.6, C4 = 16.0, C5 =16.4) for the calculation : { e.g. V = 16.4 + 16.4 + 16.5) / 3 = 16.4} AAVSO Spring Meeting 06 Automated Extraction

Design (continued) Methods of calculations - continued Weighted Mean - weight the average by the inverse of the standard errors: n Vw =  (Vi/i) * 1/(1/i + 1/i+1…+ 1/n ) i=1 where i = individual error and Vi = the individual calculated magnitudes from each comparison star AAVSO Spring Meeting 06 Automated Extraction

Design (continued) Methods of calculations - continued Aggregate – combining all comparison star intensities and magnitudes to form a virtual star to compare with the variable (also called ensemble, composite, master star): n C(total) = ( -2.5)Log10 ( 10(-Ci/2.5)) {sum comparison magnitudes} i =1 I(total) =  Ii {sum intensities} Then: Vagg = -2.5 Log10 (Iv/I(total)) + C(total) {find var mag} AAVSO Spring Meeting 06 Automated Extraction

Design (continued) Methods of calculations - continued Ensemble – (Inhomogenous Exposures - Honeycutt, 1992) combining all comparison star intensities and magnitudes from multiple images using a sophisticated weighting technique to form a reference frame to measure all stars against: m(e, s) = m0(s) + em(e) {instrumental mag} ee ss b =   [m(e, s) - m0(s) em(e)]2 w(e,s) {least sqrs} e=1 s=1 The magnitude measured of star is a function of both the intrinsic magnitude of the star m0(s), but also the magnitude difference from the individual exposure, such as air mass, seeing, instrumental error The technique is to find a least-squares fit to each star and exposure to build a reference frame to measure all stars against. AAVSO Spring Meeting 06 Automated Extraction

Format Data Format for output is specified on an AAVSO webpage: Column # 00000000011111111112222222222333333333344444444445555555555666666666677777777778 12345678901234567890123456789012345678901234567890123456789012345678901234567890 Design. Name Julian Date Magn. CommentStep Mag Charts Init.Remarks Codes or Comp Stars xxxx+xxxnnnnnnnnnnxxxxxxx.xxxx<xx.x:aaaaaaagggggggggggccccccccnnnnnxxxxxxxxxxx.. 0059+53 V723 CAS 2451777.628 14.1 SU 132,142 PD0296 WEO From the AAVSO website AAVSO Spring Meeting 06 Automated Extraction

The Software Start: AAVSO Spring Meeting 06 Automated Extraction

The Software Analysis Panel with Maxim DL: Maxim DL is started when tool starts AAVSO Spring Meeting 06 Automated Extraction

The Software Analysis Panel: Expand Analysis Panel AAVSO Spring Meeting 06 Automated Extraction

The Software Extended Main Panel: Load Photometry Data AAVSO Spring Meeting 06 Automated Extraction

The Software Load Star Data: Select File to Load AAVSO Spring Meeting 06 Automated Extraction

The Software Star Data Loaded, showing variable star info: Reference Files Observer and Comments Multiple Sequences Variable and Position Data AAVSO Spring Meeting 06 Automated Extraction

The Software Star Data Loaded, showing C1 star info: Comparison Magnitude and Position Data AAVSO Spring Meeting 06 Automated Extraction

The Software Edit Set-Up information: Set SNR Photometry Settings Calculation Types AAVSO Spring Meeting 06 Automated Extraction

The Software Choose Image Files: AAVSO Spring Meeting 06 Automated Extraction

The Software Ready for Analysis: Click on Analyze Image Files Set AAVSO Spring Meeting 06 Automated Extraction

The Software Analysis in Progress: Analysis Log Images Loaded and Aligned with Reference Image AAVSO Spring Meeting 06 Automated Extraction

The Software Analysis Complete: Maximize Log Save to File Scroll through Results AAVSO Spring Meeting 06 Automated Extraction

The Software Analysis Log: Each selected calculation is displayed Selecting fainter comparison stars Variable not detected AAVSO Spring Meeting 06 Automated Extraction

The Software Analysis Log: (continued) Signal-to-noise values known K - C minus observed K-C Signal-to-noise values AAVSO Spring Meeting 06 Automated Extraction

The Software Analysis Log: (continued) Comparison of Selected Calculation Methods AAVSO Spring Meeting 06 Automated Extraction

The Software Marking Comparison and Variable Star Positions: Click on Mark Button Ref. File Loaded Select Seq to Mark AAVSO Spring Meeting 06 Automated Extraction

The Software Marking Comparison and Variable Star Positions (continued): Maxim DL Info Panel Set Star Positions Enter Mag for Comps Click Done AAVSO Spring Meeting 06 Automated Extraction

The Software Marking Comparison and Variable Star Positions (continued): Marked Position carried over to analysis panel Save Data AAVSO Spring Meeting 06 Automated Extraction

Some Comparisons Tool vs AIP4Win: Used approximately 50 observations CY & AY Lyr: Bias Mean (AIP – Tool) Mean Difference = 0.01, Std Dev = 0.11 Aggregate (AIP – Tool) Mean Difference = 0.03, Std Dev = 0.11 Average (AIP – Tool) Mean Difference = 0.00, Std Dev = 0.13 AAVSO Spring Meeting 06 Automated Extraction

The Software Limitations and Notes: Software assumes Image Files are fully processed beforehand (Flat, Bias, Dark) Reference and Image Files must be the same scale If you change your f-ratio, you must take new reference images The 0.1 mag values of many AAVSO charts obviously limits the accuracy that could be achieved. AAVSO Spring Meeting 06 Automated Extraction

Conclusions This is a demonstration piece of software Different techniques or algorithms could have been used. It does seem to provide a straight-forward method of obtaining photometric data. As always, the photometric results are only as good as the images. It cannot pull good data out of bad images Each observer must evaluate the results in terms of the errors, consistency, and overall image quality. AAVSO Spring Meeting 06 Automated Extraction

References 1. Berry, R., Burnell, J. 2005, The Handbook of Astronomical Image Processing, 2nd Edition. 2. Crawford, T., 2006, JAAVSO Submission 3. Honeycutt, K., 1992, PASP 104, 435-440 4. Kundik, T. et al, 1995, Astrophys. J., 455, L5-L8 5. Percy, J, Kolin, D., 2000, PASP 112, 363-366 AAVSO Spring Meeting 06 Automated Extraction

Questions? AAVSO Spring Meeting 06 Automated Extraction