Real Time Photometry

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Real Time Photometry Follow-up of Variable Stars

• AAVSO Fall Meeting
• 26 -28 Oct 2006
• Steve Brady (BXS)
• Hudson, New Hampshire USA

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Contents

• Abstract
• Overview
• Design
• Observatory Automation
• Some Results
• Conclusions

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Abstract
Real Time Photometry Follow-up of Variable Stars

• An automated system for variable star observation
  with real time photometry and closed loop
  telescope scheduling is described. This new
  AutoPhotometry tool has demonstrated new
  opportunities for observatory productivity and
  discovery.
• The system uses a predefined observing strategy
  which may schedule the telescope for immediate
• Time-series observations
• Additional filter sequence observations
• A system for off-line automated photometry of
  CCD images is described
• Format observations for AAVSO submission
• Write observations to database for further data
  analysis
• Generate light curves

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Overview
Off the shelf SW components
Real time photometry Follow-up observing
strategy
New opportunities for real-time science
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Overview

• Off-line Photometry
• Run unattended or attended (preferred)
• Significantly reduce time required to perform
  manual photometry

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Overview

• Reduce operator errors such as selecting the
  wrong cmp / chk star
• Write data to a database for light curves and
  further analysis
• Format data for submission to AAVSO

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Overview

• Real Time AutoPhotometry Tool
• Photometry is performed during observing run as
  soon as image is downloaded
• Observing follow-up strategy is pre-defined for
  each target

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Overview

• Feedback to telescope scheduling software
• Time series observations
• Additional observations
• Repeat count
• Filter sequence
• Exposure time
• Goto next target

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Overview

• Currently monitor 250 targets
• AGN
• Faint CVs for outburst (SDSS, RXJ,)
• Poorly studied or rare CV outburst events
• Interesting / historical CV targets (SS Cyg, Z
  Cam)

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Design

• Requirements
• Plate solve locate stars in image
• Load reference star object information
• Filter
• Position (RA Dec)
• Standard mag
• Inner, outer aperture gap
• AAVSO designation, chart, etc.

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Design

• Place photometry apertures
• Star RA, Dec to image X,Y
• Measure
• Star intensity
• Background intensity
• SNR

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Design

• Measurement methods
• MaxIm scriptable functions
• Document.CalcInformation(X,Y, Rings)
• Integrated intensity of star
• Back ground intensity
• Signal to noise of star relative to background

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Design

• Measurement methods
• Windows based SourceExtractor (SExtractor)
• Performs astrometry photometry
• Array is returned of every star
• X,Y position
• RA Dec
• Flux after background subtraction
• Many parameters to learn and setup
• Problem with stars having low S/N

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Design

• Calculate magnitudes

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Design

• Output data to Log

Star Std RA Dec
Image RA Dec Diff
Intensity Std mag mag err CMP1
163544.08 11 26' 56.9 163544.07 11 26'
57.1 00.27 009078.67 (14.45) 14.45
0.007 CMP2 163516.74 11 26' 40.1
163516.74 11 26' 40.1 00.07 082083.47
(11.99) 12.05 0.001 CHK1 163549.48 11
28' 40.7 163549.47 11 28' 40.6 00.15
020084.42 (13.80) 13.58 0.009 OBJ1
163545.73 11 24' 58.3 163545.74 11 24'
58.0 00.35 003976.79 ------ 15.34
0.019 V849 Her
OBJ1 CHK1 CMP1 15.34 13.58 14.45
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Design

• Generate light curve

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Design

• Create AAVSO format
• Write data to database

163112 V849 HER 2453881.7174 15.34 CCD
CHK13.58 BXS ERR0.02 CMP14.45,11.99,12.77,14
.66,15.09,13.76
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Observatory Automation

• Target Scheduling ACP Scheduler
• Schedule targets based on priority and observing
  constraints
• Horizon / Air mass
• Moon distance
• Sky quality
• Meridian flip (GEM)
• Dawn/Dusk flats
• AutoFocus (FocusMax)
• Custom script for AutoPhotometry
  target follow-up scheduling

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Observatory Automation

• Target Sequencing ACP Observatory
  Control
• Telescope control via ASCOM
• Camera control image acquisition
• Filter wheel control
• Dome control

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Observatory Automation
ACP Observatory Control
Load Targets set priorities
ACP Scheduler
Image
Additional Observations ?
AutoPhotometry
Determine Follow-up Observing Strategy
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Observatory Automation
SDSS J173008624754 CVugsu
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Some Results
CV class ?
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Some Results
First night of time series observations
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Some Results
Further observations
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Some Results
BZ Uma CVugsu
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Some Results
V664 Cas CV Class ?
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Some Results
V664 Cas
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Some Results
V664 Cas period analysis
Period 0.5816
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Some Results
SDSS J080434510349 CV
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Conclusions

• Observatory automation is currently available as
  off the shelf components. This AutoPhotometry
  demonstration software is a missing link in
  current observatory automation by closing the
  loop between image acquisition and target
  planning
• Real-time image analysis
• Determine follow-up observing strategy
• Dynamic telescope scheduling based

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Conclusions

• Monitor objects of interest for change in state
• Automatically schedule follow-up
• observations using various filter sequences
  (multiple per night typical)
• Time series observations for highest priority
  targets (several per month typical)

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Conclusions

• Data is collected in real time not after the fact
  (the following night)
• Increase observatory productivity and
  contribution
• False follow-up scheduling is rare
• Concept can be applied to other targets (SNe
  search) with the detection software

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Questions?
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References / Sources

• Diffraction Limited (http//www.cyanogen.com)
• MaxIm DL
• DC Dreams (http//dc3.com/)
• PinPoint
• ACP Observatory Software
• ACP Scheduler
• FocusMax Auto-focus freeware - Steve Brady
  Larry Weber (http//www.focusmax.org)
• Peranso Period Analysis Software - CBA Belgium
  (http/www.cbabelgium.com)
• A Practical Guide to CCD Astronomy Patrick
  Martinez Alan Klotz
• Dispatch Scheduling of Automated Telescopes Bob
  Denny, DC3 Dreams
• Ensemble Photometry Option for AAVSO Amateur
  Observers Using AIP4WIN and Other Software Tim
  R. Crawford