Real Time Photometry Follow-up of Variable Stars

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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
Observatory Automation
Some Results
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
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
Off the shelf SW components

    Real time photometry
Follow-up observing strategy

   New opportunities for
    real-time science
Off-line Photometry
– Run unattended or attended (preferred)
– Significantly reduce time required to
  perform manual photometry
– 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
Real Time ‘AutoPhotometry’ Tool
 Photometry is performed during
 observing run as soon as image is
 Observing follow-up strategy is pre-
 defined for each target
Feedback to telescope scheduling software
– Time series observations
– Additional observations
    Repeat count
    Filter sequence
    Exposure time
– Goto next target
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)
  1. Plate solve & locate
     stars in image
  2. Load reference star &
     object information
     – Filter
     – Position (RA & Dec)
     – Standard mag
     – Inner, outer aperture
        & gap
     – AAVSO designation,
        chart, etc.
3. Place photometry
  –   Star RA, Dec to
      image X,Y
4. Measure
  –   Star intensity
  –   Background intensity
  –   SNR
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
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
Calculate magnitudes
  C  1 / N i  (Vi  2.5 log 10 (Ii )) avg mag constant
  Vstar  C  2.5 log 10 (I star )

  Error      σ   n  σ 
                             1      i
                                             mean value
5. Output data to Log

Star   Std RA            Dec          Image RA         Dec          Diff     Intensity   Std mag     mag    err
CMP1   16:35:44.08   11° 26' 56.9“   16:35:44.07   11° 26' 57.1“   00.27“   009078.67     (14.45)    14.45 0.007
CMP2   16:35:16.74   11° 26' 40.1“   16:35:16.74   11° 26' 40.1“   00.07“   082083.47     (11.99)    12.05 0.001
CHK1   16:35:49.48   11° 28' 40.7“   16:35:49.47   11° 28' 40.6“   00.15“   020084.42    (13.80)     13.58 0.009
OBJ1   16:35:45.73   11° 24' 58.3“   16:35:45.74   11° 24' 58.0“   00.35“   003976.79       ------   15.34 0.019

V849 Her
OBJ1       CHK1         CMP1
15.34      13.58        14.45
6. Generate light curve
 7. Create AAVSO format
1631+12 V849 HER 2453881.7174 15.34 CCD CHK:13.58 BXS ERR:0.02 CMP:14.45,11.99,12.77,14.66,15.09,13.76

 8. Write data to database
       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
        Observatory Automation
Target Sequencing          ACP Observatory Control
   – Telescope control via ASCOM
   – Camera control & image acquisition
   – Filter wheel control
   – Dome control
    Observatory Automation
Load Targets                        ACP Observatory
                   ACP Scheduler        Control
& set priorities


                   Observations ?

                                    Determine Follow-up
                                    Observing Strategy
        Observatory Automation
SDSS J173008+624754 CV:ugsu

                              16.0 mag threshold   Time series initiated
                  Some Results
CV: class ?

              15.0 mag threshold   Time series initiated
               Some Results
First night of time series observations
               Some Results
Further observations
    Some Results
BZ Uma CV:ugsu
                 Some Results
V664 Cas CV: Class ?
           Some Results
V664 Cas
                     Some Results

V664 Cas period analysis

                                Period 0.5816
       Some Results
SDSS J080434+510349 CV:
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
  – Real-time image analysis
  – Determine follow-up observing strategy
  – Dynamic telescope scheduling based
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)
Data is collected in real time not after the
fact (the following night)
Increase observatory productivity and
False follow-up scheduling is rare
Concept can be applied to other targets
(SNe search) with the detection software
         References / Sources
Diffraction Limited (
 – MaxIm DL
DC Dreams (
 – PinPoint
 – ACP Observatory Software
 – ACP Scheduler
FocusMax Auto-focus freeware - Steve Brady & Larry Weber
Peranso Period Analysis Software - CBA Belgium (http:/
 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