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 Images (S207) |
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Objects Session Notes
CCD Assisted Polar Alignment Astrometric & Photometric Monitoring
- SS Cyg (Dwarf Nova)
- BL Lac (Blazar)
- U And, W And (Mira variables)
- Z And (Variable)
- SU UMa (cataclysmic variable)
- Session duration 3.4 hr - CCD operation of -20 degC (at 67% average cooling). . - main objectives were to acquire images of selected variable stars and to perform an improved polar alignment of the telescope. - More Notes -
Polar Alignment Checks during recent sessions had established that the Scope's Polar Axis was an estimated 3.8 arc min too low and 5.8 arc min too far west. (ie out by a combined 7 arc min ). Whilst not a barrier to acquisition of star targets (due to TPoint modelling and automated star centering tools) the polar misalignment was causing stars to drift across a CCD image at rates of up to 1.5 arc sec/minute. This is equivalent to 0.6 pixel per minute drift at my normal CCD imaging setup (2x2 binning, F6.7), limiting unguided exposures to around 2-3 minutes,
To allow the acquisition of longer duration unguided exposures, and improve the quality/accuracy of photometry measurements necessary for exoplanet transit detection, an attempt was made at the end of the session to improve upon the existing polar alignment. Later Polar Alignement Checks showed that the polar misalignment had been significantly reduced, to a combined figure of under 2 arc min. More Notes and Procedure
| Images during Polar Alignment
Check (Previous Session, 2007-08-14) |
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South Sky Point Animation of 2 images taken 3 minutes apart illustrating northwards drift of 1.6 arc sec/min caused by 6.3 arc minutes misalignment in polar axis azimuth. (the slight drift in RA is either due principally to the inclination misalignment in the polar axis or Periodic Error and is ignored - it's the N-S drift that is measured) |
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| West Sky Point Animation of 2 images taken 3 minutes apart illustrating northwards drift of 1.0 arc sec/min caused by 3.8 arc minutes misalignment in polar axis inclination (the obvious drift in RA is due principally to the azimuthal misalignment in the polar axis and is ignored - it's the N-S drift that is measured) |
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| Images during Refined Polar
Alignment (This Session, 2007-08-28) showing Polar Axis Inclination Correction in progress |
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Annotated CCD Images 20 sec exposure, 2x2 binning, C Filter 2007-08-28 (#208106,111,113) |
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Images collected for Astrometric Monitoring
of Nearby Stars Project
Images collected for Photometric Monitoring
of Variable Stars
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| This Web Page: | CCD Images - Session 208 (2007-08-27) |
| Last Updated : | 2015-05-16 |
| Site Owner : | David Richards |
| Home Page : | David's Astronomy Web Site |
