David's Astronomy Pages CCD Image Notes - Session 99 (2005-10-13)

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Notes (S100)

Goto Images from 2005-10-13

Sky Condition Graph

Sky Conditions Chart (S99)

Notice  1) Limited Mag Zero Point / Sky Mag data points which are generated for C filter image    (majority of session was in V & B filters) 2) Increase in airmass as RR Lyrae moved from 64 deg altitude down to 21 deg altitude 3) Fluctuations in FWHM due to heating interior of dew shield with hair dryer to clear dew.  Analysis of previous session (S98) shown that poor attempts at refocussing had  in certain cases caused a backward step in focussing quality. During session S99  the initial focus position was retained for the entire session.

See explanation of these graphs

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RR Lyrae Photometric Analysis (2005-10-13)

The main part of session 99 examined the variation in RR Lyrae over a 5.7 hour interval, during which 366 images were taken in each of B and V filters.  The comparison star method was used to produce calibrated magnitude estimates for the variable.  As per previous session, a distinct brightening of RR Lyrae over an interval of less than 2 hours was observed, with gradual dimming thereafter.  Data seems to be consistent with the 'standard' period of 0.56686776 days. 

Data / Data QC

Calibrated V mag and B Mag data are plotted against time in the graphs below, along with control star magnitude (shifted to fit on graph). Zero Point values determined from reference star measurements that lie above a threshold level are used to distinguish higher quality data. Analysis of QC Plots below show that the RR Lyrae brightening is real (far greater than variation in control star brightness). Quality of magnitude data is slightly compromised on occasions due to temporary formation of dew on the front lens of the LX200 scope.

Magnitude Data (B & V Filters)

V mag, B mag and B-V data is plotted here against time.  The high quality data points (passing QC) are highlighted.

Magnitude / Colour Analysis including comparison with previous sessions

V mag and B-V data was combined with data from previous sessions & plotted against phase, assuming the catalog period length for RR Lyr.

[Prior Sessions :  Data/Analysis from 2005-10-08 ]

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Altair - examination of relationships between glare pattern and focus

Bright stars have been noticed to produce off-centered glare anomalies when contrast is turned up to show dim stars.  Anomaly comprises off-centered glare around the star, together with an off-centred mirror reflection/diffraction pattern. To investigate how the pattern changed with focus position a set of images of Altair were taken, moving from before-focus, through focus, to after-focus. It was noticed that the position of the secondary light circle moves close or further to the star. 

It is thought that this off-centered glare is a result of mis-collimination of the telescope, as it appears to mimic the bias in donut light pattern  shown by out-of-focus dimmer stars.  

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Star Elongation Analysis

Examination of the distribution in star elongation direction from all images in session S89, shows that there is a preferred direction of elongation towards theta=40 deg.   This corresponds to the orientation of the offset-centered anomaly noticed during analysis of images of Alair (see above)

Elongation Direction Analysis

Analysis of elongation data from previous session also shows an  elongation bias towards theta= ~ 40 deg

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Computer Crashes

Two computer crashes occurred earlier in session (seems related to hardware/driver in someway).  Connection between TheSky and LX200 telescope was lost on two occasions and USB mouse also lost connection at one stage.   Lasts 4 hour of session went smoothly.

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