Each of the measurements is taken using the Johnsons V filter. Each of the measurements has an error value associated with the magnitude measurement. This error term, when added to the magnitude value forms a plot slightly above the magnitude value curve. The error term, when subtracted, gives the lower curve.
As is clear from the large plot, the V magnitude for QQ Vul ranged from 14.72 down to 15.36 during this run.
So we have error terms and so forth. One might question the accuracy of the data making up the large chart. Might there be atmospheric factors which might affect the results? We will attempt to answer this question. We assume the camera records data in a linear fashion, and assuming this, lets look at the other charts.
Atmospherics
Atmospherics is presented in the top three charts. The leftmost measures focus quality, the center chart measures background, and the rightmost measures zero point. The X axis reflects fractional julian date and is the same scale used on the large magnitude chart. The Y axis and values are described below.
Focus Quality
Quality of focus is measured in units of Full Width at Half Magnitude, and is related to seeing conditions.
Click on the Seeing Conditions link to learn more. FWHM is computed for each image in the series and is presented in the graph. In our chart, the focus provides a seeing value of around 4 arcseconds across the entire series. Notice there is no upward trend as might be seen if focus was shifting. Focus would shift throughout a run of this length due to dropping temperatures typically experienced across a series run. For more information about this topic see the Truth About Focus.
My scope has a temperature compensating focus capability, so the focus curve is being moified as the compensation mechanism does its job. The graph pretty much tells me that shifting focus did not degrade the data being taken.
Background
Note the general form of the curve. It starts out at around fifty, and then lifts off the chart. The background value is the number of ADU per second recorded by the detector due to background light. A good evening usually produces a background of around 20. In a dark site the number may be around 9, or even less in truly dark conditions. The high value of 50 was due to the proximity of the moon. As the moon rose higher, it provided more photons per second. Other possibilities for fluctuating background in the Washington DC area is changing levels of moisture in the air. In our light polluted skies, moisture scatters the light and reflects part of it back down toward the telescope. If the chart had shown a beginning value of something like 20 gradually increasing through 40, One could reasonably conclude that the sky conditions had begun to deteriorate.
Zero Point
Another measure of seeing quality is the Zero Point. This point depicts the magnitud at which a star is completely invisible in the background. This measurement often decreases as the telescope points through increasingly more atmosphere as the series run continues. This occurrs because as the scope drops from zenith toward the west, more and more atmosphere is between the telescope and the sky. A more comprehensive discussion of zero point was given by Michael Newberry of Mirametrics. This response can be found here.
Comp Star Analysis
The three center charts deal mainly with the comparison stars used to determine the magnitude of the target (QQ Vul). I use three comparison stars to determine the magnitude of QQ Vul, but provide data only for the first two in the plots. The two comparison stars have magnitudes of 14.8 and 14.0 V.
Check Star
The Check Star plot shows the magnitudes of the two comparison stars and the target star. The point of this is to demonstrate or assure that the comparison stars do not vary. The Variable star plot adds little useful information except to demonstrate relative magnitude differences between target and comps.
DeltaMags
The DeltaMag plot shows the change in magnitude of the variable and comps over the series time. The comps should change very little over time so their lines should be flat. The polar variable, of which QQ Vul is an instance, may show considerable change in magnitude over small time intrements. This is readily demonstrated on the center plot. What is expected to be demonstrated is the the fluctguations of the variable exceed by a considerable margin the fluctuations of the check stars. If this is not the case, then atmospheric issues must surely have had significant impact on the imaging of the variable.
Error
Finally, the error across time for the variable and the two check stars is recorded. The data shown on this chart is shown on the large chart. Error data is drawn above and below the mean error line (in the center).
