7.5 Calibration Frames
89
down by 5
◦ C and repeat the cycle. Take 1, 5, 10, 30, 60, 120, and 240 s exposures
at the new temperature.
8. Continue this cycle down to the same temperature at which you took your last
bias frame.
9. Once you have downloaded all your frames, open each frame in FITS Liberator
(Fig. 7.7). The image statistics panel on the right-hand side, next to the image,
shows the Image Statistics. Record the Median and the StdDev from the Input
column for each image. This represents the median pixel value in the array and
the standard derivation of the array, i.e., how much it varies. Do this for all your
images and record the results on spreadsheets as two tables, with one table for
the bias frames and one for the darks. You can use the Image Header Tab in
FITS Liberator to confirm the temperature at which each image was taken and
the exposure time.
10. For each block of five images, for both the bias and dark frames take the mean
of the median count values and of the temperature, making a note of the spread
of the median count values (the maximum value minus the minimum value), as
this will be used for your uncertainties. Use these to make two new tables, one
for the bias frames and one for the dark frames.
11. Looking at the bias, plot the mean bias median value (y) against mean temperature (x). Your error for each point should be
±
x
2
√
N
,
(7.1)
where x is the spread of that point, and N is the number of measurements in
that point, i.e., in this case, five.
12. Think about what the point at which the line crosses the y-axis represents and
whether the temperature has a large impact on the bias. From your standard
deviation data, does the bias frame change much across the CCD? If it does,
what causes this?
13. Moving on to the dark frames. For each exposure time, plot mean bias median
value (y) against mean temperature (x) using (7.1) for your error bars. Do this
for each exposure time, plotting all seven exposure times on the same graph if
possible.
14. Keep in mind that the bias is part of the reading process, and so it appears in the
dark frames. You will need to address this in your analysis.
15. If you have access to another camera, particularly a different model of camera,
and have the time, repeat the process.
Analysis
You should write your report up in standard laboratory style: introduction, method,
results, and conclusions. You should include all your tables and your plots as well
89
down by 5
◦ C and repeat the cycle. Take 1, 5, 10, 30, 60, 120, and 240 s exposures
at the new temperature.
8. Continue this cycle down to the same temperature at which you took your last
bias frame.
9. Once you have downloaded all your frames, open each frame in FITS Liberator
(Fig. 7.7). The image statistics panel on the right-hand side, next to the image,
shows the Image Statistics. Record the Median and the StdDev from the Input
column for each image. This represents the median pixel value in the array and
the standard derivation of the array, i.e., how much it varies. Do this for all your
images and record the results on spreadsheets as two tables, with one table for
the bias frames and one for the darks. You can use the Image Header Tab in
FITS Liberator to confirm the temperature at which each image was taken and
the exposure time.
10. For each block of five images, for both the bias and dark frames take the mean
of the median count values and of the temperature, making a note of the spread
of the median count values (the maximum value minus the minimum value), as
this will be used for your uncertainties. Use these to make two new tables, one
for the bias frames and one for the dark frames.
11. Looking at the bias, plot the mean bias median value (y) against mean temperature (x). Your error for each point should be
±
x
2
√
N
,
(7.1)
where x is the spread of that point, and N is the number of measurements in
that point, i.e., in this case, five.
12. Think about what the point at which the line crosses the y-axis represents and
whether the temperature has a large impact on the bias. From your standard
deviation data, does the bias frame change much across the CCD? If it does,
what causes this?
13. Moving on to the dark frames. For each exposure time, plot mean bias median
value (y) against mean temperature (x) using (7.1) for your error bars. Do this
for each exposure time, plotting all seven exposure times on the same graph if
possible.
14. Keep in mind that the bias is part of the reading process, and so it appears in the
dark frames. You will need to address this in your analysis.
15. If you have access to another camera, particularly a different model of camera,
and have the time, repeat the process.
Analysis
You should write your report up in standard laboratory style: introduction, method,
results, and conclusions. You should include all your tables and your plots as well