Observational
Lab
with the Bengt Westerlund
Telescope (BWT)
Goals
Take images of bright
galaxies in three filters BVR. Combine them into one true color image.
Strategy
Try to achieve the best
dynamic range by adjusting the exposure time with each filter.
Calibrations
a)
Take calibration
frames for the dark current at different exposure times and derive bias level
and dark current rate. Keep track of temperature of the CCD.
b)
Take flat fields
using the same derotator position as for the targets
(see below).
Hint: if the same
derotator position is used for all targets and
filters than a single set of flat fields can be used for all observations.
Targets
a)
Go to the first
object, make sure you are there and note the current ART angle in AutoSled (Angle of the camera mount Relative
to the Telescope).
b)
Take images
(longer than 5 minute exposures require the use of offset guider) in the first
filter.
c)
Move back the derotator to the initial ART value. Take next filter
images.
d)
Repeat c) for the
last filter.
e)
Go to next
object, return the derotator in the initial position
and repeat steps b), c) and d).
Questions and topics to
include in the report
a)
What was the
level of bias and dark current derived and how did you do it?
b)
How did you
combine flat field exposures?
c)
What was the
signal-to-noise ratio in the combined (master) flat?
d)
How did you
determine the dynamic range of the target images?
e)
What was the
limiting factor for the length of a single exposure?
f)
How does the
optimal exposure time depend on the filter and why?
g)
Present images.
List of targets
The table below contains a
list of galaxies that can be observed in the evening during the winter. Columns
give name in Messier catalogue, coordinates (2000 epoch), hour (local time)
from which observations can be carried out, angular diameter (arcmin) and B magnitude.
|
Target |
a |
d |
Time |
Size in arseconds
|
Bmag |
||||||
|
M110 |
00 |
40 |
22.00 |
+41 |
41 |
07.0 |
18 |
18.62 |
x |
11.48 |
9.4 |
|
M32 |
00 |
42 |
41.87 |
+40 |
51 |
57.2 |
18 |
9.12 |
x |
6.61 |
9.2 |
|
M74 |
01 |
36 |
41.84 |
+15 |
46 |
59.6 |
18 |
10.47 |
x |
9.55 |
10.5 |
|
M81 |
09 |
55 |
33.17 |
+69 |
03 |
55.1 |
18 |
22.38 |
x |
11.48 |
8.1 |
|
M82 |
09 |
55 |
52.19 |
+69 |
40 |
48.8 |
18 |
10.47 |
x |
4.36 |
9.2 |
|
M108 |
11 |
11 |
31.29 |
+55 |
40 |
31.0 |
20 |
8.13 |
x |
2.75 |
10.7 |
|
M109 |
11 |
57 |
35.90 |
+53 |
22 |
35.0 |
20 |
7.08 |
x |
4.57 |
10.7 |
|
M106 |
12 |
18 |
57.54 |
+47 |
18 |
14.3 |
22 |
16.98 |
x |
6.46 |
9.6 |
|
M94 |
12 |
50 |
52.63 |
+41 |
07 |
09.3 |
23 |
12.58 |
x |
10.96 |
8.7 |
|
M63 |
13 |
15 |
49.28 |
+42 |
01 |
46.5 |
23 |
13.18 |
x |
7.94 |
9.7 |
|
M51 |
13 |
29 |
52.37 |
+47 |
11 |
40.8 |
23 |
8.32 |
x |
7.08 |
8.8 |
|
M102 |
15 |
06 |
29.48 |
+55 |
45 |
47.2 |
23 |
6.46 |
x |
3.16 |
11.1 |
Data files: