(i.e., how do I get data from this thing?)
Rajib Ganguly
DISCLAIMER: The purpose of this document is to assist observers at
WIRO in taking data with the Long Slit Spectrograph. It is not meant
as an official manual (since I am not part of the instrument team) and
is maintained only as a courtesy by a fellow user with an ulterior
interest of seeing interesting science come out of the
instrument. This page is also not meant to serve as a guide for what
calibration frames you should be taking or how to reduce your data
(though I am happy to discuss such issues individually). An excellent
guide to slit spectroscopy written by Phil Massey, Frank Valdes, and
Jeannette Barnes is available here. I
assume that you have some experience with slit spectroscopy and that
you are familiar with what calibration frames you need to carry out
your science.
NOTE: Because the CCD used by all the WIRO instruments seems to be
having thermal "issues," it is advised that dark frames be taken over
the course of the night in order to properly account for and remove
hot pixels in all your images (save bias frames).
NOTE 2: In the following descriptions, it is assumed that the telescope is near
zenith and the CCD dewar is pointing west (and the slit is pointed NS).
Cookbook instructions for taking data with the Long Slit Spectrograph
1. Turn stuff on: There are three switches that need to be
turned on for the full function of the instrument: power to the CCD,
power to the CuAr lamps, and power to the Aquisition/Guide Camera
(A/GC). At this stage it would also be a good idea to activate the
GUIs for both the Long Slit and the A/GC on the WIRO-Prime computer
and the Voodoo program on Claudius. For the A/GC, the MaximDL program
is typically employed. If you know another program better that is
available, feel free to use it. It is probably also a good idea to
cool the A/GC. In MaximDL, one does this by xxxxxxxxx
2. Set the slit width, open the dekker: If the resolution of
your spectra is important, then be sure to set the slit width to what
is needed for your science. To do so, open the door to the instrument
and rotate the dial to the desired number. Recall from Long
Slit page that the dial measures the width in 1000ths of an inch,
with a plate scale of 0.254 arcseconds per 1/1000 in. From my own
experience, I estimate the plate scale on the detector to be roughly 1"
per pixel. Next, open the dekker so that light passes through slit to
the grating by sliding leaf out.
3. Optimize the grating tilt: Once you have figured out (based
on your science goals) what wavelength regions you want to observed,
you need to the change the grating tilt so that you cover that
region. The wavelength coverage of a single spectrum is about 2300 A
(at 1.134 A/pix dispersion). To change the grating tilt, first unlock
the grating using the knob on bottom of the instrument on the south
face. [Forget that "lefty-loosy" rubbish. Left is not a rotational
direction. Counter-clockwise is unlocking.] Once te grating is
unlocked, change the grating angle using the micrometer at the bottom
of the instrument on the west side. If the micormeter is "all the way
in" (or flush with the instrument casing), then the grating tilt will
give you the reddest possible spectrum. Set the grating angle to your
optimal tilt and the lock the grating in position using the first knob
(rotate CLOCKWISE, "righty-tighty" is meaningless). If you want Ca II
H and K, a micrometer reading of 3 12/25 is reasonable.
You can check the wavelength coverage using either the CuAr lamp or a
solar spectrum. To use the CuAr lamp, turn on the lamp with the Long
Slit GUI and make sure the flip mirror is tilted toward the
lamp. (These are both done with buttons on the GUI. They are fairly
obvious.) Then take an image with the Voodoo interface to the CCD
camera. Analyze the image any way you want. (I prefer to bring it up
in DS9, and then using the implot task in IRAF to make cut in the
dispersion direction. Note that the blue side will be on the right and
wavelength will increase with decreaing pixel number.)
To use a solar spectrum, open the dome slit, and crack open the
primary mirror cover. Make sure the instrument flip mirror is pointed
toward the A/GC. Use the sky to get a sola solar spectrum. Please do
not open the mirror all the way and/or point the telescope directly at
the Sun. 16.6 square meters of collecting area and V=-23 object is not a
healthy combination.
4. Focus the instrument: Focusing the instrument before
attempting to collimate/focues the telescope is generally a good
idea. Instrument focus is handled through a dial that sits underneath
the CCD dewar. The dial is rotated by sticking a solid narrow object
(like an Allen wrench) in one of the holes and sliding it
sideways. THe dial also acts as a micrometer so in principle one can
take reading. However, there is significant backlash in the dial, so
be wary of this.
5. Take biases (ark-loads) and darks (Chinese junk-loads)
6. Take sky flats
7. Initialize the telescope
8. Take dome flats
9. Collimate the primary
10. Take object spectra
11. Take calibration spectra
12. Reduce data. Publish. Make yourself/UW/WIRO famous: As per
the disclaimer, I can't help you here. You have to do it yourself.
Possibly useful numbers...
|
| Grating
| ICOL
| Focus
|
|
|
| Date
| Tilt
| HA
| DEC
| Telescope
| Instrument
| Temperature
| Observer
|
| 03 June 2006
| 3 12/25
| -00:00:46.0
| -00:08:51.0
| 540
|
|
| Ganguly
|
| 04 June 2006
| -2 05/25
| -00:00:46.0
| -00:08:51.0
| 540
|
|
| Ganguly
|
| 14 July 2006
|
| -00:00:56.6
| -00:08:49.3
| 562/3
|
|
| Kinemuchi
|
| 18 July 2006
| 0 10/25
| -00:00:56.6
| -00:08:49.3
| 540
| 0.312
| 63 F
| Kiminki
|
Troubleshooting...
Symptom: There's no light in the instrument...
- Cause: This will happen if the optical axis of the telescope and instrument are not nearly perfectly aligned...
- Possible solutions:
- Check the icol numbers
- Check the pointing of the telescope (e.g., with the finder scope)
- Check the mounting of the instrument. With the instrument pointed EW (and the slit aligned NS),
the rotator plate should read zero.