MOS / OSIS quick reference sheets

MOS Run 2005 February 28 - March 09

Support Astronomers (SA): Christian Veillet and David Woodworth
Observing Assistants (OAs): Lisa Wells 2/28 - 3/3 | David Woodworth 3/4 - 3/8 | Teddy George 3/9

Feb 28 T7 (Lyo) filters: none / grisms: R300
Low-mass population studies in the Ursa Major Group and the Coma Berenices

Mar 1-3 F11 (Renner) filters: none / grisms: V150 R150-1
Physical characterisation of the Karin young asteroid family

Mar 4-5 K6 (Sohn) filters: none / grisms: O600
Spectroscopy of Early-Type Galaxies in Abell Clusters at Moderate Redshifts

Mar 6-9 C26 (Hanes) filters: 4404 , B Broadband , R Broadband / grisms: B400 , B600 , O600
Globular Clusters as Dynamical Probes of  Early-Type Galaxies: Omnipresent Dark Halos or Not?

1 GENERAL INFORMATION for the observers

1.a Accounts, passwords, configuration files

1.b Trouble reports / Emergency calls

Always check with your OA for the best procedure if you encounter problems, or need help. If you encounter problems during night, please be sure to let your SA know about it, preferably by phone, or at least by email.

Do not leave the summit for Hale Pohaku without making sure that the OA has informed your Support Astronomer of any action needed during the following day. Do not leave a problem unreported, as it could remain a problem for the next observing night (yours, or the first night of the next observer).

2 Guidance for CFHT Observers

3 MOS in numbers

Please note that STIS2 is now Dead.  The EEV1 has several advatages over STIS2: larger useable spectral range, smaller pixels (13.5 vs 21 um), faster readout (90 vs 150 seconds), and lower read noise (3 vs 9 electrons). The main disadvantage of EEV1 is the larger amount of fringing it experiences. It also has somewhat lower QE in the red. Note that, although EEV1 has 4500 rows (dispersion direction), an electronics problem prevents the readout of more than the first 3900 rows. This is still a somewhat longer dispersion range than STIS2 (52mm vs 43mm).
PIXEL SIZE  15 µm  13.5 µm 
PIXEL SCALE  0.31 arc sec  0.28 arc sec 
IMAGING FIELD: 9.4x9.5 arc min  (1790x1810)?  1990x2010 
SPECTRAL FIELD: 9.3x8.3 arc min 
(spectra can extend over the entire CCD in Y ) 
(1740x1580)?  1970x1760 
READOUT TIME (full frame)  50 sec  1.5 min 
READOUT NOISE  (7.5 e-)? 4.6 e- 
QE at 4000 Å  30%
QE at 7000 Å  95%

Orientation in imaging mode (EEV1): At bonnette angle = 0 deg, North=up (+y), East=right (+x)
Orientation of the spectral dispersion: Red=up (+y), Blue=down
Bonnette rotation: Rotating the bonnette by +30 degrees rotates the slit by +30 degrees in position angle.
Slit Orientation: At bonnette angle = 0 deg, the slit is East-West
Allowed Rotation: -90 deg to +90 deg.

Image quality: 30 to 40µm from the center to the edge, about 2 pixels.
Best focus: to be done about 3 arc min from the center.
Distortion: 0 to 120µm (from the center to the edge of the CCD)
MOS internal flexure: 0.075 arc sec/hour
MOS/Cass differential flexure: 0.2 arc sec/hour while guiding with TCS

Filters: 8 positions total: 7 filters + 1 open (5s for one position change)
Grisms: 8 positions total: 6 grisms + 1 CAF bi prism + 1 open (25s for 1 position change)
Masks: 4 positions total: 3 masks + open ( 25s for 1 position change )
Grism efficiencies: On-line MOS manual, Chapter 3, figure 6
Set up value for CAF bi-prism : 34 (since February 1997)

4 Important LAMA details

5 Some Observing procedures

Focusing with CAF: (see also Chapter 5 in the MOS on-line manual)
1) take an image of the field and find a reasonably bright star.
2) Set FRASTER sub raster of at least 300x300 pixels for MOS, 500x500 pixels for OSIS to be sure the two star images are in the field. Note that with EEV1 the standard raster (Xc,Yc = 1024,2200; Xs,Ys = 2048,3900) leaves 250 unused pixels on the ends in Y. These must be included in your calculation of the raster location.
3) Start CAF. Use the same exposure time as was used to image the field. CAF will multiply it by a factor of 10 to compensate for the loss of light in the bi-prism.
4) Select cursor then region mode in SAOIMAGE.
5) Select left-hand star image by clicking with the left mouse button.
6) Select write
7) Press Enter on the keyboard.
8) Type q in the image field.
9) WAIT for the end of the CAF process before starting another command.
10) CAF will report the best focus position. You will have to move the telescope focus to the new position with the hand paddle.
11) CAF will offer the option to try a second time. This is a good idea if the focus changed substantially (more than about 20 units).
12)When you are done with CAF, the Exposure type is left at Focus. Make sure you change it to Object or it will use the FRASTER instead of your image RASTER.

LAMA Mask preparation/cutting (see also Chapter 5 in the MOS on-line manual )
Once an image of your field has been acquired, you can process it to prepare the mask.

1) Login as "lama" on the LAMA X-terminal in the 2nd observing room.
2) Select the "Setup" form. Select the appropriate instrument (MOS/OSIS) and CCD (MIT1/EEV1).
3) Select the "Grism ENG" form and give the grism identification and parameters of your spectra: i.e. the central wavelength and wavelength range you want to cover. This will set the limits of spectra that will be overlaid on the field image when you select your objects. This is useful for defining the area of full wavelength coverage, or when you want to cut two or three series of slits per column with low dispersion grisms and/or wavelength range limited by a band pass filter. However, be aware in that case the zero order images of the slits corresponding to a given series could fall on the spectra of another series.
4) To design a mask, select "Lama Mask" from the LAMA menu bar. This form requires the following input from you: After selecting "accept" the field image will be displayed in SAOIMAGE. This SAOIMAGE is slighly different from the standard version, in particular it has a "MOS" button (for both MOS and OSIS setups). Clicking on it will give you access to the mask design menu.
5) Select the MOS button to design the mask.
6) Select, for example, "slit" in the MOS menu. This will display a GREEN slit with width and length you specified upon start-up in the image window. Drag the slit by pressing and holding down the left mouse button and positioning the cursor on the first object position; fine tune the slit position by moving the keyboard arrows, and then clicking with the left mouse button. To select this slit for later cutting type "s" on the keyboard - this will make the slit turn YELLOW. To display another GREEN slit for another object, click with the left mouse button and start again. You will not be able to move any YELLOW slit again unless you type "d" (for delete or de-select) on the keyboard: this makes the YELLOW slit GREEN again and removes this slit from the list of slits to be cut later.
7) Pan mode allows very accurate slit positioning. Click on "pan" and then on your selected object for centering the zoom window, then select high zoom magnification. Return to "MOS" for centering of the slit and validate by typing "s" on the keyboard.
8) Choose one or two "centering" bright star(s) in the field and center round apertures on them (by selecting "point" in the MOS menu and process as slits). These are invaluable to quickly set the objects into the mask apertures.
9) Once you have completed your mask design, select "do it" in the SAOIMAGE/MOS menu. The program will then create the appropriate mask design file (for instance 299742o.0l; as previously described), as well as a specially formatted "YAG" file (299742o.0ly in this case, the "y" standing for YAG) for mask cutting with the LAMA machine.
10) With the "read mask" button, you can display a previous mask file and add new apertures (perhaps with different slit geometry), thus creating a new version of the file. It is always wise to save your data from time to time when you are creating a mask with many slits in case the program or computer crashes.
11) When you are happy with the current version of your yag file, note the file name so you can find the correct file on the LAMA cutting computer.
12) Cutting the mask: The LAMA cutting machine is located on the fourth floor. Here you should find mask holders and blanks. Using the machine is quite easy: Just follow the detailed check-list for starting the machine in the LAMA manual which should be found near the machine. Ask your SA/OA to be present when doing it for the first time. When everything is ready, call up the YAG file with the file name from step 11 (299742o.0ly in our example). After finishing the mask cutting for the night do not forget to shutdown the LAMA machine

6 Additional Information

Copyright © 1997, CFHT Corporation. All rights reserved.