CCCP DBSP observing page



DBSP observing setup and tips:

Instrument default CCCP setup:

Dichroic: D55

Gratings: red side: 158/7500. blue side: 600/4000 *** Note change ! ***

Grating angles: red side 20 deg 59', blue side 27 deg 17'.*** Note change ! ***

Slit: single long slit. Choose width according to nightly seeing.

Calibrations:

Biases: at least 5 exposures, blue and red. Easiest to get using the EXPOSE command with exposure time=0 (see below).

Dome flats: light dome lamps using the HIGHLAMP command on the vax. Take 10 exposures (easiest using the FSERIES command).
Exposure times for default setting: red side 2 sec, blue side 20 sec, per image.

At the start of the night, take the following arc exposures through a *0.5"* slit:
o Blue side:
Fe-Ar (hollow cathode), 60 seconds. *** reduced exp. time following fix of the Fe-Ar power supply.
Hg, 0.5 sec.
o Red side:
He-Ne-Ar, 0.2 sec.
Hg, 0.1 sec.
Take sets of arcs following each science exposure, with the same observing setup, only if you have plenty of time. If pressed for time, skip these additional arc exposures.

If possible, obtain two arcs well before dinner and ID the lines to verify that the wavelength coverage is as expected. The default setting should provide coverage between 3400-5600 Angstrom on the blue side, and ~4800-9400 Angstrom on the red side.

Standard stars:

Please use only standards from the following list. Other stars may have lines or other complicating features that are better avoided. These stars should appear in a list available to the 200" operator through the telescope control computer. For those I know, I have added the numbers of these stars in this list in parenthesis. Please try to observe 3 (and at least 2) stars each night. When possible, I have noted suggested exposure times for the default setting in [].

Always get these (useful for red and blue sides):

BD+262606 (9902) [Red: 5 sec. Blue: 20 sec]
BD+174708 (9903) [Red: 5 sec. Blue: 20 sec]
HD 19445 (9900) [Red: 5 sec. Blue: 30 sec]
HD 84937

You should also get some of these, for the blue side:

Feige 34 (9918) [Red: 30 sec. Blue: 60 sec]
BD+284211 [Red: 5 sec. Blue: 20 sec]
HZ44
G191B2B

Of these, the first two are better then the last.


In the afternoon:

  • Try to arrive well before dinner (15:00 is a good time to aim for, earlier in winter).
  • Meet the support astronomer and/or day crew and make sure the setup is right.
  • You need help from the day crew to change gratings and set their angles, if these need to be adjusted.
  • If this is your second night, make SURE you have all YOUR data backuped on rhea, and, if possible, on campus.
  • Wipe the disk clean of images from previous nights. Ask the support astronomer how to do this making sure there is nothing there that needs to be saved.
  • Take bias frames to make sure the system works and the cameras are alive.
  • Take arcs (remember to switch aperture to "sky"). Check the wavelength range makes sense.
  • Focus DBSP. Usual values are around 450 blue, 875 red (thanks Doug and Dave). A good way is to take a series of arcs and check the FWHM of an unsaturated, unblended line. Last few runs we found the focus minimum was rather wide, so don't be alarmed if you can't decide on the absolute location of the minimum.
  • Take dome flats. Make sure the telescope is in cass focus, the mirror cover is open, and the aperture switch is set to "aperture". Use HIGHLAMP on the vax to turn on the dome lights, LAMPSOFF to turn them off.
  • After dinner, open the dome when the sun is down. The telescope operator will carry out focus and pointing tests. You can start with a bright target (e.g. a flux standard).


    Observing tips:

    Always observe at the parallactic angle.

    If you have time, take a set of arcs after each science observation, before moving to the next one.

    However, if pressed for time, it is better to skip the arcs to get more science.

    Generally, there is no need to dither along the slit, as in LRIS. However, if you want to do this, a useful tool exists on the slit viewing computer (on the rack between the vax computer and the telescope operator's console). You can mark a fiducial place on the slit with a yellow cross and have the target always fall there. You can then measure an offset along the slit using the "measure" button and moving the cursor. On the screen you will see the required RA and Dec offsets for this dither, for the given PA of the slit. Ask Jean for a demonstration if She's there.


    Useful vax commands:

    General:

    The vax system will prompt you for every required parameter of a command you print. You don't have to remember any syntax - just print the command name and the system will take care of the rest.

    In commands that involve an image being taken, you will be prompted for the display parameters for that image. The bias levels are ~3000 counts in the blue side, and a little above 5600 counts on the red side. Useful ranges to put in for convenient setting of the display grey levels are 2900-3300 counts in the blue, 5600-6000 counts in the red. After setting the grey levels, you are prompted for other, less useful parameters, which you want to leave unchanged usually. To do that, hit the backslash key (\), to the left of the enter key, then enter.

    Taking data:

    SNAP: Take an exposure using a single camera (either blue or red). The user is prompted for the camera number (1=blue, 2=red), exposure time, and object name.

    EXPOSE: Take an image with both cameras. User is prompted for exposure time (same in both cameras) and object name.

    FSERIES: Take a sequence of images with one of the cameras. User is prompted for camera number (1=blue, 2=red), exposure time and object name, which are the same for all images in the series. Useful for taking a sequence of flats while doing something else (e.g., eating dinner). Select "no" when asked if the image should be displayed, otherwise the sequence stops to wait for your input about the display parameters.

    Note: in any case, the two cameras read out in sequence, not in parallel. Using EXPOSE saves time when long and equal integrations are required on both sides, since both cameras integrate at the same time. However, when the exposure times are short (and thus negligible when compared to the readout time) and you wish have different exposure times on the red and blue side (e.g., for a standard), then using SNAP twice is more convenient.

    MOD EXP: Modify the length of an exposure while it is in progress.


    Display and quick look analysis:

    IMAGE: Displays and image on the screen. User is prompted for image name and display parameters.

    COLOUR GREY: Resets the screen grey levels, which get scrambled sometimes when the user sets the display in a way it saturates. Note the spelling of "colour"...

    EXTRACT: Perform a simple spectral extraction from an image. The user is prompted for the range of lines summed in the extraction. No background subtraction, so sky lines remain. The result is written into an output spectrum set by the user.

    YXTRACT: Same as extract, but for a cut in the y direction. Useful for finding the raws on which an object is traced.

    SPLOT: Display a spectrum created with EXTRACT .


    Data transfer:

    The files are recorded on the DBSP computer, called sam (sam.palomar.caltech.edu). You can ftp them from the vax screen using:
    ftp rhea
    user
    user
    (rhea's password, written on rhea's box)

    Alternatively, you can ftp sam from rhea using:
    ftp sam
    user ccd
    (sam's password, written on sam's screen)

    From rhea you can scp out to any campus computer.

    At the end of the night, you may want to remove the bias line from all your files using the IERASE command used in a script run on sam. Ask around how to do this if you don't know.

    If you have time, it may be a good idea to run fig2fits on rhea to transform all the images to fits format before you scp them to campus.

    Scripts: an easy way to get all the images bias-subtracted on sam using the ierase command, all in one go:

    1) Copy all your .dst files from sam to rhea using ftp.
    2) Make a list using: ls *.dst > flist
    3) make the command script by typing:

    awk '{print "ierase "S1" b"$1}' flist | sed s/.dst//g > flist.com

    4) ftp this file back to sam
    5) run it using @flist.com - this will "ierase" all your files.
    6) ftp all ierased files (bs*n.dst) back to rhea for transfer to campus.
    ***problem: last time I could not make this work. ***

    Reductions:

    To reload our CCCP directory structure onto rhea:
    Go to here and download the tar file into /home/user/cccp.

    Then run: tar -zxvf palomar.tar.gz

    and you're ready to go.

    Just follow directions you can find here and you can get quick reductions in no time at all.


    Constructed: August 2004, by: Avishay Gal-Yam , E-Mail: avishay@astro.caltech.edu