Etalon control

 

fp <etalonz>

Set the etalon position to etalonz. This is actually a script that executes the command fabry s <etalonz>, and then ensures that the setting is saved in the image header via the NIGHT variable in FIGARO. (The snvfits command then transfers the value of this keyword to the ETALONZ FITS header keyword.)

fabry [ i <etalonz> | q | r | s <etalonz>]

Directly command the CS-100 Fabry-Perot controller. There are four distinct command sequences:

i <etalonz> - increment the etalon position

q - query the etalon position

r - release computer control of the etalon controller

s <etalonz> - set the etalon position

Any command except r should enable computer control of the etalon controller, activating the ``disabled'' indicator on its front panel (see Figure 11).

fpseq <camera> <name> <startz> <deltaz> <nexp> <dcal> <time> <filter> <tcal> <calfilter> <wait> <waitdome> <display> <spawn>

Perform a sequence of Fabry-Perot observations. This is a crucial script, which is used to observe multiple frames at various Fabry-Perot etalon spacings, e.g., an entire data cube. fpseq takes care of modifying/stepping the etalon position, exposing the CCD, changing filters, and stopping for periodic images of the calibration lamp. At the 200-inch telescope, the calibration lamp is operated by the script as well. The parameters are as follows:

camera=<n>

The camera port number to use; usually 0.

name

The image title.

startz=<n>

Initial etalon position for the sequence of observations. The exact value is not important, although 10 is a typical number. If the deltaz parameter is set to zero, this parameter is ignored.

deltaz=<n>

The step between etalon settings. The value depends upon the resolution of the etalon being used at the wavelength being observed, and the desired sampling. For example, in the common case of H$\alpha$ 6563Å observations with the Palomar ET-50 etalon, the intrinsic resolution of 23 km/sec corresponds to 32 etalon steps. Therefore, for Nyquist sampling, deltaz should be set to a value of 16.

If deltaz is set to the special value of 0, the user will be prompted for the name of a text file containing the etalon settings for the data observations (one value per line). This mode of operation allows the user to easily observe partial cubes, modify the order of the observations, etc.

nexp=<n>

The total number of exposures to be taken. This value includes both calibration and data frames. The cube should usually include sufficient data frames to encompass slightly more than a free spectral range of the etalon at the wavelength being observed. For example, in the common case of H$\alpha$ 6563Å observations with the Palomar ET-50 etalon, the intrinsic free spectral range corresponds to approximately 672 etalon steps. Therefore, nexp should include about 45 data frames (assuming deltaz = 16).

dcal=<n>

Interval for calibration/stability frames. A image of the calibration lamp with the fiducial etalon spacing of 100 will be taken before every dcal-1 object frames. This number should be set so that a calibration frame is obtained approximately every 20-30 minutes during the observation. These images will be used to monitor the stability of the Fabry-Perot over the course of the observation, including such effects as temperature and humidity variations, telescope flexure, etc.

time=<n>

Exposure time for data frames. This value is typically determined so that the entire sequence of frames will fill the available time. See Section 4.2.3 for details on determining the optimal exposure time.

filter=<filter>

The filter to use for data frames.

tcal=<n>

Exposure time for calibration/stability frames. Typical values are 15 seconds for the Neon calibration lamp, 30-60 seconds for the Hydrogen lamp.

calfilter=<filter>

The filter to use for calibration/stability frames. Usually the Neon lamp is used, and the 6598.95Åemission line is observed through a filter centered at 6593Å. There is also a Hydrogen lamp that may be used, although it is fainter, so the exposure times must be lengthened accordingly (see the tcal parameter above).

wait=[no|yes]

Wait for an exposure to finish in the foreground, or create a background process? This will almost always be yes, so that exposures longer than 60 seconds will not be placed in the background, as this would allow the script to continue to the next command before an exposure has been completed.

waitdome=[no|yes]

Pause interactively for each calibration/stability frame? Usually the calibration frames are obtained by occulting the telescope with the dome and then illuminating the dome with the calibration lamp. For night-time object observations, this option is almost always set to yes, in order to allow time for the dome to be moved to occult the telescope. For non-interactive daytime calibration observations, such as a calibration cube, this option should be set to no.

display=[no|yes]

Display each frame after it is obtained? This flag is often set to yes, so that the user may monitor the progress of the data cube on the image display monitor. Alternatively, the image command may be used from another terminal to examine images manually, although this should be done only during an exposure, not during read-out of the CCD.

If the display=yes option is used, be sure to display a typical image with the image command, before running fpseq. This is to make sure that the default minimum and maximum image display values are appropriate to the data being obtained. Failure to do this may result in the display of images with inappropriate limits.

spawn=[no|yes]

Spawn an image process? If the display parameter has been set to yes, then this should be set to yes as well, so that image display processes are spawned in the background. This allows the script to proceed most rapidly with exposures, without being required to wait for images to display. Note: Due to the nature of the fpseq script, it is recommended that this parameter always be set to yes.