DIS III - Users Information

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This page last updated: February 11, 2007 - GS
This page last checked: September 27, 2004 - JMD

Basic User's Guide: DIS - 2007

Contents

Instrument Description

Basic information to know...

DIS Slit Inventory

Using DIS with TUI

UsingDIS with Remark

Lamp Calibration Spectra with DIS

DIS Quick Start Guide (PDF)

DIS Slit Orientation Calculator Page (Maintained by B.Ketzeback)

Detailed Camera Documentation

DIS Operations Manual By Robert Lupton

DIS Gratings: Blaze angle and wavelength (Russet is this info obsolete???)

DIS III Slits - photos: March 5, 2002

Craig's COMMAND QUICK COMMANDS REFERENCE PAGE.

Craig's COMMAND QUICK KEYWORDS REFERENCE SHEET.

Jon Holtzman's report on first DIS II/III characterization (note that the blue chip has changed since this report!)

Vignetting

Setting Orientation of and Placing Objects on the DIS Slit

Instrument Description

The DIS (Dual Imaging Spectrograph) was built at Princeton by Jim Gunn, Michael Carr, Brian Elms, Ricardo Lucinio, Robert Lupton, and George Pauls. It is a medium dispersion double spectrograph, which can either be used in a direct imaging mode, or as a spectrograph.

The optical path consists of a slit-mask assembly, a shutter, a dichroic (with a transition wavelength of 5350 angstroms), and two independent collimators and cameras for the blue and red sides. The gratings and mirrors are mounted on a grating turret holding two mirrors (red and blue) and two sets of two gratings. The way that the CCDs are mounted results in the dispersion in the two chips running in opposite directions.

Because the dichroic is not in a parallel beam there is a ghost image on the blue side, produced by light reflecting off the back surface of the dichroic. It's displaced by about 20 pixels to the red. When the slit is illuminated with an He arc the amplitude is about 10%; inserting the g filter totally removes the ghost. We are considering coating the back of the dichroic to reduce this effect. When using the gratings, this ghost is of course dispersed off the chip. There are also ghosts when you are taking spectra; they will also be improved by AR coating.

When being used as a spectrograph, the entrance aperture can be either a long slit or a slit mask; the total slit length is 6', and up to 5 slits of various widths can be installed.  Currently there are several available slits at APO, or users may supply their own.

Two sets of default gratings are currently installed: a Red Medium/Blue Low and a Red High/Blue High. More detailed information on the gratings can be found here.

The shutter is a rotating half-circle; this means that there is no aperture correction, even for the shortest exposures.

The slit mask assembly contains five masks; of these the first usually contains a long slit, and the second is clear. The other three are available for other, or user created, slit masks. The slit masks can be changed by on-site personnel during the afternoon checkout. All other operations can be controlled by the remote observer.

The CCDs are cooled by closed loop CryroTigers. The cameras are both cooled to approximately -100 Celsius.

More detailed information can be found here.

Basic information to know...

You should retrieve your science images off from APO computers within 7 days after they are taken, otherwise they will be deleted. We DO NOT back up data locally here. Data can be found here.

Standard Default DIS III grating setup is - Red High/Blue High & Red Medium/Blue Low.

All grating configurations and wavelength centers need to be explicity stated in your proposal. Gratings setups different than the standard must be sent requested via separate e-mail to the techstaff at APO 2 days prior to your observing run.

Please state which gratings you wish to use (eg. DIS Red - Low, Blue - Low, not DIS Low resolution gratings) and the wavelength centers you wish.

If there is a grating setup different than the standard default setup then your program time will be used, if neccessary, to make the grating change and calibrations to/from the standard default setups. Please allow approximately 25 minutes for this. The observing specialist on duty that night can advise you if/when this will need to occur.

The following are the default wavelength centers that we use for our setup calibrations, If you wish a different wavecenter or grating set, Please inform your observng Specialist at least 1 day prior to your observing run.. This gives us time to install and/or calibrate the gratings to your specifications.

DIS Spectra (Dispersion, Waverange, and (default) Wavecenters) and Offsets

The grating centers are fairly stable once set, during the start of the night, and typically do not move during instrument rotations, However movement of the turret (changing from one set of gratings to the other) can cause a grating center shift and therefore you should always repeat your cals if the turret is moved.

Rotation does cause different illumination of mirror cover flats.

Shutter times of less than 3 seconds are not repeatable.

Click the sync button (Remark) or current button (TUI) to verify your gratings, grating centers, binning, and windowing are correct. If they are not, make necessary changes in Remark/TUI and click the apply button.

Rotating DIS with Remark

+ object rotation will rotate to the star to the E.

DIS Slit Inventory

NOTES: 'Locations' were as of October 2004. "DIS" refers to slits which remain permanently availablein the so-called default slit wheel. This 'default' wheel also contains one open position for imaging-mode observations.

Using DIS with TUI

• Configuring TUI to use DIS
• Setting up DIS exposure parameters
• Taking your Calibration lamps
• Taking your Dark Frames
• Focusing DIS
• Centering your star on the slit
• Changing the DIS guider filters
• Using the auto-guider
• Setting up multiple exposures
• Taking your exposure
• Pausing an exposure
• Stopping an exposure (early Readout)
• Stopping an exposure (discarding data)
• Where does your Data go?
• Always examine your data!

DIS Quick Start Guide (PDF)

DIS III - Advanced Usage Information

Detailed Camera Documentation

• Section 1 - Photos
• Section 2 - Assembly Drawings
• Section 3 - Detail Drawings
• Section 4 - Electronics
• Section 5 - Plenums
• Section 6 - Misc. Notes 1
• Section 7 - Misc. Notes 2
• Section 8 - Installation Measurements
• Section 9 - Other Docs, Data Sheets, and Certificate of Conformance

DIS: The Double Imaging Spectrograph

Overview:

1. The Double Imaging Spectrograph

1.1 Introduction

The DIS was built at Princeton by Jim Gunn, Michael Carr, Brian Elms, Ricardo Lucinio, Robert Lupton, and George Pauls. It is a medium dispersion double spectrograph, which can either be used in a direct imaging mode, or as a spectrograph.

This manual is written in a dialect of TeX, TeXinfo, and is also available as a printed document. You can either read it using an info viewer, or through WWW (e.g. xmosaic).

1.2 Description of Instrument

The optical path consists of a slit-mask assembly, a shutter, a dichroic (with a transition wavelength of 5350 angstroms), and two independent collimators and cameras for the blue and red sides. The gratings and mirrors are mounted on a grating turret holding two mirrors (red and blue) and two sets of two gratings. The detectors are a thinned, uv-coated SITe (formerly Tektronics) 512x512 CCD with 27 micro pixels on the blue side, and a thinned 800x800 TI chip with 15 micron pixels on the red side. The gain on the blue side is 0.96 electrons/DN; on the red side it is 1.47 electrons/DN; and the readnoise is about 9.5 electrons. The electronics on the blue side misbehave for very over-full wells; the signal is set to 0, and the pixels to the side of the offending pixels are also set to 0. The way that the CCDs are mounted results in the dispersion in the two chips running in opposite directions.

The collimator focal lengths on the blue and red side are both 963mm; the camera focal lengths are 140.3mm and 141.7mm on the blue and red sides respectively; the resulting reduction is 6.865 in the blue and 6.798 in the red (the measured values are within 1/2% of this value, and vary slightly with collimator focus). The measured scales are 1.086 arcsec/pixel in the blue and 0.610 arcsec/pixel in the red. The beam diameter is 100mm, and the angle between the collimator and camera optical axes is 35 degrees. There are commands to centre given wavelength on the chips.

Because the dichroic is not in a parallel beam there is a ghost image on the blue side, produced by light reflecting off the back surface of the dichroic. It's displaced by about 20 pixels to the red. When the slit is illuminated with an He arc the amplitude is about 10%; inserting the g filter totally removes the ghost. We are considering coating the back of the dichroic to reduce this effect. When using the gratings, this ghost is of course dispersed off the chip. There are also ghosts when you are taking spectra; they will also be improved by AR coating.

When being used as a spectrograph, the entrance aperture can be either a long slit or a slit mask; the total slit length is 6', and slits of width 1.5 and 1 arcsec are installed in slit mask wheels A and B in positions A1 and B1 respectively. In imaging mode the ends of the slit are at approximately (125,250.7) and (492,251.4) in the blue chip, and (120,433.8) and (775,434.2) in the red. At the time of writing, the FWHM at the centre of the slit are about 1.4 and 1.8 pixels.

Two sets of gratings are currently installed: a 150/300 lines/mm pair, and an 830.8/1200 lines/mm pair; the blaze angles are ??. All gratings are run in first order. The low-resolution pair have dispersions of 6.2 A/pix and 7.0 A/pix for the blue and red sides; the high resolution gratings' dispersions are thus approximately 1.1 A/pix and 1.7 A/pix to within a cosine. When used for imaging, the field of view is 4'x6'.

The shutter is a rotating half-circle; this means that there is no aperture correction, even for the shortest exposures.

The slit mask assembly contains five masks; of these the first usually contains a long slit, and the second is clear. The other three are available for user-created slit masks. There are two slit wheels, which can be easily changed by on-site personnel during the night. All other operations can be controlled by the remote observer.

The CCDs are cooled by liquid nitrogen. The cameras are automatically filled from a storage dewar when empty; provided that the storage dewar is pressurised and not empty, the cameras will remain cold. The red side runs at approximately -125 Celsius; the blue side at about -100 Celsius.

There are two optical systems that must be focused in a spectrograph, the collimators and the telescope. We do not expect users to have to focus the collimators (and it can't be done remotely in any case). The telescope is focused in the usual way. Because it is not yet possible to take multiple exposures, you will have to read out the DIS after eac