UNIVERSITY OF HAWAII Institute for Astronomy. f/31 High Angular Resolution Imaging Spectrograph HARIS USER MANUAL update June 10, 1997

Transcription

1 UNIVERSITY OF HAWAII Institute for Astronomy f/31 High Angular Resolution Imaging Spectrograph HARIS USER MANUAL update June 10, 1997 To print more copies of this document, type: dvi2ps 88inch/mkoman/haris/haris

2 Contents 1 f/31 High Angular Resolution Imaging Spectrograph HARIS Introduction : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : Schematic Overview : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : Configurations : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : Cameras, Collimators and Slits : : : : : : : : : : : : : : : : : : : : : : : : Gratings and Resolution : : : : : : : : : : : : : : : : : : : : : : : : : : : : Selecting Grating Tilt Angles : : : : : : : : : : : : : : : : : : : : : : : : : 5 2 Setup Changing the LFC Camera : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : Changing the SFC camera : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : Changing the slits : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : Changing filters : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : Changing the Grating : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : Focusing the LFC : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : Focusing the SFC : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : Startup : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 11 i

3 List of Figures 1.1 Front view of the f/31 HARIS spectrograph with the components and optical paths indicated. : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : Side view of the f/31 HARIS spectrograph with the components and optical paths indicated. : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 4 ii

4 List of Tables 1.1 f/31 HARIS Spectrograph Components : : : : : : : : : : : : : : : : : : : : : : : : f/31 HARIS Spectrograph Gratings and Dispersions : : : : : : : : : : : : : : : : : : f/31 HARIS Spectrograph Grating Settings : : : : : : : : : : : : : : : : : : : : : : 8 iii

5 Chapter 1 f/31 High Angular Resolution Imaging Spectrograph HARIS 1.1 Introduction The f/31 High Angular Resolution and Imaging Spectrograph (HARIS) is an efficient and versatile two-camera spectrograph. It was built as part of an NSF research project by Dr. Alan Stockton at the IfA to take advantage of the excellent image quality of the University of Hawaii s 2.2-m telescope and f/31 tip-tilt secondary (3 arcsec/mm scale, 4 arcmin field). It can be used with the IfA s CCD and NICMOS detectors for imaging and spectroscopy of faint and/or extended objects in the wavelength range m, at spectral resolutions in the range , and angular resolution down to 0.3 arcsec. Users can select one or both of two available camera ports. The long camera port (LFC) can support a CCD detector, at a detector image scale of f/10 (9.2 arcsec/mm). The short camera port (SFC) can support a CCD detector, usually at an image scale of f/4.5 (20.9 arcsec/mm). The spectrograph may thus be configured for two alternate or complementary observing modes, and rapidly switched between them at night (by switching the grating blaze). Exchanging slits and filters, focusing cameras and tilting the grating to select wavelength may all be managed remotely via an X-window interface on a Unix workstation, communicating with a PC-BitBus controller. Exchanging gratings, switching their blaze for use in the other camera port, and rotating the cassegrain rotator to obtain specific position angles must be done manually. Slits are aligned N-S with the Cassegrain rotator in its standard (270deg) orientation. Slit Position Angles can be altered by at least 90 degrees either side of this to achieve any Sky PA however; the rotator setting appropriate to a desired slit PA can be found from the tcsi interface. Changing Position Angle must be done with the telescope at the Zenith, and necessitates recalibrating the offset guider; this process normally takes about 15 minutes. Target objects must be carefully aligned on the (known) slit position by imaging either in the detector plane, or at a small below-slit Lynxx CCD. Since HARIS operates at f/31, targets may be either slow (telescope) guided, or fast-guided on the slit, and the Atlas guider can also be used to command small alignment offsets. Calibration is currently achieved with flat-field and arc lamps attached to the telescope top-end ring, illuminating the dome. An internal system illuminating a retractable white screen in the telescope central baffle is planned. 1

6 2 1.2 Schematic Overview Light from the f/31 focus of the UH 2.2-m telescope is focussed on the slit-plane of the spectrograph, which consists of a wheel with one open position, and provision for 4 fixed slits of different widths. Maximum slit length is 80 mm (4 arcmin at the f/31 telescope scale of 3 arcsec/mm), and this field is limited by coma increasing to 0.25 arcsec at 2 arcmin off-axis. The slits are tilted to allow for future slit-viewing capability. Below the slit wheel and on a common shaft are 2 filter wheels, each containing one open position and provision for four 4-inch circular filters. The upper wheel is reserved for user filters, the lower for standard Cousins/Mould B, V, R, I filters. A field-view mirror can be inserted below the filter wheels to feed a small Lynxx CCD-TV which can be used to view and align the target object at the slit position, and to check knife-edge (telescope) focus through a wide slit. When this mirror is retracted, light proceeds to a fixed, aluminum-coated collimator of focal length 1253 mm, to form a 40 mm collimated beam. An alternate silver-coated collimator is planned for observations redwards of 4000 Å. The collimator folds the beam back to a translation stage which moves to insert either a mirror (for focal reduced imaging) or grating into the beam. The mirror can be toggled between the two (LFC and SFC) camera port positions. There are currently 14 gratings providing a range of resolutions at various blaze angles. All gratings can be (manually) inserted with blaze directed to either camera port. The reflected or diffracted beam can be directed towards either the SFC or LFC transmission cameras, which refocus the light onto a CCD detector (SFC) or CCD or NICMOS detector (LFC). Users have a choice of three 180 mm Nikon lenses for the SFC, coated for optimum performance in the Blue, Visual and Red wavelength regions respectively (these are the same as the f/10 FOS N180 camera lenses). There are currently two custom-built 400 mm lenses for the LFC, optimized for use in the Visual- Red or Infra-red wavelength regions. Another LFC camera optimized for the UV is planned. Schematic views of the f/31 spectrograph are shown in Figures 1.1 and Configurations Cameras, Collimators and Slits The available optical and slit components for the f/31 spectrograph are summarized in Table 1.1 below Gratings and Resolution The available gratings and the reciprocal dispersions they provide with LFC and SFC cameras are summarized in Table 1.2. The wavelength coverage for the Tek2048 CCD (24m pixels) and NICMOS detector (40m pixels), together with the projected slit sizes corresponding to a slit width of 1 arcsec are also given. Each grating is clearly marked with its grooves/mm, blaze wavelength and camera orientation, on both sides of the grating. When inspecting the grating through the grating access port, you should see SFC or LFC pointing towards the camera you are actually using. If not, insert the grating cover, unclamp and remove the grating, switch the cover to the alternate direction (taking care not to touch

7 1.3. CONFIGURATIONS 3 Figure 1.1: Front view of the f/31 HARIS spectrograph with the components and optical paths indicated.

8 4 Figure 1.2: Side view of the f/31 HARIS spectrograph with the components and optical paths indicated.

9 1.3. CONFIGURATIONS 5 the grating surface), and reinsert and reclamp the grating Selecting Grating Tilt Angles The Grating encoder has 450 counts/degree (8 arcsec/step), and is generally very repeatable provided it has been initialized correctly. The Grating Home position (after reset) is (tilted towards the LFC). The grating-horizontal setting is At the moment, wavelengths are selected by entering grating rotary-stage encoder (GE) settings derived from the grating equation: = 2sincos(17:5 ) 10 7 nd sin = 10 7 nd 2cos(17:5 ) or (1:1) (1:2) where is in Å, n is the order, D is grooves/mm, 17:5 is the camera-to-collimator semi-angle, and is the dispersion angle. If i is the tilt angle (away from horizontal) measured towards the camera in use, and GE is the Grating Encoder setting, then i = + 17:5 and GE = i 450 (1:3) Zero orders to short and long cameras ( = 0:0;i=17:5) are: = ( ) (SFC settings > 25875); and = ( ) (LFC settings < 25875). Grating Encoder settings for various gratings and selected wavelengths are listed in Table 1.3. Other settings can be interpolated from here.

10 6 Table 1.1: f/31 HARIS Spectrograph Components Collimator 1253mm Aluminum coated SFC N180B 180mm Nikkor ED f/ (blue: nm) cameras N180V 180mm Nikkor ED f/ (visual: nm) N180R 180mm Nikkor ED f/ (red: nm) LFC 400VR 400mm visual-red nm cameras 400IR 400mm infra-red m Slits m mm arcsec arcsec Notes: 1 Old slit made with blades; other slits are precision machined. 2 Slits machined from thinner material, shimmed to same height (focus) as other machined slits.

11 1.3. CONFIGURATIONS 7 Table 1.2: f/31 HARIS Spectrograph Gratings and Dispersions Grating Grating Blaze SFC 1 180mm Camera LFC 2 400mm Camera Ref. Pitch Wavelength Dispersion 1-arcsec Slit Dispersion 0.5-arcsec Slit No. groove/mm Å Å/mm Proj. m Å/mm Proj. m Notes: 0 Resolution and sampling information assumes a CCD with 24m pixel size. For the Tek2048 CCD, wavelength coverage is Dispersion multiplied by 50mm. The same coverage and resolution can often be obtained with either camera. The SFC will use a wider slit (more light and less spatial sampling). The LFC requires a narrower slit, provides more spatial sampling, and can reach the highest resolutions. 1 The SFC provides slit-limited resolution (2-pixel projected slit) with a 1-arcsec slit. Wavelength resolutions are 8.6, 4.3, 2.0 and 1.3 Å with the 300, 600, 1200 and 1800 line/mm gratings respectively and a 1-arcsec slit. The spatial sampling is 0.51 arcsec per 24m pixel with the 180mm SFC. 2 The LFC provides slit-limited resolution (2-pixel projected slit) with a 0.5 arcsec slit. Wavelength resolutions are 4.2, 2.1, 1.05 and 0.66 Å with the 300, 600, 1200 and 1800 line/mm gratings respectively and a 0.5-arcsec slit. The spatial sampling is 0.23 arcsec per 24m pixel with the LFC.

12 8 Table 1.3: f/31 HARIS Spectrograph Grating Settings tilt +450tilt Grating Wavelength Tilt Angle Grating Encoder No. l/mm Å Degrees LFC SFC J H K m

13 Chapter 2 Setup 2.1 Changing the LFC Camera A panel can be removed (with knurled plastic screws) from above the LFC camera port. The LFC consists of two lenses (one moveable for focus) and two fold mirrors attached to a plate which slides in grooves along the left side of the spectrograph casing. A small trigger allows a lever to be operated which causes the LFC to slide out slightly. It should then be held firmly by its handle, taking care to avoid touching any optics, and slid fully out. There are two wooden, velvet-lined boxes in the coudé slit-room cabinets, and the LFC should be carefully slid into the grooves in the appropriate visual or ir box. To put an LFC camera back, hold the camera firmly by its handle, position it carefully at the start of its guide rails, slide it fully in, and lift the lever to lock it in place. 2.2 Changing the SFC camera This can be reached from the LFC port after removing the LFC camera (which should be replaced after this operation). Reach carefully right across the inside of the spectrograph to release two knurled metal screws on the right side of the holder. The camera in its holder can then be picked up, slid out of the locating rings, and removed, taking care to avoid touching any optics. Currently there is only one holder, so put the SFC lens of choice into this holder, and replace by reversing the above procedure, taking care to secure the locking screws. it Note: The Nikon N180B, N180V and N180R lenses are the same as used in the f/10 FOS spectrograph. They remain clamped in their base holders, but the base holder must be removed (4 screws) from its FOS holder mount, and attached (4 screws) to the holder in the HARIS spectrograph from the outside (detector removed) with the holder already in place. 2.3 Changing the slits The available slits are listed in Table 1.1. The slits are screwed to tilted mount wedges (total of 5), which insert into cylindrical holders (total of 3 in some cases tape down the wedge for stability). The holders can be inserted into the spectrograph slit wheel through the wheel access port. They are inserted from below, and rotated 1/8 turn to lock into place. Slits are stored in a box in the cabinet in the coudé slit room, and holders are normally in the spectrograph. 9

14 10 CHAPTER 2. SETUP Thus you can have 5 (of 6) slits mounted on wedges, and 3 slits in the spectrograph. It takes a few minutes to remove a slit holder, swap the slit wedge, and remount the slit holder. Slit wheel positions are labelled OPEN, S1 S3. When S1 is selected in the spectrograph menu, this means that position S1 is in the beam. The slit wheel (and filter wheels) can be moved manually at the spectrograph port by pressing the appropriate button inside the door. 2.4 Changing filters Each wheel has positions for four 4-inch circular filters, which should be held quite firmly by the spring clamps. Positions are labelled F1 F4 (upper filter wheel) and F5 F8 (lower wheel). Selecting F1 in the spectrograph menu means that position F1 is in the beam. 2.5 Changing the Grating Move the grating translation stage to GRATING, and turn the grating tilt to about (horizontal). Open the grating port, insert the cover for any grating in place, release the grating lock latch, and remove the grating with its cover. Replace the new grating with its cover, lock the latch, then remove its cover. Replace the removed grating in its appropriate slot in the grating boxes. There are 14 gratings stored in 4 labelled red boxes in the coudé slit-room cabinet. Please take care to remove and replace these gratings with their gold anodized covers in their proper places, with the cover holder towards the bottom of the box, to avoid removing the cover accidentally while removing the grating. Each cover can be put on from either side, to allow inserting the grating into its holder with the blaze towards either camera (SFC or LFC). Each grating is clearly marked with its grooves/mm, blaze wavelength and camera orientation, on both sides of the grating. When inspecting the grating through the grating access port, you should see SFC or LFC pointing towards the camera you are actually using. If not, insert the grating cover, unclamp and remove the grating, switch the cover to the alternate direction (taking care not to touch the grating surface), and reinsert and reclamp the grating. Grating Encoder settings for various gratings and selected wavelengths are listed in Table 1.3. Other settings can be interpolated from here. 2.6 Focusing the LFC This is done as option F4 of the SETUP menu (option F9 in the main menu). Note that the LFC encoder is extremely fine; 10 counts/m. Focus can normally be achieved to the nearest 1000 encoder units, which represents 100 m of focal plane movement, or 10 m of image blur at the detector. LFC focal limits are -6,000 to 100,000, with decreasing numbers moving the focal plane towards the detector. 2.7 Focusing the SFC This is done as option F3 of the SETUP menu (option F9 in the main menu).

15 2.8. STARTUP 11 SFC focal limits are 0 to 5,000, where 1 encoder unit now represents 10 m of camera movement (100 timescoarser than for the LFC), and increasing numbersmoving the cameratowards the detector. Focus should normally be achieved to 5 units, representing 50 m of focal travel, or about 10 m of image blur with the 180mm cameras. 2.8 Startup The spectrograph is under BITBUS control from the f/31 BITBUS racks mounted beside the spectrograph, and controlled by a BITBUS card resident in a PC (generally the Guide Dell). Check with the crew that everything is cabled and powered up before starting to operate the spectrograph. The HARIS f/31 software can be run on the PC directly, or started as an X-window on tycho for TO control, or on halley for observer control. With DESQview running on the guide Dell, type haris to launch the control window on tycho, or halis to launch it on halley.