All Sky Automated Survey - Prototype Instrument

Prototype Instrument for the All Sky Automated Survey consists of the specially designed paralactic mount, and Pictor 416 - CCD camera equipped with 135/1.8 lens.

Mount

It is a horse-shoe design driven in both axes by the stepper motors. Main characteristics of the drive:

Outer dimensions: 550 mm x 550 mm x 550 mm
Horse-shoe diameter 490 mm
Max. telescope diameter 30 cm (28 cm - default)
Max. camera wieght ~ 10 kg
Camera bay: half sphere r ~ 170 mm
Mechanical pointing accuracy ~ 15 arcsec
Drive resolution in Hour Angle: 3.4 arcsec
Drive resolution in Declination: 112.5 arcsec
Positionning repeatibility: 5% of resolution (no backlash)
Max slewing rate in H.A.: 5 deg/sec = 180 deg/ 40 sec
Max slewing rate in Dec.: 150 deg/sec
Adjustment accuracy of the polar axis: ~ 30 arcsec
Possible observatory lattitudes:
- (+18 to +54) & (-18 to -54) on horizontal table
- (-70 to +70) on tilted table.

Mount accuracy can be jujged from the following images:

First is direct average of 20 frames, each 30 seconds exposure, separated by 4 mniutes. Time span between first and last image was 1 hour 20 minutes. Star images are elongated both in RA (improper time constant for the RA drive step) and DEC (very crude polar axis alignment during these exposures).

Second image is "shift and add" frame (obtained after applying proper offsets to each image).

Diagram diagram shows offsets (in pixels) necessary to bring all star images into the same places.

Exposures that we are going to take with this drive will be probably 3-5 minutes long, so even without further trimming star images should not be elongated.

Camera

Pictor 416 made by MEADE with Kodak KAF-0400 (512 x 768) is used in the prototype. The only possibility that MEADE provides to control camera is interactive PictorView (for Windows) program. We have developed independent library of C routines, enabling us to control camera over the fast (115 kb) RS-232 interface. We use X Window programs for interaction with camera via camera server (dedicated program, that talks to camera over the serial link). We had to add small fan to keep camera head at temperatures not higher than ambient +5C.

Lens

Sigmatel 135mm f/1.8 is used as our primary lens. It is a fast lens, providing pixel scale of 13.75 arcsec/pixel. The only major drawback of the lens is its strange PSF (triangular with two extended fingers). PSF is better if we observe with standard UBVRI filters.

Software

Our observing system consists of a set of specialized servers and client programs interacting comunnicating throught the Data Base (simple, remotely accecible data base system with "get", "put" and "subscribe" functions - see YOGI description).

Servers
- Data Base Server - organizes echchange of information
- Camera Server - talks to the Pictor camera, reads Pictor messages, gets images and stores them on the disk.
- Telescope Server - talks to the mount motors, converts telescope positioning commands to the stepper motor control commands.
- Image Server - reads stored FITS-files and sends them to the requesting clients (e.g. dATAview - image displaying tool).
Clients
- dATAview - image displaying tool
- Camera - camera control tool
- Telescope - telescope control tool
- Map - Sky_map, air-mass display and user catalogue tool
- Executor - program executing command scripts
- Analyst - data reduction and analysis tool

Grzegorz Pojmanski / gp@sirius.astrouw.edu.pl