Spartan's Frequent Asked Questions
What is the status of all 4 detectors for science?
Detector d0 is not working. Both d1 and d2 have a bad quadrant and d3 have lots of dead pixels that must be suppressed by using a bad pixel mask and adequate dithering pattern.
How to process the data?
Spartan has no data reduction pipeline. Users often use IRAF routines to perform basic data reduction. Astrometry solution and distortion correction can be done with Astromatic.net tools (SExtractor + Scamp).
Alternatively, THELI is a useful third-party software to process imaging data from a broad range of astronomical instruments (see Schirmer 2013, ApJS, 209, 21).
Is the high-resolution mode ever used?
No. The best seeing has been 500 mas. Therefore the high-resolution mode, which samples at 40 mas/pixel, is not useful.
Do I need to refocus when I change filters?
No. The focus does not depend on wavelength, since the optics with power are all mirrors. Since the filters are placed where the beam in parallel, they do not shift the focus.
What is the shortest exposure time?
How long does it take to change filters?
The filters are on a wheel with 17 slots. It takes at most 90 s to turn the wheel completely. The J, H, & K filters are adjacent on the wheel. It takes about 10 s to change between them.
How long does it take to read an image?
It takes 20 s to read an image pair, 10 s to read to measure the amount of charge without light, and 10 s to read after integrating.
How long does it take to change the focal ratio?
Changing the focal ratio takes about 1 minute, but you would do this very infrequently.
How large is the image distortion?
The skew and distortion: The maximum is 24 pixels, and the RMS is 10 pixels.
Where can I find the image distortion?
That information is in the FITS header.
How does the instrument dither?
The observer sets the dither radius. Each time the command "to xxx" is executed, the telescope points to a random location on the circumference of the circle centered on the nominal position.