HBO Instruments

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James R. Houck telescope Cassegrain focus: effective focal length 8.57m, plate scale 41 um/arcsecond (24.4 arcsec/mm).

Filters for direct imaging

Standard 2x2 inch filters
Band Wavelength
(A)
FWHM
(A)
DN
(10th Mag)
DN
(sky)
Johnson Filters
U 3600 500    
B 4300 900    
V 5480 900    
R 7000 1600    
I 9000 1500    
Narrow Band Filters
6563 few    
He II 4685 few    

Andor DU440 CCD

  • Marconi EEV 42-10 2048x512 pixels, thinned back-illuminated chip
  • Detective Quantum Efficiency: >90% between 500 and 700nm
  • Typical readnoise, < 3e- at 33kHz readout if fan off (external liquid cooling required).
  • Readout time at 33kHz clocking, about 35s full chip
  • Turnkey system, internal Peltier-effect cooling to -70C and below
  • Specification Sheet for CCD
  • Pixel Size: 13.5 x 13.5 microns
  • Pixel Scale: 0.34 arcsec/pixel
  • Field of view: 11.6 x 2.9 arcmin

Long Slit Spectrograph

Spectrum of Starburst Galaxy
Spectrum of starburst galaxy showing strong Halpha emission line. The tilt of the line is a result of the Galaxy's rotation, with one side moving at a different rate relative to us than the other. The spectrum was taken by the fall 2006 Astro4410 class.

The HBO Long Slit Spectrograph optical path consists of an entrance flip mirror with eyepiece for previewing the field, followed by a replaceable entrance slit, 307mm fl. collimator mirror, replaceable grating, then bolt plate which accepts a CCD camera with the camera lens (55, 75, 135mm options) already affixed to it when mounted. There is a CCD slit viewer for guiding, and neon and mercury lamps which illuminate the back of the eyepiece flip mirror for obtaining arc calibration images. Demagnification of the focal plane through the spectrograph is 2.28 with the 135mm lens, 5.59 with the 55mm lens.

Pixels refer to the Andor EEV camera with 13.5 micron pixels

Slit Width Grating Camera f.l. Dispersion Slit Width Image Scale
(arcsec/um) (grooves/mm) (mm) (A/pix) (pix) (arcsec/pix)
2.4/100 600 55 3.9 1.3 1.90
4.8/200 600 55 3.9 2.6 1.90
*7.2/300 600 55 3.9 3.9 1.90
*2.4/100 600 135 1.6 3.2 0.78
4.8/200 600 135 1.6 6.4 0.78
7.2/300 600 135 1.6 9.5 0.78
 
2.4/100 1200 55 2.0 1.3 1.90
4.8/200 1200 55 2.0 2.6 1.90
*7.2/300 1200 55 2.0 3.9 1.90
 
*2.4/100 1200 135 0.8 3.2 0.78
4.8/200 1200 135 0.8 6.4 0.78
7.2/300 1200 135 0.8 9.5 0.78
* These are the most useful combinations
Slit widths are 100, 200, and 300 microns in linear dimension

Wavelength Selection

*Central Wavelength, 600 l/mm grating*
waverange.png

The central wavelength of the spectrograph is adjusted through grating rotation using a rotation micrometer. Each revolution of the micrometer head moves the grating through one degree. The micrometer head is graduated in minutes of arc, and a vernier is provided, enabling precision to some 5 seconds of arc to be achieved. The head is very easy to turn, however, and a piece of scotch tape should be applied after achieving the desired setting to lock it in place.

The chart above shows the central wavelength (and extrema) for three settings, and extrapolated to additional angles. This chart is for the "standard configuration", 600 l/mm grating with 135mm camera lens and the Andor CCD Camera.

Spectrograph Slit Viewer Guider

g29w.jpg

The spectrograph is guided by a slit viewer which re-images light from the mirrored 100 or 300 micron slits at the telescope focal plane. The re-imaging demagnifies the focal plane by a factor of 3.0. This is recorded by a SBIG ST4 CCD -- a (slightly) cooled amateur-grade camera. The field of view of the guider is a square 3.22 arcminutes on a side, but the pixels are not square. The long axis of the detector (192 pixels, 13.75 um/pixels) is oriented along the long axis of the slit and has 1.007" pixels. The short axis of the detector (165 pixels, 16 um/pixel) has 1.170" pixels. The plate scale, 13.65 um/arcsecond

Guide/Spectrum mapping with 135mm lens
spec_guidemap.png

As one can see from the above mapping, the guider only sees the central 49% of the length of the slit as seen in the spectrum itself, assuming the "standard configuration" (135mm camera). It sees the rows [362:111] of the 512 on the Andor CCD, looking at increasing X coordinate in the guider.

The guider has a readout noise of approximately 40e rms. Stars to 14th magnitude can be reached in exposures of 30s with low signal to noise. More realistically, any star in the Tycho-2 catalog (limiting magnitude of about 11) is a superb guide-candidate for 5s exposures.

The camera is controlled by various software options. Most basic is the CCDops software run through DOS emulation on the control room computer. It is activated by clicking the "DOS Guider" desktop button.

There is a notable reflection present for bright guide stars, generally present at higher Y coordinate (which means upwards for FITS sign convention, downwards for CCDops sign convention). Be careful that you do not guide on a reflection!

A FITS format file with solved astrometric solution of an M57 exposure is attached here

Fiber-fed Spectrograph

(currently not available -- redesign notes at FiberSpectrographRedesign)

-- DonBarry - 2013-08-30

 
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