Advanced Telescope Supplies

Australia's Premier CCD and Astro-Imaging Experts

SBIG SGS (Self Guiding Spectrograph)


spectro_sb2.jpg (39339 bytes)

Self-Guiding Spectrograph is designed to be used with an ST-7E camera. Although it can also be used with an ST-8E, there is no advantage in bandwidth when using the larger format camera.  The spectrometer and ST-7/8 are coupled and mounted as a unit onto the telescope (See Figure 1).  The system is quite handy for collecting spectra since both the object of interest and the spectrometer entrance slit are simultaneously imaged onto the tracking CCD, allowing the object to be viewed and accurately placed onto the slit.  The slit is backlit by an LED during the setup so it clearly shows on the tracking CCD.  Once the object is maneuvered onto the slit, self guiding will then hold the object on the slit. 


For a review of the spectrograph by Sky & telescope click here to visit Sky & Telescope's web site.

      Overview of SBIG's Self-Guided Spectrograph Capabilities      
Measure Stellar Spectra:
     - Determine spectral class
     - Measure radial velocities
2, 3, 9, 10
Measure Emission Nebula:
     - Determine spectral lines
     - Measure relative line strengths
4, 5
Measure Galactic Objects:
     - Measure radial velocity (red shift) of brighter galaxies
     - Distinguish quasars from other objects
6, 7, 8


Identify Stellar Spectral Class

Spectrum of B Class Star
Bclass.jpg (12065 bytes)

Spectrum of G Class Star
Gclass.jpg (14057 bytes)
Spectrum of M Class Star
Mclass.jpg (14386 bytes)

Figure 2
Sample Stellar Spectra

Measure Stellar Radial Velocities

Stellar Radial Velocity of Selected Stars
Measured to +/- 6 km/sec with 8" SCT

Star km/sec* If you face the
celestial equator,
straight south at
sunset, you are
looking BEHIND the
earth in orbit (the
wind is against your
ATAU1 88
ATAU2 88
ATAU3 95
AORI1 54
AORI2 51
AORI3 56
GLEO1 -15
GLEO2 -30
GLEO3 -14
* Uncorrected for earth's orbital velocity 


Measure Emission Nebula

The spectra of M57 below was obtained using the low resolution grating and the narrow slit: 

RingT.jpg (77216 bytes)

Figure 4


ring.jpg (70897 bytes)

Figure 5

The top image (Figure 4) is a screen shot showing the view of the tracking CCD displaying the
slit and the object (M57) simultaneously.  The lower image (Figure 5) is a screen shot showing the
view of the imaging CCD with emission lines from M57.

Measure Galactic Objects and Distinguish Quasars

The self-guiding feature of the ST-7/8 camera makes taking long exposures relatively painless and helps to keep the object centered on the slit for extended periods of time.   This technique is necessary if one attempts to measure the red shifts of galaxies of emission lines of quasars.  The samples below of M104 show the red shift of the galaxy relative to the star Mu UMA:

Somb.jpg (59374 bytes)

Figure 6
Screen shot of spectrum obtained of M104, The Sombrero Galaxy
(The many small white spots are cosmic ray hits)


Slide18s.gif (51365 bytes)

Figure 7
Graph showing the measured red shift of M104 relative to Mu UMA


Slide22s.gif (56496 bytes)

Figure 8
Graph of emission lines in Quasar 3C273 obtained using an 8" SCT


Obtain High Resolution Spectra

Using the high resolution grating and the narrow slit the spectrograph is capable of resolving narrowly separated lines.  The sodium doublet lines in Figure 9 below are easily separated although they are only 6 angstroms apart.  The magnesium lines in the three stars shown in Figure 10 are separated by only 5.4 angstroms. 

Slide14s.gif (46832 bytes)

Figure 9


Spectra.gif (70239 bytes)

Figure 10
Spectra of Several Bright Stars Captured with a Prototype SBIG Spectrometer on 2/3/98
Parameters:  Telescope:  10 inch LX200 F/6.3, Exposure:  120 seconds


Acquisition and Analysis Software Included

The spectrograph is provided with a special version of CCDOPS for data acquisition and SBIG's Spectral Calibration Program for analysis.  These programs make the spectrograph immediately useable as an analytical instrument without the need for the user to write or obtain third party software.

Analysis.jpg (123229 bytes)

Figure 11
Screen shot of the Spectral Calibration Program supplied with the spectrograph


Optical Specifications


Two gratings are available, on a carousel for rapid selection
          - 150 lines per mm (4.3 Angstroms per pixel)
          - 600 lines per mm (1.0 Angstroms per pixel)

Slit Width
     Interchangeable slits are included
          18 microns wide (2 arcseconds at 80 inch focal length)
               Best for stellar work
          72 microns wide (8 arcseconds at 80 inch focal length)
               Best for galaxies              

Acceptance cone angle:  F/6.3 by F/10


Narrow slit & 600 lines/mm 2.4 Angstroms
Narrow slit & 150 lines/mm 10 Angstroms
Wide slit & 600 lines/mm 10 Angstroms
Wide slit & 150 lines/mm 38 Angstroms

Relative Sensitivity to Diffuse Sources:

Narrow slit & 600 lines/mm 1.0
Narrow slit & 150 lines/mm 4.0
Wide slit & 600 lines/mm 4.0
Wide slit & 150 lines/mm 16.0


General Specifications

spectrom_sb3.jpg (55338 bytes)

Figure 12
SBIG Spectrograph shown attached to an ST-7E


Description:  The spectrometer is designed to operate with the ST-7/8.  The object that is to be analyzed is viewed on the tracking CCD, simultaneously with the slit.   The slit is backlit by an LED during setup to render it clearly visible on the tracking CCD.  The object is manually maneuvered onto the slit using the telescope controls, and is held there using SELF GUIDING during a long exposure.  The spectra is recorded by the imaging CCD, oriented long-ways so the spectra falls across 763 pixels, with a height of about 16 pixels for stellar sources.  Two gratings and two slits are available for maximum versatility.  The standard grating, 150 rulings per mm, gives a dispersion of 4.3 angstroms per pixel, and allows the user to capture the entire interesting range from the calcium H and K lines to H-Alpha with a single exposure.  Depending on the slit size, the resolution will be 10 or 38 angstroms per pixel.  An interchangeable high resolution grating can also be used that gives 1.07 angstrom per pixel dispersion, with a resolution of about 2.4 angstroms when used with the narrow slit.  The spectral range is smaller, being only about 75 angstroms.  This resolution is adequate to detect the Doppler shift due to the earth’s motion around the sun when carefully calibrated, and detect spectroscopic binaries.
Dispersion: 1.07 or 4.3 Angstroms per pixel
Resolution: emission line is recorded with 2.4, 10 or 38 Angstroms Full Width at Half Maximum
Spectral coverage per frame: about 750 Angstroms with the high resolution grating, or 3200 with the low resolution grating
Center Wavelength Selection: Calibrated Micrometer Adjustment
Wavelength Range: 3800 to 7500 Angstroms
Sensitivity: Signal to noise ratio of 10:1 for a 9th Mag star, 20 minute exposure using a non-ABG ST-7 and a 10 inch (25 cm) aperture in high resolution mode.   An ABG ST-7 will reach magnitude 8.  The low resolution mode will be 1.5 magnitudes more sensitive. 
Entrance Slit: 18 micron (2.3 arcseconds wide with 63 inch focal length telescope) or 72 microns.
Dimensions: 3 x 4 x 7 inches (7.5 x 10 x 18 cm)
Weight: 3 pounds (with ST-7 head attached)
Uses:   Stellar Classification
            Analysis of Nebular Lines
            Identification of spectroscopic binaries
            Measurement of Stellar proper motion to +/- 6 km/sec accuracy
            Measurement of Emission Nebula Proper Motions
            Spectra of Laboratory and field sources    
Galactic Red Shifts: When used with the new Kodak "E" detectors red shifts of bright galaxies are possible with amateur sized telescopes.
Price:  $US3950.00 or approx $A8100 plus GST