Zlender Images

S P E C T R A

My Littrow Spectrograph (LISP-1)

To view spectral details in higher resolution I built a LIttrow SPectrograph (LISP1). Technical details: grating of 50x50mm size, 1200 lines/mm, blazed at 2800Å, an achromatic objective 330mm f/5, that serves as collimator and imaging lens (Littrow design). When a slit (broad or narrow) is used, this lens must be focused on the slit and the CCD at the same time. In the slitless mode, spectra are focused on the CCD by the telescope focuser. The position angle of the grating can be adjusted with help of a screw such that the desired spectral window can be recorded by the CCD. A detailed technical specification can be found here.

Fig.5: Ingredients of LISP1. Different adaptors can be used to attach all sorts of cameras or oculars.

Fig.6: First tests with video camera and 50mm f/2 objective.
Spectrograph is mounted on declination axis of telescope. The attachment to the telescope was changed to achieve more flexibility as can be seen in Fig.8.

Fig.7: Waiting for the Sun.

Fig.8: Here one of the slits is shown. It is made of pencil sharpener blades. Best focus is achieved with help of a small finder scope, when the grating is not build in. The scope pears through the 30mm hole, visible on the left in Fig. 10. Slit and CCD must be in sharp focus at the same time. Adjustments are made with screws visible in Fig. 6.

Fig.9: Ready to be attached to my C11.
Original Celestron Radial Guider is used to verify the object is close to the slit
or might be used for long guided exposures. The ring is used to achieve a
more rigid connection to the telescope.

Fig.10: Here a small telescope (mirror-lens) 500mm f/8 is used.
Common T2-connectors and M42 extension tubes allow flexible interchange of optics.

Fig.11: Spectrograph and CCD camera attached to telescope for the first time (8/02/2005).

Fig.12: Original electronic drive system on CG11 is replaced by a computer controlled
"Mel-Bartels-system". LX200 compatibility allows now scripted control of the whole
equipment with help of a second computer from the warm room below.

First Tests

Fig.13: Spectrum of an fluorescent energy saving bulb. Might be useful for calibration?

Click to see it full resolution
Fig.14: Spectrum of Neon. Brightest line is 5852.5Å.

Fig.15: Deep at the end of the visible red part. Atmospheric O2-telluric absorption lines around 6820 Å.

Fig.:16: Mosaic of solar spectrum in the visible range (Click to see it in full resolution).
Technical details: No Telescope in front of slit (wide slit), camera ST-8e, exp.time 1.8s, binning 2x6.

Under the Stars

First-Light was 08/30/2005. I was astonished how easy it was to obtain spectra of brighter stars. Exposure times of a few seconds were enough to obtain a good signal / noise ratio.

Fig.:17a: Spectrum of Vega in violet part of the spectrum. Hydrogen Balmer-Lines Hδ (to the extrem right) up to Hν, and a narrow Ca K-line at 3393.7Å. Distances between lines get smaller with shorter wavelength (to the left). The convergence limit is 3646Å. Vega is a dwarf star of type A0V. A relative high atmospheric pressure broadens the spectral lines and causes the diffuse appearance.

Fig.:17b: A different impression results from this spectrum, which shows the Balmer-lines of Deneb. Here the lines appear much sharper. As a supergiant Deneb is of spectral type A2Iae and ranges among the absolute brightest stars.

Fig.18: Spectrum of Vega from Fig.17a presented with Specview. Sort of a problem are the regular "lines" between Hδ and Hε, which are artifacts caused by pixel binning and correction of a slight rotation (0.°92) of the camera.

(Specview is a product of the Space Telescope Science Institute, which is operated by AURA for NASA.)

Fig.19: To be compared with Fig.18. This is the spectrum of an atmospheric model of Wega in the violet. (Source: http://gaia.esa.int/spectralib/spectralib1A/SpectraLib1a.cfm )

Fig.20: Spectrum of a model atmosphere of Deneb. As in Fig. 17b explained lines appear much shraper. There are also more Balmerlinies to count, resulting from a much lower electron presure in this atmosphere of a supergiant. (http://gaia.esa.int/spectralib/spectralib1A/SpectraLib1a.cfm )

(Specview is a product of the Space Telescope Science Institute, which is operated by AURA for NASA.)

Fig.19: Vega, 20Å around the Hα-line.
Most of the other lines result from H2O in our own atmosphere.

Spectra of the following stars were recorded until now.

Name	Spectraltype	Focus on	Instrument	Notes	Obs.-Date
42-And	B7Ve	Hα	CG11,LISP1,ST-8e	emission lines
β-Aql	G8VIvar		CG11,LISP1,ST-8e
σ-Aql	B3V		CG11,LISP1,ST-8e
γ-Cas	B0VIe	Hα	CG11,LISP1,ST-8e	emission lines
ρ-Cas	F8Iavar	Hα	CG11,LISP1,ST-8e		30.10.05
57-Cyg	B5V		CG11,LISP1,ST-8e	spectr.double*
α-Cyg	A2Ia	Hδ-H9	CG11,LISP1,ST-8e		5.9.05
P-Cyg	B1pe	Hα	CG11,LISP1,ST-8e	emission lines	16.10.05
α-Lyr	A0V	Hα	CG11,LISP1,ST-8e
β-Lyr	B7Ve+A8p	Hα	CG11,LISP1,ST-8e	emission lines
δ2-Lyr	M4IIvar		CG11,LISP1,ST-8e
ζ2-Lyr	A3		CG11,LISP1,ST-8e
κ-Del	G5IV		CG11,LISP1,ST-8e
ι-Peg	F5V		CG11,LISP1,ST-8e
ζ-Uma (Mizar)	A2V	Hα	CG11,LISP1,ST-8e	spectr.double*	20.9.,16.10.05

Tabelle 1

Improvements

In general:

Position of grating will be readable on a scale
A better match of telescope / spectrograph by introducing a Shapley-Lense (Focal Reducer). Now F/10 and F/5, then ca. F6.7 und F/5.
Guiding will allow for longer exp. times.

For usage with slit:

Interchangeable fixed slits
A fine tunable focuser for the camera would be a nice feature.
Lightpipe for illumination of the slit with a reference source (e.g.Neon).

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