I have a StarEx LR spectroscope with a 300 line/mm diffraction grating. I can usually get R~1000 based on the FWHM of a neon emission line at 5852 A. I have a Player One Ares 533 camera for it which gives a usable spectrum between 3800 and about 8000 A.
I also have a StarEx HR which has a 2400 line/mm grating, also with a Player One Ares 533 camera for it (the Player One 533 camera has a larger full well capacity than the ZWO 533 camera). This spectroscope can achieve R~20,000 when properly calibrated, although with a camera like the Ares 533, you will see only about 120 A worth of spectrum. This is great for analysing spectral line shape. The StarEx was developed by Christian Buil. His website is an enormous source of information about spectroscopy and he also has a YouTube channel, with some videos in English.
I also have a Star Analyser 100. It’s really just a diffraction grating screwed into a camera. It provides very low resolution, usually about R~100 which makes it useful for dim objects. It’s particularly well suited to classifying supernovae, although the Alpy200 is probably the most useful tool for this type of observation.
Measuring the redshift of the quasar 3C273 with an amateur telescope
3C273 is the brightest quasar in the sky. It is easily visible in a 12 inch telescope and on a dark night, even an 8 inch will show it. This is astonishing considering its enormous distance from Earth and indicates that it has a high intrinsic luminosity. The discovey of this distance was by Maarten Schmidt who realized that the emission lines he couldn’t identify were those of hydrogen alpha and beta which were very redshifted. Measuring the redshift of this quasar is relatively easy with a low dispersion spectrograph like the StarEx in low dispersion mode.
When using the StarEx LR I used subexposures of 3 minutes using a Player One Ares 533 camera. I stacked 30 of these exposures into a final image. This is probably a minimum since the image contained lots of noise. I imaged the quasar on the night of April 6 2025 when the moon was almost quarter phase. This produced some light pollution. A further complication was due to airglow, predominantly at 5577 A. However by suitable background removal, the contribution to the spectrum of these sources can be minimized. To calibrate the spectroscope I use light from a neon bulb placed at the entrance to the telescope.
The resulting spectrum shows two major emission features. One is slightly blueward of the major telluric absorption feature at 7600 A. This peak, at 7580 A, is due to Hydrogen alpha emission which is redshifted from its resting wavelength of 6562.8 A. The other major peak is at 5630 A due to the Hydrogen beta emission line which is redshifted from its resting wavelength of 4861 A.
The redshift, called z, measured using the H alpha line is (7580 – 6562.8) / 6562.8 = 0.155
Similarly, the redshift for the H beta line is z = 0.158.
The average for the two values is z = 0.157. This is pretty close to the published value of 0.158.
Below is a finder chart showing the location of 3C273. It’s inside a triangle of stars.
Be type star Alcyone in the Pleiades
Alcyone is one of the naked-eye stars of the Pleiades. It is a a hot B7IIIe star with emission lines, usually of Halpha, in its spectrum. The emission arises from a nebulous disk surrounding the star and the intensity of the Halpha emission varies. The spectrum below shows the Halpha line in emission. Superimposed are Telluric absorption lines with their wavelengths indicated in red.
Be type star FS Canis Majoris
FS Canis Majoris (HD 45677, MWC 142) is a Be type star currently (as of Nov 2024), in outburst phase. The H-alpha line is showing particularly strong emission with a well-defined central absorption. This is the prototype star for the class of variables called FS Canis Majoris variables, a class of eruptive variable star which is probably a binary star in which mass exchange occurs with at least one member being a B-type main sequence star. The hydrogen emission lines are usually much stronger than in typical Be type stars.
Telluric Absorption Lines in the Solar spectrum near 7600 A
The image below is of the telluric absorption lines around 7600 A. I obtained this image using a ZWO ASI224 colour camera to show the colour in this part of the solar spectrum. These absorption lines are usually a nuisance when imaging the spectra of stars, and this complex absorption feature at ~7600 A is particularly strong.
Hydrogen alpha line structure in the Be star Merope
The StarEx HR spectroscope has sufficiently high resolution to display absorption or emission line structure. Below is a spectrum of the hydrogen alpha emission line at 6562.8 A of the star Merope, a Be type star, during an outburst. Normally the H alpha line is an absorption feature arising from hydrogen gas encircling the star. However if the gas becomes hot enough, it will produce emission. Hydrogen gas orbiting the star, directly between us and the star, will produce an absorption feature superimposed on the emission line.
Hydrogen alpha and Hydrogen beta line emission in V1339 Aql
In some Be stars, conditions will favor emission from both the Halpha and Hbeta lines. This occurs in the Be star V1339 Aql. The spectrum below shows emission at the 4861 A and the 6862.5 A hydrogen lines. R~900. August 30 2024 (uncorrected for instrument response and/or spectral flatfield).
Methane absorption bands in Neptune spectrum
The atmosphere of Neptune is full of methane. Sunlight reflected off the upper cloud layers of Neptune is absorbed by methane leaving characteristic absorption bands in the solar spectrum. The spectrum below shows the wavelengths where these absorption bands occur (marked by dotted lines).
Emission lines in the O-type star Zeta Puppis
Zeta Puppis is an extremely hot and luminous O-type star with a O4lf(n)p spectrum type. The “f” indicates that the spectrum displays emission lines including those of helium, nitrogen and hydrogen. This frequently occurs in evolved O-type stars. The 40,000-44,000K temperature of the star leads to He n = 4 -> 3 transitions and subsequent emission at 4686A, possible in only extremely hot stars. The hydrogen absorption lines are weaker than in B-type stars since the high temperature makes the recombination of electrons with hydrogen nuclei less likely. The spectrum also shows a strong NIII emission line around 4640A and a weak hydrogen alpha emission line.
