What type of telescope is best for the Shelyak UVEX Spectroscope?
The UVEX is optimized for an F/8 focal ratio, and it is particularly suitable for Ritchey-Chretien (RC) telescopes up to 400mm in diameter (F/8). It can go up to F/5 without vignetting, at the cost of a slight degradation in quality.
How does the UVEX achieve its wide 350 nm to 1µm spectral range?
The UVEX's main optics are two spherical mirrors in a crossed Czerny-Turner layout. This is what lets it go far into the blue (UV) and red (IR), since a mirror is purely achromatic.
Can I use the UVEX to study the Balmer series in a star like Vega (Alpha Lyrae)?
Yes. Vega is a hot, A-type star with very prominent hydrogen absorption lines (the Balmer series). The UVEX's spectral range, extending down to 350 nm, covers the Balmer series from H-alpha (656.3 nm) down into the near UV; with the 600 l/mm grating, the part recorded at one time depends on the grating angle and your sensor.
How can I use the UVEX to analyze an emission-line star like Gamma Cassiopeiae (γ Cas)?
Gamma Cas is a classic Be star, characterized by strong emission lines (especially H-alpha) from a circumstellar disk. Using the UVEX with its 600 l/mm grating, you can center the grating on 656.3 nm to record the H-alpha emission line and follow how its strength changes over time.
What is the purpose of the different slit sizes on the Shelyak UVEX?
The slit width determines the balance between spectral resolution and light throughput.
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Narrow slits (25µm, 50µm): Provide higher spectral resolution, allowing you to resolve finer details and separate closely spaced lines.
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Wider slits (100µm, 300µm): Allow more light to enter the spectroscope, at the cost of lower resolution.
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Holes (25µm, 3mm): The 3mm hole is the slitless position, and the 25µm hole is mainly for test purposes.
Why does the Shelyak UVEX require a camera with a back focus of 13mm or less?
The compact optical layout puts a strong constraint on the camera backfocus: it must be 13mm maximum.
How do I change the grating in the Shelyak UVEX?
It is a simple operation: loosen and remove the black grating cap, gently remove the grating holder and put it in its box, then install the new grating (its orientation is given by the flat surface of the holder). Each grating comes with its own vernier, which you change too. The grating surface is very fragile.
Is software included with the Shelyak UVEX?
Yes, Shelyak provides the Demetra software as a free download from their website. Demetra-UVEX, the version dedicated to the UVEX, is recommended. It handles camera control (via ASCOM), observing sessions and data reduction to a calibrated spectrum.
What do I need to autoguide my observations with the UVEX?
You need the optional guiding module and a guide camera. The UVEX slit is replaced by the mirror slit that comes with the guiding module; the supplied guiding module adapter attaches the UVEX to it. The manual mentions PHD2 as guiding software.
What does the R=1710 resolving power of the UVEX let me see?
R=1710 at 650 nm means features about 0.4 nm apart can be separated there. That is enough to see the main absorption lines and bands of different stellar types and the H-alpha emission of Be stars; the 0.6 nm sodium D doublet sits close to that limit.
How do I avoid order overlap when observing in the near-infrared with the UVEX?
Above about 750 nm, the second order of blue light can overlap the first order (400 nm at second order falls with 800 nm at first order). Shelyak offers an order filter that cuts all light below 500 nm; the UVEX holds it right after the slit.
Can I operate the Shelyak UVEX remotely?
Yes. With the optional UVEX motors module, the grating angle and focus can be controlled remotely, along with the calibration module.
