Shelyak Alpy 200 Spectroscope

The Alpy 200: A Scientific Instrument for Faint Object Spectroscopy

The Alpy 200 is designed as a true scientific instrument for pro-am astronomers seeking to perform astrophysical analysis on targets at the edge of the observable universe. It is a compact, modular and easy-to-use slit spectroscope that Shelyak calls a true scientific instrument that will stay with you for a long time.

Its purpose is to open the door to advanced projects like classifying supernovae, identifying quasars, and analyzing the spectral characteristics of faint galaxies. The design is robust and insensitive to temperature variations, requiring few adjustments in the field and simplifying the process of obtaining scientifically valuable data.

The F/4 Grism: A 200 lines/mm Dispersing Element

At the heart of the Alpy 200 is a grism, an optical element that combines a prism and a diffraction grating. This specific grism uses a 200 lines/mm grating, which is the key to its low-resolution, high-sensitivity design. This on-axis configuration spreads the incoming starlight into a spectrum without deviating the beam, creating a compact and efficient optical path.

Shelyak says the optics were designed to give the best image quality over the whole visible range with a wide F/4 aperture.

R~130: Maximizing Signal from 375 nm to 750 nm

The Alpy 200 provides a resolving power (R) of approximately 130 when used with a 23µm slit. Lower resolution spreads a target's light over fewer pixels, which is why this variant suits very faint objects.

This approach allows the Alpy 200 to cover a wide spectral range, from 375 nm in the near-ultraviolet to 750 nm in the near-infrared, and capture the defining characteristics of a target's spectrum.

Slit Options from 25µm to 300µm

A slit isolates the light from your target, making the resulting spectrum independent of seeing conditions or tracking errors. The Alpy 200 includes a multi-position slit plate with several options to adapt to different observing situations.

• 25µm, 50µm, 100µm, 300µm Slits: Narrower slits give the highest spectral resolution; wider slits let more light through at the cost of resolution.
• 25µm and 3mm Holes: With the 25µm hole the spectrum stays at the same place in the image; the 3mm hole is the slitless position, which shows a larger star field.

A 200g Payload for Telescopes from 80mm

Weighing just 200g and measuring 65mm in length with a 45mm diameter, the Alpy 200 is compact and light. Shelyak says this makes it compatible with small telescopes and refractors from 80mm diameter, on modest mounts.

Shelyak adds that many scientific publications are based on observations with the Alpy 200.

T-Mount Connection with 10.5mm to 21mm Backfocus

The Alpy 200 is designed for straightforward integration into your existing imaging train. It features a standard T-mount (M42x0.75mm) thread on the camera side, a standard interface.

The spectroscope supports a mechanical backfocus range from 10.5mm to 21mm.

Matching a Camera Sensor to the Alpy 200

Shelyak says any camera with a sensor longer than 14mm and a mechanical pull between 10 and 20mm will do.

The mechanical interface is a standard T-mount (M42x0.75mm), and the required backfocus must be between 10.5mm and 21mm. Shelyak recommends the ZWO ASI533MM-Pro camera for spectra acquisition with the Alpy 200.

Optional Guiding and Calibration for a Complete Workflow

While the Alpy 200 is a complete spectroscope on its own, its capabilities can be extended with two optional modules that streamline the scientific workflow. When these modules are added, the total required backfocus for the system becomes 64mm.

• Autoguiding Module: This module allows you to see the field of view around the slit. Shelyak says its function is to let you select and track the star you wish to observe.
• Calibration Module: For precise scientific measurements, a spectrum must be calibrated in wavelength. This module lets you take spectra of flats and of an Argon-Neon calibration lamp, for rapid wavelength calibration.

Demetra: An All-in-One Acquisition and Reduction Suite

The Alpy 200 is fully supported by Demetra, a free software package developed by Shelyak Instruments. Demetra is designed to be an all-in-one tool that guides you through the entire process, from capturing images to producing a fully calibrated final spectrum.

Demetra manages your observing session, controls the camera for image acquisition, and provides real-time feedback like profile displays and saturation alerts. Its data reduction pipeline is fully automated but remains transparent, allowing you to follow the process step-by-step. This integrated approach ensures that you collect all necessary data (including darks, flats and calibration frames).

A Magnitude 18.6 Supernova Spectrum

Robin Leadbeater first suggested a variant of the Alpy 600 for weak targets, and Shelyak shows one of his results.

Shelyak shows a spectrum of a magnitude 18.6 supernova obtained by Robin Leadbeater with the Alpy 200 from 10 exposures of 600 s.

Alpy 200 vs. Alpy 600: Sensitivity vs. Resolution

The Alpy 200 was developed as a specialized version of its sibling, the Alpy 600, for a different observational goal. The choice between them is a direct trade-off between resolving power and sensitivity.

• Alpy 600 Advantage: With a resolving power of R~600, the Alpy 600 can reveal much finer detail in the spectra of bright stars. Shelyak says it shows many details in the spectral profile.
• Alpy 200 Advantage: Shelyak made the R~130 Alpy 200 for spectra of very faint objects such as supernovae, quasars and other faint galaxies.