What is the purpose of the Shelyak eShel Calibration Module?
The eShel Calibration Module provides the two light sources necessary for calibrating high-resolution echelle spectrographs. It contains a Thorium-Argon (ThAr) lamp for precise wavelength calibration plus a tungsten lamp for blaze correction and LEDs that, with the tungsten lamp, give the flat image used to locate the orders.
Can I use the eShel Calibration Module with a non-Shelyak spectroscope?
Yes. While it is designed for native integration with the Shelyak eShel and Whoppshel, the module can be used to calibrate any other fiber-fed Echelle spectroscope that requires ThAr and flat-field illumination.
How does remote control of the eShel Calibration Module work?
The module is controlled via an RS 232 serial interface from your PC. It integrates directly with acquisition software like Demetra or Audela, allowing you to turn the lamps on/off and switch the FIGU mirror between the telescope and calibration sources as part of an automated observing sequence.
Why are both a ThAr and a flat lamp needed for the eShel?
Each lamp serves a distinct purpose:
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Thorium-Argon (ThAr): Produces a spectrum with thousands of well-documented emission lines. These act as a "ruler" to accurately map pixels on your detector to specific wavelengths.
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Flat sources: LEDs plus the tungsten lamp illuminate all orders so the software can find the geometry of the spectrum; the tungsten lamp alone gives a smooth continuum used to correct each order for the blaze function.
How does the eShel Calibration Module improve measurements of a star like 51 Pegasi?
When searching for exoplanets via the radial velocity method, as was done with 51 Pegasi, incredibly small Doppler shifts in the star's spectrum must be measured. The ThAr lamp in the eShel Calibration Module provides the stable, high-precision wavelength reference required to detect these minute shifts, making such scientific work possible.
If I am building a spectral library with my Whoppshel, is this module necessary?
Yes, it is essential for creating an accurate library. The tungsten lamp gives the smooth continuum used to correct each order for the blaze function, and the LEDs with the tungsten lamp locate the orders during processing. The ThAr lamp provides the absolute wavelength calibration, so you can confidently compare your spectra to other observations and databases.
