The eShel spctro is a professional-level multi-order fiber-optic instrument.
When you can’t choose between resolution and spectral range – as in the case of exoplanet studies, for example – then you need an Echelle spectroscope, which offers numerous orders at high resolution (R = 10,000).
The eShel spectroscope covers a spectral range of approximately 390 to 700nm (orders 32 to 53).The complete eShel system includes the spectroscope itself, as well as the FIGU F/6 (Fiber Injection and Guiding Unit), the calibration module (with ThAr lamp), and the optical fibers (target 50µm and calibration 200µm, both 20m long).

A fiber-fed spectroscope

The eShel spectroscope can work over a wide spectral range (390 to 700nm) at high resolution (R = 10,000). This is made possible by the use of multiple orders (in this case from 32 to 53); an Echelle spectrum reads “like a book”: the end of one order is found at the beginning of the next. We opted for a fiber-optic solution to increase the accuracy of radial velocity measurements (the instrument is separated from the telescope, if possible in a temperature-controlled room) and for greater user comfort.We have developed this instrument based on our experience with the Musicos and Narval professional spectroscopes.

Echelle spectroscopy

This technique achieves high spectral resolution by using the >30 diffraction orders of a grating. The resulting spectrum passes through a cross disperser, which “slices” the spectrum into successive orders, occupying the entire surface of the camera’s sensor. In this way, the entire spectral range in the visible spectrum is obtained over some twenty orders (in the case of the eShel).Schematic diagram of an Echelle spectrograph (© Christian Buil)

The eShel spectroscope

The main module generates the Echelle spectrum. It covers the spectral range from approx. 390 to 700 nm with >10000 resolution (with an ATIK 460 Ex camera in 2×2 binning not included). It has an FC/PC connector for attaching 50 µm object fiber.Spectrum of delta Sco (Be star). Note the H-alpha line in emission (click on image to enlarge). Canon 40D, 9 x 300 s, telescope 0,2m (C.Buil)The eShel spectroscope must be accompanied by the FIGU – Fiber Injection and Guiding Unit – (PF0008, for example), the calibration module (PF0012) and the two optical fibers: one for the target and the other for calibration. All these elements are included in the ES0006 “eShel complete system”.

Demetra software for eShel

Easy to use and free of charge, it runs under MS Windows, and accompanies you from spectra acquisition to data reduction. It enables remote control of the various modules (FIGU and calibration module).

Examples of raw spectra

betlyr 50pc

pcyg 50pc

WR140-6

WR 140 and Nova Del 2013 1x600s SCT 0,35 m and ATIK 460EX bin 2×2 (Click to enlarge)

Example of time series of a pulsating star

Here’s a good example of evolution of a pulsating star (BW Vul, raw images, 5min exposures, 60cm f/3.5 telescope at Pic du Midi; ccd camera QSI516).

The BW Vul spectrogram over about 5h around the Sodium doublet:

Calibrations modul eShel II

It delivers the various light sources used to calibrate the spectrum:

• Thorium-Argon lamp with high-voltage power supply
• A tungsten lamp for blaze treatment

F/6 FIGU: Fiber Injection and Guiding Unit (PF0008)

It injects the target’s flux into the eShel’s optical fiber. A guiding camera (not included) ensures target centering and autoguiding on the 50 μm fiber optic input. Calibration lamps can also be injected from the calibration module via a 200 µm optical fiber also connected to the FIGU. A remote-controlled mirror allows you to switch from one source to another. (F/9 and other F-ratios available – contact us)

T-mount adapter ring for SCT

for attaching the eShel FIGU to a Schmidt-Cassegrain telescope (typically with a 0.63x focal reducer)

50µm object fiber

(20 meters, other lengths on request)

Calibration optical fiber 200µm

(20 meters, other lengths on request)

Specifications