Shelyak Whoppshel High Resolution Echelle Spectroscope

The Whoppshel spectrograph has been designed for telescopes of 0.6 to 1m in diameter class (or even beyond). The resolution R = 30000 of this instrument indeed requires a significant diameter to collect enough light.

Several times we have received the question of the accessible limit magnitude with this spectroscope on a 60cm telescope; in order not to make a purely theoretical answer, we had to make a full-scale test on a telescope of this diameter.

We had the opportunity to use for a few weeks the first Whoppshel copy on the RC600 telescope of the Hubert Reeves observatory in Mars (Ardèche – south of France).

We would like to thank the community of town Valeyrieux, owner of the telescope as well as the Mars Astronomy Club (CAM) and its president Daniel Verilhac who warmly welcomed us, assisted for installation and made observations on this great instrument.

The Hubert Reeves Observatory

Located in a small village : Mars in Ardèche (south of France) at 1 030 m above sea level, the observatory benefits a 360-degree clear horizon and a sky of great quality.A 4.50m dome houses an Italian-made Officina Stellare telescope: a Ritchey-Chretien optic, 600mm diameter open at F / 8. It is mounted on a German equatorial mount direct drive Nova 200 built by the French company Alcor System.

The RC600 on its mount Nova 200
(Copyright photo : Olivier Garde)

To inject the light collected by the telescope onto the 50μm optical fiber, we use an injection unit from Shelyak Instruments at F/6. With the telescope open at F / 8, we use an Astro-Physics CCDT67 (x 0.67) focal length reducer to reduce the focal length of the telescope to F / 5.4. Note that Shelyak Instrument can now offer injection unit with multiple openings, incorporating an internal focal length reducer. It is thus possible to have unit at F / 6, F / 7, F / 7.8 and F / 9.

The injection unit mounted on the RC600
(Copyright photo : Olivier Garde)

The injection unit is mounted with its focal reducer, on the eyepiece holder of the RC600 (2 inches). It allows to perform several tasks:

• injection of the light flux into the optical fiber “Object” connected to the spectrograph.
• Autoguiding on the target
• Realization of calibration images (Flat, spectral lamp, LED)

Whoppshel assembly

The whoppshel is an echelle spectrograph mounted on an optical bench of 2.10m long and 0.6m wide. The total mass is about 80 kg.

Assembly of the 2 optical benches
(Copyright photo : Daniel Verilhac)

The whoppshel being assembled
(Copyright photo : Olivier Garde)

The various preassembled modules of the spectrograph are fixed on the optical bench: the optical fiber injection support, the 90-degree deflection mirror, the two optics Takahashi FSQ-106, the grating module, the cross-disperser (3 prisms) and the CCD camera with its lens.

The cross-disperser module and the CCD camera
(Crédit photo : Daniel Verilhac)

The cross-disperser module, which separates the different orders, consists of 3 prisms custom designer. They are arranged in a precise manner on a support which is fixed on the optical bench of the spectrograph at the output of the second refractor FSQ-106. The CCD camera is equipped with a 135mm optics open at F / 2.

The Whoppshel once assembled
(Copyright photo : Olivier Garde)

A black metal cowling covers the entire spectrograph to protect it from stray lights and dust. The assembly is very stable mechanically, but it is preferable that the storage room is also stable in temperature during the acquisition of the spectra if one wishes to measure precise radial velocities.

The results

We tested the spectrograph for several nights thanks to the regular presence of Daniel Verilhac at the observatory. He was able to produce dozens of spectra of stars despite a weather not always favorable. Often it would have been useful to ask longer on some targets to improve the signal-to-noise ratio of the spectrum, but the passage of clouds during the observation periods prevented us from doing so. A short overview of the observations made on various stars with various astrophysical interests...

The first target was the star HD 123299 (Alpha Dra) of magnitude V = 3.68. It allowed us to calculate the instrumental response of the spectrograph by comparing its spectral profile with a theoretical spectrum of the Pickles database. It is a AOIII type profile and we realized 5 exposures of 600s with an ATIK 460ex CCD camera in binning 1×1 and cooled to -1 ° C (the ambient temperature of the room did not allow us to cool more) .

The graph below shows the corrected spectrum of the instrumental response calculated from this star (Alpha Dra). In blue, the curve obtained with the Whoppshel, in red, the curve of the Pickles database of a A0III type star.

11 Cyg

Here is the spectrum of 11 Cyg, a Be star of magnitude V = 6,03. Here we made 5 exposures of 900s, some with cloud passages. The graphs below show the profile of hydrogen lines from H Alpha (6562.8 Å) to H Epsilon (3970.07 Å).

Chi Dra

Another “fashionable” observation subject: chromospheric stars. This is to see any emissions in H & K Calcium lines (CAII). This spectrum of Chi Dra (mag V = 3.58) shows that the Whoppshel is able to go so far into the near UV.

WR 140

The Wolf-Rayet stars (WR) show broad emission lines, clearly visible in this spectrum of WR140, of magnitude V = 6.85. 3 exposures of 1200s, exactly one hour total exposure. And when we “zoom” in each strip, what details can be observed!

HD 191378

The limiting magnitude accessible with this instrument depends, of course, on the total exposure time and the desired Signal / Noise Ratio (SNR). We limited ourselves during this campaign to a duration of observations around one hour. The faintest star we observed is HD 191378, a Be star of magnitude V = 8.99 with only 4 exposures of 1200s (1h20 total exposure). We see that the spectrum is noisy in the blue … but still: magnitude 9 with a resolution of R = 30,000!

Some key numbers

Here is the calculation result provided by ISIS (version 5.9.3) for each order on the 11 Cyg spectrum. Order 47 is the first order in red, and order 86 is the last in blue. The calibration RMS is excellent with average values ​​of the order of 0.003 Å.

• Ordre #47 : RMS = .0611 – Nb. raies = 9 FWHM = 8.09 – Dispersion = .062 A/pixel – R = 14420.5
• Ordre #48 : RMS = .0677 – Nb. raies = 7 FWHM = 9.28 – Dispersion = .061 A/pixel – R = 12516.9
• Ordre #49 : RMS = .0015 – Nb. raies = 8 FWHM = 7.38 – Dispersion = .061 A/pixel – R = 15567.5
• Ordre #50 : RMS = .0073 – Nb. raies = 8 FWHM = 6.41 – Dispersion = .059 A/pixel – R = 18013.3
• Ordre #51 : RMS = .0032 – Nb. raies = 11 FWHM = 5.69 – Dispersion = .058 A/pixel – R = 20194.3
• Ordre #52 : RMS = .0032 – Nb. raies = 11 FWHM = 5.20 – Dispersion = .057 A/pixel – R = 22349.0
• Ordre #53 : RMS = .0042 – Nb. raies = 12 FWHM = 4.59 – Dispersion = .057 A/pixel – R = 24868.4
• Ordre #54 : RMS = .0017 – Nb. raies = 10 FWHM = 4.23 – Dispersion = .055 A/pixel – R = 27028.2
• Ordre #55 : RMS = .0021 – Nb. raies = 15 FWHM = 4.01 – Dispersion = .054 A/pixel – R = 28723.9
• Ordre #56 : RMS = .0007 – Nb. raies = 10 FWHM = 3.91 – Dispersion = .053 A/pixel – R = 29480.5
• Ordre #57 : RMS = .0018 – Nb. raies = 13 FWHM = 3.86 – Dispersion = .052 A/pixel – R = 29763.2
• Ordre #58 : RMS = .0024 – Nb. raies = 12 FWHM = 3.85 – Dispersion = .051 A/pixel – R = 29776.6
• Ordre #59 : RMS = .0025 – Nb. raies = 12 FWHM = 3.85 – Dispersion = .051 A/pixel – R = 29763.7
• Ordre #60 : RMS = .0016 – Nb. raies = 12 FWHM = 3.94 – Dispersion = .049 A/pixel – R = 29543.1
• Ordre #61 : RMS = .0020 – Nb. raies = 14 FWHM = 3.93 – Dispersion = .049 A/pixel – R = 29312.2
• Ordre #62 : RMS = .0029 – Nb. raies = 13 FWHM = 3.94 – Dispersion = .048 A/pixel – R = 29158.7
• Ordre #63 : RMS = .0072 – Nb. raies = 16 FWHM = 4.19 – Dispersion = .047 A/pixel – R = 27528.6
• Ordre #64 : RMS = .0054 – Nb. raies = 11 FWHM = 4.17 – Dispersion = .046 A/pixel – R = 27744.9
• Ordre #65 : RMS = .0045 – Nb. raies = 12 FWHM = 4.23 – Dispersion = .046 A/pixel – R = 27077.1
• Ordre #66 : RMS = .0029 – Nb. raies = 14 FWHM = 4.36 – Dispersion = .045 A/pixel – R = 26441.2
• Ordre #67 : RMS = .0034 – Nb. raies = 13 FWHM = 4.38 – Dispersion = .044 A/pixel – R = 26347.2
• Ordre #68 : RMS = .0218 – Nb. raies = 13 FWHM = 3.82 – Dispersion = .044 A/pixel – R = 29917.4
• Ordre #69 : RMS = .0006 – Nb. raies = 8 FWHM = 4.47 – Dispersion = .043 A/pixel – R = 25935.4
• Ordre #70 : RMS = .0018 – Nb. raies = 9 FWHM = 4.40 – Dispersion = .043 A/pixel – R = 25955.4
• Ordre #71 : RMS = .0026 – Nb. raies = 10 FWHM = 4.26 – Dispersion = .042 A/pixel – R = 26941.9
• Ordre #72 : RMS = .0007 – Nb. raies = 11 FWHM = 4.18 – Dispersion = .042 A/pixel – R = 27238.5
• Ordre #73 : RMS = .0018 – Nb. raies = 12 FWHM = 4.23 – Dispersion = .040 A/pixel – R = 27543.4
• Ordre #74 : RMS = .0055 – Nb. raies = 10 FWHM = 4.39 – Dispersion = .040 A/pixel – R = 26419.2
• Ordre #75 : RMS = .0016 – Nb. raies = 11 FWHM = 4.18 – Dispersion = .039 A/pixel – R = 27715.6
• Ordre #76 : RMS = .0011 – Nb. raies = 9 FWHM = 3.83 – Dispersion = .039 A/pixel – R = 29945.7
• Ordre #77 : RMS = .0012 – Nb. raies = 10 FWHM = 4.01 – Dispersion = .038 A/pixel – R = 28923.0
• Ordre #78 : RMS = .0021 – Nb. raies = 13 FWHM = 4.06 – Dispersion = .038 A/pixel – R = 28466.2
• Ordre #79 : RMS = .0024 – Nb. raies = 12 FWHM = 4.27 – Dispersion = .037 A/pixel – R = 27137.1
• Ordre #80 : RMS = .0034 – Nb. raies = 11 FWHM = 3.84 – Dispersion = .037 A/pixel – R = 29738.4
• Ordre #81 : RMS = .0018 – Nb. raies = 11 FWHM = 3.73 – Dispersion = .036 A/pixel – R = 31107.6
• Ordre #82 : RMS = .0036 – Nb. raies = 9 FWHM = 4.07 – Dispersion = .035 A/pixel – R = 29097.0
• Ordre #83 : RMS = .0210 – Nb. raies = 9 FWHM = 3.51 – Dispersion = .036 A/pixel – R = 32916.2
• Ordre #84 : RMS = .0958 – Nb. raies = 10 FWHM = 3.34 – Dispersion = .035 A/pixel – R = 34570.3
• Ordre #85 : RMS = .0317 – Nb. raies = 10 FWHM = 3.02 – Dispersion = .035 A/pixel – R = 37907.5
• Ordre #86 : RMS = .1350 – Nb. raies = 11 FWHM = 3.43 – Dispersion = .034 A/pixel – R = 33108.4

Conclusion

This observation campaign conducted in a beautiful observatory, on a high quality instrument, but with a rather ungrateful weather allowed us to confirm the performance of Whoppshel in real conditions – with exposure times around of one hour :

a 60 cm telescope provides resolution spectra of around 30,000 from 3900 Å to 7600 Å.
Without being in optimal weather conditions and with an object fiber of 50 microns, objects can be observed up to magnitude 9.
The potential of this same instrument with a fiber of 105 microns – of course with a lower resolution of 15,000 – is vast.
At the time of writing, we have just learned that the Nobel Prize in Physics 2019 was awarded (among others) to two Swiss researchers, Michel Mayor and Didier Queloz, for their discovery of the first exoplanet 51 peg b. This discovery was made in 1995 at the Haute Provence observatory, where we organize a Spectro Star Party every year. It is a great emotion for us: they are people who are models for us, it’s a place and a familiar instrument, and by devoting ourselves to astronomical spectroscopy, we work as a result of these researchers to better to understand the Universe around us

And you know what ? The Whoppshel is a wonderful tool to explore the world of exoplanets!

The Whoppshel was born from the demand of our customers to have a higher resolution echelle spectroscope than the eShel for telescopes of one meter class. The whoppshel, with a resolution R = 30000, is particularly adapted to radial velocity measurements.

Whoppshel is based on a few principles:

An optical White Pupil architecture, which allows to naturally compensate for certain optical aberrations (passing twice symmetrically in the optical components), and on the other hand to maintain a reasonable target size.

The use of Takahashi lens (FSQ106 at F/ 3.6) for the collimator and a high-end photo lens (Canon 135mm F/2) for the objective lens. All the high constraints on the optics are thus embedded in high quality elements manufactured in series.

The instrument is assembled on an extremely rigid optical bench.

The cross-disperser of the echelle spectrum is obtained using three prisms specially made for this spectrograph.

Optical path of Whoppshel
Like eShel, Whoppshel is a fiber optic spectrograph. It uses the same injection fiber module, the same optical fibers and the same calibration box as the eShel range.

The light collected by the telescope is injected via the 50μm optical fiber in the middle of the two Takahashi lens, a small mirror deviates the beam towards the first telescope. The beam is then spread out by the echelle grating. It is then returned to the two symmetrically mounted lens, which eliminates most of their residual aberrations. The output converges to the three prisms (cross-disperser) which separate the different orders. The 135mm photo lens open at f/2 finally retrieves the sprectrum signal in both axes to focus the spectrum on the CCD sensor of the camera.

To inject the light flux coming from the telescope, the Whoppshel uses the same injection and guiding module as the eShel spectrograph according to the f / d ratio of the telescope:

• For telescopes open at f / d 6: PF0008
• For telescopes open at f / d 9: PF0018

It is therefore necessary that the telescope approaches the f / d ratios above for maximum efficiency.

Of course, we need to add to the setup, a 50 μm optical fiber for object, a 200 μm optical fiber for calibration, and a guiding camera.

A 105μm optical fiber can also be used to take lower magnitude target, in which case the resolution of the Whoppshel will be about R = 15000.

Specifications
The Whoppshel has a resolving power of approximately R = 30000 (slightly variable according to the orders) and covers a wavelength range from 3900 Å to 7600Å.

This spectrograph has a length of 2.10m and measures 0.6m in its greatest width. It is installed on 2 optical benches, 0.9×0.6m and 1.2m x 0.3m assembled very rigidly together. The total mass of the spectrograph is 81 kg.

A Bosch profile structure (standard elements) allows the entire enclosure of the instrument to be protected from stray lights and dust.

For the spectral calibration performed with Whoppshel, the same calibration unit as the one dedicated to eShel is used. This calibration unit includes a Halogen lamp to generate flats and a Thorium / Argon spectral lamp with a very large number of lines distributed over all orders of the spectrograph. The calibration unit can be controlled remotely via an RS 232 interface.

Here’s a spectrum of the Th/Ar lamp use for wavelength calibration :

Delivery and assembly of the spectroscope
The Whoppshel is delivered in spare parts because of its dimensions (Shelyak can of course install and adjust the Whoppshel for you if necessary). An assembly instructions allows the entire spectroscope to be assembled step by step.

Since the instrument is installed on an optical bench, the installation is done by following the beam of light element by element – editing is an extremely educational exercise, particularly useful for students.

The CCD camera is mounted on its holder with its 135mm optics, it will be used during all stages of the assembling to tune the focus and alignment of each optical element. This operation is greatly facilitated by the fact that all light streams are at the same height and centered on the camera. Thanks to the AudeLA software, we can measure the FWHM of the spot after each optical element.

The ATIK 460ex CCD camera is particularly recommended for this spectrograph because of the width of its sensor, its quantum efficiency and the read noise about 5e-. Other CCD cameras can of course be used, just check that the sensor can cover all the orders of the spectrograph and also that orders can overlap from one order to another. At a minimum, the ATIK 460ex meets these criteria. If you want to use another camera, you have to take into account the distance between the optical axis of the CCD and the optical bench which is 102mm.

First try : The Sun light
Without waiting for the night, we can make a first test of the spectrograph by using the day light directly on the optical fiber placed outside. Here is the first raw spectrum obtained:

In this raw image, we have identified some lines of the solar light, such as Balmer lines (Hα, Hβ, Hγ, Hδ), the Sodium doublet (D1, D2) and the magnesium triplet.

The orders identified are from 42 to 87, the latter containing the lines H and K of the calcium.

First stellar observations
First light on Be star Zet Tau (mag. V=3,03) with a Richtey-Chretien telescope of 400mm diameter : 3 exposures of 300s with an ATIK 460ex CCD use in bin 1×1 mode.

Above, another test with the star Eta Tau, mag. V = 2.87 with the same telescope of 400mm diameter and the comparison with the spectrograph eShel R = 11000 (curve in blue). We can be seen that Whoppshel solves the telluric lines present around the H Alpha line better than the Eshel spectrograph.

Finally, an observation of P Cyg, mag. V = 4.82, still with the same telescope of 400mm of diameter.
22 exposures of 300 seconds.