UVEX test on a one meter telescope with Mag. 15-16

[Olivier GARDE]

We are currently at the Côte d'Azur observatory in south of France, on the Calern plateau (1270 m above medium see level) with Pierre Dubreuil, Pascal Le Dû and Christian Buil, to test the UVEX by Shelyak spectrograph prototype on a one meter telescope in diameter.


The C2PU building on the Calern plateau (Photo : Olivier Garde)

The uvex is attached to the telescope at f / 9 and we use an ASI 183 MM pro camera, a 35µm slit and a 600 gr/mm grating blazed at 500nm.


Olivier and Christian during the UVEX setting (Photo : Pierre Dubreuil).

The 1st spectrum was made on the andromede parachute, a gravitational lens with a redshift Z = 2.33 approximately (11 billion light years) and the magnitude of this target is around 15-16.

The seeing during exposure was very good, around 1" RMS and pics around 0.6'', but we haven't use any auto guiding system, so the accuracy is about 1.5'' .



Here's the slit during exposure, we can see the 35µm slit and the 3 components of the gravitational lens (not a single dot).


(Photo : Pascal Le Dû)

Here's the spectrum with a resolution around R=2000. (5 exposures of 900s)



Process made by Christian with ISIS V6 (CMOS process)


And a comparison with a spectrum taken on the KECK (10 m diameter telescope) in 2017



Our spectrum is quite good with maybe a better resolution. Also note the evolution of the spectrum over 3 years.

Another target : Z And (symbiotic star Mag. V=8,08)



We took 3 exposures: 900s, 600s and 300S because we were surprised by the saturation of the spectrum at 900 and 600s. Same process by Christian with ISIS V6

In conclusion, the UVEX has been tested here on a telescope which is a little outside the standards compared to its basic optical design, namely a Ritchey Chretien type telescope of 12, see 14 inches at F / d 8, not a one meter telescope... But on point targets, we were able to show that we could use this spectrograph on a one meter telescope and produce good results spectra.



The team around the one meter telescope with (from left to right) Pascal Le Dû, Olivier Garde, Pierre Dubreuil and Christian Buil (Photo : Pascal Le Dû)

[JP Nougayrede]

Excellent spectrum on the quad quasar ! Starting to see the lyman forest under 4000 A. The evolution of the absorber at 5000 (CIV)in just 4 years is quite impressive, if true.

[Christian Buil]

It's important to distinguish two situations. The observation of large surface objects (extended planetary nebulae) and the observation of stellar object.

If we compare LISA / UVEX on nebulae, LISA has an internal magnification of 0.67 (1.05 for UVEX because anamorphose) and LISA can be used at f/6 (focal reducer on the one-meters telescope), while UVEX was used at f/9. The LISA equivalent F/D ratio is 6 x 0.67 = 4.02. The F/D ratio for UVEX 9 x 1.05 = 9.45. The superiority of LISA is very clear, the luminosity is greater by a factor (9.45 x 9.45) / (4.02 x 4.02) = 5.5.

UVEX was here also used with a double spectral dispersion compared to LISA, for a LISA final equivalent gain of 5.5 x 2 = 11. The small pixels size for CMOS cameras is also not very favorable (a CCD camera allows a very efficient analog binning) (but the presence of emission lines is a complication for the analysis).

On stars and by using the big one-meter telescope, I estimate that LISA is twice as efficient for identical spectral resolution. On a 0.2-0.3 m telescope and for point sources, the detectivity is very similar.

The superiority of UVEX concerns the uniformity of the spectral resolution over a wide spectral range and the accessibility to IR and UV with the same quality, which is of great interest from an astrophysical point of view.

Christian Buil


… an image of UVEX at telescope focal plane:

[Francois Teyssier]

Trés convainquant.
On attend avec impatience la production en série par Shelyak.
Z And: est-il possible d'exploiter le spectre poura aller plus loin dans l'UV et obtenir le saut de Balmer?
Merci de me l'envoyer pour la base!

Encore bravo à toute l'équipe de conception et de mise au point,

François

[Christian Buil]

François, Je viens de t'envoyer le spectre de CH Cyg, mais il faut être bien prudent, les raies intenses sont saturées (on c'est fait piégé pas la quantité de flux collecté et il n'était pas possible de refaire).

Pour ce qui concerne l'UV, on aurait pu aller plus loin, mais le réducteur en place absorbe sensiblement (j'ai des données pour évaluer, analyse à faire). Toujours la même chose lorsqu'on traverse des lentilles...

Je t'ai aussi envoyé mon dernier spectre IR de nova Cas 2020 au Newton de 250 mm (le 1 mètre ne pouvait pas pointer à une telle déclinaison, dommage).

Christian