1. A wide field spectrograph/camera Roberto Ragazzoni, Carmelo Arcidiacono, Jacopo Farinato, Marco Dima, Emiliano DIolaiti, Giorgia Gentile, Demetrio Magrin Valentina Viotto, Matteo Quasimodo, Fernando Pedichini, Emanuele Giallongo INAF – Padova, Bologna and Roma Observatories October 22 nd, 2008 Sede di Monte Mario

2. Background… If you think to (seeing limited) wide field you immediately think to a Prime Focus…

3. Background… If you think to (seeing limited) wide field you immediately think to a Prime Focus… …and in fact we built two of them… whose optics works from U to H for half degree Field of View with 0.2arcsec optical quality

4. Scaling factors… We are in the transition to ELT era… …so we should be used to break the factor 2 syndrome… We want a FoV 2..3deg in diameter rather than a 0.5deg one… …that is up to 36 times more FoV then LBC… …or it is 9x4=36 times again more photons than a 1deg on a 4m telescope! We want it with Multi-Object, Multi-Slits or Multi- IFU spectroscopic capabilities…

5. So, what exactly we want…? We want an LSST with, in addition, 3 rd dimension (spectroscopy) too. We want it at a price and a timescale of an instrument rather than of a telescope We want it feasible with today national technological capabilities We want it with more industrial involvement to gain more momentum on raising funds Is this possible…?

6. Scaling factors… In 1984 Richardson et al. wrote a paper on the scaling subject… Size of the first lens scales linearly with the FoV… …leading to a 4.9m lens for a 3degs Prime Focus… weighting about 100tons!

7. Surprised????

8. 5.0m

9. And still the refractive part of the camera remains even more difficult and challenging as what we call a “conventional” Prime Focus…!!! Size compared with a normal (???) man… Would you really allow this person to do a WFoV camera for you???

10. …new challenge requires new solution…

11. What is difficult in a W-FoV imager? The fast focal ratio (smaller than the Cassegrain stations)  Prime Focus or Focal reducer Wide Field of View (a tautology??)  use big optics Correction of off-axis aberration  Several optical elements to control aberrations (with aspheric too) A large array or mosaic  Big buttable CCDs

12. What is difficult in a W-FoV imager? The fast focal ratio (smaller than the Cassegrain stations)  Prime Focus or Focal reducer Wide Field of View (a tautology??)  use big optics Correction of off-axis aberration  Several optical elements to control aberrations (with aspheric too) A large array or mosaic  Big buttable CCDs

13. VLT or LBT…. Secondary mirror modified to achieve an F/4 in the usual position… A trapped F/4 unit…

14. Just an explanatory picture Long F/ focal plane Short F/ focal plane

15. Extensive segmentation Each unit has the same optical elements as any other else Correcting devices are mounted in a different fashion Achievable FoV of a single element crucial for defining the instrument Designs lies in the range 2..3arcmin in size

17. 4.9 sq. degs3.14 sq. degs 4.0 sq. degs 1000 to 2000 cameras

19. 1 arcsec diameter 2.5degrees diameter

20. Multi Object Spectroscopy too!! The physical size where fibers are to be located is much smaller than the mechanical size where the positioner is to be placed Ideal condition for mechanical solutions (almost doable with off-the-shelf components) Ratio of size is ratio between long and short focal ratios (2 to 5, in our designs) Array of small FOSC spectroscopic cameras with a number of moveable multi-slits F/4 F/3 F/2

21. Options for spectroscopy Multi-fiber or multi-IFU –Simpler mechanically and optically –Requires a dedicated spectrograph(s) –Blind pointing & fiber losses –Spectral resolution and band flexible Multi-slit –Requires double relay & more mechanics –Pointing is safe and straightforward –Spectral resolution and band limited & fixed In both cases multiplexity is in the few to 10 thousands range

22. It is movie time…

23. What a detailed Phase A study should contain…? Science cases… here we are!!! Pipeline, archiving and data reduction plan Cost vs. implementation plan (ramping up of the covered FoV?) Secondary mirror feasibility, mounting design and balance requirements on the telescope Precursor experiment? (an off-axis camera) Specific for VLT How to preserve the VLTI option Specific for LBT Location (fourth bent Nasmith) Justification & plan for double foci

24. References SPIE proc.6272, 25 (2006) SPIE proc.6269, 187 (2006) SPIE proc.5492, 121 (2004) A napkin on a “restaurant” in Copenhagen (2002) How to go ahead…? Setting up a consortia or running alone? VLT, LBT or still keeping the two options open? Science is probably straightforward but, why not to “count us”…??? A WorkShop soon on the subject? A real, INAF endorsed, preliminary design phase, similar to the one for LBC.

25. Considerations This is undoubtely a HUGE projects Requires a detailed true design to go ahead Requires to setup a real conosrtium both inside and outside Italy Requires connection with data management One shot is about 1000 x 2kx2k pixels Requires sort of automatic operations One spectroscopic shot requires placing a few thousands slits. It must be automatic to a large extent!

26. List of issues (preliminary) VLT vs. LBT issue: LBT can be trapped or normal Cassegrain. (no way… trapped is by far the best but just we have to show up this) In normal Cassegrain there is need of an additional foci position and of a larger M2 and M3. Point out masses, sizes involved and feasibility. In case of VLT arguments about where is the overall cog, and effects on the interferometry. About LBT discuss how the two channels can be diversified. Wavelenght, modalities, number of slits, etc… Comparison with LSST (2.6deg is the threshold for having the same A Omega). How much can be the optical filling factor (dead strips between cameras. Also recall that due to Cassegrain blurring there is an overlap with vignetting) There is a sort of analysis carried out by Giorgia but it is still floating!!!

27. List of issues (II) Optical Design: Number of lenses. Goal quality expected to be 80% in 0.3arcsec?? Mass production of the lenses. Is there any possibility of inside the FoV correction to make the single FoV much larger?? We actually lack a REAL optical design!

29. List of Issues (III) Spectroscopy: Concept. Review multi fibers just to point out that is a problem to find out the objects. Mechanisms, positioning devices. Preparation to observations. Where and how to place slits in automatic manner. In this moment there are conecpt and fake movies (even not finished!)

30. List of issues (IV) Mechanical design: Overall design. Modularity Accessibility. Filters exchange Maintenance Piping Overall derotation Secondary mirror Can we proceed without a baseline optical design?

31. Issues (V) Detectors: Point out that the area or pixel number is invariant. Mass production. Quality tes. Certification. Testing? Thinned back illuminated or not? Can me move out from conventional CCD technology? Controllers: Engineering. Remotely programmable. Adressable. WiFi?? Certification, testing, wquality again.

32. Issues (VI) Active Optics: Just a few modules or additional little cameras for making ActOpt at a few edges. To be checked/studied Background: Just to recall that there could be a background issue. Data Management: How much data get out? Picture of the bathroom with a lot of data everytime you flush it!!!! Yellow claim one do not confgrid all the single images unless requested. Maybe this can be done anyway in a pipeline delayed?

33. Issues (VII) International Issues: VLT and LBT are so different. For LBT Germans claimed interest and Americans denied it. Competition with LSST. Peculiarity of spectroscopic option. Management: Definition of WPS Criogenic devices: Thermal budget. Pletier cooled? Money: How much it can really cost? Where can we rob the money?

34. Furthermore… Science! We all agree, BUT there is not a well defined structure Which must be OUR role? There will be a meeting somewhere, hopefully the May 13 th, 2008 Will be presented at Ringberg Will be a poster (sigh…) at Marseille…

35. First steps Define nominal figures Figure out an optical design Define a mechanical framework Setup a scientific environment Aim to set up the cost! Still the project need firm and outstanding documents/papers Who does what???

36. Open to free discussion What do you think? Which part do you like? Which is your opinion into the VLT vs. LBT issue? Who we wish to involve into this? Need to setup a minimum goal with deadline!!!