A wide field spectrograph/camera

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 22nd, 2008 Sede di Monte Mario

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

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

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…

So, what exactly we want…? • We want an LSST with, in addition, 3rd 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…?

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!

Surprised????

Surprised???? 5.0m

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

…new challenge requires new solution…

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

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

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

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

4.9 sq. degs 3.14 sq. degs 4.0 sq. degs 1000 to 2000 cameras

2.5degrees diameter 1 arcsec diameter

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/2 F/3

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

It is movie time…

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

How to go ahead…? References • 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. • SPIE proc.6272, 25 (2006) • SPIE proc.6269, 187 (2006) • SPIE proc.5492, 121 (2004) • A napkin on a “restaurant” in Copenhagen (2002)

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!

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!!!

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!

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!)

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?

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.

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?

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?

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 13th, 2008 • Will be presented at Ringberg • Will be a poster (sigh…) at Marseille…

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???

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!!!

A wide field spectrograph/camera