Re: Think spectroscopy!

Michel -- Yours is definitely an interesting suggestion. on the basis of
the tremendous information content of spectra, I spent some time when
Megaprime was being planned arguing that it made sense to have a low/med
resolution mode of spectroscopy as well. Obviously that did not succeed.
But it is worth reconsidering.

CFHT is such a high quality site (possibly having nearly the best r_0,
tau_0 known) that it also merits consideration for a more powerful
replacement telescope, as effectively acknowledged in the CFHT21
celebrations, although the form and cost of the replacement telescope
might now be less (or more) ambitious.

Michel Dennefeld wrote:
> And what about spectroscopy for "fainter" objects?
>
> I have read with great interest the preparatory document for the 2007
> user's meeting. My reading of this document is the following:
> -The scientific directions proposed for the future, if
> we keep the present 4m, are essentially building up on the present
> situation: to be short, wide-field imaging, and high-resolution
> spectroscopy
> for asterosismology or extrasolar planet searches; and possibility to
> develop interferometry (but clearly limited to "bright" objects).
> -A future 8m for wide-field spectroscopy is alluded too at the end,
> but then is presented for exoplanet imaging....?
>
> We have put many efforts into imaging surveys...where do we do the
> spectroscopic follow-up? More surveys are coming-up in the future,
> either with "small" automatic telescopes, or with larger ones
> (e.g. Pann-Starrs, or VISTA, not to quote the more distant LSST)...
> Space missions will also provide many targets to be studied.
> In particular, GAIA is coming in 2011 and will provide thousands of
> objects which will need follow-up, for classification. To give only
> one exemple, Gaia is expected to provide several thousands of Supernovae
> each year (up to mag. 20): this is an extraordinary sample of local
> SNe to study their physics, to serve as a reference for those more
> distant SNe used in cosmology studies, and to study the Star formation
> rates in the host galaxies.
> On the french side, it is claimed that our main observing tools are
> located in the south, within ESO. Yes, but we nevertheless need a
> spectroscopic access in the Northern hemisphere, even for only a
> fraction of the time. We have an aging low-dispersion spectrograph on
> a 2m, and if MOS is decommissioned or not replaced, what do we have
> left in the north?
> Nothing for low-dispersion spectroscopy! Our colleagues from Taiwan or
> Korea are in the same situation.
> Our canadian friends have a small access to Gemini, but I understand
> that the amount they have is by far not satisfying their needs...Those
> in the best situation seem to be the colleagues from UH, so I imagine
> they will not necessarily follow my line. French astronomers are,
> among the great "astronomy nations" in the West, the only ones having
> no access to a large telescope in the northern hemisphere...
>
> What can we propose:
>
> We should have a coherent view/planning of the facilities accessible
> to us, and not treat the CFHT independantly of the other facilities.
> This view may be different for the different communities involved, but
> I think we could find a convergence on the spectroscopic needs.
>
> -The idea of a spectroscopic 8m (or larger...) seems attractive to me.
> I have some doubts about the faisability in a reasonable time scale,
> in view of the financial situation, and the priority given to ELT's.
> But this should be the goal for the long term.
> But the needs are immediate, so what can we do for the short or mid-term?
> -Provide a low-dispersion spectrograph at the CFHT, at least for the
> dark time (a 4m is perfectly suited for objects in the range of
> magnitudes 18-21, which is what is needed for Gaia follow-up; a
> complementary 2m can do the brighter ones). One can discuss the kind
> of spectrograph: it can be a wide-field one, but a good use of the
> CFHT site quality would be a spectrograph behind adaptive optics,
> either standard, or IFU. Note that among 4m telescopes accessible in
> the north, the one offering IFU was forgotten in the report: Calar
> Alto has an excellent IFU (PMAS), even if the site if obviously not of
> the same quality as Mauna Kea. The WHT is presently heavily used in
> low dispersion with ISIS, but as said in the report, AO and laser
> guide stars will take more time in the future. So there is a "niche"
> for the CFHT...
> -Exchange some CFHT survey time for spectroscopic access to other 8m's.
> Some of them are looking for support from a survey telescope...but all
> depends on the "exchange rate"... and if some 8m turn into survey
> telescopes themselves, I am note sure CFHT remains competitive in this
> domain.
>
> These two options are not exclusive of each other, and others may
> emerge also.
> What is important, is the timescale, and the continued access to
> low-dispersion spectroscopy in the North. CFHT for the short term,
> and then the 8m (or larger) for the more distant future...
>
> In any case, "Think spectroscopy!"
>
> Michel Dennefeld
>