Think spectroscopy!

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
Received on Fri Apr 27 2007 - 06:19:27 HST