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Some answers to Richard's comments
Thanks Richard for the information on the UH perspective. Here
are a few comments to clarify some points you raise:
> Christian - do we have enough information about the transmission of
> the corrector (I assume we now have the CCD QE curves) to make
> progress on the u' filter design? In my past dealings with Barr in
> purchasing filters in this wavelength range, I found that they had
> trouble making high transmission filters, because suitable glasses
> were not available. Has this changed at all in the last few years?
> About 5 years ago, you could get very high transmission filters around
> 330 nm, and around 500 nm, but the wavelengths around 400 nm did not
> have very high transmission glasses.
>
Right now, the exact bandwidth of the filters is not definitively set.
Especially the u' is not because I want to first get the results
of the coating of the WFC lenses. I would like to make a wider u', as
it seems possible to have a coating good down to ~320 to 300 nm.
We have in order a couple of filters for 12K and we will see how well
REOSC can do.
> Some people in the group have been talking about using UBVRI filters.
> Do people wish to reopen the issue of filter system? If we are sure
> we will use the Sloan system, then it would help if we start using
> these systems more in our discussions of how much observing time
> various surveys would take.
>
I agree with the last statement. At this point, I would rather not reopen
the discussion on the choice of the filters. At every meeting I mentioned
the Sloan filter set choice, I got good comments. If there is a strong new
reason not to move toward these filters though, we can re-examine the issue.
> If I recall correctly, the QE of the EEV CCDs is rather poor in the z'
> region. Would it be possible to get some more information on this
> prior to the meeting? How does it compare with CFH12K? The u' and z'
> filters are clearly going to be expensive in observing time.
I don't know what you mean by rather poor. It's definitely not as good as
on 12K. As you know for 12K, there are two sets of CCD's with pretty different
QE's. I added a page with two pictures (one for MegaCam and one for 12K)
of QE curves on our web site
http://www.cfht.hawaii.edu/Science/mswg/QE.html
> 5. Christian - could you please clarify:
> a) how many nights per year will go to Korea and Taiwan
K and T time will be taken off the top... as will a little bit
of Engineering time and possibly some D time (though I would advocate
that the resident astronomers should jump into the surveys..) which
I'll round up as 3 nights a year. K+T is 17 nights a year in dark time.
Remember though that right now we have 200 "dark" nights a year with the
current definition (16 days per lunar month). It means that we are left
with 180 dark nights a year for CFH in dark time.
> b) what their relationship is to the proposed survey?
> I realize that b) is hard, but it would help to know whether we
> expect that they will want all of their time taken off the top for
> their own targeted research, or whether they want to be part of the
> survey. If the K and T time will be taken off the top, then we should
> regard the total number of dark nights on the telescope as 183 - K/2 -
> T/2 - not as 183 per year.
See above for the comment on the number of nights. It is clear that, from
the CFHT perspective, T and K are not going to be invited to participate
in the surveys. Individuals can do what they want through collaborations
though (right now a lot of astronomers from UK and the Mainland, among other
places, are observing on our telescope through collaborations).
>
> 6. I think everyone will agree that it is vital that we maximize the
> scientific output of the CFHT. I don't think that we will be able to
> come up with a survey proposal that will answer all the most
> interesting questions that can be addressed with Megacam - in other
> words, I suspect that there still needs to be room for proposals to be
> submitted by PIs in order for our communities to accept the survey.
I agree with the fact that we have to leave some space for more PI oriented
programs, though not much for the first two or three years...
> Another way of thinking of this is in the context of the discussion
> relative to VISTA. It is fine to compare what VISTA will do, but we
> have this capability a lot sooner. Therefore, I think we should be
> scooping off all the most interesting scientific problems that can be
> addressed with deep wide-field imaging before VISTA has a chance to
> do them.
See previous comment... We have to move fast!
I was supporting MOS yesterday at the summit, and one of the observers
was from UK, working on wide field imaging too. The position of the
UK community is slightly different from the one in the VISTA project
(which is where the information I gave in a previous message came from).
Many think that a visible camera is much easier to build, that the IR one
is pretty ambitious, and then that the visible camera should be the first
priority. As for dates, the beginning of 2006 for real science is a more
realistic date.
The UKIRT wide field camera is not supposed to work heavily on surveys
for a while, but there is a push from some in the UK community to move
toward UKIRT as a survey telescope much earlier...
> 7. Olivier mentions that WIRCAM is too little too late. I'm not sure
> what we can do to change this. The main limitations seem to be lack
> of money to build this, along with intrinsic limitations of the f/8
> focus of CFHT. If we can accept to work only in the J and H bands,
> then I think that it should be possible to build something with a
> wider field of view (e.g. 3x3 array of 2k). I understand that
> two-edge abuttable devices are in the works - these would help. One
> of the main money problems has been the sheer cost of the 2k devices -
> I think these are $300k each. If we really want CFHT and SAC to
> rethink WIRCAM, where will they find the money? Is it acceptable to
> lose the thermal (K) capability?
At this point, again seen from CFHT, it is clear that we want to move fast
on WIRCAM. But if the camera as it is now is not going to satisfy the
community, why should we build it? I think we should not spend too much time
redefining WIRCAM, nor should we design the CFHLS to fit WIRCAM. However,
we can, in our discussions on the CFHLS, stress the interest of IR complement
and explain what we would like WIRCAM to be.
Aloha
Christian
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Dr. Christian Veillet, CFHT Senior Resident Astronomer
Phone: (808) 885-3161 http://www.cfht.hawaii.edu/~veillet/
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