In attendance ------------- Giovanni Carraro GC Mark Casali MC Paul Dobbie PDD Richard de Grijs RDG Nigel Hambly NCH Simon Hodgkin STH Richard Jameson RFJ Mark McCaughrean MM Ian Parry IRP Apologies --------- Jerome Bouvier JB Estelle Moraux EM Agenda ------ o Overview: targets/priorities/areas/ o CFHT surveys o Complementary optical/near-IR photometry o Spectroscopic follow-up o AOB Introduction ------------ NCH kicked off the meeting by outlining the two key points he wanted us to reach agreement on: (1) choose which filters to survey with WFCAM (2) to initiate plans for complementary optical imaging Hardware Update --------------- MC confirmed a 3 month delay to the completion of WFCAM. ATC are currently in discussion with JAC to agree a delivery date - either end of Feb 2004, or end of Apr 2004. Three out of four science chips are now in Edinburgh, together with all major hardware plus all major electronics plus computers. Quantum efficiency measurements for these detectors are a high priority, one has been measured to date and looks encouraging at the blue end. The current Z-band sensitivities (as quoted on the UKIDSS www pages) should be taken with a grain of salt given uncertainty in the background, perhaps they are a little pessimistic. The Y values might be more accurate. There is no Z-filter currently - but construction is currently being investigated. The filters will initially comprise both Z and Bracket Gamma, as well as YJHK. Overview -------- It was felt that we do not need more frequent meetings, except perhaps for the construction of proposals and further downstream in the examination of the first data to come out of the pipeline. (As an addendum, GC has arranged to come to Cambridge and write the ESO placeholder proposal with MM and STH in August). STH felt it might be useful to draw up a timeline - showing WFCAM delivery date, proposal deadlines etc, to help us keep on top of this. (Addendum: it now seems obvious that we should construct a GCS www page.) (ACTION STH) ********** Priorities and Areas -------------------- In general all were happy with the existing target priorities and areas, with minor modifications (see below). There was discussion of the Hyades, specifically in the context of the CFH key programme, along the lines that the major science goals outlined in our UKIDSS proposal may already be accomplished. It was felt that the CFH survey was so much smaller in area, and somewhat deeper, that it was in fact complementary and did not impact on the UKIDSS survey. Further discussion on this area was deferred to the later discussion on filter choices. CFHT survey ----------- In the absence of JB and EM, dicussion of this area was unfortunately a little limited. NCH showed the CFH key programme targets (there are 3 sub-programmes: PMS clusters, evolved clusters and star forming regions) and their progress to date: Target Area (sq deg) ====== ============= Stephenson 1 1.3 Collinder 359 1.6 IC 4665 4.2 Rho Oph 6.5 Collinder 70 NGC2232 Taurus Perseus Serpens 5.9 Sco OB2 Hyades 14.0 The data are all procesed and currently under analsysis by members of the CFH collaboration. IR folow-up observations of some of the candidate cluster members are already (currently) ongoing. The CFH wide field infrared camera, WIRCAM, is currently scheduled to be offered in 2004. It's not clear if this is realistic given the status of the buttable Hawaii detectors. There are plans to use WIRCAM to follow-up the CFH key programme. The question was raised: will the CFH clusters data enter the public domain and if so when. NCH offered to contact JB and investigate this question. (ACTION NCH) ********** After some discussion of the sensitivity and area of the CFH key programmes, they were felt to be very compatible with the WFCAM larger area and shallower approach. It was suggested that we should prioritise UKIDSS areas coincident to existing CFH data, which would have two obvious benefits: 1) It would return quick science for the benefit of the CFH and UKIDSS teams. 2) It would enable us to check our observing strategy with respect to candidate selection. For example, do we need all of infrared ZYJHK plus optical IZ data to select candidate cluster members, or is some fraction of these filters adequate ? It was pointed out that PATT may be an alternative route to accomplish the goals defined above if the UKIDSS depth were insufficient. An action was placed on STH to investiagte which CFH targets would benefit most (if at all) from early WFCAM observations. In particular, IC4665 was identified as a target which would be observable during scheduled WFCAM start of operations. PDD pointed out that 6 square degrees of existing CFH-12K Pleiades data would provide a sensible test dataset for early WFCAM imaging. (ACTION STH) ********** STH informed the group that a RTN (Reasearch Training Network) meeting was taking place in Cambridge (Sept 8-11th). The key focus of this meeting is to discuss preliminary results from the CFH datasets and to plan the next phases of the project: follow-up plus extension of the survey. NCH was invited to attend this meeting and represent the UKIDSS GCS for a more formal introduction between the two teams. STH invited members of the GCS to attend the science part of the RTN meeting and will send out an email. (ACTION STH) ********** WFCAM filters ------------- The bulk of the meeting focussed on the issue of which filters to survey with. It was agreed that JHK alone are inadequate and will lead to large amounts of contamination of the cluster sequence by the field. After much discussion of which exact filter combinations should be preferred, it was unanimously agreed that to observe in _all_ available broadband filters made scientific, strategic and logistical sense for some of the following reasons: 1. By observing in all filters, one maximises information and makes fewer assumptions about the outcome. Candidate selection will be better informed leading to smaller overheads on large telescopes. The possibility of extracting more unexpected and surprising science will be increased. 2. No single filter was seen as indispensible, for example the H-band was initially felt to be unneccessary, but it was pointed out that the J-H, H-K diagram is important for metallicity and luminosity class discrimination. 3. By surveying in the bluer Y and Z bands, the survey could _in principle_ be performed with only one instrument. This has numerous benefits, including simplicity (it is part of an existing programme), uniformity (the data are well matched in pixel scale and can be quasi-contemporaneously observed) and certainty (one does not have to rely on another TAC to allocate the time). 4. We are not cosmologists. We do not need to pretend that we know all the answers already. The approach of using ZYJHK was felt to be the most conservative and the most rewarding. It was argued and agreed that this strategy could be modified at later times if observing in say 3 or 4 filters could be demonstrated to be as successful. It was further argued that if time could be found on optical telescopes to perform the Z imaging, then this filter could be removed from the WFCAM observing. The meeting agreed that to start with 5 filters and reduce in number would be much easier than safer than to start with fewer and find out after a year of operations that we need the extra data. The price is that the additional overhead means we must reduce either area and or clusters. By how much is not clear and will depend as much on the overheads as the additional time itself. An action was placed on NCH to investigate the overall impact on the UKIDSS case, for both the 2 year and 7 year programmes, including reprioritisation of the targets. (ACTION NCH) ********** It was further agreed that NCH would contact Steve Warren to inform him of our decision. (ACTION NCH) ********** During this part of the meeting, there was also much discussion of empirical and model cluster sequences. It was agreed that more attention should be focussed on to both existing datasets and state of the art models. This was propogated by some confusion about which models should be used for which temperature regimes, and by a general distrust of the theory in general. It was felt that investment of effort here would help the UKIDSS survey and was specifically required for the development of complementary optical imaging programmes. STH was actioned to coordinate this. (ACTION STH) ********** STH pointed out that the MSBs (Minimum Schedulable Blocks) will need to be written by delivery of WFCAM next year (e.g. February). The programme should therefore be finalised before then. Although it ought to be possbile to modify our programme relatively simple during the survey. Complementary optical imaging ----------------------------- The primary motivation for this is to aid in the discrimination of candidates. A longer baseline colour (e.g. I-K vs J-K ) enhances both cluster sequences and helps with the identification of features therein - e.g. the binary sequence, or temperature effects (dust). Recent literature supports the case for using e.g. I-J or I-K, especially in the T-dwarf regime, where pure IR colours go blue. Optical measurements can also help with the measurement of reddening, with the obvious caveat that we get no detection for faint things in a highly obscured region. By using optical telescopes as a replacement for UKIDSS filters we don't lose either area or clusters from our programme. There was some discussion of individual telescopes: INT WFC ------- was felt to be too slow, but maybe useful if we want wide-shallow imaging of some areas. Ovsersubscription is not terribly high at the moment. LBT --- german + italian involvement. 14 arcmin field of view - which is probably too small. VST --- timescale - end of 2004 sensitivity - s/n=5 in 50 secs zvega=20.4 10 secs ivega=20.6 to match in I band 25.0. Basically the VST was felt to be rather insensitive in the I and Z bands, and that WFCAM would be preferred for Z. However this would depend on the amount of time available to UKIDSS from the VST, and on the availability of a Z filter for WFCAM and the QE of all 4 chips. It was agreed that we would propose for VST time in September 2004. GC agreed to present the proposal to the ESO board (?** help). The proposal a this tage would be more of a placeholder request, with an idea of how much time we were looking for, and for which targets. GC told us that ESO are expecting a request from UKIDSS, and he anticipates that something like 150 nights spread over two years may be available initially. GC will come to Cambridge to write this proposal with MM and STH in August. (ACTION GC) ********** ESO WFI ------- VST is preferred. CFH+Megacam ----------- was felt to be the ideal telescope + instrument combination for the northern hemisphere clusters. However it is not clear how much time would be available to survey the large UKIDSS areas given the likely competition for time with Megacam _and_ WIRCAM. Hopefully these questions will become clearer with time, and discussion with the CFH clusters team may shed light on whether or not we can gain significant access. Spectroscopy ------------ No plans for spectroscopic follow-up are in place, and this section of the meeting involved a general discussion about the existing instrumentation and capabilities as well as future prospects. STH presented some calculations showing that although the numbers of brown dwarfs per cluster could be large (100s to 1000s), the number density of brown dwarfs on the sky could be low (10/sq degree). Although he pointed out that in SFRs there could be clumps with high density, and some regions including IC4665 would have much higher density. The number of candiate brown dwarfs could be much larger than the true number of brown dwarfs - this depends on both our ability to weed out contaminants from the survey photometry, as well as our chosen sample selection philosophy - one might be ultra conservative or define magnitude limited samples to avoid pre-selection bias. Instruments considered included: VLT+ISAAC, VLT+VIMOS, SUBARU+FMOS and a new instrument to be delivered soon - MOIRCS, AAT+IRIS, CIRPASS. STH showed that for an given aperture telescope, existing IR spectrographs reach further down the sequence than an optical instrument. Ian Parry presented a short talk on CIPRASS-MOS. Members of the GCS - MM and STH have observing time with the AAT (40 arcmin field of view: target Sigma Orion and Taurus) and the WHT (10 arcmin FOV: target Trapexium). CIRPASS-MOS is a fibre fed spectrograph with peak sensitivity in the range 0.9-1.65 microns (though 1.8 microns is acheivable. It has 150 fibres, to enable beam switching (for excellent sky subtraction) on 75 targets + 6 guide fibres. A range of gratings, plus an echelle give resolutions in the range 2.2 angstroms/pixel up to 0.6 angstroms/pixel. We discussed the possibility of placing CIRPASS at the WHT (1 degree field) or AAT (3 degree field) prime foci. This would require extra expense for the WHT (new fibres) and lots of extra work and expense for the AAT. IRP would think about this in some more detail. The CIRPASS-MOS web pages are at http://www.ast.cam.ac.uk/~optics/cirpass/index.html. IRP showed some comparison charts for sensitivity and for resolution, and CIRPASS seems well matched to the brightnesses of our targets, though we could do with a larger FOV than is currently available for most of our clusters..