XID Observing Run Report ------------------------ INT WFC imaging: July 25,26,27,28 2000 Observers: Mike Watson, Charlotte Hayter (Leicester) Aims: Deep optical imaging for XID programme Instrument set-up ----------------- standard WFC imaging at INT prime focus Filters (exposures) ------------------- U (1200), g(600), r(600), i(1200), Z(1200), Halpha(1200) Observing conditions -------------------- 25, 26 July: mostly excellent 27 July: clear but dusty, short interval with cloud 28 July: clouds on and off during night, dusty, probably lost > 2 hours Periods of subarcsec seeing most nights. Time lost to technical problems ------------------------------- 25 July: 40 mins (DAS) 26 July: -- 27 July: 30 mins (shutter) 28 July: >60 mins (DAS) Targets observed ---------------- Target Filters Comments *RT Ser r Z Ha *G21.5-0.9 g r Z Ha *G21.5-0.9 off1 g r Z Ha *G21.5-0.9 off2 g r Z Ha Ridge_1 g r Ha Ha nebulosity Ridge_2 g r Ha Ha nebulosity Ridge_3 g r Ha Ridge_4 g r Ha Ridge_5 g r Ha PKS2126-158 g r i Uranus ~5 arcminutes away: abandon Q2237+0305 g r i Z *G133-69 pos2 g r i Z +PHL 1092 g r i Z A2390 g r i Z CL0016+16 g r i Z A2670 g r i Z Mark 304 g r i Z PHL 5200 g r i Z A2670 r i Z A2597 g r i GB1508+5714 g r i Z RX J1701.3 r i only r exposure OK NGC 6240 r i Exposures lost to cloud Arp 220 r i Z LBQS2212-1759 g r Z HT Cas r Ha A189 r Table needs to be double-checked against obs.logs. Data quality comments are preliminary. * XMM observations already made + XMM observations scheduled WFC pointing position --------------------- The default WFC pointing posn (aka aperture 0) is the centre of chip 4. This is not completely optimum for covering an XMM field as objects > 11.4 arcminutes to the E of the pointing posn are not covered by the camera. In the 1st AXIS WFC run the team solved this by using offset field posns for the telescope posn, thus effectively moving the XMM field centre to different place in the WFC. (You need to do this as the WFC guiding system is tied in to aperture 0.) The offsets they used took the XMM field centre to the WFC rotator posn, about 4 arcminutes away in both RA and Dec. This choice ensures good coverage of MOST of the XMM field, but unfortunately introduces a small gap at the NW corner (recall that the WFC camera does not have a symmetric chiparrangement. For our run we actually used three different pointing posns: 1. the nominal CCD 4 centre 2. the WFC rotator posn 3. a compromise posn with delta RA = 2.5 arcmin, delta Dec = + 2 arcmin. Option 3 provides a close to optimum solution for getting all the XMM field inside 12.5 arcmin. radius covered by the WFC. The other 2 options were used as we initially changed our mind about which was the best choice. Other points ------------ a) Target names with "_x" indicate offset positions (i.e. options 2 or 3 as above). Once we had started a field with a particular pointing we stuck with this (except when we made a mistake) under the assumption that changing the pointing posn would only make the subsequent reduction a pain. b) We had a new version of the WFC DAS running on the 1st night (this version supports binning and windowing, although we couldn't see the need for it). This resulted in several crashes of the DAS and slow readouts, losing us time on the first night. It may also affect the FITS headers. The WFC readout with the newest DAS is supposed to be very quick. We ended up with the last but one version that was reading out in around 40-50 seconds (except when it was malfunctioning!). On the fourth night we had more DAS crashes that looked suspiciously like new s/w problems of the same type (i.e. memory leaks). c) Several of the fields we observed have brightish stars in them (7-8 mag). It's clear that stars this bright effectively ruin parts of the WFC image. The fact that this happens at 7-8 mag. surprised me. d) We tried hard to do lots of flat fields in twilight. It takes a degree of organisation to get these, but RGM has emphasized how important these are. e) We actually ran out of fields by the 4th night due to the high efficiency of the earlier part of the run. Extra GT fields were selected from the database (LEDAS version) using the usual criteria and checked on-line against various criteria (e.g. X-ray source extent, content of optical field from DSS). Summary ------- We did 10 low latitude fields and 18 high latitude fields, most of which were successfully completed in all the colours we chose. Our overall average efficiency was thus ~> 6 fields in 4 colours per night, equivalent to around 1 field completed per dark hour. Adding U exposures (which we did not do) would have added a ~30 % overhead to each field. Effectively we went for quantity. Mike Watson 31 Jul 2000