WHT, ISIS Observing Run - 23-25 January 2002 -------------------------------------------- Observers: Natalie Webb ---------- Silvia Mateos Instrument and Setup: --------------------- ISIS double spectrograph Blue arm: R300B l/mm grating, EEV12 detector, centered at 4600A Window: 600-1710, 1-4200, pixels binned up by factor 2 Red arm; R150R l/mm grating, TEK4 detector, centered at 7000A Window: 1-1124, 200-850 Dichroic at 5700 Red blocking filter (GG 495) for red arm Slit width was 1.5" Read out speed for both CCDs was slow Observing conditions: --------------------- The weather was very good: clear; very little wind; low humidity; no dust - seeing approximately 1.5" (except some of last night, when it was worse). However, an almost full moon was present until about 04:00 each night, which meant that the sky was very bright. Observing procedure: -------------------- Where possible at least 5 biasses were taken at the beginning and end of each night, in both arms - engineering work made taking biasses at the beginning of the first night impossible. Biasses at the end of the first night are also affected by some light in the dome. The telescope focus was checked and revised at the beginning of each night. CuNe and CuAr arcs were taken at each pointing in the first two nights (exposures: 40s (blue arm) and 1s (red arm)), as it was also necessary to take tungsten flats (exposures: 8s and 1.5s blue/red, with ND=1.5) for each observation, due to anomolous features on the CCD (see the technical problems below). On the third night, the problem had been corrected, so arcs and flats were taken once only per field, as requested. Twilight flats were taken at the beginning and end of each night, with the exception of the beginning of the first night, due to the engineering work. We aimed to take spectra of all the targets marked with high priority and to complete the fields. However, due to the almost full moon and the faint targets (some fainter than 22.5), even in an exposure of 1800 secs, the target was not evident above the noise of the sky (expected S/N per pixel for the extracted spectrm, from 'signal', was less than 1). For sources with magnitudes of ~20.5-21.5 two 1800 sec spectra were taken and for sources with magnitudes of ~19.0-20.5 (and where no spectrum was visible in 1800 secs) one 1800 sec spectrum was taken. For targets with magnitudes brighter than 19th, we observed for less time, according to the magnitude. We also observed 4 different standard stars (2 per night) - G191B2B, HD 95321, GD 50 and BD+33 2642. Technical Problems: ------------------- ISIS was mounted the day of our first observations. Unfortunately the polarimeter was obstructing the light path, causing vignetting and obstructing the light to the autoguider. Thus it was impossible to use the autoguider and so ISIS was taken off again and the polarimeter removed. This meant that we could only begin to observe at about ~22:00 on 23/01/02. However, all this work had caused dust to fall into the slit and cause absorption lines (depth >5% of background) to be evident in the spectral direction on both CCDs. Some of this could be removed by blowing air through the slit (as it was deemed a very long job to be able to get at the slit to clean it properly). Once a large enough region in the centre of both CCDs was available to take spectra, in the absence of the scattered lines, we started to take data (~23:30). To minimise the likelihood of these lines interfering with the data, it was recommended that we took flatfields at each pointing (these lines moved slightly (~1 pixel) as the telescope was moved). ISIS was taken down and properly cleaned on 25/01/02, hence on the last night it was possible to take flats and arcs, only once in each field. Also, the recorded value of the slit width was found to be inaccurate. The real value on the first two nights was: recorded*0.734 and the third night: recorded*0.774-0.255. Targets Observed: ----------------- (Targets not able to be identified without rigorous data reduction due to the low signal to noise). Object n23 n24 n25 Texp(sec) i mag GRB001025_019_A x 1800+1800 20.746 GRB001025_041_A x 1800+1800 21.189 GRB001025_055_C x 1800 17.363 GRB001025_066_A x 1800+1800 19.773 GRB001025_007_B&A x 1800+1800 20.125 Cl0939_022_A x 1800+1800 21.231 Cl0939_015_A x 1800+1800 21.585 G133_007_A x 1800 20.339 A399_005_A x 1800 21.098 S50836_021_A&B x 1800+1800 ? S50836_020_A x 1800 20.610 S50836_030_A x 1000 17.931 Mkn205_109_A x 1800 18.530(H) PHL1092_010_A&B x 1800+1800 22.176 PHL1092_011_A&C x 1800 21.832 Mkn3_006_A x 1800+1800 20.472 Mkn3_017_A x 1800+1800 21.186 Mkn3_024_A x x 1800+1800 20.442 Mkn3_053_A&B x 1800 22.187 Mkn3_039_A&B x 1800+1800 21.569 Mkn3_008_A&B x 1800+1800 20.89(RB) Mkn3_021_A x 500+500 15.10(RB) B21128_021_A x x 1800+1800 20.519 B21128_024_A&B x 1800+1800 21.222 B21128_026_A x 1800 22.186 B21128_015_A x 1800 21.457 B21128_014_A x 1800 20.622 B21128_033_A x 1800+900 20.917 Use of Time and Issues: ---------------------- Some time was lost in trying to put the target star behind the slit, as we used the finding charts from the AXIS web pages. It would probably be helpful if the number of each offset star was marked on the finding charts (and the offset star + neighbours were included in the finding charts), so that we could be sure that we had correctly located the offset star, especially when the pointing of the telescope is not very accurate.