The Observing Programme in the North
Survey duration: Observing began in semester 2003B. By the end of 2008, every survey field had been observed at least once. The survey will be formally complete once it is confirmed that the desired data quality has been achieved in all fields.
Survey area and resolution: This is all galactic longitudes in the Northern Plane within the latitude range -5° < b < 5°, a total of 1800 square degrees. The INT Wide Field Camera (WFC) offers a pixel scale of 0.33 arcsec per pix, allowing on-sky structures above 1 arcsec in size to be resolved.
Survey filters and observing strategy: At each pointing, sequences of narrow-band Hα, Sloan r' and i' images are obtained with the WFC. The Hα filter has a bandwidth of 95 Å and is centred at 6568 Å. For the accompanying broad-band filters we have preferred the Sloan filters because of the more nearly rectangular shape of their pass-bands. The aim is to cover the survey area twice, observing once at each of a set of specified field centres that combine to cover the plane once, and then again at a second set of offset positions. This strategy enhances our quality control and ensures that strips of sky, otherwise falling in the gaps between CCDs, are not left out altogether. The total number of field centres demanded by this strategy works out at 7635 x 2
Data attributes: The target faint-end limiting broadband magnitude is r'=20. Hα filter exposure times have been set to give a roughly matched narrow-band magnitude limit. The choices have been guided by the desires both to match the limits of the AAO UKST H&alpha survey, and to allow most of the data-taking to be carried out in bright time. Note that this policy has resulted in considerable variation of background levels in the images, which need to be dealt with before the data can be mosaicked successfully. In median seeing, saturation is likely to be at around 13th magnitude. The telescope time needed to take data at each field position (plus its offset) and move to the next field centre is approximately 10 minutes. The target seeing limit for data to be counted as meeting survey requirements is 2 arcsec. Standard star observations are typically obtained every 2-3 hours to facilitate photometric calibration of the survey data.
All imaging data obtained via this programme can be accessed from CASU by any interested researchers working in UK, Spanish or Dutch centres.
From December 2007, source catalogues as well as images from observations obtained prior to January 2006 have been made available via the Initial Data Release.
A report on the current status of the survey can be found here.