Purchase of telescope time
Observing time on SkyMapper is available for purchase, with entire nights or sections of multiple nights being available. Three different telescope queues are available:
- Time-critical observations: scheduled for specific nights/times, at the mercy of weather
- Dark-time observations: scheduled anytime the target is visible and the sky is dark
- General observations: scheduled anytime the target is visible
Currently, SkyMapper nights are selling for AU$3-6k per night, depending on type of night (dark/bright), cadence of observations, amount of data processing required, and the total number of nights purchased; please note that a minimum purchase of AU$20,000 applies. Data can be processed by the SkyMapper science data pipeline (SDP) described in publications for the SkyMapper DR1 and DR2, which will be updated further. Please contact firstname.lastname@example.org and supply a brief description of the required observations.
The SkyMapper mosaic camera contains 32 CCDs of 4096x2048 pixels with a plate scale of ~0.50 arcsec/pixel. There are small gaps between the individual CCDs and the resulting field-of view is 2.37 deg x 2.39 deg. The mosaic fill factor is 91% of a 5.68 sq. deg. field-of-view.
The SkyMapper filter curves (with atmosphere) are shown below. We have tabulated colour transformations between SkyMapper and other standard filters, as well as predicted star colours and reddening corrections -- they can be found on the page here.
Note that the u-band filter (ultraviolet) is shortward of the Hydrogen Balmer break, while the v-band (violet) is placed between the Balmer break and the Ca H&K 4000AA-break. The u-filter also has a red leak, which needs an airmass-dependent correction. The two lines shown in the figure below are effective transmission curves including atmosphere for airmasses 1 and 2. The third (inset) panel shows the difference between the apparent u-magnitudes observed at airmass 1 and airmass 2 as a function of star colour. The redder the star the brighter it appears in u-band as it is observed closer to the horizon, because calibration stars get fainter, while the red leak keeps the flux bright. Additional information on the filter set can be found in Bessell et al. (2011).
Overheads per image range from 20 to 80 sec, but 20 sec is the median overhead and routinely achieved even when moderately slewing the telescope. Filter changes do not add to the time. Telescope slews include changes on three axes: azimuth, altitude, rotation. The azimuth slew is usually the limiting factor, where a 180 deg slew adds 50 sec.
Current seeing statistics (arcsec):
Exposure times and depth:
Due to a high read-out noise (RON) of ~10 e-, short exposures and uv filters are affected by RON. Even in full Moon, noise is sky-dominated only at t > 20 sec in the u-band. Approximate saturation and 5-sigma point-source detection limits (ABmag) reached in median seeing in a 100-sec exposure under dark sky are:
Observations are normally carried out at airmass < 2, unless otherwise specified by the proposal. The dome currently vignettes the telescope aperture at airmass > 2.2, and seeing, transmission and background obviously suffer.
The default position angle for the camera should be 0 degrees, which means that North is Up, irrespective of telescope azimuth, however, other position angles can be specified in the TOB. If the requested angle cannot be reached at the time of observation, the camera will rotate by 180 degrees automatically.
The pointing position of the mosaic is in a chip gap. Survey mode proposals can just use desired field centres, while proposals for large-object imaging should offset by a half chip and centre their main object on one of the central four CCDs. Pointing precision is on the order of 1 arcmin, but has been seen to vary. Dithering is also recommended.
There is significant curvature of the focal plane. By default, best focus is put into a ring around the centre to maximise the area of best focus and minimise the run-away of the FWHM in the corners.