You are viewing an old version of this page. View the current version.

Compare with Current View Page History

« Previous Version 29 Next »

The 3Pi Steradian Survey (as described in Chambers et al. 2016)

The Pan-STARRS telescope surveyed the sky in several different areas using various observing strategies.  The 3PI survey covers the 30,000 deg2 (3 steradians) of sky north of Declination -30º in 5 filters (grizy) with approximately 10 exposures per filter to a combined depth of approximately 21-23 mag.   Data were taken over the period  between 2009-06-02 and 2014-03-31.


The survey pattern and scheduling followed two different strategies over the course of the 3π survey: the initial pattern layed out in the Design Reference Mission (DRM) Chambers & Denneau (2008) followed by the Modified Design Reference Mission (MDRM). We switched to MDRM on 2012-01-14. All exposures in the DRM were taken in pairs, with each exposure separated by a Transient Time Interval or TTI of 12 to 24 minutes, check for the purpose of detecting moving objects within the Solar System. These were referred to as “TTI pairs”.
The original plan was then to take 2 TTI pairs over an observing season with gri taken within the same lunation and separated by days to weeks. The z and y  were to be taken approximately 6 months apart to optimise stellar parallax and proper motion measurements (for low mass stars). Over 3.5 years this would give (allowing for weather interruptions) 12 exposures in each band or 60 in total over all 5 filters. In the MDRM, a series of 4 exposures, “quads”, all separated by approximately 15 minutes (therefore completed within about 1hr), were implemented for about half of the gri exposures with the express purpose of increasing the recovery of Near Earth Objects (NEOs). The relative exposure times in each were also chosen to make an asteroid of mean solar color  to have approximately the same signal-to-noise
The exposure times for each individual exposure was as follows (e.g. a TTI pair in g is composed of 2 x 43 sec exposures, separated by 12 to 24 mins)

There are typically a dozen pointings at each point of the sky in each filter over the course of the whole 3Pi survey.  The pointing centers are dithered to enable the construction of a seamless image that fills in regions of bad pixels in most parts of the sky.  AThe table below shows the mean number of pointings and its rms variation over the whole survey as a function of band [Source: P.Draper/N. Metcalfe - taken from an all sky-projection based on the PV3 summary stacks, which have a resolution of 4'' per pixel].


Below is a histogram showing the coverage distributions per summary stack pixel (blue - g; green - r; red - i; black - z; purple - y)


The Medium Deep Survey covers 10 fields, each about 7 deg2, with hundreds to thousands of exposures per filter to reach a combined depth of 24–26 mag.  Other secondary surveys (M31 survey, ecliptic plane survey, celestial north pole) also were carried out.  The initial PS1 data release includes only the 3PI survey, but other data will be released as processing is completed.


Information for this page should come from/be consistent with Chambers et al 2016. 



Parent page for description of the surveys.  Outline of things to include:

  • Summary table:
    • Bright limits
    • Locations and areal coverage versus time
    • Data-taking statistics: numbers of visits, quality, etc.
  • 3pi Survey (3PI):
    • Definition in terms of coverage maps, depth, observing cadences
  • Medium Deep Survey(MDS):
    • Location on sky, depth, observing cadences

3PI Survey



The median seeing in the images is ~1.1" FWHM (ranging from 1.3'' in g to 1.02'' in y).  The cumulative FWHM distributions in each filter are shown below (green - g; red - r;  orange - i; blue - z; yellow - y) [Source: Ken Chamber's PS1 metrics page - accessed in April 2015].

The 5σ point source depth is given in the table below for both the individual exposures and the stacked image sum.

Image Datag limitr limiti limitz limity limit
Single epoch22.222.021.520.819.8
Stacked sum23.423.222.722.021.1

Saturation occurs roughly at point source magnitudes of 14.5, 15, 15, 14, 13 for grizy respectively [Source: N. Metcalfe, priv. comm. - needs checking]

Medium Deep Survey

The 10 fields in the Medium Deep Survey are described below.  Each field was observed several times a night during the months of the year when it was observable.  In total there are hundreds to thousands of exposures in each of the 5 filters (grizy), enabling the construction of very deep stacked images.  The depth of individual exposures is the same as for the 3PI survey in the table above; the depth of the stacked image sum is shown below.

Observing Strategy

Observations of 3-5 MD filelds are taken each night and the lters are cycled through in the pattern:g and r in the same night (dark time), followed by i and z on the subsequent second and third night, respectively. Around full moon only y data are taken. An epoch consists of 8 dithered exposures of 8 times 113 seconds for g and r or 8 times 240 seconds for the other three (i,z, and y), giving nightly stacked images of 904 and 1920 seconds duration.

Field description

NameAlt NameRA (deg)Dec (deg)g limitr limiti limitz limity limitRA (J2000)Dec (J2000)Comment
PS1MD01XMM-LSS-DXS/VVDS-02h35.875-4.25025.925.826.025.624.302 23 30-04 15 00Multi-wavelength Survey Field
PS1MD02CDFS/GOODS/GEMS53.100-27.80025.625.425.825.324.103 32 24-27 48 00Multi-wavelength Survey Field
PS1MD03IFA/Lynx130.592+44.31725.825.826.025.624.308 42 22+44 19 00Radio Survey Field
PS1MD04COSMOS150.000+2.20025.825.725.825.424.010 00 00+02 12 00Multi-wavelength Survey Field
PS1MD05Lockman-DXS161.917+58.08325.825.725.925.423.910 47 40+58 05 00Multi-wavelength Survey Field
PS1MD06NGC 4258185.000+47.11725.825.625.925.323.912 20 00+47 07 00H20 Maser
PS1MD07DEEP2 Field 1/Extended Groth Strip213.704+53.08325.825.725.925.424.114 14 49+53 05 00Multi-wavelength Survey Field
PS1MD08ELAIS-N1-DXS242.787+54.95025.925.826.025.424.216 11 09+54 57 00Multi-wavelength Survey Field
PS1MD09SA22-DXS/VVDS-22h334.188+0.28326.025.926.125.624.122 16 45+00 17 00Multi-wavelength Survey Field
PS1MD10DEEP2-Field3352.312-0.43325.925.826.125.624.123 29 15-00 26 00Multi-wavelength Survey Field

The detection limits come from a 2015 January analysis by Nigel Metcalfe and will probably change in the final processing.  They are 5-sigma point source detection limits calculated from the databases by measuring (roughly) where psfflux_err/psfflux=0.2.

  • No labels