Pan-STARRS 1
Panoramic Survey Telescope &Rapid Response System
In anticipation of the public release …

Dr Nigel Metcalfe, Durham University
Chair: Data Reduction, & Analysis
Verification Group (DRAVG)

What is Pan-STARRS?
“A major goal of Pan-STARRS is to discover and characterize
Earth-approaching objects, both asteroids and comets, thatmight pose a danger to our planet”
Actually, Pan-STARRS was a University of Hawaii project for four
identical telescopes (in the end there were two). A Consortium
was put together to run the first one – PS1:
• 1.8m f4.4 Ritchey-Chretien• 3.2 degree FOV (~ 7 sq. deg.)• 1.4 gigapixel camera, 0.26” per pixel

Designed to scan the sky from Hawaii 3 times per monthScience Consortium• Not just asteroids – 12 Key Projects were set
up covering Solar System science right out toCosmology, and most things in between!
• Plenty of science still to be done …

The PS1 Camera• 60 OTAs (8x8 with the corners missing) 70”x36” gaps
• Each OTA an array of 8x8 cells (600x600 pixels) 9”x5” gaps
• That is a lot of gaps, and a lot of opportunity for things to gowrong!
• Designed for fast readout (~10 secs), with low read noise (56e⁻) and to enable charge shuffling (never really switched on)• Purpose built data reduction/analysis pipeline – GeneMagnier

The PS1 Sky• Whole sky is split into 2643 projection cells, each composedof 10x10 skycells (on a common tangent plane projection).
• These skycells are about 25’ across (~6000x6000 pixels).
Exposures are resampled/rotated onto this grid (0.25” pixels)– known as warps.
• There is a small amount of overlap between adjacent skycells(but note this is the same data!).
• (Nearly) all reduction is done on a per skycell basis.

The PS1 Surveys
SurveyArea(sq.deg.)

FiltersPercent
Time

Exposure (secs)

3p

30,000g,r,i,z,y56

43/40/45/30/30

70g,r,i,z,y

25

113/113/240/240/240

Solar System 10,000w

545

Stellar
Transit40i

415 or 30

M31

7r,i

260/60MediumDeep

Data collection started early in 2010 and completed in April 2014

Disclaimer!
• Didn’t achieve the expected seeing or depth• Problems with variable bias lead to cell-scale issues in thebackground – bad for extended objects• Ghosting, persistence. bleed trails, cross-talk mostly masked• Leads to quite a high false positive rate per exposure• Background over-subtraction around large objects
Remember – this will be the first release. SDSS are into doublefigures!

The 3p Survey• Whole sky north of Dec -30.
• Target was 4 exposures per filter per year, composed of two
15 min pairs (in the same lunation for gri, several months
later for zy).
• Ideally, at the end of the survey there should 12 visits perband, with a 6-dither pattern.

Single pointing point source modal
depths (AB mags):

Band5sBrightg

22.0

14.5

r

21.8

15.0

i

21.5

15.0

z

20.9

14.0

y

19.7

13.0

Seeing Distribution for 3pi
ModeMediang

1.18

1.31

r

1.02

1.19

i

0.96

1.11

z

0.96

1.07

y

0.96

1.02

Sky Brightness for 3p
ModeAve

g

21.86

21.82

r

21.04

20.42

i

19.68

19.58

z

19.22

19.07

y

17.85

17.94

The Three p Survey
Actual coverage per pixel over the sky – the original aim
was 12 pointings per filter (excluding masking):
FilterVisits per pixelg

9.6 +/- 3.0

r

11.8 +/- 3.8

i

17.4 +/- 6.9

z

11.2 +/- 3.0

y11.7 +/- 3.2

The Three p Survey
Histogram of g,r,i coverage per pixel over the sky :

gr

i030

The Three p Survey
This leads us to the concept of the Static Sky, which is the PS1
weighted, stacked data release.

Filter

5s stack

g23.3

r

23.2

i

23.1

z

22.3

y21.4

Median point source 5s depth (AB mag)over the whole stacked survey(assuming the median seeing):

The Three p Survey
The survey coverage is very heterogeneous, especially on small
scales. This is the coverage on a typical projection cell (4 degacross)Range is 0-17, black to white

The Three p Survey

The Three p Survey

The Three p Survey

The Three p Survey

The Three p Survey

3p Depth Relative to SDSS
Note – this is the best case!
griz

Red –Stripe82
Blue – PS1
Green – DR8

PS1 is a red
sensitive
instrument

3p Photometry relative to SDSSBest calibrated optical survey ever? Shows SDSS stripe offsets atthe few millimag level …

Eddie Schlafly, Doug Finkbeiner

The Medium Deep Fields
 10 fields (single pointing) visited 8 times every night insome band , repeating every 4 days (when up – soabout 6 months of the year). Result is several hundred
exposures per field in each band.
 Total area around 70 sq. deg.

 Good for transients etc, but will also be available asdeep stacks.
 Deepstack can be optimised for seeing. FWHM 0.9-1.4”

The Medium Deep Fields
Here are the stacked 5s depths for the deepest 2014stacks – public release will be similar:MDRADecgriz

y01

02h 23m-04⁰ 15’

25.9

25.8

26.0

25.6

24.3

02

03h 32m-27⁰ 48’

25.6

25.4

25.8

25.3

24.1

03

08h 42m+44⁰ 19’

25.8

25.8

26.0

25.6

24.3

04

10h 00m+02⁰ 12’

25.8

25.7

25.8

25.4

24.0

05

10h 47m+58⁰ 05’

25.8

25.7

25.9

25.4

23.9

06

12h 20m+47⁰ 07’

25.8

25.6

25.9

25.3

23.9

07

14h 14m+53⁰ 05’

25.8

25.7

25.9

25.4

24.1

08

16h 11m+54⁰ 57’

25.9

25.8

26.0

25.4

24.2

09

22h 16m+00⁰ 17’

26.0

25.9

26.1

25.624.1

1023h 29m

-00⁰ 26’

25.9

25.8

26.1

25.6

24.1

Medium Deep Seeing
Note the ‘tent’in the centre.

FWHM also goes
off towards theedge.

PS1 successes• PS1 continues to discover Near Earth Asteroids ….

• PS1 has over 50% of the comet discoveries since 2014 (49/94).
Denneau et al. (2013) - MOPSPS1 successes• PS1 continues to discover high redshift QSOs:• PS1 has basically doubled the number of suchquasars known.
Banados et al (2014)

PS1 successes
Nearly 2000 M31 Cepheids – Spatial Distribution
Type I Cepheids trace the spiral arms,

Kodric et al. (2013)

Type II Cepheids trace the halo

PS1 successes
Large scale structure : The CMB cold spot

Kovacs et al. (2014)32

Data Products
Catalogues – access via SQL server – PS1 has the concept ofdetections and objects:••••

Individual detections (~3.5 x1010) – grouped into “objects”.
Stacked objects (~8x109)
Forced individual detections (for objects found on stack)Difference detections
For all you will get:•••••PSF magnitude (fit to model PSF)
Total aperture-based magnitude (better for stars on stacks)
Kron magnitude
Assorted radial moments
Circular radial aperture mags (in SDSS radii, starting at 1”)

Data Products
For a s/n and galactic latitude limited subset ofobjects you will also get:

• Petrosian magnitudes/radii• DeVaucoulers/Exponential/Sersic mags/radii• Elliptical aperture mags, asymmetry parameters
Images:• Stacks, exposures as FITS files, with WCS and zeropoints.
• Also variance and mask files• Note: up to one skycell in size, no mosaicing
All will be accessed via an interface at STScIData Products

Data Products

We are working hard on the public release …
maybe Autumn this year?
Pixels are complete, just a question of the catalogues.

See Metcalfe et al (2013) MNRAS 435, 1825 fora detailed investigation of image detection andmeasurement in a 100 sq.deg. test 3p area.

The PS1 Sky

This is a gri colour image of the whole 3p survey(thanks to Danny Farrow, MPE)