PISCO and ATCA Follow-on for SPT Clusters

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PISCO and ATCA Follow-on for SPT Clusters

• Antony A. Stark
• Smithsonian Astrophysical Observatory
• 18 May 2007

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Parallel Imager for Southern Cosmology
Observations (PISCO)A Multiband Imager for
Magellan

• Antony Stark Smithsonian PI
• Christopher Stubbs Harvard PI
• Matt Holman Smithsonian Planets, exoplanets
• John Geary CCD electronics
• Andy Szentgyorgyi Engineering consultant
• Steve Amato CCD electronics
• Will High Thesis project, Harvard Physics
• Andrea Loehr PostDoc Observing algorithm
• James Battat grad student, SAO
• Armin Rest PostDoc Photo-z Software
• Steve Sansone LPPC machine shop

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PISCO System Characteristics
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Angled Dichroic Optical Layout
Optical Design of the PISCO as of September 2006.
In the region between the collimator and the
cameras, the beam is now accurately collimated,
with a maximum angular deviation for any ray in
any field 3. This eliminates ghosting by the
dichroics and filters, and greatly reduces the
alignment requirements for the cameras. The r
focus now no longer requires a fold mirror, and
is sufficiently far from the small guider housing
(at left) so as not to be a problem (check this
with F. Perez!). Focus is now telecentric.
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ADC Operation

• Can use PISCO on Clay telescope
• Consists of two rotating cylindrical prisms,
• 1 cm thick
• airspaced, multi-coated
• Initial scientific mission can be achieved
  without ADC
• ADC can be removed with re-focus

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Dichroic in Cube Optical Layout
Alternate Optical Design of PISCO. The dichroics
are embedded into cubes of fused silica, so that
there is no difference in dielectric constant on
either side of the dichroic. This allows the
dichroics to be used at 45º. The dichroics are
placed in the telecentric beam from the focal
reducer, so all field positions have identical
ranges of angle of incidence at the dichroics.
The overall length of the instrument is reduced
to 1.6 meters, and all CCDs are in a single,
medium-sized dewar.
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Controlling Systematics

• Our design is readily baffled
• Can use both field stop and pupil stop
• Suppresses stray and scattered light
• Better flatfielding
• Single common shutter near pupil
• Reduced shutter artifacts
• Single atmospheric transmission function
• Flux ratios with a single pointing and 2-3
  exposures, under all conditions!
• Even with patchy cloud cover, get good colors.
• We can measure filter transmission functions with
  high accuracy.

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Electronics are done

• We have already taken images in the lab with full
  control-to-image software.
• Readout noise is OK (3 electrons).
• Readout speed is OK ( lt 8 seconds).

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Initial detector tests look favorable

• Tested 2 3K x 6K 10 micron high-rho devices in
  Univ of Hawaii test system.
• Read noise
• Dark current vs. temperature
• CTE via Fe55 xrays
• Gain via Fe55 xrays

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Detectors work well
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Analysis Software Well build upon
SuperMacho/ESSENCE image analysis pipeline

• Battle tested over past 6 years at CTIO for SM
  and ESSENCE surveys.
• Flatten with dome flats, fringe flat and sky
  flats
• Astrometric WCS registration, warp to fixed
  plate scale
• Photometry to 1
• CVS code management, easy to add new modules
• Parallel implementation, Condor on Linux boxes
• Robust and self-tracking
• Honed on crowded fields
• Need to add (1) cluster photo-z module, and (2)
  SQL database
• Armin Rest, pipemeister, coming to CfA in Spring
  2007.

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Flow diagram for real-time cluster redshift
analysis pipeline
We expect that within 30 seconds of acquiring the
first image, we will have produce an appraisal of
whether the second 30 image will add enough
integration time to obtain a cluster photometric
redshift at the requisite SNR. We have in hand
the middleware and pipeline structure for this,
from the ESSENCE and SuperMacho surveys. We are
missing only the final segment, namely the
redshift estimator, which we will develop in
parallel with the construction of the hardware.
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Tightly coupled software/observing
Take Image 1 30 sec
Analyze Image flatten, WCS, sextractor
Galactic reddening corr. Produce z, sz OK?
Offset Take Image 2 30 sec
Offset if appropriate More images
Slew to next target
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Photometric Redshift Principle
The plots show how the observer-frame spectrum of
an early-type galaxy depends upon its redshift.
The redshifts are indicated in the upper left
corner of each panel. The flux ratios between the
g, r, i, and z bands is a good indicator of
galaxy redshift, as the 4000 Å break moves across
the spectrum. We will develop real-time analysis
code that will produce an initial cluster
redshift result within 30 seconds of the
acquisition of an image.
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Photometric Redshift for Clusters

• Photo-zs for individual galaxies tend to have
  scatter of sz/(1z)0.03, but with a few
  catastrophic outliers.
• Combination of morphology, magnitude, color and
  location can be used to establish clusters
  redshift.
• Robust statistics can be used to eliminate
  outliers.

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Uniform exposure times for clusters
Magnitudes in the four filter bands (shaded) for
L/2 early type galaxies, and exposure times (in
seconds, unshaded) to achieve SNR10, as a
function of redshift. The table assumes galaxy
flux integrated in a 2.2 arcsec diameter
aperture, in seeing of 0.8 arcsec at an airmass
of 1.2 in dark time. The numbers assume deep
depletion detectors in the z and i bands, like
those for the SMI. The exposure time needed to
achieve SNR10 is reasonably well matched across
the bands. A minimum exposure time is 5 sec.
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One night to obtain 115 cluster redshifts at z lt
1.5
The time needed to obtain 115 cluster redshifts,
in good conditions, is 8.2 hours. It will not be
possible to obtain redshifts for the 10 of
clusters with redshift z gt 1.5 these will be
flagged to obtain redshifts using other
instruments.
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Abell 267, extrapolated to various redshifts and
observed with PISCO
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Order of detection by PISCO
8 bright red galaxies detected first (green
circles) Black-circled detected next Blue dots
are cluster galaxies Black dots are foreground
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Galaxies in Color-Magnitude Diagram
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Histogram of photo-z of the first 18 galaxies and
photo-z of the color-magnitude selected galaxies.
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Science Opportunities

• Supernova followup observations
• Type Ia and type II Sne as cosmological probes
• Requires multiband images, multiple epochs
• Photometric redshifts of clusters
• 4 band imaging over 5 arcmin field
• Transient followup
• Evolution of SED for GRBs
• Microlensing light curves
• Planetary occultations
• Multiband data useful for discrimination
• Followup camera for PanSTARRS/LSST

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Masses and radii of transiting extrasolar planets
The dashed lines correspond to loci of constant
mean density. The symbols indicate the nine
known transiting planets, along with Jupiter and
Saturn. Two symbols are shown for OGLE-TR-10b.
In green is the result based on a fit to the OGLE
photometry and available radial velocities
(Konacki et al. 2005). In blue is the Holman et
al. (2005) result, based on a simultaneous fit to
Magellan photometry and the same radial velocity
measurements.
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Project timeline
The construction of our instrument is timed to
allow us to be ready for pipelined observations
of SPT-SZ clusters in early 2008.
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PISCO Current Status

• Some observing time granted in 4th quarter 2007
  for photo-z observations of clusters
• What should we observe? Need to know soon.
• Funds are available from Smithsonian to complete
  PISCO construction
• Successfully obtained private foundation grant
  for a PostDoc
• Proposals pending at NSF, DOE for ongoing support

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Australia Telescope Compact Array (ATCA)
observations of SPT clusters

• Antony Stark Smithsonian Astro Obs
• Wilfred Walsh U. New South Wales Asia
• Joe Mohr U. Illinois
• Tom Crawford U. Chicago

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Relevance to SPT Cluster Survey

• SPT system is around 100 Jy/K
• SPT-SZ survey will be 10 µK rms per beam
• Point continuum sources that are 1 mJy or
  brighter will make a significant contribution to
  the data, and possibly affect the detection of
  clusters and their derived parameters.
• The number of such sources in SPT bands is poorly
  known.
• With the ATCA, we can actually search for and
  detect such sources in SPT clusters.

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Pilot Study Completed

• We were actually awarded a significant amount of
  observing time on ATCA
• Extragalactic time slot is undersubscribed, and
  not too hard to get observing time
• We observed 24 X-ray selected moderate redshift
  clusters (Mullis et al. 2003) in redshift range
  0.05 lt z lt 0.65
• Observe at 18 GHz, because of ATCA sensitivity
  and map area possible follow-up at 90 GHz
• Detected one source at 2 mJy at 18 GHz
• Our sensitivity was primarily limited by phase
  stabilitywe will need good weather

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Current Status

• Proposal in to NSF AST for travel and publication
  expensesno decision yet.
• Additional proposals submitted for observing time.

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THE END

• http//www.tonystark.org