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Minding the Gaps
Joseph Lazio (NRL) G. Taylor (UNM), N. Kassim (NRL), D. Wilner (CfA)


Minding the Gap
Protoplanetary Disks
· Protoplanetary disks are expected to be dynamic.
­ Planetary formation ­ Planetary migration

· Planets and protoplanetary disks are a major theme in nextgeneration instruments
­ ­ ­ ­ ­ ALMA ELT JWST TPF/Darwin ...

· Astrobiology was a highlighted theme in Astronomy & Astrophysics in the New Millennium


Minding the Gap
Protoplanetary Disks
Radio wavelengths (~ 1 cm) offer unique information about planetary formation · Pebble accretion--crucial and poorly understood regime of planetary formation · Unhindered by dust obscuration


Minding the Gap
Imaging Protoplanetary Disks
Why don't pebbles destroy each other? · Relevant size scale ~ 1 cm. · VLA observations of TW Hyd at 3.5 cm detect and resolve its disk. Emission from centimeter-sized particles in disk--on-going accretion. TW Hyd is close (50 pc); insufficient sensitivity for observing more distant systems.

Wilner et al. (2005)


Long-Range Goal
A future cm-wave telescope should be built capable of addressing planetary formation in nearby protoplanetary disks.
Will require order of magnitude increase in sensitivity over existing facilities Near-term: construction of a single prototype "station"


Instrumental Requirements at Centimeter Wavelengths
Angular resolution: 5 milliarcseconds · ~ 1 AU at 150 pc
­ 1500 km at 3.5 cm ­ 600 km at 1.5 cm (20 GHz)

Sensitivity: T ~ 10 K on roughly 750 km baselines · ~ 5 mas @ 2 cm · Tsys ~ 50 K · Aeff ~ 200,000 m
2

· Easy, already achieved with VLBA

Aeff/Tsys ~ 3500 m2/K


Existing Instrumentation
· · · · EVLA ~ 10,000 m2 ATA-42 ~ 1000 m2 ATA-350 ~ 7000 m2 North American infrastructure ~ 20,000 m2
EVLA + inner VLBA + ATA-350

· EVLA: T ~ 0.2 K
240 mas

· EVLA+VLBA: T ~ 1000 K

New telescope or substantial augmentation of existing telescopes required.


Outlier Station Proposal
The First Step

+



Construct an outlier station consisting of approximately 10-m diameter dishes at a Long Wavelength Array station. Leverage LWA and EVLA infrastructure. Leverage ATA and DSNA dish construction experience. Provide a "local" testbed for various technology prototyping, demonstrations, and education/training.


Outlier Station Foundation
Allen Telescope Array · 350-element array under construction in California · 6-m hydroformed antennas · Wideband feeds: 0.5­11 GHz Long Wavelength Array · Dipole array under construction in New Mexico · Consists of phased array "stations" of dipoles; about 50 stations to be constructed. · Stations to be tied by fiber optic links to central processing facility

VLA Y


Outlier Station
Closing Technical Gaps
· · · · · · · · · Are stations the right way to proceed? Further antenna cost reductions? Improved wide-band feed performance? Cyrogenic system performance in the field? Imaging with stations? Data transport? Reliability? Station-station correlation (ATA to station)? ...?


Outlier Station Science
Closing the u-v Gap
· LWA station locations will be about 50­100 km from the EVLA. · "Pietown link" is formed from VLA + VLBA Pietown antenna
­ ~ 50 km distant, maximum baseline = 72 km ­ Popular, oversubscribed by ~ 2.5x

Outlier station location could complement VLA Pietown link. Outlier station would complement VLBA by adding needed short spacings.


Outlier Station Science
Closing the u-v Gap


Outlier Station Science
Astronomy & Astrophysics in the New Millennium · Map the galaxies, gas, and dark matter in the Universe, and survey the stars and planets in the Galaxy · Search for life beyond Earth, and, if it is found, determine its nature and its distribution in the Galaxy · Use the Universe as a unique laboratory to test the known laws of physics in regimes that are not accessible on Earth and to search for new physics.


Outlier Station Science
Closing the u-v Gap
· Sgr A* represents nearest supermassive black hole. · Intrinsic size:
­ Local environment (jets vs. RIAFs vs. ...) ­ Density of object and limits on exotic physics

(Bower et al. 2006)

· VLA+PT can just barely resolve it at cm-wavelengths (Bower et al. 2006). Beam is significantly elliptical.


Outlier Station Science
Closing the u-v Gap
Other potential science · Massive star formation (e.g., Shepherd et al.) · OH (1720 MHz) masers · Evolution of AGN · Continuum emission from starbursts · Microquasar imaging (e.g., Hjellming & Rupen; Mioduszewski et al.)

200 AU

CI Cam


Minding the Gaps
· Planetary formation is a key aspect of 21st astronomy. · Cm-wave astronomy has a unique role.
dust pebbles boulders

· Existing infrastructure is only 10% of what is needed. · Outlier station is the next step.
­ Addresses key technical issues ­ Delivers immediate science return
Basic research in radio astronomy at the NRL is supported by the Office of Naval Research.


Imaging Protoplanetary Disks
Protoplanetary disk at 140pc, with Jupiter mass planet at 5AU ALMA simulation
428GHz (= 70 µm) max. baseline: 10km = 8 GHz, t = 4 hr
Wolf et al. 2002, ApJ 566, L97

Contrast reduced at higher frequency as optical depth increases Will push ALMA to its limits
J. Richer "Scientific Requirements of ALMA, and Its Capabilities for Key-Projects: Galactic"


The Square Kilometre Array
· Imaging protoplanetary disks is a prime aspect of one of the SKA's Key Science Projects. · Considerable work being done worldwide on various technical aspects of the SKA. Only the Allen Telescope Array is addressing some of the issues relevant to obtaining large amounts of additional collecting area at the relevant frequencies. Opportunity to leverage U.S. infrastructure and knowledge to target important 21st century astronomical problem.