HARP-B/ACSIS on the JCMT:

spatially resolved chemistry

of warm gas

John Richer (Cavendish, Cambridge)On behalf of HARP and ACSIS teams

HARP and ACSIS• Motivation:

– faster spectral mapping of molecular line emission– catch up with bolometer arrays!

• HARP-B:– 16-pixel (4x4) imaging array: 28 arcsec beam spacing, 14 arcsec beam– 2 arcmin x 2 arcmin field of view, undersampled by factor of 4 wrt Nyquist– 325-375GHz coverage– Single sideband tuned (via interferometer)– K-mirror for field rotation– Under construction in Cambridge (+ATC/HIA/…), delivery this year (2005)

• ACSIS– 16-input, 2GHz bandwidth digital correlator for HARP-B– Built by DRAO and ATC– Sophisticated software pipeline– Now arrived in Hawaii

ACSIS backend• 16 IF inputs (actually 32, paired up) • Nominal bandwidth per channel: 2GHz,

in 2x1GHz hybrid configuration – Actual BW reduced by 10-20% due to

filter roll off: 1.6GHz at least• Minimum sample time: 50ms

– Allows fast mapping • Maximum output map size: 16Gbytes • Total disc space: 4Tbytes • Output data formats:

– aips++ measurement set for raw data– FITS file for reduced map

• Full data reduction and display pipeline• Programmable data reduction

Nominal Bandwidth Resolution

250MHz 30kHz

500MHz 61kHz

1GHz 500kHz

2GHz 1MHz

ACSIS Mapping Modes• Raster position switch

– For large maps, typically of bright objects– Telescope is continuously tracked – maximum map size: approx 2x2 degrees, Nyquist-sampled

• Jiggle chop (beam-switch)– For deep maps of compact objects– Secondary mirror fills in missing samples (4x4 pointings)– Creates map 120 arcsec square– K-mirror for field rotation keeps pixels in fixed grid positions

• Jiggle frequency-switch – As above, but uses FSWITCH of >200MHz– frequency switching is slower than jiggle rate

• Grid position switch – Used for deep observations of a few selected points

Project Status• ACSIS

– Shipped to Hawaii at end of 2004 after acceptance tests at DRAO• HARP-B

– Main system undergoing system integration in the lab in Cambridge– K-mirror finished

• Anticipated timeline– Now: system integration and testing in Cambridge– 2005 Q2: acceptance tests– 2005 Q3: commissioning– 2005 Q3: ? 1st call for proposals?– 2005 Q4: ? Commissioning science– 2006 Q1: ? first open science

Orion Line Survey (Schilke et al 1997)

HARP line surveys

• 30 tunings cover whole 325-375GHz range at 1MHz resolution• Single sideband so no deconvolution needed• In one shift (8 hours) reach of order 100mK sensitivity per

channel in each of the 30 fully sampled jiggle maps:– Area coverage is 2 arcmin by 2 arcmin– Cube of size 16 x 16 x 60,000 voxels– Analysis tools?

• Possible targets – with extended chemistry: Orion, Sgr B2, CSE?…

Prestellar cores: chemistry in L1498 at mm wavelengths (Tafalla et al)

Starless Core Chemistry:probing the depletion zones

• Complete CNO depletion within 2500AU?

CO, HCO+,…

N2H+, …

H2D+

D2H+

Walmsley et al. 2004; Caselli et al 2003

372GHz line

8,000AU

2,500AU

15,000AU

Submm Lines in Low-Mass Star Forming Regions (Jorgensen et al)

Chemistry in Massive Cores

• Many low mass prestellar cores, and even Class 1 objects, will be too faint in the submm, except for CO

• N2H+ survey (Pirogov et al 2003) of massive cores

• Ideal HARP targets– Warm, massive– Good match to 2 arcmin FOV

Shock Chemistry in Outflows

L1157: chemically active outflow (Bachiller et al)

Chemistry in Galaxies?

• Nearby gas-rich systems can be studied in CO, and other lines if gas dense enough

• 2 arcmin FOV avoids problem of “knowing where to look”– Spatially resolved chemistry

• Eg HNC/HCN/CN line ratios and star formation rates

Conclusions• HARP/ACSIS will offer exciting opportunities to study spatially

extended (>14 arcsec) chemistry• Ideal targets include

– Complete spectral line surveys with 2 arcmin FOV– Spatially resolved chemistry of low mass (?) and massive cores– Shock chemistry in outflows– Stellar envelopes?– Galactic Centre clouds– Comets– ISM in Galaxies

• First open science time late this year/early 2006