1. Molecular Imager: Focal Plane Array
Glen Langston
Motivation: Molecular discoveries
Focal Plane Arrays important for all observing bands
First 7 pixel Array for 18 to 26 GHz
NRAO
Glen Langston: KFPA CDR: Jan 2009

2. Molecular Discoveries: 100m
World’s most sensitive Telescope in frequency range 10 to 50 GHz
Discovered >7 new large interstellar molecules, including propenal and propanal
Widely distributed, not exclusively in compact cores
Hollis, Snyder, Remijan and Jewell
Langston, Turner 2007
Glen Langston: KFPA CDR: Jan 2009

3. Molecular Line Surveys
Daily system check observations: Two 4 minute observations.
Simultaneous four 50 MHz bandwidth
Widely separated (Delta nu > 1 GHz)
Glen Langston: KFPA CDR: Jan 2009

4. Glen Langston: KFPA CDR: Jan 2009
HC7N Isotopomers
In the HC13N observations, a family of 13C Isotopomers is detected
Ratio of HC7N and Isotopomers Abundance = 87:1
Langston and Turner (2007), Ap. J. 658, 455
Glen Langston: KFPA CDR: Jan 2009

5. K-band Focal Plane Array
Specification
Requirement
Frequency Band
GHz (complete K-Band coverage)
Instantaneous RF Bandwidth
1.8 GHz
Number of beams
7 (expandable up to 61)
TRX (each beam, not including sky)
< 25 K (75% of band)*
< 35 K (entire band)
Aperture Efficiency
>55%, any pixel
Polarization
dual, circular (axial ratio <= 1 dB)
Polarization Isolation
>25 dB
Pixel-Pixel Isolation
>30 dB
Headroom
> 30 dB (to 1 dB compression point)
Glen Langston: KFPA CDR: Jan 2009

6. Glen Langston: KFPA CDR: Jan 2009
Design Configuration
High performance multi-pixel is technically challenging
Single Pixel
Seven Pixel
Glen Langston: KFPA CDR: Jan 2009

7. Progress: 1st Pixel Completed
Project started early 2008
Development plan stages
Summer 2008 – Single Pixel Development
Fall 2008 – Single Pixel Tests on GBT
January 2009 – Critical Design Review
Spring, Summer 2009 – 7 Pixel Development
Winter 2009 – Lab tests
Early 2010 – tests on GBT
Spring, Summery 2010 – Revisions
Winter 2010 – Science mapping with 7 pixels
Spring, Summer Funding for 61 pixels (?)
Summer Start 80 – 100 GHz Array (?)
Glen Langston: KFPA CDR: Jan 2009

8. First Astronomical Tests
Peak and Focus results good.
Obs revealed IF spurs, that are now understood.
Extensive tests of interfaces.
Web based monitor
CLEO /Astrid scripts worked for test obs.
Obs on Sept 11, 2008
Glen Langston: KFPA CDR: Jan 2009

9. 1st Pixel Tests: Frequency Range
Orion A GHz
H and He Recombination Lines
Water Line and molecules
Initial tests showed IF spur problems (now fixed)
Need more data paths for full array
Glen Langston: KFPA CDR: Jan 2009

10. Glen Langston: KFPA CDR: Jan 2009
Gain and Tsys Tests
Performed intensity measurements as a function of pixel offset from center location.
Position Offset 3.8’ at 19 GHz
Gain Drop 5 +/- 2 %
Position Offset 3.8’ at 25 GHz
Gain Drop 5 +/- 2 %
Performed a sequence of obs with K0 Feed system followed by K1 sequence.
Found higher system temperatures
Cause: Low gain and IF spurs
Obs Oct 2, 2008
Glen Langston: KFPA CDR: Jan 2009

11. Glen Langston: KFPA CDR: Jan 2009
Spectral Line Tests
Configured for TMC
NH3 1-1 and 2-2 Lines, plus HC7N
Glen Langston: KFPA CDR: Jan 2009

12. 1st Pixel Tests: Line Mapping
Taurus Molecular Cloud
HC7N
NH3
Simultaneous Maps of several lines
Note High GBT Sensitivity: Only 2 seconds per pixel!
Glen Langston: KFPA CDR: Jan 2009

13. Mapping Tests: Multiple Beams
HC7N
HC5N
Software for Mapping Tests using Current Rx: See Stephanie Moats and Diana Soehl
Glen Langston: KFPA CDR: Jan 2009

14. Glen Langston: KFPA CDR: Jan 2009
IDM 2 Tests
2nd IDM showed no IF spurs
Tsys performance similar to K0
Glen Langston: KFPA CDR: Jan 2009

15. Glen Langston: KFPA CDR: Jan 2009
Mapping Large Regions
Glen Langston: KFPA CDR: Jan 2009

16. Summary: New Tools available soon!
Wide frequency (18 to 26 GHz) observations are critical for study of important large molecules and Chemistry.
NRAO support of Astro-chemistry will be advanced by:
Increasing spectrometer bandwidth
Increasing number of beams in receivers
GBT offers great capabilities for Astro-chemistry and Astro-biology, now and in the future!
Glen Langston: KFPA CDR: Jan 2009