Glen Langston: OSU 08 1 Improved Tools for Astrochemistry Glen Langston Methods for detection of families of molecules Example: HC 7 N collaboration with

Glen Langston: OSU 08 1

Improved Tools for AstrochemistryImproved Tools for Astrochemistry

Glen Langston

Methods for detection of families of molecules

Example: HC7N collaboration with Barry Turner

Wide-band Spectrometers

Focal Plane Arrays

NRAO


Molecular Discoveries: 100mMolecular Discoveries: 100mWorld’s most sensitive Telescope in frequency range 10 to 50 GHzDiscovered >7 new interstellar molecules, including propenal and propanalWidely distributed, not exclusively in compact cores

Hollis, Snyder, Remijan and Jewell 2004-2008


HCHC77N HCN HC99N HCN HC1111N and HCN and HC1313N N

Large Cyanopolyynes known to be abundant in TMC-1


HCHC99N, HCN, HC1111N and HCN and HC1313N N

Straight forward lesson: Straight forward lesson: Larger molecules exhibit more lines at lower Larger molecules exhibit more lines at lower frequencies than their simpler counterparts.frequencies than their simpler counterparts.

Wide bandwidth spectrometers needed with full Wide bandwidth spectrometers needed with full frequency coverage at high spectral resolution.frequency coverage at high spectral resolution.

Improved spectrometer is a priority for NRAOImproved spectrometer is a priority for NRAO


Updated HCUpdated HC1313N ModelN Model

Frequency (MHz)Frequency (MHz)

Inte

nsity

(K

elvi

n)In

tens

ity (

Kel

vin)

Model of HCModel of HC1313N line strength for N line strength for Taurus Molecular CloudTaurus Molecular Cloud

Models for HC13N moments of inertia and Taurus cloud temperature (9 Kelvin's) show peak of emission at 12 to 15 GHz Prediction common to all ‘large’ molecules in cold clouds:

Many lines at lower frequencies (< 20 GHz)

Spacing between HC11N lines 338 MHzSpacing between HC13N lines 214 MHz (17 lines in 3.6 GHz)


Selections of HCSelections of HC1313N observationsN observations

Simultaneous four 50 MHz bandwidth observationsSimultaneous four 50 MHz bandwidth observations

HC13N Lines are HC13N Lines are separated by 214 MHzseparated by 214 MHz


Daily System CheckDaily System Check

Daily system check observations: Two 4 minute observations.Daily system check observations: Two 4 minute observations.

Simultaneous four 50 MHz bandwidthSimultaneous four 50 MHz bandwidth

Widely separated (Delta nu > 1 GHz)Widely separated (Delta nu > 1 GHz)


HCHC77N and HCN and HC99NN

We concentrated on larger HCnN molecules with fourth band.We concentrated on larger HCnN molecules with fourth band.


HCHC77N IsotopomersN Isotopomers

In the HCIn the HC1313N observations, a family of N observations, a family of 1313C Isotopomers is detectedC Isotopomers is detected

Ratio of HCRatio of HC77N and Isotopomers Abundance = 87:1N and Isotopomers Abundance = 87:1

Langston and Turner (2007), Ap. J. 658, 455Langston and Turner (2007), Ap. J. 658, 455


K-band Focal Plane ArrayK-band Focal Plane ArraySpecification Requirement

Frequency Band 18-26.5 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)


Design ConfigurationDesign Configuration

Single PixelSingle Pixel

High performance multi-pixel is technically challengingHigh performance multi-pixel is technically challenging

Seven PixelSeven Pixel


Mapping Large RegionsMapping Large Regions


Future DirectionsFuture Directions

Lower frequency (6 to 26 GHz) observations are critical for study of important large molecules.Demonstrated detection of a class of molecules by simultaneous observation of weak lines.Isotopomers are a significant fraction for large molecules (7/50 ~ 1/7 for HC7N)Studies of Astro-chemistry will be advanced by:

Increasing spectrometer bandwidth Increasing number of beams in receiversSoftware for optimum “folded” searches of multiple lines in large molecules

Documents

Glen Langston: OSU 08 1 Improved Tools for Astrochemistry Glen Langston Methods for detection of families of molecules Example: HC 7 N collaboration with