Transcript 062409_OSU_CSOSurvey.ppt

Spectral Line Surveys with the CSO
Susanna L. Widicus Weaver, Department of Chemistry, Emory University
Matthew Sumner, Frank Rice, Jonas Zmuidzinas, Department of Physics, Caltech
Geoffrey Blake, Department of Geological & Planetary Sciences, Department of Chemistry, Caltech
The Widicus Weaver Group
Mary Radhuber
Jay Kroll
Brandon Carroll
Jake Laas
Thomas Anderson
New Receiver Technology at the CSO
• “Z-Rex” receiver designed for
external galaxy searches at high-z
• Broad frequency coverage
• High S/N
• Double sideband (DSB) receiver
Facility CSO Receivers
Tsys (K, SSB)
Spectral (IF) Bandwidth (GHz)
120
1
Z-Rex
100
4
Z-Rex is an ideal receiver for spectral line surveys!
What is a Line Survey?
Typical Observations
Individual, narrow frequency
windows targeting only a
handful of transitions.
Line Survey
A series of spectral windows pieced
together to provide spectral coverage
across a large frequency range.
Why Line Surveys?
•
More lines observed
more detection certainty
•
Uniform coverage under similar instrument conditions
minimizes calibration inconsistencies
•
Comprehensive intensity information
reliable model of physical conditions
•
Broadband spectral coverage
large amounts of info, and fast
Why New Molecular Line Surveys?
• New astrochemical models explain
formation of complex organics
• Models require complete chemical,
physical picture for input/comparison
• Physical parameters, abundances often
educated guesses
• Few surveys access differing chemical,
physical environments
Garrod, Widicus Weaver, & Herbst, ApJ 682, 2008
Our Goals:
• Conduct surveys for many different types of sources
• Achieve high spectral sensitivity (for new molecule ID)
• Obtain full picture of chemical, physical conditions for each source
• Compare results to astrochemical models
The Orion KL Region
Orion KL
star forming region
http://www.mpg.de/bilderBerichteDokumente/mul
timedial/bilderWissenschaft/2009/02/Walter0902/
Web_Zoom.jpeg
http://oobleck.ifa.hawaii.edu:8080/where/images/orion.jpg
CSO Beam Size
at l = 1 mm
From Liu, S.-Y. et al. (ApJ 576, 2002)
Previous Orion KL Surveys
>50 radio frequency Orion spectral line surveys
reported in the literature!
OVRO survey at l = 1.3 mm
215 – 263 GHz
RMS~ 150 mK
800 resolved spectral features
29 molecular species IDed
The Challenge: DSB Spectra
-IF
+IF
Lower Sideband
Upper Sideband
LO
desired line position
desired line position
Frequency sideband
+
=
Observed Double Sideband Spectrum
Image sideband
Spectra from Nummelin et al. (ApJ Supp. Series 117, 1998)
Spectral Coverage on Orion
215
220
225
230
235
240
245
Frequency (GHz)
250
255
260
265
270
Initial Deconvolution of Orion Spectra
Blake et al. OVRO survey: RMS = 150 mK, integration time ~ weeks (months?)
Our survey: RMS = 30 mK, time ~ 4 nights
Line Identification Progress
Total Lines >3s
5548
Assigned Lines (to date)
662 (11.9%)
Unidentified Lines
4886 (88.1%)
Lines Assigned in Previous Surveys
400
New Lines Assigned (to date)
262
Line Identification Progress
Molecule
CO
DNC
C17O
H2CO
CH3CCH
CH313CN
HNCO
C33S
HDO
CN
CH3CN
13CS
C34S
H2CS
13CH CN
3
CH2CO
HCOOH
C2H5CN
CH3OH
13CH OH
3
CH3CHO
CH3OCH3
Lines Previously Observed
2
1
1
1
5
2
3
1
2
11
20
1
1
7
7
4
7
60
55
11
4
20
New Lines Observed
0
0
0
0
0
0
0
0
1
1
1
1
1
2
3
5
6
22
42
42
46
61
Line Identification
Next Steps?
Orion Survey Analysis
• Finalize spectral deconvolution
incorporate baseline subtraction, test for “ghosts”
•
Analyze spectral information
determine lineshapes, intensities
•
Identify more lines from previously detected molecules
include weak lines, isotopologues, vibrational states
•
Rotational diagram analysis for each molecule
account for multiple sources, velocities, temperatures
Beyond the Orion Survey
• Line surveys of other sources
•
•
•
completed: Sgr B2(N-LMH), NGC 1333-IRAS 4, L1157
upcoming: W51 e1/e2, G34.3+0.2, W3(H2O) & W3(OH)
Laboratory spectroscopic studies
Comparison to astrochemical models
ID of new molecules
only after complete simulation of known molecules is achieved
Laboratory Spectral Cataloging
First light April 1, 2009!
1 – 50 GHz
Frequency
Synthesizer
To Computer
VDI Multiplier chain
50 GHz – 1.2 THz
Detector
Gas Flow Cell
Sample Input
To Vacuum Pump
Methanol Broadband Scan
Dimethyl Carbonate (CH3OCOOCH3)
Acknowledgements
The Widicus Weaver Group:
Mary Radhuber
Jay Kroll
Brandon Carroll
Jake Laas
Thomas Anderson
John Pearson
& Brian Drouin @ JPL
CSO Local Staff