Transcript RC10.ppt

UNIVERSITY
OF ILLINOIS
AT URBANACHAMPAIGN
Increasing Millimeter Array Sensitivity to
Large Molecules:
the Importance of Phase Correction
Y.-S. Shiao, L. W. Looney, D. N. Friedel, L. E. Snyder and E. C.
Sutton
University of Illinois at Urbana-Champaign
The 61st International Symposium on Molecular Spectroscopy
UNIVERSITY
OF ILLINOIS
AT URBANACHAMPAIGN
Motivation
• Most large molecule spectral lines are weak (< 0.5 Jy/beam).
• Interferometers provide better sensitivity for compact sources
(0.1"@230 GHz, A configuration).
• CARMA is important for large molecule detection. (Friedel’s talk
FC02 on Fri.)
The 61st International Symposium on Molecular Spectroscopy
UNIVERSITY
OF ILLINOIS
AT URBANACHAMPAIGN
Atmospheric Fluctuations
• Water vapor causes phase variation in millimeter regime.
• Current phase correction: observing astronomical sources and phase
calibrators alternately.
The 61st International Symposium on Molecular Spectroscopy
UNIVERSITY
OF ILLINOIS
AT URBANACHAMPAIGN
Example I: Phase Fluctuation
The 61st International Symposium on Molecular Spectroscopy
UNIVERSITY
OF ILLINOIS
AT URBANACHAMPAIGN
Example II: Phase Fluctuation
The 61st International Symposium on Molecular Spectroscopy
UNIVERSITY
OF ILLINOIS
AT URBANACHAMPAIGN
Phase Coherence Factor
Phase coherence factor = Measured flux / Maximum flux
The 61st International Symposium on Molecular Spectroscopy
UNIVERSITY
OF ILLINOIS
AT URBANACHAMPAIGN
Formic Acid Spectra (BIMA Data)
HCOOH 51,5-41,4
G19.61-0.23
W75N
The 61st International Symposium on Molecular Spectroscopy
Remijan et al. 2004
UNIVERSITY
OF ILLINOIS
AT URBANACHAMPAIGN
Phase Coherence Effect
Phase noise RMS 360
Phase noise RMS 700
The 61st International Symposium on Molecular Spectroscopy
UNIVERSITY
OF ILLINOIS
AT URBANACHAMPAIGN
Formic Acid Spectral Simulation
HCOOH 51,5-41,4
Phase noise RMS 700
Phase noise RMS 360
The 61st International Symposium on Molecular Spectroscopy
UNIVERSITY
OF ILLINOIS
AT URBANACHAMPAIGN
Two Spectral Line Simulation
Phase noise RMS 700
Strong line
Phase noise RMS 360
Weak line
The 61st International Symposium on Molecular Spectroscopy
UNIVERSITY
OF ILLINOIS
AT URBANACHAMPAIGN
Summary
• Phase coherence plays a key role to
interferometric observation quality.
• Phase correction improves the sensitivity of
interferometers to detect weak emission lines (a
few tenth of Jy), like formic acid and acetic acid
rotational transition lines.
• Water vapor radiometers may correct phase
variation more efficiently.
• We continue to develop water vapor radiometer
systems.
The 61st International Symposium on Molecular Spectroscopy