UNIVERSITY OF ILLINOIS AT URBANACHAMPAIGN Increasing Millimeter Array

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 61 st 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 FC 02 on Fri. ) The 61 st 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 61 st International Symposium on Molecular Spectroscopy

UNIVERSITY OF ILLINOIS AT URBANACHAMPAIGN Example I: Phase Fluctuation The 61 st International Symposium on Molecular Spectroscopy

UNIVERSITY OF ILLINOIS AT URBANACHAMPAIGN Example II: Phase Fluctuation The 61 st International Symposium on Molecular Spectroscopy

UNIVERSITY OF ILLINOIS AT URBANACHAMPAIGN Phase Coherence Factor Phase coherence factor = Measured flux / Maximum flux The 61 st International Symposium on Molecular Spectroscopy

UNIVERSITY OF ILLINOIS AT URBANACHAMPAIGN Formic Acid Spectra (BIMA Data) HCOOH 51, 5 -41, 4 G 19. 61 -0. 23 W 75 N The 61 st 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 61 st 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 61 st 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 61 st 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 61 st International Symposium on Molecular Spectroscopy