Dual frequency interferometry and

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Dual frequency interferometry and phase transfer
at the Submillimeter Array
Todd R. Hunter, Jun-Hui Zhao (CfA) Sheng-Yuan
Liu, Yu-Nung Su, Vivien Chen (ASIAA)
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Summary of present SMA operations
Antennas 8, diameter 6m, surface rms 12 to 20
microns Baselines 28, from 16m to 500m (angular
scales 0.3 to 15 _at_ 345 GHz) Receivers DSB,
1-polarization, 3 bands 180-245, 260-355,
620-695 GHz Correlator 2 GHz BW per SB 3072
channels x 2 sidebands x 2 receivers Next
proposal deadline March 2006 (http//sma1.sma.ha
waii.edu)
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Lack of Strong Gain Calibrators at High-Frequency
Interferometry requires calibration of
antenna-based phase amplitude introduced by
instrumental and atmospheric effects.
SMA sensitivity Tsys 100 K at 230 GHz (10
mJy in 5 min) (6-antennas) Tsys 2000 K at
690 GHz (200 mJy in 5 min) For good phase
solutions, we need S/N gt 10 per baseline
This requires a strong source!

0.5 Jy at 230 GHz (70 quasars with F gt 1Jy) 8 Jy
at 690 GHz (maybe 2 or 3 quasars)
Quasars are inadequate for the SMA at 690 GHz
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Other options in 690 GHz band Minor planets
Typical flux density
Typical 230 GHz 658 GHz Diameter
Callisto 4.3 Jy 33 Jy 1.1 Ganymede 4.3 32
1.2 Titan 1.6 11
0.9 Ceres 1.4 10
0.5 Vesta 1.1 9
0.5 Pallas 0.6 5 0.3
synthesized beam in compact configuration 1.1

• These objects work adequately if one of them is
  available

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Other options in 690 GHz band Water masers
658 GHz vibrationally-excited water line seen in
oxygen-rich stars (Menten Young 1995)
(v21, J110-101) 2328 K above the ground
state 13 known sources (so far) VYCMa, RLeo,
WHya, VXSgr, RCas, TXCam, RCrt, RTVir, RXBoo,
SCrB, UHer, NMLCyg, NMLTau, RAql Good candidates
not yet searched Mira, Betelgeuse, etc.
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658 GHz H2O line in R Leo (1 hour, 15 baselines)
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658 GHz H2O line in R Cas (2 hours, 15 baselines)
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The same stars also show masers in 215 GHz SiO
(5-4) v1 line
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Masers are detectable in both bands on short
timescales (30 seconds) and make good targets
for testing phase transfer
45 meters
baseline 59 meters
68 meters
16 meters
25 meters
25 meters
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Phase transfer hardware considerations
Fundamental components of the SMA dual-band
system
Common reference frequency
LO 1
YIG, DDS
10 MHz
LO 2
Co-aligned receiver feeds (lt 6 or 1/10 beam _at_
230)
Receiver Feed 2 690 GHz
Receiver Feed 1 230 GHz
Correlator 2
Duplicate paths for simultaneous
down-conversion and correlation
IF 2
Correlator 1
IF 1
Antenna
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Expected relationships for phase amplitude
Consider a small change in atmospheric water
vapor content above one antenna relative to
another
Effect on Fringe Phase The change in
excess path length (DL) is a function of the
observing frequency and leads to a ratio (RP) in
the observed phase changes RP
(DLn2/l2) / (DLn1/l1) (DLn2/DLn1)
(n2/n1) Using Scott Paines am
model for Mauna Kea (0.9733)
(658.006 / 215.595) 2.97
Effect on the Fringe Amplitude The change in
opacity (tn) is a function of the observing
frequency and elevation and leads to a ratio (RA)
in the observed amplitude changes RA
exp(-tn2,wet) / exp(-tn1,wet) exp(tn1,wet
tn2,wet) for 0.4 mm water vapor and
658 vs. 215 GHz about 3.5 (but
is a function of airmass)
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Proposed Observational strategy for Phase
transfer
Observe four sources

• 1. Strong, compact source (e.g. maser) to compare
  215 GHz and 658 GHz phase and amplitude
  relationships
• 2. Science target
• 3. Quasar near the science target, bright enough
  at 215
• 4. Strong continuum source to obtain bandpass
  information in both bands (658 Callisto,
  Ganymede, lunar limb)

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Antenna-based solutions on R Cas masers (658 vs
215 GHz phases)
Antenna 6 m 2.1
Antenna 2 m 2.6
Antenna 1 (reference)
Antenna 5 m 4.7
Phase jump
Antenna 3 m 3.4
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Example phase transfer on a calibrator
658 GHz phase transfer image (S/N21, 0.3 beam
offset)
Quasar 3C454.3 230 GHz self-cal image
Apply coefficients from R Cas to make 690 gain
table
658 GHz self-cal image (S/N27)
Self-cal recovers S/N27
5 antennas, 35 minutes on-source, F 6 Jy (beam
1.3x1.1)
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Example phase transfer on a science target
658 GHz phase transfer image (S/N 11, 0.4 beam
offset)
Take the 690 gain table derived for 3C454.3 (from
R Cas) and apply it to the raw data for the
science target, in this case another fairly
bright quasar (2232117)
658 GHz self-cal image of quasar 2232117 (S/N
16)
Self-cal recovers S/N 16
5 antennas, 30 minutes on-source, F 4 Jy
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What limits this method of calibration?

• 1. Phase jumps and drift

Sometimes seen in one band only, sometimes both.
Under investigation. Also, slow changes in phase
offset with time between the two bands may
require frequent measurement of phase transfer
coefficients.
2. Bandpass determination in extended configs.
No compact sources (lt 0.4) are bright enough !
Lunar planetary limbs sometimes give signal,
but are not ideal. Hardware noise source to
measure bandpass phases (in progess)
Autocorrelation on the ambient load for
amplitudes?
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Summary and future work
We have made a first attempt at phase transfer at
submillimeter frequencies. Need to investigate
some remaining instrumental problems. Then try
the technique in more extended configurations. Ne
w receiver band is coming! (320-420 GHz) Will
allow more frequent dual-band observations (due
to less stringent weather requirements at
230/345) and higher S/N testing of phase
transfer. Water vapor radiometry? Two ALMA
prototypes being tested at SMA
The SMA is a path-finding instrument and we
remain hopeful to realize its full potential.
Conclusion
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658 GHz maser easily detectable on long baselines
5 second integration on a 123 meter baseline
226 meter baseline
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22 GHz water masers in R Cas imaged by the VLA
0.2 arcsec
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Example 0 phase transfer using Ceres (on
itself)
Ceres 690 Selfcal
Ceres 230 Selfcal
(rms 50 mJy, S/N 260)
Derive coefficients and 690 gain table

Ceres phase transfer image
Ceres 690 uncalibrated data
Apply 690 gain table
(rms 70 mJy, S/N 193) Proof of software
function
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Example 2 phase transfer on IRAS 16293-2422
The phase transfer analyses in the previous
slides were done in Miriad. Here is an example
done in MIR / IDL (see poster 4.69 by Su
Liu). In this case, the frequency ratio (rather
than the fit) was used in the scaling.
Phase transfer from quasar 1743-038
Direct 690GHz calibration (Ceres)
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Linear fit of Ceres 690 phase vs 230 phase
Antenna Correlation Slope 1
0.97 3.0 2 0.85
2.3 3 0.95
2.4 4 0.88 2.3
5 0.94 3.2 6
reference antenna theory 1.00
3.0
USB data
Antenna Correlation Slope 1
0.94 3.1 2 0.72
2.0 3 0.85 2.0
4 0.83 2.2 5
0.85 3.3 6 reference
antenna theory 1.00 3.1
LSB data
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Investigation of Phase transfer Part II.
Search for phase relationships
1. Run phase-only selfcal on calibrator at 230
690 2. Examine correlations of 690 vs 230 phase
solutions 3. Flag any phase jumps or unstable
periods that degrade the correlation 4. Compute
slope and offset relating 230 and 690 phases on
each antenna
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Eight nights with low opacity during the recent
690 GHz Campaign
Jan 28 W Hya / Ceres / Callisto Feb 14 VY CMa
/ Titan / 0739016 Mars / Ceres / NRAO
530 Feb 15 Orion-KL / Titan / 0607-157
Arp220 / Ceres / Callisto / Mars Feb 16 G240 /
VY CMa / Titan / 0736017 Sgr A / Ganymede /
1924-292 / SgrB2N Feb 17 TW Hya / Callisto /
1037-295 Feb 18 CRL618 / 3C111 / Titan /
Callisto IRAS16293 / Ceres / 1743-038 /
Callisto Feb 19 Orion KL, Sgr A (repeat)
Mar 02 Arp220 / Ceres / Callisto / Mars
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Appendix A Phase noise measurements

• Antenna 230 GHz 690 GHz
• 1 10.8 deg 33.6 deg
• 2 9.3 27.2
• 3 10.2 25.2
• 4 11.8 32.0
• 5 11.2 30.7
• 6 11.1 30.0
• 7 12.3 24.8
• Integration range 100Hz to 10MHz from the 6-8GHz
  YIG carrier

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January 28, 2005 First dual-IF fringes
Simultaneous maser lines from W Hydra
SiO J5-4, v1 at 215 GHz
H2O 11,0-10,1 v1 at 658 GHz
These screens show only 2 of the total
correlator data product.
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First Dual-IF Phase vs. Time solutions
215 GHz maser in LSB
658 GHz maser in USB
Ant 1
Ant 1
Ant 3
Ant 3
360o
360o
About 3x larger phase change and opposite sign
(as expected)
2 hours
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Receiver Feed offsets measured by single-dish
radio pointing with the chopping secondaries
Antenna 690 vs 230 Rx pointing Number
A1(arcsec) A2(arcsec) 1
-2.7 7.0 2 -0.9
1.6 3 4.1
-0.8 4 0.3 1.0
5 4.8 -3.4 6
4.4 3.4 7
-3.5 6.8 By comparison, the SMA primary
beam at 230 GHz is 56 arcsec. The worse case
antenna is better than 1/7 beam.