SPARO Updates (1996-2003)
February 2003: SPARO Galactic Center results published in the Astrophysical Journal
The first science results from SPARO, obtained during Austral Winter 2000, are described in
a paper published in this month's issue of the Astrophysical Journal Letters.
The abstract appears below, followed by a brief summary.
FIRST RESULTS FROM SPARO: EVIDENCE FOR LARGE-SCALE TOROIDAL MAGNETIC
FIELDS IN THE GALACTIC CENTER
We have observed the linear polarization of 450 micron continuum emission from the
Galactic center, using a new polarimetric detector system that is operated on a 2 m telescope
at the South Pole. The resulting polarization map extends ~ 170 pc along the Galactic plane
and ~ 30 pc in Galactic latitude, and thus covers a significant fraction of the central
molecular zone. Our map shows that this region is permeated by large-scale toroidal magnetic
fields. We consider our results together with radio observations that show evidence for
poloidal fields in the Galactic center, and with Faraday rotation observations. We compare
all of these observations with the predictions of a magnetodynamic model for the Galactic
center that was proposed in order to explain the Galactic Center Radio Lobe as a magnetically
driven gas outflow. We conclude that the observations are basically consistent with the
A brief summary of these Austral Winter 2000 results follows:
Shown below are magnetic field vectors implied by SPARO's
450 micron polarization measurements superimposed upon a 90 cm VLA map
(LaRosa, et al 2000) tracing the hot ionized gas in the region of the
Galactic Center. The white contours show the 850 micron continuum emission
from SCUBA/JCMT(Pierce-Price, et.al).
Click image to enlarge
Due to the operation of the magnetic alignment mechanism, the
direction of polarization is perpendicular to the magnetic field
direction. The measured polarization is predominantly perpendicular
to the Galactic plane, implying that the magnetic field
is aligned with the Galactic plane, as viewed from our vantage
point in the Galactic disk. This in turn implies an azimuthal
field geometry, i.e. the magnetic field lines run in circles that
lie in the plane of the Galaxy.
The field that SPARO samples pertains to the cool neutral regions
within our Galactic nucleus, but there is also hot ionized gas
in the nucleus, coexisting with the cool neutral gas. Interestingly,
field in this hot gas is known to run perpendicular to the
Galactic plane. One way this can be seen is to note the
orientation of the radio filaments shown (in yellow) in the
radio continuum image that we have shown superposed on our
non-thermal filaments trace magnetic fields.
We conclude that there are two
orthogonal magnetic field structures coexisting in the center of
our Galaxy. In our recent paper (see above) we compare the
SPARO results, radio filament results, and Faraday rotation results,
and show that these are all basically consistent with a magnetodynamic
model for the Galactic center proposed in 1985 by Y. Uchida and
We also obtained polarimetry of NGC 6334 during Austral Winter 2000
click for index to photos
Early 2002: Success of SPARO optical upgrade is confirmed!
Austral Summer 2001-2002, observations towards the peak of the
Galactic source RCW 57 confirmed that SPARO optics upgrade
carried out in Austral Summer 2000-2001 did indeed improve
the optical efficiency by about a factor of four, as predicted
changes in bolometer
IV characteristics and measured transmission of filters.
As a result, one day of Austral winter 2002 observations
will be equivalent to one week of Austral winter 2000 observations!
For details click
Austral Winter 2000: First SPARO polarimetry at South Pole
here to see preliminary analysis of the first polarimetry data
obtained with SPARO at the South Pole. The polarimetry vectors were taken
18,(black), July 7(green), and July 26(blue). The map corresponds
to SPARO photometry data taken on May 18. The thick vectors
represent polarimetric detections of 3 sigma or greater, while the
thin vectors are below 3 sigma detection.
Austral Winter 2000: SPARO's first image of a Galactic source
The top image is SPARO's 450 micron image of RCW 57. The lower image is
the IRAS 100 micron image of the same region. The SPARO Data are a result
of median filtering of 16 1.25 hour images of this region. This is the
first true image of a galactic source taken by SPARO. The dark blue
spots surrounding the two images in the 450 micron data are artifacts of
the small (.2 degree) chopper throw used in this scan.
Fall 1999: SPARO first light at Pole!
Following the SPARO winter-over of 1999, during which
engineering tests were done
but no observations were possible due to telescope problems, first-light
observations were made by a summer-season team consisting of
Dave Chuss and Giles
Novak of NU, Greg Griffin and Matt Newcomb of CMU, and Bob Loewenstein of U.
Chicago. We observed the Moon on November 11th, and saw the bright Galactic
cloud RCW57 several days later.
During this SPARO observing run, that lasted through the
third week of November,
we carried out tests of focus, pointing, optical efficiency,
detector noise, and
many any other aspects of the experiment.
The testing went well (see details below).
We are looking forward to our first science data in a few months:
SPARO will be
operated on the telescope again beginning in late January and
continuing into the
Austral Winter 2000. We plan to observe with SPARO for the first
three months of
the winter season (through May 2000).
February 20, 1999-Despite a long wait for liquid Helium, the testing of the SPARO experiment
during Austral Summer 1998-99 was a success. Tests with the instrument in
the lab and also with it mounted on the Viper telescope showed that SPARO
and its interface to Viper are working well, and the instrument is now in
the care of winter-over personnel: Greg Griffin and John Davis. John and
Greg will install it on Viper in midwinter, after the Carnegie-Mellon HEMT
receiver ("Corona") has had a chance to carry out another round of CMBR
For details click here.
For photos click here.
November 18, 1998- Twenty-two crates left Northwestern University's
Technological Institute bound for the South Pole Station via New Zealand,
after a busy push to complete laboratory systems tests in which such
things as instrumental polarization, system noise, and array alignment
The final laboratory shakedown of SPARO was encouraging. The hold times
for both 4He and 3He are of the order of 3 days
with improvement expected in lower Antarctic ambient temperatures.
The first SPARO crew consisting of Dr. Giles Novak(P.I.), Tom Renbarger,
Jill Hanna, and Prashant Malhotra departed for New Zealand on Sunday, December
6. While there, they will keep busy integrating SPARO to the Viper
Telescope, installing the tertiary mirror on Viper, assembling and cooling
SPARO, and running total instrumental polarization tests using planetary
August 11, 1998- Northwestern University. A committee consisting of
Robert Pernic, Director of Polar Operations, Stephan Meyer, Director of CARA,
and Mark Thoma, Engineer at Yerkes observatory, decided to give the green
light to the SPARO experiment for deployment at the South Pole this Austral
summer to prepare it for winter 1999. A status report was given
for the instrument, data from the successful May CSO run were presented, and
a plan was presented for the completion of the instrument.
Those present at the meeting were: Giles Novak, Tom Renbarger, David Chuss,
Jim Jaeger, Robert Loewenstein, Jesse Wirth, Jill Hanna, Prashant Malhotra, and
May 12, 1998-
With the "T" array electronics having been installed,
SPARO performed remarkably
well during its first light tests from May 1 through May 6 at the
Caltech Submillimeter Observatory(CSO)
located at Mauna Kea in Hawaii.
Though there was high water vapor content in the atmosphere for the
duration of the run, the polarimeter and its accompanying data system
responded favorably in a gamut of tests which helped to characterize the
infant instrument. This CSO "shakedown" helped to prepare SPARO for
its eventual deployment at the South Pole.
Februray, 26, 1998 -
Jim Jaeger (NU shop) is nearly finished with the SPARO optics
on the "optics mock-coldplate". From left to right: snout with
field lens, half-wave plate cell, mirror holder, filter and pupil
lens and holders, grids and one grid holder. Mounted at the
top of the "optics shelves" is the blank-off wheel.
February 5, 1998 -
We've cycled 3He in both systems! The final temperatures
of the inner and outer stages are 0.29K and 0.40K respectively. The
inner stage can remain cold for 46 hours, the outer stage for 18.4
hours. We've also successfully cycled the dewar while it was
tilted - demonstrating that it can be cycled on the telescope and
that convection is not a heat load in the 3He systems.
We also measured a critical cooling capacity of 2 mW for the pumped
December 19, 1997 -
The bolometers are installed in the arrays (by J. Wirth).
The tensioned wires from the arrays to the work surface are also
done (by B. Hirsch).
December 11, 1997 -
We cooled the dewar down this past week. We were unable to condense
much 3He. The pumped pot didn't have enough cooling power.
The rest of the 3He system performed very well.
system behaved about as expected - the cryogen use rate implied a
hold time of 4.5 days even though we dumped a lot of heat into the
system running tests on the 3He system.
November 25, 1997 -
We packed the dewar up and moved it from Yerkes to Northwestern.
Time to start doing serious lab testing!
November 19, 1997 -
The He3 system is complete and leak checked! He3 gas has been
loaded into the system (20psi in each system for initial tests).
- Data from the cool down.
- Photos of assembly
August 10, 1997 -
We successfully mounted the dewar on the viper telescope at
July 21, 1997 -
- Dimensions of various
components of the He3 system.
July 16, 1997 -
- New pictures of the He3
system under construction.
June 10, 1997 -
- Tom's final
- Preliminary optics snout design. From Jeff S. 7/7/97
May 28, 1997 -
- Data System ask is underway! Here's Tom McMahon's
the parts. 6/10/97
- Assembly of He3 system is proceeding. The
pots are made. All
other parts are in hand, on order, or being constructed
- We have an updated assembly drawing from Jeff Sundwall. 05/28/97.
- We've decided on an optics
- J. Wirth has produced preliminary designs for the JFet board and
April 9, 1997 - Darren has made up our
bolometers. Thanks Darren!
April 8, 1997 -
Cryogenic performance data
for the last cool down.
March 26, 1997 -The dewar is still cold! Further monitoring
of the LHe usage suggests a He4 hold time of just
over 7 days. The inner vapor cooled shield is at 100K, the
outer vapor cooled shield is at 200K.
March 24, 1997 -
I cooled the dewar
again last week. There were 10
layers of MLI on every surface. The only wiring was for 5
temperature sensors. Preliminary monitoring implies a
He4 hold time of 8 days (approximately 2.5
liters per day).
March 3, 1997 -
I finally assembled the dewar and cooled it down last
week. The dewar only had 5 temperature sensors in it. I
didn't even install MLI. The inner vapor cooled shield
ran at 125K, the outer vapor cooled shield at 225K. The
He4 hold time was approximately 3 days (which
corresponds to around 6 liters per day).
I will model the cryogenic performance this week (watch
this space for results). Preliminary modeling implies
that the vapor cooling was very efficient, even with
the large neck tube. Also the bare metal emissivities were
better than anticipated.
February 15, 1997 -
This past week we have manufactured a new fill tube and a
new optics shield.
The remaining suspension parts have been designed and fabricated.
We have begun wiring thermometers.
Next week we hope to assemble the cryostat and
cool to He4. The helium is due to arrive monday!
February 8, 1997 -
All of the He4 cryostat parts have been delivered.
In the past two weeks all parts have been fit checked. Several
pieces (notably ends of the vapor cooled shields) have been altered
for improved fit. We have already redesigned the fill tube
eliminating the rotatable bolt circle on the indium seal to the
Next week we hope to assemble the cryostat and
install the suspension system.
October 9, 1996 - Our dewar reservoir was delivered!
September 16, 1996 - Our dewar case was delivered!