High angular resolution observations are essential to understand a variety of astrophysical phenomena. The resolution
of millimeter wave interferometers is limited by large and rapid differential atmospheric delay fluctuations.
At the Combined Array for Research in Millimeter-wave Astronomy (CARMA) we have employed a Paired Antenna
Calibration System (C-PACS) for atmospheric phase compensation in the extended array configurations
(up to 2 km baselines). We present a description of C-PACS and its application. We also present successful
atmospheric delay corrections applied to science observations with dramatic improvements in sensitivity and
Optical telescopes and cameras are often used to determine the initial pointing model for radio antennas. After
this initial determination, the optical systems are typically not used. The Combined Array for Research in
Millimeter-wave Astronomy (CARMA) has implemented optical oset pointing as a standard calibration option
for science observations. We report on the proof of concept testing, the method, and the typical improvements
obtained over traditional radio pointing. We conclude with a brief discussion of future directions, which may
oer further improved pointing at CARMA and at other facilities that require increased pointing accuracy.
The CARMA telescope is a heterogeneous array of 10.4, 6.1 and 3.5 m antennas,
with antenna configurations providing spacings from ~3.5 m to 2 km. This
heterogeneous array is well suited to imaging a wide range of spatial scales.
In compact configurations the heterogeneous array provides high quality short
spacing data for aperture synthesis. In extended configurations, the antennas can
be paired, with 6.1 and 10.4m antennas making science observations in the 3 mm
and 1 mm bands, while 3.5 m antennas are simultaneously observing calibration
sources within a few degrees in the 1 cm band. This unique Paired Antenna
Calibration System allows us to to correct for atmospheric phase fluctuations
and make images at 0.15 arcec resolution in a wide range of atmospheric seeing
conditions. In this paper we discuss some results and lessons learned using these
heterogeneous observing techniques. These results are relevant to all aperture synthesis
arrays, including millimeter/submillimeter wavelength arrays like ALMA,
and cm/m wavelength arrays like ATA and SKA.
We present the steps taken at the Combined Array for Research in Millimeter-wave Astronomy (CARMA)
to handle the heterogeneous nature of the array, from apriori calibrations to data reduction. We outline the
steps needed to track relevant variable quantities over time. We discuss methods for combining interferometric
visibilities and single dish data in the context of single systems designed to obtain all the necessary data,
potentially at the same time. Such an observing approach is available at CARMA and it is the intention of the
Atacama Large Millimeter-submillimeter Array (ALMA) to offer this capability as a standard observing mode.
Planned instruments such as the Atacama Large Millimeter Array (ALMA), the Large Synoptic Survey Telescope
(LSST) and the Square Kilometer Array (SKA) will measure their data in petabytes. Innovative approaches in signal
processing, computing hardware, algorithms, and data handling are necessary. The Allen Telescope Array (ATA) is a
42-antenna aperture synthesis array equipped with broadband, dual polarization receivers from 0.5 to 11 GHz. Four
independent IF bands feed 4 spectral cross correlators and 3 beamformers. In this paper we describe the automated data
processing to handle the high data rate and RFI in close to real time at the ATA.
The Combined Array for Research in Millimeter-wave Astronomy (CARMA) comprises the millimeter-wave antennas of the Owens Valley Radio Observatory (OVRO), the Berkeley-Illinois-Maryland Association (BIMA) Array, and the new Sunyaev-Zel'dovich Array (SZA). CARMA consists of six 10.4-m, nine 6.1-m, and eventually eight 3.5-m diameter antennas on a site at elevation 2200 m in the Inyo Mountains near Bishop, California. The array will be operated by an association that includes the California Institute of Technology and the Universities of California (Berkeley), Chicago, Illinois (Urbana-Champaign), and Maryland. Observations will be supported at wavelengths of 1 cm, 3 mm, and 1.3 mm, on baselines from 5 m to 2 km. The initial correlator will use field programmable gate array (FPGA) technology to provide all single-polarization cross-correlations on two subarrays of 8 and 15 antennas with a total bandwidth of 8 GHz on the sky. The next generation correlator will correlate the full 23-antenna array in both polarizations. CARMA will support student training, technology development, and front-line astronomical research in a wide range of fields including cosmology, galaxy formation and evolution, star and planet formation, stellar evolution, chemistry of the interstellar medium, and within the Solar System, comets, planets, and the Sun. Commissioning of CARMA began in August 2005, after relocation of the antennas to the new site. The first science observations commenced in April 2006.
A new Combined Array for Research in Millimeter-wave Astronomy (CARMA) interferometer is being assembled from the existing Owens Valley Radio Observatory (OVRO), the Berkeley-Illinois-Maryland Association (BIMA) millimeter interferometers and the new Sunyaev?Zeldovich Array (SZA) at Cedar Flat, a site at 2,200 m altitude in the Inyo Mountains east of OVRO. The array will consist of 23 antennas of three different diameters, 3.5, 6.1 and 10.4 m, and will support observations in the 1 cm, 3 mm and 1.3 mm bands. The fist-light correlator is a flexible FPGA based system that will process up to 8 GHz of bandwidth on the sky for two subarrays consisting of 8 and 15 elements. The array configurations will offer antenna spacings from 5 m to 1.9 km allowing unprecedented high resolution and wide field imaging at millimeter wavelengths. Radiometers observing the 22 GHz water vapor emission line will be used to measure and correct for the water vapor induced path delay along the line of sight for each telescope and thereby minimize the time lost to “bad seeing”. This university based facility will emphasize technology development and student training along with leading edge astronomical research in areas ranging from Sunyaev-Zeldovich effect galaxy cluster surveys to studying protoplanetary disks.