Abstract: This memo reviews BIMA calibration requirements for AIPS++,

Introduction

BIMA has recently completed it's 9-element array, including a long-(1 km)-baseline project. Over the next year (effectively) two new elements will be added to the array, polarization will be implemented, and 1-mm receivers may be installed. Some of these developments are described in the BIMA Memoranda Series.

BIMA special interests

• Polarization: most likely this will be done in a time-sliced fashion, measuring circular polarization (LR and RL) with a quarter-wave plate. See also Wright (1995a) for a discussion on some of the possibilities. This will likely have an impact on how flexible the AIPS++ objects must be.
• Wide-field mapping: deconvolution of mosaiced fields. Various techniques to calibrate these data will be tried out, and a flexible setup of the resulting software is needed. For example, adding a pointing parameter to the mosaic algorithm can greatly improve the achievable dynamic range in a mosaiced image. Another important obvious feature should be the ease with which single dish data can be added to interferometry data.
• VLBI: BIMA regularly participates in mm VLBI experiments. The phased array data are currently processed offline using standard VLBI techniques (Mark-xxx, ref. xxx), and whenever AIPS++ will provide VLBI data processing, BIMA should be able to use them without any major problems.
• Unusual telescope modes: We cannot assume that all telescopes in the array are the same. They may have different sizes (primary beams). Currently though all elements are 6m dishes.
• Unusual correllator modes: The correlator can be configured in many modes, and produces DSB data with a small (< 8) number of windows with different settings of the IF. An interesting method to calibrate DSB data is to use the generally much slower varying gain ratio (phase difference and amplitude ratio). Also wide band data should not be treated different from narrow band data, and methods exists to (re)compute one from the other. Individual flags shall be present for each atomic correlation.
• calibration: although some of the calibration will be done online, we need a general offline calibration package. The DSB calibration mentioned before is an example of a peculiar application. Offline phase corrections, using total power measurements (see Wright 1995b), examplify one of the many ways in which calibration needs to be flexible.

MIRIAD/Visibility Data

• Visibility file format. MIRIAD employs a very general visibility file format, where correlations (be it cross- or auto) are tagged with a rich set of (name based) variables. Variables can be multi-dimensional of any of the basic types (variables can change dimension in a dataset, in principle even type).
• Obviously, like in the FITS community, these variables need to be registered and their meaning clarified. Currently MIRIAD knows about 95 variables.
• Although it would be ideal that the telescope data be directly written in native AIPS++ format, for the forseable future we don't see this happen. We expect to use a small conversion program, while the "Telescope Management System" is being reviewed for conversion.

References

• AIPS++ Consortium User Specifications (AIPS++ memo #115; 7-apr-92)
• AIPS++ User Specifications: BIMA Version (AIPS++ memo #108, 1991)
• Welch, W.J. et al. 1996, PASP, 108, 93-103
• Wright, M.C.H., 1995a. "Polarization Switching for the BIMA array", BIMA memo #43.
• Wright, M.C.H., 1995b. "Atmospheric Phase Prediction from Total Power Measurements", BIMA memo #44.
• W. Hoffman, J. Hudson, R. K. Sharpe, A.W. Grossman, J.A. Morgan, and P.J. Teuben. Real-Time Observing at Hat Creek, in: Astronomical Data Analysis Software and Systems V, ed. G.H. Jacoby and J. Barnes. PASP Conf Series (in press, 1996).
• R.J. Sault, P.J.Teuben, and M.C.H.Wright. A Retrospective View of Miriad , in: Astronomical Data Analysis Software and Systems IV, ed. R.A. Shaw, H.E. Payne and J.J.E. Hayes. PASP Conf Series 77, 433 (1995).