Cycle 4 Solar Observing Modes

The following text is copied from the Proposer’s Guide (Sect. A.11). Please check the original document for more information. 

Proposals will be accepted for ALMA interferometric and total power observations of the Sun in Cycle 4 with the following capabilities and restrictions:

  • Solar observations will be conducted using a “campaign mode”, whereby specific dates are reserved for the execution of Solar programs so that Solar experts are available to help with program execution. Observing windows will be identified during the periods when the 12-m Array is in one of the three most compact configurations (maximum baselines less than 500 m; see configuration schedule in Section 5.3.3). The actual campaign dates will be set after the proposal review process. Time constraints can be specified only if they imply observation times within the “Solar campaign”.

  • The interferometric component of Solar observations will be conducted using a special combined array comprising both 12-m and 7-m antennas (to ensure sufficient short-spacing information is observed), and will be processed with the 64-input Correlator (Section 5.1 of the Technical Handbook). Observations with only 12-m or only 7-m Arrays are not offered.

  • To minimize shadowing of 7-m antennas, observations will be carried out between 10:00 and 17:00 CLT (13:00 UT and 20:00 UT).

  • PIs will designate a desired angular resolution. This is restricted to the range provided by one of the three most compact 12-m configurations (see Section A.2).

  • The Total Power component of Solar observations consists of fast-scanning mapping observations of the full Sun to recover the largest angular scales for interferometric observations. Proposals requesting only total-power single-dish observations will not be accepted.

  • The TP observations will be taken contemporaneously with the interferometric observation. These observations will not be executed when the Sun is at elevations above 700 because the required fast-scan azimuth slew speeds are too high. The time cadence of full-sun images obtained from total power observations is about 7 minutes for Band 3 and 10 minutes for Band 6.

  • Proposers will specify their Solar target by providing an ephemeris file. This can be a dummy ephemeris for the purposes of a proposal (one is available from the OT “template library”). The ALMA Observatory will coordinate with successful PIs to get an updated target ephemeris at least 24 hours in advance of the proposed observation.

  • Only proposals for continuum observations in Bands 3 and 6 will be accepted. For the interferometric observations these will be obtained using the low spectral resolution (TDM) mode (see Section A.6.1). The individual integration times for this mode are fixed to 2 seconds, and the frequencies are fixed to four 1875 MHz-wide spectral windows centered on the frequencies shown in Table A-6 below. The high spectral resolution (FDM) observing mode is not offered for Solar observations.

  • The observing frequencies of the total power observations are as shown in Table A-6, but the total power data only include one channel per SPW; a correlator will not be used for total power observations in Cycle 4 and so autocorrelation measurements will not be available.

  • Simultaneous observations with Bands 3 and 6 are not offered: each science goal can only include one band.

  • Observations may be performed using dual linear polarization (XX, YY) or single polarization (XX) correlations; full polarization measurements are not currently offered for Solar observations.

  • Because the WVR receivers are saturated when the antennas point at the Sun, the on-line WVR phase correction will not be applied and the off-line WVR correction for on-source (Solar) data is not possible.

  • Absolute calibration of single-dish brightness temperatures is currently no better than ~10% but is more realistically ~15%. While efforts are ongoing to improve Solar calibration, Cycle 4 science goals that require absolute temperatures more accurate than this, and in particular comparisons of absolute temperatures between Bands 3 and 6, will be difficult to carry out successfully.

  • The total observing time requested for one proposal cannot exceed 50 hours.

Published Mar. 23, 2016 1:23 AM - Last modified Mar. 31, 2016 4:33 PM