[asac][almanews] ALMA Memo 493 Released

[Stacy Oliver]

ALMA MEMO #493 

Finding Fast Switching Calibrators for ALMA 

M.A. Holdaway, C. Carilli, R. Laing 

2004-04-29 

In order to perform fast switching phase calibration effectively, we need to
have a database of bright point-like sources at millimeter wavelengths.
Optimally, this would include flux measurements at 86 GHz and spectral
information at higher frequencies. We present a sample of 31145 compact flat
spectrum radio sources with -40 < dec < +60, presumed extragalactic, which
will be likely candidates for calibrator sources. A sample of variable steep
spectrum source (ie, sources that could harbor a flat spectrum core even
though they appear to be steep spectrum) adds another 1767 sources. And a
sample of weak but highly inverted sources adds another 5296 potential
sources to observe. Hence, we have as many as 38208 sources which are likely
to be detected at millimeter wavelengths, though some of the steep spectrum
variable sources and highly inverted source candidates may be abandoned
based on detection rate. The Prototype Interferometer (PI) at the ALMA Test
Facility (ATF) may be available to verify if these sources are indeed bright
at 86 GHz. The sensitivity of the prototype receivers should permit a noise
level of about 3.5 mJy at 86 GHz and about 10 mJy at 250 GHz. We expect
about a third of the sources will be brighter than 20 mJy at 86 GHz, and
these detections will be reobserved at 86, 106, 215, and 263 GHz to
determine the spectrum at higher frequencies and to have some data on
variability. These observations should take about 80-90 days of time on the
Prototype Interferometer, and it is suggested that these observations could
be done at night in the spring and fall of 2005, subject to availability of
equipment and manpower.

View a pdf version of ALMA Memo #493. 
http://www.alma.nrao.edu/memos/html-memos/alma493/memo493.pdf
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