Many functions are available for use within your expressions, covering standard mathematical and trigonometric functions, arithmetic utility functions, type conversions, and some more specialised astronomical ones. You can use them in just the way you'd expect, by using the function name (unlike column names, this is case-sensitive) followed by comma-separated arguments in brackets, so
max(IMAG,JMAG)will give you the larger of the values in the columns IMAG and JMAG, and so on.
The functions are grouped into the following classes:
k parameter for the HEALPix functions is the
HEALPix order, which can be in the range 0<=k<=29.
This is the logarithm to base 2 of the HEALPix NSIDE parameter.
k, there are 12*4^k pixels on the sphere.
The following parameters are used:
For a flat universe,
The terms and formulae used here are taken from the paper by D.W.Hogg, Distance measures in cosmology, astro-ph/9905116 v4 (2000).
yyyy-mm-ddThh:mm:ss.s, where the
Tis a literal character (a space character may be used instead). Based on UTC.
Therefore midday on the 25th of October 2004 is
2004-10-25T12:00:00 in ISO 8601 format,
53303.5 as an MJD value,
2004.81588 as a Julian Epoch and
2004.81726 as a Besselian Epoch.
Currently this implementation cannot be relied upon to better than a millisecond.
If you want to calculate aggregating functions like sum, min, max etc
on multiple values which are not part of an array,
it's easier to use the functions from the
Note that none of these functions will calculate statistical functions over a whole column of a table.
The functions fall into a number of categories:
array, which lets you assemble an array value from a list of scalar numbers. This can be used with the aggregating functions here, but it's generally easier to use the corresponding functions from the
Some constants for approximate conversions between different magnitude scales are also provided:
JOHNSON_AB_*, for Johnson <-> AB magnitude conversions, from Frei and Gunn, Astronomical Journal 108, 1476 (1994), Table 2 (1994AJ....108.1476F).
VEGA_AB_*, for Vega <-> AB magnitude conversions, from Blanton et al., Astronomical Journal 129, 2562 (2005), Eqs. (5) (2005AJ....129.2562B).
One coverage standard is Multi-Order Coverage maps, described at http://www.ivoa.net/Documents/MOC/. MOC positions are always defined in ICRS equatorial coordinates.
MOC locations may be given as either the filename or the URL of
a MOC FITS file. Alternatively, they may be the identifier of a VizieR
table, for instance "
V/139/sdss9" (SDSS DR9).
A list of all the MOCs available from VizieR can
currently be found at
You can search for VizieR table identifiers from the
VizieR web page
note you must use
the table identifier (like "
and not the catalogue identifier (like "
Some of these resemble similar functions in the
and in some cases are interchangeable, but these are easier to use
on non-array values because you don't have to explicitly wrap up
lists of arguments as an array.
However, for implementation reasons, most of the functions defined here
can be used on values which are already
(for instance array-valued columns) rather than as comma-separated
lists of floating point values.
A listing of the functions in these classes is given in Appendix B.1, and complete documentation on them is available within TOPCAT from the Available Functions Window.