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:
yyyy-mm-ddThh:mm:ss.s
, where the T
is 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.
The following parameters are used:
For a flat universe, omegaM
+omegaLambda
=1
The terms and formulae used here are taken from the paper by D.W.Hogg, Distance measures in cosmology, astro-ph/9905116 v4 (2000).
mean
, sum
,
maximum
etc can only be used on values which are already arrays.
In most cases that means on values in table columns which are declared
as array-valued. FITS and VOTable tables can have columns which contain
array values, but other formats such as CSV cannot.
There is also a set of functions named array
with various
numbers of arguments, which let you assemble an array value from a list
of scalar numbers. This can be used for instance to get the mean of
a set of three magnitudes by using an expression like
"mean(array(jmag, hmag, kmag))
".
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).
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.