MRT Label Standards

Reasons for label standards

In addition to providing further information about a column of data, the label can be used to as a flag to provide limit checks on certain types of common astronomical data. For example, using the RAh label for a column of hours of Right ascension will tell the machine readable (MR) conversion program to flag any values greater than or equal to 24. Thus the judicious use of the predefined labels will provide an additional consistency check of the dataset. Frequently a column has associated values such as errors or uncertainty flags. In these cases a set of prefixes and suffixes can be added to the original label already in use to show the connection between the columns.

When creating labels for your MR table, first scan the list of predefined labels. If a label doesn’t exist that describes your data column follow the rules below before creating your own.

Label rules

  • A label is always a single word. In addition, there are the following character restrictions:
    • the characters  $ @ ! ` \ ^ ~ & are not accepted in a label
    • the first character of a label can’t be one of the symbols   + – * / = . # _ ‘ “
    • the last character of a label can’t be one of the symbols   , ;
    • the various kinds of parentheses and brackets   ( ) [ ] { }, when used, must be balanced
    • a label can’t be made of digits only
    • a single-character label must be alphabetic.
    • the label – – is used for filling bytes, like the colon fond sometimes between the hours and minutes, or a x existing between the major and minor axises of a galaxy.
  • Two columns can’t have the same label in the meta-data table.
  • Very long names should be avoided since there is a limited amount of space the the meta-data table but try to keep the label discriptive.

Predefined labels and their limit checks

Symbol Explanation Default Limits
RAh Part of the right ascension expressed in hours [0,24[
RAm Part of the right ascension expressed in minutes [0,60[
RAs Part of the right ascension expressed in seconds [0,60[
RAdeg Right ascension expressed in decimal degrees [0,360[
RArad Right ascension expressed in radians [0,2{pi}[
DE- Sign of declination [+-]
DEd Part of the declination expressed in degrees [0,90]
DEm Part of the declination expressed in arc minutes [0,60[
DEs Part of the declination expressed in arc seconds [0,60[
DEdeg Declination expressed in decimal degrees [-90,+90]
DErad Declination expressed in radians [-{pi}/2,+{pi}/2]
PosErr Position mean error >=0
dRA  dDE Difference in Right Ascension or Declination
oRA  oDE Offset from a reference position in R.A. or Dec.
ELON ecliptic longitude [0,360[
ELAT ecliptic latitude [-90,+90]
GLON galactic longitude [0,360[
GLAT galactic latitude [-90,+90
Epoch Epoch — write Ep-1900 for a year with 1900 offset
plx Parallax
pmRA Proper motion in Right Ascension
pmDE Proper motion in Declination
pmX Proper motion along X direction
Seq a Sequential number used e.g. to number the objects
Name the main name of an object or feature
Diam Diameter – or MajDiam and MinDiam >=0
Axis Half Diameter – also MajAxis and MinAxis >=0
PA Position Angle, normally North to East [0,360[
Rad Radius >=0
HRV Heliocentric Radial velocity
RVel Radial velocity
Sep Separation (anglular or linear) >=0
SpType Spectral type
MType Morphological type
Vmag Magnitude (apparent) in V filter
VMag Absolute Magnitude in V filter
Kmag Magnitude (apparent) in K filter …
Sp+Index Spectral index ({alpha} in relation S({nu}) = {nu} {alpha} )
Sp-Index Spectral index ({alpha} in relation S({nu}) = {nu} -{alpha} )
Text Free-format text like list of authors, titles…

Where the inclusion or non-inclusion of the default limits as acceptable values follow the standard mathematical conventions, i.e. an opening [ bracket means that the lower value is excluded, a closing ] bracket that the upper value is included.

Prefixes and suffixes for reference labels

The following prefixes are used for common associative atronomical values.

Symbol Explanation Default Limits
a_label aperture used for parameter label >=0
d_label for a number of degrees of freedom or for number of digits on parameter label >0
E_label mean error (upper limit) on parameter label >=0
e_label mean error ({sigma}) on parameter label >=0
f_label flag on parameter label
l_label limit flag on parameter label [<>]
m_label multiplicity index on parameter label to resolve ambiguities
n_label note (remark) on parameter label
o_label number of observations on parameter label >=0
q_label quality on parameter label
r_label reference (source) for parameter label
u_label uncertainty flag on parameter label [ :]
w_label weight of parameter label >=0
x_label unit in which parameter label is expressed

The following suffixes can be appended to a label to designate the components of time or angle:

.Y Year part (in order to avoid any ambiguity, the year should include all 4 digits)
.M Month name or number in range [1···12]
.D Day number in month (2 digits, range [1···31]) or year (3 digits, range [1···366])
.h Hour (range [0···24[)
.m Minutes (range [0···60[))
.s Seconds (range [0···60[))
.d Degrees (range [0···360[)

For instance, the various components of an observation date and time can be labelled Obs.Y, Obs.Y, Obs.M, Obs.D, Obs.h, Obs.m.