MRT Standards

The AAS Journal’s machine-readable tables follow most of the conventions for ASCII tables developed and used by the CDS. The meta-data header provides the key to interpreting the data that follows. Under the section labeled “Byte-by-byte Description of file:” a five column table is used to describe the data. These columns include:

  1. the starting and ending byte locations of the data column separated by a dash.
  2. the format of the data column where:
    • An represents a character string of width n
    • In represents an integer number of maximum width n
    • Fn.m represents a real number of maximum width n and m digits after the decimal.
    • En.m represents a real number of maximum width n and mdigits after the decimal
  3. the units of the data column. Most of the common astronomical units have predefined symbols. Note that the standard is to use SI units. Thus Angstroms are given as 0.1nm and ergs/s/cm2 are mW/m2. Units are written as a single word with “/” to represent division, “.” to represent multiplication, and “+” and “-” for exponential notation (e.g. 10-7 W/cm2 is written as 10-7W/cm2). In cases where the column data is a logarithm, the unit is surrounded by “[ ]”s. Unitless values are represented by “- – -“.
  4. the label or column header. Some of the most common astronomical values have predefined labels. These labels are recognized by our software and check for values exceeding certain limits (e.g. if the label Rad is used for radius, any data in the column with values less than 0 will be flagged). Data columns that reference other columns also have predefined labels. The most common is “e_label” which is given to the +/- error data of the data referenced by “label”.
  5. the explanation field provides information about the column data. If the description is followed by a number surrounded by “( )”s addition information is provided in the “Notes” section which follows this meta-header table. The description can also be preceded by other characters which have special meaning. The two most common are “?” and “[ ]”. The “?” flag is used to indicate that NULL values are allowed in a numeric (but not a string) column. The values between the brackets are the only allowed values that may appear in the data column. All other values are flagged in the data checking programs.