Description of the fields: rawdistance

PGC

Historically the Principal Galaxies Catalogue number is invented by Paturel et al. (1989, A&AS, 80, 299). We use the standard identification schema of the HyperLEDA database. Each object has an unique number, used to link the data from the different catalogues, and, in particular, to its various designations.

modulus

The true distance modulus, (m-M)0, is stored in units of mag. The published values should be corrected for extinction if it was not done.

e_modulus

One-sigma error of the measurement on distance modulus in mag.

method

The distance determination method is coded for each measurement as follow (table distance_method_codes):

use

The boolean flag reflects HyperLEDA knowlegde about reliability of the data and its usage in the homogenization procedure. The rejected measurements are marked with (!) code on output.

quality

The bit mask describes quality of published data. 0000: normal measurement, 0001: uncertain estimate, 0010: lower limit, 0100: preliminary result, 1000: compilation. Output codes it as a set of flags: `uncertain' (:), `preliminary' (p), `low-limit' ($>$), or `compilation' (c).

calib

It refers the calibration relation used for distance estimate. The codes for calibration relations are stored in the calibration table (distance_calib).

mdstd

Standardized distance modulus, in mag, obtained as mdstd = modulus - clc - dtc.

Field: dataset

dataset

Field: bibcode

bibcode

Field:

Field: calibsys

Calibration system

Field: clc

calibsys correction, in mag.

The calibsys correction consists in shifting the zero-point of the individual distance scales that we identified in the catalogue to align them with our standerd set. We suceeded to associate most measurements to a calibsys, in the other cases we could not find in the original paper an unambigous description of the distance scale, in some cases because the listed measurements were clearly not bound to an homegeneous system (e. g. in the case of some compilations). No correction is applied in these latter cases. The most populated calibsys is Freedman+2001. For each calibsys intersecting calibset on more than 5 objects, a zero-point correction is computed.

Field: dtc

dataset correction, in mag.

The dataset correction, to apply on individual series of measurements is determined by comparing each series to all the rest of the catalogue after applying the calibsys and the previously adopted dataset corrections. Unlike the calibsys correction, the determination of dtc is a supervised process, which is incremental and iterative. For all the dataset having a sufficient intersection with the rest of the catalogue, a correction is suggested, together with the significance level. Then the datasets displaying the most significant offset are carefully examined. If a zero-point correction is adequate, a dataset correction is adopted, and all the calibsys corrections and suggested dataset correction are automatically re-adjusted.

HyperLeda Questions: leda@univ-lyon1.fr