Hi all,
The most recent, largest and most accurate work on extended deep sky objects is
the
"Revised New General Catalogue and Index Catalogue"
by
Wolfgang Steinicke from
April 2004.
He is working on this since 1981!
The catalog comprises 14000 objects!
http://www.ngcic.com/steinicke/2004/explan.htm#3
It unifies Dreyer's "New General Catalogue
(NGC)", published in 1888 and its two supplements, the Index
Catalogue, published in 1895 (IC I), and the Second Index Catalogue,
published in 1908 (IC II). The NGC contains 7840 nonstellar objects,
the IC I and IC II add another 1520 and 3866 objects, respectively.
++++++++++++++++++++++++++
The main point is that besides containing lots of "criminalistic" work to
eliminate errors, Steinicke's catalog has the positions and size
parameters corrected from the
Digital (Real) Sky surveys!
++++++++++++++++++++++++++
This huge and still ongoing work is done within the so-called
The NGC/IC Project
--------------------------------------------
The aim of the NGC/IC project, headed by Dr. Harold G. Corwin
jr. (Pasadena/USA), is to clean the historical NGC and IC. All
investigations start from the historical data, e.g. the observer's
publifications. Dreyer's data are often not consistent.
For code planning purposes, I list below the catalog entries and
notably further below an explanation of the object TYPEs!
Code: Select all
FIELD Explanation
-------------------------------------------------------------------------------
NGC, IC NGC- or IC-number. Some objects have an extension letter (A,B,C,...).
C Components. If two or more different objects use the same NGC- or IC-number, these are numbered as components (1,2,3,...). This is also applied for objects associated with the main entry.
D Dreyer Object. A * marks, that this is the object which is ment in Dreyer's catalogue (many objects with extension letters are not in the original NGC/IC).
X Second Line. If more then one line is used for an object (if the space for identifications is not sufficient) the lines are counted (1,2) here.
S Status. Status of the identification (see Tab. 2)
P Precision. Flag for high precision position
CON Constellation
alpha, delta Right ascension, declination. Equinox J2000.0
Bmag Photographic (blue) magnitude
Vmag Visual magnitude
SB Surface brightness (mag/arcmin2)
a, b Larger/smaller diameter ('). If only one value (a) is given, this refers to the maximum size.
PA Position angle (?°). The position angle is only relevant for galaxies, and given if possible.
Type Type of object
PGC PGC-number. Object listed in the Catalog of Principle Galaxies [22]
ID1, ID2, ID3 Identifications
Remarks Additional information
So you can see that besides the
RA & Dec coordinates we have the
visual & photographic (blue) magnitude, surface brightness, larger/smaller diameters, the position angle and a detailed TYPE information.
The latter is richer, however than Hubble's "Tuning fork"
classification, since the catalogue contains lots of other objects besides galaxies. So we should devise the corresponding class in
Celestia flexible enough and also contemplate about "synthesizing" the
other types automatically!
The most complex type information is given
for galaxies (e.g. the Hubble type), mainly adapted from UGC, ESO and
PGC or detemined by own estimation. Generally types differ between
various sources. There is a special type for ring galaxies, following
Thompson. Types for open clusters are included according to
Tr??mpler's classification. For globular clusters the concentration
class (I...XII) is given.
Code: Select all
TYPE Explanation
--------------------------------------------------------------------
*, *2,..,*Grp Star, double star,..,star group (asterism)
C, D, E, I, P, S Galaxy: compact, dwarf, elliptical, irregular, peculiar, spiral (d=dwarf, B=bar, R=ring , M=mixed); other letters: from Hubble type or its extensions
R.., PRG Ring galaxy (see [30]), Polar ring galaxy
GxyP Part of galaxy (e.g. bright HII region)
OCL Open cluster (if no Tr??mpler class is available)
GCL Globular cluster (if no concentration class is available)
DN, EN, RN, PN Nebula: dark, emission, reflection, planetary
SNR Supernova remnant
NF Not found
Finally, the Status field gives some useful info about the actual
contents of the catalog
S Explanation NGC % IC %
---------------------------------------------------------------
1 Galaxy 6494 76.9 4124 74.3
2 Galactic nebula,
Supernova remnant 141 1.7 102 1.8
3 Planetary nebula 96 1.1 36 0.6
4 Open cluster 686 8.1 39 0.7
5 Globular cluster 118 1.4 8 0.1
6 Part of galaxy
(e.g. bright HII regions) 27 0.3 22 0.4
7 Object already in
the NGC- or IC 362 4.3 87 1.6
8 IC-object already
in the NGC 22 0.3 253 4.6
9
Star(s) 386 4.6 634 11.4
10 Not found 115 1.4 248 4.5
---------------------------------------------------------------
Sum 8447 5553
Bye Fridger
