LDN - Lynds Catalog of Dark Nebulae
This HEASARC database table is based on the updated version of the LDN Catalog created at CDS on February 22, 1996, and contains several changes and/or additions compared to the original published version: (i) the galactic co-ordinates have been revised, (ii) 15 duplicate LDN objects were removed (LDN 184, 366, 457, 465, 924, 1025, 1318, 1342, 1344, 1413, 1575, 1592, 1593, 1603, and 1792), (iii) 4 new objects have been added (these have not been assigned LDN names so that we have given them our default NN (no name) name for unnamed objects), apparently by the original author, (iii) two new parameters have been added: Run_Number, a running number in order of increasing galactic longitude, and Lynds2_Number, a number assigned by Lynds when the updated catalog was first created whose significance is unknown (notice that it is not a unique identifier).
The name of the dark nebula, constructed from the LDN prefix and the catalog number listed in the original published version. Four nebulae added after the published version have been assigned the null name NN.
The Right Ascension of the center of the cloud.
The Declination of the center of the cloud.
The galactic longitude of the center of the cloud.
The galactic latitude of the center of the cloud.
The area, in square degrees, of the cloud.
A visual estimate of the cloud opacity on a scale of 1 (lightest) to 6 (darkest). These estimates were made by Lynds based on a comparison of the neighboring fields for the particular Palomar photograph on which the cloud appeared. Both the red and the blue prints were used for this comparison. The clouds just detectable on both prints, as evidenced by a slight decrease in the surface intensity of the general field, were designated as having an opacity of 1. The darkest clouds, of opacity 6, were those within which the star density, on the average, amounted to 120 stars per square degree, down to the limiting magnitude of the red photograph. In addition to the minimum number of stars per square degree, the opacity 6 clouds are those which appear to be the darkest - many seem darker than the general background in the neighboring clear regions. The areas of the sky which contain heavy obscuration usually exhibit clouds of several degrees of opacity. In this catalog such clouds are subdivided into areas of the same opacity: thus a single cloud may consist of an area of opacity 3 covering several square degrees and contain within it smaller condenstaions of opacity 6 and areas of hundredths of a square degree. These sections are listed separately, but have been assigned a common value of the parameter ID_Number (q.v.).
An identification Number that is used to indicate whether or not the specific cloud is an isolated object, or is part of a larger cloud with several sections of different opacity, or is an object lying in the general obscuration of the Milky Way. An isolated cloud will have a unique, non-zero value of this parameter, while an object in the general obscuration of the Milky Way will have ID_Number = 0. A cloud with several sections of different opacity will have a separate entry in this catalog for each section: these entries will all have the same non-zero value for their ID_Number.
A running number in order of increasing Galactic Longitude that was created for this revised version of the LDN Catalog.
A number that B. Lynds assigned when the updated catalog was created. The significance of this number is not known. Also, it is not a unique number throughout this version of the catalog.
The numbers of the Barnard Objects that were cross-identified by Lynds with the LDN nebulae. Some LDN objects are identified with more than one Barnard Object. (The maximum is eight cross-identifications).
BROWSE classification type. All objects in the LDN Catalog have been classified with the same class: Dark Nebula.