Catalogue of bright nebulae

Beverly T. Lynds

Steward Observatory, University of Arizona

Received January 26, 1965

Abstract

A catalogue of bright nebulae has been compiled from a study of the red and blue prints of the National Geographic-Palomar Observatory Sky Atlas. This catalogue contains positions, both equatorial and galactic, for the centers of the nebulosities, values of their largest dimensions in minutes of arc and of their areas in square degrees, and estimates of their colors and surface brightness on an arbitrary scale. Total areas of the nebulae are tabulated as a function of galactic latitude for three different color classes.

A survey has been made of all bright diffuse areas detectable on the 48-inch Palomar Sky Survey prints in a manner analogous to the survey of dark nebulae (Lynds 1962). All nebulosities apparent on these prints were recorded; their size and area measured, and their brightness and color estimated on an arbitrary scale. The catalogue contains all bright diffuse objects which presumably belong to our Galaxy. An effort was made to exclude all known planetary nebulae, including the recent list of such objects published by Abell (1961). The catalogue contains known supernovae remnants (such as IC 443), reflection nebulae, and the standard H II emission nebulae. The identification of the various kinds of objects in the catalogue is possible only by their color or their filamentary nature. Objects which appear brighter on the blue plate (designated by a color of "1" in Table 1) are undoubtedly reflection nebulae; those features of about the same surface brightness on both the red and blue plates or of greater brightness on the red may be examples of transition types or purely emission regions. Those objects very much brighter on the red print are usually H II regions, with the exception of such red reflection nebulae as that associated with Antares. Therefore, from the color alone, we cannot uniquely define the emission and reflection regions.

The catalogue is not complete for the small-scale emission or reflection features such as those described in the Lick Hα surveys, but it should be complete for all extended nebulous features of surface brightness intense enough to be detected by the f /2.4 camera. The survey covers the entire sky down to the declination limit of −33° of the Palomar telescope.

Table 1 lists all of the nebulosities recorded in the survey. The tenth column represents an identification number which indicates whether or not the object is an isolated region (in which case the number is "0") or a region of different brightness located in a more extensive complex of nebulosities. For example, the entire Orion region, with its many bright areas of emission and reflection has the identification number 73. The other columns of the table are given in the tabulation at the top of page 184.

The diffuse features, as they appeared on the prints, were traced and their actual forms reduced by a factor of about 60 from the original Palomar prints. Figure 1 represents the distribution of the nebulosities recorded in Table 1. In this diagram both the red nebulosities (indicated by solid lines) and the blue nebulosities, indicated by solid lines with hachures are included. The shading represents the relative brightnesses of the regions, the darkest areas being the brightest.

The large complexes of emission regions are apparent in Figure 1. The structure and brightness distribution of these fields give rather clear evidence of the particular stars belonging to these complexes. In contrast to these are the faint nebulosities quite often found in relatively high galactic latitudes (with |b | > 30°). These features are of very

Table 1.

(pages 164-183)