Lacaille III.3

In his catalog, Nicholas Louis de Lacaille describes in the third place in his third part ("Star Accompanied by Nebulosity") a "Star of 6th magnitude, connected to another more southern one by a nebulous trace."

While in the 3rd edition of his Atlas of Deep Sky Splendors, Hans Vehrenberg classifies this object as (open) cluster, other catalogs contain no hint on this Lacaille object, and in the 4th edition, also Vehrenberg (or his succeeding editor) marks it as non-existent.

Getting curious, the present author has investigated the field around this catalog entry, which has the coordinates RA=08:42.2, Dec=-48:04 (precessed to epoch J2000.0) and is situated in the constellation Vela. The Sky Catalogue 2000.0 gives positions for the following clusters near Lacaille's position: 

     Object       RA       Dec


    [Lac III.3]   08:42.2  -48:04
     IC 2395      08:41.1  -48:12
     NGC 2660     08:42.2  -47:09
     vdB-Ha 47    08:42.6  -48:07
     NGC 2670     08:45.5  -48:47
Cluster van den Bergh-Hagen 47 is closest to Lacaille's position.

The view of a Deep Sky Survey image of the Lacaille place revealed a surprise: Well near the center of this image is a small cluster (probably vdB-Ha 47), as well as the two stars described by Lacaille. It is, however, uncertain if there is a physical connection between the stars and the cluster. Therefore, the "object" Lacaille III.3 might be an asterism of two stars and the cluster vdB-Ha 47 which Lacaille noted as nebulous trace.

Moreover, a check of the position of IC 2395 indicates that this cluster can hardly be identified in the Digital Sky Survey. The reason for this was revealed by Brian Skiff and Brent Archinal in 1995: While the original position of IC 2395 in Dreyer's catalog, determined by Solon I. Bailey in 1908, agrees considerably well with vdB-Ha 47, more modern versions of the IC (such as that in the NGC 2000.0, the Sky Catalogue 2000.0, or the first edition of Uranometria 2000.0) propagate an erroneous position by Lund.

Digital Sky Survey images of the surroundings of Lacaille III.3:

Thanks to Arnaldo Arnal for interesting discussion of this thread.

  • The "missing" Lacaille objects

    Hartmut Frommert
    Christine Kronberg
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    Definitive Version: February 14, 1998
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