Two Infrared Sources in Nebulae

Abstract

IN a systematic survey of the Caltech infrared catalogue (IRC)¹, 210 of the 5612 listed sources have been examined optically using the prints of the National Geographic Society–Palomar Observatory sky survey. Several criteria were adopted in the selection of sources for optical examination. Objects were first selected for which no previous identification was listed on the basis of comparison with star catalogues, and which further were very red as indicated by their I (0.84 µm) minus K (2.2 µm) colour index. The reddest sources among these have (I − K) ≥ 6^m.00 and all such cases were examined, whereas for the moderately red objects ((I − K) ≳ 4^m.00) only sources at high galactic latitude (|b^II| ≥ 40°), or lying in the +40° declination zone of the two micron survey, or located near stellar rings², were inspected. During the work, a number of infrared stars of (I − K) ≳ 4^m.00 but catalogued as belonging to spectral class B were also located. Examination of the sky survey prints revealed that the infrared object, in sixteen cases out of twenty investigated, was a fainter, very red star lying near the class B star in question. Some further named stars in the catalogue whose right ascension and declination offsets relative to the infrared source exceeded ∼ 6 s and/or ∼1′.2 were also examined, and again in nine cases out of fourteen a more satisfactory identification was made. On the basis of this admittedly small sample of stars with large offsets, it is suggested that such errors of identification may number about 100 stars throughout the catalogue, or about 2 per cent of the total.