Abstract
If the zero-age main sequence is expressed in the (V – I) versus (B – V) – (V – I) plane, the reddening lines are found to lie at a great enough angle to allow reasonably accurate spectral-type classification for stars later than ~ F5. Earlier spectral types can also be identified but with lower accuracy. Comparisons with the Q method of UBV photometry and with spectra of some of the programme stars show that the BVIc technique produces reliable results. As late-type stars constitute the most numerous spectral types and are plentiful in all galactic-plane directions, BVIc reddening-distances can be derived close to the desired direction (although to smaller distances than techniques that utilize early-type stars). The applicability of the technique is further enhanced by the use of CCDs which generally have a spectral response well suited for BVIc imaging observations. Using the new technique, the distance to the PN NGC 2440 was found to be (3100 ± 320) pc.
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