13 Monocerotis

13 Monocerotis (13 Mon) is a class A0 Ib (white supergiant) star in the constellation Monoceros. Its apparent magnitude is 4.5 and it is approximately 780 parsecs (2,500 ly) away.

13 Mon lies within the Monoceros OB1 stellar association, halfway between the Rosette Nebula and NGC 2264, at a distance of about 780 parsecs. It is surrounded by a small reflection nebula listed as Van den Bergh 81 (VdB 81).

13 Monocerotis has been used as a standard star for the A0 Ib spectral class.

Extended photometry of 13 Monocerotis from 1997 to 2000 shows irregular variation of up to 0.04 magnitudes and also a slight trend to become fainter over the period. All the bright A0 - A5 supergiants analysed using Hipparcos satellite data were found to be variable, but 13 Mon was the least variable.

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