Pismis 6 and the F0Ia supergiant HD 74180

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Session 58 -- The Galaxy
Display presentation, Thursday, 2, 1994, 9:20-6:30

[58.19] Pismis 6 and the F0Ia supergiant HD 74180

D. Forbes, S. Short (Memorial Univ.)

New photoelectric UBV observations of stars in the open cluster Pismis 6 and existing photometry and spectroscopy of several nearby OB stars are used to determine the intrinsic properties of the luminous supergiant HD 74180 (F0Ia). Thirty cluster members are identified in Pismis 6 and yield a distance modulus ($V_{\o}$ - $M_{\V}$) = 11.34 +/- 0.09 and mean reddening E(B-V) = 0.46 +/- 0.04. The cluster age is estimated to be (8 +/- 2)Myr. Pismis 6 appears to be part of a physical group that includes the F-supergiant and the nearby OB stars. The position of HD 74180 in the theoretical HR diagram suggests it may be a lower-mass analogue of the hypergiant IRC +10420, which Jones et al. (1993, ApJ, 411, 323) have suggested is evolving blueward in the HR diagram from the red supergiant region, possibly on its way to becoming a Wolf-Rayet star.

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