A SEARCH FOR OB ASSOCIATIONS NEAR SOUTHERN LONG-PERIOD CEPHEIDS. V. AQ PUPPIS AND V620 PUPPIS

Abstract

A photometric UBV survey is presented for 610 stars in a region surrounding the Cepheid AQ Puppis and centered southwest of the variable, based upon photoelectric measures for 14 stars and calibrated iris photometry of photographic plates of the field for 596 stars. An analysis of reddening and distance for program stars indicates that the major dust complex in this direction is ~1.8 kpc distant, producing differential extinction described by a ratio of total-to-selective extinction of R=Av/E(B-V)=3.10+-0.20. Zero-age main-sequence fitting for the main group of B-type stars along the line of sight yields a distance of 3.21+-0.19 kpc (Vo-Mv=12.53+-0.13 s.e.). The 29.97d Cepheid AQ Pup, of field reddening E(B-V)=0.47+-0.07 (E(B-V)(B0)=0.51+-0.07), appears to be associated with B-type stars lying within 5' of it as well as with a sparse group of stars, designated Turner 14, centered south of it at J2000.0 = 07:58:37, -29:25:00, with a mean reddening of E(B-V)=0.81+-0.01. AQ Pup has an inferred luminosity as a cluster member of <Mv>=-5.40+-0.25 and an evolutionary age of 3x10^7 yr. Its observed rate of period increase of 300.1+-1.2 s/yr is an order of magnitude larger than what is observed for Cepheids of comparable period in the third crossing of the instability strip, and may be indicative of a high rate of mass loss or a putative fifth crossing. Another sparse cluster, designated Turner 13, surrounds the newly-recognized 2.59d Cepheid V620 Pup, of space reddening E(B-V)=0.64+-0.02 (E(B-V)(B0)=0.68+-0.02), distance 2.88+-0.11 kpc (Vo-Mv=12.30+-0.08 s.e.), evolutionary age 10^8 yr, and an inferred luminosity as a likely cluster member of <Mv>=-2.74+-0.11. V620 Pup is tentatively identified as a first crosser, pending additional observations.