No abstract

No abstract

No abstract

We report UBVphotometry for fields surrounding four long-period Cepheids in the Southern Milky Way. No potential early-type companions are detected around XY Car, which appears to be relatively isolated. However, an anonymous group of nine B-type and two possible FG supergiant stars are detected as possible companions to GT Car, despite its location at a seemingly improbably large distance of 10 kpc. WZ Sgr is found to lie in a sparse, previously undetected cluster, 1.8 kpc distant, containing upward of 76 potential early-type member stars. Preliminary spectroscopic observations strengthen the case for cluster membership in this instance. SW Vel appears to belong to an older subgroup of the 2.5 kpc distant Vel OB5 association described by Turner (1979), with 28 B star candidates in its immediate vicinity. Derived space reddenings and luminosities for WZ Sgr and SW Vel are consistent with their group membership, and the parameters of their associated stars, as well as those for the potential companions of GT Car, indicate that they are of comparable age to their associated Cepheid. Information is provided for follow-up studies of these stellar groups. Subject headings: Cepheids-open clusters and associations: general

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 = A V /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 (V 0 − M V = 12.53 ± 0.13 s.e.). The 29 d .97 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 M V = −5.40 ± 0.25 and an evolutionary age of 3 × 10 7 yr. Its observed rate of period increase of +300.1 ± 1.2 s yr −1 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 d .59 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 (V 0 − M V = 12.30 ± 0.08 s.e.), evolutionary age 10 8 yr, and an inferred luminosity as a likely cluster member of M V = −2.74 ± 0.11. V620 Pup is tentatively identified as a first crosser, pending additional observations.