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 = 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.

A Search for Evolutionary Changes in the Periods of Five Classical Cepheid Stars: R Cru, T Cru, XZ Car, X Lac and WZ Car

“…From the figure, we found that the rate of period change dp/dt depends upon where a Cepheid is located in the instability strip. The observed period changes are deviated in a small but important way from what is expected according to predictions based upon specific stellar evolutionary models, see Turner (2001b), and Turner et al (2012). Such scatter in our result makes it difficult to use the rate of period change for individual Cepheids to identify their exact location within the instability strip.…”

The distance to the young open cluster Westerlund 2

“…5, a situation typical of stars in crowded fields or stars near the limits of reliable photometry with the detector. Yet it is noteworthy that there are also many stars that closely match the intrinsic relation for unreddened dwarfs, which is often a good test of how closely the observations match the Johnson UBV system (see Turner et al, 2012b).…”

“…The unreddened color-magnitude diagram for Westerlund 2 members with good quality UBV photometry (Fig. 9) dereddened individually to the intrinsic color-color relation (see Turner, 1996;Turner et al, 2012b) is that of an extremely young cluster. There are very few hot O-type stars evolved by more than 1 m from the ZAMS, except for the two Wolf-Rayet stars, WR 20a and WR 20b, which are akin to Otype supergiants.…”

On the effect of rotation on populations of classical Cepheids

“…The thinner lines show the locations of blue edges obtained with the frozen convection assumption, while the thicker lines show blue and red edges obtained by taking into account the perturbation of convection flux. The left panel also shows the positions of some Galactic Cepheids whose parameters are taken from Turner & Burke (2002), Turner et al (2012. 2004) adopting a distance modulus of 18.494 mag (Pietrzyński et al 2013).…”