Anchors for the cosmic distance scale: the Cepheids U Sagittarii, CF Cassiopeiae, and CEab Cassiopeiae

¹ Saint Mary’s University, Halifax, Nova Scotia, Canada
² Mount Saint Vincent University, Halifax, Nova Scotia, Canada
³ European Southern Observatory, Av. Alonso de Cordova, 3107, 19001 Casilla, Santiago, Chile
⁴ Instituto de Astronomía, Universidad Católica del Norte, Av. Angamos 0610, 1270709 Antofagasta, Chile
⁵ Departamento de Astronomia, Universidade Federal do Rio Grande do Sul, Av. Bento Gonalves 9500, 91501-970 Porto Alegre, RS, Brazil
⁶ Sternberg Astronomical Institute, Moscow M. V. Lomonosov State University, 119992 Moscow, Russia
⁷ Isaac Newton Institute of Chile, Moscow Branch, Universitetskij Pr. 13, 119992 Moscow, Russia
⁸ Dominion Astrophysical Observatory, Victoria, British Columbia, Canada
⁹ Departamento de Astronomía, Universidad de Concepción, 160 Casilla, Concepción, Chile
¹⁰ Departamento de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111, 5030 Casilla, Valparaíso, Chile
¹¹ Astronomical Observatory, Odessa National University, Odessa, Ukraine
¹² Isaac Newton Institute of Chile, Odessa Branch, T. G. Shevkenko Park, 65014 Odessa, Ukraine
¹³ Las Campanas Observatory, Carnegie Institution of Washington, Colina el Pino, 601 Casilla, La Serena, Chile

Received: 14 September 2013
Accepted: 2 November 2013

Abstract

New and existing X-ray, UBVJHK_sW_(1 − 4), and spectroscopic observations were analyzed to constrain fundamental parameters for M 25, NGC 7790, and dust along their sight-lines. The star clusters are of particular importance because they host the classical Cepheids U Sgr, CF Cas, and the visual binary Cepheids CEa and CEb Cas. Precise results from the multiband analysis, in tandem with a comprehensive determination of the Cepheids’ period evolution (dP/dt) from ~140 years of observations, helped to resolve concerns raised regarding the clusters and their key Cepheid constituents. Specifically, the distances derived for members of M 25 and NGC 7790 are 630 ± 25 pc and 3.40 ± 0.15 kpc, respectively.