Independent Distance Determinations to Milky Way Cepheids in Open Clusters and Associations.II.CF CAS in NGC 7790

Details Independent Distance Determinations to Milky Way Cepheids in Open Clusters and Associations.II.CF CAS in NGC 7790 Independent Distance Determinations to Milky Way Cepheids in Open Clusters and Associations.II.CF CAS in NGC 7790

Nov 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aj....110.2280m&link_type=abstract

Astronomical Journal v.110, p.2280

Astronomy and Astrophysics

Astronomy

4

Open Clusters And Associations: Ngc 7790, Cepheids, Binaries: Eclipsing

Scientific paper

Containing three Cepheids and an eclipsing binary, the open cluster NGC 7790 has the potential to be a Rosetta Stone for refining the zero point of the extragalactic distance scale. Unfortunately, ZAMS fitting of this relatively sparse, heavily reddened cluster is fraught with difficulty, and even modern determinations of its distance modulus based on comparable data and techniques differ by over 0.3 mag. To provide an independent calibration of the distance to NGC 7790, we have performed a surface brightness analysis of the Cepheid CF Cas (P≃4.88 days), which is widely believed to be a member of the cluster. For this analysis, we use new high-quality radial-velocity data obtained with the DAO Radial Velocity Spectrometer, as well as archival velocities and photometry. Our new measurements increase the available set of published RV data for CF Cas by over a third. We derive the distance and radius of CF Cas to be 3130±160 pc and 40.6±2.0Rsun, respectively. This radius is consistent with fundamental-mode pulsation for a Cepheid of this period, removing a possible ambiguity in mode identification which could bias a period-luminosity calibration incorporating CF Cas. We go on to estimate the absolute magnitude ( ≃ -3.05±0.10 mag) and effective temperature (log Teff ≃ 3.74±0.02) of CF Cas, although we caution that these values are sensitive to the assumed reddening (unlike our surface-brightness distance and radius). Evolutionary and Wesselink relations yield very similar values for the mass of CF Cas, near 5 Msun.

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