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J/AJ/107/2093            DL Cas                                  (Gieren+, 1994)

Independent distance determinations to Milky Way Cepheids in open clusters and associations. I. The binary Cepheid DL Cas in NGC 129 Gieren W.P., Welch D.L., Mermilliod J.-C., Matthews J.M., Hertling G. <Astron. J. 107, 2093 (1994)> =1994AJ....107.2093G (SIMBAD/NED Reference)
ADC_Keywords: Clusters, open; Stars, variable; Binaries, spectroscopic; Radial velocities Abstract: As an eight-day Cepheid which is both a component of a spectroscopic binary and a member of the open cluster NGC 129, DL Cas is potentially a very accurate calibrator of the period-luminosity (PL) relation and Cepheid mass. From 160 high-precision (sigma<1.5km/s) radial velocity observations made with the CORAVEL and DAO spectrometers - including 67 new unpublished data - we have obtained both the orbital and pulsational velocity curves of this binary Cepheid. This body of RV data makes DL Cas one of the best observed Cepheids in our galaxy. Our analysis yields an orbital period of 684.4±0.4days which confirms DL Cas as one of the shortest-period binaries containing a Cepheid. We derive new precise orbital elements which replace earlier preliminary values found by Harris et al. Isochrone fitting to the V,B-V data points of Turner et al. yields an age of NGC 129 of (7.6±0.4)x107yr and a Cepheid mass of 5.6M. Evidence from age, a possible period change, and strip crossing times suggest that DL Cas is a solar-abundance star making its third (redward) crossing through the Cepheid instability strip. Existing observational constraints from our mass function of the DL Cas system and an IUE spectrum suggest that the companion is a main sequence star in the mass range from 2.6 to 5.6M. We use the pulsational velocity curve and published photometry to derive the distance and mean radius of DL Cas with the surface brightness method, finding values of 2034±110pc and 66.0±3.5R, respectively. The radius we derive indicates that DL Cas is a fundamental-mode pulsator, removing any possible ambiguity in mode identification. The distance corresponds to a mean absolute visual magnitude of <Mv≥-4.2±0.3mag whose error is dominated by the uncertainty of the absorption correction. Since our very precise distance contributes only 0.12mag to the error in <Mv>, improved reddening studies of NGC 129 would make DL Cas a very tight calibrator of the PL relation. Our value of the gamma velocity of the DL Cas system is identical to the mean radial velocity of the stars in NGC 129, strengthening the case for cluster membership. However, our distance for DL Cas, and thus for NGC 129, is significantly larger than the 1670±13pc obtained by Turner et al. from ZAMS fitting of the cluster. Possible causes for this discrepancy, and their implications for Cepheid distance scale calibrations, are discussed. Objects concerned: ---------------------------------- RA (2000) DE Name ---------------------------------- 00 29 58.5 +60 12 43 DL Cas ---------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1 64 160 Radial velocity observations of DL Cas
Byte-by-byte Description of file: table1
Bytes Format Units Label Explanations
1- 11 F11.3 d HJD Heliocentric Julian Date 13- 18 F6.2 km/s RV Radial velocity (1) 22- 24 A3 --- Instr Instrument, 'DAO' or 'COR' 29- 33 F5.3 --- OPh Orbital phase 36- 41 F6.2 km/s OVel Orbital velocity 44- 48 F5.2 km/s O-C Orbital O-C 52- 56 F5.3 --- PPh Pulsational phase 59- 64 F6.2 km/s PVel Pulsational velocity
Note (1): The standard deviations of the individual radial velocity observations are between 0.4 and 1.5km/s, and 0.8km/s on average for both the DAO and CORAVEL instruments.
Addresses: Gieren W.P. Hertling G. Astrophysics Group, Facultad de Fisica, Pontificia Universidad Catolica de Chile, Casilla 104, Santiago 22, Chile Welch D.L. Department of Physics and Astronomy McMaster University, Hamilton, Ontario L8S 4M1, Canada Mermilliod J.-C. Institut d'Astronomie de l'Universite de Lausanne, CH-1290 Chavannes-des-Bois, Switzerland Matthews J.M. Department of Geophysics and Astronomy, University of British Columbia, 129-2219 Main Mall, Vancouver, BC, V6T 2A6, Canada Origin: AAS CD-ROM series, Volume 3, 1995
(End) Lee Brotzman [ADS] 16-Aug-1994, Patricia Bauer [CDS] 16-Feb-1995
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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