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 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including 67 new unpublished data - we have obtained both the orbital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:
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RA (2000) DE Name
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00 29 58.5 +60 12 43 DL Cas
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1 64 160 Radial velocity observations of DL Cas
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Byte-by-byte Description of file: table1
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Bytes Format Units Label Explanations
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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
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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.
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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