Browsing by Author "HERTLING, G"

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    INDEPENDENT DISTANCE DETERMINATIONS TO MILKY-WAY CEPHEIDS IN OPEN CLUSTERS AND ASSOCIATIONS .1. THE BINARY CEPHEID DL CAS IN NGC 129
    (1994) GIEREN, WP; WELCH, DL; MERMILLIOD, JC; MATTHEWS, JM; HERTLING, G
    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 < 1.5 km/s) radial velocity observations made with the CORAVEL and DAO spectrometers-including 67 new unpublished data-we have obtained both the orbital and pulsational velocity curves of this binary Cepheid.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 +/- 0.4 days 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) X 10(7) yr and a Cepheid mass of 5.6 M.. 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 5.6 M.. 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 +/- 110 pc 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 [M(V)] = -4.2 +/- 0.3 mag whose error is dominated by the uncertainty of the absorption correction. Since our very precise distance contributes only 0.12 mag 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 +/- 13 pc 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.
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    THE MEDIUM REDSHIFT CLUSTERS CL-0017-20 AND CL-0500-24
    (1994) INFANTE, L; FOUQUE, P; HERTLING, G; WAY, MJ; GIRAUD, E; QUINTANA, H
    We present magnitudes and redshifts of galaxies in the cluster of galaxies CL 0017-20 and in the double cluster CL 0500-24. Luminosity functions and velocity distributions have been derived. CL 0017-20 possesses a virial mass of 2.9 x 10(14) M(circle dot) and a V band luminosity of 2.3+/-0.5 x 10(12) L(circle dot) (M/L(V) = 127), much of it in a very compact core of size 113 kpc. Our new velocities and photometry of CL 0500-24 confirm its double nature. Our group algorithm clearly detects two subconcentrations with masses 1.9 and 2.2 x 10(14) M(circle dot). Its total V band luminosity amounts to 2.7+/-0.8 x 10(12) L(circle dot) (M/L(V) of 157). Since the crossing and collapse times in both clusters are smaller than the age of the Universe, they appear bound and virialized. It is surprising that although M/L is small in these clusters, giant arcs have been detected in both.
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    THE VISUAL APPEARANCE OF THE NUCLEI OF RING-SHAPED GALAXIES AS AN ALTERNATIVE CLASSIFICATION CRITERION
    (1992) FAUNDEZABANS, M; HERTLING, G; RAMIREZ, AC
    An alternative classification of apparent ring galaxies is introduced concerning the morphology of the main body (nucleus). For this purpose, a list of probable ring galaxies has been prepared based on visual inspection of 56 film copies of the J SRC/ESO survey. The candidate objects have also been classified following Few & Madore's (1986) criteria.