Browsing by Author "Gieren, WP"
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- ItemA direct distance to the Large Magellanic Cloud Cepheid HV 12198 from the infrared surface brightness technique(2000) Gieren, WP; Storm, J; Fouqué, P; Mennickent, RE; Gómez, MWe report on the first application of the infrared surface brightness technique on a Cepheid in the Large Magellanic Cloud, the variable HV 12198 in the young globular cluster NGC 1866. From this one star, we determine a distance modulus of 18.42 +/- 0.10 (random and systematic uncertainty) to the cluster. When the results on further member Cepheids in NGC 1866 become available, we expect to derive the distance to the LMC with a +/-3%-4% accuracy, including systematic errors, from this technique.
- ItemAn improved calibration of Cepheid visual and infrared surface brightness relations from accurate angular diameter measurements of cool giants and supergiants(1997) Fouque, P; Gieren, WPWe have calibrated optical and near-infrared surface brightness - colour relations for cool giant and supergiant stars using high-precision angular diameters of these stars determined from Michelson interferometry. We find that the giant and supergiant relations are undistinguishable over a wide range of intrinsic colours. We independently determine the slopes of these relations obeyed by Cepheid variables and find that in all the diagrams considered, these agree very well with the slopes derived from the stable giants and supergiants. Forcing the slopes to the values derived from the Cepheids, we determine a very precise value of the zero point of the surface brightness - colour relations valid for Cepheid variables, which is 3.947 +/- 0.003. This value is in agreement with the one derived from the Cepheid effective temperature scale of Pel (1978), and from the lunar occultation angular diameter of the Cepheid zeta Gem (Ridgway et al. 1982).
- ItemBV(RI)C photometry of Cepheids in the Magellanic Cloud(1998) Moffett, TJ; Gieren, WP; Barnes, TG; Gomez, MWe report BT/(RI)(C) data for a select group of 14 Cepheids in the Large Magellanic Cloud and eight in the Small Magellanic Cloud that have preexisting radial velocity curves. The photometry was obtained as part of a program to determine distances to these Cepheids by means of the visual surface brightness technique and to improve significantly the optical BV(RI)(C) light curves of Magellanic Cloud Cepheids. The data were acquired on the 0.9 m telescope at Cerro Tololo Inter-American Observatory with the CFCCD instrument and with the 1 m photometric telescope at ESO using aperture photometry. The median number of measures per Cepheid is 46 in each band, and the uncertainty in the photometry is typically +/-0.01 mag. Using these data together with data from the literature, we determined improved periods for all variables. For most of the Cepheids, these revised periods lead to excellent, low-noise light curves, but for a few variables, the periods are obviously variable.
- ItemCepheid period-radius and period-luminosity relations and the distance to the large Magellanic Cloud(1998) Gieren, WP; Fouque, P; Gomez, MWe have used the infrared Barnes-Evans surface brightness technique to derive the radii and distances of 34 Galactic Cepheid variables. Radius and distance results obtained from both versions of the technique are in excellent agreement. The radii of 28 variables are used to determine the period-radius (PR) relation. This relation is found to have a smaller dispersion than in previous studies, and is identical to the PR relation found by Laney & Stobie from a completely independent method, a fact which provides persuasive evidence that the Cepheid PR relation is now determined at a very high confidence level. We use the accurate infrared distances to determine period-luminosity (PL) relations in the V, I, J, H, and K passbands from the Galactic sample of Cepheids. We derive improved slopes of these relations from updated LMC Cepheid samples and adopt these slopes to obtain accurate absolute calibrations of the PL relation. By comparing these relations to the ones defined by the LMC Cepheids, we derive strikingly consistent and precise values for the LMC distance modulus in each of the passbands that yield a mean value of mu(0)(LMC) = 18.46 +/- 0.02.
- ItemCepheid variables in the Large Magellanic Cloud cluster NGC 1866.: I.: New BVRI CCD photometry(2000) Gieren, WP; Gómez, M; Storm, J; Moffett, TJ; Infante, L; Barnes, TG; Geisler, D; Fouqué, PWe report BV(RI)(C) CCD photometric data for a group of seven Cepheid variables in the young, rich cluster NGC 1866 in the Large Magellanic Cloud. The photometry was obtained as part of a program to determine accurate distances to these Cepheids by means of the infrared surface brightness technique and to improve the LMC Cepheid database for constructing Cepheid P-L and P-L-C relations. Using the new data together with data from the literature, we have determined improved periods for all variables. For five fundamental mode pulsators, the light curves are now of excellent quality and will lead to accurate distance and radius determinations once complete infrared light curves and radial velocity curves for these variables become available.
- ItemIndependent distance determinations to Milky Way cepheids in open clusters and associations .3. CV Mon in Anon vandenBergh(1996) Gieren, WP; Mermilliod, JC; Matthews, JM; Welch, DLAs part of a program aimed at comparing the galactic Cepheid distance scales from cluster ZAMS fitting and from independent Baade-Wesselink techniques, we have used new, high-quality light and radial velocity curves of the Cepheid CV Mon supposed to be a member of the sparse cluster Anon van den Bergh to obtain its distance and mean radius from the visual surface brightness method, We find the distance to CV Mon to be 2160+/-200 pc which is similar to 20% larger than the ZAMS-fitting distance to the cluster determined by Turner [JRASC, 72, 248 (1978)] but cluster membership of CV Mon is still possible given the uncertainties of both determinations. Our surface brightness analysis yields a mean radius of 53.5+/-3.9 R. for CV Mon. The Cepheid's absolute visual magnitude is -3.67+/-0.36 mag, whose large uncertainty is dominated by the relatively uncertain absorption correction. Use of near infrared photometry would reduce the uncertainty in the absolute magnitude. We find rather clear evidence that CV Mon is pulsating in the fundamental radial mode. There is no evidence, neither from the existing photometry nor from radial velocity observations obtained over eleven years, that there is a binary companion to the Cepheid. (C) 1996 American Astronomical Society.
- ItemVery accurate distances and radii of open cluster Cepheids from a near-infrared surface brightness technique(1997) Gieren, WP; Fouque, P; Gomez, MWe have obtained the radii and distances of 16 galactic Cepheids supposed to be members in open clusters or associations using a new optical and two near-infrared calibrations of the surface brightness (Barnes-Evans) method. We find excellent agreement of the radii and distances produced by both infrared techniques, which use the V, V-K (K on the Carter system) and the K, J-K magnitude-color combinations, respectively, with typical random errors that are as little as similar to 2%. We discuss possible systematic errors in our infrared solutions in detail and conclude that the typical total uncertainty of the infrared distance and radius of a Cepheid is about 3% in both infrared solutions, provided that the data are of excellent quality and that the amplitude of the color curve used in the solution is larger than similar to 0.3 mag. The optical V, V-R distance and radius of a given Cepheid can deviate by as much as similar to 30% from the infrared value because of large systematic and random errors caused by microturbulence and gravity variations: these affect the optical but not the infrared colors.