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The distance to NGC 4725 has been derived from Cepheid variables, as part of the Hubble Space Telescope Key Project on the Extragalactic Distance Scale.
The distance to NGC 7331 has been derived from Cepheid variables observed with HST/WFPC2, as part of the Extragalactic Distance Scale Key Project. Multi-epoch exposures in F555W(~V) and F814W (~1), with photometry derived independently from DoPHOT and DAOPHOT/ALLFRAME programs, which were used to detect a total of 14 reliable Cepheids, with periods between 11 and 42 days.
An independent distance scale for Cepheid variables is discussed. The apparent magnitude and the visual surface brightness, inferred from an appropriate color index, are used to determine the angular diameter variation of the Cepheid. When combined with the linear displacement curve obtained from the integrated radial velocity curve, the distance and linear radius are determined. The attractiveness of the method is its complete independence of all other stellar distance scales, even though a number of practical difficulties currently exist in implementing the technique.
Using the Hubble Space Telescope (HST) thirty-seven long-period Cepheid variables have been discoverd in the Fornax Cluster spiral galaxy NGC 1365.
We report on the discovery of 30 new Cepheids in the nearby galaxy M81 based on observations using the Hubble Space Telescope (HST). The periods of these Cepheids lie in the range of 10-55 days, based on 18 independent epochs using the HST wide-band F555W filter. The HST F555W and F785LP data have been transformed to the Cousins standard V and I magnitude system using a ground-based calibration. Apparent period-luminosity relations at V and I were constructed, from which apparent distance moduli were measured with respect to assumed values of mu(sub 0) = 18.50 mag and E(B - V) = 0.10 mag for the Large Magellanic Cloud. The difference in the apparent V and I moduli yields a measure of the difference in the total mean extinction between the M81 and the LMC Cepheid samples. A low total mean extinction to the M81 sample of E(B - V) = 0.03 +/- 0.05 mag is obtained. The true distance modulus to M81 is determined to be 27.80 +/- 0.20 mag, corresponding to a distance of 3.63 +/- 0.34 Mpc. These data illustrate that with an optimal (power-law) sampling strategy, the HST provides a powerful tool for the discovery of extragalactic Cepheids and their application to the distance scale. M81 is the first calibrating galaxy in the target sample of the HST Key Project on the Extragalactic Distance Scale, the ultimate aim of which is to provide a value of the Hubble constant to 10% accuracy.
Seaton distance scale for brightness of planetary nebulae in H beta recalculated, noting correction factor
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It is established by an analysis of alternative methods for the determination of absolute distances to supernovae that there exists a kinematic method, superior to that of Baade (1926), which is illustrated for the case of the Type I supernova 1975a in NGC 2207. In addition, a dynamical method is developed which employs the recently-discovered analytic solutions for Type I supernovae. The requirement that the paradigm invoked in the present study be able to reproduce both fast and slow light curves has implied a dispersion in intrinsic brightness, whose size is approximately that observed in the Virgo and Coma clusters.
We report on the discovery of Cepheids in the field spiral galaxy NGC3621, based on observations made with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope (HST). NGC 3621 is one of 18 galaxies observed as part of the HST Key Project on the Extragalctic Distance Scale, which aims to measure the Hubble Constant to 10 percent accuracy.
Developments concerning the period-luminosity (PL) relation for classical Cepheids are discussed with particular emphasis on the fact that Cepheids continue to provide the most homogeneous and reliable set of distances to many nearby galaxies. Observational programs relating to extragalactic Cepheids are also reviewed, and new distances and reddenings to individual galaxies are determined from these data using multiwavelength PL relations, based for the first time on self-consistent calibrating data sets. Three recent promising secondary extragalactic distance indicators (Tully-Fisher, planetary nebula luminosity functions, and surface-brightness fluctuations) tie their zero points to the Cepheid distance scale and give globally consistent values for the Hubble constant of about 80 km/sec/Mpc. Tying the Faber-Jackson relation and the supernova distance scales to the Leo and Virgo clusters yields similar results. Such a value for the Hubble constant is marginally inconsistent with new estimates of the ages of globular clusters, and it may prove to be a serious problem for standard cold-dark-matter models of the universe.
This paper describes the Extragalactic Distance Scale Key Project for Hubble Space Telescope which aims to employ the Cepheid period-luminosity relation to measure galaxy distances out as far as the Virgo cluster.
The Expanding Photosphere Method is applied here to determine distances to 10 Type II SNe, exploring the effects of asymmetries, extinction, and flux dilution. It is shown that blackbody corrections caused by flux dilution are small for type II SNe in the infrared, and in the optical when their color temperatures are less than 6000 K. The distance measurements to the SNe span a wide range of 50 kpc to 120 Mpc, which is unique among the methods for establishing the extragalactic distance scale. A value of H(0) = 60 +/- 10 km/s/Mpc is derived.
The metal-poor stars in the halo of the Milky Way galaxy were among the first objects formed in our Galaxy. These Population II stars are the oldest objects in the universe whose ages can be accurately determined. Age determinations for these stars allow us to set a firm lower limit, to the age of the universe and to probe the early formation history of the Milky Way. The age of the universe determined from studies of Population II stars may be compared to the expansion age of the universe and used to constrain cosmological models. The largest uncertainty in estimates for the ages of stars in our halo is due to the uncertainty in the distance scale to Population II objects. We propose to obtain accurate parallaxes to a number of Population II objects (globular clusters and field stars in the halo) resulting in a significant improvement in the Population II distance scale and greatly reducing the uncertainty in the estimated ages of the oldest stars in our galaxy. At the present time, the oldest stars are estimated to be 12.8 Gyr old, with an uncertainty of approx. 15%. The SIM observations obtained by this key project, combined with the supporting theoretical research and ground based observations outlined in this proposal will reduce the estimated uncertainty in the age estimates to 5%).
The Extragalactic Distance Scale (H(sub o)) Key Project for Hubble Space Telescope (HST) aims to employ the Cepheid period-luminosity (P-L) relation to measure galaxy distances out as far as the Virgo Cluster. The vital steps in this program are (1) to obtain precise photometry of stellar images from the Wide Field Camera (WFC) exposures of selected galaxies, and (2) to calibrate this photometry to obtain reliable distances to these galaxies from the Cepheid P-L relation. We have used the DAOPHOT II and ALLFRAME programs to determine 28 instrumental magnitudes -- 22 of F555W (of about V) and six of F785LP (of about I) -- of all stars brighter than V of about 25 in each of two 2.56 arcmin x 2.56 arcmin WFC fields of M81. The reductions use a varying point-spread function to account for the field effects in the WFC optics and yield instrumental magnitudes with single epoch precision ranging from 0.09 to 0.24 mag, at V of about 21.8 to 23.8 -- the magnitude range of the 30 Cepheids that we have now identified in M81. For brighter stars (V of about 22), single epoch magnitudes are precise to 0.09 mag. The photometric calibration onto the Johnson V and Kron-Cousins I systems was determined from independent ground-based CCD observing at the Canada-France-Hawaii Telescope (CFHT) 3.6 m (confirmed by the Kitt Peak National Observatory (KPNO) 4.0 m) and from the Palomar 5.0 m (using the wide-field COSMIC camera) and 1.5 m telescopes. Secondary standards, taken from the COSMIC and CFHT frames, were established in each of the WFC fields in V and I, allowing a direct transformation from ALLFRAME magnitudes to calibrated V and I magnitudes, giving mean V of about 23 magnitudes accurate to of about +/- 0.1 mag. The stellar populations in M81 have been analyzed in terms of the luminosity functions and color magnitude diagrams (CMD) derived from these data, from which we identify numerous supergiants, and a CMD morphology similar to M33.
Mean mass effects on accuracy of planetary nebulae distance scales
We report the unambiguous detection of individually resolved stars in the elliptical galaxy NGC 3379, a luminous member of the Leo I Group.
This paper presents initial observations, including the discovery of 30 Cepheids in the nearby galaxy M81, made using the Wide Field Camera (WFC).
This is one of the galaxies being observed as part of the Hubble Space Telescope (HST) Key Project on the Extragalactic Distance Scale which aims to determine the Hubble Constant to 10% accuracy.