منابع مشابه
The extra-galactic Cepheid distance scale from LMC and Galactic period-luminosity relations
In this paper, we recalibrate the Cepheid distance to some nearby galaxies observed by the HST Key Project and the Sandage-Tammann-Saha group. We use much of the Key Project methodology in our analysis but apply new techniques, based on Fourier methods to estimate the mean of a sparsely sampled Cepheid light curve, to published extra-galactic Cepheid data. We also apply different calibrating PL...
متن کاملAccurate Extra-Galactic Distances and Dark Energy: Anchoring the Distance Scale with Rotational Parallaxes
We investigate how the current and future uncertainty on the Hubble constant affects the uncertainty in the Equation of State (EOS) of Dark Energy (DE). We start with the approximate linear relations between the cosmological parameters as presented by (Spergel et al. 2006), and use the standard error-propagation relations to estimate the effects of improving the Cosmic Microwave Background (CMB...
متن کاملDiffuse gamma-ray emission: Galactic and extra- galactic
Here is reviewed our current understanding of Galactic and extragalactic diffuse γ-ray emission. The spectrum of the extragalactic γ-ray background above 30 MeV can be well described by a power law with photon index α=2.1. In the 2-10 MeV range a preliminary analysis of COMPTEL data indicates a lower intensity than previously found, with no evidence for an MeV bump. Most of the models of a trul...
متن کاملGalactic HI on the 50-AU scale in the direction of three extra-galactic sources observed with MERLIN
We present MERLIN observations of Galactic 21-cm H i absorption at an angular resolution of ∼ 0.1 − 0.2 arcsec and a velocity resolution of 0.5 km s, in the direction of three moderately low latitude (–8◦ < b < –12◦) extragalactic radio sources, 3C 111, 3C 123 and 3C 161, all of which are heavily reddened. H i absorption is observed against resolved background emission sources up to ∼ 2 arcsec ...
متن کاملObservational Prospects for Extra-galactic Microlensing Events
We consider the feasibility of directly observing gravitational microlensing in extra-galactic sources, whose stars are not generally resolved. This precludes use of the simple optical depth to microlensing formulation, which is applicable only to resolved stars. We, instead, extend this method to consider observational constraints, such as seeing, sky background and minimum detectable change i...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
ژورنال
عنوان ژورنال: Nature
سال: 1970
ISSN: 0028-0836,1476-4687
DOI: 10.1038/225503a0