Cepheids

Henrietta Leavitt, Harvard College Observatory, 1912, established the relation period-luminosity of Cepheid variable stars. Being a woman i.e. confined to the tedious and ridiculously paid work of examining photographic plates for the benefit of an all-male establishment, she would not be awarded credit for her milestone discovery... 

MIT Lincoln Laboratory Midwest Research Institute Applied Biosystems Navy Research Lab Cepheid... 

Polymerase Chain Reaction (LLNL, Idaho Tech, Cepheid) Combinatorial Peptides (University of Texas)... 

Abstract. We present the results of an observational campaign undertaken to assess the influence of the iron content on the Cepheid Period-Luminosity relation. Our data indicate that this dependence is not well represented by a simple linear relation. Rather, the behaviour is markedly non monotonic, with the correction peaking at about solar metallicity and declining for higher and lower values of [Fe/H]. 

We have determined the iron abundances for a sub-sample of stars 13 Galactic, 13 LMC and 12 SMC Cepheids. Our main result is summarised in the Fig.l, where we plot the V-band residuals 5(My) of our stars from the standard PL relation of [3] as a function of the iron abundance we have derived from the... 

Fig. 1. Result from the subset analysed so far. The data are binned in metallicity to reflect the typical uncertainty on our determination of [Fe/H], marked by horizontal error-bars. The median value of 5(My) in each metallicity bin is plotted as filled squares, with the vertical error-bars representing its associated error. For comparison we also plot the empirical results from [5] in two Cepheid fields in Ml 01 (open circles and solid line) and the theoretical predictions by [2] from non-linear pulsational models (dashed line)...

Figure 9. Cepheid GeneXpert for automated sample preparation and PCR analysis. (www.Cepheid.com March 18, 2004).

The emission of light from Cepheid stars has a characteristic light curve seen in Figure 4.14 for a Cepheid in the constellation of Perseus. The sawtooth pattern is characteristic of the class and enables the period of variation to be determined. The observation, however, that the luminosity and period are related has powerful consequences. The Cepheid variables fall into two classes type I classical Cepheids have periods of 5-10 days and type II have periods of 12-20 days. The two types of Cepheids initially caused problems when determining the luminosity-period relation but the relation has now been determined. Type I Cepheids follow the expression... 

A type II Cepheid variable is observed in the elliptical galaxy M49 in the Virgo cluster of galaxies with a period of 30 days. Calculate the absolute magnitude of this star. If the total flux on the Earth from the star is 4.2 x 10 22 W m-2, estimate the distance to the Virgo cluster. 

Cepheid variable Stars that have a periodic variation in their luminosity with a direct relation between the luminosity and the period. These stars are important distance markers. 

Luck R. E. and Lambert D. L. (1992). The chemical composition of Magellanic Cloud cepheids and nonvariable supergiants. Astrophysical Journal Supplement Series 79 303. 

PN nucleus, horizontal-branch and white-dwarf regions. The dotted line shows a schematic main sequence and evolutionary track for Population II, while various dashed lines show roughly the Cepheid instability strip, the transition to surface convection zones and the helium-shell flashing locus for Population I. After Pagel (1977). Copyright by the IAU. Reproduced with kind permission from Kluwer Academic Publishers. 

E. Hubble uses Cepheid period-luminosity law to demonstrate M31 is an external galaxy comparable to the Milky Way. 

D.A. Kulesh, R.O. Baker, B.M. Loveless, D. Norwood, S.H. Zwiers, E. Mucker, C. Hartmann, R. Herrera, D. Miller, D. Christensen, L.P. Wasieloski Jr., J. Huggins and P.B. Jahrling, Smallpox and pan-orthopox virus detection by real-time 3 -minor groove binder TaqMan assays on the Roche lightcycler and the Cepheid smart cycler platforms, J. Clin. Microbiol., 42 (2004) 601-609. 

Cepheids stars with variable brightness whose period is related to their luminosity... 

By identifying Cepheid variables in the globular clusters which gravitate around our own Galaxy, Harlow Shapley was able to measure their distance. He thus located their common centre and found it to be a considerable distance from us. It was clear that human beings inhabit the neighbourhood of a nondescript star, very far from the centre of the Milky Way. We are not even at the heart of our own stellar republic A second assault was thus made on human vanity, after the eviction of the Earth from the centre of the Universe. 

Edwin Hubble measured the distance of several Cepheids in the great Andromeda nebula and found that it was situated far beyond the globular clusters in the retinue of the Milky Way. It was then that the milky designation galaxy made its entry into astronomy. The age of extragalactic astronomy had... 

Figure 3 The upper part of the HR diagram with evolutionary tracks calculated by Maeder and Meynet (1987). The branch of dots in the red part is the proposed Red Supergiant Branch. Lower to the right (at log Teff 3.4) is the uppermost part of the Asymptotic Giant Branch. The hatched area near log Teff = 3.75 is the upper part of the Cepheid branch. 

The distance to the LMC has been determined by various classical methods. Extensive JHK photometry of Cepheids has yielded a very recent value of 51.8 1.2... 

Since no astronomical standard candle is known - all proposed objects have been shown to be essentially non-uniform in one way or another - we nowadays have to calculate and plot the distance modulus for the objects. The scatter around the linear expansion line is less than 0.2 magnitudes or 20% Tonry et al. 2003. Independent of our ignorance of the exact explosion mechanism or the radiation transport in the explosions this proves that SNe la can reliably be used as a distance indicator in the local universe. This situation is very much comparable to the Cepheid stars, where the period-luminosity relation is based on empirical data of objects in the Magellanic Clouds. 

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