University Hassan II, Faculty of Sciences , Ain chock
32, Ain chifa 01, Rue 04, Casablanca, Maroc
Sure
20550
Casablanca, Morroco
Presentation 1 : Short Talk
the Cepheid variables and how to use them as distance indicators by calibration of supernovae type 1a?
Balar Khalid
Abstract. In The Workshop. I will focus on the variable stars, specially “pulsating variables” and I will concentrate on one important class of pulsating stars it’s called Cepheid variable.
I am not concerned with why the stars pulsate but rather how they are used as distance indicators, because Cepheids are the best “Standard candles” on extragalactic distance scales also they are bright and easily identified, and most importantly. So the best method of determine the distance to a galaxy is by finding a Cepheid in the galaxy and applying the period-luminosity relation ship. We will know also where did this period-luminosity come from? By using the Fitting method (Chi-square method),and also by calibration of the supernovae type 1a.
Although the Cepheid variables continue to be powerful indicators of the cosmic distance scale, astronomers now tend to believe that the Cepheid in one galaxy may not be physically identical with those of the same period in another galaxy . the slope of the P-L relation may be different from one galaxy to the next, depending upon the relative abudances of the elements in each . the slopes of the P-L relations for the two populations of stars may not be the same. ( the P-L relation are not identical at all wavelengths).
From a general consideration of Stefan’s law connecting luminosity L, radius R, and effective temperature Te, and of Ritter’s equation between the pulsation period P and the mean density ń, one derives that P = f (L, M, Te).finally By applying the Theoretical P-L and P-L-C relations to available BVK data of Cepheids in the Magellanic Clouds, I eventually obtain Z=0.004, and true distance modulus DM= 19.16 for the SMC; and Z=0.008, and DM= 18.46 for the LMC.