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Hipparcos Mira Variable Stars

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Hipparcos Mira Variable Stars

ABSTRACT

From the visual and infrared light curves we are trying to find the phase changes and correlate them to Infrared shift and magutdes to see what is happing to Mira type stars as they age. Most of the radiation in the star is in the Infrared. The method being used O-C and fitting mean light curves. All mira variables pulsate undergoing rapid mass loss. In the conclusion we show that the magnitude has a positive correlation with the phase shift.

I.Introduction

Studies of Mira variables are of considerable importance in stellar astrophysics because they are pulsating stars undergoing rapid mass loss. During one cycle, which typically lasts from 200-500 days, these stars undergo significant changes in their observable properties. At some point in their lives, many if not most stars go through an unstable phase that leads to pulsation. They are evolving through the tip of the asymptotic giant branch (AGB) in the H-R diagram and are affected by two significant processes. In the interior, helium shell flashes cause large excursions in their luminosity’s and period on a timesscale of ten of thousands of years. In the outer layers, pulsation-enhanced mass loss, which reduces their envelope masses and drives their evolution to the white dwarf. The atmospheres of Mira variables are very deep and there effective diameters change markedly with wavelength because of the opacity effects. The massive

winds of Miras are believed to be driven by a combination of dust formation and shocks induced by stellar pulsation. (Willson). Understanding the nature of shocks and measuring their properties is essential to understanding the physics of pulsation and mass loss from pulsating stars.

This paper presents an analysis of visible and IR (JHKL) data for 2 Long Period Variables (LPV). The four pulsating variables chosen are classified as Miras. All Miras stars are Long period variables that exhibit a very large change in visible light because they are cool (less than or equal to 3000K), and so most of their radiation lies in the infrared. We are studying the Mira stars instead the irregular stars because to understand any star you must first start with the simplest model then expand upon that, Mira are relatively well-behaved long period variable.

II. Data Search

For this study we required stars that had already been studied intensively, so that both IR data and visual data were available for many cycles.
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