A Future of Cepeheid Variable Stars OR

A Future of Cepeheid Variable Stars OR

A Future of Cepeheid Variable Stars

Cepeheid stars are variable stars in the Cepheid variable family. They are important because they are the brightest stars of their spectral type in the sky.


Classical Cepheids exhibit a relation between period and luminosity in the sense that the longer the period of the star, the greater its intrinsic brightness; this period-luminosity relationship has been used to establish the distance of remote stellar systems. The absolute magnitude of a classical Cepheid can be estimated from its period. Once this is known, the distance of the star can be deduced from a comparison of absolute and apparent (measured) magnitudes. Population II Cepheids likewise obey a period-luminosity relationship, but it is different from that of the classical Cepheids. Since Population II Cepheids are less luminous than classical Cepheids, they are less useful as distance indicators.

www.sdss.org)So in 1908 when Leavitt discovered a relationship between the brightness (or “luminosity”) of a Cepheid variable star and the time it took to go through a full cycle of change (its “period”), her work was not immediately recognized for its significance. It took years for the mostly-male astronomy community to realize that this relationship (today known as “the Leavitt Law”) means that measuring the period of a Cepheid variable immediately gives its true brightness — and furthermore, that comparing this to its apparent brightness immediately gives its distance. (Source:


The very property of these stars that allowed Henrietta Leavitt to discover the Leavitt Law – their predictable variations in brightness — creates challenges for APOGEE. “Over a pulsation cycle of a Cepheid variable, the star’s properties change,” says Beaton. “Its temperature, surface gravity, and atmospheric properties can vary greatly over a fairly short time. So how can APOGEE properly measure them? I thought it would be an excellent summer research project to find out.”

As a result of Hartman’s findings, additional APOGEE observations of Cepheid variables are now well underway. Jen Sobeck of the University of Washington, APOGEE’s Project Manager, explains, “the survey will observe the most nearby and well studied Cepheids with observations several times a month, will target Cepheids in the Large and Small Magellanic Cloud in January, and plans to eventually target all Cepheids in all parts of the sky we observe. These observations are an important addition to the APOGEE map of the galaxy.” (Source: www.sdss.org)



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