Harvard continues legacy of Cepheid discoveries

Cepheids are important to astronomers for their key role as extragalactic distance indicators. Cepheids are variable stars that regularly brighten and dim as they pulsate rhythmically. Their pulsation period is proportional to their intrinsic brightness – the longer the period, the brighter the star. A comparison of intrinsic to apparent brightness yields the distance to the Cepheid. Ninety years ago, Harvard astronomer Henrietta Leavitt spent years painstakingly examining thousands of sky photographs to search for and study variable stars, which led to the discovery of the period-luminosity relationship for Cepheid variables. Today, another astronomer at what has become the Harvard-Smithsonian Center for Astrophysics is continuing Leavitt’s pioneering work on Cepheids. Smithsonian astrophysicist Nancy Remage Evans and colleagues used the unique capabilities of NASA’s Hubble Space Telescope to study Cepheids in known binary systems. Their goal was to find the masses of the Cepheids – a fundamental stellar property. Instead, they announced in May 2003 at the 202nd meeting of the American Astronomical Society that they have uncovered a hidden, third star in the Cepheid system Y Carinae. More surprisingly, of the 14 total star systems with the most complete orbital information, seven were found to be likely triple systems, a remarkably high percentage.