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Abstract: The flux excess of elliptical galaxies in the far-ultraviolet can bereproduced by population synthesis models when accounting for the population ofold hot helium-burning subdwarf stars. This has been achieved by Han andcoworkers through a quantitative model of binary stellar evolution. Here, wecompare the resulting evolutionary population synthesis model to the GALEXfar-near ultraviolet colors FUV-NUV of Virgo cluster early-type galaxies thatwere published by Boselli and coworkers. FUV-NUV is reddest at about thedividing luminosity of dwarf and giant galaxies, and becomes increasingly bluefor both brighter and fainter luminosities. This behavior can be easilyexplained by the binary model with a continuous sequence of longer duration andlater truncation of star formation at lower galaxy masses. Thus, in contrast toprevious conclusions, the GALEX data do not require a dichotomy between thestellar population properties of dwarfs and giants. Their apparently oppositebehavior in FUV-NUV occurs naturally when the formation of hot subdwarfsthrough binary evolution is taken into account.

Autor: Thorsten Lisker 1, Zhanwen Han 2 1 ARI-Zentrum fuer Astronomie, University of Heidelberg, 2 National Astronomical Observatories -


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