Abstract
We present an XMM-Newton observation of the eclipsing binary Algol which contains an X-ray dark B8V primary and an X-ray bright K2IV secondary. The observation covered the optical secondary eclipse and captured an X-ray flare that was eclipsed by the B star. The XMM-Newton European Photon Imaging Camera and Reflection Grating Spectrometer spectra of Algol in its quiescent state are described by a two-temperature plasma model. The cool component has a temperature around 6.4 × 106K while that of the hot component ranges from 2 to 4.0 × 107K. Coronal abundances of C, N, O, Ne, Mg, Si and Fe were obtained for each component for both the quiescent and the flare phases, generally with upper limits for S and Ar, and upper limits for C, N, and O from the hot component. F-tests show that the abundances do not need to be different between the cool and the hot component and between the quiescent and the flare phase with the exception of Fe. Although the Fe abundance of the cool component remains constant at ∼0.14, the hot component shows an Fe abundance of ∼0.28, which increases to ∼0.44 during the flare. This increase is expected from the chromospheric evaporation model. The absorbing column density NH of the quiescent emission is 2.5 × 1020cm−2, while that of the flare-only emission is significantly lower and consistent with the column density of the interstellar medium. This observation substantiates earlier suggestions of the presence of X-ray absorbing material in the Algol system.
Highlights
Algol (β Per) is a nearby eclipsing binary with an early main-sequence (B8V) primary and a cool subgiant (K2IV) secondary
In this paper we present a time resolved spectroscopy of Algol, using XMM- Newton European Photon Imaging Camera (EPIC) and Reflection Grating Spectrometer (RGS) observations of Algol
Whereas the Fe abundance of the cool component stays at ∼0.14, the best fit for the Fe abundance of the hot component is at ∼0.44, which means an increase by a factor of ∼1.6 between the quiescent and the flare phase
Summary
Algol (β Per) is a nearby eclipsing binary with an early main-sequence (B8V) primary and a cool subgiant (K2IV) secondary. That flares have different elemental abundances has been concluded from previous missions, such as GINGA (Stern et al 1992), ROSAT (Ottmann & Schmitt 1996), BeppoSAX (Favata & Schmitt 1999), Chandra Nordon & Behar 2007 and XMM-Newton Nordon & Behar 2008 They suggest that the elemental abundances of Algol’s flaring region resemble more the photospheric than the quiescent coronal abundances, which might be a consequence of chromospheric evaporation (Gudel et al 1999; Favata & Micela 2003 and references therein). Compared with the instruments used in earlier studies the EPIC cameras are the first ones to have a combination of moderate spectral resolution, wide energy coverage, and high sensitivity, while RGS provides us with unparalleled sensitivity for high resolution spectroscopy in the soft X-ray band These advantages permit us to perform a more detailed diagnosis of the plasma properties and their evolution as far as the corona of the K type secondary is concerned.
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