From the Heart of the Ghoul: C and N Abundances in the Corona of Algol B

Abstract

Chandra Low Energy Transmission Grating Spectrograph observations of Algol have been used to determine the abundances of C and N in the secondary star for the first time. In order to minimize errors arising from an uncertain coronal differential emission measure as a function of temperature, the analysis was performed relative to similar observations of an adopted '' standard '' star, HR 1099. It is demonstrated that HR 1099 and Algol are coronal twins in many respects and that their X-ray spectra are very similar in nearly all details, except for the observed strengths of C and N lines. The H-like 2p 2 P 3=2;1=2 ! 1s 2 S 1=2 transitions of C and N in the coronae of Algol and HR 1099 demonstrate that the surface abundances of Algol B have been strongly modified by CN processing, as shown earlier by Schmitt & Ness. It is found that N is enhanced in Algol B by a factor of 3 compared with HR 1099. No C lines are detected in the Algol spectrum, indicating a C depletion relative to HR 1099 by a factor of 10 or more. These C and N abundances indicate that Algol B must have lost at least half of its initial mass and are consistent with predictions of evolutionary models that include nonconservative mass transfer and angular momentum loss through magnetic activity. Based on Hlike and He-like transitions in O and Ne, it is estimated that Algol is slightly metal poor, by 0.2 dex in terms of the coronal abundances of light elements relative to HR 1099, while the Fe xvii 2p 5 3d 1 P 1 ! 2p 6 1 S 0 transition indicates a very similar Fe abundance. In reviewing coronal abundance results for active stars in the literature and drawing on an earlier Chandra study of the coronal abundances of HR 1099, it is concluded that Fe is very likely depleted in the coronae of both Algol and HR 1099 by 0.5 dex relative to their photospheric compositions, but that Ne is enhanced by a similar magnitude. Light elements such as C, N, and O are likely depleted in both stars by of order 0.3 dex. The similarities in these large-abundance anomalies in HR 1099 and Algol are notable. Despite such compositional fractionation in these coronae, the relative C and N abundances in HR 1099, determined by comparing observed line strengths with theoretical C/N line ratios, are consistent with recent solar values, indicating that differential fractionation between these elements is not significant and that little or no dredge-up of material subjected to CN processing has occurred on the subgiant component.

The Coronae of AB Doradus and V471 Tauri: Primordial Angular Momentum versus Tidal Spin‐up

“…Circumstantial evidence against such an explanation can be found in the abundance analysis of the active RS CVn-type binary HR 1099, for which independent analyses of Chandra and XMM-Newton observations obtained at different times yielded very similar values for quiescent coronal abundances (Brinkman et al 2001;Drake et al 2001). Moreover, Drake (2003b) has found similar abundances in the coronae of HR 1099 and its ''coronal twin,'' the active late-type component of the Algol binary.…”

“…For a value of ¼ 2:4, it has been found that this function represents the Chandra transmission grating instrumental profile to within photon counting statistics for lines with a few thousand counts or less (Drake 2003c). Spectra line fitting was undertaken using the FITLINES utility in the PINTofALE spectral analysis package (Kashyap & Drake 2000).…”

“…There were three modest flare events during the ASCA observation that were not filtered from the analysis of Still & Hussain (2003). It appears likely that in some flares on active stars the abundances of low-FIP elements are enhanced toward their pristine photospheric values, a result tentatively interpreted as chromospheric evaporation (e.g., reviews of Audard et al 2003;Drake 2003a). Flares, then, might temporarily raise the abundances of the dominant plasma at a given time, although the ASCA flares were rather small for this to present an immediately convincing explanation.…”

“…Drake (2003b) presented a differential analysis of the active binaries Algol and HR 1099-two binary systems whose coronally dominant components are of very similar spectral type and rotation period, but which have had quite different evolutionary histories-and found strong similarities in their quiescent X-ray spectra and coronal abundances.…”

Coronal abundances from high-resolution X-ray data: The case of Algol

“…Here we focus on the determination of the differential emission measure distribution and elemental abundances; for a comparison of the coronal spectra of HR1099 and Algol B we refer to Drake (2003).…”