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http://hdl.handle.net/20.500.12386/32217
Title: | New X-ray observations of the hot subdwarf binary HD 49798/RX J0648.0-4418 | Authors: | MEREGHETTI, Sandro Pintore, Fabio Rauch, T. LA PALOMBARA, NICOLA Esposito, P. Geier, S. Pelisoli, I. RIGOSELLI, MICHELA Schaffenroth, V. TIENGO, ANDREA |
Issue Date: | 2021 | Journal: | MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY | Number: | 504 | Issue: | 1 | First Page: | 920 | Abstract: | HD 49798/RX J0648.0-4418 is the only confirmed X-ray binary in which the mass donor is a hot subdwarf star of O spectral type and, most likely, it contains a massive white dwarf (1.28 ± 0.05 M<SUB>⊙</SUB>) with a very fast spin period of 13.2 s. Here, we report the results of new XMM-Newton pointings of this peculiar binary, carried out in 2018 and in 2020, together with a reanalysis of all the previous observations. The new data indicate that the compact object is still spinning-up at a steady rate of (-2.17 ± 0.01) × 10<SUP>-15</SUP> s s<SUP>-1</SUP>, consistent with its interpretation in terms of a young contracting white dwarf. Comparison of observations obtained at similar orbital phases, far from the ecplise, shows evidence for long-term variability of the hard (>0.5 keV) spectral component at a level of ~(70 ± 20) per cent, suggesting the presence of time-dependent inhomogeneities in the weak stellar wind of the HD 49798 subdwarf. To investigate better the soft spectral component that dominates the X-ray flux from this system, we computed a theoretical model for the thermal emission expected from an atmosphere with element abundances and surface gravity appropriate for this massive white dwarf. This model gives a best fit with effective temperature of T<SUB>eff</SUB> = 2.25 × 10<SUP>5 </SUP>K and an emitting area with a radius of ~1600 km, larger than that found with blackbody fits. This model also predicts a contribution of the pulsed emission from the white dwarf in the optical band significantly larger than previously thought and possibly relevant for optical variability studies of this system. | URI: | http://hdl.handle.net/20.500.12386/32217 | URL: | https://academic.oup.com/mnras/article/504/1/920/6219849 | ISSN: | 0035-8711 | DOI: | 10.1093/mnras/stab1004 | Bibcode ADS: | 2021MNRAS.504..920M | Fulltext: | open |
Appears in Collections: | 1.01 Articoli in rivista |
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stab1004.pdf | Pdf editoriale | 891.65 kB | Adobe PDF | View/Open |
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