Interstellar oxygen along the line of sight of Cygnus X-2

I. Psaradaki*, E. Costantini, M. Mehdipour, D. Rogantini, C. P. De Vries, F. De Groot, H. Mutschke, S. Trasobares, L. B.F.M. Waters, S. T. Zeegers

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

Interstellar dust permeates our Galaxy and plays an important role in many physical processes in the diffuse and dense regions of the interstellar medium (ISM). High-resolution X-ray spectroscopy, coupled with modelling based on laboratory dust measurements, provides a unique probe for investigating the interstellar dust properties along our line of sight towards Galactic X-ray sources. Here, we focus on the oxygen content of the ISM through its absorption features in the X-ray spectra. To model the dust features, we perform a laboratory experiment using the electron microscope facility located at the University of Cadiz in Spain, where we acquire new laboratory data in the oxygen K-edge. We study 18 dust samples of silicates and oxides with different chemical compositions. The laboratory measurements are adopted for our astronomical data analysis. We carry out a case study on the X-ray spectrum of the bright low-mass X-ray binary Cygnus X-2, observed by XMM-Newton. We determine different temperature phases of the ISM and parameterise oxygen in both gas (neutral and ionised) and dust form. We find Solar abundances of oxygen along the line of sight towards the source. Due to both the relatively low depletion of oxygen into dust form and the shape of the oxygen cross section profiles, it is challenging to determine the precise chemistry of interstellar dust. However, silicates provide an acceptable fit. Finally, we discuss the systematic discrepancies in the atomic (gaseous phase) data of the oxygen edge spectral region using different X-ray atomic databases as well as consider future prospects for studying the ISM with the Arcus concept mission.

Original languageEnglish
Article numberA208
JournalAstronomy and Astrophysics
Volume642
DOIs
Publication statusPublished - 1 Oct 2020

Bibliographical note

Funding Information:
Acknowledgements. We would like to thank our referee J. Nuth for the useful suggestions. I.P., M.M., D.R. and E.C. are supported by the Netherlands Organisation for Scientific Research (NWO) through The Innovational Research Incentives Scheme Vidi grant 639.042.525. The Space Research Organization of the Netherlands is supported financially by the NWO. The authors would like to thank E. Gatuzz for providing the cross section calculations of the atomic oxygen implemented into XSTAR, J. Garcia for valuable suggestions on atomic data and J. Wilms, R. Smith for useful information about Arcus. We thank J. de Plaa for helping with the musr model in SPEX and J. Kaastra for general instructions regarding SPEX. We also thank M. Diaz Trigo for useful information regarding Cygnus X-2.

Publisher Copyright:
© 2020 ESO.

Funding

Acknowledgements. We would like to thank our referee J. Nuth for the useful suggestions. I.P., M.M., D.R. and E.C. are supported by the Netherlands Organisation for Scientific Research (NWO) through The Innovational Research Incentives Scheme Vidi grant 639.042.525. The Space Research Organization of the Netherlands is supported financially by the NWO. The authors would like to thank E. Gatuzz for providing the cross section calculations of the atomic oxygen implemented into XSTAR, J. Garcia for valuable suggestions on atomic data and J. Wilms, R. Smith for useful information about Arcus. We thank J. de Plaa for helping with the musr model in SPEX and J. Kaastra for general instructions regarding SPEX. We also thank M. Diaz Trigo for useful information regarding Cygnus X-2.

Keywords

  • Astrochemistry
  • Dust, extinction
  • X-rays: binaries
  • X-rays: individuals: Cygnus X-2
  • X-rays: ISM

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