Coordinated UV and X-Ray Spectroscopic Observations of the O-type Giant xi Per
- We present new, contemporaneous Hubble Space Telescope STIS and XMM-Newton observations of the O7. III(n) ((f)) star xi Per. We supplement the new data with archival IUE spectra, to analyze the variability of the wind lines and X-ray flux of xi Per. The variable wind of this star is known to have a 2.086-day periodicity. We use a simple, heuristic spot model that fits the low-velocity (near-surface) IUE wind line variability very well, to demonstrate that the low-velocity absorption in the new STIS spectra of N IV lambda 1718 and Si IV lambda 1402 vary with the same 2.086-day period. It is remarkable that the period and amplitude of the STIS data agree with those of the IUE spectra obtained 22 yr earlier. We also show that the time variability of the new XMM-Newton fluxes is also consistent with the 2.086-day period. Thus, our new, multiwavelength coordinated observations demonstrate that the mechanism that causes the UV wind line variability is also responsible for a significant fraction of the X-rays in single O stars. The sequenceWe present new, contemporaneous Hubble Space Telescope STIS and XMM-Newton observations of the O7. III(n) ((f)) star xi Per. We supplement the new data with archival IUE spectra, to analyze the variability of the wind lines and X-ray flux of xi Per. The variable wind of this star is known to have a 2.086-day periodicity. We use a simple, heuristic spot model that fits the low-velocity (near-surface) IUE wind line variability very well, to demonstrate that the low-velocity absorption in the new STIS spectra of N IV lambda 1718 and Si IV lambda 1402 vary with the same 2.086-day period. It is remarkable that the period and amplitude of the STIS data agree with those of the IUE spectra obtained 22 yr earlier. We also show that the time variability of the new XMM-Newton fluxes is also consistent with the 2.086-day period. Thus, our new, multiwavelength coordinated observations demonstrate that the mechanism that causes the UV wind line variability is also responsible for a significant fraction of the X-rays in single O stars. The sequence of events for the multiwavelength light-curve minima is Si IV lambda 1402, N IV lambda 1718, and X-ray flux, each separated by a phase of about 0.06 relative to the 2.086-day period. Analysis of the X-ray fluxes shows that they become softer as they weaken. This is contrary to expectations if the variability is caused by periodic excess absorption. Furthermore, the high-resolution X-ray spectra suggest that the individual emission lines at maximum are more strongly blueshifted. If we interpret the low-velocity wind line light curves in terms of our model, it implies that there are two bright regions, i.e., regions with less absorption, separated by 180 degrees, on the surface of the star. We note that the presence and persistence of two spots separated by 180 degrees suggest that a weak dipole magnetic field is responsible for the variability of the UV wind line absorption and X-ray flux in xi Per.…
Author details: | Derck MassaORCiD, Lidia M. OskinovaORCiDGND, Raman PrinjaGND, Richard IgnaceORCiD |
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DOI: | https://doi.org/10.3847/1538-4357/ab0283 |
ISSN: | 0004-637X |
ISSN: | 1538-4357 |
Title of parent work (English): | The astrophysical journal : an international review of spectroscopy and astronomical physics |
Subtitle (English): | the Connection between X-Rays and Large-scale Wind Structure |
Publisher: | IOP Publ. Ltd. |
Place of publishing: | Bristol |
Publication type: | Article |
Language: | English |
Date of first publication: | 2019/03/06 |
Publication year: | 2019 |
Release date: | 2021/03/24 |
Tag: | X-rays: stars; stars: activity; stars: early-type; stars: winds, outflows; ultraviolet: stars |
Volume: | 873 |
Issue: | 1 |
Number of pages: | 12 |
Funding institution: | NASA through Space Telescope Science InstituteSpace Telescope Science Institute [HST-GO-14180]; Deutsches Zentrum fur Luft und Raumfahrt (DLR)Helmholtz AssociationGerman Aerospace Centre (DLR) [FKZ 15, OR 1809]; Russian Government Program of Competitive Growth of Kazan Federal University; NASANational Aeronautics & Space Administration (NASA) [NAS5-26555] |
Organizational units: | Mathematisch-Naturwissenschaftliche Fakultät / Institut für Physik und Astronomie |
DDC classification: | 5 Naturwissenschaften und Mathematik / 53 Physik / 530 Physik |
Peer review: | Referiert |
Publishing method: | Open Access / Green Open-Access |