The X-ray spectrum ofδOrionis observed by LETGS aboardChandra

Abstract

Aims. We analyze the high-resolution X-ray spectrum of the supergiant O-star δ Orionis (O9.5II) with line ratios of He-like ions and a thermal plasma model, and we examine its variability. Methods. The O-supergiant δ Ori was observed in the wavelength range 5-175 Å by the X-ray detector HRC-S in combination with the grating LETG aboard Chandra. We studied the He-like ions in combination with the UV-radiation field to determine local plasma temperatures and to establish the distance of the X-ray emitting ions to the stellar surface. We measured individual lines by means of Gaussian profiles, folded through the response matrix, to obtain wavelengths, line fluxes, half widths at half maximum (HWHM) and line shifts to characterize the plasma. We consider multitemperature models in collisional ionization equilibrium (CIE) to determine temperatures, emission measures, and abundances.Results. Analysis of the He-like triplets extended to N vi and C v implies ionization stratification with the hottest plasma to be found within a few stellar radii 3 R * (Mg xi) and the coolest farther out, far beyond the acceleration zone, up to 49 R * (N vi) and 75 R * (C v).The observed temperatures cover a range from about 0.1 to 0.7 keV, i.e., 1-8 MK. The X-ray luminosity (L x ) is ∼1.5 × 10 32 erg/s in the range from 0.07 to 3 keV covered by LETGS. Velocity widths of about 1040 km s −1 have been determined.

A COORDINATED X-RAY AND OPTICAL CAMPAIGN OF THE NEAREST MASSIVE ECLIPSING BINARY,δORIONIS Aa. I. OVERVIEW OF THE X-RAY SPECTRUM

“…2. The temperature distribution of the X-ray emitting gas can be characterized by three dominant temperatures, which agrees fairly well with the temperature distributions derived by the earlier analysis of Miller et al (2002) and Raassen & Pollock (2013).…”

“…The derived temperature distribution is similar to that found by Miller et al (2002) in their study of the 2000 January HETGS spectrum, and by Raassen & Pollock (2013) in their analysis of an LETGS spectrum from 2007 November. In general, aside from the overall weakness of the forbidden lines compared to the model spectrum (which assumes a low-density plasma with no UV photoexcitation), the overall distribution of emission line strengths, and the continuum, are described reasonably well by the model.…”

A COORDINATED X-RAY AND OPTICAL CAMPAIGN OF THE NEAREST MASSIVE ECLIPSING BINARY,δORIONIS Aa. II. X-RAY VARIABILITY

“…The 60 ks exposure time covers about 12% of the orbital period. Raassen & Pollock (2013) analyzed a Chandra LETGS observation with exposure time of 96 ks, finding some variability in the zeroth order image; they were not able to detect any variability in the emission lines between two time splits of the observation.…”

Extended Calculations of Spectroscopic Data: Energy Levels, Lifetimes, and Transition Rates for O-like Ions from Cr xvii to Zn xxiii

“…Most of them targeted atomic data for low-lying states of the (1s 2 )2s 2 2p 4 , 2s2p 5 , and 2p 6 config-urations (the n = 2 complex) (Baluja & Zeippen 1988a,b;Galavis et al 1997;Vilkas et al 1999;Zhang & Sampson 2002;Gu 2005a;Hu et al 2011;Rynkun et al 2013;Fontes & Zhang 2015). Because of their wide applications for analyzing new observations of astrophysical sources, as well as for modeling and diagnosing a variety of plasmas, energy and transition data for higher-lying states of the n ≥ 3 complexes are also eagerly needed (Phillips et al 1982;Acton et al 1985;Landi & Phillips 2005;Kotochigova et al 2007Kotochigova et al , 2010Raassen & Pollock 2013). Among the studies of the n ≥ 3 states of Fe XIX we mention the calculations of Jonauskas et al (2004) using the multiconfiguration Dirac-Hartree-Fock (MCDHF) method, the calculations of Landi & Gu (2006) using the standard relativistic configuration interaction (RCI) method, the AUTOSTRUCTURE calculations of Butler & Badnell (2008), and the relativistic Breit-Pauli calculations of Nahar (2011).…”