HST/STIS Ultraviolet Spectroscopy of the Components of the Massive Triple Star delta Ori A

Abstract

The multiple star system of delta Orionis is one of the closest examples of a system containing a luminous O-type, bright giant star (component Aa1). It is often used as a spectral-type standard and has the highest observed X-ray flux of any hot-star binary. The main component Aa1 is orbited by two lower mass stars, faint Aa2 in a 5.7 day eclipsing binary, and Ab, an astrometric companion with an estimated period of 346 years. Generally the flux from all three stars is recorded in ground-based spectroscopy, and the spectral decomposition of the components has proved difficult. Here we present HST/STIS ultraviolet spectroscopy of delta Ori A that provides us with spatially separated spectra of Aa and Ab for the first time. We measured radial velocities for Aa1 and Ab in two observations made near the velocity extrema of Aa1. We show tentative evidence for the detection of the Aa2 component in cross-correlation functions of the observed and model spectra. We discuss the appearance of the UV spectra of Aa1 and Ab with reference to model spectra. Both stars have similar effective temperatures, but Ab is fainter and is a rapid rotator. The results will help in the interpretation of ground-based spectroscopy and in understanding the physical and evolutionary parameters of these massive stars.

accepted for publication in ApJ, 18 pages, 4 figures, 3 tables

References in corpus (12)

• Accurate masses and radii of normal stars: modern results and applications
• A new calibration of stellar parameters of Galactic O stars
• A Grid of NLTE Line-Blanketed Model Atmospheres of O-type Stars
• A Grid of NLTE Line-Blanketed Model Atmospheres of Early B-type Stars
• The High Angular Resolution Multiplicity of Massive Stars
• The Galactic O-Star Spectroscopic Survey. I. Classification System and Bright Northern Stars in the Blue-Violet at R~2500
• Speckle interferometry at SOAR in 2012 and 2013
• Cross-Correlation and Maximum Likelihood Analysis: A New Approach to Combine Cross-Correlation Functions
• Fundamental Properties of O-Type Stars
• Tomographic Separation of Composite Spectra. VIII. The Physical Properties of the Massive Compact Binary in the Triple Star System HD 36486 (delta Orionis A)
• Young stars and brown dwarfs surrounding Alnilam (eps Ori) and Mintaka (del Ori)
• Calculation of the Masses of the Binary Star HD 93205 by Application of the Theory of the Apsidal Motion

Cited by in corpus (8)

• The MiMeS survey of magnetism in massive stars: Magnetic analysis of the O-type stars
• Variability of OB stars from TESS southern Sectors 1-13 and high-resolution IACOB and OWN spectroscopy
• Orbits, Distance, and Stellar Masses of the Massive Triple Star Sigma Orionis
• Models for Sixty Double-Lined Binaries containing Giants
• A Coordinated X-ray and Optical Campaign of the Nearest Massive Eclipsing Binary, delta Orionis Aa: III. Analysis of Optical Photometric MOST and Spectroscopic (Ground Based) Variations
• Lucky Spectroscopy, an equivalent technique to Lucky Imaging. Spatially resolved spectroscopy of massive close visual binaries using the William Herschel Telescope
• Spectrum of the secondary component and new orbital elements of the massive triple star Delta Ori A
• An X-ray Study of Two B+B Binaries: AH Cep and CW Cep