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UNDERSTANDING THE UNUSUAL X-RAY EMISSION PROPERTIES OF THE MASSIVE, CLOSE BINARY WR 20a: A HIGH ENERGY WINDOW INTO THE STELLAR WIND INITIATION REGION

Abstract

The problem of explaining the X-ray emission properties of the massive, close binary WR 20a is discussed. Located near the cluster core of Westerlund 2, WR 20a is composed of two nearly identical Wolf-Rayet stars of 82 and 83 solar masses orbiting with a period of only 3.7 days. Although Chandra observations were taken during the secondary optical eclipse, the X-ray light curve shows no signs of a flux decrement. In fact, WR 20a appears slightly more X-ray luminous and softer during the optical eclipse, opposite to what has been observed in other binary systems. To aid in our interpretation of the data, we compare with the results of hydrodynamical simulations using the adaptive mesh refinement code Mezcal which includes radiative cooling and a radiative acceleration force term. It is shown that the X-ray emission can be successfully explained in models where the wind-wind collision interface in this system occurs while the outflowing material is still being accelerated. Consequently, WR 20a serves as a critical test-case for how radiatively driven stellar winds are initiated and how they interact. Our models not only procure a robust description of current Chandra data, which cover the orbital phases between 0.3 and 0.6, but  More>>
Authors:
Montes, Gabriela; Ramirez-Ruiz, Enrico; De Colle, Fabio; Strickler, Rachel [1] 
  1. Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)
Publication Date:
Nov 10, 2013
Product Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 777; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; DIAGRAMS; ECLIPSE; HYDRODYNAMICS; MASS; ORBITS; RADIATIVE COOLING; STELLAR WINDS; VISIBLE RADIATION; WOLF-RAYET STARS; X RADIATION
OSTI ID:
22270585
Country of Origin:
United States
Language:
English
Other Identifying Numbers:
Journal ID: ISSN 0004-637X; CODEN: ASJOAB; TRN: US13I0743091818
Availability:
Available from http://dx.doi.org/10.1088/0004-637X/777/2/129
Submitting Site:
USN
Size:
[6 page(s)]
Announcement Date:
Oct 23, 2014

Citation Formats

Montes, Gabriela, Ramirez-Ruiz, Enrico, De Colle, Fabio, and Strickler, Rachel. UNDERSTANDING THE UNUSUAL X-RAY EMISSION PROPERTIES OF THE MASSIVE, CLOSE BINARY WR 20a: A HIGH ENERGY WINDOW INTO THE STELLAR WIND INITIATION REGION. United States: N. p., 2013. Web. doi:10.1088/0004-637X/777/2/129.
Montes, Gabriela, Ramirez-Ruiz, Enrico, De Colle, Fabio, & Strickler, Rachel. UNDERSTANDING THE UNUSUAL X-RAY EMISSION PROPERTIES OF THE MASSIVE, CLOSE BINARY WR 20a: A HIGH ENERGY WINDOW INTO THE STELLAR WIND INITIATION REGION. United States. doi:10.1088/0004-637X/777/2/129.
Montes, Gabriela, Ramirez-Ruiz, Enrico, De Colle, Fabio, and Strickler, Rachel. 2013. "UNDERSTANDING THE UNUSUAL X-RAY EMISSION PROPERTIES OF THE MASSIVE, CLOSE BINARY WR 20a: A HIGH ENERGY WINDOW INTO THE STELLAR WIND INITIATION REGION." United States. doi:10.1088/0004-637X/777/2/129. https://www.osti.gov/servlets/purl/10.1088/0004-637X/777/2/129.
@misc{etde_22270585,
title = {UNDERSTANDING THE UNUSUAL X-RAY EMISSION PROPERTIES OF THE MASSIVE, CLOSE BINARY WR 20a: A HIGH ENERGY WINDOW INTO THE STELLAR WIND INITIATION REGION}
author = {Montes, Gabriela, Ramirez-Ruiz, Enrico, De Colle, Fabio, and Strickler, Rachel}
abstractNote = {The problem of explaining the X-ray emission properties of the massive, close binary WR 20a is discussed. Located near the cluster core of Westerlund 2, WR 20a is composed of two nearly identical Wolf-Rayet stars of 82 and 83 solar masses orbiting with a period of only 3.7 days. Although Chandra observations were taken during the secondary optical eclipse, the X-ray light curve shows no signs of a flux decrement. In fact, WR 20a appears slightly more X-ray luminous and softer during the optical eclipse, opposite to what has been observed in other binary systems. To aid in our interpretation of the data, we compare with the results of hydrodynamical simulations using the adaptive mesh refinement code Mezcal which includes radiative cooling and a radiative acceleration force term. It is shown that the X-ray emission can be successfully explained in models where the wind-wind collision interface in this system occurs while the outflowing material is still being accelerated. Consequently, WR 20a serves as a critical test-case for how radiatively driven stellar winds are initiated and how they interact. Our models not only procure a robust description of current Chandra data, which cover the orbital phases between 0.3 and 0.6, but also provide detailed predictions over the entire orbit.}
doi = {10.1088/0004-637X/777/2/129}
journal = {Astrophysical Journal}
issue = {2}
volume = {777}
journal type = {AC}
place = {United States}
year = {2013}
month = {Nov}
}