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Ultraviolet Spectropolarimetry: on the Origin of Rapidly Rotating B StarsUV spectroscopy and spectropolarimetry hold the key to understanding certain aspects of massive stars that are largely inaccessible (or exceptionally difficult) with optical or longer wavelength observations. As we demonstrate, this is especially true for the rapidly-rotating Be and Bn stars, owing to their high temperatures, geometric asymmetries, binary properties, evolutionary history, as well as mass ejection and disks (in the case of Be stars). UV spectropolarimetric observations are extremely sensitive to the photospheric consequences of rapid rotation (i.e. oblateness, temperature, and surface gravity gradients), far beyond the reach of optical wavelengths. Our polarized radiative-transfer modelling predicts that with low-resolution UV spectropolarimetry covering 120–300 nm, and with a reasonable SNR, the inclination angle of a rapid rotator can be determined to within 5 degrees, and the rotation rate to within 1%. The origin of rapid rotation in Be/n stars can be explained by either single-star or binary evolution, but their relative importance is largely unknown. Some Be stars have hot sub-luminous (sdO) companions, which at an earlier phase transferred their envelope (and with it mass and angular momentum) to the present-day rapid rotator. Although sdO stars are small and relatively faint, their flux peaks in the UV making this the optimal observational wavelength regime. Through spectral modelling of a wide range of simulated Be/n+sdO configurations, we demonstrate that high-resolution high-signal-to-noise ratio UV spectroscopy can detect an sdO star even when ∼1,000 times fainter in the UV than its Be/n star companion. This degree of sensitivity is needed to more fully explore the parameter space of Be/n+sdO binaries, which so far has been limited to about a dozen systems with relatively luminous sdO stars. We suggest that a UV spectropolarimetric survey of Be/n stars is the next step forward in understanding this population. Such a dataset would, when combined with population synthesis models, allow for the determination of the relative importance of the possible evolutionary pathways traversed by these stars, which is also crucial for understanding their future evolution and fate.
Document ID
20230006136
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
C.E. Jones ORCID
(Western University London, Ontario, Canada)
J. Labadie-Bartz
(University of Oklahoma Norman, Oklahoma, United States)
D.V. Cotton
(Monterey Institute for Research in Astronomy Marina, California, United States)
Y. Nazé
(University of Liège Liège, Belgium)
G.J. Peters
(University of Southern California Los Angeles, California, United States)
D.J. Hillier
(University of Pittsburgh Pittsburgh, Pennsylvania, United States)
C. Neiner
(Laboratory of Space Studies and Instrumentation in Astrophysics Meudon, France)
N.D. Richardson
(Embry–Riddle Aeronautical University Daytona Beach, Florida, United States)
J.L. Hoffman
(University of Denver Denver, Colorado, United States)
A.C. Carciofi
(Universidade de São Paulo São Paulo, Brazil)
J.P. Wisniewski
(University of Oklahoma Norman, Oklahoma, United States)
K.G. Gayley
(University of Iowa Iowa City, Iowa, United States)
M.W. Suffak
(Western University London, Ontario, Canada)
R. Ignace
(East Tennessee State University Johnson City, Tennessee, United States)
P.A. Scowen
(Goddard Space Flight Center Greenbelt, Maryland, United States)
Date Acquired
April 20, 2023
Publication Date
December 14, 2022
Publication Information
Publication: Astrophysics and Space Science
Publisher: Springer
Volume: 367
Issue: 12
Issue Publication Date: December 1, 2022
ISSN: 0004-640X
e-ISSN: 1572-946X
Subject Category
Astrophysics
Space Sciences (General)
Funding Number(s)
WBS: 981698.01.03.51.02.07.05
CONTRACT_GRANT: NSF AST-1816944
CONTRACT_GRANT: FAPESP 2017/23731-1
CONTRACT_GRANT: 80NSSC18K0919
CONTRACT_GRANT: STScI HST-GO15659.002
CONTRACT_GRANT: STScI HST-GO-15869.001
CONTRACT_GRANT: STScI HST-AR-16131.001-A
CONTRACT_GRANT: CNPq 311446/2019-1
CONTRACT_GRANT: FAPESP 2018/04055-8
CONTRACT_GRANT: FAPESP 2019/13354-1
CONTRACT_GRANT: NSF AST-2009412
Distribution Limits
Public
Copyright
Portions of document may include copyright protected material.
Technical Review
External Peer Committee
Keywords
Ultraviolet astronomy
Ultraviolet telescopes
Space telescopes
Circumstellar disks
Early-type emission stars
Be stars
Gamma Cassiopeiae stars
· O subdwarf stars
Multiple star evolution
Stellar rotation
Spectropolarimetry
Polarimeters
Instruments: Polstar
UV spectropolarimetry
NASA: MIDEX
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