Ultraviolet Spectropolarimetry: on the origin of rapidly rotating B stars
Article
Article Title | Ultraviolet Spectropolarimetry: on the origin of rapidly rotating B stars |
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ERA Journal ID | 1059 |
Article Category | Article |
Authors | Jones, C.E., Labadie-Bartz, J., Cotton, D.V., Nazé, Y., Peters, G., Hillier, D.J., Neiner, C., Richardson, N.D., Hoffman, J.L., Carciofi, A.C., Wisniewski, J.P., Gayley, K.G., Suffak, M.W., Ignace, R. and Scowen, P.A. |
Journal Title | Astrophysics and Space Science: an international journal of astronomy, astrophysics and space science |
Journal Citation | 367 (12) |
Article Number | 124 |
Number of Pages | 28 |
Year | 2022 |
Publisher | Springer |
Place of Publication | Netherlands |
ISSN | 0004-640X |
1572-946X | |
Digital Object Identifier (DOI) | https://doi.org/10.1007/s10509-022-04127-5 |
Web Address (URL) | https://link.springer.com/article/10.1007/s10509-022-04127-5 |
Abstract | UV 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. |
Keywords | Ultraviolet astronomy; Ultraviolet telescopes; Space telescopes; Circumstellar disks; Early-type emission stars; Be stars; Gamma Cassiopeiae stars; O subdwarf stars; Multiple star evolu; Stellar rotation; Spectropolarimetry; Polarimeters; Instruments: Polstar; UV spectropolarimetry; NASA: MIDEX |
Public Notes | File reproduced in accordance with the copyright policy of the publisher/author. |
Byline Affiliations | Western University, Canada |
University of Oklahoma, United States | |
Monterey Institute for Research in Astronomy, United States | |
Western Sydney University | |
Centre for Astrophysics | |
University of Liege, Belgium | |
University of Southern California, United States | |
University of Pittsburgh, United States | |
Sorbonne University, France | |
Embry-Riddle Aeronautical University, United States | |
University of Denver, United States | |
University of Sao Paulo, Brazil | |
University of Iowa, United States | |
East Tennessee State University, United States | |
National Aeronautics and Space Administration (NASA), United States |
https://research.usq.edu.au/item/z022w/ultraviolet-spectropolarimetry-on-the-origin-of-rapidly-rotating-b-stars
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