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A Universal Transition in Atmospheric Diffusion for Hot Subdwarfs Near 18,000 K

Brown, TM, Taylor, JM, Cassisi, S, Sweigart, AV, Bellini, A, Bedin, LR, Salaris, M, Renzini, A and Dalessandro, E (2017) A Universal Transition in Atmospheric Diffusion for Hot Subdwarfs Near 18,000 K. Astrophysical Journal, 851 (2). ISSN 0004-637X

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In the color-magnitude diagrams of globular clusters, when the locus of stars on the horizontal branch extends to hot temperatures, discontinuities are observed at colors corresponding to ∼12,000 and ∼18,000 K. The former is the "Grundahl jump" that is associated with the onset of radiative levitation in the atmospheres of hot subdwarfs. The latter is the "Momany jump" that has remained unexplained. Using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, we have obtained ultraviolet and blue spectroscopy of six hot subdwarfs straddling the Momany jump in the massive globular cluster ω Cen. By comparison to model atmospheres and synthetic spectra, we find that the feature is due primarily to a decrease in atmospheric Fe for stars hotter than the feature, amplified by the temperature dependence of the Fe absorption at these effective temperatures. © 2017. The American Astronomical Society. All rights reserved..

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical And Space Sciences, 0305 Organic Chemistry, 0306 Physical Chemistry (Incl. Structural)
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: American Astronomical Society; IOP Publishing
Date Deposited: 19 Jan 2018 10:36
Last Modified: 07 Oct 2018 00:26
DOI or Identification number: 10.3847/1538-4357/aa9ce3
URI: http://researchonline.ljmu.ac.uk/id/eprint/7878

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