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

Journal
Date Issued
2017
Author(s)
Brown, T. M.
•
Taylor, J. M.
•
•
Sweigart, A. V.
•
Bellini, A.
•
•
Salaris, M.
•
Renzini, A.
•
DOI
Abstract
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.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-14759.

Volume
851
Issue
2
Start page
118
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2017ApJ...851..118B
Rights
open.access
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