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

Abstract

In the color-magnitude diagrams (CMDs) of globular clusters, when the locus of stars on the horizontal branch (HB) extends to hot temperatures, discontinuities are observed at colors corresponding to ~12,000 K 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 omega 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.

Accepted for publication in The Astrophysical Journal. 9 pages, 1 table, 10 figures. Figure 2 is shown at low resolution due to file size limits

References in corpus (5)

• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. I. Overview of the Project and Detection of Multiple Stellar Populations
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. IX. The Atlas of Multiple Stellar Populations
• NGC 6441: another indication for a very high helium content in Globular Cluster stars
• The Peculiar Horizontal Branch Morphology of the Galactic Globular Clusters NGC 6388 and NGC 6441: new insights from UV observations
• The State-of-the-Art HST Astro-Photometric Analysis of the core of ωCentauri. III. The Main Sequence's Multiple Populations Galore

Cited by in corpus (5)

• A Plague of Magnetic Spots Among the Hot Stars of Globular Clusters
• Peculiarities in the horizontal branch stars of globular cluster NGC 1851: Discovery of a Blue straggler companion to an EHB star
• HST observations of the globular cluster NGC 6402 (M14) and its peculiar multiple populations
• SHOTGLAS II. MUSE spectroscopy of blue horizontal branch stars in the core of $\omega$ Centauri and NGC 6752
• Mapping Milky Way Halo Substructure using Stars in the Extended Blue Tail of the Horizontal Branch