
Stephen Zepf
Professor of Astronomy and Physics Michigan State University
- East Lansing MI
Stephen Zepf's research is focused the areas of black holes, neutron stars in globular clusters, and globular clusters
Biography
Industry Expertise
Areas of Expertise
Education
Johns Hopkins University
Ph.D.
Physics,
1992
Johns Hopkins University
M.A.
Physics
1987
University of Notre Dame
B.S.
Physics
1985
Affiliations
- SOAR Telescope: Board of Directors
Journal Articles
Testing the Universality of the Stellar IMF with Chandra and HST
The Astrophysical Journal2017
The stellar initial mass function (IMF), which is often assumed to be universal across unresolved stellar populations, has recently been suggested to be" bottom-heavy" for massive ellipticals. In these galaxies, the prevalence of gravity-sensitive absorption lines (eg, Na i and Ca ii) in their near-IR spectra implies an excess of low-mass ($ m\lesssim 0.5$${M} _ {\odot} $) stars over that expected from a canonical IMF observed in low-mass ellipticals.
The X-ray luminosity function of low mass X-ray binaries in early-type galaxies, their metal-rich, and metal-poor globular clusters
The Astrophysical Journal2016
We present the X-ray luminosity function (XLF) of low-mass X-ray binaries (LMXBs) in the globular clusters (GCs) and fields of seven early-type galaxies. These galaxies are selected to have both deep Chandra observations, which allow their LMXB populations to be observed to X-ray luminosities of 10 37–10 38 erg s− 1, and Hubble Space Telescope optical mosaics that enable the X-ray sources to be separated into field LMXBs, GC LMXBs, and contaminating background and foreground sources.
Kinematical fingerprints of star cluster early dynamical evolution
Monthly Notices of the Royal Astronomical Society: Letters20154
We study the effects of the external tidal field on the violent relaxation phase of star clusters dynamical evolution, with particular attention to the kinematical properties of the equilibrium configurations emerging at the end of this phase. We show that star clusters undergoing the process of violent relaxation in the tidal field of their host galaxy can acquire significant internal differential rotation and are characterized by a distinctive radial variation of the velocity anisotropy.