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

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Biography

Stephen Zepf is currently Professor and Associate Chair for Astronomy in the Dept. of Physics and Astronomy at Michigan State University. He is also a member of the Board of Directors of the SOAR Telescope and recently served as President of the Board. Among recent awards, He received a University Distinguished Faculty Award in 2013, a MSU College of Natural Science Award Faculty Mentoring Award in 2014, and a Department of Physics and Astronomy Osgood Teaching Award in 2015. Earlier he was on the National Academy Panel on the Galactic Neighborhood as part of the 2010 Decadal Survey for US Astronomy and Astrophysics and served as director of the Center for the Study of Cosmic Evolution at Michigan State for five years. Before coming to MSU, He was at Yale University for four years as Asst. Professor and Director of Graduate Studies in the Astronomy Dept. He was a Hubble Fellow at UC Berkeley and a postdoctoral fellow at Durham in the UK, and I received my PhD at Johns Hopkins University.

Industry Expertise

Writing and Editing

Education/Learning

Research

Areas of Expertise

Globular Clusters

Black Holes

Intergalactic Astronomy

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 Journal

2017
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 Journal

2016
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: Letters

20154
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.