Dr. Todd Hillwig



Assistant Professor
Dept. of Physics and Astronomy
Valparaiso University
Valparaiso, IN 46383


Phone: (219) 464-5370
FAX: (219) 464-5489
E-mail: username - todd.hillwig
domain name - valpo.edu

 

Education:
Indiana University (Bloomington, IN), Ph.D.;
Ball State University (Muncie, IN), M.S.;
Anderson University (Anderson, IN), B.A.

Major field:
Astronomy (Indiana U.);
Physics (Ball State U.);
Physics and Mathematics (Anderson U.)

Teaching specialty: Astronomy, Astronomy Labs; Mechanics; First-Year Physics

Courses on-line:

  

Research activities:

Observational Astronomy; close and interacting binary stars, circumstellar nebulosity (planetary nebulae and nova shells).

Interacting Binary Stars:

SS 433 (or V1343 Aql) is a fascinating interacting binary system. It is currently believed to consist of an A-type supergiant star approximately 27 times the diameter of the Sun and a black hole. The star and black hole orbit one another in just over thirteen days. At this close proximity, the black hole in the system is pulling material from the supergiant star. This material circles the black hole forming a large disk of gas. Some of this material eventually falls into the black hole, other material is blown away from the disk in large "winds", and the remaining material is ejected perpendicular to the disk as very narrow "jets". The material in these jets is travelling at 0.26c, or 26% the speed of light!

My recent work along with a collaboration at Georgia State University and in the Netherlands, identified the supergiant star in SS 433 as well as determining that its companion is most likely a black hole. Our work was highlighted in the May 2004 issue of Sky and Telescope magazine (p 16). We are continuing our studies of SS 433 and have joined with two additional teams who are studying SS 433 in x-ray and radio wavelengths. We are in the process of analyzing data from coordinated simultaneous observations of SS 433 in 2005 using x-ray, radio, infrared, and optical observatories!

Planetary Nebula Central Stars are the focus of another project. I have been observing these stars for several years in an attempt to find binary central stars. The central stars are remnants of sunlike stars which have shed their outer envelopes. These envelopes are blown away from the star and appear to us as planetary nebulae. Many planetary nebulae have very complex shapes and we are unsure what creates the varied and fascinating structures we observe. One possibility is that there is a companion to the central star and that the orbit of these stars creates the physical conditions which shape the outflowing gas. My research has been focused on determining how many and specifically which planetary nebulae have binary central stars. Primarily this has been done by searching for specific brightness variations which are caused by close or interacting binary stars.

Close Binary Stars:

O-type stars are the most massive stars known. Unfortunately we do not know precisely what masses they do have. In collaboration with Doug Gies at Georgia State University I have been surveying groups of O-type stars to search for binary systems. The only way for us to directly determine a star's mass is if it has a companion. The specific orbital speed and the distance between the stars can tell us what the mass of each star is. The frequency of stars that are binaries can also tell us much about how the stars formed, and important issue in understanding our Universe. We have been using the spectrum of these stars to find binary systems and to determine the orbital periods.

Circumstellar Nebulosity:

The structure of nova shells was the topic of my doctoral dissertation. Nova shells are created by material being blown off the surface of a white dwarf star in a close binary system known as a cataclysmic variable. The white dwarf in the system is surrounded by an accretion disk. The gas in the disk eventually falls to the surface of the white dwarf and eventually the white dwarf undergoes a thermonuclear runaway on its surface. This ejects the material which is seen as the nova shell. My work used spectra of the different portions of nova shells to determine the shape and expansion speed of the shell. This information can help us more aaccurately understand the processes occuring during the thermonuclear runaway.

 

 


Other Interests:

See my personal page for more information about me.


Department of Physics and Astronomy
Valparaiso University