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Home > People > Faculty > John R. Thorstensen

John R. Thorstensen

Professor of Physics and Astronomy

Education

  • University of California, Berkeley: Ph.D. 1980
  • Haverford College, B. A.; Astronomy & Physics double major (both High Honors), 1974

Contact Information

Research Interests

Optical astronomy; fundamental astronomy of cataclysmic variable stars; astrometry.

For much of my career I've been observing cataclysmic variable stars (CVs), which are binary systems in which a white dwarf star accretes matter from a nearby companion star through Roche-lobe overflow. In particular, my students and I have determined reliable orbital periods for a great many of these stars, and along the way we have found many unusual and interesting specimens, some of which are described in the papers listed below.

Back in the 1990s it occurred to me that, with the jump in precision enabled by CCD detectors, the distances to the nearest CVs should be measurable with trigonometric parallax. I started taking images for the project in 1997, and by 2003 I was able to publish distances for most of the targets on the initial list. There is considerable demand for parallaxes these days, so in addition to ongoing work on an expanded list of CVs and related object, I have expanded the program by entering into collaborations. One is with Sebastien Lepine and Mike Shara (American Museum of Natural History); Sebastien has a fantastic proper motion catalog which has yielded many interesting nearby stars. Another is with Mukremin Kilic (CfA), who, in a collaboration led by Ted von Hippel (Dartmouth '84; now at Siena College), is working on the white dwarf luminosity function.

SkyCalc, JSkyCalc, -- Programs for "Coordinates, Time and the Sky"

I wrote the widely-used skycalc program, which computes time-and-the-sky information useful to optical astronomers. A couple of years ago, I developed a Java version of skycalc, which runs on almost any computer and which should be much more intuitive for most users. The older C/Python codes, which include the text-only form, Python-callable versions, a Tkinter graphical user interface, and several extensive manuals, are available in this tar.gz file.. Finally, here is a monograph on Coordinates, Time, and the Sky which is suitable for use in courses.

Other

I am the current President of the nonprofit corporation that operates MDM Observatory on Kitt Peak, Arizona. MDM operates two telescopes, a 2.4m and a 1.3m, on the southwest ridge of Kitt Peak near Tucson, Arizona. The consortium includes Ohio State University, Columbia University, the University of Michigan, and Ohio University as well as Dartmouth.

Selected Recent Publications

Here are some of my more notable and/or recent publications. You can get a complete list from the ADS .

These papers report results of the parallax program:
"11-12 Gyr old white dwarfs 30 pc away", Kilic, M., Thorstensen, J. R., Kowalski, P. M., and Andrews, J., 2012, Monthly Notices of the Royal Astronomical Society, 423, 132.    Available on arxiv.
"New Neighbors: Parallaxes of 18 Nearby Stars Selected from the LSPM-North Catalog", Lepine, S., Thorstensen, J. R., Shara, M., and Rich, R. M. 2009, Astronomical Journal, 137, 4109.     Available on arxiv.
"Parallaxes and Distance Estimates for Twelve Cataclysmic Variable Stars", Thorstensen, J. R., Lepine, S., and Shara, M., 2008, Astronomical Journal, 136, 2107.     Available on arxiv.

Here are some papers that explores the CV population, with an emphasis on finding reliable orbital periods:
"Spectroscopy and Photometry of Cataclysmic Variable Candidates from the Catalina Real Time Survey", Thorstensen, J. R., and Skinner, J. N. 2012, Astronomical Journal, 144, 81.    Available on arxiv
"SDSS unveils a population of intrinsically faint cataclysmic variables at the minimum orbital period", Gaensicke, B. et al, 2009, Monthly Notices of the Royal Astronomical Society, 397, 2170.   Available on arxiv

In this paper we laid out the mystery raised by FIRST J1023, and suggested that the primary was a neutron star. The prediction was recently confirmed by the McGill pulsar group in a spectacular manner (A. Archibald, in preparation).
"Is FIRST J102347.6+003841 Really a Cataclysmic Binary?", with E. Armstrong, 2005, Astronomical Journal, 2005, 130, 759.    Available on astro-ph.

The subject of this paper, since renamed EI Psc, proved to have an anomalously warm secondary in a very tight orbit, indicating that mass transfer began after the secondary had undergone considerable nuclear evolution; the secondary is the stripped core of a partially-evolved star.
"1RXS J232953.9+062814: A Dwarf Nova with a 64-minute Orbital Period and a Conspicuous Secondary Star", with Fenton, W. H., Patterson, J. O., Kemp, J., Krajci, T., and Baraffe, I., 2002, Astrophysical Journal Letters, 567, L49. Available on astro-ph.

My most-cited paper is the one in which Fred Ringwald and I first defined the SW Sextantis class of cataclysmics:
"PG0027+260: An Example of a Class of Cataclysmic Binaries with Mysterious, But Consistent, Behavior", with F. A. Ringwald, R.A. Wade, G.D. Schmidt, J.E. Norsworthy, Astronomical Journal 102, 272 (1991).

This paper also well-cited, since Cas A is such an important example of a young SNR. It was in many ways an outgrowth of the parallax work. The project was initiated by my co-author and Dartmouth colleague Rob Fesen, who is a leading expert on young supernova remnants.
"The Expansion Center and Dynamical Age of the Galactic Supernova Remnant Cassiopeia A", with Fesen, R. A., and van den Bergh, S., 2001, Astronomical Journal, 122, 297. Available on astro-ph.


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