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| Office: BRT 324 | Teaching schedule, Summer 2008: |
| Office hours: MWF 2 or by appointment | AST 3043, Sect. 0617, M-F 5 in FLG 280 |
| Telephone: (352) 392-2052, ext. 236 | E-mail: hsmith@astro.ufl.edu |
| USPS: Department of Astronomy, University of Florida | Courses Taught |
| P. O. Box 112055 | |
| Gainesville, FL 32611-2055 | Research |
My current research interest is the luminosity calibration problem, in particular using maximum likelihood methods with astrometric data (trigonometric parallaxes and proper motions). Recently I have studied biases associated with parallaxes, including the Trumpler-Weaver (also known as Lutz-Kelker) and Malmquist biases as well as some newer ones. In the past I have considered a Bayesian approach to the problem as well as transformation methods.
My most recent research publication is "Beware lambda-truncation! Sample truncation and bias in luminosity calibration using trigonometric parallaxes", Monthly Notices of the Royal Astronomical Society, 365, 469 (2006). It deals with the effects of sample truncation according to both apparent magnitude and relative parallax error (which I have termed lambda) on calibration using both reduced parallaxes and the so-called direct method in three forms. The figures at right, taken from the paper, show the effect of changing the upper limit on lambda with three versions of the reduced parallax method. The solid curves are for a dispersion of 0.1 magnitude in the absolute magnitudes of sample stars; the dashed curves are for 0.2, the dot-dashed curves for 0.3, and the triple dot-dashed curves for 0.4. The negative bias in absolute magnitude seen in figures (a) and (c) with the FC and AUE variants for a small value of the cutoff results from the forms of the weight factors used, which depend on the star's apparent magnitude. The bias for the p-method variant shown in figure (b) is always nonnegative and converges to the positive bias that I have termed "modelling bias" in my 2003 paper (see below) as the cutoff approaches zero.
Prior to that I authored "Is there really a Lutz-Kelker bias? Reconsidering calibration using trigonometric parallaxes," Monthly Notices of the Royal Astronomical Society 338, 891 (2003). For reprints of these papers, the relevant paper "On the estimation of distances using trigonometric parallaxes" (Monthly Notices of the Royal Astronomical Society 281, 211, 1996, with H. K. Eichhorn), or of any of my five papers from the series on the calibration problem which appeared in Astronomy & Astrophysics in 1987-88 that are referenced in these recent papers please email me at the above address.
Some other publications:
"Transformation methods for trigonometric parallaxes," from Fifth Alexander von Humboldt Colloquium proceedings, New Developments in the Dynamics of Planetary Systems, eds. R. Dvorak and J. Henrard, Dordrecht:Kluwer, 2001, pp. 349-359. (PDF file)
"The Lutz-Kelker effect in the Hipparcos era and beyond," in Modern Astrometry and Astrodynamics, eds. R. Dvorak, H. F. Haupt, and K. Wodnar, Vienna: Austrian Academy of Sciences, 1999, pp. 139-149. (PDF file)
The paper "Spectra of stretching numbers of orbits in oscillating galaxies" from Astron. Astrophys. 314, pp. 795-806 (1996) is now available in PDF form. (Be aware that this is a fairly large file.) This paper deals with a way of studying chaos in a nearly-integrable system, namely by using stretching numbers (which are like very-short-time Lyanpunov numbers). Copies may of course be obtained from me on request.
Two of my former collaborators, gone but by no means forgotten:
Heinrich Karl Eichhorn, 1927-1999
Courses taught at various times:
AST 1002 Discovering the Universe -- introductory survey of astronomy for non-science majors (GenEd physical science)
AST 3018 Astronomy & Astrophysics 1, general astronomy for majors, first semester of two-semester sequence
AST 3019 Astronomy & Astrophysics 2, general astronomy for majors, second semester
AST 3043 History of Astronomy through Newton; for non-science majors (GenEd humanities or physical science, also international)
AST 3043 (Honors) Same as AST 3043; enrollment limited to honors students.
AST 3047 (relatively new course) History of Astronomy after Newton; for non-science majors (GenEd physical science)
AST 5210 Introduction to Astrophysics -- upper-level undergraduate/graduate course in basic astrophysics, including atomic and molecular spectra, interaction of radiation with matter, and the virial theorem and stability
AST 6309 Galactic and Extragalactic Astronomy -- graduate course in galactic dynamics, the Milky Way, properties of galaxies, clusters of galaxies and superclustering
AST 6336 Interstellar Matter -- graduate course in the astrophysics of the interstellar medium, including gaseous nebulae, supernova remnants, nova shells, molecular clouds, and interstellar dust