Richard O. Gray

  • Professor of Physics and Astronomy
  • BA-Mathematics Washington State University
  • MSc-Astronomy University of Toronto
  • PhD-Astronomy University of Toronto
  • Office: CAP 311
  • grayro@appstate.edu
  • 828-262-2430

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    Teaching

    I am a Professor in the department of Physics and Astronomy at Appalachian State University.  I currently teach the following courses:  AST 1001/1002 (Introductory Astronomy), AST 2002 (Observational Astronomy: Spectroscopy),
    AST 3100 (Astrophysics), PHY 3538 (Environmental Physics) and PHY 4620 (Optics).  I also normally have one graduate student, and regularly involve undergraduates in my research.  In addition, I have developed a number of teaching resources, including some computerized introductory astronomy labs, as well as a  Digital Spectral Classification Atlas  which is useful both for advanced classes on stellar spectroscopy and for research.

    Recently, I was a member of the faculty of the Vatican Observatory Summer School during the summer of 1999  ( VOSS 99).  This is an international astronomy summer school, open to beginning graduate students in astronomy of all faiths and no faith.  I taught 24 exceptionally bright students from 20 countries about the astrophysics of single stars.

    Research

    My research is in the field of stellar spectroscopy.  My interests include the discovery and classification of chemically pecular stars, in particular the   Lambda Bootis stars, a group of Population I A-type stars which show marked underabundances in most elements with the exception of C,N,O and S, which can be of nearly solar abundance.  These stars are astrophysically important because these underabundances are most likely due to accretion of metal-depleted gas from the interstellar medium or from a protoplanetary disk.  Thus these stars may have something to tell us about protoplanetary disks and planet formation, as well as being intrinsically interesting in themselves.  In collaboration with my colleague, Dr. Chris Corbally, S.J. of the Vatican Observatory, we are trying to determine the evolutionary state of these objects.  So far we have discovered lambda Bootis stars in the Orion OB1 association, but have not been successful in finding any of these stars in intermediate-age clusters, even though many of the Lambda Bootis stars in the field must be of that age range.  This may be telling us something important about the formation and survival of protoplanetary disks in star clusters.  See below for some recent papers we have published on this subject.  Recently, another colleague of mine and I have discovered that HR 8799, a lambda Bootis star, is also a Gamma Doradus pulsator.  This has led to some insight into the nature of the pulsation mechanism in these newly discovered variables (see papers below).

    In addition to the Lambda Bootis stars, I have become interested in pre-main-sequence A-type stars, stars which are very young and are still contracting to the main sequence.  Many of these stars show emission lines in their spectra, and are known as the "Ae stars"  The two groups turn out to be connected, as Chris Corbally and I recently discovered (see papers below) one Ae star which is also a Lambda Bootis star.  Chris and I have also extended the MK spectral classification system to these Ae stars (see below).

    In addition to these observational topics, I have been involved in the modeling of stellar spectra through spectral synthesis.  I have written a spectral synthesis program  SPECTRUM , which computes the emergent spectrum given a stellar atmosphere model.  I have been using these synthetic spectra to determine the basic parameters of stars (effective temperature, gravity, [M/H] and microturbulent velocity) using the spectra I have obtained with the Gray/Miller  spectrograph  which I designed and built (with the expert help of Robert Miller, instrument maker) for the Dark Sky Observatory 32" telescope.  This research is currently being written up, and should soon be submitted for publication.
     

    Instrumentation

    During my time at ASU, I have designed and constructed two astronomical spectrographs.  The first  was the Gray/Miller cassegrain classification spectrograph  which I have used for most of my research on the Dark Sky Observatory 32" telescope.  More recently, in collaboration with my graduate student, Pam Graham, I designed and constructed a Faint Object Spectrograph for the Dark Sky Observatory.  This spectrograph is capable of obtaining very low resolution spectra of objects down to mv = 18.5.

    Here are some recent papers I have authored/co-authored on the topics listed above:

    Kaye , A.B. et al. 1999 AJ 118, 2997 "HD 62454 and HD 68192: Two New Gamma Doradus Variables"

    Gray, R.O. & Kaye, A.B. 1999 AJ 118, 2993 "HR 8799: A Link between Gamma Doradus Variables and Lambda Bootis Stars"  pdf file

    Gray, R.O. & Corbally, C.J. 1999 BAAS 194, 47.02 "A Spectroscopic Search for Peculiar A-type Stars in Open Clusters"

    Miroshnichenko, A.S. et al. 1999 A&A 347, 137 "Observations of Recently Recognized candidate Herbig Ae/Be stars"  pdf file

    Wilhelm, R.,  Beers, T.C. & Gray, R.O. 1999 AJ 117, 2308 "Spectroscopy of Hot Stars in the Galactic Halo II. The Identification and Classification of Horizontal-Branch and Other A-type Stars"

    Zwintz, K. et al. 1999 A&A 343, 899 "Hubble Deep Field Guide Star Photometry"

    Gray, R.O. & Corbally, C.J. 1998 AJ 116, 2530 "The Incidence of Lambda Bootis Stars via an Extension of the MK Spectral Classification System to Very Young A-type Stars"  pdf file

    Gray, R.O. 1998 AJ 116, 482 "The Absolute Flux Calibration of Stromgren uvby Photometry"  pdf file

    Paunzen, E. & Gray, R.O. 1997 A&AS 126, 407 "A Spectroscopic Survey for Lambda Bootis Stars I. Strategy, Techniques and First Results