W. Romanishin

University of Oklahoma, Norman, Oklahoma, United States

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Publications (71)230.79 Total impact

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    ABSTRACT: We report on our continuing program of BVR color measurement of Centaurs and KBOs. Most of our measurements have been made with the Vatican Advanced Technology Telescope (VATT). We report of new colors obtained through October 2011.
    LPI Contributions. 05/2012;
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    ABSTRACT: We present three near-infrared spectra of Pluto taken with the IRTF and SpeX, an optical spectrum of Triton taken with the MMT and the Red Channel Spectrograph, and previously published spectra of Pluto, Triton, and Eris. We combine these observations with a two-phase Hapke model, and gain insight into the ice mineralogy on Pluto, Triton, and Eris. Specifically, we measure the methane-nitrogen mixing ratio across and into the surfaces of these icy dwarf planets. In addition, we present a laboratory experiment that demonstrates it is essential to model methane bands in spectra of icy dwarf planets with two methane phases - one highly-diluted by nitrogen and the other rich in methane. For Pluto, we find bulk, hemisphere-averaged, methane abundances of 9.1 \pm 0.5%, 7.1 \pm 0.4%, and 8.2 \pm 0.3% for sub-Earth longitudes of 10\degree, 125\degree, and 257\degree. Application of the Wilcoxon rank sum test to our measurements finds these small differences are statistically significant. For Triton, we find bulk, hemisphere-averaged, methane abundances of 5.0 \pm 0.1% and 5.3 \pm 0.4% for sub-Earth longitudes of 138\degree and 314\degree. Application of the Wilcoxon rank sum test to our measurements finds the differences are not statistically significant. For Eris, we find a bulk, hemisphere-averaged, methane abundance of 10 \pm 2%. Pluto, Triton, and Eris do not exhibit a trend in methane-nitrogen mixing ratio with depth into their surfaces over the few cm range probed by these observations. This result is contrary to the expectation (Grundy & Stansberry 2000) that since visible light penetrates deeper into a nitrogen-rich surface than the depths from which thermal emission emerges, net radiative heating at depth would drive preferential sublimation of nitrogen leading to an increase in the methane abundance with depth.
    The Astrophysical Journal 03/2012; 751(1). · 6.73 Impact Factor
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    ABSTRACT: We present spectra of Eris from the MMT 6.5 m Telescope and Red Channel Spectrograph (5700-9800 Å, 5 Å pixel–1) on Mt. Hopkins, AZ, and of Pluto from the Steward Observatory 2.3 m Telescope and Boller and Chivens Spectrograph (7100-9400 Å, 2 Å pixel–1) on Kitt Peak, AZ. In addition, we present laboratory transmission spectra of methane-nitrogen and methane-argon ice mixtures. By anchoring our analysis in methane and nitrogen solubilities in one another as expressed in the phase diagram of Prokhvatilov & Yantsevich, and comparing methane bands in our Eris and Pluto spectra and methane bands in our laboratory spectra of methane and nitrogen ice mixtures, we find Eris' bulk methane and nitrogen abundances are ~10% and ~90% and Pluto's bulk methane and nitrogen abundances are ~3% and ~97%. Such abundances for Pluto are consistent with values reported in the literature. It appears that the bulk volatile composition of Eris is similar to the bulk volatile composition of Pluto. Both objects appear to be dominated by nitrogen ice. Our analysis also suggests, unlike previous work reported in the literature, that the methane and nitrogen stoichiometry is constant with depth into the surface of Eris. Finally, we point out that our Eris spectrum is also consistent with a laboratory ice mixture consisting of 40% methane and 60% argon. Although we cannot rule out an argon-rich surface, it seems more likely that nitrogen is the dominant species on Eris because the nitrogen ice 2.15 μm band is seen in spectra of Pluto and Triton.
    The Astrophysical Journal 11/2010; 725(1):1296. · 6.73 Impact Factor
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    ABSTRACT: We present new optical broadband colors, obtained with the Keck 1 and Vatican Advanced Technology telescopes, for six objects in the inner classical Kuiper Belt. Objects in the inner classical Kuiper Belt are of interest as they may represent the surviving members of the primordial Kuiper Belt that formed interior to the current position of the 3:2 resonance with Neptune, the current position of the plutinos, or, alternatively, they may be objects formed at a different heliocentric distance that were then moved to their present locations. The six new colors, combined with four previously published, show that the 10 inner belt objects with known colors form a neutral clump and a reddish clump in B-R color. Nonparametric statistical tests show no significant difference between the B-R color distribution of the inner disk objects compared to the color distributions of Centaurs, plutinos, or scattered disk objects. However, the B-R color distribution of the inner classical Kuiper belt objects does differ significantly from the distribution of colors in the cold (low inclination) main classical Kuiper belt. The cold main classical objects are predominately red, while the inner classical belt objects are a mixture of neutral and red. The color difference may reveal the existence of a gradient in the composition and /or surface processing history in the primordial Kuiper Belt, or indicate that the inner disk objects are not dynamically analogous to the cold main classical belt objects. Comment: Accepted for publication in AJ
    The Astronomical Journal 04/2010; · 4.97 Impact Factor
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    ABSTRACT: We present deep optical photometry of the afterglow of gamma-ray burst (GRB) 041006 and its associated hypernova obtained over 65 days after detection (55 R-band epochs on 10 different nights). Our early data (t < 4 days) joined with published GCN data indicate a steepening decay, approaching Fν t-0.6 at early times (t 1 day) and Fν t-1.3 at late times. The break at tb = 0.16 ± 0.04 days is the earliest reported jet break among all GRB afterglows. During our first night, we obtained 39 exposures spanning 2.15 hr from 0.62 to 0.71 days after the burst that reveal a smooth afterglow, with an rms deviation of 0.024 mag from the local power-law fit, consistent with photometric errors. After t ~ 4 days, the decay slows considerably, and the light curve remains approximately flat at R ~ 24 mag for a month before decaying by another magnitude to reach R ~ 25 mag 2 months after the burst. This "bump" is well fit by a k-corrected light curve of supernova SN 1998bw, but only if stretched by a factor of 1.38 in time. In comparison with the other GRB-related SN bumps, GRB 041006 stakes out new parameter space for GRBs/SNe, with a very bright and significantly stretched late-time SN light curve. Within a small sample of fairly well observed GRB/SN bumps, we see a hint of a possible correlation between their peak luminosity and their "stretch factor," broadly similar to the well-studied Phillips relation for the Type Ia supernovae.
    The Astrophysical Journal 12/2008; 626(1):L5. · 6.73 Impact Factor
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    ABSTRACT: As a result of our continuing photometric survey, we report here optical colors for 36 Kuiper Belt objects, increasing our sample size to 91 objects. We find that certain dynamical classes of objects exhibit distinctive colors—21 out of 21 objects on small-inclination and small-eccentricity orbits with perihelion distances larger than 40 AU exhibit red surface colors (B-R > 1.5), while 17 out of 20 objects on large-inclination and large-eccentricity orbits with aphelion distances larger than 70 AU exhibit gray surface colors (B-R < 1.5). Our observations are consistent with a primordial origin for Kuiper Belt surface colors, if we assume that gray objects formed closer to the Sun than red objects, and as Neptune migrated outward it scattered gray objects onto dynamically hot orbits. By this model, the contrasting dynamically cold and red objects beyond 40 AU remained far enough away from Neptune that they were never perturbed by the planet.
    The Astrophysical Journal 12/2008; 599(1):L49. · 6.73 Impact Factor
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    ABSTRACT: We describe optical spectroscopic observations of the icy dwarf planet Eris with the 6.5-m MMT telescope and the Red Channel Spectrograph. We report a correlation, that is at the edge of statistical significance, between blue shift and albedo at maximum absorption for five methane ice bands. We interpret the correlation as an increasing dilution of methane ice with another ice component, probably nitrogen, with increasing depth into the surface. We suggest a mechanism to explain the apparent increase in nitrogen with depth. Specifically, if we are seeing Eris 50 degrees from pole-on [Brown, M.E., Schaller, L., 2008. Science 316, 1585], the pole we are seeing now at aphelion was in winter darkness at perihelion. Near perihelion, sublimation could have built up atmospheric pressure on the sunlit (summer) hemisphere sufficient to drive winds toward the dark (winter) hemisphere, where the winds would condense. Because nitrogen is more volatile and scarcer than methane, it sublimated from the sunlit hemisphere relatively early in the season, so the early summer atmosphere was nitrogen rich, and so was the ice deposited on the winter pole. Later in the season, much of the nitrogen was exhausted from the summer pole, but there was plenty of methane, which continued to sublimate. At this point, the atmosphere was more depleted in nitrogen, as was the ice freezing out on top of the earlier deposited nitrogen rich ice. Our increasing nitrogen abundance with depth apparently contradicts the Licandro et al. [Licandro, J., Grundy, W.M., Pinilla-Alonso, N., Leisy, P., 2006. Astron. Astrophys. 458, L5–L8] result of a decreasing nitrogen abundance with depth. A comparison of observational, data reduction, and analysis techniques between the two works, suggests the difference between the two works is real. If so, we may be witnessing the signature of weather on Eris. The work reported here is intended to trigger further observational effort by the community.
    Icarus 11/2008; · 3.16 Impact Factor
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    ABSTRACT: We present the lightcurves of Centaurs (32532) Thereus and (8405) Asbolus from observations taken October 29 through November 2, 2005 on the 1.8m Vatican Advanced Technology Telescope (VATT). Our double-peaked period for Thereus of 8.32 ± 0.01h is consistent with both the period of 8.3378 ± 0.0012h of Farnham and Davies (2003 Icarus 164, 418-427) and the period of 8.3091 ± 0.0001h of Ortiz et al. (2002 A&A 388, 661-666; 2003 A&A 407, 1149-1155). The maximum amplitude of the lightcurve has increased from 0.18mag and 0.16 ± 0.02mag to 0.38mag since their observations in September through December 2001 and September through October 2001 respectively. Our double-peaked period for Asbolus of 8.94 ± 0.01h is consistent with the period of 8.9351 ± 0.0003h derived by Davies et al. (1998 Icarus 134, 213-227) but inconsistent with the period of 8.87 ± 0.02h of Brown and Luu (1997 Icarus 126, 218-224). Asbolus's lightcurve amplitude has decreased from the reported value of Davies et al. (1998) of 0.55mag to 0.32mag. We assume that the changes in amplitude are due to the changes in viewing aspects with respect to their rotational axes. We use an amplitude-aspect model to constrain rotational pole positions and axis ratios for both Centaurs. We plan additional observations in November 2008 to further constrain the pole positions. This work is based on observations with the VATT: The Alice P. Lennon Telescope and the Thomas J. Bannan Astrophysics Facility. We gratefully acknowledge support from NASA Planetary Astronomy grant NNG06G138G to Northern Arizona University and the University of Oklahoma.
    09/2008;
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    S C Tegler, W M Grundy, F Vilas, W Romanishin
    02/2008;
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    ABSTRACT: We present high signal precision optical reflectance spectra of 2005 FY9 taken with the Red Channel Spectrograph and the 6.5-m MMT telescope on 2006 March 4 UT (5000–9500 Å; 6.33 Å pixel−1) and 2007 February 12 UT (6600–8500 Å; 1.93 Å pixel−1). From cross-correlation experiments between the 2006 March 4 spectrum and a pure CH4-ice Hapke model, we find the CH4-ice bands in the MMT spectrum are blueshifted by 3 ± 4 Å relative to bands in the pure CH4-ice Hapke spectrum. The higher resolution MMT spectrum of 2007 February 12 UT enabled us to measure shifts of individual CH4-ice bands. We find the 7296, 7862, and 7993 Å CH4-ice bands are blueshifted by 4 ± 2, 4 ± 4, and 6 ± 5 Å. From four measurements we report here and one of our previously published measurements, we find the CH4-ice bands are shifted by 4 ± 1 Å. This small shift is important because it suggest the presence of another ice component on the surface of 2005 FY9. Laboratory experiments show that CH4-ice bands in spectra of CH4 mixed with other ices are blueshifted relative to bands in spectra of pure CH4-ice. A likely candidate for the other component is N2-ice because its weak 2.15 μm band and blueshifted CH4 bands are seen in spectra of Triton and Pluto. Assuming the shift is due to the presence of N2, spectra taken on two consecutive nights show no difference in CH4/N2. In addition, we find no measurable difference in CH4/N2 at different depths into the surface of 2005 FY9.
    Icarus 01/2008; · 3.16 Impact Factor
  • W. Romanishin, S. C. Tegler, G. Consolmagno
    LPI Contributions. 01/2008;
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    ABSTRACT: Minor planets on outer planet-crossing orbits, called Centaur objects, are important members of the solar system in that they dynamically link Kuiper belt objects to Jupiter-family comets. In addition, perhaps 6% of near-Earth objects have histories as Centaur objects. The total mass of Centaurs (10-4&) Earth masses) is significant, about one-tenth of the mass of the asteroid belt. Centaur objects exhibit a physical property not seen among any other objects in the solar system; their B-R colors divide into two distinct populations: a gray and a red population. Application of the dip test to B-R colors in the literature indicates there is a 99.5% probability that Centaurs exhibit a bimodal color distribution. Although there are hints that gray and red Centaurs exhibit different orbital elements, application of the Wilcoxon rank sum test finds no statistically significant difference between the orbital elements of the two color groups. On theother hand, gray and red Centaurs exhibit a statistically significant difference in albedo, with the gray Centaurs having a lower median albedo than the red Centaurs. Further observational and dynamical work is necessary to determine whether the two color populations are the result of (1) evolutionary processes such as radiation-reddening, collisions, and sublimation or (2) a primordial, temperature-induced, composition gradient.
    The Solar System Beyond Neptune, Edited by Barucci, M.~A. and Boehnhardt, H. and Cruikshank, D.~P. and Morbidelli, A. and Dotson, R, 01/2008: pages 105-114;
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    ABSTRACT: We present optical spectra of 2005 FY9 taken with the Red Channel Spectrograph and the 6.5-m MMT telescope on 2006 March 4 UT (5000-9500 A; 6.38 A per pixel) and 2007 February 12 UT (6600-8500 A; 1.93 A per pixel). From a cross correlation experiment between the 2006 March 4 spectrum and a pure CH4-ice Hapke model, we found the CH4-ice bands in the MMT spectrum are blueshifted by 3.1 +\- 1.9 A relative to bands in a pure CH4-ice spectrum. We found the bands were blueshifted by 3.3 +/- 2.3 A in our 2006 March 5 spectrum (Tegler et al., 2007, AJ, 133, 526). The higher resolution spectrum of 2007 February 12 UT enabled us measure shifts of individual CH4-ice bands. We found the 7296 A, 7862 A, and 7993 A CH4-ice bands were blueshifted by 4.0 +/- 1.6 A, 4.0 +/- 3.0 A, and 4.2 +/- 3.7 A. These small shifts are important because they suggest the presence of another ice component. Laboratory experiments show that CH4-ice bands in spectra of CH4 and N2 ice mixtures are blueshifted relative to the bands in spectra of pure CH4-ice (Quirico and Schmitt, 1997, Icarus, 127, 354). A likely candidate is N2-ice because its weak 2.15 micron band and blueshifted CH4 bands are seen in spectra of Triton and Pluto (Cruikshank et al., 1993, Science, 261, 742; Owen et al., 1993, Science, 261, 745). Our spectra show no difference in CH4/N2 (within the uncertainties) between observations taken at two rotational phases; nor can we detect any difference at different depths into the surface. We thank the NASA Planetary Astronomy and Planetary Geology and Geophysics Programs for financial support of this research.
    10/2007;
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    W. Romanishin, S. C. Tegler
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    ABSTRACT: There are now almost 1200 cataloged minor bodies in the outer solar system. There is a rich dynamical diversity, with the Centaurs crossing the orbits of the outer planets, Plutinos in resonant orbits with Neptune (as is Pluto), the classical KBOs (CKBOs) in near circular orbits away from the resonant effects of Neptune, and scattered disk objects (SDOs) possessing eccentric orbits with large perihelia, presumably scattered from smaller orbits. We have been measuring the optical colors of these objects for the last 10 years and now have measured colors for a sample of about 120 objects. I will discuss our findings concerning several questions: (1) Do the different dynamical classes have statistically different color distributions? (2) Do these objects have a bimodal or a unimodal color distribution?
    01/2007;
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    ABSTRACT: We present high signal precision optical reflectance spectra of the large Kuiper belt objects 2005 FY9 and 2003 EL61. The spectrum of 2005 FY9 exhibits strong CH4-ice bands. A comparison between the spectrum and a Hapke model indicates the CH4 bands are shifted 3.25 +/- 2.25A relative to pure CH4-ice, suggesting the presence of another ice component on the surface of 2005 FY9, possibly N2-ice, CO-ice, or Ar. The spectrum of 2003 EL61 is remarkably featureless. There is a hint of an O2-ice band at 5773A; however, this feature needs to be confirmed by future spectroscopic observations of 2003 EL61 with a higher continuum signal precision, sufficient to detect a second weaker O2-ice band at 6275A.
    The Astronomical Journal 12/2006; · 4.97 Impact Factor
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    ABSTRACT: We present optical spectra (0.40 - 0.95 micron; fwhm 0.0020 micron) of the large Kuiper belt objects 2003 EL61 and 2005 FY9. The spectra were obtained with the Red Channel Spectrograph and the 6.5 meter MMT telescope on Mt Hopkins, AZ. Five 600-sec spectra of 2003 EL61 span 40 % of its rotational period. We find no evidence of ice absorption bands in any of the spectra nor any evidence of differences between the spectra. By combining the five spectra, we achieve a continuum signal to noise ratio of 200 near 0.577 and 0.627 micron. Such a signal to noise ratio enables us to rule out the presence of O2-ice on 2003 EL61 at an abundance seen on the surface of Ganymede (Spencer et al. 1995). In addition, the lack of the 0.890 micron CH4-ice band in our spectrum allows us to set an upper limit on the thickness of a global glaze of CH 4-ice at 0.3 mm. Our spectrum of 2005 FY9 exhibits deep CH 4-ice absorption at 0.620, 0.730, 0.786, 0.799, 0.844, 0.869, 0.890, and 0.902 micron in agreement with spectra of Licandro et al. 2006. The wavelengths of these absorption bands are consistent with pure CH4-ice. In addition, our spectrum exhibits weak CH 4-ice bands at 0.54, 0.58, and 0.60 micron. This is the first detection of these weak ice bands in laboratory or astrophysical spectra. We thank the NASA Planetary Astronomy Program for financial support of this research and the Steward Telescope Allocation Committee for allocation of telescope time.
    09/2006;
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    ABSTRACT: Centaur (60558) Echeclus was discovered to be active by Choi et al. (IAUC 8656, 2006) on December 30, 2005 and subsequently renamed comet 174P/Echeclus. Observations during the next five months showed that the apparent source of activity moved away from the primary body to a maximum distance of 7 arc-seconds, a projected distance of 65,000 km at the comet, in late February, 2006. The activity source then moved back towards and past the primary to only 2.7 arc-seconds in early May, 2006. Although the apparent motion suggested an orbiting secondary, the speed with which the secondary moved over the distances involved is inconsistent with reasonable estimates of the mass of the primary, by a factor of 200 or more. We thus believe that the secondary object is more likely moving on a hyperbolic orbit relative to the primary. Plausible explanations for the existence of the active secondary are: (1) a large fragment ejected from the primary in a disruption event; (2) an impact on the primary by another small solar system body; or (3) an escaped satellite of the primary. The lack of comparable activity from the primary body at the site of the disruption or impact argues against explanations (1) and (2). Although the existence of a Centaur with a satellite is highly plausible, it is doubtful that nongravitatonal forces resulting from outgassing at that heliocentric distance would be sufficient to explain the escape. Additional details of this unusual object will be explored. This work was supported by the NASA Planetary Astronomy Program and was performed in part at the Jet Propulsion Laboratory under contract with NASA. YJC is grateful for the support of the NASA Post-doctoral Program.
    08/2006; 38:551.
  • S. Tegler, G. Consolmagno, W. Romanishin
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    ABSTRACT: IAUC 8701 available at Central Bureau for Astronomical Telegrams.
    International Astronomical Union Circular. 04/2006;
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    ABSTRACT: We compare the shapes and spin states of well-characterized asteroids with the stress/spin curves of Holsapple (2004). Applying these trends to centaurs and KBOs we infer that most have densities
    02/2006; 37:1222.
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    ABSTRACT: We have obtained broad band photometry of a large sample of KBOs using NICMOS on the Hubble Space Telescope. We have measured 84 individual KBOs using the NIC2 camera and two broad filters, the F110W and F160W, filters that approximate the J and H bands. We fit scaled model PSFs to each image, minimizing the chi square residuals to find the best solution. Approximately half of our sample was also observed at shorter wavelengths with the WFPC2 camera. We present the IR photometric results and take a first look at infrared color trends in a large, uniform sample of KBOs. This research has been supported by program 9386, funded through a grant to STScI, operated by AURA under NASA contract NAS 5-26555.
    08/2005;

Publication Stats

496 Citations
230.79 Total Impact Points

Institutions

  • 1997–2012
    • University of Oklahoma
      Norman, Oklahoma, United States
    • Vanderbilt University
      Nashville, Michigan, United States
  • 2006
    • Lowell Observatory
      Flagstaff, Arizona, United States
  • 1997–2005
    • Northern Arizona University
      • Department of Physics and Astronomy
      Flagstaff, AZ, United States
  • 1999–2000
    • University of Notre Dame
      South Bend, Indiana, United States