arXiv subjects

J. L. Elliot

Publications and source records attributed to J. L. Elliot.

11 recordsLinked to original sources

arXiv2014

De-biased Populations of Kuiper Belt Objects from the Deep Ecliptic Survey

The Deep Ecliptic Survey (DES) discovered hundreds of Kuiper Belt objects from 1998-2005. Follow-up observations yielded 304 objects with good dynamical classifications (Classical, Scattered, Centaur, or 16 mean-motion resonances with Neptune). The DES search fields are well documented, enabling us to calculate the probability of detecting objects with particular orbital parameters and absolute magnitudes at a randomized point in each orbit. Grouping objects together by dynamical class leads, we estimate the orbital element distributions (a, e, i) for the largest three classes (Classical, 3:2, and Scattered) using maximum likelihood. Using H-magnitude as a proxy for the object size, we fit a power law to the number of objects for 8 classes with at least 5 detected members (246 objects). The best Classical slope is alpha=1.02+/-0.01 (observed from 5<=H<=7.2). Six dynamical classes (Scattered plus 5 resonances) are consistent in slope with the Classicals, though the absolute number of objects is scaled. The exception to the power law relation are the Centaurs (non-resonant with perihelia closer than Neptune, and thus detectable at smaller sizes), with alpha=0.42+/-0.02 (7.5<H<11). This is consistent with a knee in the H-distribution around H=7.2 as reported elsewhere (Bernstein et al. 2004, Fraser et al. 2014). Based on the Classical-derived magnitude distribution, the total number of objects (H<=7) in each class are: Classical (2100+/-300 objects), Scattered (2800+/-400), 3:2 (570+/-80), 2:1 (400+/-50), 5:2 (270+/-40), 7:4 (69+/-9), 5:3 (60+/-8). The independent estimate for the number of Centaurs in the same H range is 13+/-5. If instead all objects are divided by inclination into "Hot" and "Cold" populations, following Fraser et al. (2014), we find that alphaHot=0.90+/-0.02, while alphaCold=1.32+/-0.02, in good agreement with that work.

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arXiv2011

Twenty-One New Light Curves of OGLE-TR-56b: New System Parameters and Limits on Timing Variations

Although OGLE-TR-56b was the second transiting exoplanet discovered, only one light curve, observed in 2006, has been published besides the discovery data. We present twenty-one light curves of nineteen different transits observed between July 2003 and July 2009 with the Magellan Telescopes and Gemini South. The combined analysis of the new light curves confirms a slightly inflated planetary radius relative to model predictions, with R_p = 1.378 +/- 0.090 R_J. However, the values found for the transit duration, semimajor axis, and inclination values differ significantly from the previous result, likely due to systematic errors. The new semimajor axis and inclination, a = 0.01942 +/- 0.00015 AU and i = 73.72 +/- 0.18 degrees, are smaller than previously reported, while the total duration, T_14 = 7931 +/- 38 s, is 18 minutes longer. The transit midtimes have errors from 23 s to several minutes, and no evidence is seen for transit midtime or duration variations. Similarly, no change is seen in the orbital period, implying a nominal stellar tidal decay factor of Q_* = 10^7, with a three-sigma lower limit of 10^5.7.

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arXiv2011

First results from the MIT Optical Rapid Imaging System (MORIS) on the IRTF: a stellar occultation by Pluto and a transit by exoplanet XO-2b

We present a high-speed, visible-wavelength imaging instrument: MORIS (the MIT Optical Rapid Imaging System). MORIS is mounted on the 3-m Infrared Telescope Facility (IRTF) on Mauna Kea, HI. Its primary component is an Andor iXon camera, a nearly 60 arcsec square field of view with high quantum efficiency, low read noise, low dark current, and full-frame readout rates ranging from as slow as desired to a maximum of between 3.5 Hz and 35 Hz (depending on the mode; read noise of 6e-/pixel and 49 e-/pixel with electron-multiplying gain=1, respectively). User-selectable binning and subframing can increase the cadence to a few hundred Hz. An electron-multiplying mode can be employed for photon counting, effectively reducing the read noise to sub-electron levels at the expense of dynamic range. Data cubes, or individual frames, can be triggered to several nanosecond accuracy using the Global Positioning System. MORIS is mounted on the side-facing exit window of SpeX (Rayner et al. 2003), allowing simultaneous near-infrared and visible observations. Here we describe the components, setup, and measured characteristics of MORIS. We also report results from the first science observations: the 24 June 2008 stellar occultation by Pluto and an extrasolar planetary transit by XO-2b. The Pluto occultation, of a 15.8 R magnitude star, has signal-to-noise ratio of 35 per atmospheric scale height and a midtime error of 0.32 s. The XO-2b transit reaches photometric precision of 0.5 millimagnitudes in 2 minutes and has a midtime timing precision of 23 seconds.

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arXiv2010

Six High-Precision Transits of OGLE-TR-113b

We present six new transits of the hot Jupiter OGLE-TR-113b observed with MagIC on the Magellan Telescopes between January 2007 and May 2009. We update the system parameters and revise the planetary radius to R_p=1.084 pm 0.029 R_J, where the error is dominated by stellar radius uncertainties. The new transit midtimes reveal no transit timing variations from a constant ephemeris of greater than 13 pm 28 seconds over two years, placing an upper limit of 1-2 M_Earth on the mass of any perturber in a 1:2 or 2:1 mean-motion resonance with OGLE-TR-113b. Combining the new transit epochs with five epochs published between 2002 and 2006, we find hints that the orbital period of the planet may not be constant, with the best fit indicating a decrease of dP/dt=-60 pm 15 milliseconds per year. If real, this change in period could result from either a long-period (more than 8 years) timing variation due to a massive external perturber, or more intriguingly from the orbital decay of the planet. The detection of a changing period is still tentative and requires additional observations, but if confirmed it would enable direct tests of tidal stability and dynamical models of close-in planets.

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arXiv2010

Lack of Transit Timing Variations of OGLE-TR-111b: A re-analysis with six new epochs

We present six new transits of the exoplanet OGLE-TR-111b observed with the Magellan Telescopes in Chile between April 2008 and March 2009. We combine these new transits with five previously published transit epochs for this planet between 2005 and 2006 to extend the analysis of transit timing variations reported for this system. We derive a new planetary radius value of 1.019 +/- 0.026 R_J, which is intermediate to the previously reported radii of 1.067 +/- 0.054 R_J (Winn et al. 2007) and 0.922 +/- 0.057 R_J (Diaz et al. 2008). We also examine the transit timing variation and duration change claims of Diaz et al. (2008). Our analysis of all eleven transit epochs does not reveal any points with deviations larger than 2 sigma, and most points are well within 1 sigma. Although the transit duration nominally decreases over the four year span of the data, systematic errors in the photometry can account for this result. Therefore, there is no compelling evidence for either a timing or a duration variation in this system. Numerical integrations place an upper limit of about 1 M_E on the mass of a potential second planet in a 2:1 mean-motion resonance with OGLE-TR-111b.

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arXiv2009

Buoyancy waves in Pluto's high atmosphere: Implications for stellar occultations

We apply scintillation theory to stellar signal fluctuations in the high-resolution, high signal/noise, dual-wavelength data from the MMT observation of the 2007 March 18 occultation of P445.3 by Pluto. A well-defined high wavenumber cutoff in the fluctuations is consistent with viscous-thermal dissipation of buoyancy waves (internal gravity waves) in Pluto's high atmosphere, and provides strong evidence that the underlying density fluctuations are governed by the gravity-wave dispersion relation.

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arXiv2007

The 2003 Nov 14 occultation by Titan of TYC 1343-1865-1. II. Analysis of light curves

We observed a stellar occultation by Titan on 2003 November 14 from La Palma Observatory using ULTRACAM with three Sloan filters: u', g', and i' (358, 487, and 758 nm, respectively). The occultation probed latitudes 2 degrees S and 1 degrees N during immersion and emersion, respectively. A prominent central flash was present in only the i' filter, indicating wavelength-dependent atmospheric extinction. We inverted the light curves to obtain six lower-limit temperature profiles between 335 and 485 km (0.04 and 0.003 mb) altitude. The i' profiles agreed with the temperature measured by the Huygens Atmospheric Structure Instrument [Fulchignoni, M. et al., 2005. Nature 438, 785-791] above 415 km (0.01 mb). The profiles obtained from different wavelength filters systematically diverge as altitude decreases, which implies significant extinction in the light curves. Applying an extinction model [Elliot, J.L., Young, L.A., 1992. Astron. J. 103, 991-1015] gave the altitudes of line of sight optical depth equal to unity: 396 +/- 7 km and 401 +/- 20 km (u' immersion and emersion); 354 +/- 7 km and 387 +/- 7 km (g' immersion and emersion); and 336 +/- 5 km and 318 +/- 4 km (i' immersion and emersion). Further analysis showed that the optical depth follows a power law in wavelength with index 1.3 +/- 0.2. We present a new method for determining temperature from scintillation spikes in the occulting body's atmosphere. Temperatures derived with this method are equal to or warmer than those measured by the Huygens Atmospheric Structure Instrument. Using the highly structured, three-peaked central flash, we confirmed the shape of Titan's middle atmosphere using a model originally derived for a previous Titan occultation [Hubbard, W.B. et al., 1993. Astron. Astrophys. 269, 541-563].

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arXiv2006

Charon's radius and density from the combined data sets of the 2005 July 11 occultation

The 2005 July 11 C313.2 stellar occultation by Charon was observed by three separate research groups, including our own, at observatories throughout South America. Here, the published timings from the three data sets have been combined to more accurately determine the mean radius of Charon: 606.0 +/- 1.5 km. Our analysis indicates that a slight oblateness in the body (0.006 +/- 0.003) best matches the data, with a confidence level of 86%. The oblateness has a pole position angle of 71.4 deg +/- 10.4 deg and is consistent with Charon's pole position angle of 67 deg. Charon's mean radius corresponds to a bulk density of 1.63 +/- 0.07 g/cm3, which is significantly less than Pluto's (1.92 +/- 0.12 g/cm3). This density differential favors an impact formation scenario for the system in which at least one of the impactors was differentiated. Finally, unexplained differences between chord timings measured at Cerro Pachon and the rest of the data set could be indicative of a depression as deep as 7 km on Charon's limb.

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arXiv2003

Procedures, Resources, and Selected Results of the Deep Ecliptic Survey

The Deep Ecliptic Survey is a project whose goal is to survey a large area of the near-ecliptic region to a faint limiting magnitude (R ~ 24) in search of objects in the outer solar system. We are collecting a large homogeneous data sample from the Kitt Peak Mayall 4-m and Cerro Tololo Blanco 4-m telescopes with the Mosaic prime-focus CCD cameras. Our goal is to collect a sample of 500 objects with good orbits to further our understanding of the dynamical structure of the outer solar system. This survey has been in progress since 1998 and is responsible for 272 designated discoveries as of March 2003. We summarize our techniques, highlight recent results, and describe publically available resources.

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arXiv2003

Resonance Occupation in the Kuiper Belt: Case Examples of the 5:2 and Trojan Resonances

As part of our ongoing Deep Ecliptic Survey (DES) of the Kuiper belt, we report on the occupation of the 1:1 (Trojan), 4:3, 3:2, 7:4, 2:1, and 5:2 Neptunian mean-motion resonances (MMRs). The occupation of the 1:1 and 5:2 MMRs is not easily understood within the standard model of resonance sweeping by a migratory Neptune over an initially dynamically cold belt. Our dynamically hot, 5:2 resonant objects can librate with modest amplitudes of 90 deg within the resonance for at least 1 Gyr. Their trajectories cannot be explained by close encounters with Neptune alone, given the latter's current orbit. The hot orbits of such 5:2 resonant KBOs, unlike hot orbits of previously known resonant KBOs, may imply that these objects were pre-heated to large inclination and large eccentricity prior to resonance capture by a migratory Neptune. Our first discovered Neptunian Trojan, 2001QR322, may not owe its existence to Neptune's migration at all. The trajectory of 2001QR322 is remarkably stable; the object can undergo tadpole-type libration about Neptune's leading Lagrange (L4) point for at least 1 Gyr with a libration amplitude of 24 deg. Trojan capture probably occurred while Neptune accreted the bulk of its mass. For an assumed albedo of 12--4%, our Trojan is 130--230 km in diameter. Model-dependent estimates place the total number of Neptune Trojans resembling 2001QR322 at 20--60. Their existence might rule out violent orbital histories for Neptune.

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arXiv2003

Scintillation Caustics in Planetary Occultation Light Curves

We revisit the GSC5249-01240 light curve obtained during its occultation by Saturn's North polar region. In addition to refractive scintillations, the power spectrum of intensity fluctuations shows an enhancement of power between refractive and diffractive regimes. We identify this excess power as due to high amplitude spikes in the light curve and suggest that these spikes are due to caustics associated with ray crossing situations. The flux variation in individual spikes follows the expected caustic behavior, including diffraction fringes which we have observed for the first time in a planetary occultation light curve. The presence of caustics in scintillation light curves require an inner scale cut off to the power spectrum of underlying density fluctuations associated with turbulence. Another possibility is the presence of gravity waves in the atmosphere. While occultation light curves previously showed the existence of refractive scintillations, a combination of small projected stellar size and a low relative velocity during the event have allowed us to identify caustics in this occultation. This has led us to re-examine previous data sets, in which we have also found likely examples of caustics.

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