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Hilo, HI, United States

Chun M.R.,University of Hawaii at Hilo | Lai O.,Gemini Observatory | Butterley T.,Durham University | Goebel S.,University of Hawaii at Hilo | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

We present high resolution optical turbulence profiles of the dome and ground-layers measured using a set of Shack- Hartmann wavefront sensors deployed over a field of view of between 0.5 and 1.0 degrees at the focal planes of the University of Hawaii 2.2-m telescope and the Canada-France-Hawaii Telescope on Maunakea, Hawaii. Observations with the experiment were made over the course of several nights on each telescope. We obtain estimates of the strength, distribution, and velocities of optical turbulence from the covariance matrices and maps of the measured wavefront gradients and a decomposition of the measured wavefronts into Zernike polynomials. We find agreement with previous measurements on Maunakea that the ground layer is largely confined within the first tens of meters above the ground and moves at the ground wind velocity. In addition, we spatially resolve the optical turbulence that arises from within the dome. For both facilities we find that the dome seeing is a major component of the overall turbulence strength accounting for more than half of the turbulence within the ground layer and that the dome seeing changes very slowly with a characteristic frequency of less than 1 Hz. While the variety of observing conditions sampled is low, we find that the characteristics of the dome seeing with observation elevation angle and the azimuth angle with respect to the ground wind are quite different on the two telescopes suggesting a different origin to the seeing within the two enclosures. © 2014 SPIE. Source


Wahhaj Z.,European Southern Observatory | Liu M.C.,University of Hawaii at Manoa | Biller B.A.,University of Edinburgh | Nielsen E.L.,University of Hawaii at Manoa | And 6 more authors.
Astronomy and Astrophysics | Year: 2014

We present J,H, CH4 short (1.578 μm), CH4 long (1.652 μm) and Ks-band images of the dust ring around the 10 Myr old star HR 4796 A obtained using the Near Infrared Coronagraphic Imager (NICI) on the Gemini-South 8.1 m Telescope. Our images clearly show for the first time the position of the star relative to its circumstellar ring thanks to NICI's translucent focal plane occulting mask. We employ a Bayesian Markov chain Monte Carlo method to constrain the offset vector between the two. The resulting probability distribution shows that the ring center is offset from the star by 16.7 ± 1.3 milliarcseconds along a position angle of 26 ± 3°, along the PA of the ring, 26.47 ± 0.04°. We find that the size of this offset is not large enough to explain the brightness asymmetry of the ring. The ring is measured to have mostly red reflectivity across the JHKs filters, which seems to indicate micron-sized grains. Just like Neptune's 3:2 and 2:1 mean-motion resonances delineate the inner and outer edges of the classical Kuiper belt, we find that the radial extent of the HR 4796 A and the Fomalhaut rings could correspond to the 3:2 and 2:1 mean-motion resonances of hypothetical planets at 54.7 AU and 97.7 AU in the two systems, respectively. A planet orbiting HR 4796 A at 54.7 AU would have to be less massive than 1.6 MJup so as not to widen the ring too much by stirring. © ESO, 2014. Source


Wahhaj Z.,European Southern Observatory | Liu M.C.,University of Hawaii at Manoa | Biller B.A.,Max Planck Institute for Astronomy | Nielsen E.L.,University of Hawaii at Manoa | And 6 more authors.
Astrophysical Journal | Year: 2013

We present high-contrast image processing techniques used by the Gemini NICI Planet-Finding Campaign to detect faint companions to bright stars. The Near-Infrared Coronographic Imager (NICI) is an adaptive optics instrument installed on the 8 m Gemini South telescope, capable of angular and spectral difference imaging and specifically designed to image exoplanets. The Campaign data pipeline achieves median contrasts of 12.6 mag at 0.″5 and 14.4 mag at 1″ separation, for a sample of 45 stars (V = 4.3-13.9 mag) from the early phase of the campaign. We also present a novel approach to calculating contrast curves for companion detection based on 95% completeness in the recovery of artificial companions injected into the raw data, while accounting for the false-positive rate. We use this technique to select the image processing algorithms that are more successful at recovering faint simulated point sources. We compare our pipeline to the performance of the Locally Optimized Combination of Images (LOCI) algorithm for NICI data and do not find significant improvement with LOCI. © 2013. The American Astronomical Society. All rights reserved.. Source


Nielsen E.L.,University of Hawaii at Manoa | Liu M.C.,University of Hawaii at Manoa | Wahhaj Z.,University of Hawaii at Manoa | Biller B.A.,Max Planck Institute for Astronomy | And 21 more authors.
Astrophysical Journal | Year: 2012

We report the discovery of two low-mass companions to the young A0V star HD1160 at projected separations of 81 ± 5AU (HD1160B) and 533 ± 25AU (HD1160C) by the Gemini NICI Planet-Finding Campaign. Very Large Telescope images of the system taken over a decade for the purpose of using HD1160A as a photometric calibrator confirm that both companions are physically associated. By comparing the system to members of young moving groups and open clusters with well-established ages, we estimate an age of 50+50 -40Myr for HD1160 ABC. While the UVW motion of the system does not match any known moving group, the small magnitude of the space velocity is consistent with youth. Near-IR spectroscopy shows HD1160C to be an M3.5 ± 0.5 star with an estimated mass of 0.22+0.03 -0.04 M⊙, while NIR photometry of HD1160B suggests a brown dwarf with a mass of 33 +12 -9 M Jup. The very small mass ratio (0.014) between the A and B components of the system is rare for A star binaries, and would represent a planetary-mass companion were HD1160A to be slightly less massive than the Sun. © 2012 The American Astronomical Society. All rights reserved. Source


Nielsen E.L.,University of Hawaii at Manoa | Liu M.C.,University of Hawaii at Manoa | Wahhaj Z.,European Southern Observatory | Biller B.A.,University of Edinburgh | And 11 more authors.
Astrophysical Journal | Year: 2014

We present new astrometry for the young (12-21 Myr) exoplanet β Pictoris b taken with the Gemini/NICI and Magellan/MagAO instruments between 2009 and 2012. The high dynamic range of our observations allows us to measure the relative position of β Pic b with respect to its primary star with greater accuracy than previous observations. Based on a Markov Chain Monte Carlo analysis, we find the planet has an orbital semi-major axis of 9.1 AU and orbital eccentricity <0.15 at 68% confidence (with 95% confidence intervals of 8.2-48 AU and 0.00-0.82 for semi-major axis and eccentricity, respectively, due to a long narrow degenerate tail between the two). We find that the planet has reached its maximum projected elongation, enabling higher precision determination of the orbital parameters than previously possible, and that the planet's projected separation is currently decreasing. With unsaturated data of the entire β Pic system (primary star, planet, and disk) obtained thanks to NICI's semi-transparent focal plane mask, we are able to tightly constrain the relative orientation of the circumstellar components. We find the orbital plane of the planet lies between the inner and outer disks: the position angle (P.A.) of nodes for the planet's orbit (211.8 ± 0.°3) is 7.4σ greater than the P.A. of the spine of the outer disk and 3.2σ less than the warped inner disk P.A., indicating the disk is not collisionally relaxed. Finally, for the first time we are able to dynamically constrain the mass of the primary star β Pic to 1.76 M . © 2014. The American Astronomical Society. All rights reserved.. Source

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