Search Publications
Polar shapelets
Refregier, Alexandre; Massey, Richard
The shapelets method for image analysis is based upon the decomposition of localized objects into a series of orthogonal components with convenient mathematical properties. We extend the `Cartesian shapelet' formalism from earlier work, and construct `polar shapelet' basis functions that separate an image into components with explicit rotational s…
High-Resolution Radio Observations of the Colliding-Wind Binary WR 140
Dougherty, S. M.; Claussen, M. J.; Zauderer, B. A. +2 more
Milliarcsecond resolution Very Long Baseline Array (VLBA) observations of the archetype W-R+O star colliding-wind binary (CWB) system WR 140 are presented for 23 epochs between orbital phases 0.74 and 0.97. At 8.4 GHz, the emission in the wind-collision region (WCR) is clearly resolved as a bow-shaped arc that rotates as the orbit progresses. We i…
Candidate Type II Quasars from the Sloan Digital Sky Survey. III. Spectropolarimetry Reveals Hidden Type I Nuclei
Hall, Patrick B.; Strauss, Michael A.; Brinkmann, J. +7 more
We have conducted spectropolarimetry of 12 type II (obscured) quasar candidates selected from the spectroscopic database of the Sloan Digital Sky Survey on the basis of their emission-line properties. Polarization was detected in all objects, with nine being highly polarized (>3%) and with polarization reaching as high as 17% in two objects. Br…
Coronal Mass Ejection Shock and Sheath Structures Relevant to Particle Acceleration
Gombosi, T. I.; Tóth, G.; Zurbuchen, T. H. +6 more
Most high-energy solar energetic particles are believed to be accelerated at shock waves driven by coronal mass ejections (CMEs). The acceleration process strongly depends on the shock geometry and the structure of the sheath that forms behind the shock. In an effort to understand the structure and time evolution of such CME-driven shocks and thei…
HS 2331+3905: The cataclysmic variable that has it all
Gänsicke, B. T.; Marsh, T. R.; Hagen, H. -J. +6 more
We report detailed follow-up observations of the cataclysmic variable HS 2331+3905, identified as an emission-line object in the Hamburg Quasar Survey. An orbital period of 81.08 min is unambiguously determined from the detection of eclipses in the light curves of HS 2331+3905. A second photometric period is consistently detected at P ≃ 83.38 min,…
The progenitor of SN 2005cs in the Whirlpool Galaxy
Smartt, Stephen J.; Maund, Justyn R.; Danziger, I. John
The progenitor of SN 2005cs, in the galaxy M51, is identified in pre-explosion Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) imaging. Differential astrometry, with post-explosion ACS High Resolution Channel (HRC) F555W images, permitted the identification of the progenitor with an accuracy of 0.006 arcsec.…
Relationship between Magnetic Power Spectrum and Flare Productivity in Solar Active Regions
Abramenko, V. I.
Power spectra of the line-of-sight magnetograms were calculated for 16 active regions of different flare activity. Data obtained by the Michelson Doppler Imager instrument on board the Solar and Heliospheric Observatory in high-resolution mode were used in this study. For each active region, the daily soft X-ray flare index, A, was calculated. Thi…
Simultaneous Chandra X ray, Hubble Space Telescope ultraviolet, and Ulysses radio observations of Jupiter's aurora
MacDowall, R. J.; Waite, J. H.; Cravens, T. E. +8 more
Observations of Jupiter carried out by the Chandra Advanced CCD Imaging Spectrometer (ACIS-S) instrument over 24-26 February 2003 show that the auroral X-ray spectrum consists of line emission consistent with high-charge states of precipitating ions, and not a continuum as might be expected from bremsstrahlung. The part of the spectrum due to oxyg…
XMM-Newton spectroscopy of high-redshift quasars
O'Brien, P. T.; Reeves, J. N.; Page, K. L. +1 more
XMM-Newton observations of 29 high-redshift (z > 2) quasars, including seven radio-quiet, 16 radio-loud and six broad absorption line (BAL) objects, are presented; due to the high redshifts, the rest-frame energy bands extend up to ~30-70 keV. Over 2-10 keV, the quasars can be well fitted in each case by a simple power law, with no strong evide…
The Discrepancy between Solar Abundances and Helioseismology
Basu, Sarbani; Antia, H. M.
There have been recent downward revisions of the solar photospheric abundances of oxygen and other heavy elements. These revised abundances along with OPAL opacities are not consistent with seismic constraints. In this work we show that the recently released Opacity Project opacity tables cannot resolve this discrepancy either. While the revision …