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Statistics of Hipparcos binaries: probing the 1-10 AU separation range
Lindegren, L.; Quist, C. F.
The observation of double stars by Hipparcos is modelled in order to check the statistics of double-star solutions in the Hipparcos Catalogue and to set quantitative limits on binary distributions. A Galaxy model is combined with models of binary distributions and of the observation process to derive the expected numbers of the different kinds of …
Electro-Mechanical Coupling Between the Photosphere and Transition Region
Tarbell, T. D.; Shine, R.; Ryutova, M.
We study the response of the chromosphere and transition region to dynamic changes in the photospheric network magnetic fields. We present results from simultaneous measurements taken by TRACE in chromospheric and transition region (C iv) images, high-resolution magnetograms taken by MDI, and spectra of chromospheric (C ii) and transition region l…
The Hubble Space Telescope Revisits the Proper Motion of Pulsar B0656+14
Caraveo, P. A.; De Luca, A.; Mignani, R. P.
We report the first successful measurement (with the Hubble Space Telescope Wide Field Planetary Camera 2) of a significant proper motion for an mV~25 object, which we had proposed as the optical counterpart of the radio pulsar PSR B0656+14. The yearly displacement of 43+/-2 mas is highly significant and, while in agreement with early r…
NOTE: Ground-Based Observations of Cloud Features on Uranus
Baines, K. H.; Sromovsky, L. A.; Fry, P. M. +1 more
NSFCAM observations at 1.7 µm in 1998 and 1999 recorded the first discrete cloud features to appear in ground-based digital images of Uranus and the brightest such feature ever observed. The differential contributions of these northern hemisphere features to Uranus' disk-integrated brightness range from 0.8±0.2% and 0.11±0.3% for two 1998 fe…
Phase Time and Envelope Time in Time-Distance Analysis and Acoustic Imaging
Duvall, Thomas L., Jr.; Chou, Dean-Yi
Time-distance analysis and acoustic imaging are two related techniques for probing the local properties of the solar interior. In this study, we discuss the relation of phase time and envelope time between the two techniques. The location of the envelope peak of the cross-correlation function in time-distance analysis is identified as the travel t…
Langmuir Waves in the Vicinity of interplanetary Shocks and the Consequences for Type II Burst Models
MacDowall, R. J.; Thejappa, G.
The in situ wave data obtained by the Ulysses Unified Radio And Plasma wave experiment in the vicinity of a large number of interplanetary shocks show that Langmuir waves (1) are observed in only ~15% of the interplanetary shocks, (2) occur mostly in the upstream regions, and (3) are produced in the vicinity of both quasi-parallel Q∥ an…
Radiometric Calibration of the Vacuum-Ultraviolet Spectrograph SUMER on the SOHO Spacecraft with the B Detector
Wilhelm, Klaus; Schühle, Udo; Curdt, Werner +3 more
The Solar Ultraviolet Measurement of Emitted Radiation (SUMER) vacuum-ultraviolet spectrograph was calibrated in the laboratory before the integration of the instrument on the Solar and Heliospheric Observatory (SOHO) spacecraft in 1995. During the scientific operation of the SOHO it has been possible to track the radiometric calibration of the SU…
Hubble Space Telescope Imaging of Central Stars of High-Excitation Planetary Nebulae with WFC and WFPC2
Groth, Edward J.; Wolff, Michael J.; Code, Arthur D.
We present observations of four high excitation planetary nebulae (IC 2165, Me 2-1, NGC 2440, NGC 7027) taken with the Wide Field Camera and the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. The high angular resolution of the instruments allows for the unambiguous identification of the central star, which was not found to be t…
Two Böhm-Vitense Gaps in the Main Sequence of the Hyades
de Bruijne, J. H. J.; de Zeeuw, P. T.; Hoogerwerf, R.
Hipparcos proper motions and trigonometric parallaxes allow the derivation of secular parallaxes that fix the distances to individual stars in the Hyades to an accuracy of ~2%. The resulting color-absolute magnitude diagram for 92 high-fidelity single members of the cluster displays a very narrow main sequence, with two turnoffs and associated gap…
Mapping Jupiter's Latitudinal Bands and Great Red Spot Using HST/WFPC2 Far-Ultraviolet Imaging
West, Robert A.; Ballester, Gilda E.; Crisp, David +16 more
Jupiter's low and mid-latitudes are examined using ultraviolet (UV) images obtained with the Hubble Space Telescope Wide Field and Planetary Camera 2 over the period of 1994-1997. Effective atmospheric pressures probed by the F160W, F218W, and F255W are estimated at 100, 165, and 370 mbar, respectively, at low latitudes. Far-ultraviolet images of …