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  • 1
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    Thirteen new BL Lacertae objects discovered by an efficient x ray/radio/optical technique (1992)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: The discovery of 13 serendipitous BL Lac objects in the Einstein IPC Slew Survey by means of x ray/radio vs. x ray/optical color-color diagrams and confirmation by optical spectroscopy are reported. These 13 BL Lacs were discovered using a technique which exploits the characteristic broad band spectra of BL Lacs. New VLA detections provide accurate fluxes (f(6 cm) is approximately 0.5 mJy) and 2 in. positions, facilitating the determination of an optical counterpart. All 13 new BL Lacs show essentially featureless optical spectra. Nine of these lie within the range of colors of known x ray selected BL Lacs. Of the remaining four, one is apparently x ray louder (by a factor of 1.5) or optically quieter (by 0.8 mags); and three are optically louder (by 1-1.3 mags) than x ray selected BL Lacs. Approximately 50 new BL Lacs in total are expected from VLA work and upcoming Australia Telescope observations, yielding a complete Slew Survey sample of approximately 90 BL Lacs.
    Schlagwort(e): ASTRONOMY
    Materialart: Smithsonian Astrophysical Observatory, The Einstein All-Sky Slew Survey; 18 p
    Format: application/pdf
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  • 2
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    The on-orbit performance of WFPC2 (1994)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-08-27
    Beschreibung: The second Wide Field and Planetary Camera (WFPC2) was successfully installed in the Hubble Space Telescope during the STS-61 servicing mission in 1993 December. The primary objective of this new camera is to provide diffraction-limited photometric imaging over a wide field and a spectral range from 0.12 to 1.0 micrometer. Here we provide an overview of the characteristics of the new instrument and offer our perspectives based on the first 6 months of operations on-orbit.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 435; 1; p. L3-L6
    Format: text
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  • 3
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    Far-ultraviolet imaging of the globular cluster NGC 6681 with WFPC2 (1994)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: We have imagined the globular cluster NGC 6681 in the far-UV and visible with Wide Field/Planetary Camera-2 (WFPC2) on the Hubble Space Telescope (HST). Our far-UV images show a sparsely populated and fully resolved central region, and we detect 122 stars. The far-UV to visible color-magnitude diagram shows a well-defined horizontal branch with no evidence for hot, more evolved descendants. We find one hot horizontal-branch star significantly below the model zero-age horizontal branch, but the rest are consistent with evolutionary models within uncertainties in calibration, distance, and reddening. The center of the cluster harbors two luminous blue stragglers. Our far-UV images graphically confirm that there is no steep density gradient at small radii among the horizontal-branch stars of this post-core-collapse cluster and show no evidence for significant color gradients.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 435; 1; p. L55-L58
    Format: text
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  • 4
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    Accurate positions and finding charts for 528 high-redshift, luminous quasars (1992)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: Finding charts and J2000 positions accurate to about 1 arcsec are presented for the 528 high-redshift (z is greater than 1), luminous (MV is less than -25.5) quasars investigated in the HST Snapshot Survey. A histogram showing the distribution of the differences between the positions determined by the Space Telescope Science Institute Astrometric Support Program and the catalog positions is provided.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 104; 678
    Format: text
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  • 5
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    First Hubble Space Telescope observations of the brightest stars in the Virgo galaxy M100 = NGC 4321 (1994)
    In:  Other Sources
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    Publikationsdatum: 2019-08-28
    Beschreibung: As part of both the Early Release Observations from the Hubble Space Telescope (HST) and the Key Project on the Extragalactic Distance Scale, we have obtained multiwavelength BVR Wide Field/Planetary Camera-2 (WFPC2) images for the face-on Virgo cluster spiral galaxy M100 = NGC 4321. We report here preliminary results from those observations, in the form of a color-magnitude diagram for approximately 11,500 stars down to V approximately 27 mag and a luminosity function for the brightest blue stars which is found to have a slope of 0.7, in excellent agreement with previous results obtained for significantly nearer galaxies. With the increased resolution now available using WFPC2, the number of galaxies in which we can directly measure Population I stars and thereby quantify the recent evolution, as well as test stellar evolution theory, has dramatically increased by at least a factor of 100. Finally, we find that the stars are present in M100 at the colors and luminosities expected for the brightest Cepheid variables in galaxies.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 435; 1; p. L31-L34
    Format: text
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  • 6
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    Various Roentgen satellite (ROSAT) related studies (1994)
    In:  CASI
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: The first six months was spent obtaining ROSAT Survey data for as many Slew Survey sources as possible. ROSAT Survey (RASS) counterparts for 605 of the 819 Slew sources (or 75 percent). were found at MPE, providing RASS positions, fluxes, and hardness ratios. The positions were used immediately to confirm or reject proposed catalog identifications from SIMBAD and NED, and to begin a program of identifying new BL Lac objects with high efficiency. In the final six months of the award, extensive analysis were preformed on the RASS counterpart data at Cambridge screening Slew sources with multiple RASS counterparts (up to 23); extended sources and sources with large discrepancies between the RASS and Slew positions. The possibly highly absorbed sources were also studied. Finally, the RASS data has helped to identify optical counterparts to Slew Survey sources - BL Lacs stars, and 'blank fields'.
    Schlagwort(e): ASTRONOMY
    Materialart: NASA-CR-196399 , NAS 1.26:196399
    Format: text
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  • 7
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    A critical review of charged particle astronomy at Saturn: The evidence for co-orbiting material in the inner satellite system (1990)
    In:  CASI
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: The charged particle observations from Pioneer and Voyager at Saturn were reassessed with a view towards providing limits on the amount of unseen dust and debris that may exist in the Saturnian system. Such estimates are crucial for planning the Cassini tour of Saturn. The data from Pioneer 11 and Voyager were reviewed, intercompared, and correlated with model predictions to set limits on the matter distribution.
    Schlagwort(e): ASTRONOMY
    Materialart: NASA-CR-187348 , NAS 1.26:187348
    Format: application/pdf
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  • 8
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    The Global Oscillation Network Group site survey, 2: Results (1994)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-24
    Beschreibung: The Global Oscillation Network Group (GONG) Project will place a network of instruments around the world to observe solar oscillations as continuously as possible for three years. The Project has now chosen the six network sites based on analysis of survey data from fifteen sites around the world. The chosen sites are: Big Bear Solar Observatory, California; Mauna Loa Solar Observatory, Hawaii; Learmonth Solar Observatory, Australia; Udaipur Solar Observatory, India; Observatorio del Teide, Tenerife; and Cerro Tololo Interamerican Observatory, Chile. Total solar intensity at each site yields information on local cloud cover, extinction coefficient, and transparency fluctuations. In addition, the performance of 192 reasonable networks assembled from the individual site records is compared using a statistical principal components analysis. An accompanying paper descibes the analysis methods in detail; here we present the results of both the network and individual site analyses. The selected network has a duty cycle of 93.3%, in good agreement with numerical simulations. The power spectrum of the network observing window shows a first diurnal sidelobe height of 3 x 10(exp -4) with respect to the central component, an improvement of a factor of 1300 over a single site. The background level of the network spectrum is lower by a factor of 50 compared to a single-site spectrum.
    Schlagwort(e): ASTRONOMY
    Materialart: Solar Physics (ISSN 0038-0938); 152; 2; p. 351-379
    Format: text
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  • 9
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    Radiative signatures from impact of Comet Shoemaker-Levy-9 on Jupiter (1994)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-24
    Beschreibung: The visible optical power emitted from the expansion plumes from 0.4 and 2 km diameter fragments of Shoemaker-Levy are expected to be, approximately 25% and comparable to, the visible solar flux reflected from Jupiter, respectively, for several minutes, and could be easily observed by sensors on the Galileo spacecraft. Earth-based observers can detect these plumes as these expand over the SW limb of Jupiter and come into earth view some minutes after impact!
    Schlagwort(e): ASTRONOMY
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 21; 14; p. 1551-1553
    Format: text
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  • 10
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    Developing technologies for lunar-based astronomy (1992)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: Prospects for lunar-based astronomy and the development of the required technologies are briefly reviewed. A systematic approach to lunar-based astronomy includes a progression in capability from small automated telescopes to the 16-meter reflector on the moon. A next step beyond the 16-meter reflector will be a Lunar Optical/Ultraviolet/Infrared Synthesis Array. Intermediate steps are represented by the Lunar Transit Telescope and the Lunar Cluster Telescope Experiment. Priorities for the required technology development are identified.
    Schlagwort(e): ASTRONOMY
    Materialart: In: Engineering, construction, and operations in space III: Space '92; Proceedings of the 3rd International Conference, Denver, CO, May 31-June 4, 1992. Vol. 2 (A93-41976 17-12); p. 1853-1864.
    Format: text
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