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  • ASTRONOMY  (132)
  • Fluid Mechanics and Heat Transfer
  • 1995-1999  (55)
  • 1990-1994  (115)
  • 1
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    Thirteen new BL Lacertae objects discovered by an efficient x ray/radio/optical technique (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: 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.
    Keywords: ASTRONOMY
    Type: Smithsonian Astrophysical Observatory, The Einstein All-Sky Slew Survey; 18 p
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  • 2
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    The on-orbit performance of WFPC2 (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: 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.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 435; 1; p. L3-L6
    Format: text
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  • 3
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    The performance and calibration of WFPC2 on the Huble Space Telescope (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The Wide Field Planetary Camera 2 (WFPC2) was installed in the Hubble Space Telescope (HST) in 1993 December. Since then, the instrument has been providing high-quality images. A significant among of calibration data has been collected to aid in the understanding of the on-orbit performance of the instrument. Generally, the behavior of the camera is similar to its performance during the system-level thermal vacuum test at JPL in 1993 May. Surprises were a significant charge-transfer-efficiency (CTE) problem and a significant growth rate in hot pixels at the original operating temperature of the CCDs (-76 deg C). The operating temperature of the WFPC2 CCDs was changed to -88 deg C on 1994 April 23, and significant improvements in CTE and hot pixels are seen at this temperature. In this paper we describe the on-orbit performance of the WFPC2. We discuss the optical and thermal history, the instrument throughput and stability, the Point Spread Function (PSF), the effects of undersampling on photometry, the properties of cosmic rays observed on-orbit, and the geometric distortion in the camera. We present the best techniques for the reduction of WFPC2 data, and describe the construction of calibration products including superbiases, superdarks, and flat fields.
    Keywords: ASTRONOMY
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 107; 708; p. 156-178
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  • 4
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    Far-ultraviolet imaging of the globular cluster NGC 6681 with WFPC2 (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: 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.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 435; 1; p. L55-L58
    Format: text
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  • 5
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    Accurate positions and finding charts for 528 high-redshift, luminous quasars (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: 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.
    Keywords: ASTRONOMY
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 104; 678
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  • 6
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    First Hubble Space Telescope observations of the brightest stars in the Virgo galaxy M100 = NGC 4321 (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: 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.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 435; 1; p. L31-L34
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  • 7
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    Various Roentgen satellite (ROSAT) related studies (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: 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'.
    Keywords: ASTRONOMY
    Type: NASA-CR-196399 , NAS 1.26:196399
    Format: text
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  • 8
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    The redshift-space neighborhoods of 36 loose groups of galaxies. 1: The data (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: We have selected 36 loose groups of galaxies (RGH89) with at least five members, and with mean redshift average value of CZ is greater than 3200 km/s. These groups all lie within the first two slices of the CfA redshift survey 8(sup h) less than or equal to alpha less than or equal to 17(sup h) and 26.5 deg less than or equal to delta less than or equal to 38.5 deg). For each of these groups, we define the redshift-space neighborhood as a region centered on the group coordinates and delimited by a circle of projected radius R(sub cir) = 1.5/h Mpc on the sky, and by a velocity interval delta (sub cz) = 3000 km/s. Here we give the redshifts of 334 galaxies in these redshift-space neighborhoods. For completeness, we also give the redshifts of the 232 original members. These data include 199 new redshifts. We demonstrate that these samples of fainter galaxies significantly increase the number of members.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 109; 4; p.1458-1475
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  • 9
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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
    Publication Date: 2019-07-13
    Description: 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.
    Keywords: ASTRONOMY
    Type: NASA-CR-187348 , NAS 1.26:187348
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  • 10
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    The Global Oscillation Network Group site survey, 2: Results (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: 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.
    Keywords: ASTRONOMY
    Type: Solar Physics (ISSN 0038-0938); 152; 2; p. 351-379
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