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  • 1
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    The unusual morphology of molecular hydrogen emission in the planetary nebula J900 (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We report new high-resolution near-infrared imaging observations of the planetary nebula J900, in broadband J, H, and K, and narrowband 2.122 micrometers (for H2 1-0 S(1)), Brackett-gamma, and continuum filters. The H2 images reveal a remarkable set of outward-extending features not detected in any previous observations of theis object. In the northwest lobe of the inner bipolar region, the H2 emission, Brackett-gamma emission, and underlying continuum are spatially resolved. The relative positions of the peaks of the line emission suggest an ionization front seen edge-on. The continuum emission, apparently located nearer to the central star, is likely due to transiently heated small dust grains. The extended H2 emission features are probably excited either by oblique shocks caused by material ejected from the nebula, or by radiation leaking from holes in the opacity surrounding the ionized shell.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 109; 3; p. 1173-1180
    Format: text
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  • 2
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    On the nature of the unidentified EGRET sources: Are they Geminga-like pulsars? (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Observations with the Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory (CGRO) show more than 30 unidentified gamma-ray sources concentrated along the Galactic plane. Based on their spatial distribution, the typical distances of the sources are found to be between 1.2 and 6 kpc. Luminosity estimates made using the estimated distances of the sources and their observed gamma-ray fluxes lie in the range (0.7-16.7) x 10(exp 35) ergs/s. These values, on the average, appear to be higher than the luminosities of the gamma-ray pulsars observed by EGRET. The luminosity estimates indicate that the low-latitude unidentified EGRET sources cannot be explained as a group of older, low-luminosity pulsars like Geminga, although the high-latitude sources may be candidates.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 441; 2; p. L61-L64
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  • 3
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    EGRET observations of the BL Lacertae objects 0716+714 and 0521-365 (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: During the Compton Observatory's viewing programs Phase 1 (1991 April to 1992 November, also known as the All-Sky Survey) and Phase 2 (1992 November to 1993 September), the BL Lac object 0716+714 was in the field of view of the EGRET telescope a total of six times, three times in Phase 1 and three more times in Phase 2, while the BL Lac object 0521-365 was in the field of view of EGRET only once in Phase 1. The source 0716+714 was detected in high-energy gamma rays by EGRET at a flux level of (2.0 +/- 0.4) x 10(exp -7) photons/sq cm/s for E greater than 100 MeV with a 6 sigma significance when it was first observed by EGRET in 1992 January 10 to 23. The corresponding spectral slope of the photon number distribution is determined to be -2.04 +/- 0.33. The gamma-ray flux of 0716+714 showed considerable time variability in subsequent EGRET observations. But the spectral slope stayed about the same within the statistical uncertainties of the EGRET data. The average spectral slope of the four viewing periods during which the photon flux of 0716+714 stayed above the EGRET detection threshold is found to be -1.85 +/- 0.20 from the combined data. The source 0521+365 was detected by EGRET in 1992 May 14 to June 4 at a flux level of (1.8 +/- 0.5) x 10(exp -7) photons/sq cm/s for E greater than 100 MeV with a 4 sigma significance. The corresponding spectral slope of the photon number distribution is found to be 2.16 +/- 0.36. Details of the observations of these two BL Lac objects with the EGRET telescope are presented.
    Keywords: ASTRONOMY
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 442; 1; p. 96-104
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  • 4
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    Palomar observations of the collision of comet Shoemaker-Levy 9 with Jupiter (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We present two papers of the near-infrared observations from Palomar observatory of the impact of fragment R of comet Shoemaker-Levy 9 with Jupiter on July 21, 1994. The first paper is concerned with the lightcurves found from these observations: Two instruments were used to image the event at 3.2 and 4.5 microns simultaneously. The lightcurves from these image sequences both show two faint precursor flashes, a bright main peak, and several oscillations over the following hour. We identify the precursor flashes with the entry of the bolide into Jupiter's upper atmosphere, and with the post-impact ejecta plume rising above the planet's limb. The main peak is due to the re-entry of the collapsing plume in Jupiter's atmosphere and the resultant shock heating. The second paper is concerned with the low-resolution spectra from the lightcurves: Low-resolution 8-13 micron spectra taken near the peak of the lightcurve show a broad emission feature that resembles the delicate silicate feature commonly seen in comets and the interstellar medium. We use this feature to estimate the dust content of the impact plume. The overall infrared spectral energy distribution at the time of peak brightness is consistent with emission from an optically-thin layer of small particles at approximately 600 K. Integrating over the spectrum and the lightcurve, we obtain a total radiated energy from the R impact of greater than or equal to 10(exp 25) ergs and a plume mass of greater than or equal to 3 x 10(exp 13) g.
    Keywords: ASTRONOMY
    Type: NASA-CR-199366 , NAS 1.26:199366
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  • 5
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    EGRET gamma-ray sources: GRO J0744+54 and GRO J0957+65 (= BL Lacertae object 0954+658) (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: EGRET detected an unidentified source, GRO J0744+54, at a significance of 6.5 sigma, during its observations from 1993 June 28 to July 12. The source was seen again in the following 2 week viewing period and was weakly evident in the earlier phase 1 of the EGRET observations. Considering the variability of its gamma-ray flux, and its location at high Galactic latitude, GRO J0744+54 is likely to be a previously undetected blazar. Its most likely identification is with the radio source 87GB 073840.5+545138. A second source, GRO J0957+65, was seen by EGRET during the same two viewing periods at a combined significance of 5.7 sigma. The most probable counterpart of GRO J0957+65 is the BL Lacertae object 0954+658. The spectra, time variability, and positions of the two sources are presented. Multiwavelength observations of 0954+658 are also presented.
    Keywords: ASTRONOMY
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 445; 1; p. 189-195
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  • 6
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    Near-infrared (Fe II) and Pa Beta imaging and spectroscopy of Arp 220 (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: We have imaged the ultraluminous infrared galaxy Arp 220 in light of the near-infrared (Fe II) 1.257 micron and Pa-beta lines, and have obtained spectra in the J- and H-band atmospheric windows. Arp 220 is a strong source of (Fe II) and Pa-beta emission, with luminosities of 1.3 x 10(exp 41) and 9.2 x 10(exp 40) ergs/s, respectively. The (Fe II) and Pa-beta emission are both extended over the central 2 sec-3 sec, but with different morphologies. We suggest that the extended (Fe II) emission is produced through the interaction of fast shocks with ambient gas in the interstellar medium (ISM) at the base of the outflowing, supernovae-driven superwind mapped by Heckman et al. (1987). The bolometric luminosity of the starburst required to power this wind is estimated to be at least 2 x 10(exp 11) solar luminosity. If the spatially unresolved (Fe II) emission is produced via a large number of supernova remnants, the implied rate is approximately 0.6/yr. The overall luminosity of such a starburst could account for a large fraction (1/2-1/3) of the Arp 220 energy budget, but the large deficit of ionizing photons (as counted by the Pa-beta luminosity) requires that the starburst be rapidly declining and/or have a low upper mass cutoff. Alternatively, dust may effectively compete with the gas for ionizing photons, or much of the ionizing radiation may escape through 'holes' in the ISM. It is also possible that a buried active galactic nuclei (AGN) produces a large fraction of the unresolved (Fe II) and Pa-beta emission. We briefly discuss these possibilities in light of these new imaging and spectroscopic data.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 440; 1; p. 200-209
    Format: text
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