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  • 1
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    Evidence for precession of the R Aquarii jet (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Several models of the R Aqr northeast jet have been proposed which attempt to explain the presence of shock excitation, resulting in a confusing picture of this nearest astrophysical jet. This paper compares observations of the jet in the R Aqr system with the HST's Faint Object Camera (FOC) and radio continuum images acquired with the VLA. The forbidden-O III jet structure is derived from restored FOC imagery, which has been convolved with an elliptical Gaussian of the same size as the restoring beam of the 6-cm VLA maps, allowing image comparison at the same spatial resolution. It is found that, at increasing distances from the central star, the forbidden O III emission knots that comprise the optical jet occur at systematically larger position angles when compared with corresponding features in the radio images. The angular separation of forbidden O III and radio continuum emission can be understood in terms of a shock formed when ejecta in the stream interacts with previously existing circumstellar material and subsequently cools by nebular line emission.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 411; 1; p. 235-238.
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  • 2
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    Confirmation of interstellar methylene (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Four spectral emission features of the N(sub KK) = 4(sub 04) -3(sub 13) rotational transition of methylene (CH2) have been detected at signal levels 5-7 sigma above noise toward the hot core of the Orion-KL nebula and the molecular cloud in proximity to the continuum source W51 M. Specifically, in both sources we have resolved the F = 6-5, 5-4, and 4-3 hyperfine transitions of the J = 5-4 fine-structure levels and detected the blended hyperfine structure of the J = 4-3 fine structure levels. At the J = 3-2 fine-structure levels, we have observed new transitions of NS, a known interstellar molecule, which severely contaminates the search for CH2 hyperfine transitions. These new sensitive observations finally confirm the existence of interstellar CH2 which was tentatively reported by us some years ago.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 438; 1; p. 259-264
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  • 3
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    The 0623 + 71 bow shock nebula (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Deep radio continuum and deep narrow-band optical emission-line images showing the cataclysmic variable 0623 + 71 engulfed in a bow shock morphology are presented. The limb-brightened H-alpha, forbidden N II and 6 cm radio continuum emission regions define the global nebular morphology, extending to much greater spatial distances than the apex-confined forbidden O III. These morphologies are consistent with shock excitation. Complementary spectroscopy (3400-7400 A) is presented for the apex and east and west limbs of the bow shock, yielding diagnostic emission-line parameters which also indicate shock excitation. Moreover, archival IUE spectra (1200-2000 A) suggest that 06231 + 71 may be in a standstill phase. A mass-loss rate of about 1.4 x 10 exp -11 solar masses/yr and a total nebular mass of about 2.4 x 10 exp -3 solar masses are derived. Thus the nebula, by virtue of its small mass and shock excited line emission, is not a planetary nebula; it is simply a cataclysmic binary system with a strong stellar wind moving supersonically with respect to the interstellar medium.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 393; 1, Ju
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  • 4
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    Comparing restored HST and VLA imagery of R Aquarii (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The maximum entropy method is applied to Hubble Space Telescope data taken of the R Aquarii binary system and its jet with the Faint Object Camera in order to restore an image in forbidden O III at 5007 A plagued by spherical aberration and detector saturation. These results are compared with 2-cm radio continuum imagery taken with the Very Large Array at the same limiting resolution of about 0.1 arcsec. The comparison suggests that shock excitation of the inner jet accounts for a spatial difference between the forbidden O III and radio continuum emission regions.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 386; 293-298
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  • 5
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    Comparisons of SiO maser and long-period variable positions in the R Aquarii and Omicron Ceti binary systems (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: It has been determined that the absolute position of the centroid of SiO maser-emitting spots toward both R Aqr and Omicron Cet are coincident with the position of the long-period variables (LPVs) in these binary systems to within the errors of measurement. The SiO positions were determined with the Hat Creek interferometer, while the LPV positions were determined with the 8-in transit circle of the US Naval Observatory. These results contradict an earlier report of a circumbinary SiO maser far removed from the LPV in the R Aqr binary system; statistical reasons for the discrepancy are suggested. High-resolution spectra of both sources are presented and possible models are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 361; 663-666
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  • 6
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    Ultraviolet and optical spectroscopy of the R Aquarii symmetrical jet (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The first ultraviolet spectrum of the southwest (SW) component of the symmetrical jet in the R Aquarii binary system has been obtained in the range 1200-2000 A with the IUE. These results are compared to more encompassing spectra of the central H II region taken at the same time and also similar spectra of the northeast (NE) jet component obtained six months earlier. Moreover, optical spectra of both the NE and SW jet components in the range 3400-9800 A were obtained within about 6 months and about 1 month, respectively, of the ultraviolet spectra. These highly complementary observations argue that excitation of the symmetrical jet may be due to shock excitation as the jet components overtake and impact the previously ionized material associated with the expanding inner nebulosity. The problems with this shock model as well as problems with competing photoionization models are discussed. It is suggested that the jet components were ejected less than 90 years ago.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 377; 227-234
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  • 7
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    Jet activity in the symbiotic variable R Aquarii (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Low-resolution ultraviolet spectra of the R Aquarii jet have been obtained with the International Ultraviolet Explorer (IUE). The most recent IUE observations indicate the ionization state of the jet is increasing. Subarcsecond, Very Large Array observations of R Aquarii have resolved the radio-continuum structure into discrete parcels of emission that are extended and nearly collinear. R Aquarii provides evidence that indicates stellar jet activity is not unique to objects associated with high-energy emission processes alone. Rather, the nature of the aligned radio-optical features that comprise the R Aquarii jet indicate that directional mass expulsion, in the form of discrete-collimated ejecta, probably reflect a general, underlying, physical process associated with a wide variety of peculiar stellar objects. As such, the R Aquarii jet constitutes a prototype for jet activity in composite or peculiar emission stars.
    Keywords: ASTROPHYSICS
    Type: Canadian Journal of Physics (ISSN 0008-4204); 64; 523-526
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  • 8
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    R Aquarii - The large-scale optical nebula and the Mira variable position (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The R Aquarii symbiotic star system is surrounded by a large-scale optical nebula. Observations of the nebular forbidden O III structure are presented and its morphological significance are discussed in context with previously observed small-scale radio-continuum features, which may be related. It is suggested that a precessing accretion disk may explain the global features of both the large-scale optical emission and the small-scale radio emission. Moreover, an accurate position has been determined of the system's Mira, which suggests that a recent theoretical model, yielding an egg-shaped central H II region for symbiotic systems with certain physical parameters, may apply to R Aquarii. The optical position of the 387 d period Mira variable is consistent with previous findings in the radio, that SiO maser emission is far removed from the Mira photosphere.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 95; 1478-148
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  • 9
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    The unusual radio outburst of Nova Vulpeculae 1984 No. 2 (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Multifrequency radio monitoring of Nova Vulpeculae 1984 No. 2 has revealed a unique radio light curve, exhibiting a strong outburst which precedes the appearance of normal radio emission from the principal ejecta of the nova by at least 100 days. The early emission is extremely optically-thick and has brightness temperature in excess of 100,000 K. A model is discussed in which the radiation is produced by a strong shock propagating outward through the principal ejecta of the nova, as a result of an interaction with a later, high velocity wind from the central source. It is shown that the general features of the radio light curve can be explained by the presence of a central wind with a mass loss rate of about 0.00001 solar masses/yr, lasting for a period of 200 to 300 days after the optical outburst. The first radio map of nova ejecta shortly after outburst is presented. Comparison of the angular expansion rate to the ejection velocity implies a distance of 3.6 kpc, and preliminary analysis of the main outburst emission indicates a mass and kinetic energy of the ejecta respectively of about 0.0008 solar masses and 8 x 10 to the 45th erg.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 183; 1, Se
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  • 10
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    Sub-arc second 2 centimeter continuum and SiO spectral line observations of R Aquarii (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: VLA observations with a limiting spatial resolution of about 0.15 arcsec were attempted along with complementary observations of SiO emission using the three-element Hat Creek interferometer to determine an accurate position of the long-period variable (LPV) of the R Aquarii binary system. The observations indicate that the LPV wind is distorted by the photoionization of the hot campanion's accretion disk, that precession of the accretion disk may occur, and that the observed v = 1, J = 2-1 transition emanates from a circumbinary layer far removed from the position of the LPV itself.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 309; L53-L57
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