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  • ASTROPHYSICS  (8)
  • 1990-1994  (8)
  • 1980-1984
  • 1970-1974
  • 1940-1944
  • 1935-1939
  • 1990  (8)
  • 1
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    WRA 751, a candidate for a new luminous blue variable (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Results are presened on spectroscopic observations (carried out with the ESO 1.52-m telescope at La Silla, Chile) and measurements made by the Infrared Astronomical Satellite on the star WRA 751. It is estimated that the T(eff) of this star is 30,000 K and its E(B-V) is 1.8 mag. Comparison with evolutionary tracks of Maeder and Meynet (1980) indicates that WRA 751 is located in the region of luminous blue variables at a lower limit of the initial mass of about 50 solar masses. Its other physical characteristics, such as the light variability, strong Fe II lines, and the extinction-free spectral energy distribution, suggest that WRA 751 is a candidate for a new luminous blue variable.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 227; 1, Ja
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  • 2
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    Constraints on large-scale clustering from the autocorrelation properties of the X-ray background (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Expectations for the angular correlation function of intensity fluctuations of the extragalacitc 2-10 keV X-ray background are discussed in relation to the two-point spatial correlation functions, xi(r), of X-ray sources. A simple analytic formula for the amplitude of intensity correlations, Gamma(theta), holding in the low-redshift, small-separation approximation, is derived. The HEAO 1 A-2 upper limits on Gamma(theta) have been exploited to derive constraints on the local xi(r) functions of rich clusters of galaxies, of AGNs, and on the AGN-cluster cross-correlation, as well as on evolution of the correlation functions with cosmic time. X-ray data are found to be compatible with the Bahcall and Soneira estimates of xi(cluster-cluster) as well as with the results of recent studies of quasar clustering.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 351; 22-30
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  • 3
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    0108 + 388 - A compact double source with surprising properties (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: 49 cm, 6 cm, and 20 cm observations of the compact double ratio source 0108 + 388 are presented. Extended emission about 20 deg to the east of the core is detected which resembles a hot spot/lobe with a bridge of emission extending back to the core. This is the first detection of extended emission associated with such a source, and it is inconsistent with the suggestion that such sources are very young classical double radio sources. The inconsistency can be reconciled if the activity in this object is recurrent and the emission is the relic of a previous epoch of activity. Alternatively, the source may be a normal-aged radio galaxy in which most of the radio-emitting plasma is currently unable to escape the nuclear regions of the galaxy. The steep low-frequency spectrum of the core is probably related to the origin of the compact double and suggests that both components are very sharply confined on both their inner and outer edges.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 232; 1, Ju
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  • 4
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    Line profiles and the kinematics of the narrow-line region in Seyfert galaxies (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: High signal-to-noise ratio and long-slit CCD spectra at about 100 km/sec resolution have been obtained for six high-ionization Seyfert galaxies. By subtracting the stellar absorption features with the aid of continuum templates, and using deblending techniques, the asymmetry indices of a number of optical emission-line profiles were measured, spanning a wide range in both ionization potential and critical density in each galaxy. The fundamental problem of the cloud-motion direction in the narrow-line region (NLR) has been studied, using these measurements and on the assumption that the preponderance of blueward profile asymmetries requires radial motion as well as a source of extinction. Simple and spherically symmetric NLR simulations are performed to demonstrate that infall and outflow models can be distinguished by comparing asymmetry indices as a function of ionization potential and critical density.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 348; 421-433
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  • 5
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    Deuterium enrichment in the primitive ices of the protosolar nebula (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: On the basis of CH3D/CH4-ratio observations in the outer planets, the present effort to estimate the D/H ratio of the protosolar nebula's primitive ices arrives at two simple, yet effectively limiting models which constrain the degree of dilution undergone by deuterated volatiles through mixing with the initial hydrogen envelopes. These volatiles would have been contributed to planetary atmospheres by evaporated primordial ices. Ice D/H ratio model results of 0.0001 to 0.001 are compared with values for other potentially primitive material-containing bodies in the solar system, as well as with D/H ratio values from interstellar polyatomic molecules.
    Keywords: ASTROPHYSICS
    Type: Icarus (ISSN 0019-1035); 86; 329-335
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  • 6
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    Additional measurements and a refined analysis of the millimeter- and submillimeter-wave spectrum of methanol (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A total of 414 previously unobserved millimeter- and submillimeter-wave transitions of (C-12)H3OH through J = 10 and v(t) = 2 are assigned. These data and previous measured spectral transitions are combined and fitted by a modified internal axis method (IAM) treatment in which the A and E substates are treated separately and a wide variety of new rotational-torsional interaction terms are employed. The modified IAM treatment reduces the overall rms deviation of the fits to the level of experimental accuracy. The resultant spectroscopic constants allow for the accurate prediction of 569 additional transitions through J = 12 or less.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 72; 797-814
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  • 7
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    Observations of formaldehyde in Comet Machholtz (1988j) (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Comet Machholtz's 1(11)-1(10) formaldehyde emission was detected with the VLA in September, 1988 at 6-cm wavelength; the small blueshift of -0.76 + or - 0.40 km/sec noted by these observations is consistent with an anisotropic outgassing of the cometary nucleus in the solar direction. The derived formaldehyde production rate for Comet Halley, which exhibits a similar emission line blueshift, was 1.5 x 10 to the 28th mol/sec, while for Comet Machholtz the production rate is about an order of magnitude higher, at 2 x 10 to the 29th mol/sec. The fading of Comet Machholtz after these observations is ascribed to its breakup.
    Keywords: ASTROPHYSICS
    Type: Icarus (ISSN 0019-1035); 86; 289-298
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  • 8
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    The submillimeter-wave spectrum of (O-16)(O-18) (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: In order to aid in the interstellar identification of molecular oxygen via its (O-16)(O-18) isotopic species, the frequencies of four rotational fine-structure lines of (O-16)(O-18) have been measured at frequencies ranging from 298 to 464 GHz. The line with the highest intensity and consequent best chance of astronomical detection lies at 401739.823 MHz. Its magnetic dipole strength is somewhat more than half that of the previously measured strong line at 233946.179 MHz.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 349; L29-L31
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