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  • 1
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    BATSE gamma-ray burst line search. 1: Search for narrow lines in spectroscopy detector data (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Analysis of data from the Spectroscopy Detectors (SDs) of the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (GRO) has found no convincing line features in the spectra of gamma-ray bursts (GRBs) in almost 3 years of operation, in contrast to expectations based on results from other experiments. In this Letter we discuss the visual search for narrow lines in the SD data. The search has examined 192 bursts, of which approximately 18 were intense enough that lines similar to those seen by instruments on the Ginga satellite would have been visible between approximately 20 and approximately 100 keV. A simplified calculation shows that the BATSE and Ginga results are consistent at the 13% level.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 433; 2; p. L77-L80
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  • 2
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    Spectral evolution of a subclass of gamma-ray bursts observed by batse (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Among the gamma-ray bursts (GRBs) observed by the Burst and Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory we define a subclass of bursts based on similar morphology: a sharp rise followed by a longer decay time. About 7% of all the gamma-ray bursts observed by BATSE fall into this subclass. We study the spectral evolution of these bursts by fitting models to time-segmented burst spectra and find no clear distinction between the spectral evolutionary properties of this subclass and those of other bursts. Further, we study the high time resolution spectral evolution of this subclass of GRBs using their spectral hardness ratios. A majority of the bursts show hardness ratio leading the counting rate and also display a continuous hard to soft evolution. The time lag between the counting rate and the hardness ratio is found to be directly correlated with the rise time of the counting rate profile. We also find, for the first time, evidence for spectral variation in a timescale of 64 ms.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 426; 2; p. 604-611
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  • 3
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    Optical transients and depth analysis (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Flaws of the depth analysis technique of distinguishing photographic plate defects are discussed. The method is shown to be unreliable in confirming or disproving the astrophysical nature of optical transients. The arguments of Greiner and of Zytkow to the contrary are criticized.
    Keywords: ASTRONOMY
    Type: In: Gamma-ray bursts - Observations, analyses and theories (A93-20206 06-90); p. 133-137.
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  • 4
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    A ROSAT Wide Field Camera search for XUV bursts (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We have searched the ROSAT Wide Field Camera all-sky survey for shorttime-scale (less than 50 s) XUV bursts down to a limiting count of 5 x 10 exp -3 count/sq arcmin, corresponding to an incident flux of about 3 x 10 exp -10 erg/sq cm. In a total observation period of 171 d covering the entire sky, we found no evidence for such events. The present results are used to place limits on the log N-log S relation for gamma-ray bursts and constraints on the spectral shape of the previously reported ultrasoft X-ray transients.
    Keywords: ASTRONOMY
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 260; 4; p. L25-L27.
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  • 5
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    Astronomy and the limits of vision (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Celestial visibility is the study of the limits of observability of objects in the sky, with application to deducing the truth about historical events or to the derivation of astronomical information of modern utility. This study is based on what is seen by ordinary humans, either in their everyday lives or at times of historical events. The results of such studies have more relevance to non-scientists than does any other area of astronomy. Celestial visibility is a young discipline in the sense that the number of interesting applications with simple solutions outnumber the solved problems; it is a broad interdisciplinary field that involves work with astronomy, meteorology, optics, physics, physiology, history, and archeology. Each of these disciplines contribute specialized mathematical formulations which quantify the many processes that affect light as it leaves a source, traverses the atmosphere, and is detected by the human eye. These formulas can then be combined as appropriate to create mathematical models for the visibility of the source under the conditions of interest. These model results can then be applied a wide variety of problems arising in history, astronomy, archeology, meteorological optics, and archeoastronomy. This review also presents a dozen suggestions for observing projects, many of which can be directly taken for individual study, for classroom projects, or for professional research.
    Keywords: ASTRONOMY
    Type: Vistas in Astronomy (ISSN 0083-6656); 36; p. 311-361
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  • 6
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    Lunar crescent visibility (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We report the results of five Moonwatches, in which more than 2000 observers throughout North America attempted to sight the thin lunar crescent. For each Moonwatch we were able to determine the position of the Lunar Date Line (LDL), the line along which a normal observer has a 50% probability of spotting the Moon. The observational LDLs were then compared with predicted LDLs derived from crescent visibility prediction algorithms. We find that ancient and medieval rules are higly unreliable. More recent empirical criteria, based on the relative altitude and azimuth of the Moon at the time of sunset, have a reasonable accuracy, with the best specific formulation being due to Yallop. The modern theoretical model by Schaefer (based on the physiology of the human eye and the local observing conditions) is found to have the least systematic error, the least average error, and the least maximum error of all models tested. Analysis of the observations also provided information about atmospheric, optical and human factors that affect the observations. We show that observational lunar calendars have a natural bias to begin early.
    Keywords: ASTRONOMY
    Type: ICARUS (ISSN 0019-1035); 107; 2; p. 388-403
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  • 7
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    Is PSR 1509-58 the remnant of supernova AD 185? (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Thorsett has recently advanced the proposal that the counterpart of the supernova recorded by Chinese astronomers in AD 185 is the pulsar PSR 1509-58 in the supernova remnant MSH 15-52. This proposal is attractive since it was claimed to better fit the visibility contraints that plagued earlier identifications and since the spin-down age of the pulsar is 1690 years. I have examined in detail the question of the visibility of a supernova at the proposed position and find that the reported dates of visibility can be matched only if the supernova appeared substantially brighter than Venus at its peak. For the distance and extinction to the pulsar, this implies M(sub V) (max) was brighter than -21.4 mag, whereas the brightest known absolute magnitude of a Type II supernova is -19.65 (H(sub 0) = 75 km/s/Mpc). Thus, the high required luminosity can be used as good evidence against the identification of SN 185 with PSR 1509-58. However, if the identification is retained, then Hubble's Constant would have to have a small value and/or the supernova had to have been a type IIP event with exceptional brilliance. The earlier identification of SN 185 with MSH 14-63 by Clark and Stephenson can also be reconciled with the visibility data.
    Keywords: ASTRONOMY
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 105; 693; p. 1238-1239
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  • 8
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    Lunar occultation visibility (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The question of lunar occultation visibility of stars is examined from both a theoretical and an observational viewpoint. The background light caused by the lunar surface, the brightness caused by the lunar glare, the brightness of the sky for dark, twilight, and daytime conditions, and the effects of the telescopic optics are taken into consideration. The results are compared to give the limit on stellar visibility at the time of a lunar occultation, and the model results are graphically demonstrated as a function of various input parameters. Comparisons with observations show good agreement, with an uncertainty of about one-third of a magnitude.
    Keywords: ASTRONOMY
    Type: Icarus (ISSN 0019-1035); 100; 1; p. 60-72.
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  • 9
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    Eclipse earthshine (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Earthshine is the sunlight reflected off the earth's surface that illuminates the dark side of the moon. In this paper, it is predicted that the earthshine is sufficiently bright during a total solar eclipse that lunar maria and craters can be distinguished visually and photographically. The predicted contrast ratio for prominent lunar features is typically 0.06. Proper shielding from glare and reasonable magnification are prerequisites for success.
    Keywords: ASTRONOMY
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 103; 315
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  • 10
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    RW Per - Nodal motion changes its amplitude by 1.4 mag (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: RW Per was found to have large secular changes in its eclipse amplitude. In blue light, for example, the amplitude was 3.2 mag in the early 1900s, 2.2 mag in the late 1960s, and 1.75 mag in 1990. Throughout this time, the brightness at maximum was constant in all colors. It is shown that the only possible explanation is nodal motion, where the inclination varies with a period of roughly 100,000 yr. The nodal motion is caused by a third star, for which the light curve, the colors, and the O - C curve already provide evidence. Thus, RW Per is only the fourth known star with large changes of eclipse amplitude and is only the second example of nodal motion.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 101; 208-213
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