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  • 1
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract SW UMa is an unusual dwarf nova in several respects. Recent observations by Robinsonet al. (1986) have established that SW UMa is an SU UMa system, while Shafter, Szkody, and Thorstensen (1986) have presented evidence suggesting that SW UMa may be a DQ Her system as well. If the DQ Her classification is confirmed then SW UMa will be the only system to have this dual classification. Finally, time resolved spectroscopy of SW UMa has revealed the presence of an S-wave component in the Hα emission which has an unexpected phasing relative to the line wings.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2011-08-18
    Description: It is suggested that observations of circular polarization can be a valuable tool for the study of circumstellar nebulae. A simple model is presented to predict the percentage of circular polarization produced by scattering from the dust contained within such nebulae; it was found that a significant component of circular polarization can be produced in nebulae which have a net linear polarization. Possible observations of the red supergiants mu Cep and alpha Ori are given as examples.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal; 85; Nov. 198
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  • 4
    Publication Date: 2019-07-12
    Description: H-alpha and B light curves are presented for 11 M31 novae, four of which were well observed near maximum. These data, along with the H-alpha light curves of two Galactic novae, demonstrate that a nova's maximum H-alpha flux occurs days or weeks after its continuum maximum at a monochromatic intensity 1-2 magnitudes above its peak flux in B. Moreover, after this maximum is achieved, a typical nova will radiate a third as many photons in H-alpha as in the entire B bandpass. The most interesting part of a nova's H-alpha light curve, however, is its decline. It is found that, regardless of a nova's speed, its H-alpha decay rate after maximum is almost identical to its decay rate in B. This behavior suggests that most of a nova's optical luminosity during early decline is continuum emission from the nebula, rather than direct radiation from the central source.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 356; 472-482
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  • 5
    Publication Date: 2019-07-12
    Description: An attempt is made here to elucidate the dwarf nova outburst time scale in terms of basic physics, and to place limits on the model by using the observed recurrence times. A simple analytical model is developed to describe the limit cycle process, and an expression is obtained for the interval between eruptions. It is shown that the smallness of the amount of mass accreted onto the central white dwarf during eruption can be explained in terms of the propagation of heating and cooling fronts. The dependency of the fraction of the disk mass accreted on the model parameters is derived, and the result is used to construct a semianalytic expression for the recurrence time.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 333; 227-235
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  • 6
    Publication Date: 2019-07-12
    Description: Time-resolved X-ray and optical photometric and optical spectroscopic observations of the ultrashort period cataclysmic variable SW UMa are reported. The spectroscopic observations reveal the presence of an s-wave component which is almost in phase with the extreme line wings and presumably the white dwarf. This very unusual phasing in conjunction with the available optical and X-ray data seems to indicate that a region of enhanced emission exists on the opposite side of the disk from the expected location of the hot spot. The photometric observations reveal the presence of a hump in the light curve occurring at an orbital phase which is consistent with the phase at which the region of enhanced line emission is most favorably seen. Changes in the hump amplitude are seen from night to night, and a 15.9 min periodicity is evident in the light curve. The optical and X-ray periodicities suggest that SW UMa is a member of the DQ Her class of cataclysmic variables.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 308; 765-780
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  • 7
    Publication Date: 2019-07-12
    Description: Evidence is presented in support of the hypothesis that the mean mass-transfer rate at a given orbital period is not continuous across the 2-3 hr gap in the orbital period distribution for cataclysmic variables. It is pointed out that although dwarf novae comprise nearly half (48 percent) of all disk systems with orbital periods less than 10 hr, only three systems out of the 22 with periods between 3 and 4 hr appear to be dwarf novae. The overall orbital period distribution for dwarf novae in conjunction with the predictions from current theories of dwarf nova eruptions are used to argue that mass-transfer rates must be generally higher for systems with orbital periods greater than 3 hr relative to systems with periods less than 2 hr. It is further argued that the mean mass-transfer rate at a given orbital period cannot increase more steeply than P exp 1.7 unless the white dwarf mass is positively correlated with orbital period.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 305; 261-266
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  • 8
    Publication Date: 2019-07-13
    Description: The Andromeda Galaxy recurrent nova M31N 2008-12a had been observed in eruption 10 times, including yearly eruptions from 2008 to 2014. With a measured recurrence period of Prec = 351+/-13 days (we believe the true value to be half of this) and a white dwarf very close to the Chandrasekhar limit, M31N 2008-12a has become the leading pre-explosion supernova type Ia progenitor candidate. Following multi-wavelength follow-up observations of the 2013 and 2014 eruptions, we initiated a campaign to ensure early detection of the predicted 2015 eruption, which triggered ambitious ground- and space-based follow-up programs. In this paper we present the 2015 detection, visible to near-infrared photometry and visible spectroscopy, and ultraviolet and X-ray observations from the Swift observatory. The LCOGT 2 m (Hawaii) discovered the 2015 eruption, estimated to have commenced at August 28.28 +/- 0.12 UT. The 2013-2015 eruptions are remarkably similar at all wavelengths. New early spectroscopic observations reveal short-lived emission from material with velocities approx. 13,000 km/s, possibly collimated outflows. Photometric and spectroscopic observations of the eruption provide strong evidence supporting a red giant donor. An apparently stochastic variability during the early supersoft X-ray phase was comparable in amplitude and duration to past eruptions, but the 2013 and 2015 eruptions show evidence of a brief flux dip during this phase. The multi-eruption Swift/XRT spectra show tentative evidence of high-ionization emission lines above a high-temperature continuum. Following Henze et al. (2015a), the updated recurrence period based on all known eruptions is Prec 174 +/- 10 days, and we expect the next eruption of M31N 2008-12a to occur around 2016 mid-September.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN44015 , The Astrophysical Journal (ISSN 2041-8205) (e-ISSN 2041-8213); 833; 2; 149
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  • 9
    Publication Date: 2019-07-12
    Description: Results from an H-alpha survey for novae in the bulge of M31 are reported, and the spatial distribution of the nova population is analyzed. It is shown that in M31's central bulge the distribution of novae follows that of the light to within about 10 arcsec of the nucleus, refuting the notion that there is a nova 'hole' near the center of the galaxy. The Hubble-Arp nova sample is reanalyzed, concluding that the novae observed in the central 30 arcmin x 15 arcmin region belong almost exclusively to the bulge population. This result is compared to the observed cataclysmic variable distribution in the Galaxy, concluding that M31's spheroidal nova population is still compatible with the thin disk distribution of cataclysmic variables measured in the solar neighborhood. Possible explanations for the high specific nova rate of the bulge are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 318; 520-530
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  • 10
    Publication Date: 2019-07-12
    Description: The surface brightness distribution in the accretion disk of V Per is reconstructed using a maximum entropy technique. The resulting brightness temperature gradient is much less steep than that from a standard steady state, optically thick disk for all reasonable mass accretion rates. A model including a rim which obscures part of the disk does not resolve this discrepancy. However, if the inner disk is disrupted out to about 0.15-0.25R sub L1 (for example by a magnetic field), the brightness temperature gradient can be very close to T sub b varies as R exp -3/4 (1-b(Rin/R)exp 1/2) law. The value of Rin needed to match this steady state distribution depends on the distance to the system, its size and brightness, and the rotation rate of the white dwarf.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 393; 2 Ju; 729-741
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