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341.
Chris Koen 《Monthly notices of the Royal Astronomical Society》2003,346(2):473-482
76 hours of CCD photometry of 11 L dwarfs and one T dwarf is described. Three objects, including the T dwarf ε Indi B, showed convincing evidence for variability. A periodicity of 8 h is clearly visible in the light curve of 2MASS J1155395−372735. 相似文献
342.
Lawson W. A. Cottrell P. L. Gilmore A. C. Kilmartin P. M. 《Journal of Astrophysics and Astronomy》1989,10(2):151-155
SY Hyi is classified as a suspected R Coronae Borealis-type variable star. Photometric and spectroscopic observations of SY
Hyi lead to the star’s reclassification as a semiregular variable of spectral type M5-6. 相似文献
343.
D. K. Witherick R. K. Prinja S. B. Howell R. M. Wagner 《Monthly notices of the Royal Astronomical Society》2003,346(3):861-870
We present results from time-series optical spectroscopy of the low-inclination, nova-like cataclysmic variable, V592 Cas. The data span the wavelength range from ∼4000 to 5000 Å, and include Balmer lines (Hβ to Hε) as well as He i and He ii . The Balmer lines are generally characterized by shallow absorption troughs with superimposed narrower central emission components. The absorption troughs are variable on time-scales of at least ∼20 min, but the fluctuations are asymmetric such that they are more dominant on the blueward side of the profile out to ∼−2000 km s−1 . Fourier analysis reveals modulation periods for emission radial velocities and absorption changes of ∼0.114 and 0.103 d; we support earlier suggestions that the latter is likely to be 1-day alias of the former, which is essentially the system orbital period. However, there is a phase lag of ∼0.3 between absorption and emission changes. The Balmer absorption changes are compared to the predicted behaviour caused by the (stream overflowing) SW Sex phenomenon. There are several discrepancies in this scenario, including the highly asymmetric nature of blueward changes, the velocity amplitudes, and the phase relation to the emission changes. The role of a disc wind in V592 Cas is also discussed; in particular, with this data set, we cannot rule in or rule out the possibility that axisymmetry of the outflow is broken because it is seated on a warped/tilted inner disc, which is implied by previous evidence for negative superhumps in this system. 相似文献
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This paper presents observations of SiO maser emission from 161 Mira variables distributed over a wide range of intrinsic
parameters like spectral type, bolometric magnitude and amplitude of pulsation. The observations were made at 86.243 GHz,
using the 10-4 m millimeter-wave telescope of the Raman Research Institute at Bangalore, India. These are the first observations
made using this telescope. From these observations, we have established that the maser emission is restricted to Miras having
mean spectral types between M6 and M10. The infrared period-luminosity relation for Mira variables is used to calculate their
distances and hence estimate their maser luminosities from the observed fluxes. The maser luminosity is found to be correlated
with the bolometric magnitude of the Mira variable. On an H-R diagram, the masing Mira variables are shown to lie in a region
distinct from that for the non-masing ones. 相似文献
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350.
Lisa A. Crause Warrick A. Lawson Arne A. Henden 《Monthly notices of the Royal Astronomical Society》2007,375(1):301-306
Decline onset times were measured in long-term visual light curves for five R Coronae Borealis (RCB) variable stars. These included RY Sgr and V854 Cen, the two RCB stars previously reported to have a relationship between dust formation events and pulsational variations. Analysis of the decline epochs showed that all decline onsets for a given star obey a linear ephemeris tied to the object's dominant radial pulsation period. Thus, in addition to confirming the pulsation–decline correlation for RY Sgr and V854 Cen, this same behaviour was demonstrated in UW Cen, R CrB and S Aps for the first time. This general result firmly establishes the connection between radial pulsation and mass loss in the RCB stars. The dominant pulsation period of ≈40 d for all of these objects therefore represents the characteristic time-scale on which these stars produce dust. 相似文献