共查询到20条相似文献,搜索用时 10 毫秒
1.
Geoffrey C. Clayton 《Astrophysics and Space Science》2002,279(1-2):167-170
The R Coronae Borealis (RCB) stars are rare hydrogen-deficient carbon-rich supergiants which undergo spectaculardeclines in brightness of up to 8 magnitudes at irregular intervals as dust forms along the line of sight.Understanding the RCB stars is a key test for any theory whichaims to explain hydrogen deficiency in post-Asymptotic Giant Branch (AGB) stars. There are two major evolutionary models for the origin of RCB stars: the Double Degenerate and the Final Helium ShellFlash. In the final flashmodel, there is a close relationship between RCB stars and Planetary Nebulae (PNe). The connection between RCB stars and PNe has recentlybecome stronger, since the central stars of three old PNe (Sakurai's Object, V605 Aql and FG Sge) have had observedoutbursts that transformed them from hot evolved central stars into cool giants with the spectral properties of an RCB star. 相似文献
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A. E. Rosenbush 《Astronomische Nachrichten》1995,316(4):213-223
The results of photometry and polarimetry of the R Coronae Borealis type stars and other interesting objects are given. The observation of the former objects are obtained at the light maximum or at a brightness lower by 2-3 mag. The polarization of R CrB stars at light maximum has interstellar origin. The absolute magnitude of V 854 Cen is estimated to Msvw = −3m, and for Y Mus it is Mv > −3m.7. ρ Cas has a variable polarization and is probably a giant (Mv ≅ 0m) rather than a supergiant. Many early stars in its surroundings are photometrically and polarimetrically variable. The protoplanetary star BD −0°3679 has a polarization with the Rayleigh component. 相似文献
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A. É. Rosenbush 《Astrophysics》2007,50(4):500-514
This is an examination of the hypothesis that the appearance of a component with a negative displacement of about −25 km/s
in the lines of the sodium resonance doublet can serve as an indicator of the near-term onset of a visual light minimum of
a star with R Coronae Borealis type variability. This effect has been observed three times since 1994 in connection with a
brightness minimum: twice for a day or a few days before the beginning of a drop in brightness (1995, 1998) and, perhaps,
once during the first days of a minimum (2003). Similar changes have been noted in one of the lines of the infrared CaII triplet
at 854.2 nm.
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Translated from Astrofizika, Vol. 50, No. 4, pp. 603–620 (November 2007). 相似文献
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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
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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
8.
D. H. Morgan D. Hatzidimitriou R. D. Cannon B. F. W. Croke 《Monthly notices of the Royal Astronomical Society》2003,344(1):325-335
Six stars out of a sample of ∼2300 carbon stars in the Magellanic Clouds have been identified as having strong C2 bands but CN bands that are very weak or absent. It is argued that five of these are likely to be R Coronae Borealis (RCB) stars on the basis of their spectral characteristics and peculiar colours. Most are variables and the Large Magellanic Cloud (LMC) members have extreme radial velocities that are more like the planetary nebula population than the carbon stars. This sample consists of four LMC members (only one of them previously recognized as an RCB star), one Small Magellanic Cloud (SMC) member (the first RCB star reported in the SMC) and one foreground Galactic star. 相似文献
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This review presents a selection of recent highlights of observations of R Coronae Borealis variables. Emphasis is placed
on an abundance analysis of a complete sample (18 stars) of the warm galactic RCBs. It is shown that 14 of the 18 have very
similar compositions: the iron mass fraction ranges about a factor of 3 around the solar value (assuming C/He = 3%) but abundance
ratios X/Fe for elements from Na to Ba show little variation. By contrast, the other 4 stars are deficient in iron but not
in Na, Si, S and some other elements. With for example, [Si/Fe] ≃ 2, the quartet is indeed ‘peculiar’. One of the quartet,
V854 Cen shows depletions of elements (other than CNO) similar to the depletions seen in interstellar medium corresponding
to average logn(H
tot) = − 1.5. Scenarios for creating RCB from normal single and double stars are summarised.
Invited review talk presented at the Asia-Pacific regional IAU meeting held at Pune from 16–20 August 1993. 相似文献
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David L. Lambert N. Kameswara Rao Sunetra Giridhar 《Journal of Astrophysics and Astronomy》1990,11(4):475-490
Moderate-resolution spectra of the C2 Swan 0-1 bandhead, the Na I D lines and the KI resonance lines near 7660 Å obtained at minimum light during the 1988–1989 decline of R CrB are discussed and interpreted in terms of a popular model for R CrB declines. High-resolution spectra obtained at maximum light show blue-shifted chromospheric emission in the cores of the Na I D and the Sc π 4246.8 Å lines 相似文献
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The amplitude of the ellipsoidal variability, the mass function and the evolutionary limits on the component masses have been used to constrain the binary system parameters of T Coronae Borealis. Contrary to all previous studies, our analysis shows that the mass ratio of T CrB is q ≡ M g / M h ≈0.6, which implies a low-mass binary system, with the stellar masses M g ∼0.7 M⊙ for the red giant and M h ∼1.2 M⊙ for the hot companion. This result strongly supports the thermonuclear runaway model for this recurrent nova, and solves all controversies about the nature of the hot component and the physical causes of its eruptions. 相似文献
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S. B. Charnley 《Astrophysics and Space Science》1995,224(1-2):439-440
Some results from studies of the gas-grain chemistry in oxygen-rich circumstellar envelopes (CSEs) are presented. 相似文献
20.
Excess mid-infrared emission in cataclysmic variables 总被引:1,自引:0,他引:1
G. Dubus † R. Campbell B. Kern R. E. Taam H. C. Spruit 《Monthly notices of the Royal Astronomical Society》2004,349(3):869-881