Observations of R Coronae Borealis stars in decline - Empirical arguments for dust formation near the stellar surface

Clayton, Geoffrey C.; Whitney, B. A.; Stanford, S. A.; Drilling, J. S.

doi:10.1086/171821

Cited by 41 publications

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“…In this connection, the report of Clayton et al (1992) on the change of the degree of polarization of R CrB at light maximum is very interesting.…”

Section: Resultsmentioning

confidence: 91%

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Observations of variable stars with the R Coronae Borealis phenomenon and other unique objects

Rosenbush

1995

Astron Nachr

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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. IntroductionThe unique behaviour of visual brightness of R Coronae Borealis and several other related stars formed the basis to distinguish the RCB variable star type. The reason for attributing a variable to the RCB group is the combination of the following features: 1) irregular brightness decreases by 1-8 mag during several tens of days with a longer recovery to the normal light; 2) peculiar abundances: a large deficit of hydrogen and a carbon excess; 3) infrared excess due to circumstellar dust (a permanent envelope). The carbon excess according to the Loreta-O'Keefe hypothesis, which has been developed by many authors, facilitates the formation of carbon-rich dust in the upper layers in the stellar atmosphere which obscures the star. The dilution of this dust in a surrounding space by the radiation pressure leads to the recovery of normal brightness. A growth of the polarization up to 10% and more is observed during the active state. The permanent circumstellar envelope is not a consequence of these rare enough events, but it is the result of permanent intense mass loss from the star. The permanent mass loss results from the pulsations of these stars (Rosenbush 1981(Rosenbush , 1984Fadeyev 1984). The luminosity of the circumstellar envelope (i.e. its mass) is related in some way to the amplitude of stellar pulsations. Variable stars with the R Coronae Borealis phenomenon are few and this is due to the fact that they are connected with a short stage of stellar evolution. Their peculiar abundance is associated with the loss of upper hydrogen-rich stellar layers and with the exposed deeper carbon-rich ones. The existence of a very cold (the effective temperature is several tens of degrees) envelope around R CrB is related just to this process (Gillett et al. 1986). Such an envelope exists around SU Tau and V348 Sgr, too (Rao and Nandy 1986).Unfortunately, an insufficiency of the information about intrinsic fundamental properties, which are not distorted by observational selection, compels some conclusions to be spread on the whole group of stars. For example, the high luminosity of RY Sgr and some members of the Large Magellanic Cloud (W Men, HV 5637 and HV 12842) are attributed to the rest of the group. But this conclusion was not confirmed by our studies (Rosenbush 1981(Rosenbush , 1989a. The RCB stars occupy a large region in the HR diagram, which may testify that they belong to different evolutionary tracks. This circumstance together with the fact known long ago that RCB photometric behaviour is observed in some novae (Rosenbush 1988) and in PU Vul (Men'shchikov et al. 1985) has served the basis for our conclusion that there is no compact group of variable stars of RCB type with respect to their physical properties, but there are stars which are at different late stages of ste...

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“…In this connection, the report of Clayton et al (1992) on the change of the degree of polarization of R CrB at light maximum is very interesting.…”

Section: Resultsmentioning

confidence: 91%

“…The stellar pulsations at light maximum have no effect on the polarization of the star (Table 1). Although there are some indications that an additional polarization may appear at light maximum (up to 0.4%) in R CrB (Clayton et al 1992). …”

Section: V854mentioning

confidence: 97%

Observations of variable stars with the R Coronae Borealis phenomenon and other unique objects

Rosenbush

1995

Astron Nachr

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“…The UV spectrum undergoes a similar evolution (Clayton et al 1992a ;Lawson et al 1999). The very early decline spectrum (E1) is dominated by blends of many emission 1 Based on observations obtained with the NASA/ESA Hubble Space T elescope, which is operated by STScI for the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.…”

Section: Introductionmentioning

confidence: 83%

“…The BL lines are often constant throughout declines but are sometimes seen to fade signiÐcantly over D100 days, indicating that a portion of the BL emission is coming from within a few AU of the star (Herbig 1949 ;Clayton et al 1992a ;Lawson et al 1999). The extended C II emission regions reported here bear some resemblance to the BL region deduced for V854 Cen by Rao & Lambert (1993) using forbidden lines.…”

Section: Discussionmentioning

confidence: 99%

“…On the other hand, V854 Cen is the least hydrogen-deÐcient RCB star, with H/C D 2 while He/ C D 10È60, with the lower value the most likely (Asplund et al 1998). Perhaps related to the high hydrogen abundance, the UV-decline spectra of V854 Cen di †er from those of RY Sgr (and R CrB) in an important respect : the presence of strong BL emission from C II] j2325 and C I j2965 (Clayton et al 1992a(Clayton et al , 1992b.…”

Section: Target Starsmentioning

confidence: 99%

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Long‐Slit Observations of Extended Ciiλ1335 Emission around V854 Centauri and RY Sagittarii

Clayton

Ayres

2001

ApJ

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We have obtained long-slit far-ultraviolet (1150È1730 spectra of the R Coronae Borealis (RCB) A ) stars V854 Cen and RY Sgr near maximum light and pulsational phase zero with the Space Telescope Imaging Spectrograph on board the Hubble Space T elescope. The far-UV spectrum of each star shows a photospheric continuum rising steeply toward longer wavelengths and a prominent emission feature at C II j1335. RY Sgr displays a second, but fainter, emission attributed to Cl I j1351 (which is radiatively Ñuoresced by C II j1335), but Cl I is weak or absent in V854 Cen. Most surprisingly, the C II emission of V854 Cen is signiÐcantly extended along the slit by about 6 ] 103 AU at the distance of the star.2A .5, The C II feature of RY Sgr exhibits no such gross extension. Nevertheless, subtle broadenings of the C II emissions beyond the point response proÐle suggest inner clouds of radius (250 AU) around both D0A .1 stars. V854 Cen is only the third RCB star after R CrB and UW Cen known to have a resolved shell.

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Size scale of the R Coronae Borealis variables

Rosenbush

1995

Astron Nachr

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The radius of R CrB is estimated to 90-100 radii of the Sun. The dust layer, which is the cause of the deep minimum in the visible light of R Coronae Borealis-type stars, has a radius of about 6 radii of the star. This follows from the delay of the infrared light increase after the visual minimum and also from the analogy with the dust formation in novae. The emission lines appearing in the minimum have an origin analogous to the metal emissions in the comets of 1882 I1 and 1965 VIII in which they were observed at a distance of 20-30 Ro. The permanent dust shell has a radius about of 26 stellar radii.

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Observations of R Coronae Borealis stars in decline - Empirical arguments for dust formation near the stellar surface

Cited by 41 publications

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Observations of variable stars with the R Coronae Borealis phenomenon and other unique objects

Observations of variable stars with the R Coronae Borealis phenomenon and other unique objects

Long‐Slit Observations of Extended Ciiλ1335 Emission around V854 Centauri and RY Sagittarii

Size scale of the R Coronae Borealis variables

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