Les étoiles R CrB
R Coronae Borealis (RCB) are very unusual type of variable star, in
that the variability is caused by the formation of a cloud of carbon
dust in the line of sight. The cloud is formed near the stellar
photosphere, condenses (dimming the star's visual brightness by
several magnitudes) and then dissipates as it moves away from the
star. These star are hydrogen-poor, carbon- and helium-rich,
high-luminosity stars which are simultaneously eruptive and pulsating
variables. All RCB stars are variable at maximum light because
presence of pulsations phenomena, typically with periods of 40 to 100
days and amplitudes of a few tenths of a magnitude. They show slow
nonperiodic fadings by 1-9 mag in V lasting from a month or more to
several hundred days. The decline is sharp.
At maximum light the typical spectrum looks
like a F or G supergiant but the Balmer lines are very weak or
absent. The spectrum is dominated by C2 and CN bands and many lines
of neutral atomic carbon.
At the decline period a rich emission-line
spectrum appears consisting of singly ionized and neutral metals
(CaII H&K, NaI D in the visible part of the spectrum).
R CrB is the prototype of these stars. The
number of know R CrB stars is small (26 only in the GCVS). Below a
list of brighter members.
HD name
R.A. Delta Range
Spectral
25878 XX Cam 04 08 39
+53 21 39 8.1-9.8 G1I(C0-2,0)
247925 SU Tau 05 49 06 +19 04 00 9.1-16.9
G0-1Iep(C1,0 HD)
UW Cen 12 43 17 -54 31 38 9.1-14.5 K
V854 Cen 14 34 50 -39 33 19 7.1-14.1 Pec
141527 R CrB 15 48 34 +28 09 25 5.7-14.8
C0,0(F8pep)
RS Tel 18 18 51 -46 34 06 9.0-14.0 C(R0)
GU Sgr 18 24 16 -24 15 27 11.3 15.0
C(R0)
MV Sgr 18 44 32 -20 57 17 12.0-16.0
B2p(HDCe)
180093 RY Sgr 19 16 33 -33 31 19 5.8-14.0
G0Iaep(C1,0)
U Aqr 22 03 20 -16 37 40 10.5-14.5 Pec
UV Cas 23 02 15 +59 36 39
11.8-16.5 F0Ib-G5Ib
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