Peripatus Home Page  pix1Black.gif (807 bytes)  Astronomy Page >> Carbon Stars Updated: 6 Aug 2003 

Carbon Stars


Abstract

The defining characteristics of carbon stars are presented and interpreted in an evolutionary context. Some occurences are listed with their known physical properties.

Keywords: carbon stars

Introduction

Carbon stars, also known as type C stars, overlap with late G, K and M stars in most respects but are distinguished by compositional differences, typically an unusually high concentration of carbon.

Characteristics

Spectra

C stars, known as carbon stars, overlap with late G, K and M stars in most respects but are distinguished by compositional differences, typically an unusually high concentration of carbon.

Type R is the approximate carbon analogue of the K stars, and is very rare; N is the approximate carbon analogue of the M stars (see Table 1).

 
 

Related Topics


Further Reading

Related Pages

Other Web Sites

 
 
Harvard Type Keenan & Morgan Type Equivalent Normal Star
 
R0

R3
R5
 
R8

Na
Nb

Nc
C0
C1
C2
C3

C4
C5
C6

C7
C8

C9
G4 – G6
G7 – G8
G9 – K0
K1 – K2

K3 – K4
K5 – M0
M1 – M2

M3 – M4
Table 1: Approximate equivalence between carbon stars (Harvard and Keenan & Morgan classifications) and normal stars, after Kaler 1989 (Table 3.4). Equivalence is "only approximate, and for the later classes very much so. There is good evidence that the N stars correspond to M classes later than given here. The C-type responds to both carbon abundance and temperature and consequently there is a large and essentially unknown temperature range for each carbon subclass."

Mass and Luminosity

xxx.

Variability/Mass Loss

Carbon stars are typically long period variables.

Interpretation

During late phases of stellar evolution, ‘ordinary’ stars (i.e. excluding the super-massive stars which take the LBV–WR route) become long period variables on the AGB. "Because of the sudden increase in energy flux from the helium-burning shell during a flash episode, a convective zone is established between it and the hydrogen-burning shell. At the same time, the depth of the envelope convection zone increases with pulse strength. For stars that are massive enough (M > 2M), the convection zones will merge and eventually extend down into regions where carbon has been synthesized, carrying freshly processed material to the surface. This third dredge-up phase appears to explain the difference between oxygen-rich giants (Xo > Xc) and carbon-rich giants (Xc > Xo), called carbon stars..." (Carroll & Ostlie 1996, p. 504).

Occurrence/Examples

The following table provides a little additional information about some bright examples of these rare stars. Examples are provided for both southern and northern observers.

Star Coordinates Distance Magnitude (period) Spectrum Reference
RU Vir 12:47:18.4
+4:08:41.3
  9.0–14
(437 days)
R3ep  
HD 52432 7:01:1.95
-3:15:09
  7.2 R5  
S Cam     8.1–11.0
(326 days)
R8e  
TX Psc 23:46:23.5
+3:29:16
(1000 l.y.) 5.5–6.0
(irr.)
N0 (C6,2) Burnham 1992
BL Ori 6:25:28.1
+14:43:19.2
  6.3–7.0
(irr.)
N0 (C6,3)  
SS Vir 12:25:19.6
+0:47:51.7
    C6,3  
Y Pav 21:24:16.6
-69:44:04
  6.1–6.7
(233 days?)
C5,2  
U Ant 10:35:12.9
-39:33:46'
    C5,3 Hoffleit et al. 1991
Y CVn
(La Superba)
12:45:07.8
+45:26:24.2
(400–600 l.y.) 5.0–6.4
(158 days)
N3 (C5,4) Burnham 1989a
V Aql 19:04.4
-05:41
  6.6–8.4
(353 days)
N6 Tirion 1991
SS Vir 12:25.3
+00:48
  6.0–9.6
(354.7 days)
N6 Tirion 1991
U Hya          
V Hya 10:51:37.3
-21:15:01.1
(1300 l.y.) 6.5–12
(533 days)
N6e (C6,3) Burnham 1989b
R Lep (Hind’s Crimson Star) 4:59:36.7
-14:48:22
(1500 l.y.) 5.9–11
(432 days)
N6e (C7,4) Burnham 1989b
S Cep 21:35:12.6
+78:37:28.2
(2000 l.y.) 7.4–12.9
(487 days)
N8e (C7,4) Burnham 1989a
Table 2: Table of bright carbon stars.

References

Burnham, Robert 1989a: Burnham’s Celestial Handbook. Volume 1 – Andromeda to Cetus. Dover.

— 1989b: Burnham’s Celestial Handbook. Volume 2 – Chamaeleon to Orion. Dover.

— 1992: Burnham’s Celestial Handbook. Volume 3 – Pavo to Vulpecula. Dover.

Carroll, Bradley W.; Ostlie, Dale A. 1996: Introduction to Modern Astrophysics. Addison Wesley.

Hoffleit et al. 1991: The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version).

Kaler, James B. 1997: Stars and Their Spectra. Cambridge. (Corrected paperback ed.) 300 pp.

Tirion, Wil 1991: Cambridge Star Atlas 2000.0. Cambridge.


  Peripatus Home Page  pix1Black.gif (807 bytes)  Astronomy Page >> Carbon Stars Contact me.