Dredge-up


Dredge-up

Dredge-up refers to a period in the evolution of a star where a surface convection zone extends down to the layers where material has undergone nuclear fusion. As a result, the fusion products are mixed into the outer layers of the stellar atmosphere and these nuclides can appear in the spectrum of the star.

The first dredge-up occurs when a main sequence star enters the red giant branch (RGB). As a result of the convective mixing, the outer atmosphere will display the spectral signature of hydrogen fusion: the 12C/13C and C/N ratios are lowered, and the surface abundances of lithium and beryllium may be reduced.

The second dredge-up occurs in stars with 4 – 8 solar masses of material. When helium fusion comes to an end at the core, convection mixes the products of the CNO cycle.[1] This second dredge up results in an increase in the surface abundance of 4He and 14N, while the amount of 12C and 16O decreases.[2]

The third dredge-up occurs after a massive star enters the asymptotic giant branch (AGB) and a flash occurs along a helium burning shell. This dredge-up causes helium, carbon and the s-process products to be brought to the surface. The result is an increase in the abundance of carbon relative to oxygen, which can create a carbon star.[2]

The names of the dredge-ups are set by the evolutionary and structural state of the star in which each occurs, not by the sequence experienced by the star. As a result, lower-mass stars experience the first and third dredge-ups in their evolution but not the second.

References

  1. ^ Lambert, D. L. (1992). "Observational Effects of Nucleosynthesis in Evolved Stars". In Mike G. Edmunds and Roberto J. Terlevich. Elements and the Cosmos. University of Cambridge. pp. 92–109. ISBN 052141475X. 
  2. ^ a b Kwok, Sun (2000). The origin and evolution of planetary nebulae. Cambridge University Press. p. 199. ISBN 0521623138. 

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • dredge — dredge1 [drej] n. [prob. < MDu dregge, akin to DRAG] 1. a device consisting of a net attached to a frame, dragged along the bottom of a river, bay, etc. to gather shellfish, marine plant specimens, etc. 2. an apparatus for scooping or sucking… …   English World dictionary

  • dredge — [dredʒ] v [Date: 1500 1600; Origin: Perhaps from Old English dragan to pull ] 1.) [I and T] to remove mud or sand from the bottom of a river, ↑harbour etc, or to search for something by doing this ▪ They were dredging for oysters. 2.) [T + with]… …   Dictionary of contemporary English

  • dredge — ► VERB 1) clean out the bed of (a harbour, river, etc.) with a dredge. 2) bring up or remove with a dredge. 3) (dredge up) bring (something unwelcome and forgotten) to people s attention. ► NOUN ▪ an apparatus for bringing up objects or mud from… …   English terms dictionary

  • Dredge — (dr[e^]j), v. t. [imp. & p. p. {Dredged} (dr[e^]jd); p. pr. & vb. n. {Dredging}.] To catch or gather with a dredge; to deepen with a dredging machine. R. Carew. [1913 Webster] {Dredging machine}, a machine (commonly on a boat) used to scoop up… …   The Collaborative International Dictionary of English

  • Dredge — Dredge, n. [OE. dragge, F. drag[ e]e, dredge, also, sugar plum; cf. Prov. dragea, It. treggea; corrupted fr. LL. tragemata, pl., sweetmeats, Gr. tragh mata, fr. trw gein to gnaw.] A mixture of oats and barley. [Obs.] Kersey. [1913 Webster] …   The Collaborative International Dictionary of English

  • Dredge — (drɛdʒ) ist ein aus dem Englischen stammender Begriff für: ein über den Boden von Gewässern gezogenes Schleppnetz zur Probenentnahme, siehe Dredge (Schleppnetz) das Ausbaggern oder Absaugen von Material aus dem Gewässergrund, z. B. zum… …   Deutsch Wikipedia

  • Dredge — Dredge, v. t. To sift or sprinkle flour, etc., on, as on roasting meat. Beau. & Fl. [1913 Webster] {Dredging box}. (a) Same as 2d {Dredger}. (b) (Gun.) A copper box with a perforated lid; used for sprinkling meal powder over shell fuses. Farrow.… …   The Collaborative International Dictionary of English

  • Dredge — (dr[e^]j), n. [F. dr[ e]ge, dreige, fish net, from a word akin to E. draw; cf. D. dreg, dregge, small anchor, dregnet dragnet. [root]73. See {Draw}.] 1. Any instrument used to gather or take by dragging; as: (a) A dragnet for taking up oysters,… …   The Collaborative International Dictionary of English

  • dredge up — (something) 1. to remember something from the past. He hates it when people dredge up the crimes that happened here 20 years ago. You re not dredging that old idea up again, are you? Usage notes: often said about something unpleasant 2. to find… …   New idioms dictionary

  • dredge — dredge; dredge·man; …   English syllables


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.