Patuljasta nova

Ultravioletni snimak patuljaste nove Z Cam

Patuljasta nova je vrsta zvijezda koju karakterizuje nagla promjena sjaja. Ubrajaju se u nove, njihova sjajnost iznosi 2-5 magnituda. Promjena sjaja, koja je djelimično periodična, nastaje višestrukim erupcijama na površini bijelog patuljka. Do sada je otkriveno nekoliko stotina patuljastih nova. Dok se kod klasičnih i intervalnih nova promjena sjaja odvija termonuklearnim procesima na njihovoj površini, kod patuljastih postoje imaju dva različita modela[1]:

  • Model nestabilnog diska (en. disk instability model)
  • Model prenosa materije erupcijom (en. mass transfer burst model)


Model nestabilnog diska

U ovom slučaju akrecioni disk okružuje bijelog patuljka koji je u stanju primiti velike količine gasa. Ovisno o gravitaciji, kod veće je skupljane gasa intenzivnije, dolazi do porasta elektromagnetnog zračenja (en. outburst). Kada se gas u akrecionom disku potroši, dolazi do stabilizacije procesa i opadanja sjaja. Kada akrecioni disk sakupi dovoljno gasa, proces se pokreće iznova.[1]


Model prenosa materije erupcijom

Kod ovog modela dolazi, zbog gravitacije bijelog patuljka, do naglog porasta prenosa materijala s hladne zvijezde. Dolazi do brzog kolapsa akrecionog diska. Većom brzinom se gas i skuplja oko bijelog patuljka, tako da pod utjecajem jače gravitacije dolazi do izbijanja nove (en. nova outburst).[1]

Kategorizacija

Razlikuju se podvrste[2]:

SU Ursae Majoris

U Geminorum

Z Camelopardalis

Pored pojačane aktivnosti karakteriše ih i prosječna jačina sjaja koja se duže zadrži (naziva se i "stajanje"). Ovo stajanje pojavljuje se obično nakon izbijanja i traje do 1000 dana. Prosječna energija zračenja, u fazi stajanja, jača je nego tokom pojačane aktivnosti. Period stajanja pojavljuje povećavanjem toka materije, s crvenog u pravcu bijelog patuljka. Poznati zastupnik ove podgrupe je Z Camelopardalis (Z Cam) iz sazviježđa Žirafe. Z Cam je dvostruka zvijezda, gdje bijeli patuljak spektralnog tipa G s oko 1,17 Sunčeve mase kruži oko druge patuljaste zvijezde s periodom od 7 sati i 21 minute.[3]


Reference

  1. ^ a b c Dwarf Novaeastronomy.swin.edu.au,pristupljeno 6.12.2014 (en)
  2. ^ Zwergnovaetechniklexikon.net,pristupljeno 6.12.2014 (de)
  3. ^ Astronomie - Planeten, Sterne, Galaxien. Mannheim: Der Brockhaus. 2006. str. 539. ISBN 3-7653-1231-2. Provjerite vrijednost datuma u parametru: |date= (pomoć)


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