BY Draconis değişeni

BY Dra tipi değişken yıldız V1297 Her'ün TESS ışık eğrisi

BY Draconis değişenleri tayflarında hidrojen salma çizgileri ile karakterize olan, dKe ve dMe tayf türünden geç tür cüce yıldızlardır. Bu yıldızlarda izlenen parlaklık değişimi, tekdüze olmayan yüzey parlaklık dağılımlarından kaynaklanmaktadır. Fotosferlerine oranla daha soğuk olan güneş benzeri leke bölgelerinin, yıldızın yarımkürelerinden birinde daha fazla yer alması halinde, dönme modülasyonu etkisiyle ışık değişimi ortaya çıkmaktadır. BY Draconis değişenleri ileri düzeyde kromosferik etkinliğe sahip yıldızlardır. Hem tek hem de çift sistem üyesi olabilmektedirler. Bu türden yıldızların kromosferik etkinlik gösterebilmeleri için ekvatoryal dönme hızlarının 5 km/sn değerinin üstünde olması gerekmektedir.[1]

BY Draconis yıldızlarının çoğu, UV-Ceti türü flare etkinlikleri de göstermektedir. Grubun prototipi BY Dra'nın, ışık değişimine sahip olduğu ilk kez 1966'da Pavel Fedorovich Chugainov'un gözlemlerinden anlaşılmıştır. Chugainov, gözlenmekte olan ışık değişiminin karanlık lekelerden kaynaklandığını da ortaya koymuştur. 1926’da keşfedilen YY Gem bir örten çift olarak sınıflandırılmıştır. Aslında bileşenlerinin tayf türleri dM1e+dM2e olan çift bir BY Dra değişenidir. Kron 1952'de, tutulmalar dışında kalan ışık değişiminin, leke kökenli dalga biçimindeki bozulmadan kaynaklandığını göstermiştir.[2]

Örnekler

  • BY Draconis: K4V+K7.5 bileşenlerinden oluşma çift bir sistemdir. Yörünge dönemi 5.975 gündür. Tutulma göstermemektedir. Leke dalgasının dönemi (fotometrik dönem) ise 3.827 gündür. Yörünge basıklığı e=0.31 civarındadır. Sistemin ortalama parlaklığı 50-60 yıllık bir çevrimle değişmektedir.
  • CC Eri: Yörünge dönemi 1.56 gün olan, K7Ve+? tayf türünden tek çizgili bir tayfsal çifttir. Tutulma göstermemektedir. BY Dra’dan önce ışık değişimi keşfedilmiştir.
  • OU Gem: K3V+K5V tayf türünden bileşenlere sahip çift bir sistemdir ve yörünge dönemi 6.99 gündür. Tutulma göstermemektedir. Leke dalgasının dönemi (fotometrik dönemi) 7.36 gündür.

Kaynakça

  1. ^ Lopez-Morales, Mercedes; Morrell, N. I.; Butler, R. P.; Seager, S. (2006), "Limits to Transits of the Neptune-mass planet orbiting Gl 581", Publications of the Astronomical Society of the Pacific, 118 (849), s. 1506, arXiv:astro-ph/0609255 $2, Bibcode:2006PASP..118.1506L, doi:10.1086/508904, BY Draconis variable. This type of variable is characterized by quasiperiodic photometric variations over time scales from less than a day to months, and amplitudes ranging from a few hundredths of a magnitude to 0.5 mags. 
  2. ^ Hoffmeister, Cuno; Richter, Gerold; Wenzel, Wolfgang (1984), Veränderliche Sterne, Springer 
  • Samus N.N., Durlevich O.V., et al. Combined General Catalog of Variable Stars (GCVS4.2, 2004 Ed.)

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