* Astronomy

Title: BK Lyncis: The Oldest Old Nova?... And a Bellwether for Cataclysmic-Variable Evolution
Authors: Joseph Patterson (1), Helena Uthas (1), Jonathan Kemp (1), Enrique de Miguel (2), Thomas Krajci (3), Jerry Foote (3), Franz-Josef Hambsch (3), Tut Campbell (3), George Roberts (3), David Cejudo (3), Shawn Dvorak (3), Tonny Vanmunster (3), Robert Koff (3), David Skillman (3), David Harvey (3), Brian Martin (4), John Rock (3), David Boyd (3), Arto Oksanen (3), Etienne Morelle (3), Joseph Ulowetz (3), Anthony Kroes (3), Richard Sabo (3), Lasse Jensen (3) ((1) Columbia Univ., (2) Univ. de Huelva, (3) Centre for Backyard Astrophysics, (4) King's Univ. Coll.)

We summarise the results of a 20-year campaign to study the light curves of BK Lyncis, a nova-like star strangely located below the 2-3 hour orbital period gap in the family of cataclysmic variables. Two apparent "superhumps" dominate the nightly light curves - with periods 4.6% longer, and 3.0% shorter, than P_orb. The first appears to be associated with the star's brighter states (V~14), while the second appears to be present throughout and becomes very dominant in the low state (V~15.7).
Starting in the year 2005, the star's light curve became indistinguishable from that of a dwarf nova - in particular, that of the ER UMa subclass. Reviewing all the star's oddities, we speculate: (a) BK Lyn is the remnant of the probable nova on 30 December 101, and (b) it has been fading ever since, but has taken ~2000 years for the accretion rate to drop sufficiently to permit dwarf-nova eruptions. If such behaviour is common, it can explain other puzzles of CV evolution. One: why the ER UMa class even exists (because all members can be remnants of recent novae). Two: why ER UMa stars and short-period novalikes are rare (because their lifetimes, which are essentially cooling times, are short). Three: why short-period novae all decline to luminosity states far above their true quiescence (because they're just getting started in their postnova cooling). Four: why the orbital periods, accretion rates, and white-dwarf temperatures of short-period CVs are somewhat too large to arise purely from the effects of gravitational radiation (because the unexpectedly long interval of enhanced postnova brightness boosts the mean mass-transfer rate). These are substantial rewards in return for one investment of hypothesis: that the second parameter in CV evolution, besides P_orb, is time since the last classical-nova eruption.

Read more (758kb, PDF)