Spectroscopy and eclipse-mapping of the mass-exchanging binary star V361 Lyr

Ronald William Hilditch, Andrew Collier Cameron, G Hill, SA Bell, TJ Harries

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We present the first spectroscopic investigation of the short-period (P = 0.309614 d) mass-exchange binary system V361 Lyr. From observations over two complete orbits, we show that he system is double-lined, with the stars having minimum masses of m(1)sin(3)i = 1.25 +/- 0.03 M. and m(2)sin(3)i = 0.87 +/- 0.03 M.. The mass ratio m(2)/m(1) = 0.69 +/- 0.02 and the projected semimajor axis of the relative orbit is a sin i = 2.47 +/- 0.05 R.. The spectral type of the primary component is estimated to be F8-G0. The H alpha line profile clearly shows two absorption components when the system is at its brightest and bluest stage, around orbital phases 0.35-0.45. The published V and I light curves are analysed with LIGHT2 to show that the primary component (T = 6200 K) fills its Roche lobe, whilst the secondary (T = 4500 K) is detached and fills approximate to 57 per cent of the available Roche volume. Eclipse maps of both stellar surfaces are derived via DOTS from light curves obtained in 1988, 1989 and 1992. These show that the secondary has a persistent elongated hot structure on its equator with an estimated temperature of 10000 K that is consistent with the expectations of a theoretical mass transfer stream leaving the primary at its inner Lagrangian point and falling on to the secondary. The accretion luminosity of approximate to 0.5 L. from that impacting stream, as estimated from the observed decrease in orbital period and the derived stellar masses, it about twice the luminosity of the structure inferred from the light curves and the surface-image reconstructions. The eclipse maps for the primary illustrate small changes in the cool spot structures that are typical of magnetic activity observed in other rapidly-rotating solar-type stars that are single or are members of binary systems (e.g. AB Dor, XY UMa). This model for V361 Lyr predicts successfully the phase-dependent variations observed in the H alpha line.

The properties of this mass-exchanging semidetached binary are compared with the near-contact and the contact systems of the W UMa type for the purpose of establishing whether or not it represents the short-lived phase of evolution into contact for the first time, or the broken-contact stage of a thermal-relaxation oscillation. The derived locations of both components on the zero-age main sequence would favour the former interpretation. V361 Lyr is reddened by E(B - V) = 0.43 and lies at a distance of 520 +/- 40 pc.

Original languageEnglish
Pages (from-to)749-762
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 11 Nov 1997


  • accretion, accretion discs
  • binaries, close
  • stars, fundamental parameters
  • stars, individual, V361 Lyr
  • stars, late-type


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