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Corrected parameters for delta Velorum In 2000 we publshed (with Paul Fieseler and Chris Lloyd) the discovery of delta Velorum as an eclipsing binary. The main goal was to alert astronomers to study the new variable. One of the papers used to inform on the multiple status of the star was that from Tango et al. (1979) .They claimed the discovery of a subarcsecond companion (0.6") and "guessed" that the known B companion had been left outside of the camera's field so it didn't interfere with the measures. (!) On the other hand, Hipparcos data give a similar separation (0.7") but the magnitude was the same as the known component (5.5). The most intriguing thing was the abscence of the B component on Hipparcos' data. If the satellite did observe the closer "a" star, it was too strange that it didn't record the other more distant one.... It turns out that the "a" star was actually B in another position of its 142 year apparent orbit around the primary (which now can be safely called "Aa") Argyle et al. (2002) came to the rescue with an excellent paper last year. I only discovered it now that I found delta Vel's eclipses are total (well, one is total the other is a transit) Being aware of this confussion, one should rest one star worth of mass and brightness to obtain the real picture of the system. We get: Aa: V= 1.99, A0V+A5V B: V= 5.45, G0V (Spectra according to Argyle et al., 2002) V mag. out of eclipse: AaB= 1.95 Aa = 1.99 A = 2.33 a = 3.43 B = 5.45 During primary eclipse: AaB= 2.46 Aa = 2.53 A = 3.16 (partially eclipsed) a = 3.43 (transiting) B = 5.45 During secondary eclipse: AaB= 2.27 Aa = 2.33 A = 2.33 (total eclipse) a = invisible B = 5.45 Now a better picture could be made with the brightness differences between A and B during the transit and knowing that the eclipses' durations are very different: Primary (Phase 0.000) = 0.51 days (+/-0.05, only visual coverage and a rough estimation from Galileo's 2000 data) Secondary (Phase 0.435) = 0.91 days (+/-0.01, almost complete coverage by Galileo in 1989) Accurate photometry is needed to know the exact duration of the totality phases (that seem to last a couple of hours) This is an eccentric orbit, so the secondary eclipse appears at phase 0.435 and the primary eclipse is shorter because it happens near periastron when the stars are moving faster in their orbits. Refined elements: Min I = JD 2452798.555 + 45.150 x E Min II = JD 2452818.194 + 45.150 x E Delta Vel is near (80 ly) and this gives us a good idea of its true distance (great parallax) and it will put constraints to its parameters. A deep study of this eclipsing star would be very worth doing. We now know the apparent magnitudes of each of the stars with little uncertainty (the companion star problem has disappeared) and this allows us to know its absolute visual magnitude, since we know its distance. A: mV= 2.33, MV= 0.39 a: mV= 3.43, MV= 1.49 B: mV= 5.45, MV= 3.51 We can obtain these additional (only approximate) parameters: Spec= A0V, Lo = 60 , Mo= 3.9, Ro= 2.5 Spec= A3V, Lo = 20.8, Mo= 2.7, Ro= 2.0 Spec= F9V:, Lo = 3.3 , Mo= 1.4, Ro= 1.1 Argyle et al. values for Mo are lower (A= 2.7, a= 2.0, B= 1.0) and are based on the orbital parameters. They are probably better (I was based on the M/L relationship only) I hope other Southern astronomers follow Argyle's steps and observe intensively this star, both photometrically and spectroscopically. The system that turned out to be quintuple not sextuple. Sebastián Otero, Wezen 1 88 - CEA - LIADA. June 2003 References: Argyle, R.W., Alzner, A., Horch, E.P., Orbits for five southern visual binaries, 2002, A&A 384, 171 Otero, S.A., Fieseler, P.D., Lloyd, C., 2001, IBVS Nº 4999 Tango, W.J., Davis, J., Thompson, R.J., Hanbury, R., A "Narrabri" Binary Star Resolved by Speckle Interferometry", 1979, Proc. ASA 3, 323
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