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Astron. Astrophys. 346, 134-138 (1999)

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6. Photometric classification

The physical parameters of HR 1960 can be derived from the photometric multicolour measurements. By using the calibrations of Cramer (1997, 1999) for B-type stars, the following values have been derived:

  • [FORMULA] = +0.03 [FORMULA] 0.20

  • [FORMULA] = 4.020 [FORMULA] 0.02

  • [FORMULA] = 3.8 [FORMULA] 0.2

  • [FORMULA]  (Geneva system), thus

  • [FORMULA]  (UBV system)

  • [FORMULA]  (Extinction in the V band)

  • A0 IV-III  ("Photometric spectral type")

From these values, using the calibrations by North & Cramer (1981), a mass of about 3 [FORMULA] and an age of [FORMULA] can be derived. The evolutionary stage of HR 1960 corresponds to the end of the main sequence.

The parallax [FORMULA] of HR 1960 has been determined by the Hipparcos satellite (ESA, 1997). Thus, the distance d of the star can be derived directly and its absolute magnitude [FORMULA] may be calculated by using in addition the value obtained above for the interstellar extinction [FORMULA]. The values are the following:

  • [FORMULA] = 3.81 [FORMULA] 0.47 mas

  • d = 262 -28/+37 pc

  • [FORMULA] = -0.89 +0.25/-0.29 mag

The value of [FORMULA] results from the colours of HR 1960, while the value of [FORMULA] comes from the parallax. Thus, [FORMULA] and [FORMULA] correspond respectively to the absolute magnitudes of the primary component and the two components taken togheter. The difference between these two values, [FORMULA]0.9 [FORMULA] 0.4, is an indication of the duplicity of the star, with nearly equal brightness of the secondary and the primary stars. This conclusion is an additional argument supporting the model of the binary system proposed in Sect. 5 explaining the photometric variability of HR 1960. It must be noted that the "Photometric spectral type" indicates a star slightly more evolved than the B9.5 V value determined by Houk & Cowley (1975). This difference could also be due to the effect of light provided by the secondary component.

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© European Southern Observatory (ESO) 1999

Online publication: May 6, 1999
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