Astron. Astrophys. 356, 146-156 (2000)

3. Atmospheric models

The determination of stellar parameters has been accomplished through the application of the uvbybeta photometric calibration of Moon & Dworetsky (1985) as improved by Napiwotzki et al. (1993). Hoffleit & Jaschek identified HR 1094 to be of B9V spectral classification but Hill & Blake measured a magnetic field and classified it as an Ap star. A recent photometric study (Adelman 1999) implies the photometric uvby colour variations to be approximately 0.01 magnitude over the rotational period. This colour amplitude translates into a temperature variation of 300 K, using the calibration by Napiwotzki et al., which is typically within the error margins of the temperature determination for B-type stars.

If both HR 1094 and HR 5049 have effective temperatures exceeding 9500 K we can assume to be a suitable gravity indicator while the or index measures effective temperature. The Johnson (U - B) and (B - V) indices for HR 1094 are taken from Haggkvist & Oja (1969) while corresponding indices for HR 5049 and HR 3383 are from Johnson et al. (1966). All Strömgren indices were taken from Hauck & Mermilliod (1980). We used expressions developed by Napiwotzki et al., based on a reference frame of Ap stars, to determine an effective temperature for HR 1094 of 12 000 K. Moon & Dworetsky presented a calibration grid of the surface gravity using the index. From this grid HR 1094 is assign a log g of 4.2 0.2, where the error margin is an estimated read-out uncertainty.

Similar calculations have been performed for HR 5049 and HR 3383 yielding = 10 500 K and a log= 4.0 for HR 5049 and = 9 750, log= 4.0 for HR 3383. For each star an interpolated model was chosen from the ATLAS9 grid of Kurucz (1993) under the assumption of no turbulent velocity.

© European Southern Observatory (ESO) 2000

Online publication: March 28, 2000
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