Table 1.

Best-fit parameters for Roche–von Zeipel models of Altair. Parameter descriptions: Inclination (0° is pole-on, 90° is edge-on) and position angle (degrees east of north) describe our viewing angle, Tpole and Rpole describe the temperature and radii of the pole (alternatively, one can describe the temperature and radii at the equator as Teq and Req), ω is the angular rotation rate as a fraction of critical breakup rate, and β is the gravity-darkening coefficient. Models assumed stellar mass = 1.791 M (15), metallicity [Fe/H] = –0.2 (32), and distance = 5.14 pc (33).

Parameterβ fixedβ free
Inclination 62.7° ± 1.5° 57.2° ± 1.9°
Position angle -61.7° ± 0.9° -61.8° ± 0.8°
Tpole (K) 8710 ± 160 8450 ± 140
Rpole (R) (mas) 1.661 ± 0.004 1.634 ± 0.011
1.503 ± 0.004 1.479 ± 0.010
Teq (K) 6850 ± 120 6860 ± 150
Req (R) (mas) 2.022 ± 0.009 2.029 ± 0.007
1.830 ± 0.008 1.835 ± 0.007
ω 0.902 ± 0.005 0.923 ± 0.006
β 0.25 (Fixed) 0.190 ± 0.012
Model V-band photometric magnitude 0.765 0.765
Model H-band photometric magnitude 0.225 0.220
Model v sin i (km/s) 241 240
Reduced χ2:
    Total 1.79 1.37
    Closure phase 2.08 1.73
    Vis2 1.48 1.10
    Triple amp 2.14 1.58