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While it is known that the sharp-line star Vega (vsini ~ 20km/s) is actuallya rapid rotator seen nearly pole-on with low i (< 10 deg), no consensus has yetbeen accomplished regarding its intrinsic rotational velocity (v_e), for whichrather different values have been reported so far. Methodologically, detailedanalysis of spectral line profiles is useful for this purpose, since theyreflect more or less the v_e-dependent gravitational darkening effect. However,direct comparison of observed and theoretically simulated line profiles is notnecessarily effective in practice, where the solution is sensitively affectedby various conditions and the scope for combining many lines is lacking. Inthis study, determination of Vega's v_e was attempted based on an alternativeapproach making use of the first zero (q_1) of the Fourier transform of eachline profile, which depends upon K (temperature sensitivity parameter differingfrom line to line) and v_e. It turned out that v_e and vsini could beseparately established by comparing the observed q_1^obs and calculated q_1^calvalues for a number of lines of different K. Actually, independent analysisapplied to two line sets (49 Fe I lines and 41 Fe II lines) yielded resultsreasonably consistent with each other. The final parameters of Vega's rotationwere concluded as vsini = 21.6 (+/- 0.3) km/s, v_e = 195 (+/- 15) km/s, and i =6.4 (+/- 0.5) deg.

Determination of Vega's rotational velocity based on the Fourier analysis of spectral line profiles