Astronomy and Astrophysics, volume 285, 415-439 (1994/5-2)
New radial velocities for classical cepheids. Local galactic rotation revisited.
PONT F., MAYOR M. and BURKI G.
Abstract (from CDS):
New centre-of-mass radial velocities are calculated for 107 classical cepheids from CORAVEL observations. We generally determine these velocities from four to six measurements carefully spaced in phase, by fitting a "typical" radial velocity curve or the mirror image of the light curve. A decomposition in Fourier series is used for stars with more than 10 measurements. Distances are then computed through a period-luminosity-colour relation for 278 classical cepheids with known radial velocity, and an axisymmetric galactic rotation model is applied to the sample, using a generalised non-linear least square method with uncertainties on both the velocities and the distances. The best results, with a rotation curve modelled as a third order polynomial, are: R☉=8.09 ±0.30 kpc, A=15.92 ±0.34 km/s/kpc, 2A R☉=257 ±7 km/s, A2=d2θ(R)/d R2=-3.38 ±0.38 km/s/kpc2, A3=d3θ(R)/d R3=1.99 ±0.62 km/s/kpc3, u0=9.32 ±0.80 km/s, v0=11.18 ±0.65 km/s. The effect of modifying the distance scale of cepheids, the absorption coefficient or the fitting procedure algorithm are examined. It appears that the product 2 A R☉ is very robust towards these changes. The extended sample of classical cepheids with known radial velocity presented in this paper seems to imply a higher value for A than anterior studies. The radial velocity residuals show a systematic k-term of about 2 km/s. New evidence from cluster cepheids excludes an intrinsic cause for this shift, and a dynamical cause is proposed from a comparison with a N-body simulation of the Galaxy. The simulation shows that a systematic bias of this magnitude is typical. The structure of the local residual velocity field is examined in some detail.