Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...285..415p&link_type=abstract
Astronomy and Astrophysics 285, 415-439 (1994)
Astronomy and Astrophysics
Astrophysics
80
Stars: Kinematics, Stars: Variables: Cepheids, Galaxy: Kinematics And Dynamics
Scientific paper
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: Rsun_=8.09 +/-0.30 kpc, A=15.92 +/-0.34 km/s/kpc, 2A Rsun_=257 +/-7 km/s, A2=d^2theta(R)/d R^2^=-3.38 +/-0.38 km/s/kpc^2^, A3=d^3theta(R)/d R^3^=1.99 +/-0.62 km/s/kpc^3^, u_0_=9.32 +/-0.80 km/s, v_0_=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 Rsun_ 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.
Burki Gilbert
Mayor Marcel
Pont Frederic
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