Abstract. We present a method for simultaneous measurement of the vertical distribution of the optical turbulence

We present the results of monitoring optical-turbulence profiles at San Pedro Mártir, Mexico, during 11 nights in 1997 March and April, and 16 nights in 2000 May. The data were collected using the generalized scintillation detection and ranging (SCIDAR) technique from Nice University at the 1.5 and 2.1 m telescopes. A total of 6414 turbulence profiles were measured and statistically analyzed. The principal results are as follows: the seeing produced by the turbulence in the first 1.2 km at the 1.5 m and 2.1 m telescopes, not including turbulence inside the domes, have median values of and , respectively. The 0Љ .63 ‫ע‬ 0Љ .01 0Љ .44 ‫ע‬ 0Љ .02 dome seeing at those telescopes have median values of and. The median values of the 0Љ .64 ‫ע‬ 0Љ .01 0Љ .31 ‫ע‬ 0Љ .02 seeing produced above 1.2 km and in the whole atmosphere are and. The isoplanatic 0Љ .39 ‫ע‬ 0Љ .01 0Љ .71 ‫ע‬ 0Љ .01 angle for full-correction adaptive optics has a median value of. The decorrelation time (defined as 1Љ .87 ‫ע‬ 0Љ .04 the time lag for which the temporal correlation drops to 50%) of the turbulence strength at altitudes below and above 16 km above sea level is approximately equal to 2 and 0.5 hr, respectively. The isoplanatic-angle decorrelation time is estimated to be equal to 2 hr. The turbulence above ∼8 km remained notably calm during nine consecutive nights, which is encouraging for adaptive optics observations at the site. The results obtained here places San Pedro Mártir among the best suited sites for installing next-generation optical telescopes.

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Aims. Previous studies have found that the coefficients and intrinsic dispersions of both the Kormendy relation and the Fundamental Plane depend on the magnitude range within which the galaxies are contained. We study whether this type of behaviour is also present for the Faber-Jackson relation. Methods. We take a sample of early-type galaxies from the Sloan Digital Sky Survey (SDSS-DR7, ∼90 000 galaxies) spanning a range of approximately 7 mag in both g and r filters and analyse the behaviour of the Faber-Jackson relation parameters as functions of the magnitude range. We calculate the parameters in two ways: i) we consider the faintest (brightest) galaxies in each sample and we progressively increase the width of the magnitude interval by inclusion of the brighter (fainter) galaxies (increasing-magnitudeintervals); and ii) we consider narrow-magnitude intervals of the same width (ΔM = 1.0 mag) over the whole magnitude range available (narrow-magnitude-intervals). Results. Our main results are that: i) in both increasing and narrow-magnitude-intervals the Faber-Jackson relation parameters change systematically, ii) non-parametric tests show that the fluctuations in the values of the slope of the Faber-Jackson relation are not products of chance variations. Conclusions. We conclude that the values of the Faber-Jackson relation parameters depend on the width of the magnitude range and the luminosity of galaxies within the magnitude range. This dependence is caused, to a great extent by the selection effects and because the geometrical shape of the distribution of galaxies on the M − log(σ 0 ) plane depends on luminosity. We therefore emphasize that if the luminosity of galaxies or the width of the magnitude range or both are not taken into consideration when comparing the structural relations of galaxy samples for different wavelengths, environments, redshifts and luminosities, any differences found may be misinterpreted.