G. Theureau

Extragalactic database - VII. Reduction of astrophysical parameters

The Lyon-Meudon Extragalactic database (LEDA) gives a free access to the main astrophysical parameters for more than 100 000 galaxies. The most common names are compiled allowing users to recover quickly any galaxy. All these measured astrophysical parameters are first reduced to a common system according to well defined reduction formulae leading to mean homogeneized parameters. Further, these parameters are also transformed into corrected parameters from widely accepted models. For instance, raw 21-cm line widths are transformed into mean standard widths after correction for instrumental effect and then into maximum velocity rotation properly corrected for inclination and non-circular velocity. This paper presents the reduction formulae for each parameter: coordinates, morphological type and luminosity class, diameter and axis ratio, apparent magnitude (UBV , IR, HI) and colors, maximum velocity rotation and central velocity dispersion, radial velocity, mean surface brightness, distance modulus and absolute magnitude, and group membership. For each of these parameters intermediate quantities are given: galactic extinction, inclination, K-correction etc.. All these parameters are available from direct connexion to LEDA and distributed on a standard CD-ROM (PGC-ROM 1996) by the Observatoire de Lyon via the CNRS.

Kinematics of the local universe XII. 21-cm line measurements of 586 galaxies with the new Nançay receiver

This paper presents 586 new 21-cm neutral hydrogen line measurements carried out with the FORT receiver of the meridian transit Nancay radiotelescope in the period July 2000-March 2003. This observational programme is part of a larger project aiming at collecting an exhaustive and magnitude-complete HI extragalactic catalogue for Tully-Fisher applications. It is associated with the building of the MIGALE spectroscopic archive and database.

Long-term timing of four millisecond pulsars

We have timed four millisecond pulses, PSRs J1721−2457, J1745−0952, J1810−2005, and J1918−0642, for up to a total of 10.5 years each using multiple telescopes in the European Pulsar Timing Array network: the Westerbork Synthesis Radio Telescope in The Netherlands, the Nancay Radio Telescope in France and the Lovell telescope at Jodrell Bank in the UK. The long time span has enabled us to measure the proper motions of J1745−0952 and J1918−0642, indicating that they have transverse velocities of 200(50) and 54(7) km s −1 respectively. We have obtained upper limits on the proper motion of J1721−2457 and J1810−2005, which imply that they have transverse velocities less than 140 and 400 km s −1 respectively. In all cases, the velocities lie in the range typical of millisecond pulsars. We present pulse profiles for each pulsar taken from observations at multiple frequencies in the range of 350 to 2600 MHz, and show that J1810−2005 shows significant profile evolution in this range. Using our multi-frequency observations, we measured the spectral indices for all four pulsars, and for J1810−2005 it appears to be very flat. The flux density of J1918−0642 shows extensive modulation which we attribute to the combined effects of refractive and diffractive scintillation. We discuss the possible use of including J1721−2457 or J1918−0642 in a pulsar timing array, and find that J1918−0642 will be useful to include when the timing precision of this pulsar is improved over the next few years. We have searched archival optical observations to detect companions of the binary pulsars, but none were detected. However, we provide lower limits on the masses of the white dwarf companions of PSRs J1745−0952 and J1918−0642.

Revisiting the optical depth of spiral galaxies using the Tully-Fisher B relation

Aims. We attempt to determine the optical depth of spiral galaxy disks by a statistical study of new Tully-Fisher data from the ongoing KLUN+ survey, and to clarify the difference between the true and apparent behavior of optical depth. Methods. By utilizing so-called normalized distances, a subsample of the data is identified to be as free from selection effects as possible. For these galaxies, a set of apparent quantities are calculated for face-on positions using the Tully-Fisher diameter and magnitude relations. These values are compared with direct observations to determine the mean value of the parameter C describing the optical depth. Results. The present study suggests that spiral galaxy disks are relatively optically thin τB ≈ 0.1, at least in the outermost regions, while they appear in general to be optically thick τB > 1 when the apparent magnitude and average surface brightness are studied statistically.

Interprétation de la structure de galaxies entourant le Superamas Local

After numerical simulations by E. Praton, we interprete the cocoon-like structure observed for the distribution of galaxies around us as an effect of infall velocities onto clusters. In this view structures like the Cocoon (or even like the Great-Wall) could be interpreted as observationnal artefacts.