Showing papers by "Alberto Krone-Martins published in 2009"

Kinematic analysis and membership status of TWA22 AB

Abstract: Context. TWA22 was initially regarded as a member of the TW Hydrae association (TWA). In addition to being one of the youngest ( 8 Myr) and nearest ( 20 pc) stars to Earth, TWA22 has proven to be very interesting after being resolved as a tight, very lowmass binary. This binary can serve as a very useful dynamical calibrator for pre-main sequence evolutionary models. However, its membership in the TWA has been recently questioned despite due to the lack of accurate kinematic measurements. Aims. Based on proper motion, radial velocity, and trigonometric parallax measurements, we aim here to re-analyze the membership of TWA22 to young, nearby associations. Methods. Using the ESO NTT/SUSI2 telescope, we observed TWA22 AB during 5 di erent observing runs over 1.2 years to measure its trigonometric parallax and proper motion. This is a part of a larger project measuring trigonometric parallaxes and proper motions of most known TWA members at a sub-milliarcsec level. HARPS at the ESO 3.6m telescope was also used to measure the system’s radial velocity over 2 years. Results. We report an absolute trigonometric parallax of TWA22 AB, = 57:0 0:7 mas, corresponding to a distance 17:5 0:2 pc from Earth. Measured proper motions of TWA 22AB are cos( ) = 175:8 0:8 mas/yr and = 21:3 0:8 mas/yr. Finally, from HARPS measurements, we obtain a radial velocity Vrad = 14:8 2:1 km/s. Conclusions. A kinematic analysis of TWA22 AB space motion and position implies that a membership of TWA22 AB to known young, nearby associations can be excluded except for the Pictoris and TW Hydrae associations. Membership probabilities based on the system’s Galactic space motion and/or the trace-back technique support a higher chance of being a member to the Pictoris association. Membership of TWA22 in the TWA cannot be fully excluded because of large uncertainties in parallax measurements and radial velocities and to the uncertain internal velocity dispersion of its members.

Kinematic analysis and membership status of TWA22ABR

Abstract: TWA22 was initially regarded as a member of the TW Hydrae association (TWA). In addition to being one of the youngest (~8Myr) and nearest (~20pc) stars to Earth, TWA22 has proven to be very interesting after being resolved as a tight, very low-mass binary. This binary can serve as a very useful dynamical calibrator for pre-main sequence evolutionary models. However, its membership in the TWA has been recently questioned despite due to the lack of accurate kinematic measurements. Based on proper motion, radial velocity, and trigonometric parallax measurements, we aim here to re-analyze the membership of TWA22 to young, nearby associations. Using the ESO NTT/SUSI2 telescope, we observed TWA22AB during 5 different observing runs over 1.2 years to measure its trigonometric parallax and proper motion. This is a part of a larger project measuring trigonometric parallaxes and proper motions of most known TWA members at a sub-milliarcsec level. HARPS at the ESO 3.6m telescope was also used to measure the system's radial velocity over 2 years. We report an absolute trigonometric parallax of TWA22AB, 57.0mas, corresponding to a distance 17.5pc from Earth. Measured proper motions of TWA22AB are -175.8mas/yr in right ascension and -21.3mas/yr in declination. Finally, from HARPS measurements, we obtain a radial velocity 14.8km/s.

Kinematic parameters and membership lists of open clusters in the Bordeaux Carte du Ciel zone

Abstract: In the study of open clusters, the distinction between cluster and field members and the assignment of membership probabilities for each individual star in the relevant region are central issues. Here, we present an analysis based on the use of a fully automated method that relies on a hybrid heuristics, based on genetic algorithms and hill-climbing optimisation, as well as different probability distribution functions for the observables. We analysed the use of some variations for the parameterisation of those distribution functions. Finally, a catalogue comprising kinematic parameters and associated membership probability lists for all the open clusters in the Bordeaux PM2000 region was derived.