Poster Abstracts

Name/Affiliation:  Nicolas Lodieu (IAC, Tenerife)

Title:  An homogeneous view of the IMF across the hydrogen-burning limit in nearby open clusters

Abstract:
The latest release of the UKIDSS Galactic Clusters Survey (GCS) made public near-infrared photometry in six passbands (ZYJHK1K2) and accurate proper motions measured from the multiple epochs obtained by the GCS. The main scientific goal of the GCS is to investigate the shape and universality of the Initial Mass Function in the low-mass and substellar regimes. We analysed the photometric and astrometric data in six galactic clusters among the 10 regions surveyed by the GCS: sigma Orionis (3-5 Myr, 352 pc; Lodieu et al. 2009), Upper Scorpius (age=5 Myr, d=145 pc; Lodieu et al. 2007, 2008, 2013), IC4665 (27 Myr, 350 pc; Lodieu et al. 2011), Alpha Per (85 Myr, 170 pc; Lodieu et al. 2012b), the Pleiades (125 Myr, 120 pc; Lodieu et al. 2012), and Praesepe (590 Myr, 182 pc; Boudreault et al. 2012). We selected hundreds of member candidates in these regions in an homogeneous manner based on their positions in colour-magnitude and vector point diagrams. We derived the luminosity and mass functions for all these regions, using the latest state-of-the-art isochrones to convert magnitudes into masses. We find that all mass functions are very similar in the 0.6-0.03 Msun mass interval and in agreement with the log-normal form of the field mass function by Chabrier (2005), pointing towards a universal mass function. This talk will focus on key results from our homogeneous study and present preliminary optical spectroscopy: 1) comparison of the mass functions in the low-mass and substellar regimes 2) comparison of the cluster sequences with the most recent BT-Settl models from the Lyon group 3) comparison of the photometric binary fractions in the low-mass and brown dwarf regimes with hydrodynamical simulations of Bate (2012) 4) discussion on the K-band variability as a function of age for low-mass stars and brown dwarfs