A deep all-sky census of the Hyades

Abstract

Aims. On the basis of the PPMXL catalogue we perform an all-sky census of the Hyades down to masses of about 0.2 m in a region up to 30 pc from the cluster centre. Methods. We use the proper motions from PPMXL in the convergent point method to determine probable kinematic members. From 2MASS photometry and CMC14 r -band photometry, we derive empirical colour-absolute magnitude diagrams and, finally, determine photometric membership for all kinematic candidates. Results. This is the first deep (r ≤ 17) all-sky survey of the Hyades allowing a full three-dimensional analysis of the cluster. The survey is complete down to at least M Ks = 7.3 or 0.25 m . We find 724 stellar systems co-moving with the bulk Hyades space velocity, which represent a total mass of 435 m . The tidal radius is about 9 pc, and 275 m (364 systems) are gravitationally bound. This is the cluster proper. Its mass density profile is perfectly fitted by a Plummer model with a central density of 2.21 m pc −3 and a core radius of r co = 3.10 pc, while the half-mass radius is r h = 4.1 pc. There are another 100 m in a volume between one and two tidal radii (halo), and another 60 m up to a distance of 30 pc from the centre. Strong mass segregation is inherent in the cluster. The present-day luminosity and mass functions are noticeably different in various parts of the cluster (core, corona, halo, and co-movers). They are strongly evolved compared to presently favoured initial mass functions. The analysis of the velocity dispersion of the cluster shows that about 20% of its members must be binaries. As a by-product, we find that presently available theoretical isochrones are not able to adequately describe the near-infrared colour-absolute magnitude relation for those cluster stars that are less massive than about 0.6 m .

Simulations of the Hyades

“…The contamination with field stars in the observational data file is negligible for r < 9 pc, 7.5% at 9 pc < r < 18 pc, and 30% at 18 pc < r < 30 pc (with respect to the number of stars; Röser et al 2011), where r is measured from the center of the cluster. Three comparisons of the cumulative mass profiles are shown in Fig.…”

“…The three values are consistent with the fact that the velocity dispersion in the core is higher than in the halo within the Jacobi radius and rises again outside of the Jacobi radius. The values can be compared with those given in Röser et al (2011). Figure 7 shows the average realization of the Kroupa (2001) IMF of the ensemble en3000W6 with lowest mass m l = 0.08 M and initial particle number N 0 = 3000.…”

“…In addition, he introduces a small scatter in both V and B − V. We cannot directly compare to the observations since the data in B − V are missing for the data set used in the present study. Figure 11 show the comparison of the present-day luminosity functions (PDLFs) for the ensemble en3000W6 and the observations by Röser et al (2011). In the top, middle and bottom panels stars within a radius of 30, 9 (Jacobi radius) and 3 pc (core) from the cluster center have been used in the statistics.…”

“…The top panel of Fig. 13 shows the analysis of the evolved (for 625 Myr) ensemble en3000W6, while the bottom panel shows an analysis of the observational data of Röser et al (2011). Each single plot contains on the left-hand side the "cumulative" Γ MST (points) for the 5, 10, 20, 50, 100, 200, 500, and all most massive stars (black).…”

Reliable probabilistic determination of membership in stellar kinematic groups in the young disk

“…We found that II Tau is a good kinematic candidate of the Hyades stream. Even if this source was already listed as a Hyades candidate by Röser et al (2011), its membership is still not clear because of the disagreement between its estimated age and that of the Hyades. Due to their very low probability of membership in the AB Doradus association, we proposed GJ 3136 and 1RXS J235133.3+312720 AB as being candidates of the Pleiades MG, mainly because both Eggen's criteria are also fulfilled for this group.…”