Towards a complete stellar mass function of the Hyades

Abstract

Aims. The Hyades cluster is an ideal target to study the dynamical evolution of a star cluster over the entire mass range due to its intermediate age and proximity to the Sun. Methods. We wanted to extend the Hyades mass function towards lower masses down to 0.1 M and to use the full three-dimensional spatial information to characterize the dynamical evolution of the cluster. Results. We performed a kinematic and photometric selection using the PPMXL and Pan-STARRS1 sky surveys, to search for cluster members up to 30 pc from the cluster centre. We determined our detection efficiency and field star contamination rate to derive the cluster luminosity and mass functions down to masses of 0.1 M . The thorough astrometric and photometric constraints minimized the contamination. A minimum spanning tree algorithm was used to quantify the mass segregation. Conclusions. We discovered 43 new Hyades member candidates with velocity perpendicular to the Hyades motion up to 2 km s −1 . They have mass estimates between 0.43 and 0.09 M , for a total mass of 10 M . This doubles the number of Hyades candidates with masses smaller than 0.15 M . We provide an additional list of 11 possible candidates with velocity perpendicular to the Hyades motion up to 4 km s −1 . The cluster is significantly mass segregated. The extension of the mass function towards lower masses provided an even clearer signature than estimated in the past. We also identified as likely Hyades member an L0 dwarf previously assumed to be a field dwarf. Finally we question the membership of a number of previously published candidates, including a L2.5-type dwarf.

LACEwING: A New Moving Group Analysis Code

“…First, that all the groups are similarly complete down to spectral type K7; this will cause more rarely studied groups like 32 Ori and χ 01 For to be underpredicted. Second, that the initial mass function of all of these groups has the same slope; this will overpredict membership in groups with known top-heavy mass functions like the Hyades (Goldman et al 2013), and in theory underpredict membership in any group with a bottom-heavy mass function. Third, that a K7 spectral type refers to the same mass at the age of every group.…”

“…Based on analyses of Röser et al (2011) and Goldman et al (2013), there are 724 known members of the Hyades, of which 260 are BAFGK members (including giants and white dwarfs). The hottest stellar member (excluding white dwarfs) isθ 02 Tau, an A7III giant.…”

Spectroscopy of Hyades L dwarf candidates★

“…The mean proper motion of the L dwarf candidates is (µα cos δ,µ δ ) = (106.10,−19.35) mas/yr with an intrinsic dispersion (after removing proper motion errors) of 25.5 mas/yr and 7.4 mas/yr in right ascension and declination, respectively (total is 26.5 mas/yr). For comparison, the total intrinsic dispersion of Hyades members from Goldman et al (2013) in the area covered by Hogan et al (2008) with masses in the 2.6-2.0 M⊙, 2.0-1.0 M⊙, 1.0-0.5 M⊙, and 0.5-0.2 M⊙ are 17.96 mas/yr, 19.67 mas/yr, 23.82 mas/yr, and 26.89 mas/yr, respectively.…”

“…We overplotted in that figure the known Hyades members published by Goldman et al (2013) with small grey crosses. We can observe the large dispersion of the members, centered around (100,−25) mas/yr.…”

“…However, this search was limited in magnitude to V ∼20 mag, yielding a catalogue of 364 stars within the tidal radius of the cluster, down to 0.2 M⊙ corresponding to a spectral type of M4. This work was recently extended by Goldman et al (2013) down to lower masses (∼0.09 M⊙) by combining PPMXL with PanStarrs (Kaiser et al 2002) to derive the cluster mass function in the low-mass regime. Gizis et al (1999) attempted to select photometrically L dwarf candidates in the Hyades from a photometric search in the Two Micron All Sky Survey (2MASS; Cutri et al 2003;Skrutskie et al 2006) but did not confirm any of the candidate as spectroscopic member.…”