22 April 2015

Alexander Binks
Identifying the Debris Disk Fraction Amongst M-dwarfs in Moving Groups

In this talk I present, for the first time, the fraction of debris disks for M-dwarfs in nearby moving groups (MGs) as a function of age. Although much work has focused on the disk frequencies of Solar-type stars, little is known of the M-dwarf debris disk fractions, because they are too faint to be studied in open clusters and until recently few were confirmed as members of MGs. Searches to identify new members in these groups in the last five years have revealed a swathe of new M-dwarfs members, which provide excellent tests for pre-main-sequence evolution of low-mass stars and surrounding substellar material. Infrared photometry is used to reveal disc excesses and SED fits are made to distinguish primordial and transitional disks from debris disks. Simulations show however that debris disks around M-dwarfs are not present above a WISE W1-W4 colour of ~2.5 and because the majority of field M-dwarfs have W1-W4 ~ 0.5 this means that debris disks can only be observed in a narrow W1-W4 window. This makes the absolute fraction of debris disks difficult to measure. The fractions are placed into a more general context with Solar-type stars to investigate both the age and mass dependency of the presence of debris disks. Whilst the M-dwarf disk fraction in this work was found to be ~5% in MGs younger than 40 Myr, there were no disks found in the groups older than 40 Myr, a result which rejects the null hypothesis at 90%. The debris disk dissipation timescale appears to be faster than for higher-mass stars and to conclude this talk I provide possible explanations for the more rapid decay timescale observed in M-dwarfs.