Cool Stars 14 - Submitted Abstract # 323
This version created on 05 October 2006

Disks Around Cool Stars and Brown Dwarfs


Daniel Apai, University of Arizona
Kevin Luhman, Penn State University

The aim of the session is to present the newest results and
organize them into an evolutionary sequence contributing toward
the understanding of planet formation around cool stars. The
discussion-oriented session will be led by key speakers and
summarized in a written review by the convenors Apai and Luhman.

Understanding the properties of planetary systems around cool
stars requires answering four fundamental questions: How
frequent are disks around cool stars and brown dwarfs? How often
do these disks evolve into planetary systems? What is the least
massive star that can harbor planetary systems? How will the
architecture of planetary systems vary with the varying stellar
and disk parameters?

These exciting questions motivated substantial observational and
theoretical effort since Cool Stars 13 and significant progress
has been achieved partly by the Spitzer Space Telescope. These
studies and results include largeÐscale thermal infrared imaging
demonstrating that about 50% of the young brown dwarfs are
surrounded by warm dust disks [e.g. 1] and evidence that disks
can be found even around planetaryÐmass objects [2]. Spitzer
infrared spectroscopy has revealed surprisingly processed dust
in the inner brown dwarf disks, resembling dust at the epoch of
the cometÐformation in our Solar System [3]. Optical and
nearÐinfrared spectroscopy identified a correlation between
stellar mass and accretion rate extending from Herbig stars to
young brown dwarfs [4,5].

Recent years brought mounting evidence for planetary systems
around very low-mass stars and even brown dwarfs: the direct
imaging of the faint companion of 2MASS1207 demonstrated the
presence of planetary-mass objects on wide orbits around brown
dwarfs [6,7]; radial velocity surveys of M-stars identified 4
close-in giant planets [8] and the direct imaging of the debris
disk around the nearby M--dwarf AU Mic highlighted the existence
of giant planets and planetesimals [9,10]. Gravitational lensing
experiments detected a 5 Earth-mass planet around an M-dwarf,
suggesting that cool stars may harbor terrestrial planets more
frequently than their more massive counterparts do [11].

Motivated by the observations, intense theoretical work explored
the efficiency of planet formation around MÐdwarfs [e.g. 12,13]
and brown dwarfs [e.g. 14] and the accretion rateÐstellar mass
correlation [e.g. 15]. The discoveries and the emerging
understanding of disk evolution and planet formation around cool
objects highlighted the potential of comparative disk studies.
This rapidly developing field will greatly benefit from a forum
that brings together its yet diverse community.

The splinter session proposed here aims to provide a venue for
the community studying circumstellar disks around cool stars and
brown dwarfs to: i, review the latest results from Spitzer, HST,
and ground-based facilities; ii, cast these results in a
coherent evolutionary sequence; iii, discuss the recent results
and their implications in detail, developing a better
understanding of the processes. The proposed session will be
dominated by 15-minute discussions on eight key topics:
protostellar phase, disk frequency and life time, disk structure
and mineralogy, disk masses, transition disks, planet formation,
and debris disks. Each topic will be introduced in a 6-minute
review by an expert.

References: [1] Luhman et al. 2005 ApJL 631, 69 [2] Luhman et
al. 2005 ApJL 620, 51 [3] Apai et al. 2005 Science 310, 834 [4]
Muzerolle et al. 2005 ApJ 625, 906 [5] Natta et al. 2004 A&A
424, 603 [6] Chauvin et al. 2005 438, 25 [7] Extrasolar Planets
Encyclopedia [8] Liu 2004 Science 305, 1442 [9] Kalas et al.
2004 Science 303, 1990 [10] Beaulieu et al. Nature 2006 439, 437
[11] Boss 2006 ApJ 643, 501 [12] Laughlin et al. 2004 612, 73
[13] Lodato & Clarke 2005 MNRAS 353, 841 [14] Armitage et al.
2006 ApJ 639, 83 [15] Dullemond et al. 2006 ApJ, in press 

Website: http://nautilus.as.arizona.edu/DisksCoolStars/index.html

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