TY - JOUR
T1 - The long-lived disks in the η chamaeleontis cluster
AU - Sicilia-Aguilar, Aurora
AU - Bouwman, Jeroen
AU - Juhsz, Attila
AU - Henning, Thomas
AU - Roccatagliata, Veronica
AU - Lawson, Warrick A.
AU - Acke, Bram
AU - Feigelson, Eric D.
AU - Tielens, A. G.G.M.
AU - Decin, Leen
AU - Meeus, Gwendolyn
PY - 2009
Y1 - 2009
N2 - We present Infrared Spectrograph spectra and revised Multiband Imaging Photometer photometry for the 18 members of the η Chamaeleontis cluster. Aged 8Myr, the η Cha cluster is one of the few nearby regions within the 5-10Myr age range, during which the disk fraction decreases dramatically and giant planet formation must come to an end. For the 15 low-mass members, we measure a disk fraction 50%, high for their 8Myr age, and four of the eight disks lack near-IR excesses, consistent with the empirical definition of "transition" disks. Most of the disks are comparable to geometrically flat disks. The comparison with regions of different ages suggests that at least some of the "transition" disks may represent the normal type of disk around low-mass stars. Therefore, their flattened structure and inner holes may be related to other factors (initial masses of the disk and the star, environment, binarity), rather than to pure time evolution. We analyze the silicate dust in the disk atmosphere, finding moderate crystalline fractions (10%-30%) and typical grain sizes 1-3 μm, without any characteristic trend in the composition. These results are common to other regions of different ages, suggesting that the initial grain processing occurs very early in the disk lifetime (<1Myr). Large grain sizes in the disk atmosphere cannot be used as a proxy for age, but are likely related to higher disk turbulence. The dust mineralogy varies between the 8-12 μm and the 20-30 μm features, suggesting high temperature dust processing and little radial mixing. Finally, the analysis of IR and optical data on the B9 star η Cha reveals that it is probably surrounded by a young debris disk with a large inner hole, instead of being a classical Be star.
AB - We present Infrared Spectrograph spectra and revised Multiband Imaging Photometer photometry for the 18 members of the η Chamaeleontis cluster. Aged 8Myr, the η Cha cluster is one of the few nearby regions within the 5-10Myr age range, during which the disk fraction decreases dramatically and giant planet formation must come to an end. For the 15 low-mass members, we measure a disk fraction 50%, high for their 8Myr age, and four of the eight disks lack near-IR excesses, consistent with the empirical definition of "transition" disks. Most of the disks are comparable to geometrically flat disks. The comparison with regions of different ages suggests that at least some of the "transition" disks may represent the normal type of disk around low-mass stars. Therefore, their flattened structure and inner holes may be related to other factors (initial masses of the disk and the star, environment, binarity), rather than to pure time evolution. We analyze the silicate dust in the disk atmosphere, finding moderate crystalline fractions (10%-30%) and typical grain sizes 1-3 μm, without any characteristic trend in the composition. These results are common to other regions of different ages, suggesting that the initial grain processing occurs very early in the disk lifetime (<1Myr). Large grain sizes in the disk atmosphere cannot be used as a proxy for age, but are likely related to higher disk turbulence. The dust mineralogy varies between the 8-12 μm and the 20-30 μm features, suggesting high temperature dust processing and little radial mixing. Finally, the analysis of IR and optical data on the B9 star η Cha reveals that it is probably surrounded by a young debris disk with a large inner hole, instead of being a classical Be star.
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U2 - 10.1088/0004-637X/701/2/1188
DO - 10.1088/0004-637X/701/2/1188
M3 - Article
AN - SCOPUS:70449900303
SN - 0004-637X
VL - 701
SP - 1188
EP - 1203
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
ER -