73 research outputs found
Disk evolution in the Ori OB1 association
We analyze multi-band photometry of a subsample of low mass stars in the
associations Ori OB1a and 1b discovered during the CIDA Orion Variability
Survey, which have ages of 7 - 10 Myr and 3 - 5 Myr, respectively. We obtained
UBVRcIc photometry at Mt. Hopkins for 6 Classical T Tauri stars (CTTS) and 26
Weak T Tauri stars (WTTS) in Ori OB1a, and for 21 CTTS and 2 WTTS in Ori OB1b.
We also obtained L band photometry for 14 CTTS at Mt. Hopkins, and 10um and
18um photometry with OSCIR at Gemini for 6 CTTS; of these, all 6 were detected
at 10um while only one was detected at 18um. We estimate mass accretion rates
from the excess luminosity at U, and find that they are consistent with
determinations for a number of other associations, with or without high mass
star formation. The observed decrease of mass accretion rate with age is
qualitatively consistent with predictions of viscous evolution of accretion
disks. We find an overall decrease of disk emission from Taurus to Ori OB1b to
Ori OB1a. This decrease implies that significant grain growth and settling
towards the midplane has taken place in the inner disks of Ori OB1. We compare
the SED of the star detected at both 10um and 18um with disk models for similar
stellar and accretion parameters. We find that the low <= 18 um fluxes of this
Ori OB1b star cannot be due to the smaller disk radius expected from viscous
evolution in the presence of the FUV radiation fields from the OB stars in the
association. Instead, we find that the disk of this star is essentially a flat
disk, with little if any flaring, indicating a a significant degree of dust
settling towards the midplane, as expected from dust evolution in
protoplanetary disks.Comment: 35 pages, 11 figures, to appear in the Astronomical Journal. Full
resolution figures in http://www.cida.ve/~briceno/publications
The Evolution of Protoplanetary Disks: Probing the Inner Disk of Very Low Accretors
We report FUV, optical, and NIR observations of three T Tauri stars in the
Orion OB1b subassociation with H equivalent widths consistent with low
or absent accretion and various degrees of excess flux in the mid-infrared. We
aim to search for evidence of gas in the inner disk in HST ACS/SBC spectra, and
to probe the accretion flows onto the star using H and He I
10830 in spectra obtained at the Magellan and SOAR telescopes. At the
critical age of 5 Myr, the targets are at different stages of disk evolution.
One of our targets is clearly accreting, as shown by redshifted absorption at
free-fall velocities in the He I line and wide wings in H; however, a
marginal detection of FUV H suggests that little gas is present in the
inner disk, although the spectral energy distribution indicates that small dust
still remains close to the star. Another target is surrounded by a transitional
disk, with an inner cavity in which little sub-micron dust remains. Still, the
inner disk shows substantial amounts of gas, accreting onto the star at a
probably low, but uncertain rate. The third target lacks both a He I line or
FUV emission, consistent with no accretion or inner gas disk; its very weak IR
excess is consistent with a debris disk. Different processes occurring in
targets with ages close to the disk dispersal time suggest that the end of
accretion phase is reached in diverse ways.Comment: 13 pages, 3 figures. Accepted for publication in The Astrophysical
Journa
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