133 research outputs found
Demographics of Transition Objects
The unusual properties of transition objects (young stars with an optically
thin inner disc surrounded by an optically thick outer disc) suggest that
significant disc evolution has occured in these systems. We explore the nature
of these systems by examining their demographics, specifically their stellar
accretion rates (Mdot) and disc masses (Mdisc) compared to those of accreting T
Tauri stars of comparable age. We find that transition objects in Taurus occupy
a restricted region of the Mdot vs. Mdisc plane. Compared to non-transition
single stars in Taurus, they have stellar accretion rates that are typically
~10 times lower at the same disc mass and median disc masses ~4 times larger.
These properties are anticipated by several proposed planet formation theories
and suggest that the formation of Jovian mass planets may play a significant
role in explaining the origin of at least some transition objects. Considering
transition objects as a distinct demographic group among accreting T Tauri
stars leads to a tighter relationship between disc masses and stellar accretion
rates, with a slope between the two quantities that is close to the value of
unity expected in simple theories of disc accretion.Comment: 11 pages, 4 figures, to appear in MNRA
High-resolution Spectroscopy of [Ne II] Emission from TW Hya
We present high-resolution echelle spectra of [Ne II] 12.81 micron emission
from the classical T Tauri star (CTTS) TW Hya obtained with MICHELLE on Gemini
North. The line is centered at the stellar radial velocity and has an intrinsic
FWHM of 21\pm 4 km/s. The line width is broader than other narrow emission
lines typically associated with the disk around TW Hya. If formed in a disk,
the line broadening could result from turbulence in a warm disk atmosphere,
Keplerian rotation at an average distance of 0.1 AU from the star, or a
photoevaporative flow from the optically-thin region of the disk. We place
upper limits on the [Ne II] emission flux from the CTTSs DP Tau and BP Tau.Comment: Accepted by ApJ. 18 pages, including 2 figures and 2 table
- …