Abstract
The transition between massive Class II circumstellar disks and Class III debris disks, with dust residuals, has not yet been clearly understood. Disks are expected to dissipate with time, and dust clearing in the inner regions can be the consequence of several mechanisms. Planetary formation is one of them that will possibly open a gap inside the disk. According to recent models based on photometric observations, T Cha is expected to present a large gap within its disk, meaning that an inner dusty disk is supposed to have survived close to the star. We investigate this scenario with new near-infrared interferometric observations. We observed T Cha in the H and K bands using the AMBER instrument at VLTI and used the MCFOST radiative transfer code to model the SED of T Cha and the interferometric observations simultaneously and to test the scenario of an inner dusty structure. We also used a toy model of a binary to check that a companion close to the star can reproduce our observations. The scenario of a close (few mas) companion cannot satisfactorily reproduce the visibilities and SED, while a disk model with a large gap and an inner ring producing the bulk of the emission (in H and K-bands) close to 0.1 AU is able to account for all the observations. With this study, the presence of an optically thick inner dusty disk close to the star and dominating the H and K- bands emission is confirmed. According to our model, the large gap extends up to ~ 7.5 AU. This points toward a companion (located at several AU) gap-opening scenario to explain the morphology of T Cha.
Highlights
Using the IRAS space observatory, Strom et al (1989) have reported that several pre-main-sequence stars show a lack of emission in the mid-infrared (IR) compared to their far-IR flux, owing to a lack of warm dust indicative of the early stages of planetary formation
T Cha was observed at the VLTI, using the AMBER instrument that allows the simultaneous combination of three beams in the near-IR with spatial filtering (Petrov et al 2007)
We present K- and H-bands observations taken in the low spectral resolution mode (LR; R ∼ 35) with the 8.2 m Unit Telescopes (UTs), coupled with the use of adaptive optics
Summary
Using the IRAS space observatory, Strom et al (1989) have reported that several pre-main-sequence stars show a lack of emission in the mid-infrared (IR) compared to their far-IR flux, owing to a lack of warm dust indicative of the early stages of planetary formation. Thanks to the great sensitivity of the Spitzer Space Telescope, fainter T Tauri stars were found to present such behavior (e.g., Brown et al 2007). Several mechanisms can be responsible for dust clearing, such as a binary companion (Jensen & Mathieu 1997) which is the case for CoKu Tau 4 (Ireland & Kraus 2008), or photo-evaporation processes (Alexander et al 2006) These mechanisms will clear the disk as probed by submillimeter and millimeter observations (e.g., Andrews et al 2009; Hughes et al 2009; Brown et al 2009). In this Letter, we present the first near-IR interferometric observations of a T Tauri star by the AMBER instrument, installed at the Very Large Telescope Interferometer (VLTI, Schöller 2007).
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