High-Resolution Spectroscopy in Tr37: Gas Accretion Evolution in Evolved Dusty Disks

Abstract

Using the Hectochelle multifiber spectrograph, we have obtained high-resolution (R~34,000) spectra in the Halpha region for a large number of stars in the 4 Myr-old cluster Tr 37, containing 146 previously known members and 26 newly identified ones. We present the Halpha line profiles of all members, compare them to our IR observations of dusty disks (2MASS/JHK + IRAC + MIPS 24 micron), use the radial velocities as a membership criterion, and calculate the rotational velocities. We find a good correlation between the accretion-broadened profiles and the presence of protoplanetary disks, noting that a small fraction of the accreting stars presents broad profiles with Halpha equivalent widths smaller than the canonical limit separating CTTS and WTTS. The number of strong accretors appears to be lower than in younger regions, and a large number of CTTS have very small accretion rates (dM/dt<10^{-9} Msun/yr). Taking into account that the spectral energy distributions are consistent with dust evolution (grain growth/settling) in the innermost disk, this suggests a parallel evolution of the dusty and gaseous components. We also observe that about half of the "transition objects" (stars with no IR excesses at wavelengths shorter than ~6 micron) do not show any signs of active accretion, whereas the other half is accreting with accretion rates <10^{-9} Msun/yr. These zero or very low accretion rates reveal important gas evolution and/or gas depletion in the innermost disk, which could be related to grain growth up to planetesimal or even planet sizes. Finally, we examine the rotational velocities of accreting and non accreting stars, finding no significant differences that could indicate disk locking at these ages.

51 pages, 13 (reduced resolution) figures, 2 tables. AJ in press

References in corpus (4)

• Photoevaporation of protoplanetary discs II: evolutionary models and observable properties
• Stellar Multiplicity and the IMF: Most Stars Are Single
• Photoevaporation of protoplanetary discs I: hydrodynamic models
• Mid-Infrared Spectroscopy of Disks around Classical T Tauri Stars

Cited by in corpus (16)

• Theory of Star Formation
• Dust dynamics during protoplanetary disc clearing
• Very Low-Mass Objects in the Coronet Cluster: The Realm of the Transition Disks
• On the Semimajor Axis Distribution of Extrasolar Gas Giant Planets: Why Hot Jupiters Are Rare Around High-Mass Stars
• Disk Dispersal and Planet Formation Time Scales
• A Search for Mid-Infrared Molecular Hydrogen Emission from Protoplanetary Disks
• From discs to planetesimals I: evolution of gas and dust discs
• Disk Truncation and Planet Formation in gamma Cephei
• Accretion properties of T Tauri stars in sigma Ori
• The Rapid Outbursting Star GM Cep: An EX-or in Tr 37?
• Properties of protostars in the Elephant Trunk globule IC 1396A
• MBM 12: young protoplanetary discs at high galactic latitude
• Discovery of Gas Accretion Onto Stars in 13 Myr old h and chi Persei
• A Search for NIR Molecular Hydrogen Emission in the CTTS LkHa 264 and the debris disk 49 Cet
• A GLIMPSE into the Nature of Galactic Mid-IR Excesses
• 10 $\mu$m interferometry of disks around young stars