A Census of the Low Accretors. II: Accretion Properties

Abstract

Much is known about the processes driving accretion from protoplanetary disks onto low-mass pre-main-sequence stars (T Tauri stars). Nevertheless, it is unclear how accretion stops. To determine the accretion properties and their relation to stellar properties and gain insight into the last stages of accretion, we present a detailed analysis of 24 low and possible accretors, previously identified using the He I $\lambda$10830 line. We model moderate-resolution H$\alpha$ profiles of these stars using magnetospheric accretion flow models that account for the chromospheric contribution at the line center. Based on parameters derived from the fits of 20 stars that can be reproduced with the models, we find a power-law relation between the disk truncation radius and the mass accretion rate consistent with predictions from theory and simulations. Comparing the corotation and truncation radii, we find that most of our targets are accreting in the unstable regime and rule out the propeller as the main process stopping accretion. For the truncation radius to be the same as the magnetic radius, the dipole magnetic field and/or the efficiency parameter $\xi$ need to be smaller than previously determined, suggesting that higher-order fields dominate in low accretion rates. Lastly, we determine that the lowest accretion rates that can be detected by H$\alpha$ line modeling are $1-3\times 10^{-11}{M}_{\odot }y{r}^{-1}$ for M3 stars and $3-5\times 10^{-11}{M}_{\odot }y{r}^{-1}$ for K5 stars. These limits are lower than the observed accretion rates in our sample, suggesting that we have reached a physical lower limit. This limit, $\dot{M}\sim 10^{-10}{M}_{\odot }y{r}^{-1}$, is consistent with EUV-dominated photoevaporation.

arXiv commentAccepted for publication in The Astrophysical Journal

References in corpus (41)

• Astropy: A Community Python Package for Astronomy
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• A new extensive library of PHOENIX stellar atmospheres and synthetic spectra
• Optimal Techniques in Two-dimensional Spectroscopy: Background Subtraction for the 21st Century
• Very Low Mass Stars and Brown Dwarfs in Taurus-Auriga
• APOGEE Data and Spectral Analysis from SDSS Data Release 16: Seven Years of Observations Including First Results from APOGEE-South
• X-Shooter spectroscopy of young stellar objects in Lupus: Accretion properties of class II and transitional objects
• Photoevaporation of Circumstellar Disks by FUV, EUV and X-ray Radiation from the Central Star
• Three-dimensional Simulations of Disk Accretion to an Inclined Dipole: II. Hot Spots and Variability
• Protoplanetary disc evolution and dispersal: the implications of X-ray photoevaportion
• Three-dimensional Simulations of Disk Accretion to an Inclined Dipole: I. Magnetospheric Flow at Different Theta
• The Evolution of Early-Type Galaxies in Distant Clusters II: Internal Kinematics of 55 Galaxies in the z=0.33 Cluster CL1358+62
• X-Shooter study of accretion in Chamaeleon I: II. A steeper increase of accretion with stellar mass for very low mass stars?
• Unstable Disk Accretion to Magnetized Stars: First Global 3D MHD Simulations
• X-Shooter spectroscopy of young stellar objects: II. Impact of chromospheric emission on accretion rate estimates
• X-Shooter study of accretion in Chamaeleon I
• The Gaia-ESO Public Spectroscopic Survey: Motivation, implementation, GIRAFFE data processing, analysis, and final data products
• Non-stationary dynamo & magnetospheric accretion processes of the classical T Tauri star V2129 Oph
• Multidimensional models of hydrogen and helium emission line profiles for classical T Tauri Stars: method, tests and examples
• The Gaia-ESO Survey: Chromospheric Emission, Accretion Properties, and Rotation in $\gamma$ Velorum and Chamaeleon I
• Accretion to Stars with Non-dipole Magnetic Fields
• Analytical Hot Spot Shapes and Magnetospheric Radius from 3D Simulations of Magnetospheric Accretion
• Boundary between Stable and Unstable Regimes of Accretion. Ordered and Chaotic Unstable Regimes
• Accretion dynamics in the classical T Tauri star V2129 Oph
• Fundamental properties of pre-main sequence stars in young, southern star forming regions: metallicities
• An extensive VLT/X-Shooter library of photospheric templates of pre-main sequence stars
• Modeling the Halpha line emission around classical T Tauri stars using magnetospheric accretion and disk wind models
• The magnetic fields of intermediate-mass T Tauri stars : I. Magnetic detections and fundamental stellar parameters
• The non-dipolar magnetic fields of accreting T Tauri stars
• Properties of Strong and Weak Propellers from MHD Simulations
• Stellar Rotation of T Tauri stars in the Orion Star-Forming Complex
• A Correlation Between Circumstellar Disks and Rotation in the Upper Scorpius OB Association
• Characterising the surface magnetic fields of T Tauri stars with high-resolution near-infrared spectroscopy
• How do T Tauri stars accrete
• Variable Accretion onto Protoplanet Host Star PDS 70
• Magnetic braking of accreting T Tauri stars: Effects of mass accretion rate, rotation, and dipolar field strength
• Magnetic fields of intermediate mass T Tauri stars
• A Census of the Low Accretors. I: The Catalog
• X-Shooter spectroscopy of young stellar objects - VI - HI line decrements
• Complex Magnetospheric Accretion Flows in Low Accretor CVSO 1335
• The rotation period distributions of 4--10 Myr T Tauri stars in Orion OB1: New constraints on pre-main-sequence angular momentum evolution

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