Evolution of the Accretion Rate of Young Intermediate Mass Stars: Implications for Disk Evolution and Planet Formation

Abstract

This work presents a study of the evolution of the stellar accretion rates of pre-main-sequence intermediate-mass stars. We compare the accretion rate of the younger intermediate-mass T Tauri stars (IMTTSs) with the older Herbig stars into which they evolve. We find that the median accretion rate of IMTTSs (1.2$\times$10${}^{-8}$ M${}_{\odot }$ yr${}^{-1}$) is significantly lower than that of Herbig stars (1.9$\times$10${}^{-7}$ M${}_{\odot }$ yr${}^{-1}$). This increase stands in stark contrast with canonical models of disk evolution that predict that the stellar accretion rate declines with age. We put forward a physically plausible scenario that accounts for the systematic increase of stellar accretion based on the increase of the effective temperature of the stars as they evolve towards the zero-age main sequence. For example, the temperature of a 2M${}_{\odot }$ star will increase from 4900~K in the IMTTS phase to 9100~K during the Herbig phase. Thus, the luminosity of the far ultraviolet (FUV) radiation will increase by orders of magnitude. We propose that this increase drives a higher stellar accretion rate. The scenario we propose to account for the increase in the stellar accretion rate solves the lifetime problem for Herbig disks because the increasing stellar accretion rates require lower initial disk masses to account for present-day disk masses. This work highlights the importance of the role FUV radiation has in driving the accretion rate, predicts a large population of pre-main-sequence non-accreting A stars, and has implications for interpreting disk morphologies that may serve as signposts of embedded gas giant planets in Herbig disks.

13 pages, 4 figures, to be published in the Astronomical Journal

References in corpus (31)

• X-Shooter spectroscopy of young stellar objects in Lupus: Accretion properties of class II and transitional objects
• The Magnetic Fields of Classical T Tauri Stars
• Accretion in the Rho-Oph pre-main sequence stars
• A new library of theoretical stellar spectra with scaled-solar and alpha-enhanced mixtures
• On the gas content of transitional disks: a VLT/X-Shooter study of accretion and winds
• High-Resolution Spectroscopy in Tr37: Gas Accretion Evolution in Evolved Dusty Disks
• Tracing Slow Winds from T Tauri Stars via Low Velocity Forbidden Line Emission
• Five steps in the evolution from protoplanetary to debris disk
• Near-Infrared Interferometric, Spectroscopic, and Photometric Monitoring of T Tauri Inner Disks
• The protoplanetary disk population in the rho-Ophiuchi region L1688 and the time evolution of Class II YSOs
• Demographics of Transition Discs in Ophiuchus and Taurus
• Accretion-related properties of Herbig Ae/Be stars. Comparison with T Tauris
• Evidence for Early Circumstellar Disk Evolution in NGC 2068/71
• A spectroscopic survey of Herbig Ae/Be stars with X-Shooter II: Accretion diagnostic lines
• Photoevaporative Dispersal of Protoplanetary Disks around Evolving Intermediate-mass Stars
• Reflections on nebulae around young stars: A systematic search for late-stage infall of material onto Class II disks
• The mass and size of Herbig disks as seen by ALMA
• A Statistical Spectropolarimetric Study of Herbig Ae/Be Stars
• Herbig Stars: A Quarter Century of Progress
• Dynamical stellar masses of pre-main sequence stars in Lupus and Taurus obtained with ALMA surveys in comparison with stellar evolutionary models
• The temporal requirements of directly observing self-gravitating spiral waves in protoplanetary discs with ALMA
• BEAST begins: Sample characteristics and survey performance of the B-star Exoplanet Abundance Study
• No Transition Disk? Infrared Excess, PAH, H2, and X-rays from the Weak-Lined T Tauri Star DoAr 21
• On the Mass Accretion Rates of Herbig Ae/Be Stars. Magnetospheric Accretion or Boundary Layer?
• Tracing Accretion onto Herbig Ae/Be Stars Using the Brγ Line
• Mapping the merging zone of late infall in the AB Aur planet-forming system
• Relation between metallicities and spectral energy distributions of Herbig Ae/Be stars. A potential link with planet formation
• Linear spectropolarimetry across the optical spectrum of Herbig Ae/Be stars
• X-Shooter Survey of Young Intermediate Mass Stars -- I. Stellar Characterization and Disc Evolution
• Linear line spectropolarimetry of Herbig Ae/Be stars
• Intermediate mass T Tauri disk masses and a comparison to their Herbig disk descendants