Twenty-five Years of Accretion onto the Classical T Tauri Star TW Hya

Abstract

Accretion plays a central role in the physics that governs the evolution and dispersal of protoplanetary disks. The primary goal of this paper is to analyze the stability over time of the mass accretion rate onto TW Hya, the nearest accreting solar-mass young star. We measure veiling across the optical spectrum in 1169 archival high-resolution spectra of TW Hya, obtained from 1998–2022. The veiling is then converted to accretion rate using 26 flux-calibrated spectra that cover the Balmer jump. The accretion rate measured from the excess continuum has an average of 2.51 × 10−9 M ⊙ yr−1 and a Gaussian distribution with an FWHM of 0.22 dex. This accretion rate may be underestimated by a factor of up to 1.5 because of uncertainty in the bolometric correction and another factor of 1.7 because of excluding the fraction of accretion energy that escapes in lines, especially Lyα. The accretion luminosities are well correlated with He line luminosities but poorly correlated with Hα and Hβ luminosity. The accretion rate is always flickering over hours but on longer timescales has been stable over 25 years. This level of variability is consistent with previous measurements for most, but not all, accreting young stars.

A Multiwavelength, Multiepoch Monitoring Campaign of Accretion Variability in T Tauri Stars from the ODYSSEUS Survey. I. HST Far-UV and Near-UV Spectra

“…Despite this relative stability in the accretion structure, there is variability in the accretion rate up to a factor of four within 2 days. This is consistent with previous reports that accretion is variable on all timescales probed (Costigan et al 2014;Hartmann et al 2016;Zsidi et al 2022;Herczeg et al 2023). Specifically, Venuti et al (2014) find that accretion variability is typically about 0.5 dex on timescales of days-weeks, and our results are consistent with this.…”

“…TW Hya is old (8-10 Myr; Sokal et al 2018), yet it is still actively accreting from a surrounding accretion disk beyond the assumed 5 Myr life span of protoplanetary disks (Evans et al 2009;Williams & Cieza 2011) and therefore challenges our understanding of disk dispersal mechanisms. The range of measured accretion rates in TW Hya is (0.05-0.6) × 10 −8 M e yr −1 (Ingleby et al 2013;Manara et al 2014;Herczeg et al 2023;Sousa et al 2023). This accretion is thought to primarily occur through a single, large, poleward flow (Donati et al 2011;Sicilia-Aguilar et al 2023), along with many smaller, more sporadic accretion tongues near the equator (Siwak et al 2018).…”

Revisiting the Helium and Hydrogen Accretion Indicators at TWA 27B: Weak Mass Flow at Near-freefall Velocity

“…Interestingly, the L acc corresponding to the 3σ upper limit on F Hα is lower than the average L acc by 1 or 0.5 dex according to the planetary or CTTS relationships, respectively. This apparent discrepancy could be explained by time variability (the Hα was measured in 2011, the other lines in 2023), wavelength-dependent absorption due to dust (see Figure 9(b) of given the low accretion rate, absorption is likely negligible), or differences in the emission mechanism for Hα compared to the other lines (at least for TW Hydra, Hα does not correlate as well as the other lines with L acc ; Herczeg et al 2023). No strong arguments can be made for or against these factors.…”

The Accretion History of EX Lup: A Century of Bursts, Outbursts, and Quiescence

“…Table 4 compares our accretion rates with selected accretion rates from the literature and from other spectroscopic diagnostics. The accretion rates presented in this work are much more likely to be underestimated than overestimated due to the exclusion of lowdensity flows (see Espaillat et al 2021;Pittman et al 2022 and references therein) and the exclusion of line emission (see discussions in Alcalá et al 2014 andHerzceg et al 2023).…”