Measuring Accretion in Young Substellar Objects: Approaching the Planetary Mass Regime

By J. Muzerolle, K. Luhman, C. Briceño, L. Hartmann, N. Calvet. 2005

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We present observations of Hα emission-line profiles taken at Magellan Observatory for a sample of 39 young low-mass stars and brown dwarfs in the Taurus and Chamaeleon I star-forming regions. We have identified 11 new substellar accretors, more than tripling the number of known brown dwarfs with measurable accretion activity. These include the lowest-mass objects yet seen with accretion, with masses down to ~0.015 M☉. Using models of Hα emission produced in magnetospheric accretion flows, the most widely applicable primary calibrator now available, we determine the first estimates of mass accretion rates for objects at such extremely low masses. For the six objects with masses ≲0.03 M☉, we find accretion rates of ~5 × 10-12 M☉ yr-1, among the smallest yet measured. These new results continue the trend of decreasing mass accretion rate with decreasing (sub)stellar mass that we have noted previously for samples of more massive objects; the overall correlation is ∝ M2.1, and it now extends over a mass range of over 2 orders of magnitude. Finally, the absence of a discontinuity in the distribution of accretion rates with mass tends to suggest that stars and brown dwarfs share similar formation histories.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/0473f009fb9b6c700285e622204096fc5e455463

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Citations in the corpus

Accretion Rates in Herbig Ae stars (2006, methodology): “3 plotsṀacc as a function of M⋆ for the HAe stars, together with objects in Ophiuchus (Natta et al. 2006), Taurus (Muzerolle et al. 2005 and references therein; Mohanty et al. 2005) and IMTTS in Orion and Taurus (Calvet et al. 2004).”
Dust dynamics during protoplanetary disc clearing (2007, background): “In recent years, observations of disc properties, such as accretion rates and disc masses, have expanded to cover a much wider range in stellar mass than was previously possible (e.g. Muzerolle et al. 2005; Scholz, Jayawardhana & Wood 2006), and a number of trends with stellar mass are now known.”
A Decreased Probability of Habitable Planet Formation around Low-Mass Stars (2007, background): “Additional clues come from the observed stellar accretion rate Ṁ , which scales as Ṁ ∝ M2⋆ , with a large dispersion (Muzerolle et al. 2003, 2005, Natta et al. 2006).”
A spectroscopic survey of Herbig Ae/Be stars with X-shooter – I. Stellar parameters and accretion rates (2015, result): “When considering the HAeBes as a whole, the relationship found between Ṁacc and M⋆ is a factor of ∼2.0 larger in exponent than in low mass PMS stars, where Ṁacc ∝ M 2.0±0.2 ⋆ (Muzerolle et al. 2005; Natta, Testi & Randich 2006).”
TIME EVOLUTION OF VISCOUS CIRCUMSTELLAR DISKS DUE TO PHOTOEVAPORATION BY FAR-ULTRAVIOLET, EXTREME-ULTRAVIOLET, AND X-RAY RADIATION FROM THE CENTRAL STAR (2009, background): “This scaling is motivated by observations of a correlation between the accretion rate and central star mass, Ṁacc ∝ M2∗ (Muzerolle et al 2003, Natta et al 2004, Calvet et al. 2004, Muzerolle et al 2005, Natta et al 2006).”
The Stellar Population of the Chamaeleon I Star-forming Region (2007, background): “The details of the observations are the same as those described by Muzerolle et al. (2005) for other targets observed on that same night.”
The Formation and Early Evolution of Low-Mass Stars and Brown Dwarfs (2012, background): “Similar objects have been found during other spectroscopic surveys of late-type field dwarfs (Allers et al. 2010; Nakajima, Tsuji & Yanagisawa 2004; Reiners & Basri 2010).”
EPISODIC ACCRETION AT EARLY STAGES OF EVOLUTION OF LOW-MASS STARS AND BROWN DWARFS: A SOLUTION FOR THE OBSERVED LUMINOSITY SPREAD IN H–R DIAGRAMS? (2009, result): “…results are compared to recent surveys of LMS and BDs between ∼ 0.01 M and 1 M in various SFRs, with characteristic ages of a few Myr, namely Taurus and Chamaeleon I (Muzerolle et al. 2005), ρ Ophiucus (Gatti et al. 2006), Orion molecular cloud (Peterson et al. 2008), σ-Orionis (Gatti et al. 2008).”
Accretion-driven turbulence as universal process: galaxies, molecular clouds, and protostellar disks (2009, background): “We compare it with data from Calvet et al. (2004), Mohanty et al. (2005), Muzerolle et al. (2005), and Natta et al. (2006) as displayed in Fig.”
Accretion in the ρ-Ophiuchi pre-main sequence stars (2006, methodology): “When compared to accretion measurements in Taurus (see Muzerolle et al. 2005, and references therein), we find that the two regions look very similar, at least for objects with M >∼ 0.1 M .”
UV Excess Measures of Accretion onto Young Very Low Mass Stars and Brown Dwarfs (2008, methodology): “Instead, accretion has been been measured based on magnetospheric models of the Hα line profile (Muzerolle et al. 2000, 2003, 2005), by extending relationships between Ṁ and line luminosities established at higher masses to brown dwarf masses (Natta et al. 2004, 2006; Mohanty et al. 2005), or in a…”
The Disk Population of the Chamaeleon I Star-forming Region (2008, background): “Because of the relatively low extinction, optical wavelengths are accessible for the spectral classification of the stellar population (Comerón et al. 2004; Luhman 2004a, references therein) and for measuring diagnostics of accretion (Mohanty et al. 2005; Muzerolle et al. 2005).”
On the formation of Hα line emission around classical T Tauri stars (2006, methodology): “Velocity broadened, asymmetric Hα profiles in brown dwarfs (BDs) are used as an indicator of ongoing MA, and the same models that are used for CTTS are applied to these systems in order to determine mass-accretion rates (e.g. Lawson, Lyo & Muzerolle 2004; Muzerolle et al. 2005).”
Accretion onto Pre-Main-Sequence Stars (2016, background): “Modeling the Hα line profile (see Muzerolle et al. 2005 and the references therein) provides results that are internally self-consistent but may have systematic differences with accretion rates calculated from direct measurements of the accretion continuum, in large part because of the ad hoc…”
X-ray emission from T Tauri stars and the role of accretion: inferences from the XMM-Newton extended survey of the Taurus molecular cloud (2006, background): “Similarly, Muzerolle et al. (2003) and Muzerolle et al. (2005) found Ṁ ∝ M2 and Ṁ ∝ M2.”
PHOTOEVAPORATION OF CIRCUMSTELLAR DISKS BY FAR-ULTRAVIOLET, EXTREME-ULTRAVIOLET AND X-RAY RADIATION FROM THE CENTRAL STAR (2008, methodology): “…observational data characterizing FUV luminosity as a function of stellar spectral type or mass, we use a mass-accretion defined FUV flux as described in GH08, i.e. we use the empirically derived accretion rate versus mass relation of Muzerolle et al. (2003, 2005) and assume that Ṁacc ∝ M2∗ .”
Star and Protoplanetary Disk Properties in Orion's Suburbs (2009, background): “Power law fits of the formṀacc∝Mα∗ have yielded values in the range 1.0−2.1 for the exponentα (White & Basri 2003; Muzerolle et al. 2003; Calvet et al. 2004; Muzerolle et al. 2005; Mohanty et al. 2005; Natta et al. 2006; Garcia Lopez et al. 2006; Herczeg & Hillenbrand 2008; Gatti et al. 2008).”