Constraining the sub-au-scale distribution of hydrogen and carbon monoxide gas around young stars with the Keck Interferometer

Abstract

We present Keck Interferometer observations of T Tauri and Herbig Ae/Be stars with a spatial resolution of a few milliarcseconds and a spectral resolution of ∼ 2000. Our observations span the K-band, and include the Brγ transition of Hydrogen and the v = 2 → 0 and v = 3 → 1 transitions of carbon monoxide. For several targets we also present data from Keck/NIRSPEC that provide higher spectral resolution, but a seeing-limited spatial resolution, of the same spectral features. We analyze the Brγ emission in the context of both disk and infall/outflow models, and conclude that the Brγ emission traces gas at very small stellocentric radii, consistent with the magnetospheric scale. However some Brγ-emitting gas also seems to be located at radii of 0.1 AU, perhaps tracing the inner regions of magnetically launched outflows. CO emission is detected from several objects, and we generate disk models that reproduce both the KI and NIRSPEC data well. We infer the CO spatial distribution to be coincident with the distribution of continuum emission in most cases. Furthermore the Brγ emission in these objects is roughly coincident with both the CO and continuum emission. We present potential explanations for the spatial coincidence of continuum, Brγ, and CO overtone emission, and explore the implications for the low occurrence rate of CO overtone emission in young stars. Finally, we provide additional discussion of V1685 Cyg, which is unusual among our sample in showing large differences in emitting region size and spatial position as a function of wavelength.

Probing the accretion-ejection connection with VLTI/AMBER

“…Moreover, this model is also able to approximately reproduce the visibilities and small 1 From now on, we useṀ w for the modelled total mass-loss rate anḋ M out for the observed value from the literature. differential phase of previous Keck interferometric observations of this source (Eisner et al 2010(Eisner et al , 2014. However, it slightly overpredicts the pure Brγ line visibilities for the longest baseline (see Fig.…”

“…3 shows that the entire disc wind emitting region extends to an outer radius of ∼15 R * or ∼0.16 AU. The modelled disc wind emitting region is more compact than the inner continuum dust rim radius reported in the literature (R rim ∼ 0.19-0.45 AU; Benisty et al 2010;Eisner et al 2010Eisner et al , 2014Tannirkulam et al 2008a,b). Our modelling does not exclude that some of the Brγ emission is produced in the magnetosphere.…”

“…Similarly, by fitting a ring model with a ring width of 20% of the inner ring radius, an inner radius of 0.7 ± 0.2 mas or ∼0.08 ± 0.02 AU, is found. This radius is smaller than the inner continuum dust rim radius of R rim ∼ 0.19-0.45 AU reported in the literature (Tannirkulam et al 2008a,b;Benisty et al 2010;Eisner et al 2014). …”

“…Previous spectro-interferometric studies of HD 163296 at medium resolution had also detected an increase of the visibility within the Brγ line (Kraus et al 2008;Eisner et al 2014). Our HR mode AMBER observations have, however, allowed us to measure the visibilities and phases in ∼30 different spectral channels across the Doppler-broadened Brγ line, helping us to better distinguish the contribution of the line to that of the continuum.…”

“…Renard et al 2010;Benisty et al 2010;Eisner et al 2010Eisner et al , 2014Tannirkulam et al 2008a,b). It is within this region that the extended Brγ emission is being emitted (Kraus et al 2008;Eisner et al 2014), although, the exact origin of the line emission, and the nature of the innermost gaseous disc are still unclear.…”