Blinded by the light: on the relationship between CO first overtone emission and mass accretion rate in massive young stellar objects

Ilee, J. D.; Oudmaijer, R. D.; Wheelwright, H. E.; Pomohaci, Robert

doi:10.1093/mnras/sty863

Cited by 16 publications

(20 citation statements)

References 53 publications

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“…In particular, the CO ro-vibrational emission in the wavelength range ∼ 2.25-2.45 µm observed in a few HAeBes is probably coming from the innermost disk regions, based on spectral modelling (see, e.g., Carr 1989;Bik & Thi 2004;Ilee et al 2014). However, none of the five stars in our sample show signatures of CO emission in the GRAVITY data, which is in agreement with the low detection rate in HAeBes (Ilee et al 2014(Ilee et al , 2018. In fact, spatially resolved interferometric observations of CO are only available for one HAeBe star to date (see the works on 51 Oph by Tatulli et al 2008;GRAV-ITY Collaboration et al 2020), which prevents us from making a comparative study.…”

Section: Inner Gas Probed Through Spectro-interferometrysupporting

confidence: 76%

K-band GRAVITY/VLTI interferometry of “extreme” Herbig Be stars

Marcos-Arenal

Mendigutía²,

Koumpia³

et al. 2021

A&A

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Context. It has been hypothesized that the location of Herbig Ae/Be stars (HAeBes) within the empirical relation between the inner disk radius (rin), inferred from K-band interferometry, and the stellar luminosity (L*), is related to the presence of the innermost gas, the disk-to-star accretion mechanism, the dust disk properties inferred from the spectral energy distributions (SEDs), or a combination of these effects. However, no general observational confirmation has been provided to date. Aims. This work aims to test whether the previously proposed hypotheses do, in fact, serve as a general explanation for the distribution of HAeBes in the size–luminosity diagram. Methods. GRAVITY/VLTI spectro-interferometric observations at ~2.2 μm have been obtained for five HBes representing two extreme cases concerning the presence of innermost gas and accretion modes. V590 Mon, PDS 281, and HD 94509 show no excess in the near-ultraviolet, Balmer region of the spectra (ΔDB), indicative of a negligible amount of inner gas and disk-to-star accretion, whereas DG Cir and HD 141926 show such strong ΔDB values that cannot be reproduced from magnetospheric accretion, but probably come from the alternative boundary layer mechanism. In turn, the sample includes three Group I and two Group II stars based on the Meeus et al. SED classification scheme. Additional data for these and all HAeBes resolved through K-band interferometry have been compiled from the literature and updated using Gaia EDR3 distances, almost doubling previous samples used to analyze the size–luminosity relation. Results. We find no general trend linking the presence of gas inside the dust destruction radius or the accretion mechanism with the location of HAeBes in the size–luminosity diagram. Similarly, our data do not support the more recent hypothesis linking such a location and the SED groups. Underlying trends are present and must be taken into account when interpreting the size–luminosity correlation. In particular, it cannot be statistically ruled out that this correlation is affected by dependencies of both L* and rin on the wide range of distances to the sources. Still, it is argued that the size–luminosity correlation is most likely to be physically relevant in spite of the previous statistical warning concerning dependencies on distance. Conclusions. Different observational approaches have been used to test the main scenarios proposed to explain the scatter of locations of HAeBes in the size–luminosity diagram. However, none of these scenarios have been confirmed as a fitting general explanation and this issue remains an open question.

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Section: Inner Gas Probed Through Spectro-interferometrysupporting

confidence: 76%

K-band GRAVITY/VLTI interferometry of “extreme” Herbig Be stars

Marcos-Arenal

Mendigutía²,

Koumpia³

et al. 2021

A&A

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“…Interestingly, the only source of the sample without signs of the CO bandheads (G301.8147) shows the strongest Brγ emission. Increasing accretion rates (e.g., stronger Brγ; see, Mendigutía et al 2011) or evolutionary stage (Cooper 2013;Cooper et al 2013) are known to influence the detection rate of the CO bandheads towards MYSOs (Ilee et al 2018b).…”

Section: G301mentioning

confidence: 99%

The first interferometric survey of massive YSOs in the K-band

Koumpia

Wit

Oudmaijer

et al. 2021

A&A

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Context. Circumstellar discs are essential for the formation of high mass stars, while multiplicity, and in particular binarity, appears to be an inevitable outcome, as the vast majority of massive stars (>8 M⊙) are found in binaries (up to 100%). Our understanding of the innermost regions of accretion discs around massive stars and the binarity of high-mass young stars is sparse because of the high spatial resolution and sensitivity required to trace these rare and distant objects. Aims. We aim to spatially resolve and constrain the sizes of the dust and ionised gas emission from the innermost regions of a sample of massive young stellar objects (MYSOs) for the first time, and to provide high-mass binary statistics for young stars at 2–300 au scales using direct interferometric measurements. Methods. We observed six MYSOs using long-baseline near-infrared K-band interferometry on the VLTI (GRAVITY, AMBER) in order to resolve and characterise the 2.2 μm hot dust emission originating from the inner rim of circumstellar discs around MYSOs, and the associated Brγ emission from ionised gas. We fitted simple geometrical models to the interferometric observables, and determined the inner radius of the dust emission. We placed MYSOs with K-band measurements in a size–luminosity diagram for the first time, and compared our findings to their low- and intermediate-mass counterparts (T Tauris and Herbig AeBes). We also compared the observed K-band sizes (i.e. inner rim radius) to the sublimation radius predicted by three different disc scenarios: a classical thick flattened structure with oblique heating in action, and direct heating from the protostar via an optically thin cavity with and without backwarming effects. Lastly, we applied binary geometries to trace close binarity among MYSOs. Results. The characteristic size of the 2.2 μm continuum emission towards this sample of MYSOs shows a large scatter at the given luminosity range. When the inner sizes of MYSOs are compared to those of lower mass Herbig AeBe and T Tauri stars, they appear to follow a universal trend in that the sizes scale with the square-root of the stellar luminosity. The Brγ emission originates from a similar or somewhat smaller and co-planar area compared to the 2.2 μm continuum emission. We discuss this new finding with respect to a disc-wind or jet origin. Finally, we report an MYSO binary fraction of 17–25% at milli-arcsecond separations (2–300 au). Conclusions. The size–luminosity diagram indicates that the inner regions of discs around young stars scale with luminosity independently of the stellar mass. The observed fraction of MYSO binaries in K-band is almost ‘flat’ for a wide range of separations (2–10 000 au). At the targeted scales (2–300 au), the MYSO binary fraction is lower than what was previously reported for the more evolved main sequence massive stars, which, if further confirmed, could implicate predictions from massive binary formation theories. Lastly, with this study, we can finally spatially resolve the crucial star–disc interface in a sample of MYSOs, showing that au-scale discs are prominent in high-mass star formation and are similar to their low-mass equivalents, while the ionised gas can be linked to disc wind and disc accretion models similar to Herbig AeBes.

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“…Carr 1989;Ishii et al 2001;Connelley & Greene 2010;Cooper et al 2013). A plausible reason for this low detection rate, at least in the case of HMYSOs, is that the CO emission seems to be sensitive to the mass accretion rate (Ṁ acc ) of the system; because this rate A&A 633, A128 (2020) is a moderate value ofṀ acc ∼ 10 −5 M yr −1 it best produces the most prominent CO emission (Ilee et al 2018). Therefore, adding objects with CO detection represents both a challenge and an important contribution.…”

Section: Introductionmentioning

confidence: 99%

Mirror, mirror on the outflow cavity wall

Fedriani

Garatti

Koutoulaki

et al. 2020

A&A

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Aims. The inner regions of high-mass protostars are often invisible in the near-infrared, obscured by thick envelopes and discs. We aim to investigate the inner gaseous disc of IRAS 11101-5829 through scattered light from the outflow cavity walls. Methods. We observed the immediate environment of the high-mass young stellar object IRAS 11101-5829 and the closest knots of its jet, HH135-136, with the integral field unit VLT/SINFONI. We also retrieved archival data from the high-resolution long-slit spectrograph VLT/X-shooter. We analysed imaging and spectroscopic observations to discern the nature of the near-infrared CO emission. Results. We detect the first three bandheads of the υ = 2−0 CO vibrational emission for the first time in this object. It is coincident with continuum and Brγ emission and extends up to ~10 000 au to the north-east and ~10 000 au to the south-west. The line profiles have been modelled as a Keplerian rotating disc assuming a single ring in local thermodynamic equilibrium. The model output gives a temperature of ~3000 K, a CO column density of ~1 × 1022 cm−2, and a projected Keplerian velocity vK sin idisc ~ 25 km s−1, which is consistent with previous modelling in other high-mass protostars. In particular, the low value of vK sin idisc suggests that the disc is observed almost face-on, whereas the well-constrained geometry of the jet imposes that the disc must be close to edge-on. This apparent discrepancy is interpreted as the CO seen reflected in the mirror of the outflow cavity wall. Conclusions. From both jet geometry and disc modelling, we conclude that all the CO emission is seen through reflection by the cavity walls and not directly. This result implies that in the case of highly embedded objects, as for many high-mass protostars, line profile modelling alone might be deceptive and the observed emission could affect the derived physical and geometrical properties; in particular the inclination of the system can be incorrectly interpreted.

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Blinded by the light: on the relationship between CO first overtone emission and mass accretion rate in massive young stellar objects

Cited by 16 publications

References 53 publications

K-band GRAVITY/VLTI interferometry of “extreme” Herbig Be stars

K-band GRAVITY/VLTI interferometry of “extreme” Herbig Be stars

The first interferometric survey of massive YSOs in the K-band

Mirror, mirror on the outflow cavity wall

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