Context. T Tauri stars are low-mass young stars whose disks provide the setting for planet formation. Despite this, their structure is poorly understood. We present new infrared interferometric observations of the SU Aurigae circumstellar environment that offer resolution that is three times higher and a better baseline position angle coverage than previous observations. Aims. We aim to investigate the characteristics of the circumstellar material around SU Aur, constrain the disk geometry, composition and inner dust rim structure. Methods. The CHARA array offers unique opportunities for long baseline observations, with baselines up to 331 m. Using the CLIMB three-telescope combiner in the K -band allows us to measure visibilities as well as closure phase. We undertook image reconstruction for model-independent analysis, and fitted geometric models such as Gaussian and ring distributions. Additionally, the fitting of radiative transfer models constrain the physical parameters of the disk. For the first time, a dusty disk wind is introduced to the radiative transfer code TORUS to model protoplanetary disks. Our implementation is motivated by theoretical models of dusty disk winds, where magnetic field lines drive dust above the disk plane close to the sublimation zone. Results. Image reconstruction reveals an inclined disk with slight asymmetry along its minor-axis, likely due to inclination effects obscuring the inner disk rim through absorption of incident star light on the near-side and thermal re-emission and scattering of the far-side. Geometric modelling of a skewed ring finds the inner rim at 0.17 ± 0.02 au with an inclination of 50.9 ± 1.0° and minor axis position angle 60.8 ± 1.2°. Radiative transfer modelling shows a flared disk with an inner radius at 0.18 au which implies a grain size of 0.4 μ m assuming astronomical silicates and a scale height of 15.0 at 100 au. Among the tested radiative transfer models, only the dusty disk wind successfully accounts for the K -band excess by introducing dust above the mid-plane.
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A Millimeter-multiwavelength Continuum Study of VLA 1623 West
Abstract VLA 1623 West is an ambiguous source that has been described as a shocked cloudlet as well as a protostellar disk. We use deep ALMA 1.3 and 0.87 mm observations to constrain its shape and structure to determine its origins better. We use a series of geometric models to fit the uv visibilities at both wavelengths with GALARIO . Although the real visibilities show structures similar to what has been identified as gaps and rings in protoplanetary disks, we find that a modified flat-topped Gaussian model at high inclination provides the best fit to the observations. This fit agrees well with expectations for an optically thick, highly inclined disk. Nevertheless, we find that the geometric models consistently yield positive residuals at the four corners of the disk at both wavelengths. We interpret these residuals as evidence that the disk is flared in the millimeter dust. We use a simple toy model for an edge-on flared disk and find that the residuals best match a disk with flaring that is mainly restricted to the outer disk at R ≳ 30 au. Thus, VLA 1623W may represent a young protostellar disk where the large dust grains have not yet had enough time to settle into the midplane. This result may have implications for how disk evolution and vertical dust settling impact the initial conditions leading to planet formation.
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- NSF-PAR ID:
- 10437855
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 937
- Issue:
- 2
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 104
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract We present high-resolution Karl G. Jansky Very Large Array (VLA) observations of the protostar L1527 IRS at 7 mm, 1.3 cm, and 2 cm wavelengths. We detect the edge-on dust disk at all three wavelengths and find that it is asymmetric, with the southern side of the disk brighter than the northern side. We confirm this asymmetry through analytic modeling and also find that the disk is flared at 7 mm. We test the data against models including gap features in the intensity profile, and though we cannot rule such models out, they do not provide a statistically significant improvement in the quality of fit to the data. From these fits, we can, however, place constraints on allowed properties of any gaps that could be present in the true, underlying intensity profile. The physical nature of the asymmetry is difficult to associate with physical features owing to the edge-on nature of the disk, but it could be related to spiral arms or asymmetries seen in other imaging of more face-on disks.more » « less
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null (Ed.)Context. Recent years have seen building evidence that planet formation starts early, in the first ~0.5 Myr. Studying the dust masses available in young disks enables us to understand the origin of planetary systems given that mature disks are lacking the solid material necessary to reproduce the observed exoplanetary systems, especially the massive ones. Aims. We aim to determine if disks in the embedded stage of star formation contain enough dust to explain the solid content of the most massive exoplanets. Methods. We use Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 (1.1–1.3 mm) continuum observations of embedded disks in the Perseus star-forming region together with Very Large Array (VLA) Ka -band (9 mm) data to provide a robust estimate of dust disk masses from the flux densities measured in the image plane. Results. We find a strong linear correlation between the ALMA and VLA fluxes, demonstrating that emission at both wavelengths is dominated by dust emission. For a subsample of optically thin sources, we find a median spectral index of 2.5 from which we derive the dust opacity index β = 0.5, suggesting significant dust growth. Comparison with ALMA surveys of Orion shows that the Class I dust disk mass distribution between the two regions is similar, but that the Class 0 disks are more massive in Perseus than those in Orion. Using the DIANA opacity model including large grains, with a dust opacity value of κ 9 mm = 0.28 cm 2 g −1 , the median dust masses of the embedded disks in Perseus are 158 M ⊕ for Class 0 and 52 M ⊕ for Class I from the VLA fluxes. The lower limits on the median masses from ALMA fluxes are 47 M ⊕ and 12 M ⊕ for Class 0 and Class I, respectively, obtained using the maximum dust opacity value κ 1.3 mm = 2.3 cm 2 g −1 . The dust masses of young Class 0 and I disks are larger by at least a factor of ten and three, respectively, compared with dust masses inferred for Class II disks in Lupus and other regions. Conclusions. The dust masses of Class 0 and I disks in Perseus derived from the VLA data are high enough to produce the observed exoplanet systems with efficiencies acceptable by planet formation models: the solid content in observed giant exoplanets can be explained if planet formation starts in Class 0 phase with an efficiency of ~15%. A higher efficiency of ~30% is necessary if the planet formation is set to start in Class I disks.more » « less
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Context. T Tauri stars are low-mass young stars whose disks provide the setting for planet formation, which is one of the most fundamental processes in astronomy. Yet the mechanisms of this are still poorly understood. SU Aurigae is a widely studied T Tauri star and here we present original state-of-the-art interferometric observations with better uv and baseline coverage than previous studies.Aims. We aim to investigate the characteristics of the circumstellar material around SU Aur, and constrain the disk geometry, composition and inner dust rim structure.Methods. The MIRC-X instrument at CHARA is a six-telescope optical beam combiner offering baselines up to 331 m. We undertook image reconstruction for model-independent analysis, and fitted geometric models such as Gaussian and ring distributions. Additionally, the fitting of radiative transfer models constrained the physical parameters of the disk.Results. Image reconstruction reveals a highly inclined disk with a slight asymmetry consistent with inclination effects obscuring the inner disk rim through absorption of incident star light on the near side and thermal re-emission/scattering of the far side. Geometric models find that the underlying brightness distribution is best modelled as a Gaussian with a Full-Width Half-Maximum of 1.53 ± 0.01 mas at an inclination of 56.9 ± 0.4° and a minor axis position angle of 55.9 ± 0.5°. Radiative transfer modelling shows a flared disk with an inner radius at 0.16 au which implies a grain size of 0.14 μm assuming astronomical silicates and a scale height of 9.0 au at 100 au. In agreement with the literature, only the dusty disk wind successfully accounts for the near infrared excess by introducing dust above the mid-plane.Conclusions. Our results confirm and provide better constraints than previous inner disk studies of SU Aurigae. We confirm the presence of a dusty disk wind in the cicumstellar environment, the strength of which is enhanced by a late infall event which also causes very strong misalignments between the inner and outer disks. -
Aims. We present a detailed visible and near-infrared spectro-interferometric analysis of the Be-shell star o Aquarii from quasi-contemporaneous CHARA/VEGA and VLTI/AMBER observations. Methods. We analyzed spectro-interferometric data in the H α (VEGA) and Br γ (AMBER) lines using models of increasing complexity: simple geometric models, kinematic models, and radiative transfer models computed with the 3D non-LTE code HDUST. Results. We measured the stellar radius of o Aquarii in the visible with a precision of 8%: 4.0 ± 0.3 R ⊙ . We constrained the circumstellar disk geometry and kinematics using a kinematic model and a MCMC fitting procedure. The emitting disk sizes in the H α and Br γ lines were found to be similar, at ~10–12 stellar diameters, which is uncommon since most results for Be stars indicate a larger extension in H α than in Br γ . We found that the inclination angle i derived from H α is significantly lower (~15°) than the one derived from Br γ : i ~ 61.2° and 75.9°, respectively. While the two lines originate from a similar region of the disk, the disk kinematics were found to be near to the Keplerian rotation (i.e., β = −0.5) in Br γ ( β ~ −0.43), but not in H α ( β ~ −0.30). After analyzing all our data using a grid of HDUST models (BeAtlas), we found a common physical description for the circumstellar disk in both lines: a base disk surface density Σ 0 = 0.12 g cm −2 and a radial density law exponent m = 3.0. The same kind of discrepancy, as with the kinematic model, is found in the determination of i using the BeAtlas grid. The stellar rotational rate was found to be very close (~96%) to the critical value. Despite being derived purely from the fit to interferometric data, our best-fit HDUST model provides a very reasonable match to non-interferometric observables of o Aquarii: the observed spectral energy distribution, H α and Br γ line profiles, and polarimetric quantities. Finally, our analysis of multi-epoch H α profiles and imaging polarimetry indicates that the disk structure has been (globally) stable for at least 20 yr. Conclusions. Looking at the visible continuum and Br γ emission line only, o Aquarii fits in the global scheme of Be stars and their circumstellar disk: a (nearly) Keplerian rotating disk well described by the viscous decretion disk (VDD) model. However, the data in the H α line shows a substantially different picture that cannot fully be understood using the current generation of physical models of Be star disks. The Be star o Aquarii presents a stable disk (close to the steady-state), but, as in previous analyses, the measured m is lower than the standard value in the VDD model for the steady-state regime ( m = 3.5). This suggests that some assumptions of this model should be reconsidered. Also, such long-term disk stability could be understood in terms of the high rotational rate that we measured for this star, the rate being a main source for the mass injection in the disk. Our results on the stellar rotation and disk stability are consistent with results in the literature showing that late-type Be stars are more likely to be fast rotators and have stable disks.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3847/1538-4357/ac905c
