Article Published: 07 October 2020

Four annular structures in a protostellar disk less than 500,000years old

Dominique M. Segura-Cox , Anika Schmiedeke, Jaime E. Pineda, Ian W. Stephens, Manuel

Fernández-López, Leslie W. Looney, Paola Caselli, Zhi-Yun Li, Lee G. Mundy, Woojin Kwon &

Robert J. Harris 

Nature  586, 228–231(2020)

2282 Accesses 408 Altmetric Metrics

Abstract

Annular structures (rings and gaps) in disks around pre-main-sequence stars have beendetected in abundance towards class II protostellar objects that are approximately1,000,000 years old . These structures are often interpreted as evidence of planetformation , with planetary-mass bodies carving rings and gaps in the disk . Thisimplies that planet formation may already be underway in even younger disks in theclass I phase, when the protostar is still embedded in a larger-scale dense envelope of gasand dust . Only within the past decade have detailed properties of disks in the earlieststar-forming phases been observed . Here we report 1.3-millimetre dust emissionobservations with a resolution of five astronomical units that show four annularsubstructures in the disk of the young (less than 500,000 years old) protostar IRS 63.IRS 63 is a single class I source located in the nearby Ophiuchus molecular cloud at adistance of 144 parsecs , and is one of the brightest class I protostars at millimetre

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wavelengths. IRS 63 also has a relatively large disk compared to other young disks(greater than 50 astronomical units) . Multiple annular substructures observed towardsdisks at young ages can act as an early foothold for dust-grain growth, which is aprerequisite of planet formation. Whether or not planets already exist in the disk ofIRS 63, it is clear that the planet-formation process begins in the initial protostellarphases, earlier than predicted by current planet-formation theories .

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Data availability

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This paper makes use of ALMA data with the project code:ADS/JAO.ALMA#2015.1.01512.S. The archival data are available athttp://almascience.eso.org/aq/ by querying the project code. The final calibratedversion of the data analysed in this work is available from the Harvard Dataverse athttps://doi.org/10.7910/DVN/LPVDSF. Other material in this work is available fromthe corresponding author on reasonable request .

Code availability

The radiative-transfer modelling makes use of RADMC-3D, which is publicly availableat http://www.ita.uni-heidelberg.de/~dullemond/software/radmc-3d/. The radiative-transfer modelling also uses the Pandora framework for the setup of and interfacing withRADMC-3D; Pandora is not open source and is available upon request. The MCMCmodelling uses emcee, which is publicly available athttps://emcee.readthedocs.io/en/stable/.

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Acknowledgements

ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS(Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republicof Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory isoperated by ESO, AUI/NRAO and NAOJ. D.M.S.-C., A.S., J.E.P. and P.C. are grateful forsupport from the Max Planck Society. L.W.L. acknowledges support from NSF AST-1910364. Z.-Y.L. is supported in part by NASA 80NSSC18K1095 and NSF AST-1910106.This research made use of Astropy, a community-developed core Python package forastronomy.

Author information

Affiliations

1. Center for Astrochemical Studies, Max Planck Institute for Extraterrestrial Physics,Garching, Germany

Dominique M. Segura-Cox, Anika Schmiedeke, Jaime E. Pineda & Paola Caselli

2. Department of Astronomy, University of Illinois, Urbana, IL, USA

Dominique M. Segura-Cox, Leslie W. Looney & Robert J. Harris

3. Center for Astrophysics | Harvard & Smithsonian, Cambridge, MA, USA

Ian W. Stephens

4. Instituto Argentino de Radioastronomía (CCT-La Plata, CONICET; CICPBA),Buenos Aires, Argentina

Manuel Fernández-López

5. Astronomy Department, University of Virginia, Charlottesville, VA, USA

Zhi-Yun Li

6. Astronomy Department and Laboratory for Millimeter-wave Astronomy, Universityof Maryland, College Park, MD, USA

Lee G. Mundy

7. Department of Earth Science Education, Seoul National University (SNU), Seoul,Republic of Korea

Woojin Kwon

8. Korea Astronomy and Space Science Institute (KASI), Daejeon, Republic of Korea

Woojin Kwon

Contributions

D.M.S.-C. led the observing proposal and project, led the analysis, reduced the ALMAdata, and wrote the manuscript. A.S. performed the radiative-transfer modelling. J.E.P.performed the MCMC modelling. I.W.S., M.F.-L., L.W.L., Z.-Y.L., L.G.M., W.K. and R.J.H.contributed to the ALMA proposal. P.C. provided discussion and interpretation of theresults. All authors discussed the results and implications, and commented on themanuscript.

Corresponding author

Correspondence to Dominique M. Segura-Cox.

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Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature thanks Jonathan Williams and the other, anonymous,reviewer(s) for their contribution to the peer review of this work. Peer reviewer reportsare available.

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Extended data figures and tables

Extended Data Fig. 1 Asymmetry remains after re-centring the best radiative-transfer model.a, The residual of the data minus the best radiative-transfer model, which had a centroidset to the Gaussian fit centre (same as Fig. 2c). b, The residuals of the best radiative-transfer model with a shifted centroid from minimizing the r.m.s. of the data minusmodel residuals. The asymmetry to the northwest portion of the disk is clear in bothcases.

Extended Data Fig. 2 Posterior distributions of the analytic disk modelparameters.From left to right, the parameters are: normalization factor Σc, surface density gradient γ,

characteristic radius Rc, the coordinates of the centroid of the fit x0 and y0, disk position

angle PA and disk inclination angle IA.

Extended Data Fig. 3 A geometrically flat analytic model shows asymmetry inthe residuals.a, The original dust continuum data (same as Fig. 2a). b, The image of the flat analyticmodel, generated from the median parameter values resulting from the MCMC fit. c, Theresiduals of the observed data minus the analytic model. Again, here the annularsubstructures and the asymmetry with excess emission to the northwest are seen.

Extended Data Fig. 4 Position–intensity cuts of the dust continuum imagecentred at the position of the peak intensity.The centroid is (α(2000), δ(2000)) = (16 h 31 m 35.6577 s, −24° 01′ 29.897″). a–c, The cutsare taken at position angles of 150.0° or along the minor axis (a), of 60.0° or along theminor axis (b), and of 105.0° or along a cut from the southeast to northwest (c). d, Theorientation of these cuts across the disk are shown in blue, orange and green,corresponding to a–c, respectively. The radii in a–c are deprojected assuming a diskinclination angle of 45.0° and are measured starting from the centroid outwards. Thegrey shaded areas represent the resolution of the observations, and the black horizontal

lines show the 1σ noise level of 18.4 μJy per beam. We plot the radial intensities alongeither side of the centroid for each cut (solid and dashed lines). The 105.0° cut in c, alongthe southeast to northwest direction, shows the highest difference in intensities on eitherside of the centroid, and is consistent with the asymmetric and excess emission to thenorthwest previously seen in the residuals from the disk models.

Extended Data Fig. 5 Position–intensity cuts of the dust continuum imagecentred at the Gaussian fit position.As in Extended Data Fig. 4, with a centroid of (α(2000), δ(2000)) = (16 h 31 m 35.6572 s,−24° 01′ 29.896″).

Extended Data Fig. 6 Position–intensity cuts of the dust continuum imagecentred at the centre determined from the MCMC fit to the analytic model.As in Extended Data Fig. 4, with a centroid of (α(2000), δ(2000)) = 16 h 31 m 35.6575 s,−24° 01′ 29.901″.

Extended Data Fig. 7 Radial properties derived from observations.a–c, The radial profiles of the in-band spectral index (α, a), the optical depth (τ, b) andthe temperature (T, c) derived from the observational data. The grey shaded arearepresents the resolution of the observations, and the vertical grey dashed and dottedlines show the positions of the bright annular substructures R1 and R2 and dark annularsubstructures G1 and G2. For the spectral index the light-blue ribbon represents the localstandard deviation of each bin, and the horizontal dashed grey line shows the α = 2blackbody Rayleigh–Jeans limit. Optical depth is determined from a greybody fit to theintensity profile of the two in-band wavelengths. The temperature profile is determinedfrom the greybody fit at radii where τ > 3 (solid blue line), and extrapolated to largerradii, r, as an inverse square-root law (dot–dash black line). For optical depth andtemperature, the light-blue ribbons reflect the 10% amplitude uncertainty of theobservations. The orange shaded region shows the location of the CO snowline based ondust temperature, reflecting the range of gas densities used to compute the condensationtemperature.

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Segura-Cox, D.M., Schmiedeke, A., Pineda, J.E. et al. Four annular structures in aprotostellar disk less than 500,000 years old. Nature 586, 228–231 (2020).https://doi.org/10.1038/s41586-020-2779-6

Received 05 March 2020 Accepted 05 August 2020 Published 07 October 2020

Issue Date 08 October 2020 DOI https://doi.org/10.1038/s41586-020-2779-6

Nature ISSN 1476-4687 (online)

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