Confirmation of a ring structure in the disk around MP Mus (PDS 66) with ALMA Band 7 observations

¹ Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111, Valparaíso, Chile
² Instituto de Astrofisica, Departamento de Fisica y Astronomia, Facultad de Ciencias Exactas, Universidad Andres Bello. Av. Fernandez Concha 700, Las Condes, Chile
³ Millennium Institute of Astrophysics, Nuncio Monseñor Sotero Sanz 100, Of. 104, Providencia, Santiago, Chile
⁴ Departamento de Física, Universidad Técnica Federico Santa María, Avenida España 1680, Valparaíso, Chile
⁵ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁶ Center for Imaging Science, Rochester Institute of Technology, Rochester, NY 14623, USA
⁷ School of Physics and Astronomy, Rochester Institute of Technology, Rochester, NY 14623, USA
⁸ Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, USA
⁹ Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile
¹⁰ Millennium Nucleus on Young Exoplanets and their Moons (YEMS), Chile
¹¹ Departamento de Física, Universidad de Santiago de Chile, Av. Víctor Jara 3493, Santiago, Chile
¹² Center for Interdisciplinary Research in Astrophysics & Space Exploration (CIRAS), Universidad de Santiago de Chile, Chile
¹³ Telespazio UK S.L. for European Space Agency (ESA), Camino bajo del Castillo, s/n, Urbanización Villafranca del Castillo, Villanueva de la Cañada, 28692 Madrid, Spain
¹⁴ Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA
¹⁵ First Center for Autism and Innovation, Vanderbilt University, 2414 Highland Avenue, Suite 115, Nashville, TN 37212, USA
¹⁶ Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile

^★ Corresponding authors: aurora.aguayov@gmail.com; zhen.guo@uv.cl; jhk@cis.rit.edu

Received: 11 March 2025
Accepted: 17 April 2025

Abstract

Context. Young stellar objects (YSOs) are surrounded by protoplanetary disks, which are the birthplace of young planets. Ring and gap structures are observed among evolved protoplanetary disks, often interpreted as a consequence of planet formation.

Aims. The pre-Main Sequence (pre-MS) star MP Mus hosts one of the few known examples of protoplanetary disks within 100 pc. Previously, a disk ring structure, with a radius of 80–85 au, was detected in scattered light via near-infrared polarimetric imaging. This ring structure may be indicative of the disk clearing process. Although such ring structures were not seen in the ALMA Band 6 images, some features were detected at ∼50 au.

Methods. In this paper, we analyzed new ALMA Band 7 observations of MP Mus in order to investigate the details of its disk substructures.

Results. By subtracting the continuum profile generated from Band 7 data, we discovered a ring structure in the Band 7 dust continuum image at ∼50 au. We calculated the overall dust mass as 28.4 ± 2.8 M_⊕ at 0.89 mm and 26.3 ± 2.6 M_⊕ at 1.3 mm and the millimeter spectral index α_{0.89–1.3 mm} ∼2.2 ± 0.3 between 0.89 mm and 1.3 mm. Moreover, we display the spatial distribution of the spectral index (α_mm), estimating values ranging from 1.3 at the inner disk to 4.0 at a large radius. Additionally, we observed an extended gas disk up to ∼120 au, in contrast with a compact continuum millimeter extent of ∼60 au.

Conclusions. We conclude that there are strong indicators for an active radial drift process within the disk. However, we cannot discard the possibility of a dust evolution process and a grain growth process as responsible for the outer disk structures observed in the ALMA continuum imaging.