Discovery of carbon monoxide emission from five debris disks around young A-type stars

¹ HUN-REN Research Centre for Astronomy and Earth Sciences, Konkoly Observatory, MTA Centre of Excellence, Konkoly-Thege Miklós út 15–17, 1121 Budapest, Hungary
² ELTE Eötvös Loránd University, Institute of Physics and Astronomy, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
³ Department of Astrophysics, University of Vienna, Türkenschanzstraße 17, 1180 Vienna, Austria
⁴ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁵ National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan
⁶ Astronomy Department and Van Vleck Observatory, Wesleyan University, 96 Foss Hill Drive, Middletown, CT 06459, USA
⁷ Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK
⁸ LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS, 92190 Meudon, France
⁹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France

^★ Corresponding author: moor.attila@csfk.org

Received: 28 March 2025
Accepted: 21 August 2025

Abstract

Context. Over the past 15 years, surveys mainly at millimeter wavelengths have led to the discovery of ~20 gas-bearing debris disks, most of them surrounding young intermediate-mass stars. Exploring the properties and origin of this gas could be fundamental to better understanding the transition between the protoplanetary and debris disk phases, the evolution of icy planetesimal belts, and the formation of planetary atmospheres.

Aims. To expand the list of known CO-bearing debris disks and to improve our knowledge of the environmental conditions under which they can form, we targeted 12 dust-rich debris disks around young (<50 Myr) intermediate-mass stars.

Methods. Using the ALMA 12m Array we performed millimeter continuum and CO line observations to search for dust and gas and to measure their quantity and spatial distribution.

Results. We discovered CO gas in five disks. Two of them have a low CO content of a few times 10⁻⁵ M_⊕, similar to that of β Pic. The other three disks, however, are CO-rich with M_CO > 10⁻³ M_⊕. By combining our results with those of other studies we concluded, in agreement with previous findings, that the detection rate of CO gas is significantly higher for disks around stars with 6.5 L_⊙ < L_* < 21.9 L_⊙ (~A8–A0 spectral type) than for disks around less luminous stars (0.18 L_⊙ < L_* < 6.4 L_⊙, K7–A9). A comparison of the measured CO masses and the estimated mass loss rates of solids in disks with low CO content (<10⁻⁴ M_⊕) suggests that collisions may play a role in CO gas production in such systems. Interestingly, however, the estimated mass loss rates of CO-rich debris disks are not higher than those of systems with low CO content. In light of this finding, we speculate on what could lead to the formation of CO-rich debris disks.