CO outflows from young stars in the NGC2023 cluster

¹ Institute for Astronomy, University of Hawaii at Manoa, 640 N. Aohoku Place, Hilo, HI 96720, USA
e-mail: gsandell@hawaii.edu
² Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
³ Max Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Received: 19 November 2023
Accepted: 12 March 2024

Abstract

Context. Young early-type HAeBe stars are still embedded in the molecular clouds in which they formed. They illuminate reflection nebulae, which shape the surrounding molecular cloud and may trigger star formation. They are therefore ideal places to search for ongoing star formation activity.

Aims. NGC 2023 is illuminated by the Herbig Be star HD 37903. It is the most massive member of a small young cluster with about 30 PMS stars, several of which are Class I objects that still heavily accrete. It might therefore be expected that they might drive molecular outflows. We examined the whole region for outflows.

Methods. We analyzed previously published APEX data to search for and characterize the outflows in the NGC 2023 region. This is the first systematic search for molecular outflows in this region. Since the outflows were mapped in several CO transitions, we can determine their properties quite well.

Results. We have discovered four molecular outflows in the vicinity of NGC 2023, three of which are associated with Class I objects. MIR-63, a bright mid-infrared and submillimeter Class I source, is a binary with a separation of 2″.4 and drives two bipolar outflows orthogonal to each other. The large southeast–northwest outflow excites the Herbig-Haro flow HH 247. MIR-73, a Class I object, which is also a far-infrared source, drives a pole-on outflow. MIR-62 is a Class II object with strong infrared excess and a luminosity of 7 L_⊙. It is not detected in the far-infrared. The Class I sources have bolometric luminosities of about 20 L_⊙ or lower, that is, they are all low-mass stars. One other far-infrared source, MIR-75, may have powered an outflow in the past because it now illuminates an egg-shaped cavity.

Conclusions. The four outflows are all powered by young stars and are located in the immediate vicinity of NGC 2023. They are at a similar evolutionary stage, which suggests that their formation may have been triggered by the expanding C II region.