Low mass stars and brown dwarfs in the star forming region Corona Australis. The study “The substellar population in Corona Australis” of K. Muzic (Universidade de Lisboa) appeared on A&A
A new study on the low mass stellar population of the star forming region Corona Australis shed light on the formation of brown dwarfs
In recent years, several studies of star-forming regions near the Sun have revealed that a significant fraction of the stellar population of the Milky Way consists of brown dwarfs—objects whose cores do not reach the pressure and temperature conditions required to ignite thermonuclear reactions. These are difficult bodies to detect and identify, as they are much smaller and less luminous than true stars.
One of the unresolved questions regarding brown dwarfs concerns their formation mechanism and the extent to which the environment may influence their production. It is commonly accepted among researchers that more massive brown dwarfs form through processes similar to those of stars. This is suggested by the many similarities observed between young stellar objects and young brown dwarfs. At lower masses, however, it is still unclear whether brown dwarfs form like stars or like planets. Several scenarios have also been proposed in which the surrounding environment could influence their formation: for example, high-energy radiation (mainly ultraviolet) from nearby massive stars, capable of heating and altering the physical properties of the nebulae where stars form, or gravitational interactions between stars, which are more frequent in denser stellar environments (e.g. more stars per elements of volume).
To address these questions, a team of researchers led by astrophysicist K. Muzic of the University of Lisbon carried out a search for hidden brown dwarfs in the nebulae of the Corona Australis star-forming region, located about 500 light-years from the Sun. The study is based on photometric observations obtained with the SuprimeCam instrument on the Subaru telescope and the VISTA Hemisphere Survey, spectroscopic observations with the KMOS instrument mounted on the Very Large Telescope of the ESO and with the FLOYDS spectrograph installed at the 2m
Faulkes South telescope, part of the Las Cumbres Observatory, and astrometric data from the Gaia satellite of the European Space Agency. Thanks to this large dataset, the researchers were able to determine the region stellar mass function, i.e., the distribution of stars as a function of mass (called initial mass function) down to 10 Jupiter masses, and to estimate the star-to-brown dwarf ratio, which is about 2. By comparing these results with those from other regions with different stellar environments, the study concludes that the efficiency of brown dwarf formation does not depend on the environment—at least within 5 orders of magnitude in the intensity of high-energy radiation from massive stars and 2 orders of magnitude in stellar surface density (number of stars per unit area). The study is described in the article “The substellar population in Corona Australis”, recently published in Astronomy & Astrophysics, co-authored also by astrophysicist V. Almendros Abad of INAF – Osservatorio Astronomico di Palermo.
The cover figure (click here to view the full image) shows an I-band image of Corona Australis taken with Subaru’s SuprimeCam, combined with J- and K-band data from the VISIONS survey. The observed field spans about 36.1 × 29.1 square arcminutes. Orange circles indicate the positions of stars associated with Corona Australis, as identified in a 2022 study. White star symbols mark the stars observed with FLOYDS/LCO, while white circles mark those observed with KMOS.
Mario Giuseppe Guarcello
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