The earliest evolution of low mass stars

The first 100,000 years of low-mass protostars

One of the big open questions in the formation of young low-mass stars is when circumstellar disks form and how they evolve. Low-mass stars like our Sun are formed in the centers of dark clouds of dust and gas that obscure their visible light. Deep observations at infrared and submillimeter wavelengths are uniquely suited to probe the inner regions of these young stellar objects and unravel their structures. These earliest stages - the first 100,000 years after the stars have formed - are particularly interesting: It is for example during this stage that the final mass of the star and the properties of its disk - and thus ability to form planets - are determined.

Over the last couple of years a group led by Jes Jørgensen has performed a large survey of 20 deeply embedded protostars using the Submillimeter Array (SMA) on Mauna Kea in Hawaii. With these high angular resolution observations the team has mapped the dust continuum on few hundred AU scales and, with the use of detailed radiative transfer modeling, constrained the physical structures of the protostellar disks and envelopes including their masses.

A particular interesting result of this study is that the disk masses are comparable to those around more evolved T Tauri stars and also that very little evolution is seen of the disk parameters with age during these first 100,000 years.

This suggests that disks are formed and grow to significant sizes early in the evolution of the protostars, but also are very efficient in channeling matter onto the central stars. A paper describing these results has recently been submitted to Astronomy & Astrophysics. This survey will serve as an important pathfinder for studies with the Atacama Large Millimeter Array (ALMA) currently being built in Chile and expected to start early science operations 2011. With this array it will be possible to perform more complete censuses of the thousand of known young stellar objects in nearby molecular clouds to, e.g., study the effects of environment on star/disk formation and furthermore zoom-in on individual sources at much higher resolution (a few AU) compared to current data. This will be one of the central research topics of the group of Jes Jørgensen at the Centre for Star and Planet Formation.