A Case Study of Low‐Mass Star Formation

Abstract

This article synthesizes observational data from an extensive program aimed toward a comprehensive understanding of star formation in a low-mass star-forming molecular cloud. New observations and published data spanning from the centimeter wave band to the near-infrared reveal the high-and low-density molecular gas, dust, and premain-sequence stars in L1551. The total cloud mass of $160 M contained within 0.9 pc has a dynamical timescale, t dyn ¼ 1:1 Myr. Thirty-five pre-main-sequence stars with masses from $0.1 to 1.5 M are selected to be members of the L1551 association constituting a total of 22 AE 5 M of stellar mass. The observed star formation efficiency, SFE ¼ 12%, while the total efficiency, SFE tot , is estimated to fall between 9% and 15%. L1551 appears to have been forming stars for several t dyn , with the rate of star formation increasing with time. Star formation has likely progressed from east to west, and there is clear evidence that another star or stellar system will form in the high column density region to the northwest of L1551 IRS 5. High-resolution, wide-field maps of L1551 in CO isotopologue emission display the structure of the molecular cloud at 1600 AU physical resolution. The 13 CO emission clearly reveals the disruption of the ambient cloud by outflows in the line core and traces the interface between regions of outflow and quiescent gas in the line wings. Kinetic energy from outflows is being deposited back into the cloud on a physical scale k peak % 0:05 pc at a rate,Ė input % 0:05 L . The remaining energy afforded by the full mechanical luminosity of outflow in L1551 destroys the cloud or is otherwise lost to the greater interstellar medium. The C 18 O emission is optically thin and traces well the turbulent velocity structure of the cloud. The total turbulent energy is close to what is expected from virial equilibrium. The turbulent velocities exist primarily on small scales in the cloud, and the energy spectrum of turbulent fluctuations, E(k) / k À , is derived by various methods to have % 1 2. The turbulent dissipation rate estimated using the results of current numerical simulations isĖ diss %Ė input . This study reveals that stellar feedback is a significant factor in the evolution of the L1551 cloud.

Low-mass protostars and dense cores in different evolutionary stages in IRAS 00213+6530

“…Therefore, the initial assumption that star formation occurs in an isolated mode may not be appropriate to describe the I00213 region when the region is studied with high angular resolution. This poses the question of to what extent we can adopt the isolated mode in the theories of star formation, as this high angular resolution study together with a large number of recent studies (e.g., Huard et al 1999;Djupvik et al 2006;Teixeira et al 2007;Carrasco-González et al 2008;Chen et al 2008Chen et al , 2009Forbrich et al 2009;Gutermuth et al 2008;Swift & Welch 2008;Girart et al 2009) suggest that isolated star formation seems to be rare in the Galaxy, even in low mass star-forming regions. The three YSOs are spatially ordered from youngest (east) to oldest (west), suggesting that an external agent could be inducing star formation in MM1.…”

Radiation-Hydrodynamic Simulations of Protostellar Outflows: Synthetic Observations and Data Comparisons

“…However, other simulations of jets indicate that well-collimated outflows drive supersonic turbulence very inefficiently, although they may contribute significant energy at lower velocities (Banerjee et al 2007). However, observations of some molecular clouds suggest that the energy injected by outflows is insufficient by an order of magnitude or more than the observed cloud turbulence (Arce et al 2010;Ginsburg et al 2011, but see also Swift & Welch 2008;Nakamura et al 2011). Such estimations include corrections for inclination effects and mass underestimations that amount to a factor of four.…”

“…Consequently, the discrepancy we demonstrate here is unlikely to account for the turbulent deficit measured in clouds 10 pc. In addition, outflows must not only account for the magnitude of the energy injection but the appropriate range of scales (Matzner 2002;Swift & Welch 2008). If measured outflow extents range from ∼0.1 to 2 pc then they will not contribute driving motions on larger scales.…”

An Exploration of the Statistical Signatures of Stellar Feedback

“…However, from an observational prospective, stellar feedback is messy and identifying clear feedback signatures is complex for the reasons mentioned above. Disentangling feedback signatures from the turbulent background and assessing their impact is challenging since any low-velocity motions excited by feedback are often lost in the general cloud turbulence (Swift & Welch 2008;Arce et al 2010Arce et al , 2011.…”