---
author:
- 'A. Crapsi'
- 'P. Caselli'
- 'C.M. Walmsley'
- 'M. Tafalla'
- 'C.W. Lee'
- 'T.L. Bourke'
- 'P.C. Myers'
date: 'Received ;Accepted'
title: 'Observations of L1521F: a highly evolved starless core'
---

Introduction
============

The pre–stellar core L1544 has recently been the subject of much study because while apparently in hydrostatic equilibrium, there are indications that it is close to the “critical” state at which it will become gravitationally unstable and from which it will dynamically collapse (see discussions by Tafalla et al. [@taf98]; Ciolek & Basu [@cb2000]; Caselli et al. [@cas02a]; Caselli et al. [@cas02b]). If correct, this is of fundamental importance because it defines the initial conditions for the formation of a protostar, which affects many theoretical studies of low mass star formation.\
Clearly trying to extrapolate general trends from a single object is difficult and a larger number of L1544-like cores (preferably with the same external environment) should be studied. Unfortunately there are rather few other objects with similar properties due to the short timescale of this phase. According to the Ciolek & Basu ([@cb2000]) model, for example, (contraction of a disk driven by ambipolar diffusion) L1544–like properties fit the model structure of 