Pulsar observations and small-scale structure in interstellar H I

Abstract

If small-scale structure is present in H I clouds, then H I absorption profiles toward pulsars with large proper motions should show changes on a time-scale of a few years. We have compared absorption measurements, made with an interval of about four years, toward two pulsars and find a marginal difference in one of them. If confirmed, this could imply structures on the scale of about 1000 AU in H I clouds.