The results are presented of a molecular line survey to search for the spectral signature of infall towards 77 850 µm continuum sources believed to be candidate high mass protostellar objects. Up to six different transitions, HCO + J = 1 → 0, J = 3 → 2 and J = 4 → 3, H 2 CO 2 12 − 1 11 , N 2 H + J = 1 → 0 and H 13 CO + J = 3 → 2, were observed towards each source. Towards the peak of the 850 µm emission, N 2 H + was typically strong, with a peak antenna temperature of ∼1.5 K, with a typical linewidth of ∼2 km s −1 . The good agreement between the velocity and velocity width of the N 2 H + and H 13 CO + emission suggests that both species are tracing similar material in the sources. With respect to the velocity of the N 2 H + , there is a statistically significant excess of blue asymmetric line profiles in both the HCO + J = 1 → 0 and H 2 CO transitions. This excess reaches levels similar to that seen towards samples of low mass protostars, and suggests that the material around these high mass sources is infalling. We identify 22 promising candidate infall sources which show at least one blue asymmetric line profile and no red asymmetric profiles. The infall velocity is estimated to be in the range of 0.1 km s −1 to 1 km s −1 with an implied mass accretion rate of between 2 × 10 −4 M /yr and 10 −3 M /yr.

Abstract. We present maps of the 850 µm and 450 µm continuum emission seen towards a sample of 68 high-mass protostellar candidates with luminosities ranging from 10 2.5 L to ∼10 5 L . Most of these candidate high-mass stars are in the earliest stages of evolution, and have not yet developed an ultra-compact HII region. We observe a variety of continuum emission morphologies, from compact symmetric sources through to multiple cores embedded in long filaments of emission. We find on average there is a 65% probability of an IRAS point-source having a companion detection at submillimetre wavelengths. The ratio of integrated flux to peak flux for our detections shows no strong dependence on distance, suggesting the emission we have observed is primarily from scale-free envelopes with power-law density structures. Assuming a near kinematic distance projection, the clumps we detect vary in mass from ∼1 M to over 1000 M , with a mean clump mass of 330 M , column density of 9 × 10 23 cm −2 and diameter of ∼0.6 pc. The high luminosity and low mass of the smallest clumps suggests they are accompanied by a minimal number of stellar companions, while the most massive clumps may be examples of young protogroups and protoclusters. We measure the spectral index of the dust emission (α) and the spectral index of the dust grain opacity (β) towards each object, finding clumps with morphologies suggestive of strong temperature gradients, and of grain growth in their dense inner regions. We find a mean value for β of 0.9, significantly smaller than observed towards UCHII regions.

This paper quantifies the expected impacts of climate change, climate variability and salinity accumulation on food production in coastal Bangladesh during the dry season. This forms part of a concerted series of actions on agriculture and salinity in Bangladesh under the UK funded Ecosystems for Poverty Alleviation programme and the British Council INSPIRE scheme. The work was undertaken by developing simulation models for soil water balances, dry season irrigation requirements and the effectiveness of the monsoon season rainfall at leaching accumulated salts. Simulations were run from 1981 to 2098 using historical climate data and a daily climate data set based on the Met Office Hadley Centre HadRM3P regional climate model. Results show that inter-seasonal and inter-annual variability are key factors that affect the viability of dry season vegetable crop growing. By the end of the 21(st) century the dry season is expected to be 2-3 weeks longer than now (2014). Monsoon rainfall amounts will remain the same or possibly slightly increase but it will occur over a slightly shorter wet season. Expectations of sea level rise and additional saline intrusion into groundwater aquifers mean that dry season irrigation water is likely to become more saline by the end of the 21(st) century. A study carried out at Barisal indicates that irrigating with water at up to 4 ppt can be sustainable. Once the dry season irrigation water quality goes above 5 ppt, the monsoon rainfall is no longer able to leach the dry season salt deposits so salt accumulation becomes significant and farm productivity will reduce by as a much as 50%, threatening the livelihoods of farmers in this region.

No abstract