Protostellar accretion traced with chemistry: Comparing synthetic C18O maps of embedded protostars to real observations

Context: Understanding how protostars accrete their mass is a central question of star formation. One aspect of this is trying to understand whether the time evolution of accretion rates in deeply embedded objects is best characterised by a smooth decline from early to late stages or by intermittent bursts of high accretion. Aims: We create synthetic observations of deeply embedded protostars in a large numerical simulation of a molecular cloud, which are compared directly to real observations. The goal is to compare episodic accretion events in the simulation to observations and to test the methodology used for analysing the observations. Methods: Simple freeze-out and sublimation chemistry is added to the simulation, and synthetic C$^{18}$O line cubes are created for a large number of simulated protostars. The spatial extent of C$^{18}$O is measured for the simulated protostars and compared directly to a sample of 16 deeply embedded protostars observed with the Submillimeter Array. If CO is distributed over a larger area than predicted based on the protostellar luminosity, it may indicate that the luminosity has been higher in the past and that CO is still in the process of refreezing. Results: Approximately 1% of the protostars in the simulation show extended C$^{18}$O emission, as opposed to approximately 50% in the observations, indicating that the magnitude and frequency of episodic accretion events in the simulation is too low relative to observations. The protostellar accretion rates in the simulation are primarily modulated by infall from the larger scales of the molecular cloud, and do not include any disk physics. The discrepancy between simulation and observations is taken as support for the necessity of disks, even in deeply embedded objects, to produce episodic accretion events of sufficient frequency and amplitude.Comment: Accepted for publication in A&A, 11 pages, 8 figures; v2 contains minor updates to the languag

COMPARISON OF GROWTH PERFORMANCE OF BEEF CALVES FROM DIFFERENT GENETIC STRAINS REARED UNDER ORGANIC CONDITIONs (D. 3.2)

The objective of the present study was to compare growth performance of 15 Danish Holstein bull (DHB) calves, 15 Limousine x Danish Holstein crossbred bull (CB) calves and 15 Limousine x Danish Holstein crossbred heifer (CH) calves reared under organic conditions. Spring-born calves were puchased at private farms and arrived at approximately 20 days of age with an average initial body weight of 52.9, 58.5 and 56.1 kg, (SEM 2.6) for DHB, CB and CH, respectively. Calves were kept indoor until weaning at 3 months of age. Calves were gradually introduced to a grass-silage based ration from 3 to 4 months of age. From 4 to 7 months calves were kept on mix grass pasture of ryegrass and white clover. There were significant differences between treatment groups in terms of average daily gain (ADGP1) during the first summer pasture period, average daily gain (ADGI) during the indoor winter period, and average daily gain (ADGP2) during the second summer pasture period (first 7 weeks). Thus, CB had significantly greater ADG than CH for all three periods with DHB being in between. CB had greater values than DHB and CH in terms of LWP1 144, 140 and 135 (SEM 4) kg, ADGP1 1.15, 1.04 and 0.95 (SEM 0.05) kg/d, LW Indoor 222, 213, and 201 (SEM 5) kg and ADGI 1.06, 1.02 and 0.95 (SEM 0.02) kg/d, LWP2 462, 445 and 414 (SEM 9) kg and ADGP2 1.24, 0.98 and 0.68 (SEM 0.04) kg/d for CB, DHB and CH, respectively. The final live weight were not different between CB and DHB but was significantly lower for CH than DHB and CB (483, 539 and 582 (SEM 8) kg, for CH, DHB and CB, respectively). Overall growth performance across all periods was 13% higher for CB than CH

The autonomous vision system on TeamSat

The second qualification flight of Ariane 5 blasted off-the European Space Port in French Guiana on October 30, 1997, carrying on board a small technology demonstration satellite called TeamSat. Several experiments were proposed by various universities and research institutions in Europe and five of them were finally selected and integrated into TeamSat, namely FIPEX, VTS, YES, ODD and the Autonomous Vision System, AVS, a fully autonomous star tracker and vision system. This paper gives short overview of the TeamSat satellite; design, implementation and mission objectives. AVS is described in more details. The main science objectives of the AVS were to verify, in space, multiple autonomous processes intended for spacecraft applications such as autonomous star identification and attitude determination, identification and tracking of non-stellar objects, imaging and real-time compression of image and science data for further ground analysis. AVS successfully determined the attitude and attitude dynamics of TeamSat