The 12C/ 13C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry

A study has been conducted of 12C/13C ratios in five complex molecules in the Galactic center. H2CS, CH3CCH, NH2CHO, CH2CHCN, and CH3CH2CN and their 13C-substituted species have been observed in numerous transitions at 1, 2, and 3 mm, acquired in a spectral-line survey of Sgr B2(N), conducted with the telescopes of the Arizona Radio Observatory (ARO). Between 22 and 54 individual, unblended lines for the 12C species and 2–54 for 13C-substituted analogs were modeled in a global radiative transfer analysis. All five molecules were found to consistently exhibit two velocity components near VLSR ∼ 64 and 73 km s−1, with column densities ranging from Ntot ∼ 3 × 1014 − 4 × 1017 cm−2 and ∼2 × 1013 − 1 × 1017 cm−2 for the 12C and 13C species, respectively. Based on 14 different isotopic combinations, ratios were obtained in the range 12C/13C = 15 ± 5 to 33 ± 13, with an average value of 24 ± 7, based on comparison of column densities. These measurements better anchor the 12C/13C ratio at the Galactic center, and suggest a slightly revised isotope gradient of 12C/13C = 5.21(0.52) DGC + 22.6(3.3). As indicated by the column densities, no preferential 13C enrichment was found on the differing carbon sites of CH3CCH, CH2CHCN, and CH3CH2CN. Because of the elevated temperatures in Sgr B2(N), 13C isotopic substitution is effectively “scrambled,” diminishing chemical fractionation effects. The resulting ratios thus reflect stellar nucleosynthesis and Galactic chemical evolution, as is likely the case for most warm clouds.NSF [AST-1515568, AST-1140030]; NSF University Radio Observatories (URO) program [AST-1140030]; NASA [NNX15AD94G]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Late gestation conditions leading to postpartal subclinical ketosis in dairy cows affects offspring growth and performance

Ketosis is a common disease associated with NEB in peripartal dairy cows, and the onset of this condition is linked to prepartal preconditions such as decreased intake and excessive fat mobilization. Likely the same prepartal endocrine peripheral changes that predispose cows to subclinical ketosis (SK) postpartum will affect fetal development and colostrum biosynthesis. Thus, the objective of this retrospective study was to evaluate the effects of maternal SK in peripartal dairy cows on offspring growth and development. Twelve Holstein dairy cows (n = 6/group) were monitored during the peripartal period. Cows were housed in bedded pack pens and fed the same close-up diet (0.63 Mcal/kg DM and 12.3% CP). After parturition cows were moved to a freestall barn and fed a lactation diet (0.73 Mcal/ kg DM and 15.6% CP). Precision Xtra was used to measure blood BHB at 1, 3, 5, 7, 9, and 11 d postpartum and cows were classified as subclinically-ketotic (KET; \u3e 1.4 mmol/L) or non-ketotic (NONKET; \u3c 1.4 mmol/L). Dairy calves were enrolled if calving difficult \u3c 3, BW ≥ 32kg, single calf, colostrum quality ≥ 21% Brix refractometer, and 3.8 L of colostrum intake from the same dam. Calves born to dams in KET and NONKET groups were assigned accordingly. Calves were monitored from 1 to 8 wk of age. Calves were fed 2.8 L/d of milk replacer 2x/d from 1 to 6 wk, 1x/d in 7 wk, and weaned at 8 wk. Calves had ad libitum access to starter and water. The BW and withers height (WH) were measured weekly until wk 8. Health checks were performed daily. Data were analyzed using the MIXED procedure of SAS. Birth BW was greater (P = 0.05; 42.9 vs 37.9 kg) in KET calves than NONKET. However, a slower (P = 0.02) growth rate was observed in KET calves than NONKET from 1 to 8 wk (53.1 vs 56.2 kg). The latter was reflected in a lower (P = 0.05) final BW at 8 wk in KET than NONKET (71.3 vs 74.8 kg). Overall, offspring’s WH was not affected (P = 0.016) by maternal SK. Results suggest that prepartal endocrine and metabolic mechanisms predisposing dairy cows to postpartal SK may produce long-lasting effects on the offspring’s growth and development