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标题：Physical and chemical modeling of the starless core L 1512 ★
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作者：Sheng-Jun Lin ; Laurent Pagani ; Shih-Ping Lai 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2020
卷号：635
页码：1-20
DOI：10.1051/0004-6361/201936877
语种：English
出版社：EDP Sciences
摘要：Context.The deuterium fractionation in starless cores gives us a clue to estimate their lifetime scales, thus allowing us to distinguish between dynamical theories of core formation. Cores also seem to be subject to a differential N2and CO depletion, which was not expected from the models.Aims.We aim to create a survey of ten cores to estimate their lifetime scales and depletion profiles in detail. After describing L 183, located in Serpens, we present the second cloud of the series, L 1512, from the star-forming region Auriga.Methods.To constrain the lifetime scale, we performed chemical modeling of the deuteration profiles across L 1512 based on dust extinction measurements from near-infrared observations and nonlocal thermal equilibrium radiative transfer with multiple line observations of N2H+, N2D+, DCO+, C18O, and13CO, plus H2D+(110–111).Results.We find a peak density of 1.1 × 105cm−3and a central temperature of 7.5 ± 1 K, which are higher and lower, respectively, compared with previous dust emission studies. The depletion factors of N2H+and N2D+are 27−13+17and 4−1+2in L 1512, which are intermediate between the two other more advanced and denser starless core cases, L 183 and L 1544. These factors also indicate a similar freeze-out of N2in L 1512, compared to the two others despite a peak density one to two orders of magnitude lower. Retrieving CO and N2abundance profiles with the chemical model, we find that CO has a depletion factor of ~430–870 and the N2profile is similar to that of CO unlike that toward L 183. Therefore, L 1512 has probably been living long enough so that N2chemistry has reached steady state.Conclusions.N2H+modeling is necessary to assess the precise physical conditions in the center of cold starless cores, rather than dust emission. L 1512 is presumably older than 1.4 Myr. Therefore, the dominating core formation mechanism should be ambipolar diffusion for this source.
关键词：Key wordsenastrochemistryISM: individual objects: L 1512ISM: cloudsISM: structureISM: abundancesISM: kinematics and dynamics