Volume 635, March 2020
|Number of page(s)||20|
|Section||Interstellar and circumstellar matter|
|Published online||02 April 2020|
Physical and chemical modeling of the starless core L 1512★
Institute of Astronomy, National Tsing Hua University,
No. 101, Section 2, Kuang-Fu Road,
2 LERMA & UMR8112 du CNRS, Observatoire de Paris, PSL University, Sorbonne Universités, CNRS, 75014 Paris, France
3 Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38400 Saint-Martin d’Hères, France
4 LOMC – UMR 6294, CNRS-Université du Havre, 25 rue Philippe Lebon, BP 1123, 76063 Le Havre, France
Accepted: 29 January 2020
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 N2 and 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, and 13CO, plus H2D+ (110–111).
Results. We find a peak density of 1.1 × 105 cm−3 and 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+17 and 4−1+2 in 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 N2 in L 1512, compared to the two others despite a peak density one to two orders of magnitude lower. Retrieving CO and N2 abundance profiles with the chemical model, we find that CO has a depletion factor of ~430–870 and the N2 profile is similar to that of CO unlike that toward L 183. Therefore, L 1512 has probably been living long enough so that N2 chemistry 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.
Key words: astrochemistry / ISM: individual objects: L 1512 / ISM: clouds / ISM: structure / ISM: abundances / ISM: kinematics and dynamics
Based in part on observations obtained with WIRCam, a joint project of CFHT, Taiwan, Korea, Canada, France, at the Canada–France–Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institute National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. The observations at the Canada–France–Hawaii Telescope were performed with care and respect from the summit of Maunakea which is a significant cultural and historic site.
© ESO 2020
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