DUTREY, Anne; HENNING, Thomas; GUILLOTEAU, S.; SEMENOV, Dmitry; PIÉTU, Vincent; SCHREYER, Katharina; BACMANN, A.; LAUNHARDT, Ralf; PETY, Jerome; GUETH, Frederic

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DUTREY, Anne
Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux [L3AB]
Observatoire aquitain des sciences de l'univers [OASU]
Laboratoire d'Astrophysique de Bordeaux [Pessac] [LAB]

HENNING, Thomas

GUILLOTEAU, S.
Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux [L3AB]
Observatoire aquitain des sciences de l'univers [OASU]
Laboratoire d'Astrophysique de Bordeaux [Pessac] [LAB]

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Article de revue

Ce document a été publié dans

Astronomy and Astrophysics - A&A. 2007, vol. 464, n° 2, p. 615-623

EDP Sciences

Résumé en anglais

Aims: To constrain the ionization fraction in protoplanetary disks, we present new high-sensitivity interferometric observations of N$_2$H$^+$ in three disks surrounding DM Tau, LkCa 15, and MWC 480. Methods: We used the IRAM PdBI array to observe the N$_2$H$^+$ J=1-0 line and applied a $\chi^2$-minimization technique to estimate corresponding column densities. These values are compared, together with HCO$^+$ column densities, to results of a steady-state disk model with a vertical temperature gradient coupled to gas-grain chemistry. Results: We report two \ndhp detections for LkCa 15 and DM Tau at the $5 \sigma$ level and an upper limit for MWC 480. The column density derived from the data for LkCa 15 is much lower than previously reported. The [N$_2$H$^+$/HCO$^+$] ratio is on the order of 0.02--0.03. So far, HCO$^+$ remains the most abundant observed molecular ion in disks. Conclusions: All the observed values generally agree with the modelled column densities of disks at an evolutionary stage of a few million years (within the uncertainty limits), but the radial distribution of the molecules is not reproduced well. The low inferred concentration of N$_2$H$^+$ in three disks around low-mass and intermediate-mass young stars implies that this ion is not a sensitive tracer of the overall disk ionization fraction.< Réduire

Mots clés en anglais

MWC 480

Stars: circumstellar matter

planetary systems: protoplanetary disks

individual: LkCa 15

DM Tau

Stellar PropertiesRadio-lines: stars

Origine

Importé de hal

Unités de recherche

Laboratoire d'Astrophysique de Bordeaux (LAB) - UMR 5804