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    The diagnostic potential of Fe lines applied to protostellar jets*


    Giannini, T. and Nisini, B. and Antoniucci, S. and Alcalá, J.M. and Bacciotti, F. and Bonito, R. and Podio, L. and Stelzer, B. and Whelan, Emma (2013) The diagnostic potential of Fe lines applied to protostellar jets*. Astrophysical Journal Supplement, 778 (71). ISSN 0067-0049

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    Abstract

    We investigate the diagnostic capabilities of iron lines for tracing the physical conditions of shock-excited gas in jets driven by pre-main sequence stars. We have analyzed the 3000-25000 Å, X-shooter spectra of two jets driven by the pre-main sequence stars ESO-Hα 574 and Par-Lup 3-4. Both spectra are very rich in [Fe II] lines over the whole spectral range; in addition, lines from [Fe III] are detected in the ESO-Hα 574 spectrum. Non-local thermal equilibrium codes solving the equations of the statistical equilibrium along with codes for the ionization equilibrium are used to derive the gas excitation conditions of electron temperature and density and fractional ionization. An estimate of the iron gas-phase abundance is provided by comparing the iron lines emissivity with that of neutral oxygen at 6300 Å. The [Fe II] line analysis indicates that the jet driven by ESO-Hα 574 is, on average, colder (T e ~ 9000 K), less dense (n e ~ 2 × 104 cm–3), and more ionized (x e ~ 0.7) than the Par-Lup 3-4 jet (T e ~ 13,000 K, n e ~ 6 × 104 cm–3, x e < 0.4), even if the existence of a higher density component (n e ~ 2 × 105 cm–3) is probed by the [Fe III] and [Fe II] ultra-violet lines. The physical conditions derived from the iron lines are compared with shock models suggesting that the shock at work in ESO-Hα 574 is faster and likely more energetic than the Par-Lup 3-4 shock. This latter feature is confirmed by the high percentage of gas-phase iron measured in ESO-Hα 574 (50%-60% of its solar abundance in comparison with less than 30% in Par-Lup 3-4), which testifies that the ESO-Hα 574 shock is powerful enough to partially destroy the dust present inside the jet. This work demonstrates that a multiline Fe analysis can be effectively used to probe the excitation and ionization conditions of the gas in a jet without any assumption on ionic abundances. The main limitation on the diagnostics resides in the large uncertainties of the atomic data, which, however, can be overcome through a statistical approach involving many lines.

    Item Type: Article
    Additional Information: Citation: T. Giannini et al 2013 ApJ 778 71 * Based on observations collected with X-shooter at the Very Large Telescope on Cerro Paranal (Chile), operated by the European Southern Observatory (ESO). Program ID: 085.C-0238(A).
    Keywords: ISM: individual objects (ESO-Hα 574, Par-Lup 3-4); ISM: jets and outflows; ISM: lines and bands; stars: pre-main sequence;
    Academic Unit: Faculty of Science and Engineering > Experimental Physics
    Item ID: 9889
    Identification Number: https://doi.org/10.1088/0004-637X/778/1/71
    Depositing User: Emma Whelan
    Date Deposited: 07 Sep 2018 14:27
    Journal or Publication Title: Astrophysical Journal Supplement
    Publisher: Institute of Physics
    Refereed: Yes
    URI:

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