Research ArticleASTROPHYSICS

Laboratory unraveling of matter accretion in young stars

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Science Advances  01 Nov 2017:
Vol. 3, no. 11, e1700982
DOI: 10.1126/sciadv.1700982
  • Fig. 1 Laboratory investigation of magnetized accretion dynamics and comparison with scaled astrophysical simulation of the same phenomenon highlighting the formation of a shocked core and of a surrounding shell.

    (A) Arrangement of the laboratory experiment and of the diagnostics. (B) Snapshot of the modeling of the laboratory experiment by the GORGON code (shown is the mass density in kg/m3). (C) Measured maps, at different times (as indicated), of laboratory plasma electron density, embedded in a homogeneous and steady 20-T magnetic field. The contours displayed on the first two panels highlight the core (contour at 1019cm−3) and the shell (contour at 3 × 1018cm−3). Here, the obstacle is a CF2 target, whereas the stream is generated from a laser-irradiated PVC (C2H3Cl)n target. (D) Simulated plasma density (left-half panels) and temperature (right-half panels) maps, also at different times, and extracted from a 2D astrophysical simulation (using the PLUTO code). In all panels, the initial magnetic field is uniform and oriented along the z axis; the white (resp. black) lines in (A) and (C) (resp. B) represent the magnetic field lines. In all, the obstacle/chromosphere is located at the bottom, at z = 0, and t = 0 corresponds to the moment when the stream hits the obstacle/chromosphere.

  • Fig. 2 Visible and x-ray emissions produced simultaneously by the shocked core and shell plasmas as recorded in the laboratory.

    (A) Visible [time- and space-resolved; here, the obstacle is a CF2 target, whereas the stream is generated from a PVC (C2H3Cl)n laser-irradiated target] and (B) x-ray (integrated in time and in space over 0 < z < 1 mm, that is, near the obstacle but spectrally resolved) emissions from the laboratory plasma. Note that, here, contrary to (A), the obstacle is a PVC (C2H3Cl)n target, whereas the stream is generated from a laser-irradiated CF2 target. However, we observe that the plasma density dynamics and characteristics (density and temperature) are the same whenever the laser target and obstacle targets are swapped. In (B), the configuration using a CF2 stream-source target is used because the spectrometer records the spectrum corresponding to the fluorine ions and that most (95 %) of the plasma seen above the obstacle is composed of stream material, as precisely analyzed by recording F-ion emissions solely originating from stream or obstacle material. The spectrum shown in (B) uses the configuration of a CF2 stream-source target because it leads to stronger emissions compared to when using the reverse configuration of a CF2 obstacle target. Overlaid are the simulations of the emissions produced by two plasma components having the densities of the core and shell, respectively, and temperatures of 0.58 MK (50 eV) and 3.7 MK (320 eV), respectively. Note that the modeled spectra are offset along the photon energy scale for better visibility (note also that the Lyα line corresponds to the emission of H-like state F ions and that the He series to the emission of He-like state F ions). a.u., arbitrary unit.

  • Fig. 3 Simulation of reduced x-ray emissivity from a young star due to local absorption in the shell.

    (A) Time-integrated x-ray emissivity maps (the color bar is in erg/s per grid cell) (23) postprocessed from the astrophysical simulation shown in Fig. 1D and looking along an axis perpendicular to the incident stream. (B) Same as (A) but taking into account the local absorption effect (see Materials and Methods). (C) The emitted spectrum, synthesized from the numerical model used for (A) and (B), in the energy range of the He-like O VII triplet and using the response function of the medium energy grating (MEG) of the Chandra satellite, with (red) and without (blue) the local absorption. Observation capabilities of maps such as (A) and (B) are unlikely, in contrast to spectra that can be directly compared with astrophysical data, such as the one shown in the inset of (C), which displays the spectrum from the CTTS TW Hydrae observed by MEG/Chandra (9). The unit of the ordinates of the inset is counts per bin.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/11/e1700982/DC1

    Supplementary Information

    section S1. Astrophysical accretion modeling using the PLUTO code

    section S2. Experimental diagnostics

    section S3. Comparative table of the laboratory and astrophysical plasma parameters

    section S4. Temporal animation of the 2D-resolved plasma electron density measurements of the magnetized accretion of the laboratory plasma at 20 T

    section S5. Temporal animation of the 2D-resolved density and temperature simulated maps of magnetized accretion dynamics in young stars

    section S6. Experimental observations in the case of a 6- or 30-T applied magnetic field

    section S7. Laboratory 3D MHD simulations using the GORGON code

    fig. S1. Sketch of the astrophysical simulation box.

    fig. S2. Radiative losses per unit EM for an optically thin plasma.

    fig. S3. Cartoon showing the top view of the central coil region of the experimental setup and the diagnostics paths.

    fig. S4. Shocked plasma density profiles as measured in the laboratory and simulated at the surface of a young star.

    fig. S5. Illustration of the step transition observed in the transmitted x-rays between the target and vacuum or an ablated plasma expanding toward vacuum.

    fig. S6. Results of the analysis of the x-ray radiographs.

    fig. S7. Spectral response of the combined streak camera and filter set system used in the SOP diagnostic.

    fig. S8. Best fit of the x-ray spectrum measured near the obstacle (PVC target, the stream being generated from a CF2 target) in the case of a magnetic field strength of B = 20 T and as obtained by the PrismSPECT code in steady-state mode for an electron temperature of 200 eV or 2.32 MK.

    fig. S9. Comparison of experimental spectra (in black) recorded near the obstacle target for the cases of 20 T (left, here the obstacle is a PVC target, whereas the stream is generated from a CF2 target) and 6 T (right, here the obstacle is an Al target, whereas the stream is still generated from a CF2 target) applied B field, together with simulations (in red) of the He-like line series obtained using a recombination plasma model.

    fig. S10. The spectrum measured for an applied magnetic field of 20 T (here, the obstacle is a PVC target, whereas the stream is generated from a CF2 target), in the range from 14.5 to 15.4 Å and containing the Lyα line and its dielectronic satellites.

    fig. S11. Laboratory observation of magnetized accretion dynamics using a 6-T strength for the applied magnetic field.

    fig. S12. Laboratory observation of magnetized accretion dynamics for various strengths of the applied magnetic field and using a larger distance between the stream-source target and the obstacle.

    fig. S13. 2D slices of the decimal logarithm of the electron density of the accretion shock region at three different times for a carbon plasma.

    fig. S14. 2D slices of ion and electron temperatures as well as plasma thermal beta at t = 22 ns (that is, 12 ns after the stream impacts the obstacle).

    table S1. Parameters for the MHD models of accretion impacts.

    table S2. Parameters of the laboratory accretion, with respect to the ones of the accretion stream in CTTSs for three distinct regions, namely, the incoming stream, the score, and the shell.

    table S3. Parameters, experimentally retrieved from the interferometry diagnostic, of the jet, shell, and core in the case of an applied magnetic field of 20 T.

    table S4. Parameters, experimentally retrieved from the interferometry diagnostic, of the jet, shell, and core in the case of an applied magnetic field of 6 T.

    movie S1. An animation of the accretion dynamics recorded as a function of time in the laboratory in the case of an applied 20-T magnetic field.

    movie S2. An animation of the accretion dynamics recorded as a function of time in the astrophysical simulation (case D5e10-B07 of table S1, that is, as for Fig. 1D of the main text).

    References (5782)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Information
    • section S1. Astrophysical accretion modeling using the PLUTO code
    • section S2. Experimental diagnostics
    • section S3. Comparative table of the laboratory and astrophysical plasma parameters
    • section S4. Temporal animation of the 2D-resolved plasma electron density measurements of the magnetized accretion of the laboratory plasma at 20 T
    • section S5. Temporal animation of the 2D-resolved density and temperature simulated maps of magnetized accretion dynamics in young stars
    • section S6. Experimental observations in the case of a 6- or 30-T applied magnetic field
    • section S7. Laboratory 3D MHD simulations using the GORGON code
    • fig. S1. Sketch of the astrophysical simulation box.
    • fig. S2. Radiative losses per unit EM for an optically thin plasma.
    • fig. S3. Cartoon showing the top view of the central coil region of the experimental setup and the diagnostics paths.
    • fig. S4. Shocked plasma density profiles as measured in the laboratory and simulated at the surface of a young star.
    • fig. S5. Illustration of the step transition observed in the transmitted x-rays between the target and vacuum or an ablated plasma expanding toward vacuum.
    • fig. S6. Results of the analysis of the x-ray radiographs.
    • fig. S7. Spectral response of the combined streak camera and filter set system used in the SOP diagnostic.
    • fig. S8. Best fit of the x-ray spectrum measured near the obstacle (PVC target, the stream being generated from a CF2 target) in the case of a magnetic field strength of B = 20 T and as obtained by the PrismSPECT code in steady-state mode for an electron temperature of 200 eV or 2.32 MK.
    • fig. S9. Comparison of experimental spectra (in black) recorded near the obstacle target for the cases of 20 T (left, here the obstacle is a PVC target, whereas the stream is generated from a CF2 target) and 6 T (right, here the obstacle is an Al target, whereas the stream is still generated from a CF2 target) applied B field, together with simulations (in red) of the He-like line series obtained using a recombination plasma model.
    • fig. S10. The spectrum measured for an applied magnetic field of 20 T (here, the obstacle is a PVC target, whereas the stream is generated from a CF2 target), in the range from 14.5 to 15.4 Å and containing the Lyα line and its dielectronic satellites.
    • fig. S11. Laboratory observation of magnetized accretion dynamics using a 6-T strength for the applied magnetic field.
    • fig. S12. Laboratory observation of magnetized accretion dynamics for various strengths of the applied magnetic field and using a larger distance between the stream-source target and the obstacle.
    • fig. S13. 2D slices of the decimal logarithm of the electron density of the accretion shock region at three different times for a carbon plasma.
    • fig. S14. 2D slices of ion and electron temperatures as well as plasma thermal beta at t = 22 ns (that is, 12 ns after the stream impacts the obstacle).
    • table S1. Parameters for the MHD models of accretion impacts.
    • table S2. Parameters of the laboratory accretion, with respect to the ones of the accretion stream in CTTSs for three distinct regions, namely, the incoming stream, the score, and the shell.
    • table S3. Parameters, experimentally retrieved from the interferometry diagnostic, of the jet, shell, and core in the case of an applied magnetic field of 20 T.
    • table S4. Parameters, experimentally retrieved from the interferometry diagnostic, of the jet, shell, and core in the case of an applied magnetic field of 6 T.
    • Legends for movies S1 and S2
    • References (57–82)

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1(.mp4 format). An animation of the accretion dynamics recorded as a function of time in the laboratory in the case of an applied 20-T magnetic field.
    • movie S2 (.mp4 format). An animation of the accretion dynamics recorded as a function of time in the astrophysical simulation (case D5e10-B07 of table S1, that is, as for Fig. 1D of the main text).

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