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University of Groningen

Constraining the stellar energetic particle flux in young solar-like stars

Rab, Ch.; Padovani, M.; Güdel, M.; Kamp, I.; Thi, W.-F.; Woitke, P.

Published in:

Origins: From the Protosun to the First Steps of Life. Proceedings of the International Astronomical Union

DOI:

10.1017/S174392131900156X

IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below.

Document Version

Final author's version (accepted by publisher, after peer review)

Publication date: 2020

Link to publication in University of Groningen/UMCG research database

Citation for published version (APA):

Rab, C., Padovani, M., Güdel, M., Kamp, I., Thi, W-F., & Woitke, P. (2020). Constraining the stellar energetic particle flux in young solar-like stars. In Origins: From the Protosun to the First Steps of Life. Proceedings of the International Astronomical Union: From the Protosun to the First Steps of Life. Proceedings of the International Astronomical Union (Vol. 345, pp. 310-311). (Proceedings of the International Astronomical Union; Vol. 14). Cambridge University Press.

https://doi.org/10.1017/S174392131900156X

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arXiv:1902.00914v1 [astro-ph.SR] 3 Feb 2019

Origins: from the Protosun to the First Steps of Life Proceedings IAU Symposium No. 345, 2019

Bruce G. Elmegreen, L. Viktor T´oth, Manuel G¨udel, eds.

c

2019 International Astronomical Union DOI: 00.0000/X000000000000000X

Constraining the stellar energetic particle

flux in young solar-like stars

Rab Ch.

1

and Padovani M.

2

and G¨

udel M.

3

and Kamp I.

1

and

Thi W-F.

4

and Woitke P.

5

1

Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen, The Netherlands, email: rab@astro.rug.nl

2

University of Vienna, Dept. of Astrophysics, T¨urkenschanzstr. 17, 1180 Wien, Austria

3INAF-Ossevatorio Astrofisico di Arcetri, Largo E. Fermi, 5 - 50125 Firenze, Italy 4

MPE, Giessenbachstrasse 1, 85748 Garching, Germany

SUPA, School of Physics & Astronomy, University of St. Andrews, St. Andrews KY16 9SS, UK

Abstract.Anomalies in the abundance measurements of short lived radionuclides in meteorites indicate that the protosolar nebulae was irradiated by a large number of energetic particles (E & 10 MeV), often called solar cosmic rays. The particle flux of the contemporary Sun cannot explain these anomalies, but, similar to T Tauri stars, the young Sun was more active and proba-bly produced enough high energy particles. However, the stellar particle (SP) flux of young stars is essentially unknown. We model the impact of high-energy ionization sources on the chemistry of the circumstellar environment (disks and envelopes). The model includes X-ray radiative transfer and makes use of particle transport models to calculate the individual molecular hydro-gen ionization rates. We study the impact on the chemistry via the ionization tracers HCO+

and N2H+. We argue that spatially resolved observations of those molecules combined with detailed

models allow for disentangling the contribution of the individual high-energy ionization sources and to put constraints on the SP flux in young stars.

Keywords.stars: pre–main-sequence, (stars:) circumstellar matter, stars: activity, astrochem-istry, radiative transfer, methods: numerical

1. Introduction & Methods

Our Sun can accelerate particles to energies similar to galactic cosmic rays (E & 10 MeV), hence this stellar energetic particles (SP) are also called solar cosmic rays. Abundance measurements of short-lived radionuclides in meteorites indicate that the protosolar

neb-ulae experienced an about 105

times higher SP flux than the Sun produces nowadays (see e.g. Feigelson et al. 2002, Gounelle et al. 2006). Similar to T Tauri stars (young so-lar analogues) the young Sun was likely more active and was probably able to produce the SP flux required to explain the abundance anomalies measured in meteorites. This scenario is also supported by the observed high X-ray luminosities of T Tauri stars

(G¨udel et al. 2007). However, contrary to X-rays, the SP flux in T Tauri stars cannot be

directly measured, and is not well constrained.

We present 2D radiation-thermo chemical models to study the impact of SPs on the

ionization structure of the circumstellar environment. We use PRODIMO

(PROtoplan-etary DIsk MOdel, Woitke et al. 2009, Kamp et al. 2017) to calculate the temperature structure, chemical abundances and to produce synthetic observables. We include the

main H2ionization sources: X-rays, galactic cosmic-rays (CR) and SPs. To calculate the

H2 ionization rate we use X-ray radiative transfer (Rab et al. 2018) and make use of

particle transport models (Padovani et al. 2009). This allows us to study the individual 1

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2 Ch. Rab et al.

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ISM CR+X-rays

N2H+hole N 2H+peak

stellar particles

Figure 1.Synthetic N2H+J= 3 − 2 integrated intensity maps for an envelope model (Class

0/I) without SP irradiation (left panel) and the same model with SPs (right panel).

contributions of the ionization agents to the total ionization rate and on the chemistry

of observable molecules such as HCO+

and N2H+.

2. Results & Conclusions

In Rab et al. (2017), we show that SPs can be the dominant H2 ionization source in

the upper layers of a protoplanetary disk. Differently to X-rays and CRs, SPs cannot penetrate down to the midplane as they originate close to the star and are not scattered

towards the midplane. With observations of two molecules, HCO+, which traces the upper

disk layers and N2H+, which traces deeper layers of the disk, it is therefore possible to

measure the impact of SPs and to constrain the SP flux in young stars.

Herschel observations of Ceccarelli et al. (2014) for the deeply embedded Class 0

pro-tostar OMC-2 FIR 4 show very low HCO+/N

2H+ line ratios. They explained their

ob-servations with a strongly elevated H2 ionization rate of 10−14− 10−12s−1, produced

by a high flux of SPs. We used the same approach as for our disk models but now for an envelope structure (see Rab et al. 2017a for details) to simulate the conditions for embedded sources. We find that indeed a high SP flux is required to reproduce the low

HCO+

/N2H+ ratios observed by Ceccarelli et al. (2014). In Fig. 1, we present ALMA

simulations for this model showing that spatially resolved N2H+ observations should

clearly show the signatures of SP ionization in embedded sources. We plan to also in-clude different particle transport methods in our model (e.g. Rodgers-Lee et al. 2017) to test if they produce yet other observable signatures.

References

Ceccarelli, C., Dominik, C., L´opez-Sepulcre, A., Kama, M. et al. 2014, ApJ (Letters), 790, L1 Feigelson, E. D., Garmire, G. P., Pravdo, S. H. 2002, ApJ, 572, 335-349

Gounelle, M., Shu, F. H., Shang, H., Glassgold, A. E. et al. 2006, ApJ, 640, 1163-1170 G¨udel, M., Briggs, K. R., Arzner, K., Audard, M., Bouvier, J. et al. 2007, A&A, 468, 353-377 Kamp, I., Thi, W.-F., Woitke, P., Rab, C., Bouma, S., M´enard, F. 2017, A&A, 607, A41 Padovani, M., Galli, D. & Glassgold, A. E. 2009, A&A, 501, 619-631

Rab, Ch., Elbakyan, V., Vorobyov, E., G¨udel, M., Dionatos, O. et al. 2017a, A&A, 604, A15 Rab, Ch., G¨udel, M., Padovani, M., Kamp, I., Thi, W.-F. et al. 2017, A&A, 603, A96 Rab, Ch., G¨udel, M., Woitke, P., Kamp, I., Thi, W.-F., Min, M. et al. 2018, A&A, 609, A91 Rodgers-Lee, D., Taylor, A. M., Ray, T. P., Downes, T. P. 2017, MNRAS, 472, 26-38 Woitke, P., Kamp, I., & Thi, W.-F. 2009, A&A, 501, 383

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