Detailed Plasma and Fluorescence Diagnostics of a Stellar X-Ray Flare

1. Detailed Plasma and Fluorescence Diagnostics of aStellar X-Ray Flare Paola Testa(1) Fabio Reale(2), Jeremy Drake(3), Barbara Ercolano(3), David Huenemoerder(1), David Garcia-Alvarez(3,4) 1MIT, 2Universita’ di Palermo (Italy),3SAO, 4 Imperial College July 11 2007 - CXC X-ray spectroscopy workshop

2. Rationale HETGS observation of the G1 III giant HR 9024 Hertzsprung gap giant,3M, 13R, peak Lx~1032ergs/s (see also Ayres et al 2007, Nordon & Behar 2006) Motivations: • X-ray activity in evolved intermediate mass stars • Coronal structuring • Physics of stellar flares • Plasma diagnostics, and geometry diagnostics: • hydrodynamic loop modeling (Testa et al. 2007, ApJ, 663) • fluorescence emission Diagnostic Tools: Comparison of results from the two independent analyses July 11 2007 - CXC X-ray spectroscopy workshop

3. HETGS Spectrum HR 9024:Hertzsprung gap giant,3M, 13R, peak Lx~1032ergs/s July 11 2007 - CXC X-ray spectroscopy workshop

4. Light curve and hardness ratio HR 9024:Hertzsprung gap giant,3M, 13R, peak Lx~1032ergs/s July 11 2007 - CXC X-ray spectroscopy workshop

5. X-ray activity of intermediate-mass giants • HR 9024: Hertzsprung gap giant,3M, 13R, Lx~1032ergs/s • Evolved intermediate mass star: what are the characteristics of the X-ray production mechanisms? How is the corona structured (typical size, filling factors, …)? (e.g., Ayres et al. 1998, Ayres et al. 2007) • These giants are thought to develop a dynamo when they enter the convective region of the H-R diagram, also given their typical fast rotation in MS (when they are non-coronal late-B/early-A dwarfs) • Variability: flares are very unusual in these massive evolved giants July 11 2007 - CXC X-ray spectroscopy workshop

6. Hydrodynamic Modeling • For the hydrodynamic modeling we use information mainly from the continuum that is strong, and it probes the hot flaring plasma: • we derive T and EM by fitting the continuum in line-free regions (according to both APED and CHIANTI) • Loop Model: • start with an educated guess for the parameters • synthesize the HETG spectrum of the solution • repeat the analysis carried out on the observed spectrum and compare the same quantities • refine the model if needed July 11 2007 - CXC X-ray spectroscopy workshop

7. Hydrodynamic Modeling MEG cts/s T T vs. n EM • (Testa et al. 2007, ApJ, 663, 1232)

8. Hydrodynamic Modeling • Model parameters: • loop semi-length L = 5· 1011 cm • ~R/2, as in normal coronae • cross-section radius r ~ 4.5· 1010 cm, i.e. aspect ratio r/L~0.1 as in typical solar loops • impulsive heating (15 ks; starting 8 ks before the beginning of the observation) at the footpoints; volumetric heating ~ 4 erg/cm3/s, heating rate ~ 1033 erg/s July 11 2007 - CXC X-ray spectroscopy workshop

9. Hydrodynamic Modeling • Cross-check of results: • light curves in strong spectral features: • Fe XXV, • Si XIV, • Mg XII • (Testa et al. 2007, ApJ) July 11 2007 - CXC X-ray spectroscopy workshop

10. Hydrodynamic Modeling • Cross-check of results: • EM(T) • (flare) • (Testa et al. 2007, ApJ) July 11 2007 - CXC X-ray spectroscopy workshop

11. Hydrodynamic Modeling • Cross-check of results: • cross-section radius - we derive estimates from the normalization of different light curves: • (a) integrated MEG counts (r ~ 4.9· 1010 cm), • (b) EM from continuum (r ~ 4.3 · 1010 cm), • (c) single spectral features (r ~ 4.8 · 1010 cm); • they all agree with each other within a 15% July 11 2007 - CXC X-ray spectroscopy workshop

12. Geometry Diagnostics from Fluorescence In the HEG spectrum there is evidence of Fe K fluorescence (1.94Å, 6.4keV) that provides an independent diagnostic for the coronal geometry HEG July 11 2007 - CXC X-ray spectroscopy workshop

13. Geometry Diagnostics from Fluorescence • the fluorescence efficiency depends on (e.g., Bai 1979): • the solid angle subtended by the cold material as seen by the X-ray source h • the inclination angle at which the reflecting surface is viewed by the observer  • the Fe abundance of the cold material July 11 2007 - CXC X-ray spectroscopy workshop

14. Measured value (1) Prediction from hd model Geometry Diagnostics from Fluorescence July 11 2007 - CXC X-ray spectroscopy workshop

15. Results • the X-ray characteristics of HR9024 are typical of normal coronae but scaled up to the larger stellar radius • HETGSallows for the first time to test HD models predictions for single spectral features: we find very good agreement at least for the hottest feature of FeXXV • the HEG spectrum shows evidence of Fe K fluorescence emission, and its analysis provides an independent check of the results of the hydrodynamic modeling: • the fluorescence efficiency predicted from the HD model is in agreement with the observed one within the uncertainties July 11 2007 - CXC X-ray spectroscopy workshop

16. Thank you! July 11 2007 - CXC X-ray spectroscopy workshop

17. Hydrodynamic Modeling • Cross-check of results: • light curves in strong spectral features: • Fe XXV,Si XIV, Mg XII

18. Hydrodynamic Modeling t=0-10ks Comparison of MEG observed spectrum with predictions of loop model t=10-15ks t=15-30ks t=30-45ks

19. Hydrodynamic Modeling t=0-10ks Comparison of MEG observed spectrum with predictions of loop model t=10-15ks t=15-30ks t=30-45ks

20. Hydrodynamic Modeling Apex T Apex ne max v Apex p

21. Hydrodynamic Modeling