Post on 18-Dec-2015
Detailed Plasma and Detailed Plasma and Fluorescence Diagnostics Fluorescence Diagnostics of aof a Stellar X-Ray FlareStellar X-Ray Flare
Paola Testa (1)
Fabio Reale(2), Jeremy Drake(3), Barbara Ercolano(3), David Huenemoerder(1), David Garcia-Alvarez(3,4)
1 MIT, 2 Universita’ di Palermo (Italy), 3 SAO, 4 Imperial College
July 11 2007 - CXC X-ray spectroscopy workshop
Rationale
• 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 emissionJuly 11 2007 - CXC X-ray spectroscopy workshop
HETGS observation of the G1 III giant HR 9024 Hertzsprung gap giant, 3M, 13R, peak Lx~1032ergs/s
Diagnostic Tools:
Comparison of results from the two independent analyses
Motivations:(see also Ayres et al 2007, Nordon & Behar 2006)
HETGS Spectrum
July 11 2007 - CXC X-ray spectroscopy workshop
HR 9024: Hertzsprung gap giant, 3M, 13R, peak Lx~1032ergs/s
Light curve and hardness ratio
July 11 2007 - CXC X-ray spectroscopy workshop
HR 9024: Hertzsprung gap giant, 3M, 13R, peak Lx~1032ergs/s
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
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:
1. start with an educated guess for the parameters
2. synthesize the HETG spectrum of the solution
3. repeat the analysis carried out on the observed spectrum and compare the same quantities
4. refine the model if needed
July 11 2007 - CXC X-ray spectroscopy workshop
MEG cts/sMEG cts/s TT
EMEM T vs. nT vs. n
Hydrodynamic Modeling
(Testa et al. 2007, ApJ, 663, 1232)
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
Hydrodynamic Modeling
July 11 2007 - CXC X-ray spectroscopy workshop
Cross-check of results:
• light curves in strong spectral features:
Fe XXV,
Si XIV, Mg XII
Hydrodynamic Modeling
July 11 2007 - CXC X-ray spectroscopy workshop(Testa et al. 2007, ApJ)
Cross-check of results:
• EM(T) (flare)
Hydrodynamic Modeling
July 11 2007 - CXC X-ray spectroscopy workshop(Testa et al. 2007, ApJ)
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%
Hydrodynamic Modeling
July 11 2007 - CXC X-ray spectroscopy workshop
Geometry Diagnostics from Fluorescence
July 11 2007 - CXC X-ray spectroscopy workshop
HEGHEG
In the HEG spectrum there is evidence of Fe K fluorescence (1.94Å, 6.4keV) that provides an independent diagnostic for the coronal geometry
Geometry Diagnostics from Fluorescence
July 11 2007 - CXC X-ray spectroscopy workshop
• 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
the fluorescence efficiency depends on (e.g., Bai 1979):
Geometry Diagnostics from Fluorescence
July 11 2007 - CXC X-ray spectroscopy workshop
Measured value (1)
Prediction from hd model
• the X-ray characteristics of HR9024 are typical of normal coronae but scaled up to the larger stellar radius
• HETGS allows 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 Fe XXV
• 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
Results
July 11 2007 - CXC X-ray spectroscopy workshop
Thank you!
July 11 2007 - CXC X-ray spectroscopy workshop
Hydrodynamic Modeling
Cross-check of results:
• light curves in strong spectral features:
Fe XXV, Si XIV, Mg XII
tt=0-10ks=0-10ks
tt=10-15ks=10-15ks
tt=15-30ks=15-30ks
tt=30-45ks=30-45ks
Hydrodynamic Modeling
Comparison of MEG observed spectrum with predictions of loop model
Hydrodynamic Modeling
Comparison of MEG observed spectrum with predictions of loop model
t=0-10kst=0-10ks
t=10-15kst=10-15ks
t=15-30kst=15-30ks
t=30-45kst=30-45ks
Hydrodynamic Modeling
Apex TApex T Apex nApex nee
Apex pApex p max vmax v
Hydrodynamic Modeling