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Detailed Plasma and Fluorescence Diagnostics of a Stellar 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.

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detailed plasma and fluorescence diagnostics of a stellar x ray flare

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

slide2

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

slide3

HETGS Spectrum

HR 9024:Hertzsprung gap giant,3M, 13R, peak Lx~1032ergs/s

July 11 2007 - CXC X-ray spectroscopy workshop

slide4

Light curve and hardness ratio

HR 9024:Hertzsprung gap giant,3M, 13R, peak Lx~1032ergs/s

July 11 2007 - CXC X-ray spectroscopy workshop

slide5

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

slide6

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

slide7

Hydrodynamic Modeling

MEG cts/s

T

T vs. n

EM

  • (Testa et al. 2007, ApJ, 663, 1232)
slide8

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

slide9

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

slide10

Hydrodynamic Modeling

  • Cross-check of results:
  • EM(T)
  • (flare)
  • (Testa et al. 2007, ApJ)

July 11 2007 - CXC X-ray spectroscopy workshop

slide11

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

slide12

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

slide13

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

slide14

Measured value (1)

Prediction from hd model

Geometry Diagnostics from Fluorescence

July 11 2007 - CXC X-ray spectroscopy workshop

slide15

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

slide16

Thank you!

July 11 2007 - CXC X-ray spectroscopy workshop

slide17

Hydrodynamic Modeling

  • Cross-check of results:
  • light curves in strong spectral features:
  • Fe XXV,Si XIV, Mg XII
slide18

Hydrodynamic Modeling

t=0-10ks

Comparison of MEG observed spectrum with predictions of loop model

t=10-15ks

t=15-30ks

t=30-45ks

slide19

Hydrodynamic Modeling

t=0-10ks

Comparison of MEG observed spectrum with predictions of loop model

t=10-15ks

t=15-30ks

t=30-45ks

slide20

Hydrodynamic Modeling

Apex T

Apex ne

max v

Apex p