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Introduction Stellar flares Summary X-RAYING THE STELLAR CORONAE Lalitha Sairam Tata Institute of Fundamental Research 06 February 2014 1

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Page 1: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

X-RAYING THE STELLAR CORONAE

Lalitha SairamTata Institute of Fundamental Research

06 February 2014

1

Page 2: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

X-rays across the HR diagram

-0.5 0.0 0.5 1.0 1.5 2.0B-V Colour

20

15

10

5

0

-5

-10

Ab

solu

te M

agn

itu

de

BSC/Gliese detections

2

Page 3: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

Flaring star – Algol

• System – short period eclipsing binary

• B-type star – lack surface convective envelope

• Magnetically active secondary – major flares

3

Page 4: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

General picture

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Coronal loop

Acceleration

Coronal X−ray source

Precipitating electrons

Evaporation

Flare footpoint

4

Page 5: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

Temporal variation

Hudson et al. (1998)

FSXR ∝

∫FHXR(t)dt

or

d

dtFSXR(t) ∝ FHXR(t)

5

Page 6: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

Temporal variation

Proxima Centauri

6.1 6.2 6.3 6.4 6.5Time (h since MJD 54904)

-2

0

2

4

6

Sca

led

flu

x

EPIC LC derivativeEPIC LCUVES-B LC

AB Doradus A

2.6 2.8 3.0 3.2 3.4 3.6Time (h since MJD 55160)

-2

0

2

4

6

Sca

led

flu

x

EPIC LC derivativeEPIC LCUVES continuum LC

6

Page 7: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

Algol as observed with SXT

Quiescence

1Energy [keV]

0.0001

0.0010

0.0100

0.1000

1.0000

10.0000

Co

un

ts/s

/keV

Flare

1Energy [keV]

0.01

0.10

1.00

10.00

100.00

Co

un

ts/s

/keV

7

Page 8: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

Abundance variation – Fe K complex

5.5 6.0 6.5 7.0 7.5Energy [keV]

0.001

0.010

0.100

1.000

10.000

Co

un

ts/s

/keV

8

Page 9: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

Abundance variation – Fe K complex

5.5 6.0 6.5 7.0 7.5Energy [keV]

0.001

0.010

0.100

1.000

10.000

Co

un

ts/s

/keV

9

Page 10: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

Abundance variation – Fe K complex

5.5 6.0 6.5 7.0 7.5Energy [keV]

0.001

0.010

0.100

1.000

10.000

Co

un

ts/s

/keV

10

Page 11: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

Abundance variation – Fe K complex

5.5 6.0 6.5 7.0 7.5Energy [keV]

0.001

0.010

0.100

1.000

10.000

Co

un

ts/s

/keV

11

Page 12: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

Abundance variation – Fe K complex

5.5 6.0 6.5 7.0 7.5Energy [keV]

0.001

0.010

0.100

1.000

10.000

Co

un

ts/s

/keV

12

Page 13: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

Abundance pattern

• Sun, inactive or low activity level stars - a normal FIPeffect - elements with a low first ionization potential (FIP)are enhanced in the corona

• Active stars - inverse FIP effect - enhanced high-FIPelements and depleted low-FIP elements

5 10 15 20 25FIP[eV]

0

1

2

3

4

Ab

un

da

nc

e r

ela

tiv

e t

o s

ola

r

MgFeSi S C O N Ar Ne

AB Doradus A

Proxima Centauri

13

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Introduction Stellar flares Summary

Flare energy distribution

Parker model - nanoflare for the Sun – < 1027 erg

N(> E) =∫∞

E

dN

dEdE = KE−α+1

• In Solar context

→ α = 1.5− 1.6 for a normal flare (Crosby et al. 1993)

→ α = 2.3− 2.6 for small events in the quiescent corona

(Krucker et al. 1998)

• Solar analogs:

→ α = 2.2 for solar analogs EK Dra and 47 Cas

(Audard et al. 1999)

• M dwarfs:

→ α = 1.6 for X-ray flares using EXOSAT observations

(Collura et al. 1988)

14

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Introduction Stellar flares Summary

Flare energy distribution

1033 1034

E [erg]

10-36

Rat

e [e

rg-1 y

ear-1

]

N (> E) ~ E - 1.93 +/- 0.06

15

Page 16: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

Summary

• overall picture of the atmosphere from the chromosphere tothe corona - the X-ray and optical/UV light curves ofactive low mass stars during the flare onset

• abundances, emission measures, and temperatures of flaringplasma

• short term energy release and their role in heating of theatmosphere of active stars.

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Page 17: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

Appendix

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Introduction Stellar flares Summary

X-raying stellar coronae with SXT

2T XSPEC model + APEC

• Case 1 – Bright coronal X-ray source

• Case 2 – RS CVn and dMe

• Case 3 – Sun-like stars

• Case 4 – Late-type stars

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Page 19: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

Case 1 – Bright coronal X-ray source

1Energy [keV]

0.0001

0.0010

0.0100

0.1000

1.0000

10.0000

Co

un

ts/s

/keV

Fx=1×10−10 ergs cm−2 s−1, nH=6×1018 cm−2

T1=0.6 keV, T2=2.5 keV, EM2=2EM1

Exposure – 10 ks19

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Introduction Stellar flares Summary

Case 2 – RS CVn and dMe

1Energy [keV]

10-5

10-4

10-3

10-2

10-1

100

Co

un

ts/s

/keV

Fx=1×10−11 ergs cm−2 s−1, nH=1×1019 cm−2

T1=0.5 keV, T2=2.0 keV, EM2=EM1

Exposure – 20 ks20

Page 21: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

Case 3 – Sun-like stars

1Energy [keV]

0.0001

0.0010

0.0100

0.1000C

ou

nts

/s/k

eV

Fx=1×10−12 ergs cm−2 s−1, nH=1×1019 cm−2

T1=0.5 keV, T2=2.0 keV, EM2=EM1

Exposure – 50 ks21

Page 22: X-raying the stellar coronaeastrosat.iucaa.in/~astrosat/Astrosat_BaselineScienceMeeting_6-7Fe… · Introduction Stellar flares Summary X-rays across the HR diagram-0.5 0.0 0.5 1.0

Introduction Stellar flares Summary

Case 4 – Late-type stars

1Energy [keV]

10-5

10-4

10-3

10-2

Co

un

ts/s

/keV

Fx=1×10−13 ergs cm−2 s−1, nH=3×1019 cm−2

T1=0.5 keV, T2=2.0 keV, EM2=EM1

Exposure – 100 ks22

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Introduction Stellar flares Summary

Temperature and emission measure variation

0 2 4 6 8 10 12 14Time bin

0

2

4

6

8

10

12

14

T [

keV

]

0 2 4 6 8 10 12 14Time bin

0

5

10

15

EM

[10

54 c

m-3]

23