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Surface features from high-precision photometry
Klaus G. Strassmeier , Leibniz-Institute for Astrophysics Potsdam (AIP)
in collaboration with Igor Savanov, Thomas Granzer and John Rice

1. The old game: data precision vs. model accuracy
2. Inversion tests with synthetic light-curves

3. Warm and cool ,,spots" from white light?
4. Differential rotation vs. spot changes and faculae

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


Photometry from Antarctica (Dome C): July 2007

25cm telescope 243 hours continuous @ 98%

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


-83C

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


1. The old game: precision vs. accuracy

· Ground-based automatic photoelectric telescopes (APTs) ext1-5 mmag (V0m-10m).

· CoRoT 0.25 mmag (10m-14m),

· KEPLER 0.03 mmag (10m) ­ 0.06 (12m) ­ 0.12 (14m)

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


The old game: data precision vs. model accuracy

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


17 years of BVI =5mmag photometry of HD208472 vs. 145 nights of CoRoT photometry with =0.24 mmag of CoRoT-6

HD208472 ­ APT: жzdarcan et al. 2010, AN 331, 794

CoRoT-6 ­ CoRoT: Lanza et al. 2010, A&A 525, A14

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


The old game: precision vs. accuracy

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


2. LC-tests: 10-20 single-rotation inversions

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


Single-rotation test-light-curve inversions
Phase=0 0.5 pole -on

V

f 20

Input

From Savanov & Strassmeier (2008): Data w/ (V)=5mmag, f=fractional surface area (0
10

As above but ,,peppered star" without concentrated spots.

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


More test inversions with V-band data but ... a) Tphot and Ts 250K
pot

lowered by

b) log g lowered by -0.5dex (3.5 instead of 4.0) c) Increased = 20 mmag (=5)
d) Inclination lowered by 15 (45 instead of 60). Shown with = 0 mmag ,,data". e) Vunspotted brighter by 0.2mag (6.8m instead of 7.0m)
K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


Reconstructions for V1355 Ori from V-band ... 1997 - 2007

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


... but also for different bandpasses

(V-I)(Prot) constrains Tphot Tspot
Real data: V-band

I-band

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


However, (V-I)0 may also be variable

HD123351: Strassmeier et al. (2011), A&A

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


A comparison with Doppler images: V1355 Ori Doppler images Light-curve images

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


A comparison with Doppler images: V1355 Ori Doppler images Light-curve images

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


A comparison with Doppler images: V889 Her
Observed Doppler image Forward light curve Reconstructed LC image

Jeffers et al. (2011), MNRAS 411, 1301

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


3. Warm and cool ,,spots" from white light?

Plages/faculae T=+1000K

Spots T=1000K

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


The Sun in photospheric and chromospheric light

Red light

Ca II H&K
Jones et al. (2008), SP 248, 323

Intensity images of the full-disk Sun (CSUN/SFO)

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


The Sun as a star: ACRIM data = bolometric
W illson R. C. (2003), www.acrim.com

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


The Sun as a star: reconstructions of P(rot) from spots
Strassmeier & Olah (2003), in 2nd Eddington workshop, ESA SP538

All data

Spot max

Spot min
Spot maximum Spot minimum

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


The cause: warm ,,spots"

· Do stellar plages or other ,,bright points" exist? And
V410Tau

· Solar plages have different lifetimes than sunspots.

· This demodulates a (white)light curve based on spot transits.
K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


4. Differential surface rotation Simulation

Strassmeier & Bopp (1992) A&A 259, 183
K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


Time series from the ground

HD 17433, K3-4 IV, P=16.4 days

Strassmeier & Bopp (1992)
K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


Differential rotation of Eri with MOST:





=0.11
Best two spot model fit with P = 11.35 & 11.55 d

Croll, Walker et al. (2006)
K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


CoRoT-6: differential rotation vs. ,,facular" component

=

Lanza et al. (2011)
K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


CoRoT-6: differential rotation vs. ,,facular" component

Q = 1.5: Q = 4: (Q
Sun





= 0.12 ± 0.02 = 0.09 ± 0.02

= 9)

Lanza et al. (2011)
K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012


Summary and conclusions

K. G. Strassmeier, Surface features from high-precision photometry., IAU GA2012, Special Session 13, August, 2012