The Dwarf project: Eclipsing binaries - precise clocks to discover exoplanets

1. The Dwarf project: Eclipsing binaries - precise clocks to discover exoplanets Theodor Pribulla Astronomical Institute of the Slovak Academy of Sciences, Tatranská Lomnica, Slovakia Science with meter-class telescopes, September 18-21, 2012, Belgrade, Serbia

2. Circum-binary exoplanets =planets simultaneously orbiting both stars (mass center) of a binary, the planetary orbital period is much longer than that of the binary... • Detection techniques to detect circum-binary exoplanets are: • (i) RV measurements to detect the wobble of the binary center - problem with close binaries: component spin-up • (ii) photometric detection of transit(s) of the planet(s) across the disk of the inner binary: requires satellite photometry - Kepler, CoRoT, MOST • (iii) timing of the inner binary eclipses

4. Timing technique • LITE - timing of pulses, eclipses or pulsations • timing variations of eclipses of the binary system orbited by a substellar body due to the finite velocity of light • enables determination of the orbital parameters similar to spectroscopic elements • sensitive to long-period objects • the exoplanet encyclopedia lists (as of September 15, 2012) 14 planetary systems (16 planets/4 multiple planetary systems) detected by timing.

5. V471 Tau • Post-common-envelope system containing a WD and a MS late-type dwarf • enables very precise timing because of short ingress and egress durations. ...a BD companion with M3 = 0.045 ± 0.015 MSun and P3 = 33.4 yr (Kaminski et al. 2007)

6. HW Vir • two-planet system orbiting the short-period sdB + M dwarf • HW Vir b: Mb = 19.2±0.2 MJ and HW Vir c: MC = 8.5±0.4 MJ (Lee et al. 2009)

7. Object “rating” Chances to discover a circum-binary substellar body depend mostly on 3 factors: • (i) precision and number of minima • (ii) semi-amplitude of the LITE caused by the body • (iii) intrinsic variability of the binary

8. Precision of a triangular minimum timing • It can be shown (Pribulla et al., 2012, AN, in press) that: • where Fλ is number of photons from a mλ = 0 star per square meter and second outside Earth atmosphere, d is the depth and D duration of the minimum, A diameter of the telescope, X is airmass, kl the extinction coefficient and t (0, 1) throughput of the system

9. LITE amplitude • The full amplitude DT (Max-Min, or peak-to-peak) of expected LITE caused by another body orbiting a binary with edge-on orbit is: • The total mass of the under-lying binary is important: having 8 times more massive inner binary decreases the LITE amplitude four times. • DT=4-8 seconds for our sample of stars and a Jupiter-mass planet on a 10-years orbit

10. Intrinsic variability of the binary star • Spots and flares in the late-type K or M dwarfs: The advantage of low-mass binaries is offset by their surface activity • pulsations in sdB stars • Applegate's (1992) mechanism: spurious cyclic variability DK CVn, Terrell et al., 2005, IBVS 5642

11. Suitable types of objects The following three groups of objects with sharp minima were included: • (i) systems with K or/and M dwarf components • (ii) systems with a hot subdwarf (sdB or sdO) and K or M dwarf component • (iii) post-common-envelope systems with a white dwarf (WD) component

12. Important issues... • Red noise: LCs are affected (at the 0.01 mag level) by the red noise (atmosphere transparency changes, lack of auto-guiding in some of the telescopes) and the second-order extinction) - PCA approach by Tamuz, Mazeh & Zucker (2005) ? • Inhomogeneity of data: the CCD frames will be obtained at several observatories with different setups • Exact time: shutter delay, time reference UTC ==> BJD in TDB, at least 1 sec accuracy • flux-weighted time of exposure ?

13. Accurate minimum timing: fitting LC by itself • advantages: (1) timing from any non-constant part of LC (2) LC itself is the best fitting template (3) possibility to include systematic trends and scaling differences in the data (e.g., because of the filter transparencies) • A simple fitting function can be: • where T(x) is the template LC and A,B,C,D coefficients allow vertical and horizontal shift, trend and vertical scaling

14. Project strategy & philosophy • involving large number of instruments (now 40+) • selecting several dozens of most promising targets • involving amateur observers to survey preliminary list of objects (from NSVS, HAT, KIC, ASAS etc.) • follow-up of interesting objects with 2m-class telescopes • 5-10 years duration

15. Observing network 40+ instruments at 33 observatories mostly in Europe, 20-200cm diameters

16. A sample of LC obtained at the Stará Lesná observatory

17. Additional science • study of spot cycles in the RS CVn-like late-type stars binaries, detection of flares • detection of new low-mass EBs crucial to better define the empirical lower main sequence: determination of absolute parameters of the components • detection of WD and sdB/sdO • detection of of eclipsing binaries with pulsating components • detection of new variables • ...

18. Conlusions • The chances to detect circum-binary bodies depend several factors - brightness, duration and depth of minima, mass of the binary, its intrinsic noise • circum-binary planets down to the Jupiter mass orbiting on a 10-year orbits with meter-class telescopes can be detected • More info at: http://www.ta3.sk/~pribulla/Dwarfs/ http://astronomy.science.upjs.sk/projectdwarf/

19. Thank You !