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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

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=planets simultaneously orbiting both stars (mass center) of a binary, the planetary orbital period is much longer than that of the binary...

Circum-binary exoplanets

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

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✷ 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.

Timing technique

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✷ Post-common-envelope system containing a WD and a MS late-type dwarf

✷ enables very precise timing because of short ingress and egress durations.

V471 Tau

...a BD companion with M3 = 0.045 ± 0.015 MSun and P3 = 33.4 yr (Kaminski et al. 2007)

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✷ 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)

HW Vir

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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

Object “rating”

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✷ It can be shown (Pribulla et al., 2012, AN, in press) that:

Precision of a triangular minimum timing

✷ 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, λthe extinction coefficient and (0, 1) throughput of the system

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✷ The full amplitude T (Max-Min, or peak-to-peak) of expected LITE caused by another body orbiting a binary with edge-on orbit is:

LITE amplitude

✷ The total mass of the under-lying binary is important: having 8 times more massive inner binary decreases the LITE amplitude four times.

✷ T=4-8 seconds for our sample of stars and a Jupiter-mass planet on a 10-years orbit

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✷ 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

Intrinsic variability of the binary star

DK CVn, Terrell et al., 2005, IBVS 5642

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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

Suitable types of objects

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✷ 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 ?

Important issues...

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✷ 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:

Accurate minimum timing: fitting LC by itself

✷ where T(x) is the template LC and A,B,C,D coefficients allow vertical and horizontal shift, trend and vertical scaling

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✷ 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

Project strategy & philosophy

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Observing network

40+ instruments at 33 observatories mostly in Europe, 20-200cm diameters

16A sample of LC obtained at the Stará Lesná observatory

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✷ 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✷ ...

Additional science

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✷ 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/

Conlusions

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Thank You !