The DWARF project: VidojevicaVince Oliver, Astronomical observatory of Belgrade

Outline

* Will talk about the Serbian side of the DWARF project

The DWARF: “Definition”

• DWARF is an international project aimed at detection of circumbinary extrasolar planets using the timing of the minima of low-mass eclipsing binaries.

The DWARF: Recall

• In general, we can consider 2 types of binary-planet configurations:

S-type (planet orbit one star and Pbin>>Ppla) P-type (planet orbit both stars and Ppla>>Pbin)

P-type = circumbinary extrasolar planet (Kepler-16: Saturn-mas planet orbitin K+M dwarfs with P~229days)

The DWARF: Program stars• Starting sample of program stars consist 45 stars that

can be sorted into 3 groups:

(i) systems with K or/and M dwarf components (ii) systems with hot subdwarf (sdO or sdB) and K or

M dwarf components, (iii)post-common envelope systems with a white dwarf

(WD) component.

The DWARF: Program stars

Porbit < 5 days => to cover the minimaR=10-17mag => 20-200cm telescopes

The DWARF: Detection

In general, we have 3 principal techniques: (i) precise radial-velocity measurements to

detect the wobble of the binary mass center, (ii) Photometric detection of transits of the

planet(s) across the disks of the components of the inner binary, and

(iii) timing of the inner binary eclipse

BUTThe timing technique proved to be the best

for detecting circumbinary planets

• The timing technique = precisely measure of the exact instant of some well-defined and repeating feature of the binary light curve (e.g. minimum)

e.g. Kepler 16

The DWARF: Timing technique

The DWARF: MembersHuge network consisting of 37 institutes/observatories

18 countries1. Slovakia2. Germany3. Russia4. Ukraine5. Turkey6. Egipt7. Italy8. Croatia9. Greece10. Bulgaria11. Austria12. Korea13. Poland14. Romania15. Portugal16. Czech Republic17. Hungary18. Serbia

The DWARF: Teles/Instruments

• Telescope sizes: 20 – 200 cm.• Types: Cass, Schmidt-Cass, RC, few Newtons• FOV: 7’x7’ – 132’ x 132’

AOB: Serbian side of the DWARF project

• Project ”Stellar Physics” at the AOB participate in the DWARF project since may 2012

• People currently involved in the project: Dr Gojko Djurasevic Dr Istvan Vince Monika Jurkovic

Dr Oliver Vince

ASV: Equipment1. Observatory is on the Vidojevica mountain: 1150m2. 60cm telescope (Cass, Astro System Austria)3. ALTA Apogee U42 (2048x2048, 15’x15’ FOV, 0.46 “/pix)4. Optec filter wheel (Bessel filters: B V R I)

ASV: Controlling softwares

• Telescope control: Autoslew control. soft. (P. Keller)• Camera/filter control: MaxImDL imaging softw. • Dome control: DomeControl soft. (Nikola & Laza)

ASV: Observation• Automatized inVisual Basic Scripting language

Calibration module

Master frame

module

Pre-observation

module

Observation module

- Setup the accurate time-Waits the sunset (using TheShy6 planetary program)-Takes 5 FF frames with 5sec exposures in each band with highest S/N-Takes 10 dark frames with 5sec exposure for making master flat-Takes 10 bias frames for master bias-Takes 10 dark frames with 180sec exposure for scalable master dark

- Makes master bias, dark and flat frames

-Chose the object which has an observable minima on that day -Slew the telescope to the object-Checks the FOV and correct it if needed-Automatically finds the optimal exposure time for each filter

LOOP -Makes an exposure -Calibrates the images -Do photometry on the fly - corrects the exposure time if needed -Check RA, DEC and correct if there is a shiftNEXT

ASV: VBScript output

HAT-192-0001841Binary system: K+M dwarfsObserved in I bandWithout binningVmax = 14 magP ~ 0.31 daym ~ 0.6 mags~ 0.02 mag

So far we have minima of 3 objects:

1. HAT-192-0001841; Vmax=14; I band; texp=45s; S/N=254; no binning2. HS 2231+2441; Vmax=14; V band; texp=23s; S/N=79; with binning3. NSVS 14256825; Vmax=13.2; V band ; texp=23; S/N=180; with binning

Final reduction, calibration and photometry is performed in the IRAF package

This project is the first automatized project in Serbia astronomy

• Our experience shows that there are at least 3 negative effects for observation:

1. Shutter delay: affects the timing of the minima2. Shutter effect: affects the LC3. Non-linearity of the CCD : affects the LC

ASV: Our experience

ASV: Our experience

1. Shutter delay: is a result of finite time for shutter to START to open

e.g. ALTA Apogee E47 has 0.42 sec delaye.g. ALTA Apogee U42 has nearly 0 sec delay

Consequently: OBS-TIME written in the image header is not the true one

Opinion: Each DWARF member should test their CCD for this effect and correct it if needed

2. Shutter effect: is a result of a finite time for shutter to open and close – it is not instant event but it is a process

e.g. FF with 0.02s (still present for 3sec exposure time)When to wary?: FF frames are usually taken with 1-5 sec where

the effect is still severeConsequence: Calibration and photometry is incorrectOpinion: Small exposures should be avoided or to correct for

this effect

ASV: Our expirience

3. Non-linearity: for instance, if we want 0.01 photometric precision we need to be within 1% of the linarity range with both, Comp and Variable star

e.g. ALTA Apogee U42 is linear 3000-47000

ASV: Our experience

ASV: How can 1.5m telescope help in this project?

Theory: Expected precision of the minimum

ANt ~

Practice: We can calculate the recommended texpfor a given telescope, CCD, and star brightness combination in order to achieve the required precision

N-number of the sampling points; A-aperture size

ASV: How can 1.5m telescope help?

Our case: in order to achieve t < 1s, the program stars can be rawly divided into 4 groups:

30s, 60s, 120s, 240s

However: there are problematic cases: - faint stars producing small S/N - stars observed in I band (CCD is ~20% less sensitive then in V band)

Solution:- binning can help in some cases (faster readout, greater S/N)- Larger aperture (greater S/N, better sampling)

Conclusions

• Serbia became eligible to be a part of nice observational projects like DWARF with the 60cm telescope

• 1.5m telescope will improve the current position in the observation