PHOTOMETRY OF SYNCHRONOUS BINARY ASTEROID (8474) RETTIG IN 2015

1. PHOTOMETRY OF SYNCHRONOUS BINARY ASTEROID(8474) RETTIG IN 2015 V. G. Chiorny1, Yu. N. Krugly1, V. Benishek2, P. Pravec3, P. Kusnirak3, A. Galad3, J. Oye4, R. Groom4 V. Reddy5, D. Pray6, W. Cooney7, J. Gross7, R. Inasaridze8, V. Aivazyan8, V. Zhuzhunadze8, D. Terrell9, R. Montaigut10, A. Leroy10, I. Molotov11 1 Institute of Astronomy of Kharkiv National University , Sumska Str. 35, Kharkiv 61022, Ukraine 2 Belgrade Astronomical Observatory, Volgina 7, 11060 Belgrade 38, Serbia 3 Astronomical Institute, Academy of Sciences of the Czech Republic, Fricova 1, CZ-25165 Ondrejov, Czech Republic 4 Blue Mountains Observatory, Leura, NSW, Australia 5 Planetary Science Institute, Tucson, AZ 85719, USA 6 Sugarloaf Mountain Observatory, South Deerfield, MA 01373, USA 7 Sonoita Research Observatory, 77 Paint Trail, Sonoita, AZ 85637, USA 8 Kharadze Abastumani Astrophysical Observatory, Ilia State University, G. Tsereteli str. 3, Tbilisi 0162, Georgia 9 Department of Space Studies, Southwest Research Institute, Boulder, CO 80302, USA 10 OPERA Observatory, 33820 Saint Palais, France 11 Keldysh Institute of Applied Mathematics, Russian Academy of Sciences, Miusskaya sq. 4, Moscow 125047, Russia The 4th Workshop on Binaries in the Solar System Prague, Czech Republic 2016 June 21-23

2. Synchronous binary asteroids Both components are approximately equal size D2/ D1 = 0.8 1.0 synchronous rotationP1 = P2 = Porb Currently knows 14 similar objects : The biggest: (90) Antiope (MBA) D1 ~ D2 ~ 80 km (Merline W.J. et al., 2000) (617) Patroclus (Trojan)D1 ~ D2 = 120 km(Merline W.J. et al., 2001) The smallest: (69230) Hermes (NEA) D1 ~ D2 ~ 0.6 km(Margot J.-L. et al., 2003; Pravec P. et al.,2003) The small main-beltasteroids(MBA)withD1 ,D2 <13 km - 11syncronous pairs (809) Lundia(Kryszczynska A. et al., 2005) ;(1139) Atami(Manzini F. et al., 2006); (854) Frostia, (1089) Tama, (1313) Berna, (4492) Debussy(Behrend R. et al, 2006); (3905) Doppler(Franco L. et al., 2013) The Photometric Survey of Asynchronous Binary Asteroids(Pravec P., 2005) : (4951) Iwamoto(Reddy V. et al., 2007); (2478) Tokai(Higgins D. et al, 2007); (7369) Gavrilin(Higgins D. et al, 2008);(8474) Rettig(Chiorny V. et al., 2015)

3. Photometry of (8474) Rettig in 2015 Main-belt asteroid (8474) Rettig Orbital elements: Observational circumstances: a = 2.2245 AU 2015, May 18.8 – July 23.9 i = 5.9109 deg Phase angles - 7.0– 29.0 deg e = 0.1717 Visual magnitude - 15.3m – 16.6m

4. Kharkiv Observatory (Ukraine)(founded in 1883) Location : 36.94° E ; 49.62° N: Observatory code - 121 CCD camera ML 8300 (FLI) 0.7 –meter reflector telescope Pixels –3326 x 2404 Pixel size – 5.4 mm Sensor size – 17.9 x 13.5 mm Sensor Quantum Efficiency ~ 55 % The field of view – 21.5' x 16.2 ' Newtonian fokus (f/4) Filterwheel CFW-1 (FLI) - VR (BI) – filters of the standard Jonson-Cousins photometric system

5. Photometry of (8474) Rettig in 2015 Synchronous rotations of the components with the orbital period Porb = 30.54 hours Amplitude of the combined primery and secondary rotational lihtcurve A1 + A2 = 0.34 mag at solar phases from 7 to 15 degrees (809) Lundia in 2005 Deep mutual eclipse/occultation eventsm = 0.60 – 0.93mag m = 2.5 log (1 + k2) k = D2/ D1 The ratio of mean diameters D2/D1 ≥ 0.86 (Kryszczynska A. et al., 2009)

6. Photometry of (8474) Rettig in 2015 Standardization of photometric observations in the V and R-filters The measured color index V – R = 0.52± 0.02 The estimated mean absolute magnitude HR = 13.55 ± 0.06 HV = 14.07 ± 0.07 Log D(km) = 3.1235 – 0.2HV – 0.5 *Log(pV) pV = 0.20 for S-type (Warner et al., 2009) D= D1(1 + k2)1/2 k = D2/ D1 The estimated mean diameters of components D1= 3.5 ± 0.9 km D2= 3.0 ± 0.8 km

7. The parameters of the small main-belt synchronous binary asteroids (Kryszczynska A. et al., 2005) (Behrend R. et al, 2006) (Manzini F. et al., 2006) (Reddy V. et al., 2007) (Higgins D. et al, 2007) (Higgins D. et al, 2008) (Franco L. et al., 2013) (Chiorny V. et al., 2015) D1 and D2 from (Warner B. et al., 2009) , updated 2016

8. Summary Photometry of small main-belt asteroid (8474) Rettig – synchronous bynary system: 2015, May 18. 8795 UT – July 23. 8511 UT more than 2 months of observations 35 lightcurves Collaboration of 10 observatory, located in Europe, Australia and North America Physical parameters– Absolute magnitude H = 14.07 mag Color index V – R = 0.52 mag The ratio of mean diameters D2/ D2 ≥ 0.86 Rotation period P1 = P2 = Porb = 30.54 hours Amplitude A1 + A2 = 0.34 mag Diameters D1 = 3.5 km ; D2 = 3.0 km ; _

9. Discussion Abundance of synchronous binary asteroids : BinAst program - 4 synchronous < 1 % (N > 500) (www.asu.cas.cz/~asteroid/) Joint program of Geneva Observatory - 4 synchronous < 1 % (N ~ 450) (Behrend R. et al., 2006) These objects are unique …??? … !!! “ Because these systems are doubly synchronous, there are strong biases against discovery; only mutual events reveal the presence of the satellite. Thus they are possibly significantly under-represented amongst known asteroid binaries. ” (Walsh K.J. & Jacobson S.A., 2016) “ These binaries formed via rotational fission and so share a common parent body. If binaries are trapped in a long-term stable equilibrium, then binary creation could be infrequent.” (Jacobson S.A. & Scheeres D.J., 2011) (Jacobson S.A., 2014)

10. Thank you !