CCD observations of the satellites of Saturn and Uranus with 26-inch refractor

Transcription

1 CCD observations of the satellites of Saturn and Uranus with 26-inch refractor I.S. Izmailov, E.A. Grosheva Central Astronomical Observatory of the Russian Academy of Sciences at Pulkovo This works have been carried out with the support of RFBR N

2 Equipment 26-inch refractor D=65 cm F=10413 mm M=19.78 /mm CCD-camera FLI Pro Line 'x12' 3056x3056 px 1px = 12 x 12 m (0.24 )

3 Observations Object Period of observations Number Number of Exposures of nights CCD images 20 sec Uranus 30 Sep sec 04 Jan sec 0.5 sec Saturn 03 Jan sec 25 April sec

4 Measurements All measurements were made by the software package IZMCCD (I.S. Izmailov). This screenshot demonstrates the program window with opened CCD image. The image of seven satellites of Saturn was taken at 24 April 2008, 18 h 41 m 45 s UT

5 The excluding of planet halo Some images of satellites are immersed in the light scattered by the planet and this is the main problem of image processing. To exclude influence of planet halo the IZMCCD approximates it by a square-law polynomial. CCD image of Uranus before and after procedure of excluding planet halo.

6 Measurements and reduction Images of satellites and reference stars were measured by means of a structure set by function of Lorentz (Franz O. G., 1973) C I( x, y) = + D a (1 + Ar) r = ( x + (1 + B)( y I(x,y) brightness of element (x,y) x 0, y 0 center of image a,a, B, C, D, E parameters of the model. The equatorial coordinates of satellites were calculated by the method of H.H. Turner. The UCAC2 catalog (Zacharias et al, 2004) was used as a reference one. Average accuracy of obtained coordinates is 2 j x 0 ) 2 j y 0 ) 2 + E( x j x 0 )( y j y 0 ) 66 mas (in α)and 55 mas (in δ).

7 Total number of average positions obtained during observational period for every observed satellite and average accuracy of coordinates Uranian satellites number of positions σ x σ y Saturnian satellites number of positions σ x σ y

8 Comparison with a theory All theoretical positions of Uranus, Saturn and their satellites were taken at Natural Satellites Ephemeride Server MULTI-SAT (IMCCE, by N.Emelyanov, Ephemeris of Uranian satellites were calculated with theory TASS1.6 (A.Vienne, L.Duriez, 1995) Ephemeris of Saturnian satellites were calculated with theory GUST 06, improved GUST86 (Laskar J., Jacobson R.A., 1987 ) Theoretical positions of Uranus and Saturn were calculated with planet motion theory INPOP06 (Fienga A. et al, 2008)

9 Average residuals Observed minus Calculated Uranian satellites (O-C)x, mas (O-C)y, mas ± ± ± ± ± 45-2 ± 76 Saturnian satellites (O-C)x, mas (O-C)y, mas 2 84 ± ± ± ± ± ± ± ± ± ± ± ± ± ± 46

10 Positions of Uranus and Saturn The planet images at all CCD images were oversaturated and therefore not measurable. Positions of the planets were obtained from observed positions of satellites and their theoretical diffential coordinates, provided by Natural Satellites Ephemeride Server. Obtained positions of planet were compared with theoretical ones (INPOP06). Average O-C residuals of positions of Uranus (without positions, calculated with Umbriel): (O-C)x = -3 ± 50 mas (O-C)y =- 5 ± 74 mas Average O-C residuals of positions of Saturn (without positions, calculated with Hyperion): (O-C)x = - 37 ± 80 mas (O-C)y = 19 ± 86 mas

11 Conclusions More than 2700 CCD images of Saturnian and Uranian systems were carried out during 22 nights in the period from September 2007 to April The equatorial coordinates (J2000) of 2 nd, 3 rd, 4 th satellites of Uranus and positions of 2 nd till 8 th Saturnian satellites were obtained. Average accuracy was about 66 mas in RA and and 55 mas in D. These observations are available at Pulkovo Database of Observations of Solar System Bodies

12 Acknowlegements We thank the IMCCE and the SAI for developing the Natural Satellites Ephemeride Server MULTI-SAT the Russian Foundation for Basic Research for financial support Also we are grateful to all observers on 26-inch refractor at Pulkovo

13 Positions of Uranus. O-C in tangential plane 0.25 Average O-C residuals of positions of Uranus (without positions, calculated by Umbriel): Y() (O-C) x / (O-C) y / X () calculated by position of Oberon calculated by position of Umbriel calculated by position of Titania theoretical position by INPOP

14 Positions of Saturn. O-C residuals in tangential plane 0.60 Y, Average O-C residuals of positions of Saturn (without positions, calculated with Hyperion): (O-C) x / (O-C) y / X, calculated by position of Hyperion calculated by position of Rhea calculated by position of Titan calculated by position of Iapetus calculated by position of Dione calculated by position oftethys calculated by position of Enceladus theoretical position by INPOP

15 References Измайлов И. С. IZMCCD - программный пакет для астрометрической обработки числовых изображений небесных объектов // (2005) Zacharias, N.; Urban, S. E.; Zacharias, M. I. et al). The Second US Naval Observatory CCD Astrograph Catalog (UCAC2) // A.J., V. 127, pp , Franz O. G., Observational Procedures for Visual Double-Star Work // J. R. Astr. Soc. Can., 67, 81, Н.В. Емельянов. «Эфемериды естественных спутников планет MULTI- SAT IMCCE - ГАИШ МГУ» (программа вычисления эфемерид) // A.Vienne,L.Duriez TASS1.6: Ephemerides of the major Saturnian satellites // A&A,v.297, p.588 (1995) Laskar J., Jacobson R.A. GUST86 - An analytical ephemeris of the Uranian satellites. // A&A., v. 188, p (1987) Fienga A.; Manche H.; Laskar J.; Gastineau M. INPOP06: a new numerical planetary ephemeris. // A&A, 477, (2008)

16 Oberon. O-C residuals in α year Oberon. O-C residuals in δ year

17 Titania. O-C residuals in α year Titania. O-C residuals in δ year

18 Umbriel. O-C residuals in α year Umbriel. O-C residuals in δ year

19 Enceladus, O-C residuals in α year - Enceladus, O-C residuals in δ year -

20 Tethys, O-C residuals in α year - Tethys, O-C residuals in δ year -

21 Dione, O-C residuals in α year - Dione, O-C residuals in δ year -

22 Rhea, O-C residuals in α year - Rhea, O-C residuals in δ year -

23 Titan, O-C residuals in α year - Titan, O-C residuals in δ year -

24 Hyperion, O-C residuals in α year - Hyperion, O-C residuals in δ year -

25 Iapetus, O-C residuals in α year - Iapetus, O-C residuals in δ year -