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JENAM 2011, European Week of Astronomy and Space Science, 4-8 July 2011, St. Petersburg, Russia

Forthcoming mutual events of planets and astrometric radio sources
Z. Malkin, V. L'vov, S. Tsekmejster
Pulkovo Observatory, St. Petersburg, Russia Abstract. Radio astronomy observations of close approaches of the Solar system planets to compact radio sources as well as radio source occultations by planets may be of large interest for planetary scien ces, dynamical astronomy, and testing gravity theories. In this p aper, we present extended lists of occultations of astrometric radio sources observed in the framework of various astrometric and geode tic VLBI programs by planets, and close approaches of planets to radio sources expected in the nearest years. Computations are made making use of the EPOS software package.

Introduction Very long baseline interferometry (VLBI) and single dish radio observations of close approaches of the Solar system bodies (planets, satellites, asteroids) to compact radio sources, as well as radio source occult ations by planets may be of large interest for planetary sciences, dynamical astronomy, and testing gravity theories. In this paper we present a new extended version of the list of occultations of astrometric radio sources (i.e. having reliable coordinates at the milliarcsecond level of accur acy) by planets, and close approaches of planets to radio sources expected in the nearest 40 years co mpiled at the Pulkovo Observatory. Previous lists presented in [1, 2] were substantially revised in two respects. First, a new version of software to find occultation and approaches was used. Second, the list of astrometric radio sources was extended. All computations of the mutual events circumstances have been made at the Pulkovo Observatory making use of the EPOS software package (http://www.gao.spb.ru/personal/neo/ENG/ESUPP/main.htm) and other programs. The list of astrometric radio sources has been taken from the OCARS catalog available at http://www.gao.spb.ru/english/as/ac_vlbi/ocars.txt. Occultations of astrometric radio sources by planets Observations of occultations of compact radio sources by Solar system planets may be interesting for several astronomical and physical applications, such as testing GR [1], improvement of planet orbits and their tie to the International Celestial Reference Frame (ICRF) [3], and planetary researches [4, 5]. List of nearest expected events is shown in Table 1 along with the elongation from the Sun. The latter is important for planning of radio astronomy observations. If the radio source is too close to the Sun, it may be impossible to observe it. Nevertheless, we include all the events found during our calculations for completeness. Occultations of radio sources by planets, like solar eclipses, generally speaking can only be observed in a limited region. A map of the shadow path and detailed circumstances for each VLBI station situated on the shadow path for several selected occultations that will occur in regions with several stations and hence most interesting for radio astronomy experiments are given in [2]. One can see that occultations of astrometric radio sources by planets, especially by outer planets, suitable for radio observations are rare events. However, some physical applications do not require knowledge of accurate source coordinates. For such studies, any compact radio source can be observed, which makes experiment scheduling much easier. Close angular approaches of planet to astrometric radio sources During close angular approaches of Solar system planets to astrometric radio sources, the apparent positions of these sources shift due to relativistic effects. Thus, these events may be used for testing gravity theories, see, e.g., [1] and paper cited therein. This fact was successfully demonstrated in the experiments on the measurements of radio source position shifts during the approaches of Jupiter carried out in 1988 and 2002 [6, 7]. Basic circumstances for the coming events (10 years in advance for Jupiter and 15 years for

other planets) are shown in Table 2.

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Table 1. Occultations of astrometric radio sources by planets

Planet Venus Mercur Venus Jupiter Venus Venus Mercur Jupiter Mercur Saturn Mercur Venus Mercur Mercur Mercur Jupiter y

y y y y y y

Dat Y 2012 2014 2015 2016 2020 2020 2022 2025 2027 2028 2029 2029 2029 2029 2030 2033

e, UT MD 12 24.4 07 30.2 08 06.8 04 10.4 01 16.7 07 17.7 11 14.7 09 18.6 03 21.7 10 24.8 01 14.3 02 28.2 04 16.1 12 27.9 02 27.6 02 04.2

Source 1631­208 0750+218 0947+064 1101+077 2220­119 0446+178 1529­195 0725+219 2220­119 0223+113 1958­179 2221­116 0243+181 1858­212 2208­137 2104­173

Elongation, deg 23W 11W 15E 144E 38E 42W 4E 65W 27W 173W 5E 6W 19E 8E 9W 1W

Summary In this paper, we present new lists of found mutual events of astrometric extragalactic radio sources and Solar system planets. The circumstances of both occultations and close angular approaches have been calculated. For these computations, we considered only astrometric radio sources having reliable coordinates at the milliarcsecond level of accuracy. Observations of these sources are used when the tie to the ICRF is important. For other, mainly physical, studies any compact source may be suitable for observations, see, e.g., [3]. For various tasks, VLBI or single-dish radio observations can be performed. Different observing techniques and strategies may require pre-computation of different circumstances of the event of interest. These data can be calculated as well on request using the EPOS software and associated programs developed at the Pulkovo Observatory. Tables presented above contain only basic circumstances for events expected in limited period of time. Full version of these Tables for all the events found for the period till 2050 with more details is available at the Pulkovo Observatory Web site http://www.gao.spb.ru/english/as/ac_vlbi/#Approaches. Besides, detailed computation of the circumstances for selected events of special interest, including also small Solar system bodies and extended lists of radio sources, can be performed on request. References 1. Malkin Z. M., L'vov V. N., Tsekmejster S. D. Forthcoming Close Angular Approaches of Planets to Radio Sources and Possibilities to Use Them as GR Tests. // Solar System Research. 2009. V. 43. No. 4, P. 313­318. 2. L'vov V., Malkin Z., Tsekmeister S. Forthcoming Occultations of Astrometric Radio Sources by Planets. // D. Behrend, K. D. Baver (eds.), IVS 2010 General Meeting Proc., NASA/CP-2010-215864, 2010, P. 320­324. 3. Linfield R. Occultation of a compact radio source by Venus. // Astron. J. 1992. V. 104. P. 880­890. 4. Leblanc Y., Ladreiter H. P. Neptune's radio emissions. // Adv. in Space Res. 1992. V. 12. P. 23­36. 5. Black G., Campbell D., Nicholson P., Sault R. New Long-Wavelength Radio Source Occultations by Saturn's Rings. // Bull. Amer. Astron. Soc., V. 32, P. 1086. 6. Treuhaft R. N., Lowe S. T. A Measurement of Planetary Relativistic Deflection. // Astron. J. 1991. V. 102. P. 1879­1888. 7. Fomalont E. B., Kopeikin S. M. The Measurement of the Light Deflection from Jupiter: Experimental Results. // Astrophys. J. 2003. V. 598. P. 704­711.

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Table 2. Close angular approaches of planets to astrometric radio sources. In this table, d is the angular distance between the planet and radio source, E is the elongation from the Sun

Planet Jupiter

Saturn

Uranus

Neptune

Dat Y 2011 2011 2011 2011 2012 2012 2012 2013 2013 2013 2013 2013 2014 2014 2014 2016 2017 2019 2019 2020 2020 2020 2020 2021 2021 2021 2013 2014 2015 2015 2017 2019 2021 2021 2021 2021 2022 2022 2023 2023 2024 2024 2024 2013 2013 2016 2016 2017 2024

e, UT MD 07 03.6 08 16.8 09 13.1 11 27.2 02 04.0 02 20.3 04 22.5 02 28.1 03 29.5 10 23.0 11 07.2 11 22.1 07 26.1 08 22.8 09 09.3 10 19.2 10 13.7 10 20.5 10 28.4 01 30.3 02 15.0 08 02.0 10 24.2 02 19.9 03 16.0 11 29.8 12 05.8 08 26.3 06 19.1 11 19.1 12 13.3 11 16.6 08 10.7 08 19.0 12 01.0 12 08.1 03 11.2 05 29.1 04 13.3 04 18.2 01 04.6 03 18.5 03 28.0 05 05.4 10 03.3 07 11.8 08 16.9 04 12.8 09 02.7

Source 0210+119 0229+131 0229+131 0156+105 0201+113 0210+119 0300+162 0420+210 0435+217 0723+219 0725+219 0723+219 0814+201 0839+187 0854+178 1229­021 1352­104 1717­229 1723­229 1853­226 1907­224 1922­224 1922­224 2104­173 2126­158 2147­144 1459­149 1459­149 1548­177 1614­195 1752­225 1907­224 2044­188 2042­191 2042­191 2044­188 2126­158 2147­144 2221­116 2223­114 0220­119 2252­090 2256­084 0036+030 0036+030 0127+084 0127+084 0127+084 2354­021

d, arcsec 341 488 149 285 490 342 115 216 563 123 388 351 488 360 310 506 69 222 184 542 91 78 355 149 528 79 525 486 156 64 73 240 20 441 382 114 521 288 33 276 370 158 388 558 362 313 259 499 498

E, deg 66W 104W 130W 147E 78E 64E 16E 88E 63E 100W 114W 130W 1W 21W 35W 18W 10E 55E 48E 27W 39W 160E 79E 17W 36W 77E 26W 75E 152E 10E 8E 53E 171E 163E 60E 53E 31W 103W 49W 54W 50E 16W 25W 35W 179W 86W 120W 2E 162W

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