1995AJ 110.1875C University, Sumskayastr.35,Kharkov 310022, Ukraine. and ß,thehelio-geocentric distancesrandA,the for themidtimeoflightcurve: theeclipticcoordinatesX Stellarum 1950.0(Vehrenberg1970). to theequinox1950.0,theirVmagnitudesandnumbers The equatorialcoordinatesofthecomparisonstarsreferred ordinates oftheuncataloguedstarsweretakenfromAtlas of thephotometricalstandardsaregiveninTable1.Theco- made bothonthenightswhenasteroidwasobservedand Address ofcorrespondence:Astronomical ObservatoryofKharkovState after thefulfillmentofwholeprogramobservations. were used.Thephotometricalstandardizationofstarswas measurements ofbrightnesswerecarriedoutusingthe reflector ofSanglokMountainObservatory(SMO)the publications onthephotometryofEarth-approachingaster- 1875 Astron.J.110 (4),October1995 0004-6256/95/110(4)/1875/4/$0.90 ©1995Am.Astron. Soc.1875 KhAO) oranearestphotometricalstandardstar(atSMO) described indetailbyKayumovetal.(1989)andVelichko ments andthereductiontechniqueofobservationsare method ofdifferentialphotometryintheBVbands the 0.7mreflectorofAstronomicalObservatory Institute ofAstrophysicsinDushanbe(Tajikistan)andwith et al.1990;Velichko1992). oids (Lupishkoetal.1986;Lupishko1988;Velichko standard photometricsystem.Theprecisionofthemeasure- Kharkov University,Ukraine(KhAO).Thephotoelectric Ganymede and1627Ivarwerecarriedoutwiththe1m (1991). THE ASTRONOMICALJOURNAL © American Astronomical Society • Provided by the NASA Astrophysics Data System Table 2containstheaspectdata oftheobservedasteroids As comparisonstarsnearesttotheasteroidfieldstar(at New observationsoftheAmor-groupasteroids1036 This paperisacontinuationofseriestheauthor’s ä0 mag deg\respectively.©1995AmericanAstronomicalSociety. Ganymede ando:*18-54forIvararerepresentedbythecoefficients0.020±0.0020.024±0.002 contrast, Ivarlightcurvesarerathersymmetricandshowverylargeamplitudewithconsiderablechanges obtained compositelightcurveofGanymedeismarkedlyasymmetricwithanamplitude0.13mag.By carried outon10nightsin1989May-Julyand191990May-August,respectively.The The photometricobservationsofAmorasteroids1036Ganymede(BVbands)and1627Ivar(Vband)were (from 1.05to1.4mag).Magnitude-phasedependencesobtainedatphaseanglerangesofa*«10°-30°for Department ofPhysicsandAstronomy,FacultyScience,UniversityGaryounis,P.O.Box9480,Benghazi,Libya PHOTOMETRY OFAMORASTEROIDS1036GANYMEDEAND1627IVAR Astrophysical Institute,TajikAcademyofSciences,BukhoroStrasse22,Dushanbe734670,Tajikistan 1. INTRODUCTION Astronomical ObservatoryofKharkovUniversity,SumskayaStrasse35,310022,Ukraine Yu. N.Krugly,D.F.Lupishko,V.G.Shevchenko,andRVelichko Received 1995February23;revisedMay22 G. RChernovaandN.Kiselev Electronic mail:[email protected] Electronic mail:[email protected] VOLUME 110,NUMBER4 1 R. A.Mohamed ABSTRACT with albedoof0.14-0.17anddiameterabout38.5km can beobtainedbysendingtherequesttoYu.N.Krugly. In addition,adatafilecontainingtheoriginalobservations Ganymede isclassifiedasanS-typeasteroid(Tholen1989), extremum (seeFigs.1,and3-5),thenumberofcompari- tude V(l,a)ofthelightcurveextremum,notation phase anglea.Thistablealsocontainsthereducedmagni- son star,andthesitewhereobservationswerecarriedout. This asteroidisthelargestEarth-approachingobject. Comparison Note: O,Blancoetal.(1968);©,Kazanasmas etal.(1982); star 15 1349.8+104912.14 16 1354.3+83711.63ROSS838 [O] 14 1346.7+12109.85 13 46.3+122811.72BD+13 2698, HD121109[O] 12 1455.5+150012.35 11 1405.1+141512.38 10 1407.8+135712.65 7 1456.9+60811.43Ne544,684SAI07[©] 4 1525.3-01310.80 2 1530.8-13013.04 9 1420.3+11529.47HD124066A[O] 6 1515.2+14912.26Ne2,3NGC5904[©] 3 1529.0-05510.79 8 1457.1+60711.93 5 1519.1+11110.84HD136834[O] 1 15Î3878-3°23'11759HD140850[O] ©, Moffett&Bames(1979). «le Table 1.Comparisonstars. 2.1 1036Ganymede $19 2. RESULTS V Standard star OCTOBER 1995 1995AJ 110.1875C period andanamplitudeestimate of0.13mag.Wewereun- has anordinaryformwithtwo pairs ofextremaperrotation data points(solidline).Theasteroid compositelightcurve with changingaspectandthelackofevidenceforsurface tude of0.4magtotheformwiththreepairsextremaand From theanalysisoflightcurvesitisknownthat Ganymede. Afourth-orderFourier serieswasfittedtothe albedo variations(Hahnetal1989)mayindicatethatthe an amplitudeof0.13mag.Suchevolutionthelightcurve change greatlyfromasimplesinusoidalformwithanampli- curves obtainedinthe1985opposition(Hahnetal1989) the surfacemineralogicalcomposition(Chapman&Gaffey metric datapointouttheexistenceofsilicatesonsurface scribed byatriaxialellipsoid(Ostro etal1988). shape ofGanymedeisrathercomplexandnotwellde- asteroid hasaretrogradesenseofrotationwithperiod of thisasteroidandtheabsencelargescalevariations Table 2.Aspectdataandthemeasuredmagnitudesofobserved (Veeder etal1989;Kiselev1994).Thespectrophoto- asteroids. 1979; McFaddenetal1984;Vilas&1992). 10.31 hr(Lupishkoetal1988;Hahn1989).Thelight 1876 CHERNOVAETAL.\1036GANYMEDEAND1627IVAR 08 12.70 06 22.87 05 25.87230.017.42.2941.3249.610.01M3 07 22.76 07 19.75 07 18.75 07 15.74 06 29.88 06 23.76 06 22.77 06 21.77 06 17.83 06 16.88 05 23.88 05 22.91 05 13.90 05 01.80 07 10.73219.622.11.9951.40228.610.39M 06 02.92227.118.72.2431.31013.310.14M5 05 28.89228.917.92.2751.31710.910.02M4 05 23.84230.717.02.3071.3318.8-2 05 16?91233°215?62.3511.3626.7-1KhAO 07 14.75 06 15.76 05 11.82 07 09.74219.722.02.0011.39828.310.40M 07 08.74219.722.02.0081.39428.010.40M 07 07.75219.722.02.0151.38927.710.40M7,8SMO 06 06.88225.819.32.2181.30815.210.14M6 Note: KhAO,KharkovAstronomicalObservatory;SMO,SanglokMountainObservatory. Date © American Astronomical Society • Provided by the NASA Astrophysics Data System Figure 1showstheobtained composite lightcurveof UT 233.8 216.0 213.9 213.3 211.4 210.8 203.5 201.2 201.2 200.9 200.1 200.8 201.0 201.4 203.8 204.5 208.3 199.9 199.7 20.6 20.4 20.6 20.8 21.6 21.8 22.0 25.0 25.1 25.3 25.2 24.4 13.1 14.0 14.2 15.1 15.4 19.1 5.9 1.238 1.242 1.242 1.382 1.387 1.446 1.123 1.147 1.154 1.156 1.164 1.167 1.215 1.246 1.263 1.267 1.272 1.435 1.500 AU r 1036 Ganymede(1989) 1627 Ivor(1990) 0.409 64.114.89 0.428 61.614.78 0.432 60.614.78 0.435 59.714.78 0.449 53.914.21 0.453 51.014.29 0.454 50.614.18 0.454 50.614.18 0.455 50.114.09 0.431 60.814.78 0.436 59.414.76 0.457 48.013.09 0.457 47.513.83 0.458 46.913.94 0.476 32.413.63 0.478 31.713.57 0.494 25.313.48 0.499 23.913.46 0.530 17.813.28 AU A V(l,
LO COCT)
Rotational phase Date UT, 1990 Magnitude shift 0 - May 1.80 -0.185 O - Jun 15.76 -0.245 □ - May 11.82 0.000 □A - Jun 16.8817.83 -0.350-0.280 +¿ - May 22.9113.90 0.1100.020 + - Jun 21.77 -0.095 * - May 23.88 0.165 ■x - Jun 22.8722.77 0.000 *0 - Jun 23.7629.88 0.0300.110 Fig. 3. Composite light curve of 1627 Ivar in 1990 May. The zero phase corresponds to JD 2448023.2753 corrected for light time. Fig. 4. Composite light curve of 1627 Ivar in 1990 June. The zero phase corresponds to JD 2448064.1968 corrected for light time. Figure 2 shows the magnitude-phase dependence of Ganymede plotted using the reduced values V(l,a) of the The light curve in May (near the opposition, Fig. 3) has a maximum M of the light curve. The obtained phase coeffi- symmetrical form with equal levels of extrema, an amplitude cient is /3=0.020±0.002 mag deg-1 and V( 1,0) =9.81 mag. of about 1.12 mag and it coincides with data obtained by The phase coefficient value coincides with the one deduced Hoffmann & Geyer (1990). The measured amplitude is about by Lupishko et al. (1988) according to the 1985 data and is twice as large as the value obtained from the observation in one of the lowest values for known asteroids. The value 1985 (Hahn et al. 1989). This indicates that in the 1990 op- ß=0.025 mag deg-1 published by Hahn et al. (1989) is a bit position the asteroid had an aspect approaching to the equa- different from the one we obtained. This difference can be torial one. However, when the asteroid moved farther apart explained by rather large aspect changes of Ganymede from the opposition the brightness variation increased to 1.45 brightness during the time interval of Hahn et al. observa- mag (see Fig. 4), but aspect change insignificantly. This may tions (the aspect changes of magnitude were comparable indicate that asteroid 1627 Ivar has no accurate pole position with the phase angle changes, contrary to our 1989 observa- determination. tions). The magnitude-phase dependence of 1627 Ivar (Fig. 6) was plotted using the reduced magnitude of Ml maximum according to the observations at KhAO. The obtained phase 2.2 1627 Ivar relation within a=180-54° gives /?=0.024±0.002 Ivar is classified as an 5-type asteroid (Tholen 1989), pos- sessing albedo 0.12 and diameter of about 8.1 km (Veeder et al. 1989). According to the results of Ivar observations during its previous approach to the Earth in 1985, it was found that it has a rotation period of about 4.8 hr, prograde = o sense of rotation and pole coordinates X.0 333 , )Ö0=18°, (Lupishko et al. 1986; Hahn et al. 1989; Velichko & Lu- pishko 1989). Radar observations show that the asteroid has a complex shape and they qualitatively confirm the estimate of its pole coordinates (Ostro et al. 1990). New observations of Ivar were carried out from May till August at 1990 opposition. The visibility conditions (season of short nights), faint asteroid brightness, and a close com- mensurability of the asteroid rotation period to the Earth day did not allow to observe the complete light curve from one O - Jul 14.75 -0.020 site. Therefore, observations at both observatories which are □ - Jul 15.74 0.000 two hours apart in longitude, could finally give the possibil- A - Jul 18.75 0.000 *+ - Jul 22.7619.75 0.000 ity to obtain a complete coverage of the light curve. Figures x - Aug 12.70 0.110 3, 4, and 5 show the composite light curves of Ivar plotted according to the observations in 1990 May, June, and July- Fig. 5. Composite light curve of 1627 Ivar in 1990 July-August. The zero August, respectively. phase corresponds to JD 2448088.1899 corrected for light time.
© American Astronomical Society • Provided by the NASA Astrophysics Data System 1995AJ 110.1875C -1 Lupishko, D.E,Velichko,F.R,&Shevchenko,V.G.1988,Astron.Vestn. Lupishko, D.E,Velichko,F.P,&Shevchenko,V.G.1986,Kinem.Fiz. largest amongtheEarth-approachingasteroids,1036 mag degobtainedbyHahnetal1989. mag deg\whichagreecloselywith/3=0.022±0.001 Hoffmann, M.,&Geyer,E.1990,AcA,40,389 Hahn, G.,etal1989,Icarus,78,363 Chapman, C.R.,&Gaffey,M.J.1979,inAsteroids,editedbyT.Gehrels Blanko, V.M.,Demers,S.,Douglas,G.G.,&Fitzgerald,M.P.1968,Publ. Ganymede. Ontheotherhand,realshapesof1036 Kiselev, N.N.,Chernova,G.P,&Lupishko,D.F.1994,Kinem.Fiz. Kazanasmas, M.S.,Zavershneva,L.A.,&Tomak,F.1982,Atlasand Kayumov, V.V.,Kiselev,N.N.,Pushnin,PA.,Rakhimov,J.,Siklitski, 1878 CHERNOVAETAL:1036GANYMEDEAND1627IVAR Nebesn. Tel2,39 Nebesn. Tel10,35 Astrophys., TadjikAcad.Sei.No.78,10 I., Tarasov,K.V.,Chernova,G.P,&Yakutovich,V.N.1989,Bull.Inst,of 22, 167 Kiev), p.220 Catalogue ofMagnitudesPhotometricalStandards(NaukovaDumka, US NavalObs.21,772 (University ofArizonaPress,Tucson),p.655 At present,therearenopolecoordinateestimatesforthe © American Astronomical Society 3. CONCLUSION Provided bythe NASA Astrophysics Data System REFERENCES 1 phase dependenceofanyEarth-approachingasteroidis pronounced forGanymedewhichhas/3=0.020magdeg”. results ofeachasteroidintwooppositions)turnedouttobe problem, thereliableshapeandpolecoordinateestimatesare far lessthanthoseofthemainbeitSasteroids.Thisismore pect, epochsofextrema,etc.)aregreatinterestinsolving termination ofIvar’spolecoordinates.Therefore,theob- meaningless unlessaspectmagnitudechangesaretakeninto lar case.Thereisagoodprobabilitythatthemagnitude- into considerationaspectmagnitudechangesineachparticu- needed, whichwillgiveapossibilitytosimulateandtake changes foreachasteroidinbothoppositions.Tosolvethis It isunknownwhetherthisexplainedbytheparticular these problems. tained data(lightcurveamplitudes,theirchangeswithas- triaxial ellipsoid(Ostroetal1988),whichwasusedforde- Vilas, E,&McFadden,L.A.1992,Icarus,100,85 Velichko, F.R,&Lupishko,D.E1989,Kinem.Fiz.Nebesn.Tel5,90 Velichko, ER,Krugly,Yu.N.,Lupishko,D.E,&Mohamed,R.A.1990, Velichko, F.R,Krugly,Yu.N.,&Chiomij,V.G.1992,Astron.Tsirk.No. Velichko, F.R1991,Ph.D.thesis,KharkovUniversity,p.198 Vehrenberg, H.1970,AtlasStellarum,1950.0(Treugesell,Dusseldorf),p. Veeder, G.J.,Hanner,M.S.,&Matson,D.L.1989,AJ,97,1211 Tholen, D.1989,inAsteroidsII,editedbyR.RBinzel,T.Gehrels,andM. Moffett, T.J.,&Barnes,G.1979,AJ,84,627 McFadden, L.A.,Gaffey,M.J.,&McCord,T.B.1984,Icarus,59,25 grants fromtheAmericanAstronomicalSociety. The worksofYu.K.andD.F.L.werepartlysupportedby grateful forthesupportbyLibyanEmbassystaffinKiev. observing theasteroid1036Ganymede.R.A.M.isvery account. surface characteristicsorbydifferentaspectmagnitude Ganymede and1627Ivarmayconsiderablydifferfromthe Ostro, S.J.,Connelly,R.,&Dorogi,M.1988,Icarus,75,30 Ostro, S.J.,Campbell,D.R.,Hine,A.A.,Shapiro,I.L,Chandler,J.E, 450 Astron. Tsirk,No.1546,39 Werner, C.L.,&Rosema,K.D.1990,AJ,99,2012 S. Mathews(UniversityofArizona,Tucson),p.1139 1553, 37 The authorswouldliketothankA.V.Shulgaforhelpin Ganymede andIvarphasecoefficients(accordingtothe 1878