STUDY OF SPECTRAL VARIABILITY OF THE PLANETARY NEBULA

STUDYOFSPECTRALVARIABILITYOFTHEPLANETARYNEBULA

IC4997OVER25YEARS(1972–1996)

E.B.Kostyakova

SternbergAstronomicalInstitute,1199,Moscow,Universitetskijpr.,13,Russia(ekost@sai.msu.su).

ThespectrumoftheplanetarynebulaIC4997wasobservedphotographicallyinCrimeain1972–1996.Theobjectiveprismspectro-gramswereusedforestimationofthefluxinelevenbrightemissionlinesoftheneb-aulaandinthecontinuumofthecentralstar.ñeMostspectralcharacteristicswerefoundtoP mchangeintime.TheratioRofthe[OIII]aiλ4363andHγfluxesexhibitedthegreatestriM changeover1972–1996;thisratioreacheda& ,maximum(logR=+0.28)in1992.Inthesotrnextyearsitbegantodecrease.IncreasesinaMtheexcitationandionizationdegreesofthe ocnebulaweredetected.

raMThechangeinthemainphysicalparametersof ,otheobjectwasestimated.Overtheperiod1972–cn1992thetotalelectrondensitychangedfromNe󰀃arF(2–6)×105cm−3toNe󰀃(1–3)×106cm−3,andthe éstotalelectrontemperaturerosefromTe󰀃12000KoJ ,toTe󰀃14000K.Thesetofspectroscopicdatasug-yengeststhattheeffectivetemperatureofthecentralnestarrosefromT∗󰀃40000KtoT∗≥60000K,overH mtheperiod1972–1992.

ailliW :srotidETheintensificationofthenebula’sspectralactiv-ity,whichstartedinthelate1960’s,appearstohavestoppedintheearly1990’s,whilein1993–2000theactivitybegantodecrease.

OurphotometricandspectralstudyofthenebulaIC4997isinprogress.TheresultsofspectralstudyofIC4997arepublishedinKostyakova(1999).

ResultsofourphotometricUBVstudyofvari-abilityintheplanetarynebulaNGC6572,IC4997,Hu2-1,NGC61,IC3568,NGC6720,andNGC6543,over30yearsarepublishedbyKostyakova(1990,1991,1997)andArchipovaetal.(1994).

REFERENCES

Arkhipova,V.P.,Kostyakova,E.B.,&Noskova,R.I.

1994,Pis’mavAstron.Zh.,20,122

Kostyakova,E.B.1990,Pis’mavAstron.Zh.,16,1085

.1997,inIAUSymp.180,PlanetaryNebulae,

eds.H.F.Habing&H.J.L.M.Lamers,(Dordrecht:Kluwer),251

Ionized Gaseous Nebulae (Mexico City, 21-24 November 2000)