Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009arep...53.1155k&link_type=abstract
Astronomy Reports, Volume 53, Issue 12, pp.1155-1164
Astronomy and Astrophysics
Astronomy
Scientific paper
We present the results of our many-year (1968-2008) photoelectric photometry and absolute spectrophotometry of the young variable planetary nebula IC 4997, performed in uniform systems. Integrated line energy fluxes in the range 3727-5007 Å are tabulated, along with the integrated (star + nebula) continuum flux at 4500 Å, and time variations investigated. We study the time behavior of fluxes in the hydrogen, HeI, [OIII], [OII], [NeIII] emission lines. Variations of the line intensity ratio R = F([OIII]4363 Å)/ F(Hγ) between 1938 and 2008 are presented. We estimate the nebula's electron density N e and electron temperature T e for 1972-1992: the mean nebula N e increased by the factor of five, from ˜4 × 105 to ˜2 × 106 cm-3, while the mean T e increased from 12 000 to 14 000 K. The color temperature of the exciting star, measured from the 4000-4900 Å continuum, increased from 37 000-40 000 K to 47 000 K during the time interval covered by our observations, as is confirmed by the growth of ionization of HeI, NeIII, and OIII (from the 4363 Å line). V-band variations of the object's integrated (nebula + star) light with an amplitude about 0.5 m can essentially be fully explained as being due to changing contributions from variable fluxes in the [OIII] 5007 and 4959 Å lines. The V magnitude in 2009 (after 40 years) happened to be the same as at the start of our observations in 1968. A period of the order of 50 years can also be noted in log R( t). This may provide evidence for binarity of the central star and be related to its orbital period.
Arkhipova V. P.
Kostyakova E. B.
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