Computer Science
Scientific paper
Jul 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995hst..prop.6055p&link_type=abstract
HST Proposal ID #6055
Computer Science
Hst Proposal Id #6055 Hot Stars
Scientific paper
We will study the extraordinary event occurring in the central star of the LMC-PN N66. Before 1987, it showed a weak continuum with a T(eff) >= 120000 K and L(bol) ~eq 25000 solar luminosities. Recently it developed strong W-R features typical of a WN4.5 star (P -Cygni profiles in N V Lambda 1240 and C IV Lambda 1550 lines and wide He II emission lines). Simultaneously, the visual and UV continuum intensities increased by large factors. The present T(eff) is 50000 K. The ejected wind consists of highly H-deficient He- and N-rich material. This is most unusual since all the known PNe with W-R nucleus show He- and C-rich winds. To explain these changes Pena et al. (1994a) proposed that the star is undergoing a ``final thermal pulse". This is the first time that such an event is observed. The nebular emission lines have not changed in the last 20 years so the recent stellar activity has not altered the nebula yet. Small aperture observations with HST are needed to obtain the stellar spectrum without contamination of the nebular emission. We plan to use the FOS with a combination of gratings to cover the wavelength range 1150-7000 Angstrom with a resolving power of 1300. The spectrophotometric data will be used to determine the present stellar parameters (mass loss, T(eff), L(bol) and to analize the chemical composition of the atmosphere. We propose to re-observe the object in Cycle 6 since the star is undergoing important changes in time scales of 1 year or less.
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