Other
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aas...185.4710h&link_type=abstract
American Astronomical Society, 185th AAS Meeting, #47.10; Bulletin of the American Astronomical Society, Vol. 26, p.1385
Other
Scientific paper
With its rich UV-optical-IR spectrum, NGC 7027 has been the target of choice for study of important physical processes including charge-exchange, dust-quenching of nebular lines, PDR's, extended-red emission, etc. Surprisingly little, though, is known about the central star, because the star is embedded in such a bright nebula. With the success of the HST servicing mission, it is now possible to carry out direct studies of the central star. Here, we report on HST/FOS spectroscopy of the central star. In August 1994, we obtained FOS/G400H, G570H spectra of NGC 7027 with the central star centered in the 1farcs 0 aperture. The spectra cover the wavelength range, 3250-6750 Angstroms. The spectra are of excellent quality. For example, at lambda 4800 Angstroms, the S/N=76 per resolution element, and the star contributes 94% of the observed continuum flux. Other very hot stars, i.e. PG 1159 stars, are known to show high-ionization lines, such as O VI lambda lambda 3811,3834, C IV lambda 4441, or C V lambda 4945, etc. To our surprise, these lines are absent in the spectrum of the central star. In fact, the stellar spectrum is apparently featureless. We have therefore used the absence of spectral features to put limits on effective temperature and chemical composition of the central star. We are constructing a small grid of line-blanketed NLTE model atmospheres for the effective temperatures range 100,000 K < T_eff < 250,000 K, 5.8 < log g < 7.5, and for two compositions: (i) a H-rich (solar) composition, and (ii) a C-O enriched atmosphere, typical of PG 1159 stars. We will report on the results of this analysis.
Heap Sally R.
Hubeny Ivan
Lanz Thierry
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