Transcript The Central Star of A63 – UU Sge Don Pollacco, Ralf

The Central Star of A63 – UU Sge
Don Pollacco (Queens University Belfast, UK), Ralf Napiwotzki (Banberg, Germany), Steve Bell (HMNAO, UK)
Katrina Exter (Queens University Belfast, UK)
UU Sge is unique amongst central star in that it is a totally
eclipsing binary. Hence physical parameters for the
components can be derived, in principle, with great accuracy.
The morphology of A63 is extreme, exhibiting an aspect ratio
of some 7:1!
This result is consistent with the
light curve solutions derived
using a 6000K secondary – as
derived from spectra obtained
during the brief (but faint) total
eclipse.
These results imply a distance of
2.4 kpc (±20%).
Model atmosphere fits to the spectrum of the sdO star (near
phase 0) require Teff~70000K. At other phases emission lines
from the irradiated phase contaminate absorption lines and in
the case of OIV and CIV lines, fill them in completely!
The spectra here were obtained
near phase 0.5 (top) and around
0.0 (middle). The difference
shows the irradiated spectrum
(bottom). Double peaked
hydrogen lines and narrow
forbidden lines arise high in the
atmosphere of the secondary star.