Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.5903h&link_type=abstract
American Astronomical Society, AAS Meeting #211, #59.03; Bulletin of the American Astronomical Society, Vol. 39, p.841
Astronomy and Astrophysics
Astronomy
Scientific paper
VV Cephei is an eclipsing binary system composed of an M2Iab supergiant primary with an extended atmosphere and wind and a hot companion, probably an early B main-sequence star. The system was observed with the HST/STIS spectrograph at 21 epochs between 1997 and 2003, which included observations from total eclipse through and beyond first quadrature. Two-dimensional processing of the spectra reveals spatial extension at some wavelengths in all 21 observations.
During total eclipse, a rich emission-line spectrum is observed. Strong lines with lower energy levels up to 2 eV (and even some very strong lines with somewhat higher excitation) are cut by blue-shifted absorption from the expanding M-supergiant circumstellar envelope. As the hot component approaches egress from eclipse, the emission on the short-wavelength side of the line profiles strengthens, presumably due to gas in the vicinity of the hot component itself beginning to emerge.
The spatial extent of the continuum seen outside eclipse is consistent with the spatial point-spread function of the STIS spectrograph. The blue-shifted emission which increases as the hot component nears third contact is also consistent with the STIS spatial point-spread function and thus does appear localized in extent. The spectral features which do show extended emission are generally those with blue-shifted circumstellar absorption, and the extended emission appears longward of this absorption, near line center. This extended emission is mostly due to singly-ionized elements in the iron group. Both the radial velocity and the strength of the extended emission is correlated with the position angle of the aperture at the time of observation, offering the possibility of mapping the structure of the M-star wind at a scale of a few tens of M-star radii.
This work was based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute.
Bennett David P.
Gull Ted R.
Hagen Bauer Wendy
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