Abstract
Light, color, and radial velocity data (2007–2015) for HD 161796, V887 Her, and HD 331319, three oxygen-rich post-AGB stars, have thus far not provided direct support for the binary hypothesis to explain the shapes of planetary nebulae and severely constrain the properties of any such undetected companions. The light and velocity curves are complex, showing similar periods and variable amplitudes. Nevertheless, over limited time intervals, we compared the phasing of each. The color curves appear to peak with or slightly after the light curves, while the radial velocity curves peak about a quarter of a cycle before the light curves. Thus it appears that these post-AGB stars are brightest when smallest and hottest. The spectra of these objects are highly variable. The H α line has multiple, variable emission and absorption components. In these oxygen-rich post-AGB stars atmospheric lines, such as near-infrared Ca ii triplet and low-excitation atomic lines, also have multiple components and sometimes show line doubling, indicative of shocks induced by pulsation.
Highlights
Stars at the proto-planetary nebula (PPN) phase evolve from the Asymptotic Giant Branch towards the PN phase becoming hotter at almost constant luminosity
High-resolution spectra were obtained at the Dominion Astrophysical Observatory 1.2 m telescope since 2007 and with the HERMES Spectrograph on the 1.2 m Mercator telescope (Raskin et al [8], Van Winckel et al [9]) since 2009
The present observations do not provide direct support for the binary hypothesis to explain the shapes of thes PPNe
Summary
Stars at the proto-planetary nebula (PPN) phase evolve from the Asymptotic Giant Branch towards the PN phase becoming hotter at almost constant luminosity. These low mass stars are surrounded by a circumstellar envelope ejected during the AGB phase. The objects have spectral energy distributions typical for “shell” objects: they are double peaked, with a peak in the visible arising from the (reddened) photosphere and a second peak in the mid-infrared arising from re-radiation from cool (T ≤ 200 K) dust. They have no Galaxies 2018, 6, 131; doi:10.3390/galaxies6040131 www.mdpi.com/journal/galaxies. If it turns out that these PPNe are not binaries, it raises the possibility that there may be more than one way to produce bipolar PNe
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
