Where are the Binaries? Results of a Long-term Search for Radial Velocity Binaries in Proto-planetary Nebulae

Abstract

We present the results of an expanded, long-term radial velocity search (25 yrs) for evidence of binarity in a sample of seven bright proto-planetary nebulae (PPNe). The goal is to investigate the widely-held view that the bipolar or point-symmetric shapes of planetary nebulae (PNe) and PPNe are due to binary interactions. Observations from three observatories were combined from 2007−2015 to search for variations on the order of a few years and then combined with earlier observations from 1991−1995 to search for variations on the order of decades. All seven show velocity variations due to periodic pulsation in the range of 35−135 days. However, in only one PPN, IRAS 22272+5435, did we find even marginal evidence found for multi-year variations that might be due to a binary companion. This object shows marginally-significant evidence of a twoyear period of low semi-amplitude which could be due to a low-mass companion, and it also displays some evidence of a much longer period of >30 years. The absence of evidence in the other six objects for long-period radial velocity variations due to a binary companion sets significant constraints on the properties of

The binary fraction of planetary nebula central stars - III. the promise of VPHAS+

“…Hillwig et al 2017, high precision observations and careful reduction techniques are required for wider binaries (e.g. Hrivnak et al 2017). This means that sample sizes are small, making statistical analysis of the total PN population difficult.…”

Surveying Planetary Nebulae Central Stars for Close Binaries: Constraining Evolution of Central Stars Based on Binary Parameters

“…The CSs of PPNe are observed to be single objects and stable over at least several decades through direct observation (though many show pulsations). They do not show evidence of binarity, significant mass transfer, or large-scale changes, and the circumstellar envelope has detached from the CS [32]. If these objects entered a CE in the past, they are now at a stage after the CE has been ejected.…”

“…Various photometric, spectroscopic, and radial velocity studies of PPNe to search for close binaries that may be responsible for shaping have all ended with the absence of any evidence for close binary cores [31,32], or in fact for any binary systems with orbital periods less than years.…”

Spectroscopic and Photometric Variability of Three Oxygen Rich Post-AGB “Shell” Objects

“…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. Radial velocities of the HERMES spectra were determined via the cross-correlation technique using a mask in the range 477-655 nm for F0-type stars and fitting the peak of the obtained correlation function with a gaussian (Hrivnak et al [1]). Radial velocities of DAO spectra were also obtained via cross correlation with a set of bright IAU RV standards observed with the same instrumentation.…”

“…We selected seven bright (V < 10 mag) post-AGB stars observable with 1-m class telescopes from the northern hemisphere (Hrivnak et al [1]). They all have F-and G spectral types.…”