Variability in Proto-planetary Nebulae. V. Velocity and Light Curve Analysis of IRAS 17436+5003, 18095+2704, and 19475+3119

Abstract

We have obtained contemporaneous light, color, and radial velocity data for three proto-planetary nebulae (PPNe) over the years 2007 to 2015. The light and velocity curves of each show similar periods of pulsation, with photometric periods of 42 and 50 days for IRAS 17436+5003, 102 days for IRAS 18095+2704, and 35 days for IRAS 19475+3119. The light and velocity curves are complex with multiple periods and small, variable amplitudes. Nevertheless, at least over limited time intervals, we were able to identify dominant periods in the light, color, and velocity curves and compare 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. Similar results were found previously for two other PPNe, although for them the light and color appeared to be in phase. Thus, it appears that PPNe are brightest when smallest and hottest. These phase results differ from those found for classical Cepheid variables, where the light and velocity differ by half a cycle, and are hottest at about average size and expanding. However, they do appear to have similar phasing to the larger-amplitude pulsations seen in RV Tauri variables. Presently, few pulsation models exist for PPNe, and these do not fit the observations well, especially the longer periods observed. Model fits to these new light and velocity curves would allow masses to be determined for these post-AGB objects, and thereby provide important constraints to post-AGB stellar evolution models of low-and intermediate-mass stars.

Variability in Proto-Planetary Nebulae: VII. Light Curve Studies of Five Medium-bright, Oxygen-rich or Mixed-chemistry Post-AGB/Post-RGB Objects

“…In this paper, we report on the search for periodic brightness variations in the light curves of five medium-bright PPN candidates which appear to have O-rich or mixed chemistries. This follows our earlier variability studies of four bright (V = 7-11 mag) O-rich PPNe (Hrivnak et al 2015b(Hrivnak et al , 2018. Most of our previous variability studies have been of C-rich PPNe in the Milky Way Galaxy (Hrivnak et al 2010(Hrivnak et al , 2013(Hrivnak et al , 2020 and in the Magellanic Clouds (Hrivnak et al 2015a).…”

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

“…The RV amplitudes are small (<4.0 km/s, Hrivnak et al [12]) and the periods found in the RV data are in the range 35 to 103 days, similar to the pulsation periods of the objects. So far, no clear evidence for long-period RV variations due to binary companions has been found in any of these objects.…”

“…However, over limited time intervals during 2007-2015, we were able to identify dominant periods in the light, color, and velocity curves and compare the phasing of each. See figures in Hrivnak et al [12] which shows the phased light, color, and velocity curves of the objects. The color curves appear to peak with or slightly after the light curves while the RV curves peak about a quarter of a cycle before the light curves.…”

“…The complex spectral variability and lack of stable periods in the light and velocity curves makes the temporal changes hard to phase. Provisionally, in Figure 3 we phased V887 Her to the period of 102.3 days and the same epoch as Hrivnak et al [12]. We searched for evidence for a jet as seen in BD+46 442 (Bollen et al [17]), in which a broad absorption with a velocity up to ∼−400 km/s is observed.…”

Variability in Proto-planetary Nebulae. VI. Multitelescope Light Curve Studies of Several Medium-bright (V = 13–15), Carbon-rich Objects

“…Studies of pulsation in PPNe have also been published by Arkhipova and collaborators (e.g., Arkhipova et al 2010Arkhipova et al , 2011. For the brighter ones (V ≤ 10.5 mag), we have also compared their radial velocity curves with their light curves to determine the phase relationship between their brightness, temperature, and size (Hrivnak et al 2013(Hrivnak et al , 2018). Here we present our observed light curves for five medium-bright objects.…”