Studies of Variability in Proto-Planetary Nebulae. Ii. Light and Velocity Curve Analyses of Iras 22272+5435 and 22223+4327

Abstract

We have carried out a detailed observational study of the light, color, and velocity variations of two bright, carbon-rich proto-planetary nebulae, IRAS 22223+4327 and 22272+5435. The light curves are based upon our observations from 1994 to 2011, together with published data by Arkhipova and collaborators. They each display four significant periods, with primary periods for IRAS 22223+4327 and 22272+5435 being 90 and 132 days, respectively. For each of them, the ratio of secondary to primary period is 0.95, a value much different from that found in Cepheids, but which may be characteristic of post-AGB stars. Fewer significant periods are found in the smaller radial velocity data sets, but they agree with those of the light curves. The color curves generally mimic the light curves, with the objects reddest when faintest. A comparison in seasons when there exist contemporaneous light, color, and velocity curves reveals that the light and color curves are in phase, while the radial velocity curves are ∼0.25 P out of phase with the light curves. Thus they differ from what is seen in Cepheids, in which the radial velocity curve is 0.50 P out of phase with the light curve. Comparison of the observed periods and amplitudes with those of post-AGB pulsation models shows poor agreement, especially for the periods, which are much longer than predicted. These observational data, particularly the contemporaneous light, color, and velocity curves, provide an excellent benchmark for new pulsation models of cool stars in the post-AGB, proto-planetary nebula phase.

The Evolved Pulsating Cemp Star Hd 112869

“…The variations are semiregular, with some changes from cycle to cycle and a significant scatter of velocities near the velocity extremums, which exceeds the standard error of measurements. Similar velocity variations and scatter are observed for two protoplanetary nebulae-HD 235858 and BD+42°4388 (Hrivnak et al 2013). The velocity variations of HD 112869 are accompanied by light and color variations.…”

“…A comparison of the light, color, and velocity curves reveals that the light and color curves are about in phase, while the radial velocity curve is out of phase with the light curve. Thus, the radial velocity and light/color variations display the correlations observed for the pulsating evolved stars (see Hrivnak et al 2013, and references therein).…”

“…All the velocity measurements for HD 112869, as a function of phase, resulting from the approximation by a sine wave with a period of 114.9 days, are plotted in Figure 5 (top panel). The radialvelocity monitoring shows with certainty that HD 112869 is a pulsator with a dominating pulsation period of about 115 days and a variability pattern typical of the evolved low mass stars (see Hrivnak et al 2013 and references therein).…”

Peculiarities of the atmosphere and envelope of a post-AGB star, the optical counterpart of IRAS 23304+6347

“…The overwhelming majority of the radial velocities used by Hrivnak et al (2013) were obtained with CORAVEL-type spectrometers. For definiteness, consider the results obtained by these authors for V354 Lac (IRAS 22272+5435).…”

“…A fundamental shortcoming of the single-channel methods is a mismatch between the scales of the spectrum and the shifted spectral mask arising at any change in the stellar radial velocity. In the period 1991-1995, Hrivnak et al (2013) used the DAO cross-correlation photometer (Fletcher et al 1982;McClure et al 1985). The above mismatch between the scales was partly compensated for by a special design of the mask (a with a system of tall slits in the range 4000-4600Å, slope changing with distance from the mask center) and a special law of mask motion (at 45 o to the spectrum axis).…”