A Herschel study of Planetary Nebulae

We present Herschel PACS and SPIRE images of the dust shells around the planetary nebulae NGC 650, NGC 6853, and NGC 6720, as well as images showing the dust temperature in their shells. The latter shows a rich structure, which indicates that internal extinction in the UV is important despite the highly evolved status of the nebulae.Comment: 2 pages, 1 figure, 2012, proceedings IAU Symposium 283 Planetary Nebulae: An Eye to the Futur

JWST observations of the Ring Nebula (NGC 6720): I. Imaging of the rings, globules, and arcs

We present JWST images of the well-known planetary nebula NGC 6720 (the Ring Nebula), covering wavelengths from 1.6$\mu$m to 25 $\mu$m. The bright shell is strongly fragmented with some 20 000 dense globules, bright in H$_2$, with a characteristic diameter of 0.2 arcsec and density $n_{\rm H} \sim 10^5$-$10^6$ cm$^{-3}$. The shell contains a thin ring of polycyclic aromatic hydrocarbon (PAH) emission. H$_2$ is found throughout the shell and in the halo. H$_2$ in the halo may be located on the swept-up walls of a biconal polar flow. The central cavity is shown to be filled with high ionization gas and shows two linear structures. The central star is located 2 arcsec from the emission centroid of the cavity and shell. Linear features (`spikes') extend outward from the ring, pointing away from the central star. Hydrodynamical simulations are shown which reproduce the clumping and possibly the spikes. Around ten low-contrast, regularly spaced concentric arc-like features are present; they suggest orbital modulation by a low-mass companion with a period of about 280 yr. A previously known much wider companion is located at a projected separation of about 15 000 au; we show that it is an M2-M4 dwarf. The system is therefore a triple star. These features, including the multiplicity, are similar to those seen in the Southern Ring Nebula (NGC 3132) and may be a common aspect of such nebulae.Comment: 25 pages, 23 figures. Submitted to Monthly Notices of the Royal Astronomical Society. Corrected typos in metadat

A stubbornly large mass of cold dust in the ejecta of Supernova 1987A

We present new Herschel photometric and spectroscopic observations of Supernova 1987A, carried out in 2012. Our dedicated photometric measurements provide new 70 micron data and improved imaging quality at 100 and 160 micron compared to previous observations in 2010. Our Herschel spectra show only weak CO line emission, and provide an upper limit for the 63 micron [O I] line flux, eliminating the possibility that line contaminations distort the previously estimated dust mass. The far-infrared spectral energy distribution (SED) is well fitted by thermal emission from cold dust. The newly measured 70 micron flux constrains the dust temperature, limiting it to nearly a single temperature. The far-infrared emission can be fitted by 0.5+-0.1 Msun of amorphous carbon, about a factor of two larger than the current nucleosynthetic mass prediction for carbon. The observation of SiO molecules at early and late phases suggests that silicates may also have formed and we could fit the SED with a combination of 0.3 Msun of amorphous carbon and 0.5 Msun of silicates, totalling 0.8 Msun of dust. Our analysis thus supports the presence of a large dust reservoir in the ejecta of SN 1987A. The inferred dust mass suggests that supernovae can be an important source of dust in the interstellar medium, from local to high-redshift galaxies.Comment: ApJ accepted, 8 page

<i>JWST</i> observations of the Ring Nebula (NGC 6720): I. Imaging of the rings, globules, and arcs

We present $\textit{JWST}$ images of the well-known planetary nebula NGC 6720 (the Ring Nebula), covering wavelengths from 1.6$\mu$m to 25$\mu$m. The bright shell is strongly fragmented with some 20 000 dense globules, bright in $H_2$, with a characteristic diameter of 0.2 arcsec and density $n_H$ ∼ $10^5$–$10^6$ $\textit{cm}$$^{-3}$. The shell contains a narrow ring of polycyclic aromatic hydrocarbon (PAH) emission. $H_2$ is found throughout the shell and also in the halo. $H_2$ in the halo may be located on the swept-up walls of a biconal polar flow. The central cavity is filled with high ionization gas and shows two linear structures which we suggest are the edges of a biconal flow, seen in projection against the cavity. The central star is located 2 arcsec from the emission centroid of the cavity and shell. Linear features (‘spikes’) extend outward from the ring, pointing away from the central star. Hydrodynamical simulations reproduce the clumping and possibly the spikes. Around ten low-contrast, regularly spaced concentric arc-like features are present; they suggest orbital modulation by a low-mass companion with a period of about 280 yr. A previously known much wider companion is located at a projected separation of about 15 000 au; we show that it is an M2–M4 dwarf. NGC 6720 is therefore a triple star system. These features, including the multiplicity, are similar to those seen in the Southern Ring Nebula (NGC 3132) and may be a common aspect of such nebulae

PROPERTIES OF POST-AGB STARS WITH IRAS COLORS TYPICAL OF PLANETARY NEBULAE.

We have investigated the infrared properties of a sample of objects with IRAS colors typical of planetary nebulae. The selected objects have not yet evolved to the planetary nebula stage since they have no detectable radio continuum emission and they are therefore likely post-AGB stars. 1

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

© 2018 by the authors. Light, color, and radial velocity data (2007-2015) for HD161796, V887 Her, and HD331319, 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 Hα 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.status: publishe

Spectroscopic and photometric variability of three oxygen rich post-AGB “Shell” objects

Light, color, and radial velocity data (2007–2015) for HD161796, V887 Her, and HD331319, 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 Ha 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

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

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 Hα 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