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Register a new userSymbiotic Miras vs. Planetary Nebulae in the Near Infrared
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While symbiotic Miras and planetary nebulae are hard to distinguish by optical spectroscopy, their near infrared colors differ. We propose the near infrared two-color diagram to be an excellent tool to easily distinguish these two classes of objects.
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This paper continues our study of the behaviour of near infrared helium recombination lines in planetary nebula. We find that the 1.7007um 4^3D-3^3P HeI line is a good measure of the HeI recombination rate, since it varies smoothly with the effective temperature of the central star. We were unable to reproduce the observed data using detailed photoionisation models at both low and high effective temperatures, but plausible explanations for the difference exist for both. We therefore conclude that this line could be used as an indicator of the effective temperature in obscured nebula. We also characterised the nature of the molecular hydrogen emission present in a smaller subset of our sample. The results are consistent with previous data indicating that ultraviolet excitation rather than shocks is the main cause of the molecular hydrogen emission in planetary nebulae.
Number of known symbiotic stars (SySt) is still significantly lower than their predicted population. One of the main problems in finding complete population of SySt is the fact that their spectrum can be confused with other objects, such as planetary nebulae (PNe) or dense H II regions. The problem is reinforced by a fact that in significant fraction of established SySt the emission lines used to distinguish them from other objects are not present. We aim at finding new diagnostic diagrams that could help separate SySt from PNe. Additionally, we examine known sample of extragalactic PNe for candidate SySt. We employed emission line fluxes of known SySt and PNe from the literature. We found that among the forbidden lines in the optical region of spectrum, only the [O III] and [N II] lines can be used as a tool for distinguishing between SySt and PNe, which is consistent with the fact that they have the highest critical densities. The most useful diagnostic that we propose is based on He I lines which are more common and stronger in SySt than forbidden lines. All these useful diagnostic diagrams are electron density indicators that better distinguishes PNe and ionized symbiotic nebulae. Moreover, we found six new candidate SySt in the Large Magellanic Cloud and one in M81. If confirmed, the candidate in M81 would be the furthest known SySt thus far.
Planetary nebulae (PNe) are powerful tracers of evolved stellar populations. Among the 3000 known PNe in the Galaxy, about 600 are located within the 520 square-degree area covered by the VVV survey. The VVV photometric catalogue provides an important new dataset for the study of PNe, with high-resolution imaging in five near-infrared bands. Aperture photometry of known PNe in the VVV area was retrieved from source catalogues. Care was taken to minimise any confusion with field stars. The colours of the PNe we are determined for H-Ks, J-H, Z-Y, and Y-J, and compared to stars and to other types of emission line objects. Cloudy photo-ionisation models were used to predict colours for typical PNe. We present near-infrared photometry for 353 known PNe. The best separation from other objects is obtained in the H-Ks vs. J-H diagram. We calculated the emission-line contribution to the in-band flux based on a model for NGC 6720: we find that this is highest in the Z and Y bands at over 50%, lower in the J band at 40%, and lowest in the H and Ks bands at 20%. A new view of PNe in the wavelength domain of the Z and Y bands is shown. Photo-ionisation models are used to explore the observed colours in these bands. The Y band is shown to be dominated by HeI 1.083 mu and HeII 1.012 mu, and colours involving this band are very sensitive to the temperature of the ionizing star. The VVV survey represents a unique dataset for studing crowded and obscured regions in the Galactic plane. The diagnostic diagrams presented here allow one to study the properties of known PNe and to uncover objects not previously classified.
Near-infrared (2.5-5.0$,mu$m) low-resolution ($lambda/Deltalambda{sim}100$) spectra of 72 Galactic planetary nebulae (PNe) were obtained with the Infrared Camera (IRC) in the post-helium phase. The IRC, equipped with a $1{times}1$ window for spectroscopy of a point source, was capable of obtaining near-infrared spectra in a slit-less mode without any flux loss due to a slit. The spectra show emission features including hydrogen recombination lines and the 3.3-3.5$,mu$m hydrocarbon features. The intensity and equivalent width of the emission features were measured by spectral fitting. We made a catalog providing unique information on the investigation of the near-infrared emission of PNe. In this paper, details of the observations and characteristics of the catalog are described.
Recombination lines (RLs) of C II, N II, and O II in planetary nebulae (PNs) have been found to give abundances that are much larger in some cases than abundances from collisionally-excited forbidden lines (CELs). The origins of this abundance discrepancy are highly debated. We present new spectroscopic observations of O II and C II recombination lines for six planetary nebulae. With these data we compare the abundances derived from the optical recombination lines with those determined from collisionally-excited lines. Combining our new data with published results on RLs in other PNs, we examine the discrepancy in abundances derived from RLs and CELs. We find that there is a wide range in the measured abundance discrepancy Delta(O+2) = log O+2(RL) - log O+2(CEL), ranging from approximately 0.1 dex up to 1.4 dex. Most RLs yield similar abundances, with the notable exception of O II multiplet V15, known to arise primarily from dielectronic recombination, which gives abundances averaging 0.6 dex higher than other O II RLs. We compare Delta(O+2) against a variety of physical properties of the PNs to look for clues as to the mechanism responsible for the abundance discrepancy. The strongest correlations are found with the nebula diameter and the Balmer surface brightness. An inverse correlation of Delta(O+2) with nebular density is also seen. Similar results are found for carbon in comparing C II RL abundances with ultraviolet measurements of C III].
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