2–45 Micron Infrared Spectroscopy of Carbon‐rich Proto–Planetary Nebulae

Abstract

Infrared Space Observatory (ISO) 2È45 km observations of seven protoÈplanetary nebulae (PPNs) and two other carbon-rich objects are presented. The unidentiÐed emission features at 21 and 30 km are detected in six sources, including four new detections of the 30 km feature. This previously unresolved 30 km feature is now resolved and found to consist of a broad feature peaking at 27.2 km (the "" 30 km ÏÏ feature) and a narrower feature at 25.5 km (the "" 26 km ÏÏ feature). This new 26 km feature is detected in eight sources and is particularly strong in IRAS Z02229]6208 and 16594[4656. The unidentiÐed infrared (UIR) emission features at 3.3, 6.2, 7.7, and 11.3 km, which are commonly observed in planetary nebulae and H II regions, are also seen in these PPNs. However, their strengths relative to the continuum plateaus at 8 and 12 km are weaker than in planetary nebulae. The 6.9 km feature, seen almost exclusively in PPNs, is strong. New millimeter CO and HCN observations were made ; they support the carbon-rich nature of the objects and yield the expansion velocities of the gaseous envelopes. The spectral energy distributions of these PPNs were Ðtted with a radiative-transfer model, taking into account the emission features at 21, 26, and 30 km. A signiÐcant fraction of the total energy output is emitted in these features : as high as 20% in the 30 km feature and 8% in the 21 km feature. The fact that so much energy is carried in these features suggests that the material responsible for these features must be made of abundant elements and most likely involves carbon. appears to be ruled out as the emitter of the SiS 2 21 km feature due to the absence of a predicted companion feature.

Infrared light on the composition of the dust surrounding carbon-rich stars

“…In view of the difference in approach, the envelope mass they find The circumstellar envelope of HD 56126 and our mass determination are compatible. Hrivnak et al (2000) derive a mass-loss rate of 3.6 10 −5 M /yr at the distance of 2 kpc, which corresponds to 5 10 −5 M /yr at 2.5 kpc, about half of the value that we find. Jura et al (2000) model the density in the envelope as the result of a "dying" wind, i.e.…”

“…Lastly, these sources exhibit a strong, broad feature between 23−45 µm (Omont et al 1995;Szczerba et al 1997;Hrivnak et al 2000), called the "30" µm feature. The carrier of the "30" µm feature is identified with magnesium sulfide (MgS) (see Chapter 6 and references therein).…”

“…Nuth et al 1985; Goebel & Moseley 1985;Begemann et al 1994). Hrivnak et al (2000) show that the "30" µm feature in the 21 µm objects consists of a 26 and a 30 µm component. An extensive survey of the "30" µm feature in a wide range of C-rich evolved objects shows that its peak position can vary from 26 µm to 34 µm (Chapter 6), see To compare the features we observe in NGC 40 and NGC 6369 with other sources we extract the profiles of the excess emission.…”

“…is commonly found in C-rich post-AGBs and PNe however with varying band shapes and varying feature to continuum ratios (Goebel & Moseley 1985; Waters et al 2000;Hrivnak et al 2000;Volk et al 2002) Goebel & Moseley (1985 proposed solid magnesium sulfide (MgS) as the possible carrier of the "30" µm feature. Their suggestion is based on the coincidence of the emission feature with the sole IR-resonance of MgS (Nuth et al 1985;Begemann et al 1994) and the fact that MgS is one of the expected condensates around these objects (Lattimer et al 1978; Lodders & Fegley 1999).…”

TheWISEview of RV Tauri stars

“…The expansion velocity of the gas as well as the mass-loss rates can be determined by CO observations (Bujarrabal 1999). A typical expansion velocity for the circumstellar shell is 10 to 15 km/s (Hrivnak et al 2000;He et al 2014). We made an extensive literature survey for optically bright objects for which the envelope kinematics are studied using the rotational transition of CO (see Table 1).…”