CO emission from evolved stars and proto-planetary nebulae

Knapp, G. R.; Sutin, Brian M.; Phillips, T. G.; Ellison, Brian N.; Keene, J.; Leighton, Robert B.; Masson, C. R.; Steiger, Walter R.; Veidt, B.; Young, Kaisa E.

doi:10.1086/167052

Cited by 21 publications

(13 citation statements)

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“…However, if the ionized nebula is optically thick at 21 cm, any H i gas present in this zone would be invisible. Knapp & Bowers (1983) previously attempted unsuccessfully to detect R Aqr in H i using the VLA, and unlike the other four stars in our present survey, R Aqr has never been detected in CO (Knapp et al 1989;Young 1995). Figure 10 shows an image of the 1.4 GHz (21 cm) continuum emission in the R Aqr field.…”

Section: Introductionmentioning

confidence: 68%

Very Large Array Observations of Hiin the Circumstellar Envelopes of Asymptotic Giant Branch Stars

Matthews

Reid

2007

Astron J

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We have used the Very Large Array to search for neutral atomic hydrogen (H i) in the circumstellar envelopes of five asymptotic giant branch stars. We have detected H i 21 cm emission coincident in both position and velocity with the S-type semiregular variable star RS Cnc. The emission comprises a compact, slightly elongated feature centered on the star with a mean diameter of $82 00 (1:5 ; 10 17 cm), plus an additional filament extending $6 0 to the northwest. If this filament is associated with RS Cnc, it would imply that a portion of its mass loss is highly asymmetric. We estimate M H i % 1:5 ; 10 À3 M and a mass-loss rateṀ % 1:7 ; 10 À7 M yr À1 . Toward three other stars (IRC+10216, EP Aqr, R Cas) we have detected arcminute-scale H i emission features at velocities consistent with the circumstellar envelopes, but spatially offset from the stellar positions. Toward R Cas, the emission is weak but peaks at the stellar systemic velocity and overlaps with the location of its circumstellar dust shell and thus is probably related to the star. In the case of IRC+10216, we were unable to confirm the detection of H i in absorption against the cosmic background previously reported by Le Bertre & Gérard. However, we detect arcs of emission at projected distances of r $ 14 0 Y18 0 ($2 ; 10 18 cm) to the northwest of the star. The large separation of the emission from the star is plausible, given its advanced evolutionary status, although it is unclear if the asymmetric distribution and complex velocity structure are consistent with a circumstellar origin. For EP Aqr, the detected H i emission comprises multiple clumps redward of the systemic velocity, but we are unable to determine unambiguously whether the emission arises from the circumstellar envelope or from interstellar clouds along the line of sight. Regardless of the adopted distance for the H i clumps, their inferred H i masses are at least an order of magnitude smaller than their individual gravitational binding masses. We did not detect any H i emission from our fifth target, R Aqr (a symbiotic binary), but measured a 1.4 GHz continuum flux density of 18:8 AE 0:7 mJy. R Aqr is a previously known radio source, and the 1.4 GHz emission likely arises primarily from free-free emission from an ionized circumbinary envelope.

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Section: Introductionmentioning

confidence: 68%

Very Large Array Observations of Hiin the Circumstellar Envelopes of Asymptotic Giant Branch Stars

Matthews

Reid

2007

Astron J

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“…From discussion in Knapp et al (1989), we infer that the units in Knapp et al (1990) are equivalent to T mb . The CO extent is unknown, but optical and radiocontinuum images are very small, 1-2 , see de Marco et al (1997) and Bedding & Zijlstra (1994), so we will assume that the CO shell is also much smaller than the telescope resolution in those observations (32 ).…”

Section: He 2-113mentioning

confidence: 94%

Mass, linear momentum and kinetic energy of bipolar flows in protoplanetary nebulae

Bujarrabal

Castro-Carrizo

Alcolea

et al. 2001

A&A

268

356

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Abstract.We have studied the CO emission from protoplanetary nebulae (PPNe). Our sample is composed of 37 objects and includes, we think, all well identified PPNe detected in CO, together with the two yellow hypergiants emitting in CO and one young PN. We present a summary of the existing CO data, including accurate new observations of the 12 CO and 13 CO J = 1-0 and J = 2-1 lines in 16 objects. We identify in the nebulae a slowly expanding shell (represented in the spectra by a central core) and a fast outflow (corresponding to the line wings), that in the well studied PPNe is known to be bipolar. Excluding poor data, we end up with a sample of 32 sources (including the 16 observed by us); fast flows are detected in 28 of these nebulae, being absent in only 4. We present a method to estimate from these data the mass, "scalar" momentum and kinetic energy of the different components of the molecular outflows. We argue that the uncertainties of our method can hardly lead to significant overestimates of these parameters, although underestimates may be present in not well studied objects. The total nebular mass is often as high as ∼1 M , and the mass-loss rate, that (presumably during the last stages of the AGB phase) originated the nebula, had typical values ∼10 −4 M yr −1 . The momentum corresponding to this mass ejection process in most studied nebulae is accurately coincident with the maximum momentum that radiation pressure, acting through absorption by dust grains, is able to supply (under expected conditions). We estimate that this high-efficiency process lasts about 1000-10 000 yr, after which the star has ejected a good fraction of its mass and the AGB phase ends. On the other hand, the fast molecular outflows, that have probably been accelerated by shock interaction with axial post-AGB jets, carry a significant fraction of the nebular mass, with a very high momentum (in most cases between 10 37 and 10 40 g cm s −1 ) and very high kinetic energy (usually between 10 44 and 10 47 erg). In general, yellow hypergiants and post-AGB objects with low initial mass show nebular masses and momenta that are, respectively, higher and lower than these values. We compare the momenta of the fast outflows with those that can be supplied by radiation pressure, taking into account the expected short acceleration times and some effects that can increase the momentum transfer. We find that in about 80% of PPNe, the fast molecular flows have too high momenta to be powered by radiation pressure. In some cases the momentum of the outflow is ∼1000 larger than that carried by radiation pressure; such high factors are difficult to explain even under exceptional conditions. Wind interaction is the basic phenomenon in the PN shaping from the former AGB envelopes; we conclude that this interaction systematically takes place along a dominant direction and that this process is not powered by radiation pressure. Due to the lack of theoretical studies, the possible momentum source remains a matter of speculation.

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“…Extensive surveys have been performed, and presently more than 500 objects have been detected (e.g., Knapp & Morris 1985;Leahy et al 1987;Nguyen-Q-Rieu et al 1986;Knapp et al 1989;Loup et al 1990;Margulis et al 1990;Likkel et al 1991;Bujarrabal et al 1992;Nyman et al 1992;Kastner et al 1993;Olofsson et al 1993;van der Veen et al 1993;Volk et al 1993;Bieging & Latter 1994;Hu et al 1994; Kahane & Jura 1994;Sahai & Liechti 1995;Young 1995;Groenewegen et al 1996;Kerschbaum et al 1996c;Bieging et al 1998;Groenewegen & de Jong 1998;Josselin et al 1998; Knapp et al 1998;Kerschbaum & Olofsson 1998). A significant fraction of this work was catalogued by Loup et al (1993, hereafter L93).…”

Section: Introductionmentioning

confidence: 99%

Oxygen-rich semiregular and irregular variables

Kerschbaum

Olofsson²

1999

Astron. Astrophys. Suppl. Ser.

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Abstract. Using the SEST, the Onsala 20 m telescope, the JCMT, and the IRAM 30 m telescope we have carried out a survey of circumstellar CO(J = 1 − 0, 2 − 1, 3 − 2, and 4 − 3) emission on a large sample of oxygen-rich semiregular (SRa and SRb) and irregular variables (Lb). A total of 109 stars were observed in at least one CO line: 66 were shown to have circumstellar CO line emission (7 SRa, 36 SRb, and 23 Lb variables), ∼ 60% of the semiregulars and all but one of the irregulars were detected for the first time. Most stars were observed in at least two transitions. There is a total of 138 detected CO lines. For twelve stars strong interference from interstellar CO emission precluded detection.We present here a catalogue of all observational data and the spectra of all detections, as well as brief discussions on detection statistics (including its dependence on variability type, period, IRAS-colour, IRAS LRS-class, and M-subclass), line profiles (including line shape asymmetry, multi-component line shapes, and line intensity ratios), gas expansion velocity distributions, and correlations between CO line and IR continuum fluxes (including implications for the mass-loss mechanism).

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CO emission from evolved stars and proto-planetary nebulae

Cited by 21 publications

References 0 publications

Very Large Array Observations of Hiin the Circumstellar Envelopes of Asymptotic Giant Branch Stars

Very Large Array Observations of Hiin the Circumstellar Envelopes of Asymptotic Giant Branch Stars

Mass, linear momentum and kinetic energy of bipolar flows in protoplanetary nebulae

Oxygen-rich semiregular and irregular variables

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