Mass loss from evolved stars. II - Radio continuum emission and evolution to planetary nebulae

Spergel, David N.; Giuliani, J. L.; Knapp, G. R.

doi:10.1086/161536

Cited by 45 publications

(31 citation statements)

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“…There is no other known radio lines, although they have been searched for (H 2 O, SiO, HCN, H 2 S, SO 2 , etc.). Finally, RS Cnc has not been detected in the radio continuum neither at 2.6 mm (Neri et al 1998), 2 cm (Drake et al 1991) or 6 cm (Spergel et al 1983). …”

Section: Letter To the Editormentioning

confidence: 84%

The H I emission profile of RS Cnc

Gérard

Bertre

2003

A&A

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Abstract. The H I line at 21 cm has been detected in the direction of the S-type AGB star RS Cnc with the Nançay Radio Telescope (NRT). The profile is composite and similar to the CO rotational line profiles. It is composed of a narrow rectangular component overimposed on a wider Gaussian one, both centred on the stellar radial velocity. The narrow component has a width of 4 km s −1 and is unresolved (with the NRT beam size of 4 in α). The Gaussian component has a width (FWHM) of 12 km s −1 and seems resolved by the NRT. These components trace at least 2 different episodes of mass loss by RS Cnc. We argue that the atomic hydrogen responsible for the narrow rectangular profile was likely formed in the stellar atmosphere which could thus be devoid of molecular hydrogen, although we cannot strictly exclude that up to 25% may have been produced by photodissociation of H 2 . As predicted 20 years ago by Glassgold & Huggins, such a situation should be common to giants with stellar effective temperature larger than 2500 K. This property is relevant to the atmospheric structure of these sources and probably also to the characteristics of their winds.

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Section: Letter To the Editormentioning

confidence: 84%

The H I emission profile of RS Cnc

Gérard

Bertre

2003

A&A

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“…In addition, both have radial velocities offset from the peak of the Galactic interstellar emission along the line of sight (Hartmann & Burton 1997), and neither has any strong neighboring 20 cm continuum sources (Condon et al 1998) whose sidelobes might complicate the detection of weak, extended stellar H i signals. An additional motivation for targeting R Aqr is that it is part of a symbiotic binary system, with the orbit of the hot companion lying within the cool giant's circumstellar envelope (e.g., Spergel et al 1983;Hollis et al 1986). It has been suggested that the primary source of the H i emission detected from the weakly symbiotic AGB star o Ceti could be H 2 photodissociated by its hot companion Gérard & Le Bertre 2003); hence, it is of interest Michalitsianos et al (1980;R Aqr) or from Table 3 of Knapp et al (1998;all other stars).…”

Section: Sample Selectionmentioning

confidence: 99%

“…Although R Aqr is surrounded by extensive nebulosity (extending to at least 2 0 ; e.g., Wallerstein & Greenstein 1980;Hollis et al 1985), the current mass-loss rate of the star is rather low. Based on ultraviolet spectroscopy and radio continuum observations, respectively, both Michalitsianos et al (1980) and Spergel et al ( 1983) estimatedṀ $ 6 ; 10 À8 M yr À1 . However, these determinations may underestimate the actual massloss rate by as much as an order of magnitude, depending on the fraction of the wind that is ionized (e.g., Dougherty et al 1995).…”

Section: Introductionmentioning

confidence: 99%

“…At the distance of R Aqr, the lower boundary for this region would lie well within one VLA synthesized beam. Models by Spergel et al (1983) predict that, close to the R Aqr primary (r P 4:5 ; 10 13 cm), an additional zone of neutral gas may be present. However, if the ionized nebula is optically thick at 21 cm, any H i gas present in this zone would be invisible.…”

Section: Introductionmentioning

confidence: 99%

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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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“…The expansion velocity of the ionization front in CRL 618, estimated from radio continuum mapping with high angular resolution in different epochs, has decreased with time: from 50-74(D/0.9 kpc) (Kwok & Feldman 1981) to 26(D/0.9 kpc) km s À1 (Spergel, Giuliani, & Knapp 1983). Expanding at this rate, the ionization front will never reach the lobes, which are moving much faster (up to 200 km s À1 ), and the molecules will reform in the shocked gas sooner or later.…”

Section: Future Circumstellar Evolution Of Crl 618mentioning

confidence: 99%

Physical Structure of the Proto–Planetary Nebula CRL 618. I. Optical Long‐Slit Spectroscopy and Imaging

Contreras¹,

Sahai²,

Paz³

2002

ApJ

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In this paper we present optical long-slit spectroscopy and imaging of the proto-planetary nebula CRL 618. The optical lobes of CRL 618 consist of shock-excited gas, which emits many recombination and forbidden lines, and dust, which scatters light from the innermost regions. From the analysis of the scattered H emission, we derive a nebular inclination of i ¼ 24 AE 6 . The spectrum of the innermost part of the east lobe (visible as a bright, compact nebulosity close to the star in the H Hubble Space Telescope image) is remarkably different from that of the shocked lobes but similar to that of the inner H ii region, suggesting that this region represents the outermost parts of the latter. We find a nonlinear radial variation of the gas velocity along the lobes. The largest projected LSR velocities (with respect to the systemic velocity), $80 km s À1 , are measured at the tips of the lobes, where the direct images show the presence of compact bow-shaped structures. The velocity of the shocks in CRL 618 is in the range $75-200 km s À1 , as derived from diagnostic line ratios and line profiles. We report a brightening (weakening) of [O iii] 5007 ([O i] 6300) over the last $10 years that may indicate a recent increase in the speed of the exciting shocks. From the analysis of the spatial variation of the nebular extinction, we find a large density contrast between the material inside the lobes and beyond them: the optical lobes seem to be '' cavities '' excavated in the asymptotic giant branch (AGB) envelope by interaction with a more tenuous post-AGB wind. The electron density, with a mean value n e $ 5 Â 10 3 10 4 cm À3 , shows significant fluctuations but no systematic decrease along the lobes, in agreement with most line emission arising in a thin shell of shocked material (the lobe walls) rather than in the post-AGB wind filling the interior of the lobes. The masses of atomic and ionized gas, respectively, in the east (west) lobe are >1:3 Â 10 À4 (>7 Â 10 À5 ) and $6 Â 10 À5 ($4 Â 10 À5 ) M . The shocks in CRL 618 are in a radiative regime and may lead in the future to the evolution of the optically emitting lobes into a fast, bipolar molecular outflow. The time required by the dense, shocked gas to cool down significantly is d2 yr, which is substantially lower than the kinematical age of the lobes (d180 yr). This result suggests that a fast wind is currently active in CRL 618 and keeps shocking the circumstellar material.

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Mass loss from evolved stars. II - Radio continuum emission and evolution to planetary nebulae

Cited by 45 publications

References 0 publications

The H I emission profile of RS Cnc

The H I emission profile of RS Cnc

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

Physical Structure of the Proto–Planetary Nebula CRL 618. I. Optical Long‐Slit Spectroscopy and Imaging

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