Evidence for the early onset of aspherical structure in the planetary nebula formation process: Spectropolarimetry of post-AGB stars

Trammell, Susan R.; Dinerstein, H. L.; Goodrich, Robert W.

doi:10.1086/117128

Cited by 90 publications

(111 citation statements)

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“…(2005) to explain the P Cygni-like profile of H and other recombination lines in the YPN M1-92, which shows a very broad, blue absorption feature well detached from the emission component that cannot result from the single stellar wind scenario used to explain typical P Cygni profiles. Our interpretation is also consistent with the fact that most PPNs exhibit intrinsic polarization of the continuum as well as some emission lines, which are most likely due to scattering off dust grains (Trammell et al 1994). In particular, Balmer lines seem to come from an H ii region close to the star, which is blocked from direct view by, e.g.,the thick equatorial dust waists commonly present in these objects, and are seen in reflection off the nebular dust (see also, e.g., Sánchez Contreras et al 2002).…”

Section: Correlationssupporting

confidence: 90%

“…] on the SEDs of nonspherically symmetric nebulae). High polarization values, implying mostly scattered light, are indeed observed for some objects in our sample (e.g., Trammell et al 1994;Gledhill 2005;Oppenheimer et al 2005;Bieging et al 2006 and references therein).…”

Section: Luminosity and Distancesupporting

confidence: 66%

“…H emission was not present in the spectrum of the C-rich variable star IRC +10216 observed by Trammell et al (1994) but was detected by Cohen & Schmidt (1982) (Cohen 1980;Cohen & Schmidt 1982;Trammell et al 1994). In our ESI spectrum, H appears much weaker than in earlier works and is blended with other (presumably metallic) lines with similar intensity.…”

Section: Variability Of the H Profilementioning

confidence: 89%

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Echelle Long‐Slit Optical Spectroscopy of Evolved Stars

Contreras

Sahai²,

Paz

et al. 2008

Astrophysical Journal Supplement Series, The

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We present echelle long-slit optical spectra of a sample of objects evolving off the asymptotic giant branch (AGB), most of them in the preplanetary nebula ( PPN ) phase, obtained with the ESI and MIKE spectrographs at the 10 m Keck II and 6.5 m Magellan-I telescopes, respectively. The total wavelength range covered with ESI (MIKE) is $3900Y10900 8 ($3600Y7200 8). In this paper, we focus our analysis mainly on the H profiles. Prominent H emission is detected in half of the objects, most of which show broad H wings (with total widths of up to $4000 km s À1 ). In the majority of the H -emission sources, fast, post-AGB winds are revealed by P-Cygni profiles. In $37% of the objects H is observed in absorption. In almost all cases, the absorption profile is partially filled with emission, leading to complex, structured profiles that are interpreted as an indication of incipient post-AGB mass loss. The rest of the objects ($13%) are H nondetections. We investigate correlations between the H profile and different stellar and envelope parameters. All sources in which H is seen mainly in absorption have F-G type central stars, whereas sources with intense H emission span a larger range of spectral types from O to G, with a relative maximum around B, and also including very late C types. Shocks may be an important excitation/ionization agent of the close stellar surroundings for objects with late type central stars. Sources with pure emission or P Cygni H profiles have larger J À K color excess than objects with H mainly in absorption, which suggests the presence of warm dust near the star in the former. The two classes of profile sources also segregate in the IRAS color-color diagram in a way that intense H -emitters have dust grains with a larger range of temperatures. Spectral classification of the central stars in our sample is presented. For a subsample (13 objects), the stellar luminosity has been derived from the analysis of the O i 7771Y7775 8 infrared triplet. The location in the HR diagram of most of these targets, which represent $30% of the whole sample, is consistent with relatively high final (and, presumably, initial) masses in the range M f $ 0:6 Y0:9 M (M i $ 3Y 8 M ).

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Section: Correlationssupporting

confidence: 90%

Section: Luminosity and Distancesupporting

confidence: 66%

Section: Variability Of the H Profilementioning

confidence: 89%

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Echelle Long‐Slit Optical Spectroscopy of Evolved Stars

Contreras

Sahai²,

Paz

et al. 2008

Astrophysical Journal Supplement Series, The

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“…Aspherical symmetries such as found by Trammeil, Dinerstein & Goodrich (1994) for post-AGB stars from spectropolarimetry may then be naturally understood, as they are already present in earlier stages. The observed, more obvious non-spherical symmetries in Protoplanetary and Planetary Nebulae (PPN) studied in the optical and IR (Kwok 1993) and also seen in optical polarimetry of evolved objects (Johnson h Jones 1991; Trammell et al 1994) are also consistent with the origin of the asymmetries being early in the AGB phase.…”

Section: Introductionmentioning

confidence: 57%

Asymmetries around Luminous Red Variables

Magalhães

Nordsieck

2000

Symp. - Int. Astron. Union

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Abstract. Departures from spherical symmetry are known to exist around Luminous Red Variables (LRVs). One of the earliest pieces of evidence came from the discovery that light from these objects is polarized. Additional evidence comes from other techniques and observations of related objects. This talk briefly reviews these data and focuses on the mechanisms that produce polarization in LRVs. Emphasis is given on recent spectropolarimetric monitoring data of selected key objects and what we have learned about the LRV environment from such data.

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“…It is the second brightest carbon star at 12 fim, next to IRC+10216, and is believed to be undergoing an early phase of the transition between asymptotic giant branch stars and planetary nebulae (Trammell et al 1994). However, because of its unusual color characteristics, it can be rather easily observed in optical wavelengths, contrary to other extreme carbon stars.…”

Section: Introductionmentioning

confidence: 99%