Spectropolarimetry of the post-main-sequence bipolar nebulae GL 618, M2-56, and M1-92

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

doi:10.1086/172128

Cited by 36 publications

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“…Considering that our slit is a factor of $2.5 smaller than theirs and the size of the nebula (2>5-3 00 in the direction perpendicular to the slit), we must conclude that the intensity of the [O iii] lines is now a factor of 2-3 larger than 9 years ago. Trammell et al (1993) also found upper limits for the flux of the [O iii] lines that are also much smaller than our measurements in spite of their broader slit (2 00 ). We also derive an [O iii]/H line ratio (less dependent on the slit width) a factor of $2 larger than that obtained by Kelly et al (1992) …”

Section: Line Identification and Flux Measurementscontrasting

confidence: 64%

“…Previous spectropolarimetric observations indicate that $40% of the total H flux is polarized (with a line polarization of about 15%; Trammell et al 1993); i.e., it is light scattered by nebular dust. The polarization of the forbidden lines is, however, much lower, and this would explain the absence of these features in these cases.…”

Section: Scattered and Local Emission Componentsmentioning

confidence: 99%

“…The high-excitation nebula (atomic and ionized gas) is composed of (1) a compact H ii region, visible through radio continuum emission, elongated in the east-west direction with an angular size of 0>2-0>4 that is increasing with time (Kwok & Feldman 1981;Martín-Pintado et al 1993), and (2) multiple lobes with shock-excited gas that produces recombination and forbidden line emission in the optical (e.g., Goodrich 1991;Trammell, Dinerstein, & Goodrich 1993;Kelly, Latter, & Rieke 1992;Trammell 2000). From previous spectroscopic data, the inner H ii region and the lobes are known to be expanding with velocities of $20 and up to $120 km s À1 , respectively Carsenty & Solf 1982, hereafter CS82).…”

Section: Introductionmentioning

confidence: 99%

“…From spectropolarimetric observations it is known that a fraction of the flux of the Balmer lines is also scattered light originally arising from the inner, compact H ii region (Schmidt & Cohen 1981;Trammell et al 1993). The polarization of the forbidden lines is negligible, indicating that they are almost entirely produced by the shock-excited gas in the lobes with a small or insignificant contribution by scattered photons from the H ii region (the high density in this region, $10 6 cm À3 , produces collisional de-excitation of most forbidden lines).…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Line Identification and Flux Measurementscontrasting

confidence: 64%

Section: Scattered and Local Emission Componentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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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“…10 and 11, we present a set of diagnostic diagrams, involving several emission-line ratios commonly used to discriminate photoionized nebulae from shock-excited objects. In (Riera et al 1995(Riera et al , 2006, triangles: M 1-92, M 2-56 and OH 238.1+4.2 (Trammell et al 1993;Sánchez Contreras et al 2000), stars: CRL 618 (Riera et al, in prep.)]. The red symbols correspond to ground-based spectroscopic data of NGC 6543 (circles), NGC 7009 (triangles) and IC 4634 (squares) are taken from Balick et al (1994), Gonçalves et al (2001), Guerrero et al (2008).…”

Section: A Comparison With Observed Line Ratiosmentioning

confidence: 99%

Line ratios from shocked cloudlets in planetary nebulae

Raga

Riera

Mellema

et al. 2008

A&A

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Context. Some PNe and PPNe show compact knots, travelling at high velocities away from the central sources.Aims. We compute a number of models from which we obtain predictions of the emission-line spectrum, which can be compared with the spectra of the observed knots. Methods. We completed a series of 11 axisymmetric simulations of an initially spherical cloudlet, travelling away from a photoionizing source, into a uniform medium. The simulations included a multi-frequency transfer of the ionizing radiation, and a 33 species non-equilibrium ionization network. Results. From our simulations, we computed emission maps and spatially-integrated emission-line spectra. The predictions show a transition from spectra similar to those of shock wave models (for simulations with lower photoionization rates) to spectra similar to those of photoionized regions (for simulations with higher photoionization rates). Conclusions. The spectra from our photoionized cloudlet models have a range of line ratios that agree approximately with the observed spectra when shown in two-line ratio diagnostic diagrams. The predicted and observed spatial distributions of the emission (with high ionization lines extending more towards the source than lower ionization lines) agree in a qualitative way.

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The Physical and Chemical Properties of Circumstellar Envelopes

Huggins

1995

Circumstellar Matter 1994

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Spectropolarimetry of the post-main-sequence bipolar nebulae GL 618, M2-56, and M1-92

Cited by 36 publications

References 0 publications

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

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

Line ratios from shocked cloudlets in planetary nebulae

The Physical and Chemical Properties of Circumstellar Envelopes

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