A magnetically collimated jet from an evolved star

P.J. Diamond (Jodrell Bank) & H. Imai (Kagoshima University); W.H.T. Vlemmings (Jodrell Bank)

REVIEW

A magnetically collimated jet from an evolved star

W.H.T. Vlemmings (Jodrell Bank), P.J. Diamond (Jodrell Bank) & H. Imai (Kagoshima University)

Astrophysics · Submitted 28 Feb 2006 · 31 references

Pith's verdict: First measurement of both field direction and strength in a collimated jet, but the toroidal-field claim rests on a 90-degree ambiguity and the 'direct evidence' wording overstates what the data show.

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arXiv IDastro-ph/0603003 (version 1)

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CitationP.J. Diamond (Jodrell Bank) & H. Imai (Kagoshima University), W.H.T. Vlemmings (Jodrell Bank). "A magnetically collimated jet from an evolved star." arXiv:astro-ph/0603003 (2006). https://pith.science/paper/DF7H3YGL

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Editor's note

read the letter

You should know this paper: it reports the first measurement of both magnetic field direction and strength in any collimated jet, using VLBA polarimetry of 22 GHz water masers around W43A. The core observation is real and new: the masers lie at the two tips of the precessing jet, and their linear polarization vectors are consistently perpendicular to the jet axis, implying a toroidal field. A 90-degree flip across the brightest maser feature provides an internal consistency check. The Zeeman detection in one feature gives B|| = 85 ± 33 mG and, with a model estimate of theta ≈ 65°, B ≈ 200 ± 75 mG. The error bars include a systematic calibration term. That is a genuinely useful measurement.

What is new: no prior paper gets both direction and strength in a jet; this one does. The technique is established maser polarimetry, so this is a first application to an evolved-star jet rather than a new method. The data appear to be handled competently.

Soft spots: the direction identification carries a real 90-degree ambiguity. Goldreich-Keeley-Kwan allows the linear polarization to be either parallel or perpendicular to the sky-projected field; the paper uses the rule that the strongest polarization is perpendicular and concludes the field is toroidal. That is a plausible reading, but the flip across the brightest feature only shows that both orientations occur—it does not label which one is the field. If the parallel solution applies, the same measurement puts B along the jet, and the geometric support for collimation disappears. The low polarization fraction (0.66 ± 0.07%) does not strongly constrain which regime we are in. So the letter's phrase 'direct evidence' is too strong. The data are consistent with a toroidal field, not a proof of one.

The field strength also depends on the same model: theta ≈ 65° comes from a polarization-model fit, and the pressure ratio 2-200 spans two orders of magnitude because n is uncertain. That does not undercut the B|| measurement, but the headline numbers are softer than they look.

The paper's own text actually flags most of this, but it does so quickly; a referee should push the authors to put the ambiguity up front and soften 'direct evidence' to 'evidence consistent with.' The citation pattern is fine; self-citations are to earlier method papers that are legitimately prior. Extrapolation to the stellar surface assumes r^-1 scaling and an opening angle, which is speculative but clearly labeled.

Verdict: this is a solid observational result that deserves a serious referee. The 90-degree ambiguity is a genuine weakness, but it is not a fatal one—the geometry and the flip make the toroidal reading the natural one. If I were editor, I would send it out; I would ask the referees to push on the language and the model dependence, not on the data.

Referee report

Significance

If the geometric interpretation holds, this would be one of the first measurements of both the direction and strength of the magnetic field in a collimated stellar jet, directly supporting magnetohydrodynamic collimation models for evolved stars and their role in planetary-nebula shaping. The paper's strengths include high-angular-resolution VLBI observations, an explicit 8-degree systematic calibration error, use of a non-thermal-equilibrium maser radiative transfer model for the Zeeman fit, and an attempt to relate the measured field to both the jet base and possible pre-shock conditions. The central result, however, rests on the assumed orientation rule for maser linear polarization, and the current text does not resolve the parallel/perpendicular ambiguity.

Major objections (3)

[Section 2, paragraph beginning 'The 22 GHz H2O masers...'] The identification of the sky-projected field direction is the load-bearing step, and it is not uniquely determined by the data. The paper adopts the rule that strong linear polarization occurs when the E-vector is perpendicular to B, but the cited theory (Goldreich, Keeley & Kwan 1973) also allows the E-vector to be parallel to B. With E-vectors aligned with the jet, the parallel solution would place B along the jet, removing the toroidal interpretation and with it the geometric support for magnetic collimation. The observed 90-degree flip demonstrates that both relative orientations occur across a single feature, but it does not by itself label which orientation corresponds to the field. The low linear polarization fraction (0.66 ± 0.07%) does not by itself select the perpendicular regime. Please provide a quantitative argument from the polarization model—for example, the expected fractional polarization in the parallel versus perpendicular branches for the measured intensity, beaming, and saturation—or substantially weaken the 'direct evidence' claim.
[Section 3, paragraph beginning 'We have also detected...'] The total field B ≈ 200 ± 75 mG depends on θ ≈ 65 degrees, which is inferred 'using the linear polarization fraction... and our polarization model fit results.' If the model's predicted relation between fractional linear polarization and orientation is itself based on the perpendicular-branch assumption, then the Zeeman measurement and the total-field estimate are not independent of the geometric ambiguity raised above. Please state explicitly how θ is constrained by the model and give the range of total B that results if the parallel-branch solution is admitted.
[Section 4, paragraph beginning 'H2O masers at 22 GHz are excited...'] The concluding argument depends on the statement that magnetic pressure dominates gas pressure by a factor of 2-200. The lower end of this range is only a factor of about two, which is weak evidence for collimation, and the factor depends on assumed hydrogen number densities and on the uncertain field magnitude. The stronger evidence is the inferred field geometry, so the abstract and conclusion should separate the geometric evidence from the pressure-balance argument and should avoid claiming direct evidence for magnetic collimation until the orientation ambiguity is resolved.

Minor objections (5)

[Figure 1 caption, sentence beginning 'The perpendicular magnetic field direction of the Northern-most maser feature...'] This sentence is difficult to parse. It seems to say that the northernmost feature has a magnetic field direction along the projected jet, but the word 'perpendicular' is ambiguous. Please rephrase to state explicitly which quantity (polarization vector or magnetic field vector) is perpendicular to which reference direction.
[Abstract and first paragraph of Section 1] The phrase 'direct evidence' is used repeatedly. Because of the orientation ambiguity noted above, consider reserving 'direct' for the unambiguous part of the measurement and stating the model-dependent step explicitly in the abstract.
[Section 3, Zeeman fitting paragraph] The paper does not give the number of independent spectral channels or a goodness-of-fit statistic for the circular-polarization model. A sentence providing the reduced chi-square or equivalent would help the reader judge the quality of the Zeeman fit.
[Section 2, sentence 'The strongest linear polarization is typically found...'] The word 'typically' would benefit from a citation or a statement of the maser regime in which this result holds, especially since the measured fractional linear polarization is small.
[Figure 1 caption, model parameters] The model parameters for the precessing jet (v = 145 km/s, inclination 39 degrees, position angle 65 degrees, precession 5 degrees, period 55 years) are given without uncertainties; please state whether these are fixed in the analysis.

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The paper

The paper claims

Magnetic fields, not gas pressure, collimate the jet of the evolved star W43A.

The reading

This paper reports the first direct measurement of both the direction and the strength of the magnetic field in a collimated jet, made in the precessing jet of the evolved star W43A. Using polarization of 22 GHz water masers in two gas clumps at the opposite tips of the jet, roughly 1,000 AU from the star, the authors infer a magnetic field lying almost perpendicular to the jet, consistent with a toroidal field wrapped around the outflow. A Zeeman measurement in one maser yields a total field of about $200 \pm 75$ mG, strong enough for magnetic pressure to exceed gas pressure by a factor of 2-200. If the interpretation is right, this is direct observational support for the long-standing idea that magnetic fields, not gas pressure alone, collimate jets from evolved stars and shape asymmetric planetary nebulae.

What carries the argument

The load-bearing mechanism is maser polarimetry. The 22 GHz H$_2$O masers in the jet act as small magnetometers: their linear polarization vectors encode the sky-projected magnetic field direction through the standard maser-theory rule (the vector is either parallel or perpendicular to the field, and the strongest linear polarization occurs when it is perpendicular), and their circular polarization, via the Zeeman effect, encodes the line-of-sight field strength. A non-LTE water maser radiative transfer code is used to fit the circular polarization spectrum, yielding $B_\parallel$; the linear polarization fraction then supplies the angle $\theta$ that converts this to the total field $B \approx 200 \pm 75$ mG. Two auxiliary scalings carry the measurement beyond the maser spot: $B \propto n^{0.47}$ relates the compressed maser-region field to the surrounding envelope, and the toroidal component $B_\phi \propto r^{-1}$ (with the radial component falling as $r^{-2}$) extrapolates the field back to the stellar surface, where it can be compared with dynamo expectations.

Extended reading notes

Core claim

Working on the evolved star W43A, which is rapidly transitioning from an asymptotic giant branch star to a planetary nebula, the paper claims to have found direct evidence of magnetic jet collimation. Observations of 22 GHz H$_2$O masers in two clumps at the opposing tips of the precessing jet, about 1,000 AU from the star, show linear polarization vectors whose median error-weighted position angle corresponds to a sky-projected magnetic field at $-27^\circ \pm 12^\circ$, almost perpendicular to the jet. The paper interprets this, via the standard maser-theory direction rule, as a toroidal field wrapped around the outflow; the observed $90^\circ$ flip of the polarization angle across the brightest feature is the predicted signature of the parallel-to-perpendicular transition. Zeeman circular polarization in one southern-tip maser gives $B_\parallel = 85 \pm 33$ mG and, with an inferred inclination $\theta \approx 65^\circ$, a total field $B \approx 200 \pm 75$ mG. Depending on the density of the maser gas, magnetic pressure then exceeds gas pressure by a factor of 2-200, the regime the authors identify as magnetic collimation; extrapolating the toroidal field back to the stellar surface yields a field of order 1.5 G in the swept-up case (or 70 mG in the shock case), consistent with earlier maser-based field estimates. The conclusion is that W43A provides direct evidence that magnetic fields can collimate jets from evolved stars.

Load-bearing premise

The load-bearing assumption is the maser-theory direction rule: the paper assumes that the observed linear polarization vectors are perpendicular to the sky-projected magnetic field, rather than parallel to it; a 90-degree error in that rule would put the field along the jet and remove the geometric evidence for a toroidal, collimating field.

Editorial extensions

If this is right

W43A becomes the first object in which both the direction and the strength of a jet's magnetic field have been directly observed, providing an observational template for magnetic collimation.
The field is consistent with a toroidal configuration wrapped around the jet, with magnetic pressure 2-200 times the gas pressure in the maser gas; such a field is strong enough to pinch the outflow.
Extrapolating the field with $B_\phi \propto r^{-1}$ implies a field of about 1.5 G at the base of the jet (70 mG if the masers arise in shocks), with implied equatorial surface fields of 35 G or 1.6 G that match earlier maser-polarization estimates.
The result supports theoretical models in which magnetic fields, rather than gas pressure or an unseen companion, collimate the jets that give planetary nebulae their asymmetric shapes.
Because similar magnetic field strengths are found in star-forming regions, the paper concludes that magnetic collimation likely operates in protostellar jets as well.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

If this reading is right, the precession of the W43A jet might be a magnetic effect: a rotating or tilted dipole on the star would sweep the jet around, which could be tested by monitoring the polarization angle through the 55-year precession cycle.
The 90-degree ambiguity inherent in maser polarization means sky-projected field maps can only pin the field axis, not its orientation; W43A is the cleanest case only because the Zeeman detection and pressure argument break the degeneracy, and similar dual measurements in other sources are needed.
The paper's extrapolated surface field of order a few Gauss sits in the regime where an evolved-star dynamo can generate it; if future spectropolarimetric stellar-surface measurements confirm such fields, the dynamo-to-nebula shaping link becomes testable.
Comparable H2O-maser jets in young stellar objects show similar field strengths, so if this mechanism is general, the same toroidal-collimation signature should appear there; searching for it would extend the result beyond evolved stars.

Original abstract

Planetary nebulae often have asymmetric shapes, which could arise due to collimated jets from evolved stars before evolution to the planetary nebula phase. The source of jet collimation in these stars is unknown. Magnetic fields are thought to collimate outflows that are observed in many other astrophysical sources, such as active galactic nuclei and proto-stars, although hitherto there are no direct observations of both the magnetic field direction and strength in any collimated jet. Theoretical models have shown that magnetic fields could also be the dominant source of collimation of jet in evolved stars. Here we report measurements of the polarization of water vapour masers that trace the precessing jet emanating from the asymptotic giant branch star W43A at 2.6 kpc from the Sun, which is undergoing rapid evolution into a planetary nebula. The masers occur in two clusters at opposing tips of the jets, ~1,000 AU from the star. We find direct evidence that the magnetic field is collimating the jet.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13.0 via TypeSafe API, question bank abstract-p1-20260923, 2026-09-23: 1 request, 5,620 input tokens.

What the abstract itself states, as probabilities: claims first 0.59 · states limitation 0.12 · human participants 0.01 · controlled comparison 0.02 · randomized assignment 0.01 · states quantitative result 0.75 · compares with prior results 0.35 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v1. Results and the main claim are underlined; show every role.

Planetary nebulae often have asymmetric shapes, which could arise due to collimated jets from evolved stars before evolution to the planetary nebula phase. The source of jet collimation in these stars is unknown. Magnetic fields are thought to collimate outflows that are observed in many other astrophysical sources, such as active galactic nuclei and proto-stars, although hitherto there are no direct observations of both the magnetic field direction and strength in any collimated jet. Theoretical models have shown that magnetic fields could also be the dominant source of collimation of jet in evolved stars. Here we report measurements of the polarization of water vapour masers that trace the precessing jet emanating from the asymptotic giant branch star W43A at 2.6 kpc from the Sun, which is undergoing rapid evolution into a planetary nebula. The masers occur in two clusters at opposing tips of the jets, ~1,000 AU from the star. We find direct evidence that the magnetic field is collimating the jet.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#	sentence	role	the authors' own work	states the main conclusion	strength
s0	Planetary nebulae often have asymmetric shapes, which could arise due to collimated jets from evolved stars before evolution to the planetary nebula phase.	background 1.00	0.04	0.02	hedged possibility 1.00
s1	The source of jet collimation in these stars is unknown.	gap 0.95	0.04	0.02	asserted 0.93
s2	Magnetic fields are thought to collimate outflows that are observed in many other astrophysical sources, such as active galactic nuclei and proto-stars, although hitherto there are no direct observations of both the magnetic field direction and strength in any collimated jet.	gap 0.90	0.03	0.02	hedged possibility 0.86
s3	Theoretical models have shown that magnetic fields could also be the dominant source of collimation of jet in evolved stars.	background 0.99	0.04	0.04	hedged possibility 0.98
s4	Here we report measurements of the polarization of water vapour masers that trace the precessing jet emanating from the asymptotic giant branch star W43A at 2.6 kpc from the Sun, which is undergoing rapid evolution into a planetary nebula.	contribution 0.97	0.97	0.05	asserted 1.00
s5	The masers occur in two clusters at opposing tips of the jets, ~1,000 AU from the star.	result 0.53	0.63	0.02	asserted 0.99
s6	We find direct evidence that the magnetic field is collimating the jet.	result 0.92	0.97	0.96	asserted 1.00

What kind of paper the classifier reports this is: empirical study 1.00 · evidence from observation or experiment 1.00.

What was examined, and what was not

sources read

arXiv listing abstract v1

not examined

full text
figures and tables
references and citing sentences
relations to other papers

levels run

P abstract

not run

S sections
T body sentences
C citations
R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

References

Works cited (31)

[1]

Sahai, R. & Trager, J. T. Multipolar bubbles and jets in low-excitation planetary nebulae: toward a new understanding of the formation and shaping of planetary nebulae. Astron. J. 116, 1357-1366 (1998)

View on Pith 1998
[2]

Imai, H., Obara, K., Diamond, P. J., Omodaka, T. & Sasao, T. A collimated jet of molecular gas from a star on the asymptotic giant branch. Nature 417, 829 831 (2002)

View on Pith 2002
[3]

The source of jet collimation in these stars is unknown. Magnetic fields are thought to collimate outflows that are observed in many other astrophysical sources, such as active galactic nuclei4-7 and proto-stars8, 9, although hitherto there are no direct observations of both the magnetic field direction and strength in any collimated jet. Theoretical mode...

View on Pith
[4]

Miranda, L. F., Gómez, Y., Anglada, G. & Torrelles, J. M. Water-maser emission from a planetary nebula with a magnetized torus. Nature 414, 284-286 (2001)

View on Pith 2001
[5]

Pearson, T. J. & Readhead, A. C. S. The milliarcsecond structure of a complete sample of radio sources. II - First-epoch maps at 5 GHz. Astrophys. J. 328, 114-142 (1988)

View on Pith 1988
[6]

Blandford, R. D. & Payne, D. G. Hydromagnetic flows from accretion discs and the production of radio jets. Mon. Not. R. Astron. Soc. 199, 883-903 (1982)

View on Pith 1982
[7]

Xu, C., Livio, M. & Baum, S. Radio-loud and radio-quiet Active Galactic Nuclei. Astron. J. 118, 1169-1176 (1999)

View on Pith 1999
[8]

Gabuzda, D. C., Murray, É. & Cronin, P. Helical magnetic fields associated with the relativistic jets of four BL Lac objects. Mon. Not. R. Astron. Soc. 351, L89-L93. (2004). 6

View on Pith 2004
[9]

Ouyed, R., Pudritz, R. E. & Stone, J. M. Episodic jets from black holes and protostars. Nature 385, 409-414 (1997)

View on Pith 1997
[10]

Zinnecker, H., McCaughrean, M. J. & Rayner, J. T. A symmetrically pulsed jet of gas from an invisible protostar in Orion. Nature 394, 862-865 (1998)

View on Pith 1998
[11]

Blackman, E. G., Frank, A., Markiel, J. A., Thomas, J. H. & Van Horn, H. M. Dynamos in asymptotic-giant-branch stars as the origin of magnetic fields shaping planetary nebulae. Nature 409, 485-487 (2001)

View on Pith 2001
[12]

García-Segura, G., López, J. A. & Franco, J. Magnetically driven winds from post- asymptotic giant branch stars: solutions for high-speed winds and extreme collimation. Astrophys. J. 618, 919-925 (2005)

View on Pith 2005
[13]

Diamond, P. J., Norris, R. P., Rowland, P. R., Booth, R. S. & Nyman, L.-A. The circumstellar envelopes around OH/IR stars. Mon. Not. R. Astron. Soc. 212, 1-21 (1985)

View on Pith 1985
[14]

Vlemmings, W. H. T., Diamond, P. J., van Langevelde, H. J. & Torrelles, J. M. The magnetic field in the star-forming region Cepheus A from H2O maser polarization observations. Astron. Astrophys. accepted (2005)

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[15]

Vlemmings, W. H. T., Diamond, P. J. & van Langevelde, H. J. Circular polarization of water masers in the circumstellar envelopes of late type stars. Astron. Astrophys. 394, 589-602 (2002)

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[16]

Vlemmings, W. H. T., van Langevelde, H. J. & Diamond, P. J. The magnetic field around late-type stars revealed by the circumstellar H2O masers. Astron. Astrophys. 434, 1029-1038 (2005)

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[17]

Nedoluha, G. E. & Watson, W. D. The Zeeman effect in astrophysical water masers and the observation of strong magnetic fields in regions of star formation. Astrophys. J. 384, 185-196 (1992). 7

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[18]

Goldreich, P., Keeley, D. A. & Kwan, J. Y. Astrophysical masers. II. polarization properties. Astrophys. J. 179, 111-134 (1973)

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[19]

Kemball, A. J. & Diamond, P. J. Imaging the magnetic field in the atmosphere of TX Cam. Astrophys. J. 481, L111-LL114 (1997)

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[20]

Elitzur, M. Astronomical Masers (Kluwer Academic, Dordrecht, 1992)

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[21]

Crutcher, R. M. Magnetic fields in molecular clouds: observations confront theory. Astrophys. J. 520, 706-713 (1999)

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[22]

Elitzur, M., Hollenbach, D. J. & McKee, C. F. Planar H2O masers in star-forming regions. Astrophys. J. 394, 221-227 (1992)

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[23]

Reid, M. J. et al. Stellar OH masers and magnetic fields – VLBI observations of U Orionis and IRC +10420. Astrophys. J. 227, L89-L92 (1979)

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[24]

Chevalier, R. A. & Luo, D. Magnetic shaping of planetary nebulae and other stellar wind bubbles. Astrophys. J. 421, 225-235 (1994)

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[25]

García-Segura, G., Langer, N., Rózuczka, M. & Franco, J. Shaping bipolar and elliptical planetary nebulae: effects of stellar rotation, photoionization heating, and magnetic fields. Astrophys. J. 517, 767-781 (1999)

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[26]

Sahai, R. Bipolar and multipolar jets in protoplanetary and planetary nebulae. Rev. Mex. Astron.Astrofis. 13, 133-138 (2002)

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[27]

Blackman, E.G. in Asymmetrical Planetary Nebulae III: Winds, Structure and the Thunderbird, APS Conference Series (eds Meixner, M., Kastner, J. H., Balick, B. & Soker, N.) Vol. 313 401-407 (Astronomical Society of the Pacific, San Francisco, 2004)

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[28]

Imai, H., Nakashima, J., Diamond, P. J., Miyazaki, A. & Deguchi, S. A biconically expanding flow in W43A traced by SiO maser emission. Astrophys. J. 622, L125-L128 (2005). 8

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[29]

Lery, T. et al. Magnetised protostellar bipolar outflows. I. Self-similar model with Poynting flux. Astron. Astrophys. 350, 254-274 (1999)

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[30]

Lebedev, S. V. et al. Magnetic tower outflows from a radial wire array Z-pinch. Mon. Not. R. Astron. Soc. 361, 97-108 (2005)

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[31]

Asada, K. et al. A helical magnetic field in the jet of 3C 273. Publ. Astron. Soc. Jpn. 54, L39-L43 (2002). Acknowledgements: NRAO is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. W.V. was financially supported by a Marie-Curie Intra- European fellowship. Competing interests statement:...

View on Pith 2002

How the literature uses it

2 arXiv papers cite this in 3 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers whose main result relates to this one's

Found among the papers closest to this one by title and main claim. Pith's classifier compared each pair's main results and a second model family confirmed the relation; checked against two further families, shown conflicts agreed 118 times in 120 and shown same results 218 times in 239. The quoted sentence is the other paper's main claim.

States the same result 1 paper

This is the first direct observational evidence for magnetic collimation in the jets, that likely play an important role in shaping planetary nebulae.

A magnetically collimated jet from the evolved star W43A · 0.97

Papers citing it · 2 sentences without a confident label

Cites it as support 1 paper

There is direct evidence for jets surrounded by winds in AGN [ref] , YSOs [ref] , pulsars [ref] , or embedded in stellar environments, including post AGB and planetary nebula [ref] , and SN and GRB [ref] .

Persistent mysteries of jet engines, formation, propagation, and particle acceleration: have they been addressed experimentally? · What jet collimation mechanisms operate in nature? · 0.99

Discussion

Disagree with the review, or know something it missed? Leave a comment, highlight any passage above to comment on it, or challenge this review formally.

[1] [1]

Sahai, R. & Trager, J. T. Multipolar bubbles and jets in low-excitation planetary nebulae: toward a new understanding of the formation and shaping of planetary nebulae. Astron. J. 116, 1357-1366 (1998)

View on Pith 1998

[2] [2]

Imai, H., Obara, K., Diamond, P. J., Omodaka, T. & Sasao, T. A collimated jet of molecular gas from a star on the asymptotic giant branch. Nature 417, 829 831 (2002)

View on Pith 2002

[3] [3]

The source of jet collimation in these stars is unknown. Magnetic fields are thought to collimate outflows that are observed in many other astrophysical sources, such as active galactic nuclei4-7 and proto-stars8, 9, although hitherto there are no direct observations of both the magnetic field direction and strength in any collimated jet. Theoretical mode...

View on Pith

[4] [4]

Miranda, L. F., Gómez, Y., Anglada, G. & Torrelles, J. M. Water-maser emission from a planetary nebula with a magnetized torus. Nature 414, 284-286 (2001)

View on Pith 2001

[5] [5]

Pearson, T. J. & Readhead, A. C. S. The milliarcsecond structure of a complete sample of radio sources. II - First-epoch maps at 5 GHz. Astrophys. J. 328, 114-142 (1988)

View on Pith 1988

[6] [6]

Blandford, R. D. & Payne, D. G. Hydromagnetic flows from accretion discs and the production of radio jets. Mon. Not. R. Astron. Soc. 199, 883-903 (1982)

View on Pith 1982

[7] [7]

Xu, C., Livio, M. & Baum, S. Radio-loud and radio-quiet Active Galactic Nuclei. Astron. J. 118, 1169-1176 (1999)

View on Pith 1999

[8] [8]

Gabuzda, D. C., Murray, É. & Cronin, P. Helical magnetic fields associated with the relativistic jets of four BL Lac objects. Mon. Not. R. Astron. Soc. 351, L89-L93. (2004). 6

View on Pith 2004

[9] [9]

Ouyed, R., Pudritz, R. E. & Stone, J. M. Episodic jets from black holes and protostars. Nature 385, 409-414 (1997)

View on Pith 1997

[10] [10]

Zinnecker, H., McCaughrean, M. J. & Rayner, J. T. A symmetrically pulsed jet of gas from an invisible protostar in Orion. Nature 394, 862-865 (1998)

View on Pith 1998

[11] [11]

Blackman, E. G., Frank, A., Markiel, J. A., Thomas, J. H. & Van Horn, H. M. Dynamos in asymptotic-giant-branch stars as the origin of magnetic fields shaping planetary nebulae. Nature 409, 485-487 (2001)

View on Pith 2001

[12] [12]

García-Segura, G., López, J. A. & Franco, J. Magnetically driven winds from post- asymptotic giant branch stars: solutions for high-speed winds and extreme collimation. Astrophys. J. 618, 919-925 (2005)

View on Pith 2005

[13] [13]

Diamond, P. J., Norris, R. P., Rowland, P. R., Booth, R. S. & Nyman, L.-A. The circumstellar envelopes around OH/IR stars. Mon. Not. R. Astron. Soc. 212, 1-21 (1985)

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