Near-IR spectroscopy and imaging photometry of M 1-16: Bipolar H2 jets in a post-AGB transition object

Details Near-IR spectroscopy and imaging photometry of M 1-16: Bipolar H2 jets in a post-AGB transition object Near-IR spectroscopy and imaging photometry of M 1-16: Bipolar H2 jets in a post-AGB transition object

Oct 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...278..255a&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 278, no. 1, p. 255-266

Astronomy and Astrophysics

Astrophysics

12

Astronomical Photometry, Gas Jets, Hydrogen, Infrared Spectroscopy, Line Spectra, Planetary Nebulae, Astronomical Models, Color-Color Diagram, Infrared Spectrometers, Stellar Winds

Scientific paper

We present near-IR long-slit spectroscopy and imaging photometry of the transition object/proto-planetary nebula M1-16. This object has recently been found to possess multiple bipolar lobes seen in the optical as high-velocity (+/- 250 km/s) shock-excited line emission. We have discovered that M1-16 also possesses spatially extended near-IR emission primarily from vibrationally excited molecular hydrogen (H2). The H2 emission extends approximately 25 arcseconds into each optical emission lobe and appears as symmetrically opposed collimated bipolar jets whose direction is not co-linear with the axis of any of the optical features. From studies of H2 line ratios along the jets, we suggest that the H2 emission may not be pre-dominantly shock-excited rather, the ratios seem to indicate a two component model of stronger fluorescent and weaker shock emission. Measurements of the v = 1-0 S(1) H2 emission line at high spectral resolution using an echelle have revealed velocity structure along the bipolar jets. The H2 jets appear red-shifted in the northwest bipolar lobe and blue-shifted in the southeast lobe with a velocity, relative to the central star, increasing linearly with distance from the source to a maximum of +/- 28 km/s. We propose two models to explain the morphology and emission structure of M1-16 in the near-IR. Both models require that the H2 jets define the current axis of the collimated stellar wind, and the velocity increase along the jets is physical rather than geometric suggesting that the molecular gas is entrained in the stellar wind. The first model implies that the H2 jets may be the result of a non-isotropic UV illumination/excitation of the expanding red giant envelope, while the second interprets the jets as physical density enhancements in a focussed stellar wind with a more isotropic irradiation by UV flux.

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