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R. Sahai (Jet Propulsion Laboratory/ CALTECH)
We report the serendipitous discovery of an object which has the morphology of a young stellar object (YSO) like HH30, but which has been classified as a planetary nebula (PN) since 1964! This object, He2-90, discovered by K.G. Henize in 1964, has been listed as a PN by Perek and Kohoutek (1967, Catalogue of Galactic Planetary Nebulae, Publ. House Czech. Acad. Sci.) and in the more recent compilation by Acker et al (1992, Strasbourg-ESO Catalog of Galactic Planetary Nebulae, ESO, Garching). Acker et al subjected their catalogued PNe to morphological and spectroscopic tests, selecting 1143 out of an initial list of 1820 objects which had at least once been classified as PNe. These authors list He2-90 as a PN with a diameter of 10 arcsec, however in a subsequent narrow-band imaging study, Schwarz, Corradi & Melnick (1992, A&AS, 96, 23) find the object to be stellar.
We imaged He2-90 as part of a SNAPSHOT imaging survey of young planetary nebulae with the Wide-Field & Planetary Camera 2 onboard the Hubble Space Telescope (HST) (Sahai & Trauger 1998, AJ, 116, 1357). Our HST image, taken with the F656N (H\alpha) filter, shows an object resembling a classical YSO -- a bipolar nebula bisected by a flaring dark lane, and a highly collimated bipolar jet structure oriented orthogonal to the dark lane. The jet is knotty, showing at least five pairs of emission knots located symmetrically on either side of the central (obscured) star. He2-90 lies towards, but slightly outside, the Coalsack dark cloud region. If it is indeed a YSO, then it may be associated with molecular clouds belonging to the Sagittarius-Carina arm which lie in its direction (at distances of probably 1-2 kpc). We present our HST imaging of He2-90 and discuss its morphology in the context of formation models for low-mass stars and planetary nebulae. We summarise new multi-wavelength observations which we are undertaking to further investigate the nature of this mysterious object.
Funding for this work has been provided by NASA through grant GO 08345.01-97A from STScI (operated by AURA, under contract from NASA).
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The author(s) of this abstract have provided an email address for comments about the abstract: sahai@grandpa.jpl.nasa.gov