Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000apj...538l.145s&link_type=abstract
The Astrophysical Journal, Volume 538, Issue 2, pp. L145-L149.
Astronomy and Astrophysics
Astronomy
38
Stars: Circumstellar Matter, Ism: Planetary Nebulae: General, Stars: Agb And Post-Agb, Stars: Mass Loss
Scientific paper
Using the Hubble Space Telescope, we have obtained Hα imaging of the object Hen 2-90, which has long been classified as a planetary nebula (PN). We find that the morphology of Hen 2-90 does not look like that of any known PN, but resembles that of a classical young stellar object (YSO)-a bipolar nebula bisected by a flaring disklike structure and a highly collimated bipolar jet perpendicular to the disk. The linear jet shows at least six pairs of emission knots located symmetrically on either side of the nebular center. Taking a kinematic distance of 2.5 kpc, we find that the gas density in the knots decreases steadily from about 104 cm-3 in the knots closest to the center to 1.1×103 cm-3 in the more distant knots, and their masses lie in the range of (0.7-3.6)×10-6 Msolar. The jet opening angle is about 4°, from which we estimate its speed to be ~150 km s-1. Hen 2-90's near- and mid-infrared fluxes imply the presence of a massive dusty nebula containing ``warm'' (183 K) and ``hot'' (513 K) dust in components with masses 5×10-3 and 2.4×10-5 Msolar, respectively (assuming a gas-to-dust ratio of 100); the source luminosity is 5280 Lsolar. Millimeter-wave line observations show no molecular gas directly associated with the source and the absence of star-forming activity, indicating that Hen 2-90 is probably not a YSO. The most likely hypothesis for explaining Hen 2-90 requires a binary with a cool giant and a compact companion with an accretion disk. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universitites for Research in Astronomy, Inc., under NASA contract NAS5-26555.
Nyman Lars-Ake
Sahai Raghvendra
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