IRAS 17423-1755 has been recognized as a new bipolar nebula during a multi-wavelength observational program of unidentified IRAS sources with far infrared colours similar to those of known planetary nebulae.
B, V, R and H alpha CCD images show a clearly marked bipolar structure with a total extension of similar to 11 arcsec. The spectrum of the core shows strong emission lines of HI (Balmer and Paschen series), HeI, FeII, [FeII], OI, CaII and [CaII], Strong P-Cygni profiles are clearly seen in the Balmer lines and in some other emission lines, indicating the presence of a strong mass outflow. This is confirmed by the presence of a very steep density gradient in the nebula, strong near infrared excess and the detection of highly symmetric bipolar emission at very large velocities in the lobes (greater than or similar to 425 km s(-1)).
The highest velocity, however, is observed in the innermost region of the bipolar outflow, where a jet-like structure is detected with v = 870 km s(-1), while its velocity decreases to 750 km s(-1) a few arcsecs away from the central star. This has been interpreted as the result of sporadic mass loss events with a time-dependent ejection velocity. The position-velocity diagram is well reproduced assuming an inclination angle of 150 degrees. The emission observed in the lobes shows an extraordinary line width and double-peaked profiles, indicating that the emission arises from the cooling region behind a bow-shock.
From the high values of the [NII]/H alpha ratios, we deduce that the outflowing material is nitrogen enriched gas of stellar origin, which can only be explained if IRAS 17423-1755 is an evolved star and not a young stellar object. The morphology and kinematics closely resemble those observed in well known bipolar proto-planetary nebulae, while the luminosity is far below the values found in known LBV's (Luminous Blue Variables). The characteristics of the OH maser emission found in IRAS 17423-1755 are consistent with the presence of an equatorial disk of neutral material (perpendicular to the bipolar axis) expanding at v(e) = 50 km s(-1), which could be the responsible for the collimation of the outflow.
|Number of pages||17|
|Journal||Astronomy & astrophysics|
|Publication status||Published - Oct-1995|
- STARS, AGB, POST-AGB
- STARS, MASS LOSS
- STARS, IRAS 17423-1755
- INTERSTELLAR MEDIUM, JETS AND OUTFLOWS
- PLANETARY NEBULAE, IRAS 17423-1755
- ACTIVE GALACTIC NUCLEI
- NEAR-INFRARED SURVEY
- CA-II EMISSION
- PERMITTED LINES