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Astron. Astrophys. 358, 1035-1048 (2000)
ISO Spectroscopy of the young bipolar nebulae S106 IR and Cep A East *
M.E. van den Ancker 1,2,
A.G.G.M. Tielens 3,4,5 and
P.R. Wesselius 4
1 Astronomical Institute "Anton Pannekoek", University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138, USA
3 Kapteyn Astronomical Institute, Groningen University, P.O. Box 800, 9700 AV Groningen, The Netherlands
4 SRON, P.O. Box 800, 9700 AV Groningen, The Netherlands
5 NASA Ames Research Center, MS 245-3, Moffett Field, CA 94035, USA
Received 23 February 2000 / Accepted 2 May 2000
Abstract
We present the results of ISO SWS and LWS grating scans towards the
embedded Young Stellar Objects (YSOs) S106 IR and Cep A East.
Emission from the pure rotational lines of H2 and the
infrared fine structure lines of [C II ],
[O I ], [S I ], [Si II ]
and [Fe II ], as well as absorption bands due to
H2O, CO and CO2 ice were detected toward
Cep A. In S106 we detected emission lines of H2, CO,
H I , and a large number of ionized species including
Fe, O, N, C, Si, S, Ne and Ar. S106 also shows many of the infrared
PAH bands in emission. Excitation temperatures and molecular hydrogen
masses were derived from the low-lying pure rotational levels of
H2 and are 500 and 730 K and 8 and 3
![[FORMULA]](img1.gif)
10-3 M![[FORMULA]](img2.gif)
for S106 and
Cep A, respectively. Since both objects are expected to have
several solar masses of H2 in their environment, we
conclude that in both cases the bulk of the H2 is cooler
than a few hundred Kelvins. Excitation temperatures and line ratios
were compared with those predicted by theoretical models for PDRs and
dissociative and non-dissociative shocks. The [S I ]
25.2 µm/[Si II ]
34.8 µm ratio is a particularly useful shock versus
PDR discriminant and we conclude that S106 IR is dominated by PDR
emission while Cep A East has a large shock component. From an
analysis of the ionic lines in S106 we conclude that the central star
must have a temperature around 37,000 K, corresponding to a
spectral type of O8. From its luminosity it is concluded that the
driving source of Cep A must also be a massive early-type star.
The absence of strong high-ionization ionic lines in its ISO spectrum
shows that Cep A has not yet created a significant
H II region and must be younger than S106, illustrating
the process of the clearing of the surroundings of a massive young
star.
Key words: shock
waves 
stars: circumstellar
matter
stars:
formation
ISM: H ii
regions
ISM: jets and
outflows
infrared: stars
* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.
Send offprint requests to: M.E. van den Ancker (mario@astro.uva.nl)
Contents
- 1. Introduction
- 2. Observations and data
- 3. Solid-state features
- 4. Hydrogen recombination lines
- 5. Molecular hydrogen emission
- 6. Carbon-monoxide emission lines
- 7. Atomic fine structure lines
- 8. Discussion and conclusions
- Acknowledgements
- References
© European Southern Observatory (ESO) 2000
Online publication: June 20, 2000
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