Issue |
A&A
Volume 483, Number 1, May III 2008
|
|
---|---|---|
Page(s) | 199 - 208 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20078457 | |
Published online | 02 January 2008 |
A HST study of the environment of the Herbig Ae/Be star LkHα 233 and its bipolar jet*
1
Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany e-mail: melnikov@tls-tautenburg.de
2
Ulugh Beg Astronomical Institute, Astronomical Str. 33, 700052 Tashkent, Uzbekistan
3
INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
4
Dipartimento di Matematica, Università degli Studi di Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
5
Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland
Received:
9
August
2007
Accepted:
26
October
2007
Context. LkHα 233 is a Herbig Ae/Be star with a collimated bipolar jet. As such, it may be a high-mass analogue to the classical T Tauri stars and their outflows.
Aims. We investigate optical forbidden lines along the LkHα 233 jet to
determine physical parameters of this jet (electron density , hydrogen ionisation fraction
, electron temperature Te). The knowledge of these parameters allows us a direct comparison of a jet from a Herbig star with those from T Tauri stars.
Methods. We present the results of HST/STIS and WFPC2 observations of
LkHα 233 and its environment. These are the first
observations of this object with a spatial resolution of ≤ at
optical wavelengths. Our STIS data provide spectroscopic maps that allow us
to reconstruct high angular resolution images of the bipolar jet from
LkHα 233 covering the first ≈2000 AU from the star in the
blueshifted outflow lobe and ≈4000 AU in the redshifted
lobe. These maps are analysed with a diagnostic code that yields
,
, Te, and mass density
within the jet.
Results. The WFPC2 images in broad-band filters clearly show a dark
lane caused either by a circumstellar disk or a dust torus. The
circumstellar environment of LkHα 233 can be interpreted as a conical
cavity that was cleared by a bipolar jet. In this interpretation, the
maximum of the optical and near-infrared brightness distribution does not
coincide with the star itself which is, in fact, deeply extincted. In the
blueshifted lobe, ne is close to or above the critical density for [SII] lines (2.5
) in the first arcsecond and
decreases with distance from the source. The ionisation
gently rises for the first 500 AU of the flow and shows two
re-ionisation events further away from the origin. The electron temperature
varies along the flow between
and 3
. The
is between 3
103 and
, and the mass flux
. The (radial) outflow velocities
are ≈
, and they appear to
increase with distance from the source. In the redshifted lobe, the excitation
conditions are quite different:
,
,
, and
are all lower than in the blueshifted
lobe, but have the same order of magnitude.
Conclusions. All these derived parameters are just beyond or at the upper limits of those observed for classical T Tauri star jets. This may indicate that the flows from the higher mass Herbig stars are indeed scaled-up examples of the same phenomenon as in T Tauri stars.
Key words: ISM: jets and outflows / stars: pre-main sequence / stars: main-loss
© ESO, 2008
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