Issue |
A&A
Volume 421, Number 1, July I 2004
|
|
---|---|---|
Page(s) | 187 - 193 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20034386 | |
Published online | 11 June 2004 |
Observations of the Brackett decrement in the Class I source HH100 IR*
1
INAF-Osservatorio Astronomico di Roma, 00040 Monteporzio Catone, Italy
2
Università degli Studi “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
Corresponding author: B. Nisini, nisini@mporzio.astro.it
Received:
24
September
2003
Accepted:
3
March
2004
The Brackett decrement in the Class I source HH100 IR
has been observed and analyzed to set constraints on the
origin of the IR HI emission in this young object.
We have used both low resolution ( 800) observations of the
Brackett lines from Brγ to Br24, and medium resolution (
9000)
spectra of the Brγ, Br12 and Br13 lines. The dereddened fluxes
indicates that the lines remain moderately thick up to
high quantum numbers. Moreover, the profiles of the three
lines observed in medium resolution are all broad and nearly symmetric, with
a trend for the lines at high n-number to be narrower than the Brγ line. With the assumption that the three lines have different optical
depths and consequently trace zones at different physical depths,
we interprete the observed profiles as evidence that the ionized gas velocity in the HI emitting region is increasing as we move outwards, as
expected in an accelerating wind more than in an infalling gas.
We have modelled the observed line ratios and velocities with a simplified
model for the HI excitation from a circumstellar gas with a velocity law
. Such a comparison indicates
that the observations are consistent with the emission coming from
a very compact region of 4–6
, where the gas has been
already accelerated to velocities of the order of 200 km s-1, with an associated
mass flow rate of the ionized component of the order of
10
yr-1. This implies that the observed lines
should originate either from a stellar wind or from the inner part
of a disk wind, providing that the disk inner truncation radius is close
to the stellar surface. It is also expected that the gas ionization fraction
is relatively high as testified by the high rate of ionized mass loss derived.
Our analysis, however, does not resolve the problem of how to reproduce
the observed symmetrical line profiles, which
at present are apparently difficult to model by both wind and
accretion models. This probably points to the fact that the real situation
is more complicated than described in the simple model presented here.
Key words: line: formation / stars: circumstellar matter / stars: individual: HH100-IR / infrared: stars / stars: formation / stars: winds, outflows
© ESO, 2004
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