Received 19th March 1998
Abstract.
Results of observations of the neutral hydrogen in the Milky Way with the
Effelsberg 100 m
radiotelescope are presented.
In the 4° × 4° field in the plane of our Galaxy 7 new
H
I shells have been identified.
In this paper we show
lb and
pv diagrams of two selected
structures.
1. Introduction
The first systematic study of H I shells in the Milky Way
was performed by Heiles (1979), who used the H I survey
of Weaver and Williams (1973) with angular resolution of 36 arcmin.
We reobserved one of the shells, GS061+00+51, with the
Effelsberg 100 m
radiotelescope to confirm the identification and to get data with
the higher resolution (both spatial and velocity) which may serve for
a comparison with our numerical models of expanding shells.
At the same time we also hoped we would be able to identify new structures in
the observed field.
2. Observations
Observations were made with the
100 m radiotelescope
in Effelsberg during March and June 1997 in collaboration with
W. Huchtmeier from
MPIfR.
At the 21 cm wavelength the telescope has an angular resolution of
9.4 arcmin (FWHM).
Spectra cover the range -164 km s-1 to
+164 km s-1 with respect to LSR at
a velocity resolution of 0.64 km s-1.
We measured the emission over galactic longitudes
59°≤l≤63° and galactic latitudes
-2°≤b≤+2°.
Spectra were taken every 4 arcmin both in latitude and longitude.
The integration time was 15 s. A linear baseline was removed.
3. Identification of H I shells
So far we have identified 8 H I structures in the observed
field.
One was known before (Heiles' shell GS061+00+51).
We are aware of the problems and incompleteness caused by our small field.
Especially larger shells are affected and it may turn out later
(when observations of the larger field will be available),
that some of our shells are actually parts of larger structures.
Here we present figures of two shells, whose identification is quite clear.
The first one, GS59.9-1.0+38 (Fig. 1),
is a small spherical shell in the inner Galaxy.
As it lies near the tangential point, its distance is determined quite
precisely (d = 4.3 kpc).
The radius of the shell is then 30 pc and the expansion velocity is
9 km s-1.
We suppose the shell was created by one SN explosion 2 or 3 Myr ago
(Ehlerová et al. 1998).
[Click here to see Fig. 1!]
The shell GS60.0-1.1-54 (Fig. 2) is
an example of a structure whose shape was significantly influenced by the ISM
distribution.
Using the rotation curve of Wouterloot et al. (1990), we derive the distance
towards the shell to be nearly 14 kpc and then its dimensions are
450 pc (in the l direction) and 550 pc (in the direction
perpendicular to the galactic plane).
The shell GS60.0-1.1-54 is very similar to the Aquila supershell observed
by Maciejewski et al. (1996).
Numerical simulations which would explain its particular shape will be
published elsewhere.
[Click here to see Fig. 2!]
References
- Ehlerová S., Huchtmeier K.W., Palous J., 1998,
to be published in the proceedings of the 30th YERAC conference
- Heiles C., 1979, ApJ 229, 533
- Maciejewski W., Murphy E.M., Lockman F.J., Savage B.D., 1996, ApJ 469, 238
- Weaver H.F., Williams D.R., 1973, A&AS 8, 1
- Wouterloot J.G.A., Brand J., Burton W.B., Kwee K.K., 1990, A&A 230, 21
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| First version: | 06th | July, | 1998
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| Last update: | 29th | September, | 1998
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Jochen M. Braun &
Tom Richtler
(E-Mail: jbraun|richtler@astro.uni-bonn.de)