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    {\small\rm\zihao{6}\songti\thepage\hfill
    \quad\quad ACTA ASTRONOMICA SINICA \hfill
    \hspace{2mm} Vol.44\vspace{2mm}}}} %%%%%%%
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    {\small\rm \zihao{6}\songti suppl.\hfill E. F\"{u}rst: The 100-m Effelsberg Telescope and the Milky Way %%（作者：题目名称）
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    \normalsize\rm
\zihao{5}\songti

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    \small\rm
    \zihao{6}\songti
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    Vol.44~ Suppl.
    \hfill\hspace{8mm} %%% if ``October/January'' then \hspace{8/10 mm} July
    \small ACTA ASTRONOMICA SINICA
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      Feb.,~2003 \\[-1.5 true mm] %%January
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\vs\vs\vs \bc {\Large\bf
The 100-m Effelsberg Telescope and the Milky Way    %%（文题）
%\\[1ex]
%$\!\!^*$
}

\vs\vs{\normalsize Ernst F\"{u}rst}  %%（本文作者）

\vs
({\footnotesize {\it Max-Planck-Institute for Radioastronomy, D-53121, Bonn, Germany)}} \\%%（本文作者单位）
\vs\vs \ec

\normalsize
\begin{quotation}

 \no{\bf A{\scriptsize\bf BSTRACT }}~~~\small
The Effelsberg 100-m radio telescope was built almost 30 years ago
for radio observations at centimeter wavelength. Observations are
possible from the primary as well as the secondary focus. Some
technical details of the telescope are described.
%\noindent
Since the beginning, observations with the 100-m radio telescope
contribute to all
fields of radio astronomy: radio continuum, spectroscopy, pulsar
research and VLBI. The telescope is well suited to map large areas
of the sky in the radio continuum, in total intensity and
polarization.  As an example, the radio maps of the plane of the
Milky Way are presented. Such data in combination with follow-up
measurements at other radio frequencies provide spectral and
polarization information on various objects of the Milky Way. As
an example the remnants of supernova explosions are discussed.
%\noindent
With the 100-m telescope, observations at wavelengths shorter than
1~cm become more and more important. Large feed arrays will help
to speed up mapping of extended areas. A proposal exists to
improve the sensitivity of the 100-m radio telescope especially at
short wavelengths. Comments on this project are given.

 %\vn
 %\no{\bf Key words}~~  pulsar-mode  change-spectrum
\end{quotation}




\para{\normalsize\bf{1}~~ The 100-m Radio Telescope}

\vs\vs
The Effelsberg 100-m radio telescope (Figure~1, Hachenberg
et al. 1973) began it's astronomical operation in 1971. For about
30 years it was the largest fully steerable
\begin{figure}[h]
\center {\includegraphics [bb=0 87 408 480,scale=0.5]{fig1a.eps}}

   %\parbox[tb]{12cm}
   %{\hspace{3.5cm}
   {\center
   \footnotesize

      Fig.\,1~~ The 100-m-Radio telescope Effelsberg}

    \end{figure}
radio telescope.  The telescope consists of a main paraboloid
reflector of 100-m size and a gregorian subreflektor of 6.5~m
size, which provides easy access to the primary (PFK) and to the
secondary (SFK) focus. In the primary focus (focal length = 30~m)
only one receiver can be installed at the same time. The available
receivers/frequencies range between 800~MHz and 86~GHz. A change
between receivers/frequencies needs manual work. The focal length
of 385m of the secondary focus allows the permanent
installation of many receivers/frequencies (see Figure 2), which
all are ready for observations. Optical errors are small even at
large distances from the optical axis. The 100-m radio telescope
is the first telescope built according
\begin{figure}[h]
\center {\includegraphics [bb=0 219 408 444,scale=0.8]{fig2.eps}}

   %\parbox[tb]{12cm}
   %{\hspace{3.5cm}
   {\center
   \footnotesize

      Fig.\,2~~ The secondary focus of the 100-m-RT}

    \end{figure}
to the so-called homologeous principle. When tilting the telescope
from 90$^\circ$ to it's lower limit of 7$^\circ$ elevation the
maximal distortion at the edge of the reflector due to gravity is
8~cm. The best-fit paraboloid, fitted to the distorted surface,
shows systematic deviations of about $\pm$2~mm. The resulting mean
deviation from the best-fit paraboloid is 0.45~mm at 32$^\circ$
elevation for the central region of 40~m radius. At the elevation
of 32$^\circ$ the panels of the reflector are adjusted according
to holographic measurements using geostationary satellites.
Towards 90$^\circ$ elevation the mean deviation increases due to
gravity up to 0.83~mm. The outer region of the reflector was
recently filled with panels of perforated aluminium with holes of
7~mm and a filled fraction of about 50\%. This part of the
reflector will be adjusted during 2003. The pointing accuracy of
the telescope is about 2-3~arcsec for low wind speeds.
Observations have to be stopped at wind speeds larger than 16~m/s.
The instrumental polarization of the telescope is usually
$<$0.7\%. For many observations a cleaning of the polarization for
instrumental effects is not necessary.


Mapping of extended objects is one of the main tasks of the 100-m-RT.
Over the last 30 years the 100-m-RT has contributed to the 408~MHz all-sky survey (Haslam et al. 1982) and
various surveys of the Galactic plane. Nummerous individual extended Galacitc objects and external
galaxies have also been mapped in total intensity and polarization.
Here only the Galactic plane and supernova remnants (SNRs) are discussed.


\para{\large\bf{2}~~The Galactic Plane and Supernova Remnants}

\vs\vn The Galactic plane has been observed with the 100-m-RT at
2.695~MHz in the years from 1982 to 1990 (Reich et al. 1984, 1990;
F\"{u}rst et al. 1990).
 The entire region visible from Effelsberg has been mapped.
The analysis of the whole region in total intensity was finished in 1994.
The linear polarization has been analysed for the first quadrant of the
Galaxy. A small section of the survey is shown in Figure~3. The various
scientific goals motivating this
survey were the study of HII regions
\begin{figure}[h]
\center {\includegraphics [bb=0 195 408 451,scale=0.7]{fig3d.eps}}

   %\parbox[tb]{12cm}
   %{\hspace{3.5cm}
   {\center
   \footnotesize Fig.\,3~~ Part of the Galactic plane at 2695~MHz in total intensity}

    \end{figure}
and SNRs as well as the study
of the extended and diffuse emission.

\vs\vn{\bf{2.1~~Supernova remnants}}

 An exciting example of SNRs is the well-known object S147 at
the anti-centre of the Galaxy (Figure~4). The sensitive 2.695~GHz
radio map corresponds even in details
\begin{figure}[h]
\center {\includegraphics [bb=0 193 408 451,scale=0.6]{fig4.eps}}

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   %{\hspace{3.5cm}
   {\center
   \footnotesize Fig.\,4~~ The SNR S147 in radio (F\"{u}rst and Reich 1986) and optical light (van den Bergh 1973)}

    \end{figure}
with the optical H$_\alpha$ map. A pulsar is located inside the
remnant, possibly associated with it (Anderson et al. 1996). It is
one of few SNRs with detectable optical emission. In most cases
the identification of SNRs relies on radio astronomical tools: the
spectral index of the radio flux density $S_\nu$ ($S_\nu \propto
\nu^\alpha$), the low infrared emission compared with HII regions,
and the radio polarization.

\no 2.1.1~~The radio flux density spectral index
\begin{figure}[th]
\center {\includegraphics [bb=0 182 408 455,scale=0.6]{fig5.eps}}

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   %{\hspace{3.5cm}
   {\center
   \footnotesize Fig.\,5~~ The radio spectrum of S147}

    \end{figure}
The radio spectrum of SNRs is typically a power law with a
spectral index $\alpha$ between -0.1 and -1.0 depending on the SNR
type. In rare cases a break or bend towards high frequencies is
observed. In Figure.~5 the radio flux density spectrum of S147 is
shown. The power law and the spectral index  are intimately
related to the acceleration of electrons in the SNR shock wave,
the magnetic field in the emitting regions, and the aging effects
during various periods of the SNR lifetime.
 In case of S147
the detected emission can be separated into thin radio/optical filaments and
extended
diffuse emission (F\"{u}rst and Reich 1988). The spectral index maps of both
components are different (see Figure~6).
In Figure~6 the temperature
spectral index
\begin{figure}[h]
\center {\includegraphics [bb=0 244 408 437,scale=0.7]{fig6a.eps}}

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   %{\hspace{3.5cm}
   {\center
   \footnotesize Fig.\,6~~ The two spectral components of S147}

    \end{figure}
$\beta$ is used
($T_B \propto \nu^{\alpha-2} = \nu^\beta$).
The
flux density spectral index of the filaments is close to $\alpha = -0.5$,
the canonical value for
Fermi accelerated electrons. The diffuse emission shows a much steeper spectrum.
A possible
interpretation is the exchange of electrons between filaments and the extended
component and the corresponding action
of compression (strong aging effects) and expansion. This mechanism may shift
the possible break
frequency of the extended component to low frequencies, F\"{u}rst el al. 1988).
\begin{figure}[h]
\center {\includegraphics [bb=0 242 408 438,scale=0.8]{fig7.eps}}

   %\parbox[tb]{12cm}
   %{\hspace{3.5cm}
   {\center
   \footnotesize Fig.\,7~~ The Galactic plane in radio and infrared}

    \end{figure}

\no 2.1.2~~The infrared emission

The infrared emission may be used as a second tool to separate HII regions from
SNRs (F\"{u}rst et al. 1987). In Figure~7 we show the radio map of a section of
the Galactic plane
 \begin{figure}[h]
\center {\includegraphics [bb=0 56 408 489,scale=0.43]{fig8a.eps}}

   %\parbox[tb]{12cm}
   %{\hspace{3.5cm}
   {\center
   \footnotesize Fig.\,8~~ The SNR HB9 in total and polarized intensity}

    \end{figure}
filled with HII regions
and SNRs. At 60~micron (IRAS) the region look very similar. The
two maps may be scaled in such a way that HII regions in the two
maps have about the same amplitude. Subtracting the scaled
60~micron map from the radio map let all the HII regions
disappear, while all the SNRs (circles) remain visible. Some
relicts of the strong HII regions are still visible, may be as a
result of intrinsic differencies between 60~micron and radio
emission or small pointing differencies.
\begin{figure}[h]
\center {\includegraphics [bb=0 216 408 445,scale=0.7]{fig9a.eps}}

   %\parbox[tb]{12cm}
   %{\hspace{3.5cm}
   {\center
   \footnotesize Fig.\,9~~ Part of the Galactic plane in total and polarized intensity}

    \end{figure}

\no 2.1.3~~The linear polarization

Possibly the most convincing tool to identify SNRs is the linear
polarization of the synchroton emission. One example for a
polarization map of SNRs is shown in Figure~8 (Reich et al. 1984).
The linear polarization of SNRs may reach a high percentage of
order 50\% or more. The exact value depends on the geometry of the
SNR's magnetic field as well as on the action of the Faraday
effect within the source and between the object and the observer.
\begin{figure}[h]
\center {\includegraphics [bb=0 90 408 480,scale=0.5]{fig10a.eps}}

   %\parbox[tb]{12cm}
   %{\hspace{3.5cm}
   {\center
   \footnotesize Fig.\,10~~ Tycho-SNR at 32 GHz with the 100-m-RT}
    \end{figure}
More about Faraday effects is presented by Wielebinski and by W.
Reich (this volume). In a certain sense the linear polarization of
the SNR's is related to the ambient Galactic magnetic field, in
particular in late phases of the SNR evolution. However, studies
of the Galactic magnetic field using the Effelsberg 2695 MHz
survey shows a very complicated nature of the observed field
(Figure~9, Junkes et al. 1987, Duncan et al. 1999). Various
effects contribute to this caotic view: Intrinsic variations of
the magnetic field in intensity and direction, Faraday effects
along the line of sight within the emission regions and caused by
ionized gas along the line of sight or by randomly distributed
Farady screens.

\no 2.1.4~~High frequency measurements

A break or bend in the SNR radio spectrum is, if any, observed at
high frequencies, in most case above 10~GHz. Observations at high
frequencies, particularly at 30~GHz and beyond become more and
more important. New sensitive receivers at these frequencies allow
mapping of extended sources in a reasonable time. As an  example
the SNR Tycho is shown in Figure~10 at 32~GHz. Observations at
32~GHz are made with a multi-feed system from the SFK. At present
such observations are limited by a relative low antenna gain at
high elevations, caused by the distortions of the not perfect
homology of the main dish. The insufficient quality of the
gregorian subreflektor causes an additional decrease of the gain.
\begin{figure}[h]
\center {\includegraphics [bb=0 128 408 469,scale=0.6]{fig11.eps}}

   %\parbox[tb]{12cm}
   %{\hspace{3.5cm}
   {\center
   \footnotesize Fig.\,11~~ The distortion of the main reflector
   at 70$^\circ$ elevation}

    \end{figure}

\para{\large\bf{3}~~Possible Improvements of the 100-m-RT}

\vs\vs The insufficient quality of the subreflector and the
remaining distortions of the homologeous main reflector contribute
to a low gain particularly at high elevations. Figure~11 shows the
distortions of the main reflector at the elevation of 70$^\circ$.
Variations of about $\pm$2~mm are visible, which contribute
significantly to the mean deviation. These deviations are
uncritical for frequencies below about 10~GHz, for which the
telscope was designed. Beyond 10~GHz, especially at the highest
frequency of 86~GHz the beam pattern is strongly affected by these
destortions. An example, the beam pattern at 86~GHz caused by
these effects is shown in Figure~12. The
 beam
pattern is calculated from the surface distortions shown in the upper left
panel using common diffration theory and shows only the effect of
incomplete homology. If such observation are moved to the SFK, an improvement is
possible
if the subreflektor is equipped with active elements. If using 96 activators the
improvement of the surface and the beam pattern are shown in the right panels of
Figure~12.
\begin{figure}[h]
\center {\includegraphics [bb=0 128 408
469,scale=0.6]{fig12a.eps}}

   \vs%\parbox[tb]{12cm}
   %{\hspace{3.5cm}
   {\center
   \footnotesize Fig.\,12~~ The improvement of the antenna beam pattern with an
active subreflector}

    \end{figure}

The following improvements are currently being discussed or in progress:

\begin{itemize}
\item Replacement of the subreflektor including it's mount

\item Active surface of subreflector

\item Automatic focus change

\item Adjustment of the panels of the main reflector (Holography)

\item Multichannel polarimeters

\item 7-feed 21cm system for the primary focus

\item 90 feed array at 32~GHz for the secondary focus
\end{itemize}

\bc {\bf References} \ec

\vspace{-4mm} \no \fns

 \nref Anderson S.B., Cadwell B.J.,  Jacobe B.A., et al.,  ApJ, 1996,
 468, L55
 \nref Duncan A.R.,  Reich R.,  Reich W., et al.,  A\&A, 1999,
350, 447
 \nref  F\"{u}rst E.,  Reich W.,  A\&A, 1986, 163, 185
 \nref F\"{u}rst E.,  Reich W.,  A\&AS, 1987, 71, 63
 \nref  F\"{u}rst E.,   Reich W.,  in Supernova shelles
and their birth events.  W. Kundt ed., Lecture Notes in Physics.
Springer Verlag, 1988, 316, p33 \nref  F\"{u}rst E.,  Reich W.,
A\&AS, 1990, 85, 691 \nref  Hachenberg O., Wielebinski R.,  Grahl
B.H.,  The 100-m radio telescope Effelsberg, Proc. I.E.E.E., 1973,
61, 1288 \nref  Haslam C.G.T.,  Salter C.J.,  Stoffel H., et al.,
A\&AS, 1982, 47, 1 \nref  Junkes N.,  F\"{u}rst E.,  Reich W.,
A\&AS, 1987, 350, 447 \nref  Reich W.,  F\"{u}rst E.,  Sieber W.,
IAU Symp, 1984, 101, 376 \nref  Reich W.,  F\"{u}rst E.,  Steffen
P., et al.,  A\&AS, 1984, 58, 197 \nref  Reich W.,  F\"{u}rst E.,
Reich P., et al.,  A\&AS, 1990, 85, 633 \nref  van den Bergh S.,
Marschner A.P.,  Terzian Y.,  ApJS, 1973, 26, 19

%\end{CJK}
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