L. Kohoutek
Hamburg Observatory, Hamburg, Germany
Abstract:
The nebula He 2-104 (RA=140833.5,
D=
511219.1, PK 315+91,
PN G 315.4+09.4), known as the Southern Crab since the
discovery of its large bipolar structure by Schwarz et al.(1989),
originally discovered in 1964 by Henize (1967) and classified
also as a symbiotic star (SS, Allen, 1984), is a typical
example of objects classified simultaneously as PN and SS.
The nebula was observed with the 0.9 m tel.+ CCD at La Silla in Apr./May 1995 (scale: 1 pixel = 0.443). The shape of it, clearly visible in the light of [OIII] 5007A line, is bipolar with bright central arcs together with two main condensations. These condensations (N1, S1) lie exactly at the ``poles'' of the nebula. The dimensions of the main structure are 80x34 in p.a. 120.8; the total extension of the nebula may be 105 if the outer faint condensations N13 and S13 are also taken into account. The space between the main condensations N1 and S1 and the arcs is filled out by some matter. If the radiation of this is in the continuum, which seems to be probable, its nature would be dust. Further investigation is planned in order to prove this.
We identified altogether 26 condensations or clouds. They appear in pairs, which means that to each northern condensation a southern counterpart can be found. The condensations are nearly symmetrical towards the centre of the nebula. A common origin of the pairs of condensations is very probable. The presence of condensations in [OIII] 5007A indicates their high excitation state.
The central object is not starlike but somewhat extended: only 0.40 in X- and 0.49 in Y-direction if FWHM of it is compared with those of the surrounding stars.
Adopting the distance d=800 pc we get 0.41 pc for the total extent of the nebula, and 0.035 x 0.029 pc for its inner core. We believe that the name ``symbiotic proto-PN'' (Schwarz et al., 1989) is justified for He 2-104.
The nebula He 2-104 (RA = 140833.5,
D =
511219.1=120.8
FWHM
The condensations are
substantially larger than the
seeing disc of the stars: the mean value in x-direction is 3.6
The condensations appear in pairs, which means that to each
northern condensation a southern counterpart can be found. The
association between the northern and the southern condensations may
be in principle rather uncertain and is at present only preliminary,
because we do not know the velocity of the condensations. The
association Nn with Sn (n=1
The condensations lie nearly symmetrically towards the centre
of the nebula (x
An independent check for the existence of nebular condensations
was based on star counts: we counted altogether 82 stars in the
field of He 2-104. The star density in our photometric system was
therefore 118 arcsec
The structure of the central arcs is dotted with several condensations
as seen in the paper of Corradi, Schwarz (1993, Fig.1).
The arcs extend in all four directions to about 24 arcsec from the
centre of the nebula. They have no sharp ends and their width is
between 2.3
The space between the main body of the nebula (the arcs) and the condensations N1 and S1 is filled out by some matter (see Fig.2). If the radiation of this is in the continuum, which seems to be probable, its nature would be dust. Further investigation is planned in order to prove this. In that case dust would be present not only in the assumed equatorial torus, but also in the polar directions.
The central object
is not
starlike but somewhat extended: only 0.40
If we adopt the distance d=800 pc of He 2-104 (Schwarz et al., 1989) we get
0.41 pc for the total extent of the nebula, and 0.035 (towards the poles) x 0.029 pc for the dimension of its inner core. The idea of high-velocity
jets and the calculated dimensions of the inner nebulosity are both compatible with the
common conception of small proto-PN, so that we believe that the name
``symbiotic proto-PN'' (Schwarz et al., 1989), considering also the
M-component of the central star (see Whitelock, 1988), is justified for
He 2-104.
Con. | |
|
|
FWHM |
R | |||
|
|
|||||||
N1 | +18.0 | 3.7 | 2.8 | * | ||||
N2 | +17.3 | |
* | |||||
N3 | |
+14.6 | +2.7 | 2.2 | 4.1 | |||
N4 | |
+13.7 | +2.6 | 7.1 | 1.3 | * | ||
N5 | |
+24.1 | +23.1 | |||||
N6 | |
+20.0 | +30.8 | 1.1 | 6.9 | * | ||
N7 | |
+17.5 | +27.8 | 3.6 | 9.7 | : | ||
N8 | |
+11.3 | +8.3 | 2.9 | : | 2.8 | ||
N9 | |
+5.9 | |
1.9 | 1.3 | |||
N10 | |
+13.5 | +8.8 | * | ||||
N11 | |
+3.6 | * | |||||
N12 | |
|
||||||
N13 | |
+31.7 | +7.7 | |||||
S1 | +32.6 | +1.1 | 4.0 | 13.0 | * | |||
S2 | +32.4 | |
* | |||||
S3 | +23.8 | +10.1 | 7.5 | 2.4 | ||||
S4 | +19.3 | +3.2 | 5.4 | 0 | : | * | ||
S5 | +16.0 | +20.4 | 2.7 | 6.1 | ||||
S6 | +9.6 | +38.0 | ||||||
S7 | +12.3 | +24.3 | 3.9 | 1.8 | ||||
S8 | +14.2 | +13.2 | 1.1 | 0 | : | |||
S9 | +9.4 | |
|
|||||
S10 | +17.8 | +11.2 | * | |||||
S11 | +23.5 | |
3.8 | 3.8 | ||||
S12 | +22.0 | +1.4 | ||||||
S13 | +39.0 | +10.7 | * |
Remarks : | |
N1 | interacting with N2 |
N2 | interacting with N1, separate condensation? |
N4 | association with S4 uncertain, may also be with S10 |
N6 | together with a star |
N10 | very faint and small; association with S10 uncertain, may also be with S4 |
N11 | two centres? |
S1 | interacting with S2 |
S2 | interacting with S1, separate condensation? |
S4 | association with N4 uncertain, may also be with N10 |
S10 | association with N10 uncertain, may also be with N4 |
S13 | very faint |
* Based on data collected at the European Southern Observatory, La Silla, Chile.
Fig.1: Bipolar shape of He 2-104 with 26 condensations in pairs: read N1...N13, S1...13. [OIII] 5007A filter.
Fig.2: He 2-104 in the light of [OIII] 5007A; the space between the main nebular body and the condensations N1+N2 and S1+S2 is filled out by some matter, probably dust. Position in pixels, scale: 1 pixel = 0.443'' orientation as Fig.1 (north at the top, east on the right).