In the following we discuss in detail the long-slit spectra of the 9 TTSs
(Haro 6-10, XZ Tau, UZ Tau E, HN Tau, DO Tau, DP Tau, UY Aur, RW Aur and
V536 Aql) for which the most detailed information is available on the
spatial distribution of the FEL regions in the lines of [OI]
, 6363, [NII] 
and the [SII]
, 6731 and also on the outflow direction. In the latter
case long-slit spectra at sufficiently large number of orientations have
been taken to determine the unknown outflow direction (see also Hirth et al.
1994a), unless the outflow direction is known from narrow-band
imaging. First results on DO Tau, DP Tau and RW Aur have been briefly
discussed elsewhere (Hirth et al. 1994b). A detailed
discussion of the data for CW Tau is given in Hirth et al.
(1994a). The following examples also give the reader an idea of the
sometimes rather complex spatial and kinematic structure of the FEL region
of the investigated TTSs and the often strong differences between individual
objects.
Haro 6-10 (HH 184) is an embedded TTS with strong FELs surrounded by a small
nebula consisting of a mixture of HH emission and scattered continuum light.
It has a deeply embedded IR companion which is much fainter at H and K than
at L and M (Seperation 2'', 
, 
; Leinert & Haas 1989). More details about
previous studies are given in Strom et al. (1986),
Leinert & Haas (1989) and Reipurth (1994).
Direct images of Haro 6-10 presented by Elias (1978) and Strom
et al. (1986) show a HH knot some 50'' southeast from the source
at 
and a much fainter and extended feature at about
170'' distance at 
. On the basis of these images we
assumed that the outflow is oriented at around 
and
placed the slit at through Haro 6-10 and the HH knot.
Note that spatial and kinematic data derived from spectra of the FELs have
not been available before our survey.
Figure 1: Position-velocity map of the [SII] 
and [SII]
lines of Haro 6-10 and its associated HH object extracted
from data taken with the 3.5 m Cassegrain twin spectrograph in December 1988
(). The stellar continuum has been subtracted. The
spacing of the contours is logarithmic corresponding to a factor 20.5
in the intensity. Relative positions and velocities are quoted with respect
to the stellar position and stellar velocity, respectively. On the right
hand side the electron densities of various emission line features are
given
Figure 2: Spatial width (top part), spatial offset (middle part) and
spatially integrated intensity (lower part) of the [OI] 
,
[NII] and [SII] line emission of Haro 6-10 as
a function of the radial velocity (). The dotted line
in the plots of the spatial width indicates the lower limit for which
changes in width with velocity can be reliably measured. The radial velocity
has been measured relative to the stellar velocity. The data are extracted
in part from the continuum-subtracted position-velocity map displayed in
Fig. 1 (click here)
The long-slit spectra of Haro 6-10 were obtained with the 3.5 m Cassegrain
twin spectrograph in December 1988. From the PV map shown in Fig. 1 (click here)
one clearly sees that in the [SII] , 6731 lines the
emission region is spatially extended along . The
FELs of the above mentioned HH knot have been detected as well, permitting
us to deduce its kinematic properties for the first time. The radial
velocities at 47'' and at 52'' distance from the outflow source are
and 
, respectively. The electron
densitites derived for this HH knot (
) are
relatively low compared to the values for the emission near the stellar
position (
). Note that for the highly blueshifted gas at
lower electron densities were derived (
) compared to the values of for the peak
emission at 
.
Details about the kinematic and spatial properties of the FEL region of Haro
6-10 are shown in Fig. 2 (click here). The plots display the spatial width
(
), the offset y and the spatially integrated
intensity I as a function of the radial velocity with respect to the
stellar velocity. All quantities are derived by a Gaussian line fit over the
FEL region in spatial direction of the continuum-subtracted spectrogram as
described in Sect. 2 (click here).
The [OI] , [NII] and the [SII] lines show line emission over a very broad range of velocities with
blue wings extending up to 
in [NII] .
However, a well separated LVC and HVC is not evident in the line profiles of
[OI] and [SII] like for example in V536 Aql
(see Figs. 20 (click here) and 21 (click here)).
Among the studied FELs the [NII] line is the best diagnostic
tool for the investigation of the HVC (or the high-velocity gas in general),
since to our knowledge this line never forms a LVC. The [NII]
line peaks at 
and we therefore assume a
radial velocity of 
for the HVC, which is in line with
the velocity of the HH object. Therefore the broad emission peak of the [OI]
and [SII] lines at 
probably represents the
blend from both a LVC and a HVC where the LVC is more spatially compact.
Such a blended LVC and HVC would also explain why the offset and spatial
width in the [SII] and [OI] lines is slowly but systematically increasing
between 0 and 
. At velocities between -120 to
the offset in the [OI] and [SII]
lines increases strongly and reaches values of about 2''
in both lines at velocities of . Although for these
high velocities no significant differences between the spatial properties of
the [OI] and [SII] lines are detected this is
not the case at low velocities where the offset and spatial width of the
peak emission of the [SII] line are nearly as twice as large
as the corresponding values for the [OI] line. In the [NII]
line the offset of the line emission is even higher around
the peak of the emission when comparing with the [OI] and
[SII] lines. A similar trend has been observed for several
other TTSs (see Sect. 4.1 (click here) below).
We finally like to note that it is rather unclear why the gas at radial
velocities of about has such a large offset and why
it has so much higher radial velocities than the HH object or the HVC (i.e.
the peak of the [NII] emission). Maybe there was a phase of much higher
outflow velocities in the past. It is also possible that we observe an
independent HVC from the companion of Haro 6-10.
XZ Tau is a double star. The two components are separated by about 0.3''
in 
and differ in K-magnitude by about a factor
of 3 (Leinert et al. 1993). Profiles of the FELs have first
been published by Appenzeller et al. (1984). Deep [SII]
, 6731 CCD images of XZ Tau were first published by
Mundt et al. (1988) and Mundt et al. (1990).
These authors show that XZ Tau is associated with a bipolar outflow with a
for the blueshifted part of the flow. Because of
the low luminosity of the binary component XZ Tau B, the component A is more
likely the source of the outflow. Previous long-slit spectra of the FELs of
XZ Tau have been discussed by Solf (1989) and Mundt et
al. (1990).
Since the ouflow direction at is known
from CCD imaging we have taken deep long-slit spectrograms only close to
this position angle at 
. PV maps of the [OI]
line, [NII] and [SII] lines
of XZ Tau derived from these long-slit spectra are shown in Fig. 3 (click here).
In the [NII] line the very broad red emission is rather
prominent.
Figure 3: Position-velocity maps of the [OI] , [NII]
and [SII] lines of of XZ Tau extracted from
data taken with the 3.5 m Cassegrain twin spectrograph in November 1993
(). The stellar continuum has been subtracted.
Contours, positions and velocities as in Fig. 1 (click here)
Figure 4: Spatial width (top part), spatial offset (middle part) and
spatially integrated intensity (lower part) of the [OI] ,
[NII] and [SII] line emission of XZ Tau as a
function of the radial velocity (). The dotted line in
the plots of the spatial width indicates the lower limit for which changes
in width with velocity can be reliably measured. The radial velocity has
been measured relative to the stellar velocity. The data are extracted from
the continuum-subtracted position-velocity maps displayed in
Fig. 3 (click here)
Figure 5: Position-velocity maps of the [OI] , [NII]
and [SII] lines of UZ Tau E extracted from
data taken with the 3.5 m Cassegrain twin spectrograph in December 1988
(
). The stellar continuum has been subtracted. Contours,
positions and velocities as in Fig. 1 (click here)
The spatial and kinematical properties of the bipolar outflow are shown in
more detail in Fig. 4 (click here). Note that due to the spectral resolution of
about 
in the Cassegrain twin spectra the line profiles
of the [OI] and [SII] line are not resolved
into a LVC and HVC. However, data from coudé spectra with a higher
spectral resolution clearly show a double-peaked line profile with a HVC at
in the [SII] line and 
in
the [OI] line, and with a LVC at 
and
, respectively (see Figs. 22 (click here)f and g).
The bipolarity of the outflow is most clearly evident in the [NII]
line by the corresponding changes in the sign of the offset.
In most other TTSs of our sample the offset (and often the spatial width) is
largest in the [NII] line and smallest in the [OI]
line. For XZ Tau this is the case for the blueshifted part of
the bipolar outflow but not for the redshifted part where similar values in
[SII] and [NII] are observed.
Like in many other TTSs studied here, the spatial width for the HVC is much
larger in the [NII] and [SII] lines than in
the [OI] line. In the [NII] line the spatial
width is 
for the blueshifted part while the corresponding
value for the [OI] line is only 
. In the
velocity range of the LVC of the [OI] and [SII]
lines one recognizes a local minumum in the spatial width.
This trend is already expected from previous studies (e.g. CW Tau in Hirth
et al. 1994a) where the LVC shows a smaller offset and spatial width
than the HVC.
Observations of the [OI] line of UZ Tau E were first
discussed in Appenzeller et al. (1984). They detected a LVC and
a broad HVC. Recent data on the FELs of this TTS have been published by
Hartigan et al. (1995). Information on the spatial properties
of the FELs of UZ Tau E is so far not available.
Long-slit spectra of UZ Tau E have been taken at four position angles
(, 
, 
and 
).
Since we have found evidence for a bipolar outflow only in our north-south
oriented slit, as illustrated in Fig. 5 (click here), we believe that the
blueshifted part of the bipolar outflow is roughly oriented towards . The PV maps in Fig. 5 (click here) show that the bipolar nature of
the outflow is most clearly evident in the [NII] line. This
is further illustrated in Fig. 6 (click here) where more details about the
kinematic and spatial properties of the FELs are displayed. From this figure
it is evident, that the bipolar outflow is also indicated in the [OI]
line but the offsets are half as large as in the [SII]
line. In the plots of the spatial width
versus radial
velocity (see Fig. 6 (click here)) one can recognize that in the [OI] and [SII] lines the spatial width is smallest around
the stellar velocity. As already mentioned above, this behaviour is also
observed in other TTSs in our sample.
Figure 6: Spatial width (top part), spatial offset (middle part) and
spatially integrated intensity (lower part) of the [OI] ,
[NII] and [SII] line emission of UZ Tau E as a
function of the radial velocity (). The dotted line
in the plots of the spatial width indicates the lower limit for which
changes in width with velocity can be reliably measured. The radial velocity
has been measured relative to the stellar velocity. The data are extracted
from the continuum-subtracted position-velocity maps displayed in
Fig. 5 (click here)
The [OI] and [SII] lines do not show a
pronounced double-peaked line profile, presumably due to the moderate
spectral resolution of the Cassegrain twin spectra (
). However, it is known from high-resolution spectroscopic
studies (see Appenzeller et al. 1984 and Hartigan et al.
1995) that both a HVC and a LVC exist at velocities of -90 and
, respectively. From a two-component Gaussian fit to our [OI]
data we derive a radial velocity of 
for the HVC and 
for the LVC. For the [SII] line the corresponding values are 
and 
, respectively. For the [NII] line only a HVC at
has been detected. For the redshifted part of the bipolar
outflow no distinct HVC is evident in the line intensity profile shown in
Fig. 6 (click here). But the broad redshifted wing reaches to velocities of
about 
in all lines. Note that in the spectra of
Hartigan et al. (1995) one can see the redshifted emission in
both the [OI] and [SII] lines at similar
radial velocities.
Jensen et al. (1996) have argued on the basis of their
observations that UZ Tau is sourrounded by a disk with
the disk plane being oriented at about 
,
i.e., approximataly at our derived outflow direction. They furthermore argue
that such a disk orientation is strongly supported by the measured position
angles of the electric polarization vector which often has a similar
orientation as the disk plane (see e.g. Bastien 1989). This
result clearly contradicts our derived disk orientation of about 
(assuming that the disk is oriented perpendicular to the bipolar
outflow). We suggest that the data of Jensen et al.
(1996) can also be explained by a bipolar outflow and that there is
no convincing argument that their data can only be interpreted by disk
rotation. Furthermore the available polarization data are not useful to
argue for a certain disk orientation, since in these polarization studies
the combined light of both UZ Tau E and W has been measured. In summary we
believe that the data of Jensen et al.
(1996) and our data can be understood, if the blueshifted part of
the outflow from UZ Tau E is oriented at 
.
HN Tau is one of the TTSs in our sample with the strongest forbidden line
emission (
for the [OI]
line) and has therefore been selected for our studies. Previous
high-resolution [OI] and [SII] line profiles of this star published by
Edwards et al. (1987) and Hartigan et al. (1995)
do not show a double-peaked line profile as observed for other TTSs but only
display a very broad blueshifted emission with a weak red wing in [OI]
. First long-slit spectra were discussed by Solf
(1989).
With the 3.5 m Cassegrain twin spectrograph we have taken long-slit spectra
at , , and 
.
Furthermore we have obtained two high-resolution coudé spectrograms at
and 
. From the observed offset of the
high-velocity emission in these spectra we conclude that the blueshifted
part of the outflow is oriented between 
and
.
Figure 7: Position-velocity maps of the [OI] , [NII]
and [SII] lines of HN Tau extracted from
data taken with the 2.2 m coudé spectrograph in September 1992 ( and ). The stellar continuum has been subtracted.
Contours, positions and velocities as in Fig. 1 (click here)
Figure 8: Position-velocity maps of the [OI] , [NII]
and [SII] lines of HN Tau extracted from
data taken with the 3.5 m Cassegrain twin spectrograph in December 1988
(). The stellar continuum has been subtracted. Contours,
positions and velocities as in Fig. 1 (click here)
Figure 9: Spatial width (top part), spatial offset (middle part) and
spatially integrated intensity (lower part) of the [OI] ,
[NII] and [SII] line emission of HN Tau as a
function of the radial velocity (). The dotted line in
the plots of the spatial width indicates the lower limit for which changes
in width with velocity can be reliably measured. The radial velocity has
been measured relative to the stellar velocity. The data are extracted from
the continuum-subtracted position-velocity maps displayed in
Fig. 8 (click here)
Figure 7 (click here) shows the PV diagrams of the [OI] , [NII]
and the [SII] lines at
derived from the coudé spectra. For comparison the PV diagram of the
[SII] line at is also shown. The PV
maps of the [OI] and the [SII] lines at
clearly illustrate the increase of the offset with
increasing blueshift of the emission. The PV diagram of the [SII]
line at shows, as expected, that
there is no significant offset at a position angle approximately
perpendicular to the outflow direction.
Due to their lower spectral resolution the PV maps of the [OI]
, [NII] and the [SII] lines
derived from the Cassegrain twin spectrograms do not clearly show the
increase of the offset with increasing velocity (see Fig. 8 (click here)). But
the effect is evident in the [NII] and the [SII] lines as better illustrated in Fig. 9 (click here). The offsets of the
[SII] line plotted seems to suggest a bipolar outflow, since the redshifted
parts of the emission has apparently positive offsets. However, such a
bipolar outflow is not supported by the nearly constant offset measured in
the [OI] line (see Fig. 9 (click here)) and by the PV map of the
[SII] line shown in Fig. 7 (click here).
A comparison of the line intensity profiles shown in Fig. 9 (click here) and
Fig. 22 (click here)h shows that the [NII] line peaks at much larger negative
radial velocities than the [OI] lines ( as compared to
, see also Fig. 7 (click here)). It is known that the [NII] line in
TTSs shows normally no LVC (see also Sect. 4 (click here)). Therefore the lower radial
velocity of the [OI] line can be explained by a strong LVC in that line
which is spectroscopically unresolved from the HVC due to the large internal
velocity widths of both components. In the [SII] lines a LVC is probably
also present. The existence of a LVC in both the [OI] and [SII] lines is
also consistent with the smaller offsets and smaller spatial widths observed
at velocities between and (see
Fig. 7 (click here) and Fig. 9 (click here)).
DO Tau is a classical TTS (CTTS) associated with an arc-like reflection nebula (see POSS). Profiles of FELs have first been published by Appenzeller et al. (1984) and Edwards et al. (1987). First results on the spatial properties of the FELs, based on long-slit spectra obtained with the Cassegrain twin spectrograph, have been discussed by Hirth et al. (1994b).
Figure 10: Position-velocity maps of the [OI] , [OI]
, [SII] and [SII] lines of DO
Tau extracted from data taken with the 3.5 m Cassegrain twin spectrograph in
December 1988 (). The stellar continuum has been
subtracted. Contours, positions and velocities as in Fig. 1 (click here)
Spectrograms have been taken at seven different slit positions in December
1988 (
, 
, 
, 
,
, 
and 
). They show the existence of
a bipolar outflow with the blueshifted part being oriented at 
. Note that the determined outflow direction is nearly
perpendicular to the polarization angle of 
found by
Bastien (1985).
The outflow is detected in the [SII] , 6731 and in the
[OI] , 6363 lines but neither in 
nor in
the [NII] 
, 6583 lines.
PV maps of the [OI] , 6363 and the [SII]
, 6731 lines are shown in Fig. 10 (click here). These
diagrams show that DO Tau has a bipolar outflow, with the blueshifted part
being much more prominent than the redshifted one. The bipolar outflow
extends up to 4'' from the star and, like in the case of RW Aur (Hirth et
al. 1994b), shows asymmetries both in morphology and kinematics on
either side of the star. In particular, in the [SII] lines the blueshifted
part of the outflow shows radial velocities of 
at
1.5'' distance from the star, whereas, at the same position in the
redshifted part of the outflow, the corresponding value is 
.
Figure 11: Spatial width (top part), spatial offset (middle part) and
spatially integrated intensity (lower part) of the [OI] and
[SII] line emission of DO Tau as a function of the radial
velocity (). The dotted line in the plots of the
spatial width indicates the lower limit for which changes in width with
velocity can be reliably measured. The radial velocity has been measured
relative to the stellar velocity. The data are extracted from the
corresponding continuum-subtracted position-velocity maps displayed in
Fig. 10 (click here)
Figure 12: Position-velocity maps of the [SII] 
, 4076
lines of DO Tau extracted from data obtained with the blue channel of the
3.5 m Cassegrain twin spectrograph in December 1992 (). Contours, positions and velocities as in Fig. 1 (click here)
We note that, in contrast to the blueshifted part, the redshifted part of the outflow can not be continously traced back to the stellar position. This is probably due to the existence of a circumstellar disk occulting the redshifted emission near the star, unless the gap in redshifted emission is due to an intrinsic faintness because of unfavourable excitation conditions.
In the blueshifted part of the outflow the HVC shows different kinematic
properties in the [OI] and [SII] lines.
Compared to the [SII] line the radial velocities in the [OI] line is lower
by 10 to 
. Furthermore, the velocity dispersion in the
[OI] lines is about two times larger than in the [SII] lines. This might be
the result of an increasing jet collimation with increasing distance from
the outflow source, as discussed in Mundt & Hirth (1997).
High resolution line profiles of the [OI] and [SII]
lines of DO Tau are shown in Fig. 22 (click here)i. These data
are extracted from coudé spectra which have a 2.5 times higher spectral
resolution compared to the deep 3.5 m Cassegrain twin spectrograph data
shown in Fig. 11 (click here). The higher spectral resolution of the coudé
spectra probably explains why we observed a double-peaked line profile in
the [OI] lines, i.e. a HVC and a LVC. In the [SII] lines only a HVC has been
found. However, the emission in the red wing of the HVC in the [SII] lines
(between and ) might indicate the
existence of a very weak LVC (see Fig. 22 (click here)i). Note that, contrary to
the case of the Cassegrain twin spectra, the redshifted part of the outflow
could not be detected in the coudé spectra due to the relatively low S/N
ratio. We like to mention that in most other TTSs the LVC is observed in
[SII] too. The only other examples among our investigated stars where a LVC
is only observed in [OI] and not in [SII] is FN Tau (see Fig. 22 (click here)a)
and RW Aur (see Sect. 3.8 (click here) ).
Figure 11 (click here) shows more details about the spatial characteristics of
the bipolar outflow of DO Tau deduced from the PV diagrams shown in
Fig. 10 (click here). (We again note that in these data a double-peaked line
profile in the [OI] line could not be resolved because of the
lower spectral resolution). From Fig. 11 (click here) it is evident that the
spatial offset and spatial width of the [SII] line are much
larger than the corresponding values of the [OI] line, a
result which was found for most other stars in our sample.
The data permit us to derive the electron densities (
) in both
parts of the bipolar outflow. In the blueshifted part of the outflow
decreases from 
to about 
between 2'' and 4'' distance from the star. At comparable distances in
the redshifted part densities of about 
have been
derived but no significant spatial variation of the electron density has
been detected between 2'' and 4'' distance from DO Tau.
In addition, we measured the [SII] /[OI] line
ratio in the blueshifted part of the outflow. This ratio increases from 0.2
at the stellar position up to 1.5 at 2'' distance from DO Tau. Further out
the [OI] line flux decreases very fast making a determination of the
[SII]/[OI] line ratio impossible. In the redshifted part of the outflow an
increase of the line ratio from 1.3 to about 3.0 at distances between 2''
and 4'' has been detected. These values are comparable with those
measured in HH objects and are in line with the results obtained for CW Tau
(see Hirth et al. 1994a) and RW Aur (see below). In all these
cases, the increase of the [SII]/[OI] line ratios with increasing distance
from the source can most probably be explained by a corresponding decrease
in electron density (see Sect. 3.8 (click here) and Mundt et al. 1990).
Furthermore the [SII] , 4076 lines of DO Tau have been
observed with the blue channel of the 3.5 m Cassegrain twin spectrograph in
December 1992 (see Fig. 12 (click here)). Whereas the much fainter [SII]
line appeares spatially resolved, this is not the case for
the [SII] 
line. The equivalent width for the [SII] line is 
. The radial velocity relative to the star is
and the velocity dispersion at FWHM is 
.
However, the [SII] line is heavily disturbed by Fe I
emission in the blue and Fe I 
emission in the
red wing. Therefore the values for the equivalent width and the velocity
dispersion are quite uncertain. The same holds for the [SII]
line, which is disturbed by Sr II 
emission in the red wing.
The equivalent width for the [SII] line is 
. The radial velocity and velocity dispersion are 
and 
, respectively. Note the lower negative
radial velocities and the much higher velocity dispersions of the short
wavelength [SII] FELs compared to the [OI] , 6363 and
[SII] , 6731 lines (cf. Table 2 (click here)). Due to the
relatively large velocity dispersion of the [SII] ,
4076 lines and/or the large internal line width it is possible that we
observe in these lines unresolved double-peaked line profiles. Data of
higher spectral resolution of CW Tau and DG Tau show that a double-peaked
line profile can also be present in the [SII] line. In these
two cases such a profile is observed also in the [SII] , 6731 lines (Hamann 1994). Note also that in the PV map
of the [SII] line a weak spatial gradient of the radial
velocity in outflow direction is suggested. However, such a feature was not
observed in the [SII] , 6731 lines (see
Fig. 10 (click here)).
DP Tau is a CTTS of spectral type M0 with strong line emission in [OI]
(
; Cohen & Kuhi
1979).
First results of long-slit spectroscopic observations have been published in
Hirth et al. (1994b). They have taken three long-slit
spectrograms with the 4.2 m ISIS spectrograph of the WHT at position angles
of 
, 
and 
. The orientations of
the slit have been selected on the basis of a short exposure [SII]
, 6731 image taken with the ISIS before the long-slit
spectra. This image and the long-slit spectra suggest a PA of
for the blueshifted part of the bipolar outflow. This result
has been recently confirmed by narrow-band images in the [SII]
, 6731 lines obtained by Mundt & Eislöffel
(1997). Their deep images clearly show a bipolar outflow at a PA of
and 
.
Continuum-subtracted PV maps of the , [NII] and
[SII] , 6731 lines have been published in Hirth et al.
(1994b). Here we only show the PV maps of the [OI] , 6363 and the [SII] , 6731 lines (see
Fig. 13 (click here)). As in the case of RW Aur and DO Tau, the asymmetric
morphology of the bipolar outflow on either side of the star is obvious. As
discussed in Hirth et al. (1994b) at distances larger than
5'' from the star the line shows different radial velocities
in the redshifted and blueshifted part of the outflow: In the blueshifted
part, velocities between -90 and 
are measured whereas at similar distances the redshifted part
of the outflow shows a radial velocity of about 
only.
Due to the strong stellar emission, the emission from the
bipolar jets cannot be traced in much closer to the star than
about 2'' - 3''. This is not the case for the lines of [OI]
, 6363 and [SII] , 6731 shown in
Fig. 13 (click here). A comparison of these lines with the 
data in Fig. 3 (click here) of Hirth et al. (1994b)
shows that the [SII] and [NII] data resemble each other. Therefore we will
concentrate here on the comparison between the [SII] and [OI] lines shown in
Fig. 13 (click here).
Figure 13: Position-velocity maps of the [OI] , [OI]
, [SII] and [SII] lines of DP
Tau extracted from data taken with the 4.2 m ISIS Cassegrain spectrograph in
September 1993 (
). The stellar continuum has been
subtracted. Contours, positions and velocities as in Fig. 1 (click here)
Figure 14: Spatial width (top part), spatial offset (middle part) and
spatially integrated intensity (lower part) of the [OI] ,
[NII] and [SII] line emission of DP Tau as a
function of the radial velocity (). The dotted line in
the plots of the spatial width indicates the lower limit for which changes
in width with velocity can be reliably measured. The radial velocity has
been measured relative to the stellar velocity. The data are extracted from
the continuum-subtracted position-velocity maps displayed in
Fig. 13 (click here)
The PV maps show significant differences between the [OI] and [SII] lines.
These differences are presumably due to the higher density traced by the
[OI] lines. Firstly, only the [OI] lines show the existence of a clear LVC
with a radial velocity of 
. This component almost
certainly represents a LVC since no significant offset and spatial width has
been measured (see also the more detailed presentation of the spatial
properties in Fig. 14 (click here)). Furthermore in both the [SII] and [NII]
lines no similar velocity component at the stellar velocity has been
detected. We note that the component at about in the
[SII] lines is most probably a redshifted HVC since it shows a relatively
large offset of about +0.2''. Furthermore, a velocity component with
similar spatial and kinematic characteristics is observed in the [NII]
lines. However, it cannot be excluded, that in the [SII] line at low radial
velocities we are observing a superposition of a faint LVC and the beginning
of the high-velocity redshifted emission of the bipolar outflow. Similar to
most other TTSs in our sample, Fig. 14 (click here) shows that the offset in
[NII] and [SII] are much larger than in [OI]
. The same trend is observed in the blueshifted part of the
outflow for the spatial widths of these three FELs.
Note that although the spatial offset of the redshifted part of the outflow
is similar in the [SII] and [NII] lines, the
offset of the blueshifted part of the outflow is nearly twice as large in
[NII] compared to [SII] (see Fig. 14 (click here)). Such an asymmetry in the
spatial properties of the bipolar outflow on either side of the star has
been also detected in V536 Aql and in the case of UZ Tau E for the [NII]
line.
Figures 13 (click here), 14 (click here) and 22 (click here)j show that there is a
prominent blue wing in the [OI] line extending to velocities
of 
(offset 
; see
Fig. 14 (click here)). The blue wing is relatively faint and diffuse in the
[SII] line and may be absent in the [SII]
line.
From the PV maps of the [NII] and the [SII] lines it is also
evident that the velocity asymmetries between the two parts of the bipolar
outflow are already detectable at distances of about 1'' from DP Tau. In
particular on the blueshifted side in the [SII] lines one observes gas with
velocities of -70 to while on the redshifted side
velocities of are observed. The data on the
redshifted side suggest in addition that strong velocity variations have
taken place in the flow, e.g. at large distances from the star higher
velocities (
) are observed than at smaller
ditances (
). Also for the blueshifted side
the data of Hirth et al. (1994b) indicate
variations in the outflow velocity. Furthermore it is interesting to note
that in the velocities of the redshifted flow (for distances
) are half as small as the corresponding values in the [SII] and
[NII] lines. This latter result makes the whole situation
rather confusing and suggests that in addition to a complex behaviour of
velocity variations and asymmetries between the two sides of the outflow
there may be some unusual excitation and density effects at work.
For the redshifted part of the outflow we have also determined the electron
densities (). This quantity decreases from the upper limit of the
[SII] line method (
) at the stellar position
down to 
at 0.8'' distance from DP Tau and down to
and 
at 4'' and 5.5'' distance
further out. Furthermore, the [SII] /[OI] line
ratio increases from 0.4 at the stellar position up to 1.3 at 2''. For
the blueshifted part of the outflow the electron density and the
[SII]/[OI] line ratio have not been determined due to the low S/N ratio. As
in the case of CW Tau (see Hirth et al. 1994a), RW Aur and DO
Tau, these results imply that the density in the outflow is decreasing with
increasing distance from the star (see also Sect. 3.8 (click here) ).
UY Aur is a binary. The components are separated 0.89'' in 
and differ by about a factor of 1.5 in visual magnitude (Herbig
& Bell 1988; Leinert et al. 1993). Cohen &
Kuhi (1979) measured an equivalent width of the [OI]
line of 
. Profiles of the FELs have been first published by Appenzeller
et al. (1984), Edwards et al. (1987) and Hartigan et
al. (1995).
Our long-slit spectrograms of UY Aur obtained at position angles of 
, 
, 
and 
suggest
the existence of a bipolar outflow at 
.
Figure 15 (click here) shows the PV maps of UY Aur in the [OI]
and [SII] lines at extracted from a
spectrogram taken with the 3.5 m Cassegrain twin spectrograph in December
1988. Note that only a redshifted HVC at 
is visible
in [SII] whereas a blueshifted HVC has not been detected.
However, in a Cassegrain twin spectrogram taken in December 1992 (not shown
here) high-velocity blueshifted gas with velocities between -100 to is clearly evident in the [SII] line profile.
The differences in the PV map between the [OI] and [SII]
line are rather significant, with the [OI] map
showing a prominent emission extending up to . Why
such an emission has not been detected in [SII] in December
1988 is not fully understood. In part it could be due to the relatively low
S/N ratio of the data and the relatively weak [SII] flux. But
certainly the physical conditions in the blueshifted part of the flow may
also play a significant role. In particular, this part of the flow must be
of relatively high density and low excitation in order to explain the
strength of the [OI] line and the absence of the [NII]
line. It would be also interesting to find out by further
observations whether the velocity asymmetries observed by Hirth et al.
(1994b) for many bipolar outflows from YSOs are also present in UY
Aur. They could explain the smaller velocity extent of the [OI] line in the redshifted side.
Figure 15: Position-velocity maps of the [OI] and [SII]
lines of UY Aur extracted from data taken with the 3.5 m
Cassegrain twin spectrograph in December 1988 ().
The stellar continuum has been subtracted. Contours, relative positions and
velocities as in Fig. 1 (click here)
Figure 16: Spatial width (top part), spatial offset (middle part) and
spatially integrated intensity (lower part) of the [OI] and
[SII] line emission of UY Aur as a function of the radial
velocity (). The dotted line in the plots of the
spatial width indicates the lower limit for which changes in width with
velocity can be reliably measured. The radial velocity has been measured
relative to the stellar velocity. The data are extracted from the
continuum-subtracted position-velocity maps displayed in Fig. 15 (click here)
Further details about the kinematic and spatial properties of the [OI]
and [SII] line emission regions are displayed
in Fig. 16 (click here). Due to the medium resolution of the deep Cassegrain
twin spectra no clear distinction between a HVC and a LVC is evident. From
the change of the sign of the offset in the middle part of Fig. 16 (click here)
the bipolar nature of the outflow is evident especially in the [OI] line. As observed in many other TTSs, the offset of the (redshifted)
HVC in the [SII] line is larger than the HVC in the [OI]
line. However, note that the spatial width is similar for
both lines.
The data extracted from our coudé spectrograms indicate further
interesting details in the line profiles (see Fig. 22 (click here)k). In the
[OI] line a broad redshifted wing with velocities extending
up to 
is observed, while the blueshifted side of the
emission extends up to 
. Furthermore the blueshifted
part of the line profile indicates narrow peaks (
) at 
, 
and 
. Possibly, the data indicate multiple HVCs. In the [SII]
line no corresponding features have been detected.
The bright TTS RW Aur is a relatively isolated object (Herbig
1977). It is a hierachical triple system with the primary A having a
separation of about 1.4'' in 
from the close binary
B&C (separation: 0.12''; Ghez et al. 1993). The
latter two components are about 2 - 3 magnitudes fainter than the primary
component. Profiles of the FELs of RW Aur have been first published by
Hamann (1994). These data clearly show both a blueshifted and
a redshifted HVC and a slightly blueshifted LVC (see also below). The radial
velocities of these two HVCs are 
and 
, respectively. Although one could have already concluded from the
data of Hamann (1994) that RW Aur has a bipolar jet, the
existence of such a jet has been first realized by Hirth et al.
(1994b) from their long-slit spectroscopic observations. In their
paper a preliminary discussion of some of the data shown here has been
outlined.
A [SII] , 6731 image of the bipolar jet of RW Aur has
been obtained by Mundt & Eislöffel (1997). From this image
a PA of and a projected length of 106'' have been derived
for the southeastern blueshifted jet. On the opposite side the flow can be
traced over at least 50''.
The five long-slit spectrograms of RW Aur (
,
, 
, and 
) have been taken
before the above mentioned [SII] image. The analysis of these spectra
resulted in a PA of 
for the blueshifted part
of the bipolar outflow in good agreement with the imaging data. In the
long-slit spectra the bipolar jet can be traced over a distance of 20''
only in each direction. This is not only due to the limited S/N ratio of the
spectroscopic data but also due to the imperfect match of the PA of the slit
with the outflow direction. From the variation of the offsets of the blue
and redshifted emission centroids measured for different slit PA we
conclude that RW Aur A is most probably the source of the bipolar outflow.
This is particularly evident from the spectrogram obtained at 
(not shown here) for which the slit passes through component A
and the closeby binary B&C. Although this spectrogram does not resolve the
component A and the 
fainter binary B&C the measured offsets
of the HVC in the [SII] line of only 
from
component A clearly show that the bipolar outflow must originate from RW Aur
A. Note that unlike other TTSs with bipolar outflows, RW Aur shows no
detectable reflection nebula on the continuum CCD frames obtained by Mundt
& Eislöffel (1997).
A very surprising result of the data analysis of
Hirth et al.
(1994b) is the fact that the radial velocity of the HVC in the blue-
and redshifted part of the outflow differs by about a factor of 2. This
behaviour has been observed in several other TTSs as well but no
satisfactory explanation for this unusual asymmetry between the two sides of
the outflow has been found.
Further details on the variation of various spatial properties of the
redshifted (
) and blueshifted (
) jet are shown in Fig. 17 (click here). From this
figure it is evident that the two sides of the bipolar outflow differ not
only in radial velocity but also in intensity, in , and in the
[SII]/[OI] line ratio. In addition, the 
line ratio differs between the two sides and values of that ratio
ranging from 0.2 to 0.8 and from 1.0 to 3.3 have been measured for the
redshifted and blueshifted jet, respectively. The direct images presented by
Mundt & Eislöffel (1997) also show asymmetries between the
redshifted and blueshifted jet in both the spatial extent and morphology.
Somewhat surprising and unusual is the fact that the maximum of
the redshifted part of the flow is not located at the stellar position but
at a distance of -0.9'' from the star. The same behaviour is observed in
the line intensity. On the other hand the [SII]/[OI] line ratio seems to be
smallest at the stellar position as expected from observations of other
TTSs.
As already discussed by Mundt et al. (1990) the decrease of
the [SII]/[OI] line ratio with decreasing distance from the star probably
results from a strong increase of towards the star. As mentioned
in that publication, this density effect only works near the critical
density of the [SII] lines (
) which
is roughly 100 times lower than the critical density of the [OI] lines.
Therefore, for 
the [OI] line can
still become stronger than the [SII] line provided a low
excitation is prevailing in the jet or the HH object. We note that the
values of the [SII] /[OI] ratio deduced for the
more distant and therefore more tenuous parts of the redshifted outflow are
typical for HH objects (
; for more details see Dopita
1978; Brugel et al. 1981; Dopita et al.
1982).
In Fig. 18 (click here) the PV maps of the [OI] , 6363 and
[SII] , 6731 lines are displayed. Further details on
the spatial properties (spatial width and offset) in the [OI]
and [SII] lines are shown in Fig. 19 (click here). Interestingly,
a LVC is only observed in the [OI] lines but not in the [SII] lines. Similar
results have been obtained only for DO Tau (see Sect. 3.5 (click here) ) and FN Tau (see
Fig. 22 (click here)a). We note that in the [OI] line the LVC
appears weaker relative to the [OI] line (see
Fig. 18 (click here)). This presumably results from a blend with a weak
(allowed) emission near 6300 Å (or is due to an underlying absorption
feature near 6363 Å). As in most other TTSs discussed here the HVC shows
a much larger spatial width and offset in the [SII] lines than in the [OI]
lines.
V536 Aql is a CTTS of spectral type K7 which is known for its relatively
strong forbidden line emission in [OI] (
; Cohen & Kuhi 1979) and for its large degree of
polarization (
; Bastien 1982). Ageorges et al.
(1994) have shown that V536 Aql is a double star. The components are
separated by 0.52'' in 
and differ by about a factor
of five in luminosity. Already Appenzeller et al. (1984)
reported that the blueshifted [OI] centroid is offset from
the stellar position by about 1'' in .
Long-slit spectra of the FELs of V536 Aql taken at various position angles
(, 
, , ,
and 
) suggest the existence of a bipolar
outflow with the blueshifted part at a PA of 
. This outflow direction has been confirmed by recent
narrow-band [SII] , 6731 images of V536 Aql by Mundt &
Eislöffel (1997). These images show a few faint HH knots in 
at a distance of about 10'' to 15'' from the
star. We note that the outflow direction derived from our long-slit spectra
could not be determined that accurately as for several other cases (e.g.
like in the case of CW Tau; cf. Hirth et al. 1994a). This may
be due to the large opening angle of the outflow of V536 Aql. It is also
possible that light scattering of the emission from the FEL region in a
compact reflection nebula is important, resulting in misleading offset
values for the FELs. The latter is not unconceivable considering the large
degree of polarisation of V536 Aql. Interestingly the outflow direction of
is not perpendicular to the position angle of the
electric polarization vector of 
(Bastien 1982),
as observed for many outflows from YSOs (see e.g. Bastien
1989).
Figure 17: Spatial variation of the velocity width (FWHM), the radial velocity
of the [SII] HVC, the [SII] /[OI]
line ratio, the electron density , and the spatially
integrated [SII] intensity for the redshifted and blueshifted
part of the bipolar outflow of RW Aur extracted from data taken with the 3.5
m Cassegrain twin spectrograph in November 1993 (
).
Positions and velocities as in Fig. 1 (click here). The velocity dispersion is
corrected for the instrumental profile. The intensity is given in arbitrary
units
Figure 18: Position-velocity maps of the [OI] , [OI]
, [SII] and [SII] lines of RW
Aur extracted from data taken with the 3.5 m Cassegrain twin spectrograph in
November 1993 (). The stellar continuum has been
subtracted. Contours, relative positions and velocities as in
Fig. 1 (click here)
Because of the much larger luminosity of the component A we presume that
this component is the outflow source. Figure 20 (click here) shows
continuum-subtracted PV maps of V536 Aql in the [OI] , [NII]
and [SII] lines taken in September 1993 at a
PA of . The bipolar nature of this outflow is evident from the
opposite spatial offsets of the blueshifted and redshifted emission.
Interestingly the peak emission of the redshifted part of the outflow shows
a radial velocity which is about 60% higher relative to V536 Aql compared
to the blueshifted part. Similar asymmetries in the outflow velocities on
either side of the bipolar outflow have been detected in several other TTSs
(see e.g. Hirth et al. 1994b).
The spatial and kinematic properties of the [OI] , [NII]
and [SII] lines derived from the corresponding
PV maps are shown in more detail in Fig. 21 (click here). The intensity
profiles show a double-peak in both the [OI] and [SII]
lines. The centroid velocities for the HVC and LVC where
determined to 
and for the [OI] line and
and 
for the [SII]
line, respectively. For the [NII] line, as observed in all
other investigated TTSs, only a HVC with a velocity of 
has been detected. In the [NII] and in the [SII]
lines the redshifted part of the outflow can be traced up to
, which is not the case for the [OI]
line. Maybe the highly redshifted gas is relatively tenuous
and of higher excitation and therefore not strongly emitting in [OI]
because of the higher critical density of the latter FEL.
Figure 21 (click here) shows that the offset value in all three FELs changes its
sign at about the rest velocity of the star which clearly illustrates the
bipolar nature of the outflow. In the blueshifted part of the outflow, the
offset of the [SII] HVC reaches values of up to 0.6''. For
the blueshifted [NII] HVC slightly higher offset values have
been measured, whereas for the [OI] HVC the offset is about
half as large as in the other two FELs. As already mentioned above, this
trend has been observed in most stars studied here (see Sect. 4.1 (click here) for more
details).
Figure 19: Spatial width (top part), spatial offset (middle part) and
spatially integrated intensity (lower part) of the [OI] and
[SII] line emission of RW Aur as a function of the radial
velocity (). The dotted line in the plots of the
spatial width indicates the lower limit for which changes in width with
velocity can be reliably measured. The radial velocity has been measured
relative to the stellar velocity. The data are extracted from the
continuum-subtracted position-velocity maps displayed in Fig. 18 (click here)
The corresponding offsets for the LVC of the [OI] and [SII]
lines are very small (0.1'' and 0.2'', respectively). The
differences between the spatial properties of the HVC and the LVC are also
illustrated in Fig. 21 (click here) where the offset and the spatial width as a
function of the radial velocity are shown. In these plots a local minimum in
the spatial width is observed in the radial velocity range of the LVC. As
already mentioned above, similar results have been obtained for several
other TTSs discussed here and elsewhere (Solf & Böhm 1993;
Böhm & Solf 1994; Hirth et al. 1994a).
Finally, an offset value of 0.5'' of the [SII] HVC has been
deduced from our observations in September 1993. Comparing this value with
the value of 0.7'' derived under similar observational conditions in
September 1992 suggests that changes in the spatial structure of the outflow
have occured within one year. However, further observations are required to
prove the reality of this effect.