UV Emission line shifts of symbiotic binaries

Abstract

Relative and absolute emission line shifts have been previously found for symbiotic binaries, but their cause was not clear. This work aims to better understand the emission line shifts. Positions of strong emission lines were measured on archival UV spectra of Z And, AG Dra, RW Hya, SY Mus and AX Per and relative shifts between the lines of different ions compared. Profiles of lines of RW Hya and Z And were also examined. The reality of the relative shift between resonance and intercombination lines of several times ionised atoms was clearly shown except for AG Dra. This redshift shows a well defined variation with orbital phase for Z And and RW Hya. In addition the intercombination lines from more ionised atoms and especially OIV are redshifted with respect to those from less ionised atoms. Other effects are seen in the profiles. The resonance-intercombination line shift variation can be explained in quiescence by P Cygni shorter wavelength component absorption, due to the wind of the cool component, which is specially strong in inferior conjunction of this cool giant. The velocity stratification permits absorption of line emission. The relative intercombination line shifts may be connected with varying occultation of line emission near an accretion disk, which is optically thick in the continuum. Comment: 14 pages, 11 figures, to appear in A&A

Full text

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arXiv:1001.0310v1 [astro-ph.SR] 2 Jan 2010
Astronomy & Astrophysics manuscript no. mfried
January 2, 2010
c ? ESO 2010
UV Emission line shifts of symbiotic binaries
M. Friedjung1, J. Miko? lajewska2, A. Zajczyk3, and M. Eriksson4
1Institut d’Astrophysique de Paris -UMR 7095, CNRS/Universit´ e Pierre et Marie Curie, 98 bis Boulevard Arago,
75014 Paris France
2Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland
3Nicolaus Copernicus Astronomical Center, Rabia´ nska 8, 87-100 Toru´ n, Poland
4University College of Kalmar, 391 82 Kalmar, Sweden
Received , Accepted...
ABSTRACT
Context. Relative and absolute emission line shifts have been previously found for symbiotic binaries, but their cause
was not clear.
Aims. This work aims to better understand the emission line shifts.
Methods. Positions of strong emission lines were measured on archival UV spectra of Z And, AG Dra, RW Hya, SY
Mus and AX Per and relative shifts between the lines of different ions compared. Profiles of lines of RW Hya and Z
And were also examined.
Results. The reality of the relative shift between resonance and intercombination lines of several times ionised atoms
was clearly shown except for AG Dra. This redshift shows a well defined variation with orbital phase for Z And and RW
Hya. In addition the intercombination lines from more ionised atoms and especially Oiv are redshifted with respect to
those from less ionised atoms. Other effects are seen in the profiles
Conclusions. The resonance-intercombination line shift variation can be explained in quiescence by P Cygni shorter
wavelength component absorption, due to the wind of the cool component, which is specially strong in inferior conjunc-
tion of this cool giant. The velocity stratification permits absorption of line emission. The relative intercombination
line shifts may be connected with varying occultation of line emission near an accretion disk, which is optically thick
in the continuum.
Key
Z And - CI Cyg – AG Dra – RW Hya – SY Mus – AX Per
words.
Stars: binaries:symbiotic– Stars:mass loss Stars:- accretion– Stars: individual:
1. Introduction
The variations of the radial velocities of the emission lines
formed in symbiotic systems are not easy to interpret. The
lines are emitted in moving plasma, due to winds and/or
gas streams, which do not need to have the same motion
as either stellar component. In addition the lines can be
affected by absorption of overlying material such as the
absorption of other lines of the iron forest as well as by ra-
diative transfer effects. The line profiles are as a result not
necessarily simple, affecting radial velocity measurements.
The present work was undertaken in order to better under-
stand both radial velocities and in some cases line profiles.
Among the effects previously found, there is a system-
atic redshift of the wavelengths of resonance emission lines
of highly ionized atoms with respect to those of intercombi-
nation emission lines in the ultraviolet spectra of a number
of symbiotic binaries (Friedjung, Stencel and Viotti 1983).
The former lines might be expected to be optically thick, so
it appeared that such a redshift might be explainable in an
expanding medium, either by the presence of absorption at
the short wavelength edge of the resonance emission lines
or by a radiative transfer effect, associated with the scat-
tering of radiation in this expanding medium. The latter
can occur only if the optical thickness is very large.
Send offprint requests to: M. Friedjung
Correspondence to: fried@iap.fr
More recently a GHRS/HST spectrum and a number of
IUE spectra of the symbiotic binary CI Cyg were studied
by Miko? lajewska, Friedjung and Quiroga (2006). The red-
shift was confirmed for that binary. The resonance lines had
an almost constant radial velocity during an orbital cycle,
interpreted as being most probably due to the presence of
a blueshifted absorption component, produced in a circum-
binary region. According to the interpretation proposed,
the circum-binary region appeared to be mostly expand-
ing, while in addition, a part appeared to be contracting.
Other radial velocity effects in the emission lines were also
investigated and interpreted in that paper.
In the present work we examine the radial velocities
of other symbiotic binaries, comparing mean radial veloci-
ties of emission lines of different ions, in order to look for
optical thickness and ionisation potential dependent strat-
ification effects. We can in this connection note that ac-
cording to Nussbaumer et al (1988), among the emission
lines, which interest us Ciii, Civ, Niii,Niv and Oiii are
expected to be formed in the same region for a temperature
of the source of ionising radiation of not less than 60000K
and an electron density of around 109cm−3. In addition
the critical densities, where most emission of the intercom-
bination lines is produced, are of the order of 109cm−3.
This paper together with our previous paper on CI Cyg
(Miko? lajewska, Friedjung, and Quiroga) (2006), completes
the study of radial velocity shifts in all symbiotic binaries

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2 Friedjung et al.: Symbiotic line shifts
which have strong emission lines and for which high reso-
lution ultraviolet spectra exist.
2. The data
We have used the MAST archive, containing IUE and HST
spectra. Among the IUE spectra only those, having a high
resolution, taken with the large aperture and the SWP cam-
era, were analysed. HST spectra were available for AG Dra
and RW Hya. This left 41 spectra of Z And, 44 spectra of
AG Dra, 11 spectra of RW Hya, only 7 spectra for SY Mus
and even fewer (3) for AX Per.
Z And had two outbursts between JD 45797 and JD
46596, while AG Dra had more than one outburst dur-
ing the period studied. AX Per, SY Mus and RW Hya are
eclipsing systems. Near infrared photometry indicates elip-
soidal variations for SY Mus and RW Hya with Roche lobe
filling factors near unity of 0.83 and 0.91 respectively ac-
cording to Rutkowski, Miko? lajewska and Whitelock (2007),
while Miko? lajewska (2007) gives reasons for believing that
the cool components of most S type systems fill their Roche
lobes.
The radial velocities were measured by Gaussian fits to
the whole profile, using the SPLOT programme of IRAF,
This averages over any real or instrumental assymmetry.
Saturated lines were measured by fitting to the wings. We
have checked that the radial velocities determined in this
way closely agree with the line centroid radial velocities. It
is because of our method that we were able to use emission
lines, whose centres are saturated. The nature of our IUE
spectra does not enable us to do anything more precise.
Let us note however that the HST/STIS spectra of AG
Dra suggest some assymmetry of the resonance emission
line profiles, with line centres being shifted by apparent
absorption on the low wavelength side (Young 2006, private
communication as well as the MAST archive).
The errors, indicated in the radial veocity tables, corre-
spond to 1 σ errors of the respective mean values. They do
not indicate systematic errors, such as for instance those of
errors in the absolute wavelength scale. However the mean
values are based on data of different transitions, so their σ
values include that due to uncertainty of laboratory wave-
lengths. The other systematic errors due to the absolute
wavelength scale, have been estimated by comparing our
radial velocity estimates from different spectra of the same
target, taken at the same epoch. In particular we found 14
pairs of IUE spectra (4 for Z And, 10 for AG Dra) taken on
the same day or one day later. The offset in radial velocity
for these pairs is between ∆v ∼ 0 − 20kms−1, with an off-
set for 10 pairs of 2-8 kms−1, a median value of around 5
km s−1and a mean of ∼ 6.7 ± 1.3kms−1. There is no dif-
ference in the offset between saturated and non-saturated
lines, when we compare a spectrum on which a particular
line is saturated and another spectrum on which it is not
saturated. The corresponding offset for 2 HST/STIS spec-
tra of AG Dra taken on the same day is only 1.7 kms−1.
3. Results
Our measured radial velocity means and their 1 σ errors are
tabulated in table 1 for AX Per, SY Mus and RW Hya, in
table 2 for Z And and in table 3 for AG Dra. The phases of
the tables are from the ephemeris of Miko? lajewska (2003),
0
10
20
30
40
-0.5 0 0.5

1 1.5
Vrad [ km s-1 ]
CIV
0
10
20
30
40
-0.5 0 0.5

1 1.5
Vrad [ km s-1 ]
NV
-10
0
10
20
30
-0.5 0 0.5
φ
1 1.5
Vrad [ km s-1 ]
HeII
Fig.1. Radial velocities for SY Mus. The dashed line shows
the orbital velocity of the cool giant. The symbols are ex-
plained in the text.
with respect to inferior conjunction of the giant. The last 8
lines in table 1 for RW Hya and the last 2 lines in table 3 for
AG Dra are based on HST/STIS spectra. The wavelength of
the Heii 1640˚ A line used, is a mean wavelength of the fine
structure, given by Clegg et al (1999). Let us note that this
mean is fairly insensitive to the exact physical conditions of
line formation; ranges of electron density from 104to 109
cm−3and temperatures from 10 000 to 30 000K give for
case B line formation a shift of 0.007˚ A or 1.3 km s−1.
Some radial velocities in the tables, including means and
the radial velocity of the Heii 1640˚ A line, plotted against
orbital phase, are shown in fig 1, for SY Mus, while radial
velocity differences with much less scatter are shown in figs.
2 and 3 for the same symbiotic. Similar figures shown, are
4, 5 and 6 for Z And and 7, 8 and 9 for AG Dra. The
difference graphs are with respect to the resonance doublet
of Civ, as measurements of the strong lines belonging to
this doublet could be made for all the spectra studied by us.
Shifts, such as those of the intercombination lines relative
to Civ, depend on the shift of Civ itself. The values for
Siiv are not plotted, but their behaviour can be seen from
the tables.

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Friedjung et al.: Symbiotic line shifts3
Table 1. Radial velocities of the UV emission lines (in units of kms−1) for AX Per, SY Mus and RW Hya.
MJD
IP[eV]
φ
Siiii]
16.3
Ciii]
24.4
Niii]
29.6
Oiii]
35.1
Niv]
47.4
AX Per
Oiv]
54.1
Siiv
33.5
Civ
47.5
Nv
77.5
Heii
54.4
44156
45642
48226
0.000
0.183
0.979
-123
-137
-111
-121
-131
-110
-120(2)
-134(1)
-116(2)
-124(2)
-136(5)
-111(2)
-106 -105(2)
-107(4)
-103(2)
-113
-137
-113
-135
-111
SY Mus
8
-10
7
10
13
13
-5
RW Hya
-8
8
24
17.7
16.1
17.1
20.0
19.8
23.2
25.0
26.2
-135-111(1)
-104(2)
44767
45020
48451
48473
48629
48623
50187
0.340
0.746
0.240
0.275
0.525
0.675
0.018
7 15
-6
10
19
16
14
5
7 9(1)1319(1) 22(2)
20(1)
23(2)
27(1)
23(1)
23(1)
23(1)
16(3)3
2
-6
3
12
8
-3
9 2(1)
13(1)
16(1)
11(1)
-2
14
16
11
0
14 26 28
16(1)
9
-15
21(1)
18(2)
22(4)
21(1)
44118
44256
44692
52012∗
52016∗
52020∗
52024∗
52028∗
52032∗
52036∗
52040∗
For saturated lines the radial velocities (itallic) were obtained by fitting their wings.
1-σ errors of the mean values are in brackets.
∗– HST STIS spectra.
0.437
0.809
0.987
0.749
0.760
0.771
0.782
0.793
0.803
0.814
0.825
10
7
14
11
6
23
3
7
2(1)
6(2)
18(1)
11.9(0.5)
8.7(0.3)
9.5(0.8)
11.9(1.1)
10.3(1.3)
12.8(1.4)
13.8(1.3)
14.7(1.5)
-3(2)
32(2)
47(1)
35.3(0.1)
34.0(0.5)
35.4(0.5)
39.2(0.5)
39.9(0.5)
43.5(0.6)
45.0(0.9)
46.0(0.7)
17(1)
24
26(3)
36(1)
45(3)
40.0(1.2)
38.0(1.3)
39.0(0.9)
42.6(0.8)
42.1(0.5)
45.3(0.4)
46.4(0.2)
46.7(0.2)
19(1)
32(7)
-26
34
55
40.4
39.0
40.2
43.7
44.3
48.1
49.7
51.0
17
29.0(1.0)
29.4(0.4)
30.3(0.2)
33.9(0.5)
32.9(0.6)
34.4(0.7)
36.6(0.4)
34.6(1.4)
46.5 (0.4)
48.1(0.4)
50.1(0.5)
52.9(0.9)
53.3(1.3)
57.6(1.5)
61.9(0.9)
63.3(1.1)
-10
0
10
20
30
40
-0.5 0 0.5

1 1.5
Vrad [ km s-1 ]
CIV-NV
0
10
20
30
40
50
-0.5 0 0.5
φ
1 1.5
Vrad [ km s-1 ]
CIV-HeII
Fig.2. Nv and Heii radial velocity differences for SY Mus.
The dashed line shows the orbital velocity of the cool giant.
The symbols are explained in the text.
In the graphs mentioned, the open circles are of fits of
the line centres to a Gaussian for IUE observations in quies-
cence, while in the cases of IUE observations of Z And and
AG Dra, the filled circles are for IUE observations in out-
burst. Open and filled triangles denote corresponding fits of
the line wings in quiescence and outburst, when the centres
are saturated. Finally an X is used to plot HST/STIS data
of AG Dra. The dotted curve in these figures is the radial
velocity curve of the cool component from Belczy´ nski et al
(2000), taking phase 0 as that of inferior conjuction of that
component.
We mainly show and study the difference graphs and
values, which are much less affected by the systematic er-
rors, as shown above. In the case of SY Mus, Fig. 1 shows
that the Civ radial velocity is redshifted and almost con-
stant, while Heii tends to follow the hot compoment with
a blueshift. One can see from Fig. 2 that the mean Civ
and Nv redshifts are almost the same without systematic
variations with orbital phase, while in addition the table 1
Civ - Siiv differences are small and slightly positive. The
Fig. 2 Civ - Heii 1640˚ A radial velocity graph shows a rel-
ative redshift of Civ with a minimum perhaps near phase
0.5, this being a reflection of the radial velocity variation of
Heii by itself. The redshift of the Civ resonance with re-
spect to the intercombination lines of SY Mus varies fairly
smoothly with orbital phase, with a maximum approaching
30 kms−1somewhat before phase 0 and a much smaller
minimum (Fig.3).
There are far more measurements for Z And which
shows comparable effects. The Oiv] and Heii 1640˚ A radial
velocities show a maximum which seems to be in phase with
the radial velocity of the hot component at least during qui-
escence (Fig.4). The Heii line may have a small tendency
to have a blueshift. The difference graphs of Z And give
clear results. Shifts of Nv relative to Civ in Fig. 5 are at
least during quiescence almost always small and indepen-

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4 Friedjung et al.: Symbiotic line shifts
Table 2. Radial velocities of the UV emission lines (in units of kms−1) for Z And.
MJD
IP[eV]
43922
44075
44402
44480
44719
45797∗∗
45863∗∗
45946
45948
46232
46233
46283
46595∗∗
46596∗∗
46715
46778
46962
47081
47101
47195
47327
47713
47845
47885
48092
48929
48997
49163
49229
49617
49678
49728
49898
49963
50104
50104
For saturated lines the radial velocities (itallic) were obtained by fitting their wings.
1-σ errors of the mean values are in brackets.
∗∗– spectra taken during outbursts. The profiles on spectra taken during the outburst on MJD46353–46462 are very complex and
they cannot be characterised by single radial velocity.
φ
Siiii]
16.3
-6
-13
0
-5
9
-24
-9
-8
6
-6
5
10
-13
-7
-21
-8
7
0
-10
-23
-33
-2
-8
-16
-1
-9
-7
6
7
-30
-7
-6
-21
-3
-16
-21
Ciii]
24.4
-7
-14
-1
1
10
-18
-11
-17
10
-1
4
3
-20
-15
-27
-16
11
0
-16
-18
-37
-2
-8
-18
3
-8
7
8
10
-18
-7
0
-14
3
-7
-25
Niii]
29.6
-6
-14
-9
-4
Oiii]
35.1
-2.6(0.1)
-13.4(1.0)
-1.8(1.1)
-1.7(4.0)
4
-27.1(5.1)
-10.6(2.0)
-10.0(1.0)
4.1(0.2)
-1.9(1.5)
12.1(4.0)
6
-19.4(1.6)
-11.4(1.2)
-19.4(1.9)
-6.2(0.1)
10.4(1.7)
-1.0(3.1)
-8.3(1.5)
-15
-31
-3.3(2.5)
-6.8(1.90)
-26
-4
-7
-3.9(0.3)
3.7(2.3)
11.0(0.4)
-21
-14.9(0.1)
-9.3(1.5)
-18.3(1.3)
-5.1(0.6)
-13.4(2.6)
-17.0(0.6)
Niv]
47.4
-8
-11
-7
0.8
8
-29
-11
-16
2
-7
6
14
-23
-11
-28
-8
7
-5
-13
Oiv]
54.1
5.3(1.1)
-4.4(1.4)
10.1(2.5)
7.9(1.0)
Siiv
33.5
7.3(2.6)
2
11.6(2.6)
6.9(6.0)
Civ
47.5
Nv
77.5
0.4(2.0)
-0.2(2.0)
8.1(1.1)
5.9(0.6)
15
12.3(4.6)
12.5(3.5)
2.7(0.8)
16.3(3.5)
11.8(1.7)
22.7(1.6)
21.5(0.9)
12.1(4.8)
Heii
54.4
-6
-12
-12
-12
1
-4
1
-14
-3
5
1
3
-20
-11
-21
-20
-8
6
-3
-16
-33
-8
-7
-20
-4
-20
-9
-8
5
-24
-18
-17
-30
-12
-16
-18
0.655
0.856
0.287
0.391
0.706
0.126
0.213
0.323
0.325
0.700
0.701
0.767
0.178
0.179
0.336
0.419
0.662
0.819
0.845
0.969
0.143
0.650
0.825
0.878
0.150
0.254
0.343
0.563
0.650
0.161
0.241
0.307
0.523
0.617
0.802
0.802
10.1(1.3)
7.1(1.6)
14.2(0.1)
13.1(0.9)
17.9(0.3)
17.7(1.7)
30.7(4.3)
16.5(5.4)
21.7(0.4)
11.2(0.8)
24.1(1.3)
25.9(3.1)
4.4(3.8)
18.5(2.4)
-2.3(1.4)
8.1(0.4)
24.0(0.7)
19.0(1.8)
11.1(1.0)
4.4(0.1)
-6.6(0.8)
11.4(1.2)
11.1(2.6)
-1.5(1.5)
25.1(0.5)
10.8(4.6)
12.2(1.0)
15.4(0.5)
20.4(0.3)
2.2(1.1)
7.0(0.2)
7.8(0.5)
0.2(1.7)
7.9(1.0)
4.6(0.2)
-1.4(1.0)
-21 -21.8(0.9)
-1.9(2.1)
-1.5(1.5)
11.1(1.6)
6.1(1.0)
17
26.2(3.9)
-10.9(0.1)
-3.5(1.6)
-12.8(1.3)
-1.1=(1.1)
16.8(4.3)
10
-0.1(3.1)
18.0(4.5)
9.0(0.1)
7.6(3.8)
17.6(1.3)
11.4(2.8)
23.1(2.7)
-11.8(0.5)
-14
5
-0.5(2.8)
-4
1
-24.6(1.7)
-14.7(1.4)
-19.4(1.9)
-6.3(2.1)
11
-2
-13
5.4(5.0)
10.7(1.3)
-4.3(1.7)
5.0(0.8)
22.5(0.5)
-2.5(0.1)
3.7(2.8)
19.2(2.3)
16.3(4.7)
9.4(5.3)8
-34
-11
-8
-15
-39
-5
-12
-21
-8
-30.3(2.1)
2.5(1.2)
-2.7(0.8)
-17(3.7)
2
0
10.5(0.5)
8.4(0.1)
23.1(1.0)
-15
-10.3(2.3)
-0.2(1.9)
-9
-13.5(1.2)
4.6(3.5)
7.1(0.1)
-13
7.4(1.1)
6.4(1.3)
-3
-7
-4
0
5
10.9
7.6(3.0)
9.8(0.4)
18.8(1.2)
-1
0
9
-27
-18
-2
-20
-13
-11
-18
9.4(0.9)
10.3(2.8)
20.5(0.5)
-4 6.8
4.5(0.2)
-8.3(4.0)
6
1.0(4.0)
-8.8(1.1)
2
-20
-15
-19-11.3(4.2) -3.0(0.2)3.0(0.6)
dent of orbital phase. We may note that the Civ - Siiv
differences from the table have a certain amount of scatter,
but are usually small (less than 10 km s−1and positive).
Fig. 5 shows that the Civ - Heii radial velocity is in phase
with the cool component, or that the Heii radial velocity
relative to that of Civ is in phase with the hot component.
The situation is somewhat less certain for Oiv], which may
reach a maximum radial velocity relative to that of Civ
earlier. Civ is however redshifted with respect to Oiv] at
most orbital phases. Fig. 6 shows radial velocity differences
between Civ and other intercombination lines, which have
a similar orbital phase dependence, but which are generally
more positive than the Oiv] difference. Let us note that the
phase dependence would appear to be somewhat different
than that of SY Mus. In connection with these results let us
note that IUE wavelengths of Oiv] are usually less accurate
than those of Heii.
AG Dra shows fewer clear effects. Unlike in quiescence
there are enough Heii and Oiv] measurements during out-
burst, to indicate that they appear to follow the hot com-
ponent at least at such times (Fig. 7). The difference graphs
of Fig. 8 show constant differences at almost all times, Civ
having a small redshift relative to Heii. This constancy is
violated during outburst between JD 49538 and 49613 at
phases of 0.7-0.9 (Table 1). Fig. 9 shows the radial velocity
shift between the Civ and intercombimation lines exclud-
ing Oiv]; except perhaps for Ciii] in outburst, no clear
sign of any orbital variation is seen, while there might be
a significant redshift for line centre meaurements of Civ
relative to Ciii] in quiescence. As can be seen in Table 3
the higher quality HST/STIS spectra show a clear redshift
of Oiv] relative to the other intercombination lines, due to
ions with a lower ionization potential.
Figures are not shown for the other symbiotics for which
the observations have poor phase coverage. However most
RW Hya measurements, based on HST/STIS spectra are
very accurate. The radial velocity Civ - Siiv differences
are small and positive, with very little variation between
8.7 and 12.1 km s−1. The Civ - Nv difference shows how-
ever a more complex behaviour. The first 2 values, based on
IUE spectra are similarly small (7 and 4 kms−1), while the
later values from HST/STIS spectra as well as being closely
spaced in time at phases not very far from that of the second
IUE spectrum, but taken two decades later, are curiously

Page 5

Friedjung et al.: Symbiotic line shifts5
Table 3. Radial velocities of the UV emission lines (in units of kms−1) for AG Dra.
MJD
IP[eV]
44418
44418
44698∗∗
44700∗∗
44719∗∗
44719∗∗
44820∗∗
44944∗∗
44950∗∗
44950∗∗
45492
46138
46155
46374
47827
47828
48225
48812
48878
48898
48960
49058
49533∗∗
49533∗∗
49538∗∗
49540∗∗
49543∗∗
49543∗∗
49546∗∗
49561∗∗
49562∗∗
49613∗∗
49693∗∗
49693∗∗
49846∗∗
49846∗∗
49927∗∗
49928∗∗
49928∗∗
49975∗∗
50016∗∗
50064∗∗
50128∗∗
52756∗
52756∗
For saturated lines the radial velocities (itallic) were obtained by fitting their wings.
1-σ errors of the mean values are in brackets.
∗– HST STIS spectrum.
∗∗– spectra taken during outbursts.
φ
Siiii]
16.3
-138
-142
Ciii]
24.4
Oiii]
35.1
Niv]
47.4
-137
-142
-159
-154
-156
-155
-161
-168
-162
-166
-145
-152
-148
-154
-163
Oiv]
54.1
Siiv
33.5
-132
-142
Civ
47.5
Nv
77.5
Heii
54.4
-149
-155
-162
-152
-158
-159
-168
-185
-188
-179
-158
-165
-168
-149
-164
-159
-151
-157
-140
-139
-154
-166
-143
-153
-152
-173
-120
-130
-165
-158
-169
-154
-154
-157
-162
-169
-155
-161
-161
-159
-170
-155
-147
-151
-152
0.421
0.421
0.932
0.934
0.969
0.969
0.154
0.379
0.390
0.390
0.378
0.554
0.585
0.984
0.631
0.632
0.355
0.424
0.545
0.581
0.695
0.873
0.737
0.737
0.748
0.750
0.755
0.755
0.762
0.789
0.791
0.884
0.029
0.029
0.307
0.307
0.456
0.456
0.456
0.541
0.618
0.705
0.823
0.608
0.608
-141.8(0.9)
-143.1(1.3)
-156.3(4.8)
-153.0(1.9)
-153
-153.5(1.4.0)
-156.5(1.3)
-166.3(0.3)
-160.4(1.7)
-157
-146.6(0.5)
-151.3(0.7)
-133.9(2.0)
-137.0(1.5)
-151.4(0.7)
-143.8(1.2)
-146.1(4.6)
-144.2(0.8)
-149.6(1.6)
-162.1(0.6)
-158.3(3.0)
-160
-137.1(1.7)
-142.2(3.2)
-148
-136
-148.9(5.9)
-131.9(0.6)
-138.2(1.0)
-149.9(0.1)
-144.3(0.1)
-147.5(1.1)
-144.7(1.4)
-152.5(0.2)
-170.6(0.1)
-160.6(1.5)
-159.7(1.0)
-141.7(0.7)
-148.0(0.7)
-150.7(1.4)
-137.0(0.3)
-150.5(0.8)
-148.1(7.7)
-135.9(0.4)
-149.6(7.1)
-137.3(2.9)
-125.4(3.4)
-139.4(2.2)
-150.9(2.0)
-142.7(0.6)
-148.0(1.3)
-144.9(0.1)
-164.3(1.6)
-136.5(0.8)
-143.0(0.7)
-164.6(6.0)
-147.2(3.5)
-154.8(0.9)
-137.9(0.1)
-134.6(1.0)
-140.8(0.6)
-145.5(1.2)
-152.5(0.9)
-148.2(1.2)
-141.0(0.3)
-138.5(1.1)
-150.9(0.5)
-150.3(0.7)
-131.4(0.9)
-130.8(0.9)
-138.4(1.5)
-140.1(1.6)
-145.3(5.0)
-145.0(2.9)
-149.6(1.7)
-147.9(3.0)
-146.3 (0.6)
-142.9(0.1)
-158.0(2.6)
-169.7(1.0)
-168.3(3.9)
-160.0(4.6)
-145
-153
-153.1(3.8)
-139
-150
-157
-132.1(3.1)
-157
-128
-126
-138.9(1.0)
-149
139.2(0.7)
-150
-134.9(1.3)
-154.6(2.9)
-110.5(1.8)
-130
-143
-132
-148.0(5.6)
-138
-133.5(0.8)
-140.9(2.1)
-151
-154
-153.0(1.2)
-145
-137
-145
-154
-145
-144
-145
-179
-161
-156.7(1.8)
-144.6(0.6)
-148.7(0.4)
-145.4(1.2)
-154.7(2.3)
-163.3(1.5)
-159.3(1.8)
-150.7(2.7)
-145.8(0.1)
-149.9(0.8)
-148
-141
-146
-157
-160
-153
-154
-143
-144
-153
-140
-152-157
-156
-152
-134
-160.7(0.8) -152
-145.7(1.3) -140
-149
-140
-137
-124
-142
-161
-140
-146.2
-165.7(3.6)
-145
-154
-150
-172.4(0.2)
-170
-167
-168
-143
-164
-145.6(4.7)
-141.9(0.4)
-149.0(1.5)
-154
-158.1(2.0)
-162.6(1.4)
-154
-161
-160.5(0.4)
-157.6(1.5)
-143.1
-151
-148.2(0.1)
-150.0(0.1)
-148
-163
-144
-153
-153
-167
-144
-148
-138.2(1.4)
-152.2(4.4)
-140.8(2.1)
-142
-138.2(2.9)
-153.4(5.3)
-125
-140
-143
-157
-134 -146.7(4.6)
-148
-142.9(1.6)
-163.3(1.1)
-143
-133.7(1.6)
-133
-164
-143
-151
-144
-151
-132
-140
-147
-153
-154
-157
-146
-152
-154
-151
-140
-147
-146
-146
-160
-145
-143
-149
-154
-154
-161
-156
-154 -153.4(4.5)
-146.6(5.3)
-130
-144.7(0.2)
-145.3(3.9)
-134.9(0.5)
-141(3.1)
-144.0(0.5)
-147.7(0.9)
-150.5(1.8)
-143
-142
-147
-138
-151.8(0.7)
-151.9(0.4)
-143
-137
-150
-128
-160
-160
-143
-145
-148.4
-150.0
-153.0(1.8)
-151.8(1.4)
-134.7(0.3)
-135
-138.9(0.6)
-140.1(0.9)
-154.9(3.4)
-151.1(1.3)
-134.2(4.5)
-136
-141.8(1.0)
-143.4(0.6)
-152.8(2.6)
-152
-138.4(1.2)
-133
-134.9(0.6)
-136.1(0.6)
negative, decreasing between the phases 0.749 and 0.825
from -6.5 to -16.6 km s−1. In this way Nv appears to be
more redshifted with respect to the intercombination lines
than Civ. The Civ redshift relative to the intercombina-
tion lines, deduced from the HST/STIS spectra, decreases
with the ionization potential of the corresponding ions, be-
ing much less for Oiv] than for Oiii] and Niv]. The Heii
1640˚ A line appears to be for all but the first observation
strongly redshifted with respect to the systemic radial ve-
locity of 12.4 or 12.9 km s−1, but its radial velocity may
be compatible with that of the compact component at the
phases of the observations, if this component is much less
massive than the cool one. However the radial velocity vari-
ations of Heii and the intercombination lines, deduced from
the HST/STIS spectra, would appear to be in phase with
the orbital radial velocity variations of the cool one.
The AX Per spectra are all for phases very close to con-
junction. The Civ, Nv and Siiv lines have similar radial
velocities, which are redshifted with respect to the inter-
combination lines, including Oiv.
A few line profiles of Z And and RW Hya, obtained
from the spectra, are shown in figs. 10 and 11. They will be
considered in the discussion of our results in order to better
understand the reasons for the radial velocity shifts.

Page 6

6 Friedjung et al.: Symbiotic line shifts
0
15
30
45
-0.5 0 0.5

1 1.5
Vrad [ km s-1 ]
CIV-CIII]
0
15
30
45
-0.5 0 0.5

1 1.5
Vrad [ km s-1 ]
CIV-OIII]
0
15
30
45
-0.5 0 0.5
φ
1 1.5
Vrad [ km s-1 ]
CIV-NIV]
Fig.3. Intercombination line radial velocity differences for
SY Mus. The dashed line shows the orbital velocity of the
cool giant. The symbols are explained in the text.
4. Discussion
Let it first be emphasized, that the differences between the
Civ mean resonance line radial velocity and the means of
other resonance doublets, are generally much smaller than
the difference between the Civ resonance line mean and
the intercombonation line means in many orbital phases
for SY Mus, Z And and AX Per. This clearly indicates that
any explanation of the relative shift between the resonance
and the intercombination line radial velocities, which is not
the same for the different resonance line doublets, cannot
work. The shift is in many orbital phases much larger than
the 1 σ errors given in the tables, which shows in addition
that shifts between either the different resonance or the
intercombination lines of the same ion are small.
We can immediately draw the conclusion that it may be
difficult to explain the relative radial velocity shift between
the optically thick resonance lines and the intercombination
lines by a resonance line radiative transfer effect, because
the different optical thicknesses of the resonance line might
be expected at first sight to produce different shifts.
Line radial velocities can be influenced by various ef-
fects. We need to first examine such effects, before dis-
-40
-20
0
20
40
-0.5 0 0.5

1 1.5
Vrad [ km s-1 ]
OIV]
-40
-25
-10
5
20
-0.5 0 0.5
φ
1 1.5
Vrad [ km s-1 ]
HeII
Fig.4. Intercombination Oiv] and Heii radial velocities
for Z And. The dashed line gives the orbital velocity of the
cool giant. The symbols are expained in the text.
cussing what is observed. Among the former we shall in
the first three subsections consider the following.
4.1. Effects due to the presence of interstellar lines on shifted
resonance line
Interstellar absorption components can be superposed on
the resonance emission lines and can distort the line pro-
files. Such an effect should not be present for the symbiotic
systems with large systemic velocities (-116.5 and -148.3
kms−1of AX Per and AG Dra respectively). In the case
of the others we can look for narrow at least partly inter-
stellar absorption lines in stars, which are close in the sky,
but which do not have smaller linear distances from the
observer. Let us note that this test for the effect of inter-
stellar absorption is not completely watertight. Radiation
from the hot component of a symbiotic binary could ionize
the nearby interstellar medium, so producing interstellar
absorption from highly ionized atoms, without such lines
being seen in the spectra of other stars in similar lines of
sight.
The estimated distance of SY Mus is 850 pc according to
Schmutz et al (1994), while TU Mus, a β Lyr type eclipsing
variable with a O star component, has a distance of 2.1 kpc
according to Penny et al (2008) and is only 0.3oin the sky
from SY Mus. The stronger Nv 1238˚ A doublet resonance
line absorption of TU Mus is weak as is also the stronger
Siiv 1393˚ A doublet resonance line. The shifts of Nv and
Siiv relative to Civ of SY Mus are both near zero however,
suggesting hardly any effect of interstellar absorption in the
direction of TU Mus and SY Mus.
High resolution HST/STIS spectra are available for RW
Hya and we can directly inspect the spectra for the pres-

Page 7

Friedjung et al.: Symbiotic line shifts7
-20
0
20
40
60
-0.5 0 0.5

1 1.5
Vrad [ km s-1 ]
CIV-OIV]
-20
0
20
40
-0.5 0 0.5

1 1.5
Vrad [ km s-1 ]
CIV-NV
-20
0
20
40
60
-0.5 0 0.5
φ
1 1.5
Vrad [ km s-1 ]
CIV-HeII
Fig.5. Intercombination Oiv] as well as Nv and Heii ra-
dial velocity differences for Z And. The dashed line shows
the orbital velocity of the cool giant. The symbols are ex-
plained in the text.
ence of narrow absorption lines. In fact extremely narrow
absorption lines are seen, superposed on Nv 1242˚ A emis-
sion as well as in other places, though they may rather be
circumstellar (see discussion below on the iron forest).
Z And has a distance of 1.5 kpc according to
Miko? lajewska and Kenyon (1996), while HD218195, sep-
arated 10.3oin the sky, has a distance of 2.9 kpc (2001).
There is neither any sign of Nv absorption nor of that of
Civ within the noise. In any case the relative shifts of Nv,
Civ and Siiv in the Z And spectra, which might be ex-
pected not to be affected in the same way by interstellar
absorption, are usually small at many orbital phases com-
pared with the shift between Civ and the intercombination
lines.
4.2. Effects due to the absorption component of a P Cygni
profile of shifted resonance lines
It should first be noted that any explanation involving a P
Cygni absorption component of a line at a shorter wave-
length than the line emission studied has a difficulty when
-20
0
20
40
60
-0.5 0 0.5

1 1.5
Vrad [ km s-1 ]
CIV-CIII]
-20
0
20
40
60
-0.5 0 0.5

1 1.5
Vrad [ km s-1 ]
CIV-OIII]
-20
0
20
40
60
-0.5 0 0.5
φ
1 1.5
Vrad [ km s-1 ]
CIV-NIV]
Fig.6. Intercombination line radial velocity differences of
less ionized atoms for Z And. The dashed line shows the
orbital velocity of the cool giant. The symbols are explained
in the text.
the continuum is weak. In that case, line absorption can
however still be produced by an overlying layer with the
same radial velocity as regions from which part of the line
emission comes. It is this kind of explanation, which we
shall use to understand many observations of the resonance
lines. In this connection, we can mention that Young et al
(2005) suggest that the Ovi P Cygni profile of AG Dra is
affected by absorption of a false continuum, that is by a
continuum enhanced by the presence of electron scattering
wings of the line. However the 1/e width of electron scat-
tering wings is 550 kms−1at 10000K for one scattering. If
much narrower line emission is only seen, with no evidence
of wings with at least this width, such an explanation will
not work for any geometry of an electron scattering region
relative to that of line formation. In particular in the case
of CI Cyg, previously studied by Miko? lajewska, Friedjung
and Quiroga (2006), there is no evidence of broad wings
for the Civ resonance lines, extending to much more than
100 km s−1in the HST/GHRS spectrum (see Fig. 1 of that
paper).

Page 8

8 Friedjung et al.: Symbiotic line shifts
-180
-160
-140
-120
-100
-0.5 0 0.5

1 1.5
Vrad [ km s-1 ]
OIV]
-200
-180
-160
-140
-120
-100
-0.5 0 0.5
φ
1 1.5
Vrad [ km s-1 ]
HeII
Fig.7. Oiv] intercombination line and Heii radial veloci-
ties for AG Dra. The dashed line shows the orbital velocity
of the cool giant. The symbols are explained in the text
4.3. Analysis of iron forest absorption and plausible line shifts
of lines producing pumping by accidental resonance
(PAR)
The importance of iron forest absorption by the low ve-
locity wind of the cool component, leading to pumping by
accidental resonance (PAR), needs to be checked. The ef-
fect of the iron forest is well known since the work of Shore
and Aufdenberg (1993). In principle such an effect could
be quite large, though in fact we shall find usually no large
influence of this kind of effect on the radial velocities of
the lines studied by us. A major problem of the Shore
and Aufdenberg calculations is moreover that the oscilla-
tor strengths, used for the lines, are not always reliable.
This is for instance the case for the 4s-4p∗transitions in-
volving high parent terms (sometimes refered to as 4s∗and
4p∗transitions) superposed on short wavelength region IUE
emission lines. We can in such a way explain why for in-
stance lines excited or “pumped” as a result of absorption
of emission by the Civ 1548˚ A line are generally observed
unlike those from the Civ 1550˚ A line (Erikson, Johansson
and Wahlgren 2006).
We can, in order to test for effects of the iron forest,
firstly look for the presence of emission lines, emitted in
the wind of the cool component by levels “pumped” as
a result of absorption of the emission of lines, studied in
this paper. The amount of pumping clearly depends on the
widths of the lines which can pump. Pumping is summa-
rized for different symbiotic binaries by Eriksson, Johansson
and Wahlgren (2006).
In the case of Z And, Civ 1548˚ A pumps two channels,
while Siiv 1393˚ A probably pumps another channel. The
3d7a4F9/2- 3d6(3G) 4p y4H11/2channel pumps 10 ob-
served Feii emission lines at 2772, 2493, 2481, 2459, 2436,
-30
-15
0
15
30
-0.5 0 0.5

1 1.5
Vrad [ km s-1 ]
CIV-OIV]
-30
-15
0
15
30
-0.5 0 0.5

1 1.5
Vrad [ km s-1 ]
CIV-NV
-30
-15
0
15
30
45
Vrad [ km s-1 ]

CIV-HeII
-160
-140
-0.5 0 0.5
φ
1 1.5
Fig.8. Intercombination line Oiv], Nv, Heii radial veloc-
ity differences with the orbital radial velocity of the cool
giant for AG Dra. The symbols are explained in the text.
2228, 2220, 2211, 2168 and 1975˚ A. The 3d7a4P1/2- 4p
w2D3/2channel, pumped by the same Civ line produces
the observed 2979.95, 2483, 2479.98 and 1965˚ A lines. The
3 Feii lines probably pumped by Siiv through the 3d6
(5D) 4s a6D7/2- 3d6(1G) 4p x2H9/2channel are at 2588,
25492 and 1793˚ A. Correcting the fluxes for the radiation
absorbed from the pumping lines, before being re-emitted
in the pumped lines, gives nearly ”optically thin” flux ra-
tios near 2 for the Civ and Siiv doublets, except for the
Civ doublet near phase zero in outburst, when probably
blueshifted P Cygni absorption (see Fig. 10) is visible. In
addition pumping by the Oiii] intercombination line at
1660˚ A may be responsable for weak emission features in
the spectrum of Z And at 2784.5 and 2728.2˚ A . However

Page 9

Friedjung et al.: Symbiotic line shifts9
-40
-20
0
20
40
-0.5 0 0.5

1 1.5
Vrad [ km s-1 ]
CIV-CIII]
-20
0
20
40
60
-0.5 0 0.5

1 1.5
Vrad [ km s-1 ]
CIV-OIII]
-15
0
15
30
45
Vrad [ km s-1 ]

CIV-NIV]
-160
-140
-0.5 0 0.5
φ
1 1.5
Fig.9. Intercombination line radial velocity differences of
less ionized atoms with the orbital radial velocity of the
cool giant for AG Dra. The symbols are explained in the
text.
we do not see any systematic velocity shift of the Oiii] line
with respect to the other intercombination lines.
Pumping by the first 1548˚ A Civ line channel produced
4 observed Feii emission lines in the spectrum of SY Mus.
The Civ flux ratio, correcting for pumping again gives an
”optically thin” value of 2.
Obtaining a clear result is more difficult for AG Dra.
Emission lines, which could be produced by pumping, are
also observed sometimes in absorption. However in a pri-
vate communication P.R. Young states that he sees lines
pumped by Civ, Heii 1640˚ A and 1085˚ A, N IV] 1486˚ A
and O III] 1660˚ A. We have however seen no sign of Feii
lines pumped by two possible Heii 1640˚ A channels for AG
Dra so any effect of pumping on the Heii profile is small. In
any case, let us note that pumping may be less important
for this metal underabundant symbiotic system.
The Civ 1548˚ A line pumps the Feii y4H11/2chan-
nel in the spectrum of RW Hya, but lines pumped by this
mechanism are not observed in the spectrum of AX Per,
suggesting no strong iron forest absorption for the latter
symbiotic. We must in the former RW Hya case note in
addition, that the HST/STIS spectra show strong narrow
absorption components, superposed especially on the Nv
1242˚ A profile and on the last date on the Siiv profile.
In any case we can note, that the already mentioned
small 1 σ values for the radial velocities of the two lines of
the same resonance doublet and also of the intercombina-
tion lines of the same ion as well as the usually small values
of the Civ radial velocity mean - mean resonance doublet
radial velocities of other ions, would be hard to explain, if
effects on radial velocities of the iron forest, which should
not be the same for differnt lines, were important.
4.4. Clues about the nature of the observed radial velocity
shifts for different systems
More clues concerning the nature of the shifts can be ob-
tained from the time variations and line profiles, for which
we have information especialy from the observations of Z
And and RW Hya.
The periodic variation of the Z And Civ resonance dou-
blet -intercombination line radial velocity means suggests
a maximum at phases not long after conjunctions when
the cool component is nearer the observer. This might
be understood if the increased redshift of Z And at such
phases is due to larger cool component wind line absorp-
tion on the short wavelength side of resonance line emis-
sion for strongly ionised atoms, with perhaps additional
effects behind the cool giant at that phase. Among such
effects there is wind focussing towards the orbital plane,
with a three dimensional spiral stream, which occurs when
the cool component does not quite fill its Roche lobe
(Gawryszczak, Miko? lajewska, R´ o˙ zyczka 2003). This inter-
pretation is not contradicted by the Civ and Nv fluxes
found by Fernandez-Castro et al (1988) including a mini-
mum near phase zero, confirmed by later more numerous
observations. However, Fernandez-Castro et al (1988) also
find simlar minima for the intercombnation lines, so some-
thing else than line absorption is also involved.
There has been a certain amount of disagreement and
uncertainty about the causes of the outbursts of Z And
and similar symbiotic systems. Our ultraviolet line study
may be relevant to this question. According to Sokoloski et
al (2006), based on later observations after the end of the
life of IUE, outbursts of Z And can be understood as disk
instabilites, which in the case of major outbursts are fol-
lowed by thermonuclear burning. The V magnitude of one
outburst, studied by these authors, became brighter than
about 9.7, when according to them thermonuclear burning
started. Bisikalo et al (2006) also suggested an increase in
thermo-nuclear burning during outbursts as well as effects
of colliding winds. They made fairly detailed calculations.
Fig 10 shows the IUE profiles of the Civ resonance dou-
blet of Z And at three epochs. The first in the upper panel
is at phase 0.961 during a major outburst, when according
to Sokoloski et al (2006) thermonuclear burning could have
occured. On this date the line profiles were faint and com-
plex so we do not attempt to give radial velocities in table

Page 10

10 Friedjung et al.: Symbiotic line shifts
Fig.10. Civ doublet profiles of Z And for 3 dates. The
upper panel is for phase 0.960 during a major outburst, the
middle panel for phase 0.178 at a fainter stage of outburst
and the lower panel for phase 0.523 in quiescence.
2. The middle panel shows the profiles at phase 0.171, in a
fainter stage of outburst, while the bottom panel shows the
profiles at phase 0.523 in quiescence. The greater width of
lines in outburst, previously detected by Fernandez-Castro
et al (1995), is clearly seen even through the presence of
very weak wings in the fainter stage of outburst and is gi-
gantic during what could be a thermo-nuclear burning stage
according to Sokoloski et al. Fig. 10 shows particularly a
large quantity of redshifted emission. However we can note
in addition to faint red wings, the presence of what looks
like blue shifted absorption superposed on weak line emis-
sion in the fainter stage of the outburst. Fernandez-Castro
et al (1995) suggested that envelopes were ejected during
outburst; another interpretation is discussed below.
We may try to understand the changing profiles, shown
in Fig. 10, as due to a decrease in ionising radiation near
the maximum of outburst, corrsponding to a lower photo-
spheric temperature of an expanded white dwarf. In addi-
tion we expect the optical thickness of the Civ resonance
lines to be probably very large; because taking an elec-
tron density of the order of 1010cm−3from Altamore et
al (1981) and Fernandez-Castro et al (1988), a solar abun-
dance of carbon, and assuming 10 percent of carbon three
times ionised, would lead to the weaker line becoming op-
tically thick for distances of only 2 109cm, which is small
compared wth the binary separation times the sine of the
inclination of 7 1012cm of Mikolajewwska (2003). The
fractional abundance of carbon in the form of C+++used,
is of the order of that calcuated for different conditions by
Nussbaumer (1982). Therefore the enlargement of what is
still visible of the Civ ion doublet lines towards the red, in
very probable conditions of large optical thicknesses near
the cool component at that time, might be due to radiative
transfer in an expanding medium such as the cool compo-
nent wind or a region of collision between the winds from
the components rather than an optically thinner ejected
shell. Iron forest absorption can be expected to also play
a role in the profile. An explanation only involving line
emission due to the wind from the hot component is un-
likely, because the escape velocity from the photosphere of
the outbursting component would for a largest measured
radius of 0.36 solar radii and a white dwarf mass of 0.65
solar masses (taking the estimates of Sokoloski et al 2006)
be then around 830 kms−1. A wind from that component
might be expected to be probably faster, while in outburst
the red sides of those resonance line profiles, which are un-
affected by any classical P Cygni absorption, do not extend
to more than about 300 kms−1.
We may note in this connection that Lamers et al
(1995), in their study of wind terminal velocities of hot
stars near the main sequence, found ratios of the terminal
to escape velocity, decreasing from around 2.7 at an effec-
tive temperature of more than 40 000K and highly ionized
winds to 0.7 at an effective temperature of 8000K and much
less ionized winds, which produce P Cygni spectral line pro-
files of Cii, Aliii and Mgii. In addition Dumm et al (2000)
state that the terminal velocities of central stars of plane-
tary nebulae are typically 2.5 times the escape velocity. Let
it be noted however that the hot component wind could
be concentrated towards the polar axis by the white dwarf
magnetic field and/or the accretion disk, so the observed ra-
dial velocity would be then the above expected value times
the cosine of the inclination and so smaller.
We may also note that Sokoloski et al (2006) observed
P Cygni profiles for Z And in outburst in the far ultravio-
let, using the FUSE satellite. An enhanced continuum was
seen by them during outburst, classical P Cygni blueshifted
absorption being strong at phases 0.116 to 0.155, when the
continuum was also strong. Pv 1117˚ A absorption, indicat-
ing the presence of a not very fast wind, is clearly visible
to about -270 km s−1at phase 0.116 in their Fig. 6.
We can compare our AG Dra results with results given
in previous papers for that system. Let us note that Viotti
et al (1984) found that the Nv lines were broader when
the luminosity of AG Dra was higher like for Z And. These
authors found in addition P Cygni profiles for all epochs
of Nv 1238˚ A with a terminal velocity of 170 kms−1for
the stellar wind supposed to produce it and line assymme-
try suggesting P Cygni absorption of line emission, which
was also present when the continuum was weak. Young et
al (2005) observed AG Dra with FUSE and saw a redshift
of the Ovi resonance doublet (which had a P Cygni pro-
file) relative to the intercombination Nev and Nevi lines.
However their measurements indicated no redshift for the
Siv and Svi zero energy lines. These last mentioned au-
thors suggest that the Ovi P Cygni absorption is only that
of the resonance doublet, superposed on a false continuum,
produced by electron scattering wings. We may finally note
that the geometry of this system with a fairly small pre-
ferred orbital inclintion of 30-45oaccording to Miko? lajewska
et al (1995) and a low metal abundance, may play a role in
reducing shifts between the resonance and intercombination
lines.
We shall here just emphasize one of the results for SY
Mus. The constancy of the Civ radial velocity mean at dif-
ferent orbital phases reminds us of the resonance line mean
constant velocity, found by Miko? lajewska, Friedjung and
Quiroga (2006) for CI Cyg, which like SY Mus is a high
inclination eclipsing system. Unlike in the case of CI Cyg,
we do not have very high resolution HST spectra for SY
Mus, but we may be able to invoke a similar explanation

Page 11

Friedjung et al.: Symbiotic line shifts11
Fig.11. HST/STIS profiles for RW Hya on MJD 52040
(phase 0.825). The full line shows the Civ 1551˚ A profile,
the dotted line the Niv] 1486˚ A profile and the dashed line
the Oiv 1401˚ A profile
to that given by Miko? lajewska, Friedjung and Quiroga, ex-
plaing the redshift of the resonance doublet emission lines
by the presence of a circum-binary region. Such a region
could be near the plane of the orbit.
As far as RW Hya is concerned, the observations avail-
able, do not enable us to say anything certain about
the variation of redshift with orbital phase. According to
Dumm et al (2000 low resolution UV spectra indicate a
flux decrease in the continuum between 1250˚ A and 1290
˚ A at phase 0.78 relative to phase 0.71, which was almost
over at phase 0.81. They interpreted this result as due to
additional apparent extinction by Rayleigh scattering of
neutral hydrogen and due to iron forest absorption in an
accretion wake produced by wind accretion. Our exami-
nation indicates no large variation in the values of Civ-
intercombination line radial velocity between phases in the
range 0.749 to 0.825 on the high resolution HST/STIS spec-
tra. In any case, there is no accretion wake, if accretion is
by Roche lobe overflow, as suggested by the observations
of ellipsoidal light variability in the near infrared accord-
ing to Rutkowski, Miko? lajewska and Whitelock (2007) and
another explanation is required for the observations of ul-
traviolet fluxes in such a case than that of Dumm et al
(2000). Another possibility is absorption due to impact of
the stream. In addition Dumm et al (1999) suggest that
the density distribution around the M giant of SY Mus
is assymetric with additional extinction than that due to
Rayleigh scattering, which they suggest is produced by the
iron forest.
Unlike most of the spectra studied here, those of RW
Hya did have a significant continuum, with P Cygni ab-
sorption components superposed on it, which could have
contributed to some measured velocities of the Nv and Siiv
lines. The edge velocities relative to the systemic velocity
are lower than 200 km−1. Let us note also the presence
of broad wings of more than 20˚ A wide around the Civ
resonance lines. It remains to be seen whether that can be
explained by electron scattering.
The high resolution HST/STIS spectra of RW Hya can
be used to look at the line profiles, in order to better under-
stand the radial velocity shifts. Fig. 11 shows profiles of the
Civ 1551˚ A , Niv 1586˚ A and Oiv] 1401˚ A lines. The weak
continuum fluxes of less than 2% the line centre fluxes have
been subtracted, the profiles being insensitive to the contin-
uum and unaffected by the iron forest absorption. The Civ
profile was divided by 3 and the Oiv] profile by 1.7, so as
to make their red wings coincide approximately. One sees
that the blue wings of the Civ and Oiv] lines are reduced
with respect to Niv]. The Civ line is optically thick, so the
reduction appears to be due to P Cygni absorption of line
emission, starting at radial velocities which are positive rel-
ative to the systemic velocity of 12.4 or 12.9 km s−1(both
values being given as alternatives by Belczynski et al (2000)
and Mikolajeswska (2003)) and a cool giant radial velocity
7.8 km s−1smaller than those values at phase 0.825. This
could suggest the presence of a line absorbing wind from the
cool component absorbing some of of the line emission com-
ing from regions rotating not very rapidly around the white
dwarf with perhaps a contribution to the absorption at cer-
tain orbital phases by a stream from the inner Lagrangian
point. The latter is possible for high inclination eclipsing
systems like RW Hya if the cool component fills its Roche
lobe (Rutkowski, Mikolajewska and Whitelock (2007). Let
us note that the wind from the cool component can be de-
viated by the gravitational field of the compact component.
The Oiv] line is optically thin, so no explanation, invovlv-
ing absorption can work for this line. The effect may be ex-
plainable by a large part of the intercombination emission
line flux coming from the already mentioned wind from the
cool component in front of an accretion disk, with the latter
being opticaly thick in the continuum, so occulting emis-
sion behind it, plus a possible contribution to line emission
due to the presence of the already mentioned stream from
the inner Lagrangian point in front of the disk. Such effects
might produce other emission line shifts. Let us finally note
that it is not quite clear to what extent the small absolute
redshift of the Niv] line centre relative to the systemic and
cool giant velocities is real. In any case the very incomplete
phasing of the HST/STIS spectra makes it hard to draw
more conclusions.
5. Conclusions
A number of new results have been obtained, from a more
detailed analysis of relative emission line shifts, which con-
clude the study of suitable ultraviolet spectra, which are
available.
The relative shift between the radial velocities of the
resonance lines and the intercombination lines of multiply
ionised atoms is confirmed for most systems and appears
to be not due to various artifacts. It is rather probably
due to the absorption component of P Cygni profiles of
the cool component’s wind, which must in many cases be
able to absorb emission from the emission part of line pro-
files and not only radiation from the continuous spectrum.
That places strong constraints on the geometry, which we
might try to interpret as for instance involving absorption
of line radiation from near the outer edge of an accretion
disk. The variation of the shifts with orbital phase, espe-
cialy for Z And, can be understood as due to a greater
optical thickness of regions connected with the cool com-
ponent’s wind on its far side with respect to the compact

Page 12

12 Friedjung et al.: Symbiotic line shifts
component. However the wide redshifted profile of Civ of
Z And near phase zero during outburst may still be due to
a radiative transfer effect.
Ionisation potential dependent stratification of radial
velocity is present for the intercombination lines, Oiv] be-
ing much more redshifted than intercombination lines of
less ionised atoms. This could be connected with occulta-
tion by an accretion disk, which is optically thick in the
continuum. However let us note that our data do not en-
able us to be certain about any difference for Z And and
AG Dra in outburst, if a comparison is made with quies-
cence We might expect that as a change in the properties
of an accretion disk might be expected.
Differences can be due to different geometries and metal
abundances. AG Dra in particular has a strong metal un-
derabundance. Streams and cool component winds affected
by the presence of the hot component, may play a major
role. However the sample of symbiotic systems with high
spectral resolution ultraviolet observations at many differ-
ent orbital phases is very small, making it difficult to look
for correlations with the properties of these systems. It is
therefore probably not convenient to make more detailed
speculations at the present time.
Acknowledgements. This research has been partly supported by
Polish research grants 1P03D 017 27 and N203 395539, and by the
European Associated Laboratory “Astrophysics-Poland-France”. It
also made use of the NASA Astrophysics Data System and SIMBAD
database. We thank Peter Young for giving information on line pro-
files and other possible channels of possible pumping of excited Fe
II levels in AG Dra. J. Zorec must also be thanked for supplying a
computer programme, while a friend helped in the preparation of one
figure.
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