The C IV lambda lambda 1548.2,1550.8 resonance doublet in a symbiotic stars was shown to exhibit anomalous line intensity ratios in which I (lambda 1548.2)/I(lambda 1550.8) less than 1, or less than the optically-thick limit of unity. The R Aquarii-central HII region and RX Puppis exhibit this phenomena. The I(lambda 1548.2)/I(lambda 1550.8) ratio in RX Puppis is found to vary inversely with the total C IV line intensity, and with the FES-visual light, as the object declined over a 5 yr period following a brightening in UV and optical emission which peaked in 1982. This doublet intensity behavior could be explained by a wind which has a narrow velocity range of 600 approx. less than sup v wind approx. less than 1000 km/sec, or by the pumping of the Fe II (mul. 45.01) transition a sup 4 F sub 9/2 - y sup 4 H(o) sub 11/2 by C IV lambda 1548.2, which effectively scatters C IV photons into the Fe II spectrum in these objects

Fahey, R. P.

Kafatos, M.

Michalitsianos, A. G.

English

NASA Technical Reports Server

/I _t / " ") / 385
• t
N89 - 1076 1
Till'; ANOMAI,OIlS C IV IN'I'I':NSITY RA'I'IO IN SYblB]OTIC STARS
1
A.C. Michalitsianos
2
hi. Kafatos
1
R.P. Fahey
ILaboratory for Astronomy and Solar Physics
NASA Coddard Space Flight Center
Greenbelt, Maryland USA
2Department of Physics
Ceorge Mason University
Fairfax, Virginia USA
ABSTRACT
The C IV _1548.2,[550.8 resonance doublet in a
few symbiotic stars exhibit anomalous line
intensity ratios in whlqh T(_1548.2)/I(_1550.8)
_$I, or less than the bptically-thick limit of
unity. Both the R Aquarli-centra] HII region and
RX Puppls exhibit this phenomena. The
I(_[548.2)/I(_1550.8) ratio in RX Puppls was found
to vary inversely wlth the total C IV line
Intensity, and with the FES-visua] light, as the
object declined over a five year period following
a brightening in UV and optical emission which
peaked in 1982. Thls doublet intensity behavior
could be explained by a wind which has a narrow
velocity range of 600 _v i__ _|000 km s -l, or by
the pumping of the Feil _m_. 45.01) transition
a4F9/2 - y4H°ll/2 by C IV _|548.2, which
effectively scatters C IV photons into the Fe If
spectrum In these objects.
Key words: Symbiotic Stars, Stars, Atomic
Spectra, Bowen Pumping, Stellar Winds
1. Introduction
Spaceborne ultraviolet spectroscopy in
the near and far-UV has afforded Investigators
an opportunity to explore the complex emission
llne spectrum of symblotlc stars. These
objects are believed to be a class of
Interacting binary, which contain a r_d giant
or Mira variable, and a hot companion _. At
optlca] wavelengths, the presence of an
ionizing radiation source In these systems is
indicated by the presence of strong nebular
emission, which includes [0 II], [0 III],
[N Ill, [N III] [SII], He I, He If and strong
Balmer series emission. In the IUE wavelength
sensitivity range, the spectra of symbiotic
stars are characterized by an assortment of
Intercomblnatlon lines, which Include C III]
X_1907,1909, Si IiI] X1892, NIIl] _1749-
1750, N IV] )1487, 0 lllJ _X1660,1666, 0 IV]
%%1398-1401, as well as the permitted lines of
N V _1238,1240, SI IV %1398, C IV _548,1550,
He II _1640 and Mg II _%2795,2802. Often, the
Bowen flourescent llnes of 0 III are also
quite prominent. A number of symblotlcs are
sufflclently bright in the UV that high
resolution spectra (A_ ~ 0.1A resolution) are
feasible with IUE.
In at least a few of these systems2'3;
there Is a growing body of evidence from the
line profile structure of the strong high
excitation lines of C IV kX1548,1550 and He II
_1640 for the presence of high velocity winds
of _900 km s-l; velocities of this magnitude
are probably associated with mass expulsion
from the hot companion in the system, rather
than the extended atmosphere of the late type
star. For example, the C IV llne profile
structure in RX Puppls 4, AG Pegasi 5 and
_I Cyg 6 and Z And 7 exhibit broad - complex
emission structure, which is probably related
to mass motions in these systems, perhaps in
the form of streamers or rings, formed as
result of accretlon onto the hot companion .
In addition to the complex velocity
structure suggested in the emlss_on llne
profiles of RX _ippls, the C IV resonance
doublet exhibits additional anomalous
properties. Michalltslanos et al. (ref. fl)
have noted a curious effect in which the C IV
doublet Intensities I(_1548.2)/I(_1550.8) in
RX Puppls and R Aquarli (central HII region)
are less than the theoretical optically thick
limit of one. Anomalous C IV doublet
Intensities, where I(XI548.2)II(k_550.8) ¢1,
have a_so been reported in CH Cyg , Z And and
AG Peff J. In the case of RX Puppls, however,
the C IV intensity ratio was
I(_1548.2)/I(_1550.8) ~ 0.6, during an
enhanced phase of UV and optical emission, and
became larger, acquiring a value of
I(%1548.2)/I(_1550.8) ~ 1,.as the star
declined In UV and visual 11ght over a flve
year period; i.e. the I(_1548.2)/I(_1550.8)
was found to vary inversely with the C IV
absolute intensity, and with the IUE-FES
visual magnitude. _is behavior we propose to
call the "C IV Doublet Intensity Effect"
(ref. 8). The anomalous C IV intensities in
RX Puppls have been explained in terms of a
high velocity wind which has an expansion
velocity !_ the range 600_Vwlnd,_
1000 km s . As such, the broad P-Cygnl
absorption trough of the X1550.8 red doublet
member absorbs emission from the _1548.2 blue
doublet line 8, in a manner similar to _hat
proposed for 0 and B-type stellar winds _.
However, a high velocity wlnd model imposes
several Important conditions on both the upper
and lower llmltlng wind velocities, as well as
the optical depth properties of the expanding
gas.
A Decade of UV Astronomy with IUE, Proc. Celebratory Symposium, GSFC, Greenbelt, USA, 12-15 April 1988, ESA SP-281, Vol. 1 (June 1988)
https://ntrs.nasa.gov/search.jsp?R=19890001390 2020-03-20T06:08:32+00:00Z
386 A G MICHALITSIANOS, M KAFATOS & R P FAHEY
We wish to re-examlne thls Interpretation
and consider an alternate possibility, in
which the C IV doublet Intensity effect could
be exp]alned if C IV _1548.2 pumps a high
order multtplet (multiplet 45.0l) of
Fe II in a Bowen type mechanism I0. Tnls
process is suspected to occur in RR Tel and
VI016 Cyg, based upon the presence of number
of flourescently excited Fe [I lines in the
LWP _2000-3200 corresP9nding to the downward
cascades of the FeiI y4H°ll/2 transition of
multlplet 45.01 IU, even though the C IV
doublet ratios in these objects do not appear
obviously anomalous.
The merits of both models are discussed
in context with our observations of RX Puppls,
which have been obtained by monitoring
RX Puppls In the HIRES and LORES mode of iUE.
Recently, anomalous C IV ratios,
I(XI548.2)/I(x1550.8) ~ 0.6 have been observed
in the central HII region in R Aquaril. On the
other hand, the extended 6_5 nebular jet II in
this symbiotic system indicates optically-
thin emission in C IV, where
I(XI548.2)/I(XI550.8) ~ 2, appropriate to a
photoexclted gas 8. Thus, the R Aquarll system
affords an opportunity to spatially
differentiate the C IV llne forming regions
within its nebulosity In a manner not possible
with other more distant, and spatially
unresolved symbiotic stars, such as RX Puppls.
2. Discussion
A description of our five year IUE
monitoring program of RX Puppls, and the first
successful HIRES exposure of R Aquarii are
described by Mlchalltslanos et al. (ref. 8).
In Figure I, [top: R Aquaril-Hll Region;
bottom: RX Puppls] we have overplotted the
k1548.2 and _1550.8 lines In order to compare
their structure In velocity space. The
vertical arrows indicate the laboratory rest
wavelength. High frequency noise was reduced
by a 5-polnt running average which acts as a
digital low-pass filter. The formal fit errors
of velocity are i0.5 km s -l, the Instrument
velocity resolution at C IV for determining
peak emission in well exposed-narrow emission
lines is _ i2.0 km s -1. Thus, the peak
emission for both C IV members is consistent
with the radial velocity of R Aquarll of
V R = -23 km s-l,.and V R = +II km s -I for
KX Puppls.
2.1 Line profile Structure
The 5-polnt smoothing applled to the
profiles ensures that high frequency noise has
been removed. Therefore, the narrow emission
components which survive this smoothing are
likely real; this profile structure is also
evident in photowrlte SWP-HIRES images of both
objects. The llne profile structure of the
C IV doublet in RX Puppls consists of at least
three distinct emission components, which have
average veloclty separations of Av ~
40 km s -i, which over a 5-year period were
always seen redward of the rest wavelength.
The velocities of these components combine to
produce a broadened profile whose base width
extends up to + ~125 km s -I. R Aquarli-HIl
region exhibits slmilar structure, but the
secondary emission component obtained by
double-gausstan fitting is blueward of the
rest wavelength by a velocity separation Av ~
-50 km s -I .
The velocity separation of the Individual
emission components which form the C IV llne
profile structure In RX _ippls and R Aquarll
are roughly the same, which suggests that the
kinematics of the C IV forming regions are
probably similar in both objects. If the
individual C IV components correspond to
discrete parcels of highly ionized gas, which
are ejected from the system at roughly regular
Intervals of time, the predominance of redward
displaced emission in the case of RX Puppis,
and blueward displaced emission in R Aquarii,
might reflect the orientation of ejection if
the parcels are emitted successively in a one-
sided stream or jet. This is consistent with
high resolution radio continuum maps obtained
with the Very Large Array (VLA) of
KX Puppts and R Aquarii. The 6-cm radio
morphology of R Aquarii and its jet clearly
suggests that most of the streaming activity
is confined to one side of the central objgct
in the form of discrete knots of emission"Z;
this is reminiscent of one-sided radio tails
in extragalactic jets. Recently obtained high
resolution ..O'gl, 1.3 and 2-cm radio continuum
observations of RX Puppis also indicate one-
sided morphology of a similar nature 13. The
relatlonship between radio continuum knots and
C IV emitting regions could be established only
with high resolution sub-arcsecond imaging in
the C IV lines, now only possible with HST.
However, these results provide a preliminary
indication establishing a corresondance
between radio and UV emission from streaming
material in these systems.
2.2 The C IV Doublet Member Intensities
2.2.1 The P-Cygni Profile Interpretation
In Figure 1, the shaded area formed by
the superposition of the line profiles shows
the velocity range over which the doublet
ratio I(XI548.2)/l(xI550.8) is less than the
optically-thick limit of unity. In the case of
KX Puppis, the intensity ratio was
i(X1548.2)/I(x1550.8) ~ 0.6, when the object
was at maximum IJV emission around March 1982.
Over a five year period, KX Puppis gradually
declined in UV line emission. In Figure 2, the
i(_1548.2)/I(_1550.8) has been plotted against
the total C IV doublet Intensity for the
observing epochs indicated. A linear
relationship is evident between the doublet
intensity ratio and UV light, in Figure 3, a
similar relationship was found between
I(x1548.2)/I(_1550.8) and the FES-visual
magnitude for this period as well.
If the "doublet ratio intensity effect"
is explained by a wlnd, a minimum wind speed
of 600 to 700 km s -I is required for the
doublet wavelength separation of 2.6A, in
order for the absorption trough of the X1550.8
line to absorb emission at _1548.2. However,
continuum adjacent to the C IV doublet has not
been detected in long duration SWP-HIRES
exposures with sufficient slgnal to confirm
the presence of broad P-Cygnl structure; far-
UV continuum was not detected in a ~15-hour
HIRES-SWP exposure in 1987. Similar duration
HIRES-SWP exposures of R Aquarli-HII region
also failed to detect adjacent continuum which
could support tbls interpretation. On the
ANi)MAI.()US (" IV IN rI:.NSITY RATIO IN SYMBIOTIC STARS 387
other hand, T.ORES-,_dP (Ak = 6A resolution)
qpectra of RX lhlpplq and R Aquarli clearly
indicate the presence of strung UV cont inunm
emission In both obiect_.
Moreover, If sucb a high _peed wtnd ig
present, the curious abqence of C IV P-Cy_ni
_tructure in I.ORES-SWP spectra In both RX
F_lppls and R Aquarii places strong upper
limits on v . . for both stars of
_1OOO km g , gecause of the limitin[_
resolution of LORES IUE spectra. For example,
_1000 km s -1 - P-CyRnf wind profiles are
detectable In LORES-SWP spectra of the
planetary nebula [C 418 14,15. Accordingly, a
narrow range of wind velocities of 600 _Vwind
1OO0 km s -1 must exist, which places tight
constraints on the wind velocities, such that
the Vw_nd is sufficiently large compared with
the doublet wavelength separation, but not
large enough to be detectab]e in LORF. S-SWP
I
o3
Z
uJ
F-
ZI
<
uJ
spectra.
70
60
50
40
30
2O
10
O0
-I0
-20
i 1
77
-200 -150 -100 -50
i I I I I
1 R AQUARII
HII REGION
-27 km s 1
j IV R = -23 km s I)
-10
i I i I
0 +50 -;-100 4-150 +200
VELOCITY (km s -_)
>-
I
u)
z
L_
Z
LU
>
<_
,,-I,
70
60
50
40
30
20
10
0.0
-10
-20
i i i 1 i i
-o
RX Puppls
+37
(V R = *11 kl'q S -1 }
+78
+1i4 km s'l
i
-100 -50
i [ i i i i i
O +50 +100 +150 +200 +250 +300
VELOCITY (kin s -1)
_ I: C IV red and blue doublet
lines overplotted in velocity space.
The vertical arrows indicate the radial
velocity of the star. The shaded area
indicates the velocity range over
which the doublet intensity _s less than
unity. ]'he velocities shown correspond
to the velocity of individual C IV
emitting regions that combine to produce
the broadened profile.
_3
>
L3
2.2.2 C IV Bowen l_mping of Fe I[
,fohansson (ref. lO) identified a number
Fe I[ emi_sfon lines of multiplet 45.01 at
_2436.20, 2458.78, 2481.N0, 2492.28, 2771.15
in IIIRES-LWP spectra of the symbiotic
VIOI6 Cy_ obtained by Nussbaumer and
Schild "_" . _/eqe and four additional
flourescently formed lines have also been
identified in RR Tel IO; they are formed by
the downward cascade of the excited Fe II,
y4tt°ll/2 level. Emission from C lV X1548.2 was
e.... d by Jgbansson _ref. 10) to _electively
pnmp the a qF9/2 - Y_ Oil ll/2 transition of Fe 1[
tn a Bowen mechanism.
Close examination II[RES-LWP £pectra of
_X _ippls taken in March, 1982, when the
obiect was at maximum UV emission, and when
the C iV [(XI54g.2)/T(xI55Q.8) ratio had Its
maximum deviation below the optically-thlck
limit of one, Indicated only the possible
presence of tile second strongest line from the
group identified by .lohansson (ref. 10) In
V1016 Cyg and RR Tel, which is Fe II _2771.2.
The strongest member of the series Fe [1
X2458.78 was not detected. However, the tlIRES-
IMP exposure of 180-minutes in March, I982 wag
significantly underexposed, making
identification difficult for relatively weak
featureq. Accordingly, the only manifestation
of the Bowen puming of Fe TI by the blue
doublet member of C [V could be the anomalous
C IV intensity ratio.
1.O
09
0.8
0.7
0.6
05
0,5
I I I i I I I I I
RX Puppis
C IV )&1548,1550
A
0
O 2 July 87
[] 9 May 86
&. 11 Mar 84
0 29 Oct 83
• 20 Sept 80
• 22 Ma_ 82
• 11 June 81
I I I I I I I I
1.0
C IV FLUX 0',1548+X1550) Normalized to
Epoch 20 September 1980
Figure 2: The C IV doublet intensities
I(X1548.2)/I(X1550.8)-seven observing epochs
plotted against the combined C IV emission
line intensity.
5
388 A G MICHALITSIA_IOS, M KAFATOS & R P FAHEY
RX PUPPIS
80O
700
co 6O0
F-.-
Z
g 500
0
400
L,t-
- 300
2OO
100
IT "t
0 Oq5 016 I I I 104 07 08 09 10
C IV I(X1548 2)
1(X1550 8)
o9
:s
>
u3
IdJ
Id..
11_
12
Figure 3: C IV doublet intensity plotted
against the FES-magnitudes (top) and the
FES counts (bottom).
Similarly, ~15-hour exposures required to
detect the strongest emission lines in
R Aquarii-HII region in the LWP and SWP HIRES
cameras encounter similar difficulties.
However, in the case of RX Puppis, IUE has
sufficient sensitivity that longer expoures of
_4 hours, for a S/N ~ I0, are possible in the
LWP-HIRES camera. If a direct correlation can
be established between the C IV
I(_1548.2)/I(I1550.8) and the strength of the
flourescent Fe II lines, the redistribution of
C IV energy into the Fe II spectrum of
RX Puppls would be important to establish.
Because the C IV I(I1548.2)/I(I1550.8) ratio
is related to the intrinsic UV llne
brightness, such a correlation cou]d be used
to determine concentration of Fe II along the
absorbing pathlength during slow outbursts of
the system. IUE observations are continuing to
investigate this phenomena in greater detail.
3. Conclusions and Summary
The C IV _X1548.2,1550.8 emission lines
in a select number of symbiotic stars exhibit
complex profiles, suggestive of complex
kinematic motions In the form 9f streamers,
accretion rings and/or a disk 4. The C IV
I(I1548.2)/I(I1550.8) intensity ratio also
appears anomalous in a number of these
systems, where the ratio is less than the
8
theoretical optlcally-thick limit of unity
In RX Puppls, where this effect has been
studied most extensively, the C IV
I(_1548.2)/I(x1550.8) ratio appears to vary
Inversely with the total UV line emission.
We have s.g_ested two possible
explanations of this behavior which we propose
to call the 'C IV doublet intensity effect :
I) the broad P-Cygni absorption trough absorbs
emission at _1548.2, thus reducing the doublet
ratio below the optically thick limit of unity
during slow outbursts; the wind velocity in
thls case _nst he in the range 600^_Vwind
lO00 km s-', or, II) that owing to_ z,_
wavelength coincidence between Fe It and C IV,
4 4 o
Fe 11 (multiplet 42.01) a F9/2 - y H 11/2
transition can be pumped by the blue doublet
C IV at %1548.2 llne 10, effectively
redistributing C IV _1548.2 photons into the
Fe II spectrum in a Bowen-type mechanism.
Present IUE observations can not resolve this
Issue, and HIRES exposures In the LWP and _dP
cameras of IUE, or with the HiF_h Resolution
Spectrophraph of liST, will be required to
probe this effect in greater depth.
References
i. Kenyon, S.J. 1986, The Symbiotic Stars
(Cambridge U. Press.: New York).
2. Penston, M.V. et al. 1983, M.N.R.A.S.,
202, 833.
3. Penston, M.V. and Mien, D.A. 1985,
M.N.R.A.S., 212, 939.
4. Kafatos, M., Micha]itsianos, A.G. and
Fahey, R.P. 1985, Ap.J. Suppl. 59, 785.
5. Keyes, C.D. and Plavec, M.J. ]980, In The
Universe at Ultraviolet Wavelengths,
ed. R.D. Chapman (NASA CP 2171), p. 443.
6. Selvelli, P.L. 1988, in Proc. of IAU
Colloq. 103 "The Symbiotic Phenomena",
eds. MikolajewskI, J. eta]. (D. Rediel
Pub. Co.-Holland), In press.
7. Cassatella, A., Fernandez-Castro, T.,
Gimenez Riestra, Jlmenez 1988, In Proc.
of IAU Colloq. 103 "The Symbiotic
Phenomena", eds. bllkolajewski, J. et al.
(D. Reidel Pub. Co. - Holland), In press.
g. YHchalltslanos, A.G., Kafatos, M., Fahey,
R.P., Viottl, R., Cassatella, A. and
Altamore, A. 1988, Ap.J., in press.
9. Olson, G.L. 1982, Ap.J., 255, 267.
I0. Johansson, S. 1983 _qRAS, 205. 71p.
II. Michalitsianos, A.G. 1984, Comments on
Astrophys., I0, 85.
12. Hollis, J.M., Michalitsianos, A.G.,
Kafatos, M., M.C.H. Wright and Welch,
W.J. 1986, Ap.J. (Letters), 309, L53.
13. Hollis, J.M., Yusef-Zadeh, F., Cornwe]l,
T.J., Oliversen, R.J., Michalitsianos,
A.G. and Kafatos, M. 1988, Ap.J., in
press.
14. Harrington, J.P., Lutz, J.H., Seaton,
M.J. and Stickland, D.J. 1980, MNRAS,
191, 13.
15. Flower, D.R. 1983, in Atoms in
Astrophysics, eds. Burke, P.G. aad
Eissner, W.B., Hummer, D.G. and
Percival, I.C. (Plenum Press-New York),
Chap. 6, p. 303.
16. Nussbaumer, H. and Schild, H. 1981,
Astron. As trophys., I01, 118.


The anomalous C 4 intensity ratio in symbiotic stars

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