The preliminary results of the study of several high resolution spectrograms (lambda 3500 - lambda 7000 A), obtained at the Haute Provence Observatory (OHP) in France, at different epochs before, during and after the eclipse are reported. Some of these spectrograms are compared with corresponding IUE high resolution observations, in order to study the effects of the intrinsic UV activity, towards the longer wavelengths

Ferluga, S.

Hack, M.

English

NASA Technical Reports Server

THE ECLIPSE OF EPSILON AURIGAE 
VISIBLE SPECTROSCOPY AND ULTRAVIOLET ACTIVITY 
S. Ferluga and M. Hack 
Trieste University, Institute of Astronomy - Via Tiepolo 11, 134131 Trieste,Italy 
We report the preliminary results of the study of several high-resolution 
spectrograms ( A3500 - A7000 A ) ,  obtained at the Haute Provence Observatory 
(OHP) in fiance, at different epochs before, during and after the ecli?se. 
We also compare some of these spectrograms with corresponding IUE high-resolu- 
tion observations, in order to study the effects of the intrinsic UV activity, 
towards the longer wavelengths. 
1. - The Visible Spectrum 
As during the previous eclipses, we have observed the appearance of 
sharp absorption components on the red side of the strong low-excitation 
lines and of the Balmer lines during the ingress phase, and on the violet 
side during the egress phase (Ferluga and Hack, 1985: Paper I). This additional 
spectrum, which we call "shell spectrum", appears only during the eclipses 
and is very well observable during the partial phases of the eclipse. During 
totality it is observable as a strong deepening of the absorption cores 
of the strongest lines, especially the Balmer lines. The shell spectrum 
is explained by a gaseous envelope surrounding the eclipsing body and rotating 
in the same sense as the orbital motion. Since the shell spectrum appears 
before the beginning and disappears after the end of the photometric eclipse, 
the gaseous envelo2e must be more extended than the occulting body (a dusty 
disk, as suggested by the IR observations by Backman et al. 1984). The shell 
has about the same excitation temperature of the photosphere of the FOIa 
primary, but a much lower density. This is indicated by the fact that the 
quantum number of the last resolved Balmer line is n = 31 in the photospheric 
spectrum and n p 50 in the shell spectrum; moreover,the high excitation 
lines and all the faint lines do not present the shell component. (Fig.1) 
The shell responsible for the additional spectrum has an absolute value 
of the rotational velocity lower before totality than after it (e.g., 277 
days before mid eclipse the shell RV is +15 km/s and, 269 days after it, 
it is -35 km/s; 227 days before it, it is +17 km/s, and 221 days after it, 
it i s  -37 km/s). that is, the part of the shell which follows in the orbital 
notion rotates faster than the preceeding one. Moreover, both parts of the 
shell show a rotational velocity which increases from the outer part to 
the inner one, reaches a maximum and then decreases again (Fig. 2). The 
general behaviour and the values of the RV are the same as observed by St- r uve 
et al. (1958) during the 1955-57 eclipse. 
At the epoch of the brightening on Jan. 1984 near the end of totality 
A 
(Oki et al., 1984) the shell has the maximum negative RV and also maximuni 
intensity. Weak low-excitation lines which generally do not show the shell 
components show it in the spectrum (GB 8177) taken at the OHP on Jan 24, 
1984 ( * I  . This fact could indicate that in correspondence of a diminution 
of the density of the dusty disk we observe the absorption of the FO Ia 
(*) Note. The saae behaviour i s  shown i n  the  UV by the  spectrum LWP 2673,  obta ined w i t h  the  
IUE a t  h i g h  r e s o l u t i o n  on Jan 20, 1984. 
https://ntrs.nasa.gov/search.jsp?R=19860002706 2020-03-20T16:08:47+00:00Z
F i g  1 - The s h e l l  spectrum. An a d d i t i o n a l  component i s  super imposed o v e r  t h e  s t r o n g e r  l o w - e x c i t a -  
t i o n  l i n e s .  T h i s  component i s  r e d - s h i f t e d  on i n g r e s s  (Hov 19. 1982) and v i o l e t - s h i f t e d  on eg ress  
 arch 29. 1984). The spect rum t a k e n  o u t  of  e c l i p s e  ( Jan  4. 1981) i s  r e p o r t e d  f o r  comparison. 
. .  . ( .  
F i g .  2  - The r a d i a l  v e l o c i t y  c u r v e  d u r i n g  t h e  e c l i p s e  ( t o g e t h e r  w i t h  t h e  W l i g h t - c u r v e  r e p o r t e d  a t  
t h e  b a t t o n  f o r  compar ison [ E  AUI. N ~ Y S L . I I ~ ~  - 32]). he s h e l l  components o f  tid.Hp, HT9 ( 8 )  and 
of  o t h e r  l i n e s  (0 ) .  have r a d i a l  v e l o c i t i e s  u i c h  a r e  p o s i t i v e  on i n g r e s s  and n e g a t i v e  on egress .  
A t  t h e  same t i m e  t h e  s t e l l a r  l i n e  Mg I1 r( 4481 (+),and t h e  o t h e r  l i n e s  w i t h  dominant  s t e l l a r  
component (x) ,shou a  remarkab l y  s l o w e r  v a r i a t i o n ,  due t o  t h e  o r b i t a l  mot ion .  
44 
Fig .  3  - The b e h a v i o u r  o f  H a  a t  e g r e s s .  A p o s t - e c l i p s e  p r o f i l e  ( s o l i d  l i n e )  i s  compared wi th  t h e  
p r o f i l e s  a t  e g r e s s  ( d a s h e d )  and a t  e a r l y  e g r e s s  ( d o t t e d )  . P r o f i l e s  on t o t a l i t y  a r e  
shown i n  p a p e r  I ,  u h i l e  t h e  p r o f i l e s  on i n g r e s s  a r e  g iven  by Boehm,Ferluga,l984(1BYS 2326) 
LOG1 +C 1 I I I 
light from a part of the shell close to the orbital plane where the density 
and the rotational velocity are probably higher than above and below the 
plane. 
The strongest lines in the photospheric spectrum, H and K of Ca XI, 
during the partial phases of the eclipse appear to be predominantly due 
to the FO Ia spectrum, while the contrary is true for the Balmer lines. 
Moreover, they have a complex structure also out of eclipse . In fact, the 
spectrum taken in Jan 1981 shows that the H and K lines have a violet-shifted 
component at about -30 km/s, probably of CS origin, which was observed also 
by Struve in 1950 (Struve 1951) and by Adams in 1940. The presence of a 
CS shell is confirmed by the UV emissions 01 A1302 and ElgII A2800 which 
are not affected by the eclipse. 
The general behaviour of H a  (Fig. 3) is very similar to that described 
by Wright and Kushwaha (1957) during the previous eclipse. The RV of the 
various absorption components, the half-width and intensity of absorptions 
and emissions are given in paper I. 
During the UV phases of activity observed with IUE the lines of low 
excitation are weaker, while the lines of higher excitation are not we;ker 
or are just slightly weakened. The weak lines which are all FO Ia photospheric 
lines (i.e. without sl~ell components) remain unchanged. This suggests (see 
the next section) that the UV activity of the companion increases the state 
of excitation of the shell. The same effect can be produced by the activity 
of a hot spot on the surface of the primary, hypothesized by Parthasarathy 
and Lambert in 1983 as an alternative explanation of the UV excess observed 
at A shorter than about 1600 A.  
It 5 
0.0 - * 
- 0.5 
R i l  
- \I : I - 
I f 1 
\ 1 n.n.es - 
t ' 29.3.84 - -- - 
24.1.84 .- .-..-.-.- 
- 1.0 - - 
1 1  1 1 1 1 1  1 1 l l l l  I I I I I  1 1 1 1 1 1  
6550 6555 6580 6565 6570 WAVELENGTH ( A  ) 
LOG F, 
-10.5 
LOG F, 
-10.5 
2965 2970 2975 -XId) 
Fig. 4  - Line var iat ions  during UV a c t i v i t y .  With respect  t o  the quiescent  phase on Sep 6 ,  1984 
(-....-), the p r o f i l e s  of Fe I UV 1 resonance l i n e s  are " f i l l e d N  during a c t i v i t y  on March 12, 
1982 (- ), and they are s t i l l  AOre f i l l e d  during the a c t i v i t y  peak on March 26, 1982 ( - - - - )  
Note that  the " f i l l i n g ' 1  a c t s  on the doppler-shifted part of the l i n e s .  
2. The "active spectrumg1 
As happens for the depth of the eclipse, also the determination of 
the shell spectrum, in principle, is affected by the problem of separating 
the effects of the eclipse from those related with the intrinsic far-UV 
activity. The influence of this activity, over the spectral lines of the 
system, can be studied in correspondence of the two active periods which 
have been observed in the UV since now: the first occurred before the eclipse, 
on March 1982, while the second occurred during totality, on March 1983. 
Since for the active period in totality it is difficult, if not impossible, 
to separate the effects of the eclipse and of the activity, here we shall 
discuss the pre-eclipse activity period in some detail. 
The activity phase in 1982 was the strongest and reached its observed 
maximum, A m = 1.75 mag at 1500 8, on March 26 (Boehm, Ferluga, Hack, 1984) ; 
two weeks before, on March 12, the activity was weaker, A m = 1.25 mag at 
1500 A.  It is then particularly interesting to compare these two IUE high- 
resolution spectra, LWR 12777 and LWR 12866, taken in 1982 on March 12 and 
March 26 respectively (spectral range Ah 2600 5 3100 A ) ;  unfortunately, we 
do not have optical spectrograms at that epoch. Since both spectra are "activett, 
there are no large variations in the line profiles (paper I); but a detailed 
inspection reveals that some groups of lines appear to change their relative 
intensities slightly. 
In particular, we may notice that, in correspondence of a higher degree 
of activity, the stronger mid-UV lines of Fe I, such as X A  2966.9 - 2973.1 i\ 
resonances or the kultiplet V9, ;. seem to be partially "filledIg . The same 
thing happens to several low-excitation lines of Ti 11, and in particular 
to the strong low-excitation lines of V I1 belonging to the multiplets 
UV 3-10-11-12 (EP 6 0.4 eV) and V 26-27-34-42. Also the absorption wings 
4 6 
of the Fe I1 A 2599 1 resonance line, and particularly the large absorption 
wirigs of the Mg I1 ,I 2800 1 resonance doublet, appear to be flattened by 
the effect of activity. The filling occurs generally on the red side o f 
the lines, and on both wings of the Fe I1 and Mg I1 resonances; the effect 
is about 0.2 - 0.3 magnitudes, between March 12 and March 26, 1982. At the 
same time, the continuum is raised by about 0.1 mag, in the "window" around 
3080 - 3087 1. 
Such effects are greatly enlarged, if we compare these active pre-eclipse 
spectra, with a quiescent post-eclipse spectrum: in our case let us consider 
LWP 4158, obtained with IUE at high resolution on September 6,1984. After 
overcoming some calibration problems (the last spectrum was taken with a 
different IUE camera), there still remains a difference of about 0.5 mag, 
between the mid-UV continuum enhanced by activity (1982). and the quiescent 
one (1984); then, while the continuum is raised, the behaviour of the line- 
components of the mid-UV spectrum, with respect to activity, can be classified 
as follows. 
( i )  NormaZ. The majority of the lines apparently follow the variation of 
the continuum, increasing their central flux by I-U 0.5 mag in activity, with 
no remarkable variation in the profile. 
( ii ) Filled. This is the case (Fig. 4) of the already-mentioned lines of 
Fe I, Ti 11, V 11, and wings of Fe I1 - Mg I1 resonance lines, which are 
filled in pre-eclipse activity by N 1 mag. (*)  
( iii ) &changed. Activity does not affect remarkably the central flux of 
some high-excitation lines, such as Fe I1 multiplets W 62 and higher 
(EP 3 1 e~), or Cr I1 multiplets UV 5 and higher (EP 2 1.5 e~); so these 
lines appear to be deepened, with respect to the enhanced continuum. This 
effect should be dominant in the far UV, producing the deepening of lines 
observed at low resolution. Moreover, these lines do not show any remarkable 
doppler shift depending on activity (or on eclipse phase). 
( iv ) Circwnstellar. Also the circumstellar emission components of strong 
resonance lines, such as Fe I1 A 2599 A and Mg I1 A 2800 A, remain unchanged 
by activity, as well as 0 I A1302 A (observed in the low-resolution mode). 
These observed effects can be easily explained by the presence of an 
additional spectrum, produced by the source of far-UV variability, and super- 
imposed over the spectrum of the system. This active spectrum should be 
very s i m i l a r  to that ofthe primary, in order to leave it practically identical; 
the only difference should be a slightly higher temperature ( bgether with 
the absence of absorption wings in Fe I1 and Mg I1 resonance lines). 
As a consequence, one would have ( ii ) fainter low-excitation lines, 
producing the observed filling (and the wihgs of Fe I1 and Mg I1 resonances 
would be filled as well) ; moreover, one would also have stronger high-excita- 
tion lines, adding no appreciable flux (iii) to the underlying stellar ~pe~trum. 
(*) Note. The behaviour o f  an even l a r g e r  number o f  l o w - e x c i t a t i o n  l i n e s ,  known t o  possess a  
v i o l e t - s h i f t e d  s h e l l  component i n  t h e  post -ec l ipse  spectrum o f  Sept 1984, i s  apparent ly  
s i m i l a r .  The same behaviour i s  shown, symmetr ica l ly ,  i n  t h e  p r e - e c l i p s e  spectra  
o f  Harch 1982. Just because t h e  s h e l l  absorpt ion i s  weaker a t  ingress,  on comparing 
a  p r e - e c l i p s e  spectrum u i t h  a  post -ec l ipse  one, these l i n e s  appear t o  be l l f i l l e d f l  
on t h e  v i o l e t  s i d e  b e f o r e  t h e  e c l i p s e :  t h i s  e f f e c t  has noth ing t o  do w i t h  a c t i v i t y ,  
and i t  should be d i s t i n g u i s h e d  from case ( i i ) .  
Intermediate situations would generate case ( i 1 ,  while circumstellar emission 
components (iv ) would clearly remain unaffected. Finally, we note that in 
case ( ii ) the residual line is not red-shifted in pre-eclipse activity, 
since the "filling11 acts on the doppzer-shifted part of' the line (~ig. 4) ; 
also in case ( iii ) there is no shift during activity. This should mean that 
the hot source .is either on the primary, or at the center of the companion, 
but in any case not rotating with the shell. 
3. - Conclusions 
From the results of the present and previous eclipses of Epsilon A u r  
it is evident that the sgectroscopic and photometric observations are completely 
explained by the presence of the following bodies: 
a )  the FO Ia primary, whose spectrum is always observable; 
b )  a cool body (T N 500 K) which is responsible for the photometric eclipse 
of the primary (Bakman et al., 1984). This dusty disk or ring must be made 
of particles much larger than those present in the IS dust, because no ad- 
ditional reddening is observed at 2200 A during the eclipse; 
c) a gaseous envelope more extended than the dusty disk, which is responsible 
for the additional spectrum appearing during the eclipse; 
d) an extended envelope surrounding the whole system, where the emissions 
of 01 11302 and MgII 1 2800 are formed; 
e )  a faint hot body which is not eclipsed and whose radiation dominates 
at X 6 1500 8. In fact the depth of the eclipse tends to become zero at 
X $1500A,thus indicating that the excess in the UV is real and not due simply 
to scattered light from longer wavelengths in the spectrum of the primary, 
or in other-words, it is not simply an instrumental effect. This hot body 
may be a star (as suggested by Hack and Selvelli, 1979) or a binary system 
(as suggested by Lissa uer and Backman, 198 5 1, whose radiation, escaping 
from the poles, excites and ionizes the gaseous envelope, producing the 
shell spectrum; or it may be a hot spot on that part of the surface of the 
primary which is not occulted by the dusty disk (as suggested by Parthasarathy 
and Lambert, 1983). The hot body (star, binary system or hot spot) is variable 
in light. 
l h i s  work i s  based on obse rva t i ons  made a t  t h e  Haute Provence Obs. (France), and w i t h  t h e  IUE 
s a t e l l i t e  f rom VILSPA (Madr id) .  Data a n a l y s i s  uas performed. a t  t h e  ASTRONET p o l e  o f  T r i e s t e , I t a l y .  
References 
Adams. W.S., 1940, p r i v .  com. quoted by Struve, 0.: 1951 Astroph. J. - 113. 699. 
Backman, D.E., Beck l i n ,  E.E., Cruikshank. 0.0.. Jo ice ,  R.R., Simon, T., Tokunaga. A.: 1984. ~ s t r o p h .  
J. 284. 799. 
-
Boehm, C., Fer luga,  S., Hack, M.: 1984, Astron. Astroph. - 130, 419: Paper I 
Fer luga,  S. and Hack, M.: 1985. Astron. Astroph. i n  press. 
Hack, M. and S e l v e l l i ,  P.L.: 1979, Astron. Astroph. - 75, 316 
L issauer ,  J.J. and Backman, 0.: 1985, Astroph. J. i n  press.  
ski, I., Sek i ta ,  I., Hirayama, K.: 1984, .c Aur Campaign Newsl. no. 11, p. 17 
Par thasara thy ,  M. and Lambert, D.L.: 1983, Publ. Astron. Soc. P a c i f i c  95, 1012 
St ruve.  0.: 1951, Astroph. J. 113, 699. 
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Struve,  O., P i l l a n s ,  H., Zebergs, V.: 1958, Astroph. J. - 128, 287 
Wr ight ,  K.A. and Kushwaha, R.S.: 1957, LiCge C o l l .  N 8, p. 421. 


The eclipse of Epsilon Aurigae visible spectroscopy and ultraviolet activity

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