Infall from the circumstellar envelope onto the bright B0.5 IVe star, HD 58978 was studied. The IUE data indicate that the star was surrounded by a low and moderately ionized circumstellar shell at least 12 times between 1979 and 1988. During 6 of these episodes, the signatures of cool circumstellar material were redshifted with respect to the photosphere by 20 to 80 km/sec. The data indicate that the transition from infall to minimal shell absorption can occur in under 10 days, and are consistent either with infall phases lasting up to 6 months, or with infall episodes shorter than 10 to 15 days. The long term behavior of the shell episodes is compared with variability in the stellar wind

Bjorkman, K. S.

Grady, C. A.

Henrichs, H. F.

Peters, G. J.

English

NASA Technical Reports Server

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I(E(JUI(I(KNT Slll.',l,l, INI::\I,I, l,]k:liN 15 IN A BIJ %, ,%T:\I¢. lid ,5S'J78 I!JT<)-1988
C.A Gtady
astlononiy })ro_ralns, (_olllplltcr _Clell( e% (R_I pol,ll,R)n,
,rod IUI'; ()bs(:l,.'atuiy, C,o([d,ud Sly,ice l"[ight Cent('l v
1_ S Blorklu_n
Center for Astrophy.qcs <rod Sp,..e Astrunonly,
Unlvelslt3 of (h,lot.do
A BS 1'1l ACT
\,Ve present a sludy of mfall hen) the cucumstellar enve-
lope elite the brigh_ B0.5 IVo star, liD 58':)78. The ,ivai],lble
IUE data indi,'.ate that kS(, st,u has been surioun(h'd 17y a
low ,rod moderately _onized circumstellar shell at least 12
times between 1979 and 1988. l)urmg six of th(-.se episodes,
the signatures of cool circuinstellar material weie redshifte(1
with respect to the photosl)here by 20 to 80 km sec-1 The
available data indicate that the transition from infall to lmn-
imal shell absorption can occur in _<10 days, and are consis-
tent either with infall phases lasting up to 6 months, or with
uifall episodes shorter than 10 to 15 clays. The long lernl
behavior of the shell episodes is compared with variability
m the stellar wind.
[(eg'_t:o?'d.q: Be Stars, outer atmospheres; cu'cumstellar
material, mass infall
1 1NTt/OI)UCTION
lid 58978 (FY CMa, ltR 2855, B0.5IVe, v sin , =280
km sec -I (Ref. 1)) is eLcomparatively early-type, bright lie
star, which has been the subject of sporadic IUE observa-
tions from 1979 and into 1986. More frequent observations
began m 1986 and will continue rote 1989. Peters (Ref. 2)
first noted the presence of multiple, low velocity discrete
absorption components in C IV arid N V. Subsequent IUE
spectra have shown that this star has a strong and dramati
cMly variable stellar wind with complex absorption profiles.
The wind profiles in this star are characterized by' variable
high velocity absorption seen in N V, and C IV. Multiple
low velocity (0 to -400 km sec -1) discrete absorption com-
ponents are present in all of the 1UE spectra, although the
absorption depth ranges from essentially saturated features
to 20 percent below the continuuln level. This star is un-
usual among the early-type Be stars surveyed by Grady,
Bjorkman, and Snow (Ref. 3) in showing variable emis-
sion in N V, and possibly also C IV. Unlike most of the
B0.5e stars observed with IUE, low ionization material is
frequently present in outflow, and is particularly easily de-
tected in Si 1II A1206 at velocities up to -600 km sec -1.
Space _(l(211ces (',(211t(;l _
1./Nixetsi b' ot Stoutheln ('ahfornia
]I.F Ih'niichs
:\stiorloillic,d hlstitule, Unl\'eislly of Amsl.ei(ldin
4 • __
5 /b
3
225
15
075
0 __l ...... ,___ i
1230 1955 1240 1245
',VO vele ngt h (A)
-_..... r r -- -_
f"./ir'v-
V ,a i9b7 Me/ 3
cv'v )_>#,% ......
j _Q 19_7 Nov /
125(2 1255
Figure 1 N V resonance profiles ill IlD 58978 for three
dates in 1987 to 1988. Note the variations in the emission
luw strength, the aniount of absol'l)t_on in the low velocity
diH:rete absorption coniponents, and in the anlount of high
velo(lty wind absorption.
2. LOW IONIZATION IN1;'AI, I_
In an effort to better understand the cornl)lex wind pro-
tile% and dramatic resonance profile variations, regular inon
ltormg of tins star was be.gun in 1986. Red shifted abc.orl>
lion re,(lures m lines of low and moderately iomzed species
were first noted in an IUE SWP observation made on 1987
May 3, which showed unusually strong absorption m the
vicinity of the S 111 lines at 1202 _ . Further inspection of
the spectrum showed that similar absorption features were
present in all lines of S 11I (1)_ 1200, Si llI (4)A 1300, C II,
AI lllMd854, 1862, and several t?e III multiplets, especially
multiplet 34. Comparison with the IUE spectrum obtained
on 1987 March 6 (SWP 30443) showed that the low ion-
ization features had not been present in March (Figure 2).
Sharp absorption features in these ions, particularly the ex-
cited state lines, are normally not seen in the UV spectra of
stars as hot as HD 58978 (Ref. 3), and indicate the presence
of a moderately ionized circumstellar envelope.
The shell features observed on 1987 May 3 have radial
velocities corresponding to the absorption maximuni rang-
ing from +85 to +110 km sec -1. This range of absorption
maxima is a real feature of the stellar sl)ect,'um , since in-
terstellar lines observed in both that spectrum, and in the
A Decade of UV Astronomy with IUE, Prec. Celebratory Symposium, GSFC, Greenbelt, USA, 12-15 April 1988, ESA SP-281, 14)1.1 (June 1988)
https://ntrs.nasa.gov/search.jsp?R=19890001361 2020-03-20T06:09:05+00:00Z
_'.f¢"
258 C_ F-'CO_ QUALFr'Y C A GRADY ET AL
z?qo _?o_ 1 too ,_o', , %,a
',vq.ol_,,n- (,a)
l"lgure 2 1987 May 3 Si lIl (UV 4) line profiles for lID 59878
(solid) and 1987 March 6 (dashed) showing the redslnfted
absorption present in the May spectrum, l,eader lines in-
dicate the heliocentric wavelength_ of the Si III transitions.
The unmarked sharp abso]ption h:atnres 1]1 the spectl'un/
are interstella:.
cool circmustellar envelope, since this line does ]lot have a
_t]ong photospheric component, lies in a portion of the IUE
spectrum with good signal to noise, and is not blended with
other cu cumsteliar or interstellar lines.
The cool circumstellar absorption is present over a wide
range of radial velocity in this star. Inspection of the pro-
files has shown that the radial velocity corresponding to the
absorption maximum is variable, and is frequently displaced
redward of both the hehocentric line center, and the stellar
radial velocity of 29 km sec -1 (Ref. 5). Of the 23 spectra
with appreciable Fe III absorption, 9 had Fe III circumstel-
lar absorption centroid radial velocities displaced more than
20 km sec -I redward o[ the photospheric radial velocity,
and thus unambiguously indicate the presence of infalling
circumstellar materiah The remaining spectra showed com-
pm atively undisplaced absorption, which following the op-
tical terlninology for Be stars is termed "shell" absorption.
Eleven spectra showed no significant circumsteltar Fe III
absorption.
IUE spectrum of the same star obtained on 1987 March 6
agreed to mthin 4 to 5 km s -I , an accuracy typical of IUE's
pointing (Ref. 4). Inspection of the absorption components
revealed that the absorption was not distributed in the form
of a single approximately" gaussian component, but showed
considerable red-asymmetry (Figure 3).
cq
O
q-
x
to_
Y_
35
5
25
2
15
]
O5
0
I I i
O0 0 1O0 200
RQdLol Velocity (kin/s)
,00
Figure 3: Distribution of infalhng mater:al as a func-
tion of radial velocity on 1987. The 1987 May 3 spectrum
is shown in bold, A comparison spectrum taken in 1987
November (SWP 323t7) was obtained at a tram when the
low ionization mfall was mimmal. The strong absorption
feature centered at +29 km sec -1 is interstellar.
Since the discovery of low ionization infall in the spec-
trum of this star, we have continued to momtor the low
ionization lines in this star, and have extended our analysis
to the previously acquired IUE data. As shown in Figure 3;
the Fe III (34) line at 1895.456 _ is particularly suitable for
monitoring the strength and velocity characteristics of the
Figure 4a shows the circumstellar Fe Ill A 1895.456
equivalent widths as a fimction of time. Radial velocities
of the absorption maximum as a function of time are shown
in Figure 4b. The 1987 data show that several successive
spectra can show infall signatures. As a result, we define in-
fMl episodes to be time intervals where all IUE spectra show
mfall s:gnatures and separated by IUE spectra without in-
fall signatures, or where the interval between observations is
moie than approximately 2 months. Shell episodes are de-
fined as intervals where the 1UE spectra indicate the pres-
ence of cool undisplaced circumstellar material. By these
criteria, the available IUE spectra, correspond to 12 shell
anti infall episodes, six of which are infall events. Our data
are consistent either with infall episodes shorter than 10 to
15 days, the characteristic separation of the 1987 and 1988
data, or at least as long as 41 days, and possibly as long
as s:x months. The IUE spectra obtained in 1987 Novem-
ber indicate that the signatures of low ionization infall can
vanish quickly, in as httle as 7 days.
<
-(
5
.c
L,
d
05
0':
05
F
O"
O:
Ol <
o r
I
< c
<.... _, _I
c <¢<
o:, _ o <, e' 4, <' I
ii a
g , 4 S3 5 B5 2 571 g?
],m.. of O:s:',,a:,o_ ('rec's)
Figure 4a: Fe 111 (3,l))_ 1895 456 absorption eqmvalent
widths as a function of time.
RECURRENTSHELLINFALLEVENTSINAB05ESTAR 259
%-
[
"a
d'
%
w
c,
E
llO
6L ¢
¢,
44
O
22_
0 ___l_
7£ E1 a
¢
¢
¢,
¢,
$ e,<,
¢
¢,
$
g2,3 kS? g"
7 rne o' Obse,,cboq (_,cc'-')
Figure 4b: Fe Ill (34) A 1895.456 absorption cem.roid ra&,,I
velocities as a function of time
3. IIIGII IONIZATION INFALL
Four IUE spectra, SWP 6963 (1979 day, 296), SWI'
28457 (1986 day 159), SWP 30:/92 (1987 (lay 57) and SWP
:12317 (1987 (lay 318), show no slgniticaut low ionization
infall. Instead. these spectra show strong absoiption coln-
ponents in N V wH, h centroid velocities of +50, +7 with a
strong asymmetric tail extending to +113 km scc -1, +150
and +50 kmsec -1 respectlw.qy In the 1987 Februaw spec-
trum, infalling material is visible out to at least, +260 kin
sec -1 (Figure 5). The three mole lecc'nt spectia showiug
tile high ,oniz,ttion infall are separated by multiples of ap-
ploxmlately 260 days from observation to observation The
available IUE data are too sparse to currently deternunc
whether this interval represents a periodic l)hem)nmnon in
the stellar envelope, although 1U E observations pl,mned fol
the remainder of the tenth aim l.he eleventh episode may he
able to address this (luest_on
x
D
u_
HD
1 2
- I
E-9
E-9
8
E-10
6
E 10
4
E-IO
2
E-lO
0 i
1 2,50 1255
©55978 1987 Feb. _5
I I
1240 1245 1250
Wovelength (A)
l"lgure 5: N V protih." for Ill) 58978 obtained on 1!187 Febru-
ary 25 showing the lughly redshffted absorl)tion [eatule 1|1
ad&tion to the more typical low velocity, (outflow) discrete
absorption con|pone||ts.
4. COI/RI_;I,ATION O1" INFAI,I, EV, EN'I_S
WITII WIND VARIATIONS
Correlating the behavior of the cool c|rcumstellar enve-
lope with the stellar wind is complicated by the complexity
of the wind profiles, and by the dramatic variab|lity of all
portions of the stellar wind profiles. Of the resonance lines,
the N V do||blet is the most promising for analysis since the
resonance lines are infrequently saturated, and the signal to
noise m that part of the spectrum is good. The absorption
portion of the C IV profile tends to be saturated at low ra-
dial velocities in outflow, precluding reliable measurement.
The Si IV profiles are dominated by the strong photospheric
absorption profiles, making evaluation of the w|nd absorp-
turn more difficult. All of the available IUE spectra show
absorption from low velocity (outflow) discrete absorption
components which are particularly pronounced in N V. No
weak wind episodes, characterized by the absence of (hscrete
absorption con|t)Olmnts have been observed in the nearly
nine years of 1UE observations, in contrast to tile I)ehavior
of many otlmr early-type Be stars.
The discrete colnl)onents are the most obviously vari-
able port|o/| of the N V profile Figure 6 shows the total
equivalent width for the low wzlocity discrete absorption fc'a-
tu|es. This measurement inch|des the low velocity (outflow)
cnmt)onents , any undlsplaced c|rcumstellar absorption fea-
t|ues, and any red-shifted absorption features. The contin-
u||m level f,or the mcasuremcmts was determined using tim
local photospheric contlnuuln outside the resonance profile.
Due to the |mcertai| h and variable number of absorptio||
components the equivalent widths are not easily l.ranslated
it|to column densities. Figure 7 shows the Fe III k 1895.456
circumstelhtr materiM equivalent width plotted against the
sumnmd N V discrete component equivalent widths. De-
spite the scatter in the N V data, the larger N V equiva-
h.'nt widths tend to be associated with the smaller clrcum-
stellar Fe l lI equivahmt widths. This |s also SUl)ported hy
the detection of red-shifted N V absorption features only
in spectra with no detectable Fe Ill absorption. These re-
s||lts suggest that the ionization balance in the vicinity of
the star is variable, per[laps indicating the presence of Lran-
smut shocks At present the data are conMstent eit, her with
temporal variations_ or with variabdlty as a result of orbital
|notion. A more reliable estmmte of the periodicity of the N
V |ed shifted abboiption featu|e w|ll be required to separate
ten|imral variations, which are not uncommon in Be stellar
wi|lds, from any orbll.al effects.
5. DISCUSSION
lnfalling material in main sequence stars with apprecia-
ble c|rcun|stellar n|atcrial have been reported in interacting
binary stats (t{ef 6), and it| the protoplanetary disk/A
shell star 3 Pie (Ref. 7, 8). Signatures of infalling material
were present in IUt" high dispersion spectra of/3 Pic from
1984 December through 1985, and were also visible in Ca
11 profiles (Ref. 8). The absorption profiles, and velocity
r,|)lge obsel ved in these lines are similar to those seen in the
u|ajorlty of our spectra. Ihgh ion|zation infall has not been
reported in/3 Pic, and would be unlikely from the erosion of
a comparatively cool dust and gas disk, unless that mate-
260 c A GRADY ET AL
_%
2-
_2
i,
9
_J
L.I
Y
O
C_
F
o
u
22
2
i
O5
0
lY80
ti[) bn978
r r i
o
+e,e,
o
0 _," <"
¢'¢" o
¢, e,
o
o
,5 o
o
o -
2
e,¢,
o4,
r r L __
_b81 1985 1965 1987 198g
]_r-nc Of Ob±_rvaNOn
Figure 6: N V M238.821 discrete absorption component
eqnivalent width as a function of time. This measurement
includes both the low velocity material in outflow, and any
redshifted absorption. The lcr uncertainty in the measure-
ments due to continuum placement in 0.3_.
v
_: 2
:3
g
E 1
aJ
c:
O5
o
{J
) 0
0
HD 539?8 1_..7 J- 1988
T ] i
o
o
• o
•;22, :_ :'_l' _,",
,.,_,..,. '_ ._, ,,.
r
• __ M____I__ _t .... i____
0 I 02 05 0 _ 0b
[C III [quw(slu'rq WIr_lth (A)
Figure 7: N V discrete component equivalent width plot-
ted as a function of the Fe Ill cii cumstellar equivalent width.
rial were to encounter a high density stellar wind moving at
sufficiently high velocity to produce x-rays m the collision
The available infrared data on I-ID 58978 (Ref. 9) are consis-
tent with an infrare&_xce_d_,,t:_tuc.e.d,.5.v free-free emission
• - _'_" .- ,_r_'_': _ .,
from a gas d,sk, rat_tJ,_e _r_e_.._.,_ large dust
disk, as is observed in/3' Pic.-'_lll_fist_es0,1_',_o_.N_er with the
ionization variations in HD 58978's wind and circumstellar
environment suggest that this star may be an interacting
binary system.
Interpretation of this star as an interacting binary is
supported by by the similarity of the resonance profiles to
some known interacting Be-binary systems. Cool and mod-
erately ionized infalling material is present in the UV spec-
trum of HD 41335 (HR 2142), where the infall is present at
a limited number of phases, and outflow is present in the
same lines at other times (Ref. 10). No high ionizatmn in-
fall has been detected in this star. The bright Be star ¢
Per (Ref. 11), which is somewhat cooler than HD 58978,
has C IV profiles similar to the N V profiles seen in this
star, complete with emission, and strong low velocity ab-
sorption in outflow. Redshifted absorpbon features are seen
in some of the IUE spectra. Further confirmation of the bi-
nary interpretation for this star will require additional IUE
spectra, in order to establish which portions of the complex
circumstellar envelope show signs of periodic variability.
6. IMPLICATIONS FOR OTHER Be STARS
Grady, Bjorkman, and Snow (Ref. 3) found several Be
tars, not known to be interacting binaries, which had wind
,outflow) profiles similar to ttD 58978. These stars had
emission in at least one resonance profile which was more
highly ionized than would be expected in a normal B star
of comparable spectral type and luminosity class, and also
had strong and extremely low velocity discrete absorption
components. These stars also showed wind signatures over a
wide ionization range, and in at least one case infalling ma-
terial is present. The other stars have been insufficiently ob-
served to determine whether infall is present at some times
or phases. If all of these objects can be shown to be inter-
acting binary stars, the wind peculiarities may reflect the
presence of a hot and luminous secondary in the system, a
hot spot caused by the collision of the stellar wind and the
mass transfer stream, or the presence of an accretion disk.
The available IUE database on stellar winds in B stars is
now sufficiently complete, that single observations of the C
IV or N V resonance profiles can identify stars with peculiar
_inds. Since the integration times to acquire IUE spectra
tend to be shorter than those required for x-ray observa-
tions, UV spectral surveys of early-type stars may prove
to be an efficient way of identifying such interacting binary
syst.ems for future study.
REFERENCES
1 Slettebak, A., 1982, Ap. J Suppl., 50, 55.
2 Peters, C.J. 1982h, in Be Stars (IAUSymposzum No. 98),
ed. M. Jasdlek and tt.G. Groth (Dordrecht: Reidel),
p. 353.
3 Crady, C.A., Bjorkman, K.S., and Snow, T.P. 1987,
Ap. J., 320, 376.
,1. Ilarris, A. and Sonneborn, C. 1987, "How to Use IUE
Data" in Ezplorm 9 the Unzverse w_th the IUE Satel-
hte, ed. Y. Kondo (Dordrecht: Reidel), 729.
5..lenkins, E.B 1978, Ap. J., 219, 845.
6. McCluskey, G.E., Jr. and Sahade, J. 1987, "Interact-
ing Binaries" in Explor_r_g the Unzverse w_th the IUE
Satelhte, ed. Y. Kondo (Dordrecht: Reidel), 427.
7. I£ondo, Y., and Bruhweiler, F.C. 1985, Ap. J. (Letters),
291, L1.
8. Lagrange, A.M., Ferlet, R., and Vidal-Madjar, A. 1986,
in New Iuszghts zn Astrophysics: Ezght Years of UV
Astronomy wzth IUE, ESA SP-263, (Paris: European
Space Agency) 569.
9. Cote, J. and Waters, L.B.F.M. 1987, Astr. Ap., 176, 93.
10. Peters, C.J. 1981, in The Uuwerse at Ultraviolet Wave-
lengths: The F_rst Two Years of lUE NASA CP-2171,
ed. R.D. Chapman, 157.
11. Peters, G.J. and Pohdan, R.S. 1982, in Be Stars (IAU
Symposmm No. 98), eds. M. Jaschek and H.-G. Groth,
(Dordrecht: Reidel), 405.


Recurrent shell infall events in a B0.5e star: HD 58978 1979-1988

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