Ultraviolet observations of the red giant HR 3126 are combined with multi-wavelength data in order to provide a firmer basis for explaining the arc-minute sized nebula surrounding the object. Possibilities as to the location of HR 3126 on the Hertzsprung-Russel diagram, and to the formation mechanisms of the reflection nebula IC 2220 associated with it, are summarized

Dachs, Joachim

Doggett, Jesse

Mundt, Reinhard

Pesce, Joseph E.

Stencel, Robert E.

Walter, Frederick M.

Whitelock, Patricia A.

English

NASA Technical Reports Server

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253
MULTI-WAVELENGTH
OBSERVATIONS OF THE PECULIAR
RED GIANT HR 3126
Joseph E. Pesce, Robert E Stcncel,
Frederick M. Walter
Center for Astrophysics and Space Astronomy
University of Colorado, Boulder, U S A.
.Jesse Dogger%
Joachim Dachs,
Astronomisches
Institut, Ruhr Univ.
Bochum FRG
Patricia A. Whitelock,
South African
Astronomical
Observatory
Remhard Mlmdt
Max Planck Institut
filr Astrononfie
Heidelberg FRG
ABSTRACT
New ultraviolet observations of the red giant HR 3126 are
reported and co,nbined with multi wavelength data in or-
der to provide a firmer basis for explaining the unique, arc-
minute sized nebula surrounding the object.
Keywords: ultraviolet spectrum; peculiar red giant; stel
lar evolution; symbiotic stars; hybrid stars.
on extinction are too large. Their estimate of the nebular
mass based on the surface brightness, assuming graphite as
the dust materi_d, is _ 0.01 Me, which could be produced
in the current mass loss phase of HR 3126.
A light curve between 1963-1977 has been constructed
for HR 3126 by Dachs et al (1978), who concluded that
the star is an irregular variable (V ranges from 6.2 to 7 1),
possibly due to variations in the circumstellar extinction,
which may occassionally amount to 0'_.10 per day. This
behavior is similar Co the M0 Iab supe.rgiant CPD 57 ° 3507
in NGC 3293 or to tt_e M2e Ia supergiant, IL Cep. The light
curve of HR 3126 has remained quasi-constant during the
1980's, near V = 6.5 (Dachs 1986, private conmmnication).
N
1. INTRODUCTION
The M2 II star HR 3126 (HD 65750, V341 Car, SAO
235638, CPD 57 ° 1028) is remarka|)le because it sits near
the center of a butterfly-shaped nebula of several are nfin-
utes extent (Dachs et aI 1978) (Figure 1). While other
red objects are known to have nebulae (e.g. OH0739-14,
Cohen et al. 1985), most are much snmller and often ex-
plained in terms of binary star ejection mechanisms. If HR
3126 is a member of the nearby open cluster NGC 2516, the
distance (375 pc), main sequence turnoff age (_ l0 s years)
and implied mass (_ 5Mo) suggest that HR 3126 is a red
bright giant past the initiation of helium burning in its core
and on the Asymptotic Giant Branch (AGB). Observations
of circumstellar lines in the optical spectrum of HR 3126
indicate a nmss ejection rate of 2-4 x 10 -r M o yr -l and a
wind velocity of 13 km s -1 (Reimers 1977).
Tile reflection nebula, lC 2220, associated with HR 3126,
has a mass estimated to be 0.7M o from the mean redden-
ing of the starlight produced in the nebula. Perkins ct al
(1981) proposed the existence of a circumstellar disk, im
plying that previous mass estimates (of the nebula) based
E
\
\
Figure 1. Photograph, of HR 3126 and surrounding nebula,
IC 2220, in the V (yellow) spectral region. From a CTIO
Schmidt plate of Dachs.
A Decade of UV Astronomy wtth IUE, Proc. Celebratory Sympostum. GSFC, Greenbelt, USA, 12-15 April 1988, ESA SP-281, Vol. 1 (June 1988)
https://ntrs.nasa.gov/search.jsp?R=19890001360 2020-03-20T06:09:03+00:00Z
254 J E PESCE ET AL
The essentially constant brightness of IC 2220 does not
follow the brightness variations of its central star, neither
immediately nor with some fixed delay. The B-V and U-
B colors of the nebula are bluer than those of HR 3126,
as is expected from a pure reflection nebula. Dachs and
colleagues have suggested that the nebula appears to be
structured by a magnetic field. A spectrum between 5865
and 6745 _i of the brightest knot of IC 2220, about 40"
south of the star, was obtained by R. Mundt at ESO on
1987 February 25. The spectrum of the nebula resembles
that of the star showing Na-D and Ha absorption as well
as tile TiO band at 6159_t.
From Dachs (1973) the color differences between nebula
and star are,
(B-V) = --0m.23 ± Om.03
(U-B) = 0m.98 4- 0m.ll
and their ratio,
y = 4.3 =t=0.8
are much larger than the nebulosity around the Pleiades.
This difference may be due to the fact that a larger frac-
tion of radiation at shorter wavelengths may be scattered
by reflection nebulae around M-type stars than around B
type stars, or IC 2220 may not be a pure reflection nebula.
Perkins et al (1981) statc that the degree of polarization is
typical of reflection nebulae, indicating that the dust grains
reflecting the central starlight are not unusual. Excitation
of the gas of the nebula by an unknown, faint, blue compan-
ion of HR 3126 may contribute to the ultraviolet radiation
of the nebula.
Only a few reflection nebulae connected with red giants
are known. Late-type giants are known to lose mass and
develop dusty shells which are quite close to the star (arc-
sec rather than arc-min scales). HR 3126 and IC 2220 offer
a unique and interesting environment in which to observe
these processes under extreme conditions.
We have obtained IUE and other wavelength data to
test the hypothesis that the nebula surrounding HR 3126
is a fossil of a rapid mass loss epoch during hydrogen shell
burning, several million years ago.
2. OBSERVATIONS
Ultraviolet observations were obtained 1987 Sept. 28
by Stencel and Pesce [IUE program MLJRS]: SWP 31915
(30 minute exposure) and LWP 11744 (159 minute expo-
sure). We infer from the lack of signal in the SWP exposure
that the central object is not an interacting binary, such as
a symbiotic star (@ Nussbaumer and Stenccl 1988), be-
cause the exposure time was more than adequate to reveal
bright emission lines in most of the known members of this
class of active binary stars. In the LWP image, only Mg II
emission and a photospheric continuum longward of about
2700A were detected. The Mg II emission appears normal
for the spectral type, suggesting a chromosphere is present
(see Figure 2).
Doggett obtained visual (3800-5200) reKion) spectra of
HR 3126 on 1987 September 25th and 26th at CTIO. They
appear to be typical red giant spectra with the Ca II H and
K features, and TiO bands at 4461, 4954 and 5000_L The
Ba II feature at 4554A is present and is possibly enhanced
compared to other M giants (see Figure 3). In addition,
a 5640-7040A region spectrum was obtained by Walter at
Cerro 1"ololo (1987 April 4). The spectrmn is normal except
for an overly strong Li I line at 6707_i. Abnormally high
lithium abundances have been seen in weak G band and S-
type stars (Hartoog 1978, Boesgaard 1970). According to
Pilaehowski et el (1984), a normal K giant [HD 112127] and
similar stars show high lithium abundance with otherwise
normal spectra. High lithium abundances in evolved stars
have been taken as evidence that the stars have undergone
helium shell flashes and are second ascent giants. However,
strong lithium lines were observed by Pilachowski et al in
several giants in the old galactic cluster, NGC 7789, indicat-
ing an abnormally high lithium abundance on the red giant
branch (RGB). These observations remove the constraint
that the weak G band stars and the HDl12127 stars must
be ascending the AGB. In addition, Pilachowski et al con-
clude that lithium abundance declines with temperature on
the upper RGB.
In the infrared region, Ten JHKL observations obtained
between 1975 and 1982, at the South African Astronomical
Observatory, indicate that HR 3126 is a low amplitude vari-
able with AJ _ 0.2 mag. Whiteloek observed HR 3126 on
1987 September 15/16 and comparison of (J-H), (H-K) and
(K-L) colors with a standard star show longwave excesses.
She further reports that, although the colors could be those
of a Mira variable, the lack of large amplitude variablility
and the IR spectrum clearly indicate this is not the case. A
low resolution (AA/A _ 0.01) spectrum from 1.2 - 4.0 /ml
obtained in December 1981 at South Africa is typical of an
M giant, the CO strength indicates a type of M3 and there
is no sign of Mira-like H20 absorption.
Finally, lIRAS observed this object as well, detecting it
in all four bands, 12 to 100 pm and with the Low Reso-
lution Spectrograph (LRS). Ttie infrared colors suggest a
far infrared excess remains after a 3250K blackbody is sub-
tracted Further analysis suggest the source was spatially
resolved by the IRAS detectors at all frequencies. In addi-
tion, in the LRS spectrum, there is no evidence of the 9.7#m
feature associated with silicate dust or the 10.3pro feature
associated with dust composed of SiC. However, spectra
obtained by Humphries and Ney (1974) with the 40-inch
reflector at Las Campanas Observatory on a system de-
scribed by Ney and Stein (1968) show the 9.7 and 18 #m
features associated with silicate grains. Their beam size is
15", and the spectrum they obtain is probably not contam-
inated by light from the nebula. Surprisingly_ Thomas et
al (1976), in observations obtained with the IR photometer
attached to the 1.25m telescope at Mr. Stromlo and Siding
Springs Observatory, find an infrared excess in the 8- to
MULTI-WAVELENGTH OBSERVATIONS OF THE PECULIAR RED GIANT HR 3126 255
a
l= 11
E-to
_. ,-,_
,_?o
E-I_
o
HR 3126
i J
o" o;, o', o_', o" o3',
WAV_t_NGTH _m)
Figure 2 Ultraviolet spectrum of HR 3126 (LWP 11744).
Note the presence of the Mg II ennssion feature and the
lack of other lngh temperature emission lines, which might
indicate a hot companion star/ionized nebula.
14- #m region, associated wlth carbon-rich materiah How-
ever, it is unclear what their beam size was and, therefore.
whether their spectra were contaminated by IC 2220. LRS
has a large aperature and probably observed the entire re-
gion of HR 3126, including IC 2220. Separate observations
of HR 3126 and IC 2220 need to be made m order to clarify
the existing, contradictory, data.
Figme 4 is a multi-wavelength plot of HR 3126, combin
ing all of the observations. In the Infrared, the points that
do not, fit on the curve are the LRS data. There appears
either to be some calibiation error, or a broad emission lea-
tree is present in the short wave infrared Fie observation
seems necessary.
The IRAS 601an adds(an profile (Figure 5) shows the
expected source extension. Tile full width at 10% maxi
mum corresponds to a shell dimension of 4.12 arc-minutes,
compared to 2.49 arc-minutes for the point source, Ceres
(see Stencel et al 1988 for a thorough discussion of Red
Giant/Supergiant infrmed source exten'_ions). At 375 pc,
this cot re_ponds to a shell of 0.45 pc diameter, or twice the
&ameter of the optical shell. Assunfing the current expan-
sion velocity, the age of the shell is approximately 3.2 x 104
years.
3. CONCLUSION
Several possibihties exist as to the location of ttR 3126
on the H-R diagram and to the formation mechanisms of
IC 2220:
• HR 3126 is a red giant branch star, having ejected
part of its envelope upon initiation of the first dredge-up
(at the base of the RGB) 32 000 years ago. This scenario is
consistent with the enhanced lithimn abundance observed.
However, the problem that remains is the mechamsm for
ejection: it is not clear that the fizst dredge up could power
ejection of such a large nebula.
• HR 3126 passed through a red giant ph_e and is now
evolving blueward from the top of the RGB. Comparatively
high mass loss and dust production during the previous
epoch and the eont,inued expansion of that (lust shell is the
present day IC 2220 nebula. Tile problem with this al-
ternative is the lithium, which should have been depleted
(according to Pilaehowski et al 1984) as the star neared
helium-core ignition (and beyond). The ejection mecha-
nism could be provided by the commencement of core he-
lium fusion_ either blowing-off a large amount of material
or leading to a mass loss rate approximately two orders of
magnitude greater than observed today.
• HR 3126 is at the top of the AGB, perhaps at the
beginning of the planetary nebula ejection phase. In this
scenario, IC 2220 can easily be explained by the period of
thermal pulses that AGI'I stars experience. Since the star
g"
7 ¢_=
'fl
z
-a L
E-_a a
fIR 312g
g , i ,
t"igm e 3
obtained by Doggett. Note the Ba II featme at 4554,5_
,," o'_ o_, o', 0', 0" o_
WAVELENGTII Otto)
Portion of the blue visual spectrum of HR 3126
possesses no Mira-hke qualities it t>robably is not in the
midst, of the AGB, but given the uncertainties in mass and
Mb_ ((M_ot) = -4".4 (Retmers, 1977)), HR 3126 could eas-
ily be at the base of the AGB or at the top. However, we
again run into the problem of non-depleted lithium abun-
ddllces.
In a recent paper by Whitelock and Catchpole (1985),
the three superqithium-rich stars observed are Mira vari-
ables, or AGB stars. Contrary to the Pilachowski et el
(1984) analysis, these observations support our hypothe-
sis that HI1 3126 is somewhere on the AGB. It should be
stressed that the effects of stellar evolution on lithium abun-
dances do not appear to be understood, but they are pIob-
ably an important clue to the evolutionary stage of a red
giant star. Could it be that lithimn becomes depleted on
the upper RGB but is again enhanced as the star moves
up the AGB (due to the second dredge-up and thermal
pulses)? Much more work needs to be done to determine
lit,hium's significance and variations with evolution. The
multiwavelength data appears to offer the possibility to test
atmospheric response to evolutionary changes.
256 J E PESC'E ET AL
...... i
o
HR 3126
O
o
O
o
tO
WAVEL,ENGTH (/*m)
Figure 4: Multiwavelength plot of HR 3126. Filled dia-
monds are IRAS point source fluxes, open diamonds mag-
nitudes from Gezari et M 1987, and filled circles are from
the LRS spectrum.
100
We are please to acknowledge NASA support for some
of this work under grants NAG5-816; NGT-70005 and JPL
957632, to the University of Colorado. In addition, the
I U.E. Regional Data Analysis Facility (operated for NASA
raider contract NAS5-28731) at Colorado provided con>
puter support fo_t_ich-wve are grateful. Helpful comments
from Dr. Carl Hansen are acknowledged.
P
c_
g
--tt -9 -7 -s -_ -1 i 3 5 7 0 tt
DISTANCE
Figure 5:60 ym Addscan l')rofile of HR 3126. The abc>,_a
is sic-minutes and the ordinate is \V m -2
4. REFERENCES
Boesgaard, A.M., 1970 Ap J 161, 1003.
Cohen, M.. Dopita, M., Schwartz, R. and Tmlens. A. 1985
Ap.J 297,702.
Dachs, J., 1972 Aatron. Astrophy_. 21,373.
Dachs, J., Isserstedt, J.. 1973 Astron. A.,trophys 23,241.
Dachs, J., Isserstedt, J., and Rahe, J., 1978 Astron. Astro
phys. 63, 353.
Gezari, D. Y., Schmitz, M., and Mead, J. M., 1987 "Catalog
of Infrared Observations," N.A.S.A. referencc publica
tion 1196.
Hartoog, M.R., 1978 PubI.A S.P. 90, 167.
Hmnphries, R. M., and Ney, E. P., 1974 Aatron. Astrophy_
30, 159.
Jura, M., aacoby, G., 1976 Aatrophy_. £ett. 18, 5.
Ney. E. P., and Stein, W A., 1968 Ap. J. £ctter_ 152, L21.
.,Nu>sbaumer, H., and Stencel. R. E., 1988 in "'Exploring
the Universe with the IUE Satellite", ed. Y. Kondo (D.
Reidcl, Dordrecht). 203.
Pctkms, H. G., King, D J., Scarrott, S. M., 1981 Mon.
Not R. Aatron. Soc. 196, 403.
Pllachowski. C. A , Mould, J. R., and Siegel, M. a , 1984 .
J. Le.ttcrs 282, L17.
Reimers. D., 1977 A_tron. Aatrophys. 54,485.
Stenccl, R. E.. Pesce, J. E., and Bauer, W. H., 1988 dstron.
J. 95, 141.
Thomas, J. A., Robinson, G., Hyland, A. R., 1976 Mon.
Not. R. astr Soc. 174. 711.
\Vhm_qock, P. A, Catchpole, R. M., 1985 Mort. Not R.
astr. Soc. 212,873.


Multi-wavelength observations of the peculiar red giant HR 3126

Multi-wavelength observations of the peculiar red giant HR 3126

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