Two projects in conjunction with the International Ultraviolet Explorer Satellite are discussed. These projects were to: (1) study the properties of the H2 and H2+ quasi-molecular absorption features at lambda lambda 1600 and 1400 in the ultraviolet spectra of the hydrogen-rich DA white dwarfs and to search for additional spectroscopic features in the spectra of these stars; and (2) use the ultraviolet portion of the spectrum of the peculiar rare earth-rich late F type star, HR6560 (HD159870), to establish whether or not the element abundance anomalies are produced in conjunction with its having a white dwarf binary companion. The data show that HR6560 is probably not associated with any hot subluminous or degenerate star

Wegner, Gary A.

English

NASA Technical Reports Server

Semi-Annual Report 
f o r  NASA Grant NAG5-287 
Nat ional  Aeronautics and Space Adminis t ra t ion 
IUE Guest Observer Program 
Goddard Space F l i g h t  Center  
Greenbelt,  MD 20771 
A Study of t h e  U l t r a v i o l e t  Absorptions 
i n  t h e  Spectra  of DA White Dwarfs 
and 
U l t r a v i o l e t  Spectra  of t h e  S t a r  HR6560 
Submitted by: Gary A. Wegner 
Associate Professor  
S.S. # 
Depart cs 
and Astronomy 
Phone: 603-646-3329 
Trustees  of Dartmouth College 
PO Box 7 
Hanover, NH 03755 
Duration: One Year 
Ju ly  1, 1986 t o  December 31, 1986 
~ r i n c i ~ a i  Inves t iga to r  
Date 
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AESOf iPTICBS I@ 'Xhk S P E f T B i  CI f a  tdHXTE 
CFaPPS AH@ UETRBVXOEE3 SPECIIiA CP IRE ST48 
Hi36549 S e ~ i a a ~ u a l  Bapozt, 3 JlaB, - 31 Dee, Unclas 
1586 [BartaaontB Cell,) "B p CSCL 038 63/89 43344 
https://ntrs.nasa.gov/search.jsp?R=19870009040 2020-03-20T11:25:28+00:00Z
J 
.* 
ABSTRACT 
During t h e  l a s t  semi-annual per iod ,  t h e  r e s e a r c h  work 
connected wi th  Grant NAG5-287 from t h e  Nat iona l  Aeronaut ics  and 
Space Adminis t ra t ion has been t o  c a r r y  out  two p r o j e c t s  i n  
conjunct ion wi th  t h e  I n t e r n a t i o n a l  U l t r a v i o l e t  Explorer 
S a t e l l i t e .  These are:  
H2+ quasi-molecular absorpt ion f ea tu res  a t  hhl600 and 1400 i n  t h e  
u l t r a v i o l e t  s p e c t r a  of t h e  hydrogen-rich DA whi te  dwarfs  and t o  
search  f o r  a d d i t i o n a l  spectroscopic  f e a t u r e s  i n  t h e  s p e c t r a  of 
t h e s e  stars,  and ( 2 )  use  t h e  u l t r a v i o l e t  p o r t i o n  of t h e  spectrum of 
t h e  p e c u l i a r  rare ea r th - r i ch  l a t e  F t ype  s t a r ,  HR6560 (HD159870), 
t o  e s t a b l i s h  whether o r  not  t h e  element abundance anomalies are 
produced i n  conjunctio'n with i t s  having a white  dwarf b ina ry  
companion. The data show t h a t  HR6560 i s  probably no t  a s s o c i a t e d  
with any hot  subluminous o r  degenerate s t a r .  
(1) t o  study t h e  p r o p e r t i e s  of  t h e  H 2  and 
2 
INTRODUCTION 
The purpose of t h e  DA white dwarf research  being repor ted  here  
has been t o  complete sys temat ic  observa t ions  of t h e  u l t r a v i o l e t  
s p e c t r a  of t h e  hydrogen-rich DA w h i t e  dwarfs w i t h  the  
International Ultraviolet E x p l o r e r  ( I U E )  . T h i s  was o r i g i n a l l y  
proposed a s  a fol low up on thw work repor ted  i n  Nelan and Wegner 
(1985) t h a t  t h e  s t r o n g  found near hh1600 and 1400 i n  t h e  s p e c t r a  of 
t h e  coo le r  examples of t h e  DA whited dwarfs a r e  absorp t ions  
produced by t h e  H2 and H2' quasi-molecules. The observat ions of 
a d d i t i o n a l  DA white dwarfs progressed w e l l  and were completed 
dur ing  t h e  pe r iod  recovered by t h i s  r epor t  and t h e  new observa t ions  
obta ined  w i t h  t h e  I U E  under  t h e  auspices  of NASA Grant NAG5-287 
a r e  summarized i n  Table I .  
Observations of t h e  u l t r a v i o l e t  spectrum of t h e  p e c u l i a r  s t a r  
HR6560 (HD159870) were a l s o  completed.  These along w i t h  
measurements of t h e  comparison s t a r ,  HD141004 a r e  summarized i n  
Table 2 .  The o p t i c a l  spec t r a  of HR6560, s tud ied  i n  co l l abora t ion  
w i t h  C .  R .  Cowley who had obtained ground based s p e c t r a  of t h e  
o b j e c t ,  showed t h a t  t h i s  s t a r  was of l a t e  s p e c t r a l  type ,  about F8, 
but  has  a spectrum r i c h  i n  r a r e  e a r t h  l i n e s ,  s i m i l a r  t o  t h e  Ap 
s t a r s .  One then asks  t h e  question a s  t o  whether t h e  abundance 
anomalies a r e  due t o  i n t r i n s i c  s t e l l a r  phenomena o r  a r i s e  from 
m a t e r i a l  from an evolved s t a r  being dumped onto t h e  ou te r  l a y e r s  of 
HR6560 a s  i n  some o b j e c t s ,  e.g. t h e  barium s t a r s .  
... 
3 
11. OBSERVATIONAL RESULTS 
The IUE u l t r a v i o l e t  s p e c t r a  of t h e  DA white dwarfs have 
continued t o  reveal t h e  presence of t h e  n l 6 0 0  and 1400 absorp t ions  
i n  the coo le r  examples of t h i s  class of stars. Some of t he  newer 
s p e c t r a  are shown i n  Figure 1 where t h e  spectra of t h e  stars are 
arranged approximately i n  order  of e f f e c t i v e  temperature  according 
t o  ( B - V ) .  There it can be seen t h a t  t h e  u l t r a v i o l e t  abso rp t ions  
are f a i r l y  ubiqui tous  i n  the spec tyra  of t he  DA white dwarfs and 
tha t  there is a marked temperature dependance. 
A t  p re sen t ,  p rog res s  i s  being made towards sys t ema t i ca l ly  
modelling a l l  of t h e  DA spec t r a  obtained for t h i s  p r o j e c t  
c o l l a b o r a t i v e l y  w i t h  D r .  E.  P. Nelan of the  Computer Sciences 
Corporation a t  the Space Telescope Science I n s t i t u t e .  Earlier work 
on model atmospheres and the subsequent f i t t i n g  of t h e  s p e c t r a  of a 
f e w  objects has been described i n  previous reports and i n  Nelan and 
Wegner (1985).  B r i e f l y ,  t h i s  work makes u s e  of a computer code 
s p e c i f i c a l l y  developed by Nelan t o  s tudy  w h i t e  dwarf atmospheres 
and employs t h e  absorp t ion  c o e f f i c i e n t s  der ived by Sando & 
Wormhoudt (1973) and Stewart ,  Peek, and Cooper (1973) t o  model t h e  
u l t r a v i o l e t  quasi-molecular f ea tu re s  near  n l 6 0 0  and  1400. T h i s  
work should be completed during t h e  upcoming year  of 1987. One of 
t h e  primary ques t ions  t o  be answered is whether or not t h e  
u l t r a v i o l e t  absorp t ions  def ine a simple seqquence t h a t  only depends 
on t h e  temperature  of t h e  s t a r .  
The u l t r a v i o l e t  p o r t i o n  of the  continuum s p e c t r a l  energy 
d i s t r i b u t i o n  of HR6560 i s  shown i n  Figure 2 .  This  is based on t h e  
4 
r e c e n t l y  obta ined  low re so lu t ion  LWP and SWP images. I t  i s  p o s s i b l e  
t o  compare t h i s  with t h e  images of t h e  GO s t a r  H D 1 4 1 0 0 4  used f o r  
comparison and with o the r  s t a r s  of s p e c t r a l  type i n  t h e  range FO t o  
G O ,  publ ished i n  t h e  IUE U l t r a v i o l e t  S p e c t r a l  A t l a s  by Wu e t  
a l .  (1983) .  The over lap  i n  t h e  LWP and SWP s p e c t r a  a r e  not  
p a r t i c u l a r l y  good f o r  HR6560, but from t h i s ,  it can be seen t h a t  
t h e  energy d i s t r i b u t i o n  of HR6560 matches well  w i t h  o b j e c t s  of 
s p e c t r a l  c l a s s  near  F8. This i s  somewhat h o t t e r  than  t h e  s p e c t r a l  
type of F8 determined by Cowley ( 1 9 7 6 )  and Cowley & Bidelman 
( 1 9 7 9 ) ,  but  c e r t a i n l y  within t h e  range admissible  a s  t h e  spectrum 
of t h e  o b j e c t  i s  complicated b y  t h e  presence of r a r e  e a r t h  l i n e s  
and has  l e d  t o  somewhat d i f f e r e n t  poss ib l e  hypotheses about t h e i r  
formation.  With t h e  present  data,  it appears t h a t  HR6560 i s  not a 
composite o b j e c t  w i t h  a hot subluminous companion. The absence of 
t h i s  companion w i l l  have important impl ica t ions  on t h e  o r i g i n  of 
i t s  p e c u l i a r  m e t a l l i c  l i n e  spectrum. With t h e  p r e s e n t l y  a v a i l a b l e  
information,  a cause i n t r i n s i c  t o  t h e  s t a r  i t se l f  seems a more 
l i k e l y  explana t ion .  
111. CONCLUSIONS 
During t h e  las t  ha l f  of 1 9 8 6 ,  work has continued t o  be 
conducted on white dwarf s t a r s .  The bas i c  r e s u l t s  of t hese  
i n v e s t i g a t i o n s  can be summarized b r i e f l y  a s  fo l lows:  
1) Observations have been completed on t h e  cool  DA w h i t e  
dwarfs and they  a l l  show t h e  presence of t h e  hh1400 and 1600  
a b s o r p t i o n s .  
,. 
5 
2 )  T h e  u l t r a v i o l e t  spectrum of t h e  pecu l i a r  l a t e  F type  
metall ic l i n e  star H R 6 5 6 0  do no t  s h o w  any evidence f o r  t h e  presence 
of a hot  subluminous c o m p a n i o n .  
REFERENCES 
C o w l e y ,  A .  P .  1976, P u b l .  A s t r o n .  SOC. P a c . ,  88, 95. 
C o w l e y ,  A .  P .  and B i d e l m a n ,  W .  P .  1979, P u b l .  A s t r o n  Soc. P a c . ,  
91, a3 
N e l a n ,  E .  P .  and Wegner, G .  1985, A s t r o p h y s .  J. ( L e t t e r s ) ,  
289, ~ 3 1 .  
Sando, K .  M .  and Wormhoudt, J .  C . ,  1973, P h y s .  R e v .  A ,  7, 1889. 
S t e w a r t ,  J .  C., Peek ,  J .  M., and C o o p e r ,  J., 1973, A s t r o p h y s .  J., 
179, 983. 
Wu, C . - C . ,  e t  a1.,1983, The IUE U l t r a v i o l e t  S p e c t r a l  A t l a s ,  
NASA N e w s l e t t e r  N o .  22, I U E  O b s e r v a t o r y :  NASA G o d d a r d  Space 
F l i g h t  C e n t e r .  
.. 
6 
Tab le  I 
DA White D w a r f s  O b s e r v e d  w i t h  IUE under  t h e  auspices of G r a n t  
NAG5-287 
( O c t o b e r  1, 1985 - A p r i l  30, 1986) 
White D w a r f  D a t e  of I U E  Image 
o r  name Obse rvat i o n  N o .  SDectral TvDe 
BPM6082 
BPM6082 
G210-36 
G210-36 
LP 5 50- 5 
G116-52 
G116-52 
LP 5 50- 5 
LTT7987 
LTT7987 
G185-32 
LHS2333 
LHS2333 
L970-30 
L970-30 
G148-7 
LHS3254 
N o v .  22, 1985 
N o v .  22, 1985 
N o v .  22, 1985 
N o v .  2 2 ,  1985 
N o v .  23 ,  1985 
N o v .  23, 1985 
N o v .  23, 1985 
N o v .  23 ,  1986 
A p r .  16, 1986 
A p r .  16, 1986 
A p r .  16, 1986 
A p r .  16, 1986 
A p r .  16, 1986 
A p r .  17, 1986 
A p r .  17, 1986 
A p r .  17, 1986 
A p r .  17, 1986 
SWP27161 
LWP7171 
SWP2 7 162 
LWP7172 
SWP27163 
LWP7176 
SWP27167 
LWP7177 
LWP8041 
SWP28181 
LWP8042 
LWP8043 
SW28182 
SWP28184 
LWP8046 
SWP28185 
LWP8047 
DA 
DA 
DA 
DA 
DA 
DA 
DA 
DA 
DA 
DA 
DA 
DA 
DA 
DA 
DA 
DA 
DA 
7 
Table I1 
IUE Observations Obtained of HR6560 and Associated Objects for 
Grant NAG5-287 
(October 1, 1985 - April 30, 1986) 
Date of IUE Image Spectral Res. 
Star Observation No. Type Model 
HD15 98 70 Nov. 23, 1985 LWP7173 F8 Low 
HD15 9870 Nov. 23, 1985 SWP27164 F8 Low 
HD15 98 70 Nov. 23, 1985 LWP7174 F8 High 
HD15 98 7 0 Nov. 23, 1985 SWP27165 F8 L o w  
HD141004 April 1’7, 1985 SWP28187 GO Low 
HD14 10 04 April 17, 1985 LWP804 9 GO Low 
G
116-52 
0
.0
7
 
I
F
F
 
II 
L
T
T
7
9
8
7
 0.07 
L970-30 
0
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6240-51 
0
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210-36 
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A Study of the Ultraviolet Absorptions in the Spectra of DA White Dwarfs and Ultraviolet Spectra of the Star HR6560

Systematic investigations of the ultraviolet spectra of the hydrogen-rich white dwarfs were conducted with the International Ultraviolet Explorer satellite (IUE). This is to follow up on the work reported in Nelan and Wegner (1985) that the strong absorptions found earlier near lambda lambda 1600 and 1400 (cf. Greenstein 1980; Wegner 1982 and 1984, b) in the spectra of the cooler DA are absorptions produced by the H2 and H2(+) quasi-molecules. Observations of new DA white dwarfs obtained with the IUE are summarized

Wegner, G. A.

Semi-Annual Report
for NASA Grant NAG5-287
National Aeronautics and Space Administration
IUE Guest Observer Program
Goddard Space Flight Center
Greenbelt, MD 20771
A Study of the Ultraviolet Absorptions
in the Spectra of DA White Dwarfs
Submitted by: Gary A. Wegner
Associate Professor
S.S. 
Department of Physics
and Astronomy
Phone: 603-646-3329
Trustees of Dartmouth College
PO Box 7
Hanover, NH 03755
Duration: One Year
April 1, 1985 to September 30, 1985
^ YNASA-CR- 177276) A S I U D Y OF IHE U L T R A V I O L E T N86-28038
AESOEPTIONS IM TEE SPFCTBA OF IA W H I T E
D W A R F S Semiannual Report , 1 Apr. ,- 30 Sep. .
1985 {Dartmouth Coll.) 14 p EC A02/MF A01 Dnclas
CSCL 03A G3/89 43125
Gary A.
Principal Investigator
Date ^^ »^. /a
https://ntrs.nasa.gov/search.jsp?R=19860018566 2020-03-20T14:19:42+00:00Z
ABSTRACT
During the interval of time, April 1, 1985 to September 30,
1985, the research effort connected with Grant NAG5-287 from the
National Aeronautics and Space Administration has been to study the
properties of the XX1600 and 1400 absorptions in the ultraviolet
spectra of the hydrogen rich DA white dwarfs using the
International Ultraviolet Explorer satellite and to search for
additional new spectroscopic features, the observed properties of
which can be.matched quite well with the absorptions of the H2 and
H2+ quasi-molecules.
I. INTRODUCTION
The purpose of the research reported here has been to
continue systematic observations of the ultraviolet spectra of the
hydrogen-rich DA white dwarfs with the International
Ultraviolet Explorer satellite (IUE) . This is to follow up on
the work reported in Nelan and Wegner (1985) that the strong
absorptions found earlier near XX 1600 and 1400 (Cf. Greenstein
1980; Wegner 1982 and 1984a,b) in the spectra of the cooler DA are
absorptions produced by the H£ and H2+ quasi-molecules.
Observations of new DA white dwarfs summarized in Table I were
obtained with the IUE under the auspices of NASA grant NAG5-287.
Some of the results have been presented as papers and are listed in
Appendix I. .
II. OBSERVATIONAL RESULTS
These ultraviolet spectra of DA white dwarfs with the IUE
have revealed the existence of a number of ultraviolet
spectroscopic features that were not previously suspected from the
classical ground based observations in the visible. This began
with Greenstein's (1980) discovery of the X1400 feature in the
spectrum of the well studied Teff = 16,900 °K DA star 40 Eri B.
Subsequently/ this depression was observed in the ultraviolet
spectra of numerous other DA white dwarfs with varying degrees of
Table I
Objects Observed with IUE under the Auspices of Grant NAG5-287
(July 11, 1983-July 29, 1985)
White Dwarf/
Coordinates
L481-06
L481-06
BPM1266
BPM1266
L19-2
L19-2
0039+04
0039+04
0039+04
GD279
GD279
G2-17
G2-17
G8-8
G8-8
GD64
GD64
L870-2
L870-2
BPM2819
BPM2819
BPM2819
L997-21
L997-21
BPM2819
BPM2819
BPM2819
LFT158
LFT158
LFT158
G240-51
LHS2594
LHS2594
G240-51
Date of
Observat
Jul.
Jul.
Jul.
Jul.
Jul.
Jul.
Jul.
Jul.
Jul.
Jul.
Jul.
Jan .
Jan.
Jan .
Jan .
Jan .
Jan.
Jul.
Jul.
Jul.
Jul.
Jul.
Aug.
Aug.
Aug.
Aug.
Aug.
Jul.
Jul.
Jul.
Jul.
Jul.
Jul.
Jul.
11,
11,
11,
11,
11,
11,
11,
11,
11,
11,
11,
22,
22,
22,
22,
22,
22,
1,
1,
2,
2,
2,
29,
29,
30,
30,
30,
29,
29,
29,
29,
29,
29,
29,
IUE
i on
1983
1983
1983
1983
1983
1983
1983
1983
1983
1983
1983
1984
1984
1984
1984
1984
1984
1984
1984
1984
1984
1984
1984
1984
1984
1984
1984'
1985
1985
1985
1985
1985
1985
1985
Image
No.
SWP20441
LWR16327
SWP20442
LWR16328
SWP20443
LWR16329
SWP20444
LWR16330
SWP20445
SWP20446
LWR16331
LWP2695
SWP22077
LWP2696
SWP22078
LWP2697
SWP22079
LWP3695
SWP23380
LWP3697
LWP3698
SWP 23381
SWP23819
LWP4102
SWP23820
LWP4103
SWP23821
LWP6516
SWP26503
LWP6517
SWP26504
LWP6518
SWP26505
LWP6519
Spectral Type,
DA
DA
DA
DA
DA
DA
Sd
sd
sd
DA
DA
DA
DA
DA
DA
DA
DA
DA
DA
DA
DA
DA
DA
DA
DA
DA
DA
DA
DA
DA
DA
DA
DA
DA
4-
strength (Wegner 1982; 1984a,b; Sion et al. 1983). Basically, the
observations show that A.1400 is prominant at effective temperatures
near 13,000 °K and decreases in 'equivalent width for higher
reaching the limit of detectability with the low resolution mode of
IUE near Teff = 19000 °K (Wegner 1984a) .
For lower temperatures, i.e. Teff < 13000 °K, an additional
clue was the discovery of the feature near X1600 which begins to
dominate the spectra of DA stars for Teff < 12000 °K. Although
A.1600 occurs in the spectra of many DA stars hotter than this, its
strength drops rapidly with increasing Teff. Holm et al. (1983;
1985) reported this and it has been further described in
Wegner (1984a,b) . Some examples of DA stars of different effective
temperature that show these ultraviolet depressions in their
spectra are given in Figure 1 .
A number of earlier theories regarding the origin of the
XX1400 and 1600 absorptions were proposed, as summarized in Wegner
(1984a,b), but all of them run into serious difficulties when
considered in detail quantitatively. However, a quite natural
explanation is that the observed ultraviolet depressions are
produced by the quasi-molecular features of hydrogen and this
identification was published in Nelan and Wegner (1985) . Further
details on the model atmospheres employed can be found in Nelan
-1 I I I 111 I I Til I 1 I I I I 1 I I I I I I I I
§
o
O>
o
-7
log g: 8.0
-4
CO
c.
O -5
o
O)
-7
T = 10000 K
eff
( a ) ( b )
FIG. I;- Ultraviolet spectral energy .distributions from -Ne Ian anfi;Wegner ,(1985); .(a)
Computed energy distributions" for pure hydrogen models'with log g = 8.0 for
Teff = {«} 12000.°K, (b)-U.OOO OK, ..("c) .9500 °K. Onl-y continuum, points a-re
.plotted although the calculstr.ons were carried: out..for fully, line blanketed
models. • - . • . . . . . . .
(b) The same as Fig. lOa, but at fixed Teff and log g = (a) 7.4, (b)
. 8.0, (c) 8.6.
-3
-4
§-5
o
U - 6
CO
o
-7
M I I i I I I i i i i i e i i i i i i i i i i t I i Ml TIi
L481-60
Teff = 10 50° °K
logg = 8.0
3
^ iS
ra
u
w 2
0)
G8-8
Te f f=13000 °K
log g = 8.0
1400
1/A ( P ')
(c)
1500
( d )
1800 2000
(c) Comparison between the observed energy distribution of white dwarf L481-60
(WD1544-37) from Wegner (1984b) Shown as open circles and a pure H model wii-h
Teff an<^ Io9 9" as indicated.
(d) The same as Fig. lOc, except for the star G8-8 (WD0401+25).
(1985) which is a Ph. D. thesis partially based on the data
obtained for this project. Holm et al. (1985) were the first to
suggest A.1600 as the resonance broadening of the Ly aline.
Koester et al. (1985) have independently presented conclusions
similar to those reached in Nelan and Wegner (1985).
Quasi-molecular features are a well known spectroscopic
effect, but one little used in astrophysics. In the case of the DA
stars, the approach of two ground-state hydrogen atoms perturbs the
n=l and n=2 energy levels giving rise to the LyCC line broadening.
However, for small interatomic differences, the conventional
description for resonance broadening (Jeffreys 1968) is
inapproptiate. In Nelan and Wegner (1985), the semi-classical
theory of Sando and Wormhoudt (1973) was applied to the hydrogen
quasi-molecule. The maximum of the predicted features occurs near
X1623. Similarly, the H2+ quasi-molecule produces the strong
satellite band to Ly a at X1404.9 with other weaker ones near
XX1233 and 1240. The absorption profile for this from Stewart,
Peek, and Cooper (1973) has been included in the calculations.
The spectral energy distributions from the resulting model
atmospheres reported in Nelan and Wegner (1985) agree well with the
observed properties of XX1600 and 1400. In this study, it was found
that the use of fully line blanketed models was important. The
main results are summarized in Figure I. In Figure la, the
temperature dependance at log g = 8 can be seen. At relatively low
Teff -^1600 is strong, but fades rapidly in strength for
temperatures above 11000 °K with increasing hydrogen ionization.
In agreement with the observations, the hydrogen ion
quasi-molecular feature near X.1400 persists to higher Teff since it
is governed by both the proton and neutral hydrogen densities.
Figure Ib shows the dependance of M,1400 and 1600 on gravity for
Teff fixed at 10000 °K. Figures Ic and Id compare the results from
our models with the observed spectra of two stars from which it is
concluded that in nearly all cases studied so far, pure hydrogen
atmospheres without metals agree well with the observations.
III. FURTHER OBSERVATIONS OF ULTRAVIOLET FEATURES IN THE SPECTRA OF
THE DA WHITE DWARFS
Work on the H2 and H2+ quasi-molecular features in the
ultraviolet spectra of the cool DA stars by both obtaining new
obsaervations and producing more sophisticated model atmospheres is
continuing. There appears to be ample room for such work because a
large enough sample of interesting cool DAs that can be reached
with the IUE still exists and in the spectra of some of the
objects already studied, additional spectroscopic features have
been identified which it is hoped that the model atmospheres can
eventually be used to explain.
Two examples of such objects recently observed and still under
analysis are shown in Figures 2 and 3. The first star, L870-2
(=EG11), has been known to have an anomalously large radius on the
basis of its photometry and trigonometric parallax as discussed in
Schulz and Wegner (1980) who found Teff = 7500 °K and log R/RQ =
-1.5. Greenstein, Boksenberg, et al. (1977) have also commented
that Ha shows an emission core. This object is also discussed in
Greenstein (1984) . Figure 2 combines recent JUE ultraviolet
spectra with ground based data from Oke (1974). None of the pure or
mixed hydrogen and helium models from Nelan and Wegner (1985) can
fit the energy distribution. One possible solution to this puzzle
is that L870-2 is composite.
The second star, G2-17, has been described by Wegner and Nelan
(1984) and its energy distribution can be fit with a Teff = 8000 °K
hydrogen model. Besides showing the strong cutoff at X.1600,
illustrated in Figure 3, this object displays a broad shallow
depression near A.2500. Also L870-2 seems to show a feature near
XlSOO. Consequently, the search for additional ultraviolet
spectroscopic features should be continued and it is intended to
continue to utilize the IUE to systematically search the
u>
o
-24
-25
-26
-27
-28
-25
?-26
-27
L 8 7 0 - 2
0
0 I 2 3 4 5 6 7 8
FIG. 2 . -
Combined visual and IUE ultra-
violet low resolution spectra
of the cool DA L870-2. The
solid curve is visual data
from Oke (1973). Open circles
denote LWP data and filled
circles are for the SWP.
i i i i n r n
X2500
AI600
o
° •• „
G2-I7
i i i i i r i
2 3 4 5 6 7 8
FIG. 3 - The same as Fig. 13, except crosses denote Strb'mgren
photometry from Wegner (1983a). The position of the
suspected feature near A 2500 is indicated-.
10
ultraviolet spectral region of the DA white dwarfs in order to
understand the presently known quasi-molecular absorptions and to
search for new ones.
11
REFERENCES
Greenstein, J. L. 1980, Astrophys. J., 241, L89.
Greenstein, J. L. 1984, Astrophys. J., 276, 602.
Greenstein, J. L., Boksenberg, A., Carswell, R., and Shortridge, K.
1977, Astrophys, J.t 212, 186.
Holm, A. V., Panek, R. J., Schiffer, F. H., Ill, and Kemper, E. E.
1983, Bull. Amer. Astron. Soc., 15, 646.
Holm, A. V., Panek, R. J., Schiffer, F. H., Ill, Bond, H. E., and
Grauer, A. D. 1985, Astrophys. J., 289, 774.
Jeffreys, J. T. 1968, Spectral Line Formation, (Blaisdell Publ.
Co.: Waltham, Mass.), p. 85.
Koester, D., Weidemann, V., Zeidler-K.T., E.-M., and Vauclair, G.
1985, Astron. Astrophys., 142, L5.
Nelan, E. P. 1985, Ph. D. Thesis, Dartmouth College.
Nelan, E. P. and Wegner, G. 1985, Astrophys. J., 289, LSI.
Oke, J. B. 1974, Astrophys. J. Suppl., 27, 21.
Sando, K. M.'and Wormhoudt, J. C. 1973, Phys. Rev. A., 9, 1103.
Schulz, H. and Wegner, G. 1980, Astron. Astrophys., 94, 272.
Sion, E. M., Wesemael, F., and Guinon, E. F. 1984, Astrophys. J.,
279, 758.
Stewart, J. C., Peek, J. M., and Cooper, J. 1973, Astrophys. J.,
179, 983.
Wegner, G. 1982, Astrophys. J., 261, L87.
Wegner, G. 1984a, Astron. J., 89, 1050.
Wegner, G. 1984b, Astrophys. J., 284, L43.
Wegner, G. and Nelan, E. P. 1984, Bull. Amer. Astron. Soc., 16,
510.
12
APPENDIX I
Summary of Research Publications
The following is a list of research papers published since the
last Semi-annual Report. All investigations were supported at
least partially by NASA Grant NAG5-287. Reprints of the published
papers are attached to this document.
A. Published Papers
Liebert, J., Wesemael/ F., Sion, E.M., and Wegner, G., "GD323, A
White Dwarf with a Stratified H/He Atmosphere," Astrophys. J.,
277, 692 (1984) .
Nelan, E.P. and Wegner, G., "Identification of the 1400 and 1600 A
Features in the Ultraviolet Spectra of DA White Dwarfs,"
.Astrophysicsf J., 289, LSI, (1985)
Wegner, G., "The Absorption Near 1400 A in the Spectra of
Additional White Dwarfs," Astron. J.. 89, 1050 (1984).
Wegner, G., "The Discontinuity near 1600 A in the Spectral of DA
White Dwarfs," Astrophys. J. (Letters), 281, 243 (1984).
Wegner, G. and Yackovich, F.H., "The Cool White Dwarf Stein 205
IB," Astrophys. J.. 275, 240 (1983).
B. Papers being Submitted for Publication or in Preparation:
Wegner, G. and Nelan, E.P., "Ultraviolet and Visual Spectroscopy of
DB White Dwarf."
C. Abstracts or Titles of Papers Presented at Meetings:
Wegner, G. and Nelan, E.P., "Ultraviolet and Visual Spectroscopy of
DB White Dwarfs," Bull. Amer. Astron. Soc., 16, 510 (1984).
Nelan, E.P. and Wegner, G., "Ultraviolet Features in the Spectra of
Cool DA White Dwarfs," Bull. Amer. Astron. Soc.. 16, 510
(1984) .
13
Wegner, G. and Nelan, E.P., "Identification of the 1400 and 1600 A
Features Observed in the Ultraviolet Spectra of DA White
Dwarfs," Bui. Amer. Astron. Soc.. 16, 894 (1984).
D. Ph.D. Thesis Completed:
Nelan, E.P., "Ultraviolet Spectra of DA White Dwarfs," Dartmouth
College, May, 1985.


A Study of the Ultraviolet Absorptions in the Spectra of DA White Dwarfs and Ultraviolet Spectra of the Star HR6560

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