The outburst for a nova discovered in Nov. 1987 and followed since then is summarized. Although it was possible to observe it with the IUE at maximum, its ultraviolet energy faded rapidly, and after the first 2 weeks it was impossible to observe it at IUE wavelengths. It is observed to form a thick dust shell and is in the nebular stage

Ferland, Gary

Gallagher, J. S.

Gehrz, Robert D.

Sonneborn, G.

Sparks, Warren M.

Starrfield, S.

Stryker, L. L.

Wade, R.

Wagner, R. M.

Williams, R. E.

English

NASA Technical Reports Server

5189- 107 1 1 171
OPTICAL AND ULTRAVIOLET OBSERVATIONS OF NOVA VUL 1987
S. Starrfield and L. L Stryker
Department of Physics, Arizona State University
G. Sonneborn
IUE Observatory, Goddard Space Flight Center
Warren M. Sparks
Applied Theoretical Physics Division
Los Alamos National Laboratory
R. M. Wagner and Gary Ferland
Department of Astronomy, Ohio State University
J. S. Gallagher
Lowell Observatory
R. Wade
Steward Observatory, University of Arizona
R. E. Williams
Cerro Tololo Interamerican Observatory
Robert D. Gehrz and Edward P. Ney
Department of Astronomy, University of Minnesota
Scott Kenyon
Center for Astrophysics, Harvard University
James W. Trurnn
Department of Astronomy, University of Illinois
C. - C. Wu
Space Telescope Science Institute
ABSTRACT
We present a brief summary of the outburst for a
nova that was discovered in November 1987 and has
been followed since that time. Although we were able
to observe it with the IUE at maximum, its ultraviolet
energy faded rapidly and after the first two weeks we
were no longer able to observe it at IUE wavelengths.
It was observed to form a thick dust shell and
currently is in the nebular stage.
1. Introduction
This currently bright novae was first detected in
outburst on November 15. 1987 (UT: IAU Announcement
Card #4488). The position of 6the nova was found tobe at cz - 19 h 02 m 32. s and - +21041'39. - (1950.0).
These co-ordinates were determined by Gehrz (IAU
Announcement Card #4501). By coincidence, one of us
(S. S.) was at the I_.U_E_Observatory to obtain ultravio-
let data on bright novae. We obtained a very underex-
posed LWP spectrum at this time and about one week
later we obtained two sets of slightly underexposed
SWP and LWP spectra two nights apart. After
analysis, we found that the ultraviolet energy had
decreased by nearly a factor of 2 between these two
nights. This rate of decline is unprecedented when
compared to the other novae that have been observed
in the earliest stages of their outburst. In fact, the
rapid rate of decline in the ultraviolet was more like
that of SNi987A than that of a typical "fast" nova.
Over the same time period, we also obtained optical
and infrared data. Gin_a did not detect the nova but
this was probably caused by the low energy cutoff of
the satellite of 2 kev (Dupree 1988, private communica-
tion).
2. Ultraviolet and Optical Observations
In this paper we report on our observations of this
nova over the first four months of its outburst. The
optical data showed major changes in line intensities
and line ratios over the first two weeks. As already
mentioned, the first attempt to obtain a spectrum of
this nova was during the second half of the US 2 shift
on November 16, 1987. The exposure times were
chosen based on our previous experience with novae at
maximum. However, because we were able to observe
this nova so soon after discovery, we did try to be
conservative and not overexpose the image. To our
amazement, there was no detection in the SWP camera
and only a faint image was present in the LWP camera.
Unfortunately, there was not enough time left in the
shift to obtain additional exposures.
We were granted additional time on Monday, November
23, 1987 and Sonneborn obtained the SWP and LWP
spectra shown in Figure la and lb. The SWP image is
still underexposed after an exposure time of 10
minutes. The LWP image is better but required 2
minutes. Both of these times are long for a nova
observed at a visual magnitude, determined from the
FES, of about 8.2m. The appearance of the spectra is
not unusual, as compared to other early spectra of
novae, although the continuum appears somewhat
flatter than those shown in the paper by Stryker et al.
(1988; these proceedings).
On November 25, 1987 there was a false report of a
supernova in M31. The IUE satellite mobilized to
observe it but found no sign of any supernova at the
reported location. By that time, it was too late to
return the shift to the scheduled astronomer and it
was decided to obtain two more exposures of Nova Vul
87. Sonneborn increased the exposure times by a large
A Decade of UV Astronomy with IUE, Prec. Celebratory Symposium, GSFC, Greenbelt, USA, 12-15 April 1988, ESA SP-281, Vol. 1 (June 1988)
https://ntrs.nasa.gov/search.jsp?R=19890001340 2020-03-20T06:08:45+00:00Z
172 S STARRF1ELD ET AL
factor (SWP:. 50min; LWP: 2min 30s) but again found
that the spectra were underexposed• These spectra are
shown in Figure 2a and 2b and a glance at both scales
shows why we were being continuously fooled in
determining an optimum exposure time. The nova had
faded by a factor of 2 in the two nights separating
these two series of images. No previous nova has
faded so fast in the ultraviolet and this rapid decline
is analogous to the behavior of SN 1987A in the first
observations (the supernova declined much more
rapidly, of course)•
Almost immediately after the report of the discovery,
Garcia and co-workers at the Whipple Observatory
began obtaining spectra. They found strong P-Cygni
profiles in Ha but all of the other hydrogen lines were
in absorption (IAU Announcement Card #4489). We
(Wade and Starrfield) obtained our first spectrum at
the 2.1-m telescope of the Steward Observatory on the
evening of the 30th of November 1987 and found that
P-Cygni profiles were apparent for some of the strong
lines• This spectrum is shown in Figure 3. In
addition, a continuing series of optical spectra were
obtained by Wagner at the 1.8-m Perkins Reflector of
the Ohio Wesleyan and Ohio State Universities at the
Lowell Observatory (IAU Announcement Card ;,4501).
One interesting feature of the spectral evolution of
this nova is that the initial Whipple Observatory
spectra showed deep P-Cygni profiles which gradually
disappeared for a short time (Garcia 1987, private
communication). However, they were again obvious by
the time that we obtained the spectrum shown in
Figure 3. Figure 4 shows a spectrum obtained (at the
1.8-m Perkins Reflector by Wagner and Starrfield) in
late December when the P Cygni profiles were again
weak. The appearance, disappearance, and reappearance
of the P-Cygni profiles suggests that more than one
ejection event probably took place• These spectra
also showed lines of Fe II, Mg I, and O I in addition
to the Balmer lines• Andrillat also reported lines of
Cr I, Cr II, He I, and Mg II (IAU Announcement Card
#451 l).
At about this time, the nova became too close to the
sun for further observations in the optical• When the
nova reappeared late in January, it was reported to be
fainter than 14th. Our only explanation for this rapid
decrease was that it had formed dust• This hypothesis
was confirmed by the observations of Gehrz with the
2.34-m Wyoming Infrared Telescope on February 24
(IAU Announcement Card #4557) which showed that it
had formed an optically thick dust shell with a
temperature of about 600K.
Wagner obtained another optical spectrum with the
Perkins 1.8-m telescope, on March 13.5 (IAU Announ-
cement Card #4573), and found that it was definitely
nebular• This spectrum is shown in Figure 5. In
Figure 6, we show an early optical spectrum on the
same scale as this last spectrum• The differences are
obvious. The strong lines are due to [O III], [O I], and
[N II]. He reported that the magnitude had continued
to drop and was currently about 17. In addition and
very important, the emission line wavelengths appeared
slightly blueshifted which was consistent with a thick
shell of dust obscuring the redshifted material in the
ejecta.
3. Discussion
Although we continue to claim in our nova Target of
Opportunity proposals that every recent nova outburst
has been unique, we ourselves are still surprised when
a new nova justifies this claim. The rapid decline of
the ultraviolet energy suggests both that it was
somewhat reddened and that a relatively thick shell
was ejected during the outburst• The rapid decline in
the optical, once dust had formed, is analogous to the
behavior of DQ Her during its outburst. In fact, when
the shell was first detected by Gehrz, it was radiating
more energy in the infrared than had been observed at
maximum light in the optical. The dust is probably
carbon dust and this nova most likely ejected material
enhanced in the CNO nuclei. Further analysis of this
outburst is in progress•
Acknowledgements
This study would not have been possible without the
rapid response of the IUE Observatory to the request
for Target-of-Opportunity observations of Nova Vul
1987 and we are grateful for their continued support of
nova observations• The data were reduced with the
facilities of the RDAF at the University of Colorado,
which are supported by NASA Grant NAS5-28731, and
the assistance of T. Armitage. We also acknowledge
partial support for this research from NASA, NSF, and
the DOE through grants to our various institutions•
I _, ol ,, [,_
/'i
!i
if_ ,
J
. .ii i
Figure la. This SWP spectrum was obtained on
November 23, 1987 and is a 10 minute exposure•
Figure lb. This LWP spectrum was also obtained on
November 23, 1987. It is a 2 minute exposure. Note
that all of the spectra have different vertical scales.
ORIGINAl. PAGE IS
oe moR qukdTv OPTICAL & UV OBSERVATIONS OF NOVA VUL 1987 173
2
o _
o /L,, ]
Figure 2a. This SWP spectrum was obtained on
November 25, 1987 and the FES magnitude of the nova
was still about 8. This is an exposure of 50 minutes
and note that the fluxes have decreased by about a
factor of two since the image in Figure la.
2
_400
Figure 2b. This LWP spectrum is a 2.5 minute exposure
on the same day as the SWP spectrum in Figure 2a.
Note that the fluxes have also decreased between this
figure and Figure lb.
E_r,v_ _u_lo. _r_. PLOT O_ V_S_AT B-_ _
I
_-L
40o0 SOO0 6000 700¢_ t_ooo
_AVI I kN(,IH (,_)
Figure 3. This optical spectrum was obtained on the
2.l-m telescope of Steward Observatory on November
30, 1987.
_ _[_7_--rI_ ' ' _ ' I ' I I _lI_
,h
F
o =
R
___i_Ll__l__t__, I i i i i I i __
40O0 5000 6000 ?000 8000
"aAVF LLNGTII (_)
Figure 4. This spectrum was obtained on December 23,
1987 at the 1.8-m Perkins telescope. The P-Cygni
profiles for many of the lines had decreased in
strength since the spectrum shown in Figure 3.
I
3'
-i
'i;_ , , ', ,_
, , I , , ' , , , I ' , , , I , , ,_-I
Figure 5. This optical spectrum was obtained at the
1.8-m Perkins telescope. The nova had definitely
entered the nebular stage and the strongest lines are
due to [O III I.
<_
z
;¢(i_ t _'IHI,_(,ILI, IrlJl/
_ _ _ _ _ J F_ _ _ i _
,d'lJ"
',' I'--_-_:-_I'-'-_-:_I_'-_-'I-_-_-', P'-_--I-
_. ,.... i I
i
...... : ....... ', i .... :, i ....... _..... _,
I()(}(I I c,(Io %f)13() %DO0 bOoo O'_(JO
I_AVI I I N(,IIi {X)
Figure 6. This montage shows a comparison of two
optical spectra of Nova Vul 87. One was obtained
early in the outburst and the other is also shown as
Figure 5. Once dust formed in the expanding shell
(see text), this nova experienced an extremely rapid
decline in its optical magnitude.


Optical and ultraviolet observations of nova Vul 1987

Optical and ultraviolet observations of nova Vul 1987

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