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Vol 3, No.  13  August 27, 1993                          ISSN 1065-3597

	by Dr. Barry Welsh

We are pleased to announce the Extreme Ultraviolet Explorer has observed
its first Target of Opportunity (TOO), the dwarf nova SS Cygni. TOOs are
astronomical events, such as the appearance of a new comet or a
supernova outburst, that cannot be scheduled in advance. In the present
case, SS Cygni, a close binary consisting of a K dwarf and white dwarf
with an accretion disk formed around the white dwarf from material lost
by its companion, went into outburst on August 16th. This sudden
increase in brightness was observed by many amateur astronomers around
the world and was immediately reported to Janet Mattei, the head of the
American Association of Variable Star Observers. This information was
then relayed to Dr. Ron Oliversen, the EUVE deputy project scientist at
Goddard Space Flight Center (GSFC), and the EUVE Science Operations
Center (ESOC) at UC Berkeley.  The coordinated efforts of the ESOC and
the Flight Operations Team at GSFC enabled EUVE to slew to SS Cygni and
start observations only 8 hours after being alerted to the outburst. 

The possibility of making EUVE observations of SS Cygni in outburst was
originally proposed by Dr. Christopher Mauche of Lawrence Livermore
National Laboratory in California. He is now the proud owner of nearly
200,000 seconds of EUVE spectral data on SS Cygni obtained over a 6 day
period, during which the optical brightness of the source rose slowly to
maximum and the EUV light was observed to turn on. This outburst is
considered anomalous in that it took about 5 days to reach maximum
intensity instead of the usual 1-2 days for a dwarf novae outburst.
Additionally, near-simultaneous ultraviolet spectroscopy of SS Cygni was
obtained by the IUE satellite, assuring both EUV and UV spectra of a
dwarf novae outburst will enter the archives. 

The emission detected by the EUVE spectrometers is thought to be caused
by hot gas in the innermost regions of the accretion disk of SS Cygni,
and of the boundary layer between the accretion disk and the surface of
the white dwarf. These new data will assist Mauche and his co-workers to
understand the temperatures, luminosities, and emission processes of
these components of the binary, as well as the radiation transfer
processes of the EUV radiation through the wind of SS Cygni. 


	by Mary Samuel, Science Planner

This TOO had a significant effect on the planned EUVE schedule.  Four
priority 1 GO observations, and several short calibration pointings
were replaced by the TOO. 

The following is the revised schedule for EUVE.  All time-critical
requests for coordinated observations communicated to the EGO Center
have been honored.  The targets up until HD_7672 starting on 
September 28, 14:45 UT, are locked in the short-term schedule. 

All priority 1 targets previously scheduled are included with the
exception of the calibration target WD1845+019.  This target remains in
the calibration program and will be observed again as soon as possible. 
Most of the priority 2 targets which had been in the schedule have been dropped
to accommodate the remaining priority 1 targets. 

Short term schedule:

NAME		      ID		     START TIME

SS_CYG                SS_Cyg                 1993:229:01:50:00  Target of Opportunity 
CYG_1992              Nova_Cyg               1993:235:15:14:24
GRB_250392            GRB_250392             1993:237:00:57:36
RE_2214-491           RE_2214-491            1993:238:10:19:12
MOON                  moon1993:240:03:34:00  1993:240:02:42:00	1 orbit moon observation 
RE_2214-491           RE_2214-491-a          1993:240:05:00:00
EQ_PEG                EQ_Peg                 1993:241:04:41:00
WD_2309+105           WD_2309+105-1          1993:242:14:50:00
R_AQUARII             R_Aquarii              1993:243:12:00:00
MOON                  moon1993:244:02:23:00  1993:244:01:40:00  1 orbit moon observation 
R_AQUARII             R_Aquarii-a            1993:244:03:50:24
HD_15638              HD_15638               1993:245:14:58:24
EF_ERI                EF_Eri                 1993:248:13:42:48
EV_LAC                EV_Lac                 1993:252:17:19:00
WD_2111+498           WD_2111+498            1993:256:20:52:48
HR_1099               HR_1099-1              1993:259:10:30:00
HR_1099               HR_1099-2_0.02_0       1993:262:06:28:48	Off-boresight DSS calibration/GO observation 
HR_1099               HR_1099-3_0.02_90      1993:263:12:30:00 	Off-boresight DSS calibration/GO observation 
RE_2237               RE_2237                1993:264:16:20:00
RE_2303               RE_2303                1993:265:17:30:24
AM_HER                AM_Her                 1993:266:17:58:00
MOON                  moon1993:271:13:24:00  1993:271:12:35:30	1 orbit moon observation
HD_7672               HD_7672                1993:271:14:45:48
Intermediate/Long term schedule:

TARGET                     START TIME           POINTING ANGLE    PRIORITY 
						from ANTISUN
WD_2309+105                1993:274:14:24:00    20.929556            1
II_PEG                     1993:275:14:24:00    26.594879            1
II_PEG                     1993:277:12:00:00    26.519253            1
II_PEG                     1993:278:12:00:00    26.563685            1
RE_1938-461                1993:279:12:00:00    85.300376            1
PSR1929+10                 1993:282:14:24:00    80.979948            1
RE_2201                    1993:283:19:12:00    53.632935            1
AR_LAC                     1993:287:16:48:00    55.269941            1
AR_LAC                     1993:289:14:24:00    55.841075            1
AR_LAC                     1993:290:14:24:00    56.157254            1
FEIGE_24                   1993:291:14:24:00    16.332339            1
LAMBDA_AND                 1993:292:14:24:00    44.310491            1
WD_0004+330                1993:296:12:00:00    32.346905            1
RE_0503-285                1993:298:09:36:00    60.533060            1
AB_DOR                     1993:300:07:12:00    86.798902            1
G191-B2B                   1993:305:07:12:00    49.579803            1
MCT_0455-2812              1993:307:04:48:00    55.217498            1
RE_0847                    1993:309:02:24:00    77.226777            1
RE_0431                    1993:309:21:36:00    68.348674            1
EPSILON_ERI                1993:310:16:48:00    27.954151            1
SIRIUS_B                   1993:313:00:00:00    65.465631            1
HD_220140                  1993:314:21:36:00    66.769865            1
NGC_1360                   1993:317:19:12:00    44.172578            1
FEIGE_24                   1993:321:16:48:00    20.715778            1
LAMBDA_ERIDANI             1993:322:19:12:00    36.072341            2
71_TAU                     1993:324:07:12:00    11.094795            1
WD_1057+719                1993:328:04:48:00    75.128008            1
IX_VEL                     1993:332:02:24:00    88.176276            1
P_ENCKE                    1993:337:21:36:00    19.044020            1
BETA_CMA                   1993:339:09:36:00    46.495764            1
H1504+65                   1993:341:07:12:00    88.534963            1
CAPELLA                    1993:343:04:48:00    23.255085            1
CAPELLA                    1993:345:02:24:00    22.994276            1
CAPELLA                    1993:346:02:24:00    22.888991            1
HD_82558                   1993:347:02:24:00    70.263107            1
G191-B2B                   1993:352:21:36:00    30.437353            1
RE_0623-374                1993:353:21:36:00    60.149408            1
HD_66811                   1993:355:09:36:00    69.826702            1
ALGOL                      1993:357:19:12:00    41.477805            1
AG_DRA                     1993:360:21:36:00    86.039155            1
GEMINGA                    1993:364:19:12:00    5.563279             1
VELA                       1994:011:09:36:00    66.792805            1
RE_1309                    1994:019:02:24:00    74.357756            1
RE_1016-053                1994:019:21:36:00    40.133305            1
PG_1520+525                1994:023:19:12:00    83.191660            1
PSR_J0437-4713             1994:027:16:48:00    85.154381            1

As this schedule is translated into science plans and locked into the
short-term schedule, it will vary to some degree.  The duration on
target needed to deliver the requested exposure may change from the
predicted value due to orbital considerations and other effects (e.g.
SAA).  This may cause reordering of the targets, a simple change in the
start time, or the the introduction or removal of a target
(e.g. priority 2) to fill an unanticipated gap in the schedule. The 
schedule will be updated regularly, and the updated version 
will be available in the FTP site. The files are 
named targets_scheduled_longterm.tbl and targets_scheduled_shortterm.tbl
and are located in the pub/nra/docs.appG directory.

If you wish to plan a coordinated observation based on this schedule,
please communicate your plans to the EGO Center.  This will help us
minimize the impact of the schedule changes for tightly constrained
observations.  We will attempt to meet your request; however, we cannot
guarantee time-critical requests that were not included in the original


	by Dr. Ron Oliversen, Deputy Project Scientist @GSFC

Some confusion has arisen over what to do with the Target Summary List
since the form was not included in the table on page C-3 of the NRA for 
page limits. The target summary form is to be submitted electronically to 
and included in the hard copy to EUVE Project Scientist at GSFC.


	by Eric Olson, EGO Center

  Wavelength calibration of EUVE is done using both pre-launch calibration
data and observations of calibration targets in orbit. The wavelength
solution currently in use for the nominal reduction of near-boresight
observations contains RMS errors of 0.3 A (4 pixels) in the SW
spectrometer, 0.7 A (5 pixels) in the MW, and 0.8 A (3 pixels) in the LW.

  The errors are not evenly distributed across the detector; distortions
near the detector edges cause the errors to be as much as 4--5 times
larger than the above values in such regions of the spectrum.  In
addition, there can be systematic shifts of the entire spectrum along the
spectral direction by up to 5 pixels due to changes in the orientation of
the telescope boresight with respect to the detectors.  These shifts will
vary for each observation and for each detector within an observation.

  Spectral imaging angles are also not derived perfectly with the current
solution, for the same reasons.  This can cause the spectrum to be curved
and to fail to appear at an imaging angle of 0.0 degrees.

  No in-orbit off-boresight (> 5 arcmin ) observations of calibration
targets have been performed or are scheduled at this time.  Some
pre-launch calibration data is available for such pointings.  This data
indicates that the quality of the solution for observations at less than
0.2 deg off-boresight should be similar to that for the on-boresight case.
At larger angles, the errors in the solution become larger.  The
calibration data is less complete at such angles and conclusions drawn
must be considered approximate, but the data indicates RMS errors will
increase by at least 2--3 times for extreme off-boresight angles (>0.5

  An effort to improve the on-boresight wavelength calibration is
currently underway.  The increased number and variety of bright
calibration targets available after several months of observing should
provide better coverage of the detector.  This will both improve the
calibration near the detector edges and minimize the systematic errors due
to boresight changes.

The EUVE Electronic Newsletter is issued by the Center for Extreme
Ultraviolet Astrophysics, University of California, Berkeley, CIA 94720,
USA. The opinions expressed are those of the authors. Publishers: 
R. Malina, C. Stuart Bowyer. Funded by NASA Contracts NAS5-30180 and
NAS5-29298. Send newsletter correspondence to: ceanews@cea.Berkeley.Edu
EUVE Public Archive via FTP: ftp.cea.Berkeley.Edu, pub/archive.
EUVE is managed by NASA's GSFC. The GSFC Project Manager: Paul Pashby,
Project Scientist: Dr Yoji Kondo, Deputy Project Scientist: Dr Ronald
Oliversen. NASA HQ Program Scientist: Dr Robert Stachnik, Dep. Program
Scientist: Dr D Buzasi, Program Manager: Dr G Riegler. GSFC Project
Operations Director: Mr Kevin Hartnett. Information on the EUVE Guest
Observer Program is available from: Dr Y Kondo, Mail Code 684, GSFC,
Greenbelt, MD 20771 (301)286-6247; email to euve@stars.SPAN.NASA.GOV

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