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ELECTRONIC NEWSLETTER OF THE EUVE OBSERVATORY
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Vol 4, No. 11 16 Nov 1994 ISSN 1065-3597
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Notes from the Editor
=====================
by Brett A. Stroozas, EUVE Data Archive and Science Support (DASS) Manager
Welcome to the electronic newsletter for NASA's Extreme Ultraviolet Explorer
(EUVE) satellite, which is compiled and published monthly by the EUVE Science
Archive group at the Center for EUV Astrophysics (CEA) at the University of
California, Berkeley, CA. The contents of this issue of the newsletter are as
follows:
1. Recent EUVE Science Highlights
2. Update on EUVE Test-Bed Activities
3. Notes from the EUVE Guest Observer Center
3.1 EUVE Cycle III NRA
3.2 EUVE GO Program at the Senior Science Review
4. Notes from the EUVE Science Archive
4.1 GO Data Release List for 1 December 1994
4.2 EUVE Science Archive Guest Investigator (GI) Program
4.3 New Services Available via the World Wide Web
4.4 Accessing the Archive
5. Abstracts of Recently *Accepted* EUVE Papers
The EUVE observatory performed well throughout the month of October,
completing observations of the following Guest Observer (GO) targets (alternate
name and spectral type information taken from the SIMBAD or internal CEA
databases):
-----------------------------------------------------------------
Target Alternate Spectral Observation
Name Name Type GMT Date(s) Notes
-----------------------------------------------------------------
beta Cet HD 4128 K0III 30 Sep - 06 Oct 1994 --
VY Ari HD 17433 K0 06 Oct - 12 Oct 1994 --
SURVEY -------- ---- 12 Oct - 13 Oct 1994 E1
Moon -------- SS 13 Oct - 13 Oct 1994 --
kappa Cet HD 20630 G5Vvar 13 Oct - 18 Oct 1994 --
epsilon CMa HD 52089 B2Iab 18 Oct - 19 Oct 1994 E2
Moon -------- SS 19 Oct - 19 Oct 1994 --
UX Ari HD 21242 G5IV 19 Oct - 22 Oct 1994 --
PSR J0437-4713 -------- Pulsar 23 Oct - 12 Nov 1994 --
-----------------------------------------------------------------
E1: Engineering test to aid in determining the proper ground
software conversion factor for the high voltage power supply
on the long-wavelength spectrometer.
E2: Engineering test to aid in determining the gain degradation
at the boresight of of the deep survey imaging detector.
-----------------------------------------------------------------
To comment on or make suggestions for the EUVE electronic newsletter, please
send e-mail to ceanews@cea.berkeley.edu (Internet).
1. Recent EUVE Science Highlights
=================================
by Dr. Antonella Fruscione, EUVE Scientist
The following are recent science highlights from the EUVE mission:
o The paper "A Volume-Limited Survey of High Galactic Planetary Nebulae with
EUVE" (Fruscione, A. et al. 1994; CEA publication #609) will appear in the
February issue of the Astrophysical Journal. It reports the detection of
seven Planetary Nebulae (PN) during the EUVE all-sky survey, two of which
are newly discovered EUV sources. The emission from the objects is
consistent in all cases with that of a point source and therefore is most
probably originating from the PN central stars. From the observed values
of the EUV count rates and from assumption about the absorption occurring
in the interstellar medium between the Earth and the stars, the authors
derive temperatures of about 100,000 degrees for the emitting stars.
o The prototype eclipsing binary Algol was observed by the EUVE spectrometers
over nearly 1.5 orbital periods. Dr. R. Stern and collaborators, in an
abstract submitted for the 1995 meeting of the American Astronomical Society,
report that emission lines from high ionization states of iron, formed at
high temperature (up to 20 million degrees), are clearly detected in the
overall spectrum and that a quiescent continuum is present which increases
towards shorter wavelengths. Using synthesized spectra of optically thin
line and continuum emission, Dr. Stern and collaborators find that the iron
in the corona of Algol is under-abundant by factors of ~2-4 relative to the
Sun, unless an unreasonably large quantity of coronal plasma at temperatures
greater than 30 million degrees is present in the quiescent spectrum. The
latter possibility is, however, inconsistent with available X-ray data.
o Dr. M. Mathioudakis and collaborators (in a paper recently submitted to
Astronomy and Astrophysics) reports the detection of 23 new main-sequence
stars observed with EUVE during the all-sky survey, increasing the total
number of main-sequence stars detected in the EUV by ~12%. The authors
used the EUVE data to computed EUV fluxes (a measure of the star's activity)
for a total of 74 main-sequence stars with known rotational period to study
the connection between activity and rotation. They find that, as seen in
the EUV, saturation (the maximum level of activity in a star) in
chromospheric fluxes occurs in lower rotational velocities than it does in
coronal fluxes. One of the detected stars is the low activity M dwarf star
Gl 685. The EUVE observation indicates that this star has a cool corona at
less than about 2.5 million degrees and that the most significant amount of
radiative losses in the corona of this dwarf star emerges in the EUV.
2. Update on EUVE Test-Bed Activities
====================================
by Tom Morgan, EUVE Test-Bed Manager
The EUVE test-bed continues operations with the Low Earth Orbit Demonstrator
(LEO-D) at the Jet Propulsion Laboratory (JPL). This test-bed is attempting
to use a fully automated system of low-cost weather satellite ground stations
for the transmission of data from low-earth orbit astronomy satellites.
Pointed and non-pointed tests in both the GN (ground network) and spread
spectrum (NASA Tracking and Data Relay Satellite System-compatible) modes will
continue through November. Preliminary results indicate good potential for
success in pointed spread spectrum mode. Drs. Karen and Richard Hackney from
the NASA Kentucky Space Grant Consortium recently visited CEA to investigate
EUVE progress on the LEO-D project.
Evaluation continues with the JPL Space Craft Health Inference Engine (SHIE).
This is an augmented intelligence (AI) rule-based software application which
performs actions based in response to how the rules apply to the incoming data
stream. Initial testing indicates the inferencing speed of the application
would make it a valuable tool in systems having a requirement for elevated
processing speeds.
Evaluation continues of the JPL Selective Monitor (SelMon). Unlike other
traditional systems, this AI software application improves upon existing
monitoring systems by employing several techniques for recognizing abnormal
behavior and, when noted, focusses attention on the anomaly to provide critical
information in the early stages of a potential emergency. Initial "ground
truths" testing indicate SelMon responds correctly 100% of the time to known
anomalies. Testing continues to assess the SelMon capabilities to detect
anomalies previously undetected by EUVE software, but later detected by manual
engineering analysis.
3. Notes from the EUVE Guest Observer (EGO) Center
==================================================
by Anne Miller, EGO Technical Writer
3.1 EUVE Cycle III NRA
----------------------
The EUVE Project office at Goddard Space Flight Center (GSFC) received 106
proposals in response to NASA Research Announcement (NRA) 94-OSS-13. This NRA
allows researchers to propose for large programs of research using all four
EUVE telescopes -- the three imaging "scanners" and the Deep Survey/Spectrometer
(DS/S). This is the first opportunity for researchers to propose for pointed
scanner observations, which are carried out via the Right Angle Program (RAP;
so named because the scanners are mounted at right angles to the DS/S).
Technical and scientific reviews of the Cycle III proposals are underway and
the final Peer Review and Selection of targets is scheduled for 8-9 December.
3.2 EUVE GO Program at the Senior Science Review
------------------------------------------------
The EUVE Users Group presented an exciting plan for the science to be done
with EUVE in case of an extended mission. The presentation, made by Dr. Harry
Shipman (Chair of the Users Group) and supported by Dr. Andrea Dupree, was
delivered to the NASA Astrophysics Division Senior Review Panel. The current
EUVE mission is scheduled to end in February 1996; an extended mission would
continue for a few additional years.
4. Notes from the EUVE Science Archive
======================================
by Brett Stroozas, DASS Manager
4.1 GO Data Release List for 1 December 1994
--------------------------------------------
The table below lists the GO observations which become public on 1 December
1994; all have been reprocessed with the most recent versions of the EGO Center
software and reference data. For each entry is given the target name, the
approximate exposure time in kiloseconds, the GMT start and end date(s) for
the observation, the spectral type of the target, and the data identification
code. All public data sets may be ordered from the archive via the World Wide
Web (WWW) and electronic or postal mail (see addresses below). Please be sure
to include in your order the DataID(s) of interest.
The data rights policy for GO observations states that GO's have proprietary
rights to the data for one year from the date (s)he receives it. It is often
the case that long observations are broken up over many months; e.g., an
observation approved for 60 ksec may actually be observed for 10 ksec one
month, 20 ksec the next and 30 ksec three months later. In such cases the
one-year proprietary period begins after the GO receives the final piece of
the complete observation.
===============================================================
Target ~Exp Observation Date(s) SpT DataID
Name (ksec) Start End
===============================================================
Data Sets Available 1 Dec 1994:
71_TAU 108 Oct 24 1993 - Oct 28 1993 F0V go0116
AB_DOR 195 Nov 4 1993 - Nov 11 1993 K1 go0117
ALGOL 130 Oct 30 1993 - Nov 4 1993 B8V go0118
EPSILON_ERI 60 Oct 22 1993 - Oct 24 1993 K2V go0119
MOON 2 Aug 28 1993 - Aug 28 1993 SS go0120
MOON 2 Sep 1 1993 - Sep 1 1993 SS go0121
MOON 2 Sep 28 1993 - Sep 28 1993 SS go0122
MOON 1 Oct 4 1993 - Oct 4 1993 SS go0123
MOON 2 Oct 27 1993 - Oct 27 1993 SS go0124
MOON 2 Oct 29 1993 - Oct 29 1993 SS go0125
MOON 2 Nov 3 1993 - Nov 3 1993 SS go0126
MOON 3 Nov 29 1993 - Nov 29 1993 SS go0127
PSR1929+10 39 Oct 10 1993 - Oct 12 1993 Pulsar go0128
RE0503-285 52 Oct 20 1993 - Oct 22 1993 WD go0129
WD0004+330 44 Oct 19 1993 - Oct 20 1993 WD go0130
===============================================================
4.2 EUVE Science Archive Guest Investigator (GI) Program
--------------------------------------------------------
In order to promote research using EUVE data, CEA is pleased to announce the
EUVE Guest Investigator (GI) Science Program. The purpose of the GI Program as
an educational service which provides to researchers education and training in
the use of public EUVE data. (The basic EUVE data sets are skymaps and
"pigeonholes" -- photon event lists -- from the the all-sky and deep surveys
and multi-channel spectra from the Guest Observer Program.) In effect, the
GI Program offers CEA's technical experience and intricate knowledge of the
EUVE instrumentation and data to the external research community.
As GIs, researchers will receive from CEA a standard package of support to
assist them with their data analysis. This standard package includes up to
one week (five working days) of free access -- either as a local visitor or
remotely -- to various CEA resources including computer processing power, up
to 500 megabytes of disk space, and access to one technical research assistant
who will assist the researcher in understanding and using the EUVE data. At
the end of the five days, GIs should be fully able to analyze EUVE data
themselves at their home institutions.
Researchers interested in analyzing EUVE data are encouraged to apply for
the GI program. Since CEA resources are limited, a maximum of three GIs will
be actively supported at any one time. For more information on how to become
a GI, contact the EUVE Science Archive via telephone at (510) 642-3032 or by
e-mail at archive@cea.berkeley.edu.
The timing of the implementation of the EUVE GI Program coincides well
with the last month's NRA (94-OSS-17) from the NASA Astrophysics Data Program
(ADP) which includes EUVE data in its call for proposals. More information
on the ADP and the proposal process is available via anonymous ftp at
ftp.astrophysics.hq.nasa.gov in the directory /pub/NRAs/ADP/94-OSS-17. All
proposals are due by 25 January 1995.
4.3 New Services Available via the World Wide Web (WWW)
-------------------------------------------------------
The "Monsignori-Fossi and Landini Plasma Emission Model in the EUV Range"
is now available in the "Software and Services" section of the Archive on
the CEA WWW site (http://www.cea.berkeley.edu). This tool calculates the
spectrum of an optically thin plasma in the EUVE spectral range (60-760 A) for
a user-specified logarithmic plasma temperature, electron density, logarithmic
emission measure (EM), distance, and intervening interstellar medium (ISM)
hydrogen and helium column densities.
The spectrum is derived using emissivity tables from the X-ray/EUV spectral
code by Landini and Monsignori-Fossi (1990), recently revised using more
accurate atomic data computations (Monsignori-Fossi & Landini, 1994). Spectra
may be calculated for isothermal models in the temperature range log(T) =
4.5-8.0. The ISM attenuation is performed by the same routines used by the
ISM tool (Rumph, Bowyer, & Vennes 1994), also available in this archive.
The resolution of the output spectrum is currently fixed at 0.5 A across the
whole wavelength range. This value was chosen because it corresponds to the
maximum resolution of the EUVE spectrometers. The output spectrum may be in
either photon or energy units. The user has the option of having the output
spectrum as well as the emissivity tables corresponding to the chosen input
temperature sent to them by e-mail.
4.4 Accessing the Archive
-------------------------
Listed below are the various methods for accessing EUVE archival material:
o CEA World Wide Web URL:
http://www.cea.berkeley.edu (Mosaic/lynx remotely)
telnet www.cea.berkeley.edu 200 (lynx locally at CEA)
o NASA's Astrophysics Data System:
http://adswww.colorado.edu/adswww/adshomepg.html (Mosaic/lynx)
o CD-ROM Series: Volumes 1.1, 2.1, and 2.2 (seven separate CDs) available
o e-mail: archive@cea.berkeley.edu
o anonymous FTP (or gopher): ftp.cea.berkeley.edu
o EUVE Electronic Newsletters:
Subscriptions: majordomo@cea.berkeley.edu ("subscribe euvenews")
Post message to all subscribers: euvenews@cea.berkeley.edu
o Postal Mail:
The EUVE Public Science Archive
Center for EUV Astrophysics
2150 Kittredge St.
Berkeley, CA 94720
510-642-3032 (voice) or 510-643-5660 (fax)
archive@cea.berkeley.edu
5. Abstracts of Recently *Accepted* EUVE Papers
===============================================
Included below are abstracts of EUVE-related papers recently *accepted*
for publication. For those papers authored by CEA scientists, the EUVE
publication numbers are indicated. Unless otherwise noted, researchers may
obtain preprints of CEA papers by sending an e-mail request containing the
publication number(s) of interest to pub@cea.berkeley.edu.
Researchers are encouraged to contribute *accepted* EUVE-related abstracts
for inclusion in future editions of this newsletter; abstracts or full papers
will also be posted under the CEA WWW Home Page. Please send all abstracts
or papers to archive@cea.berkeley.edu.
--------------------------------------------------------------
IRON IN THE EUVE SPECTRUM OF PG1234+482
S. Jordan and D. Koester
Astronomische Gesellschaft, Abstract Series No. 10, p. 60, 1994.
White dwarfs of spectral type DA are defined as showing only Balmer lines
of hydrogen in the optical part of the spectrum. However, the optical part
of the spectrum is quite insensitive to small traces of helium or heavier
elements so that the evidence for additional absorbers in hot DAs rests
entirely on observations in the soft X-ray, EUV and UV. The flux in the
soft X-ray region has the strongest dependence on small traces of absorbers
heavier than hydrogen. For some hot white dwarfs with T_eff >= 38,000 K
measurements with the EINSTEIN, EXOSAT, and ROSAT satellites clearly
indicated the presence of absorbing material at wavelengths below about
300 A. Unfortunately, the limited energy resolution of these detectors
did not allow a unique determination of the chemical composition. Therefore
the analysis of the X-ray data was mostly restricted to hydrogen atmospheres
with small traces of helium. Direct evidence for such absorbers was the
detection of ions of heavier elements NV, SiIV, CIV, and FeV in IUE high
resolution spectra of G191-B2B. PG1234+482, after being classified as a
sdB was found to be a hot DA by our group. From the optical spectrum we
determined an effective temperature of 50,000 +/- 3,000 K, which is compatible
with the IUE low resolution spectrum. ROSAT pointed observation could not
be reproduced by assuming model atmospheres containing only hydrogen and
helium. With the limited energy resolution of ROSAT it was, however, not
possible to determine the metal abundance unambiguously. With its much
higher spectral resolution the EUVE satellite is able to detect spectral
lines in the extreme UV. Significant flux could be detected with the short
and medium wavelength spectrograph between about 75 and 300 A. We compared
the measurement in the short wavelength to a synthetic spectrum containing
only small traces of the iron group elements in an otherwise pure hydrogen
atmosphere. Perfect agreement between theory and observation cannot be
expected due to fixed pattern noise in the observation and due to uncertainties
of the iron opacities. However, the energy distribution and several strong
absorption features can be reproduced by the model. By varying the parameters
we conclude that the iron abundance is about 1.5-3.0E-7, lower than predicted
by Chayer et al. (1994, preprint) by detailed calculations of the radiative
forces in hot DA white dwarf atmospheres. A more complete paper by Jordan
S., Koester D., Finley D., Werner K. is in preparation.
--------------------------------------------------------------
EUVE OBSERVATIONS OF NGC 5548
J.S. Kaastra, R. Mewe, J. Heise, F.J.M. Alkemade, C.J. Schrijver, and T. Carone
IAU Symposium No. 159, Active Galactic Nuclei Across the Electromagnetic
Spectrum, Geneva, 30 Aug - 3 Sep 1993.
The first extreme ultraviolet spectrum of NGC 5548 obtained by EUVE is
presented.
--------------------------------------------------------------
ON THE PREDICTED ABUNDANCES OF IRON AND NICKEL SUPPORTED BY RADIATIVE
LEVITATION OF HOT DA WHITE DWARFS
P. Chayer, F. LeBlanc, G. Fontaine, F. Wesemael, G. Michaud, and S. Vennes
To appear in Astrophysical Journal Letters [CEA Publication #613]
We present the results of detailed radiative forces calculations for iron
and nickel levitating in hot DA white dwarf atmospheres. This follows from
the determination of the iron abundance in a handful of hot DA stars by a
number of authors and, more particularly, from the recent identification and
abundance analysis of nickel carried out by Werner & Dreizler for these same
stars. Our calculations are based on the extensive atomic data set compiled
by Kurucz for the iron group elements. We show that radiative levitation is
more than sufficient to account for the abundances of iron and nickel observed
in hot DA white dwarfs. However, we also find that the observations exhibit
an abundance pattern which cannot be explained in detail by the predictions
of radiative levitation theory. This finding adds to mounting evidence that
other mechanisms must be at work in the atmospheres of these objects and
compete with radiative levitation and gravitational settling.
--------------------------------------------------------------
LOW-COST OPERATIONS APPROACHES AND INNOVATIVE TECHNOLOGY TEST-BEDDING AT THE
EUVE SCIENCE OPERATIONS CENTER
R.F. Malina
Presented at the 45th International Astronautical Congress, IAA Symposium on
Small Satellite Missions, Session on "Low Cost Approaches for Small Satellite
Mission Operations and Data Analysis," Jerusalem, Israel, 9-14 Oct 1994.
[CEA Publication #614; not preprinted]
The NASA Astrophysics Program faces harsh realities in the new NASA budget
environment. Even though there is an increasing number of successfully operating
NASA astrophysics satellites, the Astrophysics Division mission operations and
data analysis budget will be decreasing annually over the next few years. As
a result the NASA Astrophysics Division must either terminate operation of
successful and highly productive observatories or develop techniques for
operating satellites at radically lower costs. The NASA Extreme Ultraviolet
Explorer (EUVE) astronomy satellite, which is presently operating flawlessly
and returning a stream of scientific breakthroughs in the new field of EUV
astronomy, is currently slated to be turned off in 1996. The EUVE project has
adopted an aggressive plan to find ways of operating EUVE at lower cost. The
EUVE project at the University of California, Berkeley (UCB; which has
responsibility for EUVE science operations), and Dr. Ronald Polidan of GSFC
have laid out a new mission operations concept for EUVE that will allow EUVE's
operating costs to be lowered. It will also provide a management experiment
and technology test-bed to allow NASA to transfer lessons learned and new tested
approaches gained from EUVE to other missions. The EUVE Science Operations
Center (ESOC) at UCB, has adopted these approaches and is using new operations
software that allows semi-autonomous operations to be implemented. Under this
plan the ESOC is making a transition from a three-shift, around-the-clock
operation to a one-shift, human-tended operation with use of the RTworks
artificial intelligence (AI) software package for autonomous operations during
the untended shifts. The conversion to one-shift operations was carried out
during 1994 and has been accomplished in less than nine months. An autonomous
paging system automatically makes telephone contact with remote duty engineers
upon detection of anomalies in the telemetry stream so that response to
detected anomalies can be carried out. Additional areas of cost reduction
include that of the observatory science planning and scheduling and autonomous
monitoring and error correction in the communications and ground computer
systems. The on-board robustness of the EUVE spacecraft, a Fairchild MMS
platform, allows acceptable risk tradeoffs between on-board and ground
functions for assuring ultimate health and safety of the spacecraft and payload
system. EUVE has been selected by NASA Code X for test-bedding of innovative
software techniques for cost reduction in the operations of scientific
satellites; EUVE is currently collaborating with researchers at NASA Ames
Research Center (ARC), the Jet Propulsion Laboratory (JPL), and the Goddard
Space Flight Center (GSFC). Other areas of cost reduction include test-bedding
of direct-to-ground communications with autonomous ground stations (EUVE
currently uses the Telemetry and Data Relay Satellite System (TDRSS) for all
communications), using the on-board global positioning system (GPS) for all
orbit determination needs, and streamlining of data delivery to scientific
users via the EUVE electronic archive and provisions for remote computing
facilities. An additional critical element of the EUVE low-cost innovations
is the direct involvement of University of California undergraduate students
in all aspects of operations. The EUVE educational outreach program also uses
the ESOC as a laboratory for K-12 teacher training workshops. In this paper
we describe elements of cost reduction innovation and technology test-bedding
on EUVE as well as some lessons learned. One of the lessons we have learned
from migrating the EUVE ESOC from three to one shift is that today's AI
software allows the design and operation of a fully autonomous EUVE Science
Operations Center. We are now developing plans to migrate from one shift to
zero shifts. We believe that this will result in a more robust and lower risk
science operations concept than the original three-shift, around-the-clock
operations. Although we are suspicious of slogans, we believe that this will
be an excellent example of "less is more."
--------------------------------------------------------------
EDUCATIONAL OUTREACH ON NASA'S EXTREME ULTRAVIOLET EXPLORER SATELLITE PROGRAM
R.F. Malina, I. Hawkins, and C. Christian
Presented at the 45th International Astronautical Congress, Symposium on Space
and Education, session on "Education Structures," Jerusalem, Israel, 9-14
Oct 1994. [CEA Publication #616; not preprinted]
NASA's Extreme Ultraviolet Explorer (EUVE) satellite was launched in June
of 1992. As an intrinsic part of the operations phase of this satellite, an
education outreach program has been developed for undergraduate students, K-12
students and educators, and for the general public. These projects have been
funded by NASA's Astrophysics Division Grant Supplements for Education Program
and by the EUVE project. We review the underlying ideas that motivate our
approach in using EUVE as a tool for educational outreach. In particular we
note the need for collaborations between the research project and informal
science museums and centers who are best placed to establish long term programs
with schools and the K-12 educational community. The EUVE project has also
made a commitment to staff involvement in educational outreach, rather than
setting up a separate educational outreach activity. Finally, we emphasize
the need to carry out educational outreach for space science in an
interdisciplinary context that ties space science to other disciplines as well
as to culture at large. We describe a new program, The Science Information
Infrastructure (SII), that seeks to establish collaborations between the EUVE
project, the Harvard Smithsonian Astrophysical Observatory, and science museums
including the San Francisco Exploratorium, The Lawrence Hall of Science, The
Adler Planetarium in Chicago, the UC Museum of Paleontology, the Smithsonian
Air and Space Museum, the New York Hall of Science, and the Science Museum of
Virginia. Teachers at each of these museums will participate in workshops to
develop lesson plans and educational materials that will be disseminated
through World Wide Web sites at each of the participating institutions. A
pilot project, Science On Line, is under way involving a subset of the SII to
develop initial materials in early 1995.
--------------------------------------------------------------
THE EUVE BIBLIOGRAPHY AS OF OCTOBER 1994.
Center for EUV Astrophysics [CEA Publication #617]
NASA's Extreme Ultraviolet Explorer (EUVE) launched in June 1992. This
bibliography lists all EUVE-related publications to date. The numbers
preceding most titles are the report numbers by which the papers may be
requested from the Center for EUV Astrophysics (CEA), UC Berkeley. Papers
without numbers are by non-CEA guest observers or members of the astrophysics
community. Asterisks indicate papers using EUVE data. Papers are listed
by subject and in reverse chronological order.
--------------------------------------------------------------
EXTREME ULTRAVIOLET LIGHT CURVES OF UZ FOR: EVIDENCE FOR ACCRETION STREAM
ABSORPTION AND VERTICAL EXTENT OF THE ACCRETION SPOT
John K. Warren, Martin M. Sirk, and John V. Vallerga
To appear in Astrophysical Journal [CEA publication #620]
We report on two pointed observations of UZ For carried out by the imaging
photometers aboard the Extreme Ultraviolet Explorer (EUVE), one as part of
the EUVE Right Angle Program and one as an off-axis source during a guest
observation. Both observations lasted approximately three days and covered
a total of 72 orbits of the UZ For binary providing multiple coverage of all
the orbital phases of UZ For. The resulting high signal-to-noise, phase-folded
light curve strongly constrains the emission and absorption geometry of UZ For.
We have detected a narrow absorption dip that we attribute to the accretion
stream at the location of the stagnation region many white dwarf radii away
from the accretion spot and have also detected a broad dip caused by absorption
much closer to the white dwarf surface. Both absorption effects are variable
in time and phase. Based on the time scales of M-star eclipse ingress and
egress, the angular spot size is constrained to be < 5 deg; thus the ratio
of spot area to white dwarf surface area is <= 0.0005. To explain the light
curve phase duration given this small angular spot size, the extreme
ultraviolet (EUV) accretion spot must be raised vertically by approximately
5% of the white dwarf radius.
--------------------------------------------------------------
REFERENCES
==========
o Landini, M., and Monsignori-Fossi, B.C., 1990, Astronomy & Astrophysics,
82, 229
o Monsignori-Fossi, B.C., and Landini, M., 1994, Solar Physics, 152, 81
o Rumph, T., Bowyer, S., and Vennes, S., 1994, Astronomical Journal,
107(6), 2108
---------------------------------------------------------------------------
The EUVE Electronic Newsletter is issued by the Center for Extreme
Ultraviolet Astrophysics, University of California, Berkeley, CA 94720,
USA. The opinions expressed are those of the authors. EUVE Principal
Investigators and Newsletter Publishers: Dr. R.F. Malina and Professor
C.S. Bowyer. EGO and Archive Science Manger: C.A. Christian. Archive
Manager and Newsletter Editor: B.A. Stroozas. Funded by NASA contracts
NAS5-30180 and NAS5-29298. Send newsletter correspondence to:
ceanews@cea.berkeley.edu. The EUVE project 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, 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 at (301) 286-6247 or e-mail to
euve@stars.span.nasa.gov.
END-----------EUVE------------ELECTRONIC---------------NEWS-------------END
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