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ELECTRONIC NEWSLETTER OF THE EUVE OBSERVATORY
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Vol 5, No. 2 16 Feb 1995 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, compiled and published monthly by the EUVE Science Archive
group at the Center for EUV Astrophysics (CEA) in Berkeley, CA. The contents
of this issue of the EUVE electronic newsletter are as follows:
1. EUVE Science Highlights
2. Notes from the EUVE Science Archive
2.1 1994 in Review
2.2 GO Data Release List for 1 Mar 1995
2.3 New Archive Services Available Via WWW
2.4 On-Line Access to EUVE
3. Abstracts of Recently *Accepted* EUVE Papers
To comment on or make suggestions for the EUVE electronic newsletter, please
send e-mail to ceanews@cea.berkeley.edu (Internet).
The EUVE observatory performed well throughout the month of January 1995,
performing 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
------------------------------------------------------------------
RE 1149+284 EUVE J1149+287 CV 26 Dec - 03 Jan 1995 ERR
3C 273 EUVE J1229+020 QSO 03 Jan - 15 Jan 1995 ---
UZ For EUVE J0335-257 CV 15 Jan - 19 Jan 1995 ---
RE 0425-571 LB 1727 AGN? 19 Jan - 19 Jan 1995 ---
AZ Cnc LHS 2034 M 19 Jan - 19 Jan 1995 RAP
Survey ---------- ---- 19 Jan - 22 Jan 1995 ENG
FEIGE 24 WD 0232+035 WD 22 Jan - 24 Jan 1995 ---
PSR J0837+0610 ---------- Pulsar 22 Jan - 24 Jan 1995 RAP
CN LEO RE 1056+070 M6V 24 Jan - 29 Jan 1995 ---
PSR J0459-02 ---------- Pulsar 24 Jan - 29 Jan 1995 RAP
VW Cep RE 2037+753 K0V 29 Jan - 04 Feb 1995 ---
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Key to Notes:
ERR = previous newsletter incorrectly listed this observation
as 26 Dec - 12 Jan 1995
ENG = engineering test to calibrate star trackers
RAP = Right Angle Program target
1. EUVE Science Highlights
==========================
by Dr. Jurgen Schmitt, CEA Visiting Astronomer
Schmitt, Drake, Stern, and Haisch have studied the EUVE spectrum of the star
epsilon Eri. In the EUVE spectrum of epsilon Eri they detect emission lines
attributable to iron in the ionization stages IX to XXI, thus covering a rather
large temperature range from < 1E6 K to > 1E7 K. While the lines in the lowest
and highest ionization stages are relatively weak, the strongest lines detected
are from Fe XV and XVI, from which we infer a peak in the differential emission
measure distribution at temperatures of log T ~6.4; significant emission measure
is, however, also present at both higher and lower temperatures. This is in
contrast to both lower activity stars whose EUV spectra are dominated by cooler
Fe lines in the range 170-180 A as well as active stars whose EUV spectra are
dominated by hotter Fe lines in the range 110-135 A. Finally, a density
determination using line ratios of Fe XIII and Fe XIV results in coronal
densities for epsilon Eri which are similar to solar active region densities.
2. Notes from the EUVE Science Archive
======================================
2.1 1994 in Review
------------------
by Holly Jessop, Science Archive Research Assistant
The EUVE Science Archive at CEA became operational immediately following
the launch of the EUVE satellite, in the summer of 1992, and was established
to archive and distribute EUVE-related materials to the scientific community.
Expansion of the Archive is an on-going process, and in 1994 the number of
materials and services provided by the Archive increased dramatically. In
addition, innovative ways in which these resources are made available to the
community were developed in 1994.
The material resources of the Archive grew significantly in 1994 as more
EUVE data became non-proprietary, and as the Archive continued to accumulate
and produce relevant software and documents. These resources now include 145
public Guest Observer (GO) data sets on 95 different targets. In August the
entire data set of the EUVE All-Sky Survey became available; there have since
been requests filled for over 125 source count rate calculations, 50 skymap
sections and 175 target "pigeonholes" (photon event lists). New routines were
added to the Archive collection of software, such as tools to calculate
interstellar medium transmission at EUV wavelengths and to estimate hydrogen
column densities. The Archive's collection of documents, including various
catalogs and journal and conference abstracts and papers, also exhibited a
healthy growth rate throughout the past year.
FTP access to all of these materials increased by about 40% over the
previous year's usage, and gopher access to the Archive was utilized by over
200 users every month. Selected data and documents continued to be distributed
to the community via CD-ROM in 1994, with three volumes on seven disks, and
over 1,500 CDs delivered to date. Individual requests for public GO data sets
were received and filled at a rate of over 20 orders per month.
However, the Archive's primary area of expansion in 1994 involved the
implementation of new ways for the community to access the growing resources.
Most of these access innovations make use of the interactive features of the
World Wide Web (WWW). For example, the 1-d spectra of all the public GO data
sets can now be accessed on-line with the Archive's WWW Spectral Browser.
The Spectral Browser utilizes Mosaic's form features, and is an intuitive
point-and-click procedure. After browsing data products, users can easily
make on-line requests to receive public data. Similarly, Survey data can be
conveniently accessed on-line with the Archive's Count-Rate, Skymap and
Pigeonhole services. Software, although also available via FTP, became more
easily accessible in 1994 via the Archive's WWW on-line services: while
on-line, users can submit routine parameters and receive program results
effortlessly and rapidly. Over the past year, access to these and other WWW
Archive data and services was provided every month to over 200 users initiating
over 2,000 queries.
To further expand the ways in which Archive resources can be utilized, a
new Guest Investigator (GI) Program was initiated in 1994. The purpose of the
GI Program is to provide researchers with education and training in the use of
public EUVE data. In effect, the GI Program offers CEA's technical experience
and intricate knowledge of the EUVE data to the external research community.
So far, the Archive has served 5 GIs.
The goal of the Science Archive is to disseminate scientific data and
information in both an efficient and innovative manner. Therefore, the Archive
is committed to remotely accessible and interactive data, software, and
document retrieval methods. In 1994, The Archive was indeed successful in
implementing a number of new services that facilitated the ways in which
Archive resources can be accessed and utilized. In 1995, additional
developments are underway: look for improved WWW services to be implemented
during March.
2.2 GO Data Release List for 1 Mar 1995
---------------------------------------
by Brett Stroozas, DASS Manager
The table below lists the GO observations which become public on 1 Mar 1995.
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 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 GOs 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 completed observation.
===============================================================
Target ~Exp Observation Date(s) SpT DataID
Name (ksec) Start End
===============================================================
3C 273 177 Jan 8 1994 - Jan 14 1994 AGN go0146
beta CMa 99 Dec 19 1993 - Dec 22 1993 B1 go0147
Geminga 265 Jan 14 1994 - Jan 24 1994 SNva go0148
lambda Eri 48 Dec 25 1993 - Dec 27 1993 B2IV go0149
U Gem 35 Dec 28 1993 - Dec 29 1993 Be go0150
U Gem 158 Dec 31 1993 - Jan 5 1994 Be go0151
U Gem 36 Jan 7 1994 - Jan 8 1994 Be go0152
===============================================================
2.3 New Archive Services Available Via WWW
------------------------------------------
One of the more popular science archive services is the spectral browser on
the WWW. The browser allows researchers to conveniently select, browse and
retrieve public EUVE 1-d spectra. These spectra have been automatically batch
processed and so do not fully reflect the data buried within; a careful manual
spectral extraction can often improve the signal-to-noise ratio significantly.
In order to improve upon the quality of the public spectra products the Archive
has binned the browse spectra by seven pixels to match the resolution of the
spectrometer channels (the FITS data files remain unbinned). These binned
browse spectral products display a better representation of the spectral data,
although significant improvements can still be made upon careful manual
processing and extraction.
2.4 On-Line Access to EUVE
--------------------------
Listed below are the various methods for on-line access to EUVE:
o World Wide Web (CEA URL):
http://www.cea.berkeley.edu/ (for those with WWW browsers)
telnet www.cea.berkeley.edu 200 (for those without WWW browsers)
o anonymous FTP/gopher: ftp.cea.berkeley.edu
o EUVE Electronic Newsletters (past issues available via CEA WWW):
Subscriptions: mail majordomo@cea.berkeley.edu ("subscribe euvenews")
Post message to all subscribers: mail euvenews@cea.berkeley.edu
o For additional information contact the Archive:
The EUVE Public Science Archive
Center for EUV Astrophysics
2150 Kittredge St.
Berkeley, CA 94720-5030
510-642-3032 (voice) or 510-643-5660 (fax)
archive@cea.berkeley.edu
3. 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.
--------------------------------------------------------------
EUVE OBSERVATIONS OF THE ANOMALOUS 1993 AUGUST OUTBURST OF SS CYGNI
Christopher W. Mauche, John C. Raymond, and Janet A. Mattei
To appear in the Astrophysical Journal (20 Jun 1995).
Target-of-opportunity observations of the dwarf nova SS Cygni were made by
the Extreme Ultraviolet Explorer (EUVE) satellite between 1993 August 17.1 and
23.6 UT (MJD 9216.6 and 9223.1). The observations cover the rise and plateau
phases of an anomalous outburst which began on August ~15.5 and which reached
maximum at V ~8.3 on August ~20.5. During the observations, the brightness of
the source as measured by the Deep Survey instrument rose from ~0.015 counts/s
to ~5 counts/s. A delay of ~3 days was initially observed between the EUV and
optical light curves, but this delay decreased to zero as the light curves
approached maximum.
During the interval August 17.3 to 23.6 UT, the 72-130 A flux as measured
by the Short Wavelength Spectrometer rose from ~6E-13 to ~6.7E-11 erg cm^(-2)
s^(-1), while the 72-90 A to 90-130 A count ratio remained constant at
1.39+/-0.05. Parameterizing the EUV spectrum with a blackbody absorbed by a
column of cold neutral material, we derive the luminosity L_b and fractional
emitting area f = L_b/4*pi*R^2*sigma*T^4 of the boundary layer as a function of
temperature kT. For kT = 30 eV, N_H ~4.4E19 cm^(-2), L_b ~5E32 erg/s, and
f ~1E-4. For kT = 20 eV, N_H ~7.0E19 cm^(-2), L_b ~2E33 erg/s, and f ~1E-3.
The optical through far-UV luminosity of the accretion disk in outburst is
L_d ~ 3E34 erg/s. Therefore, while simple theory predicts that the
luminosities of the boundary layer and accretion disk should be comparable
unless the white dwarf is rotating very rapidly, zeta = L_b/L_d ~1, we find
that zeta > 0.07.
The most interesting and enigmatic aspect of these observations is the EUV
spectrum, which evolved homologously over ~2 orders of magnitude in luminosity.
The constancy of the EUV spectrum over such a wide range of brightness seems
impossible to reconcile with the standard picture of boundary layer emission.
--------------------------------------------------------------
THE EUVE SPECTRUM OF THE HOT DA WHITE DWARF PG1234+482
Stefan Jordan, Detlev Koester, David Finley, Klaus Werner, and Stefan Dreizler
To appear in "White Dwarfs", eds. D. Koester & K. Werner (Springer Verlag,
Berlin), proceedings of the 9th European Workshop on white dwarfs.
We have analyzed the EUVE spectrum of PG1234+482 with fully blanketed model
atmospheres taking into account several million lines of heavy elements. Most
of the spectral features in the short (SW) and medium (MW) wavelength spectrum
can be identified with lines of iron, nickel and calcium ions.
--------------------------------------------------------------
THE EXTREME ULTRAVIOLET EXPLORER: OBSERVING A PARTLY CLOUDY UNIVERSE
S. Bowyer, R.F. Malina, and B. Haisch
Sky and Telescope, 88(6), 36-40, 1994. [CEA publication #637; not preprinted]
Since its launch in June 1992, the Extreme Ultraviolet Explorer satellite
has opened a wide window on a largely unexplored slice of the electromagnetic
spectrum.
--------------------------------------------------------------
RADIATIVE LEVITATION IN HOT WHITE DWARFS: EQUILIBRIUM THEORY
P. Chayer, G. Fontaine, and F. Wesemael
To appear in Astrophysical Journal Supplement. [CEA publication #639]
We present the results of detailed calculations of radiative levitation in
hot white dwarfs using the extensive and homogeneous atomic data given in
TOPBASE. Radiative accelerations and equilibrium abundances have been computed
for C, N, O, Ne, Na, Mg, Al, Si, S, Ar, Ca, and Fe on grids of pure hydrogen
and pure helium stellar envelope models. The DA model grid has log g = 7.0,
7.5, 8.0, and 8.5, and spans the range of effective temperature 100,000 K >=
T_eff >= 20,000 K in steps of 2,500K. The DO/DB grid is similar but extends to
T_eff = 130,000 K. We discuss at some length the input physics used in order
to provide a good physical understanding of radiative levitation under white
dwarf conditions. We also discuss the depth dependence and the morphology of
the reservoirs of levitating elements created by an equilibrium between the
radiative acceleration and the local effective gravity in various stellar
envelopes. The important role played in the morphology of the reservoirs by
dominant ionization states in closed-shell electronic configurations is
emphasized. Our central results are presented in the form of figures showing
the behavior of the expected photospheric abundance of each element as a
function of effective temperature and surface gravity. While only a handful of
abundances are available from the few analyses of observations that have been
carried out, we are nevertheless able to infer through a detailed comparison
that equilibrium radiative levitation theory fails to explain quantitatively
the observed abundance patterns of heavy elements in hot white dwarfs. At
least one other mechanism must be competing with radiative levitation and
gravitational settling in the atmospheres/envelopes of hot white dwarfs. This
basic conclusion is not affected by the inherent uncertainties and limitations
of our calculations. Among those, we single out our neglect of the effects of
trace pollutants in the background plasma, our use of a model envelope approach
to estimate photospheric abundances, our relatively crude description of the
momentum redistribution that an ion experiences following a photoexcitation,
and our neglect of the atomic fine structure. These represent areas where
improvements may be called upon in future calculations of radiative levitation
in white dwarfs. We finally indicate promising avenues for further progress in
this chapter of the theory of spectral evolution of white dwarfs.
--------------------------------------------------------------
LESSONS LEARNED FROM THE INFUSION OF AUTONOMOUS MONITORING INTO THE EUVE
SCIENCE OPERATIONS CENTER
M. Lewis, F. Girouard, F. Kronberg, P. Ringrose, A. Abedini, D. Biroscak,
T. Morgan, and R.F. Malina
To appear in Proceedings of the 1995 Goddard Conference on Space Applications
of Artificial Intelligence and Emerging Information Technologies. [CEA
publication #640]
The University of California at Berkeley's (UCB) Center for Extreme
Ultraviolet Astrophysics (CEA), in conjunction with NASA's Ames Research
Center (ARC), has implemented an autonomous monitoring system in the Extreme
Ultraviolet Explorer (EUVE) science operations center (ESOC). The
implementation was driven by a need to reduce operations costs and has allowed
the ESOC to move from continuous, three-shift, human-tended monitoring of the
science payload to a one-shift operation in which the off shifts are monitored
by an autonomous anomaly detection system. This system includes Eworks, an
artificial intelligence (AI) payload telemetry monitoring package based on
RTworks, and Epage, an automatic paging system to notify ESOC personnel of
detected anomalies. In this age of shrinking NASA budgets, the lessons learned
on the EUVE project are useful to other NASA missions looking for ways to
reduce their operations budgets. The process of knowledge capture, from the
payload controllers for implementation in an expert system is directly
applicable to any mission considering a transition to autonomous monitoring in
their control center. The collaboration with ARC demonstrates how a project
with limited programming resources can expand the breadth of its goals without
incurring the high cost of hiring additional, dedicated programmers. This
dispersal of expertise across NASA centers allows future missions to easily
access experts for collaborative efforts of their own. Even the criterion used
to choose an expert system has wide spread impacts on the implementation,
including the completion time and the final cost. In this paper we discuss,
from inception to completion, the areas where our experiences in moving from
three shifts to one shift may offer insights for other NASA missions.
--------------------------------------------------------------
---------------------------------------------------------------------------
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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