EEEEEEEEEEE U U V V EEEEEEEEEEE
E U U V V E
E U U V V E
EEEEEEE U U V V EEEEEEE
E U U V V E
E U U V V E
EEEEEEEEEEE UUUUU V EEEEEEEEEEE
---------------------------------------------------------------------------
ELECTRONIC NEWSLETTER OF THE EUVE OBSERVATORY
---------------------------------------------------------------------------
Vol 5, No. 3 17 Mar 1995 ISSN 1065-3597
---------------------------------------------------------------------------
Notes from the Editor
=====================
by Brett A. Stroozas, ISO Manager
Welcome to the electronic newsletter for NASA's Extreme Ultraviolet Explorer
(EUVE) satellite, compiled and published monthly by the Integrated/Intelligent
Science Operations (ISO) group at the Center for EUV Astrophysics (CEA) at the
University of California, Berkeley (UCB). The contents of this issue of the
EUVE electronic newsletter are as follows:
1. Recent Science Highlights
2. Cycle 3 Approved GTO Targets
3. EUVE Papers for the IAU
4. Science Payload Instrument Health Status Report
4.1 Deep Survey Detector Reduced Gain on Boresight
4.2 Transient Hot Pixels (THPs)
4.3 Filter Degradation in Scanner A
4.4 Gain Sag in All Detectors
5. ESOC One-Shift Operations Begin on 14 Feb 1995
6. EUVE Guest Observer Center News
6.1 New EGO Program Documentation
6.2 Switch to WSZ Mode for GO Observations
6.3 TOO Observation of AM Her
7. Notes from the EUVE Science Archive
7.1 Call to Students Using EUVE Data
7.2 Prototype Data Delivery Service for the IAU
7.3 GO Data Release List for 1 Apr 1995
7.4 On-Line Access to EUVE
8. Abstracts of Recently *Accepted* EUVE Papers
9. CEA/SSL Job Listings
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 February 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
------------------------------------------------------------------
VW Cep EUVE J2037+756 K0Vvar 29 Jan - 04 Feb 1995 ---
17 Lep HD 41511 Apsh 04 Feb - 07 Feb 1995 ---
MRK 421 UGC 6132 BLLac 04 Feb - 07 Feb 1995 RAP
HZ 43 WD 1314+293 DAw 07 Feb - 09 Feb 1995 CAL
RE J0715-702 EUVE J0715-704 DA 09 Feb - 11 Feb 1995 ---
Moon -------- SolSys 11 Feb - 11 Feb 1995 ---
RE J0715-702 EUVE J0715-704 DA 11 Feb - 12 Feb 1995 ---
DH Leo HD 86590 K0V 12 Feb - 20 Feb 1995 ---
YY Gem HD 60179 C M1Ve 20 Feb - 03 Mar 1995 CY3
------------------------------------------------------------------
Key to Notes:
RAP = simultaneous Right Angle Program (RAP) imaging observation
CAL = calibration observation
CY3 = begin Cycle 3 observations
The observation of DH Leo marked another major milestone for the EUVE mission
-- the completion of two highly successful years ("Cycles") of GO observations.
In those two years EUVE has carried out nearly 300 separate exposures of ~150
different targets from 139 approved GO proposals. The subsequent YY Gem
observation initiated Cycle 3 of the EUVE GO Program.
1. Recent Science Highlights
============================
by Dr. Antonella Fruscione, CEA Scientist
Dr. Christopher Mauche (Lawrence Livermore National Laboratory) found
high-amplitude (>20%) quasi-periodic oscillations (QPO) with periods of 7-10
seconds in the count rate in the EUVE Deep Survey (DS) data from both the 1993
August and 1994 June outbursts of the cataclysmic variable SS Cygni. These
QPOs have been known about for some time from HEAO-1 and EXOSAT studies, but
no other mission has had such extensive coverage of the oscillations, or has
been able to track the evolution of the period, phase, and amplitude of the
oscillations as a function of time, outburst phase, etc. A precise knowledge
of the properties of the oscillations is crucial in order to understand the
nature, size, and mechanisms at work in the emitting region. Dr. Mauche is
also investigating the presence of QPOs in the VW Hyi DS data.
2. Cycle 3 Approved GTO Targets
===============================
by Dr. Ron Oliversen, EUVE Deputy Project Scientist (GSFC)
As EUVE Principal Investigator, S. Bowyer/UCB, is entitled to 5% (470 ksec)
of the spectroscopy time for Guaranteed Time Observations (GTO). Those GTO
targets that have been selected and approved are listed below. GTO targets
were selected after the GO peer review, thus these targets do not conflict with
GO programs.
-----------------------------------------------------
Target ID Time RA Dec
(ksec) (2000) (2000)
-----------------------------------------------------
1 TON S180 100 00 57 20.1 -22 22 56
2 DIFFUSE BKGD 100 01 15 15.9 +07 57 38
3 CGCG 0212.0-0100 10 02 14 33.0 -00 46 00
4 EUVE J0723-277 100 07 23 20.0 -27 47 22
5 MKN 110 10 09 25 12.9 +52 17 11
6 MGC +11-13-018 10 10 19 12.0 +63 58 12
7 MKN 142 10 10 25 31.3 +51 40 35
8 PG 1116+215 10 11 19 08.0 +21 09 36
9 VIRGO 10 12 30 49.4 +12 23 28
10 IRAS 13349+2438 10 13 37 18.6 +24 23 03
11 PG 1444+407 10 14 46 45.9 +40 35 06
12 NO Name 10 22 48 41.2 +51 09 54
-----------------------------------------------------
3. EUVE Papers for the IAU
==========================
The International Astronomical Union (IAU) Colloquium 152 will be held on
27-30 Mar 1995 in Berkeley, CA. The colloquium focuses on EUV astronomy and
will include ~120 oral and poster presentations. Among these presentations
will be the following from CEA:
* "New Insights on the ISM from EUV Observations," S. Bowyer.
* "Low-Cost Operations Approaches, Innovative Technology Testbedding and
Education Programs on the EUVE Project," R.F. Malina and R. Polidan.
* "The Extreme Ultraviolet Explorer Public Right Angle Program," K. McDonald,
N. Craig, E. Olson, and C. Christian.
* "The Education Outreach Program at CEA," I. Hawkins, R. Battle,
C.A. Christian, R.F. Malina, and N. Craig.
* "Adaptation of Science Data and Archive Tools for the Science Information
Infrastructure Education Outreach Program," C. Christian, I. Hawkins,
R. Malina, K. Dow, and S. Murray.
* "The Second EUVE Source Catalog," M. Lampton, S. Bowyer, J. Lewis, X. Wu,
P. Jelinsky, R. Lieu, and R.F. Malina.
* "Analysis of EUVE Light Curves of AM Her Systems," M.M. Sirk and S.B. Howell.
* "EUVE Constraints on Models of Low-Mass X-ray Binaries," D.J. Christian,
M.M. Sirk, K. McDonald, and J. Edelstein.
* "A Spectroscopic Survey in the EUV of the `Coolest' Hot DA Stars," J. Dupuis,
S. Vennes, and A.K. Pradhan.
* "The EUVE Guest Investigator Science Program," K. Anderson and B.A. Stroozas.
* "The Secrets of EUVE J2056-17.1," M. Mathioudakis et al.
* "Optical Identification of EUV Sources: Extreme Ultraviolet Explorer
Sources I," N. Craig, A. Fruscione, J. Dupuis, M. Mathioudakis,
M. Abbott, C.A. Christian, J.J. Drake, R. Green, T. Boroson, and
S. Howell.
* "High-Temperature Tails: An EUV(E) Catastrophe?," J.H.M.M. Schmitt,
J.J. Drake, and R.A. Stern.
* "Modeling of EUVE Observations of the Io Plasma Torus," R. Lieu, N. Thomas,
D.E. Innes, G.R. Gladstone, D.T. Hall, and F. Herbert.
* "The FIP Effect and Element Abundance Anomalies in Late-Type Stellar
Coronae," J.J. Drake, J.M. Laming, and K.G. Widing.
* "Searching EUVE Data for Transient/Flaring Extreme Ultraviolet Sources,"
J. Lewis, S. Bowyer, M. Lampton, and X. Wu.
* "Intense X-Ray and EUV Emission from Active Galactic Nuclei," J.P.D. Mittaz,
R. Lieu, C.-Y. Hwang, S. Bowyer, and J. Lewis.
* "EUVE Observations of the Seyfert Galaxy MRK 279," C.-Y. Hwang and S. Bowyer.
* "X-ray Selected Galaxies Observed with the Extreme Ultraviolet Explorer,"
A. Fruscione.
* "The EUVE Diffuse Radiation Mission (EURD)," J. Edelstein, S. Bowyer,
J.P. Mercader, and A. Gimenez.
* "Improved Calculations of the Equilibrium Abundances of Heavy Elements
Supported by Radiative Levitation in the Atmospheres of Hot DA White
Dwarfs," P. Chayer, S. Vennes, A.K. Pradhan, P. Thejll, A. Beauchamp,
G. Fontaine, and F. Wesemael.
* "An Optical Study of the Field Including the Source: EUVE J1027+323;
Discovery of a QSO and Hidden Hot White Dwarf," R. Genova, S. Bowyer,
S. Vennes, P. Henry, R. Lieu, and J. Beckman.
4. Science Payload Instrument Health Status Report
==================================================
by Amelia Marshall, Instrument Health Engineer
All elements of the EUVE optics and detector hardware are performing well
as the instrument surpasses its designed mission lifetime and approaches the
extended mission phase. Given the fragility of materials in the detectors,
some degradation has inevitably occurred. The detectors are carefully monitored
to ensure optimized performance and no loss of quality in science data
acquisition. The most significant EUVE instrument health issues are described
in the following sections.
4.1 Deep Survey Detector Reduced Gain on Boresight
--------------------------------------------------
The Deep Survey detector was damaged early in the mission during an
observation of the EUV-bright white dwarf HZ43. Since then, observations of
bright EUV sources have further reduced throughput on boresight; current
observations are carefully planned to avoid this "deadspot". To further
minimize any damage, observations of very bright sources are dithered (pointed
at a series of randomly chosen locations near the target instead of at a
single one for the entire observation). GOs who are concerned with high
accuracy light curves should be wary of dithered observations, according to
instrument scientist John Vallerga, as some events may impinge on the damaged
area.
4.2 Transient Hot Pixels (THPs)
-------------------------------
During times when count rates are very high, transient hot pixels are
sometimes seen in EUVE data. The count rate threshold which causes the onset
of THPs is believed to be around 200 counts per second in any given quadrant.
"THPs appear in a data set as thinly scattered single bright pixels covering
one or more quadrants of the instrument," comments GO scientist Mark Abbott.
"Excess counts in a THP are on the order of 10. The number of THPs over the
whole quadrant will depend on how many periods of high count rate have occurred
during an observation, but is typically on the order of 100."
The THP problem has been observed since launch. It is believed to be due to
an error in the on-board event processing software. Development of a software
patch is in progress.
4.3 Filter Degradation in Scanner A
-----------------------------------
Scanner A's Al/Ti/C filter has shown greatly increased UV leakage since
launch. A series of tests is underway to measure the extent to which EUV
throughput is affected by this leakage. One hypothesis under investigation
is that something caused a "cloud" of very small pinholes to appear on this
filter. For most sources, the UV leak is not a problem. It is of concern for
sources which emit at both UV and EUV wavelengths. In these cases, there is
a risk that UV emissions can overwhelm the EUV.
4.4 Gain Sag in All Detectors
-----------------------------
Pulse height thresholds, formally known as lower- (LLD) and upper-level
discriminators (ULD), can be reset to maintain calibration in order to
compensate for gain drift as detectors age. Lower thresholds were recently
adjusted for the Scanner C and Deep Survey detectors. Similar adjustments
are also anticipated as required by the other instruments.
In practice, only the lower threshold is reduced for this purpose.
Decreasing the upper thresholds would have the undesired effect of removing
stim pulser (electronic calibration) events from the data.
The other option in adjusting for detector gain sag is to increase high
voltage gain. This, however, results in a reduced signal-to-noise ratio of
the input signal. It could also increase the incidence of hotspots and spikes
in the detector output. No hotspots are now being seen in the detectors;
should any appear, they can be blanked out either in hardware or by the
on-board software.
5. ESOC One-Shift Operations Begin on 14 Feb 1995
=================================================
by Dennis Biroscak, Payload Operations Manager
On Valentine's Day, 14 February 1995, the EUVE Science Operations Center
(ESOC) completed a major goal in its drive to lower costs and improve
operations for the EUVE science payload. For over a year, UCB operations
personnel, along with hardware and software engineers, have been engaged in
reducing ESOC staffing from 24 hours/day (3 shifts) to 9 hours/day (one shift)
while maintaining the same health and safety monitoring of the payload.
Our goal was accomplished with the successful implementation of Eworks, a
suite of UCB programs based on RTworks, commercial augmented intelligence (AI)
telemetry monitoring software from Talarian Corporation. Eworks autonomously
monitors the payload and pages an Anomaly Response Coordinator if any problems
occur.
The initial selection of the RTworks software package was made in January
of 1994, although the ESOC staff began preparing for the transition several
months earlier. The first Eworks system was delivered for testing only four
months later, in June of 1994. By September, the ESOC was ready to begin a
series of one-shift simulations phases.
During the first simulation phase, the ESOC staff performed all their normal
duties while closely monitoring the performance of the new software. We began
to keep detailed records of all the tasks the ESOC staff performed, particularly
those during the evening and night shifts. During the months that followed,
all tasks other than payload monitoring were systematically eliminated or moved
to the day shift.
In December, the ESOC was "closed" at night and the Eworks software performed
all payload monitoring. The ESOC staff remained in the building in order to
respond immediately to any problems. Finally, in February 1995, after five
months of successful simulations, everyone picked up their pagers and went home
each evening.
Our transition to one shift operations required significant changes in the
roles of our operations staff. The ESOC has a dedicated crew of undergraduate
students who trained to take on more responsibility for monitoring the payload
during normal operations. The operations controllers, freed by the students
from some of their tasks, created the logic diagrams for Eworks, the
"intelligence" in the AI software. The ESOC staff and software engineers
spent many hours creating detailed test data sets, testing and correcting the
software logic until it could be trusted.
Our efforts point the way toward lower mission operations costs for all
NASA missions. Future astrophysical missions will be able to spend a greater
proportion of their budgets for science related tasks and less on operations.
Our efforts at innovation in mission operations do not end with the transition
to one shift operations. The CEA Information Systems Development (ISD) and
Integrated/Intelligent Science Operations (ISO) groups will work together to
continuously reduce operations costs by integrating and automating the entire
science operations process -- from initial observation proposal to science
planning and scheduling to instrument commanding and configuration to data
processing and delivery.
6. EUVE Guest Observer Center News
==================================
by Anne Miller, EGO Center Technical Writer
6.1 New EGO Program Documentation
---------------------------------
The EGO Center recently announced plans to update and reorganize
documentation for the EUVE GO data products, software, and reference data.
The first edition of the new EUVE Guest Observer Center Data Products Guide
has now been mailed to all EUVE GO's and many active Co-Investigators. The
Data Products Guide, like the Software User's Guide, is part of the current
IRAF/EUV software release. The current software version is number 1.5, so
the first edition of the Data Products Guide is version 1.5.
The Data Products Guide is the most current documentation for the EUVE GO
program data sets, as processed with version 1.5 of the IRAF/EUV software.
This includes GO data mailed out since the software release, and all data
sets furnished through the EUVE public data archive since December of 1994.
The Data Products Guide is also available from the CEA/EUVE anonymous ftp
site at
cea.ftp.cea.berkeley.edu
in the directory /pub/documents/docs1.5/data_guide. It can be downloaded in
a number of postscript files; see the README file in the same directory. The
complete document can be downloaded in the form of a single compressed tarfile,
datapg.tar.Z. All files are less than one Megabyte in size.
The most recent release of the EUVE Guest Observer Software User's Guide
is still release number 1.4, and much of the material remains applicable to
version 1.5 of the software. See the EUVE electronic news, 4(12), for a
summary of differences in the new software. The ftp data_guide directory
also contains a cover letter (PostScript) with a table of correspondences
between material in version 1.5 documentation and version 1.4. All data tapes
mailed by the EGO Center still include a copy of the 1.4 Software User's Guide
in postscript format, in the "documents" tarfile. Version 1.5 of the Software
User's Guide will be available later this spring.
6.2 Switch to WSZ Mode for GO Observations
------------------------------------------
Acting upon a proposal from EUVE Scientist John Vallerga, and the results
of tests on instrument data, the default instrument mode for GO Observations
was, as of 1 Mar 1995, changed to WSZ. Previously, night-time data acquisition
proceeded in XY mode, in which the payload electronics convert the raw detector
WSZ coordinate events to XY before telemetering them to the ground. The
advantage of using XY mode is that there are a significant number of additional
photon slots available in the telemetry stream. The advantage of using WSZ
mode is that the instruments report the raw charge recorded on the wedge,
strip, and zigzag portions of the detector anodes directly. This provides GOs
with a mechanism for filtering event pulse heights to remove non-EUV background
events, thereby increasing the signal-to-noise ratio in their data. "The new
method improves the quality of data acquired by the spectrometer detectors for
almost every source," comments Vallerga.
Although the switch to WSZ mode means that fewer events can be telemetered
from the detectors in each major frame (1.024 seconds) of telemetry, an
instrument software algorithm ("primbsching") that allots an equal number of
telemetry slots to each detector will allow GOs to compensate for any loss of
source data in the vast majority of cases, even if one or more detectors have
high background count rates.
The mode switch will not affect the data products delivered to GOs: detector
positions of events will be calculated in processing on the ground, and the
only change in the data products will be that columns with the W, S, and Z
values will be added to event telemetry tables. GOs will be able to reprocess
their data and filter out many background events, which have a different
pulse-height distribution from those caused by EUV photons.
6.3 TOO Observation of AM Her
-----------------------------
The target of opportunity AM Herculis was observed with the EUVE
Spectrometer/Deep Survey telescope on 8-12 March 1995 as part of proposal
94-EUVE062, "EUVE Spectroscopy of the Accretion Region in AM Herculis," for
Dr. Chris Mauche of Lawrence Livermore National Laboratory. The observation
was coordinated with UV observations by the Astro-2 mission aboard the space
shuttle Endeavor (STS-67) as well as by the ASCA and ROSAT satellites.
7. Notes from the EUVE Science Archive
======================================
7.1 Call to Students Using EUVE Data
------------------------------------
The Archive is very interested in hearing from or about any students that
are using EUVE data as part of their Masters of PhD thesis work. If you or
someone you know are in this category of students, please inform the Archive
(archive@cea.berkeley.edu).
As with any researcher interested in EUVE data analysis, these students are
encouraged and invited to become EUVE Guest Investigators (GIs). The GI
Program offers to researchers assistance from experienced CEA scientific and
technical personnel in the understanding and analysis of EUVE data products.
It is easy to become a GI; contact the Archive via e-mail at the above address
or through the CEA WWW site (http://www.cea.berkeley.edu).
7.2 Prototype Data Delivery Service for the IAU
-----------------------------------------------
by Holly Jessop, EUVE Science Archive Research Associate
The EUVE Science Archive will prototype a new data delivery service during
this month's IAU conference in Berkeley, CA: individually selected archival
GO data sets will be made available "on demand" via CD-ROM. In the past,
CD-ROM access to data was only available via mass-produced volumes containing
limited pre-selected data sets. With the new service, researchers will be
given the opportunity to individually select data sets for on-demand placement
onto CD-ROM.
During the conference, attendees will be able to browse and select data sets
from a book containing a collection of extracted spectra from ~50 of the most
interesting and popular data sets. This collection represents about one-third
of the non-proprietary GO data sets currently available. A "custom" CD-ROM
will then be individually produced for each attendee who places an order.
Delivery of CD-ROMs is expected to occur within 24 hours of a data request.
Therefore, most of those attendees requesting data will receive their CD-ROM
during the conference. Of course, the usual 8mm tape data delivery option will
be available for those who request it. In order to accommodate as many
individual researchers as possible, on-demand CD-ROM orders will be limited to
one per requester.
Following the conference, the Archive plans to continue to make data
available on CD-ROM. When researchers request archival data, they will be
given a media option of CD-ROM or 8mm tape.
While the production of "custom" CD-ROMs on an individual basis is more
cost-effective than the production of an entire new CD-ROM volume, it is also
hoped that researchers will find these personalized CD-ROMs more useful.
7.3 GO Data Release List for 1 Apr 1995
---------------------------------------
The table below lists the GO observations which become public on 1 Apr
1995; with this release all Cycle 1 observations will now be publicly available.
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
===============================================================
AG Dra 22 Dec 27 1993 - Dec 28 1993 K0 go0153
AG Dra 35 Dec 29 1993 - Dec 30 1993 K0 go0154
AG Dra 62 Feb 22 1994 - Feb 25 1994 K0 go0155
alpha Vir 47 Jan 25 1994 - Jan 26 1994 B1IV go0156
Capella 68 Dec 22 1993 - Dec 24 1993 G+G go0157
Capella 26 Dec 25 1993 - Dec 25 1993 G+G go0158
Capella 39 Feb 15 1994 - Feb 16 1994 G+G go0159
HD 82558 250 Dec 10 1993 - Dec 19 1993 K0Ve go0160
Moon 3 Dec 21 1993 - Dec 21 1993 SS go0161
Moon 2 Jan 29 1994 - Jan 29 1994 SS go0162
PG 1520+525 152 Feb 9 1994 - Feb 15 1994 WD go0163
PSR 0437-471 111 Jan 31 1994 - Feb 4 1994 Puls go0164
RE 1016-053 124 Jan 27 1994 - Jan 31 1994 WD+M go0165
RE 1309+081 30 Jan 24 1994 - Jan 25 1994 NOID go0166
sigma CrB 129 Feb 16 1994 - Feb 21 1994 G0 go0167
Vela 141 Feb 4 1994 - Feb 9 1994 SNva go0168
WD 1057+719 52 Jan 5 1994 - Jan 7 1994 WD go0169
WD 1057+719 51 Feb 21 1994 - Feb 22 1994 WD go0170
===============================================================
7.4 On-Line Access to EUVE
--------------------------
Listed below are the various methods for on-line access to EUVE:
o CEA World Wide Web (WWW) 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
8. 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.
--------------------------------------------------------------
THE COMPOSITION AND STRUCTURE OF WHITE DWARF ATMOSPHERES REVEALED BY EXTREME
ULTRAVIOLET SPECTROSCOPY
M.A. Barstow, J.B. Holberg, K. Werner, and J.A. Nousek
To appear in Advances in Space Research
The ROSAT X-ray and EUV sky survey revealed that most H-rich white dwarfs
hotter than 40,000K contain significant quantities of heavy elements in their
atmospheres. However, the ROSAT data are unable to say anything about the role
of helium in the hottest white dwarfs. Spectroscopic observations with the
Extreme Ultraviolet Explorer allow us to perform a direct and sensitive search
for HeII absorption features in DA white dwarfs. In almost all cases no trace
of He is found but G191-B2B and HZ43 may have photospheric He, which is an
important result for our views of the evolutionary relationships between H
and He-rich groups of white dwarfs. Early studies of H deficient white dwarfs
with EUVE encounter difficulties in interpreting the spectra, showing that even
more detail, in the form of additional opacity sources, needs to be included in
our state-of-the-art model atmospheres.
--------------------------------------------------------------
THE REMARKABLY LOW ABUNDANCE OF HELIUM IN THE ATMOSPHERE OF THE DA WHITE
DWARF HZ43
M.A. Barstow, J.B. Holberg, and D. Koester
To appear in Monthly Notices of the Royal Astronomical Society
We report the most sensitive search yet made for helium in the atmosphere of
the hot DA white dwarf HZ43, with observations made by the Extreme Ultraviolet
Explorer (EUVE). Prior upper limits on the presence of He in DA white dwarfs
using EUVE spectra have been affected by fixed pattern efficiency variations in
the detector system which limited the signal-to-noise which could be achieved.
Recent implementation of a new observing mode designed to circumvent this
problem has yielded an ~4-fold improvement in the effective signal-to-noise.
This allows detection of weaker absorption features than hitherto and, in the
absence of visible lines, provides dramatically improved upper limits. We find
that the He abundance (by number fraction) in HZ43 is less than ~3.0E-7. This
is completely at odds with the calculations of radiative levitation theory,
which predict a He abundance of at least 3.0E-6 for a star with the mass and
temperature of HZ43. This has important consequences for our understanding of
the physical mechanisms that determine the photospheric composition of white
dwarfs.
--------------------------------------------------------------
A PRELIMINARY REVIEW OF EUVE SCIENCE
S. Vennes, J.J. Drake, M. Mathioudakis, B. Welsh, A. Fruscione, D.T. Hall,
J. Warren, and S.B. Howell
Irish Astronomical Journal, 22(1), 7-16, 1995 [CEA publication #641; not
preprinted]
This paper presents some initial results obtained during the first year of
the EUVE Guest Observer spectroscopic program.
--------------------------------------------------------------
9. CEA/SSL Job Listings
=======================
The following Senior Fellow position is being offered at the Space Sciences
Laboratory (SSL) at the University of California, Berkeley. This listing was
taken from the American Astronomical Society (AAS) Job Register.
No. 8653
Senior Fellow Program
The University of California At Berkeley
Space Sciences Laboratory
Berkeley, CA 94720-7450
Attention: Christopher McKee, Director
Appointments will be awarded to Ph.D. scientists who have demonstrated
leadership and creativity in the space sciences, with emphasis on infrared
astrophysics, UV astrophysics, high energy astrophysics and space physics.
Fellows will receive Principal Investigator status and will be expected to
develop self-supporting research groups and participate in the supervision
of graduate student research. Some start up funds are available. The level
to be determined at the time of appointment, will be Assistant, Associate,
or Full Research Scientist, depending on qualifications. Vita bibliography,
statement of prospective research program and three letters of reference
should be sent by March 31, 1995 to Christopher McKee at the above address.
AAE/EOE
---------------------------------------------------------------------------
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 Manager: 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
[HomePage]
[Email]
[Search]
[Glossary]
Page created by webmastr@cea.berkeley.edu
Last modified 10/4/97