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 4, No. 10 18 Oct 1994 ISSN 1065-3597
---------------------------------------------------------------------------
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) in Berkeley, CA. The
EUVE observatory performed well throughout the month of September, completing
observations of the following Guest Observer (GO) targets (spectral types,
taken from the SIMBAD or internal CEA databases, are indicated in parentheses):
CF Tuc (G3:V+), FK Aqr (M0Vpe), HD220657 (F8IV), MCT0027-6341 (WD), WD0050-332
(WD), and the Moon. A daytime observation test was conducted on the target
V711 Tau (G9V).
The contents of this issue of the EUVE electronic newsletter are as follows:
1. NASA Administrator Dr. Dan Goldin Comments on EUVE
2. Education Outreach at CEA
3. Mission Operations Innovation at CEA
4. Recent EUVE Science Highlights
5. Notes from the EUVE Guest Observer Center
5.1 ISM Column Densities and Extinction
5.2 Scanner Backgrounds
5.3 Scanner/Deep Survey Calibration Data
6. Notes from the EUVE Science Archive
6.1 New Services Available via the World Wide Web
6.2 GO Data Release List for 1 November 1994
6.3 Accessing the Archive
7. 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).
1. NASA Administrator Dr. Dan Goldin Comments on EUVE
=====================================================
In a talk entitled "The Next Frontier" given on 19 Aug 1994 at the
Commonwealth Club of California in San Francisco, NASA Administrator
Dr. Dan Goldin had the following glowing comments regarding the EUVE
mission:
"And in fact today, Roger Malina, who is at the head table walked
up to me ... he is from UC Berkeley, and he said "Mr. Goldin, let
me tell you, you cut our budget on the EUVE program" ... that's the
Extreme Ultraviolet Explorer program ... it's an Astrophysical
program ... "and we're cutting into the mission operations and
data analysis budget!" If we want to start new things, we can't
keep having people employed operating the old things where the
operating budget keeps going up ... so he said "let's just cut the
operating budget!" So what he did was -- he employed artificial
intelligence and expert systems and, instead of having three shifts
operating the spacecraft, with people going around the clock, he
changed the paradigm ... Less is more, and we're getting more
reliable operations of the spacecraft with one shift instead of
three."
The audio recording of the above text is accessible electronically from the
CEA World Wide Web (WWW) Home Page (http://www.cea.berkeley.edu).
2. Education Outreach at CEA
============================
by Dr. Isabel Hawkins, CEA Education Outreach Coordinator
With funding from NASA's Astrophysics Division, CEA is sponsoring an
eight-month K-12 education outreach demonstration project. "Science On-Line
(SOL) -- Earth and Space Science for the Classroom" began in September 1994
and links together formal and informal science centers, each of them having
unique and complementary assets. The project joins the efforts of CEA, the
Lawrence Hall of Science and the U.C. Museum of Paleontology, with San
Francisco's Exploratorium, and Chicago's Adler Planetarium for the purpose
of coordinating on-line resources that respond to the needs of K-12 teachers,
students, and the general public. The project will result in coordinated
resources available through the WWW with Mosaic, including virtual museums,
NASA mission information and data, and teacher-developed lesson plans that make
use of the unique aspects of the Internet. This pilot project is a precursor
to an overarching effort entitled "Science Information Infrastructure (SII)"
which will link the Nation's science museums with research institutions to
bring coordinated resources to the K-12 and general public communities. The
SII has received partial funding from the High Performance Computing and
Communications division of NASA, and partners the Center for EUV Astrophysics
and the Smithsonian Astrophysical Observatory with the Exploratorium, Lawrence
Hall of Science, UC Museum of Paleontology, Smithsonian National Air and Space
Museum, Science Museum of Virginia, Chicago's Adler Planetarium, New York Hall
of Science, Boston Museum of Science, and the Earth Observing Satellite
Company. These projects are designed to make certain that as schools gain
access to the information superhighway, K-12 educators and students will find
appropriate resources that respond to their particular needs.
3. Mission Operations Innovation at CEA
=======================================
The EUVE Science Operations Center (ESOC) is working to complete development
and testing for single-shift 10-hour daily operations. An internal readiness
review was held at CEA on 5 October to judge the readiness of the ESOC to
move from the current triple-shift, 24-hour-a-day coverage to a single-shift
scenario without increasing the risk to the mission requirements. The panel
recommended that the ESOC proceed after meeting the self-imposed internal
criteria and after obtaining Goddard Space Flight Center (GSFC) Project Office
sign-off.
On another front, the EUVE operations test-bed team has completed evaluation
of the Jet Propulsion Laboratory's Spacecraft Health Inference Engine (SHIE).
The test-bed continues to host NASA Missions interested in low-cost operations.
Hubble Space Telescope and Lockheed support personnel visited CEA to view the
"E-works" implementation that will autonomously monitor science payload health
and safety and current test-bed activities. The SOFIA project from NASA Ames
Research Center visited CEA to investigate similarities in mission concepts that
may prove to be test-bed areas.
4. Recent EUVE Science Highlights
=================================
by Dr. Antonella Fruscione, EUVE Scientist
The following are recent science highlights from the EUVE mission:
* The detection of an ancient (5 billion years old) milli-second pulsar with
the Deep Survey Telescope during Guest Observer observations. Because old
neutron stars are expected to have cooled to non-EUVE emitting temperatures,
detection of this one indicates that highly energetic re-heating has taken
place. These observations are used to discriminate between a diverse array
of standard and exotic re-heating mechanisms, and also to elucidate the
ionization state of the interstellar medium along the path to the star
(Edelstein, et al.).
* The light curve of the intermediate polar cataclysmic variable EX Hya shows
clear evidence for eclipses by the secondary star and also by the accretion
stream. There is modulation at the white dwarf rotation period. Most of
the EUV flux probably arises in the "accretion curtain" or region between
the innermost radius of the accretion disk and the white dwarf itself, where
material begins to follow the magnetic field lines rather than rotate in
Keplerian fashion (Hurwitz, et al.).
* The paper "A SPECTROSCOPIC MEASUREMENT OF THE CORONAL DENSITY OF PROCYON"
by Schmitt, Haisch, and Drake has just come out as a report to the journal
Science (Vol. 265, pp. 1420-22). The main result is that using the ratio
of two Fe XIV lines at 211.32 and 264.79 A, the authors determined a density
of 4-7E+09 electrons/cm^3 -- a factor of 2-3 higher that in typical solar
active regions. This is the first direct measurement of the coronal density
in another solar-like star. From this value the authors estimated that
about 6% of the stellar surface is covered by about 7E+04 loops.
5. Notes from the EUVE Guest Observer (EGO) Center
==================================================
by Anne Miller, EGO Technical Writer
The following sections provide relevant information to those researchers
who have proposed in Cycle 3 of the GO Program for Scanner and Deep Survey
imaging observations.
5.1 ISM Column Densities and Extinction
---------------------------------------
For help in estimating interstellar medium (ISM) column densities and
extinctions, researchers may use the tools provided on the EGO Center WWW Home
Page via the URL http://www.cea.berkeley.edu/ego/HomePage.html. Click on the
highlighted text "ISM Hydrogen Column Density Search Tool" to use a routine
that provides several of the nearest measured ISM columns for a given position.
Click on the text "ISM" to run a program that computes the transparency of the
ISM using a commonly used model which only requires a few input parameters.
The C source code for the ISM program may also be obtained from the CEA
anonymous ftp site (ftp.cea.berkeley.edu; /pub/archive/software/ism).
5.2 Scanner Backgrounds
-----------------------
To estimate background levels for the Scanner telescopes, researchers may
use the CEA WWW "Count-Rate Request Form" from the Survey Home Page (URL above)
to obtain a data file for some sky location near their target, in which no
sources were detected. After clicking on the "Count-Rate Request Form" box in
the Home Page, read the instructions and complete the form with an RA and Dec,
using a search radius of 0.05 degrees and a confidence limit of 3.0 sigma.
The counts in each survey band-pass will be computed from survey skymaps and
will be delivered via e-mail. The flux is reported in counts/(arc minute)^2,
and the file includes a significance factor derived from chi-squared statistics.
Check the significance before using the flux as a background estimate; the
value should be less than 9.0 to insure that no sources were actually found
within the search radius.
5.3 Scanner/Deep Survey Calibration Data
----------------------------------------
Calibration data on the Scanner and Deep Survey instruments is available
by means of the CEA WWW URL (http://www.cea.berkeley.edu; click on "EUVE Survey
Home Page") or via the CEA anonymous ftp site (ftp.cea.berkeley.edu;
/pub/archive/survey/calibration_data). The available calibration data includes
effective areas, point-spread-functions, and vignetting maps. The files and
limited documentation are available separately, together, or as a single UNIX
TAR-format file.
6. Notes from the EUVE Science Archive
======================================
by Brett Stroozas, Archive Manager
6.1 New Services Available via the World Wide Web (WWW)
-------------------------------------------------------
Two new services are now available to researchers via the CEA WWW Home Page
(http://www.cea.berkeley.edu under Archive/Data). The first is a revised
version of the spectral browser which allows users to browse and retrieve
public EUVE 1-d spectra. The new revised version is much easier to use as
it allows one to search the data by spectral type and/or position. Additional
search options will soon be available.
The second new service is the availability of the published EUVE source
catalogs on the WWW via NASA's Astrophysics Data System (ADS) catalog service.
The ADS catalog service, which has recently come into operation on the WWW,
offers users with most of the capabilities of the classical ADS catalog service
but with much improved speed and ease of use. The available EUVE catalogs are
the following:
o euve_bsl -- "The Extreme Ultraviolet Explorer Bright Source List" (Malina,
et al. 1994)
o euve_cat1 -- "The First EUVE Source Catalog" (Bowyer, et al. 1994)
o euve_cat1supp -- supplement table (Table 7) to "The First EUVE Source
Catalog" (Bowyer, et al. 1994)
o euve_rap1 -- "Serendipitous EUV Sources Detected during the First Year of
the Extreme Ultraviolet Explorer Right Angle Program" (McDonald, et
al. 1994)
The ADS catalog service may be accessed directly via the URL
http://adswww.harvard.edu/catalog_service.html
or through the Archive/Data section of the CEA Home Page.
6.2 GO Data Release List for 1 November 1994
--------------------------------------------
The table below lists the GO observations which become public on 1 November
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 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 Nov 1994:
AM_HER 136 Sep 23 1993 - Sep 28 1993 CV go0106
AR_LAC 90 Oct 12 1993 - Oct 15 1993 G2IV go0107
HD7672 84 Sep 28 1993 - Oct 1 1993 G5 go0108
HR1099 81 Sep 16 1993 - Sep 19 1993 G+K go0109
HR1099 36 Sep 19 1993 - Sep 20 1993 G+K go0110
HR1099 32 Sep 20 1993 - Sep 21 1993 G+K go0111
LAMBDA_AND 90 Oct 16 1993 - Oct 19 1993 G8 go0112
R_AQU 60 Aug 31 1993 - Sep 2 1993 M7 go0113
RE1938-461 27 Aug 16 1993 - Aug 17 1993 CV go0114
RE1938-461 124 Oct 6 1993 - Oct 10 1993 CV go0115
===============================================================
6.3 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
7. 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 OPTICAL THICKNESS OF STELLAR CORONAE IN EUV LINES
C.J. Schrijver, G.H.J. van den Oord, and R. Mewe
Astronomy & Astrophysics, 1994, 289, L23-L26
Stellar coronae are commonly assumed to be optically thin. Recent
spectroscopic observations in the EUV, however, lead us to question the
validity of this approximation for strong lines. We argue that scattering
may significantly affect the strongest coronal lines in coronae composed of
magnetic loops, possibly embedded in a hot stellar wind. Even if the average
number of scatterings per photon in some coronal lines is only of order unity,
the relative line strengths and the line-to-continuum ratio can be significantly
affected in non-symmetric inhomogeneous atmospheres: photons in weak lines
and in the optically thin continuum escape without any scattering, but strong
lines can be weakened or enhanced depending on the balance between outward
traveling line photons that are scattered back toward the stellar surface (if
not lost by branching), there destroyed by absorption, and downward traveling
line photons that are scattered upward and escape. We draw attention to the
fact that line scattering due to the non-negligible optical thickness in strong
coronal lines can have severe implications for differential emission measure
models and for abundance and density determinations, while it may serve as a
diagnostic for the existence of tenuous hot winds.
Keywords: Line: formation, Radiative transfer, Scattering, Stars: coronae,
X-rays: stars
--------------------------------------------------------------
EUV SPECTROSCOPY OF COOL STARS; I. THE CORONA OF ALPHA CEN OBSERVED WITH EUVE
R. Mewe, J.S. Kaastra, C.J. Schrijver, G.H.J. van den Oord, F.J.M. Alkemade
To appear in Astronomy & Astrophysics
We perform an emission measure analysis of spectra of the coronae of the
cool star binary alpha Cen (A: HD 128620 (G2V) + B: HD 128621 (K1V)) as
observed with the Spectrometers of the Extreme Ultraviolet Explorer (EUVE).
These observations, covering the wavelength range of 60E up to 800E with a
resolution of lambda/Delta-lambda ~160-320, constrain the coronal temperature
structure between about 1E+05 Kelvin up to roughly 10 million Kelvin, while
some additional line and continuum information is available to extend that
coverage from several tens of thousands of Kelvin up to several tens of
millions of Kelvin, although the solution is ill constrained in the extended
range. We performed a re-calibration of the wavelength scale for each of the
three instrumental pass-bands by comparing the model list of emission lines
with the spectrum of alpha Cen, combined with spectra of eight other cool
stars. The high signal-to-noise ratio of the alpha Cen spectrum yielded
indications for a Lorentzian rather than a Gaussian line profile for the MW
passband. The observed spectrum was decomposed into a linear combination of
spectra emitted by isothermal plasmas in thermal equilibrium, using the SPEX
plasma emission code developed in Utrecht. The resulting differential emission
measure distribution shows: a) emission from plasma below ~5 MK with a broad
peak around ~3 MK and with a tail extending down to about 0.5 MK, b) very
little emission from plasma between 0.1 MK and 0.5 MK, c) emission from plasma
below 0.1 MK, and d) possibly a hot component exceeding several tens of million
of Kelvin which, however, may (in part) have another origin than a hot coronal
plasma component. We propose that the hot component may be an artifact of the
corona being close to unit optical thickness for scattering in the strongest
spectral lines, so that part of the line photons can be destroyed by being
scattered towards the stellar surface while the plasma remains optically thin
for continuum photons. Electron density diagnostics based on Fe X, Fe XII,
Fe XIII, and Fe XIV lines, yields values in the range 2-20E+08 cm-3 at T = 1-2
MK.
Keywords: stars: coronae, X--rays: stars, stars: activity, stars:
late--type, stars: abundances, stars: individual: alpha Cen
--------------------------------------------------------------
MASS-RADIUS RELATIONS FOR LOW MASS WHITE DWARFS WITH HELIUM AND CARBON
INTERIORS
S. Vennes, G. Fontaine, and P. Brassard
To appear in Astronomy & Astrophysics Research Notes [CEA publication #607]
We have computed static mass-radius relations for low-mass white dwarfs
defined by surface gravities in the range g = 1E+07 - 1E+08 cm/s^2. We have
assumed pure helium interiors without a hydrogen envelope and carbon interiors
with and without a hydrogen envelope. Surface boundary conditions also assume
non-zero effective temperatures at 49,000 <= T_eff <= 61,000 K. Although
generally applicable to isolated low-mass white dwarfs, these models are
particularly interesting for the interpretation of the class of low-mass He
white dwarfs that potentially emerge from close binary evolution. We discuss
in particular the case of Feige 24 for which Vennes & Thorstensen (1994a) have
proposed a low mass and large radius based on their gravitational redshift
measurement. The binary parameters of Feige 24 are consistent with the
population of He white dwarf + red dwarf close binaries predicted by theory
but also with a population having a more common carbon interior with a thick
hydrogen envelope. We demonstrate that a thin hydrogen layer is unlikely.
Keywords: stars: binaries -- white dwarfs -- interiors -- evolution
--------------------------------------------------------------
A VOLUME-LIMITED SURVEY OF HIGH GALACTIC LATITUDE PLANETARY NEBULAE WITH THE
EXTREME ULTRAVIOLET EXPLORER
Antonella Fruscione, Jeremy J. Drake, Kelley McDonald, and Roger F. Malina
To appear in Astrophysical Journal [CEA publication #609]
We present the results of a complete survey, at extreme ultraviolet (EUV)
wavelengths (58-234 A), of the high galactic latitude (|b| >= 20 deg) planetary
nebulae (PN) with at least one determination of the distance within 1 kpc of
the Sun. The sample comprises 27 objects observed during the Extreme
Ultraviolet Explorer (EUVE) all-sky survey and represents the majority of PN
likely to be accessible at EUV wavelengths. Six PN (NGC 246, NGC 1360, K 1-16,
LoTr 5, NGC 4361, and NGC 3587) were detected in the shortest EUV band (58-174
A). A seventh PN (NGC 6853), not included in the sample, was also detected
during the survey. The emission is consistent in all cases with that of a
point source, and therefore is most probably originating from the PN central
star. Accurate EUV count rates or upper limits in the two shorter EUVE bands
(centered at ~100 and 200 A) are given for all the sources in the sample.
NGC 4361 and NGC 3587 are reported here for the first time as sources of EUV
radiation. As might be expected, attenuation by the interstellar medium
dominates the PN distribution in the EUV sky.
--------------------------------------------------------------
A FIRST LOOK AT THE ELEMENTAL COMPOSITION OF STELLAR CORONAE: ABSENCE OF
THE FIP EFFECT IN THE CORONA OF PROCYON
J.J. Drake, J.M. Laming, K.G. Widing, J.H.M.M. Schmitt, B. Haisch, and S. Bowyer
To appear in Science [CEA publication #610]
The chemical composition of the Sun has been studied extensively over many
years. In recent years it has been discovered that the chemical composition
of the solar corona is not the same as that of the underlying photosphere.
Elements with a first ionization potential (FIP) <= 10 eV (e.g., Fe, Mg, Si,
Ca) are observed to be enhanced relative to those with FIP >= 10 eV (e.g.,
O, Ne, S) in the corona by factors of 3-10 with respect to the photosphere.
This phenomenon is now known as the "FIP Effect." The mechanism responsible
for it is currently unknown. Is the Sun unique, or do other stellar coronae
share a solar-like enhancement of low FIP species? Prior to the recent launch
of the Extreme Ultraviolet Explorer Satellite (EUVE) the spectroscopic
capability required to answer this question did not exist. Based on
spectroscopic observations of the corona of the nearby F5 IV star Procyon
obtained with EUVE, we have now made the first estimates of the relative
abundances of high and low FIP species in the corona of a star other than the
Sun. The results indicate that, in contrast to the Sun, the FIP effect is not
present in the corona of Procyon. The FIP effect is, therefore, not an
ubiquitous feature of late-type stellar coronae. Whether the prevailing
stellar situation is that of the Sun or that of Procyon is of fundamental
interest to the physics of stellar outer atmospheres and also has a bearing
on the origin of cosmic rays.
--------------------------------------------------------------
STELLAR CORONAL ABUNDANCES II: THE ABSENCE OF THE FIP EFFECT IN THE CORONA
OF PROCYON
J.J. Drake, J.M. Laming, and K.G. Widing
To appear in Astrophysical Journal [CEA publication #611]
We present a detailed study of element abundances in the corona of Procyon
based on spectroscopic observations obtained with the Extreme Ultraviolet
Explorer Satellite (EUVE). Emission measures (EMs) have been derived from
observed line fluxes for the elements O, Ne, Mg, Si, S, Ar, Fe and Ni, using
the most recent atomic data. The slope of the resulting EM distribution is
very similar to the well-known result of 1.5 (EM ~ T^(3/2)) found for the solar
corona for log T=5.3-6.0. The abundances in the corona of Procyon are found
to be consistent with their photospheric values. No enhancement of species
with low first ionization potentials (FIP) is observed, such as is the case
for the solar corona: the "FIP effect" appears to be absent in Procyon. We
speculate that the dominant emission from the corona and transition region in
Procyon could originate in low altitude structures analogous to the solar
supergranulation network, which does not appear to exhibit a FIP effect. A
considerable body of observational evidence suggests that Procyon is both a
"basal" star in terms of its chromospheric activity, and is on the spectral
type boundary which separates stars which exhibit activity levels correlated
with rotation and those which do not. Such stars are thought by some workers
to sustain coronae which are heated predominantly by acoustic means. We also
note that an acoustically heated outer atmosphere might not possess sufficiently
small structures to support a fractionation of elements with respect to FIP.
Our results demonstrate that the FIP effect is not an ubiquitous feature of
late-type stellar coronae. Consequently, speculations in the literature that
the FIP effect observed in cosmic rays is a result of their originating from
seed particles injected by late-type stellar coronae must await observational
confirmation that the FIP effect does indeed operate on M dwarfs, which are
likely to be the dominant particle injection source.
--------------------------------------------------------------
FIRST SPECTRAL OBSERVATIONS OF THE DIFFUSE BACKGROUND WITH THE EXTREME
ULTRAVIOLET EXPLORER
P. Jelinsky, J.V. Vallerga, and J. Edelstein
To appear in Astrophysical Journal [CEA publication #612]
We present the first results from the analysis of the spectroscopic
observations of diffuse extreme ultraviolet (EUV) emission taken with the
Extreme Ultraviolet Explorer (EUVE) spectrometers in the wavelength range of
160-740 A. Though not designed or optimized for diffuse observation, the
EUVE spectrometers are the most sensitive diffuse EUV spectrometer in orbit.
The spectral resolution for diffuse emission of the Medium and Long Wavelength
spectrometers are 17 and 34 A FWHM, respectively. During the period from 1992
July 25 to 1992 August 19, the spectrometers surveyed a 2.0 deg x 20 deg field
scanned from (l^II, b^II) = (24 deg, -28 deg) to (44 deg, -47 deg) with a total
effective exposure time of 575,232 s. The only emission lines detected were
those of HeI and HeII (584, 537, and 304 A) with intensities consistent with
local geocoronal and/or interplanetary scattering of solar radiation (584 A =
1.30 Rayleighs; 537 A = 0.040 R; and 304 A = 0.029 R).
Models of the soft X-ray background, which results from a 1E+06 K plasma
(Local Bubble) surrounding the neutral gas near the Sun (Local Cloud), predict
that most of the flux from the hot plasma appears as emission lines in the EUV.
We have compared these spectral predictions with our observations to place
limits on the emission measure vs. temperature of the proposed hot plasma.
Using the same plasma model, we derived emission measures for our data and the
C and B soft X-ray bands of the Wisconsin rocket survey. We find that our
limits for the plasma emission measure are a factor of 5 to 10 below the C and
B band emission measures over the temperature range from 1E+05.7 to 1E+06.4 K.
We explore possible scenarios that could reconcile our results with the X-ray
surveys and conclude that depletion or a non-equilibrium plasma state rather
than absorption are the more likely explanations of the discrepancy. We also
show that our spectrum is inconsistent with the spectrum from the ~1E+05 K gas
at the conductive interface between the hot Local Bubble and the cooler Local
Cloud given by Slavin (1989). In addition, we place new limits on the helium
ionization parameter in the Sun's vicinity caused by the 1E+06 K plasma in the
Local Bubble.
--------------------------------------------------------------
REFERENCES
==========
o Bowyer, S., Lieu, R., Lampton, M., Lewis, J., Wu, X., Drake, J.J., and
Malina, R.F., "The First EUVE Source Catalog", Astrophysical Journal
Supplement, 93(2), 569, 1994 [CEA publication #565]
o Malina, R.F., Marshall, H.L., Antia, B., Christian, C.A., Dobson, C.A.,
Finley, D.S., Fruscione, A., Girouard, F., Hawkins, I., Jelinsky, P.,
Lewis, J., McDonald, J., McDonald, K., Patterer, R.J., Saba, V.,
Sirk, M.M., Stroozas, B.A., Vallerga, J.V., Vedder, P.W.,
Wiercigroch, A., and Bowyer, S., "The Extreme Ultraviolet Explorer
Bright Source List", Astronomical Journal, 107(2), 751-764, 1994
[CEA publication #553]
o McDonald, K., Craig, N., Sirk, M.M., Drake, J.J., Fruscione, A., Vallerga,
J.V., and Malina, R.F., "Serendipitous EUV Sources Detected during the
First Year of the Extreme Ultraviolet Explorer Right Angle Program",
to appear in Astronomical Journal
---------------------------------------------------------------------------
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
[HomePage]
[Email]
[Search]
[Glossary]
Page created by webmastr@cea.berkeley.edu
Last modified 10/4/97