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ELECTRONIC NEWSLETTER OF THE EUVE OBSERVATORY
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Vol 3, No. 15 November 5, 1993 ISSN 1065-3597
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1. Notes from the Editor
========================
by Brett A. Stroozas (DASS/Archive Manager)
Welcome to this issue of the Extreme Ultraviolet Explorer (EUVE) electronic
newsletter. Included in this issue are an announcement from the EUVE User's
Committee, some announcements regarding the EUVE Guest Observer (EGO) Program
and the second EUVE NASA Research Announcement (NRA), some abstracts from up-
coming publications of EUVE-related papers, and some brief articles from EGO
Center staff regarding the performance of the Deep Survey/Spectrometer instru-
ment.
Highlighting some of the science coming out of the Center for EUV Astrophy-
sics (CEA) here at U.C. Berkeley, is the upcoming publication in the Astro-
nomical Journal of the EUVE survey Bright Source List paper (356 sources;
see abstract below). The first EUVE survey catalog has also recently been
completed (410 sources) and a paper (Bowyer, et al.) has been submitted to
the Astrophysical Journal Supplement. Additionally, the EUVE Science Archive
group is preparing to release the next installment in the EUVE CD-ROM series
at the January meeting of the American Astronomical Society in Washington, D.C.
This release will be a set of three CD-ROMs containing pointed spectrometer
observations of selected calibration targets from the In-Orbit Calibration
(IOC) and survey phases of the mission. These eleven observations have been
arranged thematically on the three disks: four white dwarfs on disc A; two
late-type stars on disc B; and five assorted targets on disc C.
2. EUVE User's Committee Lunch at AAS Meeting
=============================================
A special luncheon meeting is being held by the EUVE User's Committee at
the American Astronomical Society Conference on Thursday, 13 January 1994
for everyone interested in extreme ultraviolet astronomy. Planned topics of
discussion are a current update on EUVE and the ongoing efforts to extend the
EUVE mission. If the mission is not extended, EUVE observations will end af-
ter a third year of GO observations (according to the current plan). Members
of the user community are encouraged to attend as increased participation in
this meeting will enhance the possibility of additional opportunities to do
research utilizing data from EUVE. Harry Shipman is the meeting organizer
and will announce further information in the near future. We hope to see you
all there.
3. Extreme Ultraviolet Explorer Second NRA
==========================================
by Dr. Ronald Oliversen (Deputy Project Scientist at GSFC)
This September, a total of 109 proposals, including 26 proposals from for-
eign countries, were received in response to the second EUVE NRA for the Guest
Observer program. The proposals were submitted by 79 Principal Investigators
(PI's) from 45 different institutions. Thirty of the PI's had not previously
proposed to the EUVE GO program. The 109 proposals covered a wide range of
topics from the solar system (6), interstellar medium (7), subluminous stars
(16), binary systems (30), cool stars (28), hot stars (6), unidentified sour-
ces (3), to extragalactic objects (13). The number of targets per proposal
is 2.5 with an oversubscription for time requested of about 3. The peer review
of proposals will occur November 8 and 9.
4. EGO Program Announcements
============================
by Anne Miller (EGO Technical Writer)
As mentioned above, a total of 109 proposals were received from 79 PI's for
Cycle II of the EUVE Guest Observer Program. Technical evaluations by EGO
Center scientists are underway, and the NASA Peer Review is currently sched-
uled for 8 and 9 November. The Review will be conducted jointly with the 1994
IUE Peer Review.
The EGO Center wishes to apologize for a lapse in the announcements of
planned observations to PI's. The practice has been resumed, and Cycle I PI's
should receive an electronic notice that their observation has been scheduled
up to one month before the scheduled date. Any GO who is organizing coordi-
nated observations or has other scheduling concerns is urged to contact the
EGO Center via e-mail at "egoinfo@cea.berkeley.edu" (Internet) whenever in
need of assistance. Scheduling questions and problems are always addressed
as promptly as possible.
5. Abstracts of Upcoming Publications of EUVE-related Papers
============================================================
The following four abstracts regarding EUVE-related data have recently been
accepted for publication:
EXTREME ULTRA VIOLET PLASMA DIAGNOSTIC: A TEST USING EUVE CALIBRATION DATA
M. Landini (Universita di Firenze, Italy) and B.C. Monsignori Fossi
(Osservatorio Astrofisico di Arcentri, Italy)
Astonomy and Astrophysics, 275, L17-L20 (1993)
The theoretical Xray-EUV spectral code of Landini and Monsignori Fossi
(1990) has been compared with an emission spectrum of the active late type
star AU Mic obtained during the initial calibration phase of Extreme Ultra-
violet Explorer Spectrometer. This comparison has been used to test the
overall applicability of the code and to provide inputs for improvement. A
number of lines were identified in the spectrum of AU Mic including several
highly ionized iron lines.
Key words: stars; coronae; EUV radiation; emission lines identification
---------------------------------------------------
THE EXTREME ULTRAVIOLET EXPLORER SPECTRUM OF ALPHA AURIGAE (CAPELLA)
A.K. Dupree (CfA), N.S. Brickhouse (CfA), G.A. Doschek (NRL), J.C. Green
(CASA), and J.C. Raymond (CfA)
Ap. J. Letters, V417, 20 Nov 1993 (in press)
Extreme ultraviolet spectra (70-740 A) of the bright spectroscopic binary
system Capella (Alpha Aurigae), obtained with the Extreme Ultraviolet Explorer
satellite (EUVE), show a rich emission spectrum dominated by iron emission
lines: Fe XV-XXIV. The emission measure for the system reveals a continuous
distribution of plasma temperatures between 1e5 and 1e7.8 K, with a clear
minimum near 1e6 K and a local maximum at 6e6 K. Electron density diagnostics
based on Fe XXI indicate N_e ~= 4e11 to 1e13 cm^(-3) at T_e = 1e7 K.
Subject headings: stars: chromosphere -- stars: giant -- stars: mass-
loss -- stars: individual (Alpha Aurigae)
---------------------------------------------------
EARLY WHITE DWARF RESULTS FROM EUVE
D.S. Finley (CEA/UCB), Frits Paerels (UCB) and Detlev Koester (LSU)
In White Dwarfs: Advances in Observation and Theory, ed. M.A. Barstow,
Dordrecht: Kluwer Academic Publishers, pp. 191-203, 1993
Following the recent launch of the Extreme Ultraviolet Explorer satellite
(EUVE), several white dwarfs were observed (both photometrically and spectro-
scopically) as part of the In-Orbit Checkout (IOC) activities which were
carried out prior to the start of the sky survey, and also during pointed
observations which were performed during the course of the sky survey. Our
initial assessment of the data has included comparison of the EUVE measure-
ments with model predictions, and a cross-comparison of the results of analy-
ses of EUV data from EUVE, the ROSAT Wide Field Camera (WFC), and EXOSAT. The
results suggest that the in-flight results for EUVE are consistent with the
EUVE ground calibration. Comparing results for pure H white dwarfs from EUVE
with results from the WFC, we find that similar temperature ranges are ob-
tained. There is an apparent systematic bias toward larger interstellar co-
lumns for the WFC which gives columns about 0.3 dex greater than are obtained
from EUVE. We found large systematic differences between EUVE and EXOSAT.
We used the HUT and EXOSAT spectroscopic observations of HZ43 to perform a
provisional adjustment of the EXOSAT effective areas which significantly
reduced that difference. We have also analyzed EUVE photometric observa-
tions of two metal-rich hot DA white dwarfs, GD246 and G191-B2B, and we pre-
sent the first determination of metal abundances for them based on EUV mea-
surements.
---------------------------------------------------
THE EXTREME ULTRAVIOLET EXPLORER BRIGHT SOURCE LIST
R.F. Malina, H.L. Marshall, B. Antia, C.A. Christian, C.A. Dobson,
D.S. Finley, A. Fruscione, F. Girouard, I. Hawkins, P. Jelinsky, J. Lewis,
J. McDonald, K. McDonald, R.J. Patterer, V. Saba, M.M. Sirk, B.A. Stroozas,
J.V. Vallerga, P.W. Vedder, A. Wiercigroch, and S. Bowyer (CEA/UCB)
Astronomical Journal, Feb 1994 (in press)
Initial results from the analysis of the Extreme Ultraviolet Explorer (EUVE)
all-sky survey (58-740 A) and deep survey (67-364 A) are presented through the
Bright Source List (BSL). The BSL contains 356 confirmed extreme ultraviolet
(EUV) point sources with supporting information, including positions, observed
EUV count rates, and the identification of possible optical counterparts. One
hundred twenty-six sources have been detected longward of 200 A.
6. EGO Program Notes Regarding the Deep Survey/Spectrometer Instruments
=======================================================================
by Anne Miller (EGO Technical Writer)
Improved Signal-to-Noise Ratio After Spectrometer Detector Threshold Changes
----------------------------------------------------------------------------
The first assessment of the spectrometer background rates after changes
in the upper and lower software thresholds in the short- (SW) and medium-
wavelength (MW) detectors, which went into effect on 22 July 1993 indicate
that spectrometer backgrounds have dropped as expected, and the MW "smudge"
has disappeared.
After one year, some detectors were showing decreased gain, particularly
in areas which consistently saw high count rates, such as the 304 A feature
in the MW spectrometer. The hardware threshold levels were lowered to admit
the lower pulse height EUV events and eliminate some of the high energy par-
ticle background. Calibrations of Telescope Interface (TIF) deadtime were
preserved by changing the software thresholds as well.
The mean count-rate/pixel/second during the latest calibration observation
of AU Mic on 23 July 1993 was calculated for sample areas near the spectra,
and in shadowed areas where nearly all counts result from particle detections.
The statistics were compared to the same calculations made from the first ob-
servation of AU Mic a year earlier, begun on 14 July 1992.
The results showed that spectral backgrounds in the SW and MW detectors
have decreased by 35-50%, while the long-wavelength (LW) background levels
matched those of the previous observation. The count rates of airglow features
were also unaffected. Although this test is based on a single observation,
comparable decreases in background are likely to continue. The LW detector
thresholds were lowered slightly on 12 October, and backgrounds will be tested
in the next few weeks.
Tests of Dithered Pointing to Alleviate Fixed Pattern Noise
-----------------------------------------------------------
The microchannel plate detectors used in the EUVE spectrometers exhibit
a small-scale distortion which can appear in extracted spectra as semi-regular
spatial variations in the apparent sensitivity over a period of about 17
pixels. This spatial variation is caused by distortions in the microchannels
at the outside boundaries of subregions. At the subregion boundaries, the
packing of fiber bundles during manufacture of the microchannel boule distorts
some channels. The distorted channel cross-sections in turn cause shifts in
the apparent locations of events at the subregion boundaries.
Obtaining reliable flat fields for the spectrometer is impractical due to
the integration times involved. The EGO program is therefore testing the prac-
ticality of dithering the pointing slightly during an observation to "wash
out" the effects of fixed pattern noise in the spectrum.
The dithering tests will involve a small slew, on the scale of two arc
minutes, during each orbit daytime when detectors are turned off. As the
excursions will be well within the area of stability for the wavelength
solution, the effects of the dithering can be completely removed from the
spectra during standard processing with the EGO Center event pipeline, using
the reported spacecraft aspect.
Following the tests, the effectiveness of dithering will be evaluated and
guidelines will be formulated based on the results, the effects of the fixed
pattern noise on different types of observations, and the frequency of slewing
available to the spacecraft.
Analysis of Deep Survey Detector Dead Spot
------------------------------------------
Comparison of initial IOC calibrations with recent observations of white
dwarfs has shown the development of a small area of decreased gain near the
center of the deep survey (DS) detector. Shifts of the image position by as
little as 3 pixels (13 arc seconds) resulted in the Lexan/B count rate decli-
ning by as much as a factor of three. The dead spot is the result of intense
bombardment by EUV photons from bright sources, and has been observed in orbits
as early as the initial slew to HZ43 on 18 February of this year.
GO's who have received DS detector photon data and centroids from observa-
tions made after 18 February 1993 should treat all DS detector count rates as
suspect. Members of the CEA data analysis and science teams are developing a
method that will use maps of the dead spot (to be obtained during the aspect
dithering tests mentioned above), and observation aspect records to estimate
the fraction of DS counts that were lost during such observations. Spectro-
meter count rates are not affected.
At least a partial recovery of the detector gain in the dead spot is ex-
pected, but the rate of recovery is yet to be determined. In the meantime,
pointings in the next EUVE science plan, scheduled to begin after 18 November,
will be offset by one arc minute to avoid the dead spot. The spectrometer
wavelength solution is stable up to nearly one degree from boresight, so this
should have no noticeable effect on GO data quality.
-----------------------------------------------------------------------
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. Publishers:
Drs. R. Malina and C. Stuart Bowyer. Editor: B. Stroozas. Funded by
NASA contracts NAS5-30180 and NAS5-29298. Send newsletter correspondence
to: ceanews@cea.berkeley.edu. The EUVE Public Science Archive is available
via anonymous FTP: ftp.cea.berkeley.edu, pub/archive. 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, Deputy Program Scientist:
Dr. D. Buzasi, Program Manager: Dr. G. Riegler. GSFC Project Operations
Director: Mr. Kevin Hartnett. Information on the EUVE Guest Observer
Program is available from: Dr. Y. Kondo, Mail Code 684, GSFC, Greenbelt,
MD 20771 (301)286-6247; email to euve@stars.span.nasa.gov.
END-----EUVE---------ELECTRONIC---------------NEWS-----------------END
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