46 research outputs found
Observations of Diffuse EUV Emission with the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS)
The Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) was designed to study
diffuse emission from hot gas in the local interstellar cavity in the
wavelength range 90 - 265 A. Between launch in January 2003 and early 2004, the
instrument was operated in narrow-slit mode, achieving a peak spectral
resolution of about 1.4 A FWHM. Observations were carried out preferentially at
high galactic latitudes; weighted by observing time, the mean absolute value of
the galactic latitude for all narrow-slit observations combined is about 45
degrees. The total integration time is about 13.2 Msec (74% day, 26% night). In
the context of a standard collisional ionization equilibrium plasma model, the
CHIPS data set tight constraints on the emission measure at temperatures
between 10^{5.55} K and 10^{6.4} K. At 10^{6.0} K, the 95% upper limit on the
emission measure is about 0.0004 cm^{-6} pc for solar abundance plasma with
foreground neutral hydrogen column of 2 x 10^{18} cm^{-2}. This constraint,
derived primarily from limits on the extreme ultraviolet emission lines of
highly ionized iron, is well below the range for the local hot bubble estimated
previously from soft X-ray studies. To support the emission measures inferred
previously from X-ray data would require depletions much higher than the
moderate values reported previously for hot gas.Comment: 13 pages, 4 figures, 1 tabl
A New Measurement of the Average FUV Extinction Curve
We have measured the extinction curve in the far-ultraviolet wavelength
region of (900 -- 1200 A) using spectra obtained with the Berkeley EUV/FUV
spectrometer during the ORFEUS-I and the ORFEUS-II missions in 1993 and 1996.
From the complete sample of early-type stars observed during these missions,
we have selected pairs of stars with the same spectral type but different
reddenings to measure the differential FUV extinction. We model the effects of
molecular hydrogen absorption and exclude affected regions of the spectrum to
determine the extinction from dust alone. We minimize errors from inaccuracies
in the cataloged spectral types of the stars by making our own determinations
of spectral types based on their IUE spectra. We find substantial scatter in
the curves of individual star pairs and present a detailed examination of the
uncertainties and their effects on each extinction curve. We find that, given
the potentially large uncertainties inherent in using the pair method at FUV
wavelengths, a careful analysis of measurement uncertainties is critical to
assessing the true dust extinction. We present a new measurement of the average
far-ultraviolet extinction curve to the Lyman limit; our new measurement is
consistent with an extrapolation of the standard extinction curve of Savage &
Mathis (1979).Comment: 13 pages text, 7 figures 4 tables. Sent as gzipped tar, with ms.tex
and 7 figure
A Search for EUV Emission from Comets with the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS)
We have obtained EUV spectra between 90 and 255 \AA of the cometsC/2002 T7
(LINEAR), C/2001 Q4 (NEAT), and C/2004 Q2 (Machholz) near their perihelion
passages in 2004 with the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS).
We obtained contemporaneous data on Comet NEAT Q4 with the X-ray
Observatory ACIS instrument, marking the first simultaneous EUV and X-ray
spectral observations of a comet. The total CHIPS/EUV observing times were 337
ks for Q4, 234 ks for T7, and 483 ks for Machholz and for both CHIPS and
we calculate we have captured all the comet flux in the instrument
field of view. We set upper limits on solar wind charge exchange emission lines
of O, C, N, Ne and Fe occurring in the spectral bandpass of CHIPS. The spectrum
of Q4 obtained with can be reproduced by modeling emission lines of
C, N O, Mg, Fe, Si, S, and Ne solar wind ions. The measured X-ray emission line
intensities are consistent with our predictions from a solar wind charge
exchange model. The model predictions for the EUV emission line intensities are
determined from the intensity ratios of the cascading X-ray and EUV photons
arising in the charge exchange processes. They are compatible with the measured
limits on the intensities of the EUV lines. For comet Q4, we measured a total
X-ray flux of 3.7 ergs cm s, and derive from
model predictions a total EUV flux of 1.5 erg cm
s. The CHIPS observations occurred predominantly while the satellite was
on the dayside of Earth. For much of the observing time, CHIPS performed
observations at smaller solar angles than it was designed for and EUV emission
from the Sun scattered into the instrument limited the sensitivity of the EUV
measurements.Comment: 28 pages total, 4 tables, 7 figures. Accepted by The Astrophysical
Journa
Spectral Observations of Diffuse Far-Ultraviolet Emission from the Hot Phase of the Interstellar Medium with the Diffuse Ultraviolet Experiment
One of the keys to interpreting the character and evolution of interstellar
matter in the galaxy is understanding the distribution of the low density hot
(10^5 K -10^6 K) phase of the interstellar medium (ISM). This phase is much
more difficult to observe than the cooler high density components of the ISM
because of its low density and lack of easily observable tracers. Because gas
of this temperature emits mainly in the far ultraviolet (912 angstrom - 1800
angstroms) and extreme ultraviolet (80 angstrom - 912 angstrom), and (for gas
hotter than 10^6 K) X-rays, observations in these bands can provide important
constraints to the distribution of this gas. Because of interstellar opacity at
EUV wavelengths, only FUV and X-ray observations can provide clues to the
properties of hot gas from distant regions. We present results from a search
for FUV emission from the diffuse ISM conducted with an orbital FUV
spectrometer, DUVE, which was launched in July, 1992. The DUVE spectrometer,
which covers the band from 950 angstrom to 1080 angstrom with 3.2 angstrom
resolution, observed a region of low neutral hydrogen column density near the
south galactic pole for a total effective integration time of 1583 seconds. The
only emission line detected was a geocoronal hydrogen line at 1025 angstrom. We
are able to place upper limits to several expected emission features that
provide constraints on interstellar plasma parameters. We are also able to
place limits on the continuum emission throughout the bandpass. We compare
these limits and other diffuse observations with several models of the
structure of the interstellar medium and discuss the ramifications.Comment: 23 pages, LaTeX, 10 eps figures, uses aaspp4.sty and Psfig/TeX
Release 1.2, Minor editorial change
XMM- Newton Observation of the Coma Galaxy Cluster: The temperature structure in the central region
We present a temperature map and a temperature profile of the central part (r < 20' or 1/4 virial radius) of the Coma cluster. We combined 5 overlapping pointings made with XMM/EPIC/MOS and extracted spectra in boxes of 3.5' X 3.5'. The temperature distribution around the two central galaxies is remarkably homogeneous (r<10'), contrary to previous ASCA results, suggesting that the core is actually in a relaxed state. At larger distance from the cluster center we do see evidence for recent matter accretion. We confirm the cool area in the direction of NGC 4921, probably due to gas stripped from an infalling group. We find indications of a hot front in the South West, in the direction of NGC4839, probably due to an adiabatic compression
Ultraviolet number counts of galaxies from Swift UV/Optical Telescope deep imaging of the Chandra Deep Field South
Deep Swift UV/Optical Telescope (UVOT) imaging of the Chandra Deep Field
South is used to measure galaxy number counts in three near ultraviolet (NUV)
filters (uvw2: 1928 A, uvm2: 2246 A, uvw1: 2600 A) and the u band (3645 A).
UVOT observations cover the break in the slope of the NUV number counts with
greater precision than the number counts by the Hubble Space Telescope (HST)
Space Telescope Imaging Spectrograph (STIS) and the Galaxy Evolution Explorer
(GALEX), spanning a range from 21 < m_AB < 25. Number counts models confirm
earlier investigations in favoring models with an evolving galaxy luminosity
function.Comment: 20 pages, 6 figures, accepted to Ap
The X-ray spectrum of the Seyfert I galaxy Mrk 766: Dusty Warm Absorber or Relativistic Emission Lines?
Competing models for broad spectral features in the soft X-ray spectrum of
the Seyfert I galaxy Mrk766 are tested against data from a 130 ks XMM-Newton
observation. A model including relativistically broadened Ly-alpha emission
lines of OVIII, NVII and CVI is a better fit to 0.3-2 keV XMM RGS data than a
dusty warm absorber. Moreover, the measured depth of neutral iron absorption
lines in the spectrum is inconsistent with the magnitude of the iron edge
required to produce the continuum break at 17-18Angstroms in the dusty warm
absorber model. The relativistic emission line model can reproduce the
broad-band (0.1-12 keV) XMM-EPIC data with the addition of a fourth line to
represent emission from ionized iron at 6.7 keV and an excess due to reflection
at energies above the iron line. The profile of the 6.7 keV iron line is
consistent with that measured for the low energy lines. There is evidence in
the RGS data at the 3sigma level for spectral features that vary with source
flux. The covering fraction of warm absorber gas is estimated to be ~12%. Iron
in the warm absorber is found to be overabundant with respect to CNO compared
to solar values.Comment: Accepted for publication in ApJ Letter
Microchannel Plates for the UVCS and SUMER Instruments on the SOHO Satellite
The microchannel plates for the detectors in the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) and UVCS (Ultraviolet Coronograph Spectrometer) instruments aboard the Solar Orbiting Heliospheric Observatory (SOHO) mission to be launched in late 1995 are described. A low resistance Z stack of microchannel plates (MCP's) is employed in a detector format of 27 mm x 10 mm using a multilayer cross delay line anode (XDL) with 1024 x 360 digitized pixels. The MCP stacks provide gains of greater than 2 x 10(exp 7) with good pulse height distributions (as low as 25% FWHM) under uniform flood illumination. Background rates of approx. 0.6 event cm(exp -2) sec(exp -1) are obtained for this configuration. Local counting rates up to about 800 events/pixel/sec have been achieved with little drop of the MCP gain. MCP preconditioning results are discussed, showing that some MCP stacks fail to have gain decreases when subjected to a high flux UV scrub. Also, although the bare MCP quantum efficiencies are close to those expected (10%), we found that the long wavelength response of KBr photocathodes could be substantially enhanced by the MCP scrubbing process. Flat field images are characterized by a low level of MCP fixed pattern noise and are stable. Preliminary calibration results for the instruments are shown
A Mosaic of the Coma Cluster of Galaxies with XMM-Newton
The Coma cluster of galaxies was observed with XMM-Newton in 12 partially
overlapping pointings. We present here the resulting X-ray map in different
energy bands and discuss the large scale structure of this cluster. Many point
sources were found throughout the observed area, at least 11 of them are
coincident with bright galaxies. We also give a hardness ratio map at the so
far highest angular resolution obtained for a cluster of galaxies. In this map
we found soft regions at the position of bright galaxies, little variation in
the central 15 arcmin, but some harder regions north of the line NGC 4874 - NGC
4889.Comment: 6 pages, 3 figures, accepetd for publication in the A&A special issue
on XMM-Newton result