300 research outputs found
Chandra's Close Encounter with the Disintegrating Comets 73P/2006 (Schwassmann--Wachmann--3) Fragment B and C/1999 S4 (LINEAR)
On May 23, 2006 we used the ACIS-S instrument on the Chandra X-ray
Observatory (CXO) to study the X-ray emission from the B fragment of comet
73P/2006 (Schwassmann-Wachmann 3) (73P/B). We obtained a total of 20 ks of CXO
observation time of Fragment B, and also investigated contemporaneous ACE and
SOHO solar wind physical data. The CXO data allow us to spatially resolve the
detailed structure of the interaction zone between the solar wind and the
fragment's coma at a resolution of ~ 1,000 km, and to observe the X-ray
emission due to multiple comet--like bodies. We detect a change in the spectral
signature with the ratio of the CV/OVII line increasing with increasing
collisional opacity as predicted by Bodewits \e (2007). The line fluxes arise
from a combination of solar wind speed, the species that populate the wind and
the gas density of the comet. We are able to understand some of the observed
X-ray morphology in terms of non-gravitational forces that act upon an actively
outgassing comet's debris field. We have used the results of the Chandra
observations on the highly fragmented 73P/B debris field to re-analyze and
interpret the mysterious emission seen from comet C/1999 S4 (LINEAR) on August
1st, 2000, after the comet had completely disrupted. We find the physical
situations to be similar in both cases, with extended X-ray emission due to
multiple, small outgassing bodies in the field of view. Nevertheless, the two
comets interacted with completely different solar winds, resulting in
distinctly different spectra.Comment: accepted by ApJ, 44 Pages, including 4 tables and 14 figure
The Evolving Activity of the Dynamically Young Comet C/2009 P1 (Garradd)
We used the UltraViolet-Optical Telescope on board Swift to observe the
dynamically young comet C/2009 P1 (Garradd) from a heliocentric distance of 3.5
AU pre-perihelion until 4.0 AU outbound. At 3.5 AU pre-perihelion, comet
Garradd had one of the highest dust-to-gas ratios ever observed, matched only
by comet Hale-Bopp. The evolving morphology of the dust in its coma suggests an
outburst that ended around 2.2 AU pre-perihelion. Comparing slit-based
measurements and observations acquired with larger fields of view indicated
that between 3 AU and 2 AU pre-perihelion a significant extended source started
producing water in the coma. We demonstrate that this source, which could be
due to icy grains, disappeared quickly around perihelion. Water production by
the nucleus may be attributed to a constantly active source of at least 75
km, estimated to be more than 20 percent of the surface. Based on our
measurements, the comet lost kg of ice and dust during this
apparition, corresponding to at most a few meters of its surface.Even though
this was likely not Garradd's first passage through the inner solar system, the
activity of the comet was complex and changed significantly during the time it
was observed
Simultaneous Swift X-ray and UV views of comet C/2007 N3 (Lulin)
We present an analysis of simultaneous X-Ray and UV observations ofcomet
C/2007 N3 (Lulin) taken on three days between January 2009 and March 2009 using
the Swift observatory. For our X-ray observations, we used basic transforms to
account for the movement of the comet to allow the combination of all available
data to produce an exposure-corrected image. We fit a simple model to the
extracted spectrum and measured an X-ray flux of 4.3+/-1.3 * 10^-13 ergs cm-2
s-1 in the 0.3 to 1.0 keV band. In the UV, we acquired large-aperture
photometry and used a coma model to derive water production rates given
assumptions regarding the distribution of water and its dissociation into OH
molecules about the comet's nucleus.
We compare and discuss the X-ray and UV morphology of the comet. We show that
the peak of the cometary X-ray emission is offset sunward of the UV peak
emission, assumed to be the nucleus, by approximately 35,000 km. The offset
observed, the shape of X-ray emission and the decrease of the X-ray emission
comet-side of the peak, suggested that the comet was indeed collisionally thick
to charge exchange, as expected from our measurements of the comet's water
production rate (6--8 10^28 mol. s-1). The X-ray spectrum is consistent with
solar wind charge exchange emission, and the comet most likely interacted with
a solar wind depleted of very highly ionised oxygen. We show that the measured
X-ray lightcurve can be very well explained by variations in the comet's gas
production rates, the observing geometry and variations in the solar wind flux.Comment: Paper accepted for publication in Astronomy and Astrophysics, 6 March
2012, 12 pages, 8 colour figures, one tabl
Spectral Analysis of the Chandra Comet Survey
We present results of the analysis of cometary X-ray spectra with an extended
version of our charge exchange emission model (Bodewits et al. 2006). We have
applied this model to the sample of 8 comets thus far observed with the Chandra
X-ray observatory and ACIS spectrometer in the 300-1000 eV range. The surveyed
comets are C/1999 S4 (LINEAR), C/1999 T1 (McNaught-Hartley), C/2000 WM1
(LINEAR), 153P/2002 (Ikeya-Zhang), 2P/2003 (Encke), C/2001 Q4 (NEAT), 9P/2005
(Tempel 1) and 73P/2006-B (Schwassmann-Wachmann 3) and the observations include
a broad variety of comets, solar wind environments and observational
conditions. The interaction model is based on state selective, velocity
dependent charge exchange cross sections and is used to explore how cometary
X-ray emission depend on cometary, observational and solar wind
characteristics. It is further demonstrated that cometary X-ray spectra mainly
reflect the state of the local solar wind. The current sample of Chandra
observations was fit using the constrains of the charge exchange model, and
relative solar wind abundances were derived from the X-ray spectra. Our
analysis showed that spectral differences can be ascribed to different solar
wind states, as such identifying comets interacting with (I) fast, cold wind,
(II), slow, warm wind and (III) disturbed, fast, hot winds associated with
interplanetary coronal mass ejections. We furthermore predict the existence of
a fourth spectral class, associated with the cool, fast high latitude wind.Comment: 16 pages, 16 figures, and 7 Tables; accepted A&A (Due to space
limits, this version has lower resolution jpeg images.
Folding ion rays in comet C/2004 Q2 (Machholz) and the connection with the solar wind
The appearance of folding ion rays in cometary comae is still not very well
understood, so our aim is to gain more insight into the role of the local solar
wind in the formation of these structures. Comet C/2004 Q2 (Machholz) was
intensively monitored during its closest approach to Earth (January 2005) with
the CCD camera Merope mounted on the Flemish 1.2m Mercator telescope, in three
different bands (Geneva U and B and Cousins I). Spectacular ion rays, thin
ionic structures rapidly folding tailward, were recorded in the U band during
one night, January 12th. Data from the SOHO satellite that was extrapolated
corotationally to the position of the comet showed that the ion rays were
formed during a sudden change in the in-situ solar wind state. We were able to
succesfully correlate a high-speed solar wind stream with the appearance of
folding ion rays. To our knowledge, this is the first clear observational
evidence that folding ion rays in cometary comae are produced by a sudden
change in the local solar wind state.Comment: 4 pages, 4 figures, accepted by A&
Rebirth of X-ray Emission from the Born-Again Planetary Nebula A 30
The planetary nebula (PN) A30 is believed to have undergone a very late
thermal pulse resulting in the ejection of knots of hydrogen-poor material.
Using HST images we have detected the angular expansion of these knots and
derived an age of 850+280-150 yr. To investigate the spectral and spatial
properties of the soft X-ray emission detected by ROSAT, we have obtained
Chandra and XMM-Newton observations of A30. The X-ray emission from A30 can be
separated into two components: a point-source at the central star and diffuse
emission associated with the hydrogen-poor knots and the cloverleaf structure
inside the nebular shell. To help us assess the role of the current stellar
wind in powering this X-ray emission, we have determined the stellar parameters
of the central star of A 30 using a non-LTE model fit to its optical and UV
spectrum. The spatial distribution and spectral properties of the diffuse X-ray
emission is suggestive that it is generated by the post-born-again and present
fast stellar winds interacting with the hydrogen-poor ejecta of the born-again
event. This emission can be attributed to shock-heated plasma, as the
hydrogen-poor knots are ablated by the stellar winds, under which circumstances
the efficient mass-loading of the present fast stellar wind raises its density
and damps its velocity to produce the observed diffuse soft X-rays. Charge
transfer reactions between the ions of the stellar winds and material of the
born-again ejecta has also been considered as a possible mechanism for the
production of diffuse X-ray emission, and upper limits on the expected X-ray
production by this mechanism have been derived. The origin of the X-ray
emission from the central star of A 30 is puzzling: shocks in the present fast
stellar wind and photospheric emission can be ruled out, while the development
of a new, compact hot bubble confining the fast stellar wind seems implausible.Comment: 29 pages, 11 figures, 4 tables; accepted for publication by Ap
Chandra Observations of Comets 8P/Tuttle and 17P/Holmes during Solar Minimum
We present results for Chandra observations of comets, 17P/Holmes (17P) and
8P/Tuttle (8P). 17P was observed for 30 ksec right after its major outburst, on
31 Oct 2007 (10:07 UT) and comet 8P/Tuttle was observed in 2008 January for 47
ksec. During the two Chandra observations, 17P was producing at least 100 times
more water than 8P but was 2.2 times further away from the Sun. Also, 17P is
the first comet observed at high latitude (+19.1 degrees) during solar minimum,
while 8P was observed at a lower solar latitude (3.4 degrees). The X-ray
spectrum of 17P is unusually soft with little significant emission at energies
above 500 eV. Depending on our choice of background, we derive a 300 to 1000 eV
flux of 0.5 to 4.5 x 10^-13 ergs/cm2/sec, with over 90% of the emission in the
300 to 400 eV range. This corresponds to an X-ray luminosity between 0.4 to 3.3
x 10^15 ergs/sec. 17P's lack of X-rays in the 400 to 1000 eV range, in a simple
picture, may be attributed to the polar solar wind, which is depleted in highly
charged ions. 8P/Tuttle was much brighter, with an average count rate of 0.20
counts/s in the 300 to 1000 eV range. We derive an average X-ray flux in this
range of 9.4 x 10^-13 ergs/cm2/sec and an X-ray luminosity for the comet of 1.7
x 10^14 ergs/sec. The light curve showed a dramatic decrease in flux of over
60% between observations on January 1st and 4th. When comparing outer regions
of the coma to inner regions, its spectra showed a decrease in ratios of
CVI/CV, OVIII/OVII, as predicted by recent solar wind charge exchange emission
models. There are remarkable differences between the X-ray emission from these
two comets, further demonstrating the qualities of cometary X-ray observations,
and solar wind charge exchange emission in more general as a means of remote
diagnostics of the interaction of astrophysical plasmas.Comment: 37 Pages, 8 Tables, 11 Figures; Accepted in Astrophysical Journal
Supplement
Solar system Xârays from charge exchange processes
While Xâray astronomy began in 1962 and has made fast progress since then in expanding our knowledge about where in the Universe Xârays are generated by which processes, it took one generation before the importance of a fundamentally different process was recognized. This happened in our immediate neighborhood, when in 1996 comets were discovered as a new class of Xâray sources, directing our attention to charge exchange reactions. Charge exchange is fundamentally different from other processes which lead to the generation of Xârays, because the Xârays are not produced by hot electrons, but by ions picking up electrons from cold gas. Thus it opens up a new window, making it possible to detect cool gas in Xârays (like in comets), while all the other processes require extremely high temperatures or otherwise extreme conditions. After having been overlooked for a long time, the astrophysical importance of charge exchange for the generation of Xârays is now receiving increased general attention. In our solar system, charge exchange induced Xârays have now been established to originate in comets, in all the planets from Venus to Jupiter, and even in the heliosphere itself. In addition to that, evidence for this Xâray emission mechanism has been found at various locations across the Universe. Here we summarize the current knowledge about solar system Xârays resulting from charge exchange processes (© 2012 WILEYâVCH Verlag GmbH & Co. KGaA, Weinheim)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91180/1/324_ftp.pd
Cometary charge exchange diagnostics in UV and Xâray
Since the initial discovery of cometary charge exchange emission, more than 20 comets have been observed with a variety of Xâray and UV observatories. This observational sample offers a broad variety of comets, solar wind environments and observational conditions. It clearly demonstrates that solar wind charge exchange emission provides a wealth of diagnostics, which are visible as spatial, temporal, and spectral emission features. We review the possibilities and limitations of each of those in this contribution (© 2012 WILEYâVCH Verlag GmbH & Co. KGaA, Weinheim)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91138/1/335_ftp.pd
Role of charge patches in ion guiding through nanocapillaries in a PET polymer
We studied the dynamic properties of ion guiding through nanocapillaries in insulating polyethylene terephthalate (PET). The angular distribution of the transmitted ions was measured as a function of time. The temporal evolution of the angular transmission profiles was acquired for the capillary diameters of 200 and 400 nm. The tilt angle was varied from 0° to 6.5°. The transmission profiles exhibit significant changes in position as time varies. This observation is explained by the formation of temporary charge patches produced in the interior of the capillary besides the primary charge patch created in the entrance region.</p
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