511 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
Water production rates and activity of interstellar comet 2I/Borisov
We observed the interstellar comet 2I/Borisov using the Neil Gehrels-Swift
Observatory's Ultraviolet/Optical Telescope. We obtained images of the OH gas
and dust surrounding the nucleus at six epochs spaced before and after
perihelion (-2.56 AU to 2.54 AU). Water production rates increased steadily
before perihelion from molecules s on Nov. 1,
2019 to molecules s on Dec. 1. This rate of
increase in water production rate is quicker than that of most dynamically new
comets and at the slower end of the wide range of Jupiter-family comets. After
perihelion, the water production rate decreased to
molecules s on Dec. 21, which is much more rapidly than that of all
previously observed comets. Our sublimation model constrains the minimum radius
of the nucleus to 0.37 km, and indicates an active fraction of at least 55% of
the surface. calculations show a variation between 57.5 and 105.6
cm with a slight trend peaking before the perihelion, lower than previous and
concurrent published values. The observations confirm that 2I/Borisov is
carbon-chain depleted and enriched in NH relative to water.Comment: 12 pages, 3 figures, 2 tables, submitted to ApJ
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
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