201 research outputs found
TRAPPIST photometry and imaging monitoring of comet C/2013 R1(Lovejoy): Implications for the origin of daughter species
We report the results of the narrow band photometry and imaging monitoring of
comet C/2013 R1 (Lovejoy) with the robotic telescope TRAPPIST (La Silla
observatory). We gathered around 400 images over 8 months pre- and
post-perihelion between September 12, 2013 and July 6, 2014. We followed the
evolution of the OH, NH, CN, C3 , and C2 production rates computed with the
Haser model as well as the evolution of the dust production. All five gas
species display an asymmetry about perihelion, the rate of brightening being
steeper than the rate of fading. The study of the coma morphology reveals gas
and dust jets which indicate one or several active zone(s) on the nucleus. The
dust, C2 , and C3 morphologies present some similarities while the CN
morphology is different. OH and NH are enhanced in the tail direction. The
study of the evolution of the comet activity shows that the OH, NH, and C2
production rates evolution with the heliocentric distance is correlated to the
dust evolution. The CN and, to a lesser extent, the C3 do not display such a
correlation with the dust. These evidences and the comparison with parent
species production rates indicate that C2 and C3 on one side and OH and NH on
the other side could be -at least partially- released from organic-rich grains
and icy grains. On the contrary, all evidences point to HCN being the main
parent of CN in this comet.Comment: Accepted for publication in Astronomy & Astrophysics, 10 page
Coma environment of comet C/2017 K2 around the water ice sublimation boundary observed with VLT/MUSE
We report a new imaging spectroscopic observation of Oort-cloud comet C/2017
K2 (hereafter K2) on its way to perihelion at 2.53 au, around a heliocentric
distance where H2O ice begins to play a key role in comet activation.
Normalized reflectances over 6 500--8 500 AA for its inner and outer comae are
9.7+/-0.5 and 7.2+/-0.3 % (10^3 AA)^-1, respectively, the latter being
consistent with the slope observed when the comet was beyond the orbit of
Saturn. The dust coma at the time of observation appears to contain three
distinct populations: mm-sized chunks prevailing at <~10^3 km; a 10^5-km
steady-state dust envelope; and fresh anti-sunward jet particles. the dust
chunks dominate the continuum signal and are distributed over a similar radial
distance scale as the coma region with redder dust than nearby. they also
appear to be co-spatial with OI1D, suggesting that the chunks may accommodate
H2O ice with a fraction (>~1 %) of refractory materials. The jet particles do
not colocate with any gas species detected. The outer coma spectrum contains
three significant emissions from C2(0,0) Swan band, OI1D, and CN(1,0 red band,
with an overall deficiency in NH2. Assuming that all OI1D flux results from H2O
dissociation, we compute an upper limit on the water production rate Q_H2O of
~7 x 10^28 molec s^-1 (with an uncertainty of a factor of two). the production
ratio log[Q_C2/Q_CN] of K2 suggests that the comet has typical carbon-chain
composition, with the value potentially changing with distance from the Sun.
Our observations suggest that water ice-containing dust chunks (>0.1 mm) near
K2's nucleus emitted beyond 4 au may be responsible for its very low gas
rotational temperature and the discrepancy between its optical and infrared
lights reported at similar heliocentric distances.Comment: Accepted for publication in Astronomy & Astrophysic
Ground-based monitoring of comet 67P/Churyumov-Gerasimenko gas activity throughout the <i>Rosetta</i> mission
Simultaneously to the ESA Rosetta mission, a world-wide ground-based campaign provided measurements of the large scale activity of comet 67P/Churyumov-Gerasimenko through measurement of optically active gas species and imaging of the overall dust coma. We present more than two years of observations performed with the FORS2 low resolution spectrograph at the VLT, TRAPPIST, and ACAM at the WHT. We focus on the evolution of the CN production, as a tracer of the comet activity. We find that it is asymmetric with respect to perihelion and different from that of the dust. The CN emission is detected for the first time at 1.34 au pre-perihelion and production rates then increase steeply to peak about two weeks after perihelion at (1.00±0.10) ×1025 molecules s−1, while the post-perihelion decrease is more shallow. The evolution of the comet activity is strongly influenced by seasonal effects, with enhanced CN production when the Southern hemisphere is illuminated
FeI and NiI in cometary atmospheres. Connections between the NiI/FeI abundance ratio and chemical characteristics of Jupiter-family and Oort-cloud comets
FeI and NiI emission lines have recently been found in the spectra of 17
Solar System comets observed at heliocentric distances between 0.68 and 3.25 au
and in the interstellar comet 2I/Borisov. The blackbody equilibrium temperature
at the nucleus surface is too low to vaporize the refractory dust grains that
contain metals, making the presence of iron and nickel atoms in cometary
atmospheres a puzzling observation. Moreover, the measured NiI/FeI abundance
ratio is on average one order of magnitude larger than the solar photosphere
value. We report new measurements of FeI and NiI production rates and abundance
ratios for the Jupiter-family comet (JFC) 46P/Wirtanen in its 2018 apparition
and from archival data of the Oort-cloud comet (OCC) C/1996 B2 (Hyakutake). The
comets were at geocentric distances of 0.09 au and 0.11 au, respectively. The
emission line surface brightness was found to be inversely proportional to the
projected distance to the nucleus, confirming that FeI and NiI atoms are
ejected from the surface of the nucleus or originate from a short-lived parent.
Considering the full sample of 20 comets, we find that the range of NiI/FeI
abundance ratios is significantly larger in JFCs than in OCCs. We also unveil
significant correlations between NiI/FeI and C/CN, CH/HO, and
NH/CN. Carbon-chain- and NH-depleted comets show the highest NiI/FeI ratios.
The existence of such relations suggests that the diversity of NiI/FeI
abundance ratios in comets could be related to the cometary formation rather
than to subsequent processes~in~the~coma.Comment: Accepted for publication in A&A Letter
MUSE observations of comet 67P/Churyumov-Gerasimenko:A reference for future comet observations with MUSE
Observations of comet 67P/Churyumov-Gerasimenko were performed with MUSE at
large heliocentric distances post-perihelion, between March 3 and 7, 2016.
Those observations were part of a simultaneous ground-based campaign aimed at
providing large-scale information about comet 67P that complement the
ESA/Rosetta mission. We obtained a total of 38 datacubes over 5 nights. We take
advantage of the integral field unit (IFU) nature of the instrument to study
simultaneously the spectrum of 67P's dust and its spatial distribution in the
coma. We also look for evidence of gas emission in the coma. We produce a high
quality spectrum of the dust coma over the optical range that could be used as
a reference for future comet observations with the instrument. The slope of the
dust reflectivity is of 10% nm over the 480-900 nm interval, with a
shallower slope towards redder wavelengths. We use the to
quantify the dust production and measure values of 654 cm, 754 cm,
and 824 cm in the V, R, and I bands respectively. We detect several jets
in the coma, as well as the dust trail. Finally, using a novel method combining
spectral and spatial information, we detect the forbidden oxygen emission line
at 630 nm. Using this line we derive a water production rate of , assuming all oxygen atoms come from the
photo-dissociation of water.Comment: Accepted for publication in Astronomy and Astrophysic
Isotopic ratios in outbursting comet C/2015 ER61
Isotopic ratios in comets are critical to understanding the origin of
cometary material and the physical and chemical conditions in the early solar
nebula. Comet C/2015 ER61 (PANSTARRS) underwent an outburst with a total
brightness increase of 2 magnitudes on the night of 2017 April 4. The sharp
increase in brightness offered a rare opportunity to measure the isotopic
ratios of the light elements in the coma of this comet. We obtained two
high-resolution spectra of C/2015 ER61 with UVES/VLT on the nights of 2017
April 13 and 17. At the time of our observations, the comet was fading
gradually following the outburst. We measured the nitrogen and carbon isotopic
ratios from the CN violet (0,0) band and found that C/C=100
15, N/N=130 15. In addition, we determined the
N/N ratio from four pairs of NH isotopolog lines and measured
N/N=140 28. The measured isotopic ratios of C/2015 ER61 do
not deviate significantly from those of other comets.Comment: 4 pages, 4 figures, accepted to be published by A&
A Monitoring Campaign for Luhman 16AB. I. Detection of Resolved Near-Infrared Spectroscopic Variability
[abbreviated] We report resolved near-infrared spectroscopic monitoring of
the nearby L dwarf/T dwarf binary WISE J104915.57-531906.1AB (Luhman 16AB), as
part of a broader campaign to characterize the spectral energy distribution and
temporal variability of this system. A continuous 45-minute sequence of
low-resolution IRTF/SpeX data spanning 0.8-2.4 micron were obtained, concurrent
with combined-light optical photometry with ESO/TRAPPIST. Our spectral
observations confirm the flux reversal of this binary, and we detect a
wavelength-dependent decline in the relative spectral fluxes of the two
components coincident with a decline in the combined-light optical brightness
of the system over the course of the observation. These data are successfully
modeled as a combination of brightness and color variability in the T0.5 Luhman
16B, consistent cloud variations; and no significant variability in L7.5 Luhman
16A. We estimate a peak-to-peak amplitude of 13.5% at 1.25 micron over the full
lightcurve. Using a two-spot brightness temperature model, we infer an average
cloud covering fraction of ~30-55% for Luhman 16B, varying by 15-30% over a
rotation period. A Rhines scale interpretation for the size of the variable
features explains an apparent correlation between period and amplitude for
three highly variable T dwarfs, and predicts relatively fast winds (1-3 km/s)
for Luhman 16B consistent with lightcurve evolution on an advective time scale
(1-3 rotation periods). Our observations support the model of a patchy
disruption of the mineral cloud layer as a universal feature of the L dwarf/T
dwarf transition.Comment: 11 pages, 7 figures; accepted for publication in Astrophysical
Journa
TRAPPIST monitoring of comet C/2012 F6 (Lemmon)
Comet C/2012 F6 is a long-period comet that reached perihelion on March 23, 2012. The unexpected brightness of this comet since December 2012 allowed us to obtain narrowband photometry and to study its chemical composition as well as its rotation
Comets CO and CO fluorescence models for measuring the C/C isotopic ratio in CO
Context: CO is an abundant species in comets, creating CO ion with
emission lines that can be observed in the optical spectral range. A good
modeling of its fluorescence spectrum is important for a better measurement of
the CO abundance. Such a species, if abundant enough, can also be used to
measure the C/C isotopic ratio. Aims: This study uses the
opportunity of a high CO content observed in the comet C/2016 R2 (PanSTARRS),
that created bright CO emission lines in the optical range, to build and
test a new fluorescence model of this species and to measure for the first time
the C/C isotopic ratio in this chemical species with ground-based
observations. Methods: Thanks to laboratory data and theoretical works
available in the scientific literature we developed a new fluorescence model
both for CO and CO ions. The CO model can be
used for coadding faint emission lines and obtain a sufficient signal-to-noise
ratio to detect this isotopologue. Results: Our fluorescence model provides a
good modeling of the CO emission lines, allowing to publish revised
fluorescence efficiencies. Based on similar transition probabilities for
CO and CO we derive a C/C isotopic ratio of
7320 for CO in comet C/2016 R2. This value is in agreement with the
solar system ratio of 892 within the error bars, making the possibility
that this comet was an interstellar object unlikely.Comment: 11 pages, 8 figure
Dust modelling and a dynamical study of comet 41P/Tuttle-Giacobini-Kresak during its 2017 perihelion passage
Thanks to the Rosetta mission, our understanding of comets has greatly
improved. A very good opportunity to apply this knowledge appeared in early
2017 with the appearance of the Jupiter family comet 41P/TGK. We performed an
observational campaign with the TRAPPIST telescopes that covered almost the
entire period of time when the comet was active. In this work we present a
comprehensive study of the evolution of the dust environment of 41P based on
observational data from January to July, 2017. Also, we performed numerical
simulations to constrain its origin and dynamical nature. To model the
observational data set we used a Monte Carlo dust tail model, which allowed us
to derive the dust parameters that best describe its dust environment as a
function of heliocentric distance. In order to study its dynamical evolution,
we completed several experiments to evaluate the degree of stability of its
orbit, its life time in its current region close to Earth, and its future
behaviour. From the dust analysis, we found that comet 41P has a complex
emission pattern that shifted from full isotropic to anisotropic ejection
sometime during February 24-March 14 in 2017, and then from anisotropic to full
isotropic again between June 7-28. During the anisotropic period, the emission
was controlled by two strongly active areas, where one was located in the
southern and one in the northern hemisphere of the nucleus. The total dust mass
loss is estimated to be kg. From the dynamical
simulations we estimate that 3600 yr is the period of time during which
41P will remain in a similar orbit. Taking into account the estimated mass loss
per orbit, after 3600 yr, the nucleus may lose about 30 of its mass.
However, based on its observed dust-to-water mass ratio and its propensity to
outbursts, the lifetime of this comet could be much shorter.Comment: 14 pages, 13 figures. Accepted for its publication in Astronomy &
Astrophysic
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