We report on photometry and imaging of the Jupiter family comets 41P/Tuttle–Giacobini–Kresak and 45P/Honda–Mrkos–Pajdusakova with the TRAPPIST-North (TRAnsiting Planets and PlanetesImals Small ...Telescope) telescope. We observed 41P on 34 nights from February 16 to July 27, 2017, pre- and post-perihelion (rh = 1.04 au), and collected data for comet 45P after perihelion (rh = 0.53 au) from February 10 to March 30, 2017. We computed the production rates of the daughter species OH, NH, CN, C3 and C2 and we measured the dust proxy, Afρ, for both comets. The peak of water-production rate of 41P was (3.46 ± 0.20) × 1027 molecules s−1 on April 3, 2017, when the comet was at 1.05 au from the Sun. We have shown that the activity of 41P is decreasing by about 30–40% from one apparition to the next. We measured a mean water-production rate for 45P of (1.43 ± 0.62) × 1027 molecules s−1 during a month after perihelion. Our results show that these Jupiter family comets had low gas and dust activity and no outburst was detected. Relative abundances, expressed as ratios of production rates and the Afρ parameter with respect to OH and to CN, were compared to those measured in other comets. We found that 41P and 45P have a typical composition in terms of carbon-bearing species. The study of coma features exhibited by the CN gas species allowed the measurement of the rotation period of 41P, showing a surprisingly large increase of the rotation period from (30 ± 5) h at the end of March to (50 ± 10) h at the end of April, 2017, in agreement with recent observations by other teams.
Aims.
2I/Borisov (hereafter 2I) is the first visibly active interstellar comet observed in the Solar System, allowing us for the first time to sample the composition of a building block from another ...system. We report on the monitoring of 2I with the Ultraviolet-Visual Echelle Spectrograph, the high-resolution optical spectrograph of the ESO Very Large Telescope at Paranal, for four months from November 15, 2019 to March 16, 2020. Our goal is to characterise the activity and composition of 2I with respect to Solar System comets.
Methods.
We collected high-resolution spectra at 12 different epochs from 2.1 au pre-perihelion to 2.6 au post-perihelion.
Results.
On December 24 and 26, 2019, close to perihelion, we detected several OH lines of the 309 nm (0–0) band and derived a water production rate of 2.2 ± 0.2 × 10
26
molecules s
−1
. The three OI forbidden oxygen lines were detected at different epochs and we derived a green-to-red doublet intensity ratio (G/R) of 0.31 ± 0.05 close to perihelion. The NH
2
ortho and para lines from various bands were measured and allowed us to derive an ortho-to-para abundance ratio (OPR) of 3.21 ± 0.15, corresponding to an OPR and spin temperature of ammonia of 1.11 ± 0.08 and 31
−5
+10
K, respectively. These values are consistent with the values usually measured for Solar System comets. Emission lines of the radicals NH (336 nm), CN (388 nm), CH (431 nm), and C
2
(517 nm) were also detected. Several FeI and NiI lines were identified and their intensities were measured to provide a ratio of log (NiI/FeI) = 0.21 ± 0.18, which is in agreement with the value recently found in Solar System comets.
Conclusions.
Our high spectral resolution observations of 2I/Borisov and the associated measurements of the NH
2
OPR and the Ni/Fe abundance ratio are remarkably similar to Solar System comets. Only the G/R ratio is unusually high, but it is consistent with the high abundance ratio of CO/H
2
O found by other investigators.
Context. Early observations of comet C/2016 R2 (PanSTARRS) have shown that the composition of this comet is very peculiar. Radio observations have revealed a CO-rich and HCN-poor comet and an optical ...coma dominated by strong emission bands of CO+ and, more surprisingly, N2+ $\mathrm{N_2^+}$ N2+ . Aims. The strong detection of N2+ $\mathrm{N_2^+}$N2+ in the coma of C/2016 R2 provided an ideal opportunity to measure the 14N∕15N isotopic ratio directly from N2+ $\mathrm{N_2^+}$N2+ for the first time, and to estimate the N2∕CO ratio, which is an important diagnostic to constrain formation models of planetesimals, in addition to the more general study of coma composition. Methods. We obtained high resolution spectra of the comet in February 2018 when it was at 2.8 au from the Sun. We used the UVES spectrograph of the European Southern Observatory Very Large Telescope, complemented with narrowband images obtained with the TRAPPIST telescopes. Results. We detect strong emissions from the N2+ $\mathrm{N_2^+}$N2+ and CO+ ions, but also CO2+ $\mathrm{CO_2^+}$CO2+ , emission lines from the CH radical, and much fainter emissions of the CN, C2, and C3 radicals that were not detected in previous observations of this comet. We do not detect OH or H2O+, and we derive an upper limit of the H2O+∕CO+ ratio of 0.4, implying that the comet has a low water abundance. We measure a N2+/CO+ $\mathrm{N_2^+/CO^+}$N2+/CO+ ratio of 0.06 ± 0.01. The non-detection of NH2 indicates that most of the nitrogen content of the comet is in N2. Together with the high N2+/CO+ $\mathrm{N_2^+/CO^+}$N2+/CO+ ratio, this could indicate a low formation temperature of the comet or that the comet is a fragment of a large differentiated Kuiper Belt object. The CO2+/CO+ $\mathrm{CO_2^+/CO^+}$CO2+/CO+ ratio is 1.1 ± 0.3. We do not detect 14N15N+ lines and can only put a lower limit on the 14N∕15N ratio (measured from N2+ $\mathrm{N_2^+}$N2+ ) of about 100, which is compatible with measurements of the same isotopic ratio for NH2 and CN in other comets. Finally, in addition to the OI and CI forbidden lines, we detect for the first time the forbidden nitrogen lines NI doublet at 519.79 and 520.03 nm in the coma of a comet.
Context.
The eccentric massive binary HD 152248 (also known as V1007 Sco), which hosts two O7.5 III-II(f) stars, is the most emblematic eclipsing O-star binary in the very young and rich open cluster ...NGC 6231. Its properties render the system an interesting target for studying tidally induced apsidal motion.
Aims.
Measuring the rate of apsidal motion in such a binary system gives insight into the internal structure and evolutionary state of the stars composing it.
Methods.
A large set of optical spectra was used to reconstruct the spectra of the individual binary components and establish their radial velocities using a disentangling code. Radial velocities measured over seven decades were used to establish the rate of apsidal motion. We furthermore analysed the reconstructed spectra with the
CMFGEN
model atmosphere code to determine stellar and wind properties of the system. Optical photometry was analysed with the
Nightfall
binary star code. A complete photometric and radial velocity model was constructed in
PHOEBE 2
to determine robust uncertainties.
Results.
We find a rate of apsidal motion of (1.843
−0.083
+0.064
)° yr
−1
. The photometric data indicate an orbital inclination of (67.6
−0.1
+0.2
)° and Roche-lobe filling factors of both stars of about 0.86. Absolute masses of 29.5
−0.4
+0.5
M
⊙
and mean stellar radii of 15.07
−0.12
+0.08
R
⊙
are derived for both stars. We infer an observational value for the internal structure constant of both stars of 0.0010 ± 0.0001.
Conclusions.
Our in-depth analysis of the massive binary HD 152248 and the redetermination of its fundamental parameters can serve as a basis for the construction of stellar evolution models to determine theoretical rates of apsidal motion to be compared with the observational one. In addition, the system hosts two twin stars, which offers a unique opportunity to obtain direct insight into the internal structure of the stars.
Context.
Hyperactive comets are a small group of comets whose activity is higher than expected. They seem to emit more water than would normally be expected given the size of their nucleus. Comet ...46P/Wirtanen (hereafter, 46P) is among these objects of interest. Investigating its activity and composition evolution could provide clues about its origins and its formation region in the Solar nebulae.
Aims.
Given the exceptional close approach of comet 46P to the Earth in 2018, we aim to study the evolution of its activity and composition as a function of heliocentric distances before and after perihelion.
Methods.
We used both TRAPPIST telescopes to monitor the comet for almost a year with broad and narrow-band filters. We derived the production rates of five gaseous species (OH, NH, CN, C
3
, and C
2
) using a Haser model as well as the A(
θ
)f
ρ
dust proxy parameter. The comet was also observed with the two optical high-resolution spectrographs UVES and ESPRESSO, mounted on the 8-m ESO VLT, to measure the isotopic ratios of C and N, along with the oxygen forbidden-line ratios and the NH
2
ortho-to-para ratios.
Results.
Over nearly a year, we followed the rise and decline of the production rates of different species as well as the dust activity of 46P on both pre- and post-perihelion. Relative abundances with respect to CN and OH along the orbit of the comet show constant and symmetric abundance ratios and a typical coma composition. We determined the rotation period of the nucleus using high-cadence observations and long series of CN images on several nights. We obtained a value of (9.18±0.05) hours at perihelion. Using the high-resolution spectra of 46P coma, we derived C and N isotopic ratios of 100±20 and 150±30 as well as a green-to-red forbidden oxygen OI line ratio of 0.23±0.02. We measured a NH
2
ortho-to-para ratio of 3.31 ±0.03 and derived an ammonia ratio of 1.19±0.03, corresponding to a spin temperature of 27±1 K.
Conclusions.
Narrow-band observations show that comet 46P is a hyperactive comet for which 40% of its nucleus surface is active. It has a typical composition, similar to other normal comets; however, an asymmetric behavior with respect to perihelion has been seen in its activity, which is typical of seasonal effects. Photometric measurements show no evidence for a change in the rotation period of the nucleus during this apparition. High-resolution spectra show that 46P has typical NH
2
ortho-to-para, OI lines ratios, and C and N isotopic ratios.
•Asteroid Apophis was found in a non-principal axis rotation state (tumbling).•Its dynamical parameters and a shape model were derived.•Its retrograde spin calls for a further assessment of its ...impact probability.•Recent estimates of asteroid nutational damping times were reviewed and applied.•Parameters of tumbling asteroids place constraints on their evolution and properties.
Our photometric observations of Asteroid (99942) Apophis from December 2012 to April 2013 revealed it to be in a state of non-principal axis rotation (tumbling). We constructed its spin and shape model and found that it is in a moderately excited Short Axis Mode (SAM) state with a ratio of the rotational kinetic energy to the basic spin state energy E/E0=1.024±0.013. (All quoted uncertainties correspond to 3σ.) The greatest and intermediate principal moments of inertia are nearly the same with I2/I3=0.965-0.015+0.009, but the smallest principal moment of inertia is substantially lower with I1/I3=0.61-0.08+0.11; the asteroid’s dynamically equivalent ellipsoid is close to a prolate ellipsoid. The precession and rotation periods are Pϕ=27.38±0.07h and Pψ=263±6h, respectively; the strongest observed lightcurve amplitude for the SAM case is in the 2nd harmonic of P1=Pϕ-1-Pψ-1-1=30.56±0.01h. The rotation is retrograde with the angular momentum vector’s ecliptic longitude and latitude of 250° and -75° (the uncertainty area is approximately an ellipse with the major and minor semiaxes of 27° and 14°, respectively). An implication of the retrograde rotation is a somewhat increased probability of the Apophis’ impact in 2068, but it is still very small with the risk level on the Palermo Scale remaining well below zero. Apophis is a member of the population of slowly tumbling asteroids. Applying the theory of asteroid nutational damping by Breiter et al. (Breiter, S., Rożek, A., Vokrouhlický, D. 2012. Mon. Not. R. Astron. Soc. 427, 755–769), we found that slowly tumbling asteroids predominate in the spin rate–size range where their estimated damping times are greater than about 0.2Gyr. The appearance that the PA/NPA rotators transition line seems to follow a line of constant damping time may be because there are two or more asteroid spin evolution mechanisms in play, or the factor of μQ (the elastic modulus times the quality factor) is not constant but it may decrease with decreasing asteroid size, which would oppose the trend due to decreasing collisional age or excitation time.
Context.
The N
2
and CO-rich and water-depleted comet C/2016 R2 (Pan-STARRS) – hereafter “C/2016 R2” – is a unique comet for detailed spectroscopic analysis.
Aims.
We aim to explore the associated ...photochemistry of parent species, which produces different metastable states and forbidden emissions, in this cometary coma of peculiar composition.
Methods.
We reanalyzed the high-resolution spectra of comet C/2016 R2 obtained in February 2018 using the UVES spectrograph of the European Southern Observatory Very Large Telescope. Various forbidden atomic emission lines of CI, NI, and OI were observed in the optical spectrum of this comet when it was at 2.8 au from the Sun. The observed forbidden emission intensity ratios are studied in the framework of a couple-chemistry emission model.
Results.
The model calculations show that CO
2
is the major source of both atomic oxygen green and red doublet emissions in the coma of C/2016 R2 (while for most comets it is generally H
2
O), whereas, CO and N
2
govern the atomic carbon and nitrogen emissions, respectively. Our modeled oxygen green-to-red-doublet and carbon-to-nitrogen emission ratios are higher by a factor of three than what is found from observations. These discrepancies could be due to uncertainties associated with photon cross sections or unknown production and/or loss sources. Our modeled oxygen green-to-red-doublet emission ratio is close to what is seen in observations when we consider an O
2
abundance with a production rate of 30% relative to the CO production rate. We constrained the mean photodissociation yield of CO, producing C(
1
S) at about 1%, a quantity which has not been measured in the laboratory. The collisional quenching is not a significant loss process for N(
2
D) though its radiative lifetime is significant (~10 h). Hence, the observed NI doublet-emission ratio (NI 5198/5200) of 1.22, which is smaller than the terrestrial measurement by a factor 1.4, is mainly due to the characteristic radiative decay of N(
2
D).
We report on photometry and high-resolution spectroscopy of the chemically peculiar Jupiter-family comet (hereafter JFC) 21P/Giacobini-Zinner. Comet 21P is a well-known member of the ...carbon-chain-depleted family, but also displays a depletion of amines. We continuously monitored the comet over more than seven months with the two TRAPPIST telescopes (TN and TS), covering a wide heliocentric distance range from 1.60 au inbound to 2.10 au outbound with a perihelion at 1.01 au on September 10, 2018. We computed and followed the evolution of the dust- (represented by
Afρ
) and gas-production rates of the daughter species OH, NH, CN, C
3
, and C
2
and their relative abundances to OH and to CN over the cometary orbit. We compared them to those measured in the previous apparitions. The activity of the comet and its water production rate reached a maximum of (3.72 ± 0.07) × 10
28
mol s
−1
on August 17, 2018 (
r
h
= 1.07 au), 24 days before perihelion. The peak value of
A
(0)
fρ
was reached on the same date (1646 ± 13) cm in the red filter. Using a sublimation model for the nucleus, we constrained the active surface of the nucleus using the slow-rotator model. The abundance ratios of the various species are remarkably constant over a wide range of heliocentric distances before and after perihelion, showing a high level of homogeneity of the ices in the surface of the nucleus. The behaviour and level of the activity of the comet is also remarkably similar over the last five orbits. In the coma dust colour, 21P shows reflective gradients similar to JFCs. We obtained a high-resolution spectrum of 21P with UVES at ESO Very Large Telescope one week after perihelion. Using the CN B-X (0, 0) violet band, we measured
12
C/
13
C and
14
N/
15
N isotopic ratios of 100 ± 10 and 145 ± 10, respectively, both in very good agreement with the ratios commonly found in comets. We measured an ortho-para abundance ratio of NH
3
of 1.16 ± 0.02, corresponding to a nuclear spin temperature of
T
spin
= 27 ± 1 K, which is similar to other comets. While the abundance ratios in the gaseous coma reveal a peculiar composition, the isotopic and ortho-to-para ratios appear entirely normal. We performed a dynamical simulation of 21P and found that it is likely a young member of the JFC population. We favour a pristine composition scenario to explain the chemical peculiarities of this comet.
Context. (1) Ceres is the largest body in the main asteroid belt and one of the most intriguing objects in the solar system, in part because of the discovery of water outgassing by the Herschel Space ...Observatory (HSO) and its still-debated origin. Ceres was the target of NASA’s Dawn spacecraft for 3.5 yr, which achieved a detailed characterization of the dwarf planet. The possible influence of the local flux of solar energetic particles (SEP) on the production of a Cerean exosphere and water vapor has been suggested, in addition to the sublimation of water ice that depends on the temperature, meaning the heliocentric distance. Aims. We used the opportunity of both the perihelion passage of (1) Ceres in April 2018, and the presence of Dawn in its vicinity (for measuring the SEP flux in real time) to check the influence of heliocentric distance and SEP flux on water outgassing. Methods. We searched for OH emission lines near the limb of Ceres in the near-UV with the UVES spectrograph mounted on the 8-m ESO Very Large Telescope. Two spectra were recorded when Ceres was close to its perihelion, in February 2018, and with Dawn spacecraft orbiting Ceres. It was possible to simultaneously measure energetic particles around Ceres at the time of our observations. Results. Our observations did not permit detection of OH emission lines to a very high sensitivity level. This level is estimated to correspond to a global water production rate of QH2O ∽ 2 × 1026 $Q_{\textrm{H}_2O}\,{\sim}\,2\,{\times}\,10^{26}$ QH2O ~ 2 × 1026 molecules s−1, similar to the water production rate derived from HSO observations. The solar energetic particles flux measured around Ceres was negligible at the time of these observations. Conclusions. Our observations support the idea that heliocentric distance (i.e., the sublimation of water ice) does not play a major role in the water emission from Ceres. This production rate could be either related to SEP events or to other mechanisms, possibly of endogenic origin.
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