The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could harbor liquid water on their surfaces. Ultraviolet observations are essential to measuring their ...high-energy irradiation and searching for photodissociated water escaping from their putative atmospheres. Our new observations of the TRAPPIST-1 Ly line during the transit of TRAPPIST-1c show an evolution of the star emission over three months, preventing us from assessing the presence of an extended hydrogen exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape. However, TRAPPIST-1e to h might have lost less than three Earth oceans if hydrodynamic escape stopped once they entered the habitable zone (HZ). We caution that these estimates remain limited by the large uncertainty on the planet masses. They likely represent upper limits on the actual water loss because our assumptions maximize the X-rays to ultraviolet-driven escape, while photodissociation in the upper atmospheres should be the limiting process. Late-stage outgassing could also have contributed significant amounts of water for the outer, more massive planets after they entered the HZ. While our results suggest that the outer planets are the best candidates to search for water with the JWST, they also highlight the need for theoretical studies and complementary observations in all wavelength domains to determine the nature of the TRAPPIST-1 planets and their potential habitability.
Aims.
The discovery of the first active interstellar object 2I/Borisov provides an unprecedented opportunity to study planetary formation processes in another planetary system. In particular, ...spectroscopic observations of 2I allow us to constrain the composition of its nuclear ices.
Methods.
We obtained optical spectra of 2I with the 4.2 m
William Herschel
and 2.5 m
Isaac Newton
telescopes between 2019 September 30 and October 13, when the comet was between 2.5 au and 2.4 au from the Sun. We also imaged the comet with broadband filters on 15 nights from September 11 to October 17, as well as with a CN narrow-band filter on October 18 and 20, with the TRAPPIST-North telescope.
Results.
Broadband imaging confirms that the dust coma colours (
B
−
V
= 0.82 ± 0.02,
V
−
R
= 0.46 ± 0.03,
R
−
I
= 0.44 ± 0.03,
B
−
R
= 1.28 ± 0.03) are the same as for Solar System comets. We detect CN emission in all spectra and in the TRAPPIST narrow-band images with production rates between 1.6 × 10
24
and 2.1 × 10
24
molec/s. No other species are detected. We determine three-sigma upper limits for C
2
, C
3
, and OH production rates of 6 × 10
23
molec/s, 2 × 10
23
molec/s and 2 × 10
27
molec/s, respectively, on October 02. There is no significant increase of the CN production rate or A(0)f
ρ
during our observing period. Finally, we place a three-sigma upper limit on the Q(C
2
)/Q(CN) ratio of 0.3 (on October 13). From this, we conclude that 2I is highly depleted in C
2
, and may have a composition similar to Solar System carbon-chain depleted comets.
Isotopic ratios in outbursting comet C/2015 ER61 Yang, Bin; Hutsemékers, Damien; Shinnaka, Yoshiharu ...
Astronomy and astrophysics (Berlin),
01/2018, Letnik:
609
Journal Article, Web Resource
Recenzirano
Odprti dostop
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 12C/13C = 100 ± 15, 14N/15N = 130 ± 15. In addition, we determined the 14N/15N ratio from four pairs of NH2 isotopolog lines and measured 14N/15N = 140 ± 28. The measured isotopic ratios of C/2015 ER61 do not deviate significantly from those of other comets.
We present the discovery by the WASP-South survey of WASP-121 b, a new remarkable short-period transiting hot Jupiter. The planet has a mass of
$1.183_{-0.062}^{+0.064}$
M
Jup, a radius of 1.865 ± ...0.044 R
Jup, and transits every
$1.274\,9255_{-0.000\,0025}^{+0.000\,0020}$
days an active F6-type main-sequence star (V = 10.4,
$1.353_{-0.079}^{+0.080}$
M⊙, 1.458 ± 0.030 R⊙, T
eff = 6460 ± 140 K). A notable property of WASP-121 b is that its orbital semimajor axis is only ∼1.15 times larger than its Roche limit, which suggests that the planet is close to tidal disruption. Furthermore, its large size and extreme irradiation (∼7.1 109 erg s−1 cm−2) make it an excellent target for atmospheric studies via secondary eclipse observations. Using the TRAnsiting Planets and PlanetesImals Small Telescope, we indeed detect its emission in the z
′-band at better than ∼4σ, the measured occultation depth being 603 ± 130 ppm. Finally, from a measurement of the Rossiter–McLaughlin effect with the CORALIE spectrograph, we infer a sky-projected spin-orbit angle of
$257{^{\circ}_{.}} 8_{-5{^{\circ}_{.}} 5}^{+5{^{\circ}_{.}} 3}$
. This result may suggest a significant misalignment between the spin axis of the host star and the orbital plane of the planet. If confirmed, this high misalignment would favour a migration of the planet involving strong dynamical events with a third body.
SPECULOOS: Ultracool dwarf transit survey Sebastian, D.; Gillon, M.; Ducrot, E. ...
Astronomy and astrophysics (Berlin),
01/2021, Letnik:
645
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context.
One of the most promising avenues for the detailed study of temperate Earth-sized exoplanets is the detection of such planets in transit in front of stars that are small and near enough to ...make it possible to carry out a thorough atmospheric characterisation with next-generation telescopes, such as the
James Webb
Space telescope (JWST) or Extremely Large Telescope (ELT). In this context, the TRAPPIST-1 planets form a unique benchmark system that has garnered the interest of a large scientific community.
Aims.
The SPECULOOS survey is an exoplanet transit survey targeting a volume-limited (40 pc) sample of ultracool dwarf stars (of spectral type M7 and later) that is based on a network of robotic 1 m telescopes especially designed for this survey. The strategy for brighter and earlier targets leverages on the synergy with the ongoing TESS space-based exoplanet transit survey.
Methods.
We define the SPECULOOS target list as the sum of three non-overlapping sub-programmes incorporating the latest type objects (
T
eff
≲ 3000 K). Programme 1 features 365 dwarfs that are small and near enough to make it possible to detail atmospheric characterisation of an ‘Earth-like’ planet with the upcoming JWST. Programme 2 features 171 dwarfs of M5-type and later for which a significant detection of a planet similar to TRAPPIST-1b should be within reach of TESS. Programme 3 features 1121 dwarfs that are later than M6-type. These programmes form the basis of our statistical census of short-period planets around ultracool dwarf stars.
Results.
Our compound target list includes 1657 photometrically classified late-type dwarfs, with 260 of these targets classified, for the first time, as possible nearby ultracool dwarf stars. Our general observational strategy was to monitor each target between 100 and 200 h with our telescope network, making efficient use of the synergy with TESS for our Programme 2 targets and a proportion of targets in our Programme 1.
Conclusions.
Based on Monte Carlo simulations, we expect to detect up to a few dozen temperate, rocky planets. We also expect a number of them to prove amenable for atmospheric characterisation with JWST and other future giant telescopes, which will substantially improve our understanding of the planetary population of the latest-type stars.
In this paper, we aim to reconstruct meteoroid trajectories using a forward scatter radio system transmitting a continuous wave (CW) with no modulation. To do so, we use the meteor echoes recorded at ...the receivers of the BRAMS (Belgian RAdio Meteor Stations) network. This system consists, at the time of writing, of a dedicated transmitter and 44 receiving stations located in and nearby Belgium, all synchronized using GPS clocks. Our approach processes the meteor echoes at the BRAMS receivers and uses the time delays as inputs to a nonlinear optimization solver. We compare the quality of our reconstructions with and without interferometric data to the trajectories given by the optical CAMS (Cameras for Allsky Meteor Surveillance) network in Benelux. We show that the general CW forward scatter trajectory reconstruction problem can be solved, but we highlight its strong ill‐conditioning. With interferometry, this high sensitivity to the inputs is alleviated and the reconstructed trajectories are in good agreement with optical ones, displaying an uncertainty smaller than 10% on the velocity and 2° on the inclination for most cases. To increase accuracy, the trajectory reconstruction with time delays only should be complemented by information about the signal phase. The use of at least one interferometer makes the problem much easier to solve and greatly improves the accuracy of the retrieved velocities and inclinations. Increasing the number of receiving stations also enhances the quality of the reconstructions.
Plain Language Summary
This paper presents a method for tracking the path and speed of meteoroids using radio observations. A simple continuous wave signal is reflected by the electrons created when the meteoroid enters the upper atmosphere and creates ionization. The reflected signal, called a meteor echo, is recorded at various locations not co‐located with the transmitter. The time delays between several echoes is used to retrieve the meteoroid trajectory and speed. In this work, we apply this method using data from Belgian RAdio Meteor Stations (BRAMS), a Belgian network of 44 receiving stations. The results are compared to accurate observations from Cameras for Allsky Meteor Surveillance, an optical network of cameras surveying the sky for meteors. Our method perfectly works with no measurement errors but small uncertainties on the time delays may significantly impact the accuracy of the reconstruction. Using a large amount of receivers and/or a radio interferometer greatly improves the results. This project is the first to tackle the meteoroid trajectory reconstruction using this type of radio system (with no range information and many receivers at different locations). This novel method is essential to fully exploit the capabilities of BRAMS for future applications such as determination of fluxes or sounding of the upper atmosphere (e.g., wind speed measurements).
Key Points
Meteoroid trajectory and speed determined with a continuous wave forward scatter radio set‐up
Trajectory reconstruction solver is validated against simulated data but the problem is ill‐conditioned
Interferometry required for an accuracy of <10% on the velocity and <2° on the inclination for most trajectories
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