ISM studies of GRB 030329 with high resolution spectroscopy

We present a series of early UVES/VLT high resolution spectra of the afterglow of GRB 030329 at redshift z=0.16867+-0.00001. In contrast to other spectra from this burst, both emission and absorption lines were detected. None of them showed any temporal evolution. From the emission lines, we determine the properties of the host galaxy which has a star formation rate (SFR) of 0.198 M_solar yr^-1 and a low metallicity of 1/7 Z_solar. Given the low total stellar host mass M_star=10^7.75+-0.15 M_solar and an absolute luminosity m_V=-16.37, we derive specific SFRs (SSFR) of log SFR/M = -8.5 yr^-1 and SFR/L = 14.1 M_solar yr^-1 L_*^-1. This fits well into the picture of GRB hosts as being low mass, low metallicity, actively star forming galaxies. The MgII and MgI absorption lines from the host show multiple narrow (Doppler width b=5-10 km/s) components spanning a range of v about 260 km/s, mainly blueshifted compared to the redshift from the emission lines. These components are likely probing outflowing material of the host galaxy, which could arise from former galactic superwinds, driven by supernovae from star forming regions. Similar features have been observed in QSO spectra. The outflowing material is mainly neutral with high column densities of log N(MgII)=14.0+-0.1 cm^-2 and log N(MgI)=12.3+-0.1 cm^-2.Comment: 11 pages, 4 figures, submitted to Ap

Study of the forbidden oxygen lines in a dozen comets observed at the VLT (ESO)

The forbidden lines are difficult to analyse because their detection requires high spectral and spatial resolutions. Their analysis is however interesting because it allows the determination of the spatial distribution and the production rate of the parent molecules, supposedly H2O which doesn't have any feature in the optical range. But as shown by Cochran [2] [3], some issues remain about the nature of the parents of the oxygen atoms. Moreover the width of the green line was found larger than that of the red lines. One of the goals of this study is to determine the parent species that photo-dissociate to produce oxygen atoms and see how this process depends on the heliocentric distance. We present here the results of the analysis of a homogeneous set of high quality spectra of 13 different comets observed with UVES at the ESO VLT since 2002 [4] [5]

A fast rotation period and large amplitude for PHA 2021 NY1

We report optical light curve observations of the near earth asteroid 2021 NY1. It was first observed with Pan-STARRS 1, Haleakala, on 2021, July 7 and has been classified by the Minor Planet Center as a potentially hazardous asteroid

Study of the forbidden oxygen lines in comets at different heliocentric and nucleocentric distances

Oxygen is an important element in the chemistry of the Solar System objects given its abundance and its presence in many molecules including H2O, which constitutes 80% of cometary ices. The analysis of oxygen atoms in comets can provide information not only on the comets themselves but also on our Solar System. These atoms have been analyzed using the three forbidden oxygen lines [OI] observed in emission in the optical region at 5577 Å (the green line), 6300 Å and 6364 Å (the red lines) [1]. These lines are difficult to analyze because their detection requires high spectral and spatial resolutions. The oxygen analysis is interesting because it allows the determination of its parent molecules

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

TRAPPIST C/2021 A1 (Leonard) comet production rates

E. Jehin, Y. Moulane, and J. Manfroid, report that they obtained on 19 December, from 00:15 to 01:15 UT, with the TRAPPIST-South (code=I40) robotic telescope (Jehin el al. 2011) located at the ESO La Silla Observatory (Chile), three sets of cometary HB narrowband filters (Farnham et al. 2000) and broad band filters (B,V,Rc,Ic) on comet C/2021 A1 (Leonard) at high airmass under photometric conditions

Comets 12^{12}CO+^+ and 13^{13}CO+^+ fluorescence models for measuring the 12^{12}C/13^{13}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 $^{12}$C/$^{13}$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 $^{12}$C/$^{13}$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 $^{12}$CO$^+$ and $^{13}$CO$^+$ ions. The $^{13}$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 $^{12}$CO$^+$ emission lines, allowing to publish revised fluorescence efficiencies. Based on similar transition probabilities for $^{12}$CO$^+$ and $^{13}$CO$^+$ we derive a $^{12}$C/$^{13}$C isotopic ratio of 73$\pm$20 for CO$^+$ in comet C/2016 R2. This value is in agreement with the solar system ratio of 89$\pm$2 within the error bars, making the possibility that this comet was an interstellar object unlikely.Comment: 11 pages, 8 figure

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 $^{12}$C/$^{13}$C=100 $\pm$ 15, $^{14}$N/$^{15}$N=130 $\pm$ 15. In addition, we determined the $^{14}$N/$^{15}$N ratio from four pairs of NH$_2$ isotopolog lines and measured $^{14}$N/$^{15}$N=140 $\pm$ 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&

Reconstructing meteoroid trajectories using forward scatter radio observations from the BRAMS network

peer reviewedIn 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

Reconstructing meteoroid trajectories using forward scatter radio observations and the interferometer from the BRAMS network

When meteoroids hit Earth's atmosphere molecules, they leave a trail of plasma behind. This region, composed of free electrons and positively charged ions, is capable of reflecting radio signals. The analysis of such signals along the meteoroid path can be used for various scientific purposes: quantification of the electron line density, analysis of the thermosphere properties, characterization of the meteor ablation process, etc. To achieve these objectives, the meteoroid trajectory needs first to be determined. The reflection on the plasma trails is usually assumed to be specular, which means that the radio wave is reflected only at a given point along the meteoroid trajectory. For forward scatter systems, the position of this specular point depends on the trajectory on the one hand, and on the position of both the emitter and the receiver on the other hand. Using non-collocated receivers, one obtains several specular points along the trajectory. The receivers will thus detect the reflected signal at different time instants on a given trajectory. In this work, we propose a method that aims at reconstructing meteoroid trajectories using only the time differences of the meteor echoes measured at the receivers of a forward scatter radio system, such as the BRAMS (Belgian RAdio Meteor Stations) network. The latter uses the forward scatter of radio waves on ionized meteor trails to study meteoroids falling in the Earth's atmosphere. It is made of a dedicated transmitter and 42 receiving stations located in and nearby Belgium. Given that all the BRAMS receivers are synchronized using GPS clocks, we can compute the time differences of the meteor echoes and use them to find the meteoroid trajectory. Assuming a constant speed motion, the position (three degrees of freedom) and the three velocity components have to be determined. This inverse problem is non-linear and requires the definition of a target objective to minimize. Two different formulations are compared: the first one is based on the minimization of the bistatic range while the second one uses a forward model, which defines the trajectory as being tangential to a family of ellipsoids whose loci are the emitter and each receiver. A Monte-Carlo analysis is performed to highlight the sensitivity of the output trajectory parameters to the input time differences. The BRAMS network also includes an interferometer in Humain (south of Belgium). Unlike the other receiving stations, it uses 5 antennas in the so-called Jones configuration (Jones et al., 1998; Lamy et al., 2018) and allows to determine the direction of arrival of the meteor echo to within approximately 1°. In that case, the problem becomes much easier to solve because the interferometer gives information about the direction of a reflection point. The benefits brought by such a system regarding the accuracy of the trajectory reconstruction are highlighted. The post-processing steps allowing to extract meteor echoes from the raw radio signals are described. An approach to properly filter out the direct beacon signal is introduced. Indeed, each receiver detects a more or less strong direct signal coming from the transmitter. This signal does not contain any information about the meteor path since it simply propagates through the atmosphere and is not reflected on the meteor trail. Knowing that the BRAMS transmitter emits a continuous cosine wave, the amplitude, the frequency and the phase are fitted in the frequency domain. The beacon signal is finally reconstructed in the time domain and subtracted. This process in illustrated in the following figure, which shows an example of spectrograms (i.e. time-frequency maps where the power is color-coded) before and after the beacon signal subtraction. The proper removal of the horizontal line at around 1005 Hz (corresponding to the direct signal) is apparent in the bottom spectrogram. Afterwards, a bandpass filter is necessary to fully exploit the echoes of the detected meteors. Indeed, the raw signal at the time of the meteor echo is noisy and can have interfering signals caused by the reflections on aircrafts. If the latter are at slightly different frequencies than the meteor echo, they produce interference beats. A windowed-sinc filter Blackman filter of high order is therefore used to remove the signal components at frequencies where the meteor echo does not appear. The time corresponding to half-peak power in the rising edge of the echo (which marks the passage of the meteoroid at the specular reflection point) is finally retrieved and the time differences are computed. To analyze the accuracy of the trajectory reconstructions, data from the optical CAMS-BeNeLux network are used. Promising results showing the reconstructed position, velocity and inclination of several meteoroid trajectories with and without the interferometer are discussed. In the following figure, an example of CAMS trajectory reconstruction obtained with our post-processing is shown. The blue line corresponds to the trajectory determined with the CAMS network, while the purple line is obtained through our analysis of the radio signals obtained at the BRAMS receivers. The reconstructed trajectory using the time differences only (method 1) is shown on the left. The trajectory obtained thanks to the combination of time differences and interferometric data (method 2) is given on the right