1σ Uncertainty Research Articles

Reeling in the Whirlpool galaxy: Distance to M 51 clarified through Cepheids and the type IIP supernova 2005cs

Context. The distance to the Whirlpool galaxy, M 51, is still debated, even though the galaxy has been studied in great detail. Current estimates range from 6.02 to 9.09 Mpc, and different methods yield discrepant results. No Cepheid distance has been published for M 51 to date. Aims. We aim to estimate a more reliable distance to M 51 through two independent methods: Cepheid variables and their period-luminosity relation, and an augmented version of the expanding photosphere method (EPM) on the type IIP supernova SN 2005cs, which exploded in this galaxy. Methods. For the Cepheid variables, we analysed a recently published Hubble Space Telescope catalogue of stars in M 51. By applying filtering based on the light curve and colour-magnitude diagram, we selected a high-quality sample of M 51 Cepheids to estimate the distance through the period-luminosity relation. For SN 2005cs, an emulator-based spectral fitting technique was applied, which allows for the fast and reliable estimation of the physical parameters of the supernova atmosphere. We augmented the established framework of EPM with these spectral models to obtain a precise distance to M 51. Results. The two resulting distance estimates are DCep = 7.59 ± 0.30 Mpc and D2005cs = 7.34 ± 0.39 Mpc using the Cepheid period-luminosity relation and the spectral modelling of SN 2005cs, respectively. This is the first published Cepheid distance for this galaxy. The obtained values are precise to 4–5% and are fully consistent within 1σ uncertainties. Because these two estimates are completely independent, they can be combined for an even more precise estimate, which yields DM 51 = 7.50 ± 0.24 Mpc (3.2% uncertainty). Conclusions. Our distance estimates agree with most of the results obtained previously for M 51, but they are more precise than the earlier counterparts. However, they are significantly lower than the TRGB estimates, which are often adopted for the distance to this galaxy. The results highlight the importance of direct cross-checks between independent distance estimates so that systematic uncertainties can be quantified. Because of the large discrepancy, this finding can also affect distance-sensitive studies and their discussion for objects within M 51, as well as the estimation of the Hubble constant through the type IIP standardizable candle method, for which SN 2005cs is a calibrator object.

Atmospheric CO2 inversion reveals the Amazon as a minor carbon source caused by fire emissions, with forest uptake offsetting about half of these emissions

Abstract. Tropical forests such as the Amazonian rainforests play an important role for climate, are large carbon stores and are a treasure of biodiversity. Amazonian forests have been exposed to large-scale deforestation and degradation for many decades. Deforestation declined between 2005 and 2012 but more recently has again increased with similar rates as in 2007–2008. The resulting forest fragments are exposed to substantially elevated temperatures in an already warming world. These temperature and land cover changes are expected to affect the forests, and an important diagnostic of their health and sensitivity to climate variation is their carbon balance. In a recent study based on CO2 atmospheric vertical profile observations between 2010 and 2018, and an air column budgeting technique used to estimate fluxes, we reported the Amazon region as a carbon source to the atmosphere, mainly due to fire emissions. Instead of an air column budgeting technique, we use an inverse of the global atmospheric transport model, TOMCAT, to assimilate CO2 observations from Amazon vertical profiles and global flask measurements. We thus estimate inter- and intra-annual variability in the carbon fluxes, trends over time and controls for the period of 2010–2018. This is the longest period covered by a Bayesian inversion of these atmospheric CO2 profile observations to date. Our analyses indicate that the Amazon is a small net source of carbon to the atmosphere (mean 2010–2018 = 0.13 ± 0.17 Pg C yr−1, where 0.17 is the 1σ uncertainty), with the majority of the emissions coming from the eastern region (77 % of total Amazon emissions). Fire is the primary driver of the Amazonian source (0.26 ± 0.13 Pg C yr−1), while forest carbon uptake removes around half of the fire emissions to the atmosphere (−0.13 ± 0.20 Pg C yr−1). The largest net carbon sink was observed in the western-central Amazon region (72 % of the fire emissions). We find larger carbon emissions during the extreme drought years (such as 2010, 2015 and 2016), correlated with increases in temperature, cumulative water deficit and burned area. Despite the increase in total carbon emissions during drought years, we do not observe a significant trend over time in our carbon total, fire and net biome exchange estimates between 2010 and 2018. Our analysis thus cannot provide clear evidence for a weakening of the carbon uptake by Amazonian tropical forests.

Measuring the photoionization rate, neutral fraction, and mean free path of H i ionizing photons at 4.9 ≤ z ≤ 6.0 from a large sample of XShooter and ESI spectra

ABSTRACT We measure the mean free path ($\lambda _{\rm mfp,H\, \small {I}}$), photoionization rate ($\langle \Gamma _{\rm H\, \small {I}} \rangle$), and neutral fraction ($\langle f_{\rm H\, \small {I}} \rangle$) of hydrogen in 12 redshift bins at 4.85 < z < 6.05 from a large sample of moderate resolution XShooter and ESI QSO absorption spectra. The fluctuations in ionizing radiation field are modelled by post-processing simulations from the Sherwood suite using our new code ‘EXtended reionization based on the Code for Ionization and Temperature Evolution’ (ex-cite). ex-cite uses efficient Octree summation for computing intergalactic medium attenuation and can generate large number of high resolution $\Gamma _{\rm H\, \small {I}}$ fluctuation models. Our simulation with ex-cite shows remarkable agreement with simulations performed with the radiative transfer code Aton and can recover the simulated parameters within 1σ uncertainty. We measure the three parameters by forward-modelling the Lyα forest and comparing the effective optical depth ($\tau _{\rm eff, H\, \small {I}}$) distribution in simulations and observations. The final uncertainties in our measured parameters account for the uncertainties due to thermal parameters, modelling parameters, observational systematics, and cosmic variance. Our best-fitting parameters show significant evolution with redshift such that $\lambda _{\rm mfp,H\, \small {I}}$ and $\langle f_{\rm H\, \small {I}} \rangle$ decreases and increases by a factor ∼6 and ∼104, respectively from z ∼ 5 to z ∼ 6. By comparing our $\lambda _{\rm mfp,H\, \small {I}}$, $\langle \Gamma _{\rm H\, \small {I}} \rangle$ and $\langle f_{\rm H\, \small {I}} \rangle$ evolution with that in state-of-the-art Aton radiative transfer simulations and the Thesan and CoDa-III simulations, we find that our best-fitting parameter evolution is consistent with a model in which reionization completes by z ∼ 5.2. Our best-fitting model that matches the $\tau _{\rm eff, H\, \small {I}}$ distribution also reproduces the dark gap length distribution and transmission spike height distribution suggesting robustness and accuracy of our measured parameters.

Depth of Magma Storage Under Iceland Controlled by Magma Fluxes

AbstractThe compositions of volcanic materials are sensitive to physical conditions in the underlying magmatic system. When basaltic melts are saturated in olivine‐plagioclase‐augite prior to eruption, their compositions can be used to estimate the pressure at which they last equilibrated. We developed PyOPAM, an open‐source tool that runs in Python, and use this refreshed liquid‐barometer to investigate the relationship between final depths of magma storage and magma flux. We first tested PyOPAM using 312 experimental glasses compiled from literature and found that the 1σ uncertainty is 1.13 kbar (±3 km). PyOPAM was then applied to a data set of 13,400 analyses from Iceland, where suspected controls on magma flux are well constrained. Of these, 3807 analyses return robust pressure estimates, constraining final pre‐eruptive magma storage depths for 23 of the 30 Icelandic volcanic systems. Our results indicate that magma storage pressures on Iceland are linked to melt‐flux from the mantle. This finding is consistent with previous models linking storage depths and spreading rates on the global mid‐ocean ridge system. In addition, we provide clear evidence that the magma flux, rather than spreading rate alone, is the key control on the distribution of melt at spreading centers. Increased melt flux is associated with shoaling of pre‐eruptive storage depths, indicating that mantle melt fluxes dictate the long‐term stabilization of extensive magmatic storage regions at depths shallower than 10 km. Quantitative relationships between mantle melt flux and storage depths can be used to test computational models of transcrustal magmatic systems.

Orbits and Masses of the Small Satellites of Pluto

We present a new orbit and mass solution for the four small satellites of Pluto: Styx, Nix, Kerberos, and Hydra. We have reanalyzed all available observations of the Pluto system obtained by the Hubble Space Telescope from 2005 to 2019 with the ACS, WFPC2, and WFC3 instruments, as well as the New Horizons LORRI images taken on approach to Pluto in 2015. We have used this high-precision astrometry to produce updated orbits and mass estimates with uncertainties for all four of the small satellites. We find that the masses of Nix and Hydra are smaller than previously published estimates, with a dynamical mass of (1.8 ± 0.4) × 10−3 km3 s−2 ((2.7 ± 0.6) × 1016 kg) for Nix and (2.0 ± 0.2) × 10−3 km3 s−2 ((3.0 ± 0.3) × 1016 kg) for Hydra. These masses are 60% and 63% of the mean estimates by Brozovic et al., respectively, although still consistent with their 1σ uncertainties, and correspond to densities of 1.0 ± 0.2 g cm−3 for Nix and 1.2 ± 0.2 g cm−3 for Hydra given the moon volume estimates from Porter et al. Although these densities are consistent with a range of ice−rock compositions, depending on the unknown bulk porosity in the moon interiors, the moons’ high albedos and predominantly icy surfaces are most easily explained if their interiors are ice-rich. The tiny masses of Kerberos and Sytx remain very poorly constrained; we find 1σ upper limits for dynamical mass of 3 × 10−5 km3 s−2 (5 × 1014 kg) for Styx and 5 ×10−5 km3 s−2 (8 × 1014 kg) for Kerberos, consistent with densities of <2.1 g cm−3 for both bodies.

Improved semi-experimental equilibrium structure and high-level theoretical structures of ketene.

The millimeter-wave rotational spectrum of ketene (H2C=C=O) has been collected and analyzed from 130 to 750GHz, providing highly precise spectroscopic constants from a sextic, S-reduced Hamiltonian in the Ir representation. The chemical synthesis of deuteriated samples allowed spectroscopic measurements of five previously unstudied ketene isotopologues. Combined with previous work, these data provide a new, highly precise, and accurate semi-experimental (reSE) structure for ketene from 32 independent moments of inertia. This reSE structure was determined with the experimental rotational constants of each available isotopologue, together with computed vibration-rotation interaction and electron-mass distribution corrections from coupled-cluster calculations with single, double, and perturbative triple excitations [CCSD(T)/cc-pCVTZ]. The 2σ uncertainties of the reSE parameters are ≤0.0007 Å and 0.014° for the bond distances and angle, respectively. Only S-reduced spectroscopic constants were used in the structure determination due to a breakdown in the A-reduction of the Hamiltonian for the highly prolate ketene species. All four reSE structural parameters agree with the "best theoretical estimate" (BTE) values, which are derived from a high-level computed re structure [CCSD(T)/cc-pCV6Z] with corrections for the use of a finite basis set, the incomplete treatment of electron correlation, relativistic effects, and the diagonal Born-Oppenheimer breakdown. In each case, the computed value of the geometric parameter lies within the statistical experimental uncertainty (2σ) of the corresponding semi-experimental coordinate. The discrepancies between the BTE structure and the reSE structure are 0.0003, 0.0000, and 0.0004 Å for rC-C, rC-H, and rC-O, respectively, and 0.009° for θC-C-H.

The ages and metallicities of the globular clusters in the Sparkler

ABSTRACT JWST observations of the strongly lensed galaxy the Sparkler have revealed a population of gravitationally bound globular cluster (GC) candidates. Different analyses have resulted in broadly similar ages but significantly different metallicities, questioning the assembly history that has led to the formation of such a population. In this letter, we reanalyse the two sets of photometry available in the literature with the code mcmame especially tailored to fit physical properties of GCs. We find the ages and metallicities from both data sets are consistent within 1σ uncertainties. A significant group of GCs is consistent with being old and metal poor ([Fe/H] ∼ −1.7). For this group, the ages do not converge, hence, we conclude that they are definitively older than 1 Gyr and can be as old as the age of the Universe. The remaining GCs have younger ages and a metallicity spread. The ages and metallicities distribution of GCs in the Sparkler are consistent with those observed in Local Group’s galaxies at similar lookback times. Comparing with predictions from E-MOSAICS simulations we confirm that the Sparkler GC population traces the self-enrichment history of a galaxy which might become a few times 109 M⊙ massive system at redshift z = 0.

WISDOM project – XIV. SMBH mass in the early-type galaxies NGC 0612, NGC 1574, and NGC 4261 from CO dynamical modelling

ABSTRACT We present a CO dynamical estimate of the mass of the supermassive black hole (SMBH) in three nearby early-type galaxies: NGC 0612, NGC 1574, and NGC 4261. Our analysis is based on Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 3–6 observations of the 12CO(2–1) emission line with spatial resolutions of 14–58 pc (0.01″–0.26″). We detect disc-like CO distributions on scales from ≲ 200 pc (NGC 1574 and NGC 4261) to ≈10 kpc (NGC 0612). In NGC 0612 and NGC 1574 the bulk of the gas is regularly rotating. The data also provide evidence for the presence of a massive dark object at the centre of NGC 1574, allowing us to obtain the first measure of its mass, MBH = (1.0 ± 0.2) × 108 M⊙ (1σ uncertainty). In NGC 4261, the CO kinematics is clearly dominated by the SMBH gravitational influence, allowing us to determine an accurate black hole mass of (1.62 ± 0.04) × 109 M⊙ (1σ uncertainty). This is fully consistent with a previous CO dynamical estimate obtained using a different modelling technique. Signs of non-circular gas motions (likely outflow) are also identified in the inner regions of NGC 4261. In NGC 0612, we are only able to obtain a (conservative) upper limit of MBH ≲ 3.2 × 109 M⊙. This has likely to be ascribed to the presence of a central CO hole (with a radius much larger than that of the SMBH sphere of influence), combined with the inability of obtaining a robust prediction for the CO velocity curve. The three SMBH mass estimates are overall in agreement with predictions from the MBH − σ* relation.

Hubble Space Telescope Proper Motion Measurements of Supernova Remnant N132D: Center of Expansion and Age

We present proper motion measurements of the oxygen-rich ejecta of the LMC supernova remnant N132D using two epochs of Hubble Space Telescope Advanced Camera for Surveys data spanning 16 years. The proper motions of 120 individual knots of oxygen-rich gas were measured and used to calculate a center of expansion (CoE) of α = 5h25m01.ˢ71 and δ = −69°38′41.″64 (J2000) with a 1σ uncertainty of 2.″90. This new CoE measurement is 9.″2 and 10.″8 from two previous CoE estimates based on the geometry of the optically emitting ejecta. We also derive an explosion age of 2770 ± 500 yr, which is consistent with recent age estimates of ≈2500 yr made from 3D ejecta reconstructions. We verified our estimates of the CoE and age using a new automated procedure that detected and tracked the proper motions of 137 knots, with 73 knots that overlap with the visually identified knots. We find that the proper motions of the ejecta are still ballistic, despite the remnant’s age, and are consistent with the notion that the ejecta are expanding into an interstellar medium cavity. Evidence for explosion asymmetry from the parent supernova is also observed. Using the visually measured proper motion measurements and corresponding CoE and age, we compare N132D to other supernova remnants with proper motion ejecta studies.

Localization Method for the Pointing Observation with the Collimated Telescopes of Insight-HXMT

An accurate target source position is sometimes useful for the pointing observation with the collimated telescopes of the Hard X-ray Modulation Telescope (Insight-HXMT), which is determined by the reliability of the instrumental response. Insight-HXMT has the unique design that all three main payloads (LE, ME and HE) consist of detector groups with three fields of views (FOVs) whose orientations differ by 60°. As the point-spread functions are different at different positions in the FOV coordinates, the count rate ratios between the detector groups depend on the position of an X-ray source in the FOVs. Based on the multi-FOV design, we develop a localization method for an X-ray source in the pointing observation of Insight-HXMT. The accuracy of the method is investigated with the pointing observations of the Crab with different exposures. We find that the statistical error decreases with the exposure, and the systematic error is dominant for the exposure >128 s. With the exposure of 1024 s, the total error is 0.°015 for the Crab. This method can effectively distinguish the Rapid Burster H 1730–333 and Slow Burster GX 354–0, which are only 0.°5 apart and can both contribute to bursts in the light curve obtained by Insight-HXMT. We also apply the pointing observation localization method to locate the X-ray counterpart of FRB 200428 with high precision. The located position is consistent with SGR J1935+2154 within 1σ uncertainty of 10′, which provides important evidence that fast radio bursts can originate from magnetars.

Group additivity values for entropy and heat capacities of C2–C8 alkanes, alkyl hydroperoxides, and their radicals

Group additivity values for the thermodynamic properties of oxygenated radicals are poorly determined due to the absence of high quality reference data. Here, a set of 58 group additive values (GAV) for the standard entropy and heat capacity of relevance to alkane oxidation is derived from fits to an extensive and accurate database of standard entropies (298.15 K) and heat capacities (300–3000 K) recently calculated with the “STAR-1D” formalism. The 192 species in this database represent the alkanes (RH), alkyl radicals (Ṙ), alkyl hydroperoxides (RO2H), alkyl-peroxy (RȮ2) and hydroperoxy-alkyl (Q˙OOH) radicals for all of the isomers of C2–C5 alkane fuels and a select number of isomers of C6–C9 species. The STAR-1D thermochemical data for this set of species was previously obtained from a coupling of scaled B2PLYPD3/cc-pVTZ vibrational analyses with scaled ωB97X-D/cc-pVTZ one-dimensional hindered rotor corrections. The 2σ uncertainties in the GAV results relative to the STAR-1D data set are 2.4 cal K–1 mol–1 for the entropies and at most 2.0 cal K–1 mol–1 for the heat capacities in the temperature range 500–800 K. The 2σ fitting uncertainties in the heat capacity gradually reduce at higher temperatures reaching a value of 0.8 cal K–1 mol–1 at 2000 K decreasing to only 0.5 cal K–1 mol–1 at 3000 K. The high degree of accuracy for the GAV representations is obtained through the introduction of various new group terms, together with the re-optimization of existing group terms. Among the full set of 58 GAV terms, 25 include non-next-nearest neighbor interactions (NNI) and β-corrections. The updated GAVs can be applied in the prediction of entropies and heat capacities for a wide range of hydrocarbons and hydroperoxide species and their radicals, which is important to the accurate prediction of fuel reactivity at low-temperatures in the range 600–1000 K.

Non-destructive analysis of spent fuel samples using a gamma-blind fast neutron detector

This paper presents the capabilities of a measurement setup built to measure the axial distribution of neutron emitters in spent fuel pins from nuclear power plants. The measurement system uses a custom gamma-blind detector based on a novel combination of silver-activated zinc sulfide scintillators and wavelength-shifting fibers for direct fast neutron detection while having a low sensitivity for gamma rays even in the strong gamma fields present during the inspection of spent fuel. A collimator with an opening of 2 cm is used to create axial resolved information. The system has been tested using UOX and MOX spent fuel samples with burn-ups between 40 and 90 GWd/t and with long cooling times (20–25 y). Measurements of the total neutron emission of the samples relative to each other achieved a 1σ uncertainty of 2%. Absolute values were measured by comparison with a calibrated 252Cf source, achieving a 1σ uncertainty of 5%. The neutron emission of the samples was previously measured using a thermal neutron detector. The results from that previous measurement agree within 2.5σ with the new results. The reconstruction of the axial neutron emission profile was performed for one of the samples. Based on the edges of the sample, the resolution of the reconstruction was estimated to be 2.5 cm. These promising results are the basis for future development of the measurement setup which should not only improve the accuracy of the results but also enable the measurement of spent fuel with much shorter cooling times of ∼1 y.

Anthropogenic heat due to energy consumption contributes to cooler and wetter summers in Southwest China

Anthropogenic heat release is the release of heat generated by anthropogenic energy consumption. The regional mean Anthropogenic heat release flux in Southwest China grew quickly from 0.06 Wm-2 in 1992 to a peak of 0.37 Wm-2 in 2019. This study examines the climatic effects and feedbacks of Anthropogenic heat release due to energy consumption in Southwest China during the boreal summer using simulations from the Community Earth System Model. The modeling results show that Anthropogenic heat release impacts on the lower-troposphere stability and affects large-scale atmospheric circulation in Southwest China, which transports more water vapor and consequently increases the humidity and low cloud cover in Southwest China. This effect impacts the energy balance at the surface by reducing the amount of incoming shortwave radiation that reaches the ground. Anthropogenic heat release decreases the average 2-m air temperature in Southwest China by 0.10 ± 0.01 K (1σ uncertainty) and also decreases the minimum and maximum air temperatures in Southwest China as well. Anthropogenic heat release contributes to cooler and wetter summers in Southwest China. The results show that Anthropogenic heat release is a non-negligible factor that impacts the climate of Southwest China. This study improves our understanding of the climate change resulting from human activities in Southwest China.

Measurement of Telescope Transmission Using a Collimated Beam Projector

With the increasingly large number of Type Ia supernova being detected by current-generation survey telescopes, and even more expected with the upcoming Rubin Observatory Legacy Survey of Space and Time, the precision of cosmological measurements will become limited by systematic uncertainties in flux calibration rather than statistical noise. One major source of systematic error in determining SNe Ia color evolution (needed for distance estimation) is uncertainty in telescope transmission, both within and between surveys. We introduce here the Collimated Beam Projector (CBP), which is meant to measure a telescope transmission with collimated light. The collimated beam more closely mimics a stellar wave front as compared to flat-field-based instruments, allowing for more precise handling of systematic errors such as those from ghosting and filter angle-of-incidence dependence. As a proof of concept, we present CBP measurements of the StarDICE prototype telescope, achieving a standard (1σ) uncertainty of 3% on average over the full wavelength range measured with a single beam illumination.

HOLISMOKES

Modeling of strong gravitational lenses is a necessity for further applications in astrophysics and cosmology. With the large number of detections in current and upcoming surveys, such as the Rubin Legacy Survey of Space and Time (LSST), it is pertinent to investigate automated and fast analysis techniques beyond the traditional and time-consuming Markov chain Monte Carlo sampling methods. Building upon our (simple) convolutional neural network (CNN), we present here another CNN, specifically a residual neural network (ResNet), that predicts the five mass parameters of a singular isothermal ellipsoid (SIE) profile (lens center x and y, ellipticity ex and ey, Einstein radius θE) and the external shear (γext, 1, γext, 2) from ground-based imaging data. In contrast to our previous CNN, this ResNet further predicts the 1σ uncertainty for each parameter. To train our network, we use our improved pipeline to simulate lens images using real images of galaxies from the Hyper Suprime-Cam Survey (HSC) and from the Hubble Ultra Deep Field as lens galaxies and background sources, respectively. We find very good recoveries overall for the SIE parameters, especially for the lens center in comparison to our previous CNN, while significant differences remain in predicting the external shear. From our multiple tests, it appears that most likely the low ground-based image resolution is the limiting factor in predicting the external shear. Given the run time of milli-seconds per system, our network is perfectly suited to quickly predict the next appearing image and time delays of lensed transients. Therefore, we use the network-predicted mass model to estimate these quantities and compare to those values obtained from our simulations. Unfortunately, the achieved precision allows only a first-order estimate of time delays on real lens systems and requires further refinement through follow-up modeling. Nonetheless, our ResNet is able to predict the SIE and shear parameter values in fractions of a second on a single CPU, meaning that we are able to efficiently process the huge amount of galaxy-scale lenses expected in the near future.

Multiwavelength Speciation in Pyrolysis of n-Pentane and Experimental Determination of the Rate Coefficient of nC5H12 = nC3H7 + C2H5 in a Shock Tube.

We report the application of a multiwavelength speciation strategy to the study of n-pentane (nC5H12) pyrolysis behind reflected shock waves in a shock tube. Experiments were conducted with 2% nC5H12/0.8%CO2/Ar (by mole) between 1150 and 1520 K in the pressure range of 1-2 atm. Utilization of laser absorption spectroscopy at eight wavelengths allowed time-resolved measurements of n-pentane, ethylene, methane, heavy alkenes, and temperature. The measured time histories were compared against the predictions of four recently developed chemical kinetic models for heavy hydrocarbons. It was found that none of the models reconciled the measured species time histories simultaneously. Sensitivity analysis was conducted to identify key reactions influencing the evolution of ethylene and other major pyrolysis products. The analysis revealed that the unimolecular decomposition of n-pentane into n-propyl and ethyl radicals has a dominating influence over the evolution of ethylene in the temperature range of 1150-1450 K. The rate coefficient of this reaction was then adjusted to match the measured ethylene time histories for each experiment. The rate coefficients thus determined, were fit against temperature using an Arrhenius expression given by k1(T) = 3.5 × 1014 exp(-67.2 kcal/RT) s-1. The average overall 2σ uncertainty of the measured rate coefficient was found to be ±35%, resulting primarily from uncertainties in the rate coefficients of secondary reactions. The measured rate coefficient, when used with the models, leads to a significant improvement in the prediction of species time histories. Further improvements in the model are possible if the rate coefficients of relevant reactions pertaining to small hydrocarbon chemistry are determined with an improved accuracy, and less uncertainty. To the best knowledge of the authors, this is the first experimental determination of the rate coefficient of C5H12 → nC3H7 + C2H5.

Probing the baryon mass fraction in IGM and its redshift evolution with fast radio bursts using Bayesian inference method

ABSTRACT We investigate the fraction of baryon mass in intergalactic medium (fIGM), using 18 well-localized fast radio bursts (FRBs) in the redshift range z ∈ (0.0039, 0.66). We construct a five-parameter Bayesian inference model, with the probability distributions of dispersion measures (DMs) of IGM and host galaxy properly taken into account. To check the possible redshift evolution, we parametrize fIGM as a mildly evolving function of redshift, fIGM = fIGM,0[1 + αz/(1 + z)]. By simultaneously constraining five parameters, we get $f_\mathrm{IGM,0} = 0.92^{+0.06}_{-0.12}$ and $\alpha = 0.49^{+0.59}_{-0.47}$, and the median value of DM of host galaxy is $\exp (\mu)=72.49^{+33.31}_{-25.62}~{\rm pc ~ cm ^ {-3}}$. By fixing two parameters that can be constrained independently with other observations, we obtain $\alpha =0.11^{+0.24}_{-0.27}$ in the three-parameter fit, which is consistent with zero within 1σ uncertainty. Monte Carlo simulations show that even 300 FRBs are not enough to tightly constrain five parameters simultaneously. This is mainly caused by the correlation between parameters. Only if two parameters are fixed, 100 FRBs are necessary to achieve unbiased constraints on the remaining parameters.

XMM-Newton Detection of X-Ray Emission from the Metal-polluted White Dwarf G 29-38

A recent analysis of Chandra X-ray data of the metal-polluted white dwarf G 29-38 has revealed X-ray emission that can be attributed to the accretion of debris from a planetary body. In the light of this detection we revisit here archival XMM-Newton observations of G 29-38 from which only an upper limit was derived in the past due to the presence of a relatively bright nearby X-ray source. An analysis of these data in multiple energy bands allows disentangling of the X-ray emission at the location of G 29-38 from that of the nearby source. The similar spectral properties of the source in the XMM-Newton and Chandra observations and their spatial shift, consistent with the proper motion of G 29-38 between these observations, strengthen the origin of the X-ray emission from G 29-38. The X-ray luminosities from both observations are consistent within the 1σ uncertainties, so too are the best-fit plasma temperatures. Although the count number is small, there is tantalizing evidence for line emission in the 0.7–0.8 keV energy band from an optically thin hot plasma. The most likely candidate for this line emission would be the Fe complex at 16 Å.

Constraining the polarisation flux density and angle of point sources by training a convolutional neural network

Context.Constraining the polarisation properties of extragalactic point sources is a relevant task not only because they are one of the main contaminants for primordial cosmic microwave background B-mode detection if the tensor-to-scalar ratio is lower thanr= 0.001, but also for a better understanding of the properties of radio-loud active galactic nuclei.Aims.We develop and train a machine learning model based on a convolutional neural network to learn how to estimate the polarisation flux density and angle of point sources embedded in cosmic microwave background images knowing only their positions.Methods.To train the neural network, we used realistic simulations of patches of 32 × 32 pixels in area at the 217 GHzPlanckchannel with injected point sources at their centres. The patches also contain a realistic background composed of the cosmic microwave background signal, the Galactic thermal dust, and instrumental noise. We split our analysis into three parts: firstly, we studied the comparison between true and estimated polarisation flux densities forP, Q, andUsimulations. Secondly, we analysed the comparison between true and estimated polarisation angles. Finally, we studied the performance of our model with the 217 GHzPlanckmap and compared our results against the detected sources of the SecondPlanckCatalogue of Compact Sources (PCCS2).Results.We find that our model can be used to reliably constrain the polarisation flux density of sources above the 80 mJy level. For this limit, we obtain relative errors of lower than 30% in most of the flux density levels. Training the same network withQandUmaps, the reliability limit is above ±250 mJy when determining the polarisation angle of bothQandUsources. Above that cut, the network can constrain angles with a 1σuncertainty of ±29° and ±32° forQandUsources, respectively. We test this neural network against real data from the 217 GHzPlanckchannel, obtaining similar results to the PCCS2 for some sources; although we also find discrepancies in the 300–400mJy flux density range with respect to thePlanckcatalogue.Conclusions.Based on these results, our model appears to be a promising tool for estimating the polarisation flux densities and angles of point sources above 80 mJy in any catalogue with very small computational time requirements.

Radiocarbon sampling efforts for high-precision lake sediment chronologies

High-resolution chronologies with the best time control are key for comparing palaeoenvironmental studies with independent high-precision historical, archaeological or climatic data. Precise chronologies are also essential for inter-site comparisons of palaeo records at decadal to centennial time scales. We present an updated sediment chronology from Burgäschisee, a small and well-studied lake in the Swiss lowlands. The new age-depth relationship was generated using a large number of new radiocarbon samples of terrestrial plant remains extracted from the Burgäschisee sediments and Bayesian age-depth modelling. The results reveal 2σ uncertainties of only ±19 years for the entire record covering the Early Bronze Age (3800 cal. BP) to the Early Middle Ages (1150 cal. BP). The differences between four age-depth modelling techniques (Bayesian and non-Bayesian) are minor (around 25 years) and remain stable with lower radiocarbon date availability. The maximum age offset between the preliminary previously published and the refined chronology from Burgäschisee is 225 years. Our results demonstrate the importance of a rigorous subsampling strategy that includes a careful selection of the best terrestrial plant material and avoiding radiocarbon calibration plateaus whenever possible. The new chronology from Burgäschisee now allows a more accurate site-to-site comparison with archaeological, historical and other palaeoecological evidence from the region.