Using CO line ratios to trace the physical properties of molecular clouds

The carbon monoxide (CO) rotational transition lines are the most common tracers of molecular gas within giant molecular clouds (MCs). We study the ratio ($R_{2-1/1-0}$) between CO's first two emission lines and examine what information it provides about the physical properties of the cloud. To study $R_{2-1/1-0}$ we perform smooth particle hydrodynamic simulations with time dependent chemistry (using GADGET-2), along with post-process radiative transfer calculations on an adaptive grid (using RADMC-3D) to create synthetic emission maps of a MC. $R_{2-1/1-0}$ has a bimodal distribution that is a consequence of the excitation properties of each line, given that $J=1$ reaches local thermal equilibrium (LTE) while $J=2$ is still sub-thermally excited in the considered clouds. The bimodality of $R_{2-1/1-0}$ serves as a tracer of the physical properties of different regions of the cloud and it helps constrain local temperatures, densities and opacities. Additionally this bimodal structure shows an important portion of the CO emission comes from diffuse regions of the cloud, suggesting that the commonly used conversion factor of $R_{2-1/1-0}\sim 0.7$ between both lines may need to be studied further.Comment: 10 pages, 8 figures, accepted to MNRA

Diagnóstico de los desembarques pesqueros artesanales en la costa del Caribe colombiano a través de indicadores

Landings of the artisanal fishery in the Colombian Caribbean from 2013 to 2021 were characterized by means of two indicators: the trophic level and the vulnerability to fishery landings. Indicators showed a statistically significant decreasing trend in vulnerability and trophic level, suggesting that the fishery is increasingly targeting species of low vulnerability and trophic level, thus moving down the food web. The overall pattern of indicators was not uniform in space. Incidence interaction of gears and species landed explained the trajectory of indicators at the scale of Departments. Fishing gears targeted different levels in the food web, with gillnets responsible for the bulk of landings. Compared to a previous study, the group of fish species supporting most of landings has changed towards species with lower vulnerability, i.e. resistant to fishing mortality due to their evolved life-history but still of predatory habits in general. A notable exception is Mugil incilis, a species with a low trophic level that has become third in importance of landings in the database.Los desembarques de la pesca artesanal en el Caribe colombiano entre 2013 y 2021 se caracterizaron mediante dos indicadores: el nivel trófico y la vulnerabilidad en los desembarques de pesca. Los indicadores mostraron una tendencia decreciente significativa en la vulnerabilidad y el nivel trófico, lo que sugiere que la pesquería se dirige cada vez más a especies de baja vulnerabilidad y nivel trófico, desplazándose así hacia abajo en la trama alimentaria. El patrón general de indicadores no fue uniforme en el espacio. La interacción de incidencia de las artes y especies desembarcadas explicó la trayectoria de los indicadores a nivel de Departamentos. Las artes de pesca capturaron a diferentes niveles de la rama alimentaria, siendo las redes de enmalle responsables de la mayor parte de los desembarques. En comparación con un estudio anterior, el grupo de especies de peces que sustentan la mayoría de los desembarques ha cambiado hacia especies con menor vulnerabilidad, es decir, resistentes a la mortalidad por pesca debido a la evolución de su historia de vida, pero aún con hábitos depredadores en general. Una excepción notable es Mugil incilis, una especie con un nivel trófico bajo que se ha convertido en la tercera en importancia de desembarques en la base de datos

Chandra X-Ray Observations of Nineteen Millisecond Pulsars in the Globular Cluster 47 Tucanae

We present spectral and long-timescale variability analyses of \textit{Chandra} ACIS-S observations of the 19 millisecond pulsars (MSPs) with precisely known positions in the globular cluster 47 Tucanae. The X-ray emission of the majority of these MSPs is well described by a thermal (blackbody or neutron star hydrogen atmosphere) spectrum with a temperature $T_{\rm eff}\sim(1-3)\times10^6$ K, emission radius $R_{\rm eff}\sim0.1-3$ km, and luminosity $L_{X}\sim10^{30-31}$ ergs s$^{-1}$. For several MSPs, there is indication that a second thermal component is required, similar to what is seen in some nearby field MSPs. The radio-eclipsing binary MSPs 47 Tuc J, O, and W show a significant non-thermal component, with photon index $\Gamma\sim 1-1.5$, which may originate in an shock formed due to interaction between the relativistic pulsar wind and matter from the stellar companion. We re-examine the X-ray--spindown luminosity relation ($L_{X}-\dot{E}$) and find that due to the large uncertainties in both parameters the result is consistent with both the linear $L_{X}-\dot{E}$ relation and the flatter $L_X\propto\dot{E}^{0.5}$ predicted by polar cap heating models. In terms of X-ray properties, we find no clear systematic differences between MSPs in globular clusters and in the field of the Galaxy.Comment: 13 pages, 6 figures, accepted for publication in the Astrophysical Journa

Economic and Social Impacts of Energy Shocks: A General Equilibrium Analysis for Chile

Oil price increases and the restrictions to natural gas imports from Argentina generate multiple effects which ripple throughout the Chilean economy. The magnitude of the aggregate, sectoral and distributive impacts associated with these changes in the energy sector is debated. In this paper, using a static general equilibrium framework, we analyze quantitatively the direct and indirect effects of these international shocks. The results show that the increase in international prices of oil and fuels generates a slightly negative impact on GDP, which is explained by the recessionary effect on consumption. The sectors most adversely affected are the fuel sector, other sectors strongly linked to the energy sectors such as transport and electricity and those geared to the provision of goods and services for final consumption. The main effect on the productive structure is a strengthening of Chile’s traditional comparative advantages based on primary sectors and natural resources. Within the energy sector, coal gains participation in the energy matrix. The impacts on the income of the poorest and its distribution are clearly negative: contractionary and regressive. The former results are magnified when both natural gas supply restrictions and high hydrocarbon prices are considered together.

Precision Timing Measurements of PSR J1012+5307

We present results and applications of high precision timing measurements of the millisecond pulsar J1012+5307. Combining our radio observations with results based on optical observations, we derive complete 3-D velocity information for this system. Correcting for Doppler effects, we derive the intrinsic spin parameters of this pulsar and a characteristic age of 8.6 +/- 1.9 Gyr. Our upper limit for the orbital eccentricity of only 8 * 10^-7 (68% C.L.) is the smallest ever measured for a binary system. We demonstrate that this makes the pulsar an ideal laboratory to test certain aspects of alternative theories of gravitation. Our precise measurements suggest deviations from a simple pulsar spin-down timing model, which are consistent with timing noise and the extrapolation of the known behaviour of slowly rotating pulsars.Comment: 9 pages, 6 figure

CO line ratios in molecular clouds: the impact of environment

Line emission is strongly dependent on the local environmental conditions in which the emitting tracers reside. In this work, we focus on modelling the CO emission from simulated giant molecular clouds (GMCs), and study the variations in the resulting line ratios arising from the emission from the J = 1–0, J = 2–1, and J = 3–2 transitions. We perform a set of smoothed particle hydrodynamics simulations with time-dependent chemistry, in which environmental conditions – including total cloud mass, density, size, velocity dispersion, metallicity, interstellar radiation field (ISRF), and the cosmic ray ionization rate (CRIR) – were systematically varied. The simulations were then post-processed using radiative transfer to produce synthetic emission maps in the three transitions quoted above. We find that the cloud-averaged values of the line ratios can vary by up to ±0.3 dex, triggered by changes in the environmental conditions. Changes in the ISRF and/or in the CRIR have the largest impact on line ratios since they directly affect the abundance, temperature, and distribution of CO-rich gas within the clouds. We show that the standard methods used to convert CO emission to H2 column density can underestimate the total H2 molecular gas in GMCs by factors of 2 or 3, depending on the environmental conditions in the clouds