The radio continuum spectrum of Mira A and Mira B up to submillimeter wavelengths

We present new measurements of the flux densities at submillimeter wavelengths based on ALMA band 7 (338 GHz) and band 9 (679 GHz) observations to better constrain the origin of the continuum emission of the Mira AB binary system and to check its orbit. We have measured the Mira A and Mira B continuum in ALMA band 7, with a resolution of ~0"31, and for the first time in ALMA band 9, with a resolution of ~0"18. We resolved the binary system at both bands, and derived the continuum spectral index of the stars and their relative position. We also analyzed ALMA SciVer data obtained in bands 6 and 3. Measurements at centimeter wavelengths obtained by other authors have been included in our study of the spectral energy distribution of the Mira components. The Mira A continuum emission has a spectral index of 1.98+-0.04 extending from submillimeter down to centimeter wavelengths. The spectral index of the Mira B continuum emission is 1.93+-0.06 at wavelengths ranging from submillimeter to ~3.1 mm, and a shallower spectral index of 1.22+-0.09 at longer wavelengths. The Mira A continuum emission up to submillimeter wavelengths is consistent with that of a radio photosphere surrounding the evolved star for which models predict a spectral index close to 2. The Mira B continuum emission cannot be described with a single ionized component. An extremely compact and dense region around the star can produce the nearly thermal continuum measured in the 0.4-3.1 mm wavelength range, and an inhomogeneous, less dense, and slightly larger ionized envelope could be responsible for the emission at longer wavelengths. Our results illustrate the potential of ALMA for high precision astrometry of binary systems. We have found a significant discrepancy of ~14 milliarcsec between the ALMA measurements and the predicted orbit positions.Comment: 6 pages, 3 figures, 2 tables, accepted for publication in Astronomy and Astrophysic

Abundance of HOCO+ and CO2 in the outer layers of the L1544 prestellar core

The L1544 prestellar core has been observed as part of the ASAI IRAM Large Program at 3 mm. These observations led to the detection of many complex molecules. In this Letter, we report the detection of two lines, at 85.5 GHz (4,0,4-3,0,3) and 106.9 GHz (5,0,5-4,0,4), respectively, of the protonated carbon dioxide ion, HOCO+. We also report the tentative detection of the line at 100.4 GHz (5,0,5-4,0,4) of DOCO+. The non-LTE analysis of the detected lines shows that the HOCO+ emission originates in the external layer where non-thermal desorption of other species has previously been observed. Its abundance is (5 +/- 2) e-11. Modelling of the chemistry involved in the formation and destruction of HOCO+ provides a gaseous CO2 abundance of 2e-7 (with respect to H2) with an upper limit of 2e-6.Comment: To appear in A&A Letter

Molecules in Bipolar Outflows

Bipolar outflows constitute some of the best laboratories to study shock chemistry in the interstellar medium. A number of molecular species have their abundance enhanced by several orders of magnitude in the outflow gas, likely as a combined result of dust mantle disruption and high temperature gas chemistry, and therefore become sensitive indicators of the physical changes taking place in the shock. Identifying these species and understanding their chemical behavior is therefore of high interest both to chemical studies and to our understanding of the star-formation process. Here we review some of the recent progress in the study of the molecular composition of bipolar outflows, with emphasis in the tracers most relevant for shock chemistry. As we discuss, there has been rapid progress both in characterizing the molecular composition of certain outflows as well as in modeling the chemical processes likely involved. However, a number of limitations still affect our understanding of outflow chemistry. These include a very limited statistical approach in the observations and a dependence of the models on plane-parallel shocks, which cannot reproduce the observed wing morphology of the lines. We finish our contribution by discussing the chemistry of the so-called extremely high velocity component, which seems different from the rest of the outflow and may originate in the wind from the very vicinity of the protostar.Comment: 15 pages, 7 figures. Contribution to the IAU Conference "The Molecular Universe" held in Toledo in June 201

Detection of the HC3_3NH+^+ and HCNH+^+ ions in the L1544 pre-stellar core

The L1544 pre-stellar core was observed as part of the ASAI (Astrochemical Surveys At IRAM) Large Program. We report the first detection in a pre-stellar core of the HCNH$^+$ and HC$_3$NH$^+$ ions. The high spectral resolution of the observations allows to resolve the hyperfine structure of HCNH$^+$. Local thermodynamic equilibrium analysis leads to derive a column density equal to (2.0$\pm$0.2)$\times$10$^{13}$cm$^{-2}$ for HCNH$^+$ and (1.5$\pm$0.5)$\times$10$^{11}$cm$^{-2}$ for HC$_3$NH$^+$. We also present non-LTE analysis of five transitions of HC$_3$N, three transitions of H$^{13}$CN and one transition of HN$^{13}$C, all of them linked to the chemistry of HCNH$^+$ and HC$_3$NH$^+$. We computed for HC$_3$N, HCN, and HNC a column density of (2.0$\pm$0.4)$\times$10$^{13}$cm$^{-2}$, (3.6$\pm$0.9)$\times10^{14}$cm$^{-2}$, and (3.0$\pm$1.0)$\times$10$^{14}$cm$^{-2}$, respectively. We used the gas-grain chemical code Nautilus to predict the abundances all these species across the pre-stellar core. Comparison of the observations with the model predictions suggests that the emission from HCNH$^+$ and HC$_3$NH$^+$ originates in the external layer where non-thermal desorption of other species was previously observed. The observed abundance of both ionic species ([HCNH$^+$]$\,\simeq3\times10^{-10}$ and [HC$_3$NH$^+$]$\,\simeq[1.5-3.0]\times10^{-12}$, with respect to H$_2$) cannot be reproduced at the same time by the chemical modelling, within the error bars of the observations only. We discuss the possible reasons for the discrepancy and suggest that the current chemical models are not fully accurate or complete. However, the modelled abundances are within a factor of three consistent with the observations, considering a late stage of the evolution of the pre-stellar core, compatible with previous observations.Comment: Accepted for publication in MNRAS, 13 pages, 9 figure

Estudio de la degradación de nitrofenoles mediante fotocatálisis heterogénea

Los isómeros 2, 3 y 4-Nitrofenol son contaminantes comunes en las aguas residuales procedentes de vertidos industriales. Su elevada toxicidad hace que las concentraciones máximas de estos compuestos estén reguladas. La biodegradabilidad de estos compuestos por técnicas convencionales es lenta. Este es el motivo por el cual se están investigando nuevas técnicas con mejores eficiencias que los procesos convencionales. Dentro de este grupo de nuevos procesos se encuentra la fotocatálisis heterogénea, que será desarrollada experimentalmente en este proyecto. Los experimentos realizados en el proyecto se pueden clasificar en tres series, dependiendo del método de degradación empleada. En una primera serie de experimentos se analizó la degradabilidad de disoluciones acuosas de los compuestos en ausencia de fuentes de radiación externas. Se comprobó que las disoluciones eran estables en intervalos de tiempo cortos (horas). Para periodos mayores, del orden de días, se han apreciado variaciones en la composición de las disoluciones de 2 y 4-Nitrofenol siendo mucho más notable esta variación en el compuesto 4-Nitrofenol. El 3-Nitrofenol no se degrada en agua en periodos largos (varias semanas). En la segunda serie de experimentos, se analizó el comportamiento de los compuestos sometidos a un proceso de fotólisis mediante su irradiación con luz ultravioleta. En este caso, las muestras fueron sometidas a radiación ultravioleta con aireación y agitación. Las experiencias se han realizado con concentraciones variables, comprobándose que la degradación en estas condiciones sigue una cinética de orden cero para todos los componentes. Por último se han estudiado los procesos de degradación utilizando fotocatálisis heterogénea. En estos experimentos las muestras fueron irradiadas con aireación y agitación, y en presencia de TiO2. Los experimentos realizados se han dividido según la concentración de los compuestos y la carga de TiO2 utilizada. Todos los procesos realizados en presencia de TiO2 han seguido una cinética de pseudo-primer orden. En los tres compuestos se ha comprobado que la presencia de TiO2 mejora la eficiencia de la degradación reduciendo considerablemente el tiempo de degradación. Se ha demostrado que el aumento de la concentración de óxido de titanio (IV) en todos los procesos, aumenta el rendimiento. Con los datos experimentales se han obtenido las constantes cinéticas de degradación. Estas constantes se han utilizado para extrapolar que valores de degradación se podrían obtener para diferentes concentraciones de TiO2. Finalmente se ha comprobado que en todos los procesos de fotólisis y fotocatálisis realizados, la degradación ha sido siempre más efectiva para disoluciones 4-Nitrofenol, seguido de 2-Nitrofenol y 3-Nitrofenol. Los procesos de fotocatálisis siempre han obtenido un mejor rendimiento que los de otras técnicas utilizadas. __________________________________________________________________________________________________________The isomers 2, 3 and 4-Nitrophenol are common contaminants in wastewater from industrial effluents. Its high toxicity makes the maximum concentrations of these compounds be regulated. The biodegradability of these compounds by conventional techniques is slow. For this reason, new techniques with better efficiency than conventional processes are being investigated. The heterogeneous photocatalysis is included in this group, and it will developed experimentally in this project. Experiments in the project have been divided into three groups. In the first series of experiments are examined the degradability of the compounds in the absence of external radiation sources. It was found that the composition of the solutions does not change for short periods (hours). For periods whit the order of days, have been noted variations in the composition in solutions of 2 and 4-Nitrophenol, the variation is more remarkable in the compound 4-Nitrophenol. The 3-Nitrophenol composition remained stable in the in the period analyzed. In the second series, we examined the behavior of the compounds undergoing a process of photolysis. In this set of experiments the samples were simultaneously subjected to ultraviolet radiation, aeration and agitation. Processes have been conducted with varying concentrations. The testing under these conditions follows a zero order kinetics for all components. Finally, there have been heterogeneous photocatalytic processes. The samples were irradiated, aerated and agitated in the presence of TiO2. Experiments have been divided according to the concentration of the compounds and the amount of TiO2 used. All processes performed in the presence of TiO2 kinetics have followed pseudo-first order. In all three compounds have shown that the presence of TiO2 improves the efficiency process by reducing the degradation times compared with those obtained in the photolysis. It has been shown that increasing the concentration of titanium oxide (IV) in the process, increases the efficiency of processes. Degradation kinetics constants have been obtained with the experimental data . These constants are used to extrapolate values for degradation that could be obtained for different concentrations of TiO2. Finally, It has been proved in all process which have been performed, the degradation has always been more effective for 4-Nitrophenol solutions, followed by 2-Nitrophenol and 3-Nitrophenol. Photocatalytic processes have always obtained better performance than other techniques.Ingeniería Industria

W40 region in the Gould Belt : An embedded cluster and H II region at the junction of filaments

We present a multiwavelength study of W40 star-forming region using IR observations in UKIRT JHK bands, Spitzer IRAC bands & Herschel PACS bands; 2.12 micron H2 narrow-band imaging; & radio observations from GMRT (610 & 1280 MHz), in a FoV of ~34'x40'. Spitzer observations along with NIR observations are used to identify 1162 Class II/III & 40 Class I sources in the FoV. The NN stellar surface density analysis shows that majority of these YSOs constitute the embedded cluster centered on the source IRS1A South. Some YSOs, predominantly younger population, are distributed along & trace the filamentary structures at lower stellar surface density. The cluster radius is obtained as 0.44pc - matching well with the extent of radio emission - with a peak density of 650pc^-2. The JHK data is used to map the extinction which is subsequently used to compute the cloud mass. It has resulted in 126 Msun & 71 Msun for the central cluster & the northern IRS5 region, respectively. H2 narrow-band imaging displays significant emission, which prominently resembles fluorescent emission arising at the borders of dense regions. Radio analysis shows this region as having blister morphology, with the radio peak coinciding with a protostellar source. Free-free emission SED analysis is used to obtain physical parameters of the overall region & the IRS5 sub-region. This multiwavelength scenario is suggestive of star formation having resulted from merging of multiple filaments to form a hub. Star formation seems to have taken place in two successive epochs, with the first epoch traced by the central cluster & the high-mass star(s) - followed by a second epoch which is spreading into the filaments as uncovered by the Class I sources & even younger protostellar sources along the filaments. The IRS5 HII region displays indications of swept-up material which has possibly led to the formation of protostars.Comment: 17 pages, 12 figures, 2 tables. Accepted for publication in The Astrophysical Journa