The infrared and molecular environment surrounding the Wolf-Rayet star WR130

We present a study of the molecular CO gas and mid/far infrared radiation arising from the environment surrounding the Wolf-Rayet (W-R) star 130. We use the multi-wavelength data to analyze the properties of the dense gas and dust, and its possible spatial correlation with that of Young Stellar Objects (YSOs). We use CO J=1-0 data from the FCRAO survey as tracer of the molecular gas, and mid/far infrared data from the recent WISE and Herschel space surveys to study the dust continuum radiation and to identify a population of associated candidate YSOs. The spatial distribution of the molecular gas shows a ring-like structure very similar to that observed in the HI gas, and over the same velocity interval. The relative spatial distribution of the HI and CO components is consistent with a photo-dissociation region. We have identified and characterized four main and distinct molecular clouds that create this structure. Cold dust is coincident with the dense gas shown in the CO measurements. We have found several cYSOs that lie along the regions with the highest gas column density, and suggest that they are spatially correlated with the shell. These are indicative of regions of star formation induced by the strong wind and ionization of the WR star.Comment: 15 pages, 12 figures, 6 Tables. Accepted for publication in MNRA

GS100-02-41: a new large HI shell in the outer part of the Galaxy

Massive stars have a profound effect on the surrounding interstellar medium. They ionize and heat the neutral gas, and due to their strong winds, they swept the gas up forming large HI shells. In this way, they generate a dense shell where the physical conditions for the formation of new stars are given. The aim of this study is to analyze the origin and evolution of the large HI shell GS100-02-41 and its role in triggering star forming processes.To characterize the shell and its environs, we carry out a multi-wavelength study. We analyze he HI 21 cm line, the radio continuum, and infrared emission distributions. The analysis of the HI data shows an expanding shell structure centred at (l, b) = (100.6 deg, -2.04 deg) in the velocity range from -29 to -51.7 km/s. We infer for GS100-02-41, a kinematical distance of 2.8 +/- 0.6 kpc. Several massive stars belonging to Cep OB1 are located in projection within the large HI, shell boundaries. The analysis of the radio continuum and infrared data reveal that there is no continuum counterpart of the HI shell. On the other hand, three slightly extended radio continuum sources are observed in projection onto the dense HI shell. From their flux density determinations we infer that they are thermal in nature. An analysis of the HI emission distribution in the environs of these sources shows, for each of them, a region of low emissivity having a good morphological correlation with the ionized gas in a velocity range similar to the one where GS100-02-41 is detected. The origin of GS100-02-41 could have been mainly due to the action of the Cep OB1 massive stars located inside the HI shell. The obtained age difference between the HI shell and the HII regions, together with their relative location, led us to conclude that the ionizing stars could have been created as a consequence of the shell evolution.Comment: Accepted for publication in A&

Searching for evidence of interaction between the of star HD 229196 and the interstellar medium

Massive stars with strong stellar winds are expected to have a huge impact on their interstellar surroundings, an effect which, in a surprisingly large number of cases, is not observed. This work is part of a concerted effort to obtain a better and more homogeneous observational data base with which to test the predictions of theoretical models. Analysis of the interstellar medium around the Of star HD 229196 shows that it coincides (in projection) with a region of lower radio continuum emission. This suggests that the star has shaped the surrounding interstellar medium via its ionizing flux and stellar wind. However, we find no clear evidence of the star's action in atomic hydrogen images. The radio continuum morphology and absence of a clear expanding H i shell are consistent with the possibility that the star, which is travelling supersonically at ∼30 km s-1 with respect to its local interstellar medium, is creating a weak bow shock. We cannot however rule out the possibility that the observed asymmetry is due to an inhomogeneous interstellar density distribution. We use data from the Canadian Galactic Plane Survey to carry out this study.Facultad de Ciencias Astronómicas y GeofísicasInstituto Argentino de Radioastronomí

Searching for evidence of interaction between the of star HD 229196 and the interstellar medium

Massive stars with strong stellar winds are expected to have a huge impact on their interstellar surroundings, an effect which, in a surprisingly large number of cases, is not observed. This work is part of a concerted effort to obtain a better and more homogeneous observational data base with which to test the predictions of theoretical models. Analysis of the interstellar medium around the Of star HD 229196 shows that it coincides (in projection) with a region of lower radio continuum emission. This suggests that the star has shaped the surrounding interstellar medium via its ionizing flux and stellar wind. However, we find no clear evidence of the star's action in atomic hydrogen images. The radio continuum morphology and absence of a clear expanding H i shell are consistent with the possibility that the star, which is travelling supersonically at ∼30 km s-1 with respect to its local interstellar medium, is creating a weak bow shock. We cannot however rule out the possibility that the observed asymmetry is due to an inhomogeneous interstellar density distribution. We use data from the Canadian Galactic Plane Survey to carry out this study.Facultad de Ciencias Astronómicas y GeofísicasInstituto Argentino de Radioastronomí

Triggered star formation in a molecular shell created by a SNR?

We present a study of a new molecular shell, G 126.1-0.8-14, using available multiwavelength Galactic plane surveys and optical Gemini observations. A well-defined shell-like structure is observed in the CO(1-0) line emission at (l,b) = (126°.1, -0°.8), in the velocity range -10.5 to -15.5 km s-1. The H I emission shows a region of low emissivity inside G 126.1-0.8-14, while radio continuum observations reveal faint non-thermal emission possibly related to this shell. Optical spectra obtained with Gemini South show the existence of B-type stars likely to be associated with G 126.1-0.8-14. An estimate of the stellar wind energy injected by these stars shows that they alone cannot be able to create such a structure. On the other hand, one supernova explosionwould provide enough energy to generate the shell. Using the MSX, IRAS and WISE point source catalogues we have found about 30 young stellar object candidates, whose birth could have been triggered by the expansion of G 126.1-0.8-14. In this context, Sh2-187 could be a consequence of the action on its surroundings of the most massive (and thus most evolve) of the stars formed by the expanding molecular shell.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La PlataInstituto Argentino de Radioastronomí

Physical characterization of S169: A prototypical IR bubble associated with the massive star-forming region IRAS12326-6245

With the aim of studying the properties of Galactic IR bubbles and their impact in massive star formation, we present a study of the IR bubble S169, associated with the massive star forming region IRAS12326-6245. We used CO(2-1),$^{13}$CO(2-1), C$^{18}$O(2-1), HCN(3-2), and HCO+(3-2) line data obtained with the APEX telescope to study the properties of the molecular gas in the nebula and the IRAS source . To analyze the properties and distribution of the dust, we used IRAC-GLIMPSE, Herschel, and ATLASGAL data. The properties of the ionized gas were studied using images obtained from the SUMSS survey and SuperCOSMOS database. In our search for stellar and protostellar objects in the region, we used IR and optical point source calalogs. The new APEX observations allowed us to identify three molecular components associated with the nebula, namely: at $-$39 km/s (component A), $-$25 km/s (component B), and $-$17 km/s (component C). Six molecular condensations (MC1 to MC6) were identified in component A, with MC3 (the densest and more massive one) being the molecular counterpart of IRAS12326-6245. For this source, we estimated an H$_2$ column density up to 8$\times$10$^{23}$ cm$^{-2}$. To explain the morphology and velocity of components A, B, and C, we propose a simple model consisting of a partially complete semisphere-like structure expanding at ~ 12 km/s. The introduction of this model has led to a discussion about the distance to both S169 and IRAS12326-6245, which was estimated to be ~ 2 kpc. Several candidate YSOs were identified, projected mostly onto the molecular condensations MC3, MC4, and MC5, which indicates that the star-formation process is very active at the borders of the nebula. A comparison between observable and modeled parameters was not enough to discern whether the collect-and-collapse mechanism is acting at the edge of S169.Comment: 17 pages, 12 figures. Accepted for publication in A&

GS305+04-26:Revisiting the ISM around the CenOB1 stellar association

Massive stars deeply modify their surrounding ISM via their high throughput of ionizing photons and their strong stellar winds. In this way they may create large expanding structures of neutral gas. We study a new large HI shell, labelled GS305+04-26, and its relationship with the OB association CenOB1. To carry out this study we have used a multi-wavelenght approach. We analyze neutral hydrogen (HI) line data retrieved from the Leiden-Argentina-Bonn (LAB) survey, new spectroscopic optical observations obtained at CASLEO, and make use of proper motion databases available via Internet. The analysis of the HI data reveals a large expanding structure GS305+04-26 centered at (l,b)=(305^{\degr}, +4^{\degr}) in the velocity range from -33 to -17 km/s. Based on its central velocity, -26 km/s, and using standard galactic rotation models, a distance of 2.5(+-)0.9 kpc is inferred. This structure, elliptical in shape, has major and minor axis of 440 and 270 pc, respectively. Its expansion velocity, total gaseous mass, and kinetic energy are ~8 km/s, (2.4(+-)0.5)x10^5 Mo, and (1.6(+-)0.4)x10^{50} erg, respectively. Several stars of the OB-association CenOB1 are seen projected onto, and within, the boundaries of GS305+04-26. Based on an analysis of proper motions, new members of CenOB1 are identified. The mechanical energy injected by these stars could have been the origin of this HI structure.Comment: 14 pages, 6 figures, A&A (in press

A multiwavelength study of the star forming region IRAS 18544+0112

This work aims at investigating the molecular and infrared components in the massive young stellar object (MYSO) candidate IRAS 18544+0112. The purpose is to determine the nature and the origin of this infrared source. To analyze the molecular gas towards IRAS 18544+0112, we have carried out observations in a 90" x 90" region around l = 34.69, b = -0.65, using the Atacama Submillimeter Telescope Experiment (ASTE) in the 12CO J=3-2, 13CO J=3-2, HCO+ J=4-3 and CS J=7-6 lines with an angular resolution of 22". The infrared emission in the area has been analyzed using 2MASS and Spitzer public data. From the molecular analysis, we find self-absorbed 12CO J=3-2 profiles, which are typical in star forming regions, but we do not find any evidence of outflow activity. Moreover, we do not detect either HCO+ J=4-3 or CS J=7-6 in the region, which are species normally enhanced in molecular outflows and high density envelopes. The 12CO J=3-2 emission profile suggests the presence of expanding gas in the region. The Spitzer images reveal that the infrared source has a conspicuous extended emission bright at 8 um with an evident shell-like morphology of ~ 1.5 arcmin in size (~ 1.4 pc at the proposed distance of 3 kpc) that encircles the 24 um emission. The non-detection of ionized gas related to IRAS 18544+0112, together with the fact that it is still embedded in a molecular clump suggest that IRAS 18544+0112, has not reached the UCHII region stage yet. Based on near infrared photometry we search for YSO candidates in the region and propos that 2MASS 18565878+0116233 is the infrared point source associated with IRAS 18544+0112. Finally, we suggest that the expansion of a larger nearby HII region, G034.8-0.7, might be related to the formation of IRAS 18544+0112.Comment: 14 pages, accepted for publication in A&A. Figures degraded to reduce file siz

Early cephalopod evolution clarified through Bayesian phylogenetic inference

Background: Despite the excellent fossil record of cephalopods, their early evolution is poorly understood. Different, partly incompatible phylogenetic hypotheses have been proposed in the past, which reflected individual author's opinions on the importance of certain characters but were not based on thorough cladistic analyses. At the same time, methods of phylogenetic inference have undergone substantial improvements. For fossil datasets, which typically only include morphological data, Bayesian inference and in particular the introduction of the fossilized birth-death model have opened new possibilities. Nevertheless, many tree topologies recovered from these new methods reflect large uncertainties, which have led to discussions on how to best summarize the information contained in the posterior set of trees. Results: We present a large, newly compiled morphological character matrix of Cambrian and Ordovician cephalopods to conduct a comprehensive phylogenetic analysis and resolve existing controversies. Our results recover three major monophyletic groups, which correspond to the previously recognized Endoceratoidea, Multiceratoidea, and Orthoceratoidea, though comprising slightly different taxa. In addition, many Cambrian and Early Ordovician representatives of the Ellesmerocerida and Plectronocerida were recovered near the root. The Ellesmerocerida is para- and polyphyletic, with some of its members recovered among the Multiceratoidea and early Endoceratoidea. These relationships are robust against modifications of the dataset. While our trees initially seem to reflect large uncertainties, these are mainly a consequence of the way clade support is measured. We show that clade posterior probabilities and tree similarity metrics often underestimate congruence between trees, especially if wildcard taxa are involved. Conclusions: Our results provide important insights into the earliest evolution of cephalopods and clarify evolutionary pathways. We provide a classification scheme that is based on a robust phylogenetic analysis. Moreover, we provide some general insights on the application of Bayesian phylogenetic inference on morphological datasets. We support earlier findings that quartet similarity metrics should be preferred over the Robinson-Foulds distance when higher-level phylogenetic relationships are of interest and propose that using a posteriori pruned maximum clade credibility trees help in assessing support for phylogenetic relationships among a set of relevant taxa, because they provide clade support values that better reflect the phylogenetic signal.Peer reviewe