E-BOSS: An Extensive stellar BOw Shock Survey. II. Catalogue second release

Context. Stellar bow shocks have been studied not only observationally, but also theoretically since the late 1980s. Only a few catalogues of them exist. The bow shocks show emission along all the electromagnetic spectrum, but they are detected more easily in infrared wavelengths. The release of new and high-quality infrared data eases the discovery and subsequent study of new objects. Aims. We search stellar bow-shock candidates associated with nearby runaway stars, and gather them together with those found elsewhere, to enlarge the list of the E-BOSS first release. We aim to characterize the bow-shock candidates and provide a database suitable for statistical studies. We investigate the low-frequency radio emission at the position of the bow-shock features, that can contribute to further studies of high-energy emission from these objects. Methods. We considered samples from different literature sources and searched for bow-shaped structures associated with stars in the Wide-field Infrared Survey Explorer (WISE) images. We looked for each bow-shock candidate on centimeter radio surveys. Results. We reunited 45 bow-shock candidates and generated composed WISE images to show the emission in different infrared bands. Among them there are new sources, previously studied objects, and bow shocks found serendipitously. Five bow shocks show evidence of radio emission. Conclusions. Stellar bow shocks constitute an active field with open questions and enormous amounts of data to be analyzed. Future research at all wavelengths databases, and use of instruments like Gaia, will provide a more complete picture of these objects. For instance, infrared spectral energy distributions can give information about physical parameters of the bow shock matter. In addition, dedicated high-sensitivity radio observations can help to understand the radio-$\gamma$ connection.Comment: 20 pages, 11 figures, and 8 tables. Accepted for publication in A&

Looking for evidence of high-mass star formation at core scale in a massive molecular clump

We present a comprehensive physical and chemical study of the fragmentation and star formation activity towards the massive clump AGAL G338.9188+0.5494 harbouring the extended green object EGO 338.92+0.55(b). The presence of an EGO embedded in a massive clump, suggests, at clump scale, that high-mass star formation is occurring. The main goal of this work is to find evidence of such high-mass star formation, but at core scale. Using mm observations of continuum and lines obtained from the ALMA database at Bands 6 and 7, we study the substructure of the massive clump. The angular resolution of the data is about 0.5'', which allow us to resolve structures of about 0.01pc ($\sim$ 2000 au) at the distance of 4.4 kpc. The continuum emission at 340 GHz reveals that the molecular clump is fragmented in five cores, labeled from C1 to C5. The $^{12}$CO J=3--2 emission shows the presence of molecular outflows related to three of them. The analysis of the CH$_3$CN and CH$_3$CCH emissions suggests temperatures of about 340 and 72~K, respectively, for C1, showing that the methyl cyanide would trace a gas layer closer to the protostar than the methyl acetylene. The obtained mass of core C1 ranges from 3 to 10 M$_{\odot}$. We found that the discovered molecular outflow arising from core C1 should be the main responsible for the 4.5 $\mu$m extended emission. The average mass and energy of such a molecular outflow is about 0.5 M$_{\odot}$~and $10^{46}$~erg, respectively, which suggest that 10 M$_{\odot}$ is the most likely mass value for core C1. Additionally we found that the region is chemically very rich with several complex molecular species. Particularly, from the analysis of the CN emission we found strong evidence that such a radical is indirectly tracing the molecular outflows, more precisely the border of the cavity walls carved out by such outflows.Comment: Accepted for publication in A&A (July 5, 2023

E-BOSS: an Extensive stellar BOw Shock Survey. I: Methods and First Catalogue

Context: Bow shocks are produced by many astrophysical objects where shock waves are present. Stellar bow shocks, generated by runaway stars, have been previously detected in small numbers and well-studied. Along with progress in model development and improvements in observing instruments, our knowledge of the emission produced by these objects and its origin can now be more clearly understood. Aims: We produce a stellar bow-shock catalogue by applying uniform search criteria and a systematic search process. This catalogue is a starting point for statistical studies, to help us address fundamental questions such as, for instance, the conditions under wich a stellar bow shock is detectable. Methods: By using the newest infrared data releases, we carried out a search for bow shocks produced by early-type runaway stars. We first explored whether a set of known IRAS bow shock candidates are visible in the most recently available IR data, which has much higher resolution and sensitivity. We then carried out a selection of runaway stars from the latest, large runaway catalogue available. In this first release, we focused on OB stars and searched for bow-shaped features in the vicinity of these stars. Results: We provide a bow-shock candidate survey that gathers a total of 28 members which we call the Extensive stellar BOw Shock Survey (E-BOSS). We derive the main bow-shock parameters, and present some preliminary statistical results on the detected objects. Conclusions: Our analysis of the initial sample and the newly detected objects yields a bow-shock detectability around OB stars of $\sim$ 10 per cent. The detections do not seem to depend particularly on either stellar mass, age or position. The extension of the E-BOSS sample, with upcoming IR data, and by considering, for example, other spectral types as well, will allow us to perform a more detailed study of the findings.Comment: A&A accepted (25-NOV-2011), 15 pages, 4 tables, 11 figure

Unveiling the substructure of the massive clump AGAL G035.1330−00.7450

Context. It is known that high-mass stars form as the result of the fragmentation of massive molecular clumps. However, it is not clear whether this fragmentation gives rise to cores that are massive enough to directly form high-mass stars, or if leads to cores of low and intermediate masses that generate high-mass stars by acquiring material from their environment. Aims. Detailed studies of massive clumps at the early stage of star formation are needed to collect observational evidence that sheds light on the fragmentation processes from clump to core scales. The infrared-quiet massive clump AGAL G035.1330−00.7450 (AGAL35) located at a distance of 2.1 kpc is a promising object for studying the fragmentation and the star formation activity at early stages. Methods. Using millimeter observations of continuum and molecular lines obtained from the Atacama Large Millimeter Array database at Bands 6 and 7, we studied the substructure of the source AGAL35. The angular resolution of the data at Band 7 is about 0.′′7, which allowed us to resolve structures of about 0.007 pc (~1500 au). Results. The continuum emission at Bands 6 and 7 shows that AGAL35 harbors four dust cores, labeled C1 to C4, with masses lower than 3 M⊙. Cores C3 and C4 exhibit well-collimated, young, and low-mass molecular outflows related to molecular hydrogen emission-line objects that were previously detected. Cores C1 and C2 present CH3CN J = 13–12 emission, from which we derive rotational temperatures of about 180 and 100 K, respectively. These temperatures allow us to estimate masses of about 1.4 and 0.9 M⊙ for C1 and C2, respectively, which are about an order of magnitude lower than those estimated in previous works and agree with the Jeans mass of this clump. In particular, the moment 1 map of CH3CN emission suggests the presence of a rotating disk towards C1, which is confirmed by the CH3OH and CH3OCHO (20–19) emissions. On the other hand, the CN N = 2–1 emission shows a clumpy and filamentary structure that seems to connect all the cores. These filaments might be tracing the remnant gas of the fragmentation processes taking place within the massive clump AGAL35 or the gas that is being transported toward the cores, which would imply a competitive accretion scenario. Conclusions. The massive clump AGAL35 harbors four low- to intermediate-mass cores with masses lower than 3 M⊙, which is about an order of magnitude smaller than the masses estimated in previous works. This study shows that in addition to the importance of high-resolution and sensitivity observations for a complete detection of all fragments, it is very important to accurately determine the temperature of these cores for a correct mass estimation. Finally, although no high-mass cores were detected toward AGAL35, the filamentary structure connecting all the cores means that high-mass stars might form through the competitive accretion mechanism

Multiple molecular outflows and fragmentation in the IRDC core G34.43+00.24 MM1

Context. The fragmentation of a molecular cloud that leads to the formation of high-mass stars occurs on a hierarchy of different spatial scales. The large molecular clouds harbor massive molecular clumps with massive cores embedded in them. The fragmentation of these cores may determine the initial mass function and the masses of the final stars. Therefore, studying the fragmentation processes in the cores is crucial to understanding how massive stars form. Aims. Detailed studies toward particular objects are needed to collect observational evidence that shed light on star formation processes on the smallest spatial scales. The hot molecular core G34–MM1, embedded in the filamentary infrared dark cloud (IRDC) G34.34+00.24 located at a distance of 3.6 kpc, is a promising object for studying fragmentation and outflow processes. Methods. Using data at 93 and 334 GHz obtained from the Atacama Large Millimeter Array (ALMA) database we studied in great detail the hot molecular core G34–MM1. The angular resolution of the data at 334 GHz is about 0.′′8, which allows us to resolve structures of about 0.014 pc (~2900 au). Results. We found evidence of fragmentation toward the molecular hot core G34–MM1 on two different spatial scales. The dust condensation MM1–A (about 0.06 pc in size) harbors three molecular subcore candidates (SC1 through SC3) detected in 12CO J = 3–2 emission, with typical sizes of about 0.02 pc and an average spatial separation among them of about 0.03 pc. From the HCO+ J = 1–0 emission, we identify, with better angular resolution than previous observations, two perpendicular molecular outflows arising from MM1–A. We suggest that subcores SC1 and SC2, embedded in MM1–A, respectively harbor the sources responsible for the main and the secondary molecular outflow. Finally, from the radio continuum emission at 334 GHz, we marginally detected another dust condensation, named MM1–E, from which a young (tdyn ~ 1.6 × 103 yr), massive (M ~ 5 M⊙), and energetic (E ~ 6 × 1046 ergs) molecular outflow arises. Conclusions. The fragmentation of the hot molecular core G34–MM1 at two different spatial scales, together with the presence of multiple molecular outflows associated with it, would support a competitive accretion scenario. Studies like this shed light on the relation between fragmentation and star formation processes occurring within hot molecular cores, only accessible through high angular resolution interferometric observations

Megahertz emission of massive early-type stars in the Cygnus region

peer reviewedMassive, early-type stars have been detected as radio sources for many decades. Their thermal winds radiate free-free continuum and in binary systems hosting a colliding-wind region, non-thermal emission has also been detected. To date, the most abundant data have been collected from frequencies higher than 1 GHz. We present here the results obtained from observations at 325 and 610 MHz, carried out with the Giant Metrewave Radio Telescope, of all known Wolf-Rayet and O-type stars encompassed in area of $˜$ 15 sq degrees centred on the Cygnus region. We report on the detection of 11 massive stars, including both Wolf-Rayet and O-type systems. The measured flux densities at decimeter wavelengths allowed us to study the radio spectrum of the binary systems and to propose a consistent interpretation in terms of physical processes affecting the wide-band radio emission from these objects. WR 140 was detected at 610 MHz, but not at 325 MHz, very likely because of the strong impact of free-free absorption (FFA). We also report—for the first time—on the detection of a colliding-wind binary system down to 150 MHz, pertaining to the system of WR 146, making use of complementary information extracted from the Tata Institute of Fundamental Research GMRT Sky Survey. Its spectral energy distribution clearly shows the turnover at a frequency of about 600 MHz, that we interpret to be due to FFA. Finally, we report on the identification of two additional particle-accelerating colliding-wind binaries, namely Cyg OB2 12 and ALS 15108 AB