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Register a new userE-BOSS: an Extensive stellar BOw Shock Survey. I: Methods and First Catalogue
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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.
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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.
Bow shocks and related density enhancements produced by the winds of massive stars moving through the interstellar medium provide important information regarding the motions of the stars, the properties of their stellar winds, and the characteristics of the local medium. Since bow shocks are aspherical structures, light scattering within them produces a net polarization signal even if the region is spatially unresolved. Scattering opacity arising from free electrons and dust leads to a distribution of polarized intensity across the bow shock structure. That polarization encodes information about the shape, composition, opacity, density, and ionisation state of the material within the structure. In this paper we use the Monte Carlo radiative transfer code SLIP to investigate the polarization created when photons scatter in a bow shock-shaped region of enhanced density surrounding a stellar source. We present results assuming electron scattering, and investigate the polarization behaviour as a function of optical depth, temperature, and source of photons for two different cases: pure scattering and scattering with absorption. In both regimes we consider resolved and unresolved cases. We discuss the implication of these results as well as their possible use along with observational data to constrain the properties of observed bow shock systems. In different situations and under certain assumptions, our simulations can constrain viewing angle, optical depth and temperature of the scattering region, and the relative luminosities of the star and shock.
We present an extensive catalog of non-parametric structural properties derived from optical and mid-infrared imaging for 4585 galaxies from the MaNGA survey. DESI and WISE imaging are used to extract surface brightness profiles in the g, r, z, W1, W2 photometric bands. Our optical photometry takes advantage of the automated algorithm AutoProf and probes surface brightnesses that typically reach below 29 mag/arcsec^2 in the r band, while our WISE photometry achieves 28 mag/arcsec^2 in the W1 band. Neighbour density measures and central/satellite classifications are also provided for a large sub-sample of the MaNGA galaxies. Highlights of our analysis of galaxy light profiles include: (i) an extensive comparison of galaxian structural properties that illustrates the robustness of non-parametric extraction of light profiles over parametric methods; (ii) the ubiquity of bimodal structural properties suggesting the existence of galaxy families in multiple dimensions; and, (iii) an appreciation that structural properties measured relative to total light, regardless of the fractional level, are uncertain. We study galaxy scaling relations based on photometric parameters, and present detailed comparisons with literature and theory. Salient features of this analysis include the near-constancy of the slope and scatter of the size-luminosity and size-stellar mass relations for late-type galaxies with wavelength, and the saturation of the central surface density, measured within 1 kpc, for elliptical galaxies with M* > 10.7 Msol (corresponding to Sigma_1 ~ 10^{10} Msol/kpc^2). The multi-band photometry, environmental parameters, and structural scaling relations presented are useful constraints for stellar population and galaxy formation models.
We present a deep radio-polarimetric observation of the stellar bow shock EB27 associated to the massive star BD+43 3654. This is the only stellar bow shock confirmed to have non-thermal radio emission. We used the Jansky Very Large Array in S band (2 - 4GHz) to test whether this synchrotron emission is polarised. The unprecedented sensitivity achieved allowed us to map even the fainter regions of the bow shock, revealing that the more diffuse emission is steeper and the bow shock brighter than previously reported. No linear polarisation is detected in the bow shock above 0.5%, although we detected polarised emission from two southern sources, probably extragalactic in nature. We modeled the intensity and morphology of the radio emission to better constrain the magnetic field and injected power in relativistic electrons. Finally, we derived a set of more precise parameters for the system EB27-BD+43 3654 using Gaia Early Data Release 3, including the spatial velocity. The new trajectory, back in time, intersects the core of the Cyg OB2 association.
We study the polarization produced by scattering from dust in a bow shock-shaped region of enhanced density surrounding a stellar source, using the Monte Carlo radiative transfer code SLIP. Bow shocks are structures formed by the interaction of the winds of fast-moving stars with the interstellar medium. Our previous study focused on the polarization produced in these structures by electron scattering; we showed that polarization is highly dependent on inclination angle and that multiple scattering changes the shape and degree of polarization. In contrast to electron scattering, dust scattering is wavelength-dependent, which changes the polarization behaviour. Here we explore different dust particle sizes and compositions and generate polarized spectral energy distributions for each case. We find that the polarization SED behaviour depends on the dust composition and grain size. Including dust emission leads to polarization changes with temperature at higher optical depth in ways that are sensitive to the orientation of the bow shock. In various scenarios and under certain assumptions, our simulations can constrain the optical depth and dust properties of resolved and unresolved bow shock-shaped scattering regions.Constraints on optical depth can provide estimates of local ISM density for observed bow shocks. We also study the impact of dust grains filling the region between the star and bow shock. We see that as the density of dust between the star and bow shock increases, the resulting polarization is suppressed for all the optical depth regimes.
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