Two possible planetary nebulae (PN G035.5-00.4 and IRAS 18551+0159), one newly re-identified supernova remnant (SNR G35.6-0.4), and one HII region (G35.6-0.5) form a line-of-sight-overlapped complex known as G35.6-0.5. We analyze 21 cm HI absorption spectra towards the complex to constrain their kinematic distances. PN G035.5-00.4 has a distance from 3.8+/-0.4 kpc to 5.4+/-0.7 kpc. IRAS 18551+0159 is at 4.3+/-0.5 kpc. We discuss the distance for SNR 35.6-0.4, for which the previous estimate was 10.5 kpc, and find plausible for it to be 3.6+/-0.4 kpc. The new distance of SNR G35.6-0.4 and the derived mass for the ~55 km/s CO molecular cloud can accommodate an association with HESS J1858+020. We also conclude that SNR G35.6-0.4 is unlikely associated with PSR J1857+0210 or PSR J1857+0212, which are projected into the SNR area.
On the non-thermal kappa-distributed electrons in planetary nebulae and HII regions: the kappa index and its correlations with other nebular properties
We determine the radial abundance gradient of helium in the disc of the Galaxy from published spectra of 19 $\text{H}\thinspace \text{II}$ regions and ring nebulae surrounding massive O stars. We revise the Galactocentric distances of the objects considering {\it Gaia} DR2 parallaxes and determine the physical conditions and the ionic abundance of He$^{+}$ in a homogeneous way, using between 3 and 10 $\text{He}\thinspace \text{I}$ recombination lines in each object. We estimate the total He abundance of the nebulae and its radial abundance gradient using four different ICF(He) schemes. The slo…
One of the key methods for determining the unknown nature of Type Ia supernovae (SNe Ia) is the search for traces of interaction between the SN ejecta and the circumstellar structures at the resulting supernova remnants (SNRs Ia). So far, the observables that we receive from well-studied SNRs Ia cannot be explained self-consistently by any model presented in the literature. In this study, we suggest that the circumstellar medium (CSM) being observed to surround several SNRs Ia was mainly shaped by planetary nebulae (PNe) that originated from one or both progenitor stars. Performing two-dimensi…
A very small fraction of (runaway) massive stars have masses exceeding $60$-$70\, \rm M_{\odot}$ and are predicted to evolve as Luminous-Blue-Variable and Wolf-Rayet stars before ending their lives as core-collapse supernovae. Our 2D axisymmetric hydrodynamical simulations explore how a fast wind ($2000\, \rm km\, \rm s^{-1}$) and high mass-loss rate ($10^{-5}\, \rm M_{\odot}\, \rm yr^{-1}$) can impact the morphology of the circumstellar medium. It is shaped as 100 pc-scale wind nebula which can be pierced by the driving star when it supersonically moves with velocity $20$-$40\, \rm km\, \rm s…
Star-forming regions are often associated with nebulosity. In this study, we investigated infrared diffuse emission in Spitzer IRAC images. The infrared nebula L1527 traces outflows emanating from a low-mass protostar. The nebular color is consistent with the color of a stellar photosphere with large extinction. Nebulae around the HII region W5-East are bright in the infrared. These colors are consistent with the model color of dust containing polycyclic aromatic hydrocarbon (PAH). The strength of ultraviolet irradiation of the nebulae and the small dust fraction were deduced from the infrared…
Pinpointing a pulsar in its parent supernova remnant (SNR) or resulting pulsar wind nebula (PWN) is key for understanding its formation history, and the pulsar wind mechanism. Yet, only about half the SNRs and PWNe appear associated with a pulsar. We aim to find the pulsars in a sample of eight known and new SNRs and PWNe. Using the LOFAR radio telescope at 150 MHz, each source was observed for 3 hours. We covered the entire remnants where needed, by employing many tied-array beams to tile out even the largest objects. For objects with a confirmed point source or PWN we constrained our search …
We present some results of an ongoing project devoted to reassess the radial abundance gradients in the disc of the MilkyWay based on deep spectroscopy of Hii regions. The data have been taken with large aperture telescopes, mainly with the GTC and VLT. The sample contains about 35 objects located at Galactocentric distances from 5 to 17 kpc. We determine the electron temperature for all nebulae, allowing the precise calculation of chemical abundances. In this paper, we present and discuss results mostly concerning the radial gradients of O, N and C.
Accurate distance estimates of astrophysical objects such as planetary nebulae (PNe), and nova and supernova remnants, among others, allow us to constrain their physical characteristics, such as size, mass, luminosity, and age. An innovative technique based on the expansion parallax method, the so-called distance mapping technique (DMT), provides distance maps of expanding nebulae as well as an estimation of their distances. The DMT combines the tangential velocity vectors obtained from 3D morpho-kinematic models and the observed proper motion vectors to estimate the distance. We applied the D…
Atomic ionised regions with strong continuum emission are often associated with regions of high-mass star formation and low-frequency (<2GHz) observations of these regions are needed to help build star formation models. The region toward the Vela Supernova Remnant is particularly interesting as it is a complex structure of recent supernova explosions and molecular clouds containing a number of HII regions that are not well characterised. We searched publicly available catalogues for HII regions, both candidate and identified, which also have low-frequency emission. In the area of ~400 square d…
An analytic calculation is made of the effect of plasma density fluctuations on some spectroscopic diagnostics commonly used in the study of HII regions and planetary nebulae. To permit an analytic treatment, attention is restricted to the case of density fluctuations possessing an exponential probability distribution function (pdf). The present investigation is made in support of a completely numerical and more extensive study of nebular diagnostics by Bergerud et al (2019). Results from this paper are presented in terms of graphs of the observed quantity (spectroscopic line ratio) versus mea…
Large-scale radio continuum surveys provide data to get insights into the physical properties of radio sources. HII regions are prominent radio sources produced by thermal emission of ionised gas around young massive stars. We identify and analyse HII regions in the Sino-German 6cm polarisation survey of the Galactic plane. Objects with flat radio continuum spectra together with infrared and/or Halpha emission were identified as HII regions. For HII regions with small apparent sizes, we cross-matched the 6cm small-diameter source catalogue with the radio HII region catalogue compiled by Paladi…
The fact that infrared ring nebulae (IRRNs) are frequently associated with HII regions, provides us the opportunity to study dust at the interface between ionized and neutral gas. In this paper, we analyze the infrared radiation in the range from 8 to 500~$μ$m in outer and inner parts of 32 IRRNs showing round shape. We aim to determine the morphology of these objects and possible dust evolution processes on the base of the comparison of IR radiation towards the ionized and neutral regions. We calculate six slopes between adjacent wavelengths in their spectral energy distributions to trace the…
The VISTA Magellanic Cloud (VMC) survey is assembling a deep, multi-epoch atlas of YJKs photometry across the Magellanic Clouds. Prior to the VMC survey only the brightest Magellanic Cloud PNe (MCPNe) were accessible at near-infrared (NIR) wavelengths. It is now possible for the first time to assemble the NIR properties of MCPNe and to identify contaminating non-PNe mimics which are best revealed at NIR wavelengths (e.g. HII regions and symbiotic stars). To maintain the unique scientific niche that MCPNe occupy these contaminants must be removed. Here we conduct a VMC-led, multi-wavelength stu…
The post-asymptotic giant branch (AGB) phase is arguably one of the least understood phases of the evolution of low- and intermediate- mass stars. The recent post-AGB evolutionary sequences computed by Miller Bertolami (2016) are at least three to ten times faster than those previously published by Vassiliadis & Wood (1994) and Bloecker (1995) which have been used in a large number of studies. This is true for the whole mass and metallicity range. The new models are also $\sim$0.1-0.3 dex brighter than the previous models with similar remnant masses. In this short article we comment on the mai…
