Search

During a search for previously unknown Galactic emission nebulae, we discovered a faint 36' diameter Halpha emission nebula centered around the periodic variable YY Hya. Although this star has been classified as RR-Lyr variable, such a classification is inconsistent Gaia distance of ~450 pc. GALEX image data also shows YY Hya to have a strong UV excess, suggesting the existence of a hot, compact binary companion. In addition to our discovery image data, we obtained image of the region with CHILESCOPE time-series spectroscopy at MDM observatory. Also, we used data from various space missions to derive an exact orbital period and a SED. We find that YY Hya is a compact binary system containing a K dwarf star which is strongly irradiated by a hot WD companion. The spectral characteristics of the emission lines, visible only during maximum light of the perfectly sinusoidal optical}light curve shows signatures much like members of the BE UMa variable family. These are post common envelope pre-cataclysmic variables. However the companion star here is more massive than found in other group members and the progenitor of the white dwarf must have been a 3 to 4 Mo star. The nebula seems to be an ejected common envelope shell with a mass in the order of one Mo and an age of 500000 years. This makes it to be the biggest hitherto known such shell. Alignment of neighboring nebulosities some 45' to the northeast and southwest of YY Hya suggests that the system had strong bipolar outflows. We briefly speculate it might be related to the 1065 BP "guest-star" reported in ancient Chinese records as well., 18 pages, 17 figures accepted for publication in A&A

We develop a 3D hydrodynamical code written in C programming language to study the expansion of supernova remnants (SNRs) in the surrounding medium. It is based on the MUSCL-Hancock finite volume scheme with the HLLC Riemann solver. The code initiates the supernova remnant already in the Sedov phase and simulates hydrodynamics of the subsequent remnant expansion. The simulation is optimized for studies of large scale interaction of a supernova remnant with the interstellar medium (ISM). After a detailed description of the code, and three tests of hydrodynamics, we present the results for a single remnant expanding into a uniform and fractally structured ISM, as the first application of the code. The simulation of SNR expanding in a uniform medium is compared with the Sedov law of expansion and Sedov self-similar solution to density, velocity and pressure profiles. The results indicate that the simulation presented here reproduces well the hydrodynamics of the supernova remnant expansion and is very practical due to its simplicity and speed. The SNR evolution in fractal ISM shows that clumps disturb the blast wave and produce interference of bow shocks, resulting in turbulent motions and inhomogenities inside the remnant. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 176005: Emission nebulae: structure and evolution]

We investigate the dust attenuation in both stellar populations and ionized gas in kpc-scale regions in nearby galaxies, using integral field spectroscopy data from MaNGA MPL-9. We identify star-forming (HII) and diffuse ionized gas (DIG) regions from MaNGA datacubes. From the stacked spectrum of each region, we measure the stellar attenuation, $E(B-V)_{\rm star}$, using the technique developed by Li et al.(2020), as well as the gas attenuation, $E(B-V)_{\rm gas}$, from the Balmer decrement. We then examine the correlation of $E(B-V)_{\rm star}$, $E(B-V)_{\rm gas}$, $E(B-V)_{\rm gas}-E(B-V)_{\rm star}$ and $E(B-V)_{\rm star}/E(B-V)_{\rm gas}$ with 16 regional/global properties, and for regions with different $\rm H{\alpha}$ surface brightnesses ($\Sigma_{\rm H\alpha}$). We find a stronger correlation between $E(B-V)_{\rm star}$ and $E(B-V)_{\rm gas}$ in regions of higher $\Sigma_{\rm H\alpha}$. Luminosity-weighted age ($t_L$) is found to be the property that is the most strongly correlated with $E(B-V)_{\rm star}$, and consequently with $E(B-V)_{\rm gas}-E(B-V)_{\rm star}$ and $E(B-V)_{\rm star}/E(B-V)_{\rm gas}$. At fixed $\Sigma_{\rm H\alpha}$, $\log_{10}t_L$ is linearly and negatively correlated with $E(B-V)_{\rm star}/E(B-V)_{\rm gas}$ at all ages. Gas-phase metallicity and ionization level are important for the attenuation in the gas. Our results indicate that the ionizing source for DIG regions is likely distributed in the outer-skirt of galaxies, while for HII regions our results can be well explained by the two-component dust model of Charlot & Fall (2000)., Comment: accepted by ApJ

With a metallicity of 12 + Log(O/H) $\approx$ 7.1-7.2, I Zw 18 is a canonical low-metallicity blue compact dwarf (BCD) galaxy. A growing number of BCDs, including I Zw 18, have been found to host strong, narrow-lined, nebular He II ($\lambda$4686) emission with enhanced intensities compared to H$\beta$ (e.g., He II($\lambda$4686)/H$\beta$ > 1%). We present new observations of I Zw 18 using the Keck Cosmic Web Imager. These observations reveal two nebular He II emission regions (or He III regions) northwest and southeast of the He III region in the galaxy's main body investigated in previous studies. All regions exhibit He II($\lambda4686$)/Hbeta greater than 2%. The two newly resolved He III regions lie along an axis that intercepts the position of I Zw 18's ultraluminous X-ray (ULX) source. We explore whether the ULX could power the two He III regions via shock activity and/or beamed X-ray emission. We find no evidence of shocks from the gas kinematics. If the ULX powers the two regions, the X-ray emission would need to be beamed. Another potential explanation is that a class of early-type nitrogen-rich Wolf-Rayet stars with low winds could power the two He III regions, in which case the alignment with the ULX would be coincidental., Comment: 9 pages, 4 figures, accepted for publication in ApJL

SITELLE is a novel integral field unit spectroscopy instrument that has an impressive spatial (11 by 11 arcmin), spectral coverage, and spectral resolution (R=1-20000). SIGNALS is anticipated to obtain deep observations (down to 3.6x10-17ergs s-1cm-2) of 40 galaxies, each needing complex and substantial time to extract spectral information. We present a method that uses Convolution Neural Networks (CNN) for estimating emission line parameters in optical spectra obtained with SITELLE as part of the SIGNALS large program. Our algorithm is trained and tested on synthetic data representing typical emission spectra for HII regions based on Mexican Million Models database(3MdB) BOND simulations. The network's activation map demonstrates its ability to extract the dynamical (broadening and velocity) parameters from a set of 5 emission lines (e.g. H{\alpha}, N[II] doublet, and S[II] doublet) in the SN3 (651-685 nm) filter of SITELLE. Once trained, the algorithm was tested on real SITELLE observations in the SIGNALS program of one of the South West fields of M33. The CNN recovers the dynamical parameters with an accuracy better than 5 km s-1 in regions with a signal-to-noise ratio greater than 15 over the H{\alpha}line. More importantly, our CNN method reduces calculation time by over an order of magnitude on the spectral cube with native spatial resolution when compared with standard fitting procedures. These results clearly illustrate the power of machine learning algorithms for the use in future IFU-based missions. Subsequent work will explore the applicability of the methodology to other spectral parameters such as the flux of key emission lines., Comment: 14 pages, 11 figures Accepted in ApJ

We present sub-arcsecond optical images and low- to moderate-resolution spectra of the compact, X-ray and optically bright supernova remnant known as S8 in the nearby dwarf galaxy IC 1613. Deep H$\alpha$ images of the remnant show a sharply defined crescent shaped nebula, while narrow passband images reveal a coincident and unexpectedly bright continuum nebulosity exhibiting a size and morphology like that seen for the remnant's line emissions. Low-dispersion spectra covering 3600 - 9000 A show numerous low-ionization line emissions such as [O I] and [Fe II], along with higher-ionization emission lines including He II and optical coronal lines [Fe VII], [Fe X], [Fe XI], and [Fe XIV]. This suggests the presence of a wide range of shock velocities from $\sim$ 50 to over 350 km s$^{-1}$, corresponding to preshock densities of $\sim1 - 30$ cm$^{-3}$. Higher resolution spectra indicate an expansion velocity around 180 km s$^{-1}$ with a $\sim45$ km s$^{-1}$ wide central cavity. H$\alpha$ emission spans rest frame velocities of $+120$ to $-240$ km s$^{-1}$ and we estimate a total nebula mass of $119 \pm 34$ M$_{\odot}$. We conclude S8 is a relatively young supernova remnant ($\simeq2700 - 4400$ yr) exhibiting properties remarkably like those seen in the young LMC remnant N49, including age, physical size, shock velocities, filament densities, optical line strengths, X-ray and optical luminosities, and coronal line and continuum emissions., Comment: 19 pages, 6 figures, and 5 tables. Accepted for publication in ApJ

Escaping Lyman continuum photons from galaxies likely reionized the intergalactic medium at redshifts $z\gtrsim6$. However, the Lyman continuum is not directly observable at these redshifts and secondary indicators of Lyman continuum escape must be used to estimate the budget of ionizing photons. Observationally, at redshifts $z\sim2-3$ where the Lyman continuum is observationally accessible, surveys have established that many objects that show appreciable Lyman continuum escape fractions $f_{esc}$ also show enhanced [OIII]/[OII] (O$_{32}$) emission line ratios. Here, we use radiative transfer analyses of cosmological zoom-in simulations of galaxy formation to study the physical connection between $f_{esc}$ and O$_{32}$. Like the observations, we find that the largest $f_{esc}$ values occur at elevated O$_{32}\sim3-10$ and that the combination of high $f_{esc}$ and low O$_{32}$ is extremely rare. While high $f_{esc}$ and O$_{32}$ often are observable concurrently, the timescales of the physical origin for the processes are very different. Large O$_{32}$ values fluctuate on short ($\sim$1 Myr) timescales during the Wolf-Rayet-powered phase after the formation of star clusters, while channels of low absorption are established over tens of megayears by collections of supernovae. We find that while there is no direct causal relation between $f_{esc}$ and O$_{32}$, high $f_{esc}$ most often occurs after continuous input from star formation-related feedback events that have corresponding excursions to large O$_{32}$ emission. These calculations are in agreement with interpretations of observations that large $f_{esc}$ tends to occur when O$_{32}$ is large, but large O$_{32}$ does not necessarily imply efficient Lyman continuum escape., Comment: 12 pages, 5 figures, submitted to ApJL on September 15, 2020

We present a detailed study of the binary central star of the planetary nebula ETHOS 1 (PN G068.1+11.0). Simultaneous modelling of light and radial velocity curves reveals the binary to comprise a hot and massive pre-white dwarf with an M-type main-sequence companion. A good fit to the observations was found with a companion that follows expected mass–temperature–radius relationships for low-mass stars, indicating that despite being highly irradiated, it is consistent with not being significantly hotter or larger than a typical star of the same mass. Previous modelling indicated that ETHOS 1 may comprise the first case where the orbital plane of the central binary does not lie perpendicular to the nebular symmetry axis, at odds with the expectation that the common envelope is ejected in the orbital plane. We find no evidence for such a discrepancy, deriving a binary inclination in agreement with that of the nebula as determined by spatio-kinematic modelling. This makes ETHOS 1 the ninth post-common-envelope planetary nebula in which the binary orbital and nebular symmetry axes have been shown to be aligned, with as yet no known counter-examples. The probability of finding such a correlation by chance is now less than 0.000 02 per cent., With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)

This review presents the fundamentals of the particle acceleration processes active in interstellar medium (ISM), which are essentially based on the so-called Fermi mechanism theory. More specifically, the review presents here in more details the first order Fermi acceleration process -- also known as diffusive shock acceleration (DSA) mechanism. In this case, acceleration is induced by the interstellar (IS) shock waves. These IS shocks are mainly associated with emission nebulae (HII regions, planetary nebulae and supernova remnants). Among all types of emission nebulae, the strongest shocks are associated with supernova remnants (SNRs). Due to this fact they also provide the most efficient manner to accelerate ISM particles to become {high energy particles}, i.e.~cosmic-rays (CRs). The review therefore focuses on the particle acceleration at the strong shock waves of supernova remnants., Comment: Accepted for publication in Astrophysics and Space Science

High-resolution optical integral field units (IFUs) are rapidly expanding our knowledge of extragalactic emission nebulae in galaxies and galaxy clusters. By studying the spectra of these objects -- which include classic HII regions, supernova remnants, planetary nebulae, and cluster filaments -- we are able to constrain their kinematics (velocity and velocity dispersion). In conjunction with additional tools, such as the BPT diagram, we can further classify emission regions based on strong emission-line flux ratios. LUCI is a simple-to-use python module intended to facilitate the rapid analysis of IFU spectra. LUCI does this by integrating well-developed pre-existing python tools such as astropy and scipy with new machine learning tools for spectral analysis (Rhea et al. 2020). Furthermore, LUCI provides several easy-to-use tools to access and fit SITELLE data cubes., Submitted to RNAAS Extensive documentation can be found at https://crhea93.github.io/LUCI/index.html

We analyze the chemical composition of the planetary nebula (PN) NGC 5315, through high-resolution (R = 40000) optical spectroscopy with UVES at the Very Large Telescope, and medium-resolution (R = 4800) near-infrared spectroscopy with FIRE at Magellan Baade Telescope, covering a wide spectral range from 0.31 to 2.50 micron. The main aim of this work is to investigate neutron (n)-capture element abundances to study the operation of the slow n-capture ("s-process") in the AGB progenitor of NGC 5315. We detect more than 700 emission lines, including ions of the n-capture elements Se, Kr, Xe, and possibly Br. We compute physical conditions from a large number of diagnostic line ratios, and derive ionic abundances for species with available atomic data. The total abundances are computed using recent ionization correction factors (ICFs) or by summing ionic abundances. Total abundances of common elements are in good agreement with previous work on this object. Based on our abundance analysis of NGC 5315, including the lack of s-process enrichment, we speculate that the most probable scenario is that the progenitor star is in a binary system as hinted at by radial velocity studies, and interactions with its companion truncated the AGB before s-process enrichment could occur. However there are other two possible scenarios for its evolution, that cannot be ruled out: i) the progenitor is a low-mass single star that did not undergo third dredge-up; ii) the progenitor star of NGC 5315 had an initial mass of 4--6 solar masses, and any s-process enhancements were heavily diluted by the massive envelope during the AGB phase., 31 pages, 6 figures, 15 tables. Accepted for publication in MNRAS

Background/Objective: Planetary nebulas are glowing shell of gases that are ejected from the central star. The main objective of this paper is to present a model for NGC6369 planetary nebula. Methods: The central star is an old star (type O) with magnitudes between -3 and +5. These stars are quickly evolving into white dwarfs. In this paper, dynamic and ionized structure of NGC 6369 planetary nebula based on the interaction model of two stellar winds is discussed. Results: This high velocity wind will collide with a super stellar wind after a while, and creates a dense area, where this area is the same nebula under study. The stellar wind begins to blow at a mass loss rate of 1 x 10 -5 Msun/yr and a speed of 10 km/ s. After a while, the wind ends, and a high velocity wind starts blowing. Conclusion: If the problem assigned a typical velocity of 2000 km/ s, it has achieved a mass loss rate of 4.5 x 10 -9 Msun/yr.

The first wind nebula around a magnetar was recently discovered in X-rays around Swift~J1834.9$-$0846. We study this magnetar's global energetics and the properties of its particle wind or outflows. At a distance of $\sim4\;$kpc, Swift~J1834.9$-$0846 is located at the center of the supernova remnant (SNR) W41 whose radius is $\sim 19\;$pc, an order of magnitude larger than that of the X-ray nebula ($\sim2\;$pc). The association with SNR W41 suggests a common age of $\sim5-100\;$kyr, while its spin-down age is $4.9$~kyr. A small natal kick velocity may partly explain why a wind nebula was detected around this magnetar but not around other magnetars, most of which appear to have larger kick velocities and may have exited their birth SNR. We find that the GeV and TeV source detected by Fermi/LAT and H.E.S.S., respectively, of radius $\sim11\;$pc is most likely of hadronic origin. The dynamics and internal structure of the nebula are examined analytically to explain the nebula's current properties. Its size may naturally correspond to the diffusion-dominated cooling length of the X-ray emitting $e^+e^-$ pairs. This may also account for the spectral softening of the X-ray emission from the nebula's inner to outer parts. Analysis of the X-ray synchrotron nebula implies that (i) the nebular magnetic field is $\gtrsim 11\;\mu$G (and likely $\lesssim30\;\mu$G), and (ii) the nebula is not powered predominantly by the magnetar's quiescent spin-down-powered MHD wind, but by other outflows that contribute most of its energy. The latter are most likely associated with the magnetar's bursting activity, and possibly dominated by outflows associated with its past giant flares. The energy source for the required outflows cannot be the decay of the magnetar's dipole field alone, and is most likely the decay of its much stronger internal magnetic field., Comment: 33 pages, 15 figures. Accepted for publication in MNRAS

A nova is a cataclysmic event on the surface of a white dwarf in a binary system that increases the overall brightness by several orders of magnitude. Although binary systems with a white dwarf are expected to be overabundant in globular clusters (GCs) compared to the Galaxy, only two novae from Galactic globular clusters have been observed. We present the discovery of an emission nebula in the Galactic globular cluster M 22 (NGC 6656) in observations made with the integral-field spectrograph MUSE. We extract the spectrum of the nebula and use the radial velocity determined from the emission lines to confirm that the nebula is part of NGC 6656. Emission-line ratios are used to determine the electron temperature and density. It is estimated to have a mass of 1 to $17 \times 10^{-5}$ solar masses. This mass and the emission-line ratios indicate that the nebula is a nova remnant. Its position coincides with the reported location of a 'guest star', an ancient Chinese term for transients, observed in May 48 BCE. With this discovery, this nova may be one of the oldest confirmed extrasolar events recorded in human history., 7 pages, 3 figures; accepted for publication in Astronomy & Astrophysics

We present XMM-Newton and Chandra observations of the born-again planetary nebula A 30. These X-ray observations reveal a bright unresolved source at the position of the central star whose X-ray luminosity exceeds by far the model expectations for photospheric emission and for shocks within the stellar wind. We suggest that a “born-again hot bubble” may be responsible for this X-ray emission. Diffuse X-ray emission associated with the petal-like features and one of the H-poor knots seen in the optical is also found. The weakened emission of carbon lines in the spectrum of the diffuse emission can be interpreted as the dilution of stellar wind by mass-loading or as the detection of material ejected during a very late thermal pulse., Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe, 563

We present detection of 67 HII regions and two optical supernova remnant (SNR) candidates in the nearby irregular galaxy NGC 2366. The SNR candidates were detected by applying [SII]/H$\alpha$ ratio criterion to observations made with the 2-m RCC telescope at Rozhen National Astronomical Observatory in Bulgaria. In this paper we report coordinates, diameters, H$\alpha$ and [SII] fluxes for detected objects across the two fields of view in NGC 2366 galaxy. Using archival XMM-Newton observations we suggest possible X-ray counterparts of two optical SNR candidates. Also, we discard classification of two previous radio SNR candidates in this galaxy, since they appear to be background galaxies., Comment: 12 pages, 6 figures, accepted for publication in Serbian Astronomical Journal

Motivated by the discovery of rare enormous Lyman α nebulae (ELAN) around z ̃ 2 quasars, we initiated a long-term campaign with the MUSE/VLT instrument to directly uncover the astrophysics of the gas around quasars. We present here the first 61 targets under the acronym QSO MUSEUM. These quasars are characterized by a median redshift z = 3.17, absolute i magnitude in the range -29.67 ≤ Mi(z = 2) ≤ -27.03, and different levels of radio-loudness. This sample unveils diverse specimens of Ly α nebulosities extending for tens of kpc around these quasars (average maximum projected distance of 80 kpc) above a surface brightness SB > 8.8 × 10-19 erg s-1 cm-2 arcsec-2(2σ). The bulk of the Ly α emission is within R < 50 kpc, and is characterized by relatively quiescent kinematics, with average velocity dispersions Ly α> < 400 km s-1. Therefore, the motions within all these Ly α nebulosities have amplitudes consistent with gravitational motions expected in dark matter haloes hosting quasars at these redshifts, possibly reflecting the complexity in propagating a fast wind on large scales. Our current data suggest a combination of photoionization and resonant scattering as powering mechanisms of the Ly α emission. We discover the first z ̃ 3 ELAN, confirming a very low probability ({̃ }1{{ per cent}}) of occurrence of such systems at these redshifts. Finally, we discuss the redshift evolution currently seen in extended Ly α emission around radio-quiet quasars from z ̃ 3 to z ̃ 2, concluding that it is possibly linked to a decrease of cool gas mass within the circumgalactic medium of quasars from z ̃ 3 to z ̃ 2, and thus to the balance of cool versus hot media. Overall, QSO MUSEUM opens the path to statistical surveys targeting the gas phases in quasars' haloes along cosmic times.

In this paper we present new optical observations of the galaxy NGC 185 intended to reveal the status of supernova remnants (SNRs) in this dwarf companion of the Andromeda galaxy. Previously, it was reported that this galaxy hosts one SNR. Our deep photometric study with the 2m telescope at Rozhen National Astronomical Observatory using narrow-band H$\alpha$ and [SII] filters revealed complex structure of the interstellar medium in the center of the galaxy. To confirm the classification and to study the kinematics of the detected nebulae, we carried out spectroscopic observations using the SCORPIO multi-mode spectrograph at the 6m telescope at the Special Astrophysical Observatory of the Russian Academy of Science, both in low- and high-resolution modes. We also searched the archival X-ray and radio data for counterparts of the candidate SNRs identified by our optical observations. Our observations imply the presence of one more SNR, one possible HII region previously cataloged as part of an SNR, and the presence of an additional source of shock ionization in one low-brightness PN. We detected enhanced [SII]/H_alpha and [NII]/H_alpha line ratios, as well as relatively high (up to 90 km s$^{-1}$) expansion velocities of the two observed nebulae, motivating their classification as SNRs (with diameters of 45 pc and 50 pc), confirmed by both photometric and spectral observations. The estimated electron density of emission nebulae is 30 - 200 cm$^{-3}$. Archival XMM-Newton observations indicate the presence of an extended, low-brightness, soft source in projection of one of the optical SNRs, whereas the archival VLA radio image shows weak, unresolved emission in the center of NGC 185., Comment: 15 pages, 14 figures, accepted for publication in A&A

Tenuous wind bubbles, which are formed by the spin-down activity of central compact remnants, are relevant in some models of fast radio bursts (FRBs) and super-luminous supernovae. We study their high-energy signatures, focusing on the role of pair-enriched bubbles produced by young magnetars, rapidly-rotating neutron stars, and magnetized white dwarfs. (i) First, we study the nebular properties and the conditions allowing for escape of high-energy gamma-rays and radio waves, showing that their escape is possible for nebulae with ages of >10-100 yr. In the rapidly-rotating neutron star scenario, we find that radio emission from the quasi-steady nebula itself may be bright enough to be detected especially at sub-mm frequencies, which is relevant as a possible counterpart of pulsar-driven SNe and FRBs. (ii) Second, we consider the fate of bursting emission in the nebulae. We suggest that an impulsive burst may lead to a highly relativistic flow, which would interact with the nebula. If the shocked nebula is still relativistic, pre-existing non-thermal particles in the nebula can be significantly boosted by the forward shock, leading to short-duration (maybe millisecond or longer) high-energy gamma-ray flashes. Possible dissipation at the reverse shock may also lead to gamma-ray emission. (iii) After such flares, interactions with the baryonic ejecta may lead to afterglow emission with a duration of days to weeks. In the magnetar scenario, this burst-in-bubble model leads to the expectation that nearby (, 15 pages, 6+1 figures, 1 table, published in MNRAS (arXiv on 03/28/2016), free-free absorption recalculated with more realistic parameters (conclusions unchanged), arXiv version with comments on FRB 121102

Two southern objects are studied. The first, the planetary nebula PK 349-01.1, is of interest because it has a chain of jets ejected from the central star. 12C(1-0) observations of the vicinity of this object reveal red- and blue-shifted molecular outflows. The second object is a star formation region consisting of two groups of IR stars. These groups have a trapezium-like configuration. Two stars in one of these groups are associated with a ring-shaped nebulae. This star formation region is associated with a new radial system of dark globules.

We present deep XMM-Newton EPIC observations of the Wolf-Rayet (WR) bubble NGC6888 around the star WR136. The complete X-ray mapping of the nebula confirms the distribution of the hot gas in three maxima spatially associated with the caps and northwest blowout hinted at by previous Chandra observations. The global X-ray emission is well described by a two-temperature optically thin plasma model $T_1$=1.4$\times$10$^{6}$ K, $T_{2}$=8.2$\times$10$^{6}$ K) with a luminosity of $L_{\mathrm{X}}$=7.8$\times$10$^{33}$ erg s$^{-1}$ in the 0.3--1.5 keV energy range. The rms electron density of the X-ray-emitting gas is estimated to be $n_\mathrm{e}$=0.4 cm$^{-3}$. The high-quality observations presented here reveal spectral variations within different regions in NGC6888, which allowed us for the first time to detect temperature and/or nitrogen abundance inhomogeneities in the hot gas inside a WR nebula. One possible explanation for such spectral variations is that the mixing of material from the outer nebula into the hot bubble is less efficient around the caps than in other nebular regions., 10 pages, 4 figures, 2 tables; Accepted to MNRAS

Cassiopeia A (Cas A) is one of the best studied young Galactic supernova remnants. While providing a rare opportunity to study in detail the remnant of a Type IIb supernova, questions remain regarding the nature of its progenitor, its mass-loss history, and its pre-SN evolution. Here we present an optical investigation of the circumstellar environment around Cas A and find clumpy and filamentary Halpha emission nebulosities concentrated 10-15 pc (10-15 arcminutes) to the north and east. First reported by Minkowski as a faint H II region, these nebulosities exhibit distinct morphological and spectroscopic properties relative to the surrounding diffuse emissions. Compared to neighboring H II regions, these nebulae show stronger [N II] 6548, 6583 A and [S II] 6716, 6731 A emissions relative to Halpha. We show that Cas A's highest-velocity ejecta knots are interacting with some of the closest projected emission nebulae, thus providing strong evidence that these nebulae lie at the same distance as the remnant. We interpret these surrounding nebulosities to be the remains of the progenitor's red supergiant wind which accumulated against the southern edge of a large extended H II region located north of Cas A. Our findings are consistent with the view that Cas A's progenitor underwent considerable mass-loss, first from a fast main-sequence wind, then from a slower, clumpy red supergiant wind, and finally from a brief high-velocity wind, like that from a yellow supergiant., Comment: 19 pages, 9 figures, accepted to ApJ

To date, over 220 emission nebulae in M33 have been identified as supernova remnants (SNRs) or SNR candidates, principally through [SII]:Halpha line ratios that are elevated compared to those in H II regions. In many cases, the determination of a high [SII]:Halpha line ratio was made using narrow-band interference filter images and has not been confirmed spectroscopically. Here we present MMT 6.5 m optical spectra that we use to measure [SII]:Halpha and other line ratios in an attempt to determine the nature of these suggested candidates. Of the 197 objects in our sample, 120 have no previously published spectroscopic observations. We confirm that the majority of candidate SNRs have emission line ratios characteristic of SNRs. While no candidates show Doppler-broadened lines expected from young, ejecta-dominated SNRs (> 1000 km/s), a substantial number do exhibit lines that are broader than H II regions. We argue that the majority of the objects with high [SII]:Halpha line ratios (>0.4) are indeed SNRs, but at low surface brightness the distinction between H II regions and SNRs becomes less obvious, and additional criteria, such as X-ray detection, are needed. We discuss the properties of the sample as a whole and compare it with similar samples in other nearby galaxies., 43 pages, including 2 tables and 14 figures. Accepted for publication in ApJ

Massive stars play an important role in both cluster and galactic evolution and the rate at which they lose mass is a key driver of both their own evolution and their interaction with the environment up to and including their SNe explosions. Young massive clusters provide an ideal opportunity to study a co-eval population of massive stars. We performed 3mm continuum observations with the Atacama Large Millimetre/submillimetre Array of the Galactic cluster Westerlund 1, to study the constituent massive stars and determine mass-loss rates for the diverse post-main sequence population. We detected emission from 50 stars in Westerlund 1, comprising all 21 Wolf-Rayets within the field of view, eight cool and 21 OB super-/hypergiants. Emission nebulae were associated with a number of the cool hypergiants while, unexpectedly, a number of hot stars also appear spatially resolved. We measured the mass-loss rates for a unique population of massive post-main sequence stars at every stage of evolution, confirming a significant increase as stars transition from OB supergiant to WR states. The range of spectral types exhibited provides a critical test of radiatively driven wind theory and the reality of the bi-stability jump. The extreme mass-loss rate inferred for the interacting binary Wd1-9 in comparison to other cluster members confirmed the key role binarity plays in massive stellar evolution. The presence of compact nebulae around a number of OB and WR stars is unexpected; by analogy to the cool super-/hypergiants we attribute this to confinement and sculpting of the stellar wind via interaction with the intra-cluster medium/wind. Given the morphology of core collapse SNe depend on the nature of the pre-explosion circumstellar environment, if this hypothesis is correct then the properties of the explosion depend not just on the progenitor, but also the environment in which it is located., Comment: 35 pages, 20 figures, accepted for publication in A&A

In this paper, the integrated continuum radio spectrum of supernova remnant (SNR) W44 was analyzed up to 70 GHz, testing the different emission models that can be responsible for its particular shape. The observations by the Planck space telescope made possible to analyze the high frequency part of radio emission from SNRs. Although the quality of radio continuum spectrum (a high scatter of data points at same frequencies) prevents us to make definite conclusions, the possibility of spinning dust emission detection towards this remnant is emphasized. In addition, a concave-down feature, due to synchrotron losses, can not be definitely dismissed by the present knowledge of the integrated radio continuum spectrum of this SNR., submitted to Serb. Astron. J.; minor revision

We present new observations of the nebula around the Magellanic candidate Luminous Blue Variable S61. These comprise high-resolution data acquired with the Australia Telescope Compact Array (ATCA), the Atacama Large Millimetre/Submillimetre Array (ALMA), and VISIR at the Very Large Telescope (VLT). The nebula was detected only in the radio, up to 17 GHz. The 17 GHz ATCA map, with 0.8 arcsec resolution, allowed a morphological comparison with the H$\alpha$ Hubble Space Telescope image. The radio nebula resembles a spherical shell, as in the optical. The spectral index map indicates that the radio emission is due to free-free transitions in the ionised, optically thin gas, but there are hints of inhomogeneities. We present our new public code RHOCUBE to model 3D density distributions, and determine via Bayesian inference the nebula's geometric parameters. We applied the code to model the electron density distribution in the S61 nebula. We found that different distributions fit the data, but all of them converge to the same ionised mass, ~0.1 $\rm M\odot$, which is an order of magnitude smaller than previous estimates. We show how the nebula models can be used to derive the mass-loss history with high-temporal resolution. The nebula was probably formed through stellar winds, rather than eruptions. From the ALMA and VISIR non-detections, plus the derived extinction map, we deduce that the infrared emission observed by space telescopes must arise from extended, diffuse dust within the ionised region., Comment: 17 pages, 9 figures. Authors list corrected. In press in MNRAS. RHOCUBE code available online ( https://github.com/rnikutta/rhocube )

Characteristics of the flares of gamma rays detected from the Crab Nebula by the AGILE and Fermi-LAT satellite instruments are compared with those of a gamma ray burst recorded by several air shower arrays on February 23, 1989 and with one recent observation made by the ARGO-YBJ array. It is demonstrated that though pulsar-periodicity and energy spectra of emissions at 100 MeV (satellite gamma ray telescopes) and 100 TeV (EAS arrays) are different, their time structures seem to be similar. Moreover, maybe the difference between “flares” and “waves” recently found in the Crab Nebula emission by the AGILE team also exists at ultra-high energies.

We performed long-slit optical spectroscopy (GTC-OSIRIS) of 6 radio-loud QSOs at redshifts $2

We have conducted a detailed multi-wavelength study of the peculiar nebula Abell 48 and its central star. We classify the nucleus as a helium-rich, hydrogen-deficient star of type [WN4-5]. The evidence for either a massive WN or a low-mass [WN] interpretation is critically examined, and we firmly conclude that Abell 48 is a planetary nebula (PN) around an evolved low-mass star, rather than a Population I ejecta nebula. Importantly, the surrounding nebula has a morphology typical of PNe, and is not enriched in nitrogen, and thus not the `peeled atmosphere' of a massive star. We estimate a distance of 1.6 kpc and a reddening, E(B-V) = 1.90 mag, the latter value clearly showing the nebula lies on the near side of the Galactic bar, and cannot be a massive WN star. The ionized mass (~0.3 M_Sun) and electron density (700 cm^-3) are typical of middle-aged PNe. The observed stellar spectrum was compared to a grid of models from the Potsdam Wolf-Rayet (PoWR) grid. The best fit temperature is 71 kK, and the atmospheric composition is dominated by helium with an upper limit on the hydrogen abundance of 10 per cent. Our results are in very good agreement with the recent study of Todt et al., who determined a hydrogen fraction of 10 per cent and an unusually large nitrogen fraction of ~5 per cent. This fraction is higher than any other low-mass H-deficient star, and is not readily explained by current post-AGB models. We give a discussion of the implications of this discovery for the late-stage evolution of intermediate-mass stars. There is now tentative evidence for two distinct helium-dominated post-AGB lineages, separate to the helium and carbon dominated surface compositions produced by a late thermal pulse. Further theoretical work is needed to explain these recent discoveries., 19 pages, 10 figures, to appear in MNRAS. Version 3 incorporates proof corrections

Models for the spectral energy distributions of four stellar objects in the bright compact H nebula Cep B are constructed. With a high probability, three of them are found to be very young stellar objects of evolutionary class 0/I with ages of 10 4 -10 5 years, comparable to the kinematic age of the ionization front of the nebula itself. The IRAS 22551+6221 source associated with Cep B is initiated by heated dust. An intermediate-mass (B2-B3) star of evolutionary class III lies at the center of the ionization front. The local density of PMS stars in the immediate neighborhood of the Cep B nebula exceeds that for the cluster as a whole. It is highly probable that this zone is a local source of a new star-formation stage.

We present observations of the portion of the nearby spiral galaxy IC342 using narrow band [SII] and H$\alpha$ filters. These observations were carried out in November 2011 with the 2m RCC telescope at Rozhen National Astronomical Observatory in Bulgaria. In this paper we report coordinates, diameters, H$\alpha$ and [SII] fluxes for 203 HII regions detected in two fields of view in IC342 galaxy. The number of detected HII regions is 5 times higher than previously known in these two parts of the galaxy., Comment: 9 pages, 3 tables, 4 figures. Table 3 corrected + small corrections in the text

Abell 14 is a poorly studied object despite being considered a born again planetary nebula. We performed a detailed study of its 3D morphology and ionization structure using the SHAPE and MOCASSIN codes. We found that Abell 14 is a highly evolved, bipolar nebula with a kinematical age of $\sim$19,400 yr for a distance of 4 kpc. The high He abundance, and N/O ratio indicate a progenitor of 5 $M_{\odot}$ that has experienced the third dredge-up and hot bottom burning phases. The stellar parameters of the central source reveal a star at a highly evolved stage near to the white dwarf cooling track, being inconsistent with the born again scenario. The nebula shows unexpectedly strong [N I] $\lambda 5200$ and [O I] $\lambda 6300$ emission lines indicating possible shock interactions. Abell 14 appears to be a member of a small group of highly evolved, extreme Type-I PNe. The members of this group lie at the lower-left corner of the PNe regime on the [N II]/H$\alpha$ vs. [S II]/H$\alpha$ diagnostic diagram, where shock--excited regions/objects are also placed. The low luminosity of their central stars, in conjunction with the large physical size of the nebulae, result in a very low photo-ionization rate, which can make any contribution of shock interaction easily perceptible, even for small velocities., Comment: 12 pages, 9 figures and 4 tables, accepted for publication in MNRAS

This paper presents the Spitzer IRS (Infra Red Spectrograph) detection of mid-infrared polycyclic aromatic hydrocarbon (PAH) emission features and H2 associated with dense knots in the ring of the "oxygen-rich" (C/O~0.6-0.8) planetary nebula (PN) NGC6720 (Ring Nebula). We explored a further three oxygen-rich extended PNe with similar dataset available. These turned out to be non-detection of PAHs, although two of these do contain H2 emission knots. The presence of PAHs is discussed in the context of a bottom-up formation mechanism, in which first small hydrocarbons, and later PAHs, are formed in warm dense knots inside the ionised regions of PNe.

10 pages, 6 figures, RWT 152 is one of the few known planetary nebulae with an sdO central star. We present subarcsecond red tunable filterHa imaging and intermediate-resolution, long-slit spectroscopy of RWT 152 obtained with OSIRIS/GTC (Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy/Gran Telescopio Canarias) with the goal of analysing its properties. The Ha image reveals a bipolar nebula with a bright equatorial region and multiple bubbles in the main lobes. A faint circular halo surrounds the main nebula. The nebular spectra reveal a very low excitation nebula with weak emission lines from H+, He+ and double-ionized metals, and absence of emission lines from neutral and single-ionized metals, except for an extremely faint [NII] lambda 6584 emission line. These spectra may be explained if RWT 152 is a density-bounded planetary nebula. Low nebular chemical abundances of S, O, Ar, N and Ne are obtained in RWT 152, which, together with the derived high peculiar velocity (similar to 92-131 km s(-1)), indicate that this object is a halo planetary nebula. The available data are consistent with RWT 152 evolving from a low-mass progenitor (similar to 1 M-circle dot) formed in a metal-poor environment., This paper has been partially supported by grant AYA 2011-24052 (AA, ES), AYA 2011-30228-C3-01 (LFM), ESP2014-55996-C2-2-R (AU) and AYA2014-57369-C3-3-P (LFM) of the Spanish MINECO (all them co-funded by FEDER funds). We also acknowledge support from grant IN-CITE09 312191PR (AU, LFM, AA) of Xunta de Galicia, partially funded by FEDER funds, from grant PRX15/00511 (AU) of the Spanish MECD, and from grant 12VI20 (AU, LFM, AA) of the University of Vigo. AA also acknowledges support from FONDECYT through postdoctoral grant 3160364. This research has made use of the SIMBAD data base, operated at the CDS, Strasbourg (France), Aladin, NASA's Astrophysics Data System Bibliographic Services and the Spanish Virtual Observatory supported from the Spanish MINECO through grant AYA2011-24052.

43 stellar objects with Hα emission are discovered by slitless spectroscopy in a 14’ × 14' area near the nebula GM 2-41 located in the HII region DR 15 at the southern edge of the Cyg OB2 association. Emission is detected for the first time for 30 of these objects. Based on VI and JHK photometric data, the overwhelming majority of these objects are classified as young stellar objects in spectral classes F7-M3 with ages of ~1 Myr. The stars are distributed nonuniformly and form two groups which have the same coordinates as the UCHII regions G0.79 + 0.3 and G79.2 + 0.4.

Water fountains are evolved stars showing water masers with velocity spanning more than ~100 km/s. They usually appear at the end of the Asymptotic Giant Branch (AGB) phase or at the beginning of the post-AGB phase, and their masers trace the first manifestation of axisymmetric collimated mass-loss. For the first time, masers with water fountain characteristics have been detected towards a PN (IRAS 15103–5754), which might require a revision of the current theories about jet formation and survival times. IRAS 15103-5754 was observed using the ATCA interferometer at 22 GHz (both continuum and water maser). The main results of these observations are summarized here. The evolutionary classification of this object is also discussed.

We present new optical spectra of the nearby, bright, planetary nebula NGC 6778. The nebula has been known to emit strong recombination lines for more than 40 years but this is the first detailed study of its abundances. Heavy element abundances derived from recombination lines are found to exceed those from collisionally excited lines by a factor of ~20 in an integrated spectrum of the nebula, which is among the largest known abundance discrepancy factors. Spatial analysis of the spectra shows that the abundance discrepancy factor is strongly, centrally peaked, reaching ~40 close to the central star. The central star of NGC 6778 is known to be a short period binary, further strengthening the link between high nebular abundance discrepancy factors and central star binarity., 11 pages, 5 figures, 6 tables. Accepted for publication in the main journal of MNRAS

We report spectrophotometric observations made with SOFIA/FORCAST on 2011 June 2 UT. Optical measurements have previously shown that the abundance discrepancy factor (adf) varies with position in several high-adf PNe, and is highest close to the central star. The very low electron temperature inclusions postulated to explain the abundance discrepancy, must be cooled predominantly by fine structure IR lines. These SOFIA data will map mid-IR FS lines (and our related Herschel program will add several far-IR FS lines) in the bright, well-characterized, high-adf PN NGC 7009. We will compare these IR results with FS optical line measurements in order to correlate ratios of IR to optical fluxes with position, and thus correlate with where the adf peaks.

We report on the current status of the search for planetary nebulae (PNe) in the IPHAS survey, the 1800 square degree H-alpha survey of the Northern Galactic Plane carried out at La Palma Observatory. The first major installment of the “IPHAS Catalogue of Extended Nebulae” is presented. This includes a complete census of emission-line nebulae in 320 square degrees toward the inner regions of the Galaxy. In this area, more than 450 emission nebulae have been catalogued including 100 known PNe, and 155 new IPHAS candidate PNe.A vigorous programme of spectroscopic confirmation of IPHAS candidate PNe over the entire survey area is underway using a number of telescopes worldwide. So far, around one hundred new PNe over the whole IPHAS area have been spectroscopically confirmed. Their main properties, some outstanding examples, as well as the relevance of the IPHAS survey to determine the total PN population in the Galactic disc and its chemical gradient is discussed.

Using the data from the NOAO Local Group Survey, we have measured the Hα fluxes of 291 nebulae associated with 21 of the van den Bergh OB associations. We have combined these data together with six-color HST WFPC2 photometry, in order to identify the most UV-bright stars in the region. The simple purpose of this article is to explore the spatial relationships between these components. We find that there are basically three types of Hα-hot star morphology. One type consists of a very bright H II region, with a tightly spaced group of hot stars at or near its center; we refer to these as monolithic structures. A second common arrangement is that of a ringlike bubble structure with an often-empty central area, where the hot stars are concentrated. We construct simple models of these objects, which show that their photometric profiles are like those of spherical shells. We refer to these as bubble structures A third morphology is a scattered distribution of small nebulae with a few hot stars that are...

In the course of the XMM-Newton survey of the Small Magellanic Cloud (SMC), a region to the east of the emission nebula N19 was observed in November 2009. To search for new candidates for high mass X-ray binaries the EPIC PN and MOS data of the detected point sources were investigated and their spectral and temporal characteristics identified. A new transient (XMMUJ005011.2-730026= SXP214) with a pulse period of 214.05 s was discovered; the source had a hard X-ray spectrum with power-law index of ~0.65. The accurate X-ray source location permits the identification of the X-ray source with a ~15th magnitude Be star, thereby confirming this system as a new Be/X-ray binary.

We uniformly analyze 136 optically detected PNe and candidates from the GLIMPSE-I survey in order to to develop robust, multi-wavelength, classification criteria to augment existing diagnostics and provide pure PN samples. PNe represent powerful astrophysical probes. They are important dynamical tracers, key sources of ISM chemical enrichment, windows into late stellar evolution, and potent cosmological yardsticks. But their utility depends on separating them unequivocally from the many nebular mimics which can strongly resemble bona fide PNe in traditional optical images and spectra. We merge new PNe from the carefully evaluated, homogeneous MASH-I and MASH-II surveys, which offer a wider evolutionary range of PNe than hitherto available, with previously known PNe classified by SIMBAD. Mid-infrared (MIR) measurements vitally complement optical data because they reveal other physical processes and morphologies via fine-structure lines, molecular bands and dust. MIR colour-colour planes, optical emission line ratios and radio fluxes show the unambiguous classification of PNe to be complex, requiring all available evidence. Statistical trends provide predictive value and we offer quantitative MIR criteria to determine whether an emission nebula is most likely to be a PN or one of the frequent contaminants such as compact HII regions or symbiotic systems. Prerequisites have been optical images and spectra but MIR morphology, colours, environment and a candidate's MIR/radio flux ratio provide a more rigorous classification. Our ultimate goal is to recognize PNe using only MIR and radio characteristics, enabling us to trawl for PNe effectively even in heavily obscured regions of the Galaxy.

The well known Crab Nebula is at the center of the SN1054 supernova remnant. It consists of a rotationally-powered pulsar interacting with a surrounding nebula through a relativistic particle wind. The emissions originating from the pulsar and nebula have been considered to be essentially stable. Here we report the detection of strong gamma-ray (100 MeV-10 GeV) flares observed by the AGILE satellite in September, 2010 and October, 2007. In both cases, the unpulsed flux increased by a factor of 3 compared to the non-flaring flux. The flare luminosity and short timescale favor an origin near the pulsar, and we discuss Chandra Observatory X-ray and HST optical follow-up observations of the nebula. Our observations challenge standard models of nebular emission and require power-law acceleration by shock-driven plasma wave turbulence within a ~1-day timescale., Comment: 23 pages (including Supporting On-line Material), 8 figures, 1 table. Version published in Science Express on January 6, 2011 (available at http://www.sciencemag.org/content/early/2011/01/05/science.1200083)

This work focusses on MWC 922, the central object in the Red Square Nebula. We obtained low and medium resolution spectra of both, the central object and the surrounding nebula, using the DIS and TSpec spectrograph. The spectra show the whole spectral range between ~3 500 Å up to ~25 000 Å. The central object shows a plethora of emission lines, including many Fe II and forbidden Fe [II] lines. Here, we present the inventory of the emission lines of the central object, MWC 922. Future work will comprise the identification of the nebula emission lines by using newly obtained X-Shooter spectra. That way we want to gain further insight into the physical and chemical conditions in this environment. A comparison of the Red Square to the Red Rectangle Nebula is anticipated and will guide our search for DIBs in emission.