TY - JOUR A1 - Bozzo, Enrico A1 - Ferrigno, Carlo A1 - Oskinova, Lida A1 - Ducci, Lorenzo T1 - Accretion of a clumped wind from a red supergiant donor on to a magnetar is suggested by the analysis of the XMM-Newton and NuSTAR observations of the X-ray binary 3A 1954+319 JF - Monthly notices of the Royal Astronomical Society N2 - 3A 1954+319 has been classified for a long time as a symbiotic X-ray binary, hosting a slowly rotating neutron star and an aged M red giant. Recently, this classification has been revised thanks to the discovery that the donor star is an M supergiant. This makes 3A 1954+319 a rare type of high-mass X-ray binary consisting of a neutron star and a red supergiant donor. In this paper, we analyse two archival and still unpublished XMM-Newton and NuSTAR observations of the source. We perform a detailed hardness ratio-resolved spectral analysis to search for spectral variability that could help investigating the structures of the inhomogeneous M supergiant wind from which the neutron star is accreting. We discuss our results in the context of wind-fed supergiant X-ray binaries and show that the newest findings on 3A 1954+319 reinforce the hypothesis that the neutron star in this system is endowed with a magnetar-like magnetic field strength (greater than or similar to 10(14) G). KW - accretion KW - stars: massive KW - stars: neutron KW - X-rays: binaries KW - X-rays: individual: 3A 1954+319 KW - X-rays: stars KW - accretion discs Y1 - 2021 U6 - https://doi.org/10.1093/mnras/stab3688 SN - 0035-8711 SN - 1365-2966 VL - 510 IS - 3 SP - 4645 EP - 4653 PB - Oxford Univ. Press CY - Oxford ER - TY - GEN A1 - Oskinova, Lida A1 - Guerrero, Martín A. A1 - Hénault-Brunet, Vincent A1 - Sun, W. A1 - Chu, You-Hua A1 - Evans, Chris A1 - Gallagher, John S. A1 - Gruendl, Robert A. A1 - Reyes-Iturbide, Jorge T1 - The slow X-ray pulsar SXP 1062 and associated supernova remnant in the Wing of the Small Magellanic Cloud T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe N2 - SXP 1062 is an exceptional case of a young neutron star in a wind-fed high-mass X-ray binary associated with a supernova remnant. A unique combination of measured spin period, its derivative, luminosity and young age makes this source a key probe for the physics of accretion and neutron star evolution. Theoretical models proposed to explain the properties of SXP 1062 shall be tested with new data. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 591 KW - stars: emission-line KW - Be KW - X-rays: binaries KW - pulsars: individual (SXP 1062) Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-415135 SN - 1866-8372 IS - 591 ER - TY - JOUR A1 - Toala, Jesús Alberto A1 - Oskinova, Lida A1 - Ignace, R. T1 - On the Absence of Non-thermal X-Ray Emission around Runaway O Stars JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters N2 - Theoretical models predict that the compressed interstellar medium around runaway O stars can produce highenergy non-thermal diffuse emission, in particular, non-thermal X-ray and gamma-ray emission. So far, detection of nonthermal X-ray emission was claimed for only one runaway star, AE Aur. We present a search for non-thermal diffuse X-ray emission from bow shocks using archived XMM-Newton observations for a clean sample of six welldetermined runaway O stars. We find that none of these objects present diffuse X-ray emission associated with their bow shocks, similarly to previous X-ray studies toward. zeta ph and BD+ 43 degrees 3654. We carefully investigated multi-wavelength observations of AE Aur and could not confirm previous findings of non-thermal X-rays. We conclude that so far there is no clear evidence of non-thermal extended emission in bow shocks around runaway O stars. KW - stars: massive KW - stars: mass-loss KW - stars: winds, outflows KW - X-rays: ISM Y1 - 2017 U6 - https://doi.org/10.3847/2041-8213/aa667c SN - 2041-8205 SN - 2041-8213 VL - 838 SP - 1 EP - 32 PB - IOP Publ. Ltd. CY - Bristol ER - TY - GEN A1 - Guerrero, Martín A. A1 - Chu, You-Hua A1 - Hamann, Wolf-Rainer A1 - Oskinova, Lida A1 - Schönberner, Detlef A1 - Todt, Helge Tobias A1 - Steffen, Matthias A1 - Ruiz, Nieves A1 - Gruendl, Robert A. A1 - Blair, William P. T1 - Ablation and wind mass-loading in the born-again planetary nebula A 30 T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 563 KW - planetary nebulae: individual (A 30) KW - X-rays: ISM Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-412341 SN - 1866-8372 IS - 563 ER - TY - JOUR A1 - Ignace, R. A1 - Toalá, Jesús Alberto A1 - Oskinova, Lida T1 - Inversion of Intensity Profiles for Bubble Emissivity JF - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015 N2 - Under the assumption of spherical symmetry, the run of intensity with impact parameter for a spatially resolved and optically thin bubble can be inverted for an "effective emissivity" as a function of radius. The effective emissivity takes into account instrumental sensitivity and even interstellar absorption. This work was supported by a grant from NASA (G03-14008X). Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88432 SP - 358 ER - TY - JOUR A1 - Guerrero, Martín A. A1 - Ruiz, N. A1 - Hamann, Wolf-Rainer A1 - Chu, Y.-H. A1 - Todt, Helge Tobias A1 - Schönberner, Detlef A1 - Oskinova, Lida A1 - Gründl, R. A. A1 - Steffen, M. A1 - Blair, William P. A1 - Toala, Jesús Alberto T1 - Rebirth of X-Ray emission from the born-again planetary Nebula A30 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - The planetary nebula A30 is believed to have undergone a very late thermal pulse resulting in the ejection of knots of hydrogen-poor material. Using multi-epoch Hubble Space Telescope images, we have detected the angular expansion of these knots and derived an age of 850(-150)(+280) yr. To investigate the spectral and spatial properties of the soft X-ray emission detected by ROSAT, we have obtained Chandra and XMM-Newton deep observations of A30. The X-ray emission from A30 can be separated into two components: a point source at the central star and diffuse emission associated with the hydrogen-poor knots and the cloverleaf structure inside the nebular shell. To help us assess the role of the current stellar wind in powering this X-ray emission, we have determined the stellar parameters and wind properties of the central star of A30 using a non-LTE model fit to its optical and UV spectra. The spatial distribution and spectral properties of the diffuse X-ray emission are highly suggestive that it is generated by the post-born-again and present fast stellar winds interacting with the hydrogen-poor ejecta of the born-again event. This emission can be attributed to shock-heated plasma, as the hydrogen-poor knots are ablated by the stellar winds, under which circumstances the efficient mass loading of the present fast stellar wind raises its density and damps its velocity to produce the observed diffuse soft X-rays. Charge transfer reactions between the ions of the stellar winds and material of the born-again ejecta have also been considered as a possible mechanism for the production of diffuse X-ray emission, and upper limits on the expected X-ray production by this mechanism have been derived. The origin of the X-ray emission from the central star of A30 is puzzling: shocks in the present fast stellar wind and photospheric emission can be ruled out, while the development of a new, compact hot bubble confining the fast stellar wind seems implausible. KW - planetary nebulae: general KW - planetary nebulae: individual (A30) KW - stars: winds, outflows KW - X-rays: ISM Y1 - 2012 U6 - https://doi.org/10.1088/0004-637X/755/2/129 SN - 0004-637X VL - 755 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Fang, X. A1 - Guerrero, Martín A. A1 - Marquez-Lugo, R. A. A1 - Toala, Jesús Alberto A1 - Arthur, S. J. A1 - Chu, Y.-H. A1 - Blair, William P. A1 - Gruendl, R. A. A1 - Hamann, Wolf-Rainer A1 - Oskinova, Lida A1 - Todt, Helge Tobias T1 - Expansion of hydrogen-poor knots in the born-again planetary nebulae A30 and A78 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We analyze the expansion of hydrogen-poor knots and filaments in the born-again planetary nebulae A30 and A78 based on Hubble Space Telescope ( HST) images obtained almost 20 yr apart. The proper motion of these features generally increases with distance to the central star, but the fractional expansion decreases, i.e., the expansion is not homologous. As a result, there is not a unique expansion age, which is estimated to be 610-950 yr for A30 and 600-1140 yr for A78. The knots and filaments have experienced complex dynamical processes: the current fast stellar wind is mass loaded by the material ablated from the inner knots; the ablated material is then swept up until it shocks the inner edges of the outer, hydrogen-rich nebula. The angular expansion of the outer filaments shows a clear dependence on position angle, indicating that the interaction of the stellar wind with the innermost knots channels the wind along preferred directions. The apparent angular expansion of the innermost knots seems to be dominated by the rocket effect of evaporating gas and by the propagation of the ionization front inside them. Radiation-hydrodynamical simulations show that a single ejection of material followed by a rapid onset of the stellar wind and ionizing flux can reproduce the variety of clumps and filaments at different distances from the central star found in A30 and A78. KW - ISM: kinematics and dynamics KW - planetary nebulae: individual (A30 and A78) Y1 - 2014 U6 - https://doi.org/10.1088/0004-637X/797/2/100 SN - 0004-637X SN - 1538-4357 VL - 797 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Oskinova, Lida A1 - Sun, W. A1 - Evans, C. J. A1 - Henault-Brunet, V. A1 - Chu, Y.-H. A1 - Gallagher, J. S. A1 - Guerrero, Martín A. A1 - Gruendl, R. A. A1 - Güdel, M. A1 - Silich, S. A1 - Chen, Y. A1 - Naze, Y. A1 - Hainich, Rainer A1 - Reyes-Iturbide, J. T1 - Discovery of x-ray emission from young suns in the small magellanic cloud JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We report the discovery of extended X-ray emission within the young star cluster NGC 602a in the Wing of the Small Magellanic Cloud (SMC) based on observations obtained with the Chandra X-Ray Observatory. X-ray emission is detected from the cluster core area with the highest stellar density and from a dusty ridge surrounding the H II region. We use a census of massive stars in the cluster to demonstrate that a cluster wind or wind-blown bubble is unlikely to provide a significant contribution to the X-ray emission detected from the central area of the cluster. We therefore suggest that X-ray emission at the cluster core originates from an ensemble of low-and solar-mass pre-main-sequence (PMS) stars, each of which would be too weak in X-rays to be detected individually. We attribute the X-ray emission from the dusty ridge to the embedded tight cluster of the newborn stars known in this area from infrared studies. Assuming that the levels of X-ray activity in young stars in the low-metallicity environment of NGC 602a are comparable to their Galactic counterparts, then the detected spatial distribution, spectral properties, and level of X-ray emission are largely consistent with those expected from low-and solar-mass PMS stars and young stellar objects (YSOs). This is the first discovery of X-ray emission attributable to PMS stars and YSOs in the SMC, which suggests that the accretion and dynamo processes in young, low-mass objects in the SMC resemble those in the Galaxy. KW - Magellanic Clouds KW - ISM: bubbles KW - H II regions KW - stars: winds, outflows KW - stars: pre-main sequence KW - X-rays: stars Y1 - 2013 U6 - https://doi.org/10.1088/0004-637X/765/1/73 SN - 0004-637X VL - 765 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Toala, Jesús Alberto A1 - Guerrero, Martín A. A1 - Todt, Helge Tobias A1 - Hamann, Wolf-Rainer A1 - Chu, Y.-H. A1 - Gruendl, R. A. A1 - Schönberner, Detlef A1 - Oskinova, Lida A1 - Marquez-Lugo, R. A. A1 - Fang, X. A1 - Ramos-Larios, Gerardo T1 - The born-again Planetary nebula A78: an X-RAY twin of A30 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We present the XMM-Newton discovery of X-ray emission from the planetary nebula (PN) A78, the second born-again PN detected in X-rays apart from A30. These two PNe share similar spectral and morphological characteristics: they harbor diffuse soft X-ray emission associated with the interaction between the H-poor ejecta and the current fast stellar wind and a point-like source at the position of the central star (CSPN). We present the spectral analysis of the CSPN, using for the first time an NLTE code for expanding atmospheres that takes line blanketing into account for the UV and optical spectra. The wind abundances are used for the X-ray spectral analysis of the CSPN and the diffuse emission. The X-ray emission from the CSPN in A78 can be modeled by a single C VI emission line, while the X-ray emission from its diffuse component is better described by an optically thin plasma emission model with a temperature of kT = 0.088 keV (T approximate to 1.0 x 10(6) K). We estimate X-ray luminosities in the 0.2-2.0 keV energy band of L-X,L-CSPN =(1.2 +/- 0.3) x 10(31) erg s(-1) and L-X,L-DIFF =(9.2 +/- 2.3) x 10(30) erg s(-1) for the CSPN and diffuse components, respectively. KW - planetary nebulae: general KW - planetary nebulae: individual (A78) KW - stars: winds, outflows KW - X-rays: ISM Y1 - 2015 U6 - https://doi.org/10.1088/0004-637X/799/1/67 SN - 0004-637X SN - 1538-4357 VL - 799 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Henault-Brunet, V. A1 - Oskinova, Lida A1 - Guerrero, Martín A. A1 - Sun, W. A1 - Chu, Y.-H. A1 - Evans, C. J. A1 - Gallagher, J. S. A1 - Gruendl, R. A. A1 - Reyes-Iturbide, J. T1 - Discovery of a Be/X-ray pulsar binary and associated supernova remnant in the wing of the small magellanic cloud JF - Monthly notices of the Royal Astronomical Society N2 - We report on a new Be/X-ray pulsar binary located in the Wing of the Small Magellanic Cloud (SMC). The strong pulsed X-ray source was discovered with the Chandra and XMM-Newton X-ray observatories. The X-ray pulse period of 1062 s is consistently determined from both Chandra and XMM-Newton observations, revealing one of the slowest rotating X-ray pulsars known in the SMC. The optical counterpart of the X-ray source is the emission-line star 2dFS 3831. Its B0-0.5(III)e+ spectral type is determined from VLT-FLAMES and 2dF optical spectroscopy, establishing the system as a Be/X-ray binary (Be-XRB). The hard X-ray spectrum is well fitted by a power law with additional thermal and blackbody components, the latter reminiscent of persistent Be-XRBs. This system is the first evidence of a recent supernova in the low-density surroundings of NGC602. We detect a shell nebula around 2dFS 3831 in H alpha and [OIII] images and conclude that it is most likely a supernova remnant. If it is linked to the supernova explosion that created this new X-ray pulsar, its kinematic age of (2-4) x 10(4) yr provides a constraint on the age of the pulsar. KW - stars: emission-line, Be KW - ISM: supernova remnants KW - Magellanic Clouds KW - X-rays: binaries Y1 - 2012 U6 - https://doi.org/10.1111/j.1745-3933.2011.01183.x SN - 0035-8711 VL - 420 IS - 1 SP - L13 EP - L17 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Toala, Jesús Alberto A1 - Oskinova, Lida A1 - Gonzalez-Galan, Ana A1 - Guerrero, Martín A. A1 - Ignace, R. A1 - Pohl, Martin T1 - X-RAY OBSERVATIONS OF BOW SHOCKS AROUND RUNAWAY O STARS. THE CASE OF zeta OPH AND BD+43 degrees 3654 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - Non-thermal radiation has been predicted within bow shocks around runaway stars by recent theoretical works. We present X-ray observations toward the runaway stars zeta Oph by Chandra and Suzaku and of BD+43 degrees 3654 by XMM-Newton to search for the presence of non-thermal X-ray emission. We found no evidence of non-thermal emission spatially coincident with the bow shocks; nonetheless, diffuse emission was detected in the vicinity of zeta Oph. After a careful analysis of its spectral characteristics, we conclude that this emission has a thermal nature with a plasma temperature of T approximate to 2 x 10(6) K. The cometary shape of this emission seems to be in line with recent predictions of radiation-hydrodynamic models of runaway stars. The case of BD+43 degrees 3654 is puzzling, as non-thermal emission has been reported in a previous work for this source. KW - stars: individual (zeta Oph, BD+43 degrees 3654) KW - stars: winds, outflows Y1 - 2016 U6 - https://doi.org/10.3847/0004-637X/821/2/79 SN - 0004-637X SN - 1538-4357 VL - 821 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Sidoli, Lara A1 - Sguera, Vito A1 - Esposito, Paolo A1 - Oskinova, Lida A1 - Polletta, Maria del Carmen T1 - XMM-Newton discovery of very high obscuration in the candidate Supergiant Fast X-ray Transient AX J1714.1-3912 JF - Monthly notices of the Royal Astronomical Society N2 - We have analysed an archival XMM-Newton EPIC observation that serendipitously covered the sky position of a variable X-ray source AX J1714.1-3912, previously suggested to be a Supergiant Fast X-ray Transient (SFXT). During the XMM-Newton observation the source is variable on a timescale of hundred seconds and shows two luminosity states, with a flaring activity followed by unflared emission, with a variability amplitude of a factor of about 50. We have discovered an intense iron emission line with a centroid energy of 6.4 keV in the power law-like spectrum, modified by a large absorption (N-H similar to 10(24) cm(-2)), never observed before from this source. This X-ray spectrum is unusual for an SFXT, but resembles the so-called 'highly obscured sources', high mass X-ray binaries (HMXBs) hosting an evolved B[e] supergiant companion (sgB[e]). This might suggest that AX J1714.1-3912 is a new member of this rare type of HMXBs, which includes IGR J16318-4848 and CI Camelopardalis. Increasing this small population of sources would be remarkable, as they represent an interesting short transition evolutionary stage in the evolution of massive binaries. Nevertheless, AX J1714.1-3912 appears to share X-ray properties of both kinds of HMXBs (SFXT versus sgB[e] HMXB). Therefore, further investigations of the companion star are needed to disentangle the two hypothesis. KW - X-rays: binaries KW - X-rays: individual: AX J1714.1-3912 Y1 - 2022 U6 - https://doi.org/10.1093/mnras/stac691 SN - 0035-8711 SN - 1365-2966 VL - 512 IS - 2 SP - 2929 EP - 2935 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Toala, Jesús Alberto A1 - Oskinova, Lida A1 - Hamann, Wolf-Rainer A1 - Ignace, Richard A1 - Sander, Andreas Alexander Christoph A1 - Shenar, Tomer A1 - Todt, Helge Tobias A1 - Chu, Y. -H. A1 - Guerrero, Martin A. A1 - Hainich, Rainer A1 - Torrejon, Jose Miguel T1 - On the Apparent Absence of Wolf-Rayet plus Neutron Star Systems BT - the Curious Case of WR124 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters N2 - Among the different types of massive stars in advanced evolutionary stages is the enigmatic WN8h type. There are only a few Wolf-Rayet (WR) stars with this spectral type in our Galaxy. It has long been suggested that WN8h-type stars are the products of binary evolution that may harbor neutron stars (NS). One of the most intriguing WN8h stars is the runaway WR 124 surrounded by its magnificent nebula M1-67. We test the presence of an accreting NS companion in WR 124 using similar to 100 ks long observations by the Chandra X-ray observatory. The hard X-ray emission from WR 124 with a luminosity of L-X similar to 10(31) erg s(-1) is marginally detected. We use the non-local thermodynamic equilibrium stellar atmosphere code PoWR to estimate the WR wind opacity to the X-rays. The wind of a WN8-type star is effectively opaque for X-rays, hence the low X-ray luminosity of WR 124 does not rule out the presence of an embedded compact object. We suggest that, in general, high-opacity WR winds could prevent X-ray detections of embedded NS, and be an explanation for the apparent lack of WR+NS systems. KW - circumstellar matter KW - ISM: jets and outflows KW - stars: massive KW - stars: evolution KW - stars: neutron KW - stars: Wolf-Rayet Y1 - 2018 U6 - https://doi.org/10.3847/2041-8213/aaf39d SN - 2041-8205 SN - 2041-8213 VL - 869 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - González-Galán, Ana A1 - Oskinova, Lida A1 - Popov, Sergei B. A1 - Haberl, F. A1 - Kühnel, M. A1 - Gallagher, John S. A1 - Schurch, Matthew A1 - Guerrero, Martín A. T1 - A multiwavelength study of SXP 1062, the long-period X-ray pulsar associated with a supernova remnant JF - Monthly notices of the Royal Astronomical Society N2 - SXP 1062 is a Be X-ray binary (BeXB) located in the Small Magellanic Cloud. It hosts a long-period X-ray pulsar and is likely associated with the supernova remnant MCSNR J0127−7332. In this work we present a multiwavelength view on SXP 1062 in different luminosity regimes. We consider monitoring campaigns in optical (OGLE survey) and X-ray (Swift telescope). During these campaigns a tight coincidence of X-ray and optical outbursts is observed. We interpret this as typical Type I outbursts as often detected in BeXBs at periastron passage of the neutron star (NS). To study different X-ray luminosity regimes in depth, during the source quiescence we observed it with XMM–Newton while Chandra observations followed an X-ray outburst. Nearly simultaneously with Chandra observations in X-rays, in optical the RSS/SALT telescope obtained spectra of SXP 1062. On the basis of our multiwavelength campaign we propose a simple scenario where the disc of the Be star is observed face-on, while the orbit of the NS is inclined with respect to the disc. According to the model of quasi-spherical settling accretion our estimation of the magnetic field of the pulsar in SXP 1062 does not require an extremely strong magnetic field at the present time. KW - stars: neutron KW - pulsars: individual: SXP 1062 KW - galaxies: individual: Small Magellanic Cloud KW - X-rays: binaries Y1 - 2017 U6 - https://doi.org/10.1093/mnras/stx3127 SN - 0035-8711 SN - 1365-2966 VL - 475 IS - 2 SP - 2809 EP - 2821 PB - Oxford University Press CY - Oxford ER - TY - JOUR A1 - Oskinova, Lida A1 - Schaerer, Daniel T1 - Ionization of He II in star-forming galaxies by X-rays from cluster winds and superbubbles JF - Astronomy and astrophysics : an international weekly journal N2 - The nature of the sources powering nebular He II emission in star-forming galaxies remains debated, and various types of objects have been considered, including Wolf-Rayet stars, X-ray binaries, and Population III stars. Modern X-ray observations show the ubiquitous presence of hot gas filling star-forming galaxies. We use a collisional ionization plasma code to compute the specific He II ionizing flux produced by hot gas and show that if its temperature is not too high (less than or similar to 2.5 MK), then the observed levels of soft diffuse X-ray radiation could explain He II ionization in galaxies. To gain a physical understanding of this result, we propose a model that combines the hydrodynamics of cluster winds and hot superbubbles with observed populations of young massive clusters in galaxies. We find that in low-metallicity galaxies, the temperature of hot gas is lower and the production rate of He II ionizing photons is higher compared to high-metallicity galaxies. The reason is that the slower stellar winds of massive stars in lower-metallicity galaxies input less mechanical energy in the ambient medium. Furthermore, we show that ensembles of star clusters up to similar to 10-20 Myr old in galaxies can produce enough soft X-rays to induce nebular He II emission. We discuss observations of the template low-metallicity galaxy I Zw 18 and suggest that the He II nebula in this galaxy is powered by a hot superbubble. Finally, appreciating the complex nature of stellar feedback, we suggest that soft X-rays from hot superbubbles are among the dominant sources of He II ionizing flux in low-metallicity star-forming galaxies. KW - galaxies KW - ISM KW - high-redshift KW - bubbles KW - X-rays Y1 - 2022 U6 - https://doi.org/10.1051/0004-6361/202142520 SN - 0004-6361 SN - 1432-0746 VL - 661 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Geist, Emily A1 - Gallagher, John S. A1 - Kotulla, Ralf A1 - Oskinova, Lida A1 - Hamann, Wolf-Rainer A1 - Ramachandran, Varsha A1 - Sabbi, Elena A1 - Smith, Linda J. A1 - Kniazev, Alexey A1 - Nota, Antonella A1 - Rickard, Matthew J. T1 - Ionization and star formation in the giant H ii region SMC-N66 JF - Publications of the Astronomical Society of the Pacific N2 - The NGC 346 young stellar system and associated N66 giant H ii region in the Small Magellanic Cloud are the nearest example of a massive star-forming event in a low metallicity (Z approximate to 0.2Z (circle dot)) galaxy. With an age of less than or similar to 3 Myr this system provides a unique opportunity to study relationships between massive stars and their associated H ii region. Using archival data, we derive a total H alpha luminosity of L(H alpha) = 4.1 x 10(38) erg s(-1) corresponding to an H-photoionization rate of 3 x 10(50) s(-1). A comparison with a predicted stellar ionization rate derived from the more than 50 known O-stars in NGC 346, including massive stars recently classified from Hubble Space Telescope far-ultraviolet (FUV) spectra, indicates an approximate ionization balance. Spectra obtained with SALT suggest the ionization structure of N66 could be consistent with some leakage of ionizing photons. Due to the low metallicity, the FUV luminosity from NGC 346 is not confined to the interstellar cloud associated with N66. Ionization extends through much of the spatial extent of the N66 cloud complex, and most of the cloud mass is not ionized. The stellar mass estimated from nebular L(H alpha) appears to be lower than masses derived from the census of resolved stars which may indicate a disconnect between the formation of high and low mass stars in this region. We briefly discuss implications of the properties of N66 for studies of star formation and stellar feedback in low metallicity environments. Y1 - 2022 U6 - https://doi.org/10.1088/1538-3873/ac697b SN - 0004-6280 SN - 1538-3873 VL - 134 IS - 1036 PB - IOP Publishing CY - Bristol ER - TY - JOUR A1 - Shrader, C. R. A1 - Hamaguchi, K. A1 - Sturner, Steven J. A1 - Oskinova, Lida A1 - Almeyda, T. A1 - Petre, R. T1 - Hifg-energy properties of the enigmatic be STAR gamma Cassiopeiae JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We present the results of a broadband X-ray study of the enigmatic Be star Gamma Cassiopeiae (herein gamma Cas) based on observations made with both the Suzaku and INTEGRAL observatories.. Cas has long been recognized as the prototypical example of a small subclass of Be stars with moderately strong X-ray emission dominated by a hot thermal component in the 0.5-12 keV energy range (L-x approximate to 10(32)-10(33) erg s(-1)). This places them at the high end of the known luminosity distribution for stellar emission, but several orders of magnitude below typical accretion-powered Be X-ray binaries. The INTEGRAL observations spanned an eight-year baseline and represent the deepest measurement to date at energies above similar to 50 keV. We find that the INTEGRAL data are consistent within statistics to a constant intensity source above 20 keV, with emission extending up to similar to 100 keV, and that searches for all of the previously reported periodicities of the system at lower energies led to null results. We further find that our combined Suzaku and INTEGRAL spectrum, which we suggest is the most accurate broadband X-ray measurement of gamma Cas to date, is fitted extremely well with a thermal plasma emission model with a single absorption component. We found no compelling need for an additional non-thermal high-energy component. We discuss these results in the context of a currently favored models for gamma Cas and its analogs. KW - gamma rays: stars KW - stars: emission-line, Be KW - stars: individual (gamma Cassiopeiae) KW - white dwarfs KW - X-rays: binaries KW - X-rays: stars Y1 - 2015 U6 - https://doi.org/10.1088/0004-637X/799/1/84 SN - 0004-637X SN - 1538-4357 VL - 799 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER -