P. Boumis

National Observatory of Athens, Athínai, Attica, Greece

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Publications (11)20.43 Total impact

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    ABSTRACT: We present simultaneous observations of H2O maser emission and radio continuum at 1.3 cm carried out with the Australia Telescope Compact Array towards two sources, IRAS 16333−4807 and IRAS 12405−6219, catalogued as planetary nebula (PN) candidates, and where single-dish detections of H2O masers have been previously reported. Our goal was to unambiguously confirm the spatial association of the H2O masers with these two PN candidates. We detected and mapped H2O maser emission in both fields, but only in IRAS 16333−4807 the maser emission is spatially associated with the radio continuum emission. The properties of IRAS 16333−4807 provide strong support for the PN nature of the object, hereby confirming it as the fifth known case of an H2O maser-emitting PN. This source is bipolar, like the other four known H2O maser-emitting PNe, indicating that these sources might pertain to a usual, but short phase in the evolution of bipolar PNe. In IRAS 12405−6219, the H2O maser and radio continuum emission are not associated with each other and, in addition, the available data indicate that this source is an H ii region rather than a PN.
    Full-text · Article · Jul 2014 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We present 3D hydrodynamical simulations of an isotropic fast wind interacting with a previously ejected toroidally-shaped slow wind in order to model both the observed morphology and the kinematics of the planetary nebula (PN) NGC 6302. This source, also known as the Butterfly nebula, presents one of the most complex morphologies ever observed in PNe. From our numerical simulations, we have obtained an intensity map for the H$\alpha$ emission to make a comparison with the Hubble Space Telescope (HST) observations of this object. We have also carried out a proper motion (PM) study from our numerical results, in order to compare with previous observational studies. We have found that the two interacting stellar wind model reproduces well the morphology of NGC 6302, and while the PM in the models are similar to the observations, our results suggest that an acceleration mechanism is needed to explain the Hubble-type expansion found in HST observations.
    Full-text · Article · May 2014 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We present 3D hydrodynamical simulations of an isotropic fast wind interacting with a previously ejected toroidally shaped slow wind in order to model both the observed morphology and kinematics of the planetary nebula (PN) NGC 6302 (so-called the Butterfly Nebula). This nebula is among the most complex ever observed in PNe. From our numerical simulations, we have obtained an intensity map for H alpha emission to make a comparison with the Hubble Space Telescope observations of this object. We have also simulated the proper-motions of nebular knots and contrast them with those measured by comparing two set of observations. We have found that based on a generalized interacting stellar wind model, the morphology as well as the Hubble-type expansion indicated by the proper-motion measurements are explained.
    No preview · Article · Mar 2014
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    I. Leonidaki · P. Boumis · A. Zezas
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    ABSTRACT: We present the largest sample of multi-wavelength Supernova Remnants (SNRs) in six nearby galaxies, based on Chandra archival data and deep optical narrow-band Hα and [Sii] images as well as spectroscopic observations. We have identified 37 X-ray selected thermal SNRs, 30 of which are new identifications and ~ 400 optical SNRs, for 67 of which we spectroscopically verified their shock-excited nature. We discuss the properties of the X-ray/optically detected SNRs in different types of galaxies and hence different environments, in order to address their dependence on their Interstellar Medium (ISM). We also discuss the SNR populations in the context of the star formation rate of their host galaxies. We cross-correlate parameters of the optically detected SNRs with parameters of coincident X-ray emitting SNRs in order to understand their evolution and investigate possible selection effects.
    Preview · Article · Dec 2013 · Proceedings of the International Astronomical Union
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    ABSTRACT: In this Letter, we explore the hypothesis that the smooth appearance of bow shocks around some red supergiants (RSGs) might be caused by the ionization of their winds by external sources of radiation. Our numerical simulations of the bow shock generated by IRC −10414 (the first-ever RSG with an optically detected bow shock) show that the ionization of the wind results in its acceleration by a factor of 2, which reduces the difference between the wind and space velocities of the star and makes the contact discontinuity of the bow shock stable for a range of stellar space velocities and mass-loss rates. Our best-fitting model reproduces the overall shape and surface brightness of the observed bow shock and suggests that the space velocity and mass-loss rate of IRC −10414 are ≈50 km s−1 and ≈10−6 M⊙ yr−1, respectively, and that the number density of the local interstellar medium is ≈3 cm−3. It also shows that the bow shock emission comes mainly from the shocked stellar wind. This naturally explains the enhanced nitrogen abundance in the line-emitting material, derived from the spectroscopy of the bow shock. We found that photoionized bow shocks are ≈15–50 times brighter in optical line emission than their neutral counterparts, from which we conclude that the bow shock of IRC −10414 must be photoionized.
    Full-text · Article · Dec 2013 · Monthly Notices of the Royal Astronomical Society
  • L. Uscanga · P. Boumis
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    ABSTRACT: Planetary Nebulae (PNe) are one of the last phases in the evolution of low/intermediate mass stars (<8Msun), characterized by extended diffuse ionized and neutral gas surrounding the dying hot cores of highly evolved stars. Their immediate precursors are stars in the asymptotic giant branch (AGB), characterized by a strong mass-loss, followed by a short (100-10000 yr) transitional post-AGB phase. While the morphology of the mass-loss processes in the AGB phase is usually spherically symmetric, PNe show complex bipolar or multipolar structures. Diverse structural components of these evolved stars can be observed at different wavelengths, i.e., 1) ionised bipolar/multipolar structures in PNe, observed from optical to cm-wavelengths; 2) maser emission tracing outflows/discs in post- AGBs/extremely young Pne, observed at cm-wavelengths; 3) circumstellar molecular gas presumably tracing dense toroidal structures towards the centre of PNe, observed at mm/submm-wavelengths. These multi wavelength studies together with theoretical modelling (3D hydrodynamical simulations, kinematical models, and radiative transfer studies) are important to derive a complete picture of the evolution of low/intermediate mass stars. The aim of THEMOS project is to determine the genesis of the asymmetry in these evolved stars by studying their physical conditions, morphology, and kinematics of ionized and neutral gas. These studies will cover a wide range of spatial scales from hundreds of AU for optical studies, down to a few AU, using radio interferometric techniques. We will present our first results from our radio interferometric observations in PNe, as well as the hydrodynamical modeling of the morphology and kinematics of the PN NGC 6302.
    No preview · Article · Sep 2013
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    I. Leonidaki · P. Boumis · A. Zezas
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    ABSTRACT: We present results from a study of optically emitting Supernova Remnants (SNRs) in six nearby galaxies (NGC 2403, NGC 3077, NGC 4214, NGC 4395, NGC 4449 and NGC 5204) based on deep narrow band H{\alpha} and [SII] images as well as spectroscopic observations. The SNR classification was based on the detected sources that fulfill the well-established emission line flux criterion of [SII]/H{\alpha} > 0.4. This study revealed ~400 photometric SNRs down to a limiting H{\alpha} flux of 10^(-15) erg sec^(-1) cm^(-2). Spectroscopic observations confirmed the shock-excited nature of 56 out of the 96 sources with ([SII]/H{\alpha})$_{phot}$> 0.3 (our limit for an SNR classification) for which we obtained spectra. 11 more sources were spectroscopically identified as SNRs although their photometric [SII]/H{\alpha} ratio was below 0.3. We discuss the properties of the optically-detected SNRs in our sample for different types of galaxies and hence different environments, in order to address their connection with the surrounding interstellar medium. We find that there is a difference in [NII]/H{\alpha} line ratios of the SNR populations between different types of galaxies which indicates that this happens due to metallicity. We cross-correlate parameters of the optically detected SNRs ([SII]/H{\alpha} ratio, luminosity) with parameters of coincident X- ray emitting SNRs, resulted from our previous studies in the same sample of galaxies, in order to understand their evolution and investigate possible selection effects. We do not find a correlation between their H{\alpha} and X-ray luminosities, which we attribute to the presence of material in a wide range of temperatures. We also find evidence for a linear relation between the number of luminous optical SNRs (10^(37) erg sec^(-1)) and SFR in our sample of galaxies.
    Full-text · Article · Nov 2012 · Monthly Notices of the Royal Astronomical Society
  • I. Leonidaki · P. Boumis · A. Zezas
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    ABSTRACT: We present the detection of new optically emitting Supernova Remnants (SNRs) in six nearby galaxies, using deep narrow band Halpha and [S II] images as well as spectroscopic observations. The SNR classification was based on the detected sources that fulfill the well-established emission line flux criterion of [S II]/Halpha > 0.4. This study revealed ~400 photometric SNRs down to a limiting flux of 10-16 erg/sec /cm2, ~350 of which are new identifications. 130 photometric SNRs were spectroscopically observed and 63 outlined their shock-excited nature, verifying that the used photometric method is a robust diagnostic tool for the preliminary identification of SNRs. We compare the derived SNR properties (such as electron density, luminosity, number of SNRs) in different types of galaxies and hence different environments, in order to investigate their interaction with the surrounding interstellar medium. We also cross-correlate parameters of the optically detected SNRs ([S II]/Halpha ratio, luminosity) with parameters (temperature, luminosity) of coincident X- ray emitting SNRs, resulted from our previous studies in the same sample of galaxies, in order to understand their evolution and investigate possible selection effects.
    No preview · Article · Jan 2012
  • I. Leonidaki · A. Zezas · P. Boumis
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    ABSTRACT: We present the results from a study of the SNR populations in six nearby galaxies (NGC 2403, NGC 3077, NGC 4214, NGC 4395, NGC 4449 and NGC 5204) based on Chandra archival data. We have detected a sample of 244 discrete X-ray sources with fluxes down to 10-17 erg s-1 cm-2. A total number of 37 X-ray detected SNRs are identified, 30 of which are new, based on their X-ray colors and spectroscopy. We discuss the SNR properties (luminosity, temperature, density) of the X-ray detected SNRs in order to obtain information on their interaction with their environment. We also compare the luminosity distributions of X-ray SNRs in different types of galaxies with the number of our X-ray detected SNRs and we indicate differences between the SNR populations in spiral and irregular galaxies. On the basis of a multi-wavelength study of SNRs, we obtained deep images in the [S II] and Hα emission lines and we initially classified a large number of optical candidate SNRs based on their [S II] / Hα ratio. Follow-up spectro-photometric observations for a number of the candidate SNRs have also been obtained and their spectral signatures suggest that the detected emission originates from shock-heated gas.
    No preview · Article · Jul 2010
  • Andreas Zezas · Panos Boumis · Ioanna Leonidaki
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    ABSTRACT: We propose to obtain optical spectra of photometrically selected SNRs in 5 nearby galaxies (NGC 3077, NGC 4214, NGC 4395, NGC 4449 and NGC 5204), based on narrow-line imaging. In that way, we will confirm these identifications and obtain an accurate sample of extragalactic SNRs. These observations will provide a 2 order-of-magnitude improvement in sensitivity over similar previous surveys and therefore a more complete and representative picture of the SNR populations in different galactic environments. They will supplement existing deep Chandra observations by confirming the X-ray classification of the identified sample of thermal X-ray SNRs and will allow us to link their X-ray properties (temperature, luminosity) to their optical properties (H(alpha) luminosity, density) and local environment.
    No preview · Article · Feb 2010
  • Ioanna Leonidaki · A. Zezas · P. Boumis

    No preview · Article · Jul 2008