arXiv subjects

P. Boumis

Publications and source records attributed to P. Boumis.

At least 55 records · Page 3Linked to original sources

arXiv2015

Modeling the cometary structure of the planetary nebula HFG1 based on the evolution of its binary central star V664 Cas

HFG1 is the first well observed planetary nebula (PN) which reveals a cometary-like structure. Its main morphological features consist of a bow shaped shell, which surrounds the central star, accompanied by a long collimated tail. In this study we perform two-dimensional hydrodynamic simulations modeling the formation of HFG1 from the interaction of the local ambient medium with the mass outflows of its Asymptotic Giant Branch (AGB) progenitor star. We attribute the cometary appearance of HFG1 to the systemic motion of the PN with respect to the local ambient medium. Due to its vital importance, we re-estimate the distance of HFG1 by modeling the spectral energy distribution of its central star, V664 Cas, and we find a distance of $ 490 \pm 50$ pc. Our simulations show that none of our models with time invariant stellar wind and ambient medium properties are able to reproduce simultaneously the extended bow shock and the collimated tail observed in HFG1. Given this, we increase the complexity of our modeling considering that the stellar wind is time variable. The wind description is based on the predictions of the AGB and post-AGB evolution models. Testing a grid of models we find that the properties of HFG1 are best reproduced by the mass outflows of a 3 Msun AGB star. Such a scenario is consistent with the current observed properties of V664 Cas primary star, an O-type subdwarf, and bridges the evolutionary history of HFG1 central star with the observables of the PN. We discuss the implications of our study in the understanding of the evolution of AGB/post-AGB stars towards the formation of O-type subdwarfs surrounded by PNe.

astro-ph.SR↗

arXiv2015

Evidence for Rapid Variability in the Optical Light Curve of the Type Ia SN 2014J

We present results of high-cadence monitoring of the optical light curve of the nearby, Type Ia SN 2014J in M82 using the 2.3m Aristarchos telescope. $B$ and $V$-band photometry on days 15-18 after $t_{max}(B)$, obtained with a cadence of 2 min per band, reveals evidence for rapid variability at the 0.02-0.05 mag level on timescales of 15-60 min on all four nights, taking the red noise estimation at face value. The decline slope was measured to be steeper in the $B$-band than in $V$-band, and to steadily decrease in both bands from 0.15 mag/day (night 1) to 0.04 mag/day (night 4) in V and from 0.19 mag/day (night 1) to 0.06 mag/day (night 4) in B, corresponding to the onset of the secondary maximum. We propose that rapid variability could be due to one or a combination of the following scenarios: the clumpiness of the ejecta, their interaction with circumstellar material, the asymmetry of the explosion, or the mechanism causing the secondary maximum in the near-infrared light curve. We encourage the community to undertake high-cadence monitoring of future, nearby and bright supernovae to investigate the intraday behavior of their light curves.

astro-ph.SR↗

arXiv2015

NELIOTA: ESA's new NEO lunar impact monitoring project with the 1.2m telescope at the National Observatory of Athens

NELIOTA is a new ESA activity launched at the National Observatory of Athens in February 2015 aiming to determine the distribution and frequency of small near-earth objects (NEOs) via lunar monitoring. The project involves upgrading the 1.2m Kryoneri telescope at the National Observatory of Athens, procuring two fast-frame cameras, and developing a software system, which will control the telescope and the cameras, process the images and automatically detect NEO impacts. NELIOTA will provide a web-based user interface, where the impact events will be reported and made available to the scientific community and the general public. The objective of this 3.5 year activity is to design, develop and implement a highly automated lunar monitoring system, which will conduct an observing campaign for 2 years in search of NEO impact flashes on the Moon. The impact events will be verified, characterised and reported. The 1.2m telescope will be capable of detecting flashes much fainter than current, small-aperture, lunar monitoring telescopes. NELIOTA is therefore expected to characterise the frequency and distribution of NEOs weighing as little as a few grams.

astro-ph.EP↗

arXiv2015

Evidence for a [WR] or WEL-type binary nucleus in the bipolar planetary nebula Vy 1-2

We present high-dispersion spectroscopic data of the compact planetary nebula Vy 1-2, where high expansion velocities up to 100 km/s are found in the Ha, [N II] and [O III] emission lines. HST images reveal a bipolar structure. Vy 1-2 displays a bright ring-like structure with a size of 2.4"x3.2" and two faint bipolar lobes in the west-east direction. A faint pair of knots is also found, located almost symmetrically on opposite sides of the nebula at PA=305 degrees. Furthermore, deep low-dispersion spectra are also presented and several emission lines are detected for the first time in this nebula, such as the doublet [Cl III] 5517, 5537 A, [K IV] 6101 A, C II 6461 A, the doublet C IV 5801, 5812 A. By comparison with the solar abundances, we find enhanced N, depleted C and solar O. The central star must have experienced the hot bottom burning (CN-cycle) during the 2nd dredge-up phase, implying a progenitor star of higher than 3 solar masses. The very low C/O and N/O abundance ratios suggest a likely post-common envelope close binary system. A simple spherically symmetric geometry with either a blackbody or a H-deficient stellar atmosphere model is not able to reproduce the ionisation structure of Vy 1-2. The effective temperature and luminosity of its central star indicate a young nebula located at a distance of ~9.7 kpc with an age of ~3500 years. The detection of stellar emission lines, C II 6461 A, the doublet C IV λλ 5801, 5812 A and O III 5592 A, emitted from a H-deficient star, indicates the presence of a late-type Wolf-Rayet or a WEL type central star.

astro-ph.SR↗

arXiv2014

H$_2$O maser emission associated with the planetary nebula IRAS 16333$-$4807

We present simultaneous observations of H$_2$O maser emission and radio continuum at 1.3 cm carried out with the Australia Telescope Compact Array towards two sources, IRAS 16333$-$4807 and IRAS 12405$-$6219, catalogued as planetary nebula (PN) candidates, and where single-dish detections of H$_2$O masers have been previously reported. Our goal was to unambiguously confirm the spatial association of the H$_2$O masers with these two PN candidates. We detected and mapped H$_2$O maser emission in both fields, but only in IRAS 16333$-$4807 the maser emission is spatially associated with the radio continuum emission. The properties of IRAS 16333$-$4807 provide strong support for the PN nature of the object, hereby confirming it as the fifth known case of a H$_2$O maser-emitting PN. This source is bipolar, like the other four known H$_2$O maser-emitting PNe, indicating that these sources might pertain to a usual, but short phase in the evolution of bipolar PNe. In IRAS 12405$-$6219, the H$_2$O 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.

astro-ph.SR↗

arXiv2014

Modelling the 3D morphology and proper motions of the planetary nebula NGC 6302

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$α$ 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.

astro-ph.SR↗

arXiv2013

On the stability of bow shocks generated by red supergiants: the case of IRC-10414

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 two, 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 fit 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 $\approx$50 ${\rm km} \, {\rm s}^{-1}$ and $\approx$$10^{-6}$ $M_\odot \, {\rm yr}^{-1}$, respectively, and that the number density of the local ISM is $\approx$3 ${\rm cm}^{-3}$. 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 $\approx$15$-$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.

astro-ph.SR↗

arXiv2012

A multi-wavelength study of Supernova Remnants in six nearby galaxies. II. New optically selected Supernova Remnants

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 Hα 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]/Hα > 0.4. This study revealed ~400 photometric SNRs down to a limiting Hα 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]/Hα)$_{phot}$> 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]/Hα 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]/Hα 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]/Hα 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 Hα 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.

astro-ph.CO↗

arXiv2012

Discovery of optical candidate supernova remnants in Sagittarius

During an [O III] survey for planetary nebulae, we identified a region in Sagittarius containing several candidate Supernova Remnants and obtained deep optical narrow-band images and spectra to explore their nature. The images of the unstudied area have been obtained in the light of Halpha+[N II], [S II] and [O III]. The resulting mosaic covers an area of 1.4x1.0 deg^2 where filamentary and diffuse emission was discovered, suggesting the existence of more than one supernova remnants (SNRs) in the area. Deep long slit spectra were also taken of eight different regions. Both the flux calibrated images and the spectra show that the emission from the filamentary structures originates from shock-heated gas, while the photo-ionization mechanism is responsible for the diffuse emission. Part of the optical emission is found to be correlated with the radio at 4850 MHz suggesting their association, while the WISE infrared emission found in the area at 12 and 22 micron marginally correlates with the optical. The presence of the [O III] emission line in one of the candidate SNRs suggests shock velocities into the interstellar "clouds" between 120 and 200 km/s, while the absence in the other indicates slower shock velocities. For all candidate remnants the [S II] 6716/6731 ratio indicates electron densities below 240 cm^{-3}, while the Halpha emission has been measured to be between 0.6 to 41x10^{-17} erg/s/cm^2/arcsec^2. The existence of eight pulsars within 1.5deg away from the center of the candidate SNRs also supports the scenario of many SNRs in the area as well as that the detected optical emission could be part of a number of supernovae explosions.

astro-ph.GA↗

arXiv2009

A new candidate supernova remnant G 70.5+1.9

A compact complex of line emission filaments in the galactic plane has the appearance of those expected of an evolved supernova remnant though non-thermal radio and X-ray emission have not yet been detected. This optical emission line region has now been observed with deep imagery and both low and high-dispersion spectroscopy. Diagnostic diagrams of the line intensities from the present spectra and the new kinematical observations both point to a supernova origin. However, several features of the nebular complex still require an explanation within this interpretation.

astro-ph.GA↗

arXiv2009

Discovery of optical emission from the supernova remnant G 32.8-0.1 (Kes 78)

Deep optical CCD images of the supernova remnant G 32.8-0.1 were obtained where filamentary and diffuse emission was discovered. The images were acquired in the emission lines of Halpha+[N II] and [S II]. Filamentary and diffuse structures are detected in most areas of the remnant, while no significant [O III] emission is present. The flux-calibrated images suggest that the optical emission originates from shock-heated gas since the [S II]/Halpha ratio is greater than 1.2. The Spitzer images at 8 micron and 24 micron show a few filamentary structures to be correlated with the optical filaments, while the radio emission at 1.4 GHz in the same area is found to be very well correlated with the brightest optical filaments. Furthermore, the results from deep long-slit spectra also support the origin of the emission to be from shock-heated gas ([S II]/Halpha > 1.5). The absence of [O III] emission indicates slow shocks velocities into the interstellar "clouds" (< 100 km/s), while the [S II] 6716/6731 ratio indicates electron densities up to ~200 cm^{-3}. Finally, the Halpha emission is measured to lie between 1.8 to 4.6 x 10^{-17} erg/s/cm^2/arcsec^2, while from VGPS HI images a distance to the SNR is estimated to be between 6 to 8.5 kpc.

astro-ph.GA↗

arXiv2009

A long trail behind the planetary nebula HFG1 (PK 136+05) and its precataclysmic binary central star V664 Cas

A deep wide-field image in the light of the Halpha+[N II] emission lines, of the planetary nebula HFG1 which surrounds the precataclysmic binary system V664 Cas, has revealed a tail of emission at least 20' long, at a position angle of 316deg. Evidence is presented which suggests that this is an ~10^5 y old trail of shocked material, left behind V664 Cas as it ejects matter whilst ploughing through its local interstellar media at anywhere between 29 and 59 km/s depending on its distance from the Sun.

astro-ph.GA↗

arXiv2009

A high-speed bi-polar outflow from the archetypical pulsating star Mira A

Optical images and high-dispersion spectra have been obtained of the ejected material surrounding the pulsating AGB star Mira A. The two streams of knots on either side of the star, found in far ultra-viollet (FUV) GALEX images, have now been imaged clearly in the light of Halpha. Spatially resolved profiles of the same line reveal that the bulk of these knots form a bi-polar outflow with radial velocity extremes of +- 150 km/s with respect to the central star. The South stream is approaching and the North stream receding from the observer. A displacement away from Mira A between the position of one of the South stream knots in the new Halpha image and its position in the previous Palomar Observatory Sky Survey (POSS I) red plate has been noted. If interpreted as a consequence of expansion proper motions the bipolar outflow is tilted at 69deg +- 2deg to the plane of the sky, has an outflow velocity of 160 +- 10 km/s and is ~1000 y old.

astro-ph.GA↗

arXiv2008

Photometric study of selected cataclysmic variables II. Time-series photometry of nine systems

We present time-series photometry of nine cataclysmic variables: EI UMa, V844Her, V751 Cyg, V516 Cyg, GZ Cnc, TY Psc, V1315 Aql, ASAS J002511+1217.12, V1315 Aql and LN UMa. The observations were conducted at various observatories, covering 170 hours and comprising 7,850 data points in total. For the majority of targets we confirm previously reported periodicities and for some of them we give, for the first time, their spectroscopic orbital periods. For those dwarf-nova systems which we observed during both quiescence and outburst, the increase in brightness was followed by a decrease in the amount of flickering. Quasi-periodic oscillations have either been discovered, or were confirmed. For the eclipsing system V1315 Aql we have covered 9 eclipses, and obtained a refined orbital ephemeris. We find that, during its long baseline of observations, no change in the orbital period of this system has occurred. V1315 Aql also shows eclipses of variable depth.

astro-ph↗

arXiv2008

First optical detection from the supernova remnant G 15.1-1.6

Deep optical CCD images of the supernova remnant G 15.1-1.6 were obtained and filamentary and diffuse emission has been discovered. The images, taken in the emission lines of Halpha+[N II], [S II] and [O III], reveal filamentary and diffuse structures all around the remnant. The radio emission at 4850 MHz in the same area is found to be well correlated with the brightest optical filaments. The IRAS 60 micron emission may also be correlated with the optical emission but to a lesser extent. The flux calibrated images suggest that the optical emission originates from shock-heated gas ([S II]/Halpha > 0.4), while there is a possible HII region ([S II]/Halpha ~0.3) contaminating the supernova remnant's emission to the east. Furthermore, deep long-slit spectra were taken at two bright filaments and also show that the emission originates from shock heated gas. An [O III] filamentary structure has also been detected further to the west but it lies outside the remnant's boundaries and possibly is not associated to it. The [O III] flux suggests shock velocities into the interstellar "clouds" ~100 km/s, while the [S II] 6716/6731 ratio indicates electron densities up to ~250 cm^{-3}. Finally, the Halpha emission has been measured to be between 2 to 7 x 10^{-16} erg/s/cm^2/arcsec^2, while the lower limit to the distance is estimated at 2.2 kpc.

astro-ph↗

arXiv2007

Deep optical observations of the interaction of the SS 433 microquasar jet with the W 50 radio continuum shell

Four mosaics of deep, continuum-subtracted, CCD images have been obtained over the extensive galactic radio continuum shell, W 50, which surrounds the remarkable stellar system SS 433. Two of these mosaics in the Halpha+[N II] and [O III] 5007 A emission lines respectively cover a field of ~2.3 x 2.5 degr^2 which contains all of W 50 but at a low angular resolution of 5 arcsec. The third and fourth mosaics cover the eastern (in [O III] 5007 A) and western (in Halpha+[N II]) filamentary nebulosity respectively but at an angular resolution of 1 arcsec. These observations are supplemented by new low dispersion spectra and longslit, spatially resolved echelle spectra. The [O III] 5007 A images show for the first time the distribution of this emission in both the eastern and western filaments while new Halpha+[N II] emission features are also found in both of these regions. Approaching flows of faintly emitting material from the bright eastern filaments of up 100 km/s in radial velocity are detected. The present observations also suggest that the heliocentric systemic radial velocity of the whole system is 56+-2 km/s. Furthermore, very deep imagery and high resolution spectroscopy of a small part of the northern radio ridge of W 50 has revealed for the first time the very faint optical nebulosity associated with this edge. It is suggested that patchy foreground dust along the ~5 kpc sightline is inhibiting the detection of all of the optical nebulosity associated with W 50. The interaction of the microquasar jets of SS 433 with the W 50 shell is discussed.

astro-ph↗

arXiv2006

Abundant dust found in intergalactic space

Galactic dust constitutes approximately half of the elements more massive than helium produced in stellar nucleosynthesis. Notwithstanding the formation of dust grains in the dense, cool atmospheres of late-type stars, there still remain huge uncertainties concerning the origin and fate of galactic stardust. In this paper, we identify the intergalactic medium (i.e. the region between gravitationally-bound galaxies) as a major sink for galactic dust. We discover a systematic shift in the colour of background galaxies viewed through the intergalactic medium of the nearby M81 group. This reddening coincides with atomic, neutral gas previously detected between the group members. The dust-to-HI mass ratio is high (1/20) compared to that of the solar neighborhood (1/120) suggesting that the dust originates from the centre of one or more of the galaxies in the group. Indeed, M82, which is known to be ejecting dust and gas in a starburst-driven superwind, is cited as the probable main source.

astro-ph↗

arXiv2006

A deep mosaic of [O III] 5007 A CCD images of the environment of the LBV star P Cygni

A mosaic of six, deep, CCD images in the light of the [O III] 5007 A nebular emission line has been obtained with the 1.3-m Skinakas (Crete) telescope of the filamentary nebulosity surrounding P Cygni. The [O III] 5007 A line discriminates against confusing galactic H II regions along the same sight-lines and the new mosaic did not include the 4.8 mag. central star; a source of artifacts in the previous lower angular resolution observations. New giant `lobes' and `shells' are found to be clustered around P Cygni which must be the relics of historic eruptions between 2400 and up to ~10^5 yr ago.

astro-ph↗