Found 9 talks width keyword planetary nebulae

Henri_MJ_Boffin_180517s
Thursday May 17, 2018
Dr. Henri M. J. Boffin
ESO, Garching

Abstract

Binarity and mass transfer appear to play a key role in the shaping and, most likely, in the formation of planetary nebulae (PNe), thereby explaining the large fraction of axisymmetric morphologies. I present the binary hypothesis for PNe and its current status. Recent discoveries have led to a dramatic increase in the number of post-common envelope binary central stars of PNe, thereby allowing us to envisage statistical studies. Moreover, these binary systems let us study in detail the mass transfer episodes before and after the common envelope, and I present the evidences for mass transfer - and accretion - prior to the common envelope phase.


Xuan_Fang_151104s
Wednesday November 4, 2015
Dr. Xuan Fang
IAA-CSIC

Abstract

Planetary nebulae (PNe) are excellent tracers to study the chemistry, kinematics, and stellar populations of galaxies.  They can be used to
constrain the properties of galactic substructures and peer into the past tidal interactions.  In this talk, I present our successful GTC observations of PNe in the Northern Spur and the Giant Stream, two
most prominent substructures of M31.  The deep spectroscopy enabled detection of the weak [O III] 4363 temperature-diagnostic line in all target PNe and as a consequence, reliable determination of elemental abundances. Our PN sample have homogeneous oxygen abundances, although
slight difference between the two substructures are marginally noticed. The study of abundances and the spatial and kinematical properties of our sample leads to the tempting conclusions: 1) their progenitors might
belong to the same stellar population, and 2) the Northern Spur and the Giant Stream may have the same origin and may be explained by the stellar orbit proposed by Merrett et al.
The dwarf satellite M32 might be responsible for the two substructures. Deep spectroscopy of PNe in M32 will help to assess this hypothesis.


jesus_toala_150716s
Thursday July 16, 2015
Mr. Jesús Toala
Instituto de Astrofísica de Andalucía

Abstract

In this talk we will present our most recent numerical and observational results on the formation, evolution, and X-ray emission from hot bubbles in nebulae around evolved stars. Our studies include hot bubbles around massive and low-mass stars, e.g., Wolf-Rayet nebulae and planetary nebulae. Our results show that the diffuse X-ray emission from these hot bubbles is a dynamic process that involves mixing of nebular material into the hot bubble due to hydrodynamical instabilities, photoevaporation, thermal conduction, and dust cooling. The formation of these hot bubbles is governed by the evolution of the stellar wind parameters, and its properties can be used to study stellar evolution.


nicholas_sterling_150707s
Tuesday July 7, 2015
Dr. Nicholas C. Sterling
University of West-Georgia, USA

Abstract

The origins of neutron(n)-capture elements (atomic number Z > 30) have historically been discerned from the interpretation of stellar spectra. However, in the last decade nebular spectroscopy has been demonstrated to be a potentially powerful new tool to study the nucleosynthesis of n-capture elements. In this talk, I will discuss exciting new advances made in this field with near-infrared and optical observations of planetary nebulae, and atomic data investigations that enable the analysis of spectroscopic data.


david_jones_150212s
Thursday February 12, 2015
Dr. David Jones
IAC

Abstract

I will report on the results of our paper published in Nature this week, outlining the discovery of a super-Chandrasekhar double-degenerate binary system at the heart of the planetary nebula Hen 2-428.  Planetary nebulae (PNe) represent the final stage in the evolution of low- and intermediate-mass stars, forming from the mass ejected by the star during its AGB evolution before being ionised by the star's, now exposed, core.  As binarity is expected to play a key role in the formation of aspherical PN morphologies, we have been intensively searching for new binary central stars in a push towards a statistical sample.  One of our newly-discovered binary systems, lying at the heart of Hen 2-428, had a further surprise to reveal, with observations and modelling showing the system to consist of twin evolved stars with a total mass greater than the Chandrasekhar limit.  The short period of the system, only 4.2 hours, means that the two stars will merge together in approximately 700 Myr, resulting in a Supernova Type Ia.  While the super-Chandrasekhar merger of two white dwarfs has long been considered a formation pathway for SN Ia, this is the first system found that is confirmed to be both massive enough and in a tight enough orbit to merge in less than a Hubble time.


andres_asensio_ramos_121122s
Thursday November 22, 2012
Dr. Andrés Asensio Ramos
IAC

Abstract

As astrophysicists, we are used to extracting physical information from the observations. The usual procedure is to propose a parametric physical model to explain the observations and use the observations to infer the values of the parameters. However, in our noisy and ambiguous universe, the solution to the inference problem is usually non-unique or diffuse. For this reason, it is important that our inversion techniques give reliable results. In this talk I present a few recent results (dusty tori of AGN, magnetic fields in central stars of planetary nebulae, oscillations of coronal loops, signal detection) in which our group is applying Bayesian ideas to extract information from the observations.


maria_jesus_martinez_110407s
Thursday April 7, 2011
Dr. María Jesús Martínez
Instituto de Astrofísica de Canarias, Spain

Abstract

This question is important because a large fraction of planetary nebulae (about 80%) are bipolar or elliptical rather than spherically symmetric. Modern theories invoke magnetic fields, among other causes, to explain the rich variety of aspherical components observed in PNe, as ejected matter is trapped along magnetic field lines. But, until recently, this idea was mostly a theoretical claim. Jordan et al. (2005) report the detection of kG magnetic fields in the central star of two non-spherical PNe, namely NGC1360 and LSS1362. We find that, contrary to that work, the magnetic field is null within errors for both stars. Then, a direct evidence of magnetic fields on the central stars of PNe is still missing — either the magnetic field is much weaker (< 600 G) than previously reported, or more complex (thus leading to cancellations), or both. The role of magnetic fields shaping PNe is still an open question.


arianna_cortesi_091218s
Thursday December 18, 2008
Dr. Arianna Cortesi
University of Nottingham, UK

Abstract

We present a detailed study of the lenticular galaxy NGC 1023 kinematics. To perform this analysis we use planetary nebulae (PNe). which can be observed in the faint outer regions of the galaxy, where traces of the galaxy past history are clearly recorded. If the circular speed is equal or lower than the stars velocity dispersion, the system is hot and it is the result of a minor merger. Otherwise, if the stellar motions are rotation dominated at large radii, a spiral galaxy is the progenitor of the lenticular. A first attempt at such an analysis was undertaken by Noordermeer et al. (2008), who found that the S0 system NGC 1023 has very peculiar kinematics in its disk, which do not seem to be consistent with either of the above scenarios. In this paper we show that that result was largely due to a contamination of the disk kinematics by stars belonging to the spheroidal component or accreted from the small companion. We present a new method based on a more sophisticated maximum-likelihood analysis that uses a full two-dimensional disk/spheroid decomposition to solve simultaneously for both disk and spheroid kinematics. This analysis reveal that NGC1023 has the kinematics expected for a stripped spiral galaxy.


valentina_luridiana_080617s
Tuesday June 17, 2008
Dr. Valentina Luridiana
Instituto de Astrofísica de Andalucía, Spain

Abstract

Common wisdom identifies hydrogen lines in photoionized region with recombination lines. However, these lines can also be excited by different atomic mechanisms, the most important of which are collisional excitation and continuum pumping by stellar photons. The relative contributions of these two mechanisms to the total Balmer intensity can be substantial in certain environments, and the associated bias can easily dominate the error budget. In this talk I will give estimates for the effectiveness of these mechanisms, defining at the same time the observational strategies that permit to minimize their contribution.


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