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Israelian, G.; Groot, M. de

doi:10.1023/a:1005223314464

Cited by 31 publications

(32 citation statements)

References 35 publications

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“…Ca ii showing a double peaked profile, indicative of a rotating disk (Aret et al 2012;Aret & Kraus 2015); 2. emission lines with P Cygni profiles indicating fast winds in the outflows (Israelian & de Groot 1999); 3. H i recombination lines tracing the extended nebula and the disk photosphere;…”

Section: Resultsmentioning

confidence: 96%

“…The transition process from H i absorption lines (H i 2-7) towards a P Cygni line profile starting with (H i 2-6) is shown. The P Cygni profiles are indicative of an extended shell of gas moving away from the central star (Israelian & de Groot 1999) detected. We plot the spectra obtained in 2010 and 2012, as well as the individual decomposed pixel spectra (see Fig.…”

Section: The Excitation Temperature Of [Fe Ii]mentioning

confidence: 92%

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Medium-resolution échelle spectroscopy of the Red Square Nebula, MWC 922

Wehres

Ochsendorf

Tielens

et al. 2017

A&A

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Context. Medium-resolution échelle spectra of the Red Square Nebula surrounding the star MWC 922 are presented. The spectra have been obtained in 2010 and 2012 using the X-shooter spectrograph mounted on the Very Large Telescope (VLT) in Paranal, Chile. The spectrum covers a wavelength range between 300 nm−2.5 µm and shows that the nebula is rich in emission lines. Aims. We aim to identify the emission lines and use them as a tool to determine the physical and chemical characteristics of the nebula. The emission lines are also used to put constraints on the structure of the nebula and on the nature of the central stars. Results. These findings put constraints on the evolution of the central objects in MWC 922. The Red Square shows strong similarities to the Red Rectangle Nebula, both in morphology and in its mid-IR spectroscopic characteristics. As for the Red Rectangle, the observed morphology of the nebula reflects mass-loss in a binary system. Specifically, we attribute the biconical morphology and the associated rung-like structure to the action of intermittent jets blown by the accreting companion in a dense shell, which has been created by the primary. We stress, though, that despite the morphological similarities, these two objects represent very different classes of stellar objects.

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Section: Resultsmentioning

confidence: 96%

Section: The Excitation Temperature Of [Fe Ii]mentioning

confidence: 92%

Medium-resolution échelle spectroscopy of the Red Square Nebula, MWC 922

Wehres

Ochsendorf

Tielens

et al. 2017

A&A

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“…2) and has not been observed to show variability on the same scales as other LBVs such as AG Car or S Dor (van Genderen et al 1992). η Car and P Cyg are unusual objects even by LBV standards -whilst both had huge outbursts hundreds of years ago, P Cyg has been roughly constant in luminosity for many years, while η Car's variability is often explained by the expanding nebula moving across our line of sight, coupled with the effects of being in a highly eccentric binary system (Israelian & de Groot 1999;Davidson & Humphreys 1997). This leaves AG Car, HR Car and HD 160529 as the only "normal" Galactic LBVs.…”

Section: Galactic Vs Extra-galactic Lbvsmentioning

confidence: 99%

Asphericity and clumpiness in the winds of Luminous Blue Variables

Davies

Oudmaijer

Vink

2005

A&A

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Abstract. We present the first systematic spectropolarimetric study of Luminous Blue Variables (LBVs) in the Galaxy and the Magellanic Clouds, in order to investigate the geometries of their winds. We find that at least half of our sample show changes in polarization across the strong Hα emission line, indicating that the light from the stars is intrinsically polarized and therefore that asphericity already exists at the base of the wind. Multi-epoch spectropolarimetry on four targets reveals variability in their intrinsic polarization. Three of these, AG Car, HR Car and P Cyg, show a position angle (PA) of polarization which appears random with time. Such behaviour can be explained by the presence of strong wind-inhomogeneities, or "clumps" within the wind. Only one star, R 127, shows variability at a constant PA, and hence evidence for axi-symmetry as well as clumpiness. However, if viewed at low inclination, and at limited temporal sampling, such a wind would produce a seemingly random polarization of the type observed in the other three stars. Time-resolved spectropolarimetric monitoring of LBVs is therefore required to determine if LBV winds are axi-symmetric in general. The high fraction of LBVs (>50%) showing intrinsic polarization is to be compared with the lower ∼20-25% for similar studies of their evolutionary neighbours, O supergiants and Wolf-Rayet stars. We anticipate that this higher incidence is due to the lower effective gravities of the LBVs, coupled with their variable temperatures within the bi-stability jump regime. This is also consistent with the higher incidence of wind asphericity that we find in LBVs with strong Hα emission and recent (last ∼10 years) strong variability.

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“…Smith et al 1998), HR Car has at least three ejecta (e.g. Voors 1999), P Cyg has four ejecta (Barlow et al 1994;Meaburn et al 1996;Skinner et al 1998; see also the review on P Cyg by Israelian & de Groot 1999). The differences in dynamical ages amount to from a few centuries to 5 10 4 yr.…”

Section: The Number Of Stellar Ejecta and Their Agesmentioning

confidence: 99%

S Doradus variables in the Galaxy and the Magellanic Clouds

Genderen¹

2001

A&A

196

105

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Abstract. The goal in writing this paper is five fold: (1) to summarize the scientific achievements in the 20th century on S Dor variables (or LBVs); (2) to present an inventory of these variables in the Galaxy and the Magellanic Clouds with a description of their physical state and instability properties; (3) to emphasize the photometric achievements of the various types of instabilities. Generally this seems to be a neglected item resulting in a number of misunderstandings continuously wandering through literature; (4) to investigate the structure of the S Dor-area on the HR-diagram; (5) to estimate the total numbers of S Dor variables in the three stellar systems. The position of the strong active S Dor variables in minimum brightness obey the following linear relation on the HR-diagram:log L/L = 1.37 log T eff − 0.03. The relatively small dispersion of less active and supposed exand dormant S Dor variables with respect to this relation is twice as large at the blue side than at the red side. This might be caused by evolution to the WR stage and/or to high rotation. S Dor variables can be subject to five types of instabilities: the very rare genuine eruptive episodes (the "SD-eruptions"), two different brightening phases caused by slow pulsations (the "SD-phases"): one on a time scale of years, the other on a time scale of decades at a more or less constant luminosity and two types of microvariations: one on a time scale of weeks, the other on a time scale of about 100 d. So far, no periodicities of light curve characteristics of any of these instabilities have ever been found. The durations of active and non-active stages are estimated for about half of the sample based on scattered magnitude estimations such as from historical records, and on modern monitoring campaigns. It would be a misunderstanding to believe that all S Dor variables should be always spectacular. It is estimated that most of them will not be spectacular at all for at least 70% of their lifetime as an S Dor variable.

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Untitled

Cited by 31 publications

References 35 publications

Medium-resolution échelle spectroscopy of the Red Square Nebula, MWC 922

Medium-resolution échelle spectroscopy of the Red Square Nebula, MWC 922

Asphericity and clumpiness in the winds of Luminous Blue Variables

S Doradus variables in the Galaxy and the Magellanic Clouds

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