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See detailHerschel observations of nebulae ejected by massive evolved stars
Vamvatira-Nakou, Chloi ULg; Hutsemekers, Damien ULg; Royer, P. et al

Poster (2013, October)

We have obtained far-infrared Herschel PACS imaging and spectroscopic observations of nebulae associated to massive evolved stars. The study of these nebulae is crucial to understand the evolution of ... [more ▼]

We have obtained far-infrared Herschel PACS imaging and spectroscopic observations of nebulae associated to massive evolved stars. The study of these nebulae is crucial to understand the evolution of these stars as it can reveal the mass-loss history. The infrared images along with available data at other wavelengths give a complete view of their morphology. The dust modeling provides the dust parameters, such as the temperature, the mass and the composition of dust. The spectroscopic analysis provides the gas C,N,O abundances and mass. Based on these observations, the evolutionary status of the star at the time of the nebula ejection can be constrained. We present here selected results of an ongoing exhaustive study of nebulae around low- and high-luminosity LBVs (AG Car, HR Car, WRAY 15-751, G79.29+0.46, HD168625), WN stars (NGC6888, M1-67, He3-519) and Of stars (NGC6164/5). [less ▲]

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See detailHerschel imaging and spectroscopy of the nebula around the luminous blue variable star WRAY 15-751
Vamvatira-Nakou, Chloi ULg; Hutsemekers, Damien ULg; Royer, P. et al

in Astronomy and Astrophysics (2013), 557

We have obtained far-infrared Herschel-PACS imaging and spectroscopic observations of the nebular environment of the luminous blue variable (LBV) WRAY 15-751. The far-infrared images clearly show that the ... [more ▼]

We have obtained far-infrared Herschel-PACS imaging and spectroscopic observations of the nebular environment of the luminous blue variable (LBV) WRAY 15-751. The far-infrared images clearly show that the main, dusty nebula is a shell of radius 0.5 pc and width 0.35 pc extending outside the Hα nebula. Furthermore, these images reveal a second, bigger and fainter dust nebula that is observed for the first time. Both nebulae lie in an empty cavity, very likely the remnant of the O-star wind bubble formed when the star was on the main sequence. The kinematic ages of the nebulae are calculated to be about 2 × 10^4 and 8 × 10^4 years, and we estimated that each nebula contains ~0.05 Msun of dust. Modeling of the inner nebula indicates a Fe-rich dust. The far-infrared spectrum of the main nebula revealed forbidden emission lines coming from ionized and neutral gas. Our study shows that the main nebula consists of a shell of ionized gas surrounded by a thin photodissociation region illuminated by an “average” early-B star. We derive the abundance ratios N/O = 1.0 ± 0.4 and C/O = 0.4 ± 0.2, which indicate a mild N/O enrichment. From both the ionized and neutral gas components we estimate that the inner shell contains 1.7 ± 0.6 Msun of gas. Assuming a similar dust-to-gas ratio for the outer nebula, the total mass ejected by WRAY 15-751 amounts to 4± 2 Msun. The measured abundances, masses and kinematic ages of the nebulae were used to constrain the evolution of the star and the epoch at which the nebulae were ejected. Our results point to an ejection of the nebulae during the red super-giant (RSG) evolutionary phase of an ~40 Msun star. The multiple shells around the star suggest that the mass-loss was not a continuous ejection but rather a series of episodes of extreme mass-loss. Our measurements are compatible with the recent evolutionary tracks computed for an ~40 Msun star with little rotation. They support the O–BSG–RSG–YSG–LBV filiation and the idea that high-luminosity and low-luminosity LBVs follow different evolutionary paths. [less ▲]

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See detailThe Nebula around the Luminous Blue Variable WRAY 15-751 as seen by Herschel
Vamvatira-Nakou, Chloi ULg; Hutsemekers, Damien ULg; Royer, P. et al

in Massive Stars: From alpha to Omega (2013, June 01)

To understand the evolution of massive stars it is crucial to study the nebulae associated to Luminous Blue Variables which can reveal the star mass-loss history. We obtained far-infrared Herschel PACS ... [more ▼]

To understand the evolution of massive stars it is crucial to study the nebulae associated to Luminous Blue Variables which can reveal the star mass-loss history. We obtained far-infrared Herschel PACS imaging and spectroscopic observations of the nebula associated with the Luminous Blue Variable star WRAY 15-751. These images revealed a second nebula, bigger and cooler, lying in an empty cavity that probably delineates the remnant of the O-star bubble formed when the star was on the Main Sequence. The dust mass and temperature were derived from the modeling of the far-infrared SED. The analysis of the emission line spectrum revealed that the main nebula consists of a region of photoionised gas surrounded by a thin photodissociation region. Both regions are mixed with dust. The calculated C, N, O abundances, together with the estimated mass-loss rate, show that the nebula was ejected from the star during a Red Supergiant phase. This is compatible with the latest evolutionary tracks for a ~40 Mo star with little rotation. [less ▲]

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See detailEjecta around evolved massive stars observed with Herschel
Vamvatira-Nakou, Chloi ULg; Hutsemekers, Damien ULg; Royer, P. et al

Conference (2012, March)

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See detailMESS (Mass-loss of Evolved StarS), a Herschel Key Program
Groenewegen, M. A. T.; Waelkens, C.; Barlow, M. J. et al

in Astronomy and Astrophysics (2011), 526

MESS (Mass-loss of Evolved StarS) is a Guaranteed Time Key Program that uses the PACS and SPIRE instruments on board the Herschel Space Observatory to observe a representative sample of evolved stars ... [more ▼]

MESS (Mass-loss of Evolved StarS) is a Guaranteed Time Key Program that uses the PACS and SPIRE instruments on board the Herschel Space Observatory to observe a representative sample of evolved stars, that include asymptotic giant branch (AGB) and post-AGB stars, planetary nebulae and red supergiants, as well as luminous blue variables, Wolf-Rayet stars and supernova remnants. In total, of order 150 objects are observed in imaging and about 50 objects in spectroscopy. This paper describes the target selection and target list, and the observing strategy. Key science projects are described, and illustrated using results obtained during Herschel's science demonstration phase. Aperture photometry is given for the 70 AGB and post-AGB stars observed up to October 17, 2010, which constitutes the largest single uniform database of far-IR and sub-mm fluxes for late-type stars. [less ▲]

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See detailThe Herschel view of nebulae around evolved massive stars
Vamvatira Nakou, Chloi ULg; Royer, P.; Hutsemekers, Damien ULg et al

Conference (2011)

The detailed study of the nebulae ejected from Luminous Blue Variables and the circumstellar bubbles around Wolf-Rayet stars, which radiate strongly in the IR due to the heating of dust, is crucial for ... [more ▼]

The detailed study of the nebulae ejected from Luminous Blue Variables and the circumstellar bubbles around Wolf-Rayet stars, which radiate strongly in the IR due to the heating of dust, is crucial for understanding the massive stars evolution. With Herschel, the largest telescope ever flown in space, we are able to study the gas and the dust in these circumstellar environments in the full far-infrared waveband. In the context of 'Mass-loss of Evolved StarS' Herschel guaranteed time key programme, we have obtained imaging and spectroscopic observations of nebulae associated with Luminous Blue Variable and Wolf-Rayet stars using PACS, one of the three instruments onboard Herschel. A description of these observations and first results of the data analysis are presented. [less ▲]

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See detailResults from the Herschel Key Program MESS
Groenewegen, M. A. T.; Waelkens, C.; Barlow, M. J. et al

in Kerschbaum, F.; Lebzelter, T.; Wing, R. F. (Eds.) Why Galaxies Care about AGB Stars II: Shining Examples and Common Inhabitants. ASPC 445 (2011)

MESS (Mass loss of Evolved StarS) is a Herschel Guaranteed Time Key Program that will image about 100, and do spectroscopy of about 50, post-main-sequence objects of all flavours: AGB stars, post-AGB ... [more ▼]

MESS (Mass loss of Evolved StarS) is a Herschel Guaranteed Time Key Program that will image about 100, and do spectroscopy of about 50, post-main-sequence objects of all flavours: AGB stars, post-AGB stars, planetary nebulae, luminous blue variables, Wolf-Rayet stars, and supernova remnants. In this review the implementation and current status of MESS is outlined, and first results are presented. [less ▲]

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