Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/research/masermeeting/web_papers/503_RHumphreys.pdf Дата изменения: Tue Apr 10 02:47:15 2007 Дата индексирования: Sun Dec 23 12:41:38 2007 Кодировка: Поисковые слова: red supergiant

The Hypergiant Masers: Episodic Mass Loss, Convective Activity and Magnetic Fields
Roberta M Humphreys University of Minnesota

VY CMa

IRC +10420 NML Cyg


The Cool Hypergiants -- lie just below the upper luminosity envelope with spectral types A to M, high mass loss rates, photometric and spectroscopic variability, large infrared excess, and some with extended circumstellar ejecta
point sources:

µ Cep Cas
HR5171a HR8752 extended sources + complex ejecta VX Sgr S Per IRC +10420 NML Cyg VY CMa


The Post Red Supergiant -- IRC +10420
Strong IR excess L ~ 5 x 105 Lsun High mass loss rate 3-6 x 10-4 One of warmest maser sources Spectroscopic variation late F

mid A

Complex CS Environment One or more distant reflection shells Within 2 " ­ jet-like structures, rays, small nearly spherical shells or arcs Evidence for high mass loss ejections in the past few hundred years
1" = 5300 AU

OH maser emission peculiar, varying intensity, distributed 1.3 ­ 1.5" from star


NML Cyg ­ Interacting with Its Environment
Optically obscured star embedded in a small asymmetric bean-shaped nebula, strong OH/IR source mass loss rate 6 x 10-5 L ~ 5 x 105 Lsun Similar in shape to HII contours (30" away) due to interaction of RSG wind with ionizing photons hot stars in Cyg OB2

0".25 = 500 AU

Schuster, Humphreys & Marengo (2006) showed this is the molecular photodissociation boundary


VY CMa -- the extreme red supergiant, powerful OH/IR source
10 "

Mass loss rate 4 x 10 L ~ 5 x 105 Lsun

-4

Famous asymmetric red nebula, > 10" across, visible in small ground based telescopes. HST/WFPC2 images revealed complex environment ­ numerous knots, filamentary arcs, prominent nebulous arc Due to multiple, asymmetric ejection episodes possibly from large-scale convective regions on the star.

1" = 1500 AU


High Resolution, Long-Slit Spectroscopy --Keck HIRES Spectrograph

A strong velocity gradient from reflected absorption lines across the NW arc.

Expanding relative to star ~ 50 km/s ~ 500 year ago


2D spectra of strong K I emission lines across the arcs
NW Arc

Arcs 1 and 2


Geometry of the Ejecta -- Comparison with Maser Maps

OH maser peaks Bowers et al 1983

H2O masers Richards et al 1998


Comparison with Maser maps
SiO emission appears bipolar but masers are N/S

Recent (Muller et al 2007) CO map is bipolar but with a very large opening angle Masers present geomet optical and CO emission to do not a consistent image of the ry and do not align with the features.


Asymmetric Mass Loss Events and the Origin of the Discrete Ejecta
Images + Doppler Velocities of VY CMa Arcs and Knots are spatially and kinematically distinct; ejected in different directions at different times; not aligned with any axis of symmetry. They represent localized, relatively massive (few x 10-3 Msun) ejections Large-scale convective activity Magnetic Fields

VY CMa -- circular polarization of H2O (Vlemmings et al 2002, 2004), -- circular polarization of SiO (Barvainis et al 1987, Kemball & Diamond (1997), -- Zeeman splitting of OH (Szymczak & Cohen 1997, Masheder et al 1999) -> ~ 8 x 103 G at the star (extrapolating from OH masers at several 1000 AU) IRC +10420 -- circular polarization of OH (Nedoluha & Bowers 1992) -> ~ 3 x 103 G at the star


Collaborators
Kris Davidson Robert Gehrz Andrew Helton George Herbig Terry J. Jones Gerald Ruch Nathan Smith George Wallerstein

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Kris Davidson Robert Gehrz Terry J. Jones Nathan Smith Michael Schuster Massimo Marengo