19 research outputs found
Very fast variations of SiO maser emission in evolved stars
Full text linkContext. Stars on the asymptotic giant branch (AGB) are long-period variables
that present strong flux variations at almost all wavelengths, including the
SiO maser lines. The periods of these variations are of 300-500 days in
Mira-type stars and somewhat shorter in semi-regular variables. The variability
of the SiO lines on short timescales has been investigated, but the data are
inconclusive. Aims. We aim to study the time evolution of the SiO maser lines
in Mira-type and semi-regular variables at short timescales. We also discuss
the origin of the observed fast variations. Methods. We observed the SiO maser
lines at 7 mm (28SiO v=1,2 J=1-0) and 3 mm (28SiO v=1 J=2-1) using the 40 m
Yebes antenna and the 30 m IRAM telescope, respectively, with a minimum spacing
of 1 day. We studied the semi-regular variables RX Boo and RT Vir and the
Mira-type variables U Her, R LMi, R Leo, and Cyg. We performed a
detailed statistical analysis of the variations on different timescales.
Results. RX Boo shows strong and fast variations in the intensity of the
different spectral features of the SiO lines at 7 mm and 3 mm. On a timescale
of one day, we find variations of >10% in 25% of the cases. Variations of
greater than 50% are often found when the observations are separated by 2
or 3 days. A similar variation rate of the SiO lines at 7 mm is found for RT
Vir, but the observations of this object are less complete. On the contrary,
the variations of the SiO maser line intensity in the Mira-type variables are
moderate, with typical variation rates around <10% in 7 days. This phenomenon
can be explained by the presence of particularly small maser-emitting clumps in
semi-regular variables, which would lead to a strong dependence of the
intensity on the density variations due to the passage of shocks
M 1–92 Revisited: New Findings and Open Questions: New NOEMA Observations of Minkowski’s Footprint
Get PDFPN M 1–92, also known as Minkowski’s Footprint, is a textbook example of a massive pre-planetary nebula. It presents all the characteristics of this type of source: non-spherical symmetry (bipolar cylindrical symmetry in this case), high-velocity gas emission, large amounts of linear momentum and kinetic energy (momentum excess), and a self-similar growing structure. We have revisited this object by performing new NOEMA observations (with half arc-second resolution) of a wealth of molecules, including the rare isotopologues of CO, as well as other less abundant species. These maps provide new insights into the origin of this source. Our findings include the discovery of molecular species in the ionised regions of the nebula, confirming its shocked origin; the structure of the massive equatorial component, including the presence of active wind collisions; and the strong evidence that the AGB evolution of the source was terminated prematurely, probably due to the huge mass loss event that resulted in the formation/acceleration of the present nebula
Recherche et cartographie VLBI des Masers OH dans les régions de formation d'étoiles massives. Observations interferométriques millimétriques de Lynds 1551
No full textLes travaux presentés dans cette thèse portent essentiellement sur l'étude des régions de formation d'étoiles massives. Pour cela nous avons etudié l'émission Maser des deux transitions principales du premier état excite du radical hydroxyl (A 6031 et 6035 mhz). Nous avons conduit un relevé sur toutes les régions HII ayant une forte luminosité dans l'infrarouge lointain, plus quelques autres sources connues pour leur émission maser dans l'état fondamental de OH. Sur les 256 sources de notre catalogue, 15 nouvelles sources furent découvertes en émission et 3 en absorption. Nous avons pu mesurer l'intensité du champ magnétique de ces régions par l'intermédiaire de l'effet Zeeman qui d'une manière globale semble en accord avec le sens de rotation de la galaxie. Nous avons etudié 6 de ces sources grâce à la technique VLBI. Nous avons obtenu des franges d'interférence pour toutes les sources et cartographie W3(OH). Les cartes laissent apparaitre une structure complexe et certains points d'émission maser apparaissent résolus. Notre résolution de 5 milliarcsecondes nous a permis de déduire sans ambiguité possible des paires Zeeman qui montrent un champ magnétique variant entre 1 et 10 milligauss. Nous avons également observé avec l'interférométre du plateau de Bure une étoile de faible masse en formation, L1551, obtenant ainsi la première carte millimétrique ayant une résolution inférieure à l'arc seconde. Nous calculons une masse à partir de nos observations de C170 mais surtout cela nous a permis de quantifier la qualité du site de l'interféromètre en nous permettant d'en estimer le seeing.pas de résum
