Browsing by Subject "Mira stars"

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    Open Access
    HST and VLT observations of the symbiotic star Hen 2–147: Its nebular dynamics, its Mira variable and its distance
    (2007) Santander-García, M; Corradi, R L M; Whitelock, P A; Munari, U; Mampaso, A; Marang, F; Boffi, F; Livio, M
    Aims. We investigate the dynamics of the nebula around the symbiotic star Hen 2-147, determine its expansion parallax, and compare it with the distance obtained via the period-luminosity relation for its Mira variable. Methods. A combination of multi-epoch HST images and VLT integral field high-resolution spectroscopy is used to study the nebular dynamics both along the line of sight and in the plane of the sky. These observations allow us to build a 3D spatio-kinematical model of the nebula, which, together with the measurement of its apparent expansion in the plane of the sky over a period of 3 years, provides the expansion parallax for the nebula. Additionally, SAAO near-infrared photometry obtained over 25 years is used to determine the Mira pulsation period and derive an independent distance estimation via the period-luminosity relationship for Mira variables. Results. The geometry of the nebula is found to be that of a knotty annulus of ionized gas inclined to the plane of sky and expanding with a velocity of similar to 90 km s(-1). A straightforward application of the expansion parallax method provides a distance of 1.5 +/- 0.4 kpc, which is a factor of two lower than the distance of 3.0 +/- 0.4 kpc obtained from the period-luminosity relationship for the Mira (which has a pulsation period of 373 days). The discrepancy is removed if, instead of expanding matter, we are observing the expansion of a shock front in the plane of the sky. This shock interpretation is further supported by the broadening of the nebular emission lines.
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    Open Access
    On the nature of the cool component of MWC 560
    (2007) Gromadzki, M; Mikołajewska, J; Whitelock, P A; Marang, F
    Context.MWC 560 (V694 Mon) is one of the most enigmatic symbiotic system with a very active accretion-powered hot component. Such activity can be supported only by a luminous asymptotic giant branch star, i.e. a Mira or SR variable, with a high mass-loss rate. It is also a very unusual jet source because the jet axis lies practically parallel to the line of sight. Aims. The aims of our study are the determination of the evolutionary status of the cool component of MWC 560. Methods. Our methods involve analysis of near-IR JHKL and optical light curves. Results. The cool component of MWC 560 pulsates with a period of ∼340 days, and it is probably a red SR variable on the thermally pulsing AGB. The high mass-loss rate expected for such a star is sufficient to power the observed activity of the hot companion.