Browsing by Author "Munari, U"

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    Historical light curve and search for previous outbursts of Nova KT Eridani (2009)
    (2012) Jurdana-Šepić, R; Ribeiro, V A R M; Darnley, M J; Munari, U; Bode, M F
    Context. Nova Eridani (2009) caught the eye of the nova community due to its fast decline from maximum, which was initially missed, and its subsequent development in the radio and X-ray wavelengths. This system also exhibits properties similar to those of the much smaller class of recurrent novae; themselves potential progenitors of Type Ia Supernovae. Aims. We aim to determine the nature and physical parameters of the KT Eri progenitor system. Methods. We searched the Harvard College Observatory archive plates for the progenitor of KT Eri to determine the nature of the system, particularly the evolutionary stage of the secondary.We used the data obtained to search for any periodic signal and the derived luminosity to estimate a recurrence timescale. Furthermore, by comparing the colours of the quiescent system on a colour-magnitude diagram we may infer the nature of the secondary star. Results. We identified the progenitor system of KT Eri and measured a quiescent magnitude of < B >= 14.7 pm 0.4. No previous outburst was found. However, we suggest that if the nova is recurrent it should be on a timescale of centuries. We find a periodicity at quiescence of 737 days which may arise from reflection effects and/or eclipses in the central binary. The periodicity and the quiescence magnitude of the system suggest that the secondary star is evolved and likely in, or ascending, the Red Giant Branch. A second period is evident at 376 days which has a sinusoidal like light curve. Furthermore, the outburst amplitude of ~ 9 magnitudes is inconsistent with those expected for fast classical novae (~ 17 magnitudes) which may lend further support for an evolved secondary. (Abridged)
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    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.