Katrina Exter

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The detection of circumstellar water vapour around the ageing carbon star IRC +10216 challenged the current understanding of chemistry in old stars, because water was predicted to be almost absent in carbon-rich stars. Several explanations for the water were postulated, including the vaporization of icy bodies (comets or dwarf planets) in orbit around the(More)
Data from the Herschel Space Observatory is freely available to the public but no uniformly processed catalogue of the observations has been published so far. To date, the Herschel Science Archive does not contain the exact sky coverage (footprint) of individual observations and supports search for measurements based on bounding circles only. Drawing on(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(More)
V471 Tauri is a short-period eclipsing binary, and a member of the Hyades. It is composed of a hot DA white dwarf (WD) and a cool main-sequence dK2 companion. HST radial velocities of the WD, in combination with the ground-based spectroscopic orbit of the K star, yield dynamical masses of MWD = 0.84 and MdK = 0.93 M . During the UV observations we(More)
We perform a comprehensive analysis of the planetary nebula (PN) NGC 6781 to investigate the physical conditions of each of its ionized, atomic, and molecular gas and dust components and the object's evolution, based on panchromatic observational data ranging from UV to radio. Empirical nebular elemental abundances, compared with theoretical predictions via(More)
We report on the detection of anhydrous hydrochloric acid (hydrogen chlorine, HCl) in the carbon-rich star IRC+10216 using the spectroscopic facilities onboard the Herschel satellite. Lines from J = 1−0 up to J = 7−6 have been detected. From the observed intensities, we conclude that HCl is produced in the innermost layers of the circumstellar envelope with(More)
Context. A planetary nebula (PN) candidate was discovered during FORS imaging of the Local Group dwarf galaxy Phoenix. Aims. Use this PN to complement abundances from red-giant stars. Methods. FORS spectroscopy was used to confirm the PN classification. Empirical methods and photoionization modelling were used to derive elemental abundances from the(More)
Herschel PACS and SPIRE images have been obtained over a 30′ × 30′ area around the well-known carbon star CW Leo (IRC +10 216). An extended structure is found in an incomplete arc of ∼22′ diameter, which is cospatial with the termination shock due to interaction with the interstellar medium (ISM) as defined by Sahai & Chronopoulos from ultraviolet GALEX(More)
A study of the blue compact dwarf (BCD) galaxy Mrk 996 based on high resolution optical VLT VIMOS integral field unit spectroscopy is presented. Mrk 996 displays multi-component line emission, with most line profiles consisting of a narrow, central Gaussian (FWHM∼110 km s) with an underlying broad component (FWHM∼400 km s). The broad H i Balmer component(More)
Recent R-matrix calculations of electron impact excitation rates in K v are used to derive the nebular emission line ratio R = I(4122.6 A)/I(4163.3 A) as a function of electron density (N(e)). This ratio is found to be very sensitive to changes in N(e) over the density range 10(3) to 10(6) cm(-3), but does not vary significantly with electron temperature,(More)