1,625 research outputs found
Nulling interferometry: impact of exozodiacal clouds on the performance of future life-finding space missions
Earth-sized planets around nearby stars are being detected for the first time
by ground-based radial velocity and space-based transit surveys. This milestone
is opening the path towards the definition of missions able to directly detect
the light from these planets, with the identification of bio-signatures as one
of the main objectives. In that respect, both ESA and NASA have identified
nulling interferometry as one of the most promising techniques. The ability to
study distant planets will however depend on exozodiacal dust clouds
surrounding the target stars. In this paper, we assess the impact of
exozodiacal dust clouds on the performance of an infrared nulling
interferometer in the Emma X-array configuration. For the nominal mission
architecture with 2-m aperture telescopes, we found that point-symmetric
exozodiacal dust discs about 100 times denser than the solar zodiacal cloud can
be tolerated in order to survey at least 150 targets during the mission
lifetime. Considering modeled resonant structures created by an Earth-like
planet orbiting at 1 AU around a Sun-like star, we show that the tolerable dust
density for planet detection goes down to about 15 times the solar zodiacal
density for face-on systems and decreases with the disc inclination. The upper
limits on the tolerable exozodiacal dust density derived in this study must be
considered as rather pessimistic, but still give a realistic estimation of the
typical sensitivity that we will need to reach on exozodiacal discs in order to
prepare the scientific programme of future Earth-like planet characterisation
missions.Comment: 17 pages, accepted for publication in A&
Improved V II log() Values, Hyperfine Structure Constants, and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937
New experimental absolute atomic transition probabilities are reported for
203 lines of V II. Branching fractions are measured from spectra recorded using
a Fourier transform spectrometer and an echelle spectrometer. The branching
fractions are normalized with radiative lifetime measurements to determine the
new transition probabilities. Generally good agreement is found between this
work and previously reported V II transition probabilities. Use of two
spectrometers, independent radiometric calibration methods, and independent
data analysis routines enables a reduction in systematic uncertainties, in
particular those due to optical depth errors. In addition, new hyperfine
structure constants are measured for selected levels by least squares fitting
line profiles in the FTS spectra. The new V II data are applied to high
resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to
determine new, more accurate V abundances. Lines covering a range of wavelength
and excitation potential are used to search for non-LTE effects. Very good
agreement is found between our new solar photospheric V abundance, log
{\epsilon}(V) = 3.95 from 15 V II lines, and the solar-system meteoritic value.
In HD 84937, we derive [V/H] = -2.08 from 68 lines, leading to a value of
[V/Fe] = 0.24.Comment: 32 pages, 7 tables (3 machine-readable), 8 figures; accepted for
publication in ApJ
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