Abstract
Detecting the presence of circumstellar dust around nearby solar-type main sequence stars is an important pre-requisite for the design of future life-finding space missions such as ESA's Darwin or NASA's Terrestrial Planet Finder (TPF). The high Antarctic plateau may provide appropriate conditions to perform such a survey from the ground. We investigate the performance of a nulling interferometer optimised for the detection of exozodiacal discs at Dome C, on the high Antarctic plateau, and compare it to the expected performance of similar instruments at temperate sites. Based on the currently available measurements of the turbulence characteristics at Dome C, we adapt the GENIEsim software (Absil et al. 2006, A&A 448) to simulate the performance of a nulling interferometer on the high Antarctic plateau. To feed a realistic instrumental configuration into the simulator, we propose a conceptual design for ALADDIN, the Antarctic L-band Astrophysics Discovery Demonstrator for Interferometric Nulling. We assume that this instrument can be placed above the 30-m high boundary layer, where most of the atmospheric turbulence originates. We show that an optimised nulling interferometer operating on a pair of 1-m class telescopes located 30 m above the ground could achieve a better sensitivity than a similar instrument working with two 8-m class telescopes at a temperate site such as Cerro Paranal. The detection of circumstellar discs about 20 times as dense as our local zodiacal cloud seems within reach for typical Darwin/TPF targets in a integration time of a few hours. Moreover, the exceptional turbulence conditions significantly relax the requirements on real-time control loops, which has favourable consequences on the feasibility of the nulling instrument.
Highlights
Nulling interferometry is considered to be the technique that can enable the spectroscopic characterisation of the atmosphere of habitable extrasolar planets in the thermal infrared, where markers of biological activity have been identified (Kaltenegger et al 2007)
The water vapour content of the Antarctic atmosphere has been measured at South Pole by radiosonde, giving an exceptionally low average value of 250 μm during austral winter (Chamberlin et al 1997; Bussmann et al 2005), where temperate sites typically have a few millimetres of precipitable water vapour (PWV)
We have investigated a potential solution to a welldefined scientific need, viz. characterising the dusty environment of candidate target stars for future life-finding missions such as Darwin or Terrestrial Planet Finder (TPF)
Summary
Nulling interferometry is considered to be the technique that can enable the spectroscopic characterisation of the atmosphere of habitable extrasolar planets in the thermal infrared, where markers of biological activity have been identified (Kaltenegger et al 2007) This is the objective of the Darwin and TPF-I missions studied by ESA and NASA, respectively (Fridlund 2004; Beichman et al 1999). Its main peculiarity with respect to the South Pole station is that it resides on a local summit of the plateau (3250 m), where katabatic winds have not yet acquired a significant velocity nor a large thickness by flowing down the slope of the plateau For this reason, it is expected that Dome C could become the best accessible site on the continent, and, given its promising environmental characteristics, it is worthwhile to investigate its potential for a ground-based nulling interferometer. Absil et al.: Nulling interferometry: performance comparison between Antarctica and other ground-based sites
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