Epsilon Indi - the nearest binary Brown Dwarf: Benchmark the coolest atmospheres in the MIR

Coordinator: M. Sterzik, M. Hartung, N. Huelamo, H.U. Kaeufl, C. Melo, D. Nuernberger, E. Pantin, R. Siebenmorgen, A. Smette

The epsIndi Ba/b is the closest (3.626pc) brown dwarf binary known, and allows to determine fundamental physical parameters like its mass, luminosity, effective temperature, and surface gravity, with unprecedented precision. Extending the analysis of the atmospheric features towards the mid-infrared offers a unique opportunity to benchmark current evolutionary model atmosphere calculations for very low temperatures. With VISIR, we can spatially resolve both components (which are separated by 0.73"), and probe the photosphere of both components in the mid-infrared for the first time simultaneously. This project will demonstrate that also VISIR - owing to its spatial resolution - will be a valuable tool in brown dwarf research.

Program is available and data products can be downloadedDescription/Scope
For the given K magnitudes of 11.3 and 13.5 and temperatures of 1250K and 850K for a/b resp. (McCaughrean et al., 2004, A\&A 413, 1029), we expect MIR fluxes of about 10-20mJy for each component, assuming a simple black-body flux distribution. Our primary goal is therefore to detect, and to resolve the MIR emission from both components. In total (at least) three N-band fluxes will be determined, and will allow to infer a crude shape of the photosphere for those cool objects for the first time. With a long integration (1h) in the imager mode of the spectrograph, we will then acquire the object in a 1" wide slit, and obtain the spectra of the two brown dwarfs simultanously over the entire N-band in low Resolution, if deemed feasable.

The photometric measurements should be possible given the current sensitivity estimates of VISIR. We note that the required sensitivities can only be reached under good atmospheric conditions, and with good seeing. Once we are successful in the detection of the sources in the most sensitive PAH1 band, we will continue to cover the N-band with PAH2 and SIV filters. The S/N obtained in the photometry will then be used to assess, if N-band low-resolution spectroscopy, or further imaging in complementary N-band filters will be performed. Standard calibrations for the photometry and spectroscopy will be interlaced with the scientific observations.

Target list
NameRA(2000)DEC(2000)ModeObs.Time (h)
eIBa/b22:04:11-56:47:00SPC-LR4 x 1.25
eIBa/b22:04:11-56:47:00IMG-N alt4 x 1.25