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Post Info TOPIC: HD 69830
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Title: Multi-Epoch Observations of HD69830: High Resolution Spectroscopy and Limits to Variability
Authors: C. A. Beichman, C. M. Lisse, A. M. Tanner, G. Bryden, R. L. Akeson, D. R. Ciardi, A. F. Boden, S. E. Dodson-Robinson, C. Salyk, M. C. Wyatt

The main-sequence solar-type star HD69830 has an unusually large amount of dusty debris orbiting close to three planets found via the radial velocity technique. In order to explore the dynamical interaction between the dust and planets, we have performed multi-epoch photometry and spectroscopy of the system over several orbits of the outer dust. We find no evidence for changes in either the dust amount or its composition, with upper limits of 5-7% (1 \sigma per spectral element) on the variability of the dust spectrum over 1 year, 3.3% (1 \sigma) on the broad-band disk emission over 4 years, and 33% (1 \sigma) on the broad-band disk emission over 24 years. Detailed modelling of the spectrum of the emitting dust indicates that the dust is located outside of the orbits of the three planets and has a composition similar to main-belt, C-type asteroids in our solar system. Additionally, we find no evidence for a wide variety of gas species associated with the dust. Our new higher SNR spectra do not confirm our previously claimed detection of H_2O ice leading to a firm conclusion that the debris can be associated with the break-up of one or more C-type asteroids formed in the dry, inner regions of the protoplanetary disk of the HD69830 system. The modelling of the spectral energy distribution and high spatial resolution observations in the mid-infrared are consistent with a ~1 AU location for the emitting material.

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HD 69830ew2
The HARPS radial velocity measurements of HD 69830 are folded with the orbital periods of the three discovered planets: 8.67, 31.6 and 197 days, respectively. In each case, the contribution of the two other planets has been subtracted. The solid line shows the best fit to the measurements, corresponding to minimum masses of 10.2, 11.8 and 18.1 Earth masses. Note that the full span of the vertical axis is only 13 m/s! Error bars indicate the accuracy of the measurements. The integration time was 4 minutes on average for the first 18 measurements (shown as open dots), and was increased to 15 minutes for the remaining points (full dots). The latter measurements are therefore of much higher quality.


HD 69830ew
Illustration of the possible formation process and present day structure of the planetary system around HD 68930. The three planets form from embryos originally located at larger distances (dashed ellipses) than the present ones (indicated by solid ellipses at 0.07, 0.18 and 0.63 the mean Earth-Sun distance). The embryos of the inner and middle planets start interior to the ice line, so that these two planets build up from rocky planetesimals and gas. The two planets consist of a central rocky core (in brown) and an envelope of gas. The embryo of the outermost planet starts beyond the ice line, and the planet accumulates a large amount of ice at the beginning of its formation. The planet finally consists of a central rocky core (brown), surrounded by a shell of water (ice or liquid - in blue), and a quite massive gas envelope.
Credit: ESO

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