Poster Presentation Astronomical Society of Australia Annual Scientific Meeting including HWWS 2013

A DEBRIS disk around the planet hosting M-star GJ 581 spatially resolved with Herschel (#271)

Elodie Thilliez 1 , Jean-François Lestrade 2 , Mark Wyatt 3 , DEBRIS TEAM 4
  1. Swinburne University of Technology, Hawthorn, VIC, Australia
  2. LERMA, Observatoire de Paris, Paris, FRANCE
  3. Institute of Astronomy, University of Cambridge, Cambridge, UK
  4. DEBRIS Team,

The Key Program DEBRIS (Disc Emission via a Bias-free Reconnaissance in the Infrared/Sub-mm) on the Herschel Space Observatory is an unbiased flux-limited survey to search for dust emission at λ = 100 and 160μm toward the nearest ∼89 stars of each spectral type A, F, G, K, M as evidence of debris disks.

As part as the observational program,  we have spatially resolved the second debris disk around a M-type star at 70, 100 and 160 μm:  GJ 581 which is hosting multiple planets. Contrary to the first M-type star dust disk detected surrounding AU Microscopii (Kalas et al. 2004) extending from 50 to 210 AU, GJ 581 is much older (2-8 Gyr), and X-ray quiet in the ROSAT data.

We fit an axisymmetric model of the disk to the three PACS images using a power-law and gaussian densities and found that the best fit model is for a disk extending radially from 25 ± 12 AU to more than 60 AU.

Such a cold disk is reminiscent of the Kuiper Belt but it surrounds a low mass star (0.3 M⊙ ) and its fractional dust luminosity Ldust /L∗ of ∼ 10−4 is much higher. This may be explained by the fact that dust cannot be expelled from the system by radiation or wind pressures because of the low luminosity and low X-ray luminosity of GJ 581.

Hosting at least 4 known planets of low masses and orbiting within 0.3 AU from the star, we suggest that the correlation between low-mass planets and debris disks recently found for G-type stars also applies to M-type stars.