Characterizing the morphology of the debris disk around the low-mass star GSC 07396-00759
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Date
2021-07-15
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Abstract
Context. Debris disks have commonly been studied around intermediate-mass stars. Their intense radiation fields are believed to e ciently
remove the small dust grains that are constantly replenished by collisions. For lower-mass central objects, in particular M-stars, the dust removal
mechanism needs to be further investigated given the much weaker radiation field produced by these objects.
Aims. We present new observations of the nearly edge-on disk around the pre-main sequence M-type star GSC 07396-00759, taken with
VLT/SPHERE IRDIS in Dual-beam Polarimetric Imaging (DPI) mode, with the aim to better understand the morphology of the disk, its dust
properties, and the star-disk interaction via the stellar mass-loss rate.
Methods. We model the polarimetric observations to characterize the location and properties of the dust grains using the Henyey-Greenstein
approximation of the polarized phase function. We use the estimated phase function to evaluate the strength of the stellar winds.
Results. We find that the polarized light observations are best described by an extended and highly inclined disk (i 84:3 0:3) with a dust
distribution centered at a radius r0 107 2 au. Our modeling suggests an anisotropic scattering factor g 0:6 to best reproduce the polarized
phase function S 12. We also find that the phase function is reasonably reproduced by small micron-sized dust grains with sizes s > 0:3 µm. We
discuss some of the caveats of the approach, mainly that our model probably does not fully recover the semi-major axis of the disk and that we
cannot readily determine all dust properties due to a degeneracy between the grain size and the porosity.
Conclusions. Even though the radius of the disk may be over-estimated, our best fit model not only reproduces well the observations but is also
consistent with previous published data obtained in total intensity. Similarly to previous studies of debris disks, we suggest that using a given
scattering theory might not be su cient to fully explain key aspects such as the shape of the phase function, or the dust grain size. Taking into
consideration the aforementioned caveats, we find that the average mass-loss rate of GSC 07396-00759 can be up to 500 times stronger than that
of the Sun, supporting the idea that stellar winds from low-mass stars can evacuate small dust grains in an e cient way.
Description
Keywords
Stars: individual: GSC 07396-00759, Stars: winds, outflows, Stars: circumstellar matter, Techniques: high angular resolution, Techniques: polarimetric