Evidence for a circumplanetary disc around protoplanet PDS 70 b. (arXiv:1905.06370v1 [astro-ph.EP])

Evidence for a circumplanetary disc around protoplanet PDS 70 b. (arXiv:1905.06370v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Christiaens_V/0/1/0/all/0/1">V. Christiaens</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cantalloube_F/0/1/0/all/0/1">F. Cantalloube</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Casassus_S/0/1/0/all/0/1">S. Casassus</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Price_D/0/1/0/all/0/1">D. J. Price</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Absil_O/0/1/0/all/0/1">O. Absil</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pinte_C/0/1/0/all/0/1">C. Pinte</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Girard_J/0/1/0/all/0/1">J. Girard</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Montesinos_M/0/1/0/all/0/1">M. Montesinos</a>

We present the first observational evidence for a circumplanetary disc around
the protoplanet PDS~70~b, based on a new spectrum in the $K$ band acquired with
VLT/SINFONI. We tested three hypotheses to explain the spectrum: Atmospheric
emission from the planet with either (1) a single value of extinction or (2)
variable extinction, and (3) a combined atmospheric and circumplanetary disc
model. Goodness-of-fit indicators favour the third option, suggesting
circumplanetary material contributing excess thermal emission — most
prominent at $lambda gtrsim 2.3 mu$m. Inferred accretion rates ($sim
10^{-7.8}$–$10^{-7.3} M_J$ yr$^{-1}$) are compatible with observational
constraints based on the H$alpha$ and Br$gamma$ lines. For the planet, we
derive an effective temperature of 1500–1600 K, surface gravity $log(g)sim
4.0$, radius $sim 1.6 R_J$, mass $sim 10 M_J$, and possible thick clouds.
Models with variable extinction lead to slightly worse fits. However, the
amplitude ($Delta A_V gtrsim 3$mag) and timescale of variation
($lesssim$~years) required for the extinction would also suggest
circumplanetary material.

We present the first observational evidence for a circumplanetary disc around
the protoplanet PDS~70~b, based on a new spectrum in the $K$ band acquired with
VLT/SINFONI. We tested three hypotheses to explain the spectrum: Atmospheric
emission from the planet with either (1) a single value of extinction or (2)
variable extinction, and (3) a combined atmospheric and circumplanetary disc
model. Goodness-of-fit indicators favour the third option, suggesting
circumplanetary material contributing excess thermal emission — most
prominent at $lambda gtrsim 2.3 mu$m. Inferred accretion rates ($sim
10^{-7.8}$–$10^{-7.3} M_J$ yr$^{-1}$) are compatible with observational
constraints based on the H$alpha$ and Br$gamma$ lines. For the planet, we
derive an effective temperature of 1500–1600 K, surface gravity $log(g)sim
4.0$, radius $sim 1.6 R_J$, mass $sim 10 M_J$, and possible thick clouds.
Models with variable extinction lead to slightly worse fits. However, the
amplitude ($Delta A_V gtrsim 3$mag) and timescale of variation
($lesssim$~years) required for the extinction would also suggest
circumplanetary material.

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