We present H band spectroscopic and H \alpha photometric observations of HD 100546 obtained with the Gemini Planet Imager and the Magellan Visible AO camera .
We detect H band emission at the location of the protoplanet HD 100546 b , but show that choice of data processing parameters strongly affects the morphology of this source .
It appears point-like in some aggressive reductions , but rejoins an extended disk structure in the majority of the others .
Furthermore , we demonstrate that this emission appears stationary on a timescale of 4.6 yrs , inconsistent at the 2 \sigma level with a Keplerian clockwise orbit at 59 au in the disk plane .
The H band spectrum of the emission is inconsistent with any type of low effective temperature object or accreting protoplanetary disk .
It strongly suggests a scattered light origin , as it is consistent with the spectrum of the star and the spectra extracted at other locations in the disk .
A non-detection at the 5 \sigma level of HD 100546 b in differential H \alpha imaging places an upper limit , assuming the protoplanet lies in a gap free of extinction , on the accretion luminosity of 1.7 \times 10 ^ { -4 } ~ { } \mathrm { L } _ { \odot } and \mathrm { M } \dot { \mathrm { M } } < 6.3 \times 10 ^ { -7 } ~ { } \mathrm { M } _ { \mathrm { Jup } } ^ { 2 } . % \mathrm { yr } ^ { -1 } for 1 \mathrm { R } _ { \mathrm { Jup } } .
These limits are comparable to the accretion luminosity and accretion rate of T-Tauri stars or LkCa 15 b .
Taken together , these lines of evidence suggest that the H band source at the location of HD 100546 b is not emitted by a planetary photosphere or an accreting circumplanetary disk but is a disk feature enhanced by the PSF subtraction process .
This non-detection is consistent with the non-detection in the K band reported in an earlier study but does not exclude the possibility that HD 100546 b is deeply embedded .