A transmission spectrum of the planet candidate WD 1856+534 b and a lower limit to its mass

The cool white dwarf WD 1856+534 was found to be transited by a Jupiter-sized object with mass at or below 14 M$_{\rm{Jup}}$. We used the GTC telescope obtain and analyse photometry low resolution spectroscopy of six transits b, intention derive slope transmission spectrum, towards an eventual detection Rayleigh scattering particles in its atmosphere. Such slope, assuming cloud-free atmosphere dominated scattering, could translated into estimation b. However, resultant spectrum is essentially flat, therefore permits only determination lower limits 2.4 M$_{\rm{Jup}}$ 2-$\sigma$ level, 1.6 3-$\sigma$. These have implications for some proposed formation scenarios object. elaborate on potential effects clouds hazes our estimations, based previous studies Jupiter Titan. In addition, we detected H$\alpha$ absorption feature combined host dwarf, that leads assignation DA classification allows derivation independent set atmospheric parameters. Furthermore, epochs five were measured sub-second precision, which demonstrates additional objects more massive than $\approx$5 periods longer $O(100)$ days through light travel time effect