Context : KELT-9 b exemplifies a newly emerging class of short-period gaseous exoplanets that tend to orbit hot , early type stars - termed ultra-hot Jupiters .
The severe stellar irradiation heats their atmospheres to temperatures of \sim 4 , 000 K , similar to the photospheres of dwarf stars .
Due to the absence of aerosols and complex molecular chemistry at such temperatures , these planets offer the potential of detailed chemical characterization through transit and day-side spectroscopy .
Detailed studies of their chemical inventories may provide crucial constraints on their formation process and evolution history .

Aims : To search the optical transmission spectrum of KELT-9 b for absorption lines by metals using the cross-correlation technique .

Methods : We analyze two transit observations obtained with the HARPS-N spectrograph .
We use an isothermal equilibrium chemistry model to predict the transmission spectrum for each of the neutral and singly-ionized atoms with atomic numbers between 3 and 78 .
Of these , we identify the elements that are expected to have spectral lines in the visible wavelength range and use those as cross-correlation templates .

Results : We detect ( > 5 \sigma ) absorption by Na i , Cr ii , Sc ii and Y ii , and confirm previous detections of Mg i , Fe i , Fe ii and Ti ii .
In addition , we find evidence of Ca i , Cr i , Co i , and Sr ii that will require further observations to verify .
The detected absorption lines are significantly deeper than predicted by our model , suggesting that the material is transported to higher altitudes where the density is enhanced compared to a hydrostatic profile , i.e .
that the material is part of an extended or outflowing envelope .
There appears to be no significant blue-shift of the absorption spectrum due to a net day-to-night side wind .
In particular , the strong Fe ii feature is shifted by 0.18 \pm 0.27 km s ^ { -1 } , consistent with zero .
Using the orbital velocity of the planet we derive revised masses and radii of M _ { * } = 1.978 \pm 0.023 M _ { \odot } , R _ { * } = 2.178 \pm 0.011 R _ { \odot } , m _ { p } = 2.44 \pm 0.70 M _ { J } and R _ { p } = 1.783 \pm 0.009 R _ { J } .

Conclusions :