Context : The globular cluster HP 1 is projected at only 3 \aas@@fstack { \circ } 33 from the Galactic center .
Together with its distance , this makes it one of the most central globular clusters in the Milky Way .
It has a blue horizontal branch ( BHB ) and a metallicity of [ Fe/H ] \approx - 1.0. This means that it probably is one of the oldest objects in the Galaxy .
Abundance ratios can reveal the nucleosynthesis pattern of the first stars as well as the early chemical enrichment and early formation of stellar populations .

Aims : High-resolution spectra obtained for six stars were analyzed to derive the abundances of the light elements C , N , O , Na , and Al , the alpha-elements Mg , Si , Ca , and Ti , and the heavy elements Sr , Y , Zr , Ba , La , and Eu .

Methods : High-resolution spectra of six red giants that are confirmed members of the bulge globular cluster HP 1 were obtained with the 8m VLT UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVES configuration .
The spectroscopic parameter derivation was based on the excitation and ionization equilibrium of Fe I and Fe II .

Results : We confirm a mean metallicity of [ Fe/H ] = -1.06 \pm 0.10 , by adding the two stars that were previously analyzed in HP 1 .
The alpha-elements O and Mg are enhanced by about +0.3 \mathrel { \hbox { \raise 2.15 pt \hbox { $ < $ } \hbox to 0.0 pt { \lower 2.15 pt \hbox { $% \sim$ } } } } [ O , Mg/Fe ] \mathrel { \hbox { \raise 2.15 pt \hbox { $ < $ } \hbox to 0.0 pt { \lower 2.15 pt \hbox { $ \sim$% } } } } +0.5 dex , Si is moderately enhanced with +0.15 \mathrel { \hbox { \raise 2.15 pt \hbox { $ < $ } \hbox to 0.0 pt { \lower 2.15 pt \hbox { $% \sim$ } } } } [ Si/Fe ] \mathrel { \hbox { \raise 2.15 pt \hbox { $ < $ } \hbox to 0.0 pt { \lower 2.15 pt \hbox { $ \sim$% } } } } +0.35 dex , while Ca and Ti show lower values of -0.04 \mathrel { \hbox { \raise 2.15 pt \hbox { $ < $ } \hbox to 0.0 pt { \lower 2.15 pt \hbox { $% \sim$ } } } } [ Ca , Ti/Fe ] \mathrel { \hbox { \raise 2.15 pt \hbox { $ < $ } \hbox to 0.0 pt { \lower 2.15 pt \hbox { $ \sim$% } } } } +0.28 dex .
The r-element Eu is also enhanced with [ Eu/Fe ] \approx + 0.4 , which together with O and Mg is indicative of early enrichment by type II supernovae .
Na and Al are low , but it is unclear if Na-O are anticorrelated .
The heavy elements are moderately enhanced , with -0.20 < [ La/Fe ] < +0.43 dex and 0.0 < [ Ba/Fe ] < +0.75 dex , which is compatible with r-process formation .
The spread in Y , Zr , Ba , and La abundances , on the other hand , appears to be compatible with the spinstar scenario or other additional mechanisms such as the weak r-process .

Conclusions :