We present spectroscopic observations of candidate F , G and K type stars in NGC 6633 , an open cluster with a similar age to the Hyades .
From the radial velocities and metal-line equivalent widths we identify 10 new cluster members including one short period binary system .
Combining this survey with that of Jeffries ( 1997 ) , we identify a total of 30 solar-type members .
We have used the F and early G stars to spectroscopically estimate [ Fe/H ] = -0.096 \pm 0.081 for NGC 6633 .
When compared with iron abundances in other clusters , determined in a strictly comparable way , we can say with more precision that NGC 6633 has ( 0.074 \pm 0.041 ) dex less iron than the Pleiades and ( 0.206 \pm 0.040 ) dex less iron than the Hyades .
A photometric estimate of the overall metallicity from the locus of cluster members in the B-V , V-I _ { c } plane , yields [ M/H ] = -0.04 \pm 0.10 .
A new estimate , based upon isochrones that are empirically tuned to fit the Pleiades , gives a distance modulus to NGC 6633 that is 2.41 \pm 0.09 larger than the Pleiades .

Lithium abundances have been estimated for the NGC 6633 members and compared with consistently determined Li abundances in other clusters .
Several mid F stars in NGC 6633 show strong Li depletion at approximately the same effective temperature that this phenomenon is seen in the Hyades .
At cooler temperatures the Li abundance patterns in several open clusters with similar ages ( NGC 6633 , Hyades , Praesepe and Coma Berenices ) are remarkably similar , despite their differing [ Fe/H ] .
There is however evidence that the late G and K stars of NGC 6633 have depleted less Li than their Hyades counterparts .
This qualitatively agrees with models for pre-main sequence Li depletion that feature only convective mixing , but these models can not simultaneously explain why these stars have in turn depleted Li by more than 1 dex compared with their ZAMS counterparts in the Pleiades .
Two explanations are put forward .
The first is that elemental abundance ratios , particularly [ O/Fe ] , may have non-solar values in NGC 6633 and would have to be higher than in either the Hyades or Pleiades .
The second is that additional non-convective mixing , driven by angular momentum loss , causes additional photospheric Li depletion during the first few hundred Myr of main sequence evolution .