We present a near-infrared ( K ^ { \prime } -band ) survey of 0.7 square degree area in the \alpha Persei open cluster ( age = 90 Myr , distance = 182 pc ) carried out with the Omega-Prime camera on the Calar Alto 3.5-m telescope .
Combining optical data ( R _ { c } and I _ { c } ) obtained with the KPNO/MOSA detector and presented in Stauffer et al .
( [ 1999 ] ) with the K ^ { \prime } observations , a sample of new candidate members has been extracted from the optical-infrared colour-magnitude diagram .
The location of these candidates in the colour-colour diagram suggests that two-thirds of them are actually reddened background giants .
About 20 new candidate members with masses between 0.3 and 0.04 M _ { \odot } are added to the \sim 400 known \alpha Per cluster members .
If they are indeed \alpha Per members , four of the new candidates would be brown dwarfs .
We discuss the advantages and drawbacks of the near-infrared survey as compared to the optical selection method .
We also describe the outcome of optical spectroscopy obtained with the Twin spectrograph on the Calar Alto 3.5-m telescope for about 30 candidates , including selected members from the optical sample presented in Barrado y Navascués et al . [ 2002 ] and from our joint optical/infrared catalogue .
These results argue in favour of the optical selection method for this particular cluster .