All plots involves ONLY point-sources detected in IC4665 which satisfy the following criteria: yClass=jClass=hClass=kClass=-1 The same criteria were used for Coma_Ber.

External photometry:

• 1a: comparison with 2MASS, refer to the plots and comments made by Tim Kendall.

I made a similar plot which compares the JHKs magnitudes from 2MASS with the GCS magnitudes in the IC4665 open cluster. See Figure ic4665_gcs_2mass_phot.ps. Same results as Tim: slight offset in J, H, and K. It could be due to the difference in the filter curve (in particular for K).

The same offsets are seen when plotting GCS magnitudes versus 2MASS JHK in Coma_Ber (see plot comaber_gcs_2mass_phot.ps).

• 1b: comparison with NIR photometry obtained with CFHT/CFHTIR within the framework of a Large Programme. This Large Programme involved studies of open clusters in the optical complemented by NIR follow-up observations. We have surveyed 3.8 square degrees in IC4665 in I and z filters (Willem-Jan de Wit and Jerome Bouvier, Grenoble). Selected cluster candidates were extracted and followed-up in JHK when possible. I cross-correlated this photometry and compared it with the UKIDSS GCS survey. The results are shown in 2 figures: ic4665_gcs_cfhtir_jhk.ps and ic4665_gcs_cfhtir_k.ps. As with 2MASS, a small offset is seen in all 3 passbands. I believe that the CFHT filters in the MKO system but it should be checked. And the CFHTIR photometry is calibrated on 2MASS so we find the same offsets as for 2MASS vs. GCS!!

Depth of the GCS survey:

• 2a: IC4665.

I have plotted the histogram of objects as a function of magnitude in YJHK for IC4665. I used no constrain on the Class of the object for those plots. The completeness limits are estimated to Z=19.0, Y=18.0, J=17.5, H=18.0, K=17.0. Those values should be compared to the foreseen depth of the GCS survey (Y=, J=19.7, H=18.8, K=18.4). (Figure ic4665_gcs_completeness.ps). The Y and J survey seem shallower than predicted.

• 2b: Coma_Ber

The same plot is provided for Coma_Ber. Completeness limits are Y=19.5, J=18.5, H=18.0, and K=17.5. (Figure comaber_gcs_completeness.ps)

• 2c: I have used the following SQL query to estimate the completeness limit of the GCS survey in IC4665. These numbers are the correct ones and displayed in the completeness plot.

SELECT CAST(ROUND(zMag*10.0,0) AS INT), LOG(COUNT(*))
FROM   gcsSource
WHERE  zMag>0.0
GROUP BY CAST(ROUND(zMag*10.0,0) AS INT)

Astrometry

• 3a: IC4665: GCS versus 2MASS

I have plotted the difference in RA and dec (in arcsec) between 2MASS and the GCS for IC4665. Figure ic4665_gcs_2mass_astrom.ps

• 3b: Astrometry as a function of magnitude

I have plotted the difference in RA and dec between 2MASS and the GCS in IC4665 as a function of magnitudes. Figure ic4665_gcs_2mass_astrom_mag.ps

• 3c: Coma_Ber: GCS versus 2MASS

I have plotted the difference in RA and dec (in arcsec) between 2MASS and the GCS for Coma_Ber. Figure comaber_gcs_2mass_astrom.ps. I have also plotted the difference in RA and dec as a function of J magnitude (figure comaber_gcs_2mass_astrom_mag.ps). These plots are the same as the one shown for IC4665.

Selection of cluster members in IC4665

• Secondly, I have used various colour-magnitude diagrams to weed out contaminants from the list of cluster members in IC 4665 drawn from the deep wide-field optical (I,z) survey (de Wit et al. 2005). Note that some near-infrared photometry was obtained for some candidates using the CFHTIR camera. Among brown dwarf candidates, 18 out of 89 have Kcfhtir-band photometry and only 4 have Jcfhtir and Hcfhtir magnitudes. I have drawn the (z-J,z) and (z-K,z) colour-magnitude diagrams to select all candidates located to the right of the 100 Myr NextGen^?+DUSTY isochrones. Out of 769 optically-selected candidates, 612 and 508 were located to the right of the NextGen^? isochrones in the (z-J,z) and (z-K,z) colour-magnitude diagrams. 483 are common to both lists (blue circles in the attached figures). I have overplotted those probable cluster members in the (Y-J,Y) and (J-K,K) colour-magnitude diagrams to further constrain their membership. Most of them clearly remain members and satisfy the new colour criteria. Nevertheless, the selection of candidates needs to be refined as some lie to the left of the isochrones, they could be classified as possible members (M?).

• I have compared the list of sources located to the right of the NextGen^? isochrones in the (z-J,z) and (Z-J,Z) colour-magnitude diagrams. 612 and 472 remain members, respectively, implying that the Z-J colour criterion tends to reject more candidates than the z-J. Which filter is the most efficient one is hard to determine at this stage. I would be happy to hear your comment and opinions on this matter. This is an important issue is the GCS plans to include an "optical" band. The (Y-J,Y) colour-magnitude diagram should also be analysed thoroughly for that matter. The same conclusions are drawn regarding the number of selected candidates in the (z-K,z) and (Z-K,Z) colour-magnitude diagrams.

• I have added proper-motion selected members in the (J-K,K) colour-magnitude diagram (red open triangles). Those objects originate from the cross-correlation between 2MASS and USNO. They were selected in a 5 mas/yr radius centred on (-0.9,-8.1) mas/yr in the vector point diagram for IC 4665. They link the high-mass members to the new probable members (blue circles) and follow the NextGen^? isochrones. Many of them are located in the sequence defined by field star but this expected due to the small proper motion of the IC 4665 cluster.

• I have attached several colour-magnitudes diagrams, the legend is as follows:
  • The solid line is the 100 Myr NextGen^? isochrone (Baraffe et al. 1998). If a second line is displayed, it is the 50 Myr one.
  • The dashed line is the 100 Myr DUSTY isochrone (Chabrier et al. 2000). If a second one is drawn, it is the 50 Myr one. Red circles represent the 769 optically-selected cluster member candidates (de Wit et al. 2005, subm. to A\&A)
  • The blue circles represent the 483 common candidates located to the right of the isochrones in the (z-J,z) AND (z-K,z) colour-magnitude diagrams. *The small black dots represent all point sources detected in the 6.8 square degree area covered in IC 4665 by the GCS. Those dots are only plotted for GCS detections as I haven't cross-correlated the optical ($I$,$z$) sources with the GCS survey.

-- NicolasLodieu - 13 Sept 2005