4 Comparing DENIS and 2MASS photometric systems

We considered the mean linear relation between DCMC and 2MASS magnitudes, restricting to the range [10, 14] in Jand [8, 12] in $K_{\rm s}$, avoiding the saturated bright stars as well as the faintest ones.

We find a systematic shift of the absolute calibration between the two catalogues. For each strip, we calculated the median of $\delta J$ and $\delta K_{\rm s}$. Figure 5 shows the histograms of the shifts found for the 119 LMC strips.

Figure 5: Histograms of the shifts between DCMC and 2MASS J and $K_{\rm s}$ magnitudes for the 119 strips covering the LMC. The bin size is $0.01^{\prime \prime }$.

The derived mean relations between the two systems are as follow:

$$\begin{eqnarray*}\lefteqn{J_{{\rm DCMC}} = J_{{\rm 2MASS}} - (0.11 \pm 0.06)} \... ...efteqn{ K_{{\rm sDCMC}} = K_{{\rm s2MASS}} - (0.14 \pm 0.05). } \end{eqnarray*}$$

These relations have been computed in the case of the DCMC catalogue and may not be valid for the whole DENIS survey. This is quite different from the relations proposed by Carpenter (2001), based on a limited preliminary sample of a few DENIS sources. Groenewegen (2000) did the comparison for a few hundred Cepheids towards the Clouds and found no significant difference between 2MASS and DENIS J, but found a 0.2 mag shift for the $K_{\rm s}$ band data. This larger shift compared to the one we find is probably due to the use of only variable stars (i.e. Cepheids).