Astronomy & Astrophysics

Table 1: The sample of the 11 young BDs, with spectral type later than M 6, surveyed with the XMM-Newton Optical/UV Monitor (OM) in the XEST (Güdel et al. 2007). Columns (1) and (2) give the BD names and the 2MASS counterparts, respectively. Column (4) is the references of the spectral types in Col. (3), with B02 = Briceño et al. (2002), G06 = Guieu et al. (2006), L06 = Luhman (2006), and M05 = Muzerolle et al. (2005). Column (5) gives the disk accretion rate when available (Mohanty et al. 2005; for 2MASS J0414, Muzerolle et al. 2005). Column (6) is the XEST field number, plus the source number if there is an X-ray detection (Grosso et al. 2007). Columns (7) and (8) indicate the duration of one single full-frame/imaging window exposure and the total number of similar exposure obtained on the BD. Column (9) gives the U-band magnitude or the U-band limiting magnitude of each window exposure for a 3 $\sigma$ point-source detection (this work). For 2MASS J0422, the limiting magnitude was computed for the broader UVW1 filter (200-400 nm), which includes the U-band.
Table 2: Optical CCD photometry of 2MASS J0414 obtained with the 1.3-m McGraw-Hill telescope at the MDM observatory on October 25, 2005. Filter values are the average of two observations obtained during the same night (05 $^{\rm h}$ 19 $^{\rm m}$ -05 $^{\rm h}$ 34 $^{\rm m}$ UT and 11 $^{\rm h}$ 46 $^{\rm m}$ -11 $^{\rm h}$ 55 $^{\rm m}$ UT).