  Errors were made in the calculations of EMs using the best fit normalizations
in XSPEC. Lists of the errors and corrections are as follows.
  (1)Tables 1, 3, and 4 in ApJ, 557, 747 and astro-ph/0104190 (YSOs in Rho
Oph): All the EMs in these tables should be multiplied by pi; the log(EM) in
the first raw in Table 1, for example, is 52.6(52.2--53.2), not
52.1(51.7--52.7).
  (2)Figures 7 and 9 in ApJ, 557, 747 and astro-ph/0104190 (YSOs in Rho Oph):
The EM plots should be systematically up-shifted by the factor of pi.
  (3)Table 3 in ApJ, 563, 361 and astro-ph/0108078 (young brown dwarfs in Rho
Oph): All the EMs in this table should be multiplied by pi; the log(EM) in the
first raw, for example, is 52.1(52.0--52.6), not 51.6(51.5--52.1).
  (4)Table 1 in ApJ, 567, 423 and astro-ph/0110462 (YSOs in Mon R2): All the
EMs in this table should be divided by 10; the log(EM) in the first raw, for
example, is 52.5(52.1--52.9), not 53.5(53.1--53.9).
  All the spectral parameters except EM are unchanged. These errors of EM do
not affect any of the conclusions of the relevant papers.
  In addition, Gregorio-Hetem, J., Montmerle, T., Casanova, S., and Feigelson,
E. D.1998, A&A, 331, 193 should be included in the reference list of ApJ, 567,
423 (astro-ph/0110462).
