Testing the variability of the proton-to-electron mass ratio from
  observations of methanol in the dark cloud core L1498
  The dependence of the proton-to-electron mass ratio, mu, on the local matter
density was investigated using methanol emission in the dense dark cloud core
L1498. Towards two different positions in L1498, five methanol transitions were
detected and an extra line was tentatively detected at a lower confidence level
in one of the positions. The observed centroid frequencies were then compared
with their rest frame frequencies derived from least-squares fitting to a large
data set. Systematic effects, as the underlying methanol hyperfine structure
and the Doppler tracking of the telescope, were investigated and their effects
were included in the total error budget. The comparison between the
observations and the rest frame frequencies constrains potential mu variation
at the level of Dmu/mu < 6 x 10^(-8), at a 3 sigma confidence level. For the
dark cloud we determine a total CH3OH (A+E) beam averaged column density of 3-4
x 10^(12) cm(-2) (within roughly a factor of two), an E- to A-type methanol
column density ratio of N(A-CH3OH)/N(E-CH3OH) = 1.00 +/- 0.15, a density of
n(H2) = 3 x 10^5 cm^(-3) (again within a factor of two), and a kinetic
temperature of Tkin = 6 +/- 1 K. In a kinetic model including the line
intensities observed for the methanol lines, the n(H2) density is higher and
the temperature is lower than that derived in previous studies based on
different molecular species; the intensity of the 1_0 --> 1_-1 E line strength
is not well reproduced.
