Extracting coefficients' standard errors from linear model

Dear all,

Hope this question is not too trivial...

In order to correct standard errors from an estimation of a fixed 
effects regression model y need to extract the vector of standard
errors of the coefficients of a simple linear model estimated using

lm(var1~var2+var3+var4)

Unfortunately I can't find out the corresponding function.

ctl <- c(4.17,5.58,5.18,6.11,4.50,4.61,5.17,4.53,5.33,5.14)
trt <- c(4.81,4.17,4.41,3.59,5.87,3.83,6.03,4.89,4.32,4.69)
group <- gl(2,10,20, labels=c("Ctl","Trt"))
weight <- c(ctl, trt)
lm.D9 <- lm(weight ~ group)

vcov(lm.D9)[2,2]

vcov(lm.D9)[2,2]^(1/2)