R help - Feb 2014 - Why does a date frame returning date with a time zone sometimes?

I may have misunderstood your question.? 

vec1 <- seq(as.POSIXct("2009-01-01 00:00:00",format="%Y-%m-%d
%H:%M:%S"),by= '12 hour', length=12)

vec1[1:3] #returns with time zone
#[1] "2009-01-01 00:00:00 EST" "2009-01-01 12:00:00 EST"
#[3] "2009-01-02 00:00:00 EST"

If you don't want the time zone info:,
strftime(vec1,usetz=FALSE)[1:2]
#[1] "2009-01-01 00:00:00" "2009-01-01 12:00:00"


Also, you can change the time zone,



Sys.setenv(TZ="GMT")
?vec1[1:2]
#[1] "2009-01-01 05:00:00 GMT" "2009-01-01 17:00:00 GMT"

It is not clear what you want.
A.K.


I have a date from which returns 
head(mt, 3) 
? ? ? ? ? ? ? ? DateW ? ? ? ? ? ? | ? ? ? ? Date ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
|tempDeg
2 2009-01-01 01:00:00 ? ? ? | ? ? ? ? 2009-01-01 01:00:00 ? ? ? ?| ? ? ? ?
?-23.6
3 2009-01-01 02:00:00 ? ? ? | ? ? ? ? 2009-01-01 02:00:00 ? ? ? ?| ? ? ? ?
?-25.7
4 2009-01-01 03:00:00 ? ? ? | ? ? ? ? 2009-01-01 03:00:00 ? ? ? ?| ? ? ? ?
?-26.5


Why does this return ?a time with MST? 

mt[1,2] 
[1] "2009-01-01 01:00:00 MST"