Syntax:

$ ./vartools -i EXAMPLES/1 -quiet \
    -converttime input jd inputsubtract 2400000. \
        output hjd outputsubtract 2400000. \
        radec fix 88.079166 32.5533 \
    -o EXAMPLES/OUTDIR1/1.hjdutc

Convert the light curve EXAMPLES/1 from JD-2400000 to HJD-2400000 (Heliocentric Julian Date; assuming an elliptical orbit for the Earth-Moon Barycenter with linear perturbations to the orbital elements) and output to EXAMPLES/OUTDIR1/1.hjdutc.

$ ./vartools -i EXAMPLES/1.UTC -quiet \
    -readformat 0 inpututc '%Y-%M-%DT%h:%m:%s' 1 2 3 \
    -converttime input jd inputsys-utc \
        output bjd outputsubtract 2400000. outputsys-tdb \
        radec fix 88.079166 32.5533 \
        ephemfile CSPICEKERNELS/de421.bsp \
        leapsecfile CSPICEKERNELS/naif0009.tls \
        planetdatafile CSPICEKERNELS/pck00009.tpc \
        observatory flwo \
    -o EXAMPLES/OUTDIR1/1.bjdtdb

Convert the time in the light curve EXAMPLES/1.UTC from UTC to Barycentric Julian Date (BJD) in the Barycentric Dynamical Time (TDB) reference system. We use the inpututc keyword to the -readformat command to specify that the input is in UTC and to provide its format; the UTC is automatically converted to JD on input. The -converttime command converts from the input JD on the UTC system to the output BJD on the TDB system. We subtract 2400000 from the output time (providing an easier to read number). For conversion to BJD we must additionally specify the RA and DEC of the source, we also need to provide CSPICE ephemeris, leap-second and planetary-data files (not included with this distribution). For completeness we also give the observatory where the observations were made, however this is a very minor correction. The time-converted light curve is output to EXAMPLES/OUTDIR1/1.bjdtdb.