Large Variety of New Pulsating Stars in the OGLE-III Galactic Disk
  Fields
  We present the results of a search for pulsating stars in the 7.12 deg^2
OGLE-III Galactic disk area in the direction tangent to the Centaurus Arm. We
report the identification of 20 Classical Cepheids, 45 RR Lyr type stars, 31
Long-Period Variables, such as Miras and Semi-Regular Variables, one pulsating
white dwarf, and 58 very likely delta Sct type stars. Based on asteroseismic
models constructed for one quadruple-mode and six triple-mode delta Sct type
pulsators, we estimated masses, metallicities, ages, and distance moduli to
these objects. The modeled stars have masses in the range 0.9-2.5 M_sun and are
located at distances between 2.5 kpc and 6.2 kpc. Two triple-mode and one
double-mode pulsators seem to be Population II stars of the SX Phe type,
probably from the Galactic halo. Our sample also includes candidates for Type
II Cepheids and unclassified short-period (P<0.23 d) multi-mode stars which
could be either delta Sct or beta Cep type stars. One of the detected variables
is a very likely delta Sct star with an exceptionally high peak-to-peak I-band
amplitude of 0.35 mag at the very short period of 0.0196 d. All reported
pulsating variables but one object are new discoveries. They are included in
the OGLE-III Catalog of Variable Stars. Finally, we introduce the on-going
OGLE-IV Galactic Disk Survey, which covers more than half of the Galactic
plane. For the purposes of future works on the spiral structure and star
formation history of the Milky Way, we have already compiled a list of known
Galactic Classical Cepheids.
