Open AccessMapping stellar kinematics across the Galactic bar: HST measurements of proper motions in 35 fields ★
Author(s) -
Kozłowski S.,
Woźniak P. R.,
Mao S.,
Smith M. C.,
Sumi T.,
Vestrand W. T.,
Wyrzykowski Ł.
Publication year - 2006
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2006.10487.x
Subject(s) - physics , astrophysics , proper motion , galactic plane , galaxy , stars , advanced camera for surveys , galactic center , bulge , astronomy , hubble space telescope
We present a proper motion mini‐survey of 35 fields in the vicinity of Baade window, ( l , b ) = (1°, −4°) , sampling roughly a 5 × 2.5‐deg 2 region of the Galactic bar. Our second epoch observations collected with the Advanced Camera for Surveys/High Resolution Channel instrument onboard the Hubble Space Telescope were combined with the archival Wide Field Planetary Camera 2/PC images. The resulting time baselines are in the range of 4 to 8 yr. Precise proper motions of 15 863 stars were determined in the reference frame defined by the mean motion of stars with magnitudes between I F 814 W = 16.5 and 21.5 along the line of sight. We clearly detect small gradients in proper motion dispersions (σ l , σ b ∼ (3.0, 2.5) mas yr −1 , and in the amount of anisotropy (σ l /σ b ∼ 1.2) . Both the longitude dispersion σ l and its ratio to the vertical motion σ b increase towards the Galactic plane. The decline of the anisotropy ratio σ l /σ b towards the minor axis of the bulge is mostly due to increasing σ b . We also find, for the first time, a significant negative covariance term in the transverse velocity field σ lb /(σ l σ b ) ≃−0.10 . Our results extend by a factor of ∼15 the number of the Galactic bar fields with good proper motion dispersions.