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Description
Discovered in the last decade as overdensities of resolved stars, the ultra-faint dwarfs (UFDs) are among the least luminous, most dark-matter dominated, and most metal-poor galaxies known today. They appear as sparse, loose objects with high mass-to-light ratios. Hercules is the prototype of the UFD galaxies. To date, there are still no firm constraints on its total luminosity due to the difficulty of disentangling Hercules bona-fide stars from the severe Galactic field contamination. To better constrain Hercules properties, we aim at removing foreground and background contaminants in the galaxy field using the proper motions of the Milky Way stars and the colour-colour diagram. We have obtained images of Hercules in the r_Sloan_ , B_Bessel_ and U_spec_ bands with the Large Binocular Telescope (LBT) and LBC-BIN mode capabilities. The r_Sloan_ new dataset combined with data from the LBT archive span a time baseline of about 5yr, allowing us to measure proper motions of stars in the Hercules direction for the first time. The U_spec_ data along with existing LBT photometry allowed us to use colour-colour diagram to further remove the field contamination. Description: The Hercules ultra-faint dwarf (UFD) galaxy (J2000 position 16:31:02.0+12:47:25.6) was observed with the Large Binocular Camera (LBC) at the LBT located on Mount Graham in Arizona. The LBC is a wide field imager (4 CCDs, 2Kx4.5K pixels each) with a FoV of ~23'x 23' and a resolution of 0.225"/pix. We employed both archival and proprietary data to have the longest available time baseline. File table2 contains the final catalogue of 528 PM-selected sources. From left to right we report: the source identity (Col. 1), right ascension and declination (Col. 2-3), U_spec_, B_Bessel_ and r_Sloan_ magnitudes with their uncertainty (Col. 4-6), displacement with its uncertainty (Col. 7)
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