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NGC 3507 and star BD+18 2441On 26 May 2025, the ESA Hubble web site released an image of galaxy NGC 3507. Near the center of this galaxy is a foreground star, catalogued as BD+18 2441, which was noticed by William Herschel when he discovered the galaxy in 1784. The star was listed in the Bonner Durchmusterung (BD) catalog in 1903, its position listed as 10h 55m 43.3s, +18d 55.0m (equinox 1855) [Note: due to equinox precession, these coordinates are different than when using today's coordinate system.] This star is known to have high proper motion, that is, the star moves slowly across the celestial sphere. The proper motion was first listed by Frank E. Ross, in a paper published in 1926, giving the star the additional catalog name Ross 105. The SIMBAD database lists its proper motion as 76.124 milliarcseconds per year for right ascension, and -196.585 milliarcseconds per year for declination, which comes from the year 2020 Gaia Early Data Release 3. This means the star has been slowly moving from NorthWest to SouthEast. I have computed the expected positions going back to discovery, and forward to the year 2325, using the 2025 HST image as a reference point. Overlayed on the image from the Hubble Space Telescope, I have approximated the predicted locations of the star in 100-year intervals. The star should move off the edge of the galaxy sometime around or after the year 2325, depending on how exactly the edge of the galaxy is defined. Computed locations by year: (all coordinates are using J2000 epoch) 1784: RA 11 03 25.82 DEC +18 08 55.89 Note: this image was rotated from the original so that North is up, East is left. .png)
The earliest clear image of NGC 3507 I could find is this one taken with the Palomar 48-inch Schmidt telescope, dated 1 March 1952. It has been magnified 3x. You can see the star's position is about where we would expect it to be relative to the galaxy's nucleus. Download the original .FITS file here.
Wikipedia page for host galaxy NGC 3507: https://en.wikipedia.org/wiki/NGC_3507 SIMBAD page for star BD+18 2441: http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=BD%2B18+2441 Page created 5/27/2025 by D. Hodges Last update: 5/27/2025
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