TITLE: GCN CIRCULAR NUMBER: 25386 SUBJECT: LIGO/Virgo S190814bv: Pan-STARRS imaging indicates DG19sevhc (AT2019npy) is a proper motion star DATE: 19/08/17 22:45:05 GMT FROM: Stephen Smartt at Queen's U/Belfast S. Smartt (QUB), D. Malesani (DARK), K. W. Smith (QUB), M. Huber (IfA, Univ. of Hawaii), K. Chambers, A. Schulz (IfA), D. R. Young, O. McBrien, J. Gillanders. S. Srivastav, D. O'Neil, P. Clark, S. Sim (QUB), T. de Boer, J. Bulger, J. Fairlamb, M. Huber, C.-C. Lin, T. Lowe, E. Magnier, R. J. Wainscoat, M. Willman (IfA, Univ. of Hawaii), T.-W, Chen (MPE), A. Rest (STScI), C. Stubbs (Harvard) In the search of the skymap of the NSBH event S190814bv (The LIGO Scientific Collaboration and the Virgo Collaboration, GCN 25333, 25324) the DECam-GROWTH team identified DG19sevhc (AT2019npy; Andreoni et al. GCN 25362) as a candidate. It was followed up by Rossi et al (GCN 25383) and Dichiara et al. (GCN 25374). The latter reported an unusual and rapid z-band rise, which drew attention. We found a previous source detection close to this position on difference images taken during the Pan-STARRS Survey For Transients (Huber et al. 2015, ATel 7153) at i=20.9, on multiple images from MJD=58335 (2018-08-05). However closer inspection revealed that the source was not a transient. There is a faint red star which is coincident with background extended flux (probably a faint, red galaxy) and the star appears to have slow proper motion. This produced a dipole source in the Pan-STARRS difference images, and triggered a new source detection. The motion between the Pan-STARRS reference and the image from MJD=58335 is visually clear (about 1.4 arcsec). We further inspected the separate Pan-STARRS 3Pi epochs (Chambers et al. 2016, arXiv:1612.05560C). Using 3 images with reasonable S/N between 2010 September and 2014 August, plus the public DECam image from 2019 August, the position of the star traces a vector towards the S-E. We estimate a proper motion of 0.07 and -0.12 arcsec/yr in RA and Dec, respectively. Hence we conclude that AT2019npy is not a transient, but resulted from the proper motion of this star leaving a positive residual in the DECam images of 2019 August, and the DECam references. The unusual spatial coincidence of the moving star and background galaxy made the original DECam identification as a transient quite understandable and reasonable.