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ASASSN1: Bright Comet Discovered by the All Sky Automated Survey for SuperNovae

ATel #10597; JJ. L. Prieto (Diego Portales; MAS), B. J. Shappee (Hubble Fellow, Carnegie Observatories), J. Brimacombe (Coral Towers Observatory), K. Z. Stanek (Ohio State), Ping Chen, Subo Dong (KIAA-PKU), T. W.-S. Holoien, C. S. Kochanek, J. S. Brown, J. V. Shields, T. A. Thompson (Ohio State)
on 25 Jul 2017; 18:58 UT
Distributed as an Instant Email Notice Comets
Credential Certification: Benjamin Shappee (bshappee@obs.carnegiescience.edu)

Subjects: Optical, Comet

During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN, Shappee et al. 2014), using data from the quadruple 14-cm "Cassius" telescope on Cerro Tololo, Chile, we discovered a new moving transient source, now confirmed as a comet. The comet appears to have been in outburst and it is now possibly fading.

Comet ASASSN1 was first discovered in images obtained on UT 2017-07-19.32 at V~15.3 mag where the centroid was moving between the ASAS-SN three 90 second, dithered discovery images and there was no counterpart in the MPC database. J. Brimacombe followed up Comet ASASSN1 as a potentially new solar system object from the Savannah Skies Observatory and recovered Comet ASASSN1 9.7 hours later 0.21 degrees away. Stacking these observations on Comet ASASSN1 revealed it had a halo at least 25 arcsec in radius, a compact core, and no clear tail. Further observations were made using the Las Cumbres Observatory 1m at CTIO 24.7 hours after discovery which recovered Comet ASASSN1 at an SDSS g-band magnitude of 15.2. J. Brimacombe again recovered Comet ASASSN1 from Savannah Skies Observatory 0.77 degrees away from Comet ASASSN1's original location 35.7 hours after discovery. ASAS-SN's Cassius unit reobserved this field 3 days after discovery and found that Comet ASASSN1 significantly brightened to V~11.9 (measured in a 1.5 arcmin aperture). In addition to brightening, the coma around Comet ASASSN1 also increased significantly to 2.5 arcmin. Finally, the quadruple 14-cm "Brutus" telescope on Haleakala Hawaii observed Comet ASASSN1 6 days after discovery and found that it appears to have faded to V~12.2 (measured in a 1.5 arcmin aperture). This figure shows the discovery and follow-up ASAS-SN images, with reference image subtracted, centered on Comet ASASSN1. The circle has a radius of 2.5 arcmin and is centered on the position of Comet ASASSN1 in each image.

JD            RA        DEC    obs./tele.          MEASURER 
2457953.82085 38.2007 -10.5322 ASAS-SN/Cassius     B. Shappee 
2457954.22695 38.3677 -10.4043 Savannah Skies Obs. J. Prieto 
2457954.85353 38.6245 -10.2044 CTIO/LCOGT 1m       P. Chen 
2457955.31208 38.8119 -10.0577 Savannah Skies Obs. J. Prieto 
2457956.82058 39.4297 -9.56808 ASAS-SN/Cassius     B. Shappee 
2457960.11530 40.7719 -8.47081 ASAS-SN/Brutus      B. Shappee 

Continued follow-up observations are encouraged.

We note that the IAU has named this comet Comet C/2017 O1 and so far has not accepted the discovery group name for this comet even though the survey's acronym has been approved by the IAU and its name follows their conventions. Furthermore, at the time of this ATel, the IAU has stripped all information about this comet's discoverers from the Comet's web page. We believe that refusing to give discovery credit and name significantly oversteps the IAU's Division F Working Group on Small Body Nomenclature (SBN) responsibilities. We encourage all to use the original name (Comet ASASSN1) when referring to this comet.

We thank Las Cumbres Observatory and its staff for their continued support of ASAS-SN. ASAS-SN is funded in part by the Gordon and Betty Moore Foundation through grant GBMF5490 to the Ohio State University, NSF grant AST-1515927, the Mt. Cuba Astronomical Foundation, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, and the Chinese Academy of Sciences South America Center for Astronomy (CASSACA). For more information about the ASAS-SN project, see the ASAS-SN Homepage and the list of all ASAS-SN transients.