watchingthesky16
SN 2018epf - Not a supernova
SN 2018epf was originally discovered by ATLAS with their internal designation of ATLAS18szp. It was posted to the Transient Domain Server (TNS) as AT 2018epf. A team called SCAT took a spectrum and their analysis was of a Type Ia/b supernova at a redshift of 0.0377. Upon sending their data to TNS the designation was changed from AT 2018epf to SN 2018epf.
However, the object flagged by the ATLAS team at RA = 16:50:31.703, Decl. = +43:03:27.18 does not look like a galaxy, but instead an orange star in the SDSS. The Gaia data for this star shows proper motion of –26.7 +/- 3.9 mas in RA and –29.7 +/- 3.9 mas in Decl. That suggests movement to the southwest. The video showing the POSS1 image (b&w) and the SDSS image (color) some 50 years apart confirms movement in that direction. The Gaia parallax suggests a distance of some 632 light-years. With a reported V magnitude of 17.14 that corresponds to an absolute magnitude of about +10.7 which suggests this star is either a late-type K or very early M dwarf. Note a fainter star to the right of the star which shows lateral movement between the frames.
Furthermore, David Bishop’s supernova site reports a follow up image that shows the object was unconfirmed. As of the moment this report was done, a click of the link to that image would not pull up.
What did the SCAT team train their instrument on? Did they take a spectrum of this star and mistake it for a supernova? Or, did they take a spectrum of another object and reported it for the wrong object? If it was the wrong object, what was the correct one? A check of the discoveries around that time found too many to say it must be this one, but a couple of possibilities are SN 2018eva (Type Ib) or SN 2018euz (Type Ia).
There is an odd thing about the SDSS image of the star. When you enlarge the image, the star is slightly oval even though other stars appear nearly circular. The PanSTARRS images also show it being oval. Maybe it is an unresolved double star of two stars of similar brightness and type. Second, there appears to be a red jet extending northwest. A check of the SDSS FITS images shows it on more than one image and it also appears on the PanSTARRS images so it must be a real object. Most likely this is a very distant background galaxy that was too faint to show up on the earlier POSS1 image.
A check of the CRTS database does not show any variability outside of the error bars, but that does not preclude a flare star. Perhaps the ATLAS team caught a flare from this star.
TNS entry for SN 2018epf: wis-tns.weizmann.ac.il/object/2018epf
SCAT ATel of the classification: www.astronomerstelegram.org/?read=11919
SDSS: skyserver.sdss.org/dr16/en/tools/explore/Summary.aspx?id=...
David Bishop’s supernova archive for 2018: www.rochesterastronomy.org/sn2018/index.html
SN 2018epf - Not a supernova
SN 2018epf was originally discovered by ATLAS with their internal designation of ATLAS18szp. It was posted to the Transient Domain Server (TNS) as AT 2018epf. A team called SCAT took a spectrum and their analysis was of a Type Ia/b supernova at a redshift of 0.0377. Upon sending their data to TNS the designation was changed from AT 2018epf to SN 2018epf.
However, the object flagged by the ATLAS team at RA = 16:50:31.703, Decl. = +43:03:27.18 does not look like a galaxy, but instead an orange star in the SDSS. The Gaia data for this star shows proper motion of –26.7 +/- 3.9 mas in RA and –29.7 +/- 3.9 mas in Decl. That suggests movement to the southwest. The video showing the POSS1 image (b&w) and the SDSS image (color) some 50 years apart confirms movement in that direction. The Gaia parallax suggests a distance of some 632 light-years. With a reported V magnitude of 17.14 that corresponds to an absolute magnitude of about +10.7 which suggests this star is either a late-type K or very early M dwarf. Note a fainter star to the right of the star which shows lateral movement between the frames.
Furthermore, David Bishop’s supernova site reports a follow up image that shows the object was unconfirmed. As of the moment this report was done, a click of the link to that image would not pull up.
What did the SCAT team train their instrument on? Did they take a spectrum of this star and mistake it for a supernova? Or, did they take a spectrum of another object and reported it for the wrong object? If it was the wrong object, what was the correct one? A check of the discoveries around that time found too many to say it must be this one, but a couple of possibilities are SN 2018eva (Type Ib) or SN 2018euz (Type Ia).
There is an odd thing about the SDSS image of the star. When you enlarge the image, the star is slightly oval even though other stars appear nearly circular. The PanSTARRS images also show it being oval. Maybe it is an unresolved double star of two stars of similar brightness and type. Second, there appears to be a red jet extending northwest. A check of the SDSS FITS images shows it on more than one image and it also appears on the PanSTARRS images so it must be a real object. Most likely this is a very distant background galaxy that was too faint to show up on the earlier POSS1 image.
A check of the CRTS database does not show any variability outside of the error bars, but that does not preclude a flare star. Perhaps the ATLAS team caught a flare from this star.
TNS entry for SN 2018epf: wis-tns.weizmann.ac.il/object/2018epf
SCAT ATel of the classification: www.astronomerstelegram.org/?read=11919
SDSS: skyserver.sdss.org/dr16/en/tools/explore/Summary.aspx?id=...
David Bishop’s supernova archive for 2018: www.rochesterastronomy.org/sn2018/index.html