Probable progenitor of ASASSN-18su detected in Gaia DR2, GALEX and other surveys
ATel #11971; R. H. Barba (Universidad de La Serena)
on 20 Aug 2018; 05:21 UT
Credential Certification: Rodolfo Barba (rbarba@dfuls.cl)
Subjects: Infra-Red, Optical, Ultra-Violet, Cataclysmic Variable
The bright transient ASASSN-18su (g~10) reported by Stanek et al. (ASAS-SN, Atel #11968) was classified as CV by Callis et al. (ePESSTO, Atel #11969) without identification of the probable progenitor.
The object is almost coincident (1.5 arcsec) with the position of an object listed in Gaia Data Release 2 (GDR2; Gaia Collaboration 2018 A+A in press, arXiv:1804.09365) as source 6185371175372936064, with magnitude G=17.90. The source has a relatively large parallax of 5.52 +/- 0.15 mas (181 +/- 5 pc without systematic correction), and large proper motion.
SkyMapper DR1 images (Wolf et al. 2018, PASA, 2018, 35, 10) available through Aladin Sky Atlas (Bonnarel et al. 2000, A+AS, 143, 33) shows a very faint object with interesting features: the R-band image is elongated, while the I-band image is also elongated but perpendicular to and centered in the R-band elongation. This structure could be indication of a bipolar nebula or outflow, due to a probable H-alpha emission contribution to the R-band. Furthermore, the source is detected particularly bright in GALEX, faint in WISE/W1/W2, and detectable in 2MASS (but shifted due to proper motion). Gaia DR2, GALEX and other survey images support that ASASSN-18su is a CV as reported in Atel #11969, but also this is a nearby CV with probable ejected material (as suggested by SkyMapper images).
Aladin mosaics in the area are available in these links:
https://drive.google.com/file/d/1AaOSwoIihoAnLn0VfqeWIkXfDe_9finQ
https://drive.google.com/file/d/1XyBljDK_A0FCsAcZXXrHcakDWlJmfLju