New Variable Nebula in Cepheus

ATel #13832; G. Borisov (MARGO observatory; Astronomical Scientific Center; Crimean Astronomical Station of SAI MSU), D. Denisenko (SAI MSU)
on 25 Jun 2020; 18:16 UT
Credential Certification: Denis Denisenko (d.v.denisenko@gmail.com)

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In course of the search for comets at MARGO observatory [MPC Code L51] located in Nauchnij, Crimea, the new nebula was discovered by GB. Observations were made with the own-made 0.65-m f/1.5 Hamiltonian reflector + 3Kx3K CCD. The object at the following position: R.A. = 21 37 18, Decl. = +66 51 57 (equinox J2000.0) was found that is not present on the digitized Palomar observatory sky survey plates. The integral magnitude measured on the unfiltered image with 180-sec exposure starting on 2020-06-21 at 20:10:55 UT was ~17m (limiting magnitude 20.3). The object had a cometary appearance with a diameter about 20 arc sec plus a jet-like tail about 40 arc sec long in PA=315 deg.

Nothing is present at this position on the digitized Palomar plates from 1954 (POSS-I) and 1991-1995 (POSS-II). Comparison of 1991 Sep. 12 POSS-II Red plate and 2020 June 21 discovery image is presented at this link: VarNebula-Cep-DSS-anim.gif

Inspection of the DSS plates shows the new nebula to be located in the formerly dark region which is a part of the cloud TGU H642. Color-combined (BRI) DSS finder chart with 10'x10' FOV is posted at VarNebula-Cep-BRIR.jpg and infrared (JHK) 2MASS image with 8.5'x8.5' FOV at VarNebula-Cep-JHK.jpg. Nothing is present at this position in Simbad and NED databases. No transient object was reported in the past within 30 arc sec. There are no variable stars in AAVSO VSX within 10 arc min from this position.

Analysis of PanSTARRS-1 images available online at http://ps1images.stsci.edu/cgi-bin/ps1cutouts (Chambers et al., 2016) shows the nebula was not present in July-August 2011, has appeared on July-August 2013 images and got brighter by October 2014. It should be noticed that it is best seen in i filter and only marginally detected in r and z filters. Animation of Pan-STARRS 1 images in i filter is posted at VarNebula-Cep-PS1-anim.gif (2'x2' FOV) and the color-combined riz image at VarNebula-Cep-PS1-riz-2x2.jpg.

The object was not seen in Halpha filter images (3x180-sec exposures with 0.61-m iTelescope T24 instrument located in Auberry, CA) obtained by DD on 2020-06-25 at 11:10-11:25 UT. This area of sky at galactic latitude b=10.8 was not covered by SDSS, IPHAS and CRTS. The multi-band deep imaging and spectroscopic analysis of this nebula is requested, as well as the search for the archival images, especially those around 2012. Identification of the star illuminating the nebula is also encouraged.