Peculiar Red Flaring Object in the field of NGC 4945
ATel #12638; D. Denisenko (Sternberg Astronomical Institute, Lomonosov Moscow State University)
on 7 Apr 2019; 20:21 UT
Credential Certification: Denis Denisenko (d.v.denisenko@gmail.com)
Subjects: Optical, Request for Observations, Cataclysmic Variable, Young Stellar Object
The new flaring object in Centaurus was detected during the observations of NGC 4945 galaxy with iTelescope.Net T31 instrument (0.50-m f/6.8 reflector + CCD + f/4.5 focal reducer) in Siding Spring, Australia at 16:06-16:09 UT on 2019 Apr. 07. The star at the position R.A. = 13 05 14.57, Decl. = -49 18 59.5 was brighter by 0.7m than on the past images, including those obtained on 2019 Apr. 04. The following magnitudes (unfiltered with the V zero point) were measured using USNO-B1.0 0406-0312380 (1' north of the variable) as the reference star with V=15.85 in APASS DR9 (Henden et al., 2016):
Obs. Date, UT Mag, CV
20190404.554 17.61
20190407.671 16.95
20190407.672 16.95
20190407.673 16.92
The new variable star was named DDE 168. Coordinates of the variable object in Gaia DR2 corrected for the proper motion are R.A. = 13 05 14.62, Decl. = -49 18 59.1 (J2000.0). Color-combined DSS finder chart is uploaded to http://scan.sai.msu.ru/~denis/DDE168-JRIR.jpg (10'x10' FOV, north up, east at left).
According to Gaia DR2, the object has a parallax of 7.997+/-0.086 mas and the proper motion of pmRA=-30.19+/-0.12, pmDE=-16.40+/-0.11 mas/yr. These numbers are strikingly close to the parameters of unusual cataclysmic variable Larin 2 (ATel #11401, arXiv:1807.04574): 7.953+/-0.128 mas, -30.51+/-0.26, -14.40+/-0.18 mas/yr. Both objects are located at 126+/-2 pc from the Sun, with the distance between them on the sky being 8.4 deg.
Larin 2 has shown a week-long outburst by 1.8 mag in March 2018. It has Mabs=12.20 in Gaia band and (BP-RP) color index of 2.72. DDE 168 is even redder, with Mabs=10.54 and BP-RP=3.27. This color index is extremely high, at the very edge of the locus of eruptive variables in Gaia DR2 (see Fig. 5 in the paper by Eyer et al., Gaia collaboration, arXiv:1804.09382). There are no flaring red dwarfs of UV Ceti type with Gaia BP-RP larger than 3.3 and no T Tauri stars beyond BP-RP=2.8. Despite being extremely red in Gaia data, DDE 168 has the following colors in 2MASS and WISE: J-K=0.87+/-0.03, W1-W2=0.21+/-0.03. DDE 168 was also detected in X-rays by XMM-Newton as 3XMM J130514.6-491859 (flux=1.75e-14 mW/m2, 3 times that of Larin 2). This area of sky in Centaurus was not observed by GALEX.
The serendipitous detection of two extremely red objects with the nearly identical proper motions implies they belong to the same stellar association, and hence are likely of the same origin and age. The photometric and spectroscopic follow up observations of both objects are strongly encouraged, as well as the search for other variable objects in this moving group.
The new variable is located 9.1' north and 2.1' west of the nucleus of NGC 4945 galaxy. Searching for the past episodes of activity in the archival images of NGC 4945 and checking the photometric databases is more than welcome.
New Variable Stars by D. Denisenko
