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TCP J21013299+3957043: new transient (12.3 mag) in Cygnus

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SPK's picture
TCP J21013299+3957043: new transient (12.3 mag) in Cygnus

TCP J21013299+3957043

RA 21h01m32.99s, DEC +39°57'04.3" (J2000.0)
2018 Feb. 24.7943 UT, 12.3 mag (CCD, unfiltered)
Discoverer: Tadashi Kojima (Gunma-ken, Japan)

"2018 02 24.794 UT
Discovered by T. Kojima, Gunma-ken, Japan, on three frames with five second exposure using Canon EOS 6D digital camera + 200-mm f/3.2 lens under the limiting mag = 13.0, who writes nothing is visible at this location on the previous frame (limit mag = 12.8) taken 2018 Feb. 23.810 and also a frame (limit mag = 13.8) on 2017 May 28 UT. There is a 2MASS star at the position of 33s.44 and 03".7 and also a star (mag = 15.5) at 34s.03 and 03".5."

Follow-up reports:

The abovementioned '2MASS star at the position of 33s.44 and 03".7' is the M-dwarf 2MASS J21013344+3957037 = LSPM J2101+3957 with a proper motion of pmRA= -151 mas/yr, pmDE= -2 mas/yr.
The IPHAS DR2 source IPHAS J210133.03+395703.8 (r=19.15, i=17.87,ha=18.20 mag) is only 0.7" away from the transient's reported position.

Spectroscopy and precise astrometry are urgently required.

Clear skies,

SPK's picture
Flare of a red dwarf?

"2018 02 24.822 UT
Although Kojima has confirmed this star on six frames on 2018 Feb. 24.794 - 24.795, but 40 minutes later he could not find a star on Feb. 24.822 UT (limiting mag.= 13.0)."

This brief brightening was possibly a flare of the M-dwarf LSPM J2101+3957.


ocn's picture
TCP J21013299+3957043: new transient (12.3 mag) in Cygnus

Good Morning All,

At position 21 01 33.17  +39 57 04.5  (VPHOT measured) on Feb 25.5007 UT approximate mag 16.01V (0.17) under heavy airmass 2.50 and at Feb 25.5019 approximate mag 12.76 Ic (0.14), both with T11 remotely at New Mexico.

kind regards,



FRF's picture
no new object down to 16.5V

No new object visible at the given position (limiting mag 16.5V) on my 2x60s CCD V images taken by using the 0.1m astrograph (T14) at Mayhill, New Mexico on 2018. Feb. 25.5112 UT

Robert Fidrich (FRF)

SPK's picture
Katsumi Yoshimoto's observation

2018 02 25.522 UT
Mag. V= 16.26, I= 12.91, position end figures 33s.20, 03".6 observed by K. Yoshimoto, Yamaguchi-ken, Japan, using 0.43-m f/6.8 Mayhill reflector with f/4.5 focal reducer, remotely, who identified with a 2MASS object (position at 33s.44 and 03".7, J mag = 10.990, H mag = 10.403, Ks mag = 10.116).

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