TCP J21040470+4631129: new transient (9.2 mag) in Cygnus

Association Francaise des Observateurs d'Etoiles Variables (AFOEV)
Fri, 07/12/2019 - 16:16

TCP J21040470+4631129 (UG:)

Spectroscopy, precise astrometry, and multiband as well as time-resolved photometry are urgently required (I renamed the transient, as it is probably a dwarf nova outburst and not a "possible supernova").

Discovery details:
R.A. 21h04m04.70s, Decl. +46°31'12.9" (J2000.0)
2019 July 12.490 UT, 9.2 mag (CCD, unfiltered)
Discoverer: Hideo Nishimura (Shizuoka-ken, Japan)

2019 07 12.490 UT
Discovered by Hideo Nishimura, Shizuoka-ken, Japan, on three frames using Canon EOS 6D Digital camera + 200-mm f/3.2 lens under the limiting mag = 14.5, who writes nothing is visible at this location on a frame taken on 2019 July 10.502 UT with the limit mag.= 15s and there is a candidate star (mag = 17) on DSS. An image will be provided later.

2019 07 12.490 UT
A discovery image at

2019 07 12.61 UT
This transient does not look like a "possible supernova", but is likely a nearby dwarf nova outburst. I strongly recommend to use the designation TCP J21040470+4631129 instead of PSN J21040470+4631129. --- Patrick Schmeer (Saarbrücken-Bischmisheim, Germany)

2019 07 12.61 UT
The likely (blue) progenitor (supposedly Nishimura-san's mag. 17 candidate star) is USNO-A2.0 1350-13375367 (Bmag. 17.7, Rmag. 17.2) with Gaia DR2 position end figures 04.688s, 13.75" (equinox J2000.0, epoch 2015.5, Gmag. 17.77, parallax 9.1337 ± 0.1156 mas (distance 109.2 ± 1.4 pc)). Other designations are USNO-B1.0 1365-0394214, GSC2.3 N31X108363 (Fmag. 15.71, Bjmag. 17.76, Vmag. 18.34), PSO J210404.693+463113.906 (gmag. 18.20, rmag. 18.01), IPHAS J210404.68+463114.0. No outbursts were recorded by the ASAS-SN Sky Patrol (Shappee et al. 2014ApJ...788...48S and Kochanek et al. 2017PASP..129j4502K) between 2015 March 20 and 2019 July 9; complete light curve at…. The transient is probably a dwarf nova outburst with an amplitude of at least 9 magnitudes (WZ Sge type?). Spectroscopy as well as multiband and time-resolved photometry are strongly recommended. --- Patrick Schmeer (Saarbrücken-Bischmisheim, Germany)

Clear skies,

American Association of Variable Star Observers (AAVSO)
Spectra of transient


I took a time-series of low-res (R=2000 or so) 100 sec spectra of that object. It is a pretty bright one by now..

Just a raw 1-D extraction is shown on graph. At very left there is Hbeta, right: Halpha and HeI 6678. When looking at the spectrum, it is quite evident that it's not a nova or supernova ;-)

Maybe some of you will find that data useful, I have it with all the calibs etc.

Best wishes,

American Association of Variable Star Observers (AAVSO)
TCP J21040470+4631129 sequence

TCP J21040470+4631129 now has a sequence....

Beware that brighter comps have close companions and color options are probably not ideal, especially for brighter comps.

Tim Crawford, Sequence Team


American Association of Variable Star Observers (AAVSO)
Visual observation

I think this star is much brighter than the original CCD 9.2, my estimate is 8.2 21h57 UTC color blue but from the Tycho II catalog.



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The Astronomer's Telegram

ATEL #12936 ATEL #12936

Title: Echelle spectroscopy of TCP J21040470+4631129
Author: Francois Teyssier (ARAS Group, Rouen, France)
Posted: 13 Jul 2019; 02:43 UT
Subjects:Cataclysmic Variable, Transient

We report optical echelle spectroscopy (R ~ 11000, 4100-7300A) the newly
reported transient TCP J21040470+4631129 (discovered on 2019 Jul.12.190
UT by Hideo Nishimura). The spectrum is consistent, obtains on 2019 Jul
12.9 UT (exposure time of 2589 sec, S/N ~ 40 hat 6100 A). The spectrum
is consistent with a large amplitude outburst of a cataclysmic variable.
The He I lines (e.g. 4471, 5013, 5876, 6678, 7065) all show symmetric
double peaks with separation 210 km/s (HWZI ~ 540 km/s). He II 4686 shows
peak separation of 310 km/s (but with there are also weak peaks coincident
with the He I lines) and broader wings, HWZI ~ 700 km/s; the redshifted
peak (+130 km/s) is slightly stronger and narrower. The profiles are centered
at 12 km/s but the wings show asymmetric extensions. The H-alpha and H-beta
profiles are asymmetric (R/V peak ~ 1.14±0.05) with separation of 160
km/s (HWZI = 600 km/s). There may be an absorption component at -30 km/s
(a similar minimum is seen on the He I lines) and H-beta and H-gamma show
an underlying broad absorption line that is redshifted relative to the
emission component by about 150±50 km/s, based on the profile asymmetry.
Additional emission includes the C III lines as a broad, featureless profile.
The precursor candidate noted in the CBAT report coincides with Gaia (DR2)
2163612727665972096 with parallax 9.134+/-0.116 (g=17.77 mag)

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