TCP J21290156+3631056: new transient (11.5 mag) in Cygnus

[Peter Somogyi]

Hello,

During last night, I've spot this alert on aavso:
https://www.aavso.org/tcp-j212901563631 ... mag-cygnus

This night I've been already using the Lhires (found it quicker switching to 150/mm grating rather than switching to my existing Alpy), with a guide camera optimized for bright stars, hence spent a lot of time making sure about the target (poor guide quality).
Fresh result using ISIS:

plot_tcpj212901_20180324_137.png (29.12 KiB) Viewed 8904 times

The object was low, I took ref.star of nearby 70 Cyg before and after (using average). Had to hurry, the 4th exposure of 600 sec (taken right after the 2nd 70 Cyg ref star) was effectively destroyed by the rising sun.
The peak at 4438A is either true, or might be an artifact of known defocus towards H-gamma by the internal doublet of LHires. Otherwise, you can assess visually the SNR as spikes amount allover the featureless continuum (only the telluric 6876A seems to be real, no outstanding Balmer feature visible).
I am wondering what kind of object this transient is, looks to be featureless and bluish.

Cheers,
Peter

[Francois Teyssier]

Hi Peter,
Looks to be a dwarf nova in outburst from the shape of the continuum
Often the continuum looks so noisy that weak lines (Balmer and He) do not appear clearly
François

[Peter Somogyi]

Hello Francois,

You are right, and as looking harder into the noise, I do may figure out an outstanding peak at H-alpha with a usual W-shape might be around H-beta (and maybe H-gamma):

marked Balmer positions with PlotSpectra

So my earlier statement "featureless" does not really stand.

Peter

[Paolo Berardi]

Congrats Peter, that is an uncomfortable observation. Your result should be reported to VSNET where there are no photometric or spectroscopic follow-up right now.

Meanwhile we have a new, relatively faint, classical nova (already confirmed, ATel #11475) in Canis Major: TCP J07134590-2112330.

Paolo

[Peter Somogyi]

Thanks Paolo, I am just registering on vsnet alerts (learning how it works), and will send a report when got through.
Peter