I’d like to get some opinions on a spectrum submitted to the TNS because there are inconsistencies between the light curve of the object in question and the conclusions based on the spectrum that I am now attaching.
I am not going to say anything about it at this point to avoid creating any kind of bias, but I can tell you that this is a quiescent spectrum of an object that underwent an outburst.
I am not good at classifying spectra so I thought it was a good chance to ask here and learn something!
This looks like a set of Helium lines, 3889 A, 4026 A, 4471 A, 5875 A, 7065 A. Most of those look split, so I would assume a shell. A sequence of observations would be fun. Could also guess at some of the other lines. It is a little hard without having the spectra to get accurate wavelengths. Might be a carbon line here.
I did try to look at if any were shifted Hydrogen lines, but that doesn’t work. So, I’ll stick with mostly Helium lines.
I have a fairly good idea of what this is, but this doesn’t totally seem like a quiescent phase.
I’m no expert in spectra either but here is my take (guess)!
Just a quick visual scan shows all the major peaks in the spectra higher than 3900A seem to have double peaks. Some have the +Doppler peak higher in flux than the -Doppler side. Some have shoulders that appear almost single but probably aren’t. That would imply maybe an accretion disk resolution where the approach/receding spectra components are resolved. Be great to know if they vary over time!
I need to figure out what elements are being shown but that requires more work and I have a luncheon to go to right now. Food wins at this point!
The ball now rolls into someone else court…
Jim (DEY)
P.S. Back from lunch… He does seem to be there, lack of H, and perhaps some other elements in this spectrum does lead to a specific type of star that does not contain any accretion disk material. Nice if that it what it is!
The star was indeed submitted to VSX as an outbursting AM CVn star (UGSU/IBWD). The problem is that the light curve is not consistent with that.
The object has also been submitted to the TNS.
I attach the ZTF light curve of its single oubturst. It took more than 100 days for the object to reach maximum, something completely atypical for a dwarf nova. The amplitude is also small, only 2.5 mag. There are no rebrightenings as those seen in AM CVn systems either:
The event lasted ~300 days. Its slow development suggest a different nature, like an AGN brightening or even a supernova with the minimum mangitude in the light curve being actually the magnitude of the host galaxy.
There is no Gaia DR3 detection and thus no parallax, because it is too faint, although its blue colors cast some doubts.
There are lots of X-ray detections too. Being a powerful X-ray source, even when it is so faint in quiescence, is also unusual. The IBWD objects in VSX with similar magnitudes do not have X-ray detections and this one is found all over the place, like quasars are…
The spectrum was taken on December 20, 2025, so the object was at quiescence again, mag. 21.5. The outburst took place in 2023.
This is a puzzle. And I think there is a chance that this spectrum belongs to a different object than the one at this position.
The only other thing it might be is a Helium flash nova. I found on the “nova” wiki page that mentions that, spectra also He dominated and H missing. V445 Pup mentioned and the AAVSO db shows one outburst, around 2001, nicely but much higher amplitude than the one you show.
By observing the position of the peaks (marked by the small vertical blue lines at the top of the graph), we can begin to identify some chemical elements:
• Balmer series of Hydrogen:
• The very broad peak around 6563 Å corresponds to H-alpha.
• The peak around 4861 Å corresponds to H-beta.
• Other hydrogen lines are visible further to the left, towards the blue and UV regions (H-gamma, H-delta).
• Helium and other metals: Emissions of helium (He I) and potentially ionized iron (Fe II) are visible, which is common in dense stellar environments.
• The Sodium Doublet: The prominent peak around 5890 Å suggests the presence of sodium (Na₂I), although it could also be helium depending on the object’s context.
The width of the spectral lines (they are not simple thin lines, but rather broad “bumps”) indicates that the gas is moving at very high speeds, probably several hundred or thousands of kilometers per second. This is what I call Doppler broadening, which can be caused by strong winds.
You say that this spectrum comes from a TSN (a Type IIn SN?),but it could also come from a cataclysmic eruption or a WNh-type WR (rarer) that is burning its remaining hydrogen.
In short, this document shows an object surrounded by very hot gas ejected at high speed.
It looks like some kind of enhanced activity episode rather than the typical superoutburst of a helium dwarf nova.
In any case, I’ll accept the classification proposed by the discoverers, and it will be interesting to see if we can find objects with similar behaviour in the future.
