GAIA transient GAIA21dxg / TNS AT2021wui

[Hamish Barker]

Thanks Robin,

There is no way for me to remove my comment re k2 spectrum. I can only add additional comments. I'll add a comment with your dereddened comparison. ok?

I posted on aras and there was no response for some days apart from Terry who had also taken spectra but we were both at a loss to explain the spectrum, so I assumed nobody here was interested as everybody is busy with RS Oph and therefore posted to TNS with what information and idea was at hand. My apologies if you think I have endangered amateur access to TNS.

There was some uncertainty about the continuum slope, and with the noise in the spectra it wasn't clear whether the departures from k2 were just the noise and continuum slope. Not having your extensive experience, and having received no responses here, I didn't know to use lines only for type ID, and not continuum slope. Has someone written a nice guide to what to do when classifying ill-fitting spectra?

Cheers,
Hamish

[Stu Todd]

Hamish,
It is imperative that you get your facts in order before posting on TNS and cc'ing professional astronomers.
I'd leave it alone and take a lesson from this.

Stu

[Peter Velez]

Here is my contribution with a few lines of interest marked.

About 2 hours taken with UVEX 600 lines/mm on a PW CDK 12.5. I have dereddened the spectrum using the ISIS Extinction tool applying a factor of 1.15 as suggested by Robin. Resolution reported by ISIS is 1024. SNR measured with the FWHM tool in ISIS is around 100 and the calibration acceptable when considering the Na I and Telluric O2 lines.

The classification as an early B star looks right to me. While not particularly obvious from the main plot, I was able to identify He I at 4 locations in the spectrum. The absorption line for He II at 5411.52 A is modest - I've included it for completeness but am not certain about it.

What I do find interesting is the profiles of the Ha and Hb lines. I've included subplots of these. The Hb absorption line has a small bump - this might be the start of an emission building but at this resolution I can't be certain.

I might check back in on this one in a week or so to see if anything has changed.

Pete

[Hamish Barker]

Thanks for the feedback. Robin and stu. I'll keep it in mind.

Super observation Peter! Definitely some hints of interesting things there.

Clearly more observations are needed. Are you set up yet at your new obsy Stu?

[Robin Leadbeater]

Hi Hamish,

If you contact Ofer Yaron via the contact form explaining the situation he will likely be able to remove or correct the comments for you
https://www.wis-tns.org/content/contact-us

Cheers
Robin

[Robin Leadbeater]

TNS is supposed to be specifically for supernovae
https://www.wis-tns.org/content/tns-getting-started

"Variable stars and CVs, including in particular Galactic nova candidates, should
be reported in the same manner done prior to January 2016, and should not be
submitted to the TNS."

The problem is that TNS is being used for all sorts of variable objects which are clearly not supernovae and even for objects like this one which is not even a fast transient. In particular many (if not most) of the Gaia reports are like this. I have asked about this and apparently it was "agreed" that Gaia could do this

If you did want to report it via TNS, a better course of action might have been to enter a classification report including the spectrum and since it is clearly not a supernova, classifying it as "other" commenting on the presence of H alpha emission at near 0 redshift as indicating a galactic source and therefore not a supernova (or a CV in outburst given the very slow small increase in brightness). That would put the spectrum on record but without added speculation.
You can see an example of this where I classified an object as a CV
https://www.wis-tns.org/object/2019vww

Cheers
Robin

[Robin Leadbeater]

I didn't know to use lines only for type ID, and not continuum slope. Has someone written a nice guide to what to do when classifying ill-fitting spectra?

The best book on the subject is perhaps Gray and Corbally "Stellar spectral classification"
https://press.princeton.edu/books/paper ... sification
but for unusual spectra, it is probably best to leave it to professionals with a knowledge of stellar astrophysics and even specialist knowledge in the particular type of object

Cheers
Robin

[Peter Velez]

Robin and Hamish

I for one have found this an extremely helpful series of posts. Apart from the discussion about TNS (the operation of which was a mystery to me), the worked example on determining extinction and using that and public data about magnitude to check up on a spectral classification was really valuable for me. I am sure other relatively amateur amateurs also picked up some useful tips. Its relatively easy to learn the principles of astronomy - absolute and relative magnitude, parallax, extinction etc - but to have it simply applied like this helps bring it all together.

I plan to keep an eye on this target for a bit - there may be nothing interesting happening, but its worth being certain about that.

Pete

[Hamish Barker]

TNS is supposed to be specifically for supernovae
https://www.wis-tns.org/content/tns-getting-started

"Variable stars and CVs, including in particular Galactic nova candidates, should
be reported in the same manner done prior to January 2016, and should not be
submitted to the TNS."

The problem is that TNS is being used for all sorts of variable objects which are clearly not supernovae and even for objects like this one which is not even a fast transient. In particular many (if not most) of the Gaia reports are like this. I have asked about this and apparently it was "agreed" that Gaia could do this

If you did want to report it via TNS, a better course of action might have been to enter a classification report including the spectrum and since it is clearly not a supernova, classifying it as "other" commenting on the presence of H alpha emission at near 0 redshift as indicating a galactic source and therefore not a supernova (or a CV in outburst given the very slow small increase in brightness). That would put the spectrum on record but without added speculation.
You can see an example of this where I classified an object as a CV
https://www.wis-tns.org/object/2019vww

Cheers
Robin

thanks for all the very useful information. I will never forget your encouraging comment to my first star analyser spectrum of an LMC or SMC nova back in 2019. This week however it seems that I am jumping into the mud with both feet in my best shoes. hopefully nobody else gets it on them.

I have notified TNS via the contact form to please delete all my comments so that I might use the classification form. I searched for how to add the classification report previously but could only see the comments buttons. once again, my apologies for sullying the good name of aras contributions.

I guess it's possible that TNS could get more kafkaesque, given that it is:
- ok for GAIA transients to be posted there, and
- also ok for ligo GW events (since I guess they might be kilonova and everyone's quite excited by them),
but
- not ok for posting a spectrum in response to the actual gaia transient report which was posted on TNS, or
- not ok to make a comment based on incomplete knowledge and skills in the comment box below a discovery report.

Demoralized,

Hamish

[Robin Leadbeater]

Don't worry Hamish,

Professionals also make mistakes. Here the MASTER team reported an independent discovery of the the planet Neptune !
https://www.wis-tns.org/object/2019vvf

and not forgetting Prof Peter Dunsby of course who famously rediscovered Mars !
https://www.astronomerstelegram.org/?read=11448


Cheers
robin