with the following comment: “Very bright, young transient, possibly a
Galactic Nova; photometry likely uncertain as the object is close
to/above saturation limit”.
The extinction in this direction is relatively low A(V) = 0.345, so a
typical classical nova peaking at absolute magnitude M_V= -7.0 at 8 kpc
distance would rise to V=7.9.
Confirmation imaging, astrometry, filter photometry and classification
spectroscopy are all highly desirable.
Best wishes,
Kirill
The transient is located southwest of Antares, at -40 degrees declination; which means that while southern hemisphere observers will have the best conditions, observers in the southern U.S. should also be able to locate it near culmination as it gets dark over the next few hours.
Just came in from observing it–it’s visible in binoculars, even low in the sky & in the city. Unfortunately VSP didn’t show any comps in the region, so I had to choose a bunch of field stars and estimate its magnitude relative to those, but it looks like it’s now brighter than mag 8.0. If you’re reading this, give it a shot!
A sequence between V= 7.5 and 11.5 has been uploaded.
Let me know if it is brighter than that, it has been difficult to find a brighter comparison star that is not variable or red…
You can re-reduce your first observation too if your comp stars are in the sequence. If they are not, let me know which ones you used so I can give you their values.
The magnitudes of your comparison stars are okay. The problem with the 72 and 74 you have chosen is that they are reddened orange giants with B-V= 1.6, that’s why I did not select them as comp stars (the 72 is a milimagnitude TESS variable). But there may not be any other option if we need to go brighter…
So your 7.9 estimate should be okay.
Makes sense, thank you for checking them! I was afraid that some of the stars would turn out to be unsuitable, so I tried to make estimates with as many as I could, but you’re right, there is not a lot to work with in that field.
Another issue with my first estimate was very poor seeing. I can’t detect ASASSN-25cm in shaky binoculars, so I stabilized my binos against the eave of the garden shed… but that meant I was looking right over its metal roof! As a result, I had to watch each star for a while to ‘see through’ the scintillation. All of this is to say that I believe 7.9 was correct within reason, but the uncertainty on that estimate is something like ± 0.15 mags, larger than I usually like.
I’m more confident in my second estimate, now that you’ve created a nice sequence for us (thank you!!). 7.8 ± 0.05! It’ll be interesting to see whether it continues to brighten from here.
No, I haven’t submitted a proposal for ASSASN-25cm to AAVSOnet—so I encourage you to submit one! It would be great to have an experienced photometrist like yourself reducing the AAVSOnet images and following along as it fades. I’ve done a little bit of photometry, but I’m better at visual observations.
Looking at today’s light curve, I see four different observers reporting visual, V, & TG observations, ranging from 7.1 to 6.7. That’s naked eye from a good dark sky!
I’m excited to see whether the nova continues to brighten. Fingers crossed for clear skies tonight!
I’m an observer in Aust. I’ve only been estimating variable stars for a year and so I’m not familiar with the procedures concerning transient events. This object is well within my range and the prediction is for clear skies for most of the next week, so I’d like to help if I can.
I can produce charts with VSP using the position and I see some comparison stars but I’m not sure how to report my observations and to whom. Is AAVSO the correct place and, if so, does this star have an AUID? Otherwise, where do I send my obs?
Thanks,
David
Yes, the AAVSO is the correct place to report your observations. This nova does have an AUID, which you can find by looking it up in the AAVSO Variable Star Index (VSX):
However, you don’t actually need the AUID to submit your observations–WebObs should accept any of the designationsthe primary designation listed in VSX.
Two other locations which collect observations of transient events are the Transient Name Server (TNS) and the vsnet mailing list. I am not very experienced with either; however, I have noticed that both seem to focus more on discovering new transients than on building a post-discovery light curve, as the AAVSO does. The AAVSO’s AID is the best place for your observations in the long term.
P.S. Thank you for helping track this target!
EDIT: I was wrong about being able to submit observations using any name which is in VSX–now that the primary designation N Lup 2025 has been assigned, attempting to submit with name “ASASSN-25cm” through WebObs 2.0 results in the error “Star ‘ASASSN-25cm’ not found in VSX. Please check spelling or try a different designation.” Live and learn!
Hi Andrew!
Always try to use the pair of stars more similar to the variable to make the final estimate.
You can use those two for a first assessment but then you can narrow down the magnitude differences by using comp stars like the 60 and the 63
Thank you for sharing your observations. It looks like it keeps brightening!
Sebastián, you’re on fire with these sequences!! Thank you so much for staying on top of this. The new comps are very helpful!
I can confirm Andrew’s observation; it seems the nova continued brightening today! I checked it earlier this evening (before the new sequence was published) and was startled to see it looking brighter than the mag 6.6 comp star HD 128819. Unfortunately my estimate was not very precise (the comps were far away, and I didn’t have long to observe before it got foggy), but since I won’t get another shot at it tonight I went ahead and submitted the observation, tagged with the “Z” code for uncertainty.
