9 replies to this topic

[mborland]

I signed up for the email alerts from the Transient Name Server. I got an alert for an object named 2023acmv, which had no classification.

https://www.wis-tns....object/2023acmv

 

I took a spectrum a few nights ago, calibrated and corrected per my usual procedures, and tried to get a classification from SNID. Here's what it gave me

 

I tried GELATO as well, but it rated the classification (Type II) as unreliable. This disagrees with SNID's classification of Type Ic.

 

The match between my spectrum and the SNID templates is pretty poor. It's possible I didn't get the right object, since it was pretty dim, but I was fairly careful.

 

Maybe this isn't a supernova. Any ideas what it might be?

 

--Michael

Edited by mborland, 22 February 2024 - 12:10 AM.

[mborland]

I compared the spectrum to the Pickles database from ISIS. The best match is to a type M1V star, so probably I didn't get the right object.

 

 

At magnitude 13, it shouldn't have been hard, but it isn't the first time I looked for something from TNS and didn't find anything there.

 

--Michael

Edited by mborland, 22 February 2024 - 12:40 AM.

[ziggeman]

[robin_astro]

That's an odd one from ZTF. The light curve is strange with constant values at mag 12/14 interspersed with "fainter than" 19-20.

https://alerce.onlin...ct/ZTF24aabuyny

 

There is a bright star just to the left of the given location of the transient. This is  L 750-42 identified in SIMBAD as a "low mass star" at V mag 13.2

https://simbad.u-str...Ident=L 750-42

which has a high proper motion of 1.5 arcsec/year

 

If we look at the colour DSS image there we see a chain of two blue stars and one red one in a line. These stars and the location of AT2023acmv form a straight line. This is typical of a star showing proper motion with the combined DSS red and blue images taken at different times. 

 

 

So I suspect this not a new transient but just a star showing proper motion, falsely picked up by ZTF in in a difference image compared with a historic reference and  you measured the right object but it has moved from where it used to be !

 

Cheers

Robin

[robin_astro]

It is an interesting and unusual star though, an M subdwarf  LHS 272

https://simbad.cds.u...AJ....157...63K

 

 

 

Robin

Edited by robin_astro, 22 February 2024 - 07:41 AM.

[robin_astro]

It is an interesting and unusual star though, an M subdwarf  LHS 272

https://simbad.cds.u...AJ....157...63K

 

 

 

 

From table 3 spectral type sdM3 with an effective temperature of 3400K  and a radius just 17% of that of the sun, fascinating !

Edited by robin_astro, 22 February 2024 - 08:21 AM.

[Fabricius]

So I suspect this not a new transient but just a star showing proper motion, falsely picked up by ZTF in in a difference image compared with a historic reference and  you measured the right object but it has moved from where it used to be !

 

+1

[mborland]

Robin,

 

Thanks, I really appreciate your insights!

 

--Michael

[yuzameh]

Yes, if you take the GAIA dr3 data which is for epoch 2016.0

 

RA   145.93572   Dec  -17.78408

Gmag     12.157
BPmag  13.403
RPmag  11.056
BP-RP      2.347
Plx   74.585  mas
pmRA  -1419.970  mas/y
pmDE    226.091  mas/y
RadVel    97.36  km/s

 

convert the pm RA and pm Dec to degrees and multiply by 8.2 to be 2024.2 and then adjust the GAIA RA you get

 

145.93248

 

with TNS RA

 

145.93242

 

a difference of 0.00006 degrees or roughly 0.2 arcseconds for 2024.2.

 

With Declination it is -17.78357 and -17.78360 respectively which is a difference of 0.00003 degrees or 0.1 arcseconds for 2024.2 (which I'm calling "now", though it's a bit rounded).

 

A quality astrometric match.

 

Most of the per day(s) time series surveys in the past suffer from false alarms due to high proper motion stars, however they were usually monotonic increases or decreases over time, basically because the PSF radius used was centred on a source from an astrometric catalogue seed and the object had different amounts included within that radius as it moved over time.  However, this one isn't one of those and is a bit strange.  Transient ones just detect changes nowadays and I think try to solve their own astrometry, after all a transient may not have a precursor in any astrometric source catalogue.  How they've coded their algorithm(s) might explain this weird near alternation of "seeing" the object over time.

Edited by yuzameh, 26 February 2024 - 01:51 PM.

[robin_astro]

That's an odd one from ZTF. The light curve is strange with constant values at mag 12/14 interspersed with "fainter than" 19-20.

https://alerce.onlin...ct/ZTF24aabuyny

 

There is a bright star just to the left of the given location of the transient. This is  L 750-42 identified in SIMBAD as a "low mass star" at V mag 13.2

https://simbad.u-str...Ident=L 750-42

which has a high proper motion of 1.5 arcsec/year

 

If we look at the colour DSS image there we see a chain of two blue stars and one red one in a line. These stars and the location of AT2023acmv form a straight line. This is typical of a star showing proper motion with the combined DSS red and blue images taken at different times. 

 

 

So I suspect this not a new transient but just a star showing proper motion, falsely picked up by ZTF in in a difference image compared with a historic reference and  you measured the right object but it has moved from where it used to be !

 

Cheers

Robin

ZTF have "discovered" another high proper motion star ! This time picked up by amateur Claudio Balcon

 

https://www.wis-tns.org/object/2024dum

https://alerce.onlin...ct/ZTF24aaeirya

 

Cheers

Robin