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View Full Version : IS SDSS J091926.58+614954.0 a bright, unknown QSO?



Jean Tate
2018-Apr-30, 09:18 PM
Or is it a radio star?

SDSS J091926.58+614954.0 (http://skyserver.sdss.org/dr14/en/tools/explore/Summary.aspx?id=1237663529727688715) (sorry I don't seem to be able to post an image).

It was posted in Radio Galaxy Zoo Talk, by A1001, a few days' ago, in a thread entitled "ARG00002po star galaxy radio source?" (link (https://radiotalk.galaxyzoo.org/#/boards/BRG0000002/discussions/DRG0000oid)). Here's how I responded:




Strange. SDSS J091926.58+614954.0

If it's a radio star (they do exist), it's a quite strong emitter.

On the other hand, if it's a QSO (it is a UV source), it's a very bright one, and strange that no one has taken a spectrum of it.

It could be an chance cosmic coincidence - a background QSO and a MW star on ~the same sightline - but somehow I doubt it.

It should be in Gaia DR2; anyone know how to find out what's there?

What do you think?

ngc3314
2018-May-01, 07:56 PM
Gaia DR2 lists it with parallax 0.22+/0.11 milliarcseconds, not correcting for the parallax bias found from, for example, known high-redshift objects (which would make the significance of this parallax even more underwhelming ). For a single source, a quick route to the Gaia DR2 numbers is entering coordinates at the top of this VizieR form (http://vizier.cfa.harvard.edu/viz-bin/VizieR-3?-source=I/345/gaia2).

The SDSS colors don't make sense for a single star, with a huge drop between r and i superimposed on a reddish continuum, or emission affecting both r and i bands. In fact, r-i=-0.96 would be odd even for a typical quasar anywhere up to z=6 (which could be why the object evaded being included in ay of the SDSS samples so far). Taking wild guesses, could be H-alpha emission from something at modest redshift? (But it would be hard to hide the galaxy). GALEX shows good detections in both near- and far-UV bands, much brighter in NUV, which mitigates against such a high redshift that Lyman absorption wipes out the UV flux.

Jean Tate
2018-May-01, 08:42 PM
Thanks very much! :)

Gaia DR2 lists it with parallax 0.22+/0.11 milliarcseconds, not correcting for the parallax bias found from, for example, known high-redshift objects (which would make the significance of this parallax even more underwhelming ). For a single source, a quick route to the Gaia DR2 numbers is entering coordinates at the top of this VizieR form (http://vizier.cfa.harvard.edu/viz-bin/VizieR-3?-source=I/345/gaia2).

The SDSS colors don't make sense for a single star, with a huge drop between r and i superimposed on a reddish continuum, or emission affecting both r and i bands. In fact, r-i=-0.96 would be odd even for a typical quasar anywhere up to z=6 (which could be why the object evaded being included in ay of the SDSS samples so far). Taking wild guesses, could be H-alpha emission from something at modest redshift? (But it would be hard to hide the galaxy). GALEX shows good detections in both near- and far-UV bands, much brighter in NUV, which mitigates against such a high redshift that Lyman absorption wipes out the UV flux.
Especially for the VizieR link; I will have a look to see if Gaia found any other sources ~within the SDSS resolution (up to ~2", say). If not, that doesn't completely eliminate the possibility of a blend of some kind (QSO+MW star, MW close binary+unrelated MW star, etc), but would certainly be better than just SDSS (haven't checked PS1, DECaLS, etc, but if Gaia says not a blend, none of those are likely to find one).

I have a call in to a radio astronomer who's interested in radio stars; from what little I know of such, this would be a very unusual radio star (if that's what it turns out to be).