Radio Galaxy Zoo Talk

stellar source of compact emission?

  • WizardHowl by WizardHowl

    Here the central compact radio source has no IR match but exactly coincides with a stellar object in SDSS DR10: SDSS J115442.75+552402.4 which has a proper motion of 134.83 ± 15.264 mas/yr which would seem to confirm its stellar nature. Whilst the possibility of an ifrs background source that exactly coincides with a faint star can only be ruled out conclusively with further observations, I'll try to examine what I can to determine the nature of this object - it would be the first time in RGZ that I have encountered a star that is a radio source, if that is what it should turn out to be. (I have checked that this is not a lobe of a separate radio source).

    Firstly, SDSS DR10 shows it as an irregular blue-ish smudge. This at first made me think it was a small galaxy. It could genuinely be a star almost exactly aligned with a quasar but the object is all one colour and does not look like a blend of multiple objects - moreover the proper motion measurement is that of a fairly nearby object, as more than 100mas/yr is what might be more typical of an object within 100 parsecs, or even closer. The proper motion measurement is obviously important so that needs to be checked - if it's unreliable for some reason, this is probably an IR-faint radio galaxy. If the proper motion is good and this is a star, it is clearly unusual and may have shell of circumstellar material or be passing by some small patch of nebulosity as it is not a normal point source.

    The USNO B1 catalogue seems to be the source of the proper motion measurement. It lists no other objects within 0.5 arcmin, so source confusion would not have resulted in an incorrect attribute being assigned and the measurement should be good. The errors on the position of the object are higher than the proper motion but these are reduced in the NOMAD1 catalogue, which may reflect a different processing pipeline - the same values of proper motion and magnitudes in Johnson B and R bands are given. I note generally from looking at the other nearby objects that the errors on the positions are not unrelated to the observed proper motions, thus I can be reasonably sure this object has a significant proper motion and is a relatively nearby stellar object. Its ID in USNO B1 is 1454-0215898.

    NED lists the closest source as 0.28 arcmin away, so source confusion is not a problem here, either. It cites the SDSS declaration that the object is a point source but there are four diameter measurements that appear to confirm what can be seen visually - it is not round. These measurements are from SDSS DR6 and disagree a bit, except for the last two that give ellipticity as ~0.95 and eccentricity as ~0.99. i.e. this object is highly elongated.

    To sum up, this appears to be a faint (B=~22mag, R=~20mag) stellar object that is highly elongated and probably in the solar neighbourhood and also a compact radio source. I do not expect these characteristics to go together! If someone can see where I'm going wrong, let me know - I must be doing a lot wrong elsewhere, also, if that is the case. What is the proper way to check an object like this?

    Posted

  • WizardHowl by WizardHowl

    Not completely trusting the proper motion measurements any more. Lesson learned thanks to http://radiotalk.galaxyzoo.org/#/subjects/ARG0001mpm

    Posted

  • DocR by DocR scientist

    Wow. we really need to sort our this proper motion question.

    Posted