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Tough Blended Object

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Tough Blended Object

Hello everyone,

I’m working on an object that seems to have a strange blending problem. I first found this object in ROTSE1: Orphans data, the phased light curve of this object from that data is attached to the first reply to this post. The problem is, the coordinates that ROTSE1 gives for this object appear between two objects of similar magnitude, and a third that appears to be much dimmer. The two main stars are about 40” apart. See the attachment to this post for an image that shows this, the purple crosshairs mark the ROTSE1 coordinates. I have been trying to figure out which of these stars this object corresponds to.

I first checked NSVS. NSVS returned data for three objects that are very close together. Upon inspection of these three light curves, none appear to be of this object. In addition, the coordinates given with these NSVS data all fall between the space between the two main stars.

SWASP data contains separate data sets for these two stars, and both of their light curves look similar to that of the ROTSE1:Orphans’, in period, and amplitude. This indicates that the ROTSE1:Orphans data is a blending of these two stars, and also that the SWASP data is blended.

Neither ASAS-SN, ASAS3, nor CRTS contain data for this object. Given all of this, I have no idea which star is the actual variable.

The object's coordinates are 12 10 38.89 +46 13 44.5

What are my options when it comes to deblending? Is this object possible to deblend?

Thank you for any feedback!


File Upload: 
Phased Light Curve

Here is the light curve of phased ROTSE1:Orphans data.

File upload: 
Sebastian Otero
Sebastian Otero's picture
Identifying variable objects in crowded fields

Hello Grant,

"NSVS returned data for three objects that are very close together. Upon inspection of these three light curves, none appear to be of this object."

What do you mean with that? Actually the three are for the blend of the two objects so you can use all (with a zero point correction between all of them) in your submission and correct them all, once you identify the variable.

The way to identify an object with similar magnitude companions is to look for independent data.
SuperWASP isn't useful to identify it because its resolution is similar or even worse than the NSVS resolution.
2MASS J12104012+4613542 is the bluest object (J-K 0.26) of the two and we can look up APASS data. It seems to be variable:


APASS data can be blended for stars 12 or 13" apart but this pair's separation is 44" so we are safe.

2MASS J12103677+4613273 is redder (J-K 0.69)


It looks constant.
The colors are different so the redder object will be brighter in ROTSE-I magnitudes than its V magnitude while the bluer object will be fainter. Convert the magnitudes to R1 before applying a correction.
When there are no APASS data available, you can compare mean results for the stars involved deriving V from astrometric catalogues like CMC15, UCAC3 (not UCAC4), Pan-STARRS1, IPHAS, VPHAS DR2, Gaia DR2, SPM 4.0 (Nc column >1) or SDSS (a spreadhseet can be provided for that). If one of the stars shows discrepancies and the other one does not, you will find the variable. The problem with working with mean magnitudes is that sometimes, even if the star is variable, the mean magnitudes will be the same among catalogues...
So APASS is better (only available for AAVSO members).

The best way, no doubt about it, is to check ASAS-SN data. Stars closer than 17" will be blended but here there is no problem. ASAS-SN is all-sky so I do not know why you say there are no observations in the ASAS-SN database. You have to enter a number like 3000 in the "Enter number of days to go back" field to get all available data (the default is 20 and there may not be observations).
Here it is, the ASAS-SN light curve of the object:

It is the bluer object that we had already identified with APASS.

So use ASAS-SN data in your analysis, combine them with ROTSE-I and NSVS (after correction) and make your submission.
There are mean magnitude changes due to spots, classify this one as EW/RS.


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