Blinking Double Star FU

by Bob Jardine

You've all heard of the Blinking Planetary, right? I've discovered the Blinking Secondary! (Well, I don't really believe the discovery is unique or original; there are probably a lot of these; but I did discover it in the sense of coming across it without foreknowledge of its existence.)

I was hunting down another H400 object, NGC 136, a dim OC in Cas. I hopped over to it via a star that is shown in Uranometria as a double, about mag 8.5 or 9.0. So, as I usually do when I hop across a star marked as a double in the chart, I bumped up the power to see what it looked like. Sure enough, it was a close double, maybe 5 or 10 arcseconds wide. Pretty colors too: very yellow and very pale blue.

Then came a surprise! While I was examining the colors, the secondary winked out. Was I just imagining it? No, it winked back on when I looked slightly away. Back off again! Just like with a light switch.

Have you ever seen this before? I'm sure it isn't very unique; in fact, I'm sure I have seen doubles before where the secondary wasn't visible without averted vision. But this one is the most dramatic instance of this that I can recall. It is really worth searching out.

The star isn't labeled in Uranometria; just an anonymous double, but you can't miss it, as it is about 5 arcminutes from NGC 136; it shows very weakly in my 9X50 finder. I looked it up in Starry Night Pro this morning, and it looks like it must be HIP 2430.

Caveat: your mileage may vary (a lot) with aperture and/or sky conditions. Just like the Blinking PN, this thing may not blink for you. I was using TOBY, my 10" CPT, with a 17mm Nagler, for a little less than 100X. More aperture could stabilize the seconary; less might make it invisible.

BTW: NGC 136, which was the original point of all this, is an OC with pretty high suck factor. I did see it, but it was just a dim unresolved patch.

Blinking Secondary FU! Two Stars! Drive-in Astronomy Awards to the primary, for being so yellow, to the secondary, for its disappearing act, and to NGC 136, for being the target, even if it is a pathetic excuse for an OC.

Joe Bob Sez: "Check it out".