Zet Crb possibly changes magnitude?

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Zet Crb possibly changes magnitude?

Post by lior » Mon Aug 09, 2004 6:42 pm

WOLF has just started to analyze magnitude changes in CI, and with the addition of the cosmic rays elimination the output seems to be effective. Checking the output might be a time-consuming task, but I hope that this application will turn to be cost-effective overall, since the probablity for discoveries might be higher than just picking random star.

Anyway, last night WOLF indicated 5 stars' magnitude changes, of which I have only examined one. The one that I checked appeared to be Zet Crb:
In the frame ci040808ut214428p.fits, Zet Crb (appears at coordinates 671,513) is about 15.5 sigmas brighter than its background. However, in the frame ci040803ut214458p.fits (taken approximately at the same sidereal time), it is only 10.6 sigmas brighter than the background. Both pictures seem clear, and the background level is approximately the same (sigma=25.5). Zet Crb neighbors do not seem to behave in the same manner.

I believe the Zet Crb is a double star, and each of the two stars has a different color. One is blue and the other is orange.

Dan Cordell
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Post by Dan Cordell » Mon Aug 09, 2004 6:56 pm

From the Alcyone.de Bright Star Catalog:
position, motion, parallax:

position (J2000) RA: 16h 22min 5.8sec DEC: +30° 53' 31''
position (B1900) RA: 16h 18min 12sec DEC: +31° 7' 26''
proper motion (J2000) RA: -0.096 arcsec/a DEC: 0.109 arcsec/a
radial velocity -29 km/s
rotational velocity <17 km/s (uncertain) (variable)
trigonometric parallax 0.016 arcsec
galactic coordinates longitude: 50.77° latitude: 44.21°


visual magnitude 4.85
(V on UBV Johnson system)

spectral / color information

spectral class K0III
B-V-magnitude 0.97
U-B-magnitude 0.8
object is infrared source (NASA merged infrared catalogue, Schmitz et al., 1978)

double/multiple star system information

separation 185.1 arcsec
mag difference (of double or brightest multiple) 7.4
note Worley (1978) update of the IDS

miscellaneous information

note (category: group membership): Hyades group.
So it's a double star but has never had its variability (if any) recorded. And the second star seems to be very dim (?).

You might have found something rather interesting here.
Dan Cordell, Giant Space Cow

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Post by RJN » Tue Aug 10, 2004 1:54 am

As we all know from experience no single measurement should be a definitive detection of variability. Anything can happen on a single frame. If this star is truly variable, then it will show variability on more than one frame. If another CONCAM saw this change at the same time, that would probably also suffice.

At first glance it is hard to believe that a member of the famous Hyades star cluster is just now being discovered to be variable. The Hyades has been used to calibribrate the distance ladder of the entire universe, and an unknown variable like this might conceivably have some effect.

Still, this star is surely not monitored very much outside the NSL project, and so if it was to vary, NSL data might be the first to find it. Possibly one of the successes of the NSL project will be to discover unexpected but bright variables like zeta Crb.

It will be interesting to see if zeta Crb variability is seen on subsequent NSL data.