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V404 Cyg and others

MUY
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Hi all,

About V404 Cyg, what is the correct quiescent magnitude? I've seen estimates in the 17's but I think that's the magnitude of the very close (1.4 arcsec) neighboring star. Can someone clear this out?

And for the obscure variable RXJ0131.4+3602, on the AAVSO chart it's noted that the quiescent magnitude is 16.5 but RXJ0131 (fainter than 18) is very close to the N of this star. Am I right?

In the VSX it's noted that MN Lac is a possible UGZ variable, but with a noted range of 14.5 to 23.0: ... The quiescent mag. must be much brighter, I suppose?

Regards,

Eddy

Companions and ranges
Sebastian Otero
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Hi, Eddy,

> About V404 Cyg, what is the correct quiescent magnitude? I've seen estimates
> in the 17's but I think that's the magnitude of the very close (1.4 arcsec)
> neighboring star. Can someone clear this out?

 

No. There are two companions. The closest one has V= 18.9 and it is too close to V0404 Cyg to be resolved in most setups V0404 Cyg varies between 18.4 and 18.8 at minimum so the combined brightness is around V= 17.9. There is another star of V= 18.5 that is only 7" from the center of the V404 Cyg+companion position.
If the 3 stars in that 7" area are measured together, the Vmag would be V~17.4.

 

 
> And for the obscure variable RXJ0131.4+3602, on the AAVSO chart it's noted
> that the quiescent magnitude is 16.5 but RXJ0131 (fainter than 18) is very
> close to the N of this star. Am I right?

 

I don't understand what you mean. Why you take 16.5 as the quiescent magnitude?
The range 16.5 - 18.9 B is very approximate as can be read in 2000A&A...362..263J (Maximum magnitude is contaminated by the companion and minimum magnitude has a 0.8 mag. error). The variable has a companion 8" to the South that has V= 16.7 or so (derived from CMC14).

There are two B observations in USNO-B1.0, ine at B= 16.9 and the other at B= 14.8. So this star needs observations. Its magnitudes are very approximate.

 
> In the VSX it's noted that MN Lac is a possible UGZ variable, but with a
> noted range of 14.5 to 23.0: ... The quiescent mag. must be much brighter,
> I suppose?
 

You are right here. This must have been a typo since there are no observations at 23.0 in the AAVSO database and the range was taken from there.
I updated it to V= 20.5, consistent with the 20.8 B in GSC2.3.

 

Best wishes,
Sebastian

 

-----------------------
Sebastian Otero
VSX Team
American Association of Variable Star Observers

MN Lac minimum magnitude
Sebastian Otero
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After receving an e-mail by Patrick Wils about the existence of very faint observations of MN Lac in the AID, I realized that the 23.0: mag. minimum figure was not a typo.

What truly happened is the following. Some months ago, both CV and V magnitudes were plotted as Vmags in the LCG. While checking the LCG to get V ranges for some stars in VSX, I used those faint points as if they were Vmags.
Now the CV and V mags can be plotted separately (although with the same green symbol) and the default VSX link to the V light curve doesn't show them. That's why I thought the 23 mag. was a typo because now I didn't see any observation as faint as that!

But the fact is that the 23.0 mag. was not V but CV. All the faint observations are from William Goff, the only one who managed to go that faint. The scatter is very large at those magnitudes though and there are some fainter datapoints that are probably not trustable (e.g. CV= 24.7). But the light curve seems to suggest that indeed MN Lac gets fainter than 22 at minimum.
I'll use a more conservative minimum of 22.5 and change the passband to CV.
Maybe if William is reading he can comment of his very faint observations, comp stars used, etc.

Cheers,
Sebastian

Light curve
Sebastian Otero
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A light curve showing the CV faint data.

Cheers,
Sebastian

 

MN Lac
MUY
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Joined: 2010-07-23

Thanks Sebastian for the info! But what's really strange, if MN Lac goes down so deep, I wonder what type it is. UGZ would be very doubtfull hence the 7-8 mag range!

Cheers,

Eddy

MN Lac
MUY
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Thanks Sebastian for the info! But what's really strange, if MN Lac goes down so deep, I wonder what type it is. UGZ would be very doubtfull hence the 7-8 mag range!

Cheers,

Eddy

Sorry for my double comment.
MUY
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Sorry for my double comment. Had problems with the site.

Eddy

MN Lac minimum
GFB
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Sebastian,

Sorry for the late response.  I made a number of these faint observations as you noted, but looking back I'm not happy with them.  I see now I should have taken some other steps.  They were done with a clear filter on a V standard.  I used the bottom of the sequence, four comps from 15.8 to 16.9.  I intend to reduce them again after the upcoming meeting.

 

Bill

AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484