V695 Cyg (31 Cyg) photometry/spectroscopy campaign - Alert Notice 851

American Association of Variable Star Observers (AAVSO)
Wed, 02/14/2024 - 23:15

Alert Notice 851 announces a campaign beginning immediately on the very bright (~3.8 V) spectroscopic eclipsing binary red supergiant V695 Cyg (31 Cyg). Please see the notice for details and observing instructions.

There is a thread for this campaign under the following AAVSO forum:

- Campaigns & Observing Reports: https://www.aavso.org/v-695-cyg-campaign-2024

Please subscribe to this thread if you are participating in the campaign so you can be updated, ask questions, and join in the discussion!

Many thanks, and Good observing,

Elizabeth O. Waagen, AAVSO HQ

American Association of Variable Star Observers (AAVSO)
Hi All

Are specific comp…

Hi All

Are specific comp and check stars being requested for this campaign in order to have reference standards for all data contributors?

thank you,


About the comps

Hi Gary,


I asked the same question about ten days ago.

You'll find the answer here :




I was surprised to see that the star 30 cyg was recommanded, as this is also a variable star (4.81 - 4.84 V), and a blue one ... but it's true that, at this brightness, there is not a large choice.


I already have a few data points those last days, but most of the time the sky is overcast here.


American Association of Variable Star Observers (AAVSO)
30 Cyg status

Hi Christophe,

It was an NSV variable. A large fraction of these suspected variables turn out to be constant or, as in this case, variable to an extent that we can neglect.
The 0.03 mag. reported amplitude was based on compiled measures in the GCPD. A constant star might show such spread in the GCPD. A more consistent dataset needs to be checked.

Hipparcos doesn't suggest variations larger than 0.01 mag.

Finally, TESS reveals that there is a periodic signal but the amplitude is in the 0.001 mag. level.

I have revised the VSX entry:


The star can be safely used as a comparison star.


American Association of Variable Star Observers (AAVSO)
eclipse is now clearly detected on Feb 20.2 UT

@Sebastian: thanks a lot for looking into the 30 Cyg comparison star magnitude

I use it since it is very conveniently located near the variable so differential extinction is no problem. What I can detect in my measures is the 2nd order extinction due to color difference. In the measures I uploaded to AID both are corrected. All measures were done with DSLR Canon 600D and camera lenses 50mm and 75mm. Every data point is the average of 10 images.

Clear skies,



Hi all, Wolfgang, I had…

Hi all, Wolfgang,


I had few time left the last couple of weeks, so I'm only extrating data right now for this star. February has been terrible here, so I could  not get a large amount of measurements, most between clouds.

I also have a Canon DSLR (650) and also will extract TriRGB data.

Which R mag did you use for the comp star 30 cyg ? Simbad reports no R mag.

Same about the check star HD192579.


Thanks in advance,



American Association of Variable Star Observers (AAVSO)
Rc values

Hi Christophe,

Get used to use the photometry tables in VSP instead of looking for magnitudes in SIMBAD or other sources.
When there is a campaign, we try to provide as much information as possible.

In VSP, check the appropriate boxes at the bottom of the form in order to get Rc magnitudes too.

For 30 Cyg, you will see that Rc= 4.756.

For the 70 comp star (HD 192579, 31 Cyg B), the Rc value is 7.076. This star is a small amplitude (0.011 TESS) SPB variable according to TESS data.


Oh ! I see.

I didn't know…

Oh ! I see.

I didn't know about this function of the VSP, using only V mag and TG for years, but a few occasions.

I know about the small variability of the star 70. This is the brigtest star in my field after 30 cyg. The variability is very small ; it should be ok as a check star only. No ?


Thanks Sebastian.


American Association of Variable Star Observers (AAVSO)
PEP Comp/Check

REVISED (original stars too faint in U)


HD 185395   19 36 26.5  +50 13 16   (=000-BCH-242)

U= 4.834 B= 4.863  V=4.480


HD 192514   20 13 18.1 +46 48 56   (=000-BCK-971)

U=5.07  B=4.92  V= 4.83


From chart X36400OC



    000-BCK-190  20:01:21.6  50:06:17
    U = 7.18
    B = 6.16
    V = 5.05

    000-BCL-427  20:22:55.5  42:59:01
    U = 7.91
    B = 7.15
    V = 6.20


American Association of Variable Star Observers (AAVSO)
V0695 Cyg comp stars

Hi Tom,

You mentioned:

 "HD 192504   20 13 18.1 +46 48 56   (=000-BCK-971)
U=5.47  B=4.92  V= 4.83"

Actually, HD 192504 has V= 7.65 and B= 8.66.

The star you quoted is HD 192514 = 30 Cyg. And the U- band magnitude is 5.07 not 5.47.

The other comp star was:

"HD 185395   19 36 26.5  +50 13 16   (=000-BCH-242)
U= 4.886 B= 4.916  V=4.512"

Those magnitudes weren't good. GCPD data are much better and they are:
U= 4.834 B= 4.863  V=4.480

VSD/VSP have been updated accordingly.


Eclipse end



Finally, it seems the eclipse comes to an end.

By JD2460422.65911053 (2024-Apr-22 03:49), the star was regaining about 0.01 mag in R, 0.03 in V, and 0.07 in B, in my system.

Last night was overcast, but the coming night looks more promising. We will see.


Clear skies,


American Association of Variable Star Observers (AAVSO)
eclipse egress

Hi Christophe, and all,


good catch on Apr. 22!

On Apr. 21.1 UT I suspected 3rd contact in my measures. On Apr. 25.1 UT egress was clearly visible despite observing through thin clouds. Today at Apr. 26.0 UT the system reached normal brightness again. Now continuing observing at a more leisurely pace.


Clear skies,

Wolfgang (VOL)