W Cygni oddly bright?

Hi

I was taking wide field images (14 degrees or so) last night to scan for
perseids and after giving up, I left the camera running over night as the
chances of rain seemed slim.

I've been going through the 200 or so images today (quite easy, most are
clouded out) and have come over something I don't quite understand regarding
the variability of W Cygni.

Starry Night Pro gives the maximum magnitude as 5.3, yet when I run some
basic photometric analysis on the image in MaximDL, it comes out at Mag
3.98 - a hairs breadth brighter than Rho Cygni at 3.96. This matches visual
inspection of the image which was taken with a ST8E in 1x1 binning.

SO ... have I discovered something odd (I doubt it). Maybe it's because the
ST8E is more sensitive to IR or something like that.

Can anyone point me at a reference for the variability of W Cygni (I can't
find one).

JPEG of my image here if you're interested.

http://moffatt.uk.net/wcygni.jpg

Regards
Roger
London
UK

www.moffatt.uk.net

Roger Moffatt wrote:

Hi

I was taking wide field images (14 degrees or so) last night to scan for
perseids and after giving up, I left the camera running over night as the
chances of rain seemed slim.

I've been going through the 200 or so images today (quite easy, most are
clouded out) and have come over something I don't quite understand regarding
the variability of W Cygni.

Starry Night Pro gives the maximum magnitude as 5.3, yet when I run some
basic photometric analysis on the image in MaximDL, it comes out at Mag
3.98 - a hairs breadth brighter than Rho Cygni at 3.96. This matches visual
inspection of the image which was taken with a ST8E in 1x1 binning.

SO ... have I discovered something odd (I doubt it). Maybe it's because the
ST8E is more sensitive to IR or something like that.

Can anyone point me at a reference for the variability of W Cygni (I can't
find one).

JPEG of my image here if you're interested.

http://moffatt.uk.net/wcygni.jpg

Regards
Roger
London
UK

www.moffatt.uk.net

Ho Roger,

AAVSO's latest data shows W Cyg currently at 6.4. Go to www.aavso.org,
type "W Cyg" in the search box, select "Recent Observations" and press
"Go". There you can check the lightcurve, and get a lot of other info.

Regards,

- Alex

"Alexander Avtanski" wrote in message
...

AAVSO's latest data shows W Cyg currently at 6.4. Go to www.aavso.org,
type "W Cyg" in the search box, select "Recent Observations" and press
"Go". There you can check the lightcurve, and get a lot of other info.


Thanks Alex - that's a handy site.

So given W cyg is listed 6.4 and Rho Cyg 4.7, I can calibrate Maxim DL to
show Rho Cyg at 4.7. On this basis, W Cyg is Mag 4.72 in my original image.
This is a magnitude and a half away from the AAVSO info - so any idea what
is wrong? Even looking at the jpeg shows it seems brighter than expected.

I'll try to image again tonight - but the cloud looks well set.

Roger

"Roger Moffatt" roger (dot) moffatt (at) zen dot coh dot uk wrote in
message ...
snip
I was taking wide field images (14 degrees or so) last night to scan for
perseids and after giving up, I left the camera running over night as the
chances of rain seemed slim.
snip

Isn't the Uk perpetually under a storm cloud? Or are you just rubbing your
clear skies in on those of us that have been under clouds for weeks in the
US?

BV.

"Benign Vanilla" wrote in message
news:2o4i4nF6tn2fU1@uni-

Isn't the Uk perpetually under a storm cloud? Or are you just rubbing your
clear skies in on those of us that have been under clouds for weeks in the
US?

Maybe you missed this?

I've been going through the 200 or so images today (quite easy, most are
clouded out)

Out of 237 images, only 10 don't have any cloud at all. I'm certainly not
rubbing my clear skies on anyone else - frankly ever since I upgraded my
camera to a ST8E 2 years ago, the weather has conspired to destroy almost
every session I have planned.

Darn global warming!

Roger
UK

Roger,
CCD cameras when used unfilterd are generally more sensitive to the
redder parts of the spectrum. Therefore, red stars such as long period
variables will usually appear brighter in ccd frames than they do visually.
W Cygni is just such a red star with a spectral type of M8. If you put a V
filter on your camera, your camera come closer to the visual magnitude
scale.
You can get a lightcurve of W Cyg and other variables by going to the
AAVSO website: http://www.aavso.org/ .

....Tim


"Roger Moffatt" roger (dot) moffatt (at) zen dot coh dot uk wrote in
:


I've been going through the 200 or so images today (quite easy, most
are clouded out) and have come over something I don't quite understand
regarding the variability of W Cygni.

Starry Night Pro gives the maximum magnitude as 5.3, yet when I run
some basic photometric analysis on the image in MaximDL, it comes out
at Mag 3.98 - a hairs breadth brighter than Rho Cygni at 3.96. This
matches visual inspection of the image which was taken with a ST8E in
1x1 binning.

SO ... have I discovered something odd (I doubt it). Maybe it's
because the ST8E is more sensitive to IR or something like that.

Can anyone point me at a reference for the variability of W Cygni (I
can't find one).

JPEG of my image here if you're interested.

http://moffatt.uk.net/wcygni.jpg

Regards
Roger
London
UK

www.moffatt.uk.net

In article , Roger Moffatt wrote:
[...]
Starry Night Pro gives the maximum magnitude as 5.3, yet when I run some
basic photometric analysis on the image in MaximDL, it comes out at Mag
3.98 - a hairs breadth brighter than Rho Cygni at 3.96. This matches visual
inspection of the image which was taken with a ST8E in 1x1 binning.

SO ... have I discovered something odd (I doubt it). Maybe it's because the
ST8E is more sensitive to IR or something like that.

That makes most sense. W Cyg is supposedly an M4 star, so its V-I would
probably be much bigger than rho Cyg (G8). I'm not sure how much, but
from browsing some photometry for G8 and M4 stars in VizieR, W Cyg could
easily have V-I of 2 or so, while rho Cyg is probably more like V-I of 1,
so it might well look a magnitude brighter to your CCD than the V magnitude
would suggest.

Tim & Stuart, many thanks for the helpful info.

Roger

"Roger Moffatt" roger (dot) moffatt (at) zen dot coh dot uk wrote in
message ...

"Benign Vanilla" wrote in message
news:2o4i4nF6tn2fU1@uni-

Isn't the Uk perpetually under a storm cloud? Or are you just rubbing
your
clear skies in on those of us that have been under clouds for weeks in
the
US?

Maybe you missed this?

I've been going through the 200 or so images today (quite easy, most are
clouded out)

Out of 237 images, only 10 don't have any cloud at all. I'm certainly not
rubbing my clear skies on anyone else - frankly ever since I upgraded my
camera to a ST8E 2 years ago, the weather has conspired to destroy almost
every session I have planned.

Darn global warming!

LOL. Sorry, I guess I am just bitter. Damn clouds.

BV.