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CG Dra: a VSS campaign

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Jeremy's picture
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CG Dra: a VSS campaign

I've just posted an article about observing this dwarf nova. This is a star that is always doing something. It has outbursts every 11 days or so, and yet has been neglected of late.

It's also a good target for those wanting to have a go at digital photometry. For several years I used a 10 cm refactor and CCD to follow this object. And you don't need to use a filter. Perhaps you can fit in a few 60 sec exposures among your other imaging projects.

Visual obs also welcome, although at it's brightest it's 15th mag, so a large telescope will be needed

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Many thanks for the article,

Many thanks for the article, Jeremy. I've scheduled a few instruments in Spain and New Mexico, so hopefully will have some data to chew on.

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That's super, Maxim. Good

That's super, Maxim. Good luck!

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Outburst

CG Dra has been slowly rising to outburst over the past couple of nights...

May 10.06UT  17.06CV

May 12.01UT  16.88CV

May 12.98UT  16.15CV

May 13.95UT  15.90CV

Uisng both the OU COAST and SLOOH 2

Gary

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Alas, poor weather at my all

Alas, poor weather at my all locations. Runs cancelled one after another. Was only able to get this today on 0.5 m in New Mexico:

CG Dra, 2021-05-16 07:04:57.000 UTC, V = 16.33 ± 0.11

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Looks like it's on the fade

Looks like it's on the fade after the peak on the 13th/14th - back at about 16.7CV early this morning (17-May-21 03:18-03:56UT).

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Got a good session on May

Got a good session on May 17th. First observation 06:02, last 09:04 UTC. I wonder, is this a ~ 0.2 mag flickering or irregular modulations or this is actually an eclipse? In case of the latter then why the exit follows by an irregular tail - clumpy accretion disk?

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Jeremy's picture
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Good to see your photometry

Good to see your photometry run, Maxim. Thank you!

My first reaction, like yours, is it's probably flickering. But time will tell

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Some results from iTEL 24

16.9 V mag on the early morning 20th May. Data is at AAVSO site. Stewart

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A few more observations -

A few more observations - moonlit sky.

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CG Dra, 2021-05-29 09:17:01

CG Dra, 2021-05-29 09:17:01.000 UTC, V = 16.71 ± 0.091

Difficult to get any good accuracy due to the Moon now.

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Outburst

It appears that the slightly overdue outburst of CG Dra has finally started...

June 16.895 UT  15.87CV  (SLOOH)

Gary

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Looks like this is a "long"

Looks like this is a "long" type outburst - appeared to be still brighter than mag 16 this morning from Spain:

Jun 23.131UT  15.84CV (+/-0.04)

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Data from AAVSOnet telescopes

Ken Menzies (AAVSO) has helped me upload images with the clear filter as CV into the AAVSO database. All fit with the existing results from other observers so I seem to have done it right. Stewart

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16.85 V early this morning.

Using iTEL 18 (Spain),  Vphot gave a V filter mag of 16.86 ( three 300s images stacked)  this morning. Stewart

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2021-07-04 23:32UTC

My first scientific observation since returning to La Palma and to a whole host of instrumental and computer problems.

V=16.85 ± 0.04 at JD 2459400.480961

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Outburst

CG Dra currently in outburst ...

Jly 04.909  16.77CV; Jly 05.951  15.98CV;  Jly 06.695  15.89CV

About 20d since previous (long) outburst.

Gary

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No longer in outburst at 16.69 last night.

iTEL 18 and Vphot report  CG Dra,      2459405.55119,     16.693 V filter

So  a short outburst that I have just missed. Still all results are useful. iTEL subscription get refreshed on the 12th so will try again.

Stewart

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CG Dra at 16.70 (V filter) this morning 19 July 2021

iTEL 18 and Vphot gave CG Dra at 16.71 very early this morning. 

Check star 147 (14.674 ) estimated at 14.679. Airmass 1.04.

Stewart

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Yes, it looks to be at the

Yes, it looks to be at the bottom of a cycle.

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Jeremy's picture
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CG Dra

Good to see the data rolling in for this star. Many thanks to all observers. It's been faint for a few days: I've have it at 16.6 yo 16.7 the last couple of nights.

Now the nights are getting a bit longer, some time-series photometry runs become possible.

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Time series photometry

Nights are moderately long (though dusty and/or smoky) in these parts.

The orbital period of 0.18864 days according to AAVSO appears well determined.  What is the value of further lengthy observation runs?  Is there a suggestion that the period may be changing or are we looking for flickering in the accretion disk?

I am prepared to spend some telescope time if it is worth my while but there other calls on it too.

(Added in edit: not that it makes any difference tonight. Complete cloud cover as of about 45 minutes ago.)

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Our earlier work suspectEd

Our earlier work suspectEd shallow eclipses. Can we confirm and does the depth vary with outburst status (outburst vs quiescence)?

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Currently in outburst.

Currently in outburst.

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V filter and CV filter: what differences do we expect?

I am occasionally contributing to the present campaign on CG Dra with a V filter on iTEL 18 in Spain. Many of the results are being gathered using the CV method. 

What systematic differences do we expect between the two?

Stewart

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Looking at the light curve

Looking at the light curve Stewart, there is not much difference. In any case, the objective of the project is to measure the time and duration of each outburst, rather than its precise mag. Thanks for your observation. If you are getting decent signal to noise ratio then stick with the V filter -after all, you are using a decent aperture scope. But no filter allows better SNR, so is often preferable with small telescopes.