AG Dra

[Tim Lester]

Here is my Mar 30th result for AG Dra compared to my last observation of Aug 8 2015
(R = 9000)

_agdra.png (7.36 KiB) Viewed 10220 times

Tim

[Tim Lester]

Result for Apr 5th. This time centred on Hbeta at R = 6300

_agdra_20160405_193_tlester.png (9.25 KiB) Viewed 10190 times

Tim

[Paolo Berardi]

Hi Tim, thanks for sharing. It appears that He II 4686 has changed a lot in the past few days. I noticed it on a low-res spectrum taken yesterday by an italian amateur (Paolo Cazzato) with an Alpy 600. Then I looked here for confirmation, finding your excellent spectrum.

The ionized helium line is a bit narrower than h-beta but the EW seems now greater anyway, contrary to what we were able to observe over the past months (years?).

On the ATel #7582 it talk about a decreasing of the very high ionization conditions when the outburst began. The He II 4686 / h-beta ratio reduced to 0.67 at the end of May (2015).

Can anyone explain the astrophysical meaning of the EW change (if real, I haven't the profile for its calculation)?

Thanks,
Paolo

[Francois Teyssier]

Hi Paolo,

You 're right for a *classical* symbiotic outburst :
In the classical model, the matter (from the wind of the giant) is accreted at the surface of the white dwarf at a high rate. The rate of accreation produces a steady "burning" (proton-proton) of Hydrogen. The matters remains "normal" (non-degenerated) and reacts as a perfect gas : when the temperature inceases (for instance because of an increase of the accretion), the burning layer at the surface expends (PV ~ T) and *cools* : the temperature decreases, the peak of energy shifts to the visible range (we call that an outburst) and the mean energy of the radiation from the white dwarf (one of the two major sources of radiation, with the interaction of the fast wind from the WD and slow wind from the red giant) decreases : less ionisation. The high ionisations lines (from He II to FeVII, Raman ...and more) vanishes. This was very clear during the two outburst of AG Peg last year. See http://www.astronomie-amateur.fr/feuill ... Peg_2.html, with an obvious decrease of Fe VII or Raman features.
When the pertubation ceases, the envelopp retracts, the temperature increase ....

This is the general model, with of course many exceptions, specificities ...

For a few symbiotics, the outburst could be produce by an accretion disk (See for example some outbursts of Z And itself)



In the case of AG Dra, it has been detected two types of outbursts : classical, often double, outbursts which have been called 'cool' outbursts (IUE observations of the high-velocity symbiotic star AG Draconis. III. A compendium of 17 years of UV monitoring, and comparison with optical and X-ray observations, http://adsabs.harvard.edu/abs/1999A%26A...347..478G). The second type of outburst is called 'hot outburst'.
This the case for the current outburst, with an increase of He II intensity, while the Raman features remains very strong

I hope it's clear

François


Selected lectures :

Spectroscopic view on the outburst activity of the symbiotic binary AG Draconis
http://adsabs.harvard.edu/abs/2016MNRAS.456.2558L
The spectroscopic evolution of the symbiotic star AG Draconis. I. The O VI Raman, Balmer, and helium emission line variations during the outburst of 2006-2008
http://adsabs.harvard.edu/abs/2010A%26A...510A..70S

[Paolo Berardi]

François, thanks a lot for you detailed explanation and paper links. I found impressive to be able to discern many different events with amateur equipment.

Paolo

[Francisco Campos]

François, excellent your explanations about the outburst of AG Dra. They are a true extra motivation to carry on observing this interesting star.

Here is a comparative of two spectra taken with a difference of two weeks. The last one its a bit noisy... It seems that most emission Balmer lines and the strong He II at 4542 A have faded, together with the continuum. But in the other side H-alpha has increased...

AG Dra .png (10.01 KiB) Viewed 9997 times

Greetings
Fran

[James Foster]

Here is a spectra, using a 150 ln/mm grating, on AG Draconis on 04May16

This spectra was calibrated and instrument response corrected.

I was wondering why my Balmer H and He lines are slightly "blue-shifted" with respect to the telluric Hg and O2 lines I calibrated against; specifically,
Hg(5460.74A), O2(6860.0A), & O2(7605.0A) lines.

I have a neon calibration image, but when applying it, the H & He's show the same displacement. I was using a 17" scope at F/6.8, with a JTW L-200
spectroscope with an SBIG ST-10xme camera.

Here is another spectra taken 23 April 2016 showing similar "displaced" H & He lines:

This was a mosaic of two spectras taken with a higher resolution 300 ln/mm grating, neon source calibrated.

James Foster
Los Angeles, CA

[AndyWilson]

Hi James,
I checked my AG Dra spectrum from 27th April and I also see a fairly sizeable blue shift of over 100km/s after heliocentric correction. I did a bit of investigation and according to SIMBAD the star has a high radial velocity of 147 km/s towards us which would explain the blue shift.

http://simbad.u-strasbg.fr/simbad/sim-i ... =submit+id

AG Dra 27th April

AG Dra 27th April

AG_Dra_Helio.jpg (52.35 KiB) Viewed 9918 times

Best wishes,
Andy

[James Foster]

To: Andy,

Thanks for the quick response! I install the latest Bass 1.93 and tried velocity correction, but it was only about 4 km/sec and did not
shift the H & He lines appreciably. Thanks for the realty check!

James