AG Dra brightening

[David Boyd]

Photometric and spectroscopic observations of AG Dra in March and April 2016 show a brightening from V=9.71 on March 17 to V=9.57 on April 12. The B-V colour index changed from 1.38 to 1.20 over the same period.

Spectra taken on those dates and flux calibrated using the above V magnitudes are compared below and show a corresponding increase in flux on the blue side of H-alpha.

_agdra_20160317+20160412_D.Boyd_flux.png (35.41 KiB) Viewed 10786 times

The emission line flux of H-alpha, H-beta and HeII (4686) are as follows (in erg/cm2/s). The flux of He I (4471) is <0.05 H-beta.
March 17
H-alpha 4.7x10-11
H-beta 7.5x10-12
He II (4686) 7.5x10-12
April 12
H-alpha 5.0x10-11
H-beta 1.1x10-11
He II (4686) 1.6x10-11

From eqn 1 in Leedjarv et al. (MNRAS 2016) these HeII/H-beta ratios indicate a temperature increase from ~193,000K in March to ~222,000K in April.

Spectra taken in 2015 show a HeII/H-beta ratio steadily increasing from 0.60 (~161,000K) to 0.76 (~175,000K) between April and October.

David

[Peter Somogyi]

Hello David,

This must be an Impressive change within 1 week!
As a comparison, here is my flux measurement on my past AG Dra spectra (very different resolution, but all rectified to 5000A-5200A, measured by IRAF/splot gauss fit):

<file> <resolution> <HeII 4686> <H-beta> <HeII 4686/H-beta>
asdb_agdra_20160207_020.fit R~1800 15.7548 15.9904 0.985266
asdb_agdra_20160226_879.fit R~1800 14.8174 13.4806 1.09916
asdb_agdra_20160317_952.fit R~1800 14.2229 15.2 0.935717
asdb_agdra_20160402_910.fit R~450 18.3107 15.6075 1.1732

(Last one not sent to the database yet.)
There was only a temporary decrease of H-beta on 02.26, and a little increase of HeII 4686 on the last weekend (didn't ring the bell for me).

Cheers,
Peter

EDIT: I've just downloaded your 03.17 spectrum, via IRAF/splot/deblend/gauss fit I can measure 6.21E-12 for HeII and 6.51E-12 for your H-beta, giving a ratio of .954 that is closer to my measurement at approx. the same time.

[David Boyd]

Hello Peter,

I am using ISIS to divide out the continuum and measure the line flux. I am not sure of the precision so only quoted figures to 1 dp.

My spectrum on March 2 also gave a HeII(4686)/H-beta ratio of 1.0.

I note that apart from your March17 spectrum you are also seeing a steady rise in the HeII(4686)/H-beta ratio from February to April. Clearly something is happening.

David

[Francois Teyssier]

Congratulations David,
That's great !
He II is very intense.
Raman OVI remains strong.
This is what Gonzales-Riestra & al. (1999) call a "hot" outburst.
Classical symbiotic outbursts consist of an expension of the hydrogen 'burning' layer which produces a decrease of the temperature : vanishing of high excitation lines.
This outburst is the contrary ; increase of the temperature so increase of high ionization lines such as He II

This is clearly seen trough the light curve (AAVSO) and your photometry with a delta B = 0.3 while Delta V is only 0.15

AGDra.PNG (6.04 KiB) Viewed 10714 times

Of course more observations are needed.
This kind of outburst is short, with a very rapid rise and decrease slower (a few tens of days)


François

[Francois Teyssier]

Advice from Steve Shore :

please concentrate on the Raman pair (both lines, it's really important), especially the ratio of 7083/6825. Also for the He I 6678 vs. He II 4686.

François

[Francois Teyssier]

Tonight spectrum

_agdra_20160416_907_.png (12.04 KiB) Viewed 10679 times

H beta and He II region

_agdra_20160416_907_4500.png (11.5 KiB) Viewed 10679 times

A few lines

_agdra_20160416_907_Halpha.png (6.15 KiB) Viewed 10679 times

_agdra_20160416_907_HeII4686.png (6.25 KiB) Viewed 10679 times

_agdra_20160416_907_RamanOVI6826_wl.png (7.56 KiB) Viewed 10679 times

François

[Peter Somogyi]

Finally I've also got - a little bit cloudy - night, here is a comparative perspective:

plot_20160226vs0416.png (4.51 KiB) Viewed 10656 times

2016.04.16: 6 x 10 minute, unbinned, lots of cloud veils went by
2016.02.26: 3 x 900s bin 2x2, clear sky

Just to confirm the HeII 4686 increase at R~1900:

plot_20160226vs0416_Hbeta.png (4.25 KiB) Viewed 10656 times

Of course, the HeII 4686 / HeI 6678 would need a local rescaling to a known continuum (I could do that when requested).
The SNR and continuum shape on 7083 both can be problemmatic, at least for now it's giving a chance to compare with the eShel result by Francois.

- Peter

[umberto sollecchia]

Bonjour à tous, placez le profil de l'étoile observée hier soir.

Profilo AG Dra.png (4.39 KiB) Viewed 10589 times

Salutations à tous.Umberto

[Francois Teyssier]

Good results and cadency !

Comparison of Raman OVI 6830 (16 & 18 -04-2016)

_agdra_20160418_831_full_Raman OVI 6828.png (17.57 KiB) Viewed 10576 times

Temperatures
(Iijima, 1981), the same than David used

16-04 : 220 000 K
18-04 : 222 000 K

Formula 2 gives 233000 and 238000 K respectively

Good agreement !

François

[Peter Somogyi]

"Red alert" - both Raman profiles started to halve by yesterday, looks to have started suddenly!

When things was yet the same (shot over the night 04.19-20 without any change...):

_agdra_20160420_869_vs_0420_031.png (5.18 KiB) Viewed 10506 times

I think I've caught when started to go down suddenly (shot over 1 night, this time I was a more lucky sleeper):

_agdra_20160420_869_vs_0421_010.png (4.98 KiB) Viewed 10506 times

Next day the difference was bigger, both of them halved:

_agdra_20160420_869_vs_0421_841.png (4.91 KiB) Viewed 10506 times

_agdra_20160420_869: 18 x 10 min (of last 1-2 exposures contain the drop, but need to look)
<took calibrations>
_agdra_20160421_010: 8 x 10 min
<daytime>
_agdra_20160421_841: 5 x 20 min

Last 3 spectra have not sent yet, need to process much better as I saw wavelength registration was not really perfect so had to switch off for the 10-minute exposures. (Fortunately I have the scripts to fix it in IRAF in a precise automated way - just need some time).
Will send the fully processed serie when I'm fixing the wavelength precision + flat movement issues soon.
Anyway, the last 3rd spectra confirming me the drop.

BTW I did check flats and with/without wavelenght registration, Raman drop is visible even on 1 exposure or the last night even by the raw image.

Hope someone can confirm the drop very soon - before coming up again, at least!

Cheers,
Peter