GK Per Outburst

[Francois Teyssier]

The semi-polar [1] cataclysmic star GK per is detected in outburst (currently V ~ 11)
Monitoring of the outburst is very welcome.
Resolution : low and high
Long time series is encouraged . The period is 2 days.
24 hours monitoring (Europe, North America) should be must.
In that purpose, it is suggested than you inform arasdatabase team (Forrest Sims, David Boyd, Christophe Boussin, François Teyssier)
of the scheduling of your observations.

The peak should be ~10 mag. The duration of the outburst until return to quiescence could be more than 2 months. The target is ideally placed in winter time for a long monitoring.

Spectra should be sent to francoismathieu.teyssier [at] gmail.com & arasdatabase [at] gmail.com
For inclusion in the database.

Best wishes for this New Year and Clear Skies!

François Teyssier

Notes :
Semi-polar is a binary system. A white dwarf is accreting matter from the main sequence M type star. Due to its magnetic field (intermediate) the accretion disk is disrupted near the WD and the matter is accreted near the magnetic poles.
The system undergone the famous 1901 nova event

AAVSO light curve showing the current and previous outburst

[Joan Guarro Flo]

Hello everyone,

These are my first results about this interesting star.

Cheers, J. Guarro.

[Forrest Sims]

Greetings,

Here is my cropped, flux calibrated spectrum of GK Per for 2023-01-09 UT taken with a Shelyak LISA. Balmer emission lines, NIII, He II, and numerous He I lines plus the Sodium D absorption lines are all present. The blended line near 4640Å would appear to be a blend of NIII 4634.2Å and CIII at 4647Å.

The LISA spectrograph with the Atik414ex does not have great sensitivity below about 3900Å. But this next plot shows the same spectrum, this time including the portion of the spectrum from about 3725Å to 3900Å. There is a bump (circled in red) in the spectrum centered at about 3800Å. We do not have a physical explanation. I checked and repeated the response correction with no change in the resulting "bump". Probably a combination of low signal and noise. But in the paper mentioned to me by David Boyd https://iopscience.iop.org/article/10.1 ... /6/143/pdf. in Figure 13, shows a spectrum of GK Per with a similar bump at about the same wavelength range. Interesting, but probably noise... Still it would be interesting if any of you have spectra, particularly with a different instrument that might cover some of this range below 4000Å.

The V magnitude of GK Per was changing rapidly during the observing period is shown in the graph below.

[Francois Teyssier]

Nice results!

Note: the period is very close to 2 days. Thus any comparison of the spectra should take in account the orbital phase. Currently ~ 0.25 and ~0.75
(Alvarez-Hernandez+ (2021, MNRAS, 507, 5805)


Photometry:
Flickering is high (truncated accretion disk + hot spot and accretion near the magnetic poles).
BVR time series could produce interesting indices.



Woody: the "hump" showed in the paper you cite is Balmer jump. It ends near 3800.
Note: for such an object, it may be misleaded to compare SED of the continuum at different activity states (quiescence and outburst)
I suggest tracing the two spectra on the same graph.


I got a series with the T1M Epsilon at C2PU observatory with a LISA. Currently in reduction phase, I'll show the result asap (but dealing with IRAF ...)

Bonne continuation!

[Francois Teyssier]

ATel describing the first spectra: https://www.astronomerstelegram.org/?read=15858



ARAS Optical spectroscopy of GK Per in its current dwarf nova-like outburst
ATel #15858; S. N. Shore (Univ. of Pisa), F. Teyssier, J. Guarro Flo, F. Sims, V. Bouttard (ARAS Eruptive Stars group)
on 14 Jan 2023; 16:41 UT
Distributed as an Instant Email Notice Novae
Credential Certification: S. N. Shore (shore@df.unipi.it)

Subjects: Optical, Cataclysmic Variable, Nova



The intermediate polar cataclysmic variable GK Per (Nova Per 1901) is currently undergoing a dwarf nova-like outburst, detected on 2022 Dec. 12 (JD JD 2459926) in the AAVSO lightcurve. The latest photometry shows this event has not yet ended (V = 11 on 2023 Jan. 11). This outburst occurred 1520 days after the last one in 2018 (Atel #11995 ). Observations have been obtained at resolutions between 1000 and 9000 (echelle) covering the wavelength interval between 3800 and 9200 A with a variety of telescopes. The spectra show strong emission lines of the Balmer series, He I, He II, a strong CIII/NIII 4639-40 blend and a blue continuum. An unidentified feature at 5687A, perhaps C III 5686.6A, shows a flux of 5.7e-14 erg/s/cm^2. A flux calibrated low resolution spectrum (spectrograph LISA R = 1000) yields continuum fluxes of 1.6, 1.47, 1.1 (in units of 1E-13 erg/s/cm^2 at 4440, 5550, 6800 A. The Balmer lines show equivalent widths and fluxes of (17.6 A 1.6e-12 erg/s/cm^2), ( 4.1, 7.9-E13), (2.6, 5.5E-13), (2.5 5.1E-13) for Halpha - Hdelta. He II 4686 is very strong (2.0 E-13) with a ratio HeII/Hbeta = 2.32, compared to HeII/Hb = 0.44 in our last spectrum secured in quiescent state on MJD 2459841; He II 4542 and 5411 are also present. The HeI 5876 A (1.4E-13 erg/s/cm^2) and 6678 A (2.5E-13) lines are the strongest in the series but the full complement are detected. The He I 6678, which is especially strong, shows a variable profile with two peaks at phase 0.75 and a shift consistent with a velocity amplitude of about 50 km/s, about what is expected with the mass ratio of the WD to the companion; the echelle spectra were secured with the NOU-T spectrograph (R = 9000), the phases use the Alvarez-Hernandez+ (2021, MNRAS, 507, 5805) ephemeris. We will continue monitoring the outburst at the highest cadence possible. The spectra are publicly available in ARAS database (see Teyssier, 2019, CoSka, 49, 217), including spectra secured during quiescent state.

ARAS Dwarf Novae: GK Per

[David Boyd]

Another spectrum of GK Per taken with a LISA (R~1000) and flux calibrated using a V magnitude concurrently recorded by Franky Dubois (AAVSO AID).

David

gkper_20230113_782_D_Boyd.png (26.46 KiB) Viewed 3596 times

[Christophe Boussin]

Hi all,

Congratulations to all the observers !!
Finally, a clear sky to observe GK Per...
The following spectrum was obtained on 13 January at 19:35 UT (resolution of 540, JJ = 2459958.3156) with my Alpy 600 and an acquisition time of 50 min (5 x 600s) :

GK Per on January 13th, 2023

_gkper_20230113_816_Christophe Boussin_3700_7565.png (117.93 KiB) Viewed 3564 times

GK Per on January 13th, 2023 (identification of some lines from PlotSpectra)

Clear skies to all !!

Christophe BOUSSIN

[David Boyd]

Here is another spectrum of GK Per taken on 20th January and calibrated in absolute flux using concurrently measured V magnitudes with a mean of V = 10.96.

gkper_20230120_842_D_Boyd.png (36.82 KiB) Viewed 3356 times

I continued to record B and V magnitudes for 1.4 hrs while recording the spectra and the resulting light curves and colour index are shown below. These show that while there are large variations in both magnitudes, presumably due to flickering(?), these are correlated and the colour remains relatively constant.

GK Per light curves 20 Jan 2023.png (136.36 KiB) Viewed 3356 times

Being curious, I carried out a period analysis of the V band light curve using the PDM method in Peranso. The results are shown below. The upper pair of plots show a strong peak at 0.01086 hr = 39.1 sec with aliases. This may be a QPO in the flickering? But I was also curious about the small broad peak around 0.1 hr. The lower pair of plots show an analysis of this peak which gives a period of 0.09792 hr = 352.5 +/- 1.0 sec. A search of the literature revealed that this is the same as the WD spin period of 351 sec found in X-rays by Watson, King & Osborne (1985). I was surprised to see this signal in the V band light curve.

GK Per Peranso PDM 20 Jan 2023.png (210.76 KiB) Viewed 3356 times

David

[Hubert Boussier]

Hello David,

About the rapid variations of the B and V magnitude you underlined, you guess that it may be due to flickering, what was the time exposure you used ?
It seems yhat the B and V are more or less related so don't you think that if it was flickering the variation would be more stochastic ?

Hubert

[David Boyd]

Hello Hubert,

According to Bruch, A&A, 266, 237 (1992) the mean B-V colour index of the flickering light source in GK Per is close to 0 so the B and V magnitudes should change together, subject to the stochastic variation inherent in the flickering process.

The exposures were alternately 10 sec in V and 20 sec in B. This means the interval between V measurements was close to the 39 sec signal which appeared in the power spectrum so it looks as though this may be the cause of that signal.

David