1. SIMULTANEOUS PHOTOMETRIC AND SPECTRAL ANALYSIS OF A NEW OUTBURST OF V1686 CYG
HASMIK ANDREASYAN
Tigran Magakian
Tigran Movsessian
Mkrtich Gevorgyan
Byurakan Astrophysical Observatory
Weetwood Hall, Leeds-UK 18 June, 2019

2. Outline Introduction Observations and data reduction
The new outburst of V1686 Cyg
The spectrum of V1686 Cyg in quiescent stage
The spectrum of V1686 Cyg in maximum
Equivalent widths and radial velocities
Conclusions
References

3. Introduction
BD+40°4124
V1318 Cyg
V1686 Cyg

4. The photometric variability of LkHα 224 was detected by Wenzel (1980); as the variable this star received V1686 Cyg designation.
The star fluctuates near the mean brightness level, sometimes (usually one time per year) demonstrating irregular Algol-like minima, which last one-two months.
Its mean level of brightness itself varies from V=12.5 down to V=15 (Hillenbrand et al. 1995; Herbst&Shevchenko 1999; Oudmaijer et al. 2001).

5. Estimates of its spectral type vary from B2 to F9 (Hernandez et al, 2004).
Emission lines in V1686 Cyg spectrum also demonstrate significant variability (Mora et al. 2001). In the work of Magakyan&Movsesyan (1997) the broad asymmetric profile of Hα emission with several superposed narrow absorption-like features is shown, suggesting the existence of expanding envelopes.

6. Observations and data reduction
Observations were carried out on 2.6-m telescope in Byurakan Observatory. We used SCORPIO spectral camera, and obtained direct images, as well as long-slit spectra.
Observations were implemented from Sept to July Spectral observations were from Sept to Dec. 2016, with different spectral resolutions: 0.50, 0.80, 1.50 and 2.65 Å/pix.
In 2015 during our observations of this field, new outburst of V1318 Cyg S was detected (Magakian et al. 2019). In parallel to this star V1686 Cyg also was observed.

7. The new outburst of V1686 Cyg
The brightness of V1686 Cyg increased for more than two magnitudes in V and then gradually returned to its previous level.

8. Date B V R I
17.22
15.88
14.68
13.27
17.18
15.96
14.87
13.56
17.03
15.61
14.48
13.07
17.42
16.05
14.76
13.00
14.82
13.50
12.48
11.58
16.34
14.98
13.62
12.49
16.99
15.66
14.63
13.53
As the analysis of the light curve of V1686 Cyg shows that perceptible brightness decreasing and increasing of this star usually have days duration, while our observations have much lower time resolution. In any case, the variability, observed by us, has unusually high amplitude (and perhaps longer duration), compared with typical values for V1686 Cyg.
The data from other surveys, combined with our measurements, allow to assume that the more or less persistent brightness level of V1686 Cyg lowered in last 15 years by 1.5 magnitude, and during our observations it became even lower at least 2.5 magnitudes below the 1999 level.

9. The spectrum of V1686 Cyg in quiescent stage
Spectra, taken before the outburst, are quite typical for this star, being similar to the previous results (Hillenbrand et al. 1995; Magakyan Movsesyan, 1997). In the red part of spectral range the most conspicuous line is a broad and strong Hα emission with superposed weak blue-shifted absorption feature. Forbidden emissions of [OI] also are present, though very strong background emission lines make uncertain the estimations of their intensity. Besides, faint emission lines of FeII (40) and CaI (18), not described before, were detected.
Spectral type of V1686 Cyg can be assumed as an early Ae.

10. Spectrum of V1686 Cyg in maximum
Maximal brightness of V1686 Cyg was reached in Aug. 24 of It keeps its appearance at least until Aug. 30 of 2016.
During the outburst V1686 Cyg spectrum is quite different and has remarkable changes especially in the profile of Hα line. The strength of iron emissions decreases, forbidden lines of [OI] nearly dissapear.
In all spectra we detected (DIB) 6284 Å (Herbig 1995), which is easily distinguished from the nearby atmospheric absorption 6278 Å

11. Low-resolution spectra (with the blue range)

12. All absorption lines, including NaD and Hα line absorption component, are disappeared. All emission lines are stronger than before emission line spectrum is very similar to the spectra of PV Cep and V350 Cep (Magakian et al. 2019)

13. Equivalent widths and radial velocities
The strength of emission lines relative to continuum significantly lowered during the maximal brightness period. The changes of EW of Hα ≈-35Å to the ≈-12Å in the end of Aug. 2016; then high values again were restored.
Heliocentric radial velocities for absorption lines (Hα, NaD) all demonstrated negative velocity near -100 km s-1.
Emission lines have positive radial velocity near +60 km s-1.

14. Conclusions
Pronounced changes in the strength of some absorption lines (NaD), explain the large range of the spectral types, assigned to this object. However, the main part of these lines definitely has non-photospheric origin.
Relation between spectral and photometric variations. Formation of dense expanding envelope around the star, with its subsequent dissipation during several months. The envelope covers up lower layers of the stellar chromosphere, making invisible and diminishing emission lines.
The existence of the blue-shifted absorption components in the Hα allows to conclude, that the similar expanding envelopes nearly always are present around V1686 Cyg star, and the described outburst differs only by its extremity.

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