The 2016 outburst of the unique symbiotic star MWC 560 (= V694 Mon), its long-term BVRI evolution and a marked 331 days periodicity

Abstract

After 26 years from the major event of 1990, in early 2016 the puzzling symbiotic binary MWC 560 has gone into a new and even brighter outburst. We present our tight BVR C I C photometric monitoring of MWC 560 (451 independent runs distributed over 357 different nights), covering the 2005-2016 interval, and the current outburst in particoular. A stricking feature of the 2016 outburst has been the suppression of the short term chaotic variability during the rise toward maximum brightness, and its dominance afterward with an amplitude in excess of 0.5 mag. Similar to the 1990 event when the object remained around maximum brightness for ∼6 months, at the time Solar conjunction prevented further observations of the current outburst, MWC 560 was still around maximum, three months past reaching it. We place our observations into a long term contex by combining with literature data to provide a complete 1928-2016 lightcurve. Some strong periodicities are found to modulate the optical photometry of MWC 560. A period of 1860 days regulate the occourence of bright phases at BVR C bands (with exactly 5.0 cycles separating the 1990 and 2016 outbursts), while the peak brightness attained during bright phases seems to vary with a ∼9570 days cycle. A clean 331 day periodicity modulate the I C lightcurve, where the emission from the M giant dominates, with a lightcurve strongly reminiscent of an ellipsoidal distortion plus irradiation from the hot companion. Pros and cons of 1860 and 331 days as the system orbital period are reviewed, waiting for a spectroscopic radial velocity orbit of the M giant to settle the question (provided the orbit is not oriented face-on).

Broad absorption line symbiotic stars: highly ionized species in the fast outflow from MWC 560

“…The decline in column density during 1990 April was likely related to (1) the 1990 January-April optical brightening, which marked both a periodic peak in the system's light curve and a unique, non-periodic, and permanent tripling of the optical luminosity (Leibowitz & Formiggini 2015;Munari et al 2016); (2) the dramatic mass ejections of 1990 January-April, which yielded detached BALs blue-shifted up to a system record of 6000 km s −1 (Tomov et al 1990a(Tomov et al , 1992; and (3) the post-outburst, year-long suppresion of optical flickering and slowing of absorption speeds to less than 1000 km s −1 in late 1990-1991 (Zamanov et al 2011a). Coverage of the spectral response to these events is incomplete; to our knowledge, no optical spectra were obtained 1990 April 4 through October 22, and no UV spectra were obtained 1990 May 1 through September 25.…”

“…with blue edges up to 6000 km s −1 shifting by thousands of km s −1 in mere days (Tomov et al 1990a), and the inner accretion disk may have been partially evacuated during that year (Zamanov et al 2011a). MWC 560 later attracted renewed interest in 2016, when it brightened to V≈9 for the first time since 1990 (Munari et al 2016). No signs of innerdisk evacuation were observed in 2016-and once the peak optical flux was reached, the Balmer BALs varied stably alongside weeks-long changes in the accretion rate, with blue edges up to 3000 km s −1 at most (Lucy et al, in preparation).…”

Fermi-Lat Gamma-Ray Detections of Classical Novae V1369 Centauri 2013 and V5668 Sagittarii 2015

“…V1369 Cen and V5668 Sgr were extensively monitored optically by the AAVSO and ARAS groups 17 and showed broadly similar multi-peaked light curves. Their respective first peaks were 3.6 mag and 4.1 mag, making them the visually brightest novae observed since V382 Vel 1999 (2.5 mag peak) and since the 2008 launch of Fermi (V339 Del 2013 peaked at 4.5 mag; see Munari et al 2015). V5668 Sgr was characterized by systematically longer timescales in its brightening and fading (see Figure 1 for an overview, and Table 1).…”

Evolution of V339 Del (Nova Del 2013) since 0.37 – 75 Days after Discovery

“…1) Initial rise (t = 0 -0.6 days); nova was suddenly brighter from V  11 (at the pre-nova phase) to 6.4 [1]. Maximum v ej measured from Balmer lines ~ 1600 -2200 km/s, from Fe II lines ~ 1000 -1900 km/s and from O I line ~ 2100 -2400 km/s.…”

“…The nova was discovered during its initial rising phase. Optical maximum was on Aug. 16.25 UT when it reached V ∼ 4.3 [1]. The nova became popular among astronomers due to its brightness.…”