An energetic stellar outburst accompanied by circumstellar light echoes

Some classes of stars, including supernovae and novae, undergo explosive outbursts that eject stellar material into space. In 2002, the previously unknown variable star V838 Monocerotis brightened suddenly by a factor of about 10^4. Unlike a supernova or nova, V838 Mon did not explosively eject its outer layers; rather, it simply expanded to become a cool supergiant with a moderate-velocity stellar wind. Superluminal light echoes were discovered as light from the outburst propagated into surrounding, pre-existing circumstellar dust. Here we report high-resolution imaging and polarimetry of the light echoes, which allow us to set direct geometric distance limits to the object. At a distance of >6 kpc, V838 Mon at its maximum brightness was temporarily the brightest star in the Milky Way. The presence of the circumstellar dust implies that previous eruptions have occurred, and spectra show it to be a binary system. When combined with the high luminosity and unusual outburst behavior, these characteristics indicate that V838 Mon represents a hitherto unknown type of stellar outburst, for which we have no completely satisfactory physical explanation.Comment: To appear in Nature, March 27, 2003. 9 pages, 6 figure

A Luminous Red Nova in M31 and its Progenitor System

We present observations of M31LRN 2015 (MASTER OT J004207.99+405501.1), discovered in M31 in January 2015, and identified as a rare and enigmatic luminous red nova (LRN). Spectroscopic and photometric observations obtained by the Liverpool Telescope showed the LRN becoming extremely red as it faded from its M(V) = -9.4 +/- 0.2 peak. Early spectra showed strong Halpha emission that weakened over time as a number of absorption features appeared, including Na I D and Ba II. At later times strong TiO absorption bands were also seen. A search of archival Hubble Space Telescope data revealed a luminous red source to be the likely progenitor system, with pre-outburst Halpha emission also detected in ground-based data. The outburst of M31LRN 2015 shows many similarities, both spectroscopically and photometrically, with that of V838 Mon, the best studied LRN. We finally discuss the possible progenitor scenarios

The photometric and spectral investigation of CI Camelopardalis, an X-ray transient and B[e] star

We combined the results of UBVR photometry of CI Cam taken at Sternberg Astronomical Institute in 1998--2001, and moderate resolution spectroscopy taken at Special Astrophysical Observatory during the same time period. Photometry as well as fluxes of Balmer emissions and of some Fe II emission lines of CI Cam in quiet state reveal a cyclic variation with the period of $1100\pm50^d$. The variation like this may be due to an orbital motion in a wide pair with a giant star companion that exhibits the reflection effect on its side faced to a compact companion. The V-band photometry also confirms the pre-outburst 11.7 day period found by Miroshnichenko earlier, but with a lower amplitude of 3 per cent. The possibility of identity of this photometric period with the period of jet's rotation in the VLA radio map of the object CI Cam was investigated. The radio map modelling reveals the inclination of the jet rotation axis to the line of sight, $i = 35-40^o$, the angle between the rotation axis and the direction of ejection of the jet, $\theta = 7-10^o$, and jet's spatial velocity of 0.23--0.26c. Equivalent widths and fluxes of various spectral lines show different amplitudes of changes during the outburst, and essentially distinct behaviour in quiescence. Five types of such behaviour were revealed, that indicates the strong stratification of a gas and dust envelope round the system . The time lag of strengthening of 50--250$^d$ in the forbidden line of nitrogen [N II] was found relatively to the X-ray outburst maximum.Comment: 15 pages, 8 figures, 3 tables, Astron. Zh., 2002, (in press), vol.79, number

Physical properties of IP Pegasi : an eclipsing dwarf nova with an unusually cool white dwarf

We present high-speed photometric observations of the eclipsing dwarf nova IP Pegasi (IP Peg) taken with the triple-beam camera ULTRACAM mounted on the William Herschel Telescope. The primary eclipse in this system was observed twice in 2004, and then a further 16 times over a 3 week period in 2005. Our observations were simultaneous in the Sloan u', g' and r' bands. By phase-folding and averaging our data, we make the first significant detection of the white dwarf ingress in this system and find the phase width phi of the white dwarf eclipse to be 0.0935 +/- 0.0003, significantly higher than the previous best value of 0.0863 < phi < 0.0918. The mass ratio is found to be q = M-2/M-1 = 0.48 +/- 0.01, consistent with previous measurements, but we find the inclination to be 83 degrees.8 +/- 0 degrees.5, significantly higher than previously reported. We find the radius of the white dwarf to be 0.0063 +/- 0.0003 R-circle dot, implying a white dwarf mass of 1.16 +/- 0.02 M-circle dot. The donor mass is 0.55 +/- 0.02 M-circle dot. The white dwarf temperature is more difficult to determine, since the white dwarf is seen to vary significantly in flux, even between consecutive eclipses. This is seen particularly in the u' band, and is probably the result of absorption by disc material. Our best estimate of the temperature is 10 000-15 000 K, which is much lower than would be expected for a cataclysmic variable star with this period, and implies a mean accretion rate of < 5 x 10(-11) M(circle dot)yr(-1), more than 40 times lower than the expected rate