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Register a new userTwo New Nova Shells associated with V4362 Sagittarii and DO Aquilae
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A classical nova is an eruption on the surface of a white dwarf in an accreting binary system. The material ejected from the white dwarf surface generally forms an axisymmetric shell. The shaping mechanisms of nova shells are probes of the processes that take place at energy scales between planetary nebulae and supernova remnants. We report on the discovery of nova shells surrounding the post-nova systems V4362 Sagittarii (1994) and more limited observations of DO Aquilae (1925). Distance measurements of 0.5p/m1.4 kpc for V4362 Sgr and 6.7 p/m 3.5 kpc -0.2 for DO Aql are found based on the expansion parallax method. The growth rates are measured to be 0.07``/year for DO Aql and 0.32``/year for V4362 Sgr. A preliminary investigation into the ionisation structure of the nova shell associated with V4362 Sgr is presented. The observed ionisation structure of nova shells depends strongly on their morphology and the orientation of the central component towards the observer. X-ray, IR and UV observations as well as optical integral field unit spectroscopy are required to better understand these interesting objects.
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Near Infrared (NIR) and optical photometry and spectroscopy are presented for the nova V1831 Aquilae, covering the early decline and dust forming phases during the first $sim$90 days after its discovery. The nova is highly reddened due to interstellar extinction. Based solely on the nature of NIR spectrum we are able to classify the nova to be of the Fe II class. The distance and extinction to the nova are estimated to be 6.1 $pm$ 0.5 kpc and $A_{rm v}$ $sim$ 9.02 respectively. Lower limits of the electron density, emission measure and ionized ejecta mass are made from a Case B analysis of the NIR Brackett lines while the neutral gas mass is estimated from the optical [OI] lines. We discuss the cause for a rapid strengthening of the He I 1.0830 $mu$m line during the early stages. V1831 Aql formed a modest amount of dust fairly early ($sim$ 19.2 days after discovery); the dust shell is not seen to be optically thick. Estimates are made of the dust temperature, dust mass and grain size. Dust formation commences around day 19.2 at a condensation temperature of 1461 $pm$ 15 K, suggestive of a carbon composition, following which the temperature is seen to gradually decrease to 950K. The dust mass shows a rapid initial increase which we interpret as being due to an increase in the number of grains, followed by a period of constancy suggesting the absence of grain destruction processes during this latter time. A discussion is made of the evolution of these parameters, including certain peculiarities seen in the grain radius evolution.
The classical nova V5583 Sgr (Nova Sagittarii 2009 No 3) has been observed during the rise phase and shortly after by NASAs STEREO/HI instruments, with later optical spectroscopy obtained with the R-C Spectrograph at CTIO, Chile. The time of peak in the STEREO passband has been constrained to within 4 hours, as a result of the high cadence data obtained by STEREO/HI. The optical spectra show the nova evolving from the permitted to the nebular phases. The neon abundance in the ejecta is [Ne/O] > +1:0, which suggests that V5583 Sgr was most likely a neon nova.
We report the detection of new 12.178, 12.229, 20.347, and 23.121 GHz methanol masers in the massive star-forming region G358.93-0.03, which are flaring on similarly short timescales (days) as the 6.668 GHz methanol masers also associated with this source. The brightest 12.178 GHz channel increased by a factor of over 700 in just 50 d. The masers found in the 12.229 and 20.347 GHz methanol transitions are the first ever reported and this is only the fourth object to exhibit associated 23.121 GHz methanol masers. The 12.178 GHz methanol maser emission appears to have a higher flux density than that of the 6.668 GHz emission, which is unusual. No associated near-infrared flare counterpart was found, suggesting that the energy source of the flare is deeply embedded.
We present a re-analysis of the H$alpha$ and [OIII] flux data from the only comprehensive study of the luminosity evolution of nova shells, undertaken almost two decades ago. We use newly available distances and extinction values, and include additional luminosity data of ancient nova shells. We compare the long-term behaviour with respect to nova speed class and light curve type. We find that, in general, the luminosity as a function of time can be described as consisting of an initial shallow logarithmic decline or constant behaviour, followed by a logarithmic main decline phase, with a possible return to a shallow decline or constancy at very late stages. The luminosity evolution in the first two phases is likely to be dominated by the expansion of the shell and the corresponding changes in volume and density, while for the older nova shells, the interaction with the interstellar medium comes into play. The slope of the main decline is very similar for almost all groups for a given emission line, but it is significantly steeper for [OIII], compared to H$alpha$, which we attribute to the more efficient cooling provided by the forbidden lines. The recurrent novae are among the notable exceptions, along with the plateau light curve type novae and the nova V838 Her. We speculate that this is due to the presence of denser material, possibly in the form of remnants from previous nova eruptions, or of planetary nebulae, As a by-product of our study, we revised the identification of all novae included in our investigation with sources in the Gaia Data Release 2 catalogue.
V341 Ara was recently recognised as one of the closest (d ~ 150 pc) and brightest (V~ 10) nova-like cataclysmic variables. This unique system is surrounded by a bright emission nebula, likely to be the remnant of a recent nova eruption. Embedded within this nebula is a prominent bow-shock, where the systems accretion disc wind runs into its own nova shell. In order to establish its fundamental properties, we present the first comprehensive multi-wavelength study of the system. Long-term photometry reveals quasi-periodic, super-orbital variations with a characteristic time-scale of 10-16 days and typical amplitude of ~1 mag. High-cadence photometry from TESS reveals for the first time both the orbital period and a negative superhump period. The latter is usually interpreted as the signature of a tilted accretion disc. We propose a recently developed disc instability model as a plausible explanation for the photometric behaviour. In our spectroscopic data, we clearly detect anti-phased absorption and emission line components. Their radial velocities suggest a high mass ratio, which in turn implies an unusually low white dwarf mass. We also constrain the wind mass-loss rate of the system from the spatially resolved [O iii] emission produced in the bow-shock; this can be used to test and calibrate accretion disc wind models. We suggest a possible association between V341 Ara and a guest star mentioned in Chinese historical records in AD1240. If this marks the date of the systems nova eruption, V341 Ara would be the oldest recovered nova of its class and an excellent laboratory for testing nova theory.
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