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Register a new userEarly spectroscopic observations of Nova (V1494) Aquilae 1999 No.2
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Low- and medium resolution spectra of the fast nova, Nova (V1494) Aql 1999 No.2 obtained approximately 6, 7, 19 and 28 days after the maximum brightness are presented and discussed. The spectrum covering the whole optical range at day 6 shows the principal plus diffuse-enhanced spectrum. The presence of strong Fe II multiplets with P-Cyg profiles suggest that V1494 Aql belongs to the ``Fe II class defined by Williams (1992). The medium-resolution profiles (lambda/Delta lambda approx 7000) of the Hgamma and Hdelta lines show well-defined sharp absorption features with the same radial velocities, while the Halpha split into two distinct emission peaks in the last two spectra (Delta t=19 and 28 days). The observed behaviour suggests an expanding equatorial ring with possible small-scale clumpiness in the nova shell. The visual lightcurve is used to deduce M_V by the maximum magnitude versus rate of decline relationship. The resulting parameters are: t_2=6.6+/-0.5 days, t_3=16+/-0.5 days, M_V=-8.8+/-0.2 mag. Adopting this value, a distance d=3.6+/-0.3 kpc is determined.
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Optical and near-infrared spectroscopic observations of the fast nova V1494 Aquilae 1999 #2 covering various phases -- early decline, transition and nebular -- during the first eighteen months of its post-outburst evolution are presented in this paper. During this period, the nova evolved in the P_fe P_fe^o C_o spectral sequence. The transition from an optically thick wind to a polar blob - equatorial ring geometry is seen in the evolution of the spectral line profiles. There is evidence of density and temperature stratification in the ejecta. Physical conditions in the ejecta have been estimated based on our observations.
We present radio light curves and spectra of the classical nova V1723 Aql obtained with the Expanded Very Large Array (EVLA). This is the first paper to showcase results from the EVLA Nova Project, which comprises a team of observers and theorists utilizing the greatly enhanced sensitivity and frequency coverage of EVLA radio observations, along with observations at other wavelengths, to reach a deeper understanding of the energetics, morphology, and temporal characteristics of nova explosions. Our observations of V1723 Aql span 1-37 GHz in frequency, and we report on data from 14-175 days following the time of the nova explosion. The broad frequency coverage and frequent monitoring show that the radio behavior of V1723 Aql does not follow the classic Hubble-flow model of homologous spherically expanding thermal ejecta. The spectra are always at least partially optically thin, and the flux rises on faster timescales than can be reproduced with linear expansion. Therefore, any description of the underlying physical processes must go beyond this simple picture. The unusual spectral properties and light curve evolution might be explained by multiple emitting regions or shocked material. Indeed, X-ray observations from Swift reveal that shocks are likely present.
We report on our Chandra and RXTE observations of the bright old nova, V603 Aql, performed in 2001 April, supplemented by our analysis of archival X-ray data on this object. We find that the RXTE data are contaminated by the Galactic Ridge X-ray emission. After accounting for this effect, we find a high level of aperiodic variability in the RXTE data, at a level consistent with the uncontaminated Chandra data. The Chandra HETG spectrum clearly originates in a multi-temperature plasma. We constrain the possible emission measure distribution of the plasma through a combination of global and local fits. The X-ray luminosity and the spectral shape of V603 Aql resemble those of SS Cyg in transition between quiescence and outburst. The fact that the X-ray flux variability is only weakly energy dependent can be interpreted by supposing that the variability is due to changes in the maximum temperature of the plasma. The plasma density is likely to be high, and the emission region is likely to be compact. Finally, the apparent overabundance of Ne is consistent with V603 Aql being a young system.
INTEGRAL observed the nova V5668 Sgr around the time of its optical maximum on March 21, 2015. Studies at UV wavelengths showed spectral lines of freshly produced Be-7. This could be measurable also in gamma-rays at 478 keV from the decay to Li-7. Novae are also expected to synthesise Na-22 which decays to Ne-22, emitting a 1275 keV photon. About one week before the optical maximum, a strong gamma-ray flash on time-scales of hours is expected from short-lived radioactive nuclei, such as N-13 and F-18. These beta-plus-unstable nuclei should yield emission up to 511 keV, but which has never been observed. The spectrometer SPI aboard INTEGRAL pointed towards V5668 by chance. We use these observations to search for possible gamma-ray emission of decaying Be-7, and to directly measure the synthesised mass during explosive burning. We also aim to constrain possible burst-like emission days to weeks before the optical maximum using the SPI anticoincidence shield (ACS). We extract spectral and temporal information to determine the fluxes of gamma-ray lines at 478 keV, 511 keV, and 1275 keV. A measured flux value directly converts into abundances produced by the nova. The SPI-ACS rates are analysed for burst-like emission using a nova model light-curve. For the obtained nova flash candidate events, we discuss possible origins. No significant excess for the expected gamma-ray lines is found. Our upper limits on the synthesised Be-7 and Na-22 mass depend on the uncertainties of the distance to the nova: The Be-7 mass is constrained to less than $4.8times10^{-9},(d/kpc)^2$, and Na-22 to less than $2.4times10^{-8},(d/kpc)^2$ solar masses. For the Be-7 mass estimate from UV studies, the distance to V5668 Sgr must be larger than 1.2 kpc. During three weeks before the optical maximum, we find 23 burst-like events in the ACS rate, of which six could possibly be associated with V5668 Sgr.
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.
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