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Register a new userInterferometric studies of novae in the infrared
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Authors
Olivier Chesneau
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The Interferometric studies of novae in the optical and near-infrared is a nascent but fast emerging field which has begun to provide new and invaluable insights into the nova phenomenon. This is particularly so in the early stages of the eruption when all the relevant physical phenomena are on the scale of milli-arcseconds and thus are amenable to be studied only by interferometric techniques. In this review the instruments and arrays involved in this domain of work are briefly described, followed by a description of the major results obtained so far. A discussion is made of the physical aspects, where the application of interferometric techniques, can bring the most valuable information. Finally, prospects for the near future are discussed.
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We review infrared observations of classical and recurrent novae, at wavelengths >3microns, including both broad-band and spectroscopic observations. In recent years infrared spectroscopy in particular has revolutionised our understanding of the nova phenomenon, by revealing fine-structure and coronal lines, and the mineralogy of nova dust. Infrared spectroscopic facilities that are, or will be, becoming available in the next 10 - 20 years have the potential for a comprehensive study of nova line emission and dust mineralogy, and for an unbiassed assessment of the extragalactic nova populations.
Binaries with circumbinary disks are commonly found among optically bright post-AGB stars. Although clearly linked to binary interaction processes, the formation, evolution and fate of these disks are still badly understood. Due to their compactness, interferometric techniques are required to resolve them. Here, we discuss our high-quality multiwavelength interferometric data of two prototypical yet very different post-AGB binaries, AC and 89 Herculis, as well as the modeling thereof with radiative transfer models. A detailed account of the data and models of both objects is published in three separate papers elsewhere; here we focus on comparing the modeling results for the two objects. In particular we discuss the successes and limitations of the models which were developed for protoplanetary disks around young stars. We conclude that multiwavelength high-angular-resolution observations and radiative transfer disk models are indispensible to understand these complex interacting objects and their place in the grand scheme of the (binary) evolution of low and intermediate mass stars.
Photometric and spectroscopic results are presented for the Be star X Per/HD 24534 from near-infrared monitoring in 2010-2011. The star is one of a sample of selected Be/X-ray binaries being monitored by us in the near-IR to study correlations between their X ray and near-IR behaviour. Comparison of the stars present near-IR magnitudes with earlier records shows the star to be currently in a prominently bright state with mean J, H, K magnitudes of 5.49, 5.33 and 5.06 respectively. The JHK spectra are dominated by emission lines of HeI and Paschen and Brackett lines of HI. Lines of OI 1.1287 and 1.3165 micron are also present and their relative strength indicates, since OI 1.1287 is stronger among the two lines, that Lyman beta fluorescence plays an important role in their excitation. Recombination analysis of the HI lines is done which shows that the Paschen and Brackett line strengths deviate considerably from case B predictions. These deviations are attributed to the lines being optically thick and this supposition is verified by calculating the line center optical depths predicted by recombination theory. Similar calculations indicate that the Pfund and Humphrey series lines should also be expected to be optically thick which is found to be consistent with observations reported in other studies. The spectral energy distribution of the star is constructed and shown to have an infrared excess. Based on the magnitude of the IR excess, which is modeled using a free-free contribution from the disc, the electron density in the disc is estimated and shown to be within the range of values expected in Be star discs.
We review the near-infrared properties of classical novae in the J, H and K bands at wavelengths between 1.08 to 2.4 micron. A classification system exists for the early post-outburst optical spectra of novae on the basis of the strength of group of non-hydrogen emission lines. A similar scheme for the near-infrared regime, which is not available at present, is presented here. In the optical system there are two principal classes, namely, Fe II and He/N for novae with either prominent Fe II lines or prominent He/N lines. There is also a small subset of the hybrid Fe IIb type. From spectroscopic observations we show the differences and similarities between these classes of novae in the near-infrared. The spectral lines common to the two principal classes arise from H, He, N and O. However, the near-IR features that separate these two classes are the numerous, and often strong, Carbon lines which are seen only in the spectra of the Fe II class of novae. The dust formation process in novae is discussed based on broad-band observations. The first-overtone carbon monoxide (CO) detections in novae are analyzed to understand the formation and evolution of this molecule in the nova ejecta and to discuss the observed 12C/13C ratio.
Novae, which are the sudden visual brightening triggered by runaway thermonuclear burning on the surface of an accreting white dwarf, are fairly common and bright events. Despite their astronomical significance as nearby laboratories for the study of nuclear burning and accretion phenomena, many aspects of these common stellar explosions are observationally not well-constrained and remain poorly understood. Radio observations, modeling and interpretation can potentially play a crucial role in addressing some of these puzzling issues. In this review on radio studies of novae, we focus on the possibility of testing and improving the nova models with radio observations, and present a current status report on the progress in both the observational front and theoretical developments. We specifically address the issues of accurate estimation of ejecta mass, multi-phase and complex ejection phenomena, and the effect of a dense environment around novae. With highlights of new observational results, we illustrate how radio observations can shed light on some of these long-standing puzzles.
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