Interacting binaries in which a white dwarf accretes material from a companion-cataclysmic variables (CVs) in which the mass donor is a Roche-lobe filling star on or near the main sequence, and symbiotic stars in which the mass donor is a late type giant-are relatively commonplace. They display a wide range of behaviors in the optical, X-rays, and other wavelengths, which still often baffle observers and theorists alike. Here I review the existing body of research on X-ray emissions from these objects for the benefits of both experts and newcomers to the field. I provide introductions to the past and current X-ray observatories, the types of known X-ray emissions from these objects, and the data analysis techniques relevant to this field. I then summarize of our knowledge regarding the X-ray emissions from magnetic CVs, non-magnetic CVs and symbiotic stars, and novae in eruption. I also discuss space density and the X-ray luminosity functions of these binaries and their contribution to the integrated X-ray emission from the Galaxy. I then discuss open questions and future prospects.

https://iopscience.iop.org/article/10.1088/1538-3873/aa6736/pdf

X-Ray Emissions from Accreting White Dwarfs: A Review

Measuring the distances to Galactic planetary nebulae (PNe) has been an intractable problem for many decades. We have now established a robust optical statistical distance indicator, the Hα surface brightness–radius or SHα–r relation, which addresses this problem. We developed thisrelationfromacriticallyevaluatedsampleofprimarycalibratingPNe.Therobustnatureof the method results from our revised calibrating distances with significantly reduced systematic uncertainties, and the recent availability of high-quality data, including updated nebular diameters and integrated Hα fluxes. The SHα–r technique is simple in its application, requiring only an angular size, an integrated Hα flux, and the reddening to the PN. From these quantities, an intrinsic radius is calculated, which when combined with the angular size, yields the distance directly. Furthermore, we have found that optically thick PNe tend to populate the upper bound of the trend, while optically thin PNe fall along the lower boundary in the SHα–r plane. This enables sub-trends to be developed which offer even better precision in the determination of distances, as good as 18 per cent in the case of optically thin, high-excitation PNe. This is significantly better than any previous statistical indicator. We use this technique to create a catalogue of statistical distances for over 1100 Galactic PNe, the largest such compilation in the literature to date. Finally, in an appendix, we investigate both a set of transitional PNe and a range of PN mimics in the SHα–r plane, to demonstrate its use as a diagnostic tool. Interestingly, stellar ejecta around massive stars plot on a tight locus in SHα–r space with the potential to act as a separate distance indicator for these objects.

/pdf/the-ha-surface-brightness-radius-relation-a-robust-53yp6vwski.pdf

The Hα surface brightness–radius relation: a robust statistical distance indicator for planetary nebulae

The total number of true, likely and possible planetary nebulae (PN) now known in the Milky Way is nearly 3000, double the number known a decade ago. The new discoveries are a legacy of the recent availability of wide field, narrowband imaging surveys, primarily in the light of H-alpha. In this paper, we summarise the various PN discovery techniques, and give an overview of the many types of objects which mimic PN and which appear as contaminants in both Galactic and extragalactic samples. Much improved discrimination of classical PN from their mimics is now possible based on the wide variety of high-quality multiwavelength data sets that are now available. We offer improved taxonomic and observational definitions for the PN phenomenon based on evaluation of these better diagnostic capabilities. However, we note that evidence is increasing that the PN phenomenon is heterogeneous, and PN are likely to be formed from multiple evolutionary scenarios. In particular, the relationships between some collimated symbiotic outflows and bipolar PN remain uncertain.

/pdf/planetary-nebulae-observational-properties-mimics-and-1tvd6xlili.pdf

Planetary Nebulae: Observational Properties, Mimics and Diagnostics

Observed mass loss rates and Galactic stellar population distributions are used to estimate the rate of injection of stardust into the ISM. M stars and RLOH/IR Stars produce most of the silicates; most of the carbon and SiC comes from carbon stars. WR stars, novae, and supernovae may eject dust with chemical anomalies. There is little observational evidence for a major stellar source of hydrocarbon grains. The Galactic dust ecology considered by comparing stellar dust injection with depletion by star formation and supernova shocks suggests that dust grains are produced by accretion in molecular clouds at 1 to 5 times the stellar rate.

Sources of Stardust in the Galaxy

Radio astronomy is an active and rapidly expanding field due to advances in computing techniques, with several important new instruments on the horizon This text provides a thorough introduction to radio astronomy and its contribution to our understanding of the universe, bridging the gap between basic introductions and research-level treatments It begins by covering the fundamentals physics of radio techniques, before moving on to single-dish telescopes and aperture synthesis arrays Fully updated and extensively rewritten, the fourth edition places greater emphasis on techniques, with detailed discussion of interferometry in particular, and comprehensive coverage of digital techniques in the appendices The science sections are fully revised, with new author Peter N Wilkinson bringing added expertise to the sections on pulsars, quasars and active galaxies Spanning the entirety of radio astronomy, this is an engaging introduction for students and researchers approaching radio astronomy for the first time

/pdf/an-introduction-to-radio-astronomy-3reqs3vamk.pdf

An Introduction to Radio Astronomy

Les observations VLA, IRAS et CCD de la nova GK Persei sont presentees. La matiere circumstellaire entourant la nova est analysee. L'origine du nuage circumstellaire comme nebuleuse planetaire est etudiee

A Detailed Study of the Remnant of Nova GK Persei and Its Environs

Classical novae are a subset of the cataclysmic variable (CV) class of objects which undergo outbursts with peak luminosities ˜5×l037–5×l038 erg s–1 every 104–105 years. Around 10–5–10–4M⊙ of material is ejected at velocities typically 1,000 km s–1 at outburst. The central system is a semi-detached binary containing a white dwarf and (usually) a late-type, main-sequence companion. The companion fills its Roche lobe, and loses material, via an accretion disk, onto the surface of the white dwarf. Orbital periods are normally found to be in the range 3–10 h with CV orbits generally of low eccentricity (see ref. 1 for a review). As part of a continuing programme of observations of the old nova GK Persei, we examined Infrared Astronomical Satellite (IRAS) images in the region of the nova, and discovered extended emission in the far infrared. These observations are interpreted in terms of an ancient planetary nebula ejected from the central binary system. If this interpretation is correct, then several unique phenomena associated with GK Per may be explained. In addition, GK Per would then provide valuable clues to the evolutionary status of classical novae, and the later stages of planetary nebula formation.

J. A. Roberts

Papers

A Detailed Study of the Remnant of Nova GK Persei and Its Environs

An ancient planetary nebula surrounding the old nova GK Persei

Nova GK Persei – A Miniature Supernova Remnant?