We employed data from the VISTA near-infrared YJKS survey of the Magellanic System to analyse the light curves of Type II Cepheids (T2Cs) in the Large and Small Magellanic Clouds (LMC and SMC, respectively). Using the T2Cs identified by the OGLE IV survey and Gaia mission, we built up a sample of about 330 pulsators belonging to both galaxies. For all these objects we obtained accurate intensity-averaged magnitudes in the YJKS bands by means of a template-fitting technique. We complemented our near-infrared data with optical photometry from the literature to calculate period-luminosity and period-Wesenheit relations for a variety of different bands and colour combinations and separately for the different T2C subclasses (BL Herculis, W Virginis, peculiar W Virginis, RV Tauri). These relations, calibrated with the LMC distance modulus, were tested using T2Cs belonging to Galactic globular clusters. We thus calculated the distances of 22 clusters and compared them with the literature values, mainly based on RR Lyrae stars, finding good agreement within 1 σ and dispersion of the order of 0.3 – 0.5 kpc, depending on the adopted period-luminosity/period-Wesenheit relation.

A significant fraction of the stars near the tip of the AGB phase become regular or semi-regular (Mira-type, SRs) pulsators. However, some of these light curves have shown intriguing secondary minima or sharp dips with much longer periods. Although this phenomenon shows some resemblance with the R CrB variables, the light curve is generally symmetric before and after the dip, whereas in R CrB the luminosity recovers slower after its minimum. More recently, high-resolution ALMA CO observations revealed a spiral structure around some of these stars, which suggests the presence of a stellar or sub-stellar companion. In these cases, the long-term light curve minima could be caused by periodic eclipses of the primary by a spiral circumstellar structure, and the long-period would be related to the orbital period. In this paper we discuss the pros and cons of the various proposed scenarios for the long-term minima of pulsating AGB stars.

Studies of white dwarfs have greatly benefited from time-domain surveys and subsequent follow-up observations. However, with the avalanche of alerts delivered by ZTF and LSST and the limited resources for follow-up, we will need brokers to select intriguing alerts that warrant follow-up in a timely manner. At the University of Arizona and NSF’s OIR Lab, we are developing the Arizona-NOAO Temporal Analysis and Response to Events System, to hunt for the rarest of the rare events in the time-domain. In this work, we provide an overview of the ANTARES system, how we use ZTF as a training set, and the way forwards to LSST.

We developed a method that allows to classify the light curves of eclipsing binaries of the W UMa type (EW) with respect to their intrinsic variability. The algorithm measures several features of light curves, such as the amplitude of the O’Connell effect, the separation and location of maxima brightness as well as depths of the minima in subsequent orbital periods. This method is capable of distinguishing systems with presumed magnetic activity present from these without it, as well as recognizing systems with starspots migration and those with other types of intrinsic variability manifestation. The classification is done in an automatic way without a time consuming, visual inspection of light curves.

Variable stars have a unique part to play in Galactic astronomy. Among the most important of these variables are the Cepheids (types I and II), the RR Lyraes and the Miras (O- and C-rich). The current status of the basic calibration of these stars in their roles as distance, structure and population indicators is outlined and some examples of recent applications of these stars to Galactic and extragalactic problems are reviewed. The expected impact of Gaia on this type of work is discussed and the need for complementary ground based observations, particularly large scale near-infrared photometry, is stressed.

This study inspects the influence of various effects and free parameters of the accretion disc and circumstellar material on the emerging light curve of eclipsing binary systems that have a circumstellar disc, by using the SHELLSPEC code. The results indicate that some of the parameters, namely the temperature and inclination of the disc, spot, jet, stream and shell, significantly affect on the emerging light curve, while some other parameters, namely the exponent of the power-law behavior of the density of the disc, microturbulence, inner and outer radius of the disc, do not noticeably affect on the emerging light curve. An application to the Algol-type eclipsing binary system AV Del and an accretion disc model for the system using the SHELLSPEC code is included.

This study inspects the light and radial-velocity curves of the eclipsing binary AV Del. In comparison with other studies already done, the study shows that the absolute elements, fundamental orbital and physical parameters of the system can be determined using the Wilson-Devinney code. Using these parameters, the configuration of the system is presented. Then, an accretion disc model for the system is introduced by using the shellspec code. The results indicate that AV Del is a semi-detached system in which an optically thick accretion disc is surrounding the primary star. The outer radius of the disc is 8.0 R⊙, corresponding to a distance of 1.1 R⊙ from the surface of the secondary. Also, the temperature of the disc is calculated to be T = 5700 K.

This document presents Java-based software called xSonify that uses a sonification technique (the adaptation of sound to convey information) to promote discovery in astronomical data. The prototype is designed to analyze two-dimensional data, such as time-series data. We demonstrate the utility of the sonification technique with examples applied to X-ray astronomy and solar data. We have identified frequencies in the Chandra X-Ray observations of EX Hya, a cataclysmic variable of the intermediate polar type. In another example we study the impact of a major solar flare, with its associated coronal mass ejection (CME), on the solar wind plasma (in particular the solar wind between the Sun and the Earth), and the Earth's magnetosphere.

We briefly present the history and activities of amateur and professionnal astronomers from the “Association Française des Observateurs d'Etoiles Variables” (AFOEV, the French society of variable star observers).

The spatial distribution of dust around a sample of well-known late-type stars has been studied with the Infrared Spatial Interferometer (ISI) located at Mt. Wilson. Currently operating with a single baseline as a heterodyne interferometer at 11.15 μm, the ISI has obtained visibility curves of these stars. Radiative transfer modeling of the visibility curves has yielded estimates of the inner radii of the dust shells, the optical depth at 11 μm, and the temperature of the dust at the inner radii. For stars in which the dust is resolved, estimates of the stellar diameter and temperature can also be made. Broadly speaking two classes of stars have been found. One class has inner radii of their dust shells very close to the photospheres of the stars themselves (3–5 stellar radii) and at a higher temperature (~ 1200 K) than previously measured. This class includes VY CMa, NML Tau, IRC +10216, and o Ceti. For the latter two the visibility curves change with the luminosity phase of the star and new dust appears to form at still smaller radii during minimum luminosity. The second class of stars has dust shells with substantially larger inner radii and very little dust close to the stars, and includes α Ori, α Sco, α Her, R Leo, and χ Cyg. This indicates sporadic production of dust and no dust formation within the last several decades.