A special class of Type Ia supernovae that is not subject to ordinary and additional intragalactic gray absorption and chemical evolution has been identified. Analysis of the Hubble diagrams constructed for these supernovae confirms the accelerated expansion of the Universe irrespective of the chemical evolution and possible gray absorption in galaxies.

Every model for the progenitors of Type Ia supernovae (SNe Ia) requires that binaries pass through an epoch during which a white dwarf (WD) orbits a non-degenerate star. Depending on the mass of the WD, the radius of its companion, and the orbital separation, the WD may lens its companion. The lensing event would be an antitransit, an increase in light from the companion that can rise to the level of a percent or more, during an interval of hours. Antitransits are periodic. By studying them we can determine the properties of both the WD and its companion, as well as the characteristics of the orbit. Lensing events of this type are almost certain to be observed by the Kepler mission, while some can even be detected by ground-based surveys. Antitransits and transits will both provide valuable insight into the end states of common envelope evolution and of stable mass transfer, resolving issues that must be understood before we can fully unravel the progenitor puzzle.

The Spitzer Space Telescope has three science instruments (IRAC, MIPS, and IRS) that can take images at 3.6, 4.5, 5.8, 8.0, 24, 70, and 160 μm, spectra over 5–38 μm, and spectral energy distribution over 52–100 μm. The Spitzer archive contains targeted imaging observations for more than 100 PNe. Spitzer legacy surveys, particularly the GLIMPSE survey of the Galactic plane, contain additional serendipitous imaging observations of PNe. Spitzer imaging and spectroscopic observations of PNe allow us to investigate atomic/molecular line emission and dust continuum from the nebulae as well as circumstellar dust disks around the central stars. Highlights of Spitzer observations of PNe are reviewed in this paper.

The ionizing star of the planetary nebula NGC 2392 is too cool to explain the high excitation of the nebular shell, and an additional ionizing source is necessary. We use photoionization modeling to estimate the temperature and luminosity of the putative companion. Our results show it is likely to be a very hot (Teff ≃ 250 kK), dense white dwarf. If the stars form a close binary, they may merge within a Hubble time, possibly producing a Type Ia supernova.

Missing from the usual considerations of nuclear burning white dwarfs as Type Ia supernovae progenitors are systems with very higher mass transfer rates, where more material than is needed for steady burning accretes on the white dwarf. This will expand the photosphere of the white dwarf, causing it to emit at longer wavelengths. Thus, we propose the name ultra-soft source (USS) for these objects.

We present a VLT/FLAMES survey looking for USSs in the SMC, selected to be bright in the far UV and with blue far UV-V colors. While we find some unusual objects, and recover known planetary nebulae and WR stars, we detect no objects with strong He II lines, which should be a signature of USSs. This null result either puts an upper limit on the number of USSs in the SMC, or shows that we do not understand what the optical spectra of such objects will look like.

We also discuss the unusual LMC [WN] planetary nebula LMC N66 as a possible example of a USS. It has a luminosity consistent with that expected, and its spectra show incompletely CNO-processed material — strong helium lines, some hydrogen, enhanced nitrogen and depleted carbon. It also shows periodic outbursts. USSs may resemble N66 in quiescence. However, it lacks a FUV excess, contrary to our predictions.

The small group of λ Bootis stars comprises late B to early F-type stars, with moderate to extreme (up to a factor 100) surface under-abundances of most Fe-peak elements and solar abundances of lighter elements (C, N, O, and S). The main mechanisms responsible for this phenomenon are atmospheric diffusion, meridional mixing, and accretion of material from their surroundings. Especially spectroscopic binary (SB) systems with λ Bootis-type components are very important to investigate the evolutionary status and accretion process in more details. Because also δ Scuti type pulsation was found for several members, it gives the opportunity to use the tools of astroseismology for further investigations. We present the results of our long term efforts of detailed abundance analysis, orbital parameter estimation and photometric time series analysis for five well investigated SB systems.

I present an overview of the techniques used for detecting and following up binaries in nearby galaxies and present the current census of extragalactic binaries, with a focus on eclipsing systems. The motivation for looking in other galaxies is the use of eclipsing binaries as distance indicators and as probes of the most massive stars.

In close eclipsing binaries, measurements of the variations in the binary's eclipse timing may be used to infer information about the existence of planets in P-Type motion. To study the possibility of detecting such planets with CoRoT and Kepler, we calculated eclipse timing variations (ETV) for different values of the mass and orbital elements of the perturbing planet. These investigations are a continuation of the work of Schwarz et al. (2011).

We report on the ongoing study of the infrared properties of different types of planetary nebulae based on the data from recent photometric and spectroscopic infrared surveys. We present our first results concerning the relation between nebular morphology and infrared properties using the observations from the AKARI mission.

The photospheric emission from the hottest central stars of planetary nebulae (CSPNe) is capable to extend into the X-ray domain, with emission peaking at 0.1-0.2 keV and vanishing above 0.4 keV. Unexpected, intriguing hard X-ray emission with energies greater than 0.5 keV has been reported for several CSPNe and for a number of white dwarfs (WDs). Different mechanisms may be responsible for the hard X-ray emission from CSPNe and WDs: coronal emission from a late-type companion, shocks in fast winds as in OB stars, leakage from underneath the star photosphere, or accretion of material from a disk, a companion star, or the circumstellar medium. Therefore, the hard X-ray emission associated with CSPNe may have significant implications for our understanding of the formation of PNe: binary companions, disks, and magnetic fields are thought to play a major role in the shaping of PNe, whereas clumping in the stellar wind may have notable effects in the PN evolution by modifying the stellar mechanical energy output. Here I present the results of different observational efforts to search for hard X-ray emission from CSPNe and discuss the different mechanisms for the production of hard X-rays.

We are presently using the Chandra X-ray Observatory to conduct the first systematic X-ray survey of planetary nebulae (PNe) in the solar neighborhood. The Chandra Planetary Nebula Survey (ChanPlaNS) is a 570 ks Chandra Cycle 12 Large Program targeting 21 high-excitation PNe within ~1.5 kpc of Earth. When complete, this survey will provide a suite of new X-ray diagnostics that will inform the study of late stellar evolution, binary star astrophysics, and wind interactions. Among the early results of ChanPlaNS (when combined with archival Chandra data) is a surprisingly high detection rate of relatively hard X-ray emission from CSPNe. Specifically, X-ray point sources are clearly detected in roughly half of the ~30 high-excitation PNe observed thus far by Chandra, and all but one of these X-ray-emitting CSPNe display evidence for a hard (few MK) component in their Chandra spectra. Only the central star of the Dumbbell appears to display “pure” hot blackbody emission from a ~200 kK hot white dwarf photosphere in the X-ray band. Potential explanations for the“excess” hard X-ray emission detected from the other CSPNe include late-type companions (heretofore undetected, in most cases) whose coronae have been rejuvenated by recent interactions with the mass-losing WD progenitor, non-LTE effects in hot white dwarf photospheres, self-shocking variable winds from the central star, and slow (re-)accretion of previously ejected red giant envelope mass.

Binary/multiple properties provide clues to the formation of stars. In the AstraLux binary survey, we use the Lucky Imaging technique to search for companions to a large sample of young, nearby M dwarfs. We present results from observations of the first sub-sample, consisting of 124 M dwarfs in the southern sky.

This paper presents the results of the analysis of (O-C) diagrams of four eclipsing variables. The diagrams are based on times of minima collected in the Cracow database, which contains times of minima found in the literature, from observations at Mt. Suhora and Ulupinar Observatories, or determined using publicly-available photometric surveys (NSVS, ASAS etc).

We have found a strong correlation between small filling factors and large t 2 values in planetary nebulae. We have also found that in general the filling factor for Type I PNe is smaller than for Type II PNe. These results imply that the abundance correction due to temperature inhomogeneities in general is larger for Type I PNe than for Type II PNe. This difference permits to reproduce the expected abundance difference between PNe of Type I and II predicted by Galactic chemical evolution models.

V2028 Cyg shows a B[e] phenomenon. Due to the presence of both cool (K7III) and hot (B4III) components in the spectra, it is supposed to be a binary. Our modelling of the time variability of Hα line bisectors shows, however, that this hybrid spectrum can originate in one star, which is surrounded by a disc.

In the 1990s of the last century, CCD cameras became more reachable. Due to many advantages of CCD cameras, astronomers began using them as the primary detector for photometry of stellar objects. A typical observatory, which operates one telescope at a time, obtained 0.5 TB of raw data during two decades, that means one million about 500 kB-sized files. There are several observatories in the Czech Republic and Slovakia (taking into account all scientific, public as well as private ones). A rough estimate of the total amount of this photometric data is 10 TB, which could be a very interesting source of observational data. Unfortunately, these data are not available online. These data are stored in observatory archives in arbitrary format. Often it is not even possible to find requested data. We have decided to change this state by establishing a common archive of raw photometric data, which would be available online together with tools for searching, listing etc. We already defined the data format, file and directory structure of our archive. We developed sophisticated tools for archive maintenance as well. Our goal is to provide data storage with simple and straightforward access and we are ready to interconnect with the VO right after the IVOA Photometry Data Model will be released.

We describe an ongoing project to migrate the emission-line analysis package nebular from its current environment, IRAF, to a modern programming environment where it can be used from command line, a local GUI, or the web. We are also updating the supporting atomic data where they have been superseded by superior calculations or measurements.

The iron depletion factors found in Galactic planetary nebulae (PNe) span over two orders of magnitude, suggesting that there are differences in the grain formation and destruction processes from object to object. We explore here the relation between the iron depletions, the infrared dust features, and the C/O abundance ratios in a sample of Galactic PNe. We find that those objects with C/O<1 show a trend of increasing depletions for higher values of C/O, whereas PNe with C/O>1 break the trend and cover all the range of depletions. Most of the PNe with C/O<1 show silicate features, but several PNe with C-rich features have C/O<1, probably reflecting the uncertainties associated with the derivation of C/O. PAHs are distributed over the entire range of iron depletions and C/O values.

Protoplanetary disks are ubiquitously observed around young solar-mass stars and are considered to be not only natural by-products of stellar evolution but also precursors of planet formation. If a forming star has close companions, the protoplanetary disk may be seriously influenced. It is important to consider this effect because most stars form as multiples. Thus, studies of protoplanetary disks in multiple systems are essential to describe the general processes of star and planet formation.

We present the direct image of an interacting binary protoplanetary system. We obtained an infrared image of a young multiple circumstellar disk system, SR24, with the Subaru 8.2-m Telescope. Both circumprimary and circumsecondary disks are clearly resolved with a 0.1 arcsecond resolution. The binary system exhibits a bridge of infrared emission connecting the two disks and a long spiral arm extending from the circumprimary disk. A spiral arm would suggest that the SR24 system rotates counter-clockwise. The orbital period of the binary is 15,000 yr. Numerical simulations reveal that the bridge corresponds to gas flow and a shock wave caused by the collision of gas rotating around the primary and secondary stars. The simulations also show that fresh material streams along the spiral arm, confirming the theoretical proposal that gas is replenished from a circum-multiple reservoir. These results reveal the mechanism of interacting protoplanetary disks in young multiple systems. Furthermore, our observations provide the first direct image that enables a comparison with theoretical models of mass accretion in binary systems. The observations of this binary system provide a great opportunity to test and refine theoretical models of star and planet formation in binary systems.