The purpose of this paper is to explore a resolution for the Faint Young Sun Paradox that has been mostly rejected by the community, namely the possibility of a somewhat more massive young Sun with a large mass loss rate sustained for two to three billion years. This would make the young Sun bright enough to keep both the terrestrial and Martian oceans from freezing, and thus resolve the paradox. It is found that a large and sustained mass loss is consistent with the well observed spin-down rate of Sun-like stars, and indeed may be required for it. It is concluded that a more massive young Sun must be considered a plausible hypothesis.

Young and massive star clusters above a critical mass form thermally unstable clumps reducing locally the temperature and pressure of the hot 107 K cluster wind. The matter reinserted by stars, and mass loaded in interactions with pristine gas and from evaporating circumstellar disks, accumulate on clumps that are ionized with photons produced by massive stars. We discuss if they may become self-shielded when they reach the central part of the cluster, or even before it, during their free fall to the cluster center. Here we explore the importance of heating efficiency of stellar winds.

A Basic Angle (BA) of 106.5° separates the view directions of Gaia's two fields of view (FoV). A precise determination of the BA variations (BAV) is essential to guarantee a correct reconstruction of the global astrometric sphere, as residual systematic errors would result in, e.g., a bias in the parallaxes of the final Gaia catalog. The Basic Angle Monitoring (BAM) device, which provides a reliable and accurate estimation of BAV, shows that there exists a ~1 mas amplitude, 6-h period BA oscillation. It's essential to verify to what extent this signal is caused by real BAV, or is at least in part an effect of the BAM device itself. Here, we propose an astrometric on-sky approach to re-determine the 6-h periodic BAV. The results of this experiment, which treated a full day (17 Oct 2016) of Gaia astrometric data, recover a value for the 6-h oscillation of 1.856±0.857 mas. This is consistent, within the errors, with the BAM finding for that day.

In a massive binary, the strong shock between the stellar winds may lead to the generation of bright X-ray emission. While this phenomenon was detected decades ago, the detailed study of this emission was only made possible by the current generation of X-ray observatories. Through dedicated monitoring and observations at high resolution, unprecedented information was revealed, putting strong constraints on the amount and structure of stellar mass-loss.

Open clusters (OCs) are important objects for stellar dynamics studies. The short survival timescale of OCs makes them closely related to the formation of Galactic field stars. We motivate to investigate the dynamical evolution of OCs on the aspect of internal effect and the external influence. Firstly, we make use of the known OC catalog to obtain OCs masses, effective radii. Additionally, we estimate OCs kinematics properties by OC members cross-matched with radial velocity and metallicity from SDSSIV/APOGEE2. We then establish the fundamental plane of OCs based on the radial velocity dispersion, the effective radius, and average surface brightness. The deviation of the fundamental plane from the Virial Plane, so called the tilt, and the r.m.s. dispersion of OCs around the average plane are used to indicate the dynamical status of OCs. Parameters of the fitted plane will vary with cluster age and distance.

We analyzed the light curves (LCs) of several radio-quiet and radio-loud quasars belonging to the same parameter space volume in the 4D Eigenvector 1 (4DE1) quasar sequence, using data from the Catalina Real-time Transient Survey (CRTS). We report preliminary results on detected variability pattern, and discuss possible cases of periodic variability.

UCDs are super massive star clusters found largely in dense regions but have also been found around individual galaxies and in smaller groups. Their origin is still under debate but consensus is that they formed either during major galaxy mergers as mergers of super massive star clusters, are simply the high mass end of the globular cluster luminosity function and formed in the same way as globular clusters, or that they formed from the threshing of galaxies and are remnant nuclear star clusters, which themselves may have formed from the mergers of globular star clusters within galaxies. We are attempting to disentangle these competing formation scenarios with a large survey of UCDs in the Coma cluster. Using ACS two-passband imaging from the HST/ACS Coma Cluster Treasury Survey, we are using colors and sizes to identify the UCD cluster members. With a large sample within the core region of the Coma cluster, we will use the population size, properties, and spatial distribution, and comparison with the Coma globular cluster and nuclear star cluster populations to discriminate between the threshing and globular cluster scenarios. In particular, previously we have found a possible correlation of UCD colors with host galaxy and a possible excess of UCDs around a non-central giant galaxy with an unusually large globular cluster population, both suggestive of a globular cluster origin. With a larger sample size, we are investigating whether the color correlation with host persists and whether the UCD population is consistent with, or in excess of, the bright end of the GCLF. We present initial results from the survey.

Gamma Cassiopeiae is an enigmatic Be star with unusually hard, strong X-ray emission compared with normal main-sequence B stars. The origin has been debated for decades between two theories: mass accretion onto a hidden compact companion and a magnetic dynamo driven by the star-Be disk differential rotation. There has been no decisive signature found that supports either theory, such as a pulse in X-ray emission or the presence of large-scale magnetic field. In a ~100 ksec duration observation of the star with the Suzaku X-ray observatory in 2011, we detected six rapid X-ray spectral hardening events called “softness dips”. All the softness dip events show symmetric softness ratio variations, and some of them have flat bottoms apparently due to saturation. The softness dip spectra are best described by either ~40% or ~70% partial covering absorption to kT ~12 keV plasma emission by matter with a neutral hydrogen column density of ~2 − 8 × 1021cm−2, while the spectrum outside of these dips is almost free of absorption. This result suggests that two distinct X-ray emitting spots in the γ Cas system, perhaps on a white dwarf companion with dipole mass accretion, are occulted by blobs in the Be stellar wind, the Be disk, or rotating around the white dwarf companion. The formation of a Be star and white dwarf binary system requires mass transfer between two stars; γ Cas may have experienced such activity in the past.

X-ray and ultraviolet transits of exoplanets allow us to probe the atmospheres of these worlds. High energy transits have been shown to be deeper but also more variable than in the optical. By simulating exoplanet transits using high-energy observations of the Sun, we can test the limits of our ability to accurately measure the properties of these planets in the presence of stellar activity. We use both disk-resolved images of the Solar disk spanning soft X-rays, the ultraviolet, and the optical and also disk-integrated Sun-as-a-star observations of the Lyα irradiance to simulate transits over a wide wavelength range. We find that for stars with activity levels similar to the Sun, the planet-to-star radius ratio can be overestimated by up to 50% if the planet occults an active region at high energies. We also compare our simulations to high energy transits of WASP-12b, HD 189733, 55 Cnc b, and GJ 436b.

We present Spitzer Space Telescope archival mid-infrared (mid-IR) spectroscopy of a sample of eleven planetary nebulae (PNe). The observations, acquired with the Spitzer Infrared Spectrograph (IRS), cover the spectral range 5.2-14.5 μm that includes the H2 0-0 S(2) to S(7) rotational emission lines. This wavelength coverage has allowed us to derive the Boltzmann distribution and calculate the H2 rotational excitation temperature (Tex). The derived excitation temperatures have consistent values ≃ 900 ±70 K for different sources despite their different structural components. We also report the detection of mid-IR ionic lines of [Ar iii], [S iv], and [Ne ii] in most objects, and polycyclic aromatic hydrocarbon (PAH) features in a few cases.

The FP-7 (Framework Programme 7 of the European Union) PERICLES project addresses the life-cycle of large and complex data sets to cater for the evolution of context of data sets and user communities, including groups unanticipated when the data was created. Semantics of data sets are thus also expected to evolve and the project includes elements which could address the reuse of data sets at periods where the data providers and even their institutions are not available any more. This paper presents the PERICLES science case with the example of the SOLAR (SOLAR monitoring observatory) payload on International Space Station-Columbus.

The Calar Alto Secondary Eclipse study was a program dedicated to observe secondary eclipses in the near-IR of two known close-orbiting exoplanets around K-dwarfs: WASP-10b and Qatar-1b. Such observations reveal hints on the orbital configuration of the system and on the thermal emission of the exoplanet, which allows the study of the brightness temperature of its atmosphere. The observations were performed at the Calar Alto Observatory (Spain). We used the OMEGA2000 instrument (Ks band) at the 3.5m telescope. The data was acquired with the telescope strongly defocused. The differential light curve was corrected from systematic effects using the Principal Component Analysis (PCA) technique. The final light curve was fitted using an occultation model to find the eclipse depth and a possible phase shift by performing a MCMC analysis. The observations have revealed a secondary eclipse of WASP-10b with depth of 0.137%, and a depth of 0.196% for Qatar-1b. The observed phase offset from expected mid-eclipse was of −0.0028 for WASP-10b, and of −0.0079 for Qatar-1b. These measured offsets led to a value for |ecosω| of 0.0044 for the WASP-10b system, leading to a derived eccentricity which was too small to be of any significance. For Qatar-1b, we have derived a |ecosω| of 0.0123, however, this last result needs to be confirmed with more data. The estimated Ks-band brightness temperatures are of 1647 K and 1885 K for WASP-10b and Qatar-1b, respectively. We also found an empirical correlation between the (R′HK) activity index of planet hosts and the Ks-band brightness temperature of exoplanets, considering a small number of systems.

Studying the internal dynamics of stellar clusters is conducted primarily through N-Body simulations. One of the major inputs into N-Body simulations is the binary star frequency and mass distribution, which is currently constrained by relations derived from field binary stars. However to truly understand how clustered environments evolve, binary data from within star clusters is needed including masses. Detailed information on binaries masses, primary and secondary, in star clusters has been limited to date. The primary technique currently available has been radial velocity surveys that are limited in depth. Using previous two-band photometry-based studies that may cover different mass ranges produce potentially discrepant interpretations of the observed binary population. We introduce a new binary detection method, Binary INformation from Open Clusters Using SEDs (BINOCS) that covers the wide mass range needed to improve cluster N-body simulation inputs and comparisons. Using newly-observed multi-wavelength photometric catalogs (0.3 - 8 microns) of the key open clusters with a range of ages, we can show that the BINOCS method determines accurate binary component masses for unresolved cluster binaries through comparison to available RV-based studies. Using this method, we present results on the dynamical evolution of binaries from 0.4 - 2.5 solar masses within five prototypical clusters, spaning 30 Myr to 3.5 Gyr, and how the binary populations evolve as a function of mass.

We present a model that solves the abundance discrepancy problem for NGC 6210. The model proposes a high abundance of CNONe elements that lowers the temperature of the central parts of the nebula. The colder gas model reproduces the observed intensity of the strong [N ii] and [O iii] emission lines, and increases the predicted weak recombination lines towards their observed values. We examine how the usual nebular diagnostic line ratios depend on model abundances.

The aim of this paper is to introduce the software and astronomical web-services developed in frame of the Ukraine Virtual Observatory (UkrVO) and VIrtual Roentgen and Gamma Observatory (VIRGO) to the broad astronomical community. We report briefly on such web-services as the public databases “Sky Maps” of X-ray observations by XMM-Newton, the Earth Orbital Parameters for International Earth Rotation System, and the UkrVO Joint Digitized Archive of astroplates. We refer to such software as the “Multi-Column View”, “Variable Stars Calculator”, “FrameSmooth” for variable star’s research and “Collection Light Technology” (CoLiTec) software for search and discovery of new Solar System bodies.

One of the important challenges that Gaia imposes on the Astrometric Catalogs, is a careful study in everything affected by parallax. A particularly important case is the necessary linkage Gaia - HCRF - ICRF2, which require methods of analysis that are accurate enough so that the provided results are at the same precision level as the work data.

Highly accreting quasars are possible cosmological probes, as their Eddington ratio is expected to saturate toward values of order unity. We present preliminary estimates of redshift- independent source luminosities and the Hubble diagram for quasars in the redshift range 0.1 ≲ z ≲ 2.6.

Most cores of very young stellar clusters contain one or more massive stars at various evolutionary stages. Observations of the Orion Nebula Cluster, Trumpler 37, NGC 2362, RCW38, NGC 3603 and many others provide the most comprehensive database to study stellar wind properties of these massive cluster stars in X-rays. In this presentation we review some of these observations and results and discuss them in the context of stellar winds and possible evolutionary implications. We argue that in very young clusters such as RCW38 and M17, shock heated remnants of a natal shell could serve as an alternate explanation to the colliding wind paradigm for the hot plasma components in the X-ray spectra.