In this work we map one of the most populated regions in the main belt - the asteroid family Themis. Computed with a good choice of parameters, the map enables us to get a refined picture of the dynamics in the family, to reexamine the role of resonances therein, to understand better the distribution of asteroids inside the region and to identify dynamical pathways along which particles can drift away.

RR Lyrae stars are powerful tools to study their host populations. Information such as distance, metallicity, reddening, and age can be obtained from their pulsation properties. Dwarf spheroidal (dSph) galaxies are the most common type of galaxy in the Local Group. They are found around massive hosts such as the Milky Way (MW) and M31 and are suggested to be the present-day counterparts to systems from which spheroids and stellar halos of larger galaxies were assembled. By comparing RR Lyraes in these dSphs with their host galaxies, we hope to understand more about the formation of these galaxies. In order to achieve this goal, we have analyzed six fields in M31 using archival imaging from the Hubble Space Telescope. Published data for M31, M33, and several M31 dSphs are also included. The results are then compared with those in the MW to better constrain the early history of these systems.

We propose induction heating of planetary interiors as an energy source in the planetary mantles. Induction heating arises when a changing magnetic field induces currents in a conducting planetary mantle which then dissipate to heat the planet, mostly within an upper layer called the skin depth. This physical process can play a role in planetary interiors around strongly magnetized stars such as low mass M dwarfs with kG magnetic fields, which are common among these stars.

. Hercules X-1 (Her X-1) was observed extensively by the Rossi X-ray Timing Explorer (RXTE) over its 17 year lifetime. Here, the archival RXTE/PCA observations of Her X-1 are analyzed with emphasis on the 35-day cycle dependence. Spectral fits are carried out and the 35-day phase dependences are characterized. The regular behaviours of the changes are interpreted in terms of the precessing accretion disk. We find that the most important variation is caused by the changing illumination of the inner edge of the disk, but other variations with different causes are also seen.

We have analyzed FUSE, COS, GHRS, and Keck/HIRES spectra of the UV-bright star Barnard 29 in M13. Fits to the star’s optical spectrum yield Teff = 20,000 ± 100 K and log g = 3.00 ± 0.01. Using modern stellar-atmosphere models, we are able to reproduce the complex shape of the Balmer H.. feature. We derive photospheric abundances of He, C, N, O, Mg, Al, Si, P, S, Cl, Ar, Ti, Cr, Fe, Ni, and Ge. Barnard 29 exhibits an abundance pattern typical of the first-generation stars in M13, enhanced in oxygen and depleted in aluminum. We see no evidence of significant chemical evolution since the star left the RGB; in particular, it did not undergo third dredge-up. Previous workers found that the star’s FUV spectra yield an iron abundance about 0.5 dex lower than its optical spectrum, but the iron abundances derived from all of our spectra are consistent with one another and with the cluster value. We attribute this difference to our use of model atmospheres without microturbulence. By comparing our best-fit model with the star’s optical magnitudes, we derive a mass M*/M=0.40 − 0.49 and luminosity log L*/L⊙=3.20 − 3.29, depending on the cluster distance. Comparison with stellar-evolution models suggests that Barnard 29 evolved from a ZAHB star of mass M*/M⊙∼0.50, placing it near the boundary between the extreme and blue horizontal branches.

Stone inscriptions from all over India provide records of eclipses, solstices and planetary conjunctions. Extending the study to South Asia, to include Cambodia, Sri Lanka, Nepal and Thailand, threw light on many new aspects such as evolution of calendars independently from the influence of Indian system of time measurement as early as the 3rd Century BCE. Many interesting records of planetary conjunctions are available. One record from Cambodia hints at a possible sighting of the 1054 supernova, while another from Thailand suggests a pre-planetary nebula event.

Theoretical and observational studies of dust condensed in outflows of AGB stars have substantially advanced the understanding of dust mixture from individual stars. This detailed information incorporated in models of the lifecycle of interstellar grains provides a flexible tool to study the contribution of AGB stars to the galactic dust budget. The role of these stars in dust production depends on the morphological type and age of galaxy. While AGB stars are sub-dominant dust sources in evolved systems as the Milky Way, the observed relation between the dust-to-gas ratio and metallicity suggests that the dust input in young dwarf galaxies with 7≲12+log(O/H)≲8 can be dominated by the AGB stars. In application to post-starburst and early-type galaxies, the models for stardust evolution in combination with modern infrared observations give insights in the origin of their high dust content and its implications for their evolutionary scenarios.

Low-mass dwarf irregular galaxies are subject to outflows, in which cosmic rays may play a very important role; they can be traced via their electron component, the cosmic ray electrons (CRe), in the radio continuum as non-thermal synchrotron emission. With the advent of sensitive low-frequency observations, such as with the Low-Frequency Array (LOFAR), we can trace CRe far away from star formation sites. Together with GHz-observations, such as with the Very Large Array (VLA), we can study spatially resolved radio continuum spectra at matched angular resolution and sensitivity. Here, we present results from our 6-GHz VLA survey of 40 nearby dwarf galaxies and our LOFAR study of the nearby starburst dwarf irregular galaxy IC 10. We explore the relation of RC emission with star formation tracers and study in IC 10 the nature of a low-frequency radio halo, which we find to be the result of a galactic wind.

Planets orbiting young, active stars are embedded in an environment that is far from being as calm as the present solar neighbourhood. They experience the extreme environments of their host stars, which cannot have been without consequences for young stellar systems and the evolution of Earth-like planets to habitable worlds. Stellar magnetism and the related stellar activity are crucial drivers of ionization, photodissociation, and chemistry. Stellar winds can compress planetary magnetospheres and even strip away the outer layers of their atmospheres, thus having an enormous impact on the atmospheres and the magnetospheres of surrounding exoplanets. Modelling of stellar magnetic fields and their winds is extremely challenging, both from the observational and the theoretical points of view, and only ground breaking advances in observational instrumentation and a deeper theoretical understanding of magnetohydrodynamic processes in stars enable us to model stellar magnetic fields and their winds – and the resulting influence on the atmospheres of surrounding exoplanets – in more and more detail. We have initiated a national and international research network (NFN): ‘Pathways to Habitability – From Disks to Active Stars, Planets to Life’, to address questions on the formation and habitability of environments in young, active stellar/planetary systems. We discuss the work we are carrying out within this project and focus on how stellar evolutionary aspects in relation to activity, magnetic fields and winds influence the erosion of planetary atmospheres in the habitable zone. We present recent results of our theoretical and observational studies based on Zeeman Doppler Imaging (ZDI), field extrapolation methods, wind simulations, and the modeling of planetary upper atmospheres.

Hot star winds are driven by the radiative force due to light absorption in lines of heavier elements. Therefore, the amount of mass lost by the star per unit of time, i.e., the mass-loss rate, is sensitive to metallicity. We provide mass-loss rate predictions for O stars with mass fraction of heavier elements 0.2 <Z/Z⊙ ≤ 1. Our predictions are based on global model atmospheres. The models allow us to predict wind terminal velocity and the mass-loss rate just from basic global stellar parameters. We provide a formula that fits the mass-loss rate predicted by our models as a function of stellar luminosity and metallicity. On average, the mass-loss rate scales with metallicity as (Z/Z⊙)0.59. The predicted mass-loss rates agree with mass-loss rates derived from ultraviolet wind line profiles. At low metallicity, the rotational mixing affects the wind mass-loss rates. We study the influence of magnetic line blanketing.

Our aim is to present a new and so far most complete catalog of optically selected young stars. The basis of this work is an extensive literature search for young stars in all the known nearby (< 2 kpc) star forming regions, included in the Handbook of Star Forming Regions [4, 5], and in 67 additional catalogs. We collected data on known young, pre-main-sequence stars detected in optical bands. The catalog contains the celestial coordinates, object names, names of the enclosing star forming region, identification methods, distances, and other information (e.g., references, binarity) for 15208 young stellar objects. It is already in use by the Gaia Photometric Science Alerts Team to identify variable young stars in the Gaia data. Our catalog was cross-correlated with the Gaia DR2 and we obtained flux and distance estimations for 86% of the stars.

We present a statistical analysis of the relative orientation between the plane-of-sky magnetic field and the filaments associated with the Galactic Cold Clumps. We separated polarization parameters components of the filaments and their background using thin optical medium assumption, the filaments were detected using the Rolling Hough Transform algorithm and we separated the clump and the filament contributions in our maps. We found that in high column density environments the magnetic fields inside the filaments and in the background are less likely to be aligned with each other. This suggests a decoupling between the inner and background magnetic fields at some stage of filaments’ evolution. A preferential alignment between the filaments and their inferred magnetic fields is observed in the whole selection if the clumps’ contribution is subtracted. Interestingly, a bimodal distribution of relative orientation is observed between the filamentary structures of the clumps and the filaments’ magnetic field. Similar results are seen in a subsample of nearby filaments. The relative orientation clearly shows a transition from parallel to no preferential and perpendicular alignment depending on the volume densities of both clumps and filaments. Our results confirm a strong interplay between the magnetic field and filamentary structures during their formation and evolutionary process.

We present the current status update of the Herschel Planetary Nebula Survey Plus project (HerPlaNS+) based on the original General Observer HerPlaNS survey program during the OT1 cycle and the follow-up exhaustive archival search of PN observations using the PACS and SPIRE instruments on-board the Herschel Space Observatory.

Protoplanetary disks are expected to form through the gravitational collapse of magnetized rotating dense cores. We discuss the structure and emission of models of accretion disks threaded by a poloidal magnetic field and irradiated by the central star, expected to form in this process (Shu et al. 2007; Lizano et al. 2016). The poloidal magnetic field produces sub-keplerian rotation of the gas which can accelerate planet migration (Adams et al. 2009). It can make the disk more stable against gravitational perturbations (Lizano et al. 2010). Also, the magnetic compression can reduce the disk scale height with respect to nonmagnetic disks. We find that the mass-to-flux ratio λ is a critical parameter: disks with a weaker magnetization (high values of λ) are denser and hotter and emit more at millimeter wavelengths than disks with a stronger magnetization (low values of λ). Applying these models to the millimeter observations of the disk around the young star HL Tau indicate the large grains are present at the external radii in order to reproduce the observed 7 mm emission that extends up to 100 AU (Tapia & Lizano 2017). In the near future, observations with ALMA and VLA will be able to determine the level of magnetization of protoplanetary disks, which will be important to understand their formation and evolution.

Radio galaxies of intermediate power dominate the radio-power injection in the Universe as a whole, due to the break in the radio luminosity function, and so are of special interest. The population spans FR I, FR II, and hybrid morphologies, resides in a full range of environmental richness, and sources of all ages are amenable to study. We describe structures and interactions, with emphasis on sources with deep high-resolution Chandra X-ray data. As compared with low-power sources there is evidence that the physics changes, and the work done in driving shocks can exceed that in evacuating cavities. A range of morphologies and phenomena is identified.

The Ultra-Violet Imaging Telescope (UVIT) is one of the payloads in Astrosat, the first Indian Space Observatory. The UVIT instrument has two 375 mm telescopes: one for the far-ultraviolet (FUV) channel (1300-1800 Å), and the other for the near-ultraviolet (NUV) channel (2000-3000 Å) and the visible (VIS) channel (3200-5500 Å). We shall discuss the issues with standardization in the UV with reference to Astrosat Observations (Cycle A04). I shall discuss the problems faced in data-analysis and how these in turn lead to serious issues dealing with the color-magnitude diagarms, membership and age of the young embedded clusters studied.

Discovered periodic sublimation activity on four main-belt primitive asteroids led us to conclusions about possible origin of those and similar bodies (or their parent bodies) near or beyond the snow line in the early Solar System making incorporated in them a considerable water ice stock. Water differentiation of the bodies owing to 26A1 decay and their internal thermal evolution might have created conditions for water soluble organics and prebiotic compounds formation. Subsequent longtime periodic changing temperature and other physico-chemical parameters (due to spinning and moving around the Sun) in the near-surface layers of primitive asteroids have led probably to formation of more complex organic compounds of astrobiological significance.