Search

The Universe, originally homogeneous and isotropic according to the observation of Cosmic Microwave Background, became structured over time. Small matter overdensities, mainly dark matter, have grown through gravitational collapse. This collapse, applied to baryonic matter, triggers the formation of stars, galaxies and ever galaxy clusters. However, the structures formation, especially the massive galaxy clusters formation, is a long process. Intermediate objects, called galaxy protoclusters, precede galaxy clusters. These are the progenitors at high redshift (z) of today’s clusters at z = 0. These objects are relevant astrophysical laboratories for studying cluster evolution scenarios, for understanding the environment impact on the galaxy evolution and possibly providing cosmological constraints.These galaxy protoclusters are large and faint structures, thus difficult to detect. There are several complementary selections to observe and study them. Among these selections, is the Planck high-z candidate catalogue (PHz). This sample of protocluster candidates is based on Planck and Herschel observations showing overdensities of star-forming galaxies associated with strong infrared (IR) and submillimetre flux.One of the most promising candidates from PHz is PLCK G256.8-33.2 (G256). It indeed contains two Herschel sources with a strong IR luminosity of about 10¹³ Solar luminosities, and a high star formation rate of about 10³ Solar masses per year for each source. At the same location there is an overdensity of red Spitzer sources, corresponding to galaxies between z = 1.3 and z = 3. This area containing both Heschel sources and the Spitzer overdensity is called the area of interest (AoI). The purpose of this thesis is therefore to determine whether there is a protocluster of galaxies in this AoI. To answer this question, visible and near-infrared observations taken at the VLT with VIMOS and HAWK-I and taken with IRAC/Spitzer are used.These observations are used to produce a catalogue of multi-wavelength galaxies, made up of flux densities measured in seven photometric bands: V, R, I, J, Ks, ch1 and ch2. With these fluxes it is possible to estimate the photometric redshift of galaxies by applying the SED fitting method. The obtained results show an overdensity on the AoI of galaxies at z = 1.3 and probably at z = 2. The potential galaxy members of the protocluster candidate are then selection among those present in this AoI. A total of 56 galaxies between z = 1 and z 2.5 are selected on the AoI.From a colour analysis it is found that most of the galaxy members are active with a high star formation rate, which is supported by the absence of a red sequence in colour-magnitude diagrams. This result is consistent with the initial PHz selection. Thus, the source G256 shows a significant overdensity of active galaxies in the AoI at z = 1.3. It would therefore appear to be a late maturing galaxy protocluster.However, questions are still open about some of the properties of G256. To go further in the analysis, it would be necessary to obtain the spectra of the 56 selected galaxy members in IR with the VLT, or in the millimetre range with ALMA.The Euclid satellite, which will be launched in 2023, will observe about 15000 deg² of the sky. This survey will be an opportunity to detect new structures such as galaxy protoclusters. Part of this thesis focuses on the detectability of G256-like structures with Euclid. The study shows that if the galaxies will be well detected, it will be necessary to develop a detection algorithm specific to galaxy protoclusters.; L’Univers, à l’origine homogène et isotrope d’après l’observation du Fond Diffus Cosmologique, s’est structuré au fil du temps. De petites surdensités de matière, principalement de la matière noire, se sont développées par effondrement gravitationnel. Cet effondrement, appliqué à la matière baryonique, provoque la formation d’étoiles, de galaxies et même d’amas de galaxies. Cependant, la formation des structures, en particulier celle des amas de galaxies massifs, un est long processus. Des objets intermédiaires, appelés protoamas de galaxies, précèdent les amas de galaxies. Il s’agit des progéniteurs à grand redshift (z) des amas d’aujourd’hui à z = 0. Ces objets sont des laboratoires astrophysiques pertinents pour étudier les scénarios d’évolution des amas, comprendre le rôle de l’environnement dans l’évolution des galaxies et potentiellement donner des contraintes cosmologiques.Ces protoamas sont des structures larges et peu lumineuses, ce qui rend leur détection difficile. Il existe différentes sélections complémentaires afin de les observer et de les étudier. Parmi ces sélections, il y a le Planck high-z candidate catalogue (PHz). Cet échantillon de candidats protoamas est obtenu à partir des observations Planck et Herschel montrant des concentrations de galaxies formant beaucoup d’étoiles associées à un fort flux infrarouge (IR) et submillimétrique.L’un des candidats les plus prometteurs de PHz est PLCK G256.8-33.2 (G256). En effet, il contient deux sources Herschel dont la luminosité IR est d’environ 10¹³ luminosités solaires, et le taux de formation d’étoiles élevé de l’ordre de 10³ masses solaires par an chacune. Au même endroit se trouve une surdensité de sources rouges Spitzer, correspondant à des galaxies situées entre z = 1.3 et z = 3. Cette zone contenant simultanément ces deux sources Herschel et la surdensité Spitzer est appelée zone d’intérêt (AoI). L’objectif de cette thèse est donc de déterminer s’il y a un protoamas de galaxies sur cette AoI. Afin de répondre à cette question des observations en visible et en proche-infrarouge prises au VLT avec VIMOS et HAWK-I et prises avec IRAC/Spitzer sont utilisées.Ces observations permettent de construire un catalogue de galaxies multi-longueur d’onde, constitué de densités surfaciques de flux mesurées dans sept bandes photométriques : V, R, I, J, Ks, ch1 et ch2. Avec ces flux il est possible d’estimer le redshift photométrique des galaxies en appliquant la méthode du SED fitting. Les résultats obtenus montrent une surdensité sur l’AoI de galaxies à z = 1.3 et probablement à z = 2. Les potentielles galaxies membres du candidat protoamas sont alors sélectionnées parmi celles présentes sur cette AoI. Au total 56 galaxies entre z = 1 et z = 2.5 sont retenues sur l’AoI.Avec une analyse en couleur il est établi que la majorité des galaxies membres sont actives avec un fort taux de formation d’étoiles, ce qui est conforté avec l’absence d’une séquence rouge dans les diagrammes couleur-magnitude. Ce résultat est compatible avec la sélection initiale PHz. Ainsi la source G256 montre une surdensité significative sur l’AoI de galaxies actives à z = 1.3. Il est probable qu’il s’agisse d’un protoamas en cours de maturation tardive.Cependant des questions restent en suspens quant à certaines propriétés de G256. Pour aller plus loin dans l’analyse, il serait nécessaire d’obtenir les spectres des 56 galaxies membres en IR avec le VLT, ou dans le millimétrique avec ALMA.Le satellite Euclid, qui sera lancé en 2023, observera environs 15000 deg² du ciel. Ce relevé sera l’occasion de détecter de nouvelles structures comme des protoamas de galaxies. Une partie de cette thèse porte sur la détectabilité des structures similaires à G256 avec Euclid. L’étude montre que si les galaxies seront bien détectées, il sera nécessaire de développer un algorithme de détection propre aux protoamas de galaxies.

We present UBVRcIc photometry of stars, down to the 20th magnitude, in the region of the intermediate-age open cluster NGC 381. The core and the cluster radii are estimated to be 2.99 ± 0.93 and 5.6 ± 0.1 arcmin, respectively. A total of 350 probable cluster member stars are identified by using proper motion from GAIA as the criterion of membership. The mean proper motion of the cluster is ūx = 1.55 ± 0.38 mas yr-1, ūy = -2.19 ± 0.39 mas yr-1. We notice an anomalous reddening as the optical total-to-selective extinction ratio in the direction of the cluster Rcluster = 3.7 ± 0.1. The reddening E(BV) = 0.35 ± 0.04 mag is found in the direction of the cluster NGC 381. The distance to the cluster is 957 ± 93 pc and the cluster has an estimated age of log(Age)=8.50 ± 0.05 years.

We present here I-band time-series photometric studies of a few very low-mass stars (VLMs) and brown dwarfs (BDs) in the young (age of 2-3 Myr) IC348 star-forming region in the Perseus Molecular Cloud. Our main aim is to explore the fast rotating (of time scale of a few hours) BDs and VLMs in the I-band. From our preliminary results, we find significant variability in the young M5 dwarf 2MASS J03443896+3203196 with a rotation period of 16.037 hours.

In recent times, many new exoplanet and eclipsing binary candidates are reported, particularly from the archival data produced by the Kepler space mission destined to detect exoplanets in the Cygnus-Lyra region of the sky. In the framework of Belgo-Indian Network for Astronomy & Astrophysics (BINA) project, we also initiated a long-term programme ”Optical characterization and Radial velocity monitoring with Belgian and Indian Telescopes (ORBIT)” which aims at collecting ground-based photometric and high-resolution spectroscopic observations of exoplanet candidates as well as low-mass eclipsing binary candidates using the Indo-Belgian telescopes. We initially focus our study on a few bright candidates for which high-precision radial velocity and photometry could be possible from the available facilities within the BINA network. Our aim is to determine the physical parameters of these candidate stars in order to derive their true nature. Having a large enough sample of low-mass objects from this survey as well as from those reported in the earlier surveys, we intend to understand the mass-radius relation which is still debated for the low-mass regime of the main-sequence stars.

Using the Optical Gravitational Lensing Experiment catalogue, two contact binaries were studied using data in the V and I bands. The photometric solutions for the V and I bands are presented for two contact binaries OGLE 003835.24-735413.2 (V1) and OGLE 004619.65-725056.2 (V2) in Small Maglellanic Cloud. The presented light curves are analyzed using the Wilson-Devinney code. The results show that the variables are in good thermal and marginal geometrical contact with features like the O’Connell effect in V1. The absolute dimensions are estimated and its dynamical evolution is inferred. They tend to be solar type marginal contact binaries. The 3.6-m Devasthal Optical Telescope and the 4.0-m International Liquid Mirror Telescope of the Aryabhatta Research Institute of Observational Sciences (ARIES, Nainithal) can facilitate the continuous monitoring of such kind of objects which will help in finding the reasons behind their period changes and their impact on the evolution of the clusters.

The similar age of the stars in star cluster system makes them interesting objects for the study of stellar evolution. However, for such studies, it is essential to reduce the field star contamination. Proper motion of the stars in the region of star clusters provides a unique possibility of getting membership information of the stars. The mean absolute proper motion of the globular cluster NGC 4590 is derived as -2.95 ± 0.54 mas yr-1 and 2.03 ± 0.52 mas yr-1 along right ascension (RA) and declination (DEC) respectively using, 111,000 stars having an error less than 7 mas yr-1. We propose a similar study of globular clusters with the CCD imager mounted on the 3.6m Devasthal Optical telescope (DOT).

We have made UBV I CCD observations for the open clusters Teutsch 1, Riddle 4 and Czernik 6 using 1.04-m Sampurnanand telescope located at the ARIES observatory (Manora peak, Nainital, India). We have used 2MASS JHKS data for the clusters Teutsch 126, Teutsch 54 and Czernik 3. For the estimation of fundamental parameters, we have plotted radial density profiles, colour-magnitude and colour-colour diagrams. Using these inputs, we have studied the structure of Milky Way Galaxy in the second Galactic quadrant. We have considered the open clusters that are younger than 1 Gyrs and lay in the longitude range from 90 to 180 deg. Our study shows that up to 3.5 Kpc, the Galactic disc bends towards the southern hemisphere while after 3.5 Kpc it bends towards the northern hemisphere. The distribution of reddening with longitude and age shows a decreasing trend with the longitude and age of the clusters. Our study also indicates that younger clusters have more reddening than older ones.

We discuss three long term observational programmes to probe the central engine and environment of active galactic nuclei (AGN) using the recently installed ARIES 1.3-m and 3.6-m telescopes. The first programme is on the photometric reverberation mapping of low luminosity AGN by mainly using the ARIES 1.3-m telescope. The major impact of this programme other than to estimate the black hole mass will be to extend the broad line region (BLR) radius-luminosity (RBLR-LAGN) relation to the unexplored low luminosity regime, and to constrain the AGN broad line region geometry. The second programme is to use long slit spectroscopy on the ARIES 3.6-m telescope to discover new high redshift quasar pairs with angular separation less than ~ 1-arcmin. Here, the background QSOs sight-line will be used to probe the environment of the foreground QSOs at kpc-Mpc scales. The major impact of this programme will be on the discovery of new pairs which have been missed in the SDSS survey due to fiber collision below 1-arcmin separation, and use them to understand about any excess overdensity around the QSO, any anisotropic emission of QSOs, and/or any episodic activity of QSOs. The third programme is related to spectral variability studies of the C IV broad absorption line (BAL) QSOs, based on low resolution spectroscopy using the ARIES 3.6-m telescope. Here, those most interesting cases will be monitored, where the BAL flow emerges afresh or disappears completely in the C IV trough of BAL QSOs sample as seen in SDSS multi-epoch observations. Continuous monitoring of such a sample will be important for our understanding of the nature and origin of the flow, along with their stability and dynamical evolution.

The Belgo-Indian Network for Astronomy and Astrophysics (BINA) is a collaboration between Indian and Belgian astronomical institutes with the main aim to optimize the scientific output of the Indo-Belgian telescopes, being the 4.0-m International Liquid Mirror Telescope and the 3.6-m Devasthal Optical Telescope. These new facilities are both located at the Devasthal Observatory near Nainital, India. In this contribution, we introduce projects that are of scientific interest for colleagues of the department “Astronomy and Astrophysics” of the Royal Observatory of Belgium (ROB). It serves as an invitation for Indian astronomers to participate. We highlight how these projects could benefit from observations with the Indo-Belgian telescopes by using instruments from the first-generation (currently offered) and/or the next-generation (development or design phase). We show that, from an ROB point-of-view, the BINA would be the most successful if the 3.6-m DOT would be equipped with an efficient optical high-resolution spectrograph.

We have carried out multi-epoch deep I band photometry of the open cluster Stock 18 to search for variable stars in star forming regions. In the present study, we identified 65 periodic and 217 non-periodic variable stars. The periods of most of the periodic variables are between 2 hours to 15 days and their magnitude varies between 0.05 to 0.6 mag. We have derived spectral energy distributions for 48 probable pre-main sequence variables. Their average age and mass are 2.7 ± 0.3 Myrs and 2.7 ± 0.2 Mo, respectively.

The Nainital-Cape Survey is a dedicated search programme initiated in 1999 in the coordination of astronomers from SAAO South Africa, ARIES Nainital and ISRO Bangalore. Over the last 17 years a total of 345 chemically peculiar stars were monitored for photometric variability, making it one of the longest ground-based survey to search for pulsation in chemically peculiar stars in terms of both time span and sample size. Under this survey, we discovered rapid pulsation in the Ap star HD12098 while δ Scuti-type pulsations were detected in seven Am stars. Those stars in which pulsations were not detected have also been tabulated along with their detailed astrophysical parameters for further investigation.

To search for optical variability on a wide range of timescales, we have carried out photometric monitoring of a dozen blazars. CCD magnitudes in B, V, R and I pass-bands were determined for > 10,000f new optical observations from 300 nights made during 2011 – 2016, with an average length of ~ 4 h each, using seven optical telescopes: four in Bulgaria, one in Greece, and two in India. We measured multiband optical flux and colour variations on diverse timescales. Blazar variability studies helped us in understanding their nature and extreme conditions within the emission region. To explain possible physical causes of the observed spectral variability, we also investigated spectral energy distributions using B, V, R, I, J and K pass-band data.

We present optical photometric (upto  410 days since Bmax) and spectroscopic (upto  235 days since Bmax) observations of a type Iax supernova SN 2014dt located in M61. The broad band light curves follow a linear decline upto  100 days after which a significant flattening is seen in the late-time (beyond 150 days) light curves of SN 2014dt. SN 2014dt best matches the light curve evolution of SN 2005hk and reaches a peak magnitude of MB -18.12±0.04 with m15 1.35±0.06 mag. The earliest spectrum at  23 days is dominated by FeII and CoII lines with the absence of the Si II 6150 Å line. Using the peak bolometric luminosity we estimate a 56Ni mass of 0.14 M in the case of SN 2005hk and the striking similarity between SN 2014dt and SN 2005hk implies that a comparable amount of 56Ni would have been synthesized in the explosion of SN 2014dt. There are several explosion scenarios proposed for these peculiar events. Being one of the brightest and closest SN, SN 2014dt is an ideal candidate for long term monitoring. Late phase observations are very essential to understand the progenitor system and the actual explosion scenario for these events.

We present the late-time Hubble Space Telescope observations of two GRB associated supernovae, GRB 030329/SN 2003dh and XRF 060218/SN 2006aj. Using the multi-color data upto  320 days after the burst, we constrain the late-time decay nature of these supernovae. The decay rates of SN 2003dh are steeper than SN 2006aj. A comparison with two other GRB supernovae, GRB 980425/SN 1998bw and the supernova associated with XRF 020903, shows that the decay rates of SN 2003dh are similar to XRF 020903 and those of SN 2006aj are similar to SN 1998bw. The late-time decay rates are steeper than the 56Co56Fe radioactive decay rate (0.0098 mag day-1) indicating that there is some leakage of gamma-rays.

We have carried out time series photometry of the some young open clusters NGC 1893, Be 59, NGC 7380, Stock 8 and NGC 281 to search for pre-main-sequence variable stars. We have detected several pre-main-sequence variables associated to the young open clusters with periods ranging from ~0.1 to ~50 days. These pre-main-sequence variables could be T Tauri stars. The association of these variable stars with the cluster has been established on the basis of two colour diagrams, a colour-magnitude diagram and spectral energy distributions. The brightness of classical T Tauri stars is found to vary with a larger amplitude in comparison to weak line T Tauri stars. It is found that the amplitude of pre-main-sequence variables decreases with increasing mass, which could be due to the dispersal of discs of massive stars. We have also detected several stars as main-sequence variables, which are classified either as slowly pulsating B stars, β Cep stars, δ Scuti stars or members of a new class of variable stars.

In this work we analyzed the Kepler light curve data of HD 73045. The raw data has been smoothened using standard filters. The power spectrum has been obtained by using a fast Fourier transform routine. It shows the presence of more than one period. In order to take care of any non-stationary behavior, we carried out a wavelet analysis to obtain the wavelet power spectrum. In addition, to identify the scale invariant structure, the data has been analyzed using a multifractal detrended fluctuation analysis. Further to characterize the diversity of embedded patterns in the HD 73045 flux time series, we computed various entropy-based complexity measures e.g. sample entropy, spectral entropy and permutation entropy. The presence of periodic structure in the time series was further analyzed using the visibility network and horizontal visibility network model of the time series. The degree distributions in the two network models confirm such structures.

We present the first period study of six contact binaries in the closest globular cluster M4 the data collected from June 1995−June 2009 and Oct 2012−Sept 2013. New times of minima are determined for all the six variables and eclipse timing (O-C) diagrams along with the quadratic fit are presented. For all the variables, the study of (O-C) variations reveals changes in the periods. In addition, the fundamental parameters for four of the contact binaries obtained using the Wilson-Devinney code (v2003) are presented. Planned observations of these binaries using the 3.6-m Devasthal Optical Telescope (DOT) and the 4-m International Liquid Mirror Telescope (ILMT) operated by the Aryabhatta Research Institute of Observational Sciences (ARIES; Nainital) can throw light on their evolutionary status from long term period variation studies.

In the present analysis we have estimated the fundamental parameters of two poorly studied open star clusters, namely Teutsch 61 and Czernik 3, using 2MASS JHKs data. We have used the color-magnitude and colour-colour diagrams to determine their fundamental parameters.

This overview provides a historical perspective highlighting the pioneering role which the fairly modest observational facilities of ARIES have played since the 1990s in systematically characterizing the optical variability on hour-like time scale (intra-night optical variability, or INOV) of several major types of high-luminosity Active Galactic Nuclei (AGN). Such information was previously available only for blazars. Similar studies have since been initiated in at least a dozen countries, giving a boost to AGN variability research.Our work has, in particular, provided strong indication that mild INOV occurs in radio-quiet QSOs (amplitude up to ~ 3 – 5 % and duty cycle ~ 10%) and, moreover, has demonstrated that similarly mild INOV is exhibited even by the vast majority of radio-loud quasars which possess powerful relativistic jets (even including many that are beamed towards us). The solitary outliers are blazars, the tiny strongly polarized subset of powerful AGN, which frequently exhibit a pronounced INOV. Among the blazars, BL Lac objects often show a bluer-when-brighter chromatic behavior, while the flat spectrum radio quasars seem not to. Quantifying any differences of INOV among the major subclasses of non-blazar type AGNs will require dedicated monitoring programs using 2 - 3 metre class telescopes.

We present the results of an analysis of photometric time-series observations for NGC 2126 acquired at the Thai National Observatory (TNO) in Thailand and the Mount Lemmon Optical Astronomy Observatory (LOAO) in USA during the years 2004, 2013 and 2015. The main purpose is to search for new variable stars and to study the light curves of binary systems as well as the oscillation spectra of pulsating stars. NGC 2126 is an intermediate-age open cluster which has a population of stars inside the  Scuti instability strip. Several variable stars are reported including three eclipsing binary stars, one of which is an eclipsing binary star with a pulsating component (V551 Aur). The Wilson-Devinney technique was used to analyze its light curves and to determine a new set of the system’s parameters. A frequency analysis of the eclipse-subtracted light curve was also performed. Eclipsing binaries which are members of open clusters are capable of delivering strong constraints on the cluster’s properties which are in turn useful for a pulsational analysis of their pulsating components. Therefore, high-resolution, high-quality spectra will be needed to derive accurate component radial velocities of the faint eclipsing binaries which are located in the field of NGC 2126. The new Devasthal Optical Telescope, suitably equipped, could in principle do this.

Stripped-Envelope Supernovae constitute the sub-class of core-collapse supernovae that strip off their outer hydrogen envelope due to high stellar winds or due to interaction with a binary companion where mass transfer occurs as a result of Roche lobe overflow. We present here the photometric and spectroscopic analysis of a member of this class : SN 2015as classified as a type IIb supernova. Light curve features are similar to those of SN 2011fu while spectroscopic features are quite similar to those of SN 2008ax and SN 2011dh. Early epoch spectra have been modelled with SYN++ which indicates a photospheric velocity of 8500 km sec-1 and temperature of 6500K. Spectroscopic lines show transitioning from H to He features confirming it to be a type IIb supernova. Prominent oxygen and calcium emission features are indicative of the asymmetry of the ejecta. We also estimate the signal to noise ratio of the 3.6m telescope data. This telescope is located at ARIES, Devasthal, Nainital at an altitude of 2450m. We also show the comparison plots of spectra taken with a 2m and 4m class telescopes to enlighten the importance of spectral features displayed by bigger diameter telescopes.

The HII region/cluster complex has been a subject of numerous investigations to study the feedback effect of massive stars on their surroundings. Massive stars not only alter the morphology of the parental molecular clouds, but also influence star formation, circumstellar disks and the mass function of low-mass stars in their vicinity. However, most of the studies of low-mass stellar content of the HII regions are limited only to the nearby regions. We study the star formation in the W4 HII region using deep optical observations obtained with the archival data from Canada - France - Hawaii Telescope, Two-Micron All Sky Survey, Spitzer, Herschel and Chandra. We investigate the spatial distribution of young stellar objects in the region, their association with the remnant molecular clouds, and search for the clustering to establish the sites of recent star formation. Our analysis suggests that the influence of massive stars on circumstellar disks is significant only to their immediate neighborhood. The spatial correlation of the young stars with the distribution of gas and dust of the complex indicate that the clusters would have formed in a large filamentary cloud. The observing facilities at the 3.6-m Devasthal Optical Telescope (DOT), providing high-resolution spectral and imaging capabilities, will fulfill the major objectives in the study of HII regions.

We have generated a catalog of young stellar objects (YSOs) in the star forming region NGC 7538 using Ha and X-ray data. The spatial distribution of YSOs along with MIR, radio and CO emission are used to study the star formation process in the region. Our analysis shows that the 03V type high mass star 'IRS 6' might have triggered the formation of young low mass stars up to a radial distance of 3 pc.

The type II supernovae (SNe) are hydrogen-rich cosmic explosions resulting from the collapse of massive stars. The impetus of studying individual events arises from its cosmological importance and the diverse understanding of the evolution and explosion mechanism of such events. In this work, we present the preliminary photometric and spectroscopic analysis of a recent type IIP explosion, PNV J01315945+3328458 in the galaxy NGC 582. While the initial phases of these energetic events are bright enough to be observed with the 1-2m class telescopes, the supernovae fade below the detection limit of these telescopes in the nebular phase. In addition, the class of sub-luminous events with Mv  -15 or the events occurring at higher redshift, fade below the detection limit of these telescopes very early in their evolution. Large aperture telescopes like the newly installed 3.6m Devasthal Optical Telescope (DOT) will ensure a longer coverage of such events and also to probe deeper into the Universe. With the 3.6m telescope installed in Devasthal (DOT), we plan to study the progenitor environment of CCSNe to infer the metallicity at the explosion site.

We report on photometric variability studies of a L3.5 brown dwarf 2MASS J00361617+1821104 (2M0036+18) in the field and of four young brown dwarfs in the star-forming region IC 348. From muti-epoch observations, we found significant periodic variability in 2M0036+18 with a period of 2.66 ± 0.55 hours on one occasion while it seemed to be non-variable on three other occasions. An evolving dust cloud might cause such a scenario. Among four young brown dwarfs of IC 348 in the spectral range M7.25 - M8, one brown dwarf 2MASS J03443921+3208138 shows significant variability. The K-band spectra (2.0-2.4 m) of nine very low mass stars (M1 - M9 V) are used to characterize the water band index (H20-K2). We found that it is strongly correlated with the surface temperature of M dwarfs.

We report about the derivation of visible (VIS) and infrared (IR) albedo maps and spectral indicators of Saturn's satellite Tethys from the complete Cassini‐Visual and Infrared Mapping Spectrometer (VIMS) data set. The application of a photometric correction is necessary to remove illumination and viewing effects from the I/F spectra, to compute spectral albedo and to correctly associate spectral variations to changes in composition or physical properties of the surface. In this work we are adopting the photometric correction proposed by Shkuratov et al. (2011, https://doi.org/10.1016/j.pss.2011.06.011) to derive albedo maps of Tethys from disk‐resolved Cassini‐VIMS data. After having applied a similar methodology to Dione's data (Filacchione et al., 2018, https://doi.org/10.1002/2017GL076869), we present here the results achieved for Tethys: surface albedo maps and photometric parameters are computed at five visible (0.35, 0.44, 0.55, 0.70, and 0.95 μm) and five infrared (1.046, 1.540, 1.822, 2.050, and 2.200 μm) wavelengths and rendered in cylindrical projection with a 0.5° × 0.5° angular resolution in latitude and longitude, corresponding to a highest spatial resolution of 4.7 km/bin. The 0.35‐ to 0.55‐ and 0.55‐ to 0.95‐μm spectral slopes and the water ice 2.050‐μm band depth maps are computed after having applied the photometric correction, in order to trace the leading‐trailing hemisphere dichotomy, to constrain the shape of the equatorial lens generated by the bombardment of high‐energy magnetospheric electrons on the leading hemisphere, and to observe the stronger water ice band depth and reddening within the floors of Odysseus and Penelope impact craters.

The rotation period derived by Mueller and Samarasinha (Mueller, B.E.A., Samarasinha, N.H. [2002]. Earth Moon Planets 90, 463–471) of the Deep Space 1 (DS1) mission target, Comet 19P/Borrelly, using ground-based data from July 28 to August 1, 2000, is improved by two orders of magnitude. This precision is reached in a multistep process. Combining all available ground-based data in 2000 decreases the error by an order of magnitude. Next, assuming that the rotation period did not change between 2000 and 2001, constraints from the HST 2001 data (Weaver, H.A., Stern, S.A., Parker, J.Wm. [2003]. Astron. J. 126, 444–451) yield three possible rotation periods: P = 1.088 ± 0.003 days, P = 1.108 ± 0.002 days, and P = 1.135 ± 0.003 days, which are consistent with our initial derivation of P = 1.08 ± 0.04 days (Mueller, B.E.A., Samarasinha, N.H. [2002]. Earth Moon Planets 90, 463–471). These three periods are further refined and the error bars further improved by another order of magnitude by linking the combined ground-based data from 2000 to the nuclear orientation of Borrelly at the DS1 encounter in 2001 (see Table 2 ). Due to aliasing, there are seven possible rotation periods around P = 1.088 days, five possible periods around P = 1.108 days, and six possible periods around P = 1.135 days, with precisions of the order of 0.0002 days (≈17 s).

The thermal emission received from a planet is a key to characterize the physical and chemical properties of its atmosphere. The spectral resolution, and therefore the spectral characterization that we can achieve for extrasolar planets is unfortunately very limited in particular for terrestrial planets. In this thesis, we study the possibility to characterize an Earth-like exoplanet by the analysis of the broadband infrared emission variability. The apparent thermal emission is indeed modulated by the seasons, the rotation of the planet, the motion and variability of atmospheric patterns and clouds, the orbital phase, and even the presence of a moon. As a reference case, we have studied the thermal emission of the Earth seen as a distant point-source, as well as the variability and the dependency of the signal on the observation geometry. We have modeled the emission of the Earth using data derived from observations and data produced by a General Circulation Models (GCMs), comparing both types of data in order to validate our simulations.As a second part of our work, we have used the GCM to model Earth-like planets that differ from the Earth by a few parameters such as different rotation rates (including tidally-locked planets), a planetary surface completely covered by ice or water, different obliquities and eccentricities. For all these virtual planets, we have studied the climate derived from the physical properties and the photometric infrared signal associated with them.The last part of the thesis is a preliminary work that no longer consider the bolometric emission but the signal from narrow spectral bands, thanks to a new generation of GCMs. Because each band probes a specific level in the atmosphere, studying how the low resolution spectrum of the planets varies by comparing the photometric variabilities between bands, we can study the dynamics, composition, distribution and evolution of the atmosphere of the planet, which it opens a yet unexplored field for the characterization of exoplanets.; Le signal thermique d'une exoplanète tellurique est une clé pour caractériser les propriétés physiques et chimiques de son atmosphère. La résolution spectrale, et donc la caractérisation spectrale que nous pouvons réaliser des planètes extrasolaires, est malheureusement très limité, en particulier pour les planètes similaires à la Terre. Dans cette thèse, j'ai étudié la possibilité de caractériser des exoplanètes telluriques par l'analyse de la variabilité de son émission infrarouge. L'émission thermique apparente est en effet modulée par les saisons, la rotation de la planète, le mouvement et la variabilité des nuages, la phase orbitale, et aussi par la présence des satellites naturels.Premièrement, nous avons étudié l' émission thermique de la Terre vue en tant que point-source distante, ainsi que la variabilité et la dépendance du signal de la géométrie d'observation. J'ai modélisé l'émission de la Terre à l'aide des données satellitaires et des données produites par des modèles de circulation général (GCMs) du Laboratoire de Météorologie Dynamique de Paris (LMD), en comparant les deux types de données afin de valider les simulations.Pendant la deuxième partie de mon travail, j'ai utilisé des donnés du GCM pour modéliser des planètes telluriques qui diffèrent de la Terre par seulement un ou deux paramètres tels que: la vitesse de rotation (y compris des planètes synchrones), une surface planétaire entièrement recouverte par la glace ou de l'eau, l'obliquité de l'axe de rotation ou l'excentricité de l'orbite. Pour toutes ces planètes virtuelles, j'ai étudié le climat, déduit les propriétés physiques de la planète, et produit et analysé les signaux intégrés associés à différentes géométries d'observation.La dernière partie de la thèse est un travail préliminaire qui consiste en ne plus considérer l'émission bolométrique mais le signal de bandes spectrales étroites, grâce à une nouvelle génération de GCM. Parce que chaque bande explore un niveau spécifique dans l'atmosphère, l'étude de la variation du spectre en comparant les variabilités photométriques entre les bandes, permet d'étudier la dynamique, la composition, la distribution et l'évolution de l'atmosphère de la planète, ce qui ouvre un champ encore inexploré pour la caractérisation des exoplanètes.

Diese Arbeit beinhaltet drei verbundene Teilbereiche, bei denen es sich um ein techn. Projekt, eine Langzeit-Beobachtungskampagne und eine neuartige Analyse von Archivdaten handelt, welche alle auf die Erforschung der Zentralregion Aktiver Galaktischer Kerne (AGN) ausgerichtet sind. Für das VYSOS 16 Teleskop der Universitätssternwarte der Ruhr-Universität Bochum wird eine Steuerungssoftware entwickelt, die tägliche robotische Beobachtung von AGN ermöglicht. Es wurden Breit- und Schmalband-Lichtkurven für die Galaxien 3C120, ARK120, PG003+199 und ESO374-G25 aufgenommen und daraus je die Entfernung der Emissionsregionen der breiten Balmer Linien zusammen mit der mittleren nukl. Leuchtkraft bestimmt. Die Ergebnisse zeigen, dass diese neuartige Methode zuverlässig anwendbar ist. Schlussendlich wurde das bisher größte Sample von AGN mit H2O Maser Emissionen statistisch untersucht. Der Vergleich von [OIV] zu Röntgenstrahlen zeigt, dass Maser häufiger in Röntgenschwachen Quellen vorkommen. This work contains three interconnected parts, spanning an engineering project, a long term observational campaign and a novel analysis of archival data, all aimed at the research of the central region of active galactic nuclei (AGN). For the VYSOS 16 of the Universitätssternwarte der Ruhr-Universität Bochum, a software has been developed, allowing daily robotic observations of AGN. Broad- and narrow-band lightcurves have been taken of the galaxies 3C120, ARK120, PG003+199, and ESO374-G25, to calculate the average distance of the broad Balmer emission regions and the average nuclear luminosity. The results show that this novel method of photometric reverberation mapping is relieable. Finally, the largest sample of AGN with H20 maser emission has been analyzed statistically. The comparison between [OIV] and X-Rays reveals that Maser are found predominantly in X-Ray absorbed sources.

The Berlin Exoplanet Search Telescope is a small-aperture, wide-field telescope dedicated to time-series photometric observations. During an initial commissioning phase at the Thueringer Landessternwarte Tautenburg, Germany, and subsequent operations at the Observatoire de Haute-Provence, France, a 3.1 {\deg} x 3.1 {\deg} circumpolar field close to the galactic plane centered at ({\alpha}, {\delta}) = (02h 39m 23s, +52{\deg} 01' 46") (J 2000.0) was observed between 2001 August and 2006 December during 52 nights. From the 32129 stars observed, a subsample of 145 stars with clear stellar variability was detected out of which 125 are newly identified variable objects. For five bright objects, the system parameters were derived by modeling the light curve., Comment: 8 pages, 5 figures, 3 tables

En collaboration avec le consortium WASP (Wide Angle Search for Planets) composés d'universités britanniques, une cinquantaine de nouvelles planètes semblables à Jupiter, mais situées sur des orbites de quelques jours seulement, ont été découvertes autour d'étoiles proche et brillantes, dans le ciel de l'hémisphère Sud. La luminosité de l'étoile hôte permet une caractérisation approfondie de ces objets. Le signal lumineux produit lors du passage d'une planète devant son étoile donne la possibilité de déduire une grande quantité de paramètres physiques et orbitaux. Utilisant l'effet Rossiter-McLaughlin, il est possible notamment de déterminer l'angle entre le plan orbital de la planète et le plan équatorial de l'étoile. En découvrant que près de la moitié des planètes découvertes se situent sur des orbites inclinées, voir même rétrograde, il est possible de déduire les processus qui menèrent à la présence de ces géantes gazeuses si proche de leur étoile et de confronter les modèles de migration planétaire par intéractions avec le disque primordial de gaz et de matière dans lequel elles se sont formées.

The CoRoT exoplanet science team announces the discovery of CoRoT-11b, a fairly massive hot-Jupiter transiting a V=12.9 mag F6 dwarf star (M*=1.27 +/- 0.05 Msun, R*=1.37 +/- 0.03 Rsun, Teff=6440 +/- 120 K), with an orbital period of P=2.994329 +/- 0.000011 days and semi-major axis a=0.0436 +/- 0.005 AU. The detection of part of the radial velocity anomaly caused by the Rossiter-McLaughlin effect shows that the transit-like events detected by CoRoT are caused by a planet-sized transiting object in a prograde orbit. The relatively high projected rotational velocity of the star (vsini=40+/-5 km/s) places CoRoT-11 among the most rapidly rotating planet host stars discovered so far. With a planetary mass of mp=2.33+/-0.34 Mjup and radius rp=1.43+/-0.03 Rjup, the resulting mean density of CoRoT-11b (rho=0.99+/-0.15 g/cm^3) can be explained with a model for an inflated hydrogen-planet with a solar composition and a high level of energy dissipation in its interior., Comment: 15 pages, 13 figures, accepted for publication in A&A

We report the discovery of CoRoT-8b, a dense small Saturn-class exoplanet that orbits a K1 dwarf in 6.2 days, and we derive its orbital parameters, mass, and radius. We analyzed two complementary data sets: the photometric transit curve of CoRoT-8b as measured by CoRoT and the radial velocity curve of CoRoT-8 as measured by the HARPS spectrometer. We find that CoRoT-8b is on a circular orbit with a semi-major axis of 0.063 +/- 0.001 AU. It has a radius of 0.57 +/- 0.02 RJ, a mass of 0.22 +/- 0.03 MJ, and therefore a mean density 1.6 +/- 0.1 g/cm^3. With 67 % of the size of Saturn and 72 % of its mass, CoRoT-8b has a density comparable to that of Neptune (1.76 g/cm^3). We estimate its content in heavy elements to be 47-63 Earth masses, and the mass of its hydrogen-helium envelope to be 7-23 Earth masses. At 0.063 AU, the thermal loss of hydrogen of CoRoT-8b should be no more than about 0.1 % over an assumed integrated lifetime of 3~Ga., Comment: 10 pages, 12 figures, accepted for publication in A&A

We present high speed photometry of the Sloan Digital Sky Survey cataclysmic variable SDSS J013701.06-091234.9 in quiescence and during its 2003 December superoutburst. The orbital modulation at 79.71\pm0.01 min is double humped; the superhump period is 81.702\pm0.007 min. Towards the end of the outburst late superhumps with a period of 81.29\pm0.01 min were observed. We argue that this is a system of very low mass transfer rate, and that it probably has a long outburst interval., Comment: 5 pages, 8 figures. Accepted for publication in MNRAS

The thermal emission received from a planet is a key to characterize the physical and chemical properties of its atmosphere. The spectral resolution, and therefore the spectral characterization that we can achieve for extrasolar planets is unfortunately very limited in particular for terrestrial planets. In this thesis, we study the possibility to characterize an Earth-like exoplanet by the analysis of the broadband infrared emission variability. The apparent thermal emission is indeed modulated by the seasons, the rotation of the planet, the motion and variability of atmospheric patterns and clouds, the orbital phase, and even the presence of a moon. As a reference case, we have studied the thermal emission of the Earth seen as a distant point-source, as well as the variability and the dependency of the signal on the observation geometry. We have modeled the emission of the Earth using data derived from observations and data produced by a General Circulation Models (GCMs), comparing both types of data in order to validate our simulations.As a second part of our work, we have used the GCM to model Earth-like planets that differ from the Earth by a few parameters such as different rotation rates (including tidally-locked planets), a planetary surface completely covered by ice or water, different obliquities and eccentricities. For all these virtual planets, we have studied the climate derived from the physical properties and the photometric infrared signal associated with them.The last part of the thesis is a preliminary work that no longer consider the bolometric emission but the signal from narrow spectral bands, thanks to a new generation of GCMs. Because each band probes a specific level in the atmosphere, studying how the low resolution spectrum of the planets varies by comparing the photometric variabilities between bands, we can study the dynamics, composition, distribution and evolution of the atmosphere of the planet, which it opens a yet unexplored field for the characterization of exoplanets.; Le signal thermique d'une exoplanète tellurique est une clé pour caractériser les propriétés physiques et chimiques de son atmosphère. La résolution spectrale, et donc la caractérisation spectrale que nous pouvons réaliser des planètes extrasolaires, est malheureusement très limité, en particulier pour les planètes similaires à la Terre. Dans cette thèse, j'ai étudié la possibilité de caractériser des exoplanètes telluriques par l'analyse de la variabilité de son émission infrarouge. L'émission thermique apparente est en effet modulée par les saisons, la rotation de la planète, le mouvement et la variabilité des nuages, la phase orbitale, et aussi par la présence des satellites naturels.Premièrement, nous avons étudié l' émission thermique de la Terre vue en tant que point-source distante, ainsi que la variabilité et la dépendance du signal de la géométrie d'observation. J'ai modélisé l'émission de la Terre à l'aide des données satellitaires et des données produites par des modèles de circulation général (GCMs) du Laboratoire de Météorologie Dynamique de Paris (LMD), en comparant les deux types de données afin de valider les simulations.Pendant la deuxième partie de mon travail, j'ai utilisé des donnés du GCM pour modéliser des planètes telluriques qui diffèrent de la Terre par seulement un ou deux paramètres tels que: la vitesse de rotation (y compris des planètes synchrones), une surface planétaire entièrement recouverte par la glace ou de l'eau, l'obliquité de l'axe de rotation ou l'excentricité de l'orbite. Pour toutes ces planètes virtuelles, j'ai étudié le climat, déduit les propriétés physiques de la planète, et produit et analysé les signaux intégrés associés à différentes géométries d'observation.La dernière partie de la thèse est un travail préliminaire qui consiste en ne plus considérer l'émission bolométrique mais le signal de bandes spectrales étroites, grâce à une nouvelle génération de GCM. Parce que chaque bande explore un niveau spécifique dans l'atmosphère, l'étude de la variation du spectre en comparant les variabilités photométriques entre les bandes, permet d'étudier la dynamique, la composition, la distribution et l'évolution de l'atmosphère de la planète, ce qui ouvre un champ encore inexploré pour la caractérisation des exoplanètes.