Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userEta Car through the eyes of interferometers
123
0
0.0
(
0
)
Authors
Olivier Chesneau
Ask ChatGPT about the research
No Arabic abstract
The core of the nebula surrounding Eta Carinae has recently been observed with VLT/NACO, VLTI/VINCI, VLTI/MIDI and VLTI/AMBER in order to spatially and spectrally constrain the warm dusty environment and the central object. Narrow-band images at 3.74 and 4.05 micron reveal the structured butterfly-shaped dusty environment close to the central star with an unprecedented spatial resolution of about 60 mas. VINCI has resolved the present-day stellar wind of Eta Carinae on a scale of several stellar radii owing to the spatial resolution of the order of 5 mas (11 AU). The VINCI observations show that the object is elongated with a de-projected axis ratio of approximately 1.5. Moreover the major axis is aligned with that of the large bipolar nebula that was ejected in the 19th century. Fringes have also been obtained in the Mid-IR with MIDI using baselines of 75m. A peak of correlated flux of 100 Jy is detected 0.3 south-east from the photocenter of the nebula at 8.7 micron is detected. This correlated flux is partly attributed to the central object but it is worth noting that at these wavelengths, virtually all the 0.5 x 0.5 central area can generate detectable fringes witnessing the large clumping of the dusty ejecta. These observations provide an upper limit for the SED of the central source from 3.8 to 13.5 micron and constrain some parameters of the stellar wind which can be compared to Hilliers model. Lastly, we present the great potential of the AMBER instrument to study the numerous near-IR emissive lines from the star and its close vicinity. In particular, we discuss its ability to detect and follow the faint companion.
rate research
Read More
The High Energy Stereoscopic System (H.E.S.S.) is an array of five imaging atmospheric Cherenkov telescopes. Since 2003 it has been operating in the configuration of four 12 m telescopes complemented in 2012 by a much bigger 28 m telescope in the centre of the array. It is designed to detect very high energy (VHE) gamma-rays in the range of ~20 GeV to ~50 TeV. Over the past decade it performed extremely successful observations of the Galactic plane, which led to the discovery of about 70 sources amongst which the most numerous classes are pulsar wind nebulae, supernova remnants and binary systems. Recently H.E.S.S. also discovered the VHE emission from the Vela pulsar, which became the second pulsar detected at TeV energies after the Crab pulsar. An overview of the main H.E.S.S. discoveries in our Galaxy and their implications on the understanding of physical processes is discussed in this paper.
The ESA Gaia mission will provide a multi-epoch database for a billion of objects, including variable objects that comprise stars, active galactic nuclei and asteroids. We highlight a few of Gaias properties that will benefit the study of variable objects, and illustrate with two examples the work being done in the preparation of the data processing and object characterization. The first example relates to the analysis of the nearly simultaneous multi-band data of Gaia with the Principal Component Analysis techniques, and the second example concerns the classification of Gaia time series into variability types. The results of the ground-based processing of Gaias variable objects data will be made available to the scientific community through the intermediate and final ESA releases throughout the mission.
Eta Car is one of the most luminous and massive stars in our Galaxy and is the brightest mid-infrared (mid-IR) source in the sky, outside our solar system. Since the late 1990s the central source has dramatically brightened at ultraviolet and optical wavelengths. This might be explained by a decrease in circumstellar dust extinction. We aim to establish the mid-IR flux evolution and further our understanding of the stars ultraviolet and optical brightening. Mid-IR images from $8-20~mu$m were obtained in 2018 with VISIR at the Very Large Telescope. Archival data from 2003 and 2005 are retrieved from the ESO Science Archive Facility and historical records are collected from publications. We present the highest angular resolution mid-IR images of $eta$ Car to date at the corresponding wavelengths ($geq 0.22$). We reconstruct the mid-IR evolution of the spectral energy distribution of the spatially integrated Homunculus nebula from 1968 to 2018 and find no long-term changes. Eta Cars bolometric luminosity has been stable over the past five decades. We do not observe a long-term decrease in the mid-IR flux densities that could be associated with the brightening at ultraviolet and optical wavelengths, but circumstellar dust must be declining in our line-of-sight only. Short-term flux variations within about 25% of the mean levels could be present.
This work describes a full Bayesian analysis of the Nearby Universe as traced by galaxies of the 2M++ survey. The analysis is run in two sequential steps. The first step self-consistently derives the luminosity dependent galaxy biases, the power-spectrum of matter fluctuations and matter density fields within a Gaussian statistic approximation. The second step makes a detailed analysis of the three dimensional Large Scale Structures, assuming a fixed bias model and a fixed cosmology. This second step allows for the reconstruction of both the final density field and the initial conditions at z=1000 assuming a fixed bias model. From these, we derive fields that self-consistently extrapolate the observed large scale structures. We give two examples of these extrapolation and their utility for the detection of structures: the visibility of the Sloan Great Wall, and the detection and characterization of the Local Void using DIVA, a Lagrangian based technique to classify structures.
NASAs New Horizons spacecraft has revealed the complex geology of Pluto and Charon. Plutos encounter hemisphere shows ongoing surface geological activity centered on a vast basin containing a thick layer of volatile ices that appears to be involved in convection and advection, with a crater retention age no greater than $approx$10 Ma. Surrounding terrains show active glacial flow, apparent transport and rotation of large buoyant water-ice crustal blocks, and pitting, likely by sublimation erosion and/or collapse. More enigmatic features include tall mounds with central depressions that are conceivably cryovolcanic, and ridges with complex bladed textures. Pluto also has ancient cratered terrains up to ~4 Ga old that are extensionally fractured and extensively mantled and perhaps eroded by glacial or other processes. Charon does not appear to be currently active, but experienced major extensional tectonism and resurfacing (probably cryovolcanic) nearly 4 billion years ago. Impact crater populations on Pluto and Charon are not consistent with the steepest proposed impactor size-frequency distributions proposed for the Kuiper belt.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
