scholarly journals Effects of fast rotation on the wind of Luminous Blue Variables

2010 ◽  
Vol 6 (S272) ◽  
pp. 56-61
Author(s):  
Jose H. Groh
Keyword(s):  
Near Infrared ◽  
Rotational Velocity ◽  
Spectral Lines ◽  
High Resolution Spectroscopy ◽  
Luminous Blue Variables ◽  
Eta Carinae ◽  
Fast Rotation ◽  
Long Baseline ◽  
Infrared Interferometry ◽  
Fast Rotating

AbstractWhile theoretical studies have long suggested a fast-rotating nature of Luminous Blue Variables (LBVs), observational confirmation of fast rotation was not detected until recently. Here I discuss the diagnostics that have allowed us to constrain the rotational velocity of LBVs: broadening of spectral lines and latitude-dependent variations of the wind density structure. While rotational broadening can be directly detected using high-resolution spectroscopy, long-baseline near-infrared interferometry is needed to directly measure the shape of the latitude-dependent photosphere that forms in a fast-rotating star. In addition, complex 2-D radiative transfer models need to be employed if one's goal is to constrain rotational velocities of LBVs. Here I illustrate how the above methods were able to constrain the rotational velocities of the LBVs AG Carinae, HR Carinae, and Eta Carinae.

scholarly journals Event horizon scale emission models for Sagittarius A*

2013 ◽  
Vol 9 (S303) ◽  
pp. 298-302
Author(s):  
J. Dexter
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Event Horizon ◽  
Near Infrared ◽  
Sagittarius A ◽  
Long Baseline ◽  
Black Hole Accretion ◽  
Emission Models ◽  
Infrared Interferometry ◽  
Sgr A

AbstractVery long baseline interferometry observations at millimeter wavelengths have detected source structure in Sgr A* on event horizon scales. Near-infrared interferometry will achieve similar resolution in the next few years. These experiments provide an unprecedented opportunity to explore strong gravity around black holes, but interpreting the data requires physical modeling. I discuss the calculation of images, spectra, and light curves from relativistic MHD simulations of black hole accretion. The models provide an excellent description of current observations, and predict that we may be on the verge of detecting a black hole shadow, which would constitute the first direct evidence for the existence of black holes.

scholarly journals Radio Molecular Line Observations of Late Type Stars

1977 ◽  
Vol 42 ◽  
pp. 495-520 ◽  
Author(s):  
A. Winnberg
Keyword(s):  
Near Infrared ◽  
Spectral Lines ◽  
Late Type ◽  
Circumstellar Envelopes ◽  
Long Baseline ◽  
The Galaxy ◽  
Infrared Wavelengths ◽  
Opening Up ◽  
Excellent Tool ◽  
Geometry And Kinematics

Radio observations of spectral lines from OH, H2O, SiO and CO have put the spot-light on late-type stars and revived the interest in them. Especially they have helped the understanding of the outer envelopes of these stars and of their mass loss. They also have revealed late-type stars that are hidden from observation at optical and near-infrared wavelengths by their dense surrounding shells of gas and dust. The strong maser lines from OH, H2O and SiO have additionally given us an excellent tool in mapping the distribution of late-type variables throughout the Galaxy. On the other hand, the interpretation of the maser amplified lines in terms of a model is difficult. Very-long-baseline interferometry (VLBI) of these lines might be a way of studying the geometry and kinematics of the envelopes but there are a few problems connected with these observations which I will point out in this paper. However, recently “thermal” microwave lines of SiO and CO have been observed from late-type stars. These lines might be easier to interpret regarding physical processes in the outer circumstellar envelopes. As so often when a new field is opening up in astronomy the solutions to several old problems have been found but at the same time many more new problems have been brought up.

scholarly journals Comparison of fringe-tracking algorithms for single-mode near-infrared long-baseline interferometers

2014 ◽  
Vol 569 ◽  
pp. A2 ◽  
Author(s):  
É. Choquet ◽  
J. Menu ◽  
G. Perrin ◽  
F. Cassaing ◽  
S. Lacour ◽  
...  
Keyword(s):  
Near Infrared ◽  
Single Mode ◽  
Long Baseline ◽  
Tracking Algorithms ◽  
Fringe Tracking

NGC 6124: a young open cluster with anomalous- and fast-rotating giant stars

2021 ◽  
Author(s):  
N Holanda ◽  
N Drake ◽  
W J B Corradi ◽  
F A Ferreira ◽  
F Maia ◽  
...  
Keyword(s):  
Isotopic Ratio ◽  
Rotational Velocity ◽  
Open Cluster ◽  
Chemical Species ◽  
Stellar Atmospheres ◽  
Lithium Abundance ◽  
Giant Stars ◽  
Analysis Technique ◽  
Young Open Cluster ◽  
Fast Rotating

Abstract We present the results of a chemical analysis of fast and anomalous rotator giants members of the young open cluster NGC 6124. For this purpose, we carried out abundances of the mixing sensitive species such as Li, C, N, Na and 12C/13C isotopic ratio, as well as other chemical species for a sample of four giants among the seven observed ones. This study is based on standard spectral analysis technique using high-resolution spectroscopic data. We also performed an investigation of the rotational velocity (v sin  i) once this sample exhibit abnormal values – giant stars commonly present rotational velocities of few km s−1. In parallel, we have been performed a membership study, making use of the third data release from ESA Gaia mission. Based on these data, we estimated a distance of d = 630 pc and an age of 178 Myr through isochrone fitting. After that procedure, we matched all the information raised and investigated the evolutionary stages and thermohaline mixing model through of spectroscopic Teff and log  g and mixing tracers, as 12C/13C and Na, of the studied stars. We derived a low mean metallicity of [Fe/H] = −0.13 ±0.05 and a modest enhancement of the elements created by the s-process such as Y, Zr, La, Ce, and Nd, which is in agreement of what has already been reported in the literature for young clusters. The giants analyzed have homogeneous abundances, except for lithium abundance [log  ε(Li)NLTE = 1.08±0.42] and this may be associated to a combination of mechanisms that act increasing or decreasing lithium abundances in stellar atmospheres.

scholarly journals Multi-Wavelength High-Resolution Spectroscopy for Exoplanet Detection: Motivation, Instrumentation and First Results

Geosciences ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 289 ◽  
Author(s):  
Serena Benatti
Keyword(s):  
High Resolution ◽  
Near Infrared ◽  
Giant Planet ◽  
High Resolution Spectroscopy ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
First Results ◽  
Multi Wavelength ◽  
Low Mass ◽  
Rocky Planets

Exoplanet research has shown an incessant growth since the first claim of a hot giant planet around a solar-like star in the mid-1990s. Today, the new facilities are working to spot the first habitable rocky planets around low-mass stars as a forerunner for the detection of the long-awaited Sun-Earth analog system. All the achievements in this field would not have been possible without the constant development of the technology and of new methods to detect more and more challenging planets. After the consolidation of a top-level instrumentation for high-resolution spectroscopy in the visible wavelength range, a huge effort is now dedicated to reaching the same precision and accuracy in the near-infrared. Actually, observations in this range present several advantages in the search for exoplanets around M dwarfs, known to be the most favorable targets to detect possible habitable planets. They are also characterized by intense stellar activity, which hampers planet detection, but its impact on the radial velocity modulation is mitigated in the infrared. Simultaneous observations in the visible and near-infrared ranges appear to be an even more powerful technique since they provide combined and complementary information, also useful for many other exoplanetary science cases.

scholarly journals On the synergy between Ariel and ground-based high-resolution spectroscopy

2022 ◽  
Author(s):  
Gloria Guilluy ◽  
Alessandro Sozzetti ◽  
Paolo Giacobbe ◽  
Aldo S. Bonomo ◽  
Giuseppina Micela
Keyword(s):  
High Resolution ◽  
Near Infrared ◽  
Major Axis ◽  
High Resolution Spectroscopy ◽  
Correlation Technique ◽  
Temperature Structure ◽  
Low Resolution ◽  
Semi Major Axis ◽  
Species Discovery ◽  
Orbital Parameters

AbstractSince the first discovery of an extra-solar planet around a main-sequence star, in 1995, the number of detected exoplanets has increased enormously. Over the past two decades, observational instruments (both onboard and on ground-based facilities) have revealed an astonishing diversity in planetary physical features (i. e. mass and radius), and orbital parameters (e.g. period, semi-major axis, inclination). Exoplanetary atmospheres provide direct clues to understand the origin of these differences through their observable spectral imprints. In the near future, upcoming ground and space-based telescopes will shift the focus of exoplanetary science from an era of “species discovery” to one of “atmospheric characterization”. In this context, the Atmospheric Remote-sensing Infrared Exoplanet Large (Ariel) survey, will play a key role. As it is designed to observe and characterize a large and diverse sample of exoplanets, Ariel will provide constraints on a wide gamut of atmospheric properties allowing us to extract much more information than has been possible so far (e.g. insights into the planetary formation and evolution processes). The low resolution spectra obtained with Ariel will probe layers different from those observed by ground-based high resolution spectroscopy, therefore the synergy between these two techniques offers a unique opportunity to understanding the physics of planetary atmospheres. In this paper, we set the basis for building up a framework to effectively utilise, at near-infrared wavelengths, high-resolution datasets (analyzed via the cross-correlation technique) with spectral retrieval analyses based on Ariel low-resolution spectroscopy. We show preliminary results, using a benchmark object, namely HD 209458 b, addressing the possibility of providing improved constraints on the temperature structure and molecular/atomic abundances.

scholarly journals High-resolution spectroscopy of the hot Am star HR 3383

2020 ◽  
Vol 500 (2) ◽  
pp. 2451-2460
Author(s):  
G M Wahlgren ◽  
K E Nielsen ◽  
D S Leckrone
Keyword(s):  
Hubble Space Telescope ◽  
Theoretical Calculations ◽  
Current Theory ◽  
Element Distribution ◽  
Spectral Lines ◽  
High Resolution Spectroscopy ◽  
Atomic Data ◽  
Stellar Spectrum ◽  
Optical Telescope ◽  
Element Abundances

ABSTRACT We present the spectrum analysis of the hot Am star HR 3383 (A1 Vm). Hubble Space Telescope STIS and Nordic Optical Telescope SOFIN data are modelled with synthetic spectra, and abundances are investigated for 78 elements. Most light elements up through oxygen show deficiencies, compared to solar abundances, followed by the general trend of increasing abundance enhancement with atomic number that levels off at a 30-fold enhancement at the lanthanide group and heavier elements. The derived element distribution is generally consistent with what is observed in other hot Am stars. Abundances for HR 3383 are also similar to what is seen for the cooler HgMn stars, with the exception of the platinum-group elements that generally show dramatic enhancements in the HgMn stars. Current theory and calculations are able to predict most observed abundances and abundance trends through the iron group. The large number of derived element abundances in this study provides a constraint for theoretical calculations attempting to explain the heavy element abundances in chemically peculiar stars. This paper includes a comprehensive description of spectral lines useful for an abundance analysis of late B and A type stars, and comments are provided on the atomic data. New data for hyperfine structure components for three lines in Lu iii and a single line in Lu ii are presented, based on laboratory spectra. In addition to the stellar spectrum, lines from the interstellar medium are noted for several of the strongest Fe ii ultraviolet transitions.

Properties of Magnetic Features from the Analysis of Near-Infrared Spectral Lines

1994 ◽  
Vol 154 ◽  
pp. 393-405
Author(s):  
Sami K. Solanki
Keyword(s):  
Near Infrared ◽  
Velocity Structure ◽  
Spectral Lines ◽  
The Past ◽  
Diagnostic Potential ◽  
Theoretical Predictions ◽  
Infrared Spectral ◽  
Magnetic Features

An overview is given of the structure and the physics of magnetic features in solar plages, as derived from observations of near-infrared lines. First, the diagnostic potential of near-infrared lines is compared with that of lines in the visible and at 12 μm. Then, the results on the magnetic and velocity structure of magnetic features obtained from 1.5 μm lines are described, discussed and compared with results of observations in the visible and with theoretical predictions. Finally, the past and present achievements of near-infrared investigations of Zeeman-split lines are summarized.

Sign in / Sign up

Export Citation Format

Share Document