scholarly journals On producers of cosmic organic compounds: exploring the boron abundance in lithium-rich K giant stars

2017 ◽  
Vol 13 (S332) ◽  
pp. 237-241 ◽  
Author(s):  
N. A. Drake ◽  
R. de la Reza ◽  
V. V. Smith ◽  
K. Cunha
Keyword(s):  
Organic Compounds ◽  
Organic Material ◽  
Emission Lines ◽  
Low Mass Stars ◽  
Strong Emission ◽  
Giant Stars ◽  
First Approximation ◽  
Low Mass ◽  
Stellar Interiors ◽  
First Time

AbstractThe element boron belongs, together with lithium and beryllium, to a known trio of important elements for the study of evolutionary processes in low mass stars. Because B is the least fragile of this trio to be destroyed in the stellar interiors, it can be used to test if the Li enrichment is of planetary origin. Here, for the first time, boron lines are examined in the UV for four giants with different degrees of large Li enrichment by means of observations with the Hubble telescope. Two main results are found in our study. One is that to first approximation B abundances appear not to be in excess, invalidating the planet engulfment mechanism. The second one is that the two stars with very large Li abundances present emission lines indicating that quite strong active chromospheres are acting in these very Li-rich giants. These new results obtained from the UV complement our recent studies in the mid-IR (de la Rezaet al.2015) where strong emission-line features of organic material were found in the spectra of some Li-rich stars.

scholarly journals [WN] central stars of planetary nebulae

2016 ◽  
Vol 12 (S323) ◽  
pp. 174-178
Author(s):  
H. Todt ◽  
B. Miszalski ◽  
J. A. Toalá ◽  
M. A. Guerrero
Keyword(s):  
Surface Composition ◽  
Planetary Nebulae ◽  
Emission Lines ◽  
Evolutionary Status ◽  
Low Mass Stars ◽  
Strong Emission ◽  
The Status ◽  
New Type ◽  
Low Mass ◽  
Central Stars

AbstractWhile most of the low-mass stars stay hydrogen-rich on their surface throughout their evolution, a considerable fraction of white dwarfs as well as central stars of planetary nebulae have a hydrogen-deficient surface composition. The majority of these H-deficient central stars exhibit spectra very similar to massive Wolf-Rayet stars of the carbon sequence, i.e. with broad emission lines of carbon, helium, and oxygen. In analogy to the massive Wolf-Rayet stars, they are classified as [WC] stars. Their formation, which is relatively well understood, is thought to be the result of a (very) late thermal pulse of the helium burning shell. It is therefore surprising that some H-deficient central stars which have been found recently, e.g. IC 4663 and Abell 48, exhibit spectra that resemble those of the massive Wolf-Rayet stars of the nitrogen sequence, i.e. with strong emission lines of nitrogen instead of carbon. This new type of central stars is therefore labelled [WN]. We present spectral analyses of these objects and discuss the status of further candidates as well as the evolutionary status and origin of the [WN] stars.

scholarly journals Isochrones for late-type stars

2008 ◽  
Vol 4 (S258) ◽  
pp. 383-394 ◽  
Author(s):  
Pierre Demarque
Keyword(s):  
Three Dimensional ◽  
Radiation Hydrodynamics ◽  
Late Type ◽  
Chemical Abundances ◽  
Low Mass Stars ◽  
Structure And Dynamics ◽  
History Of ◽  
Low Mass ◽  
The Subject ◽  
Stellar Interiors

AbstractA brief summary of the history of stellar evolution theory and the use of isochrones is given. The present state of the subject is summarized. The major uncertainties in isochrone construction are considered: chemical abundances and color calibrations, and the treatment of turbulent convection in stellar interior and atmosphere models. The treatment of convection affects the modeling of stellar interiors principally in two ways: convective core overshoot which increases evolutionary lifetimes, and the depth of convection zones which determines theoretical radii. Turbulence also modifies atmospheric structure and dynamics, and the derivation of stellar abundances. The symbiosis of seismic techniques with increasingly more realistic three-dimensional radiation hydrodynamics simulations is transforming the study of late-type stars. The important case of very low mass stars, which are fully convective, is briefly visited.

scholarly journals Measurements of the Ca ii infrared triplet emission lines of pre-main-sequence stars

2020 ◽  
Vol 72 (5) ◽  
Author(s):  
Mai Yamashita ◽  
Yoichi Itoh ◽  
Yuhei Takagi
Keyword(s):  
Main Sequence ◽  
Open Clusters ◽  
Emission Lines ◽  
Main Sequence Stars ◽  
Low Mass Stars ◽  
Chromospheric Activity ◽  
Low Mass ◽  
Pms Stars ◽  
Infrared Triplet ◽  
Narrow Emission

Abstract We investigated the chromospheric activity of 60 pre-main-sequence (PMS) stars in four molecular clouds and five moving groups. It is considered that strong chromospheric activity is driven by the dynamo processes generated by stellar rotation. In contrast, several researchers have pointed out that the chromospheres of PMS stars are activated by mass accretion from their protoplanetary disks. In this study, the Ca ii infrared triplet (IRT) emission lines were investigated utilizing medium- and high-resolution spectroscopy. The observations were conducted with Nayuta/MALLS and Subaru/HDS. Additionally, archive data obtained by Keck/HIRES, VLT/UVES, and VLT/X-Shooter were used. The small ratios of the equivalent widths indicate that Ca ii IRT emission lines arise primarily in dense chromospheric regions. Seven PMS stars show broad emission lines. Among them, four PMS stars have more than one order of magnitude brighter emission line fluxes compared to the low-mass stars in young open clusters. The four PMS stars have a high mass accretion rate, which indicates that the broad and strong emission results from a large mass accretion. However, most PMS stars exhibit narrow emission lines. No significant correlation was found between the accretion rate and flux of the emission line. The ratios of the surface flux of the Ca ii IRT lines to the stellar bolometric luminosity, $R^{\prime }_{\rm IRT}$, of the PMS stars with narrow emission lines are as large as the largest $R^{\prime }_{\rm IRT}$ of the low-mass stars in the young open clusters. This result indicates that most PMS stars, even in the classical T Tauri star stage, have chromospheric activity similar to zero-age main-sequence stars.

scholarly journals Correlation between mass segregation and structural concentration in relaxed stellar clusters

2019 ◽  
Vol 485 (4) ◽  
pp. 5752-5760 ◽  
Author(s):  
Ruggero de Vita ◽  
Michele Trenti ◽  
Morgan MacLeod
Keyword(s):  
Globular Clusters ◽  
Initial Conditions ◽  
Hubble Space Telescope ◽  
Stellar Clusters ◽  
Low Mass Stars ◽  
Best Fitting ◽  
Low Mass ◽  
The Difference ◽  
Mass Segregation ◽  
First Time

Abstract The level of mass segregation in the core of globular clusters has been previously proposed as a potential indicator of the dynamical constituents of the system, such as presence of a significant population of stellar-mass black holes (BHs), or even a central intermediate-mass black hole (IMBH). However, its measurement is limited to clusters with high-quality Hubble Space Telescope data. Thanks to a set of state-of-the-art direct N-body simulations with up to 200k particles inclusive of stellar evolution, primordial binaries, and varying BH/neutron stars, we highlight for the first time the existence of a clear and tight linear relation between the degree of mass segregation and the cluster structural concentration index. The latter is defined as the ratio of the radii containing 5 per cent and 50 per cent of the integrated light (R5/R50), making it robustly measurable without the need to individually resolve low-mass stars. Our simulations indicate that given R5/R50, the mass segregation Δm (defined as the difference in main-sequence median mass between centre and half-light radius) is expressed as Δm/M⊙ = −1.166R5/R50 + 0.3246, with a root-mean-square error of 0.0148. In addition, we can explain its physical origin and the values of the fitted parameters through basic analytical modelling. Such correlation is remarkably robust against a variety of initial conditions (including presence of primordial binaries and IMBHs) and cluster ages, with a slight dependence in best-fitting parameters on the prescriptions used to measure the quantities involved. Therefore, this study highlights the potential to develop a new observational tool to gain insight on the dynamical status of globular clusters and on its dark remnants.

scholarly journals Characterizing distant blue galaxies with HST images and Keck spectra

1996 ◽  
Vol 171 ◽  
pp. 229-232
Author(s):  
Garth D. Illingworth
Keyword(s):  
Emission Lines ◽  
Length Scales ◽  
Strong Emission ◽  
Blue Galaxies ◽  
Low Mass ◽  
Emission Line Galaxies ◽  
Galaxy Population ◽  
Measured Length ◽  
Field Galaxy ◽  
Narrow Emission

Keck spectra and HST images have been used to derive characteristic velocity and length scales for an enigmatic component of the faint, blue, field galaxy population: the compact, narrow emission-line galaxies (CNELGs). These galaxies are very luminous, but have been found to be quite low mass systems (with typical masses ∼ 109 M⊙). Their blue colors and strong emission lines indicate that they are undergoing a major burst of star formation. Following the completion of their current burst they will fade, becoming, in the absence of further major bursts, objects very similar to contemporary spheroidal galaxies. With mean sizes Re ∼ 1.4 kpc and Gaussian velocity profiles with mean σ = 45 km s–1, the length scales and velocity widths of CNELGs are also quite consistent with the measured length scales and velocity widths of current spheroidals.

The First Proto-Brown Dwarf Binary Candidate Identified through Dynamics of Jets

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Tien-Hao Hsieh ◽  
Shih-Ping Lai ◽  
Arnaud Belloche ◽  
Friedrich Wyrowski
Keyword(s):  
Binary System ◽  
Orbital Motion ◽  
Brown Dwarf ◽  
Low Mass Stars ◽  
Core Mass ◽  
Substellar Objects ◽  
Current Mass ◽  
Low Mass ◽  
Dynamical Features ◽  
First Time

AbstractThe formation mechanism of brown dwarfs (BDs) is one of the long-standing problems in star formation because the typical Jeans mass in molecular clouds is too large to form these substellar objects. To answer this question, it is crucial to study a BD at the embedded phase (proto-brown dwarf). IRAS16253 is classified as a Very Low Luminosity Object (VeLLO, Lint < 0.1L⊙), which is considered as a proto-brown dwarf candidate. We use the IRAM 30m, APEX telescopes and the SMA to probe the molecular jet/outflow driven by IRAS 16253 in CO (2–1), (6–5), and (7–6) and study its dynamical features and physical properties. We detect a wiggling pattern in the position-velocity diagrams of the jets. Assuming that this pattern is due to the orbital motion of a binary system, we obtain the current mass of the binary is ~0.026 M⊙. Together with the low parent core mass, IRAS16253 will likely form one or two proto-BD in the future. This is the first time that the current mass of a proto-BD binary system is identified through the dynamics of the jets. Since IRAS16253 is located in an isolated environment, we suggest that BDs can form through fragmentation and collapse like low mass stars.

scholarly journals Nature of Emission-Line Stars in the Outer Orion Region

1995 ◽  
Vol 148 ◽  
pp. 376-379
Author(s):  
Makoto Nakano ◽  
Peter J. McGregor
Keyword(s):  
Emission Line ◽  
Large Scale ◽  
Near Infrared ◽  
Infrared Photometry ◽  
Low Mass Stars ◽  
Strong Emission ◽  
Star Catalog ◽  
T Tauri ◽  
Low Mass ◽  
Cloud Complex

AbstractNear-infrared photometry is reported for 76 emission-line stars in outer regions of the Orion molecular cloud complex. Most of our program stars are selected from the Hα emission-line star catalog of the large-scale Kiso Schmidt survey of the Orion region. We confirm that most of the emission-line stars with strong emission detected in the Kiso survey are typical T Tauri stars with masses in the range 0.5 to 2 M⊙. Low mass stars have therefore continued to form in the outer parts of the Orion region, away from present day massive molecular clouds, until at least as recently as a few million year ago.

scholarly journals Relationships of the Active Nucleus, Galaxy, and Environment

1989 ◽  
Vol 134 ◽  
pp. 425-444
Author(s):  
K. J. Fricke ◽  
W. Kollatschny
Keyword(s):  
Radio Source ◽  
Intergalactic Medium ◽  
Emission Lines ◽  
Host Galaxies ◽  
Active Nucleus ◽  
Strong Emission ◽  
Nuclear Activity ◽  
Isolated Galaxies ◽  
First Time

35 years ago Baade and Minkowski (1954) suggested that a galaxy collision - diagnosed from the peculiar appearance of the parent object and its strong emission lines - is responsible for the strong radio-source CygA. This was the first time that gravitational interactions between galaxies were suggested to trigger nuclear activity. Over the following decades after the detection of the quasars and the gradual realization that quasars, comparable to the Seyfert phenomenon, are events at the nuclei of seemingly isolated galaxies, the collision hypothesis was abandoned. Efforts concentrated on the understanding of the activity as internal processes in the host galaxies, possibly aided by infall of gas from the intergalactic medium (cf. Rees, 1978; Gunn, 1979).

scholarly journals A Deep UV-Blue Planetary Nebula Template Spectrum from NGC 7027

2003 ◽  
Vol 209 ◽  
pp. 337-338
Author(s):  
J. R. Walsh ◽  
D. Péquignot ◽  
C. Morisset ◽  
P. J. Storey ◽  
B. Sharpee ◽  
...  
Keyword(s):  
Neutron Capture ◽  
Planetary Nebula ◽  
Surface Brightness ◽  
High Surface ◽  
Emission Lines ◽  
Low Mass Stars ◽  
Ngc 7027 ◽  
Low Mass ◽  
Vast Range

NGC 7027 is justifiably THE template spectrum for PNe. Its vast range of emission species – from molecular and neutral to ions with ionization potential > 120eV – its high surface brightness and accessibiliy for northern observatories make it the PN laboratory of choice. However the quality of the spectra from the UV to the IR is mixed, many line fluxes and identifications still remaining unchecked from photographic or image tube spectra. Very deep spectra of NGC 7027 (emission line strengths <10-4 of Hβ) in the 0.65 to 1.05μm region (Baluteau et al. 1995) showed the presence of many faint emission lines. Pequignot & Baluteau (1994) showed that heavy elements from the 4th, 5th and 6th rows of the Periodic Table have much higher abundances than Solar, confirming the synthesis of neutron capture elements in low mass stars and providing new constraints on stellar evolution theory.

scholarly journals The K2-HERMES Survey: age and metallicity of the thick disc

2019 ◽  
Vol 490 (4) ◽  
pp. 5335-5352 ◽  
Author(s):  
Sanjib Sharma ◽  
Dennis Stello ◽  
Joss Bland-Hawthorn ◽  
Michael R Hayden ◽  
Joel C Zinn ◽  
...  
Keyword(s):  
Selection Function ◽  
Population Synthesis ◽  
Low Mass Stars ◽  
Mass Scaling ◽  
Elemental Abundances ◽  
Thick Disc ◽  
Promising Tool ◽  
Low Mass ◽  
The Mean ◽  
First Time

ABSTRACT Asteroseismology is a promising tool to study Galactic structure and evolution because it can probe the ages of stars. Earlier attempts comparing seismic data from the Kepler satellite with predictions from Galaxy models found that the models predicted more low-mass stars compared to the observed distribution of masses. It was unclear if the mismatch was due to inaccuracies in the Galactic models, or the unknown aspects of the selection function of the stars. Using new data from the K2 mission, which has a well-defined selection function, we find that an old metal-poor thick disc, as used in previous Galactic models, is incompatible with the asteroseismic information. We use an importance-sampling framework, which takes the selection function into account, to fit for the metallicities of a population synthesis model using spectroscopic data. We show that spectroscopic measurements of [Fe/H] and [α/Fe] elemental abundances from the GALAH survey indicate a mean metallicity of log (Z/Z⊙) = −0.16 for the thick disc. Here Z is the effective solar-scaled metallicity, which is a function of [Fe/H] and [α/Fe]. With the revised disc metallicities, for the first time, the theoretically predicted distribution of seismic masses show excellent agreement with the observed distribution of masses. This indirectly verifies that the asteroseismic mass scaling relation is good to within five per cent. Assuming the asteroseismic scaling relations are correct, we estimate the mean age of the thick disc to be about 10 Gyr, in agreement with the traditional idea of an old α-enhanced thick disc.

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