scholarly journals Effects of Photospheric Temperature Inhomogeneities on Lithium abundance Determinations (2D)

2000 ◽  
Vol 198 ◽  
pp. 437-447 ◽  
Author(s):  
Roger Cayrel ◽  
Matthias Steffen
Keyword(s):  
Effective Temperature ◽  
Atomic Model ◽  
Radiation Hydrodynamics ◽  
Lithium Abundance ◽  
Near Future ◽  
Photospheric Temperature ◽  
The Continuum

Based on detailed 2D radiation hydrodynamics (RHD) simulations, we have investigated the effects of photospheric temperature inhomogeneities induced by convection on spectroscopic determinations of the lithium abundance. Computations have been performed both for the solar case and for a metal-poor dwarf. NLTE effects are taken into account, using a five-level atomic model for Li I. Comparisons are presented with traditional 1D models having the same effective temperature and gravity. The net result is that, while LTE results differ dramatically between 1D and 2D models, especially in the metal-poor case, this does not remain true when NLTE effects are included: 1D/2D differences in the inferred NLTE Li abundance are always well below 0.1 dex. The present computations still assume LTE in the continuum. New computations removing this assumption are planned for the near future.

scholarly journals Lithium Observations in the Sun

1968 ◽  
Vol 1 ◽  
pp. 243-246
Author(s):  
Edith A. Müller
Keyword(s):  
Unknown Origin ◽  
Absorption Feature ◽  
The Sun ◽  
Degree Of Ionization ◽  
Lithium Abundance ◽  
Resonance Doublet ◽  
Lower Temperature ◽  
Central Depth ◽  
The Continuum

The determination of the lithium abundance in the solar atmosphere is essentially based on the LiI resonance doublet at λ 6707·761 and 6707·912 Å. These two lines form a very faint absorption feature, the central depth of the stronger component being of the order of 1% of the continuum. The violet component, which is also the stronger of the two, occurs near the red wing of a faint solar line of unknown origin, and the lines appear to be blended with other faint lines including possibly the doublet of the Li6 isotope (the isotopic shift being 0·160 Å). No other line of LiI has been detected in the Fraunhofer spectum of the undisturbed solar disk. This is nothing surprising, because practically all lithium is expected to be ionized in the photosphere on account of its low ionization potential (Xion = 5·37 e.v.). In sunspot spectra the lower temperature reduces the degree of ionization of lithium and causes a strengthening of the LiI lines. In fact, the LiI resonance lines which appear as a very faint absorption feature on disk spectra are about 50 times stronger in spot spectra. Furthermore, the very weak feature at λ 6103·6 Å was identified by Dubov (1964) and by Schmahl and Schröter (1965) as due to the 2s 2S–3d 2D transition of LiI. Both the resonance doublet and the faint feature at 6103·6 Å have been used by the above-mentioned authors to derive the lithium abundance in spots.

scholarly journals Super-luminous Type II supernovae powered by magnetars

2018 ◽  
Vol 613 ◽  
pp. A5 ◽  
Author(s):  
Luc Dessart ◽  
Edouard Audit
Keyword(s):  
Light Curve ◽  
Spectroscopic Properties ◽  
Radiation Hydrodynamics ◽  
Equal Proportion ◽  
Type Ii ◽  
Standard Type ◽  
Fluid Instabilities ◽  
Dense Shell ◽  
Standard Energy ◽  
Photospheric Temperature

Magnetar power is believed to be at the origin of numerous super-luminous supernovae (SNe) of Type Ic, arising from compact, hydrogen-deficient, Wolf-Rayet type stars. Here, we investigate the properties that magnetar power would have on standard-energy SNe associated with 15–20 M⊙ supergiant stars, either red (RSG; extended) or blue (BSG; more compact). We have used a combination of Eulerian gray radiation-hydrodynamics and non-LTE steady-state radiative transfer to study their dynamical, photometric, and spectroscopic properties. Adopting magnetar fields of 1, 3.5, 7 × 1014 G and rotational energies of 0.4, 1, and 3 × 1051 erg, we produce bolometric light curves with a broad maximum covering 50–150 d and a magnitude of 1043–1044 erg s−1. The spectra at maximum light are analogous to those of standard SNe II-P but bluer. Although the magnetar energy is channelled in equal proportion between SN kinetic energy and SN luminosity, the latter may be boosted by a factor of 10–100 compared to a standard SN II. This influence breaks the observed relation between brightness and ejecta expansion rate of standard Type II SNe. Magnetar energy injection also delays recombination and may even cause re-ionization, with a reversal in photospheric temperature and velocity. Depositing the magnetar energy in a narrow mass shell at the ejecta base leads to the formation of a dense shell at a few 1000 km s−1, which causes a light-curve bump at the end of the photospheric phase. Depositing this energy over a broad range of mass in the inner ejecta, to mimic the effect of multi-dimensional fluid instabilities, prevents the formation of a dense shell and produces an earlier-rising and smoother light curve. The magnetar influence on the SN radiation is generally not visible prior to 20–30 d, during which one may discern a BSG from a RSG progenitor. We propose a magnetar model for the super-luminous Type II SN OGLE-SN14-073.

Therapeutic Approach to Castration-resistant Prostate Cancer

2009 ◽  
Vol 05 (01) ◽  
pp. 83
Author(s):  
Fred Saad ◽  
Keyword(s):  
Prostate Cancer ◽  
Cancer Patients ◽  
Androgen Deprivation Therapy ◽  
Therapeutic Approach ◽  
Advanced Prostate Cancer ◽  
Castration Resistant Prostate Cancer ◽  
Castration Resistant ◽  
Resistant Form ◽  
Near Future ◽  
The Continuum

Androgen deprivation therapy (ADT) has been and continues to be the most common treatment for men with advanced prostate cancer and is now used earlier in the continuum of care for prostate cancer. Unfortunately, the majority of prostate cancer patients on ADT will develop a castration-resistant form of the disease that is responsible for the majority of the morbidity and mortality related to prostate cancer. Given recent advances, there are now therapeutic options available that can reduce the morbidity and improve survival in patients with castrationresistant prostate cancer (CRPC). Research is intensifying in this area and further improvements can be expected in the near future. This review will briefly summarize what is currently available and propose strategies for the management of CRPC.

scholarly journals Lithium abundance patterns of late-F stars: an in-depth analysis of the lithium desert

2018 ◽  
Vol 614 ◽  
pp. A55 ◽  
Author(s):  
Claudia Aguilera-Gómez ◽  
Iván Ramírez ◽  
Julio Chanamé
Keyword(s):  
Effective Temperature ◽  
Main Sequence ◽  
Atmospheric Parameters ◽  
Lithium Abundance ◽  
Temperature Range ◽  
Abundance Patterns ◽  
Depth Analysis ◽  
Effective Temperatures ◽  
F Stars

Aims. We address the existence and origin of the lithium (Li) desert, a region in the Li–Teff plane sparsely populated by stars. Here we analyze some of the explanations that have been suggested for this region, including mixing in the late main sequence, a Li dip origin for stars with low Li abundances in the region, and a possible relation with the presence of planets. Methods. To study the Li desert, we measured the atmospheric parameters and Li abundance of 227 late-F dwarfs and subgiants, chosen to be in the Teff range of the desert and without previous Li abundance measurements. Subsequently, we complemented those with literature data to obtain a homogeneous catalog of 2318 stars, for which we compute masses and ages. We characterize stars surrounding the region of the Li desert. Results. We conclude that stars with low Li abundances below the desert are more massive and more evolved than stars above the desert. Given the unexpected presence of low Li abundance stars in this effective temperature range, we concentrate on finding their origin. We conclude that these stars with low Li abundance do not evolve from stars above the desert: at a given mass, stars with low Li (i.e., below the desert) are more metal-poor. Conclusions. Instead, we suggest that stars below the Li desert are consistent with having evolved from the Li dip, discarding the need to invoke additional mixing to explain this feature. Thus, stars below the Li desert are not peculiar and are only distinguished from other subgiants evolved from the Li dip in that their combination of atmospheric parameters locates them in a range of effective temperatures where otherwise only high Li abundance stars would be found (i.e., stars above the desert).

scholarly journals Lithium abundances in dwarfs of intermediate age open clusters

2009 ◽  
Vol 5 (S268) ◽  
pp. 345-346
Author(s):  
Giancarlo Pace ◽  
Jorge Mélendez
Keyword(s):  
Effective Temperature ◽  
Open Cluster ◽  
Open Clusters ◽  
The Other ◽  
Crucial Importance ◽  
Lithium Abundance ◽  
Dwarf Stars ◽  
Accurate Temperature ◽  
Steep Decline ◽  
Effective Temperatures

AbstractLithium abundance measurements in dwarf stars in open clusters are of crucial importance for our understanding of the mixing mechanism and have allowed us to achieve important conclusions on the matter. However, in order to further our understanding of what drives lithium depletion, lithium abundance measurements have to be coupled with accurate temperature determinations, which are best achieved when the analysis of iron lines is employed. Effective temperature estimations from photometry, on the contrary, can be affected by errors as large as several hundred kelvins due to uncertain open cluster reddening, especially when studying old open clusters, which tend to be more distant. We present lithium abundance in 12 dwarfs belonging to 4 open clusters at about 1 or 2 Gyr. The stellar effective temperatures, along with the other parameters, were estimated from the analysis of about 60 Fe I lines and 10 Fe II. Even though the few datapoints call for caution, we notice that stars in the open cluster IC 4651 seem to present a steep decline with temperature below 6000 K.

scholarly journals Effective Temperature Scales of Red Giant Stars

1999 ◽  
Vol 191 ◽  
pp. 84-90
Author(s):  
David R. Alexander ◽  
Jason W. Ferguson ◽  
Robert F. Wing ◽  
Hollis R. Johnson ◽  
Peter H. Hauschildt ◽  
...  
Keyword(s):  
Effective Temperature ◽  
Near Infrared ◽  
Narrow Band ◽  
State Of The Art ◽  
Band System ◽  
Spectral Synthesis ◽  
Giant Stars ◽  
Red Giant ◽  
Absorption Features ◽  
The Continuum

We have completed a grid of spherically symmetric AGB star atmospheres using the state of the art spectral synthesis code PHOENIX. Models are constructed for stars with masses of 1 M⊙and 1.5 M⊙, spanning the range 10 to 3300 L⊙in luminosity and 2500 to 5200 K in effective temperature. We find that grains of Al2O3and CaTiO3among other species form in atmospheres cooler than Teff= 3000 K. In the coolest models the grains cause a weakening of the TiO absorption features in the red and near infrared of up to 30% through both a depression of the continuum and a depletion of the TiO number abundance. We use spectrophotometric observations from a number of catalogs to determine effective temperature – spectral class and effective temperature – color relationships. We also compare synthetic colors calculated from our models with observations of M giants on Wing's 8-color narrow-band system of classification photometry.

scholarly journals The Effect of Scattering on the Temperature Stratification of 3D Model Atmospheres of Metal-Poor Red Giants

2010 ◽  
Vol 6 (S271) ◽  
pp. 373-374
Author(s):  
Remo Collet ◽  
Wolfgang Hayek ◽  
Martin Asplund
Keyword(s):  
3D Model ◽  
Source Function ◽  
Coherent Scattering ◽  
Thin Layers ◽  
Temperature Stratification ◽  
Radiation Hydrodynamics ◽  
Red Giants ◽  
Giant Stars ◽  
Red Giant ◽  
Photospheric Temperature

AbstractWe study the effects of different approximations of scattering in 3D radiation-hydrodynamics simulations on the photospheric temperature stratification of metal-poor red giant stars. We find that assuming a Planckian source function and neglecting the contribution of scattering to extinction in optically thin layers provides a good approximation of the effects of coherent scattering on the photospheric temperature balance.

scholarly journals Observed Lithium Abundances as a Test of Stellar Internal Structure

1988 ◽  
Vol 108 ◽  
pp. 13-14
Author(s):  
Sylvie Vauclair
Keyword(s):  
Internal Structure ◽  
Effective Temperature ◽  
Time Scale ◽  
Convection Zone ◽  
Theoretical Explanation ◽  
Diffusion Time ◽  
Lithium Abundance ◽  
Galactic Clusters ◽  
F Stars ◽  
Radiative Acceleration

The “lithium gap” observed in the Hyades and other galactic clusters by Ann Boesgaard and her collaborators (Boesgaard and Tripicco 1986, Boesgaard 1987, Boesgaard, Budge and Burck 1987) gives a challenge to theoreticians. Indeed a good fit between the theoretical results and the observations will give a clue for our understanding of the stellar internal structure and evolution.A theoretical explanation of the “lithium gap” by gravitational and radiative diffusion has been proposed by Michaud 1986. In G type stars, the convection zone is too deep for gravitational settling to take place: the density at the bottom of the convection zone is so large that the diffusion time scale exceeds the age of the star. Increasing the effective temperature leads to a decrease of the convection zone, and consequently to a decrease of the diffusion time scale. In F stars it becomes smaller than the stellar age, leading qualitatively to a lithium abundance decrease as observed. When the convection zone is shallow enough, the radiative acceleration on lithium becomes important as lithium is in the hydrogenic form of li III (while it is a bare nucleus, li IV, deeper in the star). This radiative acceleration may prevent lithium settling for hotter F stars. This is a very attractive explanation, which leads to a minimum of the lithium abundance nearly at the place where it is observed in effective temperature. However it suffers from some difficulties: the theory predicts an increase of the lithium abundance larger than normal in the hottest F stars, which is not observed, and the predicted minimum lithium abundance is one or two orders of magnitude higher than the minimum observed in the Hyades. The former may be overcome if mass loss occurs in these stars (Michaud 86). Let us focus on the latter.

scholarly journals Narrow Band Photometry of Supergiant Stars

1973 ◽  
Vol 50 ◽  
pp. 208-208
Author(s):  
E. E. Mendoza V.
Keyword(s):  
Quantum Efficiency ◽  
Effective Temperature ◽  
Narrow Band ◽  
Band System ◽  
Astronomical Observatory ◽  
Type B ◽  
Photoelectric Photometry ◽  
Interference Filters ◽  
San Pedro ◽  
The Continuum

At the National Astronomical Observatory in San Pedro Mártir, B. C. (Mexico), we have performed photoelectric photometry for 31 stars in a narrow-band system. The system allows the measurements of total absorptions of neutral oxygen at 7774 Å through three interference filters (20–25 Å half-width), one for the OI lines and two for the continuum.The preliminary results are very encouraging: Supergiant stars, ranging in spectrum from the later subdivisions of type B to early G, can be clearly separated from other luminosity classes. The total absorptions depend strongly on the stellar luminosity and, to a lesser degree on the effective temperature (spectral type) of the star. The system may be improved by using narrower filters and detectors with a higher quantum efficiency, already in existence.

scholarly journals Lithium in the Hyades L5 brown dwarf 2MASS J04183483+2131275

2018 ◽  
Vol 615 ◽  
pp. L12 ◽  
Author(s):  
N. Lodieu ◽  
R. Rebolo ◽  
A. Pérez-Garrido
Keyword(s):  
Spectral Type ◽  
Effective Temperature ◽  
Resonance Line ◽  
Resolving Power ◽  
Evolutionary Models ◽  
Maximum Mass ◽  
Brown Dwarf ◽  
Lithium Abundance ◽  
The Individual ◽  
Low Dispersion

Aims. From the luminosity, effective temperature and age of the Hyades brown dwarf 2MASS J04183483+2131275 (2M0418), substellar evolutionary models predict a mass in the range 39−55 Jupiter masses (MJup) which is insufficient to produce any substantial lithium burning except for the very upper range >53 MJup. Our goal is to measure the abundance of lithium in this object, test the consistency between models and observations and refine constraints on the mass and age of the object. Methods. We used the 10.4-m Gran Telescopio Canarias (GTC) with its low-dispersion optical spectrograph to obtain ten spectra of 2277 s each covering the range 6300–10 300 Å with a resolving power of R ~ 500. Results. In the individual spectra, which span several months, we detect persistent unresolved Hα in emission with pseudo equivalent widths (pEW) in the range 45–150 Å and absorption lines of various alkalis with the typical strengths found in objects of L5 spectral type. The lithium resonance line at 6707.8 Å is detected with pEW of 18 ± 4 Å in 2M0418 (L5). Conclusions. We determine a lithium abundance of log N(Li) = 3.0 ± 0.4 dex consistent with a minimum preservation of 90% of this element which confirms 2M0418 as a brown dwarf with a maximum mass of 52 MJup. We infer a maximum age for the Hyades of 775 Myr from a comparison with the BHAC15 models. Combining recent results from the literature with our study, we constrain the mass of 2M0418 to 45–52 MJup and the age of the cluster to 580–775 Myr (1σ) based on the lithium depletion boundary method.

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