scholarly journals A Spectroscopic Abundance Study of Dwarf Cepheid V1719 Cygni

1993 ◽  
Vol 139 ◽  
pp. 374-374
Author(s):  
Chulhee Kim ◽  
Kozo Sadakane
Keyword(s):  
Effective Temperature ◽  
Model Atmosphere ◽  
Surface Gravity ◽  
The Sun ◽  
Atmospheric Parameters ◽  
Visual Region ◽  
Blue Region ◽  
Ccd Observations ◽  
Microturbulent Velocity ◽  
Convective Model

AbstractSpectroscopic CCD observations were carried out for V1719 Cygni and the spectrum in the visual region is analysed relative to the Sun with a line-blanketed convective model atmosphere. Adopted atmospheric parameters are : an effective temperature < Teff > = 7000 K, a surface gravity logg = 3.4. Although our result is dependent on microturbulent velocity and damping constant, it was found that Mg in V1719 Cygni is nearly solar, or underabundent by 0.2 to 0.3 dex according to the analysis of 5172.684 Å MgI line which is relatively free from blending. This is inconsistent with the previous photometric result where VI719 Cygni was known as an abnormally metal rich variable. Because the analysis was given to the single magnesium line which is not a good metallicity indicator and S/N ratio was low due to poor seeing condition, the investigation for iron lines in blue region is undertaken.

scholarly journals Faint solar analogues at the limit of no reddening

2019 ◽  
Vol 629 ◽  
pp. A33 ◽  
Author(s):  
R. E. Giribaldi ◽  
G. F. Porto de Mello ◽  
D. Lorenzo-Oliveira ◽  
E. B. Amôres ◽  
M. L. Ubaldo-Melo
Keyword(s):  
Principal Component Analysis ◽  
Solar System ◽  
Effective Temperature ◽  
Flux Distribution ◽  
Principal Component ◽  
Surface Gravity ◽  
The Sun ◽  
Spectral Indices ◽  
Atmospheric Parameters ◽  
Solar System Bodies

Context. The flux distribution of solar analogues is required for calculating the spectral albedo of solar system bodies such as asteroids and trans-Neptunian objects. Ideally a solar analogue should be comparatively faint as the target of interest, but very few analogues fainter than V = 9 mag have been identified so far. Only atmospheric parameters equal to solar guarantee a flux distribution equal to solar as well, while only photometric colours equal to solar do not. Reddening is also a factor to consider when selecting faint analogue candidates. Aims. Our aim is to implement the methodology for identifying faint analogues at the limit of precision allowed by the current spectroscopic surveys. We quantify the precision attainable for the atmospheric parameters of effective temperature (Teff), metallicity ([Fe/H]), and surface gravity (log g) when derived from moderately low-resolution (R = 8000) spectra with S∕N ~ 100. We estimate the significance of reddening at 100–300 pc from the Sun. Methods. We used the less precise photometry in the HIPPARCOS catalogue to select potential analogues with V ~ 10.5 mag (located at ~135 pc). We calibrated Teff and [Fe/H] as functions of equivalent widths of spectral indices by means of the principal component analysis regression. We derived log g, mass, radius, and age from the atmospheric parameters, Gaia parallaxes, and evolutionary tracks. We evaluated the presence of reddening for the candidates by underestimations of photometric Teff with respect to those derived by spectral indices. These determinations were validated with extinction maps. Results. We obtained the atmospheric parameters Teff, [Fe/H], and log g with precision of 97 K, 0.06 dex, 0.05 dex, respectively. From 21 candidates analysed, we identify five solar analogues: HIP 991, HIP 5811, and HIP 69477 have solar parameters within 1σ errors, and HIP 55619 and HIP 61835 within 2σ errors. Six other stars have Teff close to solar, but slightly lower [Fe/H]. Our analogues show no evidence of reddening except for four stars, that present E(B−V) ≥ 0.06 mag, translating to at least a 200 K decrease in photometric Teff.

scholarly journals Detailed Analyses of Four Solar Analogs Analysed On High S/N CFH and ESO Spectra

1988 ◽  
Vol 132 ◽  
pp. 429-432
Author(s):  
C. Bentolila ◽  
G. Cayrel de Strobel
Keyword(s):  
High Resolution ◽  
Effective Temperature ◽  
The Sun ◽  
Atmospheric Parameters ◽  
Iron Abundance ◽  
Solar Type ◽  
Solar Analogs

Four solar type G stars claimed to be photometrically very similar to the Sun have been analyzed in detail on high resolution, high S/N spectra. Their atmospheric parameters : effective temperature, spectroscopic gravity, microturbulence and iron abundance, [Fe/H], have been determined.

scholarly journals Some Properties of Hot, High-Gravity, Pure Helium Atmospheres

1979 ◽  
Vol 53 ◽  
pp. 125-129
Author(s):  
F. Wesemael ◽  
H.M. Van Horn
Keyword(s):  
Effective Temperature ◽  
White Dwarf ◽  
White Dwarfs ◽  
Model Atmosphere ◽  
Surface Gravity ◽  
High Gravity ◽  
Pure Helium

Model atmosphere analyses of white dwarf spectra have contributed significantly to our understanding of the properties of degenerate stars.: In particular, the pioneering investigations of Bues (1970), Strittmatter and Wickramasinghe (1971) and Shipman (1972) have provided the first reliable determinations of the effective temperature and surface gravity of these objects (see Shipman 1979 and Weidemann 1978 for recent results). We now know with certainty that the hydrogen-rich white dwarf sequence extends at least over the range Te ∽ 6000 – 60.000K. In contrast, the hottest identified helium-rich white dwarfs seem to reach Te ~ 25.000K only, a puzzling result since the progenitors of DB white dwarfs should presumably also be helium-rich.

scholarly journals A Model-Atmosphere Analysis of the Spectrum of Arcturus

1976 ◽  
Vol 72 ◽  
pp. 19-20
Author(s):  
R. Mäckle ◽  
H. Holweger ◽  
R. and R. Griffin
Keyword(s):  
Effective Temperature ◽  
Isotope Ratio ◽  
Carbon Isotope Ratio ◽  
Model Atmosphere ◽  
Empirical Models ◽  
The Sun ◽  
Abundance Patterns ◽  
Cno Cycle ◽  
Average Factor ◽  
Low Mass

We have analysed the spectrum of Arcturus (K2 III) relatively to the Sun, using a differential technique employing empirical models for both stars. We derive an effective temperature of 4260 ± 50K and a surface gravity log g = +0.90 ±0.35; these in turn lead to a very low mass, in the range 0.1 to 0.6 M⊙. Elements are found to be underabundant by an average factor of 4 compared with the Sun. The abundance patterns in the two stars are significantly different, in keeping with the belief that Arcturus is a star of an older generation than the Sun. The carbon isotope ratio, which is as small as 5 or 6, shows that the atmospheric material of Arcturus has been processed through the CNO cycle, and theoretical arguments also indicate that Arcturus is somewhat evolved.

scholarly journals 14. White Dwarf Atmospheres

1971 ◽  
Vol 42 ◽  
pp. 81-96 ◽  
Author(s):  
V. Weidemann
Keyword(s):  
Chemical Composition ◽  
Observational Data ◽  
Effective Temperature ◽  
White Dwarf ◽  
General Information ◽  
Stellar Atmospheres ◽  
Surface Gravity ◽  
Atmospheric Parameters

We first consider the general information scheme for the interpretation of observational data (Figure 1). From the relations plotted it is evident that (in going from left to right) this scheme can only be solved if distances are known and if we are able to determine the atmospheric parameters: effective temperature, Teff, surface gravity, g, and chemical composition from observations of colors and spectra – which is the genuine task of the theory of stellar atmospheres.

Differential Curve-of-Growth Analyses of Mn-Hg Stars

1976 ◽  
Vol 32 ◽  
pp. 521-531
Author(s):  
Keiichi Kodaira
Keyword(s):  
Chemical Composition ◽  
Effective Temperature ◽  
Narrow Range ◽  
Enrichment Factors ◽  
Surface Gravity ◽  
List Type ◽  
The Sun ◽  
Type Number ◽  
Growth Method ◽  
Growth Analyses

SummarySpectra of eleven Mn-Hg stars (α And,μ Lep, 129 Tau, 14 Hya,κCnc, 30 UMa, πBoo, ι CrB, ϕ Her, ν Her, 46 Dra) are analyzed by the curve-of-growth method. The effective temperature and the surface gravity are estimated from the |u-b|- and the β-indexes and fall into ranges O.346 ≤ θe≤0.451 and 3.4≤log g≤3.8. The microturbulence velocity is found to be in a narrow range of 2 ≲ vt≲ 4.5 km/sec. The resulting chemical composition is very similar among the eleven Mn-Hg stars and shows following characteristics:1)The abundance ratios N(C):N(Si):N(Ca):N(Fe), N(Ti):N(Cr) and N(Sr):N(Y):N(Zr) are nearly identical to those of the sun.2)The enrichment factors relative to Fe are about 10 for Ti and Cr, about 100 for P, Sc, Mn, Sr, Y, and Zr, about 105for Ga, and about 103~106(varying among stars) for Hg.

scholarly journals Spectroscopic properties of a two-dimensional time-dependent Cepheid model

2018 ◽  
Vol 611 ◽  
pp. A19 ◽  
Author(s):  
V. Vasilyev ◽  
H.-G. Ludwig ◽  
B. Freytag ◽  
B. Lemasle ◽  
M. Marconi
Keyword(s):  
Effective Temperature ◽  
Spectroscopic Properties ◽  
Variable Stars ◽  
Time Dependent ◽  
Surface Gravity ◽  
Current Standard ◽  
Static Approximation ◽  
Cepheid Variables ◽  
Microturbulent Velocity ◽  
1D Model

Context. Standard spectroscopic analyses of variable stars are based on hydrostatic 1D model atmospheres. This quasi-static approach has not been theoretically validated. Aim. We aim at investigating the validity of the quasi-static approximation for Cepheid variables. We focus on the spectroscopic determination of the effective temperature Teff, surface gravity log g, microturbulent velocity ξt, and a generic metal abundance log A, here taken as iron.Methods. We calculated a grid of 1D hydrostatic plane-parallel models covering the ranges in effective temperature and gravity that are encountered during the evolution of a 2D time-dependent envelope model of a Cepheid computed with the radiation-hydrodynamics code CO5BOLD. We performed 1D spectral syntheses for artificial iron lines in local thermodynamic equilibrium by varying the microturbulent velocity and abundance. We fit the resulting equivalent widths to corresponding values obtained from our dynamical model for 150 instances in time, covering six pulsational cycles. In addition, we considered 99 instances during the initial non-pulsating stage of the temporal evolution of the 2D model. In the most general case, we treated Teff, log g, ξt, and log A as free parameters, and in two more limited cases, we fixed Teff and log g by independent constraints. We argue analytically that our approach of fitting equivalent widths is closely related to current standard procedures focusing on line-by-line abundances.Results. For the four-parametric case, the stellar parameters are typically underestimated and exhibit a bias in the iron abundance of ≈−0.2 dex. To avoid biases of this type, it is favorable to restrict the spectroscopic analysis to photometric phases ϕph ≈ 0.3…0.65 using additional information to fix the effective temperature and surface gravity.Conclusions. Hydrostatic 1D model atmospheres can provide unbiased estimates of stellar parameters and abundances of Cepheid variables for particular phases of their pulsations. We identified convective inhomogeneities as the main driver behind potential biases. To obtain a complete view on the effects when determining stellar parameters with 1D models, multidimensional Cepheid atmosphere models are necessary for variables of longer period than investigated here.

scholarly journals GD 424 – a helium-atmosphere white dwarf with a large amount of trace hydrogen in the process of digesting a rocky planetesimal

2020 ◽  
Author(s):  
Paula Izquierdo ◽  
Odette Toloza ◽  
Boris T Gänsicke ◽  
Pablo Rodríguez-Gil ◽  
Jay Farihi ◽  
...  
Keyword(s):  
Steady State ◽  
Effective Temperature ◽  
White Dwarf ◽  
Metal Pollution ◽  
White Dwarfs ◽  
Surface Gravity ◽  
Atmospheric Composition ◽  
Atmospheric Parameters ◽  
Hybrid Analysis ◽  
Helium Atmosphere

Abstract The photospheric metal pollution of white dwarfs is now well-established as the signature of the accretion of planetary debris. However, the origin of the trace hydrogen detected in many white dwarfs with helium atmospheres is still debated. Here, we report the analysis of GD 424: a metal-polluted, helium-atmosphere white dwarf with a large amount of trace hydrogen. We determined the atmospheric parameters using a hybrid analysis that combines the sensitivity of spectroscopy to the atmospheric composition, log (H/He), with that of photometry and astrometry to the effective temperature, Teff, and surface gravity, log g. The resulting white dwarf mass, radius, and cooling age are ${M_{\rm{WD}}}=0.77\pm 0.01\, {\rm{M}_{\odot}}$, ${R_{\rm{WD}}}=0.0109\pm 0.0001\, {\rm{R}_{\odot}}$, and τcool = 215 ± 10 Myr, respectively. We identified and measured the abundances of 11 photospheric metals and argue that the accretion event is most likely either in the increasing or steady state, and that the disrupted planetesimal resembles either CI chondrites or the bulk Earth in terms of its composition. We suggest that the observed 1.33 × 1022 g of trace hydrogen in GD 424 were at least partly acquired through accretion of water-rich planetary debris in an earlier accretion episode.

scholarly journals Fitting of Silicon lines in UV and Balmer Hδ Line in Optical Spectra of B supergiant HD 198478

2011 ◽  
Vol 7 (S282) ◽  
pp. 263-264
Author(s):  
Tomislav Jurkić ◽  
Mariza Sarta Deković ◽  
Dubravka Kotnik-Karuza
Keyword(s):  
Effective Temperature ◽  
Optical Spectra ◽  
Surface Gravity ◽  
Numerical Code ◽  
Atmospheric Parameters ◽  
Synthetic Spectra ◽  
Temperature Surface

AbstractAtmospheric parameters of the Galactic early B-supergiant HD 198478 (55 Cyg) were determined from the UV silicon lines and optical Balmer Hδ 4101 Å line. TLUSTY synthetic spectra were broadened using the ROTIN numerical code in order to determine effective temperature, surface gravity, rotational and macroturbulent velocity.

scholarly journals 3D spectroscopic analysis of helium-line white dwarfs

2020 ◽  
Author(s):  
Elena Cukanovaite ◽  
Pier-Emmanuel Tremblay ◽  
Pierre Bergeron ◽  
Bernd Freytag ◽  
Hans-Günter Ludwig ◽  
...  
Keyword(s):  
Effective Temperature ◽  
White Dwarfs ◽  
Energy Transport ◽  
3D Models ◽  
Spectroscopic Technique ◽  
Surface Gravity ◽  
Atmospheric Models ◽  
Physical Treatment ◽  
Spectroscopic Parameters ◽  
1D Model

Abstract In this paper, we present corrections to the spectroscopic parameters of DB and DBA white dwarfs with −10.0 ≤ log (H/He) ≤−2.0, 7.5 ≤ log g ≤9.0 and 12 000 K ≲ Teff ≲ 34 000 K, based on 282 3D atmospheric models calculated with the CO5BOLD radiation-hydrodynamics code. These corrections arise due to a better physical treatment of convective energy transport in 3D models when compared to the previously available 1D model atmospheres. By applying the corrections to an existing SDSS sample of DB and DBA white dwarfs, we find significant corrections both for effective temperature and surface gravity. The 3D log g corrections are most significant for Teff ≲ 18, 000 K, reaching up to −0.20 dex at log g = 8.0. However, in this low effective temperature range, the surface gravity determined from the spectroscopic technique, can also be significantly affected by the treatment of the neutral van der Waals line broadening of helium and by non-ideal effects due to the perturbation of helium by neutral atoms. Thus, by removing uncertainties due to 1D convection, our work showcases the need for improved description of microphysics for DB and DBA model atmospheres. Overall, we find that our 3D spectroscopic parameters for the SDSS sample are generally in agreement with Gaia DR2 absolute fluxes within 1-3σ for individual white dwarfs. By comparing our results to DA white dwarfs, we determine that the precision and accuracy of DB/DBA atmospheric models are similar. For ease of user application of the correction functions, we provide an example Python code.

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