scholarly journals Mapping the Instability Domains of GW Vir Stars in the Effective Temperature–Surface Gravity Diagram

2007 ◽  
Vol 171 (1) ◽  
pp. 219-248 ◽  
Author(s):  
P.‐O. Quirion ◽  
G. Fontaine ◽  
P. Brassard
Keyword(s):  
Effective Temperature ◽  
Surface Gravity ◽  
Temperature Surface

Stellar Parameterisation using KPCA and SVM

2017 ◽  
Vol 14 (S339) ◽  
pp. 345-348
Author(s):  
H. Yuan ◽  
Y. Zhang ◽  
Y. Lei ◽  
Y. Dong ◽  
Z. Bai ◽  
...  
Keyword(s):  
Effective Temperature ◽  
Hybrid Approach ◽  
Principal Component ◽  
Test Sample ◽  
Surface Gravity ◽  
Kernel Principal Component Analysis ◽  
Support Vector ◽  
Stellar Spectra ◽  
The Impact ◽  
Temperature Surface

AbstractWith so many spectroscopic surveys, both past and upcoming, such as SDSS and LAMOST, the number of accessible stellar spectra is continuously increasing. There is therefore a great need for automated procedures that will derive estimates of stellar parameters. Working with spectra from SDSS and LAMOST, we put forward a hybrid approach of Kernel Principal Component Analysis (KPCA) and Support Vector Machine (SVM) to determine the stellar atmospheric parameters effective temperature, surface gravity and metallicity. For stars with both APOGEE and LAMOST spectra, we adopt the LAMOST spectra and APOGEE parameters, and then use KPCA to reduce dimensionality and SVM to measure parameters. Our method provides reliable and precise results; for example, the standard deviation of effective temperature, surface gravity and metallicity for the test sample come to approximately 47–75 K, 0.11–0.15 dex and 0.06–0.075 dex, respectively. The impact of the signal:noise ratio of the observations upon the accuracy of the results is also investigated.

scholarly journals RAVE-Gaia and the impact on Galactic archeology

2017 ◽  
Vol 12 (S330) ◽  
pp. 176-180
Author(s):  
Andrea Kunder
Keyword(s):  
Radial Velocity ◽  
Effective Temperature ◽  
Milky Way ◽  
Radial Velocities ◽  
Surface Gravity ◽  
Individual Stars ◽  
Dynamic Analyses ◽  
Data Release ◽  
The Impact ◽  
Temperature Surface

AbstractThe new data release (DR5) of the RAdial Velocity Experiment (RAVE) includes radial velocities of 520,781 spectra of 457,588 individual stars, of which 215,590 individual stars are released in the Tycho-Gaia astrometric solution (TGAS) in Gaia DR1. Therefore, RAVE contains the largest TGAS overlap of the recent and ongoing Milky Way spectroscopic surveys. Most of the RAVE stars also contain stellar parameters (effective temperature, surface gravity, overall metallicity), as well as individual abundances for Mg, Al, Si, Ca, Ti, Fe, and Ni. Combining RAVE with TGAS brings the uncertainties in space velocities down by a factor of 2 for stars in the RAVE volume – 10 km s−1 uncertainties in space velocities are now able to be derived for the majority (70%) of the RAVE-TGAS sample, providing a powerful platform for chemo-dynamic analyses of the Milky Way. Here we discuss the RAVE-TGAS impact on Galactic archaeology as well as how the Gaia parallaxes can be used to break degeneracies within the RAVE spectral regime for an even better return in the derivation of stellar parameters and abundances.

scholarly journals Quantitative Stellar Classification with Low-Resolution Spectroscopy

2012 ◽  
Vol 8 (S293) ◽  
pp. 375-377
Author(s):  
Matthias Ammler-von Eiff ◽  
Daniel Sebastian ◽  
Eike W. Guenther
Keyword(s):  
Effective Temperature ◽  
Surface Gravity ◽  
Low Resolution ◽  
Quantitative Classification ◽  
Faint Object ◽  
Faint Object Spectrograph ◽  
Temperature Surface

AbstractLow-resolution spectroscopy (R ≈ 1000) is used to efficiently characterize faint stars suspected to host planets. Stellar parameters, i.e. effective temperature, surface gravity, and metallicity can be assessed from these spectra by methods of quantitative classification. For this purpose, more than 130 template stars have been observed with the faint object spectrograph at the Tautenburg 2m telescope, Germany. A large number of lines are measured and the dependence of line depths on stellar parameters is studied.

scholarly journals Simultaneous Bayesian estimation of distances and ages from isochrones: SDSS and solar neighborhood FGK stars

2007 ◽  
Vol 3 (S248) ◽  
pp. 494-495 ◽  
Author(s):  
M. Franchini ◽  
C. Morossi ◽  
P. Di Marcantonio ◽  
M. L. Malagnini
Keyword(s):  
Probability Theory ◽  
Bayesian Estimation ◽  
Spectral Type ◽  
Effective Temperature ◽  
Absolute Magnitude ◽  
Solar Neighborhood ◽  
Surface Gravity ◽  
Bayesian Probability ◽  
Self Consistent ◽  
Temperature Surface

AbstractBy using a procedure based on the Bayesian probability theory we computed reliable and self–consistent estimates of absolute magnitude and age for about 2000 FKG spectral-type stars from SDSS–DR5, ELODIE, and INDO–US surveys, with effective temperature, surface gravity, and metallicity values homogeneously derived.

scholarly journals Spectroscopic survey of Kepler stars: high-resolution observations of A- and F-type stars

2013 ◽  
Vol 9 (S301) ◽  
pp. 467-468
Author(s):  
E. Niemczura ◽  
B. Smalley ◽  
S. Murphy ◽  
G. Catanzaro ◽  
K. Uytterhoeven ◽  
...  
Keyword(s):  
Chemical Composition ◽  
High Resolution ◽  
Effective Temperature ◽  
Spectroscopic Data ◽  
Rotational Velocity ◽  
Surface Gravity ◽  
Working Groups ◽  
Space Data ◽  
Temperature Surface

AbstractBasic stellar parameters such as effective temperature, surface gravity, chemical composition, and projected rotational velocity, are important to classify stars and are crucial for successful asteroseismic modelling. However, the Kepler space data do not provide such information. Therefore, ground-based spectral and multi-colour observations of Kepler asteroseismic targets are necessary to complement the space data. For this purpose, in coordination with the KASC ground-based observational Working Groups, high-resolution spectroscopic data for more than 500 B, A, F and G-type stars were collected.

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.

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 First results from MFOSC-P: low-resolution optical spectroscopy of a sample of M dwarfs within 100 parsecs

2020 ◽  
Vol 492 (4) ◽  
pp. 5844-5852 ◽  
Author(s):  
A S Rajpurohit ◽  
Vipin Kumar ◽  
Mudit K Srivastava ◽  
F Allard ◽  
D Homeier ◽  
...  
Keyword(s):  
Effective Temperature ◽  
Spectral Synthesis ◽  
Surface Gravity ◽  
Low Resolution ◽  
M Dwarfs ◽  
Physical Research Laboratory ◽  
Fundamental Parameters ◽  
Faint Object ◽  
First Results

ABSTRACT Mt Abu Faint Object Spectrograph and Camera (MFOSC-P) is an in-house-developed instrument for the Physical Research Laboratory (PRL) 1.2 m telescope at Mt Abu, India, commissioned in 2019 February. Here we present the first science results derived from the low-resolution spectroscopy programme of a sample of M dwarfs carried out during the commissioning run of MFOSC-P between 2019 February and June. M dwarfs carry great significance for exoplanet searches in the habitable zone and are among the promising candidates for the observatory’s several ongoing observational campaigns. Determination of their accurate atmospheric properties and fundamental parameters is essential to constrain both their atmospheric and evolutionary models. In this study, we provide a low-resolution (R ∼ 500) spectroscopic catalogue of 80 bright M dwarfs (J < 10) and classify them using their optical spectra. We have also performed spectral synthesis and χ2 minimization techniques to determine their fundamental parameters regarding effective temperature and surface gravity by comparing the observed spectra with the most recent BT-Settl synthetic spectra. The spectral type of M dwarfs in our sample ranges from M0 to M5. The derived effective temperature and surface gravity range from 4000–3000 K and 4.5–5.5 dex, respectively. In most of the cases, the derived spectral types are in good agreement with previously assigned photometric classifications.

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