scholarly journals How Normal are the Peculiar a Stars

1993 ◽  
Vol 138 ◽  
pp. 126-130 ◽  
Author(s):  
G.S.D. Babu ◽  
B.S. Shylaja
Keyword(s):  
Mass Range ◽  
Physical Parameters ◽  
Effective Temperatures ◽  
Ap Stars

AbstractA comparison of various physical parameters of the normal A stars with those obtained by using the peculiarity-free zones of Ap stars indicate that the peculiar A stars may be treated as normal stars as far as their effective temperatures, radii, bolometric corrections and the mass range are concerned.

scholarly journals Physical parameters for the EXPORT sample. Rotational velocities and effective temperatures

2004 ◽  
Vol 202 ◽  
pp. 127-129
Author(s):  
E. Solano ◽  
B. Montesinos ◽  
A. Mora ◽  
Keyword(s):  
Chemical Analysis ◽  
Physical Parameters ◽  
Planetary Formation ◽  
La Palma ◽  
Effective Temperatures ◽  
Detailed Chemical

The methods used to calculate projected rotational velocities and effective temperatures for the targets observed during the 1998-1999 La Palma International Time campaign are described here. This is part of a project whose main goal is to perform a detailed chemical analysis of these objects and to study their potential implications in the planetary formation phenomenon.

Calibration of the Strömvil Photometric System

2003 ◽  
Vol 12 (4) ◽  
Author(s):  
A. Kazlauskas ◽  
V. Straižys ◽  
R. P. Boyle ◽  
A. G. Davis Philip ◽  
V. Laugalys ◽  
...  
Keyword(s):  
Physical Parameters ◽  
Photometric System ◽  
Photoelectric Photometry ◽  
Color Indices ◽  
Effective Temperatures

AbstractA calibration of color indices of the Strömvil photometric system in terms of physical parameters of stars is presented. The calibration is based on photoelectric photometry of about 1000 stars with known effective temperatures, distances, gravities and metallicities. The observations were accomplished in 2000-2003 with the 1.5 meter telescope of the Steward Observatory. The distances were taken from the Hipparcos catalog, and T

scholarly journals Statistical analysis of roAp, He-weak, and He-rich stars

2019 ◽  
Vol 487 (4) ◽  
pp. 5922-5931
Author(s):  
S Ghazaryan ◽  
G Alecian ◽  
A A Hakobyan
Keyword(s):  
Data Base ◽  
Statistical Tests ◽  
Rotation Velocity ◽  
High Resolution Spectroscopy ◽  
Published Data ◽  
Physical Parameters ◽  
Peculiar Stars ◽  
Abundance Anomalies ◽  
Chemically Peculiar Stars ◽  
Ap Stars

Abstract To enlarge our data base of chemically peculiar stars, we compiled published data concerning the He-weak and He-rich stars observed by high-resolution spectroscopy techniques during last decades. Twenty He-weak and 28 He-rich stars have been added to the data base. We have also distinguished roAp stars from stars previously identified as Ap stars. To deepen our knowledge on statistical overview of the abundance anomalies versus the physical parameters of stars, we compared our data with previous compilations. We applied statistical tests on our data and found interesting correlations for effective temperature and surface gravity for all type of stars and a few correlations for projected rotation velocity only for He-rich stars. Because of the lack of the data, we could not check whether being a member of binary system is affecting on chemical peculiarities of those stars.

High-Speed Photometry of Bright roAp Stars With Small Telescopes

2001 ◽  
Vol 183 ◽  
pp. 187-196
Author(s):  
D.W. Kurtz
Keyword(s):  
Magnetic Field ◽  
High Speed ◽  
Frequency Spectra ◽  
Photometric Observations ◽  
High Speed Photometry ◽  
Effective Temperatures ◽  
Ap Stars ◽  
The Magnetic Field ◽  
Theoretical Developments

AbstractThe rapidly oscillating Ap stars are magnetic peculiar A stars which pulsate in multiple p modes with periods in the range of about 6 to 16 minutes with their oscillation axes aligned with the oblique magnetic axes of the stars. Some of these stars have the richest frequency spectra of any non-degenerate stars other than the sun. This paper shows how photometric observations using small telescopes can be used to work on several astrophysically interesting problems posed by these stars. An example of high precision photometry is shown. The proof of oblique dipole pulsation, the distortion of pulsation modes (probably by the magnetic field), and the determination of asteroseismic luminosities are all discussed. The latter, especially when combined with new theoretical developments concerning magnetic field-pulsation interaction, suggests that Ap stars have lower effective temperatures and/or smaller radii than has been previously thought. It is pointed out that this may be related to the recently discovered extreme discrepancy in effective temperature determined from the wings and cores of the Hα line.

scholarly journals Effective temperatures of Ap stars

1998 ◽  
Vol 130 (2) ◽  
pp. 215-222 ◽  
Author(s):  
N. A. Sokolov
Keyword(s):  
Effective Temperatures ◽  
Ap Stars

scholarly journals Open cluster characterization via cross-correlation with a spectral library

2009 ◽  
Vol 5 (S266) ◽  
pp. 458-461
Author(s):  
Francisco F. S. Maia ◽  
João F. C. Santos ◽  
Wagner J. B. Corradi ◽  
Andrés E. Piatti
Keyword(s):  
Central Region ◽  
Cross Correlation ◽  
Open Cluster ◽  
Radial Velocities ◽  
Physical Parameters ◽  
Ratio Analysis ◽  
Spectral Library ◽  
Self Consistent ◽  
Effective Temperatures ◽  
Stellar Aggregate

AbstractWe present a characterization method based on spectral cross-correlation to obtain the physical parameters of the controversial stellar aggregate ESO442–SC04. The data used was obtained with GMOS at the Gemini South telescope, and includes spectra of 17 stars in the central region of the object and 6 standard stars. fxcor was used iteratively to obtain self-consistent radial velocities for the standard stars and average radial velocities for the science spectra. Spectral types, effective temperatures, surface gravities and metallicities were determined using fxcor to correlate cluster spectra with the ELODIE spectral library and select the best correlation matches using the Tonry & Davis ratio. Analysis of the results suggests that the stars in ESO442–SC04 are not bound and, therefore, they do not constitute a physical system.

scholarly journals Benchmarking the fundamental parameters of Ap stars with optical long-baseline interferometric measurements

2020 ◽  
Vol 642 ◽  
pp. A101
Author(s):  
K. Perraut ◽  
M. Cunha ◽  
A. Romanovskaya ◽  
D. Shulyak ◽  
T. Ryabchikova ◽  
...  
Keyword(s):  
Angular Resolution ◽  
Chemical Elements ◽  
Instability Strip ◽  
Fundamental Parameters ◽  
Long Baseline ◽  
Peculiar Stars ◽  
Self Consistent ◽  
Effective Temperatures ◽  
Ap Stars ◽  
Angular Diameters

Context. The variety of physical processes at play in chemically peculiar stars makes it difficult to determine their fundamental parameters. In particular, for the magnetic ones, called Ap stars, the strong magnetic fields and the induced spotted stellar surfaces may lead to biased effective temperatures when these values are derived through spectro-photometry. Aims. We propose to benefit from the exquisite angular resolution provided by long-baseline interferometry in the visible to determine the accurate angular diameters of a number of Ap stars, and thus estimate their radii by a method that is as independent as possible of atmospheric models. Methods. We used the visible spectrograph VEGA at the CHARA interferometric array to complete the sample of Ap stars currently observable with this technique. We estimated the angular diameter and radius of six new targets. We estimated their bolometric flux based solely on observational spectroscopic and photometric data to derive nearly model-independent luminosities and effective temperatures. Results. We extend to 14 the number of Ap stars for which interferometric angular diameters have been measured. The fundamental parameters we derived for the complete Ap sample are compared with those obtained through a self-consistent spectroscopic analysis. Based on a model fitting approach of high-resolution spectra and spectro-photometric observations over a wide wavelength range, this method takes into account the anomalous chemical composition of the atmospheres and the inhomogeneous vertical distribution for different chemical elements. Regarding both the radii and the effective temperatures, the derived values from our interferometric observations and from self-consistent modelling are consistent within better than 2σ for nine targets out of ten. We thus benchmark nine Ap stars for effective temperatures ranging from 7200 and 9100 K, and luminosities ranging between 7 L⊙ and 86 L⊙. Conclusions. These results will be key for the future derivation of accurate radii and other fundamental parameters of fainter peculiar stars for which both the sensitivity and the angular resolution of the current interferometers are not sufficient. Within the context of the observations of Ap stars with the Transiting Exoplanet Survey Satellite (TESS), these interferometric measurements are crucial for testing the mechanism of pulsation excitation at work in these peculiar stars. In particular, our interferometric measurements provide accurate locations in the Hertzsprung-Russell diagram for hot Ap stars among which pulsations may be searched for with TESS, putting to test the blue edge of the theoretical instability strip. These accurate locations could be used to derive masses and ages of these stars through a specific grid of models, and to test correlations between the properties of these peculiar stars and their evolutionary state.

scholarly journals Energy Distribution, Photometry and Physical Characteristics of the Sun and Solar Analogs

1986 ◽  
Vol 7 ◽  
pp. 853-861
Author(s):  
I. N. Glushneva ◽  
E. A. Markova ◽  
A. V. Kharitonov
Keyword(s):  
Solar Energy ◽  
Energy Distribution ◽  
Physical Characteristics ◽  
Photometric Data ◽  
Physical Parameters ◽  
Photometric System ◽  
The Sun ◽  
Color Indices ◽  
Effective Temperatures ◽  
Solar Analogs

AbstractColor indices of solar analogs in the Vilnius seven-color photometric system are discussed. The physical parameters (effective temperatures, radii and luminosities) for solar analogs with reliable spectrophotometric and photometric data were obtained by means of infrared fluxes. The effective temperatures of 16 Cyg A and B, which are considered to be the closest solar analogs are 5854 and 5664 K, respectively. The radii of both stars are in the range of 1 Ro < R < 1.4 Ro and luminosities 1.2Lo < L < 2.1 Lo for 16 Cyg A and Lo < L < 1.7 Lo for 16 Cyg B depending on different evaluations of the distances. We find that the relative solar energy distribution in the 0.33 – 1.25 μm range determined by Neckel and Labs (1984) is reliable enough, however the absolute fluxes are slightly too low at the maximum of energy distribution.

scholarly journals Searching for ZZ Ceti white dwarfs in the Gaia survey

2019 ◽  
Vol 15 (S357) ◽  
pp. 123-126
Author(s):  
Olivier Vincent ◽  
Pierre Bergeron ◽  
David Lafrenière
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Physical Parameters ◽  
Hydrogen Line ◽  
Instability Strip ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Effective Temperatures

AbstractThe Gaia satellite recently released parallax measurements for nearly 400,000 white dwarf stars, allowing for precise measurements of their physical parameters. By combining these parallaxes with Pan-STARRS and CFIS-u photometry, we measured the effective temperatures and surface gravities for all white dwarfs within 100 pc and identified a sample of ZZ Ceti white dwarf candidates within the instability strip. We report the results of a photometric follow-up, currently under way, aimed at identifying new ZZ Ceti stars among this sample using the PESTO camera attached to the 1.6-m telescope at the Mont Mégantic Observatory. Our goal is to verify that ZZ Ceti stars occupy a region in the logg-Teff plane where no nonvariable stars are found, supporting the idea that ZZ Ceti pulsators represent a phase through which all hydrogen-line (DA) white dwarfs must evolve.

scholarly journals Physical parameters of red supergiants in dwarf irregular galaxies in the Local Group

2019 ◽  
Vol 631 ◽  
pp. A95 ◽  
Author(s):  
N. E. Britavskiy ◽  
A. Z. Bonanos ◽  
A. Herrero ◽  
M. Cerviño ◽  
D. García-Álvarez ◽  
...  
Keyword(s):  
Local Group ◽  
Massive Stars ◽  
Physical Parameters ◽  
Agb Stars ◽  
Ic 10 ◽  
Irregular Galaxies ◽  
Red Supergiants ◽  
Effective Temperatures ◽  
Dwarf Irregular Galaxies ◽  
Fundamental Physical

Context. Increasing the statistics of evolved massive stars in the Local Group enables investigating their evolution at different metallicities. During the late stages of stellar evolution, the physics of some phenomena, such as episodic and systematic mass loss, are not well constrained. For example, the physical properties of red supergiants (RSGs) in different metallicity regimes remain poorly understood. Thus, we initiated a systematic study of RSGs in dwarf irregular galaxies (dIrrs) in the Local Group. Aims. We aim to derive the fundamental physical parameters of RSGs and characterize the RSG population in nearby dIrrs. Methods. The target selection is based on 3.6 μm and 4.5 μm photometry from archival Spitzer Space Telescope images of nearby galaxies. We selected 46 targets in the dIrrs IC 10, IC 1613, Sextans B, and the Wolf-Lundmark-Melotte (WLM) galaxy that we observed with the GTC–OSIRIS and VLT–FORS2 instruments. We used several photometric techniques together with a spectral energy distribution analysis to derive the luminosities and effective temperatures of known and newly discovered RSGs. Results. We identified and spectroscopically confirmed 4 new RSGs, 5 previously known RSGs, and 5 massive asymptotic giant branch (AGB) stars. We added known objects from previous observations. In total, we present spectral classification and fundamental physical parameters of 25 late-type massive stars in the following dIrrs: Sextans A, Sextans B, IC 10, IC 1613, Pegasus, Phoenix, and WLM. This includes 17 RSGs and 8 AGB stars that have been identified here and previously. Conclusions. Based on our observational results and PARSEC evolutionary models, we draw the following conclusions: (i) a trend to higher minimum effective temperatures at lower metallicities and (ii) the maximum luminosity of RSGs appears to be constant at log(L/L⊙)≈5.5, independent of the metallicity of the host environment (up to [Fe/H] ≈ −1 dex).

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