scholarly journals Comparison Between Observational and Theoretical (log Teff, Mbol) Diagrams

1978 ◽  
Vol 80 ◽  
pp. 313-318
Author(s):  
G. Cayrel de Strobel ◽  
M.N. Perrin
Keyword(s):  
Detailed Analysis ◽  
Effective Temperature ◽  
Metal Content ◽  
Absolute Magnitude ◽  
Bolometric Correction ◽  
Hr Diagram

In a paper by Perrinet al. (1977), we have constructed an empirical HR diagram for 138 nearby F, G and K stars, for which we had: i) an effective temperature and a metal content derived from a detailed analysis; ii) a reliable bolometric magnitude obtained from an absolute magnitude My, based on a large parallax and a rather small bolometric correction.

scholarly journals Is it Possible to Derive the Position of a Star in the HR Diagram from Multicolor Photometry?

1978 ◽  
Vol 80 ◽  
pp. 319-322
Author(s):  
M.N. Perrin ◽  
G. Cayrel de Strobel
Keyword(s):  
Absolute Magnitude ◽  
Model Atmosphere ◽  
Severe Restriction ◽  
Visual Magnitude ◽  
Effective Temperatures ◽  
Bolometric Correction ◽  
Multicolor Photometry ◽  
Hr Diagram

In the preceeding paper of this Symposium by Cayrel and Perrin (1978), HR diagrams have been discussed, in which the [Fe/H] ratio and effective temperatures are derived from model atmosphere analyses and absolute bolometric magnitude from apparent visual magnitude, parallax and bolometric correction. The use of parallaxes imposes a very severe restriction on the number of objects, as parallaxes of at least 0″.050 are needed to have an absolute magnitude good to ±0m.4.

scholarly journals The Effective Temperatures of Early Wolf-Rayet Stars

1982 ◽  
Vol 99 ◽  
pp. 23-26
Author(s):  
Werner Schmutz
Keyword(s):  
Energy Distribution ◽  
Detailed Analysis ◽  
Absorption Edge ◽  
Effective Temperature ◽  
Spherically Symmetric ◽  
Final Shape ◽  
Effective Temperatures ◽  
Atmosphere Model ◽  
Hr Diagram

Nussbaumer et al. (1981) (NSSW) have calculated temperatures of 15 Wolf-Rayet stars, which cover most subtypes in the WN and WC sequences. Some Wolf-Rayet stars are found to have a blackbody-like energy distribution and therefore their effective temperature can be well determined, others show deviation from the blackbody shape. This deviation is probably due to an extended continuum emitting region. In view of these later cases NSSW adopted a temperature which they derived from a Zanstra analysis of the He II recombination lines. According to their analysis there should be a continuum jump at 2050 å. New IUE observations of the WN 5 star HD 50896 however did not show any trace of such an absorption edge. This implies that the effective temperature of this WN 5 star and probably of all WR stars with a non blackbody energy distribution is not yet known accurately. Therefore we started a detailed analysis with a spherically symmetric atmosphere model. Though the model has not yet reached its final shape we have obtained as a first result that the location of HD 50896 in the HR-diagram is to the left of the ZAMS and that the Zanstra analysis is indeed not valid for this star.

scholarly journals The Position of the Central Stars of PN on the HR Diagram

1989 ◽  
Vol 131 ◽  
pp. 481-492
Author(s):  
S. R. Pottasch
Keyword(s):  
Effective Temperature ◽  
Critical Role ◽  
Central Stars ◽  
Hr Diagram

Central stars can be placed on the HR diagram if their effective temperature (Teff) and radii are known. Knowledge of the radius can sometimes be replaced by another indication of the luminosity. The distance, which always plays an important, really critical role, is not well known. This is the essential reason that there is so much uncertainty about the position on the HR diagram.

scholarly journals The HR Diagram

1978 ◽  
Vol 80 ◽  
pp. 101-116
Author(s):  
Jesse L. Greenstein
Keyword(s):  
Chemical Composition ◽  
Broad Band ◽  
Wavelength Region ◽  
Absolute Magnitude ◽  
Coordinate Space ◽  
Evolutionary Status ◽  
Bolometric Luminosity ◽  
The Galaxy ◽  
Stellar Masses ◽  
Hr Diagram

The HR diagram is a useful shorthand locating a star in a two-coordinate space. For the astrophysicist, the y-coordinate is bolometric luminosity, Mbol, the x-coordinate, effective temperature, Teff. Objects of given chemical composition, age (or evolutionary status) are labeled in the xy plane by mass. For an observer, y may be apparent or absolute magnitude in a certain wavelength region and x may be spectral type or color. The HR diagrams for populations differ because of age, chemical composition and stellar masses present. HR diagrams are often of mixed nature; some involve observables others derived or semi-theoretical quantities. I will display various types of HR diagrams for low-luminosity stars. For galactic or extragalactic studies the HR diagram needs a further dimension, the frequency of stars at an x,y. The mass of the Galaxy, but not its light, may be dominated by M dwarfs. HR diagrams are also interesting for their nearly empty spaces. In Fig. 1 we show as a sample, the basic results of the U.S. Naval Observatory parallax program, in which broad band (B-V) colors define the visual luminosity, My, on the main (MS) and degenerate (WD) sequences.

scholarly journals Lithium Abundance in Late-Type Stars

2000 ◽  
Vol 198 ◽  
pp. 368-369
Author(s):  
L Pompéia ◽  
B Barbuy ◽  
M. Grenon
Keyword(s):  
High Resolution ◽  
Radial Velocity ◽  
Detailed Analysis ◽  
Absolute Magnitude ◽  
Late Type ◽  
Lithium Abundance ◽  
Dwarf Stars ◽  
The Absolute

We have a list of nearby bulge-like turnoff stars with metallicities in the range −0.3 ≤ [Fe/H] ≤ +0.6, for which we have the absolute magnitude from Hipparcos, Geneva photometry (therefore temperature and metallicity), and radial velocity from Coravel (Grenon 1990, 1997). From Hipparcos data, the turnoff of these field stars indicate an age of 10-11 Gyr, which would be the age of the most metal-rich component of the bulge.We obtained high resolution échelle spectra with FEROS, with the aim to carry out detailed analysis of these stars. In this paper we present the Li abundance for 40 of these metal-rich and old dwarf stars, as a function of their temperatures.

scholarly journals Constraints on the Atmospheric Parameters of the Binary DA White Dwarf L870-2 (EG11)

1989 ◽  
Vol 114 ◽  
pp. 435-439
Author(s):  
P. Bergeron ◽  
F. Wesemael ◽  
J. Liebert ◽  
G. Fontaine ◽  
P. Lacombe
Keyword(s):  
Observational Data ◽  
Stellar Evolution ◽  
Effective Temperature ◽  
White Dwarf ◽  
Binary Systems ◽  
Absolute Magnitude ◽  
Atmospheric Parameters ◽  
Spectroscopic Binary ◽  
Short Period ◽  
Period System

The recent discovery that the cool DA white dwarf L870-2 (EG11, WD0135-052) is a double-lined spectroscopic binary composed of a detached pair of DA white dwarfs (Saffer, Liebert, and Olszewski 1988, SLO hereafter) has raised some challenging problems for stellar evolution theories of such binary systems. One first important step in the understanding of this short-period system is to establish the atmospheric parameters of each component. SLO have argued from previous determinations of the effective temperature and absolute magnitude of the system, and also from their own study of the composite Hα profile, that the two components should be similar. We wish here to reexamine this assertion by taking a new look at the constraints on the two components brought about by the available observational data.

The Hertzsprung-Russell diagram

1961 ◽  
Vol 260 (1301) ◽  
pp. 175-182
Keyword(s):  
Surface Brightness ◽  
Absolute Magnitude ◽  
Black Body ◽  
Colour Index ◽  
Similar Material ◽  
Initial Composition ◽  
Evolutionary Time ◽  
Horizontal Scale ◽  
Bolometric Correction ◽  
Stellar Masses

The theory of stellar evolution aims at predicting the luminosity L and radius R of a star as a function of its mass M , its initial composition, and its age. As the time scales are so long, comparison with observation must necessarily be indirect. A convenient method is to select clusters of stars, all born from similar material and at times close together compared with the evolutionary time scale, leaving just the mass as a parameter. However, the paucity of well-determined stellar masses forces us to eliminate the mass between the ( M, L ) and ( M, R ) relations. The ( L, R ) relation is studied indirectly by introducing the effective temperature T e , defined by L = (¼ acT 4 e ) (4 πR 2 ), where c is the velocity of light, and a the stefan-Boltzmann constant. Thus T e is the temperature of a black body having the same surface brightness as the star. The theorist’s ‘Hertzsprung-Russell diagram’ is a plot of log T e on a horizontal scale, increasing to the left, against log ( L/L ʘ ), where L ʘ is the solar luminosity. The observer’s diagram is a plot of V , the absolute magnitude in the visual waveband, against the colour index ( B ─ V ), where B is the blue magnitude. The transformation of one diagram into the other by means of the bolometric correction and the T e , ( B ─ V relation is still subject to considerable uncertainties at the extremes of high and low T e .

scholarly journals Three-Dimensional Representation of A0–G5 Stars

1973 ◽  
Vol 54 ◽  
pp. 117-119 ◽  
Author(s):  
B. Hauck
Keyword(s):  
Spectral Type ◽  
Effective Temperature ◽  
Three Dimensional ◽  
Absolute Magnitude ◽  
Dimensional Representation ◽  
Three Dimensional Representation ◽  
The Absolute

It is possible to obtain for the stars of the spectral type included between A0 and G5 three parameters respectively correlated with the effective temperature, the luminosity and the blanketing. A method to determine the absolute magnitude is given.

scholarly journals MWC 300: A Runaway Hypergiant

1986 ◽  
Vol 116 ◽  
pp. 248-248 ◽  
Author(s):  
B. Wolf ◽  
O. Stahl
Keyword(s):  
Galactic Plane ◽  
Binary Star ◽  
Supernova Explosion ◽  
Absolute Magnitude ◽  
Magellanic Clouds ◽  
Circumstellar Dust ◽  
Dust Shell ◽  
Visual Magnitude ◽  
Bolometric Correction ◽  
Binary Star System

We analysed highly resolved CASPEC spectra with a high S/N-ratio of the peculiar emission-line B-star MWC 300, which is surrounded by a circumstellar dust shell. These high quality spectra enabled us to study the photospheric spectrum of MWC 300. By comparing the absorption spectrum of MWC 300 with the ones of early B supergiants we found a close resemblance with the B1 hypergiant HD 169454. We also found luminosity sensitive fluorescence lines of Fe III 115 and 117 both in MWC 300 and in the most luminous stars of our sample, confirming the hypergiant nature of MWC 300. We estimated an absolute visual magnitude Mv = −8 for MWC 300. Assuming a bolometric correction of B.C. = −1.5 mag we derive Mbol = −9.5. This shows that MWC 300 is very similar to the B e supergiants of the Magellanic Clouds. From its absolute magnitude we derive a distance of z = 560 pc from the galactic plane. It is conjectured that MWC 300 is a runaway hypergiant, released via a supernova explosion in a very massive binary star system.

scholarly journals Two Aspects of Using Hipparcos Data for Studying Multiperiodic Stellar Pulsations

2000 ◽  
Vol 176 ◽  
pp. 46-49
Author(s):  
M. Jerzykiewicz
Keyword(s):  
Effective Temperature ◽  
Hydrogen Burning ◽  
Stellar Pulsations ◽  
Scuti Star ◽  
Frequency Ratios ◽  
Hipparcos Parallax ◽  
Multicolor Photometry ◽  
Hr Diagram

AbstractTwo aspects of using Hipparcos data for studying multiperiodic stellar pulsations involve (1) deriving frequencies of multiperiodic pulsators from Hipparcos Epoch Photometry, and (2) using Hipparcos parallaxes together with other data, such as the frequencies, frequency ratios and multicolor photometry, to identify pulsation modes. Details are examined by looking at the δ Scuti star DK Virginis. From Hipparcos Epoch Photometry, two frequencies are derived. These frequencies are then verified by showing that they also fit all available ground-based observations of the star. In addition, Hipparcos parallax and a photometric effective temperature are used to compare the position of DK Vir in the HR diagram with evolutionary tracks. The star turns out to be at the end of core-hydrogen-burning stage of its evolution or slightly beyond, with a mass of 2.2 M⊙, or somewhat smaller. The observed frequencies indicate that the two detected modes are p3 and p2, while the relatively large photometric amplitudes imply ℓ ≲ 2.

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