scholarly journals Low-Level Stellar Variability

1993 ◽  
Vol 137 ◽  
pp. 693-707 ◽  
Author(s):  
M. Grenon
Keyword(s):  
Spectral Type ◽  
Effective Temperature ◽  
Light Curves ◽  
Luminosity Class ◽  
Low Level ◽  
Variability Level ◽  
Hr Diagram

AbstractThe capability of ground-based photometry to detect and monitor low-level stellar variations is discussed in the particular case of amplitudes in the range of few magnitudes to few percent. The technical and atmospherical constraints are briefly recalled. The variability level of the so-called constant stars is discussed as function of the spectral type, the luminosity class and the effective temperature. The photometric aspects of the Hipparcos mission are presented here since this satellite allows a systematic detection of microvariables and the obtention of light curves across the whole HR-diagram with an unprecedented efficiency.

The Eclipsing Binary WX Eridani

1979 ◽  
Vol 46 ◽  
pp. 385
Author(s):  
M.B.K. Sarma ◽  
K.D. Abhankar
Keyword(s):  
Light Curve ◽  
Spectral Type ◽  
Orbital Period ◽  
Primary Component ◽  
Light Curves ◽  
Absorption Feature ◽  
Primary Star ◽  
Eclipsing Binary ◽  
The Times ◽  
Phase Angles

AbstractThe Algol-type eclipsing binary WX Eridani was observed on 21 nights on the 48-inch telescope of the Japal-Rangapur Observatory during 1973-75 in B and V colours. An improved period of P = 0.82327038 days was obtained from the analysis of the times of five primary minima. An absorption feature between phase angles 50-80, 100-130, 230-260 and 280-310 was present in the light curves. The analysis of the light curves indicated the eclipses to be grazing with primary to be transit and secondary, an occultation. Elements derived from the solution of the light curve using Russel-Merrill method are given. From comparison of the fractional radii with Roche lobes, it is concluded that none of the components have filled their respective lobes but the primary star seems to be evolving. The spectral type of the primary component was estimated to be F3 and is found to be pulsating with two periods equal to one-fifth and one-sixth of the orbital period.

scholarly journals Observed Relations Between Physical Properties and MK Classification as Functions of Metal Abundance for F5-K4 Stars

1976 ◽  
Vol 72 ◽  
pp. 75-78
Author(s):  
M. Grenon
Keyword(s):  
Physical Properties ◽  
Spectral Range ◽  
Spectral Type ◽  
Photometric System ◽  
Luminosity Class ◽  
Empirical Relations ◽  
Metal Abundance ◽  
Systematic Effects ◽  
The Absolute ◽  
Absolute Magnitudes

The Geneva photometric system has been calibrated in terms of [M/H], θeff, Mv in the spectral range F5 to K4. As the spectral type is a datum generally available, we derive empirical relations showing the coupling of θeff and [M/H] at given spectral type and luminosity class. Similar relations are offered for the absolute magnitudes and provide a more accurate means for deriving spectroscopic parallaxes. Systematic effects on the estimation of the luminosity class are also shown.

scholarly journals Interferometric Investigations of Eclipsing Binaries as a Key to an Improved Distance Scale

2006 ◽  
Vol 2 (S240) ◽  
pp. 496-498
Author(s):  
K. Shabun ◽  
A. Richichi ◽  
U. Munari ◽  
A. Siviero ◽  
B. Pacsysnki
Keyword(s):  
Spectral Type ◽  
Effective Temperature ◽  
Binary Systems ◽  
Angular Separation ◽  
Eclipsing Binaries ◽  
Multiple Systems ◽  
Long Baseline ◽  
Global Calibration ◽  
Empirical Calibration ◽  
Full Solution

AbstractBinary and multiple systems constitute one of the main tools for obtaining fundamental stellar parameters, such as masses, radii, effective temperatures and distances. One especially fortunate, and at the same time rare, occurrence is that of double-lined eclipsing binaries with well-detached components. In this special case, it is possible to obtain a full solution of all orbital and stellar parameters, with the exception of the effective temperature of one star, which is normally estimated from spectral type or derived from atmospheric analysis of the spectrum. Long-baseline interferometry at facilities such as the ESO VLTI is beginning to have the capability to measure directly the angular separation and the angular diameter of some selected eclipsing binary systems, and we have proposed such observations with the AMBER instrument. In particular, we aim at deriving directly the effective temperature of at least one of the components in the proposed system, thereby avoiding any assumptions in the global solution through the Wilson–Devinney method. We will also obtain an independent check of the results of this latter method for the distance to the system. This represents the first step towards a global calibration of eclipsing binaries as distance indicators. Our results will also contribute to the effective temperature scale for hot stars. The extension of this approach to a wider sample of eclipsing binaries could provide an independent method to assess the distance to the LMC. The observations will extend accurate empirical calibration to spectral type O9 – B0.

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 Hipparcos Positions of B/Be Stars on the HR Diagram

2000 ◽  
Vol 175 ◽  
pp. 117-128 ◽  
Author(s):  
Danielle Briot ◽  
Noel Robichon
Keyword(s):  
Spectral Type ◽  
Rotational Velocity ◽  
Absolute Magnitude ◽  
Be Stars ◽  
Class V ◽  
B Stars ◽  
Luminosity Class ◽  
The Mean ◽  
Absolute Magnitudes ◽  
Hipparcos Parallax

AbstractAbsolute magnitudes of Be and B stars are computed for each spectral type and luminosity class V and IV, using the Hipparcos parallax measurements. Some simulations have been carried out in order to estimate the effects which could bias the mean absolute magnitude calculations. As a result, only stars with σπ/π < 15% have been used. A first result is that B stars are fainter than previous estimations by about 0.5 magnitude on average. We then observe that on average Be stars are brighter than B stars of the same spectral type and this over-luminosity increases with the spectral type. A possible interpretation is proposed based on the fact that the rotational velocity of the late Be stars is near the critical rotational velocity.

scholarly journals Contact binaries of spectral type O

1979 ◽  
Vol 83 ◽  
pp. 265-269 ◽  
Author(s):  
Kam-Ching Leung ◽  
Donald P. Schneider
Keyword(s):  
Direct Measurement ◽  
Spectral Type ◽  
Time Scale ◽  
Massive Stars ◽  
Eclipsing Binaries ◽  
Light Curves ◽  
Consistent Model ◽  
Contact Binaries ◽  
Primary Attraction ◽  
V729 Cyg

The eclipsing binaries UW CMa, AO Cas, and V729 Cyg have been systems of great interest for over fifty years. The light curves are complex and suffer significant changes on a time scale of months, but the primary attraction of these systems is that both components have O-type spectra; thus they present us with some of the few possibilities for direct measurement of absolute dimensions of very massive stars. Much effort has been expended on these systems, but no really consistent model has emerged.

scholarly journals The Absolute Calibration of the HR Diagram: Fundamental Effective Temperatures and Bolometric Corrections

1978 ◽  
Vol 80 ◽  
pp. 65-76 ◽  
Author(s):  
D. S. Hayes
Keyword(s):  
Spectral Type ◽  
Absolute Calibration ◽  
Effective Temperatures ◽  
The Absolute ◽  
Hr Diagram

Scales of fundamental bolometric connections (B.C.) and effective temperatures (Teff) as a function of spectral type or color are necessary for the comparison of observations and theory in the HR diagram.

scholarly journals Some Uses of Spectral Classification in HR Diagrams

1978 ◽  
Vol 80 ◽  
pp. 3-4
Author(s):  
W.W. Morgan
Keyword(s):  
Class Diagram ◽  
Two Dimensional ◽  
Spectral Classification ◽  
Luminosity Class ◽  
Local Perturbations ◽  
The Future ◽  
Continuity Of The Spectrum ◽  
Unlimited Variety ◽  
Morphological System ◽  
Hr Diagram

The MK spectrum-luminosity class diagram (S-LC diagram) between types 09 and G0 is a two-dimensional array containing approximately 100–150 information elements; each information element is a single cell denoted by a spectral type and a luminosity class. These individual, non-dimensional cells (i.e. AO III) can be considered as carriers of observational information toward the HR diagram. Some categories of peculiar spectra (for example, spectra resembling that of the “silicon star” θ Aur) can be attached to certain cells, and can be considered as local perturbations upon the underlying continuity of the spectrum-luminosity class sequences. By such a procedure, the S-LC diagram cells can be considered open-ended, in that progressive additions to the cells can be made indefinitely into the future. Such a procedure can incorporate successfully an unlimited variety of “normal” and “peculiar” categories of spectra - both those already known and those still to be discovered. A morphological system that is unitary thus comes into existence - a system of considerable astrophysical interest. The translation of the detailed language of this system into that of the classical HR diagram is a task for the future.

scholarly journals Mass loss from early-type stars

1970 ◽  
Vol 36 ◽  
pp. 209-212
Author(s):  
J. B. Hutchings
Keyword(s):  
Mass Loss ◽  
Spectral Type ◽  
Stellar Evolution ◽  
Early Type ◽  
High Luminosity ◽  
Spectroscopic Evidence ◽  
Ob Stars ◽  
Early Type Stars ◽  
Very High ◽  
Hr Diagram

Following the detailed study of four very high luminosity OB stars, a survey has been made for spectroscopic evidence of mass loss in a number of early-type supergiants. A list of spectroscopic criteria is given and the mass loss estimates for 24 stars plotted on the HR diagram. The dependence of the phenomenon on spectral type and luminosity is discussed as well as its significance in terms of stellar evolution.

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