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.

scholarly journals Sakurai’s Object: Constraints from its Variability?

1998 ◽  
Vol 11 (1) ◽  
pp. 360-360
Author(s):  
T. Gautschy ◽  
H.W. Duerbeck ◽  
A.M. Van Genderen ◽  
S. Benetti
Keyword(s):  
Cooling Rate ◽  
Nuclear Energy ◽  
Stability Analyses ◽  
The Past ◽  
Stellar Pulsations ◽  
First Results ◽  
Effective Temperatures ◽  
Stellar Envelopes ◽  
Light Variability ◽  
Hr Diagram

The peculiar outburst of the star baptized Sakurai’s Object (SO) is a conceivable example of a late He shell flash in a post-AGB object. The new source of nuclear energy forces such objects toward high luminosities and eventually low effective temperatures; they cross the HR diagram in a comparable fashion as FG Sge did in the past - i.e., they move noticeably on the HR diagram on human timescales. From monitoring campaigns of SO during the last year, first estimates of its cooling rate were derived and in particular cyclic light variability was established. We present first results from attempts to model stellar envelopes appropriate for SO. As we hypothesize the light variability to be attributable to stellar pulsations, we aim at constraining the basic stellar parameters based on stability analyses of our envelope models. Radial, nonadiabatic stability computations provided predictions of the modal content which should be observable as SO evolves. The particular components in such mode spectra of SO as they are to appear in the coming years should indeed help to constrain basic stellar parameters such as mass and luminosity.

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 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.

scholarly journals Ultraviolet Colors of Subdwarf O Stars

1978 ◽  
Vol 80 ◽  
pp. 125-128
Author(s):  
Paul R. Wesselius
Keyword(s):  
Effective Temperature ◽  
Planetary Nebulae ◽  
Central Stars ◽  
Absolute Luminosity ◽  
Hr Diagram

The group of subdwarf O stars consisting of field stars and some central stars of old planetary nebulae does occupy an intresting place in the HR diagram. Greenstein and Sargent (1974) have tried to establish this place, and conclude that especially the hottest ones need ultraviolet data to improve the values of effective temperature and absolute luminosity.

scholarly journals ON THE NATURE OF THE HADS STAR V2455 CYG

2019 ◽  
Vol 55 (2) ◽  
pp. 193-202
Author(s):  
J. H. Peña ◽  
A. Rentería ◽  
C. Villarreal ◽  
D. S. Piña
Keyword(s):  
Secular Variation ◽  
Effective Temperature ◽  
High Amplitude ◽  
Ccd Cameras ◽  
Photoelectric Photometry ◽  
Maximum Light ◽  
San Pedro ◽  
Scuti Star ◽  
Delta Scuti Star ◽  
Delta Scuti

Using uvby − β photoelectric photometry obtained with the 0.84 m telescope of the Observatorio Astrónomico Nacional de San Pedro Mártir, México, we determined some of the physical characteristics, such as effective temperature and surface gravity of the high amplitude Delta Scuti star V2455 Cyg (=HD 204615). Newly determined times of maximum light gathered at the Observatorio Astrónomico Nacional de Tonantzintla, México with small 10 inch telescopes equipped with CCD cameras were combined with times of maxima in the literature, and used to study the secular variation of the pulsational period of the star.

scholarly journals Evolutionary study of the Be star 28 Tau

2010 ◽  
Vol 6 (S272) ◽  
pp. 274-275
Author(s):  
Nazhatulshima Ahmad ◽  
Mohd. Zambri Zainuddin ◽  
Mohd. Sahar Yahya ◽  
Peter P. Eggleton ◽  
Hakim L. Malasan
Keyword(s):  
Critical Velocity ◽  
Effective Temperature ◽  
Main Sequence ◽  
Evolutionary Model ◽  
Rotation Velocity ◽  
Photometric Data ◽  
Rapid Rotation ◽  
Evolutionary Study ◽  
Be Star ◽  
Hr Diagram

AbstractWe present an evolutionary study of 28 Tau, a Be star, in connection with its rapid rotation. The photometric data during the absence of its envelope in 1921 have been used to determine the effective temperature and luminosity of the star at the main sequence of the HR diagram. From an evolutionary model, we found that the mass and radius of the star are about 3.2 M⊙ and 3.2 R⊙ respectively. The equatorial rotation velocity of the star, νe found to be close to its critical velocity, νcr where νe/νcr ≃ 0.87.

STELLAR PULSATIONS ACROSS THE HR DIAGRAM: Part II

1996 ◽  
Vol 34 (1) ◽  
pp. 551-606 ◽  
Author(s):  
Alfred Gautschy ◽  
Hideyuki Saio
Keyword(s):  
Stellar Pulsations ◽  
Hr Diagram

scholarly journals Hd 24975: A New Delta Scuti Star? (Or A Mild Ap Star with Short Photometric Variations?)

1986 ◽  
Vol 90 ◽  
pp. 253-256
Author(s):  
C. Megessier ◽  
P. North ◽  
M. Burnet
Keyword(s):  
Clear Correlation ◽  
Comparison Star ◽  
Instability Strip ◽  
Precise Location ◽  
Short Period ◽  
Scuti Star ◽  
Delta Scuti Star ◽  
Delta Scuti ◽  
Ap Stars ◽  
Hr Diagram

Looking in the literature for short period variations of Ap stars, we found the puzzling case of HD 24975. Used as a comparison star by Weiss (1978), it had been found then to present variations with a peak-to-peak amplitude of 0.01 in U, B and V with a period of about 45mn, but with no clear correlation between the three passbands.HD 24975 has the same spectral type A2 as 21 Com which seems to present photometric variations with P ⋍ 31mn and Δ V < 0,02m (Percy, 1973, 1975). Both stars are near the blue edge of the δ Scuti instability strip in the HR diagram. The lack of photo metric data, however, prevented the precise location of HD 24975 from being found on the HR diagram.

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.

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