scholarly journals A determination of the characteristics of Cepheids from B-type companions

1981 ◽  
Vol 59 ◽  
pp. 389-395
Author(s):  
D.H. McNamara ◽  
Kent A. Feltz

Photometry (uvbyβ) of five cepheids with B-type companions has been utilized to derive the spectral types and apparent magnitudes of the companions. By utilizing the period-luminosity relation it is possible to estimate the absolute magnitudes of the companions since the differences in magnitude between the companions and cepheids are known. The spectral types and absolute magnitudes of the B-type components indicate they are all evolved from the zero-age main sequence. By utilizing the ages of the B stars we can derive the ages of the cepheids under the assumptions that both stars of a binary were formed at the same time and the cepheids are more evolved than their B components. A period-age relation of the form log tage = 8.60 - 0.83 log P is found. Minimum masses of the cepheids can also be estimated from the data. No evidence of large mass loss is evident in the intermediate-band photometry of cepheids.

1970 ◽  
Vol 38 ◽  
pp. 205-208 ◽  
Author(s):  
W. Becker ◽  
R. Fenkart

The galactic clusters and the exciting stars of H II regions are powerful indicators of the spiral structure since these objects lie on or very close to the zero age main sequence (ZAMS). For clusters this behaviour can be confirmed by direct photometric observation. The exciting stars of H II regions are probably so young as not to have evolved from the ZAMS. The coincidence of these objects with the ZAMS indicates that there is little scattering in the absolute magnitudes and, as a consequence, little uncertainty in the determination of distance. This fact reveals itself very distinctly in the case of H II regions, whose exciting stars define the spiral structure considerably better than the stars of the same early spectral types but not connected with H II regions.


1998 ◽  
Vol 11 (1) ◽  
pp. 566-566
Author(s):  
C. Jaschek ◽  
A.E. Gómez

We have analysed the standards of the MK system in the B0-F5 spectral region with the help of Hipparcos parallaxes, using only stars for which the error on the absolute magnitude is ≤ 0.3 mag. The sample stars (about one hundred) were scrutinized for companions and for interstellar extinction. We find that the main sequence is a wide band and that, although in general giants and dwarfs have different absolute magnitudes, the separation between luminosity class V and III is not clear. We conclude that there is no strict relation between luminosity class and absolute magnitude. The relation is only a statistical one and has a large intrinsic dispersion. We have analysed similarly the system of standards defined by Garrison and Gray (1994) separating low and high rotational velocity standards. We find similar effects as in the original MK system.


1995 ◽  
Vol 10 ◽  
pp. 399-402
Author(s):  
A.E. Gómez ◽  
C. Turon

The Hertzprung-Russel (HR) diagram luminosity calibration relies basically on three kinds of data: trigonometric parallaxes, kinematical data (proper motions and radial velocities) and cluster distances obtained by the zero-age main sequence fitting procedure. The most fundamental method to calculate the absolute magnitude is the use of trigonometric parallaxes, but up to now, accurate data only exist for stars contained in a small volume around the sun. Individual absolute magnitudes are obtained using trigonometric parallaxes or photometric and spectroscopic calibrations. In these calibrations the accuracy on the absolute magnitude determination ranges from ±0.m2 in the main sequence to ±0m5 in the giant branch. On the other hand, trigonometric parallaxes, kinematical data or cluster distances have been used to make statistical calibrations of the absolute magnitude. The standard error on the mean absolute magnitude calibrations ranges from ±0m3 to ±0m6 on the mean sequence, from ±0m5 to ±0m7 on thegiant branch and is of about 1mfor supergiants.Future improvements in the absolute magnitude determination will depend on the improvement of the basic data from the ground and space. A brief overview of the new available data is presented. In particular, the analysis of the first 30 months data of the Hipparcos mission (H30) (from the 37 months data of the whole mission) allows to perform a statistical evaluation of the improvements expected in the luminosity determination.


1985 ◽  
Vol 111 ◽  
pp. 479-483
Author(s):  
R. S. Polidan ◽  
J. B. Holberg

Recent results have shed new light on the status of the calibration of absolute stellar fluxes between 912 and 1200 Å. Observations of hot white dwarfs, subdwarfs and planetary nebula nuclei with the Voyager ultraviolet spectrometers provide evidence that the current calibration agrees very well with extrapolations of IUE energy distributions shortwards of 1200 Å. Voyager observations of main sequence B-stars used as flux calibration sources have revealed that many are variable in brightness in the 912–1200 Å region. We conclude there is no current observational motivation for any revision of the 912 to 1200 Å calibration described by Holberg et al. (1982).


2014 ◽  
Vol 564 ◽  
pp. A70 ◽  
Author(s):  
Jiří Krtička
Keyword(s):  

1989 ◽  
Vol 111 ◽  
pp. 121-140
Author(s):  
Allan Sandage

AbstractIt is shown that the intrinsic spread in the absolute magnitudes of the RR Lyrae variables in a given globular cluster can reach 0.5 magnitudes at a given period or at a given color, due to luminosity evolution away from the zero age horizontal (ZAHB). The size of this intrinsic luminosity spread is largest in clusters of the highest metallicity.The absolute magnitude of the ZAHB itself also differs from cluster to cluster as a function of metallicity, being brightest in clusters of the lowest metallicity. Three independent methods of calibrating the ZAHB RR Lyrae luminosities each show a strong variation of MV(RR) with [Fe/H]. The pulsation equation of P<ρ>0.5 = Q(M,Te, L) used with the observed periods, temperatures, and masses of field and of cluster RR Lyraes gives the very steep luminosity-metallicity dependence of dMv(RR)/d[Fe/H] = 0.42. Main sequence fitting of the color-magnitude diagrams of clusters which have modern main-sequence photometry gives a confirming steep slope of 0.39. A summary of Baade-Wesselink MV(RR) values for field stars determined in four independent recent studies also shows a luminosity-metallicity dependence, but less steep with a slope of dMV(RR)/d[Fe/H] = 0.21.Observations show that the magnitude difference between the main sequence turn-off point and the ZAHB in a number of well observed globular clusters is independent of [Fe/H], and has a stable value of dV = 3.54 with a disperion of only 0.1 magnitudes. Using this fact, the absolute magnitude of the main sequence turn-off is determined in any given globular cluster from the observed apparent magnitude of the ZAHB by adopting any particular MV(RR) = f([Fe/H]) calibration.Ages of the clusters are shown to vary with [Fe/H] by amounts that depend upon the slopes of the MV(RR) = f([Fe/H]) calibrations. The calibrations show that there would be a steep dependence of the age on [Fe/H] if MV(RR) does not depend on [Fe/H]. No dependence of age on metallicity exists if the RR Lyrae luminosities depend on [Fe/H] as dMV(RR)/d[Fe/H] = 0.37. If Oxygen is not enhanced as [Fe/H] decreases, the absolute average age of the globular cluster system is 16 Gyr, independent of [Fe/H], using the steep MV(RR)/[Fe/H] calibration that is favored. If Oxygen is enhanced by [O/Fe] = – 0.14 [Fe/H] + 0.40 for [Fe/H] < –1.0, as suggested from the observations of field subdwarfs, then the age of the globular cluster system decreases to 13 Gyr, again independent of [Fe/H], if the RR Lyrae ZAHB luminosities have a metallicity dependence of dMV(RR)/d[Fe/H] = 0.37.


2004 ◽  
Vol 215 ◽  
pp. 199-204 ◽  
Author(s):  
C. Aerts ◽  
R. Scuflaire ◽  
A. Thoul

In this contribution we review the current status of the determination of the rotational frequency in non-radially pulsating B stars, i.e. β Cep stars and slowly pulsating B stars. Considerable progress is currently being made in the understanding of the non-radial oscillations of main-sequence B stars by means of high-temporal, high-spatial resolution spectroscopic time series. This has led to the detection of frequency multiplets, which are interpreted as rotationally splitted non-radial modes and which allow an accurate determination of the surface rotational frequency in some stars. We outline how our future goal, i.e. the derivation of the internal rotation frequency, can be achieved.


1979 ◽  
Vol 83 ◽  
pp. 103-108
Author(s):  
A. B. Underhill ◽  
L. Divan ◽  
V. Doazan ◽  
M.L. Prévot-Burnichon

Angular diameters have been estimated for 18 O and 142 B stars using absolute intermediate-band photometry in the near infrared and they have been combined with integrated fluxes to yield effective temperatures. The effective temperatures of the O stars lie in the range 30000 K to about 47000 K. For a given subtype, the luminosity class I stars have lower effective temperatures than the main-sequence stars by about 1000 K. The absorption-line spectral types of the supergiants of types O and B reflect electron temperatures which are higher than can be maintained by the integrated flux which flows through the stellar atmosphere. Distances have been estimated for all the stars and linear diameters found. The average radius for an 08 to 09.5 supergiant is about 23.3 R⊙; the radii for luminosity class III and Class V O stars lie in the range 6.8 to 10.7⊙ R.


2000 ◽  
Vol 175 ◽  
pp. 632-635
Author(s):  
J.E. Bjorkman ◽  
B.P. Abbott

AbstractUsing the wind-compressed disk model to determine the density and velocity of a rapidly rotating wind, we calculate the 2-D ionization structure and corresponding line profiles. We find that previous estimates of the mass-loss rate based on spherically symmetric models may be a factor of 5–10 too small.


Sign in / Sign up

Export Citation Format

Share Document