Log Teff Research Articles

Red Variables

This paper will be concerned with those variables lying on the cool side of the cepheid strip in the region of the HR diagram occupied by the red giant and supergiant stars. The blue edge of the red variable region for old disk population stars has been found by Eggen (1973b) to be at (R-I)K˜ 0.9 (log Teff˜ 3.53). According to Eggen (1973a, 1973b), all giant stars cooler than this vary, although the amplitude is very small (ΔV~0.2 mag) near the blue edge. In the halo population the blue edge is considerably hotter at (R-I)K˜ 0.5 (log Teff˜ 3.62). On the other hand, some small amplitude red variables (eg. R Dor, AK Hya, IQ Her) have been found at the low temperatures (RK-RK > 1.6) where large amplitude red (Mira) variables exist. From these results, it appears that the position of the blue edge deoends on some unknown stellar parameter(s). Auman (1971) has suggested that the helium abundance may be involved.

Advanced Evolution in Globular Clusters. the Ultraviolet-Bright Stars in Eight Globular Clusters

view Abstract Citations (66) References (64) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Advanced Evolution in Globular Clusters. the Ultraviolet-Bright Stars in Eight Globular Clusters Zinn, Robert Abstract Thirty-eight ultraviolet-bright stars-i.e., stars that are brighter than the horizontal branch (HB) stars and bluer than the giant branch stars-in the globular clusters M3, M10, M13, M15, M53, M92, NGC 4147, and NGC 5466 have been observed spectroscopically at 130 A mm -`. Radial-velocity measurements indicate that 15 of these stars are cluster members. The radial velocity of NGC 5466 (+115 t 4 km ) was measured from the spectrograms of seven red giants. It is suggested that Mayall's radial velocity for M53 should be revised to -89 km s '. The effective temperatures of the ultraviolet-bright stars and the Cepheid variables with periods longer than 1 day have been derived from their broad-band colors or taken from the few published analyses. Their luminosities have been derived from the distance moduli adopted for the clusters and from bolometric corrections taken from the literature. A detailed comparison is made between post-HB evolutionary tracks and the positions of the ultraviolet- bright stars (including the Cepheid variables) in the H-R diagram. For the most part, the theoretical tracks provide adequate explanations for the ultraviolet-bright stars. This comparison has led to the following conclusions: (i) As predicted by the theory, a strong correlation exists between the presence of supra-horizontalbranch stars in a cluster and the presence of HB stars hotter than log = 4.1. (ii) The theoretical relationship between the blueness of the HB and the luminosities of the ultraviolet-bright stars with log LIL0 > 2.3 is supported by observation. (iii) The rare Population II Cepheid variables that have periods between 4 and 12 days are most likely stars that have evolved from the blue end of the HB (log Teff > 4.1). Therefore, their paucity is probably caused by the paucity of hot HB stars. Subject headings: Cepheids and W Virginis stars - globular clusters - stellar evolution Publication: The Astrophysical Journal Pub Date: November 1974 DOI: 10.1086/153197 Bibcode: 1974ApJ...193..593Z full text sources ADS | data products SIMBAD (38)

The Ages of Stars in the Neighbourhood of the Sun

This introductory paper is divided into two sections.In the first section a short summary is given of the IAU Colloquium No. 17 on Stellar Ages held in Paris-Meudon Observatory in September 1972. The summary will concern particularly those subjects relevant to this Joint Discussion.In the second part the ages of nearby stars located in the subgiant region of the (log Teff, Mbol) diagram are discussed.

The Evolutionary Status of the Blue Halo Stars

view Abstract Citations (139) References (114) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The evolutionary status of the blue halo stars. Newell, E. B. Abstract This paper presents a new approach to the observational study of the advanced evolution of Population II stars. The discussion is based on the use of the (log g, log Th )-diagram as an H-R diagram. In particular, advantage is taken of our ability to make direct comparisons, in the (log g, log Te )-plane, between observations of individual field and cluster stars and the predictions of interior theory. The distribution of the high-latitude faint blue stars over T6ff is first studied on the basis of their distribution in the [(U - B), (B - V)]-diagram. It is shown that the principal stellar sequence of the latter distribution is not uniform but displays two gaps, at colors corresponding to log Teff 4.11 (gap 1) and log Teff 4.33 (gap 2). Because globular-cluster blue-horizontal- branch sequences show significant structure at similar values of Teff it is suggested that the gaps are a horizontal-branch phenomenon. The narrow-band spectrophotometric techniques used previously to study blue-horizontal- branch (BHB) stars in globular clusters are applied to a sample of high-velocity and high4atitude faint blue stars. The atmospheric parameters g and Teff, together with the interstellar reddening, are derived for individual program stars by comparing the observed narrow-band colors with the emergent fluxes computed for a grid of approximate line-blanketed model atmospheres. An investigation of the (log g, log Th )-distribution of globular cluster and field blue stars, together with the properties of gaps 1 and 2, leads to a luminosity-independent (log g, log Teff)classification for blue halo stars. This classification, which is based on g and Teff values taken from the literature and from the present study, encompasses blue halo stars in the temperature range 4.48 > log Teff > 3.86. Five subgroups, designated HL, A, BC, D, and wd are isolated. Comparison of the observed stellar distribution in the (log g, log Te )-diagram with existing evolutionary tracks shows that current theoretical concepts of the advanced evolution of Population II stars can explain the majority of blue halo stars. The group D stars (most of which would be classified spectroscopically as subdwarf B) are difficult to fit into the evolutionary scheme. The comparison between observation and theory leads also to a tentative explanation for the gaps observed in the field star two-color diagram. This explanation depends on the sensitivity of the evolutionary behavior of low-mass (0.50 o < 0.60 e) horizontal-branch stars to the amount of matter in their hydrogen-rich envelopes. If this hypothesis is correct it indicates that the observed gap positions, once properly calibrated, can be used to study the physical and chemical properties of the blue halo stars. Subject headings: faint blue stars - globular clusters - horizontal-branch stars - stellar evolution Publication: The Astrophysical Journal Supplement Series Pub Date: August 1973 DOI: 10.1086/190279 Bibcode: 1973ApJS...26...37N full text sources ADS | data products SIMBAD (236) GCPD (1)

The (log g, log Teff)-Diagram, a Fundamental HR-Diagram

Spectroscopic and photometric parallaxes are based on the assumption that to each point in the relevant region of (g, Teff, a)-space there corresponds a unique mass. The implications of a breakdown in this assumption are discussed briefly and an alternative approach to problems that traditionally have required spectroscopic or photometric parallaxes is presented. This alternative approach involves the use of the (log g, log Teff)-diagram as an HR-diagram.

Production of Planetary Nebulae

For various reasons, we have been studying evolution in the pre-white dwarf phase at Rochester. Our attention to the relevance of this work to planetary nebulae came as a result of calculations of the evolution of a one solar-mass iron star carried out at Rochester by S. Vila. Here the neutrino processes drive the peak luminosity to log L/L⊙=4·26, at an effective temperature log Teff=5·53. Although these models are brighter than 100 L⊙ for 500 000 years, they are brighter than 1000 L⊙ for 4000 years, and exceed 10000 L⊙ for 900 years. We are therefore near the luminosity of the planetary-nebula nuclei, but considerably hotter, for a period of the order of the planetary lifetimes. Except for the temperature discrepancy, these models are in rough agreement with the observationally determined evolutionary sequence found by O'Dell (1963) and by Harman and Seaton (1964) and Seaton (1966).