Grids for the determination of effective temperature and surface gravity of B, A and F stars using uvby β photometry

Moon, T. T.; Dworetsky, M. M.

doi:10.1093/mnras/217.2.305

Cited by 395 publications

(319 citation statements)

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“…We have chosen: (1) de Jager & Nieuwenhuijzen (1987) because it was used by Cranmer (2005) to discuss the distribution of rotational velocities of Be stars; (2) the calibration of the ubvy−Strömgren photometric indices given by Moon & Dworetsky (1985) and revisited by Napiwotzki et al (1993); and (3) the effective temperatures derived from fitted visible spectral energy distributions by Adelman et al (2002), Fitzpatrick & Massa (2005), and Nieva (2013). In …”

Section: Appendix A: Fundamental Parametersmentioning

confidence: 99%

Critical study of the distribution of rotational velocities of Be stars

Zorec

Frémat

Souza

et al. 2016

A&A

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Context. Among intermediate-mass and massive stars, Be stars are the fastest rotators in the main sequence (MS) and, as such, these stars are a cornerstone to validate models of structure and evolution of rotating stars. Several phenomena, however, induce under-or overestimations either of their apparent Vsin i, or true velocity V. Aims. In the present contribution we aim at obtaining distributions of true rotational velocities corrected for systematic effects induced by the rapid rotation itself, macroturbulent velocities, and binarity. Methods. We study a set of 233 Be stars by assuming they have inclination angles distributed at random. We critically discuss the methods of Cranmer and Lucy-Richardson, which enable us to transform a distribution of projected velocities into another distribution of true rotational velocities, where the gravitational darkening effect on the Vsin i parameter is considered in different ways. We conclude that iterative algorithm by Lucy-Richardson responds at best to the purposes of the present work, but it requires a thorough determination of the stellar fundamental parameters. Results. We conclude that once the mode of ratios of the true velocities of Be stars attains the value V/V c 0.77 in the main-sequence (MS) evolutionary phase, it remains unchanged up to the end of the MS lifespan. The statistical corrections found on the distribution of ratios V/V c for overestimations of Vsin i, due to macroturbulent motions and binarity, produce a shift of this distribution toward lower values of V/V c when Be stars in all MS evolutionary stages are considered together. The mode of the final distribution obtained is at V/V c 0.65. This distribution has a nearly symmetric distribution and shows that the Be phenomenon is characterized by a wide range of true velocity ratios 0.3 V/V c 0.95. It thus suggests that the probability that Be stars are critical rotators is extremely low. Conclusions. The corrections attempted in the present work represent an initial step to infer indications about the nature of the Be-star surface rotation that will be studied in the second paper of this series.

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Section: Appendix A: Fundamental Parametersmentioning

confidence: 99%

Critical study of the distribution of rotational velocities of Be stars

Zorec

Frémat

Souza

et al. 2016

A&A

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“…For stars for which Strömgren uvbyβ photometry is available, we have computed an effective temperature using the FORTRAN code "UVBYBETANEW" of Napiwotzki, Schönberner & Wenske (1993), which is in turn based mainly on the calibrations of Moon & Dworetsky (1985). When the star has colours near the boundary of different calibrations (for example near A0), we have computed the temperature using both calibrations.…”

Section: Photometrymentioning

confidence: 99%

Searching for links between magnetic fields and stellar evolution

Landstreet¹,

Bagnulo²,

Andretta³

et al. 2007

A&A

181

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Context. The evolution of magnetic fields in Ap stars during the main sequence phase is presently mostly unconstrained by observation because of the difficulty of assigning accurate ages to known field Ap stars. Aims. We are carrying out a large survey of magnetic fields in cluster Ap stars with the goal of obtaining a sample of these stars with well-determined ages. In this paper we analyse the information available from the survey as it currently stands. Methods. We select from the available observational sample the stars that are probably (1) cluster or association members and (2) magnetic Ap stars. For the stars in this subsample we determine the fundamental parameters T eff , L/L , and M/M . With these data and the cluster ages we assign both absolute age and fractional age (the fraction of the main sequence lifetime completed). For this purpose we have derived new bolometric corrections for Ap stars. Results. Magnetic fields are present at the surfaces of Ap stars from the ZAMS to the TAMS. Statistically for the stars with M > 3 M the fields decline with advancing age approximately as expected from flux conservation together with increased stellar radius, or perhaps even faster than this rate, on a time scale of about 3 × 10 7 yr. In contrast, lower mass stars show no compelling evidence for field decrease even on a timescale of several times 10 8 yr. Conclusions. Study of magnetic cluster stars is now a powerful tool for obtaining constraints on evolution of Ap stars through the main sequence. Enlarging the sample of known cluster magnetic stars, and obtaining more precise rms fields, will help to clarify the results obtained so far. Further field observations are in progress.

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“…In view of these apparent differences in the evolutionary state between magnetic stars in different mass domains, we decided to group our sample in two sub-samples with one containing lower mass stars with M < 3 M (57 stars in all) and another one with M > 3 M (33 stars). The effective temperatures of the stars of both sub-samples have been determined from photometric data in the Geneva system through the calibration of Künzli et al (1997) corrected according to the prescription of North (1998), or, when no Geneva photometry was available, in the Strömgren system, applying the calibration of Moon & Dworetsky (1985), revised by Napiwotzki et al (1993). The luminosities have been obtained by taking into account the bolometric corrections measured by Lanz (1984).…”

Section: Basic Datamentioning

confidence: 99%

Evolution of magnetic fields in stars across the upper main sequence: II. Observed distribution of the magnetic field geometry

Hubrig¹,

North

Schöller

2007

Astron Nachr

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We re-discuss the evolutionary state of upper main sequence magnetic stars using a sample of Ap and Bp stars with accurate Hipparcos parallaxes and definitely determined longitudinal magnetic fields. We confirm our previous results obtained from the study of Ap and Bp stars with accurate measurements of the mean magnetic field modulus and mean quadratic magnetic fields that magnetic stars of mass M < 3 M are concentrated towards the centre of the main-sequence band. In contrast, stars with masses M > 3 M seem to be concentrated closer to the ZAMS. The study of a few known members of nearby open clusters with accurate Hipparcos parallaxes confirms these conclusions. Stronger magnetic fields tend to be found in hotter, younger and more massive stars, as well as in stars with shorter rotation periods. The longest rotation periods are found only in stars which spent already more than 40% of their main sequence life, in the mass domain between 1.8 and 3 M and with log g values ranging from 3.80 to 4.13. No evidence is found for any loss of angular momentum during the main-sequence life. The magnetic flux remains constant over the stellar life time on the main sequence. An excess of stars with large obliquities β is detected in both higher and lower mass stars. It is quite possible that the angle β becomes close to 0 • in slower rotating stars of mass M > 3 M too, analog to the behaviour of angles β in slowly rotating stars of M < 3 M . The obliquity angle distribution as inferred from the distribution of r-values appears random at the time magnetic stars become observable on the H-R diagram. After quite a short time spent on the main sequence, the obliquity angle β tends to reach values close to either 90 • or 0 • for M < 3 M . The evolution of the obliquity angle β seems to be somewhat different for low and high mass stars. While we find a strong hint for an increase of β with the elapsed time on the main sequence for stars with M > 3 M , no similar trend is found for stars with M < 3 M . However, the predominance of high values of β at advanced ages in these stars is notable. As the physics governing the processes taking place in magnetised atmospheres remains poorly understood, magnetic field properties have to be considered in the framework of dynamo or fossil field theories.

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Grids for the determination of effective temperature and surface gravity of B, A and F stars using uvby β photometry

Cited by 395 publications

References 0 publications

Critical study of the distribution of rotational velocities of Be stars

Critical study of the distribution of rotational velocities of Be stars

Searching for links between magnetic fields and stellar evolution

Evolution of magnetic fields in stars across the upper main sequence: II. Observed distribution of the magnetic field geometry

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