scholarly journals On the Hipparcos photometry of chemically peculiar B, A, and F stars

1998 ◽  
Vol 132 (1) ◽  
pp. 93-97 ◽  
Author(s):  
Saul J. Adelman
Keyword(s):  
Chemically Peculiar ◽  
F Stars

scholarly journals A Magnetic Snapshot Survey of F-Type Stars

2020 ◽  
Author(s):  
J M Seach ◽  
S C Marsden ◽  
B D Carter ◽  
C Neiner ◽  
C P Folsom ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Longitudinal Magnetic Field ◽  
Convection Zone ◽  
Stellar Radius ◽  
Spectral Class ◽  
Chemically Peculiar ◽  
Peculiar Stars ◽  
The Mean ◽  
Chemically Peculiar Stars ◽  
F Stars

Abstract We present a spectropolarimetric magnetic snapshot survey of 55 stars which includes 53 F-type stars ranging from spectral types F0 to F9 plus 2 chemically peculiar stars β CrB, and δ Cap. We look for magnetic fields in stars spanning a range of effective temperatures where the transition from fossil to dynamo magnetic fields is believed to occur. High-resolution spectropolarimetry using circularly polarized spectra is used to look for a magnetic detection in the Stokes V profile, determine the mean longitudinal magnetic field (Bl), and to look for correlations with stellar parameters. Surface magnetic fields are detected on 14 F-stars, and present in every spectral class from F3V-F9V ranging in strength from 0.3 ± 0.1 G (36 UMa, F8V) to 8.3 ± 0.9 G (h Dra, F8V). Thus we find photospheric magnetic fields are present in stars as early as spectral type F3V with an outer convection zone thickness less than a few per cent of the stellar radius.

Main Sequence Abundances: Observational Aspects

1988 ◽  
Vol 108 ◽  
pp. 2-2
Author(s):  
Jun Jugaku
Keyword(s):  
Chemical Composition ◽  
Effective Temperature ◽  
Main Sequence ◽  
Theoretical Models ◽  
Current Data ◽  
Main Sequence Stars ◽  
Chemically Peculiar ◽  
Peculiar Stars ◽  
Chemically Peculiar Stars ◽  
F Stars

AbstractAlthough once it was thought that main-sequence stars are remarkably homogeneous with respect to their chemical composition, the upper main-sequence stars (30000 > Te > 7000) show a variaety of chemically peculiar stars besides the so-called normal stars. Those include the Am, Ap, λ Bootis, He-deficient, and He-rich stars. This review summarizes the current data, which are necessary to construct and test the theoretical models of these stars. In the second half of the review we concentrate on Li. In the lower main-sequecnce stars abundances of Li have been determined in hundreds of stars. Some of the remarkable results are: (1) A uniform upper abundance value irrespective of stellar effective temperature, (2) abundance gap in the F stars of the Hyades, and (3) increasing depletion with smaller stellar mass for the Hyades.

scholarly journals Chemically Peculiar A and F Stars with Enhanced s-process and Iron-peak Elements: Stellar Radiative Acceleration at Work

2020 ◽  
Vol 898 (1) ◽  
pp. 28
Author(s):  
Mao-Sheng Xiang ◽  
Hans-Walter Rix ◽  
Yuan-Sen Ting ◽  
Hans-Günter Ludwig ◽  
Johanna Coronado ◽  
...  
Keyword(s):  
Chemically Peculiar ◽  
F Stars ◽  
Radiative Acceleration

scholarly journals On the first δ Sct–roAp hybrid pulsator and the stability of p and g modes in chemically peculiar A/F stars

2020 ◽  
Vol 498 (3) ◽  
pp. 4272-4286
Author(s):  
Simon J Murphy ◽  
Hideyuki Saio ◽  
Masahide Takada-Hidai ◽  
Donald W Kurtz ◽  
Hiromoto Shibahashi ◽  
...  
Keyword(s):  
Polar Field ◽  
Instability Strip ◽  
Magnetic Damping ◽  
Chemically Peculiar ◽  
F Stars ◽  
The Stability ◽  
Ap Stars ◽  
High Overtone ◽  
Rule Out ◽  
Field Strengths

ABSTRACT Strong magnetic fields in chemically peculiar A-type (Ap) stars typically suppress low-overtone pressure modes (p modes) but allow high-overtone p modes to be driven. KIC 11296437 is the first star to show both. We obtained and analysed a Subaru spectrum, from which we show that KIC 11296437 has abundances similar to other magnetic Ap stars, and we estimate a mean magnetic field modulus of 2.8 ± 0.5 kG. The same spectrum rules out a double-lined spectroscopic binary, and we use other techniques to rule out binarity over a wide parameter space, so the two pulsation types originate in one δ Sct–roAp hybrid pulsator. We construct stellar models depleted in helium and demonstrate that helium settling is second to magnetic damping in suppressing low-overtone p modes in Ap stars. We compute the magnetic damping effect for selected p and g modes, and find that modes with frequencies similar to the fundamental mode are driven for polar field strengths ≲4 kG, while other low-overtone p modes are driven for polar field strengths up to ∼1.5 kG. We find that the high-order g modes commonly observed in γ Dor stars are heavily damped by polar fields stronger than 1–4 kG, with the damping being stronger for higher radial orders. We therefore explain the observation that no magnetic Ap stars have been observed as γ Dor stars. We use our helium-depleted models to calculate the δ Sct instability strip for metallic-lined A (Am) stars, and find that driving from a Rosseland mean opacity bump at ∼5 × 104 K caused by the discontinuous H-ionization edge in bound-free opacity explains the observation of δ Sct pulsations in Am stars.

scholarly journals The Boundary between the Magnetic Fields of Ap Stars and the Fields of Solar-type Stars

1991 ◽  
Vol 130 ◽  
pp. 342-346
Author(s):  
John D. Landstreet
Keyword(s):  
Magnetic Fields ◽  
Main Sequence ◽  
Convection Zone ◽  
Frequency Of Occurrence ◽  
Main Sequence Stars ◽  
Chemically Peculiar ◽  
Solar Type ◽  
F Stars ◽  
Ap Stars

AbstractThe boundary between Ap-type magnetic fields and the magnetic fields of solar-type stars occurs near Te ~ 7000K, about where deep envelope convection develops in main sequence stars. This seems natural for solar-type stars, in which the field is generated by the convection zone. However, among magnetic Ap stars the frequency of occurrence declines from about 10% of all A stars near A0 to about 1% near F0. It is not clear what produces this decline in frequency, but the convection zone is probably not responsible. In fact, it seems likely that if global fossil fields occur in main sequence F stars, such fields should be detectable even if the stars having them are not chemically peculiar.

Photo-electric Hβ and uvby photometry

1966 ◽  
Vol 24 ◽  
pp. 170-180
Author(s):  
D. L. Crawford
Keyword(s):  
Narrow Band ◽  
Line Strength ◽  
Interference Filter ◽  
B Stars ◽  
Relative Line ◽  
The Mean ◽  
F Stars ◽  
Two Parameters ◽  
Filter Photometry ◽  
The Continuum

Early in the 1950's Strömgren (1, 2, 3, 4, 5) introduced medium to narrow-band interference filter photometry at the McDonald Observatory. He used six interference filters to obtain two parameters of astrophysical interest. These parameters he calledlandc, for line and continuum hydrogen absorption. The first measured empirically the absorption line strength of Hβby means of a filter of half width 35Å centered on Hβand compared to the mean of two filters situated in the continuum near Hβ. The second index measured empirically the Balmer discontinuity by means of a filter situated below the Balmer discontinuity and two above it. He showed that these two indices could accurately predict the spectral type and luminosity of both B stars and A and F stars. He later derived (6) an indexmfrom the same filters. This index was a measure of the relative line blanketing near 4100Å compared to two filters above 4500Å. These three indices confirmed earlier work by many people, including Lindblad and Becker. References to this earlier work and to the systems discussed today can be found in Strömgren's article inBasic Astronomical Data(7).

Spectrum synthesis of sharp-line B, A and F stars

2005 ◽  
Vol 17 ◽  
pp. 345-348 ◽  
Author(s):  
J. Silaj ◽  
A. Townshend ◽  
F. Kupka ◽  
J. Landstreet ◽  
A. Sigut
Keyword(s):  
Sharp Line ◽  
Spectrum Synthesis ◽  
F Stars

Consistent Evolution of F Stars: Diffusion, Radiative Accelerations, and Abundance Anomalies

1998 ◽  
Vol 504 (1) ◽  
pp. 559-572 ◽  
Author(s):  
S. Turcotte ◽  
J. Richer ◽  
G. Michaud
Keyword(s):  
Abundance Anomalies ◽  
F Stars

scholarly journals A circular polarization survey for radio stars with the Australian SKA Pathfinder

2021 ◽  
Vol 502 (4) ◽  
pp. 5438-5454
Author(s):  
Joshua Pritchard ◽  
Tara Murphy ◽  
Andrew Zic ◽  
Christene Lynch ◽  
George Heald ◽  
...  
Keyword(s):  
Radio Emission ◽  
Brightness Temperature ◽  
Circular Polarization ◽  
Flux Density ◽  
Wide Band ◽  
M Dwarfs ◽  
Square Kilometre Array ◽  
Population Statistics ◽  
Chemically Peculiar ◽  
Radio Stars

ABSTRACT We present results from a circular polarization survey for radio stars in the Rapid ASKAP Continuum Survey (RACS). RACS is a survey of the entire sky south of δ = +41○ being conducted with the Australian Square Kilometre Array Pathfinder telescope (ASKAP) over a 288 MHz wide band centred on 887.5 MHz. The data we analyse include Stokes I and V polarization products to an RMS sensitivity of 250 μJy PSF−1. We searched RACS for sources with fractional circular polarization above 6 per cent, and after excluding imaging artefacts, polarization leakage, and known pulsars we identified radio emission coincident with 33 known stars. These range from M-dwarfs through to magnetic, chemically peculiar A- and B-type stars. Some of these are well-known radio stars such as YZ CMi and CU Vir, but 23 have no previous radio detections. We report the flux density and derived brightness temperature of these detections and discuss the nature of the radio emission. We also discuss the implications of our results for the population statistics of radio stars in the context of future ASKAP and Square Kilometre Array surveys.

Very High Resolution Ultraviolet Spectroscopy of a Chemically Peculiar Star: Results of the χ Lupi Pathfinder Project

1999 ◽  
Vol 117 (3) ◽  
pp. 1454-1470 ◽  
Author(s):  
David S. Leckrone ◽  
Charles R. Proffitt ◽  
Glenn M. Wahlgren ◽  
Sveneric G. Johansson ◽  
Tomas Brage
Keyword(s):  
High Resolution ◽  
Ultraviolet Spectroscopy ◽  
Peculiar Star ◽  
Chemically Peculiar ◽  
Very High
Sign in / Sign up

Export Citation Format

Share Document