scholarly journals Impact of initial models and variable accretion rates on the pre-main-sequence evolution of massive and intermediate-mass stars and the early evolution of H ii regions

2016 ◽  
Vol 458 (3) ◽  
pp. 3299-3313 ◽  
Author(s):  
Lionel Haemmerlé ◽  
Thomas Peters
Keyword(s):  
Main Sequence ◽  
Early Evolution ◽  
H Ii Regions ◽  
Sequence Evolution ◽  
Intermediate Mass ◽  
Intermediate Mass Stars ◽  
Accretion Rates

scholarly journals The effects of Rotation on Wolf–Rayet Stars and on the Production of Primary Nitrogen by Intermediate Mass Stars

2004 ◽  
Vol 215 ◽  
pp. 579-588 ◽  
Author(s):  
Georges Meynet ◽  
Max Pettini
Keyword(s):  
Star Formation ◽  
Time Delay ◽  
Main Sequence ◽  
Massive Stars ◽  
Sequence Evolution ◽  
Stellar Rotation ◽  
Intermediate Mass ◽  
Intermediate Mass Stars ◽  
Solar Metallicity ◽  
Effects Of Rotation

We use the rotating stellar models described in the paper by A. Maeder & G. Meynet in this volume to consider the effects of rotation on the evolution of the most massive stars into and during the Wolf–Rayet phase, and on the post-Main Sequence evolution of intermediate mass stars. The two main results of this discussion are the following. First, we show that rotating models are able to account for the observed properties of the Wolf–Rayet stellar populations at solar metallicity. Second, at low metallicities, the inclusion of stellar rotation in the calculation of chemical yields can lead to a longer time delay between the release of oxygen and nitrogen into the interstellar medium following an episode of star formation, since stars of lower masses (compared to non-rotating models) can synthesize primary N. Qualitatively, such an effect may be required to explain the relative abundances of N and O in extragalactic metal–poor environments, particularly at high redshifts.

The Pre-Main-Sequence Evolution of Intermediate-Mass Stars

1993 ◽  
Vol 418 ◽  
pp. 414 ◽  
Author(s):  
Francesco Palla ◽  
Steven W. Stahler
Keyword(s):  
Main Sequence ◽  
Sequence Evolution ◽  
Intermediate Mass ◽  
Intermediate Mass Stars

scholarly journals Stellar Mass Loss and Pulsation

1989 ◽  
Vol 111 ◽  
pp. 63-82
Author(s):  
L.A. Willson
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Effective Temperature ◽  
Large Amplitude ◽  
Main Sequence ◽  
Massive Stars ◽  
Sequence Evolution ◽  
Intermediate Mass ◽  
Mira Variables ◽  
Intermediate Mass Stars

AbstractMass loss at rates sufficient to alter the evolution of stars is known to occur during the pre-main sequence evolution of most stars, on the main sequence for massive stars, and during advanced evolutionary phases when the luminosity is high and the effective temperature is low. While most investigations of the effects of mass loss on stellar evolution have assumed continuous (parametrized) mass loss laws apply, there is increasing evidence that mass loss rates are substantially higher for stars that are pulsating with large amplitude and/or in selected modes. Some new insights into the mass loss that terminates the AGB evolution of intermediate mass stars, and leads to the formation of planetary nebulae, come from recent detailed studies of the mass loss process from the Mira variables.

scholarly journals IPHAS A-type Stars with Mid-IR Excesses in Spitzer Surveys

2009 ◽  
Vol 5 (H15) ◽  
pp. 815-815
Author(s):  
Antonio S. Hales ◽  
Michael J. Barlow ◽  
Janet E. Drew ◽  
Yvonne C. Unruh ◽  
Robert Greimel ◽  
...  
Keyword(s):  
Cross Correlation ◽  
Main Sequence ◽  
Terrestrial Planet ◽  
Circumstellar Disks ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
Mid Infrared ◽  
Isaac Newton ◽  
Intermediate Mass Stars ◽  
Dust Disks

AbstractThe Isaac Newton Photometric H-Alpha Survey (IPHAS) provides (r′-Hα)-(r′-i′) colors, which can be used to select AV0-5 Main Sequence star candidates (age~20-200 Myr). By combining a sample of 23050 IPHAS-selected A-type stars with 2MASS, GLIMPSE and MIPSGAL photometry we searched for mid-infrared excesses attributable to dusty circumstellar disks. Positional cross-correlation yielded a sample of 2692 A-type stars, of which 0.6% were found to have 8-μm excesses above the expected photospheric values. The low fraction of main sequence stars with mid-IR excesses found in this work indicates that dust disks in the terrestrial planet zone of Main Sequence intermediate mass stars are rare. Dissipation mechanisms such as photo-evaporation, grain growth, collisional grinding or planet formation could possibly explain the depletion of dust detected in the inner regions of these disks.

scholarly journals The Pan-Pacific Planet Search – VIII. Complete results and the occurrence rate of planets around low-luminosity giants

2019 ◽  
Vol 491 (4) ◽  
pp. 5248-5257 ◽  
Author(s):  
Robert A Wittenmyer ◽  
R P Butler ◽  
Jonathan Horner ◽  
Jake Clark ◽  
C G Tinney ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Main Sequence ◽  
Giant Planets ◽  
Occurrence Rate ◽  
Velocity Measurements ◽  
Intermediate Mass ◽  
Giant Stars ◽  
Intermediate Mass Stars ◽  
Final Data ◽  
Solar Type

ABSTRACT Our knowledge of the populations and occurrence rates of planets orbiting evolved intermediate-mass stars lags behind that for solar-type stars by at least a decade. Some radial velocity surveys have targeted these low-luminosity giant stars, providing some insights into the properties of their planetary systems. Here, we present the final data release of the Pan-Pacific Planet Search (PPPS), a 5 yr radial velocity survey using the 3.9 m Anglo-Australian Telescope. We present 1293 precise radial velocity measurements for 129 stars, and highlight 6 potential substellar-mass companions, which require additional observations to confirm. Correcting for the substantial incompleteness in the sample, we estimate the occurrence rate of giant planets orbiting low-luminosity giant stars to be approximately 7.8$^{+9.1}_{-3.3}$ per cent. This result is consistent with the frequency of such planets found to orbit main-sequence A-type stars, from which the PPPS stars have evolved.

scholarly journals Convective boundary mixing in low- and intermediate-mass stars – I. Core properties from pressure-mode asteroseismology

2020 ◽  
Vol 493 (4) ◽  
pp. 4987-5004 ◽  
Author(s):  
George C Angelou ◽  
Earl P Bellinger ◽  
Saskia Hekker ◽  
Alexey Mints ◽  
Yvonne Elsworth ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Measurement Precision ◽  
Observational Constraints ◽  
Intermediate Mass ◽  
Convective Boundary ◽  
Mode Identification ◽  
Boundary Mixing ◽  
Intermediate Mass Stars ◽  
F Stars

ABSTRACT Convective boundary mixing (CBM) is ubiquitous in stellar evolution. It is a necessary ingredient in the models in order to match observational constraints from clusters, binaries, and single stars alike. We compute ‘effective overshoot’ measures that reflect the extent of mixing and which can differ significantly from the input overshoot values set in the stellar evolution codes. We use constraints from pressure modes to infer the CBM properties of Kepler and CoRoT main-sequence and subgiant oscillators, as well as in two radial velocity targets (Procyon A and α Cen A). Collectively, these targets allow us to identify how measurement precision, stellar spectral type, and overshoot implementation impact the asteroseismic solution. With these new measures, we find that the ‘effective overshoot’ for most stars is in line with physical expectations and calibrations from binaries and clusters. However, two F-stars in the CoRoT field (HD 49933 and HD 181906) still necessitate high overshoot in the models. Due to short mode lifetimes, mode identification can be difficult in these stars. We demonstrate that an incongruence between the radial and non-radial modes drives the asteroseismic solution to extreme structures with highly efficient CBM as an inevitable outcome. Understanding the cause of seemingly anomalous physics for such stars is vital for inferring accurate stellar parameters from TESS data with comparable timeseries length.

scholarly journals γ Doradus stars as a test of angular momentum transport models

2019 ◽  
Vol 626 ◽  
pp. A121 ◽  
Author(s):  
R.-M. Ouazzani ◽  
J. P. Marques ◽  
M.-J. Goupil ◽  
S. Christophe ◽  
V. Antoci ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Main Sequence ◽  
Evolutionary Models ◽  
Intermediate Mass ◽  
Angular Momentum Transport ◽  
Rotation Rates ◽  
Giant Stars ◽  
Intermediate Mass Stars ◽  
Red Giant ◽  
Core Rotation

Helioseismology and asteroseismology of red giant stars have shown that distribution of angular momentum in stellar interiors, and the evolution of this distribution with time remains an open issue in stellar physics. Owing to the unprecedented quality and long baseline of Kepler photometry, we are able to seismically infer internal rotation rates in γ Doradus stars, which provide the main-sequence counterpart to the red-giants puzzle. Here, we confront these internal rotation rates to stellar evolution models which account for rotationally induced transport of angular momentum, in order to test angular momentum transport mechanisms. On the one hand, we used a stellar model-independent method developed by our team in order to obtain accurate, seismically inferred, buoyancy radii and near-core rotation for 37 γ Doradus stars observed by Kepler. We show that the stellar buoyancy radius can be used as a reliable evolution indicator for field stars on the main sequence. On the other hand, we computed rotating evolutionary models of intermediate-mass stars including internal transport of angular momentum in radiative zones, following the formalism developed in the series of papers started by Zahn (1992, A&A, 265, 115), with the CESTAM code. This code calculates the rotational history of stars from the birth line to the tip of the RGB. The initial angular momentum content has to be set initially, which is done here by fitting rotation periods in young stellar clusters. We show a clear disagreement between the near-core rotation rates measured in the sample and the rotation rates obtained from the evolutionary models including rotationally induced transport of angular momentum following Zahn’s prescriptions. These results show a disagreement similar to that of the Sun and red giant stars in the considered mass range. This suggests the existence of missing mechanisms responsible for the braking of the core before and along the main sequence. The efficiency of the missing mechanisms is investigated. The transport of angular momentum as formalized by Zahn and Maeder cannot explain the measurements of near-core rotation in main-sequence intermediate-mass stars we have at hand.

scholarly journals Lack of close-in, massive planets of main-sequence A-type stars from Kepler

2019 ◽  
Vol 489 (2) ◽  
pp. 2069-2078 ◽  
Author(s):  
Silvia Sabotta ◽  
Petr Kabath ◽  
Judith Korth ◽  
Eike W Guenther ◽  
Daniel Dupkala ◽  
...  
Keyword(s):  
High Frequency ◽  
Main Sequence ◽  
Light Curves ◽  
Occurrence Rate ◽  
Intermediate Mass ◽  
Very High Frequency ◽  
Hot Jupiters ◽  
Intermediate Mass Stars ◽  
The Masses ◽  
Very High

ABSTRACT Some theories of planet formation and evolution predict that intermediate-mass stars host more hot Jupiters than Sun-like stars, others reach the conclusion that such objects are very rare. By determining the frequencies of those planets we can test those theories. Based on the analysis of Kepler light curves it has been suggested that about 8 per cent of the intermediate-mass stars could have a close-in substellar companion. This would indicate a very high frequency of such objects. Up to now, there was no satisfactory proof or test of this hypothesis. We studied a previously reported sample of 166 planet candidates around main-sequence A-type stars in the Kepler field. We selected six of them for which we obtained extensive long-term radial velocity measurements with the Alfred Jensch 2-m telescope in Tautenburg and the Perek 2-m telescope in Ondřejov. We derive upper limits of the masses of the planet candidates. We show that we are able to detect this kind of planet with our telescopes and their instrumentation using the example of MASCARA-1 b. With the transit finding pipeline Extrans we confirm that there is no single transit event from a Jupiter-like planet in the light curves of those 166 stars. We furthermore determine that the upper limit for the occurrence rate of close-in, massive planets for A-type stars in the Kepler sample is around 0.75 per cent. We argue that there is currently little evidence for a very high frequency of close-in, massive planets of intermediate-mass stars.

scholarly journals The Evolution of Angular Momentum of Intermediate Mass Stars: From the Birthline to the Main Sequence

2004 ◽  
Vol 215 ◽  
pp. 431-437
Author(s):  
S. C. Wolff ◽  
S. E. Strom ◽  
L. A. Hillenbrand
Keyword(s):  
Angular Momentum ◽  
Accretion Disks ◽  
Power Law ◽  
Main Sequence ◽  
Sharp Decrease ◽  
Zero Point ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
Intermediate Mass Stars ◽  
Continuous Power

Measurements of stars in the Orion OB association show that there is a continuous power law relationship between specific angular momentum (J/M) and mass (M) for stars on convective tracks having masses in the range ~0.5 to ~3 M⊙; this power law extends smoothly into the domain of more massive stars on the ZAMS. If we assume that stars are “locked” to circumstellar accretion disks via their magnetic fields until they are deposited on the stellar birthline, we can account for the observed slope and zero point of the power law fit to the upper envelope of the observed J/M vs M distribution.Pre-main sequence stars with M<2 M⊙ on radiative tracks do not follow the power law relationship. A sharp decrease in J/M with decreasing mass has been recognized for more than 30 years for older field stars, but remarkably is seen already among our Orion sample of stars that are only a few million years old. We show that this break in the power law is a consequence of loss of angular momentum on convective tracks, combined with core-envelope decoupling at the time of the transition from the convective to radiative tracks.

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