scholarly journals On the relation between rotation, convection and activity in intermediate-mass giants

2006 ◽  
Vol 2 (S239) ◽  
pp. 154-156
Author(s):  
P. Gondoin
Keyword(s):  
Binary Systems ◽  
Main Sequence ◽  
Empirical Relation ◽  
Rotation Period ◽  
Surface Flux ◽  
Type Systems ◽  
Intermediate Mass ◽  
X Ray ◽  
Red Giant ◽  
Luminosity Evolution

AbstractI found evidence that the X-ray surface flux of intermediate-mass G and K giants is correlated with their rotation period and Rossby number. Confidence in the degree of correlation is significantly higher when stellar gravity is taken into account. An empirical relation is found that accounts for the X-ray luminosity evolution of single intermediate-mass giants and giants in close or long-period binary systems, such as RS CVn-type systems, as they evolve off the main sequence towards the top of red giant branch.

scholarly journals Evolution of magnetic activity in intermediate-mass giants

2013 ◽  
Vol 9 (S302) ◽  
pp. 377-378
Author(s):  
Philippe Gondoin
Keyword(s):  
Main Sequence ◽  
Type Systems ◽  
Magnetic Activity ◽  
Surface Fluxes ◽  
Intermediate Mass ◽  
Empirical Relationships ◽  
X Ray ◽  
Rotation Periods ◽  
Red Giant ◽  
Luminosity Evolution

AbstractThe X-ray surface fluxes of intermediate-mass G and K giants are correlated with their rotation periods and Rossby numbers. Empirical relationships are presented that accounts for the X-ray luminosity evolution of single intermediate-mass giants, such as FK Comae-type stars, and of giants in close or long-period binaries, such as RS CVn-type systems, as they evolve off the main sequence towards the top of the red giant branch.

Subaru Hyper Suprime-Cam Survey for the Local Group Dwarf Galaxies: Ursa Minor

2018 ◽  
Vol 14 (S344) ◽  
pp. 94-95
Author(s):  
Yutaka Komiyama
Keyword(s):  
Binary Systems ◽  
Main Sequence ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Structural Parameters ◽  
Deep Imaging ◽  
Ursa Minor ◽  
Red Giant

AbstractWe have carried out a wide and deep imaging survey for the Local Group dwarf spheroidal galaxy Ursa Minor (UMi) using Hyper Suprime-Cam (HSC). The data cover out beyond the nominal tidal radius down to ~25 mag in i band, which is ~2 mag below the main sequence turn-off point. The structural parameters of UMi are derived using red giant branch (RGB) stars and sub-giant branch (SGB) stars, and the tidal radius is suggested to be larger than those estimated by the previous studies. It is also found that the distribution of bluer RGB/SGB stars is more extended than that of redder RGB/SGB stars. The fraction of binary systems is estimated to be ~0.4 from the morphology of the main sequences.

scholarly journals Testing the companion hypothesis for the origin of the X-ray emission from intermediate-mass main-sequence stars

2006 ◽  
Vol 452 (3) ◽  
pp. 1001-1010 ◽  
Author(s):  
B. Stelzer ◽  
N. Huélamo ◽  
G. Micela ◽  
S. Hubrig
Keyword(s):  
Main Sequence ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
X Ray

scholarly journals The origin of pulsating ultra-luminous X-ray sources: Low- and intermediate-mass X-ray binaries containing neutron star accretors

2020 ◽  
Vol 642 ◽  
pp. A174 ◽  
Author(s):  
D. Misra ◽  
T. Fragos ◽  
T. M. Tauris ◽  
E. Zapartas ◽  
D. R. Aguilera-Dena
Keyword(s):  
Mass Transfer ◽  
Neutron Star ◽  
Binary Systems ◽  
Mass Transfer Rate ◽  
Host Galaxy ◽  
Intermediate Mass ◽  
X Ray ◽  
Star Mass ◽  
X Ray Binaries ◽  
Eddington Limit

Context. Ultra-luminous X-ray sources (ULXs) are those X-ray sources located away from the centre of their host galaxy with luminosities exceeding the Eddington limit of a stellar-mass black hole (LX >  1039 erg s−1). Observed X-ray variability suggests that ULXs are X-ray binary systems. The discovery of X-ray pulsations in some of these objects (e.g. M82 X-2) suggests that a certain fraction of the ULX population may have a neutron star as the accretor. Aims. We present systematic modelling of low- and intermediate-mass X-ray binaries (LMXBs and IMXBs; donor-star mass range 0.92–8.0 M⊙ and neutron-star accretors) to explain the formation of this sub-population of ULXs. Methods. Using MESA, we explored the allowed initial parameter space of binary systems consisting of a neutron star and a low- or intermediate-mass donor star that could explain the observed properties of ULXs. These donors are transferring mass at super-Eddington rates while the accretion is limited locally in the accretion disc by the Eddington limit. Thus, our simulations take into account beaming effects and also include stellar rotation, tides, general angular momentum losses, and a detailed and self-consistent calculation of the mass-transfer rate. Results. Exploring the initial parameters that lead to the formation of neutron-star ULXs, we study the conditions that lead to dynamical stability of these systems, which depends strongly on the response of the donor star to mass loss. Using two values for the initial neutron star mass (1.3 M⊙ and 2.0 M⊙), we present two sets of mass-transfer calculation grids for comparison with observations of NS ULXs. We find that LMXBs/IMXBs can produce NS-ULXs with typical time-averaged isotropic-equivalent X-ray luminosities of between 1039 and 1041 erg s−1 on a timescale of up to ∼1.0 Myr for the lower luminosities. Finally, we estimate their likelihood of detection, the types of white-dwarf remnants left behind by the donors, and the total amount of mass accreted by the neutron stars. Conclusions. We show that observed super-Eddington luminosities can be achieved in LMXBs/IMXBs undergoing non-conservative mass transfer while assuming geometrical beaming. We also compare our results to the observed pulsating ULXs and infer their initial parameters. Our results suggest that a large subset of the observed pulsating ULX population can be explained by LMXBs/IMXBs in a super-Eddington mass-transfer phase.

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 Spectropolarimetric follow-up of 8 rapidly rotating, X-ray bright FK Comae candidates

2020 ◽  
Vol 496 (1) ◽  
pp. 295-308
Author(s):  
J Sikora ◽  
J Rowe ◽  
S B Howell ◽  
E Mason ◽  
G A Wade
Keyword(s):  
Evolutionary History ◽  
Main Sequence ◽  
Magnetic Activity ◽  
Single Star ◽  
X Ray ◽  
Spectroscopic Binary ◽  
Short Period ◽  
Show Evidence ◽  
Red Giant

ABSTRACT Our understanding of the evolved, rapidly rotating, magnetically active, and apparently single FK Comae stars is significantly hindered by their extreme rarity: only two stars in addition to FK Com itself are currently considered to be members of this class. Recently, a sample of more than 20 candidate FK Comae type stars was identified within the context of the Kepler–Swift Active Galaxies and Stars (KSwAGS) survey. We present an analysis of high-resolution Stokes V observations obtained using ESPaDOnS@CFHT for 8 of these candidates. We found that none of these targets can be considered members of the FK Comae class based primarily on their inferred rotational velocities and on the detection of spectroscopic binary companions. However, 2 targets show evidence of magnetic activity and have anomalously high projected rotational velocities (vsin i) relative to typical values associated with stars of similar evolutionary states. EPIC 210426551 has a $v\sin {i}=209\, {\rm km\, s}^{-1}$, an estimated mass of $1.07\, \mathrm{ M}_\odot$, and, based in part on its derived metallicity of [M/H] = −0.4, it is either an evolved main sequence (MS) star or a pre-MS star. KIC 7732964 has a mass of $0.84\, \mathrm{ M}_\odot$, lies near the base of the red giant branch, and exhibits a $v\sin {i}=23\, {\rm km\, s}^{-1}$. We find that these two objects have similar characteristics to FK Com (albeit less extreme) and that their rapid rotation may be inconsistent with that predicted for a single star evolutionary history. Additional observations are necessary in order to better constrain their evolutionary states and whether they have short-period binary companions.

scholarly journals Late Stages of Close Binary Systems

1976 ◽  
Vol 73 ◽  
pp. 35-61 ◽  
Author(s):  
E. P. J. Van Den Heuvel
Keyword(s):  
Angular Momentum ◽  
Mass Exchange ◽  
Binary Systems ◽  
Main Sequence ◽  
Supernova Explosion ◽  
Compact Stars ◽  
Close Binary ◽  
Close Binaries ◽  
X Ray ◽  
Loss Of Mass

The expected final evolution of massive close binaries (CB) in case B is reviewed. Primary stars with masses ≳ 12–15 M⊙ are, after loosing most of their envelope by mass exchange, expected to explode as supernovae, leaving behind a neutron star or a black hole.Conservative close binary evolution (i.e. without a major loss of mass and angular momentum from the system during the first stage of mass transfer) is expected to occur if the initial mass ratio q0 = M20/M10 is ≳ 0.3. In this case the primary star will be the less massive component when it explodes, and the system is almost never disrupted by the explosion. The explosion is followed by a long-lasting quiet stage (106–107 yr) when the system consists of a massive main-sequence star and an inactive compact companion. After the secondary has left the main-sequence and becomes a blue supergiant with a strong stellar wind, the system becomes a massive X-ray binary for a short while (2–5 × 104 yr).The numbers of Wolf-Rayet binaries and massive X-ray binaries observed within 3 kpc of the Sun are in reasonable agreement with the numbers expected on the basis of conservative CB evolution, which implies that several thousands of massive main-sequence stars with a quiet compact companion should exist in the Galaxy. About a dozen of these systems must be present among the stars visible to the naked eye. During the second stage of mass exchange, large loss of mass and angular momentum from the system is expected, leading to a rapid shrinking of the orbit. The supernova explosion of the secondary will in most cases disrupt the system. If it remains bound, the final system will consist of two compact stars and may resemble the binary pulsar PSR 1913 + 16.In systems with q0 ≲ 0.2–0.3 large mass loss from the system is expected during the first stage of mass exchange. The exploding primary will then be more massive than its unevolved companion and the first supernova explosion disrupts the system in most cases. In the rare cases that it remains bound, the system will have a large runaway velocity and, after a very long (108–109 yr) inactive stage evolves into a low-mass X-ray binary, possibly resembling Her X-1.

scholarly journals Characterizing the X-Ray Emission of Intermediate-mass Pre-main-sequence Stars

2021 ◽  
Vol 162 (4) ◽  
pp. 153
Author(s):  
Evan H. Nuñez ◽  
Matthew S. Povich ◽  
Breanna A. Binder ◽  
Leisa K. Townsley ◽  
Patrick S. Broos
Keyword(s):  
Main Sequence ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
X Ray

scholarly journals Novae and Accreting White Dwarfs as Progenitors of Type Ia Supernovae

2011 ◽  
Vol 7 (S281) ◽  
pp. 172-180
Author(s):  
Mariko Kato
Keyword(s):  
White Dwarfs ◽  
Main Sequence ◽  
Accretion Rate ◽  
Type Ia Supernovae ◽  
Light Curve Analysis ◽  
X Ray ◽  
Type Ia ◽  
Recurrent Nova ◽  
Red Giant ◽  
Ia Supernovae

AbstractI review various phenomena associated with mass-accreting white dwarfs (WDs) in relation to progenitors of Type Ia supernovae (SNe Ia). The WD mass can be estimated from light curve analysis in multiwavelength bands based on the theory of optically thick winds. In the single degenerate scenario of SNe Ia, two main channels are known, i.e., WD + main sequence (MS) channel and WD + red giant (RG) channel. In each channel, a typical binary undergoes three evolutionary stages before explosion, i.e., the wind phase, supersoft X-ray source (SSS) phase, and recurrent nova phase, in this order because the accretion rate decreases with time as the companion mass decreases. For some accreting WDs we can identify the corresponding stage of evolution. Intermittent supersoft X-ray sources like RX J0513.9−6951 and V Sge correspond to wind phase objects. For the SSS phase, CAL 87-type objects correspond to the WD+MS channel. For the WD + RG channel, soft X-ray observations of early type galaxies give statistical evidence of SSS phase binaries. Recurrent novae of U Sco-type and RS Oph-type correspond to the WD + MS channel and WD + RG channel, respectively. The majority of recurrent novae host a very massive WD (≳ 1.35 M⊙) and often show a plateau phase in their optical light curves corresponding to the long-lasting supersoft X-ray phase. These properties are indications of increasing WD masses.

scholarly journals Millisecond Pulsar Surveys

1987 ◽  
Vol 125 ◽  
pp. 13-21
Author(s):  
D. C. Backer
Keyword(s):  
Mass Transfer ◽  
Stellar Evolution ◽  
Binary Systems ◽  
Rotation Period ◽  
Millisecond Pulsar ◽  
Millisecond Pulsars ◽  
X Ray ◽  
New Class ◽  
The Past ◽  
Low Mass

In 1982 a new class of pulsars was defined by the discovery of a star with a millisecond rotation period, 1.6 ms. In the past 3.5 years two additional pulsars with millisecond periods have been discovered. The rapid spin of these pulsars is attributed to mass transfer in a low-mass binary progenitor system. This hypothesis is supported by the presence of companions in two of the three millisecond pulsars. These recent discoveries have led both to a deeper understanding of the final stages of stellar evolution in binary systems, and to closer ties between the observational study of neutron stars by radio, optical and X-ray techniques. In addition the millisecond pulsars provide precise astrophysical clocks that can be used to improve the solar-system ephemeredes and to search for a background of gravitational waves that may have been produced in the early stages of the visible universe. Old and ongoing searches for new millisecond pulsars are described in this paper.

Sign in / Sign up

Export Citation Format

Share Document