scholarly journals Spots, flares, accretion, and obscuration in the pre-main sequence binary DQ Tau

2018 ◽  
Vol 14 (S345) ◽  
pp. 314-315
Author(s):  
Á. Kóspál ◽  
P. Ábrahám ◽  
G. Zsidi ◽  
K. Vida ◽  
R. Szabó ◽  
...  
Keyword(s):  
Real World ◽  
Main Sequence ◽  
Equal Mass ◽  
Light Curves ◽  
Multiple Systems ◽  
Spectroscopic Binary ◽  
Rotational Modulation ◽  
Stellar Flares ◽  
Low Mass ◽  
Formation And Evolution

AbstractDQ Tau is a young low-mass spectroscopic binary, consisting of two almost equal-mass stars on a 15.8 day period surrounded by a circumbinary disk. We analyzed DQ Tau’s light curves obtained by Kepler K2, the Spitzer Space Telescope, and ground-based facilities. We observed variability phenomena, including rotational modulation by stellar spots, energetic stellar flares, brightening events around periastron due to increased accretion, and short dips due to temporary circumstellar obscuration. The study on DQ Tau will help in discovering and understanding the formation and evolution of other real-world examples of “Tatooine-like” systems. This is especially important because more and more evidence points to the possibility that all Sun-like stars were born in binary or multiple systems that broke up later due to dynamical interactions.

scholarly journals Testing Pre-Main Sequence Models with Young Binaries

2001 ◽  
Vol 200 ◽  
pp. 472-482
Author(s):  
Francesco Palla
Keyword(s):  
Binary System ◽  
Binary Systems ◽  
Main Sequence ◽  
Young Stars ◽  
System A ◽  
Spectroscopic Binary ◽  
Low Mass ◽  
Good Agreement

I will discuss several tests to gauge the accuracy of pre–main-sequence (PMS) models. Methods to determine the mass of young stars are overviewed, with emphasis on the information provided by double-lined, spectroscopic binary systems. A comparison of the dynamically determined masses with those estimated using the PMS models of Palla & Stahler (1999) is presented. Good agreement between empirical and theoretical masses is found. The analysis of the inferred ages from the isochrones shows a remarkable coevality within each binary system. A complete assessment of the accuracy of PMS tracks needs the identification of eclipsing systems of low-mass.

scholarly journals A spectroscopic test of the rotational modulation origin of periodic Kepler photometric variability of A-type stars

2020 ◽  
Vol 498 (2) ◽  
pp. 2456-2471
Author(s):  
J Sikora ◽  
G A Wade ◽  
J Rowe
Keyword(s):  
Light Curves ◽  
Surface Structures ◽  
Inhomogeneous Surface ◽  
Photometric Variability ◽  
Spectroscopic Monitoring ◽  
Rotational Modulation ◽  
Kepler Mission ◽  
Low Mass ◽  
Monitoring Survey ◽  
Modulated Light

ABSTRACT High-precision space-based photometry obtained by the Kepler and TESS missions has revealed evidence of rotational modulation associated with main-sequence (MS) A- and late B-type stars. Generally, such variability in these objects is attributed to inhomogeneous surface structures (e.g. chemical spots), which are typically linked to strong magnetic fields ($B\gtrsim 100\, {\rm G}$) visible at the surface. It has been reported that ≈44 per cent of all A-type stars observed during the Kepler mission exhibit rotationally modulated light curves. This is surprising considering that ≲10 per cent of all MS A-type stars are known to be strongly magnetic (i.e. they are Ap/Bp stars). We present a spectroscopic monitoring survey of 44 A- and late B-type stars reported to exhibit rotational modulation in their Kepler light curves. The primary goal of this survey is to test the hypothesis that the variability is rotational modulation by comparing each star’s rotational broadening (vsin i) with the equatorial velocities (veq) inferred from the photometric periods. We searched for chemical peculiarities and binary companions in order to provide insight into the origin of the apparent rotational modulation. We find that 14 stars in our sample have vsin i > veq and/or have low-mass companions that may contribute to or be responsible for the observed variability. Our results suggest that more than 10 per cent of all MS A- and late B-type stars may exhibit inhomogeneous surface structures; however, the incidence rate is likely ≲30 per cent.

scholarly journals New Observational Clues on Binary Formation in the Galaxy

1989 ◽  
Vol 8 ◽  
pp. 103-107
Author(s):  
David W. Latham
Keyword(s):  
Strong Dependence ◽  
Stellar Populations ◽  
Close Binaries ◽  
Major Influence ◽  
Solar Mass ◽  
Multiple Systems ◽  
Binary Formation ◽  
The Galaxy ◽  
Low Mass ◽  
Formation And Evolution

AbstractNew observations of binaries are beginning to provide new clues on the formation and evolution of binary and multiple systems in a variety of stellar populations in the Galaxy. New orbital determinations are shedding light on the frequency and orbital characteristics of binaries in the disk and the halo of our Galaxy, both in clusters and the field. These results support the view that the formation of binaries involving solar-mass stars is relatively independent of the stellar environment. Evolutionary effects can have a major influence for close binaries with periods up to at least ten days, with a strong dependence on the age of the population. Progress towards determining the frequency of low-mass companions and planetary systems is promising but still very limited.

scholarly journals Exoplanet characterisation in the longest known resonant chain: the K2-138 system seen by HARPS

2019 ◽  
Vol 631 ◽  
pp. A90 ◽  
Author(s):  
T. A. Lopez ◽  
S. C. C. Barros ◽  
A. Santerne ◽  
M. Deleuil ◽  
V. Adibekyan ◽  
...  
Keyword(s):  
Bayesian Analysis ◽  
Radial Velocity ◽  
Bright Star ◽  
Planetary Formation ◽  
Mass Measurements ◽  
Multiple Systems ◽  
Upper Limits ◽  
Low Mass ◽  
Formation And Evolution ◽  
The Masses

The detection of low-mass transiting exoplanets in multiple systems brings new constraints to planetary formation and evolution processes and challenges the current planet formation theories. Nevertheless, only a mere fraction of the small planets detected by Kepler and K2 have precise mass measurements, which are mandatory to constrain their composition. We aim to characterise the planets that orbit the relatively bright star K2-138. This system is dynamically particular as it presents the longest chain known to date of planets close to the 3:2 resonance. We obtained 215 HARPS spectra from which we derived the radial-velocity variations of K2-138. Via a joint Bayesian analysis of both the K2 photometry and HARPS radial-velocities (RVs), we constrained the parameters of the six planets in orbit. The masses of the four inner planets, from b to e, are 3.1, 6.3, 7.9, and 13.0 M⊕ with a precision of 34, 20, 18, and 15%, respectively. The bulk densities are 4.9, 2.8, 3.2, and 1.8 g cm−3, ranging from Earth to Neptune-like values. For planets f and g, we report upper limits. Finally, we predict transit timing variations of the order two to six minutes from the masses derived. Given its peculiar dynamics, K2-138 is an ideal target for transit timing variation (TTV) measurements from space with the upcoming CHaracterizing ExOPlanet Satellite (CHEOPS) to study this highly-packed system and compare TTV and RV masses.

scholarly journals Spots and Flares in Hot Main Sequence Stars Observed by Kepler, K2, and TESS

2021 ◽  
Vol 8 ◽  
Author(s):  
Luis A. Balona
Keyword(s):  
Main Sequence ◽  
Previous Analysis ◽  
Type A ◽  
Light Curves ◽  
Main Sequence Stars ◽  
Considerable Fraction ◽  
Rotation Periods ◽  
Rotational Modulation

About 22,000 Kepler stars, 7,000 K2 stars, and nearly 60,000 TESS stars from sectors 1–24 have been classified according to variability type. A large proportion of stars of all spectral types appear to have periods in their light curves consistent with the expected rotation periods. A previous analysis of A- and late B-type stars suggests that these stars are indeed rotational variables. In this paper we have accumulated data to show that rotational modulation is present in about 30–40% of A- and B-type stars. A search for flares in TESS A- and B-type stars resulted in the detection of 102 flares in 57 stars. Analysis of flare energies show that the source of the flares cannot be a cool dwarf companion nor a F/G giant. The realization that a considerable fraction of A- and B-type stars are active indicates that a revision of current concepts regarding hot star envelopes is required.

scholarly journals Cataclysmic Binaries Containing a Black-Dwarf Secondary

1983 ◽  
Vol 72 ◽  
pp. 275-278
Author(s):  
H. Ritter
Keyword(s):  
Main Sequence ◽  
Probability Of Detection ◽  
Light Curves ◽  
Space Density ◽  
Cataclysmic Binaries ◽  
Low Mass ◽  
Intrinsic Luminosity

ABSTRACTCataclysmic binaries with a black-dwarf secondary can in principle be distinguished from those containing a low-mass main-sequence secondary because of the differences of the corresponding eclipse light curves. However, due to the very low intrinsic luminosity of the systems containing a black dwarf, the probability of detection turns out to be smaller than the corresponding probability for an ordinary cataclysmic binary by about 1.5 to 3 orders of magnitude. Therefore, despite the fact that the predicted space density of these objects is quite high, systems containing a black-dwarf secondary must remain essentially undetectable.

scholarly journals Rotational modulation in TESS B stars

2019 ◽  
Vol 485 (3) ◽  
pp. 3457-3469 ◽  
Author(s):  
L A Balona ◽  
G Handler ◽  
S Chowdhury ◽  
D Ozuyar ◽  
C A Engelbrecht ◽  
...  
Keyword(s):  
Main Sequence ◽  
Large Fraction ◽  
Space Mission ◽  
Light Variation ◽  
Light Curves ◽  
B Stars ◽  
Surface Features ◽  
Rotational Modulation ◽  
Gaia Dr2

Abstract Light curves and periodograms of 160 B stars observed by the Transiting Exoplanet Survey Satellite (TESS) space mission and 29 main-sequence B stars from Kepler and K2 were used to classify the variability type. There are 114 main-sequence B stars in the TESS sample, of which 45 are classified as possible rotational variables. This confirms previous findings that a large fraction (about 40 per cent) of A and B stars may exhibit rotational modulation. Gaia DR2 parallaxes were used to estimate luminosities, from which the radii and equatorial rotational velocities can be deduced. It is shown that observed values of the projected rotational velocities are lower than the estimated equatorial velocities for nearly all the stars, as they should be if rotation is the cause of the light variation. We conclude that a large fraction of main-sequence B stars appear to contain surface features which cannot likely be attributed to abundance patches.

scholarly journals The Formation and Evolution of Binaries in Globular Clusters

1989 ◽  
Vol 8 ◽  
pp. 139-142
Author(s):  
Frank Verbunt
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Galactic Disk ◽  
Main Sequence Star ◽  
Number Density ◽  
X Ray ◽  
Close Encounters ◽  
Low Mass ◽  
Formation And Evolution ◽  
X Ray Binaries

AbstractThe number density of stars in the cores of globular clusters is high enough for close encounters between stars to be frequent. These encounters may lead to the formation of binaries. Those binaries which do not easily form via the evolution of primordial main-sequence star binaries, and are therefore rare in the galactic disk, can be common in globular clusters. Examples of such binaries are the low-mass X-ray binaries. Such binaries may evolve into radiopulsars.

scholarly journals Properties of barred galaxies in the MaNGA galaxy survey

2019 ◽  
Vol 14 (S353) ◽  
pp. 226-230
Author(s):  
Amelia Fraser-McKelvie ◽  
Michael Merrifield ◽  
Alfonso Aragón-Salamanca ◽  
Karen Masters ◽  
Keyword(s):  
Main Sequence ◽  
High Mass ◽  
Star Forming ◽  
Barred Galaxies ◽  
Wide Range ◽  
The Galaxy ◽  
Hα Emission ◽  
Low Mass ◽  
Formation And Evolution ◽  
Initial Results

AbstractWe present the initial results of a census of 684 barred galaxies in the MaNGA galaxy survey. This large sample contains galaxies with a wide range of physical properties, and we attempt to link bar properties to key observables for the whole galaxy. We find the length of the bar, when normalised for galaxy size, is correlated with the distance of the galaxy from the star formation main sequence, with more passive galaxies hosting larger-scale bars. Ionised gas is observed along the bars of low-mass galaxies only, and these galaxies are generally star-forming and host short bars. Higher-mass galaxies do not contain Hα emission along their bars, however, but are more likely to host rings or Hα at the centre and ends of the bar. Our results suggest that different physical processes are at play in the formation and evolution of bars in low- and high-mass galaxies.

scholarly journals A Note about Multiple Systems of Dense Molecular Clouds

1982 ◽  
Vol 69 ◽  
pp. 105-108
Author(s):  
Peter Vanýsek
Keyword(s):  
Main Sequence ◽  
Space Distribution ◽  
Main Sequence Stars ◽  
Solar Mass ◽  
Low Mass Stars ◽  
Multiple Systems ◽  
Ob Stars ◽  
Ir Sources ◽  
Low Mass ◽  
The Individual

AbstractThe space distribution of some small dense clouds with point-like IR sources, resembles the clustering of young OB stars. It can be assumed that such objects contain heavy obscured high-luminosity stars on the ZAMS. From the comparison of infrared and radio data it follows that in typical cases, only one B star is the source of the radiation of the cloud. The total mass of the cloud is of the order of one solar mass. If the individual fragments of the cloud are gravitationally unstable, then in the later stage of the evolution only low-mass stars are formed. One can therefore expect that young OB stars are most frequently accompanied by low-mass pre-Main Sequence stars.

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