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 Main-sequence broadening, Be stars, and stellar rotation inhand χ Persei

1994 ◽  
Vol 162 ◽  
pp. 151-152
Author(s):  
J. Denoyelle ◽  
C. Aerts ◽  
C. Waelkens
Keyword(s):  
Main Sequence ◽  
Large Fraction ◽  
Variable Stars ◽  
Theoretical Studies ◽  
Be Stars ◽  
Stellar Rotation ◽  
B Stars ◽  
Fundamental Parameters ◽  
Magnitude Diagram ◽  
Double Cluster

The double cluster h andxPersei is one of the richest clusters containing early-B stars, and therefore is important for observational and theoretical studies on the fundamental parameters of massive stars. The colour-magnitude diagram of the double cluster shows an important scatter (see Figure 1). It has long been known thathandxPersei are extremely rich in Be stars (Slettebak 1968). Our previous contention (Waelkens et al. 1990) that the large-amplitude variable stars we discovered are also Be stars, could be confirmed for a few objects. Rotation velocities for stars inhandxPersei are usually high, which is not surprising in view of the large fraction of Be stars.

scholarly journals Pulsation among TESS A and B stars and the Maia variables

2020 ◽  
Vol 493 (4) ◽  
pp. 5871-5879
Author(s):  
L A Balona ◽  
D Ozuyar
Keyword(s):  
Main Sequence ◽  
Large Fraction ◽  
Single Mode ◽  
Distinct Region ◽  
Low Frequencies ◽  
B Stars ◽  
High Frequencies ◽  
Pulsating Stars ◽  
Scuti Stars

ABSTRACT Classification of over 50 000 TESS stars in sectors 1–18 has resulted in the detection of 766 pulsating main-sequence B stars as well as over 5000 δ Scuti, 2300 γ Doradus, and 114 roAp candidates. Whereas it has been assumed that high-frequency pulsations among B-type main-sequence stars are confined to the early B-type β Cephei stars, the observations indicate that high frequencies are to be found over the whole B-star range, eventually merging with δ Scuti stars. The cool B stars pulsating in high frequencies are called Maia variables. It is shown that Maia variables are not rapidly rotating and thus cannot be β Cephei pulsators that appear to have lower temperatures due to gravity darkening. In the region where β Cephei variables are found, the proportion of pulsating stars is larger and amplitudes are higher and a considerable fraction pulsate in a single mode and low rotation rate. There is no distinct region of slowly pulsating B stars (SPB stars). Stars pulsating solely in low frequencies are found among all B stars. At most, only one-third of B stars appear to pulsate. These results, as well as the fact that a large fraction of A and B stars show rotational modulation, indicate a need for a revision of current ideas regarding stars with radiative envelopes.

scholarly journals The study of unclassified B[e] stars and candidates in the Galaxy and Magellanic Clouds†

2019 ◽  
Vol 488 (1) ◽  
pp. 1090-1110 ◽  
Author(s):  
C A H Condori ◽  
M Borges Fernandes ◽  
M Kraus ◽  
D Panoglou ◽  
C A Guerrero
Keyword(s):  
Main Sequence ◽  
Interstellar Extinction ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Light Curves ◽  
Evolutionary Stage ◽  
The Third ◽  
The Galaxy ◽  
Gaia Dr2

ABSTRACT We investigated 12 unclassified B[e] stars or candidates, 8 from the Galaxy, 2 from the Large Magellanic Cloud (LMC), and 2 from the Small Magellanic Cloud (SMC). Based on the analysis of high-resolution spectroscopic (FEROS) and photometric data, we confirmed the presence of the B[e] phenomenon for all objects of our sample, except for one (IRAS 07455-3143). We derived their effective temperature, spectral type, luminosity class, interstellar extinction and, using the distances from Gaia DR2, we obtained their bolometric magnitude, luminosity, and radius. Modelling of the forbidden lines present in the FEROS spectra revealed information about the kinematics and geometry of the circumstellar medium of these objects. In addition, we analysed the light curves of four stars, finding their most probable periods. The evolutionary stage of 11 stars of our sample is suggested from their position on the HR diagram, taking into account evolutionary tracks of stars with solar, LMC, and SMC metallicities. As results, we identified B and B[e] supergiants, B[e] stars probably at the main sequence or close to its end, post-AGB and HAeB[e] candidates, and A[e] stars in the main sequence or in the pre-main sequence. However, our most remarkable results are the identification of the third A[e] supergiant (ARDB 54, the first one in the LMC), and of an ‘LBV impostor’ in the SMC (LHA 115-N82).

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 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 Rotation: a fundamental parameter of massive stars

1997 ◽  
Vol 189 ◽  
pp. 343-348 ◽  
Author(s):  
N. Langer ◽  
A. Heger ◽  
J. Fliegner
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Large Fraction ◽  
Reasonable Doubt ◽  
Close Binary ◽  
Fundamental Parameter ◽  
Mixing Processes ◽  
B Stars ◽  
Internal Mixing ◽  
Rule Out

Massive stars are rapid rotators. Equatorial rotation velocities span the range vrot = 100–400 km s−1, with B stars rotating closest to their break-up speed vcrit (Howarth et al. 1997). During the last decade, many observations have revealed unusual surface abundances that may require additional internal mixing (beyond that of simple convection and overshooting) for their explanation, most important helium and nitrogen enrichment in main sequence O and B stars (Gies & Lambert 1992), in the SN 1987A progenitor (Fransson et al. 1989), and boron depletions in main sequence B stars (Venn et al. 1996). In particular the latter observations clearly point towards internal mixing and rule out a close binary origin of the abundance peculiarities (Fliegner et al. 1996). Altogether, the occurrence of some form of additional mixing responsible for altering the surface abundances in a large fraction, if not all massive stars appears to be beyond reasonable doubt, and mixing processes due to rotation are the most natural explanation.

Pulsation, Rotation and Flares in A Stars

2017 ◽  
Vol 14 (S339) ◽  
pp. 77-82
Author(s):  
L. A. Balona
Keyword(s):  
Differential Rotation ◽  
Large Fraction ◽  
B Stars ◽  
Rotational Modulation ◽  
Scuti Stars

AbstractNew observations of Kepler δ Scuti stars show that our understanding of pulsation in these stars is incomplete. A large fraction of A and B stars exhibit rotational modulation in light, suggesting that spots exist in stars with radiative envelopes. Flares are seen in some A stars, as may be expected if starspots are present. Differential rotation shear increases from M to F but decreases for A stars; it reaches a maximum among the γ Doradus variables. Current views of stars with radiative envelopes may need to be reviewed in the light of these observations.

scholarly journals Constraints on pre-main-sequence evolution from stellar pulsations

2013 ◽  
Vol 9 (S301) ◽  
pp. 137-144
Author(s):  
M. P. Casey ◽  
K. Zwintz ◽  
D. B. Guenther
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Sequence Evolution ◽  
B Stars ◽  
Stellar Pulsations ◽  
Pms Stars

AbstractPulsating pre-main-sequence (PMS) stars afford the earliest opportunity in the lifetime of a star to which the concepts of asteroseismology can be applied. PMS stars should be structurally simpler than their evolved counterparts, thus (hopefully!) making any asteroseismic analysis relatively easier. Unfortunately, this isn't necessarily the case. The majority of these stars (around 80) are δ Scuti pulsators, with a couple of γ Doradus, γ Doradus – δ Scuti hybrids, and slowly pulsating B stars thrown into the mix. The majority of these stars have only been discovered within the last ten years, with the community still uncovering the richness of phenomena associated with these stars, many of which defy traditional asteroseismic analysis.A systematic asteroseismic analysis of all of the δ Scuti PMS stars was performed in order to get a better handle on the properties of these stars as a group. Some strange results have been found, including one star pulsating up to the theoretical acoustic cut-off frequency of the star, and a number of stars in which the most basic asteroseismic analysis suggests problems with the stars' positions in the Hertzsprung-Russell diagram. From this we get an idea of the\break constraints — or lack thereof — that these results can put on PMS stellar evolution.

scholarly journals Photometric Study of two Southern Algol Type Binaries

1989 ◽  
Vol 107 ◽  
pp. 376-376
Author(s):  
K. D. Abhyankar ◽  
M. L. Vyas
Keyword(s):  
Spectroscopic Data ◽  
Main Sequence ◽  
Light Curves ◽  
The Other ◽  
Main Sequence Star ◽  
Photometric Study ◽  
The Absolute ◽  
Better Than ◽  
Absolute Dimensions

Complete UBV light-curves of RR-Lep and RX-Hya have been obtained during 1983-87 seasons. Preliminary elements were computed using modified Wellmann’s method. With these parameters as inputs Wilson-Devinney program was executed for Blue and Yellow passbands simultaneously in detached and semi-detached modes for both the systems. The semidetached mode fitted better than the other solution for both the systems. For RR-Lep, the absolute dimensions were computed by assuming the primary to be a slightly evolved main sequence star. For RX-Hya, the absolute dimensions were computed using Struve’s spectroscopic data. The following table gives all the elements for both the systems. The secondaries of both the systems are overluminous for their masses suggesting that they have lost considerable mass.

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