scholarly journals Spectroscopic Hα and Hγ survey of field Be stars: 2004-2008

2009 ◽  
Vol 5 (S262) ◽  
pp. 343-344
Author(s):  
Erika Grundstrom ◽  
Christina Aragona ◽  
Tabetha Boyajian ◽  
Douglas Gies ◽  
Amber ◽  
...  
Keyword(s):  
Main Sequence ◽  
Line Emission ◽  
Circumstellar Disks ◽  
Circumstellar Disk ◽  
Sequence Evolution ◽  
Be Stars ◽  
B Stars ◽  
Significant Variability ◽  
Vanderbilt University ◽  
The Universe

AbstractMassive O- and B-type stars are “cosmic engines” in the Universe and can be the dominant source of luminosity in a galaxy. Be stars are rapidly rotating B-type stars that lose mass in an equatorial, circumstellar disk (Porter & Rivinius 2003) and cause Balmer and other line emission. Currently, we are unsure as to why these stars rotate so quickly but three scenarios are possible: they may have been born as rapid rotators, spun up by binary mass transfer, or spun up during the main-sequence evolution of B stars. In order to investigate these scenarios for this population of massive stars, we have been spectroscopically observing a set of 115 field Be stars with the Kitt Peak Coudè Feed telescope in both the Hα and Hγ wavelength regimes since 2004. This time baseline allows for examination of variability properties of the circumstellar disks as well as determine candidates for closer examination for binarity.We find that 90% of the observed stars show some variability with only 4% showing significant variability over the 4-year baseline. Such values may be compared with the significant variability seen in some clusters such as NGC 3766 (McSwain 2008). Also, while 20% of the sample consists of known binaries, we find that another 15-30% of the sample shows indications of binarity.This work has been supported in part by a grant from the Vanderbilt University Learning Sciences Institute, NASA grant # NNX08AV70G, and NSF Career grant AST-0349075.

scholarly journals Spectroscopic Hα and Hγ survey of field Be stars: 2004–2009

2010 ◽  
Vol 6 (S272) ◽  
pp. 290-291
Author(s):  
Erika D. Grundstrom ◽  
Douglas R. Gies ◽  
Christina Aragona ◽  
Tabetha S. Boyajian ◽  
E. Victor Garcia ◽  
...  
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Line Emission ◽  
Circumstellar Disks ◽  
Circumstellar Disk ◽  
Sequence Evolution ◽  
Be Stars ◽  
B Stars ◽  
Significant Variability ◽  
The Universe

AbstractMassive O- and B-type stars are “cosmic engines” in the Universe and can be the dominant source of luminosity in a galaxy. The class of Be stars are rapidly rotating B-type stars that lose mass in an equatorial, circumstellar disk (Porter & Rivinius 2003) and cause Balmer and other line emission. Currently, we are unsure as to why these stars rotate so quickly but three scenarios are possible: they may have been born as rapid rotators, spun up by binary mass transfer, or spun up during the main-sequence evolution of B stars. In order to investigate these scenarios for this population of massive stars, we have been spectroscopically observing a set of 115 field Be stars with the Kitt Peak Coudè Feed telescope in both the Hα and Hγ wavelength regimes since 2004. This time baseline allows for examination of variability properties of the circumstellar disks as well as determine candidates for closer examination for binarity. We find that 90% of the observed stars show some variability with 8% showing significant variability over the 5-year baseline. Such values may be compared with the significant variability seen in some clusters such as NGC 3766 (McSwain 2008). Also, while ~20% of the sample consists of known binaries, we find that another 15–30% of the sample shows indications of binarity.

The Infancy of Solar-Type Stars and its Relevance for the Origin of Life

1997 ◽  
Vol 161 ◽  
pp. 267-282 ◽  
Author(s):  
Thierry Montmerle
Keyword(s):  
Main Sequence ◽  
Solar Nebula ◽  
Circumstellar Disks ◽  
T Tauri Stars ◽  
Necessary Condition ◽  
Sequence Evolution ◽  
T Tauri ◽  
Solar Type ◽  
Optical Domain ◽  
The Origin Of Life

AbstractFor life to develop, planets are a necessary condition. Likewise, for planets to form, stars must be surrounded by circumstellar disks, at least some time during their pre-main sequence evolution. Much progress has been made recently in the study of young solar-like stars. In the optical domain, these stars are known as «T Tauri stars». A significant number show IR excess, and other phenomena indirectly suggesting the presence of circumstellar disks. The current wisdom is that there is an evolutionary sequence from protostars to T Tauri stars. This sequence is characterized by the initial presence of disks, with lifetimes ~ 1-10 Myr after the intial collapse of a dense envelope having given birth to a star. While they are present, about 30% of the disks have masses larger than the minimum solar nebula. Their disappearance may correspond to the growth of dust grains, followed by planetesimal and planet formation, but this is not yet demonstrated.

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 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 A Study of Be Stars in Clusters

1976 ◽  
Vol 70 ◽  
pp. 31-32
Author(s):  
R. Schild ◽  
W. Romanishin
Keyword(s):  
Main Sequence ◽  
Sequence Evolution ◽  
Be Stars ◽  
Rotating Stars ◽  
Time Duration ◽  
Hydrogen Burning ◽  
Fourfold Increase ◽  
Cluster Membership ◽  
Galactic Clusters ◽  
Short Time

Calibrated spectrograms at Hα of 566 stars in 29 young galactic clusters led to the detection of 41 Be stars in clusters. Using cluster membership we have inferred ages and intrinsic (B – V) colors of Be stars to permit a discussion of their evolutionary states.Rotating stars can become Be stars in their early hydrogen burning evolution away from the main sequence. Both the fraction of stars showing hydrogen emission and the strength of emission appear to vary little during the first 80% of post main sequence evolution. However, at the onset of gravitational core contraction, both the fraction of stars showing emission and their mean emission strength undergo a fourfold increase. Many stars in the core contraction phase develop an intrinsic (B – V) excess of 0.15 mag. due to the H− free-bound continuum radiation. Because of the great strength of Hα emission and the short time duration of the effect, the extreme Be stars would be excellent probes for studies of spiral structure and would also serve as probes for studies of ages and distances of extragalactic systems.Analysis of the corrected colors of the Be stars in clusters suggests that the Lucy and Solomon (1970) mechanism for reduction of effective surface gravity by ultraviolet resonance line scattering is probably important for the hotter Be stars. However, a discrepancy exists for the cooler stars between the predicted and observed colors.

scholarly journals Study of a sample of faint Be stars in the exofield of CoRoT

2018 ◽  
Vol 613 ◽  
pp. A70 ◽  
Author(s):  
T. Semaan ◽  
A. M. Hubert ◽  
J. Zorec ◽  
J. Gutiérrez-Soto ◽  
Y. Frémat ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Main Sequence ◽  
Power Spectra ◽  
Circumstellar Disks ◽  
Light Curves ◽  
Radial Pulsation ◽  
Be Stars ◽  
Time Frequency ◽  
Mass Ejection ◽  
Low Amplitude

Context. The class of Be stars are the epitome of rapid rotators in the main sequence. These stars are privileged candidates for studying the incidence of rotation on the stellar internal structure and on non-radial pulsations. Pulsations are considered possible mechanisms to trigger mass-ejection phenomena required to build up the circumstellar disks of Be stars. Aims. Time series analyses of the light curves of 15 faint Be stars observed with the CoRoT satellite were performed to obtain the distribution of non-radial pulsation (NRP) frequencies in their power spectra at epochs with and without light outbursts and to discriminate pulsations from rotation-related photometric variations. Methods. Standard Fourier techniques were employed to analyze the CoRoT light curves. Fundamental parameters corrected for rapid-rotation effects were used to study the power spectrum as a function of the stellar location in the instability domains of the Hertzsprung–Russell (H-R) diagram. Results. Frequencies are concentrated in separate groups as predicted for g-modes in rapid B-type rotators, except for the two stars that are outside the H-R instability domain. In five objects the variations in the power spectrum are correlated with the time-dependent outbursts characteristics. Time-frequency analysis showed that during the outbursts the amplitudes of stable main frequencies within 0.03 c d−1 intervals strongly change, while transients and/or frequencies of low amplitude appear separated or not separated from the stellar frequencies. The frequency patterns and activities depend on evolution phases: (i) the average separations between groups of frequencies are larger in the zero-age main sequence (ZAMS) than in the terminal age main sequence (TAMS) and are the largest in the middle of the MS phase; (ii) a poor frequency spectrum with f ≲ 1 cd−1 of low amplitude characterizes the stars beyond the TAMS; and (iii) outbursts are seen in stars hotter than B4 spectral type and in the second half of the MS. Conclusions. The two main frequency groups are separated by δf = (1.24 ± 0.28) × frot in agreement with models of prograde sectoral g-modes (m = −1, −2) of intermediate-mass rapid rotators. The changes of amplitudes of individual frequencies and the presence of transients correlated with the outburst events deserve further studies of physical conditions in the subatmospheric layers to establish the relationship between pulsations and sporadic mass-ejection events.

scholarly journals The Evolution of Rapidly Rotating B Stars (Review Paper)

1987 ◽  
Vol 92 ◽  
pp. 486-499
Author(s):  
Robert Connon Smith
Keyword(s):  
Main Sequence ◽  
Review Paper ◽  
Rotation Axis ◽  
Evolutionary Stage ◽  
Radial Pulsation ◽  
Be Stars ◽  
Rotating Stars ◽  
B Stars ◽  
Sequence Band ◽  
Main Effects

AbstractBe stars are located in or near the main-sequence band for non-rotating stars. Although this stage of evolution is relatively well understood, there are two main effects that make it impossible to say whether all Be stars are in the same stage of evolution and, if so, what that stage is. One effect is the spread in observed magnitude and colour as a result of rotation. Correction for rotation is not possible because of the unknown inclination of any particular star's rotation axis to the line of sight and because it is not clear what the internal angular momentum distribution is or how it changes as a result of evolution. The other effect is that there are uncertainties in the theoretical evolutionary tracks because the amount of convective overshooting is unclear. Other mixing mechanisms that might in principle also confuse the tracks seem to be small near the main sequence. If Be stars are related to the β Cephei and 53 Persei stars in the same part of the HR diagram, then the non-radial pulsation properties of Be stars may give a clue to their evolutionary state. The existence of a circumstellar disc or ring, however, tells us very little about the evolutionary stage of the underlying star. A useful way forward may be to try to understand individual stars in as much detail as possible.

scholarly journals Continuous spectra of circumstellar envelopes of Be stars

1994 ◽  
Vol 162 ◽  
pp. 425-426
Author(s):  
D. Rohe-Koths ◽  
J. Dachs
Keyword(s):  
Line Emission ◽  
Circumstellar Disks ◽  
Balmer Line ◽  
Be Stars ◽  
Continuous Emission ◽  
Circumstellar Envelopes ◽  
Recombination Radiation ◽  
Infrared Spectral ◽  
Be Star ◽  
Central Stars

Line emission in Be star spectra is accompanied by continuous emission both in the Balmer continuum and in the infrared spectral region, due to the same process that is responsible for Balmer line emission, i.e. to recombination radiation from ionized hydrogen in the extended circumstellar disks surrounding the hot central stars.

scholarly journals Non-Radial Pulsation In Be Stars

1986 ◽  
Vol 7 ◽  
pp. 265-272
Author(s):  
John R. Percy
Keyword(s):  
Mass Transfer ◽  
Critical Velocity ◽  
Main Sequence ◽  
Radial Pulsation ◽  
Be Stars ◽  
Hydrogen Line ◽  
Main Sequence Stars ◽  
Rapid Rotation ◽  
B Stars ◽  
Effective Gravity

Be stars are B stars in which emission has been observed in at least one hydrogen line on at least one occasion. Some Be stars are pre-main-sequence stars, mass-transfer binaries, or supergiant stars with extended atmospheres. The majority, however, are classical Be stars: single stars on or near the main sequence. An important characteristic of these stars seems to be their rapid rotation – close to but not at the “critical” velocity at which the effective gravity vanishes at the equator.

scholarly journals Do Herbig Ae/Be Stars Have Disks?

1997 ◽  
Vol 163 ◽  
pp. 525-530 ◽  
Author(s):  
T.P. Ray ◽  
M. Corcoran
Keyword(s):  
Equivalent Width ◽  
Near Infrared ◽  
Mass Loss Rate ◽  
Line Emission ◽  
Circumstellar Disks ◽  
T Tauri Stars ◽  
Be Stars ◽  
Infrared Excess ◽  
T Tauri ◽  
Outflow Rate

AbstractThe Herbig Ae/Be stars are optically visible pre-main sequence stars of intermediate mass (M* ≈ 3−8M⊙) and are thought to be the higher mass analogues of the T Tauri stars. While there is no doubt that classical T Tauri stars, i.e. those with EW(Hα) ≳ 10 Å, are surrounded by disks, it remains controversial as to whether this is the case with the equivalent Herbig Ae/Be stars. It has even been questioned whether the powerful winds that are ejected by Herbig Ae/Be stars are driven by accretion. To address these problems we have examined a large sample of these stars with the idea of using their forbidden line emission as an indirect diagnostic for the presence of disks. Striking similarities with the classical T Tauri stars are found. For example we have discovered evidence not only for a strong correlation between near-infrared colours and the equivalent width of the forbidden line emission but also that the forbidden line emission normally arises in a blueshifted outflow component. It has already been shown in the case of the classical T Tauri stars that the correlation of near-infrared colour with forbidden line equivalent width is due to a link between the accretion rate and the outflow rate. The virtually identical relationship seen in the case of the Herbig Ae/Be stars must then also have a similar origin. Our finding that the forbidden line emission in Herbig Ae/Be stars is normally blueshifted shows not only that it arises in an outflow but, as in the classical T Tauri stars, such an asymmetry in the velocity centre of the line must be caused by the obscuring effects of a disk. We find that the correlation seen in the classical T Tauri stars between the mass-loss rate and infrared excess can be extended, when we include the Herbig Ae/Be stars, to cover almost 5 orders of magnitude in stellar luminosity. Our observations therefore broaden the findings of earlier observers for low mass young stars and indicate the presence of circumstellar disks around the majority of Herbig Ae/Be stars with forbidden line emission. A corollary of our results is that the same outflow mechanism must operate in both the classical T Tauri stars and the Herbig Ae/Be stars with forbidden line emission.

Sign in / Sign up

Export Citation Format

Share Document