On the continua and infrared excess of some bright Be stars

1988 ◽  
Vol 96 ◽  
pp. 346 ◽  
Author(s):  
P. S. Goraya ◽  
N. S. Tur
Keyword(s):  
Be Stars ◽  
Infrared Excess

scholarly journals Spectro-interferometric observations of a sample of Be stars

2019 ◽  
Vol 621 ◽  
pp. A123 ◽  
Author(s):  
Y. R. Cochetti ◽  
C. Arcos ◽  
S. Kanaan ◽  
A. Meilland ◽  
L. S. Cidale ◽  
...  
Keyword(s):  
Critical Velocity ◽  
Velocity Ratio ◽  
Density Wave ◽  
Wave Structure ◽  
Maximum Size ◽  
Rotation Velocity ◽  
Variable Stars ◽  
High Mass ◽  
Be Stars ◽  
Infrared Excess

Context. Be stars are rapid rotators surrounded by a gaseous disk envelope whose origin is still under debate. This envelope is responsible for observed emission lines and large infrared excess. Aims. To progress in the understanding of the physical processes involved in the disk formation, we estimate the disk parameters for a sample of Be stars and search for correlations between these parameters and stellar properties. Methods. We performed spectro-interferometric observations of 26 Be stars in the region of the Brγ line to study the kinematical properties of their disks through the Doppler effect. Observations were performed at the Paranal observatory with the VLTI/AMBER interferometer. This instrument provides high spectral (R ≃ 12 000) and high spatial (θmin = 4 mas) resolutions. Results. We modeled 18 Be stars with emission in the Brγ line. The disk kinematic is described by a quasi-Keplerian rotation law, with the exception of HD 28497 that presents a one-arm density-wave structure. Using a combined sample, we derived a mean value for the velocity ratio V̅/V̅c = 0.75 (where Vc is the critical velocity), and found that rotation axes are probably randomly distributed in the sky. Disk sizes in the line component model are in the range of 2–13 stellar radii and do not correlate with the effective temperature or spectral type. However, we found that the maximum size of a stable disk correlates with the rotation velocity at the inner part of the disk and the stellar mass. Conclusions. We found that, on average, the Be stars of our combined sample do not rotate at their critical velocity. However, the centrifugal force and mass of the star defines an upper limit size for a stable disk configuration. For a given rotation, high-mass Be stars tend to have more compact disks than their low-mass counterparts. It would be interesting to follow up the evolution of the disk size in variable stars to better understand the formation and dissipation processes of their circumstellar disks.

scholarly journals Near-infrared excess and emission characteristics of classical Be stars

2010 ◽  
Vol 6 (S272) ◽  
pp. 404-405
Author(s):  
Chien-De Lee ◽  
Wen-Ping Chen ◽  
Daisuke Kinoshita
Keyword(s):  
Emission Line ◽  
Near Infrared ◽  
Thermal Emission ◽  
Temporal Correlation ◽  
Circumstellar Dust ◽  
Emission Characteristics ◽  
Spectral Features ◽  
Be Stars ◽  
Infrared Excess ◽  
Fast Rotating

AbstractClassical Be (CBe) stars are fast-rotating emission-line stars associated with infrared excess often attributed to plasma free-free emission. A few with exceptionally large near-infrared excess, namely with (J–H) and (H–Ks) both greater than 0.6 mag, however, must be accounted for by thermal emission from circumstellar dust. From 2007 to 2009, spectra of more than 100 CBe stars have been collected. We present some of these spectra and discuss how temporal correlation (or lack of) among spectral features would provide possible diagnosis of the origin of the CBe phenomena.

A multiband optical polarimetric study of classical Be stars with exceptionally large near-infrared excess

2013 ◽  
Author(s):  
Chien-De Lee ◽  
C. Eswaraiah ◽  
A. K. Pandey ◽  
Wen-Ping Chen
Keyword(s):  
Near Infrared ◽  
Be Stars ◽  
Infrared Excess ◽  
Polarimetric Study

scholarly journals Infrared Emission from Four be Stars Optical Counterparts of Galactic X-Ray Sources

1982 ◽  
Vol 98 ◽  
pp. 247-251
Author(s):  
P. Persi ◽  
M. Ferrari-Toniolo ◽  
G.L. Grasdalen
Keyword(s):  
Energy Distribution ◽  
Electron Density ◽  
Stellar Wind ◽  
Infrared Emission ◽  
Circumstellar Disk ◽  
Be Stars ◽  
Infrared Excess ◽  
Infrared Observations ◽  
X Ray ◽  
Be Star

Preliminary results of our infrared observations from 2.3 up to 10 and 20 microns of the Be-X-ray stars X Per, γ Cas and HDE 245770, indicate the presence of an ionized circumstellar disk with an electron density law of the type ne ∝ r−3.5. x Per and γ Cas show besides, variable infrared excess at 10μ suggesting variability in the stellar wind. LS I+65°010 presents an anomalous infrared energy distribution for a Be star.

H? line emission and infrared excess in Be stars

1985 ◽  
Vol 113 (2) ◽  
pp. 373-381 ◽  
Author(s):  
P. S. Goraya ◽  
B. S. Rautela
Keyword(s):  
Line Emission ◽  
Be Stars ◽  
Infrared Excess

scholarly journals Ultraviolet and infrared excess emission in Be stars

1986 ◽  
Vol 222 (1) ◽  
pp. 121-141 ◽  
Author(s):  
P. S. Goraya
Keyword(s):  
Be Stars ◽  
Infrared Excess ◽  
Excess Emission

scholarly journals On the Mass Accretion Rate and Infrared Excess in Herbig Ae/Be Stars

2019 ◽  
Vol 157 (4) ◽  
pp. 159 ◽  
Author(s):  
R. Arun ◽  
Blesson Mathew ◽  
P. Manoj ◽  
K. Ujjwal ◽  
Sreeja S. Kartha ◽  
...  
Keyword(s):  
Accretion Rate ◽  
Be Stars ◽  
Infrared Excess ◽  
Mass Accretion Rate

scholarly journals Multiwavelength observations of the Be-star/X-ray binary EXO2030+375 during outburst

1994 ◽  
Vol 162 ◽  
pp. 206-207
Author(s):  
A.J. Norton ◽  
M.J. Coe ◽  
C. Everall ◽  
P. Roche ◽  
L. Bildsten ◽  
...  
Keyword(s):  
Neutron Star ◽  
Emission Lines ◽  
Be Stars ◽  
Infrared Excess ◽  
X Ray ◽  
Circumstellar Material ◽  
Spin Period ◽  
Be Star ◽  
Star Surface ◽  
X Ray Binaries

EXO2030+375 consists of a neutron star in an eccentric 46 day orbit around a 20th magnitude Be-star companion (Coe et al., 1988; Parmar et al., 1989; Stollberg et al., 1993). The Be-star is thought to be surrounded by a shell/disc of material which is responsible for the infrared excess and Balmer emission lines which are characteristic of Be-stars in general. At periastron, the neutron star passes through this circumstellar material, giving rise to enhanced accretion onto the neutron star surface. As a result of this, the X-ray emission (pulsed at the neutron star spin period of 41.8s) increases dramatically, so producing the transient, outburst behaviour which is commonly seen in Be-star / X-ray binaries.

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.

scholarly journals Paschen Decrements in Be Stars

1976 ◽  
Vol 70 ◽  
pp. 227-227
Author(s):  
D. Briot
Keyword(s):  
Theoretical Calculations ◽  
Physical Characteristics ◽  
Emission Lines ◽  
Be Stars ◽  
Infrared Excess ◽  
General Properties

We searched for the general properties of the Be stars with Paschen emission lines. First, we obtained a relation between the infrared excess of the Be stars and the presence of emission in the Paschen lines. Until now, these emission excesses could be related to no physical characteristics of classical Be stars. Then, the measures of Paschen decrements of 12 stars whose spectral types range from B0e to B5e allowed us to check several theoretical calculations about the formation of emission lines in the envelopes of Be stars. Thus we can see the prominent part played by the electronic collisions in the Sobolev theory. Indeed, only with calculations taking the electronic collisions into account, can we obtain theoretical values agreeing with both measured Paschen and Balmer decrements for the hottest stars of our sample. However, no theoretical values agree with the observed decrements for the cooler stars.

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