scholarly journals Detection of accreting circumstellar gas around weak emission-line Herbig Ae/Be stars

1994 ◽  
Vol 212 (1-2) ◽  
pp. 107-114 ◽  
Author(s):  
C. A. Grady ◽  
M. R. P�rez ◽  
P. S. Th�
Keyword(s):  
Emission Line ◽  
Be Stars ◽  
Circumstellar Gas

scholarly journals A Catalogue of Be Stars

1982 ◽  
Vol 98 ◽  
pp. 261-263 ◽  
Author(s):  
M. Jaschek ◽  
D. Egret
Keyword(s):  
Emission Line ◽  
Data Center ◽  
Be Stars ◽  
Large Effort ◽  
Set Up ◽  
Available Information

We are presently undertaking, at the Stellar Data Center, a large effort to produce the Catalogue of Stellar Groups, which is a catalogue listing all the kinds of stars with spectral peculiarities existing up to now. The work is in progress and presently about fifty groups (Ap, Am, Be, WR, H and K emission line stars, etc.) are defined, gathering more than 25000 stars. The catalogue was started with the aim to set up lists defined by homogeneous criteria, because up to now the available information is scattered through the literature. We hope that the catalogue will be useful for formulating observing programs and for further detailed research on each of the groups.

scholarly journals The FeII λ5317 line profile of nine Be stars

1994 ◽  
Vol 162 ◽  
pp. 263-264
Author(s):  
D. Ballereau ◽  
J. Chauville ◽  
J. Zorec
Keyword(s):  
Emission Line ◽  
Line Profile ◽  
Be Stars

Our aim is to analyze the FeII λ5317 emission line of nine Be stars recorded in 1990, to deduce some constraints on the modeling of their envelope and to compare them to the results obtained in 1985 and 1987 by other authors.

scholarly journals Modeling Oblique Rotators: Magnetospheres and Winds

1999 ◽  
Vol 169 ◽  
pp. 178-186
Author(s):  
Steven N. Shore
Keyword(s):  
Main Sequence ◽  
Rotational Axis ◽  
Be Stars ◽  
Polar Caps ◽  
Rotator Model ◽  
Peculiar Stars ◽  
Oblique Rotator ◽  
Circumstellar Gas ◽  
Nonthermal Radio Emission ◽  
The Magnetic Field

AbstractThe upper main sequence chemically peculiar (CP) stars display evidence of trapped circumstellar gas and nonspherical outflows. These stars are also known to possess strong magnetic fields that are often highly inclined to the rotational axis. Their phenomenology can be understood by using the oblique rotator model, which has successfully accounted for the observed behavior of the cooler CP stars. This paper reviews some features of the oblique rotator model, in which the magnetic field is assumed to provide a rigid framework for the structuring of the stellar and circumstellar gas. Corotation of circumstellar plasma is enforced out to the Alfven radius in the magnetic equatorial plane, while for the hotter stars, a radiatively driven wind emerges from the magnetic polar caps. Some observable consequences of the model are discussed, especially the Hα and ultraviolet resonance line absorption and emission periodic variability that has been observed in the He-peculiar stars and nonthermal radio emission. Magnetospheres may also be present in O stars, e.g. θ1 Ori C, and in the Herbig Ae/Be stars.

scholarly journals Simultaneous Spectroscopy and Polarimetry of Be Stars

1987 ◽  
Vol 92 ◽  
pp. 84-86
Author(s):  
D. R. Gies ◽  
David McDavid
Keyword(s):  
Mass Loss ◽  
Emission Line ◽  
Absorption Line ◽  
Line Profile ◽  
Circumstellar Envelope ◽  
Be Stars ◽  
Line Profiles ◽  
Initial Attempt ◽  
Rapid Variability ◽  
Hα Emission

Evidence is now accumulating that many Be stars display photospheric line profile variations on timescales of days or less that are probably caused by nonradial pulsations (Baade 1984; Penrod 1986). In some circumstances these pulsations can promote mass loss into the circumstellar envelope, and consequently the conditions in the inner part of the envelope may vary on similar timescales. Changes in the envelope could produce variations in the polarization and emission line profiles, and observers have reported rapid variability in both. We describe here an initial attempt to search for simultaneous variations in continuum polarization, Hα emission, and the He I λ6678 photospheric absorption line in order to investigate correlated changes on short timescales.

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.

scholarly journals Neo-R1000: A Fast And Efficient Compact Spectrograph For Emission Line Objects Study At Bosscha Observatory

2016 ◽  
Vol 27 (1) ◽  
pp. 1-8
Author(s):  
Hakim L Malasan ◽  
Imanul Jihad ◽  
Robiatul Muztaba ◽  
Irham T Andika ◽  
Evaria Puspitaningrum ◽  
...  
Keyword(s):  
Emission Line ◽  
High Speed ◽  
Focal Length ◽  
Ccd Camera ◽  
Halogen Lamp ◽  
Be Stars ◽  
Classical Novae ◽  
Transmission Grating ◽  
Cathode Tube ◽  
High Flexibility

In 2015, the Institute Teknologi Bandung (ITB) signed a Memorandum of Understanding with Sangyou Kyoto University (KSU). One realization of collaboration between ITB and KSU is observational program of Novae using a compact spectrograph NEO-R1000 (Novae and Emission line Objects with Resolution of 1000). This spectrograph is mounted at the Celestron C-11 (F/10.0) reflector and supported by a Losmandy G-11 equatorial mounting inside the GAO-ITB sliding roof building, Bosscha observatory, Lembang. The unique configuration of this spectrograph is the employment of mirror collimator and camera lens with focal length ratio of 3:1. This makes it has high speed characteristics. A slit width of 6.5 μm (4.7” @ C-11 reflector ) is combined with a fixed transmission grating of 600 grooves/mm and equipped with a ST-8 XME CCD camera (9 μm per pixel, 1530 × 1024 pixels), resulting in a resolution of R≈ 1000 at a wavelength of 5800 Å with effective spectrum wavelength coverage Δl 4000-8000 Å. NEO-R1000 spectrograph has additional peripherals such as a Fe-Ne-Ar hollow cathode tube (HTC) which is used as a comparison source. We take flat-field spectrum by using an acrylic board and a halogen lamp. The main primary aim of this spectrograph is to observe the Classical Novae in the southern sky as part of Collaborative Spectroscopic Observations for the Detection of Molecules in Classical Novae. This spectrograph can also be used to observe other emission line objects such as Planetary Nebulae, Comets, P Cygni star type, WR stars and Be stars. In June 2015, this spectrograph was successfully used to observe Nova Sgr 2015 no 2. Further developments of this spectrograph includes constructing a rotator to be attached to the flange of telescope to ensure high flexibility in observation of extended objects. In the future, a fiber optic connecting output pupil with the entrance slit of the spectrograph will be deployed to improve observational effectivity while reducing the load of spectrograph on telescope.

scholarly journals Be Star Surveys in Open Clusters with Balmer-line Photometry

2000 ◽  
Vol 175 ◽  
pp. 63-66
Author(s):  
Gemma Capilla ◽  
Juan Fabregat ◽  
Deborah Baines
Keyword(s):  
Emission Line ◽  
Main Sequence ◽  
Open Clusters ◽  
Balmer Line ◽  
Be Stars ◽  
Late Type ◽  
Efficient Tool ◽  
Be Star ◽  
Almost All ◽  
Evolutionary Interpretation

AbstractWe present CCD Hα and Hβ photometry of young open clusters. We show that the comparison of the α and β photometric indices provides an efficient tool for identifying emission line stars. We report on the discovery of several new Be stars.The preliminary results of our survey are the following: i. the younger clusters (age < 10 Myr) are almost lacking of Be stars, ii. clusters in the age interval 10–30 Myr are rich in Be stars. Almost all of them are of spectral types earlier than B5, while late-type Be stars are scarce. These results point towards an evolutionary interpretation of the Be phenomenon, in the sense that Be stars are close to the end of their main sequence lifetime.

scholarly journals Paschen and Brackett Lines in Be stars

2000 ◽  
Vol 175 ◽  
pp. 472-475
Author(s):  
L. Cidale ◽  
J. Zorec ◽  
J.P. Maillard ◽  
N. Morrell
Keyword(s):  
Emission Line ◽  
Stellar Atmosphere ◽  
Velocity Fields ◽  
Circumstellar Envelope ◽  
Be Stars ◽  
Line Profiles ◽  
Circumstellar Envelopes ◽  
Hydrogen Line ◽  
Stellar Activity ◽  
Central Stars

AbstractThe activities detected in Be stars indicate that the formation of the circumstellar envelope and its structure cannot be studied independently of the phenomena taking place in the outermost layers of the central stars. Assuming that related to the stellar activity there is an expanding atmospheric region with temperatures Te > Teff followed by an envelope with a decreasing temperature, we calculated hydrogen line profiles for different velocity fields and different positions of temperature maxima relative to the underlying photosphere. Results show that the Hα line is not very sensitive to changes introduced to the stellar atmosphere and to the nearby circumstellar layers. Moreover, the Hα emission line profiles look like those produced by disc-like circumstellar envelopes seen pole-on, although the model for the circumstellar envelope is spherical. However, the first members of the Paschen and Brackett series are strongly sensitive to any changes introduced in the photospheric and exophotospheric layers. We conclude that the study of these lines may then be valuable to obtain new insight on the activity of central stars and on the phenomena involved in circumstellar envelope formation in Be stars.

Rapid Variability of H α Emission Line in Be Stars

1994 ◽  
pp. 254-256
Author(s):  
B. G. Anandarao ◽  
A. Chakraborty ◽  
R. Swaminathan ◽  
B. Lokanadham
Keyword(s):  
Emission Line ◽  
Be Stars ◽  
Rapid Variability
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