scholarly journals Variability of Some Be Stars on High-Resolution, High S/N Spectra

1988 ◽  
Vol 132 ◽  
pp. 131-134
Author(s):  
A. M. Hubert ◽  
H. Hubert ◽  
B. Dagostinoz ◽  
M. Floquet
Keyword(s):  
Emission Line ◽  
Time Scale ◽  
Signal To Noise Ratio ◽  
Complex Structure ◽  
Ccd Camera ◽  
Brightness Distribution ◽  
Short Time Scale ◽  
Be Stars ◽  
Rapid Variability ◽  
Hα Emission

Rapid variability in Be stars could be understood by non radial pulsations or by rotation of an inhomogeous surface brightness distribution…The structure and the variability of the Hα and of the HeI λ6678 lines have been investigated with an optical fiber spectrograph and a CCD camera. The signal to noise ratio, measured in the continuum, is between 300 and 500.Weak changes in the Hα emission line profile of γ Cas have been detected on time-scale of hours and days. This line has an asymmetric profile exhibiting only one blue-shifted maximum while the HeI λ6678 has a double-peak emission, superimposed to the photospheric contribution, with a violet to red peak ratio V/R >1.The Hα emission line of φ Per exhibits a complex structure with significant changes in its core, from night to night and on a short time scale <lhr. The HeI λ6678 presents a blue-shifted asymmetric emission (red-winged) superimposed to the photospheric contribution.Furthermore the Hel photospheric line λ6678 of the B6 star o And has presented notable variations in its profile during the 2 observational campaigns, which do not seem correlated to the photometric period of 1.57 day.

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 Rapid variability of Hα emission line in Be stars

1994 ◽  
Vol 162 ◽  
pp. 254-256
Author(s):  
B. G. Anandarao ◽  
A. Chakraborty ◽  
R. Swaminathan ◽  
B. Lokanadham
Keyword(s):  
Emission Line ◽  
Emission Lines ◽  
Be Stars ◽  
Rapid Variability ◽  
Fabry Perot ◽  
Dark Counts ◽  
Hα Emission

We have initiated an observational campaign on some bright Be stars in order to investigate the rapid variability in emission lines using a Fabry-Perot spectrometer(λ/δλ = 104; FSR = 21.3Å) at the Nasmyth focus of the 1.22 m JRO telescope at Hyderabad, India. The PMT dark counts were 1 – 2sec-1. Here we report our first observations on four stars.

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.

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

scholarly journals Recent Spectroscopy of X-Ray Sources and Systems Related to Cataclysmic Variables: I

1983 ◽  
Vol 72 ◽  
pp. 21-24
Author(s):  
A.P. Cowley ◽  
D. Crampton ◽  
J.B. Hutchings
Keyword(s):  
Emission Line ◽  
Time Scale ◽  
Cataclysmic Variables ◽  
Short Time Scale ◽  
X Ray ◽  
Spectroscopic Observations ◽  
Low Mass ◽  
Short Time

ABSTRACTWe present results of recent spectroscopic observations of A) some LMC X-ray sources, B) the X-ray burster 1735-44, and C) the peculiar emission-line binary BE UMa. From the short time scale variations and inferred low mass components each shows some similarities to more classical CV's.

scholarly journals Seismology of southern Be stars

1994 ◽  
Vol 162 ◽  
pp. 104-105
Author(s):  
Eduardo Janot-Pacheco ◽  
Nelson Vani Leister
Keyword(s):  
High Resolution ◽  
Signal To Noise Ratio ◽  
Ccd Camera ◽  
High Signal ◽  
Be Stars ◽  
Signal To Noise ◽  
Photometric Variability ◽  
Spectroscopic Observations ◽  
Photometric Observations ◽  
Noise Ratio

We have started in 1990 a search for moving bumps in the HeI λ 667.8 nm of mainly southern, bright Be stars. The objects of our sample have been selected on the basis of photometric variability (Cuypers et al., 1989). High resolution (R≥ 30,000), high signal-to-noise ratio (S/R≥ 300) spectroscopic observations have been performed at the brazilian Laboratório Nacional de Astrofísica with a CCD camera attached to the coudé spectrograph of the 1.60 m telescope (e.g. Table I). Several hundred spectra have been taken during the last three years. Photometric observations simultaneous with spectroscopy were made on the same site in July 1992 with a two-channel photometer (Stromgren b filter) and a CCD camera (Johnson B filter) installed at two 0.60 m telescopes. The idea is try to disentangle the controversy between NRP and RM models with the help of simultaneous spectroscopy and photometry.

scholarly journals Observations of Rapid Variability in Be Stars (Review Paper)

1987 ◽  
Vol 92 ◽  
pp. 49-65 ◽  
Author(s):  
John R. Percy
Keyword(s):  
Time Scale ◽  
Review Paper ◽  
Spectroscopic Studies ◽  
Be Stars ◽  
Intensive Study ◽  
Rapid Variability ◽  
Photometric Variability ◽  
Ultimate Cause ◽  
Special Instrumentation ◽  
Individual Objects

AbstractPhotometric and/or spectroscopic variability on time scales of approximately 0.2 to 2 days has been observed in over 40 Be stars, and is suspected in many more. This paper reviews the observational aspects of this phenomenon: both surveys and studies of individual objects. This phenomenon is not easy to study and interpret: (i) the time scale is inconvenient (ii) there have been very few simultaneous photometric and spectroscopic studies of individual objects (iii) the photometric variability is small, often irregular and superimposed on longer-term variability and (iv) the spectroscopic variability is usually observed as absorption line profile variability, which requires special instrumentation. For these and other reasons, there is not yet a universal agreement about the nature of this phenomenon. Nevertheless, it deserves further intensive study, not only because it is common, but also because in one or two stars, there is evidence that the rapid variability may be related (causally perhaps?) to the longer-term variability in these stars - variability whose ultimate cause is still not known.

scholarly journals The GALAH survey: characterization of emission-line stars with spectral modelling using autoencoders

2020 ◽  
Vol 500 (4) ◽  
pp. 4849-4865
Author(s):  
Klemen Čotar ◽  
Tomaž Zwitter ◽  
Gregor Traven ◽  
Joss Bland-Hawthorn ◽  
Sven Buder ◽  
...  
Keyword(s):  
Emission Line ◽  
Rarefied Gas ◽  
Signal To Noise Ratio ◽  
Emission Spectra ◽  
High Signal ◽  
Physical Mechanisms ◽  
Repeated Observation ◽  
Hα Emission ◽  
The Continuum

ABSTRACT We present a neural network autoencoder structure that is able to extract essential latent spectral features from observed spectra and then reconstruct a spectrum from those features. Because of the training with a set of unpeculiar spectra, the network is able to reproduce a spectrum of high signal-to-noise ratio that does not show any spectral peculiarities, even if they are present in an observed spectrum. Spectra generated in this manner were used to identify various emission features among spectra acquired by multiple surveys using the HERMES spectrograph at the Anglo-Australian telescope. Emission features were identified by a direct comparison of the observed and generated spectra. Using the described comparison procedure, we discovered 10 364 candidate spectra with varying intensities (from partially filled-in to well above the continuum) of the Hα/Hβ emission component, produced by different physical mechanisms. A fraction of these spectra belong to the repeated observation that shows temporal variability in their emission profile. Among the emission spectra, we find objects that feature contributions from a nearby rarefied gas (identified through the emission of [N ii] and [S ii] lines) that was identified in 4004 spectra, which were not all identified as having Hα emission. The positions of identified emission-line objects coincide with multiple known regions that harbour young stars. Similarly, detected nebular emission spectra coincide with visually prominent nebular clouds observable in the red all-sky photographic composites.

scholarly journals Is HR 9070 Really Pulsating?

1987 ◽  
Vol 92 ◽  
pp. 78-81
Author(s):  
Sareyan J.P. ◽  
Alvarez M. ◽  
Chauville J. ◽  
Le Contel J.M. ◽  
Michel R. ◽  
...  
Keyword(s):  
Time Resolution ◽  
Time Scale ◽  
Short Time Scale ◽  
Be Stars ◽  
Time Constants ◽  
Systematic Survey ◽  
Short Time

As Be stars and classical β CMa variables both have a distribution peak at B2, one can wonder if there is a connection between these two phenomena. A way to solve this problem could be to carry out a systematic survey of emission on short periodic B variables,over months and years.Another way, chosen by our grouns in Nice, Ensenada and Meudon, is to improve time resolution in photometric and spectrographic observations on the Be stars already known to have short time scale variations. Special attention is paid to longitude cooperation, essential to detect or measure longer time constants.

Sign in / Sign up

Export Citation Format

Share Document