scholarly journals Long-Term Spectroscopic Monitoring and Surveys of Early-Type Stars with and without Circumstellar Envelopes

2017 ◽  
Vol 26 (1) ◽  
Author(s):  
Anatoly S. Miroshnichenko ◽  
Steven Danford ◽  
Sergei V. Zharikov ◽  
Nadine Manset ◽  
Hugo Levato ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Binary Systems ◽  
Theoretical Explanation ◽  
Evolutionary Status ◽  
Early Type ◽  
Fundamental Parameters ◽  
Spectroscopic Monitoring ◽  
Early Type Stars ◽  
Large Telescopes

AbstractOngoing studies of different groups of stars result in improving our knowledge of their fundamental parameters and evolutionary status. Also, they result in finding new phases of stellar evolution, which require theoretical explanation. At the same time, availability of large telescopes and sensitivity improvement of detectors shift the focus of many observational programs toward fainter and more distant objects. However, there are still many problems in our understanding of details of stellar evolution which can now be solved with small telescopes and observations of bright stars. Approaching these problems implies conducting surveys of large groups of stars and long-term monitoring of individual objects. In this talk, we present the results of recent international programs of photometric and spectral monitoring of several groups of early-type stars. In particular, we discuss the role of binarity in creation of the Be phenomenon and show examples of recently discovered binary systems as well as the problem of refining fundamental parameters of B and A type supergiants. Special attention will be paid to collaboration with the amateur community and use of échelle spectrographs mounted on small telescopes.

scholarly journals The Connection with B[e] stars

2000 ◽  
Vol 175 ◽  
pp. 26-36 ◽  
Author(s):  
Franz-Josef Zickgraf
Keyword(s):  
Common Property ◽  
Main Sequence ◽  
Emission Lines ◽  
Circumstellar Dust ◽  
Evolutionary Status ◽  
Be Stars ◽  
Early Type ◽  
Circumstellar Envelopes ◽  
Early Type Stars ◽  
Uniform Group

AbstractThe characteristics of the various types of B[e] stars are discussed and compared with those of classical Be stars. Both groups of stars are characterized by the presence of emission lines in their spectra, in particular of hydrogen. However, there are also significant differences between these classes. Classical Be stars lack hot circumstellar dust and strong forbidden low-excitation emission lines, which are typical characteristics produced by B[e]-type stars. While classical Be stars are a rather uniform group of early-type stars, B[e]-type stars form a quite heterogeneous group, very often of poorly known evolutionary status, comprising such diverse types of objects as near main-sequence objects, evolved lowmass proto-planetray nebulae and massive evolved hot supergiants. Even pre-main sequence Herbig Ae/Be stars sometimes find their way into the group of B[e] stars. However, despite these dissimilarities classical Be stars and B[e]-type stars, share a common property, namely the nonsphericity of their circumstellar envelopes.

scholarly journals Mass loss from early-type stars

1970 ◽  
Vol 36 ◽  
pp. 209-212
Author(s):  
J. B. Hutchings
Keyword(s):  
Mass Loss ◽  
Spectral Type ◽  
Stellar Evolution ◽  
Early Type ◽  
High Luminosity ◽  
Spectroscopic Evidence ◽  
Ob Stars ◽  
Early Type Stars ◽  
Very High ◽  
Hr Diagram

Following the detailed study of four very high luminosity OB stars, a survey has been made for spectroscopic evidence of mass loss in a number of early-type supergiants. A list of spectroscopic criteria is given and the mass loss estimates for 24 stars plotted on the HR diagram. The dependence of the phenomenon on spectral type and luminosity is discussed as well as its significance in terms of stellar evolution.

scholarly journals Be Phenomena in Young Early-type Stars: Various Forms of Interaction between the Star and the Circumstellar Gaseous Envelope

2000 ◽  
Vol 175 ◽  
pp. 344-347
Author(s):  
M. Pogodin
Keyword(s):  
High Resolution ◽  
Stellar Wind ◽  
Main Sequence ◽  
Stellar Surface ◽  
High Resolution Spectroscopy ◽  
Evolutionary Status ◽  
Be Stars ◽  
Early Type ◽  
Early Type Stars ◽  
Gaseous Envelope

AbstractNew results of high-resolution spectroscopy of four pre-main sequence Ae/Be stars are presented. An analysis of parameters of lines originating in different regions of the circumstellar (CS) envelope (Hα, Hβ, He I 5876, DNal) allows to reconstruct a picture of the interaction between the star and the CS environment which can be displayed in different forms. At least two separate processes seem to impact the structural and kinematical properties of the envelope: the stellar wind from the stellar surface and the matter infall onto the star from the CS media. A possible relation between these two phenomena is discussed in the framework of different models. Some similarity between observational phenomena in Herbig Ae/Be and classical Be stars is noted in spite of their difference in evolutionary status.

Fundamental properties and seismological analysis of three Kepler stars

2012 ◽  
Vol 8 (S294) ◽  
pp. 203-204
Author(s):  
K. Liu ◽  
S. L. Bi
Keyword(s):  
Stellar Evolution ◽  
Evolutionary Status ◽  
Rotational Period ◽  
Lithium Abundance ◽  
Fundamental Parameters ◽  
Rotation Rates ◽  
Fundamental Properties

AbstractThe lithium abundance of KIC 11395018 and KIC 10920273 are not compatible with their age, which is deduced by asteroseismology. To explain this phenomenon, we investigate the possible evolutionary status and perform seismological analysis of the three stars KIC 11395018, KIC 10273246 and KIC 10920273. Using the Yale Rotating Stellar Evolution Code (YREC), we constructed a grid of evolutionary tracks with different input physics and rotation rates. In addition to the conventional observed properties, we added two observed constraints: lithium abundance and rotational period. As a result, the lithium abundance of our rotation models agrees well with the observation. Meanwhile, we obtained a set of more accurate stellar fundamental parameters than previous studies.

scholarly journals The theory of winds in early type stars

1981 ◽  
Vol 59 ◽  
pp. 125-130 ◽  
Author(s):  
A.G. Hearn
Keyword(s):  
Mass Loss ◽  
Spectral Type ◽  
Stellar Evolution ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Optical Measurements ◽  
Early Type ◽  
Large Uncertainty ◽  
Early Type Stars ◽  
Loss Rates

I assume that the purpose of this review of the theory of winds from early type stars is to summarize the way in which the mass loss rate of a star may be included in a calculation of stellar evolution. Let me summarize my conclusions. It is not possible. One can only use estimates of mass loss rates obtained from the observations. Even these give a large uncertainty. The observed mass loss rates for different stars of the same spectral type vary. Further the mass loss rates obtained by different methods for the same star differ. An extreme example of this is 9 Sgr. The mass loss rate derived from the radio observations is forty times greater than that derived from the U.V. and optical measurements (Abbott et al. 1980).

scholarly journals A Study of Main Sequence Early Type Stars

1979 ◽  
Vol 47 ◽  
pp. 483-490
Author(s):  
Ulf Sinnerstad
Keyword(s):  
Main Sequence ◽  
Photometric Study ◽  
Line Profiles ◽  
Early Type ◽  
Fundamental Parameters ◽  
Preliminary Results ◽  
Early Type Stars ◽  
Hydrogen Lines ◽  
Line Strengths

AbstractA spectroscopic and photometric study of 75 normal main sequence B2-B6 stars has been carried out. From the spectra (12 Å/mm, 3700-4800 Å) are determined: equivalent widths of all measurable lines, line profiles of hydrogen lines and v sin i. The photometric work includes besides uvby and β photometry, also photoelectrically determined line strengths of Hα and He I 4471 Å. Some preliminary results concerning the relation between the MK types and the atmospheric fundamental parameters (Teff, log g) of the stars are briefly discussed.

Colliding winds from early-type stars in binary systems

1992 ◽  
Vol 386 ◽  
pp. 265 ◽  
Author(s):  
Ian R. Stevens ◽  
John M. Blondin ◽  
A. M. T. Pollock
Keyword(s):  
Binary Systems ◽  
Early Type ◽  
Early Type Stars ◽  
Colliding Winds

scholarly journals Megahertz emission of massive early-type stars in the Cygnus region

2020 ◽  
Vol 37 ◽  
Author(s):  
P. Benaglia ◽  
M. De Becker ◽  
C. H. Ishwara-Chandra ◽  
H. T. Intema ◽  
N. L. Isequilla
Keyword(s):  
Binary Systems ◽  
Thermal Emission ◽  
Spectral Energy Distribution ◽  
Wide Band ◽  
Type Systems ◽  
Radio Spectrum ◽  
Spectral Energy ◽  
Strong Impact ◽  
Early Type ◽  
Early Type Stars

Abstract Massive, early-type stars have been detected as radio sources for many decades. Their thermal winds radiate free–free continuum and in binary systems hosting a colliding-wind region, non-thermal emission has also been detected. To date, the most abundant data have been collected from frequencies higher than 1 GHz. We present here the results obtained from observations at 325 and 610 MHz, carried out with the Giant Metrewave Radio Telescope, of all known Wolf-Rayet and O-type stars encompassed in area of $\sim$ 15 sq degrees centred on the Cygnus region. We report on the detection of 11 massive stars, including both Wolf-Rayet and O-type systems. The measured flux densities at decimeter wavelengths allowed us to study the radio spectrum of the binary systems and to propose a consistent interpretation in terms of physical processes affecting the wide-band radio emission from these objects. WR 140 was detected at 610 MHz, but not at 325 MHz, very likely because of the strong impact of free–free absorption (FFA). We also report—for the first time—on the detection of a colliding-wind binary system down to 150 MHz, pertaining to the system of WR 146, making use of complementary information extracted from the Tata Institute of Fundamental Research GMRT Sky Survey. Its spectral energy distribution clearly shows the turnover at a frequency of about 600 MHz, that we interpret to be due to FFA. Finally, we report on the identification of two additional particle-accelerating colliding-wind binaries, namely Cyg OB2 12 and ALS 15108 AB.

scholarly journals On the perspectives of using XMM to study fundamental parameters of early-type stars

1999 ◽  
Vol 193 ◽  
pp. 90-91
Author(s):  
Gregor Rauw ◽  
Karel A. van der Hucht ◽  
Rolf Mewe ◽  
Manuel Güdel ◽  
Jean-Marie Vreux ◽  
...  
Keyword(s):  
Effective Area ◽  
Early Type ◽  
X Ray ◽  
Fundamental Parameters ◽  
Medium Resolution ◽  
Wide Range ◽  
Imaging Camera ◽  
Substantial Progress ◽  
Early Type Stars ◽  
Reflection Grating

Although substantial progress has been achieved since the discovery of X-ray emission from early-type stars with the EINSTEIN satellite, several crucial aspects of this phenomenon are still not fully understood. Considerable breakthroughs in this field are expected from observations with the X-ray Multi-Mirror satellite (XMM) due for launch in early 2000. XMM is the second cornerstone mission of the ESA Horizon 2000 science programme (see Lumb et al. 1996 and references therein for an overall description of the satellite). XMM offers a large effective area over a wide range of energies and its instrumentation provides simultaneously non-dispersive spectroscopic imaging (EPIC - European Photon Imaging Camera), medium-resolution dispersive spectroscopy (RGS - Reflection Grating Spectrometer) and optical-UV imaging (OM - Optical Monitor).

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