scholarly journals Short-Term Spectroscopic Variations of the Be Star 11 Cam

1987 ◽  
Vol 92 ◽  
pp. 93-94
Author(s):  
J. Chauville ◽  
M. Alvarez ◽  
J.P. Sareyan ◽  
L. Ballereau ◽  
R. Michel
Keyword(s):  
Spectral Type ◽  
Balmer Line ◽  
Line Profiles ◽  
Short Term ◽  
Visual Magnitude ◽  
Be Star ◽  
Long Term Variations

11 Cam (HD 32343 = HR 1622) is a so-called “pole-on” Be star known for its long term variations, already noted by Merrill and Burwell (1943). Recent determinations of visual magnitude and spectral type are V = 5.222 and B2.5Ve (Rufener, 1981). The Balmer line profiles, especially Hα, have been frequently studied; Briot (1971), for instance, measured 40 and 4.9 Å equivalent widths for Hα and Hβ respectively; the Hα/Hβ peak to continuum ratio is 6.43/2.02 according to Gray and Marlborough (1974) who give v sin i = 131 km s-1, close to the value of 140 km s-1 adopted by Kogure (1968).

scholarly journals Long-Term V/R Variations of be Stars Due to Global One-Armed Oscillations of Equatorial Disks

1993 ◽  
Vol 134 ◽  
pp. 369-370
Author(s):  
Atsuo T. Okazaki
Keyword(s):  
Nonlinear Oscillations ◽  
Balmer Line ◽  
Density Gradients ◽  
Be Stars ◽  
Line Profiles ◽  
Be Star ◽  
On Line ◽  
The One ◽  
Long Term Variations

AbstractWe study the long-term variations of Balmer line profiles due to global one-armed oscillations in Be-star disks. In order to examine the qualitative effects of oscillations on line profiles, we assume that the eigenfunctions of one-armed nonlinear oscillations are similar to those of linear oscillations. Computing the line profiles for various values of disk parameters, we find that in small disks or in disks with steep density gradients the one-armed fundamental modes cause remarkable variabilities similar to the observed V/R variations.

scholarly journals A Transient Shock-Wave in the Shell of the Be Star HD 184279

1987 ◽  
Vol 92 ◽  
pp. 95-98
Author(s):  
D. Ballereau ◽  
J. Chauville
Keyword(s):  
Shock Wave ◽  
Radial Velocity ◽  
Emission Spectrum ◽  
Short Term ◽  
Balmer Series ◽  
Spectroscopic Observations ◽  
The Past ◽  
Be Star ◽  
Long Term Variations

HD 184279 (V1294 Aql) has presented in the past an emission spectrum on the first terms of the Balmer series, and shell absorptions on the hydrogen and neutral helium lines. Their variations have been reported by Merrill (1952), Merrill and Lowen (1953) and Svolopoulos (1975). Ballereau and Hubert-Delplace (1982) evidenced long-term V/R variations with an amplitude of ∼100 km s-1. Short-term photometric variations are irregular (Tempesti and Patriarca, 1976), while long-term variations are correlated with radial velocity (RV) of shell lines (Horn et al., 1982). Ballereau and Chauville (in preparation) extended the spectroscopic observations until 1984 and confirmed the pseudo-periodic variations, the last half-period ranging over 3.4 years (April 1, 1980-August 1, 1983).

scholarly journals Long-term spectroscopic and polarimetric variations of the Be star κ Dra

1994 ◽  
Vol 162 ◽  
pp. 234-235
Author(s):  
J. Arsenijevic ◽  
S. Jankov ◽  
S. Krsljanin ◽  
A.M. Hubert ◽  
H. Hubert ◽  
...  
Keyword(s):  
Primary Component ◽  
Emission Lines ◽  
Circumstellar Envelope ◽  
Short Term ◽  
Strong Emission ◽  
Be Star ◽  
Joint Material ◽  
Long Term Variations ◽  
Different Time Scales

The bright Be star κ Dra (HD 109387, B5 III, v.sini=249 km/s) is one of the rare mid B type stars which have presented FeII emission lines during strong emission phases. Spectroscopic variations were previously reported by many authors over different time scales: years, days and hours. Juza et al. (1991) proposed that κ Dra was the primary component of a binary system with Porb. = 61.55 days. Short-term and long-term variations in the linear optical polarization were also reported by Arsenijevic et al. (1986). We have tried, with our extensive joint material, to search for correlation between long-term spectroscopic and polarimetric variations with the aim of obtaining information on the behaviour of the circumstellar envelope.

Radial Velocity Variability of K Giants

1991 ◽  
Vol 130 ◽  
pp. 386-388
Author(s):  
Artie P. Hatzes ◽  
William D. Cochran
Keyword(s):  
Radial Velocity ◽  
Active Regions ◽  
Peak Amplitude ◽  
Short Term ◽  
Rotational Modulation ◽  
Surface Active ◽  
Radial Velocity Data ◽  
Long Term Variations ◽  
K Giants

AbstractAt McDonald Observatory we have been monitoring the relative radial velocities of a sample of K giants. The technique employed uses the telluric O2 lines near 6300 Å as a reference for measuring the stellar line shifts. We demonstrate that precisions of 10 m s−1 are possible with this technique. We present radial velocity data covering a 2 year time span for α Boo, α Tau, and β Gem. All of these stars show both long term variations (~ several hundred days) with a peak-to-peak amplitude of about 400 m s−1 and short term variations (~ few days) with a peak-to-peak amplitude of about 100 m s−1. The long term variations may be due to the rotational modulation of surface active regions whereas the short term variations may be indicative of pulsations.

scholarly journals The Appearance and Disappearance of Exocomet Gas Absorption

2015 ◽  
Vol 2015 ◽  
pp. 1-20 ◽  
Author(s):  
Barry Y. Welsh ◽  
Sharon L. Montgomery
Keyword(s):  
Spectral Data ◽  
Spectral Type ◽  
Gas Absorption ◽  
Stellar Systems ◽  
Activity Levels ◽  
Line Profiles ◽  
Short Term ◽  
Line Absorption ◽  
First Time ◽  
Parent Star

CaII K-line (3933 Å) absorption profiles observed towards 15 A-type and two B-type stars with known (or suspected) debris disks, in addition to archival spectral data for three A-type stars, are presented. Inspection of the extracted CaII K-line absorption lines has determined that one late B-type (HD 58647) and four new A-type (HD 56537, HD 64145, HD 108767, and HD 109573) stellar systems exhibit short-term (night-to-night) absorption variation within these profiles. This variability is due to the liberation of gas from falling evaporating bodies (the so-called FEBs activity) on the grazing approach of exocomets towards their parent star. Also we present archival spectra of the FeIλ3860 Å and CaII K-lines towardsβPictoris (HD 39060) that, for the first time, reveal the absorption signatures of FEB activity at similar velocities inbothline profiles. FEB-hosting stars seem to be of an earlier type (on average spectral type Al.8 as compared with A3.1) than those where no FEB activity has been observed. This could be due to stellar activity levels (such as chromospheric activity or nonradial pulsations) being of a higher level within the atmospheres of these hotter A-type stars.

scholarly journals Photometric studies of Be star variability

1994 ◽  
Vol 162 ◽  
pp. 299-300
Author(s):  
John R. Percy
Keyword(s):  
Time Scales ◽  
Balmer Line ◽  
Radial Pulsation ◽  
Be Stars ◽  
Photometric Study ◽  
Short Term ◽  
Hot Stars ◽  
Be Star ◽  
Short Term Variability

Be stars are hot stars which have shown emission in at least one Balmer line on at least one occasion. As the definition implies, the Be phenomenon can be variable with time: on time scales of days to decades as the circumstellar disc develops and disperses; on time scales of days to months in a few Be stars which are interacting binaries; on time scales of 0.2 to 2 days due to non-radial pulsation or possibly rotation. The Be stars are worthy of photometric study because they are bright and numerous; the nature of the short-term variability is not yet agreed upon; the cause of the development of the disc - and its relationship to the short-term variability - is also not yet known.

Morphology and Pipeline Design Through a Dynamic Landfall Area: The Black Sea Pipeline Case

2002 ◽  
Author(s):  
Z. Chen ◽  
Marco Venturi ◽  
R. Bijker
Keyword(s):  
Sediment Transport ◽  
Environmental Impact ◽  
Black Sea ◽  
Morphological Changes ◽  
The Black Sea ◽  
Burial Depth ◽  
Short Term ◽  
Pipeline Route ◽  
Long Term Variations

The Blue Stream pipeline project is a gas transportation system for the delivery of processed gas from a gas station in the southern Russia across the Black Sea to Ankara, Turkey. The Turkish landfall of the offshore pipeline in the Black Sea is located near Samsun, see Figure 1 for the pipeline route. One of the main aspects of the design of pipeline through a morphologically dynamic area such as landfall is the required burial depth (Chen et al, 1998, 2001 and Bijker et al 1995). The burial depth is the result of an optimisation between: • safety of the pipeline (which often requires a large burial depth), and • environmental impact and trenching costs (a small burial depth means less dredging and less environmental impact). This paper presents a method of predicting the future extremely low seabed level in a morphologically dynamic landfall area, which is required to determine the burial depth of the pipeline. Both short term and long term coast evolution were assessed to quantify the expected lowest seabed level along the pipeline route in the landfall area during the pipeline lifetime of 50 years. The results were used to determine the required pipeline burial depth. The long term morphological changes originate from long term variations in the morphological system (e.g. river input), gradient in the longshore sediment transport and long term variations in the hydrodynamic conditions. The short-term morphological changes originate from beach profile variations due to cross-shore sediment transport as a result of seasonal and yearly variations in the wave and current conditions. Numerical modelling was applied to compute the longshore and cross-shore sediment transport rates and the resulting coastline evolution and cross-shore profile evolution. The longshore transport model was validated using the available data on the coastline changes in the past 20 years, which was derived from the satellite images. The 50-year lowest seabed level has been determined as the sum of the coastline retreat and the cross-shore evolution in the next 50 years.

Animal Protein and Rational Choice: Diet in the Eighteenth Century

2014 ◽  
Vol 44 (4) ◽  
pp. 427-452 ◽  
Author(s):  
Martin Bruegel ◽  
Jean-Michel Chevet ◽  
Sébastien Lecocq
Keyword(s):  
Eighteenth Century ◽  
Rational Choice ◽  
Choice Model ◽  
Meat Consumption ◽  
Short Term ◽  
Rational Choice Model ◽  
Elite Status ◽  
Changing Patterns ◽  
Long Term Variations

Analysis of the account books of the convent school of Saint-Cyr between 1688 and 1788 reveals the causes of the institution's changing patterns of meat consumption. Although a rational-choice model can explain short-term variations in the school's diet, economic variables alone are not sufficient to explain its long-term variations, as evolving tastes began to infiltrate Saint-Cyr's traditional, aristocratic diet. The unintended side effect of this development was to improve nutrition, which the school managed to do without running afoul of claims to elite status.

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