Photometric behaviour of the Be star EW Lacertae

Jeong, Jang Hae; Suh, Chang Won; Nha, Il-Seong

doi:10.1007/bf00648816

Cited by 7 publications

(5 citation statements)

References 2 publications

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“…1. EW Lac is an early-type shell star (Slettebak 1982) which has been observed since 1882 presenting spectral and pho tometric variability in different timescales: a 0.7 day pho tometric variability of 0.2 mag was reported by Walker (1958), Pavlovski et al (1993) reported multiperiodicity in this object, and Jeong et al (1986) found photometric variations of 50-60 days. Percy et al (1996) determined a 3000 day photometric period.…”

Section: The Stellar Samplementioning

confidence: 96%

SIMULTANEOUSK- ANDL-BAND SPECTROSCOPY OF Be STARS: CIRCUMSTELLAR ENVELOPE PROPERTIES FROM HYDROGEN EMISSION LINES

Granada

Arias

Cidale

2010

The Astronomical Journal

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We present medium-resolution Kand L-band spectra of a sample of eight Be stars, obtained with Gemini/ NIRI. The IR K and L bands contain many lines of different hydrogen series that are used as a diagnosis to the physical conditions in the circumstellar environments. We make an analysis on the optical depths of the line-forming regions based on the intensity ratios of Pfy and Bra lines, the behavior of Humphreys' series, and the fluxes of Bra and Bry lines. All our targets show spectroscopic and photometric long-term variability; thus, time-resolved Kand L-band spectroscopy is an ideal tool for studying the structure and evolution of the innermost regions of the envelope and to test models on the disk-forming mechanism. We note that the instrumental configuration used allowed us to obtain good quality IR observations and to take profit of Gemini band 3 observing time (allocation time for ranked programs in which the observing conditions are relaxed).

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Section: The Stellar Samplementioning

confidence: 96%

SIMULTANEOUSK- ANDL-BAND SPECTROSCOPY OF Be STARS: CIRCUMSTELLAR ENVELOPE PROPERTIES FROM HYDROGEN EMISSION LINES

Granada

Arias

Cidale

2010

The Astronomical Journal

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“…The volume fraction of the retained austenite is shown in figure 2 for the steels TRIP 5 and TRIP 7 in dependence of the cooling rate between the first and the second annealing stage and the isothermal holding time 12 at the isothermal bainite transformation temperature T2.…”

Section: Discussion Of Resultsmentioning

confidence: 99%

“…Microstructure description. Optical metallography was performed after etching with 5%HN03 + [O%sodium metabisulfide to judge the effect of the heat treatment on the microstructure development [12], whereas the volume fraction of the retained austenite was determined, using a magnetic method of Voest-Alpine Stahl Linz GmbH [13].…”

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confidence: 99%

Sheet metal forming behaviour and mechanical properties of TRIP steels

1999

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Recently various kinds of high-strength sheet steels have been developed to meet the requirements of the automotive industry such as passive safety, weight reduction and saving energy. Usually the main problem of high-strength steels is their inferior ductility. Multiphase steels however show a very good combination of strength and formability so that the applicable region of high-strength steels has been widely enlarged. Multiphase steels have been developed for various purposes because of their ability to tailor properties by adjusting the type, the amount, and the distribution of different phases. Especially new developed triple-phase steels which make use of the TRIP effect (transformation induced Qlasticity) can further improve formability as well as strength due to the transformation of retained austenite to martensite during the deformation. In this work the transformation behaviour and the mechanical properties of low alloyed TRIP steels were investigated. The influence of the annealing parameters on transformation behaviour and on the amount of retained austenite were determined. In addition the temperature dependence of the mechanical properties and the effect of testing speed on the formability were studied. The investigation was carried out on seven different TRIP steels with different chemical compositions, especially the influence of the microalloying element niobium was considered. For reasons of comparison various mild and high-strength steels were tested parallel to the TRIP steels. It was found that the investigated TRIP steels offer very attractive combinations of elongation and strength values. An interesting temperature dependence of the mechanical properties can be observed, in such a way that the elongation values of the TRIP steels possess a maximum between +50 and +100°C. Due to its effect on grain size and on precipitation behaviour the addition of niobium leads to higher strength values without a strong decrease in ductility. In general, the mechanical properties are strongly affected by the type and the distribution of the different phases. The most important parameters, however, to influence the mechanical behaviour are the amount and the stability of the retained austenite, which are mainly controlled by the heat treatment and the chemical composition. Mechanisch-technologische Eigenschaften von niedriglegiertenTRiP Stahlen. In jOngster Zeit wurden unterschiedliche hochfeste Feinblechstahlsorten entwickelt, urn die Anforderungen der Automobilindustrie wie passive Sicherheit, Gewichtseinsparnis und verminderten Energieverbrauch zu erfOlien. Oblicherweise stellt die unzureichende Umformbarkeit das Hauptproblem von hOherfesten Stahlen dar. Mehrphasenstahle weisen hingegen eine sehr gute Kombination von Festigkeit und Umformbarkeit auf, so daB der Anwendungsbereich von hochfesten Stahlen erheblich erweitert werden konnte. Mehrphasenstahle wurden fOr unterschiedliche Zwecke entwickelt, da ihre Eigenschaften in erheblichem Umfang variiert werden konnen, indem Art. Menge und Verteilung der ...

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“…In order to inspect the photometric behaviors of EW Lac during the V/R variation, we show in figure 16 the long term variations of V magnitude and colors, based on the data of Pavlovski et al (1997), Jeong et al (1986) and Stagg et al (1988). For comparison, the V/R variations are also reproduced from figure 3.…”

Section: Photometric Variations and V/r Variationsmentioning

confidence: 99%

Spectroscopic Variations of the Be-shell Star EW Lac in the V/R Variation Periods

Mon,

Suzuki,

Moritani

et al. 2013

Preprint

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EW Lac has shown remarkable V/R variations in 1976 -1986, and a similar V/R variation has started again in around 2007, after some quasi-periodic V/R variation. For the first V/R variation event, we analyze the spectroscopic behaviors of emission lines and shell absorption lines of the Balmer series. The V/R variations of the Hα through Hδ lines are characterized by the different manner of variations of the individual emission lines in time lag and in duration of the V/R phases. Weak correlation is also notable between the V/R variations and other variations of the line-profile parameter such as the peak velocities, emission line intensities and peak separations. We analyze shell absorption lines for higher members of the Balmer series for their central depths and radial velocities. The optical depth of the Hα line is in a range of 2000 to 6000, and its long-term variation discloses different behaviors as compared to the V/R variations. Combining the analyses of emission and shell absorption lines, and regarding the V/R variation as wave propagation phenomena, we find for the 1976 -1986 event that the V/R variation is of retrograde structure and a spiral structure is likely formed inside the disk in the latter half of this event. The weak correlations among physical parameters are suggestive of the disk truncated at some radius. It is noticed that remarkable stellar brightening has occurred in the latter half of the event, accompanying marked decrease of emission line intensities. As for the V/R variation appeared in around 2007, which looks like a recurrence of the previous event, we found less developed state of the disk without appreciable time lag.

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Photometric behaviour of the Be star EW Lacertae

Cited by 7 publications

References 2 publications

SIMULTANEOUSK- ANDL-BAND SPECTROSCOPY OF Be STARS: CIRCUMSTELLAR ENVELOPE PROPERTIES FROM HYDROGEN EMISSION LINES

SIMULTANEOUSK- ANDL-BAND SPECTROSCOPY OF Be STARS: CIRCUMSTELLAR ENVELOPE PROPERTIES FROM HYDROGEN EMISSION LINES

Sheet metal forming behaviour and mechanical properties of TRIP steels

Spectroscopic Variations of the Be-shell Star EW Lac in the V/R Variation Periods

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