H<i>α</i> observations of Be stars

Banerjee, D. P. K.; Rawat, S. D.; Janardhan, P.

doi:10.1051/aas:2000299

Cited by 26 publications

(47 citation statements)

References 5 publications

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“…This length would be significantly longer than the previous ones observed in the second half of the 20th century. The present descending V/R branch also suggests -consistently with the longer cycle -that the descent Rivinius et al (2006), + data compiled from Underhill (1953), Faraggiana (1969), Gray & Marlborough (1974), Slettebak & Reynolds (1978), Andrillat & Fehrenbach (1982) Hanuschik et al (1995) and Banerjee et al (2000). b) Hα and Brγ V/R variations (defined as the ratio of the full peak intensities) during the period 1995-2010.…”

Section: Long-term V/r Variations Of Emission Linessupporting

confidence: 72%

New activity in the large circumstellar disk of the Be-shell star 48 Librae

Štefl

Bouquin

Carciofi

et al. 2012

A&A

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Aims. Spectroscopic, polarimetric, and high spectral resolution interferometric data covering the period 1995-2011 are analyzed to document the transition into a new phase of circumstellar disk activity in the classical Be-shell star 48 Lib. The objective is to use this broad data set to additionally test disk oscillations as the basic underlying dynamical process. Methods. The long-term disk evolution is described using the V/R ratio of the violet and red emission components of Hα and Brγ, radial velocities and profiles of He i and optical metal shell lines, as well as multi-band BVRI polarimetry. Single-epoch broad-band and high-resolution interferometric visibilities and phases are discussed with respect to a classical disk model and the given baseline orientations.Results. Spectroscopic signatures of disk asymmetries in 48 Lib vanished in the late nineties but recovered some time between 2004 and 2007, as shown by a new large-amplitude and long-duration V/R cycle. Variations in the radial velocity and line profile of conventional shell lines correlate with the V/R behavior. They are shared by narrow absorption cores superimposed on otherwise seemingly photospheric He i lines, which may form in high-density gas at the inner disk close to the photosphere. Large radial velocity variations continued also during the V/R-quiet years, suggesting that V/R may not always be a good indicator of global density waves in the disk. The comparison of the polarization after the recovery of the V/R activity shows a slight increase, while the polarization angle has been constant for more than 20 years, placing tight limits on any 3-D precession or warping of the disk. The broad Hband interferometry gives a disk diameter of (1.72 ± 0.2) mas (equivalent to 15 stellar radii), position angle of the disk (50 ± 9)• and a relatively low disk flattening of 1.66 ± 0.3. Within the errors the same disk position angle is derived from polarimetric observations and from photocenter shifts across Brγ. The high-resolution interferometric visibility and phase profiles show a double or even multiplecomponent structure. A preliminary estimate based on the size of the Brγ emitting region indicates a large diameter for the disk (tens of stellar radii). Overall, no serious contradiction between the observations and the disk-oscillation model could be construed.

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Section: Long-term V/r Variations Of Emission Linessupporting

confidence: 72%

New activity in the large circumstellar disk of the Be-shell star 48 Librae

Štefl

Bouquin

Carciofi

et al. 2012

A&A

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“…To test for other Be star characteristics in δ Sco we checked for correlations between H alpha line parameters like v sin i vs. fullwidth, v sin i vs. halfwidth, peak to continuum intensity ratio vs. equivalent width etc. (Andrillat & Fehrenbach 1982;Banerjee et al 2000;Dachs et al 1986) and found it to exhibit standard Be star behaviour.…”

Section: Resultsmentioning

confidence: 99%

Near infra-red and optical spectroscopy of Delta Scorpii

Banerjee

Janardhan

Ashok

2001

A&A

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Abstract. Spectroscopic observations of δ Sco in the near IR and optical wavelengths, obtained shortly after its recent periastron passage are reported. The IR spectra are dominated by the HI Paschen and Brackett lines. An IR excess is seen which can be attributed to free-free emission from a circumstellar shell. The observed Paschen and Brackett line intensities deviate significantly from Case B predictions and indicate optical depth effects. These effects are modeled. The overall spectral behaviour of δ Sco at present is that of a typical Be star.

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“…In this paper, only the line strength of Hα is measured. Hα is observed in Be stars with a variety of profile shapes (Banerjee et al 2000), ranging from single and double peaked emission to absorption, where no identifiable emission component can be detected (i.e. the star is not currently in an emission phase).…”

Section: Methodsmentioning

confidence: 99%

A representative sample of Be stars

Barnsley

Steele

2013

A&A

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Aims. We attempt to determine if a dependency on spectral subtype or v sin i exists for stars undergoing phase-changes between B and Be states, as well as for those stars exhibiting variability in Hα emission. Methods. We analysed the changes in Hα line strength for a sample of 55 Be stars of varying spectral types and luminosity classes using five epochs of observations taken over a ten year period between 1998 and 2010. Results. We find i) that the typical timescale between which full phase transitions occur is most likely of the order of centuries, although no dependency on spectral subtype or v sin i could be determined due to the low frequency of phase-changing events observed in our sample; ii) that stars with earlier spectral types and larger values of v sin i show a greater degree of variability in Hα emission over the timescales probed in this study; and iii) a trend of increasing variability between the shortest and longest baselines for stars of later spectral types and with smaller values of v sin i.

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Hα observations of Be stars

Cited by 26 publications

References 5 publications

New activity in the large circumstellar disk of the Be-shell star 48 Librae

New activity in the large circumstellar disk of the Be-shell star 48 Librae

Near infra-red and optical spectroscopy of Delta Scorpii

A representative sample of Be stars

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