AMBER on the VLTI: Data Processing and Calibration Issues

Millour, F.; Petrov, Romain G.; Malbet, Fabien; Tatulli, E.; Duvert, G.; Zins, G.; Altariba, E.; Vannier, M.; Hernandez, Oscar; Causi, G. Li

doi:10.1007/978-3-540-76963-7_63

Cited by 9 publications

(10 citation statements)

References 19 publications

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“…The same methods as in Štefl et al (2009) were applied to derive absolute and differential quantities for visibilities, phases, and closure phases across the Br γ line. Following the recommendation by Tatulli et al (2007) and Millour et al (2008), only the top 50% of the frames with the best S /N were averaged for calibrators as well as science targets to derive the transfer function and obtain absolutely calibrated spectra. However, because of the setting inconsistency between the science target and the calibrator, only the differential visibilities and phases were derived for ζ Tau.…”

Section: Interferometrymentioning

confidence: 99%

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: Interferometrymentioning

confidence: 99%

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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“…This ratio provides the most stable transfer function, see discussion in Tatulli et al (2007) and Millour et al (2007). -The transfer function was estimated by averaging all observations of the calibration stars.…”

Section: Interferometrymentioning

confidence: 99%

Cyclic variability of the circumstellar disk of the Be starζ Tauri

Štefl¹,

Rivinius²,

Carciofi

et al. 2009

A&A

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Context. Emission lines formed in decretion disks of Be stars often undergo long-term cyclic variations, especially in the violet-to-red (V/R) ratio of their primary components. The underlying structural and dynamical variations of the disks are only partly understood. From observations of the bright Be-shell star ζ Tau, the possibly broadest and longest data set illustrating the prototype of this behaviour was compiled from our own and archival observations. It comprises optical and infrared spectra, broad-band polarimetry, and interferometric observations. Aims. The dense, long-time monitoring permits a better separation of repetitive and ephemeral variations. The broad wavelength coverage includes lines formed under different physical conditions, i.e. different locations in the disk, so that the dynamics can be probed throughout much of the disk. Polarimetry and interferometry constrain the spatial structure. All together, the objective is a better understand the dynamics and life cycle of decretion disks. Methods. Standard methods of data acquisition, reduction, and analysis were applied. Results. From 3 V/R cycles between 1997 and 2008, a mean cycle length in Hα of 1400-1430 days was derived. After each minimum in V/R, the shell absorption weakens and splits into two components, leading to 3 emission peaks. This phase may make the strongest contribution to the variability in cycle length. There is no obvious connection between the V/R cycle and the 133-day orbital period of the not otherwise detected companion. V/R curves of different lines are shifted in phase. Lines formed on average closer to the central star are ahead of the others. The shell absorption lines fall into 2 categories differing in line width, ionization/excitation potential, and variability of the equivalent width. They seem to form in separate regions of the disk, probably crossing the line of sight at different times. The interferometry has resolved the continuum and the line emission in Brγ and HeI 2.06. The phasing of the Brγ emission shows that the photocenter of the line-emitting region lies within the plane of the disk but is offset from the continuum source. The plane of the disk is constant throughout the observed V/R cycles. The observations lay the foundation for the fully self-consistent, one-armed, disk-oscillation model developed in Paper II.

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“…This allows us to limit the fringe smearing effect (also called "jitter" effect) and the coherence length visibility loss due to the atmospheric OPD (described in Millour et al 2007). The following steps (transfer function estimation, calibration) were completed using a new set of custom-made scripts described by Millour et al (2008 2 ); -an approach using bootstrapping, roughly explained in Tatulli et al (2007) and described in more detail in Cruzalèbes et al (2007).…”

Section: Observations and Data Reductionmentioning

confidence: 99%

δ Centauri: a new binary Be star detected by VLTI/AMBER spectro-interferometry

Meilland¹,

Millour²,

Stee

et al. 2008

A&A

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Aims. We study the Be star δ Cen circumstellar disk using long-baseline interferometry which is the only observing technique capable of resolving spatially and spectroscopically objects smaller than 5 mas in the H and K band. Methods. We used the VLTI/AMBER instrument on January 6, 8, and 9, 2008, in the H and K bands to complete low (35) and medium (1500) spectral resolution observations. Results. We detected an oscillation in the visibility curve plotted as a function of the spatial frequency which is a clear signature of a companion around δ Cen. Our best-fit soltution infers a binary separation of 68.7 mas, a companion flux contribution in the K band of about 7% of the total flux, a PA of 117.5• , and an envelope flux around the Be primary that contributes up to about 50% of the total flux, in agreement with our Spectral Energy Distribution (SED) fit. The envelope size is estimated to be 1.6 mas in K but no departure from spherical symmetry is detected.

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AMBER on the VLTI: Data Processing and Calibration Issues

Cited by 9 publications

References 19 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

Cyclic variability of the circumstellar disk of the Be starζ Tauri

δ Centauri: a new binary Be star detected by VLTI/AMBER spectro-interferometry

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