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

Abstract

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.

Photometric and spectroscopic variability of the Be star 48 Lib: The relation between photometric variations and rotation

“…48 Lib (FX Lib; HD 142 983; HIP 78 207; HR 5 941) (V = 4.94 mag) is a well-studied Be shell star. Although it is classified as a B8Ia/Iabtype supergiant (Catanzaro 2013;Lafrenière et al 2014; Peña-Guerrero & Leitherer 2013), many researchers consider the star to be an early-type sub-giant, giant, or MS object (B3III to V) (Hanuschik & Vrancken 1996;Draper et al 2014;Štefl et al 2012;Touhami et al 2013;Silaj et al 2016). Similar to most Be stars, it is a rapid rotator with a projected rotational velocity (v sin i) of around 400 km s −1 (Štefl et al 2012;Touhami et al 2013) and a critical rotational velocity of ∼500 km s −1 (Frémat et al 2005;Silaj et al 2016).…”

Early-type stars observed in the ESO UVES Paranal Observatory Project - V. Time-variable interstellar absorption

“…Stellar distances, (B − V ) and E(B − V ) values were, in most cases, taken from van Leeuwen (2007) and Hunter et al (2006), taking the most accurate measurement in each case. For some sightlines neither Hunter et al (2006) nor van Leeuwen (2007) gave distance estimates and so values were taken from the literature. These cases are referenced Table 2.…”

“…in Table 3. Most distances were calculated from the parallax recorded in van Leeuwen (2007) as these tended to be the most reliable. The distance estimates from Hunter et al (2006) were calculated using the spectroscopic parallax methodology given in Diplas & Savage (1994).…”

“…epoch interval presumed to be 20 yr as no specific observation date available for epoch 1(observed between 1987 and 1989) Distance reference codes: p -distances calculated from the parallax recorded in vanLeeuwen (2007).…”

Magnetorotational instability in decretion disks of critically rotating stars and the outer structure of Be and Be/X-ray disks

“…A similar result was derived from optical spectroscopy by Kraus et al (2010) for a B[e] supergiant LHA 115-S 65. On the other hand, the estimates of the disk extension for classical Be stars from optical and near-IR regions typically give much lower radii of the order of few stellar radii (e.g., Meilland et al 2009;Štefl et al 2012;Touhami et al 2013). However, these estimates presumably do not reflect the physical dimension of the disk, but just formation loci of individual observables (Carciofi 2011).…”