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New insight into the variability of the Be star π Aquarii: Determination of stellar and disk parameters
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DOI：10.1051/0004-6361/202452708.png)
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Abstract
En 中文
Context. The Be star pi Aquarii shows a peculiar X-ray emission (gamma Cas type) commonly attributed to its outer disk interacting with a low-mass companion star, probably a white dwarf. Aims. In this work, we study the long-term variability of the optical spectra of pi Aquarii in order to derive the stellar and disk parameters of specific epochs when the disk shows major changes. Methods. We identified several spectral lines and studied specific observation dates for Balmer, helium, silicon, and iron emission lines in detail. We determined the stellar parameters using stellar atmosphere models, considering the oblate geometry due to the fast rotation, and we derived the disk parameters through H alpha modeling and considering a viscous decretion disk parametric model. Results. We found the following stellar parameters: M = (11.0 +/- 1.9) M-circle dot, < log g >= (4.03 +/- 0.10) dex, Rp = (5 +/- 0.8) R-circle dot, R-eq = (1.15 +/- 0.088) R-p, T-p = (25 000 +/- 1174) K, v sin i = (271 +/- 13) km/s, and a omega = 0.82 +/- 0.05. Over five epochs, the H alpha emission line evolved from shell profiles to double-peaked to triple-peaked to flat-topped structures. We found that the density in the disk decays faster (with n similar to 3.9) on December 22, 2001. In this epoch, the H alpha emission line presented a low-intensity shell profile modeled with a low base surface density (Sigma(0) = 0.01g cm(-2)), indicating a small disk. Then, from 2011 to (September) 2014, the disk decreased with a slowly decaying density distribution (n similar to 3.2). The disk grew drastically from October 2014 until November 2022, increasing 18 times its initial H alpha equivalent width value. At that time, we estimated an emitting region of similar to 65 R-circle dot. We also measured the inclination angle variation in similar to 10 degrees in 20 years, with the results indicating a likely precessing disk. We found that FeII 5018 angstrom covers an emission region larger than H alpha and is the only FeII emission line showing a different shape profile than the rest of the lines. Conclusions. We assert that the disk of pi Aquarii is in a misaligned binary system going through shell profiles to double-peak separation to triple-peaked to flat-topped profiles, and it now shows an asymmetric double-peak separation profile again. The emission line FeII 5018 angstrom indicates changes in the outer disk probably related to the white dwarf. We propose that the white dwarf cross the Be disk at two points in its orbit, and it is at these moments that it captures material and temporarily increases its X-ray emission.
Keywords:
techniques: spectroscopic
stars: emission-line, Be
stars: individual: HD 212571
Journal
IF:
5.8
Papers:
5.0W
Citations:
18.3W
Organization
Cited Papers