J/ApJ/900/42 CARMENES obs. of the binary system LB-1 (Liu+, 2020) ================================================================================ Phase-dependent study of near-infrared disk emission lines in LB-1. Liu J., Zheng Z., Soria R., Aceituno J., Zhang H., Lu Y., Wang S., Hamann W.-R., Oskinova L.M., Ramachandran V., Yuan H., Bai Z., Wang S., McKee B.J., Wu J., Wang J., Lattanzi M., Belczynski K., Casares J., Gonzalez Hernandez J.I., Rebolo R. =2020ApJ...900...42L (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Binaries, spectroscopic; Spectra, optical; Spectra, infrared; Equivalent widths Keywords: Black holes; black hole physics; Stellar evolution; Be stars Abstract: The mass, origin, and evolutionary stage of the binary system LB-1 have been intensely debated, following the claim that it hosts an ~70M_{sun}_ black hole, in stark contrast with the expectations for Galactic remnants. We conducted a high-resolution, phase-resolved spectroscopic study of its Paschen lines, using the Calar Alto 3.5m telescope. We find that Pa{beta} and Pa{gamma} (after subtraction of the stellar absorption component) are well fitted with a standard double-peaked disk profile. We measured the velocity shifts of the red and blue peaks at 28 orbital phases: the line center has an orbital motion in perfect antiphase with the secondary, and the radial velocity amplitude ranges from 8 to 13km/s, for different methods of profile modeling. We interpret this curve as proof that the disk traces the orbital motion of the primary, ruling out the circumbinary disk and the hierarchical triple scenarios. The phase-averaged peak-to-peak half-separation (a proxy for the projected rotational velocity of the outer part of the disk) is ~70km/s, larger than the orbital velocity of the secondary and inconsistent with a circumbinary disk. From those results, we infer a primary mass 4-8 times higher than the secondary mass. Moreover, we show that the intensity ratio of the blue and red peaks has a sinusoidal behavior in phase with the secondary, which we attribute to external irradiation of the outer part of the disk. Finally, we discuss our findings in the context of competing scenarios proposed for LB-1. Further astrometric Gaia data will test between alternative solutions. Description: We have observed LB-1 at regular intervals (28 epochs) since November 2019 (Table 1), with the "Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Echelle Spectrographs" (CARMENES) mounted on the 3.5m telescope at the Calar Alto Observatory. The CARMENES instrument consists of two separate spectrographs covering the wavelength ranges from 0.52 to 0.96um and from 0.96-1.71um with R~80000-100000. Objects: ---------------------------------------------------------- RA (ICRS) DE Designation(s) ---------------------------------------------------------- 06 11 49.08 +22 49 32.7 LB-1 = LS V +22 25 ---------------------------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 37 100 Log of our Calar Alto observations fig3.dat 77 28 Asymmetry between the red- and blue-side emission as a function of binary phase, for both Pa{beta} and Pa{gamma} fig5.dat 148 28 Measurements and model fitting of the projected radial velocities of the secondary star and primary -------------------------------------------------------------------------------- See also: B/vsx : AAVSO International Variable Star Index VSX (Watson+, 2006-2014) VI/39 : Model Atmospheres (Kurucz, 1979) I/345 : Gaia DR2 (Gaia Collaboration, 2018) J/A+A/530/A115 : Rotating massive MS stars evolutionary models (Brott+, 2011) J/A+A/537/A146 : Stellar models with rotation. 0.8