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.
<Astrophys. J., 900, 42-42 (2020)>
=2020ApJ...900...42L 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☉ 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 Paβ and Paγ (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:
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RA (ICRS) DE Designation(s)
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06 11 49.08 +22 49 32.7 LB-1 = LS V +22 25
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File Summary:
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FileName Lrecl Records Explanations
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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 Paβ
and Paγ
fig5.dat 148 28 Measurements and model fitting of the projected
radial velocities of the secondary star and
primary
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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<M<120 (Ekstrom+, 2012)
J/A+A/545/A121 : ο Puppis spectra (Koubsky+, 2012)
J/A+A/587/A61 : Stellar-mass BH in X-ray transients (Corral-Santana+, 2016)
J/A+A/615/A78 : Spectral models for binary products (Goetberg+, 2018)
J/A+A/619/A148 : Hot stars observed by XMM-Newton. II. (Naze+, 2018)
J/A+A/639/L6 : HERMES spectra of LS V +22 25 (Shenar+, 2020)
J/A+A/649/A167 : Hubble spectroscopy of LB-1 (LS V +22 25) (Lennon+, 2021)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 A10 "Y/M/D" Date Observation date
12- 21 F10.4 d BJD [58757.6/58906.4] Barycentric modified
Julian Date of mid exposure; BJD-2400000.5
23- 26 I4 s Exp [396/1801] Exposure time
28- 33 F6.4 --- Phase Phase at mid exposure (1)
35- 37 A3 --- Band Observational band used ("VIS" or "NIR")
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Note (1): Phase of 0 corresponds to inferior conjunction of the companion star,
orbiting in a counterclockwise direction. Thus, a phase of 0.25
corresponds to its highest projected radial velocity.
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Byte-by-byte Description of file: fig3.dat
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Bytes Format Units Label Explanations
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1- 10 F10.4 d BJD Barycentric Julian Date; BJD-2400000
12- 17 F6.4 --- Phase Orbital phase
19- 25 F7.4 --- R/B-PaB Paβ red and blue peak flux difference
27- 32 F6.4 --- e_R/B-PaB Uncertainty in R/B-PaB
34- 40 F7.4 --- R/B-Pag Paγ red and blue peak flux difference
42- 47 F6.4 --- e_R/B-Pag Uncertainty in R/B-Pag
49- 55 F7.4 0.1nm EWPaB [-2.3/1.8] Paβ equivalent widths
difference (1)
57- 62 F6.4 0.1nm e_EWPaB [0.02/0.3] Uncertainty in EWPaB (1)
64- 70 F7.4 0.1nm EWPag [-1.1/0.8] Paγ equivalent widths
difference (1)
72- 77 F6.4 0.1nm e_EWPag [0.003/0.14] Uncertainty in EWPag (1)
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Note (1): Redward and blueward of the mean peak locations. Units are Angstroms.
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Byte-by-byte Description of file: fig5.dat
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Bytes Format Units Label Explanations
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1- 10 F10.4 d BJD Barycentric Julian Date; BJD-2400000
12- 19 F8.6 --- Phase Orbital phase
21- 28 F8.4 km/s V2 [-24.08/81] Secondary velocity
30- 36 F7.4 km/s V1dgb [18.16/37.3] Local Gaussian fit of Paβ mean
red & blue peak velocity
38- 43 F6.4 km/s e_V1dgb [0.4/3.8] Uncertainty in V1d-gb
45- 51 F7.4 km/s Vrgb Local Gaussian fit of Paβ half separation
between the red and blue peak velocity
53- 58 F6.4 km/s e_Vrgb Uncertainty in Vr-gb
60- 66 F7.4 km/s V1dgg [15.3/38.4] Local Gaussian fit of Paγ mean
red & blue peak velocity
68- 73 F6.4 km/s e_V1dgg [0.38/4.7] Uncertainty in V1d-gg
75- 81 F7.4 km/s Vrgg Local Gaussian fit of Paγ half separation
between the red and blue peak velocity
83- 88 F6.4 km/s e_Vrgg Uncertainty in Vr-gg
90- 96 F7.4 km/s V1dsb Extended Smak Fit of Paβ mean red & blue
peak velocity
98-103 F6.4 km/s e_V1dsb Uncertainty in V1d-sb
105-111 F7.4 km/s Vrsb Extended Smak Fit of Paβ half separation
between the red and blue peak velocity
113-118 F6.4 km/s e_Vrsb Uncertainty in Vr-sb
120-126 F7.4 km/s V1dsg Extended Smak Fit of Paγ mean red & blue
peak velocity
128-133 F6.4 km/s e_V1dsg Uncertainty in V1d-sg
135-141 F7.4 km/s Vrsg Extended Smak Fit of Paγ half separation
between the red and blue peak velocity
143-148 F6.4 km/s e_Vrsg Uncertainty in Vr-sg
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 10-Dec-2021