The Binarity of Early-type Stars from LAMOST medium-resolution Spectroscopic Survey

Abstract

Massive binaries play significant roles in many fields. Identification of massive stars, particularly massive binaries, is of great importance. In this paper, by adopting the technique of measuring the equivalent widths of several spectral lines, we identified 9,382 early-type stars from LAMOST medium-resolution survey and divided the sample into four groups, T1 ($\sim$O-B4), T2 ($\sim$B5), T3 ($\sim$B7), and T4 ($\sim$B8-A). The relative radial velocities $RV_{\rm rel}$ were calculated using the Maximum Likelihood Estimation. The stars with significant changes of $RV_{\rm rel}$ and at least larger than 15.57km s$^{-1}$ were identified as spectroscopic binaries. We found that the observed spectroscopic binary fractions for the four groups are $24.6\%\pm0.5\%$, $20.8\%\pm0.6\%$, $13.7\%\pm0.3\%$, and $7.4\%\pm0.3\%$, respectively. Assuming that orbital period ($P$) and mass ratio ($q$) have intrinsic distributions as $f(P) \propto P^\pi$ (1\textless$P$\textless1000 days) and $f(q) \propto q^\kappa$ (0.1\textless$q$\textless1), respectively, we conducted a series of Monte-Carlo simulations to correct observational biases for estimating the intrinsic multiplicity properties. The results show that the intrinsic binary fractions for the four groups are 68$\%\pm8\%$, 52$\%\pm3\%$, 44$\%\pm6\%$, and 44$\%\pm6\%$, respectively. The best estimated values for $\pi$ are -1$\pm0.1$, -1.1$\pm0.05$, -1.1$\pm0.1$, and -0.6$\pm0.05$, respectively. The $\kappa$ cannot be constrained for groups T1 and T2 and is -2.4$\pm0.3$ for group T3 and -1.6$\pm0.3$ for group T4. We confirmed the relationship of a decreasing trend in binary fractions towards late-type stars. No correlation between the spectral type and the orbital period distribution has been found yet, possibly due to the limitation of observational cadence.

The statistical properties of early-type stars from LAMOST DR8

“…Based on low-resolution observation from the LAM-OST DR5, Luo et al (2021) reported a binary fraction of 40% for O-and B-type stars in the sample using spectra with more than three observations. Later work by Guo et al (2022) utilizing the medium-resolution spectra with a cadence of more than two from the LAMOST DR7 suggests a binary fraction of 68% for the early-type OB stars.…”

“…In the work of Guo et al (2022) (Paper I hereinafter), the relative radial velocity is obtained by a Maximum Likelihood Estimation and a star is recognized as a binary according to the maximum variation of radial velocity. The intrinsic binary fraction can be obtained by correcting for any observational biases appearing in the sample using a series of Monte-Carlo simulations from Sana et al (2013).…”

“…The intrinsic binary fraction can be obtained by correcting for any observational biases appearing in the sample using a series of Monte-Carlo simulations from Sana et al (2013). Since most of the early-type star spectra from Guo et al (2022) only have two observations, significant errors would exist although the large number of the sample may reduce the errors to a certain degree. This influence has not been examined and corrected due to the small cadence number of spectra from LAMOST DR7.…”

Identification of New Classical Be Stars from the LAMOST Medium Resolution Survey

“…The major goal of this work is to identify CBe stars from the database. We selected the spectra of early-type stars from the archived sample following the procedures described in Guo et al (2022). We first adopted the estimated effective temperatures (T eff ) as given by the LAMOST stellar parameter pipeline (LASP; Wu et al 2014) to coarsely eliminate any late A-type to late F-type stars with 6500 K T eff 8000 K from the MRS sample.…”

Infrared Excess of a Large OB Star Sample

“…This huge database brings the possibility to significantly expand the scale of the OB star sample. From the LAMOST Low Resolution Spectra (LRS), about 16,000 OB stars were identified by Liu et al (2019) and from the LAMOST Mid Resolution Spectra (MRS), other ∼9000 OB stars were then identified by Guo et al (2022). For these LAMOST-OB stars, the basic stellar parameters including the effective temperature (T eff ) and surface gravity ( g log ) were determined by Guo et al (2021) by the data-driven technique Stellar LAbel Machine (SLAM) with the non-LTE TLUSTY synthetic spectra as the training data set.…”