Ph.D. candidate GUO Yanjun, from Yunnan Observatories of the Chinese Academy of Sciences, and her collaborators reported recent work on determining the atmospheric parameters of about 4,500 early-type stars using the optical spectra released from the LAMOST survey. This work was published in The Astrophysical Journal Supplement Series on December 6, 2021.

Early-type stars are massive and luminous, and they are mainly comprised of O- or B-type stars. Early-type stars are important contributors to many astronomical mechanisms. Massive early-type stars can promote the reionization of the universe and enrich the galactic element abundance. Massive early-type stars are possible progenitors of extremely compact stellar objects, such as neutron stars, black holes. Besides they are potential sources of gravitational wave events. Determining their fundamental physical parameters, such as effective temperature (Teff), surface gravity (log g), projected rotational velocity (vsini), and metallicity ([M/H]), is vital for understanding the evolutionary scenario of massive stars and constraining their location in the Hertzsprung-Russell (HR) diagram.

Hitherto, the estimate of stellar parameters for such stars was restricted to small collections of spectral observations. Estimation of the stellar labels of early-type stars determined from a comprehensive and consistent approach from a large sample of observations is lack.

The researchers adopted the data-driven technique called stellar lablel machine (SLAM) with the nonlocal thermal equilibrium TLUSTY synthetic spectra as the training data set to estimate the stellar parameters of Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) optical spectra for about 4,500 early-type stars. The researchers apply two consistency tests to verify this machine-learning method and compare stellar labels given by SLAM with the labels in the literature for several objects having high-resolution spectra.

To estimate the average statistical uncertainties of the determined results, the researchers calculated the standard deviation between the predicted stellar labels and the pre-labeled values given by the high-resolution spectra from literature. The uncertainties of the estimated parameters (Teff, log g, vsini) are 2,185 K, 0.29dex, and 11 km/s, and 1,642 K, 0.25dex, and 42 km/s, for LAMOST-MRS and LAMOST-LRS spectra, respectively. This consistent catalog of atmospheric parameters of the early-type star will provide a reference for further investigation of the physical properties and evolution of massive stars.

Contact:

GUO Yanjun, Yunnan Observatories, CAS

guoyanjun@ynao.ac.cn