Pilot Studies Of High-Luminosity Stars Based On High Precision Measurements By The Gaia Satellite

With the launch of the high-precision astrometric satellite,Gaia,the precise position,proper motion,parallax and other information of stars have been well measured.Based on such high-precision data,this paper will carry out further scientific research on the following three aspects:1.Using the cross-matched data of Gaia EDR3 and the 2MASS Point Source Catalog,a sample of Red Clump stars with parallax accuracies better than 20%is identified and used to reveal the nearby spiral pattern traced by old stars.As shown in the overdensity distribution of Red Clump stars,there is an arc-like feature extended from l～90° to～243°,which passed close to the Sun.This feature is probably an arm segment traced by old stars,indicating the Galaxy potential in the vicinity of the Sun.By comparing to the spiral arms depicted by young objects,we found that there are considerable offsets between the two different components of Galactic spiral arms.The spiral arm traced by Red Clump stars tends to have a larger pitch angle,hence a more loose wound pattern.2.Establishing the period-Wesenheit relation requires independent and accurate distance measurements of classical Cepheids.The precise distance provided by an associated open cluster independently calibrates the period-Wesenheit relation of classical Cepheids.51 classical Cepheids associated with open clusters are compiled using the constraints of five-dimensional astrometric information.By directly using Gaia DR3 parallax,the period-Wesenheit relation in the Gaia G band is calibrated as WG=(-3.06±0.11)log P+(-2.96±0.10).Compared with the results derived by directly adopting the classical Cepheid parallaxes or using distance moduli,the Wesenheit magnitudes based on the cluster-averaged parallaxes exhibit a tighter relation with the period.Besides,there is a systematic offset between the observed Wesenheit absolute magnitudes of distant Open cluster-classical Cepheids and their fitted magnitudes.After considering the parallax zero-point correction,the systematic offset can be reduced,yielding a probably better PW relation of WG=(-2.94±0.12)log P+(-2.93±0.11).3.Since the hypervelocity stars were discovered in the Milky Way,various mechanisms have been proposed to explain these runaway stars.Up to now,however,the dominant ejected mechanism of hypervelocity stars is still unclear.As the largest and closest face-on satellite galaxy of the Milky Way,the Large Magellanic Cloud serves as a good target,allowing us to study this issue.Based on the high-precision astrometric parameters provided by Gaia data release 3,we researched the proper motions of 3 119 massive O-B2-type stars in the Large Magellanic Cloud and identified 98(～3%)as having the ability to escape from the Large Magellanic Cloud,with more than 50%confidence.Furthermore,by investigating the characteristics of the identified massive stars and adopting a regression analysis,we find that the dynamic ejection scenario might be the dominant mechanism of the massive hypervelocity runaway stars in the Large Magellanic Cloud.