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Abstract <p>Galactic orbital parameters of 519 type&#xa0;II Cepheids classified asBL&#xa0;Her, W&#xa0;Vir and RV&#xa0;Tau variable stars were calculated usingBayesian distances, proper motions, and Gaia&#xa0;DR3 radialvelocities. It is shown that at least 27 BL&#xa0;Her type variables outof 100, 17 W&#xa0;Vir type variables out of 308 and 8 RV&#xa0;Tau typevariables out of 111 are characterized by a spatial distributionand galactic orbital parameters typical of the population of thethin/old disk of the Galaxy. At the same time, their luminositiesare significantly lower than those of classical Cepheids (DCEP),and correspond to the luminosities of type II Cepheids. It issuggested that the region of the instability strip occupied byshort-period Cepheids of the BL&#xa0;Her type may contain stars of theold disk with initial masses of about <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(0.95 M_{\odot}\)</EquationSource> <!--ASPBull2560035Rastorguev-m1--> </InlineEquation>, whichevolved from the main sequence to the stage of the onset of heliumburning in the core and reached the instability strip over a timeof about 9&#xa0;Gyr. The presence of evolutionary ‘‘loops’’ explainsthe existence of a number of BL&#xa0;Her type Cepheids, whichdemonstrate an evolutionary decrease in period. Thus, bothlow-mass stars in the phase of evolution of a double-layer sourceand stars at the stage of the onset of helium burning in the corewith a larger initial mass can coexist in the instability strip ofBL&#xa0;Her variables. To refine the classification of type IICepheids, more detailed evolutionary and pulsation calculationsand additional comprehensive studies are needed, including, forexample, estimates of pulsation radii.</p>

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Disk Population of Type II Cepheids in the Galaxy Based on Gaia DR3 Data

  • 期刊论文

  • 发表日期：

    2025年9月1日

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  • A. S. Rastorguev,
  • M. V. Zabolotskikh

摘要

Abstract

Galactic orbital parameters of 519 type II Cepheids classified asBL Her, W Vir and RV Tau variable stars were calculated usingBayesian distances, proper motions, and Gaia DR3 radialvelocities. It is shown that at least 27 BL Her type variables outof 100, 17 W Vir type variables out of 308 and 8 RV Tau typevariables out of 111 are characterized by a spatial distributionand galactic orbital parameters typical of the population of thethin/old disk of the Galaxy. At the same time, their luminositiesare significantly lower than those of classical Cepheids (DCEP),and correspond to the luminosities of type II Cepheids. It issuggested that the region of the instability strip occupied byshort-period Cepheids of the BL Her type may contain stars of theold disk with initial masses of about \(0.95 M_{\odot}\) , whichevolved from the main sequence to the stage of the onset of heliumburning in the core and reached the instability strip over a timeof about 9 Gyr. The presence of evolutionary ‘‘loops’’ explainsthe existence of a number of BL Her type Cepheids, whichdemonstrate an evolutionary decrease in period. Thus, bothlow-mass stars in the phase of evolution of a double-layer sourceand stars at the stage of the onset of helium burning in the corewith a larger initial mass can coexist in the instability strip ofBL Her variables. To refine the classification of type IICepheids, more detailed evolutionary and pulsation calculationsand additional comprehensive studies are needed, including, forexample, estimates of pulsation radii.