A long-period Cepheid variable in the starburst cluster VdBH222

TL;DR

This study identifies a long-period Cepheid variable in the starburst cluster VdBH222, providing insights into stellar evolution, cluster properties, and the structure of the Milky Way's inner regions.

Contribution

It reports the discovery of a long-period Cepheid in VdBH222, the first such in this cluster, and uses it to refine distance, age, and star formation history estimates.

Findings

VdBH222 hosts a long-period Cepheid with a ~23.3-day period.

Distance to VdBH222 is approximately 6 kpc, with an age of about 20 Myr.

The cluster's properties suggest recent star formation in the inner Milky Way.

Abstract

Galactic starburst clusters play a twin role in astrophysics, serving as laboratories for the study of stellar physics and also delineating the structure and recent star formation history of the Milky Way. In order to exploit these opportunities we have undertaken a multi-epoch spectroscopic survey of the red supergiant dominated young massive clusters thought to be present at both near and far ends of the Galactic Bar. Significant spectroscopic variability suggestive of radial pulsations was found for the yellow supergiant VdBH 222 #505. Follow-up photometric investigations revealed modulation with a period of ~23.325d; both timescale and pulsational profile are consistent with a Cepheid classification. As a consequence #505 may be recognised as one of the longest period Galactic cluster Cepheids identified to date and hence of considerable use in constraining the bright end of the period/luminosity relation at solar metallicities. In conjunction with extant photometry we infer a distance of ~6kpc for VdBH222 and an age of ~20Myr. This results in a moderate reduction in both integrated cluster mass (~2x10^4Msun) and the initial stellar masses of the evolved cluster members (~10Msun). As such, VdBH222 becomes an excellent test-bed for studying the properties of some of the lowest mass stars observed to undergo type-II supernovae. Moreover, the distance is in tension with a location of VdBH 222 at the far end of the Galactic Bar. Instead a birthsite in the near 3kpc arm is suggested; providing compelling evidence of extensive recent star formation in a region of the inner Milky Way which has hitherto been thought to be devoid of such activity.