Two new variable stars detected in globular cluster NGC 6558

A world workforce of astronomers has performed a survey of variable stars within the area of a globular cluster often known as NGC 6558. Consequently, they recognized dozens of variables, out of which two turned out to be new cluster members. The finding was reported in a analysis paper printed June 29 on the pre-print server arXiv.

Variable stars may supply necessary hints into points of stellar construction and evolution. They may be useful for higher understanding the space scale of the universe. Specifically, research of variable stars in star clusters are of particular curiosity for astronomers as they’ve the potential to assist establish systematic errors that have an effect on stellar distance indicators.

NGC 6558 (often known as GCL 89 or ESO 456-SC62) is a Galactic bulge globular cluster positioned some 24,100 gentle years away within the constellation Sagittarius, with an angular measurement of about 5.4 x 5.4 arcminutes. Earlier observations have discovered that NGC 6558 has a metallicity at a stage of -1.32 dex and urged that it could be one of many oldest objects within the Milky Way.

A gaggle of astronomers led by Armando Arellano Ferro of the Nationwide Autonomous College of Mexico, has investigated the stellar content material of NGC 6558, hoping to detect new cluster members. For this goal, they noticed the cluster and its environment utilizing the Nationwide Observatory of Cordoba in Argentina and the Las Campanas Observatory in Chile.

“We made a survey of the variable stars in a 13.2 x 13.2 arcmin² centered on the sector of the Galactic bulge cluster NGC 6558,” the scientists wrote within the paper.

All in all, Ferro’s workforce recognized 78 variable stars within the area of NGC 6558. Afterward, they performed correct movement evaluation and a radical exploration of those variables on the color-magnitude diagram (CMD) of the cluster. Consequently, it turned out that 9 of them are really members of NGC 6558.

Two out of the 9 recognized cluster members are new variables, designated V18 and V19. Based on the paper, V18 is an eclipsing variable with a interval of roughly 0.4 days, whereas V19 is a semi-regular variable with a interval of about 346 days.

By inspecting the member variables, the astronomers managed to calculate the space to NGC 6558 and the cluster’s metallicity. They discovered that NGC 6558 is positioned about 27,500 gentle years away and its metallicity is roughly -1.33 dex.

The researchers additionally analyzed the pattern of RR Lyrae variables of the RRab kind in NGC 6558. Primarily based on this, they discovered that the cluster is almost certainly of the intermediate Oosterhoff kind (Oo-Int). Nevertheless, additional observations are required with a view to verify this assumption.

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