No Evidence for Classical Cepheids and a New Dwarf Galaxy Behind the Galactic Disk

TL;DR

This study challenges previous claims of a dwarf galaxy behind the Galactic disk by showing that the candidate stars are not classical Cepheids but likely spotted stars, emphasizing caution in classifying variable stars based on limited near-infrared data.

Contribution

The paper demonstrates that candidate Cepheids in a suspected dwarf galaxy are misclassified, providing a revised analysis that questions the galaxy's existence and highlighting classification challenges.

Findings

None of the four candidate stars are classical Cepheids.

Two stars are non-variable, one is a spotted object, and the fourth's light curve is inconsistent with Cepheids.

The study warns about misclassification risks with limited near-infrared data.

Abstract

Based on data from the ongoing OGLE Galaxy Variability Survey (OGLE GVS) we have verified observed properties of stars detected by the near-infrared VVV survey in a direction near the Galactic plane at longitude l~-27 deg and recently tentatively classified as classical Cepheids belonging to a, hence claimed, dwarf galaxy at a distance of about 90 kpc from the Galactic Center. Three of four stars are detected in the OGLE GVS I-band images. We show that two of the objects are not variable at all and the third one with a period of 5.695 d and a nearly sinusoidal light curve of an amplitude of 0.5 mag cannot be a classical Cepheid and is very likely a spotted object. These results together with a very unusual shape of the Ks-band light curve of the fourth star indicate that very likely none of them is a Cepheid and, thus, there is no evidence for a background dwarf galaxy. Our observations show that a great care must be taken when classifying objects by their low-amplitude close-to-sinusoidal near-infrared light curves, especially with a small number of measurements. We also provide a sample of high-amplitude spotted stars with periods of a few days that can mimick pulsations and even eclipses.