Distribution of red clump stars does not support the X-shaped Galactic bulge

Abstract

CONTEXT. Claims of an X-shaped Galactic bulge were based on the assumption of red clump stars as standard candles in some lines of sight crossing the off-plane bulge. However, some doubts have been cast on whether the two peaks in star counts along the line of sight really represent a double peak in the density distribution, or whether there is something wrong with the assumption of a unique constant absolute magnitude for all of these stars. AIMS. With the advent of Gaia-DR2 parallaxes in combination with near-infrared VISTA-VVV data, we are able to check which of the hypotheses is correct. METHODS. We calculated the median absolute magnitude $M_K$ corresponding to both peaks of putative red clumps in seven lines of sight with the lowest extinction in the interesting coordinates' range. RESULTS. The difference between the absolute magnitude of the bright and the faint peak is $\Delta M_K\approx 0.4$. The selected stars in both peaks cannot be represented by the same red clump giants with constant $M_K\approx -1.6$. CONCLUSIONS. The hypothesis that the bulge contains an X-shape is based on the assumption that the faint and bright peaks of the density distribution towards the bulge are dominated by standard red clump stars. However, we show that both the faint and bright peaks cannot be dominated by standard red clump stars simultaneously.

5 pages, accepted to be published in A&A

References in corpus (8)

• Modelling the Galactic bar using OGLE-II Red Clump Giant Stars
• Red clump stars and Gaia: Calibration of the standard candle using a hierarchical probabilistic model
• A parametric description of the 3D structure of the Galactic Bar/Bulge using the VVV survey
• Testing asteroseismology with Gaia DR2: Hierarchical models of the Red Clump
• The X-Shaped Milky Way Bulge in OGLE-III Photometry and in N-Body Models
• Absence of an X-shaped Structure in the Milky Way Bulge Using Mira Variable Stars
• Common Origin of Two RR Lyrae Populations and the Double Red Clump in the Milky Way Bulge
• A case against an X-shaped structure in the Milky Way young bulge

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• Difference in chemical composition between the bright and faint red clump stars in the Milky Way bulge
• Analysing the structure of the bulge with Mira variables