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 MK 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 ΔMKâ€ ≈â€ 0.4. The selected stars in both peaks cannot be represented by the same red clump giants with constant MKâ€ ≈â€ -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.
|Journal||Astronomy and Astrophysics|
|Publication status||Published - 2019 Jul 1|
Bibliographical noteFunding Information:
Acknowledgements. Thanks are given to the anonymous referee for helpful comments. Thanks are given to Carlos González-Fernández for exchanging information with us on independent analyses of the parallax distribution red clump giants with VVV+Gaia. Thanks are given to Ruth Chester (language editor of A&A) for proof-reading of the text. MLC and FGL were supported by the grant AYA2015-66506-P of the Spanish Ministry of Economy and Competitiveness (MINECO). YWL acknowledges support from the National Research Foundation of Korea. The VVV Survey is supported by the European Southern Observatory, by BASAL Center for Astrophysics and Associated Technologies PFB-06, by FONDAP Center for Astrophysics 15010003, by the Chilean Ministry for the Economy, Development, and Tourism’s Programa Iniciativa Cientí-fica Milenio through grant P07-021-F, awarded to The Milky Way Millennium Nucleus. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www. cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.
© ESO 2019.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science