Distribution of red clump stars does not support the X-shaped Galactic bulge. (arXiv:1905.13592v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Lopez_Corredoira_M/0/1/0/all/0/1">M. Lopez-Corredoira</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lee_Y/0/1/0/all/0/1">Y.-W. Lee</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Garzon_F/0/1/0/all/0/1">F. Garzon</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lim_D/0/1/0/all/0/1">D. Lim</a>
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 $Delta M_Kapprox 0.4$. The selected stars in both peaks cannot
be represented by the same red clump giants with constant $M_Kapprox -1.6$.
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.
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 $Delta M_Kapprox 0.4$. The selected stars in both peaks cannot
be represented by the same red clump giants with constant $M_Kapprox -1.6$.
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.
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