Absence of an X-shaped Structure in the Milky Way Bulge Using Mira Variable Stars

López-Corredoira, Martín

doi:10.3847/1538-4357/836/2/218

Cited by 23 publications

(22 citation statements)

References 32 publications

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“…Because the fields are symmetrical to l = 0 • , the two RCs contribute similarly to the magnitude distribution, even though the foreground RC will contributes slightly more to the distribution at l = 1 • compared to l = −1 • ; for the background RC, the opposite is true. The X-bulge density law proposed by López-Corredoira (2017) describes well this phenomenon: by looking at Figure 13, we can clearly see how the l = 1 • line of sight will pass closer to foreground RC than to the background RC, but thanks to the viewing angle under which we observe the Bar, both RCs will be visible in the magnitude distribution, even though in different contributions. The double peaked magnitude distribution shown in yellow is the López-Corredoira (2017) model calculated using Equation 4where ρB is the X-shaped density distribution that we have shown in Figure 13.…”

Section: Data Versus Model Comparisonsupporting

confidence: 59%

A parametric description of the 3D structure of the Galactic bar/bulge using the VVV survey

Simion

Belokurov

Irwin

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We study the structure of the inner Milky Way (MW) using the latest data release of the Vista Variables in Via Lactea (VVV) survey. The VVV is a deep near-infrared, multi-colour photometric survey with a coverage of 300 square degrees towards the Bulge/Bar. We use Red Clump (RC) stars to produce a high-resolution dust map of the VVV's field of view. From de-reddened colour-magnitude diagrams we select Red Giant Branch stars to investigate their 3D density distribution within the central 4 kpc. We demonstrate that our best-fit parametric model of the Bulge density provides a good description of the VVV data, with a median percentage residual of 5 % over the fitted region. The strongest of the otherwise low-level residuals are overdensities associated with a low-latitude structure as well as the so-called X-shape previously identified using the split RC. These additional components contribute only ∼ 5% and ∼ 7% respectively to the Bulge mass budget. The best-fit Bulge is "boxy" with an axis ratio of [1:0.44:0.31] and is rotated with respect to the Sun-Galactic Centre line by at least ∼ 20• . We provide an estimate of the total, full sky, mass of the Bulge of M Chabrier Bulge = 2.36 × 10 10 M for a Chabrier initial mass function. We show there exists a strong degeneracy between the viewing angle and the dispersion of the Red Clump (RC) absolute magnitude distribution. The value of the latter is strongly dependent on the assumptions made about the intrinsic luminosity function of the Bulge.

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Section: Data Versus Model Comparisonsupporting

confidence: 59%

A parametric description of the 3D structure of the Galactic bar/bulge using the VVV survey

Simion

Belokurov

Irwin

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…Although Mira period-luminosity (PL) relations exhibit an intrinsic dispersion in the optical (de Grijs 2011), it has been found that such dispersions are smaller at near-and mid-infrared (IR) wavelengths for Miras with thin dust shells and periods of less than 400 days (Whitelock et al 2008;Matsunaga et al 2009;Whitelock 2013). Thus, their PL relations can be used to trace the structure of the Milky Way (MW) galaxy and beyond (Catchpole et al 2016;López-Corredoira 2017). Moreover, SiO masers from Mira stars have proved powerful tools for investigating stellar motions in optically obscured regions of the MW (Fujii et al 2006;Deguchi et al 2007Deguchi et al , 2008Deguchi et al , 2010Deguchi 2012).…”

Section: Introductionmentioning

confidence: 99%

Mira Variable Stars from LAMOST DR4 Data: Emission Features, Temperature Types, and Candidate Selection

Yao

Liu

Deng

et al. 2017

ApJS

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Based on an extensive spectral study of a photometrically confirmed sample of Mira variables, we find a relationship between relative Balmer emission-line strength and spectral temperature of O-rich Mira stars. The F Hδ /F Hγ flux ratio increases from less than unity to five as stars cool down from M0 to M10, which is likely driven by increasing TiO absorption above the deepest shock-emitting regions. We also discuss the relationship between the equivalent widths of the Balmer emission lines and the photometric luminosity phase of our Mira sample stars. Using our 291 Mira spectra as templates for reference, 191 Mira candidates are newly identified from the LAMOST DR4 catalog. We summarize the criteria adopted to select Mira candidates based on emission-line indices and molecular absorption bands. This enlarged spectral sample of Mira variables has the potential to contribute significantly to our knowledge of the optical properties of Mira stars and will facilitate further studies of these late-type, long-period variables.

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“…However, using similar images of the Milky Way in the infrared, Ness & Lang (2016) have more recently claimed to see an X-shaped bulge, trying to confirm more recent theories of bulge formation (e.g., Li & Shen 2015). In spite of their claims, we do not see a clear X-shape in the raw images, and we think the processed images may also show elliptical or boxy bulges depending on the subtraction of some particular disk model (López-Corredoira 2017), or the subtraction of the bulge as an ellipsoid instead of as a boxy bulge (Han & Lee 2018).…”

Section: Introductionmentioning

confidence: 69%

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

López-Corredoira

Lee

Garzón

et al. 2019

A&A

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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 ∆M K ≈ 0.4. The selected stars in both peaks cannot be represented by the same red clump giants with constant M K ≈ −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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Absence of an X-shaped Structure in the Milky Way Bulge Using Mira Variable Stars

Cited by 23 publications

References 32 publications

A parametric description of the 3D structure of the Galactic bar/bulge using the VVV survey

A parametric description of the 3D structure of the Galactic bar/bulge using the VVV survey

Mira Variable Stars from LAMOST DR4 Data: Emission Features, Temperature Types, and Candidate Selection

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

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