Graduate Research Seminar I/II

The Age and Structure of the Galactic Bulge from Mira Variables

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“The Age and Structure of the Galactic Bulge from Mira Variables” by Catchpole et al.


The standard candle properties of Mira variables are exploited, in order to use them as tracers of the galactic bulge structure. Mira period-age relation is used to understand the relation of age to different regions of the bulge.


Combined original data of 648 stars taken at Australian Astronomical Observatory (AAO) with 8057 from OGLE, MACHO, and 2MASS surveys. Data span the J-, H-, K-, and L- bands.


Extinction corrected for using 4 different methods, described in Section 5, page 5. Methods are all related to period-color or color-color relations.

Distances obtained using the P-L relation given in Equation 2, page 5. Slope obtained from LMC Miras, and zero point derived from parallaxes of nearby Miras.

Period and age are inversely correlated. In this work, young and old Miras are separated at logP > 2.6, which corresponds to ~5 Gyr.


Figure 1: Visualization of coordinate systems (page 3).

Figure 2: Identification of Miras, as those below line or inside box (page 4).

Figure 3: P-C relation (page 4).

Figure 4: Histogram of periods, note the peak at logP ~ 2.5 (page 5).

Figure 5: Distribution of all Miras used in Galactic coordinates (page 6).


Evidence of helium-enrichment in Galactic bulge. Helium-enrichment thought to interfere with period-age relation, but authors think this is not significant enough to change conclusions, as the precise ages do not matter, and they are still in the same ballpark.


Distance to the center found to be 8.9 ± 0.4 kpc.

Younger Miras are found to lie in a bar structure, while older Miras are found to form a spheroidal bulge.