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OGLE-III detection of the anomalous galactic bulge red giant branch bump: Evidence of enhanced helium enrichment

Nataf, David; Udalski, A; Gould, A; Pinsonneault, Marc H

Description

We measure the red giant branch bump (RGBB) of the Galactic bulge, the most metal-rich RGBB ever detected. The RGBB luminosity function peaks at the expected brightness, but its number density is very low relative to Galactic globular cluster calibrations, implying the Galactic bulge has a higher helium enrichment parameter ΔY/ΔZ ≥ 4.0 for Y 0.35 rather than the standard 2.0 with Y = 0.27, which we suggest may be a common feature of galactic spheroids. The RGBB is (0.71 0.02) mag fainter than...[Show more]

dc.contributor.authorNataf, David
dc.contributor.authorUdalski, A
dc.contributor.authorGould, A
dc.contributor.authorPinsonneault, Marc H
dc.date.accessioned2015-12-10T23:22:52Z
dc.identifier.issn0004-637X
dc.identifier.urihttp://hdl.handle.net/1885/66700
dc.description.abstractWe measure the red giant branch bump (RGBB) of the Galactic bulge, the most metal-rich RGBB ever detected. The RGBB luminosity function peaks at the expected brightness, but its number density is very low relative to Galactic globular cluster calibrations, implying the Galactic bulge has a higher helium enrichment parameter ΔY/ΔZ ≥ 4.0 for Y 0.35 rather than the standard 2.0 with Y = 0.27, which we suggest may be a common feature of galactic spheroids. The RGBB is (0.71 0.02) mag fainter than the red clump (RC) in I toward the densest stellar regions imaged by the OGLE-III Galactic bulge photometric survey, (|l| ≤ 4, 2 ≲ |b| ≤ 4). The number density of RGBB stars is (12.7 2.0)% that of RC stars. The brightness dispersion of the RGBB is significantly lower than that of the RC, a result that is difficult to explain as the RGBB luminosity is known to vary significantly with metallicity. Sight lines that have two RCs have two RGBBs with similar properties to one another, an expected outcome if the Milky Way's bulge is X-shaped. We also find preliminary evidence of the Galactic bulge asymptotic giant branch bump, at a brightness of 1.06 mag brighter than the RC in I and with a number density 1.5% that of the RC. Accounting for the RGBB has a small effect on the best-fit parameters of the RC, shifting its best-fit peak brightness and reducing its brightness dispersion by 0.015 mag each.
dc.publisherIOP Publishing
dc.sourceAstrophysical Journal, The
dc.subjectKeywords: Galaxy: bulge
dc.titleOGLE-III detection of the anomalous galactic bulge red giant branch bump: Evidence of enhanced helium enrichment
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume730
dc.date.issued2011
local.identifier.absfor020104 - Galactic Astronomy
local.identifier.ariespublicationU3488905xPUB1328
local.type.statusPublished Version
local.contributor.affiliationNataf, David, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationUdalski, A, Warsaw University Observatory
local.contributor.affiliationGould, A, Ohio State University
local.contributor.affiliationPinsonneault, Marc H, Ohio State University
local.description.embargo2037-12-31
local.bibliographicCitation.issue2
local.bibliographicCitation.startpage118
local.identifier.doi10.1088/0004-637X/730/2/118
dc.date.updated2016-02-24T09:59:10Z
local.identifier.scopusID2-s2.0-79953714013
CollectionsANU Research Publications

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