A Survey for EHB Stars in the Galactic Bulge

Terndrup, D. M.; An, Deokkeun; Hansen, A. V. B.; Peterson, R. C.; Walker, A. R.; Sadler, E. M.

doi:10.1023/b:astr.0000044328.04425.c1

Cited by 6 publications

(5 citation statements)

References 33 publications

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“…In the Galactic bulge, evidence of the presence of hot HB stars has been provided and discussed by Bertelli et al (1996), Terndrup et al (1999Terndrup et al ( , 2004, Peterson et al (2001), Busso et al (2005), and Busso and Moehler (2008). It should also be noted that the precise RGB mass loss recipe adopted may also significantly impact the predicted production of UV sources (see Sect.…”

Section: The M V (Rrl) − [Fe/h] Relation: Linear Quadraticmentioning

confidence: 97%

“…Another important implication of this result is that the production of hot HB sources at high metallicities, which are believed to be the main sources of the "UV upturn" (or UVX) light coming from elliptical galaxies and the bulges of spirals (see O'Connell 1999 for a review and extensive references), is importantly affected by their precise helium enrichment laws (e.g., Yi et al 1997). In the Galactic bulge, evidence of the presence of hot HB stars has been provided and discussed by Bertelli et al (1996), Terndrup et al (1999Terndrup et al ( , 2004, Peterson et al (2001), Busso et al (2005), and Busso & Moehler (2008). It should also be noted that the precise RGB mass loss recipe adopted may also significantly impact the predicted production of UV sources (see Sect.…”

Section: 34mentioning

confidence: 97%

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Horizontal branch stars: the interplay between observations and theory, and insights into the formation of the Galaxy

Catelan

2009

Astrophys Space Sci

359

432

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We review and discuss horizontal branch (HB) stars in a broad astrophysical context, including both variable and non-variable stars. A reassessment of the Oosterhoff dichotomy is presented, which provides unprecedented detail regarding its origin and systematics. We show that the Oosterhoff dichotomy and the distribution of globular clusters in the HB morphology-metallicity plane both exclude, with high statistical significance, the possibility that the Galactic halo may have formed from the accretion of dwarf galaxies resembling present-day Milky Way satellites such as Fornax, Sagittarius, and the LMC-an argument which, due to its strong reliance on the ancient RR Lyrae stars, is essentially independent of the chemical evolution of these systems after the very earliest epochs in the Galaxy's history. Convenient analytical fits to isochrones in the HB type-[Fe/H] plane are also provided. In this sense, a rediscussion of the second-parameter problem is also presented, focusing on the cases of NGC 288/NGC 362, M13/M3, the extreme outer-halo globular clusters with predominantly red HBs, and the metal-rich globular clusters NGC 6388 and NGC 6441. The recently revived possibility that the helium abundance may play an important role as a second parameter is also addressed, and possible constraints on this scenario discussed. We critically discuss the possibility that the observed properties of HB stars in NGC 6388 and NGC 6441 might be accounted for if these clusters possess a relatively minor population of helium-enriched stars. A technique is M. Catelan is John Simon Guggenheim Memorial Foundation Fellow.M. Catelan ( ) proposed to estimate the HB types of extragalactic globular clusters on the basis of integrated far-UV photometry. The importance of bright type II Cepheids as tracers of faint blue HB stars in distant systems is also emphasized. The relationship between the absolute V magnitude of the HB at the RR Lyrae level and metallicity, as obtained on the basis of trigonometric parallax measurements for the star RR Lyr, is also revisited. Taking into due account the evolutionary status of RR Lyr, the derived relation implies a true distance modulus to the LMC of (m-M) 0 = 18.44 ± 0.11. Techniques providing discrepant slopes and zero points for the M V (RRL)-[Fe/H] relation are briefly discussed. We provide a convenient analytical fit to theoretical model predictions for the period change rates of RR Lyrae stars in globular clusters, and compare the model results with the available data. Finally, the conductive opacities used in evolutionary calculations of low-mass stars are also investigated.

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Section: The M V (Rrl) − [Fe/h] Relation: Linear Quadraticmentioning

confidence: 97%

Section: 34mentioning

confidence: 97%

Horizontal branch stars: the interplay between observations and theory, and insights into the formation of the Galaxy

Catelan

2009

Astrophys Space Sci

359

432

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“…They are old objects, usually used to trace old, metal-poor structures such as the Galactic halo (Catelan 2009;Vickers et al 2012). In the Galactic bulge, although metal-rich BHB stars exist, the vast majority of them seem to be metal-poor (Peterson et al 2001;Terndrup et al 2004). Identifying old metal-poor stars in the fields of the Galactic bulge is difficult, as they make up a small fraction compared to the metal-rich component.…”

Section: Cmds Of the Galactic Bulge Fields In The Vvvmentioning

confidence: 99%

Milky Way demographics with the VVV survey

Alonso-García

Saito

Hempel

et al. 2018

A&A

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Context. The inner regions of the Galaxy are severely affected by extinction, which limits our capability to study the stellar populations present there. The Vista Variables in the Vía Láctea (VVV) ESO Public Survey has observed this zone at near-infrared wavelengths where reddening is highly diminished. Aims. By exploiting the high resolution and wide field-of-view of the VVV images we aim to produce a deep, homogeneous, and highly complete database of sources that cover the innermost regions of our Galaxy. Methods. To better deal with the high crowding in the surveyed areas, we have used point spread function (PSF)-fitting techniques to obtain a new photometry of the VVV images, in the ZY JHKs near-infrared filters available. Results. Our final catalogs contain close to one billion sources, with precise photometry in up to five near-infrared filters, and they are already being used to provide an unprecedented view of the inner Galactic stellar populations. We make these catalogs publicly available to the community. Our catalogs allow us to build the VVV giga-CMD, a series of color-magnitude diagrams of the inner regions of the Milky Way presented as supplementary videos. We provide a qualitative analysis of some representative CMDs of the inner regions of the Galaxy, and briefly mention some of the studies we have developed with this new dataset so far.

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“…Due to the high extinction, one must rely on M giants, which give a result at variance with optical studies; the mean [Fe/H] is -0.1, with σ = 0.1. While one may appeal to mass loss as the culprit for the unusual M giant abundance distribution, strong depletion of the red giant branch would require that there be a large population of extreme HB or UVbright stars; no such extraordinarily large population seems to be present (Terndrup et al 2004) though the subject is worthy of additional study. It is difficult to construct an N-body bar scenario with any abundance gradient, much less two regions with different gradients.…”

Section: Complicationsmentioning

confidence: 99%

The Bulge Radial Velocity/Abundance Assay

Rich

2011

Preprint

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The Bulge Radial Velocity/Abundance Assay (BRAVA) has accomplished a survey of 10,000 red giants in the Southern Galactic bulge, approximately spanning −8 • < l < +8 • and −3 • < b < −8 • , a region within roughly 1 kpc from the nucleus. We find that the Galactic bulge at b = −4 • displays a clear departure from solid body rotation, and that the rotation field along the major axis at b = −6 • and b = −8 • is identical to that at lower latitude; this is "cylindrical" rotation, a hallmark observed in edge-on bars. Comparison of the BRAVA dataset with an N-body bar shows that > 90% of the bulge population is in the bar, leaving little room for a "classical" bulge component. We also report on the first iron abundance and composition measurements in the outer bulge, at b = −8 • . The iron abundance in this field falls on the trend of a suspected gradient measured from high resolution spectroscopy of bulge clump stars. Further, we find that the trends of [α/Fe] vs [Fe/H] that characterize the bulge at lower latitude are present 1 kpc from the nucleus, consistent with a rapid (< 1Gyr) timescale for the formation of the bulge, even near its boundary. Although the dynamics of the bulge are consistent with those of a dynamically buckled N-body bar, the presence of an abundance gradient is not compatible with purely dynamical processes; we propose that missing baryonic physics is needed. We also report on the remarkable massive bulge globular cluster Terzan 5, which has a bimodal abundance and composition distribution, and is proposed as the remnant of a population of primordial building block stellar systems that formed the bulge. Terzan 5 is presently a unique case, and it is important to test whether the dissolution of systems similar to it populated the bulge.

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A Survey for EHB Stars in the Galactic Bulge

Cited by 6 publications

References 33 publications

Horizontal branch stars: the interplay between observations and theory, and insights into the formation of the Galaxy

Horizontal branch stars: the interplay between observations and theory, and insights into the formation of the Galaxy

Milky Way demographics with the VVV survey

The Bulge Radial Velocity/Abundance Assay

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