A Catalog of Candidate Field Horizontal‐Branch and A‐Type Stars. III. A 2MASS‐Cleaned Version

Almeida, Tiago Hendrigo de; Rossi, Silvia; Wilhelm, Ronald; Marsteller, B.

doi:10.1086/509921

Cited by 13 publications

(22 citation statements)

References 42 publications

(48 reference statements)

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“…The main criterion proposed by Beers et al (2007) to select high-likelihood BHB stars, from among their candidates from the objective-prism survey inspection, is −0.2 <(B − V) o < +0.2, which means that sources are selected according to their color temperature. On the "red" side of this color interval, there might be some contamination by A v stars, which can be identified by their larger log g values.…”

Section: Discussionmentioning

confidence: 99%

“…Although several previous papers listed catalogs of candidate FHB and A-type stars from the HK survey (Pier 1982;Beers et al 1988Beers et al , 1996, it was not until the work of Beers et al (2007) that these targets were classified according to their probability of being true BHB stars. Each HK FHB candidate was associated with a 2MASS (Skrutskie et al 2006) stellar source, and the "high-probability" BHB candidates were classified according to the criterion: −0.2 (B − V) o +0.2.…”

Section: The Samplementioning

confidence: 99%

“…However, for most stars UBV photometry was not available, so the de-reddened (B − V) o had to be estimated using a relationship between (J − H) o and (B − V) o colors. Unfortunately, the relationship between the (J − H) and (B − V) color indices is not very tight, and the errors that result from predicting (B − V) from (J − H) are intrinsically large (Beers et al 2007 estimate the error in predicted color from 2MASS, (B − V) o,2M , to be about 0.08 mag). Essentially, the criterion proposed by Beers et al (2007) represents a cutoff region in color temperature, especially intended to select stars on the "blue side" of the HB.…”

Section: The Samplementioning

confidence: 99%

“…The sample selected for this study (Table 1) consists of stars classified by Beers et al (2007) as high-probability BHB stars, with the additional restriction b < −60 • . Column 1 lists the running number of the sample; Column 2 lists the original HK-survey name, while Column 3 is the name in the 2MASS catalog; other names cited in the literature are listed in Column 4; the Galactic coordinates for each star (l, b) are listed in Columns 5 and 6, respectively; Columns 7-12 contain the 2MASS JHK photometry and associated errors; Column 13 lists, where available, the measured (B − V) reported by various authors, de-reddened according to the extinction map derived by Schlegel et al (1998).…”

Section: The Samplementioning

confidence: 99%

“…An improvement to these methods was proposed by Wilhelm et al (1999a): a hybrid technique including UBV data and synthetic spectra that are used to fit the observed stellar spectra, but unfortunately, UBV data are still lacking for a large number of FHB candidates. Beers et al (2007) analyzed a sample containing 12,000 candidate FHB/A stars identified during the course of the HK objective-prism survey, and used the Two Micron All Sky Survey (2MASS) point-source catalog colors to re-classify the HK-survey candidates as low-, medium-, and high-probability FHB candidates. In order to confirm them as FHB stars, spectroscopic observations are required, which is the main purpose of this study.…”

Section: Introductionmentioning

confidence: 99%

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A Search for Field Horizontal-Branch Stars Near the South Galactic Pole

Ortiz

Wilhelm

Costa³

et al. 2010

The Astronomical Journal

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Searches for field horizontal-branch (FHB) stars in the halo of the Galaxy in the past have been carried out by several techniques, such as objective-prism surveys and visual or infrared photometric surveys. By choosing adequate color criteria, it is possible to improve the efficiency of identifying bona fide FHB stars among the other objects that exhibit similar characteristics, such as main-sequence A-stars, blue stragglers, subdwarfs, etc. In this work, we report the results of a spectroscopic survey carried out near the south Galactic pole intended to validate FHB stars originally selected from the HK objective-prism survey of Beers and colleagues, based on near-infrared color indices. A comparison between the stellar spectra obtained in this survey with theoretical stellar atmosphere models allows us to determine T eff , log g, and [Fe/H] for 13 stars in the sample. Stellar temperatures were calculated from measured (B − V) o , when this measurement was available (16 stars). The color index criteria adopted in this work are shown to correctly classify 30% of the sample as FHB, 25% as non-FHB (main-sequence stars and subdwarfes), whereas 40% could not be distinguished between FHB and main-sequence stars. We compare the efficacy of different color criteria in the literature intended to select FHB stars, and discuss the use of the Mg ii 4481 line to estimate the metallicity.

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Section: Discussionmentioning

confidence: 99%

Section: The Samplementioning

confidence: 99%

Section: The Samplementioning

confidence: 99%

Section: The Samplementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Search for Field Horizontal-Branch Stars Near the South Galactic Pole

Ortiz

Wilhelm

Costa³

et al. 2010

The Astronomical Journal

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A spectroscopic survey of FHB stars near the south galactic pole

Rossi¹,

Ortiz

Wilhelm

et al. 2009

Proc. IAU

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Abstract. We present the results of a medium-resolution spectroscopic survey of 43 field horizontal-branch (FHB) candidates carried out near the south galactic pole, selected from the original list of FHB candidates compiled by Beers et al. (2007). The observation list includes only stars classified as "high-probability" candidates, according to their 2MASS infrared colours. Atmospheric parameters of some stars have been obtained by comparing some spectral features with theoretical models provided by Kurucz (1993). A comparison between the grid of model atmospheres with some parameters of the Hδ line allowed the determination of log g, whilst [Fe/H] was estimated by the equivalent widths of the MgII 4481 and Caii lines. About 77% of the sample have been classified as FHB stars, 10% as subdwarfs, whilst the remaining 13% are probably main-sequence A-type stars far from the Galactic plane.

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Something borrowed, something blue: The nature of blue metal-poor stars inferred from their colours and chemical abundances

Hansen

Jofré

Koch

et al. 2017

A&A

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Blue metal-poor stars (BMPs) are main sequence stars that appear bluer and more luminous than normal turnoff stars. They were originally singled out by using B − V and U − B colour cuts. Early studies found that a larger fraction of field BMP stars were binaries compared to normal halo stars. Thus, BMP stars are ideal field blue straggler candidates for investigating internal stellar evolution processes and binary interaction. In particular, the presence or depletion in lithium in their spectra is a powerful indicator as to their origin. They are either old, halo blue stragglers experiencing internal mixing processes or mass transfer (Li-depletion), or intermediate-age, single stars of possibly extragalactic origin (2.2 dex halo plateau Li). However, we note that internal mixing processes can lead to an increased level of Li. Hence, this study combines photometry and spectroscopy to unveil the origin of various BMP stars. We first show how to separate binaries from young blue stars using photometry, metallicity, and lithium. Using a sample of 80 BMP stars (T> 6300K), we find that 97% of the BMP binaries have V − K s 0 < 1.08± 0.03, while BMP stars that are not binaries lie above this cut in 2/3 of the cases. This cut can help classify stars which lack radial velocities from follow-up observations. We then trace the origin of two BMP stars from the photometric sample by conducting a full chemical analysis using new high-resolution and high signal-to-noise spectra. Based on their radial velocities, Li, α, and s-and r-process abundances we show that BPS CS22874-042 is a single star (A(Li)= 2.38 ± 0.10 dex) while with A(Li)= 2.23 ± 0.07 dex CD-48 2445 is a binary, contrary to earlier findings. Our analysis emphasises that field blue stragglers can be segregated from single metal-poor stars, using (V − K s) colours with a fraction of single stars polluting the binary sample, but not vice versa. These two groups can only be properly separated by using information from stellar spectra, illustrating the need for accurate and precise stellar parameters and high resolution, high S/N spectra in order to fully understand and classify this intriguing class of stars. Our high-resolution spectrum analysis confirms the findings from the colour cuts and shows that CS 22874−042 is single, while CD −48 2445 most likely is a binary. Moreover, the stellar abundances show that both stars formed in situ; CS 22874−042 carry traces of massive star enrichment and CD −48 2445 shows indications of AGB mass transfer mixed with gases ejected possibly from neutron star mergers.

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A Catalog of Candidate Field Horizontal‐Branch and A‐Type Stars. III. A 2MASS‐Cleaned Version

Cited by 13 publications

References 42 publications

A Search for Field Horizontal-Branch Stars Near the South Galactic Pole

A Search for Field Horizontal-Branch Stars Near the South Galactic Pole

A spectroscopic survey of FHB stars near the south galactic pole

Something borrowed, something blue: The nature of blue metal-poor stars inferred from their colours and chemical abundances

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