Evidence for an Overluminosity of the Variable Star RR Lyrae, and a Revised Distance to the LMC

Catelan, M.; Cortés, C.

doi:10.1086/587515

Cited by 70 publications

(93 citation statements)

References 37 publications

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“…This value is consistent with the value we get if we calculate M V from M bol using the bolometric correction of giant stars from Alonso et al (1999). To determine V HB we use the relation given in Catelan & Cortés (2008) which is calculated using theoretical models for RR Lyrae stars. Within its uncertainties, this relation is in excellent agreement with observations of the V HB of globular clusters (e.g., Rich et al 2005).…”

Section: Thesupporting

confidence: 82%

“…M V for these halo stars is calculated from M bol using the spectroscopically defined values for gravity and temperature and the bolometric correction of giant stars from Alonso et al (1999). Additionally their height above the horizontal branch can be approximated using their spectroscopic metallicity and the relation from Catelan & Cortés (2008). In Fig.…”

Section: Verifying the New Calibration At Low-metallicitymentioning

confidence: 99%

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The NIR Ca ii triplet at low metallicity

Starkenburg¹,

Hill

Tolstoy³

et al. 2010

A&A

228

432

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The NIR Ca ii triplet absorption lines have proven to be an important tool for quantitative spectroscopy of individual red giant branch stars in the Local Group, providing a better understanding of metallicities of stars in the Milky Way and dwarf galaxies and thereby an opportunity to constrain their chemical evolution processes. An interesting puzzle in this field is the significant lack of extremely metal-poor stars, below [Fe/H] = −3, found in classical dwarf galaxies around the Milky Way using this technique. The question arises whether these stars are really absent, or if the empirical Ca ii triplet method used to study these systems is biased in the lowmetallicity regime. Here we present results of synthetic spectral analysis of the Ca ii triplet, that is focused on a better understanding of spectroscopic measurements of low-metallicity giant stars. Our results start to deviate strongly from the widely-used and linear empirical calibrations at [Fe/H] < −2. We provide a new calibration for Ca ii triplet studies which is valid for −0.5 ≥ [Fe/H] ≥ −4. We subsequently apply this new calibration to current data sets and suggest that the classical dwarf galaxies are not so devoid of extremely low-metallicity stars as was previously thought.

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Section: Thesupporting

confidence: 82%

Section: Verifying the New Calibration At Low-metallicitymentioning

confidence: 99%

The NIR Ca ii triplet at low metallicity

Starkenburg¹,

Hill

Tolstoy³

et al. 2010

A&A

228

432

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show abstract

“…2, the mean absolute magnitude is M K = −0.57±0.12, and the LMC distance modulus is (m − M) 0 = 18.53 ± 0.13. This value, within the errors, agree very well with the LMC distance moduli of Sollima et al (2006b), (m − M) 0 = 18.54 ± 0.13; Sollima et al (2008), (m − M) 0 = 18.56 ± 0.13; Szewczyk et al (2008), (m − M) 0 = 18.58 ± 0.11; Clement et al (2008), (m − M) 0 = 18.49 ± 0.11; and Catelan & Cortés (2008), (m − M) 0 = 18.44 ± 0.11. Table 3 shows the dereddened distance moduli to the centers of our fields, where N is the number of RR Lyr stars used for the computation of the distance.…”

Section: Period-[fe/h] Relationssupporting

confidence: 76%

Properties of RR Lyrae stars in the inner regions of the Large Magellanic Cloud

Borissova¹,

Rejkuba²,

Minniti

et al. 2009

A&A

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Context. RR Lyrae variable stars are the primary Population II distance indicator. Likewise, the Large Magellanic Cloud (LMC) constitutes a key step in the extragalactic distance scale. Aims. By combining near-IR photometry and spectroscopically measured metallicities for a homogeneous sample of 50 RR Lyr stars in the LMC, we investigate the metallicity dependence of the period-luminosity relation in the near-infrared (IR), use the newly derived relations to re-derive the distance to the LMC, and compare the distance moduli obtained from RR Lyr and red clump stars. Methods. This paper presents new (single-epoch) J-band and (multi-epoch) K s -band photometry of RR Lyr stars in 7 different LMC fields, observed with the near-IR camera SOFI at ESO's New Technology Telescope. Additional K s -band data for another two LMC fields were taken with the ISPI infrared array at CTIO's Blanco 4m telescope. The near-IR photometry was cross-correlated with the MACHO and OGLE databases, resulting in a catalog of 62 RR Lyr stars with BVRI JK s photometry. A subsample of 50 stars also has spectroscopically measured metallicities. Results. In the deep JK color-magnitude diagrams of 7 fields, red giant branch, red clump and RR Lyr stars are detected. The majority of RR Lyr stars are located within the instability strip with near-IR colors between 0.14 ≤ (J − K s ) 0 < 0.32. The period-luminosity relation only has a very mild dependence on metallicity in the K band, consistent with no dependence: M Ks = 2.11(±0.17) log P + 0.05(±0.07) [Fe/H] − 1.05. In the J band the currently available data do not allow firm conclusions regarding the metallicity dependence of the period-luminosity relation. Conclusions. The distance modulus of the LMC, derived using our near-IR period-luminosity-metallicity relation for RR Lyr stars, is (m − M) 0 = 18.53 ± 0.13, in very good agreement with the distance modulus from the red clump stars, 18.46 ± 0.07. However, LMC modulus derived from the RR Lyrae stars depends on the parallax of the star RR Lyrae.

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“…The isochrones plotted in Fig. 2 show that giant stars of any metallicity or age above the HB (which will have 0 < M V < +1 typically Rich et al 2005;Catelan & Cortés 2008), and most of those below the HB, will not be found at bluer colors than V −I ∼ 0.85, corresponding to stars hotter than ∼5250 K (Ramírez & Meléndez 2005). In our following analysis, aiming at disentangling the populations of giant and dwarf stars which would be preselected photometrically, we therefore will not take temperatures >5250 K into account.…”

Section: The Lines and Their Sensitivitymentioning

confidence: 98%

Cleaning spectroscopic samples of stars in nearby dwarf galaxies

Battaglia

Starkenburg

2012

A&A

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Dwarf galaxies provide insight into the processes of star formation and chemical enrichment at the low end of the galaxy mass function, as well as into the clustering of dark matter on small scales. In studies of Local Group dwarf galaxies, spectroscopic samples of individual stars are used to derive the internal kinematics and abundance properties of these galaxies. It is therefore important to clean these samples from Milky Way stars, which are not related to the dwarf galaxy, since they can contaminate analysis of the properties of these objects. Here we introduce a new diagnostic for separating Milky Way contaminant stars, which mainly consist of dwarf stars, and red giant branch stars targeted in dwarf galaxies. As discriminator we use the trends in the equivalent width of the nIR Mg I line at 8806.8 Å as a function of the equivalent width of Ca II triplet lines. This method is particularly useful for works dealing with multi-object, intermediate-resolution spectroscopy focusing in the region of the nIR Ca II triplet. We use synthetic spectra to explore how the equivalent width of these lines changes for stars with different properties (gravity, effective temperature, metallicity) and find that a distinction among giants above the horizontal branch and dwarfs can be made with this method at [Fe/H] > −2 dex. For −2 ≤ [Fe/H] ≤ −1, this method is also valid for distinguishing dwarfs and giants down to approximately one magnitude below the horizontal branch. Using a foreground model we make predictions on the use of this new discrimination method for nearby dwarf spheroidal galaxies, including the ultra-faints. We subsequently use VLT/FLAMES data for the Sextans, Sculptor, and Fornax dwarf spheroidal galaxies to verify the predicted theoretical trends.

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Evidence for an Overluminosity of the Variable Star RR Lyrae, and a Revised Distance to the LMC

Cited by 70 publications

References 37 publications

The NIR Ca ii triplet at low metallicity

The NIR Ca ii triplet at low metallicity

Properties of RR Lyrae stars in the inner regions of the Large Magellanic Cloud

Cleaning spectroscopic samples of stars in nearby dwarf galaxies

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