Detailed chemical composition of classical Cepheids  in the LMC cluster NGC 1866 and in the field of the SMC

Lemasle, B.; Groenewegen, M. A. T.; Grebel, E. K.; Bono, G.; Fiorentino, G.; François, P.; Inno, L.; Kovtyukh, V. V.; Matsunaga, Noriyuki; Pedicelli, Stefania; Primas, F.; Pritchard, J. D.; Romaniello, M.; Silva, R. da

doi:10.1051/0004-6361/201731370

Cited by 33 publications

(28 citation statements)

References 131 publications

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“…These values are in good agreement with the values from Romaniello et al (2008) with a slight offset of +0.03 dex leading to mean abundances of the combined samples of −0.73 ± 0.02 and −0.33 ± 0.03 dex respectively. Molinaro et al (2012) also measured metallicities for three Cepheids in NGC1866 and found a mean value of −0.40 ± 0.04 in good agreement with the value of −0.36 ± 0.03 from Lemasle et al (2017). Lemasle et al (2013) has similarly determined abundances for Milky Way Cepheids and for 12 stars in common with our sample the average metallicity is −0.07 ± 0.04 dex.…”

Section: Metallicitiessupporting

confidence: 76%

The effect of metallicity on Cepheid period-luminosity relations from a Baade-Wesselink analysis of Cepheids in the Milky Way and Magellanic Clouds

Gieren

Storm

Konorski

et al. 2018

A&A

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Context. The extragalactic distance scale builds on the Cepheid period-luminosity (PL) relation. Decades of work have not yet convincingly established the sensitivity of the PL relation to metallicity. This currently prevents a determination of the Hubble constant accurate to 1% from the classical Cepheid-SN Ia method. Aims. In this paper, we want to carry out a strictly differential comparison of the absolute PL relations obeyed by classical Cepheids in the Milky Way (MW), LMC and SMC galaxies. Taking advantage of the substantial metallicity difference among the Cepheid populations in these three galaxies, we want to establish a possible systematic trend of the PL relation absolute zero point as a function of metallicity, and determine the size of such an effect in optical and near-infrared photometric bands. Methods. We are using the IRSB Baade-Wesselink type method as calibrated by Storm et al. to determine individual distances to the Cepheids in our samples in MW, LMC and SMC. For our analysis, we use a greatly enhanced sample of Cepheids in the SMC (31 stars) as compared to the small sample (5 stars) available in our previous work. We use the distances to determine absolute Cepheid PL relations in optical and near-infrared bands in each of the three galaxies. Results. Our distance analysis of 31 SMC Cepheids with periods from 4-69 days yields tight PL relations in all studied bands, with slopes consistent with the corresponding LMC and MW relations. Adopting the very accurately determined LMC slopes for the optical and near-infrared bands, we determine the zero point offsets between the corresponding absolute PL relations in the 3 galaxies. We find that in all bands the metal-poor SMC Cepheids are intrinsically fainter than their more metal-rich counterparts in the LMC and MW. In the K band the metallicity effect is −0.23 ± 0.06 mag/dex while in the V, (V − I) Wesenheit index it is slightly stronger, −0.34±0.06 mag/dex. We find some evidence that the PL relation zero point-metallicity relation might be nonlinear, becoming steeper for lower metallicities. Conclusions. Using sizeable Cepheid samples in the MW, LMC and SMC with very accurate photometric and radial velocity data we establish the metallicity sensitivity of the Cepheid PL relations in the optical and near-infrared regimes. We find a significant effect in all bands in the sense that the more metal-poor SMC Cepheids are intrinsically fainter than their LMC and Galactic counterparts. We find suggestive evidence that the metallicity sensitivity of the PL relation might be nonlinear, being small in the range between solar and LMC Cepheid metallicity, and becoming steeper towards the lower-metallicity regime.

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Section: Metallicitiessupporting

confidence: 76%

The effect of metallicity on Cepheid period-luminosity relations from a Baade-Wesselink analysis of Cepheids in the Milky Way and Magellanic Clouds

Gieren

Storm

Konorski

et al. 2018

A&A

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“…Grids have been calculated for a range of metallicities with that for an LMC metallicity being used here. As discussed by Dufton et al (2005), the atmospheric structure depends principally on the iron abundance with a value of 7.2 dex having been adopted for the LMC; this is consistent with estimates of the current iron abundance for this galaxy (see, for example, Carrera et al 2008;Palma et al 2015;Lemasle et al 2017). However we note that, although tests using the Galactic (7.5 dex) or SMC (6.9 dex) grids led to small changes in the atmospheric parameters (primarily to compensate for the different amounts of line blanketing), changes in element abundances estimates were typically less than 0.05 dex.…”

Section: Methodssupporting

confidence: 70%

The VLT-FLAMES Tarantula Survey

Dufton

Thompson

Crowther

et al. 2018

A&A

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Previous analyses of the spectra of OB-type stars in the Magellanic Clouds have identified targets with low projected rotational velocities and relatively high nitrogen abundances; the evolutionary status of these objects remains unclear. The VLT-FLAMES Tarantula Survey obtained spectroscopy for over 800 early-type stars in 30 Doradus of which 434 stars were classified as B-type. We have estimated atmospheric parameters and nitrogen abundances using TLUSTY model atmospheres for 54 B-type targets that appear to be single, have projected rotational velocities, ve sin i ≤ 80 km s−1 and were not classified as supergiants. In addition, nitrogen abundances for 34 similar stars observed in a previous FLAMES survey of the Large Magellanic Cloud have been re-evaluated. For both samples, approximately 75–80% of the targets have nitrogen enhancements of less than 0.3 dex, consistent with them having experienced only small amounts of mixing. However, stars with low projected rotational velocities, ve sini ≤ 40 km s−1 and significant nitrogen enrichments are found in both our samples and simulations imply that these cannot all be rapidly rotating objects observed near pole-on. For example, adopting an enhancement threshold of 0.6 dex, we observed five and four stars in our VFTS and previous FLAMES survey samples, yet stellar evolution models with rotation predict only 1.25 ± 1.11 and 0.26 ± 0.51 based on our sample sizes and random stellar viewing inclinations. The excess of such objects is estimated to be 20–30% of all stars with current rotational velocities of less than 40 km s−1. This would correspond to ~2–4% of the total non-supergiant single B-type sample. Given the relatively large nitrogen enhancement adopted, these estimates constitute lower limits for stars that appear inconsistent with current grids of stellar evolutionary models. Including targets with smaller nitrogen enhancements of greater than 0.2 dex implies larger percentages of targets that are inconsistent with current evolutionary models, viz. ~70% of the stars with rotational velocities less than 40 km s−1 and ~6–8% of the total single stellar population. We consider possible explanations of which the most promising would appear to be breaking due to magnetic fields or stellar mergers with subsequent magnetic braking.

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“…Different authors found slightly different values for the metal content in the cluster. Lemasle et al (2017) in their spectroscopic analysis of a sample of Cepheids in the cluster, found a very homogeneous chemical composition of [Fe/H] = −0.36 ± 0.03 dex, in agreement with previous measurement of the red giant branch stars by Mucciarelli et al (2011). The MS presents a third main feature: its extension as a broad strip towards redder colours and brighter magnitudes (the dark points in the inset of Fig.…”

Section: Ngc 1866 Photometrysupporting

confidence: 88%

“…The case of NGC 1866 has been studied recently by many authors (e.g. Milone et al 2017;Goudfrooij et al 2018), and the common findings are that both rotation and different ages are required to explain the double MS and the eMSTO at Lemasle et al (2017).…”

Section: Ngc 1866 Photometrymentioning

confidence: 99%

Multiple stellar populations in NGC 1866

Costa

Girardi

Bressan

et al. 2019

A&A

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We performed a comprehensive study of the stellar populations in the young Large Magellanic Cloud cluster NGC 1866, combining the analysis of its best-studied Cepheids with that of a very accurate colour–magnitude diagram (CMD) obtained from the most recent Hubble Space Telescope photometry. We used a Bayesian method based on new PARSEC stellar evolutionary tracks with overshooting and rotation to obtain ages and initial rotation velocities of five well-studied Cepheids of the cluster. We find that four of the five Cepheids belong to an initially slowly rotating young population (of 176 ± 5 Myr), while the fifth is significantly older, either 288 ± 20 Myr for models with high initial rotational velocity (ωi ∼ 0.9), or 202 ± 5 Myr for slowly rotating models. The complementary analysis of the CMD rules out the latter solution while strongly supporting the presence of two distinct populations of ∼176 Myr and ∼288 Myr, respectively. Moreover, the observed multiple main sequences and the turn-offs indicate that the younger population is mainly made of slowly rotating stars, as is the case of the four younger Cepheids, while the older population is made mainly of initially fast rotating stars, as is the case of the fifth Cepheid. Our study reinforces the notion that some young clusters like NGC 1866 harbour multiple populations. This work also hints that the first population, i.e. the older, may inherit the angular momentum from the parent cloud while stars of the second population, i.e. the younger, do not.

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Detailed chemical composition of classical Cepheids in the LMC cluster NGC 1866 and in the field of the SMC

Cited by 33 publications

References 131 publications

The effect of metallicity on Cepheid period-luminosity relations from a Baade-Wesselink analysis of Cepheids in the Milky Way and Magellanic Clouds

The effect of metallicity on Cepheid period-luminosity relations from a Baade-Wesselink analysis of Cepheids in the Milky Way and Magellanic Clouds

The VLT-FLAMES Tarantula Survey

Multiple stellar populations in NGC 1866

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