ABSTRACT
Classical Cepheids (DCEPs) are the most important primary indicators of the extragalactic distance scale. Establishing the dependence on metallicity of their period–luminosity and ...period–Wesenheit (PLZ/PWZ) relations has deep consequences on the calibration of secondary distance indicators that lead to the final estimate of the Hubble constant (H0). We collected high-resolution spectroscopy for 47 DCEPs plus 1 BL Her variables with HARPS-N@TNG and derived accurate atmospheric parameters, radial velocities, and metal abundances. We measured spectral lines for 29 species and characterized their chemical abundances, finding very good agreement with previous results. We re-determined the ephemerides for the program stars and measured their intensity-averaged magnitudes in the V, I, J, H, Ks bands. We complemented our sample with literature data and used the Gaia Early Data Release 3 (EDR3) to investigate the PLZ/PWZ relations for Galactic DCEPs in a variety of filter combinations. We find that the solution without any metallicity term is ruled out at more than the 5σ level. Our best estimate for the metallicity dependence of the intercept of the PLKs, PWJKs, PWVKs, and PWHVI relations with three parameters is −0.456 ± 0.099, −0.465 ± 0.071, −0.459 ± 0.107, and −0.366 ± 0.089 mag dex−1, respectively. These values are significantly larger than the recent literature. The present data are still inconclusive to establish whether or not also the slope of the relevant relationships depends on metallicity. Applying a correction to the standard zero-point offset of the Gaia parallaxes has the same effect of reducing by ∼22 per cent the size of the metallicity dependence on the intercept of the PLZ/PWZ relations.
ABSTRACT
Classical Cepheids (DCEPs) are the first fundamental step in the calibration of the cosmological distance ladder. Furthermore, they represent powerful tracers in the context of Galactic ...studies. We have collected high-resolution spectroscopy with UVES@VLT for a sample of 65 DCEPs. The majority of them are the faintest DCEPs ever observed in the Milky Way. For each target, we derived accurate atmospheric parameters, radial velocities, and abundances for 24 different species. The resulting iron abundances range between +0.3 and −1.1 dex with the bulk of stars at Fe/H ∼ −0.5 dex. Our sample includes the most metal-poor DCEPs observed so far with high-resolution spectroscopy. We complement our sample with literature data obtaining a complete sample of 637 DCEPs and use Gaia Early Data Release 3 (EDR3) photometry to determine the distance of the DCEPs from the period–Wesenheit–Metallicity relation. Our more external data trace the Outer arm at Galactocentric radius (RGC) ∼ 16–18 kpc which appears significantly warped. We investigate the metallicity gradient of the Galactic disc using this large sample, finding a slope of −0.060 ± 0.002 dex kpc−1, in very good agreement with previous results based both on DCEPs and open clusters. We also report a possible break in the gradient at RGC = 9.25 kpc with slopes of −0.063 ± 0.007 and −0.079 ± 0.003 dex kpc−1 for the inner and outer sample, respectively. The two slopes differ by more than 1σ. A more homogeneous and extended DCEPs sample is needed to further test the plausibility of such a break.
Objective:Night-shift work is associated with ischaemic cardiovascular disorders. It is not currently known whether it may be causally linked to metabolic syndrome (MS), a risk condition for ...ischaemic cardiovascular disorders. The syndrome presents with visceral obesity associated with mild alterations in glucidic and lipidic homeostasis, and in blood pressure. The aim of this study was to assess whether a causal relationship exists between night-shift work and the development of MS.Methods:Male and female nurses performing night shifts, free from any component of MS at baseline, were evaluated annually for the development of the disorder during a 4-year follow-up. Male and female nurses performing daytime work only, visited during the same time period, represented the control group.Results:The cumulative incidence of MS was 9.0% (36/402) among night-shift workers, and 1.8% (6/336) among daytime workers (relative risk (RR) 5.0, 95% CI − 2.1 to 14.6). The annual rate of incidence of MS was 2.9% in night-shift workers and 0.5% in daytime workers. Kaplan–Meier survival curves of the two groups were significantly different (log-rank test; p<0.001). Multiple Cox regression analysis (forward selection method based on likelihood ratio) showed that among selected variables (age, gender, smoking, alcohol intake, familiar history, physical activity, and work schedule) the only predictors of occurrence of MS were sedentariness (hazard ratio (HR) 2.92; 95% CI 1.64 to 5.18; p = 0.017), and night-shift work (HR 5.10; 95% CI 2.15 to 12.11; p<0.001).Conclusions:The risk of developing MS is strongly associated with night-shift work in nurses. Medical counselling should be promptly instituted in night-shift workers with the syndrome, and in case of persistence or progression, a change in work schedule should be considered.
Context.
Classical Cepheids (DCEPs) represent a fundamental tool to calibrate the extragalactic distance scale. However, they are also powerful stellar population tracers in the context of Galactic ...studies. The forthcoming Data Release 3 of the
Gaia
mission will allow us to study, with unprecedented detail, the structure, the dynamics, and the chemical properties of the Galactic disc, and in particular of the spiral arms, where most Galactic DCEPs reside.
Aims.
In this paper we aim to quantify the metallicity dependence of the Galactic DCEPs’ period-Wesenheit (PWZ) relation in the
Gaia
bands.
Methods.
We adopted a sample of 499 DCEPs with metal abundances from high-resolution spectroscopy, in conjunction with
Gaia
Early Data Release 3 parallaxes and photometry to calibrate a PWZ relation in the
Gaia
bands.
Results.
We find a significant metallicity term, of the order of −0.5 mag dex
−1
, which is larger than the values measured in the near-infrared (NIR) bands by different authors. Our best PWZ relation is
W
= ( − 5.988 ± 0.018)−(3.176 ± 0.044)(log
P
− 1.0)−(0.520 ± 0.090)Fe/H. We validated our PWZ relations by using the distance to the Large Magellanic Cloud as a benchmark, finding very good agreement with the geometric distance provided by eclipsing binaries. As an additional test, we evaluated the metallicity gradient of the young Galactic disc, finding −0.0527 ± 0.0022 dex kpc
−1
, which is in very good agreement with previous results.
Context.
Classical Cepheids (DCEPs) are the most important primary indicators for the extragalactic distance scale. Establishing the dependence on metallicity of their period–luminosity and ...period–Wesenheit (PL and PW) relations has deep consequences for the estimate of the Hubble constant (
H
0
).
Aims.
We investigate the dependence on metal abundance (Fe/H) of the PL and PW relations for Galactic DCEPs.
Methods.
We combined proprietary and literature photometric and spectroscopic data, gathering a total sample of 413 Galactic DCEPs (372 fundamental mode, DCEP_F, and 41 first-overtone, DCEP_1O) and constructed new metallicity-dependent PL and PW relations in the near-infrared adopting the astrometry-based luminosity.
Results.
We find indications that the slopes of the PL(
K
S
) and PW(
J
,
K
S
) relations for Galactic DCEPs might depend on metallicity on the basis of the comparison with the Large Magellanic Cloud relationships. Therefore we used a generalized form of the PL and PW relations to simultaneously take the metallicity dependence of the slope and intercept of these relations into account.
Conclusions.
We calculated PL and PW relations that for the first time explicitly include a metallicity dependence of the slope and intercept terms. The quality of the available data is insufficient, however, and we cannot yet present conclusive results, but they are relevant from a methodological point of view. The new relations are linked to the geometric measurement of the distance to the Large Magellanic Cloud and allowed us to estimate a
Gaia
DR2 parallax zero-point offset Δ
ϖ
= 0.0615 ± 0.004 mas from the dataset of DCEPs used in this work.
ABSTRACT
On the basis of an extended set of non-linear convective RR Lyrae pulsation models we derive the first theoretical light curves in the Gaia bands G, GBP, and GRP and the corresponding ...intensity-weighted mean magnitudes and pulsation amplitudes. The effects of chemical composition on the derived Bailey diagrams in the Gaia filters are discussed for both Fundamental and first overtone mode pulsators. The inferred mean magnitudes and colours are used to derive the first theoretical Period–Wesenheit relations for RR Lyrae in the Gaia filters. The application of the theoretical Period–Wesenheit relations for both the Fundamental and first overtone mode to Galactic RR Lyrae in the Gaia Data Release 2 data base and complementary information on individual metal abundances allows us to derive theoretical estimates of their individual parallaxes. These results are compared with the astrometric solutions to conclude that a very small offset, consistent with zero, is required in order to reconcile the predicted distances with Gaia results.
ABSTRACT
Classical Cepheids (DCEPs) are the most important standard candles in the extra-galactic distance scale thanks to the period–luminosity ($\rm PL$), period–luminosity–colour ($\rm PLC$), and ...period–Wesenheit ($\rm PW$) relations that hold for these objects. The advent of the Gaia mission, and in particular the Early Data Release 3 (EDR3), provided accurate parallaxes to calibrate these relations. In order to fully exploit Gaia measurements, the zero point (ZP) of Gaia parallaxes should be determined with an accuracy of a few $\rm \mu as$. The individual ZP corrections provided by the Gaia team depend on the magnitude and the position on the sky of the target. In this paper, we use an implicit method that relies on the Cepheid $\rm PL$ and $\rm PW$ relations to evaluate the ensemble Gaia parallax zero point. The best inferred estimation of the offset value needed to additionally correct (after the Gaia team correction) the Gaia parallaxes of the present DCEP sample amounts to $\rm -22\pm 4\, \mu as$. This value is in agreement with the most recent literature values and confirms that the correction proposed by the Gaia team overcorrected the parallaxes. As a further application of our results, we derive an estimate of the Large Magellanic Cloud distance ($\rm \mu _0=18.49\pm 0.06\, mag$) in very good agreement with the currently accepted value obtained through geometric methods.
Context.
Anomalous Cepheids (ACEPs) are intermediate-mass metal-poor pulsators that are mostly discovered in dwarf galaxies of the Local Group. However, recent Galactic surveys, including the
Gaia
...Data Release 3, found a few hundred ACEPs in the Milky Way. Their origin is only poorly understood.
Aims.
We aim to investigate the origin and evolution of Galactic ACEPs by studying the chemical composition of their atmospheres for the first time.
Methods.
We used UVES at the Very Large Telescope to obtain high-resolution spectra for a sample of nine ACEPs belonging to the Galactic halo. We derived the abundances of 12 elements, C, Na, Mg, Si, Ca, Sc, Ti, Cr, Fe, Ni, Y, and Ba. We complemented these data with literature abundances from high-resolution spectroscopy for an additional three ACEPs that were previously incorrectly classified as type II Cepheids. This increased the sample to a total of 12 stars.
Results.
All the investigated ACEPs have an iron abundance Fe/H < −1.5 dex, as expected from theoretical predictions for these pulsators. The abundance ratios of the different elements to iron show that the chemical composition of ACEPs is generally consistent with that of the Galactic halo field stars, with the exception of sodium, which is found to be overabundant in 9 out of the 11 ACEPs where it was measured. This is very similar to the situation for second-generation stars in Galactic globular clusters. The same comparison with dwarf and ultra-faint satellites of the Milky Way reveals more differences than similarities. It is therefore unlikely that the bulk of Galactic ACEPs originated in a galaxy like this that subsequently dissolved into the Galactic halo. The principal finding of this work is the unexpected overabundance of sodium in ACEPs. We explored several hypotheses to explain this feature, finding that the most promising scenario is the evolution of low-mass stars in a binary system with either mass transfer or merging. Detailed modelling is needed to confirm this hypothesis.
HD 344787: a true Polaris analogue? Ripepi, V.; Catanzaro, G.; Molnár, L. ...
Astronomy & astrophysics,
03/2021, Letnik:
647
Journal Article
Recenzirano
Odprti dostop
Context.
Classical Cepheids (DCEPs) are the most important primary indicators for the extragalactic distance scale, but they are also important objects in their own right, allowing us to place ...constraints on the physics of intermediate-mass stars and the pulsation theories.
Aims.
We have investigated the peculiar DCEP HD 344787, which is known to exhibit the fastest positive period change of DCEPs, along with a quenching amplitude of the light variation.
Methods.
We used high-resolution spectra obtained with HARPS-N at the TNG for HD 344787 and the more famous Polaris DCEP to infer their detailed chemical abundances. Results from the analysis of new time-series photometry of HD 344787 obtained by the TESS satellite are also reported.
Results.
The double-mode nature of the HD344787 pulsation is confirmed by an analysis of the TESS light curve, although with rather tiny amplitudes of a few dozen millimag. This is indication that HD344787 is on the verge of quenching the pulsation. Analysis of the spectra collected with HARPS-N at the TNG reveals an almost solar abundance and no depletion of carbon and oxygen. This means that the star appears to have not gone through first dredge-up. Similar results are obtained for Polaris.
Conclusions.
Polaris and HD344787 are both confirmed to be most likely at their first crossing of the instability strip. The two stars are likely at the opposite borders of the instability strip for first-overtone DCEPs with metal abundance
Z
= 0.008. A comparison with other DCEPs that are also thought to be at their first crossing allows us to speculate that the differences we see in the Hertzsprung-Russell diagram might be due to differences in the properties of the DCEP progenitors during the main-sequence phase.
The VMC survey Sicignano, T; Ripepi, V; Marconi, M ...
Astronomy and astrophysics (Berlin),
05/2024, Letnik:
685
Journal Article
Recenzirano
Context. Type II Cepheids (T2Cs) are the less frequently used counterparts of classical or type I Cepheids (CCs) which provide the primary calibration of the distance ladder for measuring the Hubble ...constant in the local Universe. In the era of the “Hubble tension”, T2C variables together with the RR Lyrae stars and the tip of the red giant branch (TRGB) can potentially provide non-CC-dependent calibration of the cosmic distance ladder. Aims. Our goal is to provide an absolute calibration of the period–luminosity, period–luminosity–colour, and period–Wesenheit relations (PL, PLC, and PW, respectively) of T2Cs in the Large Magellanic Cloud (LMC), which traditionally serves as a crucial first anchor of the extragalactic distance ladder. Methods. We exploited time-series photometry in the near-infrared (NIR) Y, J, and Ks bands for a sample of approximately 320 T2Cs in the Magellanic Clouds (MCs). These observations were acquired during 2009–2018 in the context of the VISTA survey of the Magellanic Clouds system (VMC), an ESO public survey. We supplemented the NIR photometry from the VMC survey with well-sampled optical light curves and accurate pulsation periods from the Optical Gravitational Lensing Experiment (OGLE) IV survey and the Gaia mission. We used the best-quality NIR light curves to generate custom templates for modelling sparsely sampled light curves in YJKs bands. Results. The best-fitting YJKs template light curves were used to derive accurate and precise intensity-averaged mean magnitudes and pulsation amplitudes of 277 and 62 T2Cs in the LMC and SMC, respectively. We used optical and NIR mean magnitudes for different T2C subclasses (BLHer, WVir, and RVTau) to derive PL/PLC/PW relations in multiple bands, which were calibrated with the geometric distance to the LMC as derived from eclipsing binaries and with the Gaia parallaxes. We used our new empirical calibrations of PL and PW relations to obtain distances to 22 T2C-host Galactic globular clusters, which were found to be systematically smaller by ∼0.1 mag and 0.03−0.06 mag than in the literature when the zero points are calibrated with the distance of the LMC or Gaia parallaxes, respectively. Better agreement is found between our distances and those based on RR Lyrae stars in globular clusters, providing strong support for using these population II stars together with the TRGB for future distance scale studies.
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