ABSTRACT We present new nonlinear, time-dependent convective hydrodynamical models of RR Lyrae stars computed assuming a constant helium-to-metal enrichment ratio and a broad range in metal ...abundances (Z = 0.0001-0.02). The stellar masses and luminosities adopted to construct the pulsation models were fixed according to detailed central He-burning horizontal-branch evolutionary models. The pulsation models cover a broad range in stellar luminosity and effective temperatures and the modal stability is investigated for both fundamental (FU) and first overtone polsators (FOs). We predict the topology of the instability strip (IS) as a function of the metal content and new analytical relations for the edges of the IS in the observational plane. Moreover, a new analytical relation to constrain the pulsation mass of double pulsators as a function of the period ratio and the metal content is provided. We derive new Period-Radius-Metallicity relations for FU and FO pulsators. They agree quite well with similar empirical and theoretical relations in the literature. From the predicted bolometric light curves, transformed into optical (UBVRI) and near-infrared (NIR; JHK) bands, we compute the intensity-averaged mean magnitudes along the entire pulsation cycle and in turn new and homogenous metal-dependent (RIJHK) Period-Luminosity relations. Moreover, we compute new dual and triple-band optical, optical-NIR, and NIR Period-Wesenheit-Metallicity relations. Interestingly, we find that the optical Period-W(V, B-V) is independent of the metal content and that the accuracy of individual distances is a balance between the adopted diagnostics and the precision of photometric and spectroscopic data sets.
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.
ABSTRACT We present new multiband (UBVI) time-series data of helium burning variables in the Carina dwarf spheroidal galaxy. The current sample includes 92 RR Lyrae-six of them are new ...identifications-and 20 Anomalous Cepheids, one of which is new identification. The analysis of the Bailey diagram shows that the luminosity amplitude of the first overtone component in double-mode variables is located along the long-period tail of regular first overtone variables, while the fundamental component is located along the short-period tail of regular fundamental variables. This evidence further supports the transitional nature of these objects. Moreover, the distribution of Carina double-mode variables in the Petersen diagram (P1/P0 versus P0) is similar to metal-poor globulars (M15, M68), to the dwarf spheroidal Draco, and to the Galactic Halo. This suggests that the Carina old stellar population is metal-poor and affected by a small spread in metallicity. We use trigonometric parallaxes for five field RR Lyrae stars to provide an independent estimate of the Carina distance using the observed reddening free Period-Wesenheit PW, (BV) relation. Theory and observations indicate that this diagnostic is independent of metallicity. We found a true distance modulus of = 20.01 0.02 (standard error of the mean) 0.05 (standard deviation) mag. We also provided independent estimates of the Carina true distance modulus using four predicted PW relations (BV, BI, VI, BVI) and we found: = (20.08 0.007 0.07) mag, = (20.06 0.006 0.06) mag, = (20.07 0.008 0.08) mag, and = (20.06 0.006 0.06) mag. Finally, we identified more than 100 new SX Phoenicis stars that together with those already known in the literature (340) make Carina a fundamental laboratory for constraining the evolutionary and pulsation properties of these transitional variables.
Context.
Globular clusters (GCs) are recognised as important tools for understanding the formation and evolution of the Milky Way (MW) because they are the oldest objects in our Galaxy. ...Unfortunately, the known sample in our MW is still incomplete, especially towards the innermost regions, because of the high differential reddening, extinction, and stellar crowding. Therefore, the discovery of new GC candidates and the confirmation of their true nature are crucial for the census of the MW GC system.
Aims.
Our main goal is to confirm the physical nature of two GC candidates: Patchick 99 and TBJ 3. Both are located towards the Galactic bulge. We use public data in the near-infrared(IR) passband from the VISTA Variables in the Via Láctea Survey (VVV), the VVV eXtended Survey, and the Two Micron All Sky Survey along with deep optical data from the
Gaia
Mission DR 2 in order to estimate their main astrophysical parameters, such as reddening and extinction, distance, total luminosity, mean cluster proper motions, size, metallicity, and age.
Methods.
We investigated both candidates at different wavelengths, allowing us to discard TBJ3 as a possible GC. We use near-IR (
K
s
vs. (
J
−
K
s
)) and optical (
G
vs. (
B
P
−
R
P
)) colour–magnitude diagrams (CMDs) in order to analyse Patchick 99. First, we decontaminated CMDs, following a statistical procedure, as well as selecting only stars which have similar proper motions (PMs) and are situated within 3′ of the centre. Mean PMs were measured from
Gaia
DR 2 data. Reddening and extinction were derived by adopting optical and near-IR reddening maps, and were used to estimate the distance modulus and the heliocentric distance. Metallicity and age were evaluated by fitting theoretical stellar isochrones.
Results.
Reddening and extinction values for Patchick 99 are
E
(
J
−
K
s
) = (0.12 ± 0.02) mag and
A
K
s
= (0.09 ± 0.01) mag from the VVV data, whereas we calculate
E
(
B
P
−
R
P
) = (0.21 ± 0.03) mag and
A
G
= (0.68 ± 0.08) mag from
Gaia
DR 2 data. We use those values and the magnitude of the RC to estimate the distance, finding good agreement between the near-IR and optical measurements. In fact, we obtain (
m
−
M
)
0
= (14.02 ± 0.01) mag, equivalent to a distance
D
= (6.4 ± 0.2) kpc in near-IR and (
m
−
M
)
0
= (14.23 ± 0.1) mag and so
D
= (7.0 ± 0.2) kpc in optical. In addition, we derive the metallicity and age for Patchick 99 using our distance and extinction values and fitting PARSEC isochrones. We find Fe/H=(−0.2 ± 0.2) dex and
t
= (10 ± 2) Gyr. The mean PMs for Patchick 99 are μ
α
= ( − 2.98 ± 1.74) mas yr
−1
and μ
δ
= ( − 5.49 ± 2.02) mas yr
−1
using the
Gaia
DR 2 data. These are consistent with the bulge kinematics. We also calculate the total luminosity of our cluster and confirm that it is a low-luminosity GC, with
M
K
s
= ( − 7.0 ± 0.6) mag. The radius estimation is performed building the radial density profile and we find its angular radius
r
P
99
∼ 10′. We also recognise seven RR Lyrae star members within 8.2 arcmin from the Patchick 99 centre, but only three of them have PMs matching the mean GC PM, confirming the distance found by other methods.
Conclusions.
We find that TBJ 3 shows mid-IR emissions that are not present in GCs. We therefore discard TBJ 3 as a GC candidate and focus our work on Patchick 99. We conclude that Patchick 99 is an old metal-rich GC situated in the Galactic bulge. TBJ 3 is a background galaxy.
ABSTRACT
We present new luminosity–metallicity (LZ; $M_{V}\!-\!\rm Fe/H$ and $M_{G}\!-\!\rm Fe/H$) relations and, for the first time, empirical, Gaia three-band (G, GBP, GRP) ...period-Wesenheit-metallicity (PWZ) relations of RR Lyrae stars (RRLs) derived using a hierarchical Bayesian approach and new accurate parallaxes published for these variables in the Gaia Early Data Release 3 (EDR3). In a previous study, we obtained Bayesian hierarchically derived LZ relations from a sample of about four hundred Milky Way field RRLs with G-band light curves and trigonometric parallaxes published in the Gaia Data Release 2 (DR2), using V mean magnitudes, metallicities, absorptions, and pulsation periods available in the literature. We now extend that study in two directions. First, we update our previous results using trigonometric parallaxes from Gaia EDR3 and incorporate the Bayesian analysis of a first empirical PWZ relation derived using those field RRLs with G, GBP and GRP time-series photometry available in Gaia DR2. Secondly, we use Bayesian inference to derive LZ relations and empirical PW Gaia three-band relations from 385 RRLs belonging to 15 Milky Way globular clusters (GC) with literature-compiled spectroscopic metallicities ranging from −0.36 to −2.39 dex and prior distances extending from 2.2 to 41.2 kpc. From the samples of RRLs analysed in this paper we infer a mean Gaia EDR3 zero-point offset of −0.028 mas with median values ranging from −0.033 (LZ and PWZ models for field stars) to −0.024 mas (LZ model in the V band for GC RRLs).
Abstract
We present the results of the χ2 minimization model fitting technique applied to optical and near-infrared photometric and radial velocity data for a sample of nine fundamental and three ...first overtone classical Cepheids in the Small Magellanic Cloud (SMC). The near-infrared photometry (JK filters) was obtained by the European Southern Observatory (ESO) public survey ‘VISTA near-infrared Y, J, K
s survey of the Magellanic Clouds system’ (VMC). For each pulsator, isoperiodic model sequences have been computed by adopting a non-linear convective hydrodynamical code in order to reproduce the multifilter light and (when available) radial velocity curve amplitudes and morphological details. The inferred individual distances provide an intrinsic mean value for the SMC distance modulus of 19.01 mag and a standard deviation of 0.08 mag, in agreement with the literature. Moreover, the intrinsic masses and luminosities of the best-fitting model show that all these pulsators are brighter than the canonical evolutionary mass–luminosity relation (MLR), suggesting a significant efficiency of core overshooting and/or mass-loss. Assuming that the inferred deviation from the canonical MLR is only due to mass-loss, we derive the expected distribution of percentage mass-loss as a function of both the pulsation period and the canonical stellar mass. Finally, a good agreement is found between the predicted mean radii and current period–radius (PR) relations in the SMC available in the literature. The results of this investigation support the predictive capabilities of the adopted theoretical scenario and pave the way for the application to other extensive data bases at various chemical compositions, including the VMC Large Magellanic Cloud pulsators and Galactic Cepheids with Gaia parallaxes.
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.
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.
ABSTRACT The "VISTA near-infrared YJKs survey of the Magellanic Clouds System" (VMC) is collecting deep Ks-band time-series photometry of pulsating variable stars hosted by the two Magellanic Clouds ...and their connecting Bridge. In this paper, we present Y, J, Ks light curves for a sample of 4172 Small Magellanic Cloud (SMC) Classical Cepheids (CCs). These data, complemented with literature V values, allowed us to construct a variety of period-luminosity (PL), period-luminosity-color (PLC), and period-Wesenheit (PW) relationships, which are valid for Fundamental (F), First Overtone (FO), and Second Overtone (SO) pulsators. The relations involving the V, J, Ks bands are in agreement with their counterparts in the literature. As for the Y band, to our knowledge, we present the first CC PL, PW, and PLC relations ever derived using this filter. We also present the first near-infrared PL, PW, and PLC relations for SO pulsators to date. We used PW(V, Ks) to estimate the relative SMC-LMC distance and, in turn, the absolute distance to the SMC. For the former quantity, we find a value of Δμ = 0.55 ± 0.04 mag, which is in rather good agreement with other evaluations based on CCs, but significantly larger than the results obtained from older population II distance indicators. This discrepancy might be due to the different geometric distributions of young and old tracers in both Clouds. As for the absolute distance to the SMC, our best estimates are μSMC = 19.01 ± 0.05 mag and μSMC = 19.04 ± 0.06 mag, based on two distance measurements to the LMC which rely on accurate CC and eclipsing Cepheid binary data, respectively.
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