Context.
Classical Cepheids (CCs) are solid distance indicators and tracers of young stellar populations. Dating back to the beginning of the 20th century, they have been safely adopted to trace the ...rotation, kinematics, and chemical enrichment history of the Galactic thin disk.
Aims.
The main aim of this investigation is to provide iron, oxygen, and sulfur abundances for the largest and most homogeneous sample of Galactic CCs analyzed so far (1118 spectra of 356 objects). The current sample, containing 70 CCs for which spectroscopic metal abundances are provided for the first time, covers a wide range in galactocentric distances, pulsation modes, and pulsation periods.
Methods.
Optical high-resolution spectra with a high signal-to-noise ratio that were collected with different spectrographs were adopted to provide homogeneous estimates of the atmospheric parameters (effective temperature, surface gravity, and microturbulent velocity) that are required to determine the abundance. Individual distances were based either on trigonometric parallaxes by the
Gaia
Data Release 3 (
Gaia
DR3) or on distances based on near-infrared period-luminosity relations.
Results.
We found that iron and
α
-element radial gradients based on CCs display a well-defined change in the slope for galactocentric distances larger than ~12 kpc. We also found that logarithmic regressions account for the variation in X/H abundances from the inner to the outer disk. Radial gradients for the same elements, but based on open clusters covering a wide range in cluster ages, display similar trends. This means that the flattening in the outer disk is an intrinsic feature of the radial gradients because it is independent of age. Empirical evidence indicates that the S radial gradient is steeper than the Fe radial gradient. The difference in the slope is a factor of two in the linear fit (−0.081 vs. −0.041 dex kpc
−1
) and changes from −1.62 to −0.91 in the logarithmic distance. Moreover, we found that S (explosive nucleosynthesis) is underabundant on average when compared with O (hydrostatic nucleosynthesis). The difference becomes clearer in the metal-poor regime and for the O/Fe and S/Fe abundance ratios. We performed a detailed comparison with Galactic chemical evolution models and found that a constant star formation efficiency for galactocentric distances larger than 12 kpc accounts for the flattening observed in both iron and
α
-elements. To further constrain the impact of the predicted S yields for massive stars on radial gradients, we adopted a toy model and found that the flattening in the outermost regions requires a decrease of a factor of four in the current S predictions.
Conclusions.
CCs are solid beacons for tracing the recent chemical enrichment of young stellar populations. Sulfur photospheric abundances, when compared with other α-elements, have the key advantage of being a volatile element. Therefore, stellar S abundances can be directly compared with nebular sulfur abundances in external galaxies.
Context. Galactic abundance gradients set strong constraints to chemo-dynamical evolutionary models of the Milky Way. Given the period-luminosity relations that provide accurate distances and the ...large number of spectral lines, Cepheids are excellent tracers of the present-day abundance gradients. Aims. We want to measure the Galactic abundance gradient of several chemical elements. While the slope of the Cepheid iron gradient did not vary much from the very first studies, the gradients of the other elements are not that well constrained. In this paper we focus on the inner and outer regions of the Galactic thin disk. Methods. We use high-resolution spectra (FEROS, ESPADONS, NARVAL) to measure the abundances of several light (Na, Al), α (Mg, Si, S, Ca), and heavy elements (Y, Zr, La, Ce, Nd, Eu) in a sample of 65 Milky Way Cepheids. Combining these results with accurate distances from period-Wesenheit relations in the near-infrared enables us to determine the abundance gradients in the Milky Way. Results. Our results are in good agreement with previous studies on either Cepheids or other tracers. In particular, we confirm an upward shift of ≈0.2 dex for the Mg abundances, as has recently been reported. We also confirm the existence of a gradient for all the heavy elements studied in the context of a local thermodynamic equilibrium analysis. However, for Y, Nd, and especially La, we find lower abundances for Cepheids in the outer disk than reported in previous studies, leading to steeper gradients. This effect can be explained by the differences in the line lists used by different groups. Conclusions. Our data do not support a flattening of the gradients in the outer disk, in agreement with recent Cepheid studies and chemo-dynamical simulations. This is in contrast to the open cluster observations but remains compatible with a picture where the transition zone between the inner disk and the outer disk would move outward with time.
Classical Cepheids, what else? Bono, G.; Inno, L.; Matsunaga, N. ...
Proceedings of the International Astronomical Union,
08/2012, Letnik:
8, Številka:
S289
Journal Article
Recenzirano
Odprti dostop
We present new and independent estimates of the distances to the Magellanic Clouds (MCs) using near-infrared (NIR) and optical–NIR period–Wesenheit (PW) relations. The slopes of the PW relations are, ...within the dispersion, linear over the entire period range and independent of metal content. The absolute zero points were fixed using Galactic Cepheids with distances based on the infrared surface-brightness method. The true distance modulus we found for the Large Magellanic Cloud—(m − M)0 = 18.48 ± 0.01 ± 0.10 mag—and the Small Magellanic Cloud—(m − M)0 = 18.94 ± 0.01 ± 0.10 mag—agree quite well with similar distance determinations based on robust distance indicators. We also briefly discuss the evolutionary and pulsation properties of MC Cepheids.
We provide homogeneous optical (
U
B
V
R
I
) and near-infrared (NIR,
J
H
K
) time series photometry for 254 cluster (
ω
Cen, M 4) and field RR Lyrae (RRL) variables. We ended up with more than 551 ...000 measurements, of which only 9% are literature data. For 94 fundamental (RRab) and 51 first overtones (RRc) we provide a complete optical/NIR characterization (mean magnitudes, luminosity amplitudes, epoch of the anchor point). The NIR light curves of these variables were adopted to provide new light-curve templates for both RRc and RRab variables. The templates for the
J
and the
H
bands are newly introduced, together with the use of the pulsation period to discriminate among the different RRab templates. To overcome subtle uncertainties in the fit of secondary features of the light curves we provide two independent sets of analytical functions (Fourier and periodic Gaussian series). The new templates were validated by using 26
ω
Cen and Bulge RRLs. We find that the difference between the measured mean magnitude along the light curve and the mean magnitude estimated by using the template on a single randomly extracted phase point is better than 0.01 mag (
σ
= 0.04 mag). We also validated the template on variables for which at least three phase points were available, but without information on the phase of the anchor point. We find that the accuracy of the mean magnitudes is also ∼0.01 mag (
σ
= 0.04 mag). The new templates were applied to the Large Magellanic Cloud (LMC) globular cluster Reticulum and by using literature data and predicted PLZ relations we find true distance moduli
μ
= 18.47 ± 0.10 (rand.) ± 0.03 (syst.) mag (
J
) and 18.49 ± 0.09 ± 0.05 mag (
K
). We also used literature optical and mid-infrared data and we found a mean
μ
of 18.47 ± 0.02 ± 0.06 mag, suggesting that Reticulum is ∼1 kpc closer than the LMC.
We present new accurate abundances for five neutron-capture elements (Y, La, Ce, Nd, Eu) in 73 classical Cepheids located across the Galactic thin disk. Individual abundances are based on high ...spectral resolution (R ~ 38 000) and high signal-to-noise ratio (S/N ~ 50−300) spectra collected with UVES at ESO VLT for the DIONYSOS project. Taking into account similar Cepheid abundances provided by our group (111 stars) and available in the literature, we end up with a sample of 435 Cepheids covering a broad range in iron abundances (−1.6 < Fe/H < 0.6). We found, via homogeneous individual distances and abundance scales, well-defined gradients for the above elements. However, the slope of the light s-process element (Y) is at least a factor of two steeper than the slopes of heavy s- (La, Ce, Nd) and r- (Eu) process elements. The s-to-r abundance ratio (La/Eu) of Cepheids shows a well-defined anticorrelation with both Eu and Fe. On the other hand, Galactic field stars attain an almost constant value and display a mild enhancement in La only when they approach solar iron abundance. The Y/Eu ratio shows slight evidence of a correlation with Eu and, in particular, with iron abundance for field Galactic stars. We also investigated the s-process index (hs/ls) and we found a well-defined anticorrelation, as expected, between La/Y and iron abundance. Moreover, we found a strong correlation between La/Y and La/Fe and, in particular, a clear separation between Galactic and Sagittarius red giants. Finally, the comparison between predictions for low-mass asymptotic giant branch stars and the observedLa/Y ratio indicate a very good agreement over the entire metallicity range covered by Cepheids. However, the observed spread at fixed iron content is larger than predicted by current models.
We gathered more than 1130 high-resolution optical spectra for more than 250 Galactic classical Cepheids. The spectra were collected with the optical spectrographs UVES at VLT, HARPS at 3.6 m, FEROS ...at 2.2 m MPG/ESO, and STELLA. To improve the effective temperature estimates, we present more than 150 new line depth ratio (LDR) calibrations that together with similar calibrations already available in the literature allowed us to cover a broad range in wavelength (5348 ≤
λ
≤ 8427 Å) and in effective temperature (3500 ≤
T
eff
≤ 7700 K). This gives us the unique opportunity to cover both the hottest and coolest phases along the Cepheid pulsation cycle and to limit the intrinsic error on individual measurements at the level of ~100 K. As a consequence of the high signal-to-noise ratio of individual spectra, we identified and measured hundreds of neutral and ionized lines of heavy elements, and in turn, have the opportunity to trace the variation of both surface gravity and microturbulent velocity along the pulsation cycle. The accuracy of the physical parameters and the number of Fe
I
(more than one hundred) and Fe
II
(more than ten) lines measured allowed us to estimate mean iron abundances with a precision better than 0.1 dex. We focus on 14 calibrating Cepheids for which the current spectra cover either the entire or a significant portion of the pulsation cycle. The current estimates of the variation of the physical parameters along the pulsation cycle and of the iron abundances agree very well with similar estimates available in the literature. Independent homogeneous estimates of both physical parameters and metal abundances based on different approaches that can constrain possible systematics are highly encouraged.
The Comet Interceptor space mission, selected by ESA in June 2019 as the first F-Class mission, will study a dynamically new comet or an interstellar object by a unique multi-point ’snapshot’ ...measurement. The mission design will allow to complement previous single spacecraft’s fly-by cometary observations. The Dust Impact Sensor and Counter (DISC), devoted to the dust coma characterization, is part of the payload selected for Comet Interceptor. It will be mounted on-board two of the three spacecraft, as part of the Dust-Fields-Plasma (DFP) suite, dedicated to understand further: 1) dust in the coma; 2) magnetic field; 3) plasma and energetic neutral atoms. DISC architecture originates from the Impact Sensor subsystems, part of the Grain Impact Analyzer and Dust Accumulator (GIADA) that successfully flew on-board the ESA/Rosetta spacecraft. DISC main scientific objectives are: 1) to define the dust mass distribution for particles in the mass range 10−15 − 10−8 kg ejected from the cometary nucleus; 2) to count dust particles with mass > 10−15 kg; 3) to constrain dust particle density/structure.
In this paper, we describe DISC design, aims, methods, feasibility and performances evaluations, carried out by real and simulated dust impacts and by retrieving the number of particles, and their corresponding momentum, using the Comet Interceptor’s Engineering Dust Coma Model.
V350 Sgr is a classical Cepheid suitable for mass determination. It has a hot companion which is prominent in the ultraviolet (UV) and which is not itself a binary. We have obtained two ...high-resolution echelle spectra of the companion at orbital velocity maximum and minimum with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope in the 1320 to 1510 region. By cross-correlating these spectra we obtained the orbital velocity amplitude of the companion with an uncertainty in the companion amplitude of 1.9 km s−1. This provides a mass ratio of the Cepheid to the companion of 2.1. The UV energy distribution of the companion provides the mass of the companion, yielding a Cepheid mass of 5.2 0.3 M . This mass requires some combination of moderate main sequence core convective overshoot and rotation to match evolutionary tracks.
The Mass of the Cepheid V350 Sgr Remage Evans, Nancy; Proffitt, Charles; Carpenter, Kenneth G. ...
The Astronomical journal,
10/2018, Letnik:
866, Številka:
1
Journal Article
Recenzirano
V350 Sgr is a classical Cepheid suitable for mass determination. It has a hot companion which is prominent in the ultraviolet (UV) and which is not itself a binary. We have obtained two ...high-resolution echelle spectra of the companion at orbital velocity maximum and minimum with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope in the 1320 to 1510 Å region. By cross-correlating these spectra we obtained the orbital velocity amplitude of the companion with an uncertainty in the companion amplitude of 1.9 km s(exp −1). This provides a mass ratio of the Cepheid to the companion of 2.1. The UV energy distribution of the companion provides the mass of the companion, yielding a Cepheid mass of 5.2 ± 0.3 solar mass. This mass requires some combination of moderate main sequence core convective overshoot and rotation to match evolutionary tracks.
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