Light elements were produced in the first few minutes of the Universe through a sequence of nuclear reactions known as Big Bang nucleosynthesis (BBN)
. Among the light elements produced during BBN
, ...deuterium is an excellent indicator of cosmological parameters because its abundance is highly sensitive to the primordial baryon density and also depends on the number of neutrino species permeating the early Universe. Although astronomical observations of primordial deuterium abundance have reached percent accuracy
, theoretical predictions
based on BBN are hampered by large uncertainties on the cross-section of the deuterium burning D(p,γ)
He reaction. Here we show that our improved cross-sections of this reaction lead to BBN estimates of the baryon density at the 1.6 percent level, in excellent agreement with a recent analysis of the cosmic microwave background
. Improved cross-section data were obtained by exploiting the negligible cosmic-ray background deep underground at the Laboratory for Underground Nuclear Astrophysics (LUNA) of the Laboratori Nazionali del Gran Sasso (Italy)
. We bombarded a high-purity deuterium gas target
with an intense proton beam from the LUNA 400-kilovolt accelerator
and detected the γ-rays from the nuclear reaction under study with a high-purity germanium detector. Our experimental results settle the most uncertain nuclear physics input to BBN calculations and substantially improve the reliability of using primordial abundances to probe the physics of the early Universe.
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FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Abstract
We collected the largest spectroscopic catalog of RR Lyrae (RRLs) including ≈20,000 high-, medium-, and low-resolution spectra for ≈10,000 RRLs. We provide the analytical forms of radial ...velocity curve (RVC) templates. These were built using 36 RRLs (31 fundamental—split into three period bins—and five first-overtone pulsators) with well-sampled RVCs based on three groups of metallic lines (Fe, Mg, Na) and four Balmer lines (H
α
, H
β
, H
γ
, H
δ
). We tackled the long-standing problem of the reference epoch to anchor light-curve and RVC templates. For the
V
-band, we found that the residuals of the templates anchored to the phase of the mean magnitude along the rising branch are ∼35% to ∼45% smaller than those anchored to the phase of maximum light. For the RVC, we used two independent reference epochs for metallic and Balmer lines and we verified that the residuals of the RVC templates anchored to the phase of mean RV are from 30% (metallic lines) up to 45% (Balmer lines) smaller than those anchored to the phase of minimum RV. We validated our RVC templates by using both the single-point and the three phase point approaches. We found that barycentric velocities based on our RVC templates are two to three times more accurate than those available in the literature. We applied the current RVC templates to Balmer lines RVs of RRLs in the globular NGC 3201 collected with MUSE at VLT. We found the cluster barycentric RV of
V
γ
= 496.89 ± 8.37(error) ± 3.43 (standard deviation) km s
−1
, which agrees well with literature estimates.
Abstract
We discuss the largest and most homogeneous spectroscopic data set of field RR Lyrae variables (RRLs) available to date. We estimated abundances using both high-resolution and low-resolution ...(
Δ
S method) spectra for fundamental (RRab) and first overtone (RRc) RRLs. The iron abundances for 7941 RRLs were supplemented with similar estimates that are available in the literature, ending up with 9015 RRLs (6150 RRab, 2865 RRc). The metallicity distribution shows a mean value of 〈Fe/H〉 = −1.51 ± 0.01, and
σ
(standard deviation) = 0.41 dex with a long metal-poor tail approaching Fe/H ≃ − 3 and a sharp metal-rich tail approaching solar iron abundance. The RRab variables are more metal-rich (〈Fe/H〉
ab
= −1.48 ± 0.01,
σ
= 0.41 dex) than RRc variables (〈Fe/H〉
c
= −1.58 ± 0.01,
σ
= 0.40 dex). The relative fraction of RRab variables in the Bailey diagram (visual amplitude versus period) located along the short-period (more metal-rich) and the long-period (more metal-poor) sequences are 80% and 20%, while RRc variables display an opposite trend, namely 30% and 70%, respectively. We found that the pulsation period of both RRab and RRc variables steadily decreases when moving from the metal-poor to the metal-rich regime. The visual amplitude shows the same trend, but RRc amplitudes are almost two times more sensitive than RRab amplitudes to metallicity. We also investigated the dependence of the population ratio (N
c
/N
tot
) of field RRLs on the metallicity and we found that the distribution is more complex than in globular clusters. The population ratio steadily increases from ∼0.25 to ∼0.36 in the metal-poor regime, it decreases from ∼0.36 to ∼0.18 for −1.8 ≤ Fe/H ≤ −0.9 and it increases to a value of ∼0.3 approaching solar iron abundance.
Abstract
We collected a large data set of field RR Lyrae stars (RRLs) by using catalogs already available in the literature and
Gaia
DR2. We estimated the iron abundances for a subsample of 2382 ...fundamental RRLs (Δ
S
method: Ca
ii
K, H
β
, H
γ
, and H
δ
lines) for which there are publicly available medium-resolution SDSS-SEGUE spectra. We also included similar estimates available in the literature, ending up with the largest and most homogeneous spectroscopic data set ever collected for RRLs (2903). The metallicity scale was validated by using iron abundances based on high-resolution spectra for a fundamental field RRL (V Ind), for which we collected X-shooter spectra covering the entire pulsation cycle. The peak (Fe/H = −1.59 ± 0.01) and the standard deviation (
σ
= 0.43 dex) of the metallicity distribution agree quite well with similar estimates available in the literature. The current measurements disclose a well-defined metal-rich tail approaching solar iron abundance. The spectroscopic sample plotted in the Bailey diagram (period versus luminosity amplitude) shows a steady variation when moving from the metal-poor (Fe/H = −3.0/–2.5) to the metal-rich (Fe/H = −0.5/0.0) regime. The smooth transition in the peak of the period distribution as a function of the metallicity strongly indicates that the long-standing problem of the Oosterhoff dichotomy among Galactic globular clusters is the consequence of the lack of metal-intermediate clusters hosting RRLs. We also found that the luminosity amplitude, in contrast with period, does not show a solid correlation with metallicity. This suggests that period–amplitude–metallicity relations should be cautiously treated.
Abstract
We present a detailed spectroscopic analysis of RR Lyrae (RRL) variables in the globular cluster NGC 5139 (
ω
Cen). We collected optical (4580–5330 Å), high-resolution (
R
∼ 34,000), high ...signal-to-noise ratio (∼200) spectra for 113 RRLs with the multifiber spectrograph M2FS at the
Magellan
/Clay Telescope at Las Campanas Observatory. We also analyzed high-resolution (
R
∼ 26,000) spectra for 122 RRLs collected with FLAMES/GIRAFFE at the Very Large Telescope, available in the ESO archive. The current sample doubles the literature abundances of cluster and field RRLs in the Milky Way based on high-resolution spectra. Equivalent-width measurements were used to estimate atmospheric parameters, iron, and abundance ratios for
α
(Mg, Ca, Ti), iron peak (Sc, Cr, Ni, Zn), and s-process (Y) elements. We confirm that
ω
Cen is a complex cluster, characterized by a large spread in the iron content: −2.58 ≤ Fe/H ≤ −0.85. We estimated the average cluster abundance as
, with
σ
= 0.33 dex. Our findings also suggest that two different RRL populations coexist in the cluster. The former is more metal-poor (Fe/H ≲ − 1.5), with almost solar abundance of Y. The latter is less numerous, more metal-rich, and yttrium enhanced (Y/Fe ≳ 0.4). This peculiar bimodal enrichment only shows up in the s-process element, and it is not observed among lighter elements, whose X/Fe ratios are typical for Galactic globular clusters.
Abstract
We provide the largest and most homogeneous sample of
α
-element (Mg, Ca, Ti) and iron abundances for field RR Lyrae (RRLs; 162 variables) by using high-resolution spectra. The current ...measurements were complemented with similar abundances available in the literature for 46 field RRLs brought to our metallicity scale. We ended up with a sample of old (
t
≥ 10 Gyr), low-mass stellar tracers (208 RRLs: 169 fundamental, 38 first overtone, and 1 mixed mode) covering 3 dex in iron abundance (−3.00 ≤ Fe/H ≤ 0.24). We found that field RRLs are ∼0.3 dex more
α
poor than typical halo tracers in the metal-rich regime (Fe/H ≥ −1.2), while in the metal-poor regime (Fe/H ≤ −2.2) they seem to be on average ∼0.1 dex more
α
enhanced. This is the first time that the depletion in
α
elements for solar iron abundances is detected on the basis of a large, homogeneous, and coeval sample of old stellar tracers. Interestingly, we also detected a close similarity in the
α
/Fe trend between
α
-poor, metal-rich RRLs and red giants (RGs) in the Sagittarius dwarf galaxy as well as between
α
-enhanced, metal-poor RRLs and RGs in ultrafaint dwarf galaxies. These results are supported by similar elemental abundances for 46 field horizontal branch stars. These stars share with RRLs the same evolutionary phase and the same progenitors. This evidence further supports the key role that old stellar tracers play in constraining the early chemical enrichment of the halo and, in particular, in investigating the impact that dwarf galaxies have had in the mass assembly of the Galaxy.
Abstract
We developed a new approach to provide accurate estimates of the metal content, reddening, and true distance modulus of RR Lyrae stars (RRLs). The method is based on homogeneous optical (
...BVI
) and near-infrared (
JHK
) mean magnitudes and on predicted period–luminosity–metallicity relations (
IJHK
) and absolute mean magnitude–metallicity relations (
BV
). We obtained solutions for three different RRL samples in
ω
Cen: first overtone (RRc, 90), fundamental (RRab, 80), and global (RRc+RRab) in which the period of first overtones were fundamentalized. The metallicity distribution shows a well defined peak at Fe/H∼−1.98 and a standard deviation of
σ
= 0.54 dex. The spread is, as expected, metal-poor (Fe/H ≤ −2.3) objects. The current metallicity distribution is ∼0.3 dex more metal-poor than similar estimates for RRLs available in the literature. The difference vanishes if the true distance modulus we estimated is offset by −0.06/−0.07 mag in true distance modulus. We also found a cluster true distance modulus of
μ
= 13.720 ± 0.002 ± 0.030 mag, where the former error is the error on the mean and the latter is the standard deviation. Moreover, we found a cluster reddening of
E
(
B
−
V
) = 0.132 ± 0.002 ± 0.028 mag and spatial variations of the order of a few arcmin across the body of the cluster. Both the true distance modulus and the reddening are slightly larger than similar estimates available in the literature, but the difference is within 1
σ
. The metallicity dependence of distance diagnostics agrees with theory and observations, but firm constraints require accurate and homogeneous spectroscopic measurements.
Abstract
We performed the largest and most homogeneous spectroscopic survey of field RR Lyraes (RRLs). We secured ≈6300 high-resolution (HR,
R
∼ 35,000) spectra for 143 RRLs (111 fundamental, RRab; ...32 first-overtone, RRc). The atmospheric parameters were estimated by using the traditional approach and the iron abundances were measured by using an LTE line analysis. The resulting iron distribution shows a well-defined metal-rich tail approaching solar iron abundance. This suggests that field RRLs experienced a complex chemical enrichment in the early halo formation. We used these data to develop a new calibration of the Δ
S
method. This diagnostic, based on the equivalent widths of Ca
ii
K and three Balmer (H
δ
,
γ
,
β
) lines, traces the metallicity of RRLs. For the first time, the new empirical calibration: (i) includes spectra collected over the entire pulsation cycle; (ii) includes RRc variables; (iii) relies on spectroscopic calibrators covering more than three dex in iron abundance; and (iv) provides independent calibrations based on one/two/three Balmer lines. The new calibrations were applied to a data set of both SEGUE-SDSS and degraded HR spectra totalling 6451 low-resolution (
R
∼ 2000) spectra for 5001 RRLs (3439 RRab, 1562 RRc). This resulted in an iron distribution with a median
η
= −1.55 ± 0.01 and
σ
= 0.51 dex, in good agreement with literature values. We also found that RRc are 0.10 dex more metal-poor than RRab variables, and have a distribution with a smoother metal-poor tail. This finding supports theoretical prescriptions suggesting a steady decrease in the RRc number when moving from metal-poor to metal-rich stellar environments.
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