The separation between RR Lyrae (RRLs) and type II Cepheid (T2Cs) variables based on their period is debated. Both types of variable stars are distance indicators, and we aim to promote the use of ...T2Cs as distance indicators in synergy with RRLs. We adopted new and existing optical and near-infrared (NIR) photometry of
ω
Cen to investigate several diagnostics (color-magnitude diagram, Bailey diagram, Fourier decomposition of the light curve, and amplitude ratios) for their empirical separation. We found that the classical period threshold at one day is not universal and does not dictate the evolutionary stage: V92 has a period of 1.3 days but is likely to be still in its core helium-burning phase, which is typical of RRLs. We also derived NIR period-luminosity relations and found a distance modulus of 13.65 ± 0.07 (err.) ± 0.01 (
σ
) mag, in agreement with the recent literature. We also found that RRLs and T2Cs obey the same period-luminosity relations in the NIR. This equivalence provides the opportunity of adopting RRLs+T2Cs as an alternative to classical Cepheids to calibrate the extragalactic distance scale.
We present new distance determinations to the nearby globular M4 (NGC 6121) based on accurate optical and near-infrared (NIR) mean magnitudes for fundamental (FU) and first overtone (FO) RR Lyrae ...variables (RRLs), and new empirical optical and NIR period-luminosity (PL) and period-Wesenheit (PW) relations. We have found that optical-NIR and NIR PL and PW relations are affected by smaller standard deviations than optical relations. The difference is the consequence of a steady decrease in the intrinsic spread of cluster RRL apparent magnitudes at fixed period as longer wavelengths are considered. The weighted mean visual apparent magnitude of 44 cluster RRLs is =13.329 ± 0.001 (standard error of the mean) ±0.177 (weighted standard deviation) mag. Distances were estimated using RR Lyr itself to fix the zero-point of the empirical PL and PW relations. Using the entire sample (FU+FO) we found weighted mean true distance moduli of 11.35 ± 0.03 ± 0.05 mag and 11.32 ± 0.02 ± 0.07 mag. Distances were also evaluated using predicted metallicity dependent PLZ and PWZ relations. We found weighted mean true distance moduli of 11.283 ± 0.010 ± 0.018 mag (NIR PLZ) and 11.272 ± 0.005 ± 0.019 mag (optical-NIR and NIR PWZ). The above weighted mean true distance moduli agree within 1σ. The same result is found from distances based on PWZ relations in which the color index is independent of the adopted magnitude (11.272 ± 0.004 ± 0.013 mag). These distances agree quite well with the geometric distance provided by Kaluzny et al. based on three eclipsing binaries. The available evidence indicates that this approach can provide distances to globulars hosting RRLs with a precision better than 2%-3%.
ABSTRACT
The technique of line depth ratios (LDRs) is one of the methods to determine the effective temperature of a star. They are crucial in the spectroscopic studies of variable stars like ...Cepheids since no simultaneous photometry is usually available. A good number of LDR-temperature relations are already available in the optical domain; here we want to expand the number of relations available in the near-infrared (NIR) in order to fully exploit the capabilities of current and upcoming NIR spectrographs. We used 115 simultaneous spectroscopic observations in the optical and the NIR for six Cepheids and optical LDRs to find new pairs of lines sensitive to temperature and to calibrate LDR-temperature relations in the NIR spectral range. We have derived 87 temperature calibrations valid in the 4800–6500 K range of temperatures. The typical uncertainty for a given relation is 60–70 K, and combining many of them provides a final precision within 30–50 K. We found a discrepancy between temperatures derived from optical or NIR LDR for pulsations phases close to ϕ ≈0.0 and we discuss the possible causes for these differences. LDRs in the NIR will allow us to spectroscopically investigate highly reddened Cepheids in the Galactic centre or in the far side of the disc.
Context. The environmental conditions for asympotic giant branch (AGB) stars to reach the carbon-rich (C-rich) phase are important to understand the evolutionary process of AGB stars. The difference ...between the spatial distributions of C-rich and oxygen-rich (O-rich) AGB stars is essential for the study of the Galactic structure and the chemical evolution of the interstellar medium. Aims. We quantitatively investigate the spatial distributions of C-rich and O-rich AGB stars in our Galaxy. We discuss the difference between them and its origin. Methods. We classify a large number of AGB stars newly detected by the AKARI mid-infrared all-sky survey. In the color–color diagrams, we define their occupation zones based on the locations of known objects. We then obtain the spatial distributions of C-rich and O-rich AGB stars, assuming that they have the same luminosity for a given mass-loss rate. Results. We find that O-rich AGB stars are concentrated toward the Galactic center and that the density decreases with Galactocentric distance, whereas C-rich AGB stars show a relatively uniform distribution within about 8 kpc of Sun. Conclusions. Our result confirms the trends reported in previous studies and extends them to a Galactic scale. We discuss the relations between our result, the Galactic metallicity gradient, and the chemical evolution of the ISM in our Galaxy.
We present homogeneous and accurate iron abundances for almost four dozen (47) of Galactic Cepheids using high-spectral resolution (R ~ 40 000) high signal-to-noise ratio (S/N ≥ 100) optical spectra ...collected with UVES at VLT. A significant fraction of the sample (32) is located in the inner disk (RG ≤ 6.9 kpc) and for half of them we provide new iron abundances. Current findings indicate a steady increase in iron abundance when approaching the innermost regions of the thin disk. The metallicity is super-solar and ranges from 0.2 dex for RG ~ 6.5 kpc to 0.4 dex for RG ~ 5.5 kpc. Moreover, we do not find evidence of correlation between iron abundance and distance from the Galactic plane. We collected similar data available in the literature and ended up with a sample of 420 Cepheids. Current data suggest that the mean metallicity and the metallicity dispersion in the four quadrants of the Galactic disk attain similar values. The first-second quadrants show a more extended metal-poor tail, while the third-fourth quadrants show a more extended metal-rich tail, but the bulk of the sample is at solar iron abundance. Finally, we found a significant difference between the iron abundance of Cepheids located close to the edge of the inner disk (Fe/H ~ 0.4) and young stars located either along the Galactic bar or in the nuclear bulge (Fe/H ~ 0). Thus suggesting that the above regions have had different chemical enrichment histories. The same outcome applies to the metallicity gradient of the Galactic bulge, since mounting empirical evidence indicates that the mean metallicity increases when moving from the outer to the inner bulge regions.
Biogenic volatile organic compounds emitted from plants are important constituents of atmospheric chemistry and play a major role in the resistance of plants against various environmental stresses. ...However, little is known about how abiotic and biotic environments on a geographic scale relate to diversifications of the emission. Here, we present variations of terpenes stored in and emitted from leaves of a single species in a common garden, using genetically differentiated local populations of Japanese cedar, the most dominant and widely distributed tree species in Japan. Furthermore, we determined the composition of fungal communities in 50 locations, based on the presence or absence of 158 fungal species inhabiting the cedar. The results showed that terpenoids, especially those that are emitted, were highly diversified and geographically structured among the 12 populations. The total amount of stored terpenes was negatively affected by warm and less-snow climates. On the other hand, variations in some emitted terpenoid species among the populations were correlated to antagonistic fungal species inhabiting the Japanese cedar. We propose that the diversification of composition and amount of stored and emitted terpenoids in the tree species is not only structured by climate, but also antagonistic fungal communities through biological interactions.
Abstract
We present the results from our time-series imaging data taken with the 1.3 m Devasthal fast optical telescope and 0.81 m Tenagara telescope in
V
,
R
c
, and
I
c
bands covering an area of ...∼18.′4 × 18.′4 toward the star-forming region Sh 2–190. This photometric data helped us to explore the nature of the variability of pre-main-sequence (PMS) stars. We have identified 85 PMS variables, i.e., 37 Class
ii
and 48 Class
iii
sources. Forty-five of the PMS variables show periodicity in their light curves. We show that the stars with thicker disks and envelopes rotate slower and exhibit larger photometric variations compared to their diskless counterparts. This result suggests that rotation of the PMS stars is regulated by the presence of circumstellar disks. We also found that the periods of the stars show a decreasing trend with increasing mass in the range of ∼0.5–2.5
M
⊙
. Our result indicates that most of the variability in Class
ii
sources is ascribed to the presence of a thick disk, while the presence of cool spots on the stellar surface causes the brightness variation in Class
iii
sources. X-ray activities in the PMS stars were found to be at the saturation level reported for the main-sequence stars. The younger counterparts of the PMS variables show less X-ray activity, hinting at a less significant role of a stellar disk in X-ray generation.
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.
PDF
