Line-depth Ratios Research Articles

Characteristics of thalweg profile and cross-sectional geometry along alluvial river bends

ABSTRACT River bends have always drawn attention for their complicated hydraulic, geometric and migration nature. Laboratory as well as field experiments have been carried out to study the geometric behaviour of channel bends. This study aims to analyse the nature of the thalweg profile, longitudinal and transverse slope and distribution of depth in the cross-sectional geometry of both single and consecutive double bends of the channel. In the single bend, the thalweg approaches to the outer bank and becomes closest after the apex of the bend whereas in the successive bends of a double bend, the thalweg is closest before the apex of the bend. These results indicate that the thalweg of a bend depends on the previous consecutive bend. The longitudinal slopes vary periodically along the river bend creating the deepest pool before the apex of the bend. The centre line transverse slope varies periodically; however, the outer transverse slope with respect to the thalweg is maximum where the thalweg is closest to the outer bank. The thalweg and outer quarter line to centre line depth ratio is higher before the apex and reduces after the apex of the bend. The inner quarter line to centre line depth ratio varies periodically with a relatively smaller amplitude.

Astrophysical calibration of the oscillator strengths of YJ-band absorption lines in classical Cepheids

ABSTRACT Newly-developed spectrographs with increased resolving powers, particularly those covering the near-IR range, allow the characterization of more and more absorption lines in stellar spectra. This includes the identification and confirmation of absorption lines and the calibration of oscillator strengths. In this study, we provide empirical values of ${{\rm log} gf}$ based on the abundances of classical Cepheids obtained with optical spectra to establish the consistency between optical and infrared abundance results. Using time series spectra of classical Cepheids obtained with WINERED spectrograph (0.97–1.35 $\mu$m, R$\sim$ 28000), we demonstrate that we can determine the stellar parameters of the observed Cepheids, including effective temperature (${T_\mathrm{eff}}$), surface gravity (${{\rm log} g}$), microturbulence ($\xi$), and metallicity (${\rm {[{\mathrm{ M}}/\mathrm{ H}]}}$). With the newly calibrated relations of line-depth ratios, we can achieve accuracy and precision comparable to optical studies, with uncertainties of $\sim$90 K and 0.108 dex for ${T_\mathrm{eff}}$, and ${{\rm log} g}$, respectively. Finally, we created a new atlas of absorption lines, featuring precise abundance measurements of various elements found in the atmosphere of Cepheids, including neutron-capture elements whose ${{\rm log} gf}$ values have been astrophysically calibrated.

Effective temperatures of classical Cepheids from line-depth ratios in the H-band

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.

Effective Temperature Estimations from Line Depth Ratios in the H- and K-band Spectra of IGRINS

Determining accurate effective temperatures of stars buried in the dust-obscured Galactic regions is extremely difficult from photometry. Fortunately, high-resolution infrared spectroscopy is a powerful tool for determining the temperatures of stars with no dependence on interstellar extinction. It has long been known that the depth ratios of temperature-sensitive and relatively insensitive spectral lines are excellent temperature indices. In this work, we provide the first extensive line depth ratio (LDR) method application in the infrared region that encompasses both the H and K bands (1.48 μm − 2.48 μm). We applied the LDR method to high-resolution (R ≃ 45,000) H- and K-band spectra of 110 stars obtained with the Immersion Grating Infrared Spectrograph. Our sample contained stars with 3200 < T eff (K) < 5500, 0.20 ≤ log g < 4.6, and −1.5 < [M/H] < 0.5. The application of this method in the K band yielded 21 new LDR–T eff relations. We also report five new LDR–T eff relations found in the H-band region, augmenting the relations already published by other groups. The temperatures found from our calibrations provide reliable temperatures within ∼70 K accuracy compared to spectral T eff values from the literature.

High-resolution near-infrared spectroscopy of globular cluster and field stars toward the Galactic bulge

Globular clusters (GCs) play an important role in the formation and evolution of the Milky Way. New candidates are continuously found, particularly in the high-extinction low-latitude regions of the bulge, although their existence and properties have yet to be verified. In order to investigate the new GC candidates, we performed high-resolution near-infrared spectroscopy of stars toward the Galactic bulge using the Immersion Grating Infrared Spectrometer (IGRINS) instrument at the Gemini-South telescope. We selected 15 and 10 target stars near Camargo 1103 and Camargo 1106, respectively, which have recently been reported as metal-poor GC candidates in the bulge. In contrast to the classical approaches used in optical spectroscopy, we determined stellar parameters from a combination of line-depth ratios and the equivalent width of a CO line. The stellar parameters of the stars follow the common trends of nearby APOGEE sample stars in a similar magnitude range. We also determined the abundances of Fe, Na, Mg, Al, Si, S, K, Ca, Ti, Cr, Ni, and Ce through spectrum synthesis. There is no clear evidence of a grouping in radial velocity – metallicity space that would indicate the characterization of either object as metal-poor GCs. This result emphasizes the necessity of follow-up spectroscopy for new GC candidates toward the bulge, although we cannot completely rule out a low probability that we only observed nonmember stars. We also note discrepancies between the abundances of Al, Ca, and Ti when derived from the H- versus the K-band spectra. Although the cause of this discrepancy is not clear, the effects of atmosphere parameters or nonlocal thermodynamic equilibrium are discussed. Our approach and results demonstrate that IGRINS spectroscopy is a useful tool for studying the chemical properties of stars toward the Galactic bulge with a statistical uncertainty in [Fe/H] of ∼0.03 dex, while the systematic error through uncertainties of atmospheric parameter determination, at ∼0.14 dex, is slightly larger than in measurements from optical spectroscopy.

Chemical properties of the central part of the Galactic nuclear stellar disc. Abundances in four classical Cepheids revisited

ABSTRACT This paper is a revised abundance analysis of four yellow supergiant stars Cepheids which are located in the Galactic nucleus. The results are based on the spectra secured with the help of Subaru telescope, which are of the better quality comparing to previously analysed spectra taken with the Infrared Telescope Facility. A significantly improved method of the effective temperature determination of program stars, which is based on the calibrating relations between the temperature and line depth ratios, was applied. The present results confirmed our previous finding about the solar metallicity level at the Galaxy centre. It is very likely that the four stars of our program were born from an interstellar medium having homogeneous chemical properties, since all the stars are located close to each other, have close pulsation periods, and hence the age. However, one of the stars has a somewhat increased abundance of all studied elements compared to the abundance in the other three stars. A possible reason of this fact is discussed.

Erratum: Effective temperatures of red supergiants estimated from line-depth ratios of iron lines in the YJ bands, 0.97–1.32 μm

Erratum: Effective temperatures of red supergiants estimated from line-depth ratios of iron lines in the <i>YJ</i> bands, 0.97–1.32 μm

From Atmospheric Evolution to the Search of Species of Astrobiological Interest in the Solar System—Case Studies Using the Planetary Spectrum Generator

The study of minor chemical species in terrestrial planets’ atmospheres can teach us about the chemistry, dynamics and evolution of the atmospheres through time. Phosphine or methane on terrestrial planets are potential biosignatures, such that their detection may signify the presence of life on a planet. Therefore, the search for these species in the solar system is an important step for the subsequent application of the same techniques to exoplanetary atmospheres. To study atmospheric depletion and the evolution of water abundance in the atmospheres of terrestrial planets, the estimation of the D/H ratio and its spatial and temporal variability is used. We used the Planetary Spectrum Generator (PSG), a radiative transfer suite, with the goal of simulating spectra from observations of Venus, Mars and Jupiter, searching for minor chemical species. The present study contributes to highlight that the PSG is an efficient tool for studying minor chemical species and compounds of astrobiological interest in planetary atmospheres, allowing to perform the detection and retrieval of the relevant molecular species. Regarding detection, it is effective in disentangling different molecular opacities affecting observations. In order to contribute to the scientific community that is focused on the study of minor chemical species in the solar system’s atmospheres, using this tool, in this work, we present the results from an analysis of observations of Venus, Mars and Jupiter, by comparison of observations with simulations in the infrared (IR). The first step was to clearly identify the position of molecular features using our model simulations, since the molecular absorption/emission features of different molecules tend to overlap. For this step, we used the method of the variation of abundances. The second step was to determine the molecular abundances and compare them with values from the literature using the retrieval method and the line depth ratio method. For Venus, our study of SO2-related observations by the Texas Echelon Cross Echelle Spectrograph (TEXES) at 7.4 μm enabled the identification of absorption lines due to sulphur dioxide and carbon dioxide as well as constrain the abundance of SO2 at the cloud top. Phosphine was not detected in the comparison between the simulation and TEXES IR observations around 10.5 μm. For Mars, both a positive and a non-detection of methane were studied using PSG simulations. The related spectra observations in the IR, at approximately 3.3 μm, correspond, respectively, to the Mars Express (MEx) and ExoMars space probes. Moreover, an estimate of the deuterium-to-hydrogen ratio (D/H ratio) was obtained by comparing the simulations with observations by the Echelon Cross Echelle Spectrograph (EXES) onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) at approximately 7.19–7.23 μm. For Jupiter, the detection of ammonia, phosphine, deuterated methane and methane was studied, by comparing the simulations with IR observations by the Infrared Space Observatory (ISO) at approximately 7–12 μm. Moreover, the retrieval of the profiles of ammonia and phosphine was performed.

Line-depth ratios as indicators of effective temperature and surface gravity

ABSTRACTThe analysis of stellar spectra depends on the effective temperature (Teff) and the surface gravity (log g). However, the estimation of log g with high accuracy is challenging. A classical approach is to search for log g that satisfies the ionization balance, i.e. the abundances from neutral and ionized metallic lines being in agreement. We propose a method of using empirical relations between Teff, log g, and line-depth ratios, for which we meticulously select pairs of Fe i and Fe ii lines and pairs of Ca i and Ca ii lines. Based on YJ-band (0.97–1.32 $\mu$m) high-resolution spectra of 42 FGK stars (dwarfs to supergiants), we selected 5 Fe i–Fe ii and 4 Ca i–Ca ii line pairs together with 13 Fe i–Fe i pairs (for estimating Teff), and derived the empirical relations. Using such relations does not require complex numerical models and tools for estimating chemical abundances. The relations we present allow one to derive Teff and log g with a precision of around 50 K and 0.2 dex, respectively, but the achievable accuracy depends on the accuracy of the calibrators’ stellar parameters. It is essential to revise the calibration by observing stars with accurate stellar parameters available, e.g. stars with asteroseismic log g and stars analysed with complete stellar models taking into account the effects of non-local thermodynamic equilibrium and convection. In addition, the calibrators we used have a limited metallicity range, −0.2 &amp;lt; [Fe/H] &amp;lt; +0.2 dex, and our relations need to be tested and re-calibrated based on a calibrating data set for a wider range of metallicities.

Projected Rotational Velocities and Fundamental Properties of Low-mass Pre-main-sequence Stars in the Taurus–Auriga Star-forming Region

Abstract The projected stellar rotational velocity ( ) is critical for our understanding of processes related to the evolution of angular momentum in pre-main-sequence stars. We present measurements of high-resolution infrared and optical spectroscopy for 70 pre-main-sequence stars in the Taurus–Auriga star-forming region, in addition to effective temperatures measured from line-depth ratios, as well as stellar rotation periods determined from optical photometry. From the literature, we identified the stars in our sample that show evidence of residing in circumstellar disks or multiple systems. The comparison of infrared measurements calculated using two techniques shows a residual scatter of ∼1.8 km s−1, defining a typical error floor for the of pre-main-sequence stars from infrared spectra. A comparison of the distributions of stars with and without companions shows that binaries/multiples typically have a higher measured , which may be caused by contamination by companion lines, shorter disk lifetimes in binary systems, or tidal interactions in hierarchical triples. A comparison of optical and infrared values shows no significant difference regardless of whether the star has a disk or not, indicating that CO contamination from the disk does not impact measurements above the typical ∼1.8 km s−1 error floor of our measurements. Finally, we observe a lack of a correlation between the , presence of a disk, and H-R diagram position, which indicates a complex interplay between stellar rotation and evolution of pre-main-sequence stars.

A photospheric and chromospheric activity analysis of the quiescent retrograde-planet host ν Octantis A

ABSTRACT The single-lined spectroscopic binary ν Octantis provided evidence of the first conjectured circumstellar planet demanding an orbit retrograde to the stellar orbits. The planet-like behaviour is now based on 1437 radial velocities (RVs) acquired from 2001 to 2013. ν Oct’s semimajor axis is only 2.6 au with the candidate planet orbiting $\nu ~{\rm Oct\, A}$ about mid-way between. These details seriously challenge our understanding of planet formation and our decisive modelling of orbit reconfiguration and stability scenarios. However, all non-planetary explanations are also inconsistent with numerous qualitative and quantitative tests including previous spectroscopic studies of bisectors and line-depth ratios, photometry from Hipparcos and the more recent space missions TESS and Gaia (whose increased parallax classifies $\nu ~{\rm Oct\, A}$ closer still to a subgiant, ∼K1 IV). We conducted the first large survey of $\nu ~{\rm Oct\, A}$’s chromosphere: 198 $\rm Ca\,{\small II}$ H-line and 1160 $\rm {H}\, \alpha$ indices using spectra from a previous RV campaign (2009–2013). We also acquired 135 spectra (2018–2020) primarily used for additional line-depth ratios, which are extremely sensitive to the photosphere’s temperature. We found no significant RV-correlated variability. Our line-depth ratios indicate temperature variations of only ±4 K, as achieved previously. Our atypical $\rm Ca\,{\small II}$ analysis models the indices in terms of S/N and includes covariance significantly in their errors. The $\rm {H}\, \alpha$ indices have a quasi-periodic variability that we demonstrate is due to telluric lines. Our new evidence provides further multiple arguments realistically only in favour of the planet.

The effect of surface gravity on line-depth ratios in the wavelength range 0.97–1.32 µm

ABSTRACT A line-depth ratio (LDR) of two spectral lines with different excitation potentials is expected to be correlated with the effective temperature (Teff). It is possible to determine Teff of a star with a precision of tens of Kelvin if dozens or hundreds of tight LDR–Teff relations can be used. Most of the previous studies on the LDR method were limited to optical wavelengths, but Taniguchi and collaborators reported 81 LDR relations in the YJ band, 0.97–1.32 µm, in 2018. However, with their sample of only 10 giants, it was impossible to account for the effects of surface gravity and metallicity on the LDRs well. Here, we investigate the gravity effect based on YJ-band spectra of 63 stars including dwarfs, giants, and supergiants observed with the WINERED spectrograph. We found that some LDR–Teff relations show clear offsets between the sequence of dwarfs and those of giants/supergiants. The difference between the ionization potentials of the elements considered in each line pair and the corresponding difference in the depths can, at least partly, explain the dependency of the LDR on the surface gravity. In order to expand the stellar parameter ranges that the LDR method can cover with high precision, we obtained new sets of LDR–Teff relations for solar-metal G0–K4 dwarfs and F7–K5 supergiants, respectively. The typical precision that can be achieved with our relations is 10–30 K for both dwarfs and supergiants.

Effective temperatures of red supergiants estimated from line-depth ratios of iron lines in the YJ bands, 0.97-1.32μm

ABSTRACT Determining the effective temperatures (Teff) of red supergiants (RSGs) observationally is important in many fields of stellar physics and galactic astronomy, yet some significant difficulties remain as a result of the model uncertainty, which originates mainly in the extended atmospheres of RSGs. Here we propose a line-depth ratio (LDR) method in which we use only Fe i lines. As opposed to the conventional LDR method, in which lines of multiple species are involved, this LDR method is insensitive to surface gravity effects and is expected to circumvent the uncertainty originating in the upper atmosphere of RSGs. Therefore, the LDR–Teff relationships that we calibrated empirically with red giants can be directly applied to RSGs, although various differences between the two groups of objects, for example caused by 3D non-local thermodynamic equilibrium (non-LTE) effects, need to be kept in mind. Using the near-infrared YJ-band spectra of nine well-known solar-metallicity red giants observed with the WINERED high-resolution spectrograph, we selected 12 pairs of Fe i lines that were the least contaminated with other lines. After applying their LDR–Teff relation to 10 nearby RSGs, the resulting Teff with an internal precision of $30\!-\!70\, \mathrm{K}$ shows good agreement with previous observational results assuming 1D LTE and with the Geneva stellar evolution model. We found no evidence of significant systematic bias caused by various differences, including those in the size of the non-LTE effects, between red giants and RSGs, except for one line pair that we rejected because the non-LTE effects may be as large as $\sim \! 250\, \mathrm{K}$. Nevertheless, it is difficult to evaluate the systematic bias, and further study is required, for example including the 3D non-LTE calculations of all the lines involved.

Ground-based infrared mapping of H2O2 on Mars near opposition

We pursued our ground-based seasonal monitoring of hydrogen peroxide on Mars using thermal imaging spectroscopy, with two observations of the planet near opposition, in May 2016 (solar longitude Ls = 148.5°, diameter = 17 arcsec) and July 2018 (Ls = 209°, diameter = 23 arcsec). Data were recorded in the 1232–1242 cm−1 range (8.1 μm) with the Texas Echelon Cross Echelle Spectrograph (TEXES) mounted at the 3 m Infrared Telescope Facility (IRTF) at the Mauna Kea Observatories. As in the case of our previous analyses, maps of H2O2 were obtained using line depth ratios of weak transitions of H2O2 divided by a weak CO2 line. The H2O2 map of April 2016 shows a strong dichotomy between the northern and southern hemispheres, with a mean volume mixing ratio of 45 ppbv on the north side and less than 10 ppbv on the south side; this dichotomy was expected by the photochemical models developed in the LMD Mars Global Climate Model (LMD-MGCM) and with the recently developed Global Environmental Multiscale (GEM) model. The second measurement (July 2018) was taken in the middle of the MY 34 global dust storm. H2O2 was not detected with a disk-integrated 2σ upper limit of 10 ppbv, while both the LMD-MGCM and the LEM models predicted a value above 20 ppbv (also observed by TEXES in 2003) in the absence of dust storm. This depletion is probably the result of the high dust content in the atmosphere at the time of our observations, which led to a decrease in the water vapor column density, as observed by the PFS during the global dust storm. GCM simulations using the GEM model show that the H2O depletion leads to a drop in H2O2, due to the lack of HO2 radicals. Our result brings a new constraint on the photochemistry of H2O2 in the presence of a high dust content. In parallel, we reprocessed the whole TEXES dataset of H2O2 measurements using the latest version of the GEISA database (GEISA 2015). We recently found that there is a significant difference in the H2O2 line strengths between the 2003 and 2015 versions of GEISA. Therefore, all H2O2 volume mixing ratios up to 2014 from TEXES measurements must be reduced by a factor of 1.75. As a consequence, in four cases (Ls around 80°, 100°, 150°, and 209°) the H2O2 abundances show contradictory values between different Martian years. At Ls = 209° the cause seems to be the increased dust content associated with the global dust storm. The inter-annual variability in the three other cases remains unexplained at this time.

HDO and SO2 thermal mapping on Venus

Since January 2012 we have been monitoring the behavior of sulfur dioxide and water on Venus, using the Texas Echelon Cross-Echelle Spectrograph (TEXES) imaging spectrometer at the NASA InfraRed Telescope Facility (IRTF, Mauna Kea Observatory). We present here the observations obtained between January 2016 and September 2018. As in the case of our previous runs, data were recorded around 1345 cm−1 (7.4 μm). The molecules SO2, CO2, and HDO (used as a proxy for H2O) were observed, and the cloudtop of Venus was probed at an altitude of about 64 km. The volume mixing ratio of SO2 was estimated using the SO2/CO2 line depth ratios of weak transitions; the H2O volume mixing ratio was derived from the HDO/CO2 line depth ratio, assuming a D/H ratio of 200 times the Vienna Standard Mean Ocean Water (VSMOW). As reported in our previous analyses, the SO2 mixing ratio shows strong variations with time and also over the disk, showing evidence of the formation of SO2 plumes with a lifetime of a few hours; in contrast, the H2O abundance is remarkably uniform over the disk and shows moderate variations as a function of time. We performed a statistical analysis of the behavior of the SO2 plumes, using all TEXES data between 2012 and 2018. They appear mostly located around the equator. Their distribution as a function of local time seems to show a depletion around noon; we do not have enough data to confirm this feature definitely. The distribution of SO2 plumes as a function of longitude shows no clear feature, apart from a possible depletion around 100E–150E and around 300E–360E. There seems to be a tendency for the H2O volume mixing ratio to decrease after 2016, and for the SO2 mixing ratio to increase after 2014. However, we see no clear anti-correlation between the SO2 and H2O abundances at the cloudtop, neither on the individual maps nor over the long term. Finally, there is a good agreement between the TEXES results and those obtained in the UV range (SPICAV/Venus Express and UVI/Akatsuki) at a slightly higher altitude. This agreement shows that SO2 observations obtained in the thermal infrared can be used to extend the local time coverage of the SO2 measurements obtained in the UV range.

The metallicity effect on line-depth ratios in APOGEE H-band spectra

Ratios of carefully selected line depths are sensitive to the stellar effective temperature (Teff). Relations established between the line-depth ratio (LDR) and Teff allow Teff to be determined precisely. LDRs can also, however, depend on metallicity and abundance ratios, which can limit the accuracy of the LDR method unless such effects are properly taken into account. We investigate the metallicity effect using H-band spectra and stellar parameters published by the APO Galactic Evolution Experiment (APOGEE) project. We clearly detect the effects of metallicity and abundance ratios: Teff derived from a given LDR depends on the metallicity, 100–800 K dex−1, and a dependence on the abundance ratios, 150–1000 K dex−1, also exists when the LDR involves absorption lines of different elements. For the 11 line pairs in the H- band that we investigated, the LDR–Teff relations with metallicity- and abundance-dependent terms added have scatters as small as 30–90 K within the range of 3700 < Teff < 5000 K and −0.7 < [Fe/H] < +0.4 dex. By comparing the observed spectra with synthetic ones, we find that saturation of the absorption lines at least partly explains the metallicity effect.

A Spectroscopic Analysis of the Hyades Cool Giants

Abstract High-resolution spectroscopic observations of the four cool giants in the Hyades cluster, taken at the Elginfield Observatory, are analyzed. The velocity of γ Tau between 2002 and 2009 is constant to a few m s−1; small variations, compatible with the planetary orbit, are seen for ε Tau. The primary-to-secondary mass ratio of θ 1 Tau is found to be 2.33 ± 0.07. Absolute radial velocities are determined for three of the giants from third-signature plots that correct for granulation blueshifts: 38,615 ± 50, 38,760 ± 100, and 38,570 ± 50 m s−1 for γ Tau, δ Tau, and ε Tau respectively. Line–depth ratios show that γ Tau is 33 ± 5 K, δ Tau is 53 ± 10 K, and θ 1 Tau is 30 ± 6 K hotter than ε Tau. Although the λ6253 line bisectors are similar for all four giants, there are significant differences in the line profiles. Fourier analysis of the profile shapes yields projected rotation rates of 2.1, 2.4, 2.8, and 2.8 km s−1 for γ Tau, δ Tau, ε Tau, and θ 1 Tau respectively, with an uncertainty of ±0.3 km s−1. The corresponding radial–tangential macroturbulence dispersions are 5.07, 5.66, 5.55, and 4.65 km s−1, with a uncertainty of ±0.10 km s−1. Scale factors for third-signature plots are close to unity, ±10%, implying that the granulation velocity gradient through their photospheres is similar to the Sun's. Bisector mapping returns flux differences between granules and lanes, with average granule-to-lane temperature differences ∼125 K.

Spectroscopy of the K0 Binary Giant α UMa

Abstract High-resolution spectroscopic observations of the K0 II–III star α UMa were taken at the Elginfield Observatory over 11 years. Radial velocities were measured for nine of these years. They do not cover enough of the 44.5 year orbital period to give definitive elements on their own, but combined with published visual orbits, the spectroscopic-orbit parameters are well constrained. The spectra show no evidence of the secondary star, which remains an unsolved puzzle. Line-depth ratios show that α UMa has temperature variations ∼3 K, possibly periodic, over the 2001–2010 interval. Fourier analysis of the line broadening gives the projected rotation velocity of 2.66 ± 0.15 km s−1 and a radial-tangential macroturbulence dispersion of 4.97 ± 0.08 km s−1. The third-granulation signature shows the granulation velocities of α UMa to be essentially solar, with a scale factor of 0.98 ± 0.10. The absolute radial velocity of the star, with granulation blueshifts removed is −10,035 ± 100 m s−1 at the mean time of the observations, 2005.2544. The line bisector of Fe i λ6253 is normal and shows the classic “C” shape with the blue-most point commensurate with its absolute magnitude. Mapping this bisector on to the third signature gives a flux deficit similar to those of other giants, with a fractional area of 0.131, suggesting a temperature difference between granules and lanes of 127 K. The velocity position of the deficit is slightly higher than that for previously analyzed giants, extending the correlation with absolute magnitude.

A new and homogeneous metallicity scale for Galactic classical Cepheids

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 ≤ Teff ≤ 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.

Method to estimate the effective temperatures of late-type giants using line-depth ratios in the wavelength range 0.97–1.32 μm

The effective temperature, one of the most fundamental atmospheric parameters of a star, can be estimated using various methods, and here we focus on the method using line-depth ratios (LDRs). This method combines low- and high-excitation lines and makes use of relations between LDRs of these line pairs and the effective temperature. It has an advantage, for example, of being minimally affected by interstellar reddening, which changes stellar colours. We report 81 relations between LDRs and the effective temperature established with high-resolution, $\lambda /\Delta \lambda \sim 28,000$, spectra of nine G- to M-type giants in Y and J bands. Our analysis gives the first comprehensive set of LDR relations for this wavelength range. The combination of all these relations can be used to determine the effective temperatures of stars that have 3700<Teff<5400K and -0.5<[Fe/H]<+0.3dex to the precision of $\pm $10K in the best cases.