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The technique of line depth ratios (LDR) 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 in order to fully exploit the capabilities of current and upcoming near-infrared spectrographs. We used 115 simultaneous spectroscopic observations in the optical and the near-infrared for six Cepheids and optical line depth ratios to find new pairs of lines sensitive to temperature and to calibrate LDR-temperature relations in the near-infrared 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 near-infrared LDR for pulsations phases close to phi ~ 0.0 and we discuss the possible causes for these differences. Line depth ratios in the near-infrared will allow us to spectroscopically investigate highly reddened Cepheids in the Galactic centre or in the far side of the disk., 17 pages, 10 figures, 4 tables. Published in MNRAS

Mapping the Galactic spiral structure is a difficult task since the Sun is located in the Galactic plane and because of dust extinction. For these reasons, molecular masers in radio wavelengths have been used with great success to trace the Milky Way spiral arms. Recently, Gaia parallaxes have helped in investigating the spiral structure in the Solar extended neighborhood. In this paper, we propose to determine the location of the spiral arms using Cepheids since they are bright, young supergiants with accurate distances (they are the first ladder of the extragalactic distance scale). They can be observed at very large distances; therefore, we need to take the Galactic warp into account. Thanks to updated mid-infrared photometry and to the most complete catalog of Galactic Cepheids, we derived the parameters of the warp using a robust regression method. Using a clustering algorithm, we identified groups of Cepheids after having corrected their Galactocentric distances from the (small) effects of the warp. We derived new parameters for the Galactic warp, and we show that the warp cannot be responsible for the increased dispersion of abundance gradients in the outer disk reported in previous studies. We show that Cepheids can be used to trace spiral arms, even at large distances from the Sun. The groups we identify are consistent with previous studies explicitly deriving the position of spiral arms using young tracers (masers, OB(A) stars) or mapping overdensities of upper main-sequence stars in the Solar neighborhood thanks to Gaia data., Accepted in A&A

We investigate the properties of the mixed-mode (RRd) RR Lyrae (RRL) variables in the Fornax dwarf spheroidal (dSph) galaxy by using $B$- and $V$-band time series collected over twenty-four years. We compare the properties of the RRds in Fornax with those in the Magellanic Clouds and in nearby dSphs, with special focus on Sculptor. We found that the ratio of RRds over the total number of RRLs decreases with metallicity. Typically, dSphs have very few RRds with 0.49$\ltsim P_0 \ltsim $0.53 days, but Fornax fills this period gap in the Petersen diagram (ratio between first overtone over fundamental period versus fundamental period). We also found that the distribution in the Petersen diagram of Fornax RRds is similar to SMC RRds, thus suggesting that their old stars have a similar metallicity distribution. We introduce the Period-Amplitude RatioS (PARS) diagram, a new pulsation diagnostics independent of distance and reddening. We found that LMC RRds in this plane are distributed along a short- and a long-period sequence that we identified as the metal-rich and the metal-poor component. These two groups are also clearly separated in the Petersen and Bailey (luminosity amplitude versus logarithmic period) diagrams. These circumstantial evidence indicates that the two groups have different evolutionary properties. All the pulsation diagnostics adopted in this investigation suggest that old stellar populations in Fornax and Sculptor dSphs underwent different chemical enrichment histories. Fornax RRds are similar to SMC RRds, while Sculptor RRds are more similar to the metal-rich component of the LMC RRds., Comment: Accepted for publication by MNRAS

We present accurate and deep multi-band ($g,r,i$) photometry of the Local Group dwarf irregular galaxy NGC 6822. The images were collected with wide field cameras at 2m/4m- (INT,CTIO,CFHT) and 8m-class telescopes (SUBARU) covering a 2 square degrees FoV across the center of the galaxy. We performed PSF photometry of $\approx$7,000 CCD images and the final catalog includes more than 1 million objects. We developed a new approach to identify candidate field and galaxy stars, and performed a new estimate of the galaxy center by using old stellar tracers finding that it differs by 1.15 (RA) and 1.53 (DEC) arcmin from previous estimates. We also found that young (Main Sequence, Red Supergiants), intermediate (Red Clump, Asymptotic Giant Branch [AGB]) and old (Red Giant Branch [RGB]) stars display different radial distributions. Old stellar population is spherically distributed and extends to radial distances larger than previously estimated ($\sim$1 degree). The young population shows a well defined bar and a disk-like distribution, as suggested by radio measurements, that is off-center compared with old population. We discuss pros and cons of the different diagnostics adopted to identify AGB stars and develop new ones based on optical-NIR-MIR color-color diagrams (CCDs) to characterize Oxygen and Carbon (C) rich stars. We found a mean population ratio between Carbon and M-type (C/M) stars of 0.67$\pm$0.08 (optical/NIR/MIR) and we used the observed C/M ratio with empirical C/M-metallicity relations to estimate a mean iron abundance of [Fe/H]$\sim$-1.25 ($\sigma$=0.04 dex) that agrees quite well with literature estimates., Comment: Accepted for publication in ApJ, 34 pages, 22 figures, 6 tables

Classical Cepheids are the most popular distance indicators and tracers of young stellar populations. The key advantage is that they are bright and they can be easily identified in Local Group and Local Volume galaxies. Their evolutionary and pulsation properties depend on their chemical abundances. The main aim of this investigation is to perform a new and accurate abundance analysis of two tens of calibrating Galactic Cepheids using high spectral resolution (R$\sim$40,000-115,000) and high S/N spectra ($\sim$400) covering the entire pulsation cycle. We focus our attention on possible systematics affecting the estimate of atmospheric parameters and elemental abundances along the pulsation cycle. We cleaned the line list by using atomic transition parameters based on laboratory measurements and by removing lines that are either blended or display abundance variations along the pulsation cycle. The spectroscopic approach that we developed brings forward small dispersions in the variation of the atmospheric parameters ($\sigma$($T_{\rm eff}$)$\sim$50 K, $\sigma$($\log{g}$)$\sim$0.2 dex, and $\sigma$($\xi$)$\sim$0.2 km/s) and in the abundance of both iron ($\lesssim$ 0.05 dex) and alpha elements ($\lesssim$0.10 dex) over the entire pulsation cycle. We also provide new and accurate effective temperature templates by splitting the calibrating Cepheids into four different period bins, ranging from short to long periods. For each period bin, we performed an analytical fit with Fourier series providing $\theta = 5040/{T_{\rm eff}}$ as a function of the pulsation phase. The current findings are a good viaticum to trace the chemical enrichment of the Galactic thin disk by using classical Cepheids and a fundamental stepping stone for further investigations into the more metal-poor regime typical of Magellanic Cepheids., Comment: 31 pages, 23 figures (out of which 11 are in the appendices A and B), to be published in the Astronomy & Astrophysics journal

The Extremely Large Telescope and the Thirty Meter Telescope will use state of the art multiconjugate adaptive optics (MCAO) systems to obtain the full D 4 advantage that their apertures can provide. However, to reach the full astrometric potential of these facilities for on-sky science requires understanding any residual astrometric distortions from these systems and find ways to measure and eliminate them. In this work, we use Gemini multiconjugate adaptive optic system (GeMS) observations of the core of NGC 6723 to better understand the on-sky astrometric performance of MCAO. We develop new methods to measure the astrometric distortion fields of the observing system, which probe the distortion at the highest possible spatial resolution. We also describe methods for examining the time-variable and static components of the astrometric distortion. When applied to the GeMS Gemini South Adaptive Optics Imager (GSAOI) data, we are able to see the effect of the field rotator at the subpixel level, and we are able to empirically derive the distortion due to the optical design of GeMS/GSAOI. We argue that the resulting distortion maps are a valuable tool to measure and monitor the on-sky astrometric performance of future instrumentation. Our overall astrometry pipeline produces high-quality proper motions with an uncertainty floor of ∼45 μas yr−1. We measure the proper motion dispersion profile of NGC 6723 from a radius of ∼10″ out to ∼1′ based on ∼12,000 stars. We also produce a high-quality optical–near infrared color–magnitude diagram, which clearly shows the extreme horizontal branch and main-sequence knee of this cluster.

Metal-deficient stars are important tracers for understanding the early formation of the Galaxy. Recent large-scale surveys with both photometric and spectroscopic data have reported an increasing number of metal-deficient stars whose kinematic features are consistent with those of the disk stellar populations. We report the discovery of an RR~Lyrae variable (hereafter RRL) that is located within the thick disk and has an orbit consistent with the thick-disk kinematics. Our target RRL (HD 331986) is located at around 1 kpc from the Sun and, with V=11.3, is among the 130 brightest RRLs known so far. However, this object was scarcely studied because it is in the midplane of the Galaxy, the Galactic latitude around -1 deg. Its near-infrared spectrum (0.91-1.32 micron) shows no absorption line except hydrogen lines of the Paschen series, suggesting [Fe/H] less than -2.5. It is the most metal-deficient RRL, at least, among the RRLs whose orbits are consistent with the disk kinematics, although we cannot determine to which of the disk and the halo it belongs. This unique RRL would provide us with essential clues for studying the early formation of stars in the inner Galaxy with further investigations, including high-resolution optical spectroscopy., 13 pages, 7 figures, 6 tables, accepted for publication in ApJ

We present our analysis of a large sample (over 150k) of candidate Galactic RR Lyrae (RRL) stars for which we derived high quality photometry at UV, optical and infrared wavelengths, using data from publicly available surveys. For a sub-sample of these stars (~2,400 fundamental mode field RRLs) we have measured their individual metallicity using the Delta S method, resulting in the largest and most homogeneous spectroscopic data set collected for RRLs. We use this sample to study the metallicity distribution in the Galactic Halo, including the long-standing problem of the Oosterhoff dichotomy among Galactic globular clusters. We also analyze the dependence of their pulsation properties, and in particular the shape of their infrared light curves, from their [Fe/H] abundance., Proc. of "The RR Lyrae and Cepheid Conference 2019: Frontiers of Classical Pulsators - Theory and Observations", held in Cloudcroft, NM, 13-18 October 2019

BackgroundWe investigated the association between cigarette smoking and risk of amyotrophic lateral sclerosis (ALS) in a pooled analysis of population-based case–control studies and explored the independent effects of intensity, duration and time-since-quitting.MethodsALS cases and controls, matched by age, sex and region, were recruited in the Netherlands, Italy and Ireland (*Euro-MOTOR project). Demographics and detailed lifetime smoking histories were collected through questionnaires. Effects of smoking status, intensity (cigarettes/day), duration (years), pack-years and time-since-quitting (years) on ALS risk were estimated using logistic regression models, adjusting for age, sex, alcohol, education and centre. We further investigated effect modification of the linear effects of pack-years by intensity, duration and time-since-quitting using excess OR (eOR) models.ResultsAnalyses were performed on 1410 cases and 2616 controls. Pack-years were positively associated with ALS risk; OR=1.26 (95% CI: 1.03 to 1.54) for the highest quartile compared with never smokers. This association appeared to be predominantly driven by smoking duration (ptrend=0.001) rather than intensity (ptrend=0.86), although the trend for duration disappeared after adjustment for time-since-quitting. Time-since-quitting was inversely related to ALS (ptrendConclusionsOur findings provide further support for the association between smoking and ALS. Pack-years alone may be insufficient to capture effects of different smoking patterns. Time-since-quitting appeared to be an important factor, suggesting that smoking may be an early disease trigger.

International audience; We present a chemo-dynamical study of the Orphan stellar stream using a catalog of RR Lyrae pulsating variable stars for which photometric, astrometric, and spectroscopic data are available. Employing low-resolution spectra from the Sloan Digital Sky Survey (SDSS), we determined line-of-sight velocities for individual exposures and derived the systemic velocities of the RR Lyrae stars. In combination with the stars’ spectroscopic metallicities and Gaia EDR3 astrometry, we investigated the northern part of the Orphan stream. In our probabilistic approach, we found 20 single mode RR Lyrae variables likely associated with the Orphan stream based on their positions, proper motions, and distances. The acquired sample permitted us to expand our search to nonvariable stars in the SDSS dataset, utilizing line-of-sight velocities determined by the SDSS. We found 54 additional nonvariable stars linked to the Orphan stream. The metallicity distribution for the identified red giant branch stars and blue horizontal branch stars is, on average, −2.13 ± 0.05 dex and −1.87 ± 0.14 dex, with dispersions of 0.23 and 0.43 dex, respectively. The metallicity distribution of the RR Lyrae variables peaks at −1.80 ± 0.06 dex and a dispersion of 0.25 dex. Using the collected stellar sample, we investigated a possible link between the ultra-faint dwarf galaxy Grus II and the Orphan stream. Based on their kinematics, we found that both the stream RR Lyrae and Grus II are on a prograde orbit with similar orbital properties, although the large uncertainties on the dynamical properties render an unambiguous claim of connection difficult. At the same time, the chemical analysis strongly weakens the connection between both. We argue that Grus II in combination with the Orphan stream would have to exhibit a strong inverse metallicity gradient, which to date has not been detected in any Local Group system.